STEEL CASTINGS MANDOOK SN mai binadamu STEEL FOUNDERS SOCIETY OF AMERICA Universiivo Michigan Libraries 1817 ARTES SCIENTIA VERITAS 391 量 ​606 STEEL CASTINGS HANDBOOK THIRD EDITION 100th Anniversary of the Steal Casting Industry in the U.S.A. LI SONDON WALLS "Y*OF AMERICA INTEGRITY RESEARCH * PROGRESS Editor Charles W. Briggs Technical and Research Director, SFSA STEEL FOUNDERS' SOCIETY OF AMERICA 606 Terminal Tower Cleveland 13, Ohio Engin. Library STEEL CASTINGS HANDBOOK TO 32 (8 Copyright 1960 C Steel Founders' Society Parts of this book may be reproduced upon written permission of the Society #1 1 The Electric Printing Company Cleveland, Ohio 1 i PREFACE Many years ago, the Steel Founders' Society saw the need for an authoritative, concise, and all-inclusive Handbook on the technology of steel castings. The first edition of 507 pages, published in 1941, provided this information on steel castings, and answered the following questions: What are the advantages of using steel castings in mechanical structures and assemblies? How can steel castings best serve the engineering industries ? What helpful information is needed as a guide to the design and materials engineer? What should the engineering college graduate know about the products of the steel foundry ? The Handbook proved so popular with engineers and users of steel castings that a second edition was prepared and distributed in 1950. World War II was responsible for many developments in steel casting production and technology, and these were included in the second edition. The steel casting industry in the United States has its 100th anniversary in 1961 and this, the third edition of the Handbook, is a tribute to the numerous achievements of the industry during these first one hundred years. Many of the technological accomplishments have been made during the past ten years because of extensive metallurgical research and the application of this information to production. This Handbook is an extensive revision of the 1950 edition, and it should be considered as a completely new book. However, this Hand- book is written—as was the first edition 20 years ago—primarily for the purchaser of steel castings, the design and materials engineers, and college engineering students, and it has the same four objectives. The sources of the material herein presented are practically co- extensive with the entire steel casting industry, and include all available literature on the subjects covered, as well as much unpublished in- formation made available by qualified individuals and companies within the steel casting industry. The book is complete and timely, and can be considered as an authoritative viewpoint of the industry on technical and design matters concerning the technology of steel castings. Special recognition and grateful appreciation is expressed to the many individuals from member companies who served as task groups for the collection of data and photographs for this edition. They co- operated fully and carried out, with dispatch, the tasks assigned by the Handbook Committee. The Steel Founders' Society is especially appreciative to the Hand- book Committee for the two years of concentrated effort which they gave to preparing the outlines, studying chapter reviews, and submitting detailed comments. Many evening hours were devoted to this activity in order to keep abreast of the exacting schedule which was set. Furthermore, the Society is indebted to Mr. William W. Heimberger, Committee Chairman, for the capable manner of directing the Commit- tee and staff in the Handbook preparation. He has been associated with the preparation of the two previous editions of the Handbook, and the Society is most fortunate to have these experiences in directing this Anniversary Edition. The Handbook Committee is as follows: William W. Heimberger, Chairman—The Buckeye Steel Castings Company Franklin H. Allison, Jr.-Blaw-Knox Company Erroll V. Black-Lebanon Steel Foundry Charles A. Faist-Burnside Steel Foundry Company Francis H. Hohn-Scullin Steel Co., Div. of Universal Marion Corporation Robert L. Lord-Wehr Steel Company Cedric G. Mickelson-American Steel Foundries David P. Miller - The Falk Corporation Leonard A. Neef-St. Louis Steel Casting Inc. Bernard C. Yearley-National Malleable & Steel Castings Co. This book is dedicated to the Engineering Profession. It is offered as a reference book and a dependable manual for the use of all who are interested in the creation of improved industrial structures of the highest quality. Charles W. Briggs, Editor Robert A. Willey Harold G. Fraunhofer Charles A. Rowe Associate Editors September 1960 VI TABLE OF CONTENTS Page Preface V Chapter 1 112B四​四​% Chapter II 3 Chapter III Chapter IV Advantages of Steel Castings in Machines Design Flexibility of Steel Castings Metallurgical Versatility and Quality Economic Benefits of Steel Castings 18 Steel Compared to Other Cast Metals 25 Casting Compared to Other Methods of Forming 29 Industrial Applications of Steel Castings 36 The Purchasing of Steel Castings 101 Fundamentals of Steel Casting Design 113 Principles of Correct Design 113 Steel Casting Design Fundamentals 116 Design for the Ultimate in Section Modulus 139 Designing for Various Services 149 Redesigning of Castings and Wrought Parts 155 Evaluation of the Steel Casting Design 169 Destructive Testing, Stress Analysis and Properties 174 Design of Steel Castings vs. Weldments 182 Patterns for Steel Castings 191 Tolerances in Steel Castings 222 Design Influences Casting Tolerances 222 Process Methods Influence Tolerances 230 Recommended Tolerances for Steel Castings 238 Normal Variations in the Properties of Cast Steel 245 Variations in Elements in Manufacturing 248 Variations in Mechanical Properties 256 Reproducibility of Properties from Coupons 265 Property Variations as Affected by Mass 269 Properties of Test Bars and Castings 281 Physical Values Pertaining to Cast Steel 292 Elastic Constants 292 Density 295 Volume Changes 298 Freezing and Melting Temperatures 304 Thermal, Electrical, and Magnetic Values 306 Atomic Radiation Effects 313 Chapter V Chapter VI Chapter VII 0. red are Chapter VIII the Chapter IX fer Structural Cast Steels—Carbon Steel Grades Chemical Composition Tensile Properties Impact Properties Fatigue Properties Hardenability Applications of Various Cast Carbon Steels 316 316 318 326 331 336 338 VI Chapter X Chapter XI Chapter XII Table of Contents-(Continued) Page Engineering Cast Steels-Low-Alloy Grades 340 Consolidated Mechanical Property Values 342 Property Data for Various Types 350 Cast Steels for Wear Resistance 376 Factors Affecting Wear Resistance 377 Steels for Wear Resistant Applications 382 Surface Hardening of Steel Castings 386 Austenitic Manganese Cast Steel 391 Cast Steels for Low Temperature Application 400 Factors Affecting Impact Resistance 401 Impact Data for Various Cast Steels 407 Cast Steels for High Temperature and Heat Resistant Applications 416 Cast Steels for Service up to 1150 Degrees F 416 Cast Steels for Service Above 1150 Degrees F 424 Cast Steels for Corrosion Resisting Service 437 Corrosion of Carbon and Low-Alloy Steels 438 Corrosion Resistant Alloy Cast Steels 443 Welding of Steel Castings 455 Chapter XIII Chapter XIV Chapter XV Chapter XVI Heat Treatment Principles and Practices 480 Principles of Heat Treatment 480 Transformation Diagrams and Hardenability 485 Liquid Quenching 492 Recommended Practice for Carbon and Low-Alloy 496 Chapter XVII The Machinability of Steel Castings 503 Chapter XVIII The Manufacture of Steel Castings Melting Practice Molding and Coremaking Finishing Operations Heat Treating Facilities and Operations Inspection and Testing 541 541 557 579 587 591 Chapter XIX Steel Castings: Yesterday, Today and Tomorrow 602 Glossary of Foundry Terms 624 Appendix—Engineering Tables 649 Compositions of Standard Wrought Steels 650 Compositions of Wrought Stainless Steels 654 Alloy Casting Institute Standard Compositions for Heat and Corrosion Resistant Castings 656 Summary of Steel Casting Specifications 658 Index 664 VIII CHAPTER I ades lues Page 340 342 350 ADVANTAGES OF STEEL CASTINGS IN STRUCTURES AND MACHINES s 376 377 382 386 391 Steel is strong; steel is tough; steel is dependable; and when steel is cast to shape it represents the most direct method of producing steel parts to final form, while still retaining all the advantages of steel. A wider range of mechanical properties can be obtained in steel castings than in any other cast metal by simply varying the carbon and alloy content of the steel, or the heat treatment of the casting. on 400 401 407 at 416 SF 416 es F 424 Casting is one of the basic processes used for the shaping of steel. It is economical both as to cost and time of production. Numerous parts are being produced as steel castings because of the advantages of the steel casting process. These advantages can best be described under three major attributes: (1) design flexibility, (2) metallurgical versa- tility and quality, and (3) economic benefits. 437 438 S 443 SECTION I 455 480 480 1 485 492 496 503 Design Flexibility of Steel Castings Design engineers have freedom of design when they use steel castings as their form of construction. The steel casting process is ideal for it lends itself to the formation of streamlined, intricate, integral parts with a strength and rigidity obtainable by no other method of fabrication. The shape and size of a part are primary considerations in design and in this category the possibilities of steel castings are un- surpassed. The flexibility of steel casting design gives the engineer wide scope in converting his ideas to the practicability of an engineered part. The design flexibility of steel castings offers a number of individual advantages that are enumerated here for reference purposes so that the design engineer may readily see the wide scope of steel casting capabilities. 541 541 557 579 587 591 602 624 1-Unlimited Range of Shapes ... Steel parts may be obtained in in- numerable shapes through the use of the casting process from cylinders, blocks, and platelike structures, to those of highly intricate forms with the most complex internal passages. Figures 1 and 2 show the two extremes of shape. Both are functional for the service intended and both must withstand exacting requirements. 649 550 554 -56 58 2-Shapes Economically Unobtainable by Other Methods ... Certain engineering designs cannot be produced except by the casting process. 54 Fig. 1—Cast steel back- ing rolls weighing ap- proximately 65,000 pounds each for use on four high strip mills. WB-8456 19920 Ser 5 RM20 RE Fig. 2-A one piece booster case weighing 19,200 pounds. Complex and intricate shapes are designs that are difficult to produce economically by other methods. Also, some parts of simplified design contain internal passageways that cannot be formed by machining but can be easily produced through the use of refractory cores positioned accurately in the casting mold cavity. In some cases these passages are so small or so shaped that metal or refractory tubes are employed to form the passages. An example of a casting with a metal insert is shown in Figure 3. Designs embodying streamlined, complex curves, especially when the wall section is varied, do not lend themselves to fabrication by Fig. 3—Turbosuper- charger nozzle ring for a Diesel engine pro- duced by casting in vanes into a hub. The mold and core assem- bly that holds the vanes in location for casting is also shown. forging, welding or machining. Only by the casting process can such parts be produced. Also, parts with undercuts and varied wall sections can be produced only as steel castings. 3—Shapes for Maximum Strength ... The metal may be distributed, in steel casting designs, to those positions where it will do the most good for maximum strength and minimum weight. The design engineer can add metal, where needed, for resistance to bending, torsion, tension or impact forces. The freedom to design as strength and section calcula- tions indicate, is available only when casting construction is employed. Also, members that tie together important sections and carry little strength can be made of suitably thin design to produce strong light- weight parts. Figure 4 is a well-balanced steel casting design for dy- namic service. . 4-Shapes for Minimum Stress Concentration . . . Notches, abrupt changes in section, and sharp angles often result in early failure of parts in dynamic service. Steel casting designs permit the use of shaped fillets and blended sections at locations of high stress. Furthermore, those designs which confer minimum stress concentration in service are Fig. 4- High-strength base and cylinder castings of well bal. anced design for maxi- mum strength. 3000 Fig. 5-A spring equa). 3000 izer casting showing indications of stress pattern by the brittle lacquer technique to indicate properly de. signed fillets and blending section. 3000 . also best from the standpoint of castability in the foundry. A highly stressed steel casting with well-radiused section junctions is illustrated in Figure 5. 5–Streamlined Shapes ... Modern streamlined design is ideal for steel castings both from the standpoint of functional application and cast- ability. An example of streamlined casting design is shown in Figure 6. Steel castings of streamlined shapes are an advantage for minimum resistance to fluid passage, such as liquid or gas flow in water pumps and steam turbines, stern frames and bow stems for ships, and castings used in high-speed transportation where air resistance is a factor. 6—Shapes Designed for Eye Appeal ... Parts designed with eye appeal are usually more readily salable, especially when the smooth contour design adds to the serviceability of the part. Figure 7 shows the ap- pearance of a steel casting contrasted with a weldment designed for the same service. Steel casting shapes appear as the optimum func- tional part that they are, and thus have an inherently pleasing sales appeal. 39157 Fig. 6—10-inch weld end valve body; weight 1552 pounds. 10 500 STEEL 18-93158 A D V A N T A GES OF STEEL CASTINGS 5 UTTER equal owing Press mbrittle de to de and Fig. 7–Comparison of a steel casting and weldment for the same service to illustrate the professional appearance necessary for sales appeal. Height 16 inches. Section thickness, 3/4 inch. Weight 100 pounds. Average unit savings by using a steel casting, $7.54. The casting customer reported, "the castings were considerably neater and stronger and were in every respect far superior to any weldments we had ever fabricated." 7-Shapes for Difficult Forming and Machining Parts ... Certain alloy steels are not readily rolled or forged and are machined with considerable difficulty. Such steels can be cast to the desired shape economically and efficiently. One example of these difficult-to-form-and-machine steels is the abrasion resistant austenitic manganese steel, a casting of which is shown in Figure 8. This steel hardens on working and is machined with such difficulty that grinding is the most usual final forming operation. Casting to the desired shape is the only economical method, and many tons of 12 percent manganese steel castings are produced yearly. 8-Shapes for Difficult Welding Compositions ... High-strength steels, deep-hardening steels and high-carbon steels are difficult to fabricate by welding so that the weld metal meets the properties of the base . Fig. 8-Dipper pro- duced out of 12 to 14 percent manganese cast steel. Capacity: 442 cu. yds. 6 ADVANTAGES OF STEEL CASTINGS metal. Also, the techniques of welding these grades are critical and require close control to avoid cracking. Furthermore, electrodes are not available in every case to develop a weld that will match the properties or composition of the base metal. These special steel parts can be most easily produced as steel castings and, as such, are readily available at an economical cost. The steel casting illustrated in Figure 9 is a 220,000 psi tensile strength steel which would be most difficult and uneconomical to produce as a weldment. s Fig. 9-Ultra high strength cast steel grouser used on crawler shoes of the moving and mining machinery. The ultra high ile strength of this casting (220,000 psi) makes highly resistant to bending and distortion as well as extremely resistant to abrasive wear. 9–Rapid Alterations in Shape ... Designing parts as steel castings permits wide design versatility. Changes can be readily made from studies of the prototype and working models so as to produce improved castings by relatively inexpensive pattern changes. For example, a pilot casting can be made and studied by brittle lacquer or strain gage techniques to determine stress concentration factors. Changes then can be made to the pattern by building up sections with plastic, or re- moving parts of the pattern, and another pilot casting can be produced. These alterations in shape can be made rapidly with a minimum delay in the final production of the castings. The advantages obtained in securing a fully engineered part, especially for dynamic service, more than justify such procedure. The casting model of Figure 10 shows de- sign alterations made to produce a casting with low stress .concentration areas. The necessary pattern changes are accomplished easily and quickly. 10—Unlimited Range of Sizes . . . Each year industries of the United States use countless thousands of steel castings ranging in weight from a few ounces each to over 250 tons each, produced to perform the tough (a) (b) Fig. 10—Steering trunion casting showing a model to which design alterations were made (a). These changes can result in rapid alterations in the pattern to produce a properly designed casting as shown in (b). jobs of industry. Figure 11 is a photograph of a large press casting, whereas Figure 12 shows, for contrast, small investment castings produced in steel. Steel castings have no practical size limitation. 11—Sizes Unobtainable by Other Methods ... Large components, such as anvil blocks, rolling mill housings, and other parts, may be so large that the size of the forging presses or mills is inadequate to produce the Fig. 11--A moving crosshead casting for a 50,000 ton hydraulic closed die forging press. One of the largest steel castings produced. Total weight of casting 357 tons. 0 Fig. 12-A series of small steel castings weighing from a few to 50 pounds for trucks parts where toughness and fatigue resistance are required. ounces 8 structure. Nevertheless, a steel casting, such as shown in Figure 13, is economical and the only way in which this large structure can be produced. 12—Minimum Weight ... Thin section, lightweight steel castings are being made available today through the able cooperation of the design and foundry engineers. Also, low-stressed sections in castings are being made low in weight by extensive coring, tapering, and thin section de- signs. A thin section casting with extensive coring for lightweight is shown in Figure 14. 13–Weight Distribution Where Needed ... The design engineer can distribute the weight of the part, when employing a casting design, with a freedom not available to other forms of fabrication. Weight distribu- tion and dynamic balancing in a part are often imperative, for example, in parts operating under high speeds or for optimum section modulus. Also, weight considerations are of premium value in transportation equipment where the flexibility of design for optimum weight distribu- tion is a much sought after function in these applications. An example Fig. 13—A single piece steel casting bed frame for a crank press. The casting is lying on its side and has a height of 20 feet and weight of 240 tons. Fig. 14—Backing plate castings for disc type aviation brake assem- bly showing thin- walled high-strength steel castings with con- siderable coring for in jet aircraft under high stress con- ditions. use of designing for dynamic balancing is illustrated in the casting of Figure 15. 14–Single Component Part ... Designing for steel castings permits unit construction, thereby providing the utmost continuity to the part, including support or reinforcing ribs for strength, coring to save weight, and varying wall sections to satisfy both weight and strength require- ments in the one-piece design. Obviously, single piece construction affords greater structural rigidity than obtained in an assembly of a number of parts, and there are no joints with the possibility of leaking or of loosening of fasteners, no misalignments or assembly errors, nor delays necessitated by a short order on one of the parts of the assembly. A single component part usually permits close tolerances and snug fit. An example of a single piece steel casting construction that replaced a multiple part assembly is illustrated in Figure 16. 15—Assembly of Castings ... Steel castings, because of their various — shapes, can be assembled into complete parts for industry. The castings Fig. 15--A 54-inch di- ameter, 16-knife chip- per, to produce pulp mill chips from sawmill woodwaste. This steel casting requires dy- namic balancing. 10 A D V ANTAGES OF STEEL CASTINGS (a) steel weldment (b) steel casting Length 24 inches Length 24 inches Fig. 16—Comparison of a single piece casting and a 6-piece weldment for a hitch yoke for airfield trucks. The weldments continually failed and the casting resisted failure because of the rigidity of one piece construction. can be fitted with little or no machining in a minimum of time with but a small amount of equipment. Such parts are rugged although nice in appearance, such as the oil well drilling hook of Figure 17. This hook, of a rated capacity of 500 tons, consists of an assembly of 25 steel castings. Assemblies of steel castings such as this example are used in many industries such as logging, earthmoving and land cleaning equipment. 16—Readily Fastened to Other Parts ... Steel castings can be readily attached to wrought steel parts by welding or bolting, thus producing a Fig. 17–Oil well drilling hook, 11'71/2" tall. An assembly of 25 steel castings. Plate Fig. 18-A hoist drum, over-all dimensions 10 feet by 5 feet 3 inches diameter. This composite fabrication shows 3 steel cast- ings welded to 23/4-inch rolled plate sections. 1 Weld 1 composite fabrication. There are numerous examples of such types of construction, for example, valve or fitting castings welded to fabricated steel pipe, or steel casting shaft-bearing housings in a plate-welded machine base. Shape requirements often make castings the most economical part to install in a composite structure. An example of a steel casting attached integrally to other parts is shown in Figure 18. 17—High Dimensional Accuracy ... Steel castings, if required, can be produced to high dimensional accuracy. Tolerances of 0.25 to 0.001 inch are possible depending on service requirements, pattern equip- ment, size of casting, casting process employed, and finishing require- ments. The reader is referred to Chapter VI for a full discussion of casting tolerances (see Figure 19). 18-Desirable Surface Finish ... A surface finish of from 1000 to 125 microinches can be produced on steel castings, depending on the casting method employed. Steel castings are obtainable on specification that can be assembled into machines with no machining of the casting what- soever. An example of a steel casting with an excellent surface finish is shown in Figure 19. 19-Few or Many Parts ... Steel castings are being produced as a — single casting or mass produced in many hundred thousand castings Fig. 19-Cast tooth bevel gears produced by the shell molding process to obtain ex- cellent surfaces and close tolerances. Weight 190 pounds. 6) s 8.1 12 ADV ANTAGES OF STEEL CASTINGS Fig. 20—Mass production of railroad steel castings to close tolerances and high quality. Several thousand truck side frame castings in various stages of the final inspection and gaging operation. from one design. Certain steel foundries make a specialty of the produc- tion of only jobbing castings where a run of 50 castings of the same design may be considered as extensive, and such foundries are well equipped to produce as few as only one to five castings of the same design. Other steel foundries are equipped with highly mechanized equipment for mass production to turn out several thousand castings of one design. These castings are true to design and the 10 thousandth casting is just as accurate to the dimensions required as the first casting produced. Figure 20 shows a view of a shop with several thousand truck side frames in various stages of the finishing operation. Those in the immediate foreground, including those at the left, have been final-inspected and gaged and are ready for shipment. It is well to plan on large numbers of steel castings because one knows that they are of uniform high quality. SECTION II Metallurgical Versatility and Quality of Steel Castings There are a number of metallurgical advantages which favor steel castings as a preferred method of constructing steel parts. These advan- tages are called to the reader's attention in the following summary: GS 13 A D V A N T A GES OF STEEL CASTINGS i 1 1-High Quality . . . Many parts for exacting service conditions are produced as steel castings. Steel castings are dependable and they are being used in many critical applications, such as the following: aircraft frames and engines; atomic energy reactors and piping; turbines, valves and pumps for high pressures and high operating temperatures of 1150 degrees F; equipment for low temperatures of -50 to -150 degrees F; and railroad transportation parts subjected to high speeds and heavy loads. A large portion of modern steel castings production is for parts which have severe dynamic service requirements. Many illustrations of steel castings for exacting service are shown in Chapter II. 2—Uniform Directional Properties ... The metallographic structure of steel castings is uniform or equiaxed in all directions. It is free from ;) the directional variation of properties found in forged or rolled shapes. Steel castings have no change between transverse and longitudinal mechanical properties such as is experienced in wrought steel products. Steel that has been rolled or forged does not have the same mechanical properties in different directions as shown in Figure 21. This directionality is called “anisotropy” and occurs in both cold- worked and hot-worked steel. The greatest interest to most buyers of wrought steel is in the variation of the properties parallel to and trans- verse to the rolling or forging direction. The tensile and yield strengths of wrought steels exhibit only slight changes in directional properties; but ductility, impact, and fatigue properties show marked anisotropy. Cast steel, which is not worked, is a mean value and shows no anisotropy. These properties decrease markedly as the angle between the test speci- men axis and the rolling or forging direction increases and approaches 90 degrees. The amount that the steel may be reduced in cross section 1 y. id e 1 2 . LONGITUDINAL CASTING PROPERTIES TENSILE TRANSVERSE 90 5 TENSILE STRENGTH TENSILE STRENGTH 80 1000 p.si 1000 p.s.i. CHARPY V-NOTCH 70 ET. LBS. IMPACT, 60 YIELD 由 ​Fig. 21—The influence of forging reduction on anisotropy for a 0.35 percent carbon wrought steel (Unckel)'. Properties for a 0.35 percent carbon cast steel are shown in the graph by a star (*) for purposes of comparison. 50 REDUCTION OF AREA, % YIELD STRENGTH YIELD STRENGTH 1000 p.s.i. 1000 p.s.1. 40 REDUCTION CHARPY 30 IMPACT, FT.-LBS. CHARPY V NOTCH ELONGATION t REDUCTION ELONGATION, % OF AREA, % 20 ELONGATION, % 10 0 12 0 4 REDUCTION RATIO BY FORGING 8 12 14 A D V A NTA GES OF STEEL CASTINGS because of rolling or forging also has an effect on the directional prop- erties. For example, in Figure 21 the reduction of area drops from 57 to 18 percent when the section thickness is reduced by a ratio of 12. Attention is also directed to the wide directional variations in the wrought steel impact values - a drop of 75 to 18 ft-lbs. The steel casting impact value, which is the mean of the wrought steel values, shows no change regardless of the testing direction, and represents a more satisfactory condition for design engineers because the steel cast- ing is equally tough in all directions. The section thickness of the wrought steel shows pronounced anisot- ropy in that the center of the section is more affected than positions near the surface. This condition can be best illustrated by Figure 22 where variations in ductility values, depending on the direction of test- ing, are more noteworthy. It should be pointed out that wrought steel properties are almost always reported as the maximum values and from specimens taken in the direction of rolling or working. A comparison of these highest wrought steel values with those of cast steel can lead an uninformed individual to assume that the properties of forged or rolled steel are higher than those of steel castings. Such is not a true statement of fact. Cast steel properties are the average of normal transverse and longitudinal properties of similar wrought steels. Directional variations of wrought steels are observed in the fatigue strength as is illustrated in Figure 23, and the center of sections con- tributes additionally to the anisotropy effect as illustrated in Figure 24. This chart compares cast and rolled steels and shows cast steels to have fatigue values which are the average of the longitudinal and transverse values of similarly rolled steel. 50 ENDURANCE LIMIT 45 40 STRESS 1000PSI WROUGHT C1030 (LONGITUDINAL) 35 CAST 1030 WROUGHT CIO30 (TRANSVERSE 30 25 60 Fig. 22—The effect of sec- tion size on longitudinal and transverse endurance properties of a 61/4 inch section of 1030 rolled steel, normalized (1600°F) and tempered (1200°F) compared to a 1030 cast steel of similar section with the same heat treat- ment. ENDURANCE RATIO 55 WROUGHT C1030 (LONGITUDINAL) 50 ENDURANCE LIMIT TENSILE STRENGTH CAST 1030 45 WROUGHT CI030 (TRANSVERSE) 40 35 1"_ + to 2 2 6 A D V A N T A GES OF STEEL CASTINGS 15 90 85 80 75 1 70 Fig. 23—Anisotropy exhibited by fatigue strength and endurance limit in SAE 4340 forged steel (Ramson and Mehl)". STRESS, 1000 psi. 65 LONGITUDINAL 60 55 50 TRANSVERSE 45 40 104 10? 105 106 CYCLES TO FAILURE 100 TENSILE STRENGTH 80 т C L STRESS, 1000 PSI YIELO POINT REDUCTION IN AREA $ 60 L 50 с PERCENT 40 30 T 20 10 50 ELONGATION IN 2 40 - 30 PERCENT 20 . T 10 - CENTER o 5" 8 ti+ 나을 ​#1 6 WROUGHT CIO30 (LONGITUDINALI WROUGHT CIO30 ( TRANSVERSE) CAST 1030 Fig. 24—The effect of specimen location on the tensile properties of a 6-inch section of cast and rolled 1030 steel, normalized (1600°F) and tempered (1200°F). 1 16 A D V ANTAGES OF STEEL CASTINGS 105 100 0- 이 ​O 95 90 85 80 0 O 75 STRESS 1000 PSI 4300 SERIES NO. 25 WROUGHT43106 YNNOTCHED NOTCHED NO.24 CAST 4337 Fig. 25—S-N curves for cast 4337 steel and rolled 4340 steel tested longi- tudinally in direction of rolling. Both steels were given the same water quench and tempered heat treatments. The tensile strengths of the steels were: No. 24--168,200 psi; No. 25—168,400 psi 70 D 65 60 NO FAILURE 55 50 45 104 106 107 105 CYCLES TO FAILURE Engineers usually are given only the longitudinal endurance prop- erties of wrought steels reported in reference books, such as in the com- parison of the upper curves in Figure 25, of a 4337 cast steel with the longitudinal properties of a 4340 rolled steel. However, in the lower curves which are for notched fatigue specimens, the cast steels show a greater notch resistance (less notch sensitivity) than the comparable wrought steels. Most structures for dynamic service are designed today on the endurance limit properties of the steel. The endurance properties readily available to the designer for wrought products are those obtained only from specimens tested in the direction of rolling or forging. Factors of safety are then applied for design application. Similar or even higher factors are applied in many cases to the values of steel castings even though there is no directional variation exhibited by cast steels. This is unfortunate because it penalizes design of the part without due regard to basic principle and demonstrated fact. A better procedure is to use ADVANTAGES OF STEEL CASTINGS 17 the endurance properties obtained by testing notched specimens. In such cases, there is no need to apply safety factors because the notch test represents more severe conditions than those obtained in the service of the part. Also, cast and wrought steel design values in fatigue would be the same, as has been amply demonstrated in the technical literature. 3—Choice of Mechanical Properties ... Cast steels are available in a wide range of mechanical properties depending on the compositions and heat treatments. Properties within the following range can be obtained: Tensile strength psi 60,000 to 280,000 Yield strength psi 30,000 to 230,000 Elongation in 2 inches % 40 to 4 Reduction of area % 65 to 5 Brinell hardness 120 to 700 Charpy V-notch impact ft-lbs 65 to 5 Endurance limit psi 25,000 to 90,000 National specifications are available covering most of the properties in the above ranges. The reader is directed to Chapters IX to XIV for detailed property information for cast steels according to their service requirements. Steels with special properties can be made by steel foundries because small furnaces usually are employed and small, tailor-made heats can be produced. Properties are available in steel castings that will fit any segment of the wide range of properties employed in the engineering design of steel parts. 4-Wide Range of Compositions ... Certain casting applications rely on the steel compositions to obtain their advantageous service prerequi- sites. Chemical compositions must be carefully considered for steels of the following service applications: Abrasion resistant (See Chapter XI) Corrosion resistant (See Chapter XIV) Heat resistant (See Chapter XIII) Magnetic and non-magnetic (See Chapter VIII) Ultra high tensile strength (See Chapter X) Steels for low temperature (See Chapter XII) Steel castings of the proper compositions are produced and are available for all of the above service applications. 5—Readily Heat Treated ... Steel castings can be readily annealed, normalized, tempered, hardened, or carburized. Special face hardening treatments can be applied. Steel foundries are fully equipped to carry on these heat treatments under the supervision of qualified metallurgical engineers. The specific heat treating procedures to obtain the properties required by the purchaser are usually the prerogative of the foundry metallurgists. . ! Fig. 26-A number of machined large cast steel ball mill gears. Diameters range from 14 to 16 feet. 6–Excellent Weldability ... All cast steels are weldable, and most compositions are readily welded because the major portion of steel castings is produced with carbon content under 0.45 percent carbon. Steel castings can be welded to each other and to other wrought steel shapes. Details of the welding of steel castings and their use in com- posite fabrications are given in Chapter XV. 7—Readily Machinable ... Steel castings are as readily machinable as wrought steels, and the machinability will depend on the microstructure, the composition, and the hardness of the steel. A machinability rating chart is given in Chapter XVII as a guide to purchasers of steel castings. Figure 26 illustrates machined cast steel gears available for shipment. SECTION III Economic Benefits of Steel Castings Single Component ... Integral, one-piece construction has a number of economic advantages over assemblies requiring the use of bolts, nuts, rivets and other types of metal fasteners. The one-piece casting eliminates machining charges necessary for close match or threading in putting parts together. Also, labor costs of the assembly of parts are eliminated and there are no assembly errors with a single component. There are many cases where a single casting has economically replaced an assembly of forged parts. An example is Figure 27 showing a single steel casting for a tractor which replaced 12 detailed parts. The ADV ANTAGES OF STEEL CASTINGS 19 3 i (a) Steel weldment (b) Steel casting Fig. 27-A single piece cutter bar frame steel casting replaces a 12-piece weldment at an over-all cost reduction of 53 percent. Length 20 inches, metal thickness 1/4 to 9/16 inch. economic benefits of using the one-piece steel casting to replace an assem- bly of parts fastened together are: - . 1- Fasteners need not be purchased; 2— Extra parts need not be purchased; 3 - Fewer inventory costs; 4– Less engineering time because one drawing supplants many drawings. No assembly instructions to prepare; 5 — No assembly costs of machining and labor; 6— Fewer handling costs; 7 — Less paper work in following fewer parts through the shop; 8 — Fewer costs for time study, time keeping, recording, indirect labor, supervision and accounting; 9— Less down time with no delay of assembly of any essential parts not delivered on time; 10 - No assembly errors with a single component casting; 11 - A single component results in a single manufacturer's respon- sibility. - - - 20 ADV ANTAGES OF STEEL CASTINGS Fig. 28—One piece cast steel fluid end for a mud pump used in the oil field industry. Length 8 feet. A single casting is a more rigid part than an assembly of parts held together by fasteners. While this feature may not be entirely an econom- ical benefit, it often results in longer life of the component which, in turn, reflects over-all savings. Certain parts are too intricate to produce by any method other than casting. If they could be made, the cost may be prohibitive. The pump casting of Figure 28 is an ideal example of a single piece casting with many internal water jacket passages which must resist high pressures. All of these requirements are satisfied by a steel casting, and there are no bolts to work loose, no rivets to shear, no extensive amount of fabrication welds to open. Another example of an integral lightweight casting is the com- bined bolster center brace and rear draft lug casting shown in Figure 29. This steel casting is located in each end of a freight car center sill at the Fig. 29—Combined bolster center brace and rear draft lug casting for freight cars illustrating integral lightweight construc- tion. Over-all length of steel casting 42 inches with an average of 1/2 inch thickness. Atten- tion is directed to the 12 sand cores sary to produce the casting. neces- A D V ANTAGES OF STEEL CASTINGS 21 body bolster and is 42 inches in over-all length and has an average sec- tion thickness of 12 inch. Attention is directed to the example of exten- sive coring necessary to produce this integral casting of lightweight. The casting weighs 265 pounds and the 12 sand cores weigh 352 pounds. Quick Delivery ... Steel castings are available shortly after the pat- terns are delivered to the foundry. No delay results from the prepara- tion of dies, special tools, machines or presses. Dependability ... Steel castings give dependable performance with low maintenance costs. Records indicate that of the few failures which occur, over 90 percent are related to improper design, such as designed- in notches and other stress raisers, the improper joining of sections, and the failure to observe the rules of good design. Steel castings are capable of giving long life in exacting service, such as the truck side frame pictured in Figure 30 which presents an outstanding example of the reliability of steel castings. Cast in March of 1916 it has already given RE BUILT 7-599 CAPY 140 F-70 © EXIT PATENTED 12-3-07 3.18 CAR COMPLETELY REBUILI 59 TRUCK SIDE FRAMES CAST - 1916 Fig. 30—A 70-ton gondola freight car side frame casting which has been in continued dynamic service and shock loading for over 40 years. 2 > over 40 years of service under a 70-ton freight car, where it has been subjected to the most rigorous shock loading imaginable. As may be noted, the car proper was rebuilt in July of 1959, indicating an expected life of around 70 years for this steel casting. Of further interest is the fact that the other three side frames on this car were also manufactured in 1916. This is far from an isolated case, since over 4000 of these cars were rebuilt by one railroad during the year 1959, employing some 16,000 truck side frames of similar age and past service. 22 ADVANTAGES OF STEEL CASTINGS Steel castings are used in numerous applications where human safety is a prime factor, such as the steel castings in the ladder-hoisting mechanism of a fire truck, or the nuclear piping components of atomic energy power stations. The cast steel valves of Figure 31 are used in many industries where safety to personnel and equipment is mandatory at normal or high pressures and temperatures. co N 1 Fig. 31-Large cast steel valves. Valve body 10 ft. high. Minimum Machining Costs ... Steel castings can be cast very close to finished dimensions, which means low machining costs. The fifth wheel of Figure 32 which is used to couple a truck to its trailer must be smooth and true for slack free coupling. These castings are produced in large numbers to very close tolerances for such a large casting. In so doing, the machining and drilling have been eliminated. Furthermore, it should be pointed out that cored holes in castings materially reduce boring costs. Also, castings produced close to final contour minimize cam milling, boring, die sinking, planing, contouring and profiling machining costs. Economical Metal ... Steel is the lowest cost, highest strength metal available for modern construction. ADVANTAGES OF STEEL CASTINGS 23 Fig. 32–Fifth wheel casting used to couple a truck to its trailer. Ap- proximately 30 inches in diameter, section 138 inches thick, weight 220 pounds. Casting produced to close tolerances, eliminating machining and drilling. Low Cost Alterations ... Castings can be quickly altered if actual service conditions show design deficiencies by modifying the patterns and making other castings. Such procedures are ideal for pilot plant operations and are low cost compared to tooling charges of other processes. Minimum Tooling ... The casting customer makes no expenditures for presses, shears or other complicated tools if he builds his structures with steel castings. Minimum Product Weight ... Organizations, such as the American railroads, whose designers have had over 50 years' experience in using steel castings, employ low safety factors and secure lightweight parts with the weight distributed exactly where needed, such as, for example, the single piece brake beam casting shown in Figure 33. The brake . Fig. 33—Single unit brake beam casting for railroad freight cars. Over-all length 70 inches. Sections 1/2 to 11/2 inches. beam is perhaps the latest of a long line of steel castings for railroads which have reduced dead weight. This could run the gamut of side frames, bolsters, couplers, yokes, hopper door frames, and many others. A notable refinement relates to the redesign of the coupler knuckle of Figure 34 with a significant 20 percent weight reduction. Fig. 34—An E50-HT standard coupler knuckle for freight cars which supplanted the Grade B design. Lightening cores are used in the new design as shown and, together with the low-alloy steel employed, a 20 percent weight reduction was made without a change in the surface contour. 12 The knuckle acts as a protective "fuse" in the draft gear assembly and on occasion is subject to replacement in the field. Any weight reduction is obviously of benefit in such cases. Also, transportation costs of castings are minimized because of low weight. Flexible Production ... Steel castings are easily and quickly produced with minimum tooling costs. Steel castings have been made in very short runs of one to three in a couple of days to repair a breakdown. Such breakdown time delays are often very costly and can be minimized with steel castings, in which case the steel castings are of considerable economic benefit to the casting buyer. Sales Appearance ... All buyers of machines or structures like to purchase nice equipment with eye appeal. Modern steel castings are designed and produced with curved and streamlined shaping and smooth surfaces which would not be possible by fabrication. An example of an attractive looking steel casting of complicated design and exacting serv- ice requirements is shown in Figure 35. Fig. 35—One piece cast steel frame for oil field mud pump containing internal structural ribbing and bracing arrangements. Over-all length 44 inches. 00 i 25 A D V A N T A GES OF STEEL CASTINGS 1 SECTION IV Steel Casting Properties Compared to Those of Other Cast Metals Steel castings seldom compete in the market of the other cast metals. There are a few areas of overlapping in the ferrous metals applications but the main reason for these conditions is the lack of understanding of the properties and design scope of the different metals together with a realization of the costs of producing castings from the different metals. Each cast metal has its own distinct advantages and it is for these advantages that parts should be designed. There are cases where gray iron castings are converted to steel castings or steel castings converted to cast iron but, in all probability, they never should have been produced in the other metal in the first place. Patterns for cast iron castings have been sent to the steel foundry for production in steel because operating conditions of the equipment employing the iron castings have changed so that higher stress levels or sudden impact loads have been encountered. The casting purchaser is truly penalizing himself by using the same design for steel as he did for cast iron simply because he wishes to use the same old pattern. Differences in modulus of rigidity, strength, endurance, and toughness would result in low safety factors for steel as compared to the much larger safety factors necessary for the brittle materials. Sections, therefore, could be materially reduced and the weight lowered in cast steel as compared to the former cast iron design and, at the same time, accommodate the higher service stresses which made steel castings necessary. Conversion of steel castings to nodular iron can be another case of improper application of the use of the property advantages of cast metals unless all pertinent factors are explored. A part for dynamic stress application produced as a steel casting would be designed with a factor of safety of 4, whereas for nodular iron design engineers would consider that a factor of 12 should be employed for the same service, because nodular iron does not have the dynamic properties possessed by steel. Thus, on the basis of a 90,000 psi tensile strength material, the allowable unit stress would be: Steel 90,000/4 =22,500 psi Nodular Iron 90,000/12= 7,500 psi A conversion, therefore, should mean a redesign of the steel casting part to take advantage of the lower factor of safety that is widely used, and a section one-third of that employed for the nodular iron could be used. Likewise, it obviously would be unsafe to convert a part for 26 ADV A N T A GES OF STEEL CASTINGS dynamic service which has been properly designed as a steel casting into nodular iron unless critical sections are increased three-fold. Con- versely, a steel casting which can be safely converted to nodular iron without change is prime evidence of poor design and excessive weight, both of which are open to correction. It follows that no conversion can be intelligently made until a careful analysis of all pertinent engineering facts and properties has been made. Attributes of Cast Metals ... Aluminum alloys have a design advantage because of their lightweight, good strength, and good machinability. The strength-weight ratio of aluminum alloys requires that the tensile strength of steel be greater than 150,000 psi to be equal with aluminum on a weight-strength basis. However, costs may be an important factor. Copper-base alloys are of advantage in corrosion resistance, thermal and electrical conductivity applications. Only certain of the copper-base alloys, such as aluminum or silicon bronzes, can be hardened by heat treatment. Magnesium-base alloys are lighter than aluminum and can be heat treated to the same strength as aluminum alloys with excellent machin- ability. These alloys are more expensive than aluminum. Gray cast iron offers excellent casting characteristics, good machin- ability, and damping capacity. Malleable and pearlitic malleable irons offer a wide range of tensile properties with some ductility. Section size is limited to about 2 inches. Nodular iron is comparable to malleable irons in properties but is not limited as to section size. Interesting prop- erties are obtainable without heat treatment. Steel castings offer a wide range of properties (Figures 36 to 43), upward of 300,000 psi tensile strength in special cases with toughness, 300 280 260 STEEL 240 3220 STEEL NODULAR IRON NICKEL BASE TENSILE STRENGTH, 1000 e.si MALLEABLE IRON COPPER BASE NODULAR IRON 240 220 200 180 760 740 120 100 80 60 COPPER BASE NICKEL BASE 200 180 160 140 120 100 80 60 40 20 GRAY IRON H MALLEABLE IRON GRAY IRON ALUMINUM BASE MAGNESIUM BASE ZINC BASE IHH ALUMINUM BASE MAGNESIUM BASE ZINC BASE 20 0 Fig. 36—The comparison of tensile strength of cast metals as to the range possible for each metal. 0 Fig. 37—The comparison of the range of yield strengths for cast metals. ADV ANT AGES OF STEEL CASTINGS 27 70 STEEL 60 COPPER BASE 55 50 45 NICKEL BASE NICKEL BASE STEEL COPPER BASE NODULAR IRON ALUMINUM MALLEABLE BASE IRON NODULAR IRON 30 MALLEABLE IRON 20 Vall MAGNESIUM BASE ZINC BASE 10 GRAY IRON GRAY IRON 0 Fig. 38-A comparison of the range of tensile elongation usual in commercial cast metals. Fig. 39—Reduction area range compari. son of cast metals. Not applicable to aluminum, magnesium or zinc alloys. 70 800 STEEL STEEL 60 700 50 600 500 COPPER BASE IMPACT ENERGY, FT.-LB. (CHARPY V-NOTCH) BRINELL HARDNESS 30 NICKEL BASE 400 NOOULAR GRAY IRON IRON MALLEABLE IRON 300 TITIS 200 ALUMINUM BASE ZINC BASE 100 MAGNESIUM BASE 0 Fig. 40-A comparison of the range of hardness commercially found in cast metals. STEEL 30 NICKEL BASE MALLEABLE IRON NODULAR IRON 25 GRAY IRON 20 COPPER BASE MODULUS, MILLION p.s.i. 15 ZINC BASE ALUMINUM BASE 10 MAGNESIUM BASE 5 NODULAR IRON MALLEABLE IRON GRAY IRON Fig. 41—The Charpy V-notch impact prop- erty range of ferrous cast metals. Standard Charpy (0.394-inch bar with 45° notch 0.08 inch deep). Test too severe for nonferrous alloys. GRAY IRON MALLEABLE IRON w8bH2D8642 COERCIVE FORCE, OERSTEDS NODULAR IRON NICKEL BASE STEEL 1 0 Fig. 42—The elastic modulus of cast metals. Fig. 43—Coercive force range of iron and nickel base cast metals. 28 A D V A N T A GES OF ST E EL CASTINGS Table I Comparison of Certain Engineering Properties of Cast Metals Damping Capacity Casting Weldability Castability Machinability Steel Excellent Fair Fair Difficult Good Good Nodular Iron Difficult Excellent Good Gray Iron Excellent-About 10 times that of steel Difficult Good Good Malleable Iron Roughly related inversely Aluminum Base to the Highly suscep- tible to cracking Excellent Good to Excellent modulus of Copper Base Careful control needed Fair to Good elasticity Fair to Good Excellent Magnesium Base Readily welded- Preheat needed Good to Excellent Fair Fair Fair Nickel Base Difficult Excellent Excellent Zinc Base ADV ANT A GES OF STEEL CASTINGS 29 endurance, and ductility values exceeding anything that can be obtained by any other cast metals. Steel is weldable, machinable, and readily avail- able in various compositions for corrosion, heat and wear resistant applications, and for services at high and low temperatures. A comparison of the properties of the normally used cast metals is given in Figures 36 to 43, and in Table 1. The reader's attention is directed to the fact that a change in one mechanical property will pro- duce a change in another property; for example, as tensile strength increases, ductility decreases. These relations do not always readily appear when data are presented in tabular or bar graph form. SECTION V Advantages of Steel Castings Compared to Other Methods of Steel Forming Steel castings can be substituted for steel as weldments, forgings, machined from bars or plates, or bolted or riveted construction, because steel has similar properties regardless of the form of construction. A 100,000 psi tensile strength forging can be duplicated as to similar prop- erties in a weldment or a casting or a part machined from bar stock. The major reason for differences in the methods of steel fabrication is that a design often lends itself to one form of fabrication more easily than to another, and perhaps at less cost. This condition is especially true if the design engineer has a particular method of fabrication in mind when the structure is designed. Steel castings have greater design freedom than other methods of steel fabrication because a casting is the most direct method of trans- posing the design into the finished part. Naturally, there are certain metallurgical advantages of the casting process over those of other methods of steel forming, and the economical advantages have been listed in Section III of this chapter. The following are summarized lists of the design and metallurgical advantages of steel castings as compared with steel sections produced by other methods of forming: Steel Castings vs. Weldments Greater Design Freedom with Steel Castings 1 - Tapered wall sections, compounded curve construction, in- ternal curve construction, cored holes and passages are avail- 30 A D V A NTAGES OF STEEL CASTINGS able when steel castings are employed. The design freedom of the dynamo casting, as illustrated in Figure 44, is an example of what may be secured by designing with steel castings. Fig. 44—Dynamo steel casting for power shovel. 40 inches diameter. - 2 – Thick sections adjacent to thin sections can be easily made such as, for example, the addition of bosses and bearing blocks. Weldments are limited by the thickness of the rolled plates employed. 3 The use of complicated sections in a design is uneconomical for weldments, especially when large amounts of welding are required. Complicated sections are produced easily as steel castings. 4 - The streamlining of a part for fluid flow is more easily accom- . plished by employing steel castings. 5 — Steel castings have reduced localized stress concentration be- cause of the smoother curved construction, well-radiused fil- lets, and section junctions. Figure 45 is a comparison of the stress concentration in a steel casting and weldment fillet. Fillets prepared by welding are flat as shown in the photo- elastic models and, therefore, may produce two sharp notches where the weld metal joins the plate. 6 - Greater structural rigidity is an inherent attribute of steel castings because of the design freedom resulting from local increasing of section thickness when necessary. 7 — Fewer internal stresses usually exist in steel castings than in fabrication weldments. Steel castings are usually stress A D V A N T A GES OF STEEL CASTINGS 31 (a) A fringe order of 3 results for a 3.39 pound load for the casting corner. (b) A fringe order of 31/2 for a 3.39 pound load for the weldment corner. (c) Method of laying the weld. Welds form a flat surface whereas castings can be produced to non-stress raising fillet radius. a Fig. 45—Corner design as produced in commercial steel castings and weldments as determined photoelastically. Weldment is 86 percent as strong as the casting. - relieved or heat treated whereas weldments are seldom stress relieved. 8 — Less distortion is encountered in steel castings than in weld- ments because of the localized effect of the heat of welding. 9 — There are no joints in steel castings, and since no human element is involved in joining, as in welding, no leaks or partial lack of attachment can occur. 32 ADV ANTAGES OF STEEL CASTINGS - 10 — No misalignment or other assembly errors are possible in the use of steel castings. 11 — Appearance appeal in steel castings is readily obtained by curves, curved edges and streamlining. - Wider Range of Metallurgical Properties with Steel Castings 1- The strength ranges possible for steel castings are not limited to weldable compositions and low strengths which is the case of low-carbon and low-alloy composition weldments. 2-Steel casting compositions are not limited to those available in rolled plate, and may be attained in any special alloy from small heats, such as austenitic manganese steel, other wear resistant steels, and special high-strength steels. 3 — Weldments have directional fiber and the grain structure of rolled plates, thereby resulting in lower transverse tensile properties than those obtained in the direction of rolling. Steel castings have the same properties in all directions. Steel Castings vs. Forgings Greater Design Freedom with Steel Castings 1— Large forgings usually are limited to simple shapes, such as blocks, cylinders, bars or rings. Internal passages in forgings require extensive machining. Such conditions do not occur in the case of steel castings. For example, Figure 46 shows a large steel casting in a shape which is not economically pro- duced as a forging. Reel por- Fig. 46—Cast-forged reel arbor casting to coil sheets from a strip mill. The arbor is 18 feet long, 10 inches in diameter at small end, and 28 inches at large end. tion is extensively cored and, necessarily, a casting from econom- ic standpoint. Spindle portion was cast as a large cylinder and then forged down to the spindle. ADV ANTAGES OF STEEL CASTINGS 33 2— Drop forgings are limited to die contour possibilities. Re- entrant pockets or internal passages must be formed by machining. Steel castings are not limited to these design restrictions. 3 - Forging size and weight are limited by available forging presses. Steel casting size is unlimited, except by transpor- tation facilities. 4— Large open die forgings are usually not supplied as close to finished contour as are steel castings and hence are subject to considerable machining time and costs. - 5 — Die forgings are not economical in few numbers or adaptable to alterations because of the high die costs. Single steel cast- ings are economical, and alterations of patterns are easily and quickly made at low cost so as to permit another casting to be made. Wider Range of Metallurgical Properties with Steel Castings 1- High-carbon, high-alloy steel compositions are difficult or impossible to forge but are readily cast. This group of steels includes abrasion-resistant, heat-resistant, and corrosion- resistant grades. 2 — Forgings have directional fiber and grain structure, resulting in low transverse properties. The forging directional flow lines are often a disadvantage when the forging has been ex- tensively machined, as the machining cuts deeply into such flow lines and results in the entire part having low properties in the direction transverse to forging (see Figure 47). Steel castings have no such directional variations, but have uniform properties in all directions regardless of the direction or amount of machining. Fig. 47—Section of a forging which kas been etched with H2SO, to show the direction flow (fiber) lines. The part has subsequently been ma- chined leaving the section (shown by the arrow) with the fiber par- allel to the direction of applied stress; the result being that the part is greatly inferior in shock-resisting properties. 34 ADVANTAGES OF STEEL CASTINGS 3 - The surface of a forging often may be at a low hardness because the surface is deeply decarburized as a result of the high forging temperatures employed and the numerous heat- ings given during the fabrication of the forging. Riveted, Bolted, Threaded, Plate and Bar Construction Greater Design Freedom with Steel Castings 1- The designer is limited to the bar and plate thicknesses pro- duced and available in rolled sections when he uses bar and plate materials in bolted construction. 2 — Tapered wall thickness, compound curves, internal curves, and cored construction are available with steel castings. Shapes produced from bars and plates must be machined out of parallel-walled sections or limited to possibilities of bending or punching forming operations. - 3 — Assembly of machined sections from bars and plates, to pro- duce a composite structure, can be much more expensive than a single component in a complex shape such as a steel casting. Also, from an assembly and economy standpoint, when parts are desired in numbers, it is better to build with steel castings. Figure 48 shows a steel casting which has replaced a built-up part held together with fasteners. a 2898 was con- Fig. 48—Whizzer bar for a clay separator chamber. Main portion of the fabricated bar is 3 sections of rolled steel bolted together. The part verted to a steel cast- ing at the same weight but outlasts the fabri- cated design 21/2 times. A total cost saving for a set of 144 castings is $918.00. 28962 1 2 34 5. 6.7 89 10 11 11 13 ADV A N T A GES OF STEEL CASTINGS 35 (a) (b) Fig. 49—Truck equalizer bars for locomotives have been shaped from: (a) rolled plate by burning and machining. A conversion to (b) steel castings resulted in the saving of 2000 pounds of dead weight per locomotive with no increase in cost. 4- The joints and overlaps in riveted and fastener construction result in stress concentration at the joint and fastener posi- tions. There is also the possibility of leaks with this type of construction, and detachment of parts through failure of the fastener is always a possibility. 5 — There are no misalignment or assembly errors if steel cast- ings are employed. 6 — Steel castings permit greater rigidity than fastener construc- tion, because there is continuity of contact at all points in a steel casting structure. 7- Curved construction, curved edges, and streamlining, such as are easily obtained in steel castings, result in attractive ap- pearing structures with greater sales appeal and often result in weight savings over plate construction (see Figure 49). CHAPTER II INDUSTRIAL APPLICATIONS OF STEEL CASTINGS Steel castings are produced regularly from thousands upon thou- sands of designs for use in many industries. They fill a definite need in all the commonly known industries such as transportation, construc- tion machinery, earth-moving equipment, rolling mills, mining, and the petroleum industry. Steel castings are used in the various processing industries where high and low temperature and pressure are encoun- tered, such as refineries, chemical plants, food and drug processing, and the power generating industry. They are also used in the new glamour applications of the modern day such as atomic energy power plants (whether land-based, marine or submarine), and in missiles and aircraft of all types. New uses for steel castings are constantly being discovered so that any list of the industry's products becomes incomplete almost as soon as tabulated. Thus, to name even the more important castings in the major product classification would require many pages. However, for practical purposes 17 major classifications of steel castings have been established, grouped according to end use. The steel casting market, with a nominal yearly sales volume of 1,500,000 tons fluctuates from 2 to 3 hundred thousand tons each year. Therefore, the major use classification varies somewhat as to its share of the market; but those classifications with the highest percent of the total usually remain the leaders. The distribution chart of Figure 50 shows the percent of the total of steel castings produced for the 17 different major end uses based on an average for the years 1950 to 1959. UNCLASSIFIED 1.98% GEAR, PINION & WORM CASTINGS 1.28% SPECIAL MACHY., PRODUCTS & COMPONENTS 4.55% MATERIAL HANDLING 1.63%, SHIP & MARINE 1.32% -AGRICULTURAL EQUIP. .96% ROLLING MILL 10.42% Fig. 50—Distribution chart of 17 major end uses of steel castings. MOTOR VEHI. CLE 3.86 % CONSTRUCTION CONSTRUCTION MACHINERY & ( STRUCTURAL EQUIPMENT COMPONENTS) 13.05 % .49% MINING & CRUSHING MACH'. 5.16% METAL SHAP FINISHG & FORMG. 2.66 OIL ELECTRICAL GAS MACH'V. & FIELD, EQUIP. 3.08% VALVES & RUBBER MILL MIL- PIPING CASTINGS.81 % ITARY 6.15% 5.54% RAILROAD. 36.06 % INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 37 The photographs used for illustrative purposes in the following pages were selected to show the characteristic types of steel castings in the 17 major classifications and to give the reader an understanding of the actual application, the range of size and complexity, and the differ- ent varieties of steel casting shapes that are produced. This array of illustrations may well stir the reader's imagination in the direction of new and broader applications. Attention is directed to the fact that the representative applications of steel castings covered in these pages are the answer for engineers whose design problems call for parts or integrated structures capable of providing outstanding physical and mechanical properties and of performing under varied and rugged service applications. Railroad Castings ... The railroads are the oldest customers of the steel casting industry in the United States, and the use of steel castings in this vital segment of our transportation system is being constantly broadened and diversified. This is only natural because railroad equip- ment is subjected to rougher usage than that of perhaps any other indus- try. Steel castings excel in this service, where resistance to shock and fatigue, high tensile strength and all-around toughness must be coupled with minimum weight. It goes without saying that safety of human life, protection of cargo' and operating economy are prime requisites in railroad equipment. That is why steel castings are used for the vital parts of freight cars, passenger cars and locomotives. An example well illustrating this statement is the list of the steel castings used in the construction of an automobile freight car as shown in Table 2. Table 2 Steel Castings Used in Construction of One Automobile Freight Car. Class A-50-13 Steel Casting Classification Unit cast steel brake beam Truck side frame Bolsters Truck side bearing Coupler Coupler yoke Coupler centering device Draft lug Draft gear (cast steel parts) Back stop and center filler Gear driver bracket Weight per car set, pounds 472 2450 1650 108 850 430 85 175 350 436 14 Total 7020 Fig. 51–6-wheel motor truck frame for Diesel locomotive. Length ap- proximately 18 feet and width about 8 feet. Steel castings are used for many of the vital parts of Diesel-electric and steam locomotives. Figure 51 is a 6-wheel motor truck frame casting for a Diesel locomotive. This structure is an integral one-piece casting best suited to meet the dynamic loads experienced in railroad service. Figure 52 illustrates a steel casting housing for the direct current trac- tion motor of a gas turbine locomotive. Fig. 52–Direct current traction motor for a gas turbine locomo tive. Pinion end view. Frame is about 242 feet wide. The all important couplings which fasten all locomotives and cars are made up of an assembly of several steel castings (see Figure 53). These castings must, and do, possess the toughness and strength to absorb the impacts and stresses of starting and stopping trains which Fig. 53—Details of the coupler casting. Fig. 54—A schematic view of the location of the coupler, striker and draft gear, truck side frame and bolster on a freight car. w PATENTES AARS-285 MONS A. NANALO frequently exceed 150 cars in length. The draft gear assembly illustrated in Figure 54 acts in the nature of a two-way shock absorber as it trans- fers the loading from coupler to car, or vice versa. These assemblies largely consist of steel castings which, over a period of many years, have proved their ability to withstand the extremely rough usage to which they are subjected in this service. Properly speaking, the coupler is a part of the complete draft gear. It is the only component normally visible, since the other parts are enclosed in the center sill of the car. The freight car truck side frames illustrated in Figures 54, 55 (a) and (b) are of one-piece cast steel construction. All three employ the NCASIL RY CF-51 PATELTED AAR 38 - (a) Truck side frame of integral journal box design, for use with plain journal bearings. (b) Truck side frame of pedestal design for application of roller bearings. Fig. 55—Truck side frame for freight cars. Size of side frame approximately 75 x 18 x 28 inches, weight 750 pounds. 40 INDUSTRIAL APPLICATIONS OF STEEL CASTINGS Fig. 56–Freight car truck bolster is 7 ft. 8 in. long. Weight 700 to 1200 pounds depending on design and load capacity of car. channel section, truss type design which has been time-proved by many years of satisfactory service in this vital application. The frames pic- tured in Figures 54 and 55 (a) are of the integral journal box type to accommodate the plain journal bearings which have been used almost exclusively in the past. The current trend is toward roller bearings, which possess the advantages of easy starting and practical freedom from hot boxes. The tight schedules and high-speed operation of today's freight trains are materially accelerating this trend. Figure 55 (b) illustrates a truck side frame designed specifically for the use of roller bearings. These are supplied as complete assemblies and inserted in the pedestal jaws at either end of the frame. Each of these truck side frames (Figures 54, 55 (a) and (b)) embodies friction control of load spring action, and permits the use of softer, long-travel springs. This combination of friction snubbing and soft springs largely protects the car body and lading from road shocks. While details may differ, friction is applied through hardened, cast steel shoes which are spring-loaded to give constant pressure against truck side frame and bolster columns. Renewable wear plates are also applied to either bolster or frame columns, depending on the location where greatest travel and consequent wear is known to occur. In the case of the side frame pictured in Figure 55 (a), wear plates are applied to each column. The bolsters shown in Figures 54 and 56 are of modern design, incorporating the friction control of load spring action discussed in connection with side frames. In each instance hardened steel wear plates are applied to the columns at the box section ends. The bolster of Figure 56 (which mates with the frame of Figure 55(b) clearly shows this application. The sizes of the trucks and truck parts vary depending upon the car design and its load capacity. For example, Figure 57 illustrates the double six-wheel truck with one-piece span bolster. This truck was designed for heavy duty cars of 290 tons load capacity. Fig. 57—Double six- wheel truck with one- piece span bolster, used on freight car of 290-ton load capacity. Golon INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 41 Fig. 58—Railroad freight car wheel, 33 inches diameter. Sections of from 1 to 7 inches thick, weight 610 pounds. 1 1 The railroad freight car wheel (Figure 58) is a steel casting of approximately 0.75 percent carbon content and 130,000 psi tensile strength, and is designed and specially cast to produce a wear resistant part for long service. Freight car underframes are frequently one-piece steel castings such as shown in Figures 59 and 60. High rigidity and resistance to dynamic stresses of all sorts are required of these parts. The stand- ard one-piece underframe of Figure 59, designed for flat and bulkhead cars, is built in lengths of 42, 53 and 60 feet. They are designed for maximum strength at minimum weight, and to provide a low car height from the rail. The simplified construction gives freedom from mainte- nance and long service life. The underframes for low platform cars of Figure 60 permit loads of maximum height. The one-piece steel casting provides great strength to meet varying stresses of heavy concentrated loads with minimum deflection. Cars of varying lengths are built in wide capacity ranges of 70 to 250 tons. Figure 61 illustrates the one-piece underframe end casting for a 70-ton mechanical refrigerator car. The body bolster, draft gear stops, striker, center filler, coupler carrier, body centerplate, and side bearing pads are all integrally cast into a single piece of steel. Fig. 59—One-piece cast steel underframe for a 50-ton capacity flat or bulkhead car. Casting 531/2 feet long. XS VANIE 299 NOK Fig. 60—One-piece steel casting underframe for a 125-ton depressed center freight car. Fig. 61–One-piece undertrame-end steel casting for a 70-ton mechanical refrigerator car. Width 7/2 feet. Certain railroad castings have become highly standardized through the application of many years of engineering and research by railroads and the steel foundries. Such castings are subjected to individually designed tests for which elaborate static and dynamic testing machines have been developed. All railroad castings are subjected to rigid inspec- tion before being placed in service. The record of long life and satis- factory performance of steel castings is well known to railroad designing engineers everywhere. The enumeration of all the steel castings for railroad service would require the naming of a large number of structural and operating parts, in fact, upwards of 250 steel casting classifications. For example, a steel casting used in large numbers of design variations is the hopper frame shown in Figure 62. From four to eight of these frames are used for each hopper car. Specifications most commonly used in the procurement of steel castings for railroads are those promulgated by the Association of American Railroads, Chicago, Illinois. INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 43 gon Fig. 62—Railroad hopper car door frame with integral door hinges. Size, approximately 3 x 4 feet, weight 150 pounds. - Track components such as automatic switching units, cross-over frogs (made of 12 - 14 percent manganese cast steel), and splicing bars are produced from assemblies of steel castings or from integrally cast units. Figure 63 is an assembled car retarder used in freight car switching. Most of the parts seen in the illustration are steel castings. The splicing bars, or step link castings, Figure 64, are used in large numbers to tie together track of various sizes and weights. Fig. 63—Car retarder for switching freight cars. All major parts are steel castings. The rail runs through the center of the two retarder bars. Fig. 64-Splicing bar steel castings to tie together track of various sizes and weights. Castings vary from 18 to 30 inches long. I 2 *** Steel castings are used in many other phases of the rail transporta- tion industry such as in subways and other rapid transit cars. The kingpin, Figure 65, rests directly on the car and is welded to the under- frame. These castings have been test loaded to 152,000 pounds. Construction Machinery and Equipment ... Equipment for earth re- moval, road building, and construction work receives very rough han- dling in the field. This equipment requires the maximum of dependable strength, shock and abrasion resistance, and weight economy. These qualifications can best be met with steel castings having proper compo- sition and heat treatment. Many parts of power shovels are steel castings such as, for example, the car body of Figure 66. Deck rings and rail segments on small to large power shovels are steel castings. Power shovels must withstand Fig. 65—Kingpin casting for rapid transit service. Length 36 inches, weight 400 pounds. Fig. 66—Power shovel car body. Dimen- sions 18 ft. x 11 ft. x 2 ft., weight 33,200 pounds. f Fig. 67—Underneath view of a crawler tractor showing deck, treads, and other steel cast- ings. Tractor body is 4 feet long and 3 feet wide. CH exceedingly high loads in operation because of the very nature of the service they are called upon to render. They are often operated at great distances from repair facilities, and because continuity of operation is of great importance, it is necessary that all parts be rugged and capable of taking severe punishment. Steel castings provide an admirable answer to these problems. Moreover, when service failures occur because of unusual loading conditions, steel castings can be readily repaired by welding, thereby reducing any interruption of operations to a minimum. The one-piece frame, body or deck castings, such as shown in Figure 66, assures permanent alignment for operating mechanisms such as shafts and bearings. Figure 67 is a rugged crawler used in underground mining and general construction where it is subjected to severe operating condi- tions. It is built almost entirely of steel castings. The photograph is an underneath view showing the rear drive portion of the deck casting and several other steel castings, including the tread castings. The steel castings in the crawler combine the advantages of design freedom, shock resistance, dimensional uniformity and low end costs. Several different designs for crawler wheels for power shovels are illustrated in Figure 68. These wheels are steel castings. Fig. 68-Crawler wheels for power shovels. About 21/2 feet in diameter. 0 Fig. 69—Dipper bucket with removable cast steel dipper teeth. 342 cu. yd. size. - Dipper buckets (Figure 69) are produced from 12 - 14 percent manganese steel castings. The teeth are replaceable and are made of low-alloy, high impact, wear resistant cast steel having strengths of over 225,000 psi. Road building and land clearing equipment is subjected to every imaginable type of impact and torsional stress such as occurs on striking rocks, tree roots and snags of all types. Many of the important, heavily stressed parts of scrapers, bulldozers, ditchers and trencher machines are steel castings. Figure 70 is the drive housing for a heavy duty tractor. This steel casting houses the drive sprocket and shaft assembly. Fig. 70–Drive housing casting for heavy duty tractor. Width 25 inches. Fig. 72—Rear wheel hub for road- building scraper. Diameter 32 inches. Weight 580 pounds. Fig. 71–Grid roller castings for compaction of earth fills. Drums outside diameter 67 inches, width of each drum 32 inches. Figure 71 is a grid roller for compaction of earth fills. The grid casting permits pressure to act on the earth and confines the movement to within the 31/2-inch square openings between the bars so that mass displacement of the fill material is avoided. Each wheel is made up of 10 alloy steel grid sections with 11/2-inch diameter bars appearing as woven open mesh. The castings are heat treated to over 300 Brinell hardness. The steel casting of Figure 72 is the rear wheel hub on a large and rugged earth scraper for highway construction. This steel casting is 32 inches in diameter. The bulldozer bracket casting of Figure 73 is produced to a mini- mum of 150,000 psi tensile strength and is held to close hardness limits. Service stability, shock resistance, and dimensional uniformity combine to give the bulldozer manufacturer a high-quality, low-cost steel casting. Weight 765 Fig. 73—Bulldozer bracket casting. pounds. Fig. 74–Drum clutch spider for a power shovel. 40-inch diameter projecting flanges at each end of a 12-inch diameter hub. Figure 74 is a photograph of a drum clutch spider for a power shovel. A 1/2-inch tolerance between the two flanges is maintained. The yoke casting (Figure 75) in a road building tractor is a very highly stressed part; however, the streamlined design of this part prevents high stress concentrations in critical locations. Close tolerances are required for this rather long and wide steel casting. Steel castings are performing satisfactorily on the tough construc- tion jobs of industry where severe stresses are encountered. When prop- erly designed and of correct specifications they usually can replace, economically, other types of construction and materials. Rolling Mill and Steel Castings... There are few industries which must use as much energy in the process of manufacturing as does the steel industry. Ingots weighing many tons are pressed or forged between dies, or are run between rolls where, in a series of passes, they are reduced to billets and then to bars, plates, sheets or various other shapes. The terrific squeezing action on the hot metal calls for equipment having the strength and toughness properties that only steel can give. Modern rolling mills are of the continuous type in which any breakdowns are Fig. 75-Yoke casting for a roadbuilding tractor. Length 34 inches, width 22 inches. Weight 355 pounds. Fig. 76-98-inch four-high continu- ous strip sheet mill in which cast steel parts are identi- fied. ont-26 A Screwdown Cap B-Screwdown Cover C-Housing D-Housing Separator E Chuck |F Back-Up Roll 0-Spindle Carrier H. Pinion Stand Cap K Pinion Stand Housing 6 exceedingly costly, and it is for this reason that the producers of wrought steel products have selected steel castings for such widespread use in rolling, forging, and other plant equipment. They have learned over the past years that steel castings are dependable and rugged, and possess the strength and toughness properties that are necessary for steel plant services. Indeed, the tonnage of steel castings sold to the steel mills is third in the list of general end use classifications of consumer industries. Rolling mill housings, rolls and many supplementary parts of steel plant equipment are steel castings. The rolling mill illustrated in Figure 76 consists of numerous steel castings. The pinion stand (Figure 77) is constituted of a number of steel castings — the housing weighing 13,750 pounds; 3 half-end covers of approximately 230 pounds each; 2 universal spindle couplings, 1400 pounds each; flexible coupling, 1200 pounds; spindle bearing and carrier castings, 500 pounds; and miscel- laneous cover and clamp castings. The multi-directional properties of steel castings permit the parts to excel for the severe service conditions to which this equipment is subjected. Four such pinion stands are required for each 4-stand mill. - Fig. 77—Pinion stand, one of four in a 4. stand mill. Over-all height 61/2 feet. Each stand contains 12 steel castings weighing 25 to 13,750 pounds. 11.11. Fig. 78—40-inch slab- bing mill and drive equipment consist mostly of steel cast- ings. The 40-inch slabbing mill with motor drive installations, as illus- trated in Figure 78, contains many different steel castings; in fact, practically all of the structural parts, housings, and rolls are steel castings. Some very highly stressed mill housings are produced as steel cast- ings. An example is the Sendzimir mill housing illustrated in Figure 79. Also, many of the rolls employed in rolling mills, an example of which is shown in Figure 80, are steel castings. Cast steel roll manufacture represents a substantial specialty industry. Most of the rolls are com- pletely machined and ground to a mirror-like finish. A new and interesting development is the sintering pallet with grate bars as shown in Figure 81. Iron ore fines, limestone and coke breeze are combined by sintering to produce a properly fluxing charge for blast Fig. 79-Sendzimir mill housing. Weight 46,250 pounds. Ap- proximately 5 x 8 feet outside dimensions. Fig. 80—Back-up roll for 4-high plate mill. Roll size, 54 x 128 inches, weight 109,740 pounds. Fig. 81–Sintering pallet with grate bars for sintering ore and fluxes for the blast furnace. Width of pallet 6 feet. The grate bars of heat resistant cast steel are cast separately. furnaces. The pallet frame, side plates and wheels are steel castings. The grate bars are a heat resistant cast steel composition of 0.85 per- cent carbon, 1.25 percent silicon, 1.75 percent nickel and 0.30 percent chromium. Other compositions also are used. Sintering temperatures are slightly below 1900 degrees F. Equipment used in the steel mills for stripping ingots from the molds and handling these ingots in and out of the soaking pits and furnaces consists largely of steel castings. Machines for such operations are illustrated in Figures 82 and 83. Steel castings are employed as the major parts of these machines because they can take the rough service that is the normal role of this equipment. Blast furnace bells and hoppers are produced traditionally as steel castings. Figure 84 shows various size bells and a hopper ready for shipment. Another blast furnace accessory is the cinder pot illustrated Fig. 82 — Soaking pit tongs that are to be operated from crane. Fig. 83—Ingot stripper and extractor on a 400-ton crane. in Figure 85. Corrugated pots of this type can be produced only as steel castings because of the extended core areas. Oil, Gas Field, Valves and Piping . Steel castings for the petroleum industry are used for heavy machinery and pressure parts. The heavy machinery castings include compressors, pumps, rotaries for drilling, and machines for the handling and pulling of well casings. The require- ments for heavy machinery castings are particularly exacting with the deep well drilling that is necessary today. Steel castings are being Fig. 84—Bell and hop- per steel castings of various sizes for use in blast furnaces. Fig. 85-400-cubic foot corrugated cinder pot. Weight about 40,000 pounds. utilized in an ever increasing number of applications in oil and gas field equipment requiring high strength and dependability with a minimum of weight. An example of the severe service requirements is the drilling of oil wells in the ocean. The steel castings shown in Figure 86 form important segments of the mechanical unit which lowers, drives and extracts the piling or hulls of the oil drilling barges. The bowl castings are a part of the barge jacking unit and are connected to piston rods. The piling passes through the bowl. The bowl components, prepared as steel castings and assembled by cast-weld construction, are shown in Figure 86. Pumps and compressors consisting of steel castings are employed in oil fields and refineries, for example, the fluid end castings for mud pumps shown in Figure 87. These castings are produced from a low- alloy steel of minimum tensile strength of 85,000 psi. Another example is the slush pump shown in Figure 88. The complicated steel casting on the fluid end is tested at 6000 psi although normal operating pressure is 2200 psi. Smooth, full streamlined passage contours give unrestricted flow and increase the efficiency of the slush pump. There are no welds, no square corners to produce turbulence and cavitation. Here again, the design freedom of steel castings has allowed the production of an end product not subject to the deficiencies of other fabrication methods, and further, has resulted in a product with long life, low maintenance and low weight. Castings are employed for pressure parts in the oil refineries, as well as the oil fields. Working pressures are some of the highest ASSEMBLY TAR UPPER BOWL Fig. 86 — Steel cast- ings for barge jack- ing units used in off- shore oil drilling operations. FIN LOWER BOWL Fig. 87—Fluid end steel castings for mud pumps. Weight 3260 pounds. encountered in any industry and steel castings have proved satisfactory for such service. The requirements for pressure castings for refinery applications are extremely varied, often including factors such as: corro- sion resistance, high strength with good shock resistance, heat resistance up to high temperatures, pressure tightness at low and elevated tempera- tures, weldability, and creep resistance at elevated temperatures. Steel castings of various carbon and alloy compositions can meet these requirements and are being produced to rigid specifications. Figure 89 is a six-stage pump with a 5-inch discharge installed in a petroleum refinery. The pump casings, valves and fittings are steel castings. This unit pumps 1650 gallons per minute of absorber oil at 120 degrees F against a total head of 2370 feet. Fig. 88—Single piece steel casting as the fluid end of a slush pump. Fig. 89—Six-stage petroleum refinery pump. Casings, valves and fittings are steel castings. C Fig. 90-A Christmas tree for an off-shore oil well consisting of steel castings. Over-all height approxi- mately 23 feet. Working pressures range up to 10,000 psi. The oil well “Christmas tree” of Figure 90 is one of the largest that has been assembled. It is a pressure control arrangement consisting of valves, fittings, flow heads, choke flanges, and clamps. The bottom por- tion of the assembly was designed for an offshore well which contained six strings of casings ranging in size from 7 to 36 inches, outside diam- eter. The upper portion of the assembly was designed for a dual com- pletion with two strings of 23/8-inch tubing. Working pressures for the assembly range upward of 10,000 psi. The compressor cylinder shown in Figure 91 is a part which is very complex internally. It was simplified by producing the part as two steel castings and welding them together. The assembly was then subjected to radiographic and magnetic particle examination, and hydrostatically tested at 1800 pounds. Greater safety and dependability have been achieved through the use of steel castings, and compressor units operate with increased capacity with only minor design modifications. Fig. 91-A cast-weld compressor cylinder for operating pressures of 1150 psi. Length 7 feet, weight 12,000 pounds. Fig. 92—12-inch plug valves installed on gas scrubbers. Fig. 93—8-inch cast steel 600-pound steam pressure gate valves for oil re- finery use. The electric power industry, water works and most manufacturing plants, as well as oil fields and refineries, use steel valves and piping castings. These steel castings are called upon to handle various corrosive liquids: steam, gases, oil and gasolines and acids at sub-zero and elevated temperatures. Moreover, they must operate under pressures ranging from partial vacuum to high pressures of several thousand pounds per square inch. Valves and piping castings operating under extremely high pressure and temperature conditions must be absolutely trustworthy, otherwise human life would be endangered. Steel castings are universally used for valves and fittings because they are produced from steels and designs that meet the exacting requirements of temperature, pressure and corrosion demanded by the service conditions. Cast steel valves and fittings are made in sizes ranging from a few pounds to many tons. There is a wide variation in the designs of valves and piping components. Figure 92 shows a series of 12-inch, worm-gear operated, plug valves installed on gas scrubbers in a compressor station. Figure 93 is a photograph of 8-inch, 600-1b. cast steel gate valves with chain wheels and roller guides as used in an oil refinery, and Figure 94 shows a 300-lb. cast steel gate valve installation in a refinery. Specifications for valve and piping steel castings are those adopted by the American Society for Testing Materials, and the American Standards Association. Special Machinery, Products and Components ... Steel castings are employed by a number of industries in machinery and components. These industries have been grouped together under this heading since the steel castings are of special design for the machinery or products of these industries. Fig. 94—300-pound steam pressure cast steel gate valve. 1 A new field is that of nuclear energy. Of course, steel castings in the form of valves and piping components are employed in the nuclear energy power applications, but there are also other classifications of castings used in connection with nuclear energy power equipment. An example is the pump casing of Figure 95 which is an important part of a nuclear reactor primary coolant pump. Three of these casings are used for each reactor, as well as a number of other steel castings, namely, impellers, diffusers and thermal barrier castings. Various types of ring castings have been produced for reactors. All these steel castings receive 100 percent radiographic and dye penetrant inspection. Diesel engine castings are used in a number of industries. It is next to impossible to build an engine without using steel castings in the design, and they are found in great numbers in every type of power unit. Steel castings are ideal for use in engine parts because they com- bine the advantages of high strength, high rigidity and fatigue resistance into one structure that can withstand high pressures and temperatures. Figure 96 shows a six cylinder straight-in-line Diesel engine crankcase Fig. 95—Nuclear reactor primary cool. ant pump casing. 47 inches O.D. at top, 5-inch thick wall section. cent chromium, 8 percent nickel steel casting. 18 per Fig. 96—Six cylinder straight-in-line Diesel engine crankcase. Weight 4600 pounds. aba Fig. 101-Logging-rigging castings. Choker socket and sling hook for l-inch cable. 1 Fig. 102-High-speed impeller for refrig. eration equipment. Operates at 12,500 rpm. Refrigeration equipment requires parts that must have excellent properties at sub-zero temperatures. There are several cast steels of varying compositions that will produce the required properties. An example of the steel castings required for refrigeration equipment is the third-stage high-speed impeller of Figure 102 which attains speeds of 12,500 rpm. This particular casting was produced in a ceramic type mold to obtain close tolerance dimensional control, as well as fine surface finish. Steel castings for pressure containing parts suitable for low tem- perature service are often ordered to the specification requirements of ASTM A352. Food processing equipment incorporates steel castings for bakery machinery, bottle washing and filling machines, candy making, dairy equipment, and meat packing machinery. Figure 103 shows stainless th Shaft tapering from 3 Fig. 103—60-inch long stainless steel screws for a macaroni press. to 2% inches while maintaining a 6-inch diameter flight. Fig. 104—Bowl, cover and lock ring cast- ings for a centrifuge separator for pro cessing starch. Diameter 40 inches. steel screw castings for a macaroni screwpress. The use of steel castings for screws permitted the angles and pitch on the flights to be produced as designed. Such conditions were not possible by any other fabricating method and in this instance, castings improved the operation of the machine and a higher quality product was obtained at a lower cost. The machine production costs also dropped considerably. Another example of steel castings in food processing machinery is Figure 104 showing the bowl, cover and locking as parts of a centrifuge used as a separator in the processing of starch. The separator develops up to 9000 times the force of gravity and runs continuously for periods of 24 hours. Sugar mill equipment includes many heavy steel castings among which are gears, shredders and digestors. Figure 105 shows an assembled sugar mill. In the center foreground, assembled in place, OD Fig. 105–Assembled sugar mill. Structures seen are steel castings. Fig. 106- Planetary strander cradle steel casting for wire rope machinery. are the following steel castings: bedplates, mill housing, top and bottom roll bearing chairs, side caps, top cap, and roll shells. Steel castings not shown are gears, hydraulic cylinders and returner bar. Sugar mills are often situated in remote places, such as Hawaii, Puerto Rico, and Cuba where breakdown would occasion excessive delay before repairs could be made, and because of these conditions mill operators have found steel castings practically indispensable for equipment because of their dependability. A special machinery part is the planetary strander cradle used in wire fabricating machinery (Figure 106). A number of steel castings are employed in wire manufacturing equipment as wire rope and cable accessories. Many different steel castings form parts of foundry equipment such as shown in Figure 107 illustrating a jolt-rollover and draw machine. Such machines are made in various sizes from 20 to 30 inches with 750 pound rollover capacity to 10 to 12 feet with 40,000 pounds rollover capacity. Individual steel castings in the equipment illustrated include turnover plates, arms and extensions, links, flask clamps, equalizers and beams. Another interesting foundry equipment machine is the automatic soil pipe machine shown in Figure 108. This machine has about a Fig. 107—Steel castings are the main parts of jolt-rollover and draw molding machines for the foundry industry. INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 63 Fig. 108-Automatic soil pipe machine for the foundry industry, containing 163 steel castings representing about 75 percent of the machine weight. thousand different parts of which 163 are steel castings representing about 75 percent of the weight of the machine. The reason for using steel castings is because of the excellent combination of strength and toughness, and the ease with which they can be welded to other components. Ruggedness and strength, abrasion and impact resistance are prime requisites for equipment application in the foundry. It is for these reasons that steel castings are universally employed in machines for foundry use. The heat treating and industrial furnace equipment industry em- ploys many steel castings as furnace parts. A large proportion of these parts is produced from heat resistant steels such as the roller shaft assembly for annealing furnaces as illustrated in Figure 109. These shafts are produced in various lengths from centrifugally cast 25 per- cent chromium-12 percent nickel tubes. The trunnions and tube ends are statically cast and welded in place. Mining and Crushing Equipment...A very spectacular mining machine is the strip mining shovel which has the huge proportions of a 70-cu. yd. dipper and 140-ft. boom. This stripping shovel is the largest mobile land machine ever built, and the dipper can fill two railroad cars in one pass. The shovel can fill its dipper up a bank as high as a 12-story building. Fig. 109—Roller shaft assembly for an- nealing furnace. Tubes are centrifugally cast. Heat resistant 25-12 percent chro- mium-nickel cast steel. vvv Fig. 110—The crawler for a 60 cubic yard mine stripping shovel. Crawler 8 feet by 23 feet. Treads 5 feet wide. These stripping shovels have moved over 2 million cu. yds. of overburden on coal seams in a single month. The builders of this equipment turn to steel castings for many of their structural parts. Figure 110 shows a crawler for a 60-cu. yd. shovel, 8 ft. high and 23 ft. long, which is produced from steel castings. This includes the 60-inch width treads, crawler wheels, idlers, bearings, and other parts. The total crawler- bearing area is 782 sq. ft. and the bearing pressure is 58 psi. The truck axle (Figure 111) is mounted in the crawler of Figure 110. Four of these axles support 5 million pounds on the eight crawlers. These axles are produced from tough nickel-vanadium cast steel and heat treated to high strength. The hoisting drums for the 60-cu. yd. shovel are produced primarily from steel castings. These are shown in Figure 112. The gears for the hoists are about 13 ft. in diameter. The steel castings used in rock and ore crushers, some of them exceptionally massive, are designed to withstand compressive stresses, impact, flow and severe abrasion. Each application is considered on its merits in order that correct grades of steel may be used. So-called Fig. 111-Crawler truck axle steel casting for the 60 cubic yard mine stripping shovel. Fig. 112—Hoists for a large mine stripping shovel. Cast steel gears about 13 feet in diameter. TODADICE LITTLE “tramp iron” occasionally finds its way into these crushers causing impact loads of unknown magnitude which must be absorbed by these machines. Abrasion is the chief cause of wear in crushing operations and crusher jaws are often made of high manganese (12 to 14 percent) steel which under continuous peening action develops special wear resist- ant qualities. Jaw crushers are employed extensively in the mining industry and Figure 113 is an example of many types that are in use. The frame, fly wheels, pitman, adjusting nuts, covers, hopper and crusher jaws are all steel castings. Figure 114 shows a swing jaw casting for a large jaw crusher. The Fig. 113—A small jaw crusher weighing 6200 pounds of which 4800 pounds are carbon and manganese steel castings. Crushers are produced in various sizes from 6000 to 200,000 pounds. Fig. 114—A swing jaw steel cast- ing for a jaw crusher. 17 x 7 x 5 feet over-all dimensions. Weight 72,000 pounds. MINI is 10S14 BALL BLOMMER TACONTE Fig. 116—Ball mill. The feed head and the gears are steel castings. Fig. 115—Gyratory crusher. Spider and shells are steel castings. 1 steel casting over-all length is 17 feet and it weighs 72,000 pounds. Jaw crushers have heavy compression and shear loads applied and one- piece steel castings have proved exceedingly advantageous in maintain- ing rigidity under such high loads. The gyratory crusher is another type of primary crushing unit suitable for crushing moderately abrasive and hard ore such as hematite and taconite iron ores. The gyratory crusher of Figure 115 is comprised of a number of steel castings. The hollow box design of the steel spider casting affords maximum strength construction. The spider arms are cast integrally with the heavy outer rim, and because the spider and top shell castings are interlocked they reinforce each other to provide maximum stability and rigidity. Other steel castings are the spider cap, head center, sleeves, rim liners, mantles, liners and various bevel gears. Another mill employed in the mining industry is the ball mill for pulverizing ores to a fine particle size. One type is illustrated in Figure 116. The feed head and the gears for these mills are produced as steel castings. The grinding balls that are used in these mills are also steel cast- ings. The balls shown in Figure 117 are heat treated, solid cast alloy steel produced in various sizes from 11/2 to 4 inches in diameter. These balls are produced in large quantities for the mining industry in the grinding of very hard ores, such as quartz in gold mining. The surface hardness of the balls is 61 Rockwell C. Fig. 117—Heat treated, solid cast, alloy steel grind- ing balls. 11/2 to 4-inch diameter. Fig. 118—Cement mill supporting roll 80-inch OD with 36-inch face. Typical steel castings used in cement mills include riding rings or tires, feed and discharge end heads, gears, rollers, liners, as well as a great variety of special fittings. The supporting roll of Figure 118 is for a cement mill. The weight with shaft is 45,000 pounds. Steel castings are used extensively in mining equipment and a very good example is shown in Figure 119 which is a photograph of the Colmol continuous mining machine for mining coal seams of heights of 28 inches to 44 inches. Such a machine has a mining capacity of 900 tons of coal per shift. The machine consists of a total of 19,300 pounds of steel castings representing 21 percent of the machine weight. Steel castings include the gathering head, drive and chain flight, motor trans- mission, breaker head and drives, breaker arms and bit holders, and cusp cutter bar. These castings have high strength requirements to- gether with excellent toughness so as to withstand the excessive shock loading that is normal in the mining operations. Metal Shaping, Finishing and Forming ... Steel castings in large num- bers are components in machinery and equipment producing manu- factured goods. Such machines to name a few, are presses of all types, STEEL CASTING 1 STEEL CASTING STEEL CASTING -STEEL CASTING STEEL CASTING STEEL CASTING STEEL CASTING Fig. 119—Continuous Colmol coal mining machine for mining seams 28 to 44 inches thick, showing steel castings used in its construction. ::: . Fig. 120–Giant forging press, 50,000-ton capacity, containing 7,000,000 pounds of steel castings. The photograph shows only that portion of the press above the floor. An equal portion of the press is below the floor. mills, upsetting machines, punches, riveters, shears, and welding ma- chines as well as anvils, dies and hammers. Gears, bearings, housings, toggles, levers, arms, and a host of subsidiary structural parts are products of the foundry. Structural strength is of prime importance in some of this equip- ment; in others, maximum rigidity is essential. Still others require resistance to shock loading, abrasion resistance, high hardness or other specific properties. Steel castings are often selected as the construction materials because cast steel is capable of fulfilling all the specific properties. Presses, such as forging, extruding, punching, straightening, etc., contain many steel castings, some of which are very large. For example, Figure 120 is a photograph of a giant forging press of 50,000 tons capac- ity containing 7,000,000 pounds of steel castings. Another forging press is the 140,000-pound forging machine of Figure 121. The frame and other parts are steel castings. Fig. 121–Forging press showing the frame produced as a steel casting. INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 69 နမ်း Fig. 122—Piercing mill with a steel casting housing. Weight 74,000 pounds. Other presses are the piercing mill of Figure 122, the housing of which is a steel casting weighing 74,000 pounds, and the 2,750-ton oil hydraulic extrusion press (Figure 123) showing primarily two castings: the die container and the cylinder which is about 10 feet long, 4 feet in diameter. Fig. 123—2,750-ton extrusion press showing 10-foot long, 4-foot diameter cylinder and the die container which are steel castings. o Fig. 124–Injection molding machine for making plastic articles. steel casting. The frame is a one-piece The press of Figure 124 is a cold chamber injection molding ma- chine for producing plastic shapes. The advantages of the one-piece steel casting according to the press builder are that: (1) full rated clamping tonnage can be attained over long periods without failure or undue wear; (2) extra high effective clamping tonnage can be employed to prevent flashing and die wear; (3) it reduces risk of human error in dies setup to absolute minimum; (4) unobstructed die space is obtained without any sacrifice in locking tonnage; and (5) permanent accuracy in die alignment during opening, closing and locking over long periods of years is secured without failure or undue wear. The press shown in Figure 125 is a swaging press of 500-ton capacity produced from steel castings. Fueno Fig. 125—500-ton swaging press produced from steel castings. 14078 SA YES E FA SE Fig. 126—Cast-to-shape die holder for a die casting machine. This steel casting is 6 ft. 7 in. x 6 ft. 3 in., and 2 ft. 1 in. thick. Weight 14,730 pounds. Fig. 127-A chuck jaw produced as a shell molded steel casting and as a forging. Weight 2 pounds. A 50 per- cent saving resulted in converting to a steel casting. Many cast-to-shape die holders are used in die casting machines and extrusion presses. The steel casting of Figure 126 is a die holder made from a 70,000 psi tensile strength, low alloy Ni-Cr-Mo cast steel. This casting is a conversion from a machined part affording a 70 percent savings in machining cost. A small die part which is a steel casting, shown in Figure 127, was produced in a shell mold. The forging which was previously used is also shown. A 50 percent cost saving resulted from using the steel casting. i The largest existing tensile testing machine, installed at Lehigh University, is illustrated in Figure 128. It has a capacity of 5 million pounds. Weight of the machine and accessories is approximately 925,000 pounds. The height is approximately 60 feet above the test floor and 16 feet below, a total of 76 feet. Structures up to 40 feet high can be tested in tension. The steel castings which are a part of the machine to insure strength, rigidity and stability weigh approximately 700,000 pounds, and consist of the columns, upper crosshead, adjustable cross- head, yoke and the hydraulic cylinder and booster cylinder which are located below the floor. There are also a number of accessory steel castings such as bearing castings, etc. Military ... Steel castings have always been extensively used in mili- tary components; however, developments since the Korean action have been more pronounced in aircraft and missile parts than in ordnance equipment. Steel castings used in aircraft, either as engine parts or in airframe construction, are produced of special alloy analyses, often heat treated to very high strengths. 22 ! Fig. 128—Universal testing machine, 5,000,000 pounds capacity. Total weight 925,000 pounds of which 700,000 pounds are steel castings. Height 60 feet above test floor and 16 feet below floor, a total of 76 feet. 1 Aircraft and missile parts are not procured in large numbers because simulated and service testing often result in design changes to improve the performance of the machine. Rapid design changes are less expensive and more readily attained by steel casting pattern alterations than is possible in the case of other fabricating and machining methods. Steel castings can be produced to an intricate low-weight design, such as shown in Figure 129, without extensive machining. This casting is an aircraft brake backing plate produced of high-alloy steel, subjected to high instantaneous stresses. 'ig. 129—A jet aircraft brake backing plate onsisting of Cr-Mo-V cast steel. Fig. 130—Jet engine track support. Cast steel 4140. 1 Fig. 132—Explosive sizing die for mis- sile fuel tanks. 30- inch diameter by 12 feet long. Weight 30,000 pounds. 1 Fig. 131-Bearings housings for jet engine. Cast steel 17-4 PH. Many of the aircraft steel castings are produced by the investment casting and ceramic casting processes. The low-alloy steel casting of Figure 130 is a jet engine track support. Shown in Figure 131 are bearing housing castings for a jet engine, produced from a 17-4 PH cast steel heat treated to 180,000 psi tensile strength. Some large steel castings for missile development are being pro- duced, such as, for example, the explosive sizing die for missile fuel tanks, Figure 132, cast in low-alloy steel. A large portion of the Army Ordnance tank is made up of steel cast- ings. Some are armor castings, such as hulls, turrets, cupolas and other Fig. 133 — Army Ord- nance M60 tank show. ing armor castings. . Fig. 134—Front wheel arm steel casting. 1 exposed parts plus various brackets, machinery parts, crawler wheels and treads. The cast armor developed during World War II allowed the designer to utilize all the desirable characteristics of castings in building the greatest possible protection into the contour of the tank armor. The casting of large complete sections eliminated considerable welding and thus reduced the cost and time for fabrication. Figure 133 illustrates a recent model of a tank showing a number of armor steel castings. One of the ballistic exposed parts of the tank, as shown in Figure 134, is the front wheel arm assembly which is produced from steel castings. Centrifugal steel castings have been produced in large numbers for tank parts since they can be easily made to various diam- eters, wall thicknesses and lengths. Figure 135 illustrates: (a) recoil piston (b) recoil sleeve, and (c) recoil cradle body for a tank. These parts are produced of low-alloy cast steel and are completely machined. Fig. 135—Centrifugal steel castings for tank gun armament. (a) recoil piston, (b) recoil sleeve, and (c) recoil cradle body. Fig. 136-Cradle for 155 mm gun. 20 inches long. 1612 -7%y- p=-1034 Fig. 137—Track tension compensator casting for ordnance vehicles. Another ordnance casting, shown in Figure 136, is a cradle casting for the 155 mm gun. The following illustration, Figure 137, shows a track tension compensator casting for ordnance vehicles. It is produced to Federal Specification QQ-S-681b Class 404 of 150,000 tensile strength and it must withstand continual shock loading in service. The casting consists of such wide variations in section thickness that it presented a difficult problem in heat treatment. 76 INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 12 Fig. 138—Radome hub for a radar antenna shelter, 24 inches diameter, weight 119 pounds. The radome hub of Figure 138 is a component of a shelter for a ra- dar antenna in a warning system to detect approaching aircraft or mis- siles. It is produced from a low-alloy steel cast in a shell mold to minimize . machining, and heat treated to 105,000 psi tensile strength. Castings for Motor Vehicles ... Automotive steel castings are parts used in the construction of trucks, trailers and buses where strength and dependability are primary essentials. Many different steel castings are made for motor vehicle service, but a few examples will be sufficient to illustrate their wide application in the automotive industry. a The front axle assembly for a motor truck is shown in Figure 139, and consists of an axle center beam casting (1800 pounds), two steering arms (332 pounds), a spindle (195 pounds) produced from low-alloy cast steel of 100,000 psi tensile strength, the wheel and hub caps and end tie rods,—all of which total 3,784 pounds of steel castings. The rear axle assembly (not illustrated) consists of 25 steel castings. Fig. 139–Front axle assembly for a motor truck consisting of 10 steel castings. La Fig. 140—Spring equalizer, equalizer hanger, forward and rear spring hangers and wheel spider castings in place in a motor truck. Figure 140, illustrating other automotive steel castings, shows the spring equalizer casting in position between the two springs, the equal- izer hanger casting, the forward and rear spring hangers and the wheel spider castings. Both the spring equalizer casting and the hanger brackets operate under high loads. These castings were redesigned from weldments after careful stress coat analyses were made on pilot castings. Truck and trailer wheel spider castings, which are subjected to dynamic loading, are produced in large quantities. Two to four wheel spiders are used for each trailer and four to six for each truck. The wheel spiders are original designs prepared by the steel casting manufacturer and produced from carbon cast steel. The high fatigue strength of cast steel enables the steel casting to compete with wrought aluminum parts in weight reduction. A heavy duty axle housing for a truck is shown in Figure 141. This casting is typical of many similar designs used by truck and earthmoving equipment manufacturers throughout the country. This axle unit is produced from a low-alloy cast steel heat treated to 80,000 psi tensile strength. Fig. 141—Heavy duty axle housing casting. Length 45 inches, weight 560 pounds. Fig. 143—Rear axle brake spider casting. Weight 150 pounds. Fig. 142–Front axle spindle for a dump truck. Spindle diameter 6 inches. Weight 195 pounds. a The illustration of Figure 142 is a front axle spindle for a 28-cubic yard dump truck. This part is produced from low-alloy cast steel which is heat treated to a minimum tensile strength of 100,000 psi. Figure 143 shows another truck casting which is a rear axle brake spider produced for equipment used in open pit mining. Figure 144 is a brake shoe casting for heavy duty trucks. The casting was the result of a redesign from a fabricated brake shoe with a cost saving of 37 percent. Fig. 144—Brake shoes for a heavy duty truck. Outside diameter 24 inches, weight, each halt, 95 pounds. INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 79 Fig. 145—Cast steel rear axle housing for a heavy duty truck. Low alloy cast steel heat treated to a minimum of 100,000 psi tensile strength. Weight 2,500 pounds. Another very important steel casting for powerful heavy duty trucks is the rear axle housing illustrated in Figure 145. Big trucks, such as earth and rock haulers, are designed to insure minimum mainte- nance for daily operations. It is logical therefore, that, because of their exceptional dependability in rugged service applications, steel castings be used for front and rear axle parts. Electrical Machinery and Equipment Castings ... Steel castings play a major role in the field of electrical machinery. They are applied as parts in equipment ranging from small electric motors to large power generators. Armature parts, commutator rings, couplings, stator and rotor parts, motor frames, housings and bases are a few of the more common steel castings required by builders of electrical machinery. Examples of electrical machinery steel castings are the split frame castings of Figure 146 for DC armored motors. This motor is used in mill applications, and the frame is of extra thickness to safeguard the motor from damage if struck by moving material. Fig. 146—Split frame castings for DC armored motors. Total weight about 1400 pounds. Fig. 147—Runner for hydroelec- tric power plant. Weight 46,200 pounds. Some of the largest and most intricate steel castings are produced for the hydroelectric power plant field. Many of these structures are so large that they have to be divided into several parts for shipment. Steel castings in this service must withstand vibratory stresses and heavy impact loads, and also have long service life. The demand for continuous service requires that the steel castings for hydroelectric application be produced to exacting specifications. The photograph of Figure 147 is an integral steel casting employed as a runner for a hydroelectric power plant. Figure 148 illustrates a reversible pump turbine runner-impeller, 753 ETA S 398*XXV EIE Fig. 148-A reversible pump turbine runner- impeller, showing two of the three sections as- sembled. Fig. 149—Nozzle dis- tributor assembly for impulse turbine. Aver- age diameter of spiral distributor 26 feet. with two of the three section castings assembled. Each of these section castings weighed 76,000 pounds, finished. An interesting application of steel castings is the nozzle assembly for an impulse turbine as shown in Figure 149, where several castings are bolted together. The nozzle castings are produced from ASTM 217 Grade WC1 steel, or a low-alloy suitable for high pressure service. The weight of the largest single casting is 46,500 pounds and the water flow in the nozzle is 430 cubic feet per second. An impulse wheel, similar to one employed with the nozzle assembly of Figure 149, is illustrated in Figure 150. The buckets are steel cast- ings produced to ASTM specification A296-Grade CA-15 which requires a 13 percent chromium cast steel. The turbine speed for this wheel is 327 rpm with a water velocity of 400 feet per second. Turbines require structural material possessing outstanding ability to resist high temperatures and high pressures. Steel castings have provided a logical answer. Turbine shell castings are produced in all sizes from those of large multi-stage turbines to small units, which often serve only as standby equipment to drive important pumps which are regularly propelled by electric motors. Power plant castings must be Fig. 150–Impulse turbine with separate steel casting buckets. Bucket weight 1,400 pounds, wheel diameter 131/2 feet. Fig. 151-Low-alloy steel case for small turbine. o 12 INCHESE entirely dependable because uninterrupted service to customers must be maintained. Part of the reason that power generating stations have acquired a reputation for continuous day-in-day-out service is the fact that steel castings are so largely used in their equipment. A series of different size turbine castings is shown in Figures 151 to 154. The steel castings for turbine casings are usually produced from alloy steels with excellent creep properties at elevated temperatures, Fig. 152—Cover and base turbine castings. Total weight 7000 pounds. 3231-6 160 o 1 Fig. 153—Steam tur- bine castings. Total weight 85,000 pounds. Subject to pressures of 1200 psi. b 2 Fig. 154—Half head cover hydroelectric tur- bine. Casting weight 91,300 pounds. such as cast steels for ASTM specification A356T, “Heavy Walled Carbon and Low-Alloy Steel Castings for Steam Turbines”. Most of these castings require radiographic examination and magnetic particle inspection testing. Materials Handling Equipment ... Steel castings are well adapted for use in equipment that conveys materials from one place to another. Belt and apron conveyors, hooks, chains, buckets, tow and lift trucks and other materials handling equipment must be strong, durable, shock and wear resistant and, in these applications, cast steel parts have proven to be an ideal combination. Examples of steel castings that are used in the handling of materials are presented in the next several figures. The hook casting of Figure 155 is traditionally thought of as a forging but many cast steel hooks are used in capacity sizes of from 1 to 500 tons. Cast hooks are produced from low-alloy steel, quenched and tempered to 120,000 to 150,000 psi Fig. 155—5-ton capacity crane hook steel casting. Quenched and tempered to 120,000 to 150,000 psi tensile strength. 5 TON Fig. 156—5ton capacity balanced coil hook casting. tensile strength. Hooks are well adapted to castings because they can be produced to a continuous contour, thereby permitting no edges for stress concentration. Another type of hook produced as a steel casting is shown in Figure 156 for handling coils of wire, strips, etc. These balanced coil hooks are produced in capacity sizes up to 20 tons. The steel cylinder casting in the photograph of Figure 157 houses a steel hydraulic ram casting, which lifts boxcars for unloading. The ram, by moving vertically upward, tips a superstructure containing the boxcar so that grain or any other bulk material will flow from the open car door into a bin. The centrifugally cast steel ram and the cylin- der are 20 feet long. Other steel castings in the assembly are end cast- ings, flange and guide ring castings. The photograph of Figure 158 shows a steel casting employed as a housing for an electromagnet. The punishing side blows to which a magnet is subjected call for a tough, rugged body to protect the coil and prolong the life of the magnet. The body housings are produced from dynamo steel cast in various shapes ranging from circular to rectangular. Another method of handling standard size containers for loading them into ships by cable lifting is to attach a frame to the container 7 Fig. 157–Centrifugally cast hydraulic cylinder contain- ing a cast steel ram to lift and tip freight cars, length- wise and sidewise, so that bulk grain, etc., may be un- loaded. Cylinder 31 1/2-inch OD, ram 261/4-inch OD, 2234- inch ID. 20 feet long. 33 } N INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 85 Fig. 158—Housing for an electromagnet. Made as steel castings in sizes up to 77 inches in diameter and 15 x 76 inches in rectangular types. as illustrated in Figure 159. A number of small castings are incor- porated in this speedloader. The steel casting in Figure 160 is a ram mounted on the front of a lift truck for transporting coils of strip steel or wire. It is produced from a low-alloy cast steel and heat treated to a tensile strength of NA SHEAVE COUPLER LATCH HOUSING ALIGNING WING TOP-CORNER CASTING COMMERCIAL CONTAINER BOTTOM-CORNER CASTING Fig. 159—A speedloader system of container handling containing a number of small steel castings. Fig. 160-A ram casting in- stalled on lift trucks for trans- porting coils of steel strip or wire. Fig. 161–Steering knuckle casting for tow and lift trucks. Weight 170 pounds. 1 100,000 psi. The steering knuckles (Figure 161) of tow and lift trucks are produced as steel castings. The billet manipulator, shown in Figure 162, which moves billets at forging heat from the furnaces to the forging hammer or press, con- sists of an assembly of steel castings. The tongs, as well as the base for the tong shaft, are also steel castings. Ship and Marine Castings... Some of the most rangy castings produced in the steel foundry are used on ships. These castings must be strong and rigid. Other marine castings must be made from corrosion-resistant steels to withstand sea water corrosion. Castings for propelling engines must operate under high pressures and temperatures. Since steel cast- 1 • 1] 17 1 Fig. 162—Billet manipulator. The tongs and frame base for the tongs are assembly of steel castings. an Fig. 163—Hawse pipe casting for cargo ship. ings can furnish the answers to all these problems, they are used for many of the vital parts of the hull and the operating mechanism on ships. The ship stem is a steel casting, and the stern frame is composed of one or more steel castings. The rudder frame, hawse pipes, davits, struts, chocks, cleats, bitts, propellers, and anchors are all integral steel castings or assemblies of two or more steel castings. Turbines, piping components, pumps, compressors and other operating machinery contain many steel castings. The steel casting in Figure 163 is a one-piece hawse pipe for a cargo ship through which the anchor chain operates. Anchors of all types and sizes are produced as steel castings from those used in small pleasure boats to those for big aircraft carriers. Figure 164 is an example of a stockless anchor weighing 40,000 pounds. Propellers of various sizes Fig. 164–A 40,000-pound stockless anchor produced as three steel castings. Fig. 165—A stainless steel pro- peller casting, 5 feet in diam- eter. Fig. 166—Stern frame casting for a 730-foot long iron ore carrier. Weight, 29 tons. are also made as steel castings and many are produced from corrosion resisting steel. Figure 165 is an example of a cast steel propeller. A tremendous pressure exists against the face of the rudder when the helmsman puts the wheel hard down in a heavy sea. The rudder post and frame must sustain such suddenly applied loads, for repairs at sea are usually impossible. Naval and marine engineers entrust the tough- est assignments to steel castings, indicating the reliance and faith they have in the ability of cast steel to perform satisfactorily under over- load conditions. The stern frame of Figure 166 is a steel casting for a 730-foot long, 75-foot beam ore carrier. Cast link anchor chain (Figure 167), in various link sizes of section thicknesses of 1 to 5 inches, is regular equipment on all ships. Long lengths of this chain are tested in tension to ascertain if proof test loads are met prior to their acceptance. Builders of tugs, dredges, scows, and barges all employ steel cast- ings extensively in their construction. The following three figures show photographs of steel castings employed in these hard working marine C DC Fig. 167—Cast link anchor chain. Integrally cast without open links, by an ingenious process, for a service requiring toughness, high tensile strength and resistance to impact. INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 89 - Fig. 168–Pump casing for a dredge. Weight 27,000. pounds. units. The pump casing of Figure 168 is essential equipment for the large dredge. The kort nozzle of a Mississippi river towboat (Figure 169) permits an increased propeller thrust at low speeds. The nozzle is installed in a 2400 horsepower twin screw Diesel engine tug. This steel Fig. 169—Kort nozzle for a Mississippi river towboat. It is 15 feet wide, 12 feet high and 1442 long. > casting is a conversion of a weldment. The cutter head, shown in Figure 170, is for use on a dredge. Note the casting positions for the cutter points. Some cutters are designed as blades and do not have the "teeth.” It should be mentioned also that spuds having lengths up to 75 feet are produced as single piece steel castings for anchoring dredge boats. Rubber Mill Castings ... The manufacture of rubber products involves the application of both heat and pressure. Builders of rubber mill ma- 1 Fig. 171-Steel castings for rubber mill molds for bathing caps. Fig. 170—Cast-weld cutter head for dredging use. Steel casting weight, 18 tons. 1 chinery have an excellent material in steel castings with which to con- struct their equipment since steel castings are well known for their ability to operate under conditions of heat and pressure. Cast steels of selected grades have excellent creep resistance properties. Pneumatic and solid automobile tire molds are made of steel castings. Vulcanizing presses, dies and molds, rim rollers, slitting and cutting machines and mixers are, in a large measure, composed of steel castings. An interest- ing example of the use of steel castings in bathing cap molds is shown in Figure 171. All types and sizes of molds for rubber goods, weighing up to several tons, are being produced as steel castings. The tire mold shown in Figure 172 is produced from a free machin- Fig. 172—Tire molds are produced from free machining steel cast- ings. ha INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 91 olo Fig. 173—Bladder mold for curing green rubber for tires. A three-part mold consisting of steel castings. ing grade of cast steel (0.10 to 0.12 percent sulfur). The mold consists of two halves and the tread and side-wall designs are machined on the inside surface of each mold. Another rubber mold is shown in Figure 173. This is a bladder mold which operates under steam pressures of 150 to 200 pounds and is used for curing green rubber for tires. These molds are produced in various sizes using steel castings to ASTM specification A216, WCB grade. Another steel casting used in rubber mill equipment (Figure 174) is a rotor for a rubber mill mixer. These rotors are employed in huge mixers to prepare the rubber prior to vulcanizing. Rubber mill operators buy shrewdly. Their mass production meth- ods demand high quality tools since breakdowns on continuous pro- duction lines are expensive and must be kept to a minimum. It is not by mere chance, therefore, that steel castings are so popular in the rubber production industry. Steel castings have demonstrated eco- nomical and satisfactory performance under exacting service conditions. Their reputation for long life, and hence their low unit cost, is widely recognized Gears, Pinions and Worms... Wherever mechanical power trans- mission is required, gears are usually necessary. Gears in service are subjected to compression, shearing, torsional and shock loading stresses, as well as to abrasion and sliding wear. It is desirable that they be quiet in operation and that they be capable of withstanding heavy overloading conditions. Fig. 174–Rotor for a rubber mill mixer. Length 9 feet; weight 3940 pounds. Fig. 175-Group of spur and bevel gear castings weighing from less than a pound to many hundreds of pounds. 1 1 Cast steel is widely used for gears because it is noted for its high structural strength, rigidity, and excellent impact resistance, and is, accordingly, an ideal material to withstand stresses of all kinds. It is also adaptable to differential heat treatments by which almost any de- gree of hardness may be imparted to different parts of the same casting. Thousands upon thousands of cast steel gears are made every year, weighing many tons. Some of these gears have the teeth cast-to-shape by the foundry. These cast tooth gears are sometimes put into service without any machining of the teeth but, in those circumstances where machining is necessary, the machining expense is very materially re- duced by casting close to shape. Other gear castings are produced as blanks, the teeth being sub- sequently cut by special machine tools. Cast steel is exceptionally well suited for such cut tooth gears because, unlike wrought steel products, it does not possess "lines of flow” which, in cases where such lines run parallel to the periphery, constitute potential cleavage planes extending transversely across the teeth and existing as focal points of possible tooth breakage. Figures 175 and 176 show groups of steel casting gears of various designs. Fig. 176-An assort- ment of steel gear castings of special de- sign. a Fig. 177—Crawler gears for a large power shovel. Large gears weigh 2800 pounds and the small gears 1900 pounds. AXX Differential heat treatment of cast steel gears permits different hardness values to be imparted to the rim, the arms or web, and the hub. High hardness on the rims means added wear resistance on the tooth surface. Flame hardening and case hardening (nitriding and carburizing) can be performed on cast steel gear teeth. Many gears are of irregular and unusual design. Even among the more conventionally shaped gears there is an almost infinite variety of sizes and contours. There are gears with herringbone, spiral and spur teeth. There are worms and pinions of every sort, racks (with external or internal teeth or both) and sprockets of every size and description. Cast steel is exceptionally well suited as a material for these applications. Design variations do not present problems for the steel foundry. Carbon and alloy steels, plus a variety of heat treatments, are available for the purpose of developing mechanical properties exactly suited to individual service requirements. The strength and rigidity of cast steel mean quiet operation and durability. The crawler gears shown in Figure 177 drive the tracks of a large power shovel. The wear surfaces of these steel castings are heat treated to a high hardness to withstand the abrasion encountered in mining operations. The gear casting of Figure 178 is produced from NANO Fig. 178—Herringbone gear castings for a slush pump. 94 INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 1 O Fig. 179—Combination counterweight sheave and gear for a vertical lift railroad bridge. Diameter 14 feet. an SAE 4130 cast steel, water quenched and tempered to 280 BHN, after which the herringbone teeth are machined. The photograph of Figure 179 shows a large combination counterweight sheave and gear for a vertical lift railroad bridge. Four of these are required, one on each corner of the bridge. A cast steel of 0.45 percent carbon content was employed for this application. Agricultural Equipment ... Increasingly severe conditions have been imposed upon harvesting, tilling and various other types of agricultural tools and machinery due to high speed methods attendant upon the use of modern, more efficient motorized farming. Obviously, structural castings must be kept light but strong enough to withstand extreme torsional, tensile, shock and fatigue stresses, and to resist wear where that quality is required. Steel castings are being used in ever increasing numbers for agricultural machinery parts. Steel castings in the agricultural field are used in combine ma- chines, corn pickers, plows, stump pullers, and other land clearing equipment, and wherever light, weight-reducing metal sections are desired without sacrifice of the high mechanical properties which cast steel provides. Illustrations of a few applications of steel castings for agricultural equipment are shown in the next few figures. An example of land clearing equipment is the all-purpose rooter of Figure 180. The rooter castings are bolted into a steel frame casting which is mounted to the front of a tractor. They make short work of clearing rocks, boulders and stumps from the land. Fig. 180 — All-purpose rooter for land clear- ing. The hydraulic lift arm of Figure 181 is a steel casting part for a farm implement tractor. It is produced from a 0.35 percent carbon cast steel and weighs 11 pounds. Many other steel castings of similar sizes and weights are used in farm implements. The scarifier assembly part illustrated in Figure 182 consists of two steel castings, the scarifier bar and the replaceable tip. These castings are made of a manganese-molybdenum cast steel and heat treated to a Brinell hardness of 300 for the scarifier and 500 for the tip. A new tip can be easily attached as the old tip wears out. 0 Fig. 181—Hydraulic lift arm for farm implement tractor. Weight 11 pounds. 674 השניצ?למישות Fig. 182—A scarifier assembly of steel castings to prepare heavy and rocky ground. The replaceable tips are also steel castings. 96 INDUSTRIAL APPLICATIONS OF STEEL CASTINGS Fig. 183—Axle extension spindle for garden trucks. Length 191/2 inches, diameter of large flange 7 inches. Note integrally cast spring seat. Wide wheel spacing of truck wheels is an advantage in the harvest- ing of row-planted vegetables. Using the spindle of Figure 183 is a simple method of axle extension so that a truck can go down between the rows and, likewise, be used on the highways. Formerly, standard axles were extended to the required width by a time-consuming and expensive six-operation sequence involving machining and welding. Now, through the use of two steel castings that fit snugly over present spindles, the extension can be accomplished quickly and easily.. Construction Castings ... This category encompasses those steel cast- ings produced for bridges, locks and dams, and other similar building construction. Steel castings of almost all kinds, shapes and sizes are used in the construction of mammoth public works. Bridges of all types from the small highway types to the huge suspension spans employ steel castings. Lift, pivot, and other break-in-floor types of bridges use steel castings for many of their structural and operating parts. Such bridge members as cable bend saddles, rockers, pedestals, strand shoes, rope sockets, and bearing blocks must be absolutely de- pendable, and steel castings have proved thoroughly dependable for these uses. Examples of bridge castings are illustrated in the following two photographs. Figure 184 is a cable bend saddle for the Mackinac Fig. 184—Cable bend saddle for a suspen- sion bridge. Weight 27,500 pounds. 0. O. Fig. 186—Sector gear and rack castings for operation of a mitre gate on locks. Gear size 10 feet pitch diameter. Rack size 102/2 feet long. Fig. 185—Center cable band and suspension cable band for a high- way bridge. Weight 6700 pounds. bridge. Four of these saddles were required. The castings of Figure 185 are a center cable band and suspension cable band for a highway bridge. Steel castings for locks and dams are often very large and many are subjected to hydraulic pressures. Steel castings for this field are hydraulic slide gates, butterfly valves, bulk headgates, gate hanger devices and racks and rims for roller gates. The photograph of Figure 186 shows steel castings produced as a sector gear and rack for mitre gate machinery. Steel castings for building construction require high strength and ability to withstand shock loading. There are many steel castings ideally suited for this industry. Figure 187 is a pile follower used in the driving of timber piles below ground level. This casting was a redesign from another form of steel construction and a 400 percent Fig. 187—Pile follower casting. A construction tool for driving pipe or timber piles below ground level. 45-inch length. Weight 1050 pounds. 98 INDUSTRIAL APPLICATIONS OF STEEL CASTINGS 31 Fig. 188—Lift-slab collar casting for lifting floors into position. Produced in various sizes from 18 inches OD, round or square, to 36 inches OD. increase in life was obtained because of the greater shock resistance obtained in designing the part as a steel casting. Also two piles can now be driven in the time it formerly took to drive one pile, because one operation using the steel casting takes the place of three steps when using the previous type. The second example is the lift-slab collar of Figure 188 which is a steel casting used in erecting a building where all floors and roof are constructed of reinforced concrete at ground level and then positioned with hydraulic jacks. The essential supporting device is the lift-slab collar. These steel castings provide maximum safety under extreme loads and at the same time they are parts suitable for field welding to supporting columns. Miscellaneous ... Steel castings are used in many miscellaneous serv- ices as parts for equipment or for plant installations. Many of these parts have been designed as steel castings, because the engineer has be- come impressed with the flexibility of casting design and the outstanding intrinsic properties of steel castings. Also, in some cases, the designing engineer has worked with the steel foundry engineers and developed optimum designs based on the advantages of the steel casting process. A few examples of steel castings for miscellaneous service may indicate the wide potential of the product of the steel foundry in parts Fig. 189—Steel castings for briquette rolls. Fig. 190—Castings for automatic glass press- ing. for engineering construction. The wheel shaped castings of Figure 189 are briquette rolls. These castings were made from an original design and are produced from a 12 to 14 percent chromium cast steel. The steel castings illustrated in Figure 190 are dies used in the automatic pressing of glass. These dies were converted from forgings to castings because a special steel analysis was desired. Small quantities of special chemical analysis steel can be obtained for such parts as dies when produced as steel castings. The ability to core out unneeded metal in a die is also an important feature. Nonmagnetic parts can be produced as steel castings from austenitic manganese steel or from the austenitic type of stainless steel. The castings of Figure 191 are assorted cylinders for a Navy nonmagnetic Diesel engine and the cast steel is an 18-8 austenitic stainless com- position. The steel castings of Figure 192 are of heat resistant chemical compositions and are used as grids in carburizing automotive pinions. Fig. 191—Nonmagnetic (austenitic stainless steel) cylinder castings for a Diesel engine which powers a mine sweeper. Weights, 35 to 150 pounds. עשבוננו Fig. 192—Steel grid castings used in carbu- rizing automotive pin- ions. 3 1 16 13 20 21 22 They are produced from a steel of 38 percent nickel and 18 percent chromium. Another heat resistant application is the radiant tube as- sembly, as shown in Figure 193. This tube assembly is made by the fabrication of two centrifugally cast tubes with statically cast U-bends and firing legs. The firing leg is the tapered portion at one end of some of the tubes. The steel is 25 percent chromium, 12 percent nickel, or in some cases it may be 35 percent nickel and 15 percent chromium steel. The last illustration, Figure 194, is a steel casting flywheel used on a Diesel engine. It is held to close tolerances and is well balanced even though it is 71/2 feet in diameter and weighs 71/2 tons. Fig. 194—Steel flywheel casting for a Diesel engine, 71/2 feet in diameter, weight 792 tons. Fig. 193—Radiant tube assemblies produced from centrifugally cast tubes and statically cast U-bends. Lengths about 15 feet. CHAPTER III THE PURCHASING OF STEEL CASTINGS Purchaser's Requirements Steel castings make up the machines and structures of heavy in- dustry for the simple reason that they are best fitted to meet the desired service requirements with safety and dependability. They are, accord- ingly, hard goods which bear no likeness to consumer items such as TV sets, for example. Indeed it has been aptly stated that no individual buys a steel casting because he wants to own one. The purchasing officials of heavy industry buy steel castings because they are strong, tough, rugged, and streamlined structures which will afford many years of trouble-free service under a wide variety of severe service applica- tions. The purchasing official of a company thinks primarily of buying steel castings in terms of: cost, quality, delivery and service. His own product must be competitive, it must be readily available, and it must be of the best quality that his competitive price can permit. At the very least, it must be of adequate quality for the service intended. Cost ... Steel castings are specially designed and manufactured parts, and, therefore, unlike standardized consumer goods, the cost of castings will depend upon the purchaser's requirements. Accurate cost accounting has become a necessity in steel foundries. The effect of variables in design and service and quality requirements for steel castings plus the increased complexity of cost item distribution, particularly in the field of manufacturing overheads, demand definite knowledge in the field of cost determination. Steel castings are primarily tailor made objects. A foundry seldom produces castings of a specific type which can be sold to more than one customer. Therefore, each casting has its own distinct cost of manu- facture and an accurate cost analysis is necessary. The cost of one casting cannot necessarily be compared to the cost of another casting although similar in weight and shape, because differences in design complexity and quality requirements may exist. Two castings which look alike may have different costs because the service requirements are entirely different, and the quality and tolerance requirements of one may be of a distinctly different order than those of the other. Steel casting costs reflect variations resulting from differences in material specifications, type of pattern equipment, tolerance limitations, complexity of casting design, labor, materials, inspection, and accept- ance standards. 102 PURCHASING OF STEEL CASTINGS Quality ... The service requirements for castings are so varied that a number of quality levels are possible. It is important, therefore, that the foundry know what quality level is considered by the purchaser when steel castings are specified. Steel Founders' Society has prepared and made available to all possible purchasers of steel castings a "Recommended Minimum Stand- ard for Commercial Carbon Steel Castings".* This voluntary quality standard is applicable to steel castings commonly referred to as "com- mercial carbon steel castings." It applies only when customer specifica- tions do not call for another grade of quality. Quality levels go upward from this minimum standard to the extremely high level requirements, such as aircraft quality and atomic energy castings. There are many quality levels between these two extremes. Points to consider in determining various quality levels are as follows: 1. Mechanical properties of the steel from 60,000 to 250,000 psi tensile strength, including alloy content, heat treatment, test specimen location, number and type of mechanical tests, micro- structures, fatigue and impact testing, and processing require- ments. 2. Tolerance limitations, such as dimensions, weight, casting and machining allowances. 3. Surface conditions, which include smoothness and finish. 4. Welding requirements, such as procedures, steel compositions, electrode requirements and qualification tests. 5. Pressure testing requirements, including special leak detection. 6. Nondestructive testing, which includes radiography, magnetic particle examination, penetrant testing and ultrasonic inspec- tion. 7. Gages. 8. Special tests, such as machining; high or low temperature properties; magnetic, heat or corrosion properties; stress analysis using strain gage or brittle lacquer testing, and destruc- tive testing. Testing to insure exceptional quality requirements demands skilled workmen and staff personnel, additional production time and expensive materials and equipment. Narrow ranges of acceptability are usually coincident with high quality levels, and a higher percentage of rejected and reworked castings is a possibility. Naturally, these costs will be reflected in the price of the castings. However, necessary quality re- quirements should not be compromised in order to obtain a low price. * Available upon request from the office of Steel Founders' Society of America PURCHASING OF STEEL CASTINGS 103 A purchaser of steel castings certainly should not order to a higher level of quality than is demanded by the service, because ad- ditional quality requirements are costly. It is for this reason that the steel foundry should be advised of the purchaser's definite requirements so that a realistic price can be determined. . Delivery and Service . . . The foundry must receive all pertinent facts which govern casting delivery, such as quantity on order, delivery schedule, type of pattern equipment, inspection requirements, and ex- ceptions to material specifications. Failure on the part of the buyer to furnish all such data will usually result in delivery delays. The supply of pattern equipment by the purchaser is frequently the cause of a delay in the delivery of castings. The foundry often finds that the pattern equipment is in poor shape and requires repair, or that it may not be adequate to comply with recent changes in quality require- ments or in the quantity of castings desired by the purchaser. Services offered by the foundry create the opportunity for close cooperation between the foundry engineer and the customer. A regular visit to the customer's plant often results in the elimination or reduction of additional costs, such as those arising from: 1. misunderstanding of order details, 2. delays caused by improper maintenance of pattern equipment, 3. failure to make minor changes (finish allowances) which would reduce finishing and machining costs, and 4. specifying other than the most suitable type of steel. Valuable services can be rendered the casting buyer by permitting the foundry engineer free access to the customer's plant, and by giving him the opportunity to visit with the customer's engineers and produc- tion personnel. In this way the foundry engineer can offer early assist- ance in casting design and pattern construction when new castings are being developed, and supply information on metal properties and on metallurgical problems. Production Factors Affecting the Cost of Steel Castings A number of factors affect the cost of producing castings. These factors are not apparent in an itemized fashion in a price quotation, but they are there, and as such should be listed here for reference, so that they are available for review by the purchasing agent. The production of castings is, in large measure, a joint undertaking of the buyer and seller inasmuch as it is customary for the buyer to 104 PURCHASING OF STEEL CASTINGS furnish the pattern equipment and, in certain cases, the flasks, straightening dies, gages, and similar equipment. The foundry engineer must have knowledge of the pattern and other equipment which the buyer possesses, or is to furnish, before he can intelligently quote a price on the casting. Costs of production are dependent upon the condi- tion of the buyer's equipment as well as on the casting design and material requirements. Close cooperation between the buyer and seller is vital in keeping costs to a minimum and quality high. These lines of communication can be kept open through the efforts of the purchasing agent. The foundry engineer must depend upon the buyer for full facts and detailed information covering the requirements. Failure on the part of the buyer to supply this information may result in higher costs, inferior quality and unsatisfactory delivery. Today there is a gratifying trend toward consultation between the buyer and the producing foundry in matters pertaining to casting design. The head of the buyer's purchasing department should establish an affable relationship between the foundry and the buyer's design and engineering department heads to consider the possibilities of design modifications, changes in existing pattern equipment, materials, and other details. Such a conference can result in improved quality and appearance of the casting, in shorter delivery time, and in ultimately increased economy to the buyer by allowing the foundry to more fully utilize approved casting techniques. Factors influencing the total cost of the casting are listed below: t 1. casting design: size, weight and castability, 2. pattern equipment and molding methods, 3. type of steel, 4. tolerances and finish requirements, 5. quality levels, 6. inspection requirements including nondestructive tests, 7. quantity and delivery requirements. Pilot Castings ... Some foundries and certain buyers make a practice of requiring the production of a pilot or sample casting. The purpose of this is to show the buyer's engineers what was the reality of their design so that they may check the dimensional accuracy of the casting and ascertain whether the casting is ready for subsequent machining opera- tions. The buyer should send his approval to the foundry regarding the casting so that the foundry may start production. The pilot casting will assist the foundry in meeting the buyer's requirements as to de- livery and costs. } PURCHASING OF STEEL CASTINGS 105 Orders for Castings Which Previously Have Not Been Made The foundry industry welcomes the opportunity to assist the de- signers and engineers of structures for the metal industry in the development of a casting design by: 1. reviewing the design from the standpoint of castability, 2. assisting in pattern requirements and construction, 3. aiding in establishing quality levels, and quality standards of acceptability, 4. assisting in establishing mechanical test levels and appropriate acceptance standards, and 5. recommending a standard specification comparable to service conditions and mechanical test limits. Presenting the foundryman an opportunity to become familiar with a new job from its inception will result in lower cost, improved delivery and quality. The designer and engineer will usually determine the service condi- tions to be imposed on the casting, such as static and dynamic forces; make a tentative choice of the type of steel; check stresses and deflec- tion, if they are critical; and consider general appearance from the standpoint of utility and sales appeal. When these basic facts have been established, it is to the advantage of both the buyer and the foundry to call in the foundry engineer for consultation. Casting Design ... The designer cannot be expected to have a basic knowledge of how metal flows in molds and solidifies, nor does he understand casting design from the standpoint of castability. By main- taining a close liaison with the foundry engineers, the designer can en- courage the foundryman to suggest changes which may reduce the complexity of the design, increase its castability, and decrease the over- all cost without affecting utility. Such consultations result in the de- velopment of a practical streamlined design with lower ultimate cost. Design is the largest single area where cost is influenced. The foundry engineer studies the blueprint of a new casting design from the standpoint of the complexity of core work and whether the design can be molded by an inexpensive method or whether it requires special, more costly molding methods. He must consider whether the distribu- tion of metal will allow the casting to be produced by simple, less costly feeding systems or whether more costly, special systems must be used. Often slight changes in the exterior shape will eliminate the necessity for using costly molding methods, and, similarly, a slight change in metal distribution may eliminate the requirement for costly feeding systems. There is good evidence that designs which can be readily produced by the 106 PURCHASING OF STEEL CASTINGS simplest casting methods are also designs which possess the highest resistance to fatigue failures. Many times the foundry engineer can suggest simple design changes which would eliminate expensive manu- facturing operations. Material and Quality Levels ... It is highly desirable that the design . engineer work closely with the foundry engineer in establishing the actual mechanical properties required by a design. Once the actual property requirements are determined by the designer, it is then possible for the designer and the foundry engineer to agree on actual mechanical properties which can be established for the sections involved in the new design. It is recommended that no steel analysis be selected by the designer until he has reviewed this subject with the engineer of the supplying foundry as to what cast steels (carbon or alloy) are regularly available or the foundry regularly produces which will meet the estab- lished requirements. This will not only permit better scheduling, but will enable the foundry to fully utilize its experience in the production of these cast steels. Appreciable cost savings may be realized by allow- ing the foundry engineer to select a grade of steel which is a foundry standard. There are many possible chemical combinations which pro- duce the same end result in mechanical properties. The chief criteria of casting quality are soundness of sections, accuracy of dimensions (tolerances), metal properties, and surface appearance. Often the designer, because of his unfamiliarity with the foundry process, specifies a quality level higher than the design demands. Such cost raisers can be held to a minimum, if a close liaison exists be- tween the buyer and the foundry during the development of a new design. Specifying quality or strength levels beyond the functional demand of the design increases casting cost. The buyer can obtain a more favorable price and delivery by specifying only the mechanical property requirements (tensile bar, hardness, hardenability, impact, etc.), which are based on the design and service application of the structure. This can be best accomplished by selection of an ASTM specification which meets the mechanical test requirements. Thus, the foundry engineer is free to choose the proper alloy steel, the carbon range and the heat treatment according to his best judgment. This generally results in selecting a less expensive alloy, one which is regularly and quickly produced and heat treated, and which can be easily processed through the cleaning department. Information on any special inspection requirement is needed to establish the quality level required by the buyer. Too often, the buyer calls for nondestructive inspection without indicating the acceptance standard to be applied. Only when the foundry staff has a clear defini- PURCHASING OF STEEL CASTINGS 107 tion of the quality level required, can an intelligent cost and production schedule be estimated. Production and cost are definitely influenced by the acceptance standard, the number or percent of castings subjected to nondestructive testing, and by the extent or degree of such a test, e.g., 100 percent radiographic or magnetic particle tests, or tests only in areas indicated as critical. Such information must be known before the casting is placed in production. If additional quality limits or an increase in the nondestructive testing are required, a renegotiation of the price and delivery is obviously necessary, as the added limitation invariably re- sults in increased costs, longer processing times and additional pro- duction problems. All of these facts are vital in determining a cost estimate of the casting, in establishing a delivery schedule acceptable to the buyer, and in establishing a thorough understanding of the quality level desired by the purchaser. Specifications ... All orders, regardless of service applications, should make reference to an acceptance specification. The specification should be in line with the service and quality requirements of the castings. Specifying a higher quality level or higher mechanical properties than is necessary for a particular application will result in higher cost and slower delivery. For example, requiring a 100 percent magnetic particle testing when none is needed, or when only one highly stressed fillet area requires magnetic particle testing will increase the cost and slow down production. Furthermore, specifying a need of an alloy steel when a carbon steel would be entirely satisfactory, increases the cost of the casting. This is due to the alloy additions required in the steel as well as to increased processing costs. Delivery may be slowed down because of scheduling a special heat and the necessity of special heat treating procedures. The specifications of the American Society for Testing Materials, should be prescribed whenever possible, since the purchasing require- ments of ASTM cover many widely diversified applications for steel castings. Consultation with the foundry engineer is highly desirable as to which ASTM specification is applicable to the service and test requirement of the design. When there are special rejection limitations, other than those speci- fied in an ASTM specification, these should be definitely spelled out. The buyer should be aware of the fact that special chemical and mechan- ical limitations increase costs which must be passed along to the purchaser. 0 Application and Service Requirements ... This type of information is often very difficult to secure from the buyer. However, a thorough 108 PURCHASING OF STEEL CASTINGS understanding of how and where the casting is stressed will assist the foundry in selecting its methods of producing the casting. Information on the type of service, such as hydraulic pressure, service temperature (high, low or room temperature), fatigue and corrosion, will guide the foundry staff in its founding technique as well as in the choice of materials and thus permit the selection of the lowest cost production method. Furnishing this type of information to the foundry will be bene- ficial to the buyer as it will assist the foundry in establishing its in- spection procedure, in arranging its production schedule to meet the buyer's delivery requirements, and in determining the foundry pro- cedures to be employed. This can result in the improvement of casting quality and in establishing a fair price for the casting. Patterns for New Designs ... Problems relating to pattern construction should be discussed with the foundry engineer at the same time he is invited to comment on the proposed design for a new job. New patterns can be best constructed after consulting with the foundry, and sub- mitting prints to them. The foundry staff, in turn, can mark the prints as to processing information for the pattern manufacturers. An im- portant consideration in pattern construction is the question of how many castings are to be made from the pattern in order to determine the pattern material to be used (see Chapter V). Detailed Drawings ... Two or three legible and detailed drawings, which give the actual or estimated weight of the casting, casting dimen- sions, machined surfaces, finish allowances and nonmachined tolerances, and specification reference, should be submitted to the foundry by the purchaser. Special requirements, such as nondestructive testing, sur- face finish, gaging, grinding, cleaning, painting, etc., must be indicated on the drawing or furnished to the foundry in writing. 1 A drawing should be furnished to the foundry which clearly in- dicates the areas to be given nondestructive testing, the number of castings subject to nondestructive testing and a standard of accept- ability, when radiography, magnetic particle inspection or other non- destructive tests are required. The method of pressure testing, and the pressures employed must be clearly stated when a casting is purchased to pressure test requirements. Delivery Requirements ... The purchasing agent should indicate the delivery schedule on the order, together with the number of castings to be ordered from each pattern, the customer's inventory requirements, whether castings will be accepted in advance of schedule, and what quantity will be acceptable over or under the quantity ordered. PURCHASING OF STEEL CASTINGS 109 The buyer can expect a more favorable price if larger quantities at one time are ordered. Thus, it is better to order a larger quantity for delivery every three months than a smaller quantity on a monthly basis. Interplant Visitations ... The purchasing of castings is not a simple matter of supplying patterns, and it is beneficial to have men on both sides (buyer and producer) familiar with each other's problems. As has been repeatedly pointed out, the buyer's engineers should talk to the foundry staff at every possible opportunity. The foundryman should have an opportunity to visit the buyer's inspection department. Many times the critical requirements of the customer's quality standards, which seem unimportant to the uninformed foundryman, are seen to be valid after observing the buyer's plant operations. Visitations to the foundry by the buyer will also help to understand the problems of the foundry, and the designer may better understand why suggested minor changes in the pattern or casting design have a bearing on castability. Orders for Castings Which Have Been Made Previously The steel foundry needs a complete description of the pattern equipment even though the casting has been made previously by another foundry and accurate information pertaining to delivery requirements so as to effectively plan a balanced production schedule, and intelligently compute the price of the finished castings. Incomplete information usually results in delays in production, unnecessary correspondence, and misunderstandings, apart from its effect upon estimated costs and quoted prices. Any inquiry for a casting should be complete in its notations of all essential information. Patterns ... Furnishing the foundry with complete information on the pattern equipment also has a definite bearing on the quality, delivery, and price of the casting. This information indicates the number of pieces which can be made simultaneously, as well as the size and type of flask equipment to be used, the production rate, the production schedule, and the surface quality. The buyer should furnish an adequate description of the variable pattern equipment and its condition. This information should include: 1. Type of Pattern 1.1 Loose (number of patterns) and whether suitable for mounting 1.2 Gated (number of the patterns on a gate and over-all di- mensions) 1.3 Mounted on plate (number of patterns on a plate, size of plate, and whether gates and patterns are removable) 110 PURCHASING OF STEEL CASTINGS - 1.4 Machine, cope and drag (number of patterns on equipment, size of board, and whether patterns are removable) 2. Pattern Material 2.1 Wood (hard, soft, metal reinforced) 2.2 Metal (state kind) 2.3 Plastic or other material 3. Number of Cores per Casting, with Description of Core Boxes 3.1 Number of cores per core box 3.2 Core box material 3.3 If designed for core blower or core shooter 3.4 Core dryers — number, kind and material 4. Type of metal for which pattern was originally made (steel, iron, malleable iron, ductile iron, etc.) and patternmaker's shrinkage used in pattern construction. 5. Miscellaneous Data 5.1 Condition of pattern 5.2 Pattern age in terms of number of molds produced Patterns should be kept in good repair because off-dimensions may increase the machining and finishing costs, adversely affect the appear- ance of the casting and impair the quality. The buyer should heed the foundry's recommendations concerning pattern repair and replacement. Specifications ... All orders should specify a standard specification, preferably an ASTM specification. The purchasing requirements of ASTM cover many widely diversified applications of steel castings, in- cluding several grades of carbon and alloy steel. 1 The common ASTM specifications for purchasing steel castings are listed below. Details of these specifications are listed in the Summary of Steel Casting Specifications (see Engineering Tables in the Appen- dix). ASTM Specifications A 27-58 Mild to Medium-Strength Carbon-Steel Castings for General Application A 148-58 High-Strength Steel Castings for Structural Purpose A 216 Carbon-Steel Castings Suitable for Fusion Welding for High-Temperature Service A 217 Alloy Steel Castings for Pressure Contained Parts Suit- able for High-Temperature Service A 351 Ferritic and Austenitic Steel Castings for High-Tem- perature Service A 352 Ferritic Steel Castings for Pressure Containing Parts Suitable for Low-Temperature Service PURCHASING OF STEEL CASTINGS 111 Castings which have been made previously to no specifications should be called to the buyer's attention, because it is to his best interest that a standard specification be indicated. The foundry will welcome the . opportunity to suggest an applicable specification, such as the SFSA "Recommended Minimum Standard for Commercial Carbon Steel Castings". The buyer should clearly indicate to the foundry whether the in- spection of the casting is to be made at the foundry, and whether by representatives of the purchaser. The buyer will often get better results by relying on the foundry's inspectors, who know castings well and are responsible for enforcing the purchaser's specifications and standards. Packing and Marking ... The details of the requirements affecting packing and marking of castings should be fully described to the foundry, if it is not familiar with the buyer's requirements. Other Requirements ... Information on detailed drawings, materials and quality levels, casting design, and service requirements was given in the section on new casting design. Check List ... The following items constitute a good, general basis for the purchasing agent to follow in getting the best quality, delivery and price: 1. Use standard specifications set up by ASTM or SAE, if special properties are not imperative. 2. Understand thoroughly the quality to be purchased. Specify acceptance standards of quality—radiography, ASTM E-71, magnetic particle testing, ASTM E-125, etc. 3. Spell out any additional rejection limits other than those speci- fied in the acceptance specification. 4. Explain in detail any permissible exceptions to ASTM or other specifications. Such exceptions might help to reduce the cost or eliminate production hazards. 5. Furnish a pattern constructed for casting steel. Accuracy and dimensional tolerances cannot be held, if the pattern is con- structed for casting another metal. 6. List all inspection requirements, and provide special gages and fixtures to insure the required quality and tolerances. 7. Be sure that the locating points are shown on the drawing and used by the layout or setup man, inspector and patternmaker. 8. Do not request immediate delivery of the whole order unless it is absolutely necessary. 9. Both quality and cost are affected if all essential information is not made available to the foundry. If not supplied, the foundry has to make assumptions. 112 PURCHASING OF STEEL CASTINGS Summary ... It is evident that buying castings is not a simple matter of a buyer looking at a requisition, determining the pattern location and then issuing a purchase order for his requirements. Modern casting problems have become more complex so that more information—not only of the foundry process, but also of the end use of the castings—is increasingly more important. A number of factors must be considered to assist the buyer in securing all the pertinent data for the foundry- man. The buyer's purchasing agent should maintain close liaison be- tween his engineers and the foundry's sales and process engineers. r CHAPTER IV FUNDAMENTALS OF STEEL CASTING DESIGN SECTION I Principles of Correct Design Correct steel casting design is of paramount importance, since it is responsible for satisfactory casting service and economical casting pro- duction. The field of application of steel castings, as engineered parts for industry, is constantly expanding as design and foundry engineers approach a better understanding of their mutual and respective prob- lems, adjusting objectives of the one to the facilities and techniques of the other. > It is not essential that the design engineer be thoroughly versed in steel foundry practice or that the foundry engineer be qualified as machine designer. Their common interest is in the economical produc- tion of a steel casting which will embody the characteristics of quality and utility. Whole-hearted cooperation will result in the avoidance of high production costs. Consultation between the design engineer and the foundry engineer, while the design is in the process of development, will improve both castability and casting quality. Design: A Cooperative Effort ... Close and effective cooperation be- tween design engineers and steel foundrymen is highly desirable for the following reasons: (1) The service of a structure is largely dependent upon its design. Designs which achieve the proper placement of metal reduce localized stress concentrations in the part. (2) A quality product can best be produced when fundamental principles of acceptable engineering design are incorporated in the casting drawing. (3) Manufacturing costs and, hence, selling prices are influenced measurably by casting design. Adherence to casting design fundamentals is compatible with reduced manufacturing costs. (4) Requirements of weight saving and increased service stresses make it highly desirable that knowledge of correct steel casting design be available and put to use. The use of higher strength cast steels, in a correct design, can further increase weight savings. (5) An appreciation of casting designs permits familiarity in the redesign and replacement of weldments, or forgings, by cast- ings; takes advantage of economic considerations, cast-to-shape O Fig. 195—Consultation of designing engineer and foundry engineer on a steel casting design. 1 advantages (minimum machining), lower weights, uniformly improved service life, and dependability afforded by steel cast- ing construction. Advantages of Steel Casting Design ... The steel casting process has tremendous advantages of economic importance that are significant to the design engineer, and which no other fabrication process can dupli- cate. These advantages are: (1) Design freedom. Utilization can be made of the proper distri- bution of metal to obtain the optimum weight-strength ratio. Intricate shapes can be made which are not possible except by the casting process. (2) Reduction of stress concentration. Adequate fillets, streamlined shapes, blending contours, one-piece construction, and section thickness modifications are features that the designer may use to reduce stress concentrations. (3) Low end cost. Tooling costs (patterns vs. dies, or jigs and fix- 3 tures) are lower, and small quantities can be made economically. Steel castings substituted for other methods of fabrication give excellent service performance and are low in end cost. (4) Uniform strength. Steel castings have uniform strength in all directions. There is no differential between transverse and DESI GN 115 longitudinal properties in steel castings, as exists with forg- ings, extrusions and rolled shapes. (5) Wide choice of properties. Cast steel with strength properties from 60,000 to 250,000 psi is readily available for wide design variations. Analysis of Design ... The design engineer considers the following points when designing a new component or redesigning an old part: (1) manufacturing method, (2) quantity required, (3) service requirements, (4) weight requirements, and (5) costs. It is suggested that these items be examined briefly with steel castings in mind as the method of construction. 2 Fig. 196—Consultation of foundry operating executives as to the production procedures of a casting. Manufacturing Method... It is advisable that the numerous advantages of the steel casting process, as listed and set forth in full in Chapter I, be kept in mind. Perhaps the most important of these advantages is that the casting process is the most direct method of producing either simple or intricate parts. Once the decision is made to employ a steel casting, the efforts of the design engineer and the foundry engineer should be directed toward a correct casting design. Quantity Required ... The number of duplicate parts required is im- portant in determining the manufacturing method. Parts produced on a pilot basis should be re-evaluated as to manufacturing method after new quantities have been determined. Service Demands ... The part must function properly and carry the necessary service loads. The design will have considerable effect on the 116 DESIGN service life of the part, and design fundamentals will determine whether the part can be produced economically. Weight Allotments ... Weight is as important as maximum strength in many machines, and minimum weight is usually desirable. However, indiscriminate weight slashing is not always a complement to correct cast design. A careful study of design fundamentals will show that both padding and coring, the two extremes, are useful tools of design. Cost ... Minimum cost is obtained when the part is properly designed because it is almost axiomatic that the correct design, from the stand- point of service stresses, is also the proper design for economical production. The design engineer, after making the analysis of the design prob- lem, is now in a position to develop the design of the part. The first step is to produce freehand sketches which provide latitude not found on the drawing board. Sections can be blended, and joining sections can be designed in accordance with the specific rules given in the next section. Consultation with the foundry engineer at this stage is beneficial because ways of improving the proposed design often are possible in order to utilize the advantages of the steel casting process (Figure 195). These suggestions create the point of union between good design and good foundry practice. Discussions as to pattern equipment and layout also can proceed at this time. The design is now ready for final drafting. SECTION II Steel Casting Design Fundamentals The designer can do his part toward the fulfillment of the basic concepts of solidifying steel by following the fundamentals of steel cast- ing design. If practical application forbids strict adherence, it is sug- gested that the designer consult with the foundry engineer concerning the special techniques that need to be employed to circumvent these rules which, at the same time, will produce acceptable castings. Good steel castings can be, and have been, made of designs that violate the principles of good design set forth in this chapter but the special methods which must be employed will frequently increase pro- duction costs. Minimum Section Thickness ... The rigidity of a section often governs the minimum thickness to which a section can be designed. There are cases, however, when a very thin section will suffice, depending upon strength and rigidity calculations. However, it is necessary that a limit of minimum section thickness per length be adopted in order that cast steel sections will fill out completely. DESIGN 117 Molten steel cools rapidly as it flows through a mold; thus a thin section close to the gate which delivers the hot metal will run readily whereas the same thin section at a distance from the gate may not run. Since the design engineer has no knowledge regarding the location of the gate, a minimum thickness of 14 inch must be suggested for de- sign use. It should be pointed out that for a given thickness, steel flows best in a narrow, rather than in a wide web. If the 14-inch thick section is longer than 12 inches then a greater thickness is necessary in accordance with the values of Figure 197. The curve of this chart represents the best of design conditions wherein molten steel enters at one position on the casting and must run the lengths prescribed on the chart. It must be realized by the designer that provisions may be made by the foundryman through the application of special tech- niques to pour even longer members through thinner sections than indicated by the graph. However, such applications are usually respon- sible for increased costs of production. 3/8 MINIMUM THICKNESS OF CAST STEEL 14 SECTIONS AS A FUNCTION OF THEIR LARGEST DIMENSION % 144 / 12 24 · INCHES MINIMUM THICKNESS - seo o no seu mat o 那么​如 ​50 100 150 200 250 300 LENGTH OF SECTION IN INCHES Fig. 197—Minimum thickness of sections as a function of their largest dimension. Note: The curve represents the best of design conditions wherein molten steel enters at one position on the casting, and must run the lengths prescribed on the chart. Special techniques will permit the running of thinner sections than shown. Uniform Thickness in Casting Design ... The designer has no previous knowledge of the manner in which the casting is to be positioned in the mold; therefore, the ideal casting design is one having only a single thickness. A good rule to follow is to hold the number of varying thicknesses in a structure to a minimum. The reason for doing this is that positions of abrupt changes in thickness are also positions of stress concentration. An example of nonuniform sections is shown in design A of Figure 198 which incorporates four different thicknesses. The outer flanges 118 DESIGN 西西 ​5/8" A B Fig. 198—Uniform section design is recommended. are too thick as compared to the walls and it was necessary to rib the flanges to prevent foundry problems. Design B is the correct design. The diameters of the flanges have been reduced and the ribs omitted. Also, only two different thicknesses have been employed and use has been made of the taper at joining sections. Changes in Section Size ... While it is desirable that all sections in a steel casting be designed with a uniform thickness, it is recognized that there are times when the designer has no alternatives and sections must vary in thickness. The examples in Figure 199 indicate the accepted methods of section change. Sharp corners and small radii in a change of section should be avoided whenever possible because they are often responsible for stress concentration and casting hot spots. A radius of 1 inch, or a 15-degree taper, is an acceptable method of design when changes are made on both sides of the section. POOR DESIGN NOT RECOMMENDED Kr:1"OR GREATER FAIR DESIGN FAIR DESIGN GOOD DESIGN NO CHANGE OF SECTION- RECOMMENDED RECOMMENDED DESIGN Fig. 199—Section changes. It will be observed from Figure 199 that the best method of tackling the problem of section change is to make the change take place entirely on one side. Again, the change of section size must be progressive and gradual in order to avoid localized positions of stress concentration. This can be accomplished by employing a 15-degree taper if the thin member is less than 23 the thickness of the thick member. DESIGN 119 The values given in Figure 200 are recommended for design use. However, in no case should one employ in sketch A a joining section ratio greater than 2 to 1 (D/d) unless the principle employed in example sketch C is used. If the ratio of 2:1 is employed in sketch A, the radius should be r=1 inch. A D • Aim B riz" D d) D D d>%D IF D > 1.5" AND d > 9/3D THEN P: IF D< 1.5" AND D D THEN Pila" 8 roep с 15 DEGREE SLOPE BLEND IN D d : IF DX 1.5" AND d < THEN P: WITH A 15 DEGREE SLOPE BETWEEN THE TWO PARTS, FOR EXAMPLE: d:'2", D:2", r: 믈 ​3 : 0.7 Fig. 200—Section changes on one side. Research has shown that section changes, other than on one side, such as Figure 199 (Fair Design), are poor design practice as such designs create adverse temperature gradients and stress concentration during solidification. However, when the designer must join sections at locations other than at the base of the heavier section, a radius of 1 inch or greater should be used. Thus: When d=1/2 inch and D 32 inches then R =1 inch or > 1 inch Cylindrical sections of different section sizes may be joined success- fully, under certain limitations, without causing positions of excessive stress concentration. In joining cylinders the ratios of sections, as well as the size of the joined cylindrical section, must be taken into account. Increasing cylindrical sections in castings of constant ratio (D/d) will improve the casting design. For example, a 1-inch diameter section joined to a 2-inch diameter section will usually cause foundry problems at the junction unless a 15-degree taper is used. However, a 2-inch diameter section joined to a 4-inch diameter section may be accom- plished successfully, regardless of the radius employed at the intersection. 120 DESIGN . Joining cylinders whose ratio (D/d) is held constant at 2:1 should be designed as shown in Figure 201(a). The behavior of a particular section ratio (D/d) in one size range is definitely not translatable into similar behavior for the same ratio in other size ranges. D -d- 7 r (a) Joining cylinders ratio (D/d) of 2:1 D d 1 12 15 degree taper 2 1 15 degree taper 4 2 42 to 192 inches W h 1 (b) Joining plate sections Fig. 201-Changes in section. Joining a small diameter cylinder to a larger diameter cylinder must be done by the use of a 15-degree taper. Thus a 15-degree taper is required to join cylinders when the smaller diameter (d) is less than 1 inch and the larger diameter (D) is 15/8 inch or less. This design rule may be expressed as follows: When d=1 inch and D 315/8 inch then R =15-degree taper Cylinders greater in diameter than 15/8 inch cannot be successfully joined to a 12-inch diameter section, as fillets are no longer effective in eliminating discontinuities at the junction. In fact, increasing the radius is poor design in this instance. The use of a taper greater than 15 degrees is ineffective in joining cylinders and should not be used. Stress Concentration in the Changing of Sections The joining of bar and plate sections must be considered carefully because the serviceability of a part depends mainly upon its ability to withstand sudden and repeated loads. The stress concentration result- DESIGN 124 ing from the abrupt change in section thickness may, accordingly, reduce the serviceability of the part. Metal overloaded in fatigue fails at loads lower than expected from its tensile properties. Therefore, tensile properties, even yield strength, become relatively minor factors in the dynamic load-carrying ability of ductile metals; and fatigue strength, together with resistance to notch brittle fracture, become major factors. The shape of the part largely governs stress concentration and is, accordingly, the predomi- nant factor influencing fatigue strength and notch brittle fracture. Table 3 refers to Figures 201(a) and 201 (b); and it shows the stress concentration values for a change in section of two cylinders and two plates of different diameters, and plate widths joined together by various radii. It is evident from the table that as the radius (r) in- creases the concentration factor (K) is reduced. Table 3-Stress Concentration at Junctions of Cylinders and Plates When Loaded in Bending, Torsion and Tension Two Joining Cylinders (Fig. 201a) D/d 2 Type of Loading Bending Torsion Tension r/d Ki Ki ܚܪ ܘܘ ܕܪ Kt 2.40 1.27 1.20 1.13 1.25 1.15 1.10 1.07 1.55 1.40 1.30 1.20 1.0 Two Joining Plates (Fig. 2015) Type of Loading Bending Tension h/r=0.5 h/r=3.5 h/r=0.5 h/r=3.5 r/w .3 .5 .7 1.0 Kt 1.47 1.35 1.27 1.19 Κ. 1.70 1.50 1.36 1.25 K 1.32 1.21 1.15 1.08 K. 1.42 1.30 1.21 1.12 The casting process excels when it comes to producing parts with cast-to-shape radii as desired. No other forming process can produce radii necessary to minimize stress concentration with equal efficiency. This advantage in load carrying ability is by no means minor. The difference in theoretical stress concentration (K) resulting from increas- ing the fillet radius of joining cylinders with a 1-inch smaller cylinder (d) from 0.1 to 1.0 inch, is Kt 1.90 to 1.13. This difference is equal 122 DESIGN to an increase in load carrying ability, particularly in fatigue, of 68 percent. This is equivalent to increasing the fatigue strength of steel from 28,000 psi to 47,000 psi. Such an increase in fatigue strength requires an increase in tensile strength, at 45 percent endurance ratio, from 70,000 psi to 118,000 psi. It is for these reasons that care must be taken in designing the radius at the positions of change in section thickness and at joining sections. The Designing of Joining Sections ... Anything that a design engineer can do towards eliminating pronounced isolated hot spots, either in a casting section or at joining sections will assist greatly in the elimina- tion of foundry problems, with consequent reduction in final cost of casting. Figure 202 indicates that use can be made of inscribed circles to determine the size of the hot spot or the importance of mass effect. st S S moet polen r fize (9)*:(:) : 2.25 ()*:(27) * 3.24 (3)*: (3:)*: 4.00 INCREASE OF MASS 125% INCREASE OF MASS 224% INCREASE OF MASS 300% Fig. 202—The use of inscribed circles to determine the effect of mass. The relation of the mass of metal in two different places in the same section is approximately equal to the ratio of the area of the corres- ponding inscribed circles (ratio of the square of the radius) that can be drawn in the sections. The method of inscribed circles has proved most effective for design use. The designer may easily evaluate, with sufficient approximation by a graphic method, the effect that increased mass or a designed hot spot may have on casting quality. > There are only five ways in which sections may be joined. These may be exemplified by the following letters of the alphabet: L, T, V, X and Y. All other modes of connection are merely modifications of the above possibilities. "L" Sections ... The L junction occurs very often in the design of parts. The most commonly found L design in steel castings is the one illustrated in sketch D, Figure 203. Stress concentration values (K) of the L shape are influenced by the radii of the fillets as illustrated by the graph of Figure 204. (18, 19) The value K, denotes the increase in over-all stress resulting from the design geometry modified by surface discon- DESIGN 123 d 《 A B с D FAIR DESIGN GOOD DESIGN GOOD DESIGN POOR DESIGN WHERE dat AND 7:0 WHERE det WHERE dit AND á á < 0.40 کی AND WHERE d:7 : 1.0 AND á : 1.0 . NOTE + : THE SECTION THICKNESS AT THE JOINT Fig. 203—Evolution of the L design for maximum fatigue life. 2.4 2.2 r:0.2d Kt. 2.03 2.0 1.8 TORSION r: 0.5d Kf = 1.40 Fig. 204—The stress concentra- tion factors of an L section (Caine)." STRESS CONCENTRATION FACTOR • 1.6 16 r:1.0d Ky: 1.20 TENSION 1.2 . 11 1 EXTRAPOLATED 1.0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 13 14 RADIUS OF FILLET/THICKNESS - /d tinuities on the part, type of load application, overloads and misalign- ments. For example, a Kt factor of 2.0 on the L design in Figure 204 indicates that for every 1000 pounds of over-all load the metal at the surfaces of the junction of the two members is subjected to twice the over-all stress, or to a stress of 2000 pounds. A stress concentration factor of unity (1.0) denotes no stress concentration and the load is distributed evenly throughout the shape. Figure 204, therefore, indicates that as the inside radius of the L section is increased the concentration factor decreases. A change in the concentration factor from 2.00 to 1.20 results in an increase in the load carrying ability of about 70 percent for the particular L section under consideration. However, it should be pointed out that as the radius increases in size, the mass of metal (hot spot) at the junction 124 DE SIGN also increases so that it becomes inadvisable to pursue the idea of dropping the concentration factor to an absolute minimum. It will be observed from Figure 204 that the stress concentration factor does not change much at values of r/d greater than 1.0. There- fore, the radius of the fillet to the thickness of the section (r/d) should in no case exceed the 1.0 value, which in this case is a concentra- tion factor of Kt=1.2. The size of the hot spot at the junction, there- fore, can be limited. However, on the other hand, the load-carrying ability of the section should not be reduced greatly. This condition can be fulfilled if an r/d value of 0.5 is selected as the minimum. The L design of Figure 204 shows that for r/d=0.5, a stress concentration factor of 1.4 is obtained which is only a 17 percent reduction in the load-carrying ability, when compared to the 1.2 factor at a radius of 1.0d. L sections radii should be within values of 0.5d and 1.0d. Higher stress concentration factors are obtained under torsion stresses (18) as shown in Figure 204, but the values are relative for the junction radii under consideration. Stress concentration factors have actually been determined on steel casting L sections. The designs studied are illustrated in Figure 205 and the test specimen design is shown in Figure 206. The stress concentra- tion factors are given in Table 4. " Kt:2.03 Ky=1.21 Ky-1.23 90 ° IN Bing 1 6 Fig. 205—Corner type designs for cast steel L specimens. " 17 Kj: 1.58 K4 = 1.73 900 Kt:1.36 4 5 Table 4-Stress Concentration Factors of Steel Casting L Designs K. Determined by: Corner Design Photoelasticity Strain Measurement 1L 1.21 1.171 2L 1.23 1.22 3L 1.36 1.338 1.58 1.60 5Lt 1.73 4L † Outside radius same as 4L but with a 90-degree inside corner. Comparable design in a box section gave a Ků value of 1.37. § Comparable design in a box section gave a Kį value of 1.40. DESIGN 125 LOAD LOAD inloo Fig. 206—Dimensions of the cast steel L specimens tested. Section depth is l-inch. 442" OR LOAD 100 LOAD -1 4'2" It will be observed that the strain measurement values are very close to those predicted by photoelastic techniques. This means that steel castings can be produced to any fillet radius desired by the design engi- neer. Also, it is observed that it is not necessary that an outside corner be a part of the L design just because it normally appears this way in the design of many structures. Design 3L has a Kt value of 1.36 which is below the K=1.40 value previously set as the upper limit for the L junction design. Furthermore, the relative strength diagram and the data on the limited life fatigue tests of Figure 207 indicate that design 3L should be given careful consideration as an alternative casting design to those of 1L and 2L. 100 10,000,000 Fig. 207—Property comparison of L 75 design castings 1,000,000 (a) Relative strength of casting 50 designs. 100,000 (b) Limited life fatigue tests of steel castings at a constant preload of 1170 pounds. 0 10,000 LLLLLLLL LLLLLL 1 2 3 4 1 2 3 4 (a) (b) Design D of Figure 203 (1L of Figure 205) and Design 2L of Figure 205 give the highest fatigue life and relative strength as proved by ex- tensive testing of steel casting L sections. Design 3L of Figure 205 gives very good results in fatigue testing and, although its relative strength is 80 percent of the full section, it has an added feature: it presents RELATIVE STRENGTH - PERCENT CYCLES TO FAILURE - 1170 LB. PRELOAD 25 126 DESIGN fewer foundry problems. However, there are many cases where the ex- terior angle of the L section cannot be rounded, such as a flange joint, etc., and in such cases design D of Figure 203 is employed. Section thick- nesses of less than 1 inch should be designed so that the radii at the inside junction will be from 1/2 to 1 inch as shown in sketch A of Figure 204. Section thicknesses greater than 1 inch should have an inside radius equal to 1 inch regardless of the thickness of the section. A B D LE r:1" OR r: ot BUT NOT < 1" BLEND IN SLOPE 15° WHEN di 1", r:d. WHEN > 2 EMPLOY 15° SLOPE WHEN d >>" BUT < 2" D-d : MIN. LENGTH OF SLOPE THEN a 3.5 BUT < 1.0 WHEN D > 2", :.5 Dd Fig. 208–L designs with exterior corners. Figure 208, sketch B, illustrates the correct design if the size of one arm of the L is greater than twice the thickness of the other. Foundry problems can be minimized if the D/d ratio is less than 2. However, when the design dictates that the thickness of one leg of the L be greater than twice the thickness of the other, then the design should contain a 1-inch inside radius. The radius is then connected by a taper of 15 de- grees to the lighter section such as is shown in sketch B of Figure 208. External Corners . . . Hardenable metals, such as steel, form high ther- mal gradients across the section when sharp external corners cool from high temperatures. The elimination of these high temperature gradients by employing an external radius will do more than any other single step to prevent corner cracks. Rounded corners usually require an additional chamfering operation in any other forming process than casting. Most rounded cast corners can be made on the pattern with a simple template and a piece of sandpaper. The two exceptions, sharp corners formed at partings, and where the cores leave the casting cavity, can be remedied in the original construction of the pattern, if properly specified by the designer. This detail usually can be covered by a blanket notation on the drawing. An external corner radius of between 0.10 and 0.20d (d=section thickness) is necessary to avoid high thermal gradients. The 19-inch external radius on the 5/3-inch section of Figure 205 Design IL was pre- DESIGN 127 pared with this in mind and the stress concentration factor obtained experimentally for this design is similar to the theoretical value for a sharp external corner. “V” Sections ... The best V section design to use for steel castings is that shown in sketch A, Figure 209. In no case should an outside corner be used if the junction angle is less than 90 degrees. The recommended design values of sketch B should be employed if one arm is larger than the other. The inner radius must not be less than 1 inch in any V design. "V" SECTION D d d R De R А B r:1.5d BUT NOT LESS THAN 1" r. Did BUT NOT LESS Rir+d THAN /" R:r+d R,:r+D Fig. 209–Recommended V designs. 8 “T” Sections ... Sections joining in the form of a T have stress concen- tration values in relation to the fillet radii very similar to those of the L junction, as can be observed from Figure 210.(18) The values also level 2.4 r: 0.2d Kt:1.5-1.9 *12.2 & (a) 2.0 1:0.5d Kr: 1.3-1.45 1.8 (6) 1:1.0d Kyil.1-1.25 STRESS CONCENTRATION FACTOR: Kt 1.6 yok d TENSION 1.4 BENDING (C) h * 1.2 1 1 1 I EXTRAPOLATED 1.0 O 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 RADIUS OF FILLET / THICKNESS- 1% Fig. 210—Stress concentration factors for T sections (Caine).16 128 DESIGN off at a fillet radius of about 1.0d and there is little to be gained with larger radii as far as stress concentration is concerned. It is also known that the hot spot size increases at the junction as the radius of the fillet increases and, therefore, it is advisable that the fillet radius be kept to a minimum. Research on casting sections has shown that the minimum fillet radius to be employed is 1 inch, even though the arms and legs of the T should be less than 1 inch thick and the concentration factor would be less than K=1.2. It is necessary, from a foundry standpoint, not to permit harmful notch effects which would come from small radii. Also, the same research studies have shown that the fillet radius should not be larger than 1 inch regardless of the widths of the joining sections (up to about 3 inches) in order to prevent the detrimental effect of increased mass. Three-inch joining sections with a 1-inch radius would result in a not too serious stress concentration factor of K=1.6. Con- centration factors of more than K=1.6 probably should not be used, and a radius larger than 1 inch would become necessary even though undesirable. - The rules for the design of T junctions, therefore, can be illustrated as set forth in Figure 211. The best T joint has the dimension of the arm (D) in Figure 211 equal to the dimension of the leg (d) of the T. Thus, for T-Sections d=D. K 347 15° TAPER -D-> I'd 가뷁 ​에 ​: A B WHEN D:d, r SHOULD EQUAL "/" WHEN D IS EQUAL TO OR LESS THAN THREE TIMES d, THEN r :/ INCH, AND A 15.DEGREE TAPER IS EMPLOYED AS SHOWN IN SKETCH "B" Fig. 211–Recommended T designs when D=d and when D is greater than d. It is not always possible for the designer to employ a uniform sec- tion size when the sections form a T. Under these circumstances it is absolutely necessary that the dimension of the arm (D) of the T-section be equal to, or greater than, the dimensions of the leg (d). Thus, for alternate T-sections Dsd. DES I GN 129 No matter what radius is employed at the intersection of a T section in which the arm (D) of the T is of smaller cross section than the leg (d), foundry problems occur. Such design is to be avoided. A practical example of a proper T design is the 54-inch diameter gear of Figure 212. Normally, the gear would be designed as illustrated 14" VINZ 2'3" 1 7 R 2%" 자 ​IR 110 54 DIA. CL А B Fig. 212—Changes effected in the design of a large steel casting gear. in sketch A. The circle shows the large accumulation of mass (hot spot) to be 10.3 sq. in. Sketch B is designed with the web divided into two thin arms with greatly reduced hot spots of 7.6 sq. in. The radius be- tween the leg and arms is 1 inch in both cases; but in the B design, a taper is also employed. The B design is a manifest improvement over A. Design of Reinforcing Members... Tie-in members, ribs, or webs, usually join the walls of a casting in a T section and a hot spot is formed. Figure 213 illustrates that the hot spot is less when the web is thin as com- T ir 2"- 서법​에 ​Fig. 213—Tie-in members in the form of T sections. pared to the side wall and a more "thermally neutral" junction is ob- tained. The reduction of the size of the hot spot in the case of the example is 21 percent. It is suggested that stiffening ribs, brackets, or tie-in sections be thin sectioned. Also, extra heavy sections in the main casting design may not be necessary if use is made of section reinforce- 130 DESIGN ment. An example of this principle is given in Figure 214. Sketch A is an orthodox design which employs varying sections for strength re- quirements. Sketch B illustrates a uniform section with the employ- / 12 A RIBS OR BRACKETS TK 产 ​/" B Fig. 214—The use of brackets in steel casting design. ment of ribs or brackets. The bracket on the right of the design, sketch B, shows a cored hole at the inner radius of the L section. This is a good design feature as it prevents an accumulation of mass at that point. Coring will not impair the stiffening features of webs or brackets. Figure 215 is an enlargement of the junction of the bracket and the L section to show the shape of the cored construction. -Rib or Bracket A Fig. 215-Cored rib construction. Cored Construction Ribs are suspected of increasing stress concentration; but, if they must be used, a simple rule is to make the rib section 25 percent of the section of the main member, unless this rule results in a section too thin to cast, such as illustrated in sketch (a) of Figure 216. If the rib stif- feners differ widely in thickness, then designs of sketches (b) and (c) should be employed so as to take advantage of "thermally neutral” junc- DESIGN 131 tions for varying rib heights. If the rib junctions are proportioned, as shown in Figure 216, the junction solidifies at the same rate as the thicker member, solving many castability problems. However, regard- less of rib thickness, it is always advisable to stagger the ribs, as also illustrated in Figure 216. RIBS (a) ldk D (6) >dk (c) P:/4 tdk :/" 1:1" " h D D D WHEN D :/4D THERMALLY NEUTRAL UNTIL h : 4D WHEN d:120 WHEN : 3/4 D THERMALLY NEUTRAL THERMALLY NEUTRAL UNTIL h :1.5D UNTIL h:0.50 D நத்து F70 MINE Fig. 216—Design of ribs (Caine).16 Brackets, or webs, employed in joining T or channel sections, are shown in Figure 217. It is recommended that the design correspond to the values listed in the illustration. KLA D- CHANNEL SIDE BRACKET (d): 30 MIN. D: 1.Od THERMALLY NEUTRAL UNTIL : 0.5 d +34 MIN. D-1.3 d THERMALLY NEUTRAL UNTIL 1 : 0.33d 30 MIN. D : 2.0d THERMALLY NEUTRAL UNTIL A : 0.10 d Fig. 218—Design of bosses, r= 1/2 D in all cases (Caine).18 pared by Caine. (16) If this is done, casting problems will be minimized and the cost of chills and special risering decreased. The design sug- gestions of Figure 218 are based on heat transfer data. “Y” Sections ... The Y section is a modification of the T intersection. . It is a much more difficult design for the foundryman to handle, and it is suggested that design engineers, whenever possible, use the T design in place of the Y design. The recommended design for Y junctions is shown in Figure 219. The rules for the V and T junction are combined to develop the Y design. Sketch B of Figure 219 illustrates the manner in which the Y design can be changed into a T design. "Y" SECTIONS Y Y ri B. A p:1.50 BUT NOT 3d Fig. 221-Recommended X design. is a hot spot if it cannot be fed by a riser, and will result in the usual foundry difficulties. Offsetting the arms permits the foundryman to use external chills at the inner radii to produce acceptable sections. The arms must be completely offset, such as in sketch C, to form separate T sections. Insufficient improvement is accomplished if a design such as shown in sketch B is used. The radii for X section designs that are not modified should be 1 inch, regardless of section size. The designer may find that in certain instances the offset arm design cannot be used. In such cases the designs of Figure 222 are sug- gested, and modified Y sections are used. 134 DES I GN A design which contains several joining X sections, such as exhibited in the rectangular checkering of Figure 223, may be redesigned to re- place the X sections with the Y (hexagonal), or even a circular design CORED (OPENING 14* MIN. CORE Fig. 222—Cored X design. to bo avoided KIGO good resistanco to bonding (11 110 110 BIIIIIIINT to be avoided RC bending and torsional resistance improved as compared with 6. excellent torsional resistance but requiros the use of a core Fig. 224—Various methods of joining two walls by means of open or closed sec- tions.(2) 1000 Fig. 223—Rectangular design replaced by hexagonal de- sign. and still retain the same moments of inertia. Also, Figure 224 indicates various methods of joining two walls by means of open or closed sec- tions without using X junctions. The Y and X junctions in a commercial steel casting (sketch (a), Figure 225) are often found in connecting links, levers and similarly DESIGN 135 shaped castings because of the design engineer's desire for improved stiffness. Such junctions are always positions of stress concentration and increase foundry difficulties during manufacture of the casting. Sketch (b) changes the Y junction to a more proper design, and the X section is eliminated entirely. Stress analysis on this casting showed that the ribbing as employed in sketches (a) and (b) was of little value in the over-all load-carrying ability of the casting and, additionally, was introducing locations of high local stress concentration. Maximum stress was in torsion in the area AA of sketches (a) and (b). The complete redesign of sketch (c) of Figure 225 showed lower unit torsional stresses in the area AA than in the ribbed I-beam construc- tion. All ribs are removed, eliminating 10 points of stress concentration and a corresponding number of trouble areas for the foundry. The ob- jection to design (c) is that it "looks funny," This is because of its simplicity without the crisscrosses of ribbing which are so familiar to everyone. Another example of X sections designed to T sections in steel cast- ings is illustrated in Figure 226 which shows a portion of a casting X JUNCTION 个 ​Y JUNCTION А A ! SECTION A-A (a) (6) 究 ​13 B A, SECTION BB A, SECTION A,-A, (c) Fig. 225—The redesign of a steel casting to eliminate the X and Y junctions. 136 DESIGN TDI MOTE Fig. 226—A grid casting designed with T instead of X junctions. containing extensive grids. A modification of the grid casting is shown in Figure 227 where curved ribs are used which materially reduce the tension at the T junctions in the grid and at the junctions of the grid with the heavy frame. Isolated Masses ... A design is occasionally encountered in which an area of heavy metal is attached on all sides to members of much smaller thickness, and so located that the foundryman has no opportunity to insure solidity of the heavy portions by means of feed reservoirs. Such a condition is distinctly one of improper design. The heavy section should be either cored or more closely investigated to ascertain whether it can be made lighter. Wave Construction ... Wave construction is a design principle that should be mentioned in connection with the relief of internal stresses in cast structures. This design calls for the use of members which are slightly waved or curved. Fig. 227 — Another grid casting with curved ribs to eliminate the X junction and to reduce tension stresses. DESIGN 137 A very good example of this type of construction is the use of curved spokes (Figure 228) in many classes of wheels. In such castings the rim, the hub, and the spokes may each cool at a different rate, because of differences in their cross sectional areas, thus subjecting the casting to considerable internal stress. The use of the wave construction mini- mizes these internal stresses by allowing movement of the casting after solidification. POOR - RIGID DESIGN C Fig. 228—Wave construction -Elastic design. [ [ D GOOD - ELASTIC DESIGN B А Design of Cored Openings ... A possible source of high stress concen- tration is a hole in a flat plate, as shown in Figure 229, by Caine (16) Theoretical stress concentration in tension (K) can reach a value of 3.0 and over 2.6 times the over-all stress in bending. These values are higher 3.0 2.8 2.6 2.4 UNREINFORCED HOLE TENSION $:0.25 2.2 STRESS CONCENTRATION FACTOR, K. UNREINFORCED HOLE BENDING 2.0 18 -2.0 1.8 이디 ​/ . 1.3h 1.6 W 20 d REINFORCED HOLE TENSION 1.4 X=KF VALUE FOR WROUGHT STEEL tonte d/w: 0.1 0.2 0,3 0.4 0.5 0.6 Fig. 229—Theoretical stress concentration induced by a hole in a flat plate stressed in tension and bending (Caine).16 138 DES I GN than any previously given for other shapes. A few reported decreases in fatigue strength (Ke) are lower than the theoretical values of Kt, as shown by the X's in Figure 229. However, the decrease in fatigue strength is substantial, i.e., 30 to 50 percent. One solution, well adapted to casting, is the reinforcing boss. The decrease in stress concentration for one such reinforcing boss is shown in Figure 229 as being substantial. These bosses can be proportioned according to the recommendations of Figure 218. The minimum diameter core which can be successfully used in steel castings is dependent upon three factors: (1) the thickness of the metal section surrounding the core, (2) the length of the core, and (3) the special precautions and procedures used by the foundry. The thermal conditions which the core must withstand increase in severity as the metal thickness increases and the core diameter decreases. This, of course, is the result of an increasing amount of heat to be dissipated in heavier sections, and a decrease in the ability of the core to absorb and dissipate this heat as the diameter decreases. As the severity of the thermal conditions increases, the cleaning of the casting and core re- moval become much more difficult. The thickness of the metal section surrounding the core, and the length of the core, both affect the bending stresses induced in the core by buoyancy forces and, therefore, the ability of the foundry to obtain the tolerances required. The size of the core must be large enough to facilitate rodding of the core to withstand these stresses until the steel freezes. Naturally, as the metal thickness and the core length increase, the amount of rodding required also increases. Therefore, the minimum diameter core must also increase to accommodate the extra reinforcing. The curves shown in Figure 230(a) indicate the recommended mini- mum core diameters to be used in cylindrical or boss sections in steel castings as a function of the metal section thickness and the core length. > 8 Ta) (6) Minimum core diameter, in. 4 L : up to 6 in. -L=6 to 18 in. W equal to or greater than 5T 1 L = 18 to 36 in. 4 6 8 2 8 10 12 0 2 4 6 10 12 Section thickness surrounding core, in. Plote thickness, in. (a) (b) Fig. 230—a) Recommended minimum diameter for horizontal cores supported at ends only, in cylindrical or boss sections of steel castings. Minimum core diameters shown in the three curves can be reduced by 25 percent if the core is vertical in the mold. (b) Recommended minimum core diameter for plate sections in steel castings. DE SIGN 139 Thus, the minimum core diameter recommended for normal foundry practice in a particular application can be determined by locating the point at which the curve representing the desired core length crosses a vertical line representing the section thickness involved. These curves were prepared for cores placed in the horizontal plane only. Minimum core diameters determined from these curves can be reduced by 25 per- cent if the core is to be used vertically. A similar curve for cores in plate sections of steel castings is also shown in Figure 230. It is important to realize that these curves represent the minimum core diameter recommended for normal steel foundry practice. Smaller core diameters can be used, but they involve the use of special practices which may affect the price of the castings. Applications which require smaller cores than those recommended here should be discussed with the producing foundry. SECTION III Casting Design for the Ultimate in Section Modulus A combination of the junctions discussed in Section II, and adher- ence to the basic principles expressed therein, will result in a dependable design for connecting members of steel castings. The design engineer, in laying out a casting design, concentrates his attention on one or more important portions of the layout and then ties these portions together with a framework. For example, the lever in Figure 231 as prepared by Caine (13) is a specific case where the design engineer is interested primarily in the two ends, their dimensions and bearings. For this lever to be a load-carrying member, the ends must be connected. A properly designed web not only must utilize the funda- mentals of steel in order to produce the proper support for the ends, but in doing so make it castable as well. Many design engineers who are not familiar with casting design would employ the conventional oval section or I-beam sections of Figure 231 (a) and (b). The static load-carrying ability of the part can be estab- lished by the maximum fiber stress in tension and because the values under discussion are relative, the exact values are of secondary importance. A load of 21,000 pounds on the lever of design (a) Figure 231 results in a fiber stress of about 100,000 psi. The average stress throughout the section will be half the maximum fiber stress, or about 50,000 psi. This lever, therefore, should be made of a cast steel with a yield strength of 100,000 psi to carry the load with no factor of safety. This load may be reduced in practice to compensate for unexpected overloads or for a number of other factors. 140 DE SIGN 21,000 LB LOAD RESULTS IN A MAXIMUM FIBER STRESS OF 100,000 PSI AT THIS POINT. 21,000 LB LOAD RESULTS IN A MAXIMUM FIBER STRESS OF 34,000 PSI AT THIS POINT. 23** Lic 373 o lo 43/32 -X ho 21,000 LB 21,000 L8 VaR A. OVAL SECTION. AREA 4.9 SQ IN. Sx = 1.9 IN3 8. I BEAM SECTION. AREA 4.5 SQ IN. 1x: 2.9 IN ly: 12 IN Sy : 1.2 IN 1x: 12.1 IN. Ty : 1.9 IN Sx: 5.5 IN Sy: 1.4 IN 3 21,000 LB LOAD RESULTS IN A MAXIMUM FIBER STRESS OF 39,000 PSI AT THIS POINT. +234 21,000 LB LOAD RESULTS IN A MAXIMUM FIBER STRESS OF 37,000 PSI AT THIS POINT. 23** 716 Lot 2432 21,000 LB 21,000 LB C. CAST "C" SECTION. AREA 4.6 SO IN. O-LES O D. CAST BOX SECTION. AREA 4.6 SQ IN. 1x : 11.2 IN4 1x = 10.5 IN." ly : 1.3 IN.4 Sx: 4.8 IN Sy : .70 IN 3 S: 5.1 IN 3 Sy : 3.4 IN 3 Ix: 4.6 IN 4 -548 IN 21,000 LB LOAD RESULTS IN A MAXIMUM FIBER STRESS OF 44,000 PSI AT THIS POINT. 438" -5/16 E. CAST "U" SECTION. AREA 4.6 SQ IN. 1.9.1 IN4 by : 6.2 IN." Sx: 4.2 IN 3 Sy : 5.0 IN IT 21,000 LB Fig. 231—How design affects the stress in a lever and its load-carrying ability (Caine).": The lever probably is loaded dynamically, so that fatigue must be considered, and thus the load must be reduced to about 8,500 pounds while the cast steel must continue to possess a yield strength of 100,000 psi and a tensile strength of 125,000 psi. These conditions would be factual regardless of whether the part is forged or cast. Again, no fac- tor of safety has been considered. It is evident that if the lever of sketch (a) is to withstand the loads just discussed, it must be made of a steel heat treated to a minimum hardness of 250 BHN. Such hardness usually demands a liquid quenched and tempered alloy steel. Consider what can be done by redesign of the connecting member: the ends are accepted as is; the lever can be cast or forged with an I-beam connecting member, as in sketch (b). The over-all dimensions of this connecting member are increased, but to no larger than the over-all dimensions of the two ends. When this is done, the maximum fiber stress is decreased to 34,000 psi with the same over-all load. A more economical normalized carbon steel can be substituted for the quenched and tempered alloy steel. There are two objections to this design. If DESIGN 141 the part is forged, the more complicated multipass dies increase die costs many times. This drastic increase in initial cost is not reflected in pattern cost for casting, but the I-beam section is open to improve- ment when the best in casting design is employed. > Flexibility of the casting process permits any number of shapes that are better load-carrying members than the I-beam, for they can be streamlined for maximum dynamic load-carrying ability. The C-section in sketch (c) is perhaps the simplest. This cast section allows the use of a steel of equally low strength and cost, as the I-beam section of sketch (b), when only the principal (vertical) load is considered. If this lever must withstand appreciable thrust at right angles to the principal load or torsional deflection, the C-section also is inadequate. It is not necessary, in many cases, to have equal load-carrying ability in all phases, and the C-section of Figure 231(c) will be adequate. In cases where stiffness and load-carrying ability about both the X and Y axis are required, the box section of sketch (d) is considered the best. The reader, other than a design engineer, may not be familiar with the significance of the X and Y axis or the terms: moment of inertia (I) and section modulus (S). It is sufficient to describe the moment of inertia as the measure of the loading of the metal, and section modulus as the portion of the section carrying the maximum stress. The higher either or both values, the greater is the load-carrying ability. A load can be applied in all directions; therefore, it can be resolved about two axes, and I and S must be considered in relation to these two axes, X and Y, which represent loads acting in two planes at right angles to each other. The box or tubular sections are castable. In fact, the ability of the casting process to form rounded corners, unequal wall sections, and streamlined designs, makes the cast tube or box section very attractive to the designer. Cost is the only drawback to this design. Production costs can be high because of the use of cores and their removal from large castings. Therefore, other sections which offer approximately equal design properties, and can be cast without cores, are of interest. One such section, the U-section, is shown in Figure 231(e). A comparison of the values for the moment of inertia (I) of the five designs of Figure 231 shows that the box or tubular section is the best, but the I values can be approached, as shown by a comparison of the Ix values for the U and tubular sections (9.1 in4 vs. 11.2 in). The difference in imposed load is not great — 44,000 psi for the U vs. 37,000 . psi for the tubular section. This difference can be overcome at prac- tically no additional cost by heat treatment. It merely means varying the heat treatment to insure an increase in yield strength of 7,000 psi. 142 DESIGN The slight decrease in the I value about the X axis is more than offset by an increase about the Y axis. The U-section is stiffer and better able to handle side thrust than is the tubular section. This con- dition is of general adaptability and not limited to just the design of Figure 231; furthermore, most casting designs have the open ends of the U-section supported by connection to other parts of the casting. Designs (b), (c), (d), and (e) of Figure 231 have better load-carry- ing ability in fatigue than design (a) because the 14 inch radius imposes a stress concentration factor of about 1.6, whereas the other streamlined designs impose very little stress concentration. This difference increases the load-carrying abilities of the other designs by 60 percent regardless of other factors, such as strength of the metal, surface, and sequence of load application. . Design Properties of Cast Sections The uniform thickness junction section of the L design, such as shown in 3L of Figure 205, is excellent from the standpoint of a com- bination of streamlined design, low stress concentration, and castability. The uniform section of the rounded corners also permits a section modulus of 79 percent of the square corner. This 21 percent decrease can be easily overcome by increasing one over-all dimension a small fraction of an inch. The four streamlined cast sections to be compared in the following paragraph are not advanced as the very ultimate in cast design, but they are applicable to steel castings under static and dynamic conditions of loading, and they are being used in advanced designs for very highly stressed parts under exacting service conditions. One reason that streamlined, load-carrying casting sections have not been used extensively in the past is the laborious calculations neces- sary to determine their design properties. Although the casting process allows for an infinite number of shapes, standardization is advantageous if for no other reason than to save design time. The C-section design has been selected as the best of several dozen cast-to-shape equivalents of rolled channels and I-beams. For example, the cast C-section shown in Figure 232 exhibits moments of inertia, section moduli, overall dimen- sions, and weights comparable to rolled I-beams. The cast C-sections afford appreciably lower stress concentration, if positioned correctly, than the standard rolled channel and I-beam sections because of their rounded corners. An increase of the depth of the standard rolled sec- tions results in the development of high stiffness and load-carrying ability about the Y axis. In fact, when the depth of the C-section is in- creased to about 1.5 times its height, the section exhibits approximately equal properties about both the X and Y axes. The C-section eliminates DESIGN 143 -2.8". 2.8 .29" 44", 378" 1.05 33" Fig. 232—Comparison of an I-beam section with a cast C section as to dimensions and weight. I=moment of inertia and S=section modulus (Caine)." ly AREA 2.9 IN. WT-9.7"/FT 44" 12", 4"x25/8"-9.5*,FT Ix-6.7 Sx-3.3 ly-.91 Sy-.65 Ix-7.5 ly-1.7 SX-3.6 Sy-.95 the sharp corners of the rolled channel and the two T junctions of the I-beam section with a corresponding improvement in castability. The channel, or C-section, is thought to be vulnerable to concen- trated loads on the unsupported sides. This is true when used in long lengths as is the case with rolled channels. This objection is minimized in cast design because the C-section is always incorporated in a more complex casting. The flange members are supported by their connections to the rest of the casting, and the unsupported lengths are relatively short. The box, omega and U-sections of Figure 233 are improvements on the C-section when nearly equal properties are needed about both X and Y axes. These sections were compared by Caine(17) as to moment of inertia and section modulus as shown in Figure 233. The box or tubular section has the highest section modulus about both the X and Y axes. 4"x4"X12 TUBE WT.-1.8#/IN. 1x.12.1 S.-6.0 ly: 2: Sy-6.0 4"x4"x12 OMEGA WT.- 1.9/IN. Ir-11.5 S.-5.8 ly-23.6 Sy-79 4"x4"x12" u WT.-1.8* /IN. Ix-10.3 SX-5.2 ly-18.3 Sy-7.3 AMA 4 x 8 x 12 TUBE WT.-2.9/IN. 1x - 74.8 Sx-le.7 ly-24.3 Sy-122 4*x80x1/2" OMEGA WT.-3.1 ZIN. 1x - 75.8 SX-19.0 ly - 36.3 Sy-12.1 T 4*X8'x12' u WT.-2.9*IN. Ix-68.1 Sx-171 ly-30.7 Sy 123 Fig. 233—Design properties of cast tubular, omega and U sections of two sizes are compared. 1=moment of inertia and S=section modulus (Caine)." 17 144 DESIGN Cast tubular sections have only one drawback: cost. All require cores. The omega and U-sections can be cast without cores, and have properties approaching those of the tubular section, and improved as compared to the C-section (see Table 5). This table is prepared on the basis of 1/2 inch thick sections and permits a direct comparison of the four section designs on the basis of equal widths and varying heights. Also, value changes are possible, resulting from an equal height and a variation in the widths. The C-section is designed with a ratio of 1:1.5 selected between the web and flange thickness (see Table 5) so that the metal is placed where it will do the most good. The Y axis is also dis- placed from the web member, thereby permitting this member to be- come a fairly efficient load-carrying member about the Y axis. Table 5 shows that the properties of the tubular sections cannot be equalled by any other section of the same overall dimensions and weight. If the overall dimensions are not crucial, the omega section is an ideal section; but if overall dimensions are critical, the U-section is the best compromise in regard to overall dimensions, stress concentration and cost. The radii of gyration of the box, or tubular sections are equal about the X and Y axes, if the sections of Table 5 are to be used in compression or torsion. Comparable omega sections show radii of gyration about the X axis to be nearly equal to those of the tubular sections. Omega radii of gyration about the Y axis are higher than those for tubular sections. Equal radii of gyration about both axes are obtained with the U-section when H is 1/2 to 1 inch greater than D. The C-section D4-H8 is not particularly efficient. The 8 x 12 inch web is actually detrimental for it pulls the center of gravity too close to one side. It would be better to make the H dimension less than 1/2 inch thick — such as 14 inch thick — so as to keep the center of gravity near the geometric center. The 1/2 inch section cast members are too thick for structures weighing less than 500 pounds. Table 6 includes some design data for 14 inch sections. These sections are more applicable on a strength-weight basis for the usual steel casting. Many 5 to 200- pound steel castings are now being made with 14 to 5/16 inch connect- ing members. The properties of the sections were calculated by Caine (17) for a two to three degree pattern draft. This amount of draft may not be sufficient in certain instances, depending on the overall dimensions of the section. The omega section is particularly adapted to deep pockets that require more than minimum pattern draft. Pattern draft, pattern manufacture, and positioning of the pattern in the mold usually are not considered in the realm of design. However, DESIGN 145 Table 5-Properties of Cast Steel 1/2 Inch Thick Sectionst (Caine) 17 u у 1-Moment of Inertia S-Section Modulus R-Radius of Gyration (a) Tubular Sections (b) C - Sections (c) U - Sections D=4 H 6 D=6 H=6 D=6 H=6 (c) Omega Sections D=4 H H H 4 6 8 D=4 H 6 D=6 H=6 H 4 D=6 H=6 H 8 H 4 H 8 D=4 H 6 H 4 H 8 X Axis Y Axis I in* S in R in I in* S in R in Area in 12.1 35.3 74.8 49.2 6.0 11.8 18.7 16.4 1.4 2.0 2.7 2.2 12.1 18.0 24.3 49.2 6.0 9.0 19.2 16.4 1.4 1.4 1.5 2.2 6.4 8.6 10.4 10.8 1.8 2.4 2.9 3.0 15.2 43.0 85.6 63.1 7.6 14.3 21.4 21.0 1.5 2.3 3.1 2.4 7.8 9.2 8.6 33.1 3.5 3.8 3.3 9.4 1.1 1.1 1.7 7.2 8.5 9.2 11.2 2.0 2.5 2.6 3.1 0.9 11.5 34.5 75.8 46.9 5.8 11.5 19.0 15.7 1.3 2.0 2.6 2.1 23.6 30.4 36.3 83.4 7.9 10.1 12.1 18.5 1.8 1.8 1.8 2.8 6.9 9.0 10.9 10.3 1.9 2.5 3.1 2.9 6 6 6 9 12 12 12 1/2 1 1 1 1 Wt. psi 10.3 32.0 68.1 40.7 5.2 10.7 17.1 13.6 1.3 1.9 2.6 2.0 18.3 24.7 30.7 70.0 7.3 9.9 12.3 20.0 1.7 1.7 1.7 2.6 6.4 8.6 10.4 10.4 1.8 2.4 2.9 2.9 5 5 5 7 12 12 1/2 12 42 12 12 58 1 1 1 1 1 1 142 12 12 1/2 12 1 1 1 2.0 3.0 4.0 2.7 12 12 12 1/2 吃 ​42 / 12 34 D. in t in ti in tz in h in r in 12 34 吃​晚​1地​18 % 1 % 1 42 1 % 1 rı in / / % 42 1.77 1.6 12 % 1.43 2.5 12 1 1.9 42 1 3.0 12 1 4.1 % 1 3.0 а † Preliminary properties subject to correction (a) X and Y axes on centerlines (b) X axis on centerline; Y axis as given (c) X axis as given; Y axis on centerline 146 DESIGN Table 6_Properties of Cast Steel 14 Inch Thick Sectionst (Caine) 17 1-Moment of Inertia S-Section Modulus R-Radius of Gyration (a) (b) (c) Tubular Sections C-Sections Omega Sections D=4 D=6 D=4 D=6 D=4 H H H H=6 H H H=6 H H H 4 6 8 4 6 4 6 8 ! D=6 H=6 4.5 X I in* Axis S in R in Y 1 in Axis S in R in Area în Wt. psi D t in ti in rin ri in 9.0 23.5 46.1 30.6 7.8 11.8 10.2 1.6 2.3 2.9 2.3 9.0 12.0 15.2 30.6 4.5 6.0 7.6 10.2 1.6 1.6 1.6 2.3 3.5 4.6 5.6 5.6 .98 1.3 1.6 1.6 10.3 27.0 38.0 5.2 9.0 . 12.7 1.7 2.5 2.6 5.3 5.7 18.2 2.2 2.3 5.0 1.2 1.1 1.8 3.79 4.47 5.80 1.1 1.25 1.60 7.8 13.5 45.5 30.2 3.8 5.4 11.4 10.1 1.5 1.8 2.9 2.3 12.5 14.8 20.5 47.1 4.2 4.9 6.8 10.5 1.8 1.9 1.9 2.8 3.7 4.7 5.6 5.8 1.0 1.3 1.6 1.6 6 6 44 44 14 44 42 12 12 12 14 14 44 14 12 12 42 1/2 1.8 2.9 4.0 3.1 ... 9 44 14 14 14 % 14 42 6驻​吃吃吃 ​14 12 44 12 14 38 14 142 1.61 14 12 14 14 36 378 14 14 12 12 1.48 2.35 а. † Preliminary properties subject to correction (a) X and Y axes on centerline (b) X axis on centerline; Y axis as given (c) X axis as given; Y axis on centerline the design engineer should be familiar with some of the fundamentals. For example, the C-section can be molded in two ways, as in Figure 234. One method involves double draft on the members that are molded ver- tically. This position of molding may be unacceptable in some instances, because the double draft will decrease section modulus too much. A so- lution is to make the section shown in sketch (a) Figure 234. This molding method gives uniform sections. It may be necessary to make the C-section with double draft in some instances because of the com- plexity of the casting as a whole and this is one of the many points requiring consultation between the designer and foundry engineer. The omega and U-sections require a complex parting and always can be made with uniform sections as shown in the (b) sketch of Figure 234. The proper blending of the section discussed above to other parts or sections of castings must also be considered. In many instances, these junctions are also critically stressed areas and must be considered in de- sign studies. Proper blending of these junctions will tend to equalize stresses throughout the casting. Moments of inertia and overall dimen- sions usually do not limit the blending radii, and they can be large. DES I GN 147 COPE COPE P- DRAG ---P DRAG DRAG DRAG lal PATTERN DRAFT PATTERN DRAFT COPE COPE Р DRAG -P DRAG D.P: PARTING LINE OF MOLD DRAG DRAG CORE PATTERN DRAFT PATTERN DRAFT (6) B P COPE -P DRAG PATTERN AND CORE DRAFT COPE COPE -P DRAG DRAG TUBULAR SECTION OMEGA SECTION COR U SECTION The draft is exaggerated for Fig. 234—Details of pattern draft required for cast sections. clarity (Caine)." Application Examples ... The cast sections discussed above have wide application such as levers, cranks, brackets and numerous other stiffen- ing members. The omega section can be applied to gear cases, covers, gear and wheel webs, and many box or tubular sections such as frames could be considered as C-, U- or omega sections. The higher moments of inertia and section moduli of these cast sections cause lower applied stress. This lower stress can be used to increase load-carrying capacity, decrease weight, or allow the use of a lower strength, more economical cast steel. The bell crank casting of Figure 235 was redesigned by Caine (17) to a C-section to eliminate a point of stress concentration and poor castability through the X axis which is shown in the cross section A-A sketch. Figure 236 shows an application by Marek (20) of an omega section to a bracket. Use of the omega section decreases stress concentration and eliminates a core. The forged I-beam section of Figure 237(a) is common. Like all I-beam sections it is quite efficient. The substitution of a cast C-section of the same overall dimensions, like that of Figure 237(b), offers some advantage. The higher section modulus of the C-section decreases im- posed load by 10 percent about the X axis and 3 percent about the Y axis at a sacrifice of only 2 percent additional weight. OSOHO 148 D O DESIGN AREA-17.4 IN.2 1143.5 Su 20.5 ly 80.5 Sy= 10.9 CORE (a) H SECTION A-A Fig. 236—Redesign of a bracket cast- ing employing an omega section to de- crease stress and eliminate need for a core (Marek).20 AREA -15.5 IN. 2 11.41.0 S119.7' ly12.1 Sy- 21.1 SECTION B-B Fig. 235Redesign of a bell crank casting to a C section eliminates a point of stress concentra- tion and poor castability (Caine)." 2 DRAFT 2 DRAFT 12" 9/16" 1. DRAFT 11/16" 2 DRAFT 3/8", 42", lu 10. DRAFT 578" 61- 4 5/16" 18" A12" by 12", 34 2 DRAFT 2. DRAFT 1 (0) (b) (c) (d) 448 AREA - 7.47 IN2 11=172 Sx - 80 y 8.2 Sy- 40 2 DRAFT 418 AREA - 757 IN 2 ir - 19.2 SK-89 - 8 4 Sy-41 412" AREA - 6 8 IN 2 T-270 SX-108 - 3.0 Sy-5.6 AREA - 7.6 IN 2 11-18.8 SI-1.5 Ty - 2i 6 Sy-86 Fig. 237—Comparison of forged I-beam section with cast sections (Caine)." If the overall dimensions of the part allow just a slight increase in one, or both dimensions of the section, appreciable decreases in imposed load and increases in load-carrying ability are possible. Figure 237(c) shows that increasing the overall dimensions of Figure 237 (b) by just fractions of an inch along with a slight decrease in section thickness, increases the load-carrying ability, as determined by section modulus, 30 to 35 percent with a 9 percent decrease in weight. This increase is significant and should interest the designer. Weight can be decreased (limited by castability), load-carrying ability can be increased, or a DESIGN 149 softer, cheaper grade of steel possibly can be substituted. The latter possibility is quite attractive if a high-strength steel is used at present because it means better machinability. For example, a carbon steel can be substituted for a heat treated alloy steel because of the increased section modulus of Figure 237(c), compared with Figures 237(a) and (b). Attention is directed to the rounded corners of the section designs of Figure 237, and to the topic "External Corners" discussed on page 126. The corner radii of the sections in Figure 237 are from 10 to 20 percent of the section thickness. Any value within this range constitutes a proper design. SECTION IV Designing for Various Service Conditions Parts of a machine may have different load-carrying requirements than the entire machine and since steel castings are usually parts for a complex unit, it is possible that if several castings were a part of the unit, each casting would be reactive to different loads. > Some steel castings are loaded only statically and the stresses are normal, being tensile stress (+) and compressive stress (). Other steel castings are loaded dynamically with shearing, torsional, impact or cyclic fatigue stresses. Static... Examples of steel castings designed for static loading are the support bracket of Figure 238 and the holding arm of Figure 239. Many other steel castings such as foundation bases, hangers, hinges, spacers Fig. 239—Holding arm casting; 20-inch length. Fig. 238—Support bracket casting; 15-inch overall length. 150 DESIGN Fig. 240—Spring equalizer casting for a tandem motor trailer. and castings of similar classification are also subject to static loading. The stresses acting on these castings are either tension or compression. These castings can be best tested in tension, if such testing is re- quired. Normally static loads can be calculated, and there is little need for testing the entire casting if a ductile metal such as steel is used. Dynamic ... Dynamic loading pertains to a force not in equilibrium; for example, the rapid application and release of a load, or the application of a varying load to a component. The action of a spring on a truck or a trailer is a typical example of dynamic loading. Figure 240 is a photo- graph of a spring equalizer casting used in motor trailers. The flexing of the springs during operation applies varying loads to the spring seats which are at the ends of the casting. The center of the casting is at- tached to the trailer body. Castings dynamically loaded can be tested by applying a static load or by dynamic testing using strain gages. Static testing can be done by supporting the ends and applying a load at the center sufficient to cause failure of the casting. Multiplying this ultimate load by the appropriate endurance ratio number will give the approximate maximum dynamic load that the casting can carry. The casting can be dynamically tested by placing the strain gages at the weakest area of the casting while it is in operation. The maximum stress generated can then be used to de- termine the maximum dynamic load the casting can carry. Another example of a casting operating under dynamic loading is the railroad freight car brake beam (Figure 33 Chapter 1). The Ameri- can Association of Railroads' specifications require these brake beams to be fatigue tested for a minimum of 750,000 load cycles. Figure 241 shows a brake beam mounted in a fatigue testing machine undergoing a test at a load of 18,000 pounds. Service Applications ... The design engineer must adapt the component design to certain special service requirements as well as its load-carrying Fig. 241-Brake beam casting being tested in fatigue for a minimum of 750,000 load cycles. ability. Steel castings are designed and produced to meet the require- ments of liquid or gas pressures, ultra-high strengths, high or low tem- perature operation, wear service, and corrosion resistant applications. An example of a steel casting subject to hydraulic pressures is the press cylinder of Figure 242. The loads and the test requirements can be determined for such castings within very close limits. This casting is subjected to a hydrostatic test. A water pressure, greater than the service pressure, is employed and this pressure is maintained for varying periods of time depending on customers' requirements. The steel casting shown by the photograph of Figure 243 is a con- tainer used for compressing a non-fluid, non-homogeneous material under high pressures. This casting is subjected in use to a variable pressure over its length, ranging from little pressure at the wide end to many thousands of pounds per square inch at the small end. The testing of this casting was accomplished by making various strain gage measure- ments under actual operating conditions. Fig. 242–Hydraulic cylinder for a press. Weight 40,300 lbs. 152 DESIGN Fig. 243—A steel casting container for compressing a non-fluid, non-homogeneous material. Large end 50 inches diameter, 6 feet long. Section thickness 41/2 inches. An example of castings for high strength service is the one-piece dipper tooth for a power shovel illustrated in Figure 244. The entire lifting force of a power shovel may occasionally be placed on one tooth lifting a large boulder, and it is for this reason that high strength is Fig. 244—Dipper tooth for power shovel with strain gages mounted. required of the casting in addition to wear resistance. Testing for ac- ceptability of the casting is carried on by mounting the tooth on a dummy dipper lip in a fixture as shown in Figure 245, and loading it statically in a test machine. Stresses are measured in critical areas with strain gages and brittle lacquer. The Pitman arm for crushers (Figure 246) is another steel casting subject to high stresses resulting from excessive tension, compression and torsional loading caused many times by accidental overloads. The casting is also subject to fatigue loading and susceptibility to stress con- centration at low temperatures since these components are used at tem- peratures as low as —50 degrees F. Fig. 245—Dipper tooth mounted in a fixture and loaded statically in a compression testing ma- chine. The size of the Pittman castings makes most standard tests mean- ingless. The only method of evaluation is stress analysis of a model. A design free of stress concentration will insure maximum resistance to fatigue and low temperature brittle rupture. Magnetic particle testing of production castings will insure freedom from stress raisers. A number of steel castings for high temperature service and heat resistant applications are illustrated in Chapter XIII. Applications con- stitute refinery valves and fittings, fans, furnace rollers and many others. The design requirements are primarily reflected in the proper selection of an alloy based on: (1) required life of the part, (2) range and speed of temperature cycling, (3) atmosphere and contaminants therein, (4) complexity of casting design, and (5) cost limitations. The design engineer will be aided in his choice by providing the foundry with as much pertinent information as possible on intended operating condi- tions before reaching a definite decision to use a particular alloy. Fig. 246—Pitman arm casting for crushers. Weight 5000 lbs. 0 154 DESIGN Oxidation tests can be made on steel samples at temperatures and atmospheres to be employed under production conditions, and they will indicate the scaling loss over certain periods of time. Another test is a short-time elevated temperature tensile strength study. Such values can be used as the basis for application of safety factors. There are many cases where steel castings are employed in machines which operate at low temperatures. Well-known examples are the chemi- cal and refinery equipment. Other examples are in earthmoving, mining and crushing equipment which must operate at sub-zero temperatures. The track or crawler shoe shown in the photograph of Figure 247 is re- quired to perform satisfactorily over a wide range of temperatures. The operating temperature determines to a great extent the type of com- position required. Fig. 247—Track shoe for earthmoving equipment. Whether or not a steel is satisfactory for low temperature use de- pends upon its heat treatment, such as quenching and tempering tech- nique and the ductile-to-brittle transition characteristics of the steel, as determined by impact testing over a range of temperatures. The main objective in producing steel castings for sub-zero operation is the avoid- ance of brittleness. The best test to safeguard against these conditions is the notch-bar impact test, conducted at temperatures similar to those encountered in actual service. This provides an accurate criterion of toughness. Steel castings subject to wear are exemplified by the grouser pad for a track-type tractor (Figure 248). There are too many types of wear to generalize on the design requirements for wear resistance and how a steel casting could be tested for this service. The only reliable test is an actual service test of the casting in the intended service. DESIGN 155 Fig. 248—Grouser pad for a track type tractor. Corrosion service applications are in a similar category to that of wear. There are too many services and compositions to generalize, and actual service is the only test that can be trusted. . SECTION V Redesigning of Castings and Wrought Parts The design engineer is well aware that a design produced as a part occasionally may result in a malfunction or defective component. In a similar way a steel casting design may not produce the desired results and a redesign is indicated. The redesigning of an existing steel casting may be advisable so as to: (1) improve the casting quality, (2) decrease production costs, (3) save weight, (4) improve service life, and (5) im- prove the load-carrying ability. Casting redesign is carried on frequently, often at the suggestion of the foundry engineer because he is close to the operational problems that develop with unsatisfactory design. A few examples of the redesign of castings to secure the five ad- vantages given above are presented to illustrate the importance of de- sign fundamentals in steel casting production. Casting Redesign for Improved Quality ... The cylinder head steel cast- ing of Figure 249(a) operates under 1,000 psi hydrostatic pressure. The original design resulted in a casting that leaked at the base of the lugs on test and in use. The engineer will observe from the original design that the lug section is not in proper proportion to the outer rim section where feeding risers are located. Metal solidifies at the thin section first and impairs feeding action from the outer rim, causing uncontrolled shrinkage in the lug. 156 DESIGN Fig. 249(a)-Cylinder head casting-Original design. Fig. 249(b)-Cylinder head casting-Redesign for quality improvement The redesigned casting, Figure 249(b), resulted in an increased metal section toward the outer rim for proper directional solidification and a reduction of the heavy lug section was made without loss of strength. The quality of the casting was improved because of the elimination of conditions permitting leakage and the reduced casting and machining losses permitted a cost reduction of 9.4 percent for each casting. Another example of what can be done to improve casting quality by redesign is illustrated (Figure 250) in the half-model of a large casting that was to be produced. A small scale model is an excellent way in which to illustrate the need for redesign of a casting. The problems become very real and the design engineer can easily see and understand the foundry problems and, therefore, is readily willing to approve changes in casting design. The upper portion of Figure 250 is the origi- nal design and the lower half of the model is the suggested redesigned casting. The original design did not incorporate a sufficient number of FIED Fig. 250—A small scaled model for a 6-foot ID casting. The top portion shows the original design and the lower half illustrates the desirable features of a redesigned casting for quality improvement. cored holes to permit the proper support of cores and the cleaning out of the core after the casting had been made. Also, the two ribs are not positioned properly for attaining freedom from shrinkage and tearing problems. Improved casting quality and lower production costs were the result of redesigning the casting. Casting Redesign for Cost Reduction ... The photograph of Figure 251 (a) is a cast steel hinge butt which was too expensive to produce as originally designed. The number of cores required by having the bosses on the outside added greatly to the cost of production. The stress load on the casting was so directed that internal and external ribs were placed Fig. 251(a)—Hinge butt casting-Original design. Fig. 251(b)—Casting after redesigning with a cost saving of 15.9 percent. 158 DESIGN in bending strain rather than in direct tension or compression because the cored pinholes were not in line and parallel to the triangular shaped base. The redesigned casting, shown in Figure 251 (b), had the bosses placed on the inside, thereby eliminating two cores. Also, the cores for the pinholes and main base were made integrally. This insured holes being parallel with the base and in perfect alignment with one another. The ribs were placed in such a position that they formed a single com- ponent which was constantly under direct compressive stress. Produc- tion costs were lowered because of the elimination of two cores and the combining of other cores. The foundry engineered design reduced the casting weight from 12.2 to 9.8 pounds and the part was improved in quality because the ribs no longer were a serious problem as stress raisers. Furthermore, the total cost of the part was reduced 15.9 percent. Casting Redesign for Weight Reduction ... The small spring equalizer casting of Figure 252, is used on tandem trailers for automobiles. This casting as originally designed weighed 3 pounds. The redesigned cast- ing (lower view) weighed 2 pounds, 10 ounces: a reduction of 121/2 percent. The original casting was stress analyzed using brittle lacquer Fig. 252 upper-Small spring equalizer casting-Original design. 610,900 10,900 Fig. 252 lower—Casting after redesign with a net weight saving of 1242 percent. to find the areas of maximum and minimum stress. Metal was removed from the low stress areas and the section thickness was increased at the high stress areas; the redesigned casting was lighter and strength was actually increased by 25 percent. Further reductions in weight can be accomplished by reducing section sizes until the strength of the rede- signed component is comparable to the original designed part. Casting Redesign for Increased Service Life ... The dipper tooth point shown in the left view of Figure 253 constitutes the original design and the redesigned point appears at the right of the photograph. The longer, Fig. 253—Original design (left) of dipper tooth point. Redesigned point (right) increased the service life of the casting. PEARL hollow-ground redesigned tooth point resulted in longer service life and greater digging efficiency. It reduced the cost of operation for the cus- tomer. The redesigned tooth point is the same weight as the original. Another example of casting redesign is the cast steel knuckle arm. on a die casting machine. The original design, Figure 254(a), failed fre- quently in service because of improper design. The bar type construction rendered the part too rigid to readily absorb normal operating stresses and strains. The redesigned casting, as engineered by the foundry and shown in Figure 254 (b), eliminated the service failures, reduced the weight of the casting by 28 pounds and, at the same time, improved its strength. The total cost of the part was reduced 19.3 percent. Fig. 254—a) Knuckle arm, original design. Note break in casting. Fig. 254—(b) Redesigned to compensate for highly stressed area and give improved service life. Fig. 255—(a) Original design of a fifth wheel for a truck. Fig. 255—(b) Redesign to decrease stress concentration and provide higher strength. Casting Redesign to Reduce Stress Concentration ... The steel casting of Figure 255 (a) is the original design of a fifth wheel for a truck, with the critical fillets outlined by ink. These areas were determined by the use of brittle lacquer coatings. The foundry engineered redesign (Figure 255b) employs a stronger cross member. The outline peak stress areas in this photograph were obtained at a much higher load than used for the original design. Fillet design has been discussed at considerable length in another section of this chapter. However, it is a subject of great importance from the standpoint of stress reduction. An example of its importance can be obtained by a study of the steel casting in Figure 256(a). The casting is a tractor rail for use on crawler type tractors. A casting of the original design (Figure 256b) with 3/8 inch radius fillets was stress analyzed with brittle lacquer, and stress concentrations were very prominent at the fillets. Enlarging the fillets to a 1-inch radius reduced the stress concentration at the design load) from 56,700 psi to 48,600 psi, or a reduction of 14 percent. Redesign of Castings for Cast-Weld Construction ... Steel castings should be redesigned using cast-weld construction under the following circumstances: (a) If a casting is so intricate that producing a one-piece casting is costly and time-consuming; ORIGINAL DESIGN 7 (a) (b) Fig. 256–a) Tractor rail casting; (b) original design with small radii fillets. (b) If hot spots and high residual internal stresses cannot be eliminated. Cast steel is the only commercial cast metal that is readily weldable. Because of this, steel castings can be joined by welding to produce components that meet the service requirements of many applications. An example of the redesign of a steel casting for cast-weld con- struction is shown in Figure 257. This 380-pound conveyor belt pulley (a) Original steel casting. (b) Redesigned cast-weld construction. Fig. 257—Conveyor belt pulley casting. . 162 DESIGN was originally designed as a one-piece casting, making it difficult and expensive to produce. The one-piece casting could not be gated and solidified in a manner to insure a homogeneous casting; the elements of design were just too much for the laws of solidification. Further- more, the large center cores were costly and could not be properly anchored to insure dimensional stability. The foundry re-engineered the casting to a cast-weld design (Figure 257b). The pulley was cast in two halves and welded together, forming a single unit. The improved foundry procedure required less expensive pattern equipment and resulted in a 13.6 percent saving over the original method. Figure 257(b) has a cutaway portion to show the section thickness and the core area. The half casting eliminated the large center core and, at the same time, afforded better gating and solidification possibilities. An example of the redesign of a large casting to cast-weld construc- tion is shown in Figure 258. The lower casting is the cover of a turbine casing for the power industry. The upper casting, swinging from the crane, is a valve chest. They are to be welded together to produce the cast-weld construction. This structure produced as a single casting would be most difficult to make, especially to the high order of quality required by high-temperature, high-pressure service. Forging Redesign to a Casting ... A traditional forging is the crane a hook; however, one manufacturer has converted his line of hooks of from 5 to 75 tons capacity, to steel castings. The steel casting hooks (Figure 259) are designed with a safety factor of 3 on the yield strength and a stress concentration factor for curvature of about 1.5. The cast steel hook was redesigned by straight engineering mathematical calcula- . Fig. 258—Cast-weld construction of a cylinder and valve chest to produce a single structure. DESIGN 163 Fig. 259-A 50-ton cast steel hook with shackle. tions. After the hook was designed and cast, destructive testing showed that the hook was 11/2 times stronger than design calculations had predicted. During tests, at yield point load, the hook opened up without cracking, assuring a visible overload warning before ultimate failure. An alloy cast steel of 120,000 psi was selected for this application. (b) Fig. 260—Nozzle face side of (a) forged nozzle box; (b) steel casting nozzle box. (a) 164 DESIGN Another conversion from a forging to a steel casting is the nozzle box for high-pressure, high-temperature steam turbines. Figure 260(a) illustrates the nozzle face side of the forged nozzle box. The cast nozzle box is shown in Figure 260 (b). The forgings are solid, except for a slight depression on the nozzle face side. Castings are cored out, leaving a minimum of stock for finish. There is a 36 percent reduction of weight from the rough forging (440 pounds) to the casting (280 pounds). The conversion saved 911/2 percent in cost of material. Furthermore, the designer is given the freedom of making a greater variety of nozzle boxes to the exact design requirements without being penalized by high die costs. A low-alloy cast steel was used and no difficulties have been encountered in operating service. . Bolted or Riveted Plate Structures Redesigned as Steel Castings . Overall structural and weight savings constitute excellent reasons for the redesigning of steel plates fastened by bolting or riveting to steel castings. An example of such redesign is shown in Figure 261. The cast steel drawbar weighs 97.5 pounds less than the structural steel drawbar assembled by riveting. The casting makes a better looking component, does the same work, and represents less dead weight to haul. Fig. 261—(a) Draw-bar produced in plate and bolted construction. Fig. 261—(b) Draw-bar as a steel casting. DESIGN 165 Redesign of Weldments as Steel Castings . . . Weldments should be redesigned for production as steel castings under the following cir- cumstances: (a) If the structure is too intricate to be economically practical as a commercial weldment; (b) If the jig and fixture costs are excessive; (c) If a large number of units are required; (d) If the combination of properties and composition requirements make the securing of plates and bar stock difficult or costly. a An example of the redesign of a weldment for production as a steel casting is the mowing machine wheel arm support, as illustrated in Figure 262. The employment of the tubular form in the casting design resulted in greater load-carrying ability for the part, plus the added strength where needed. The casting design has far greater sales appeal, and cost savings of 33 percent were also realized by this conversion. (a) Original - steel weldment. C D (b) Conversion - steel casting. Fig. 262—Mowing machine wheel arm support. 166 DESIGN This redesign also permitted the spindle and ears to be welded to the casting, a further advantage considering that the spindle and ears were welded on one side for right, and the other side for left wheel support. There are numerous examples of the conversion of weldments to steel castings in the industry. Many other examples are given in Chapter XV. Originally designed as a weldment from 13 pieces of steel plate, the weldment rockers are shown in place in the hopper in Figure 263(a). The weldment design required right and left-hand parts, adding materially to the cost of the finished product. Weight, an important factor in materials handling equipment, was 117 pounds. The foundry engineered design is a one-piece steel casting, as shown in Figure 263(b), which can be readily welded in place in the final assembly. The steel casting rockers and stop brackets are completely interchangeable. They have given greater service life and the accuracy of the steel castings has eliminated machining and misfits, enabling (a) Original - steel weldment. (b) Conversion - steel casting. Fig. 263—Rockers and stop brackets for an end dump hopper. DESIGN 167 the customer to increase the production rate of completed hoppers. The weight was reduced 8.6 percent with a better weight-strength ratio, and the total cost of the part was reduced 23.4 percent. Redesign of Weldments for Composite Fabrication ... Weldments should be redesigned for composite fabrication including steel castings under the following circumstances: (a) When a particular part of a weldment is intricate and does not lend itself to simplification by the use of standard shapes and forms; (b) When the dimensions of a certain section of a structure are compact to the extent that the welding operation cannot be performed satisfactorily; (c) When a weldment requires a number of similar units to com- plete the structure. An interesting example of composite fabrication, and one of many that has been produced in this field, is the rock ripper frame illustrated in Figure 264. This machine, pulled by a tractor, is capable of breaking B K G H Fig. 264—Composite fabrication of steel castings and plate steel to form by welding a rock ripper frame. A and B formed plate steel; G, H, I, J and K, steel castings. earthen formations of any type preparatory to scraping operations. The ripper frame is a composite of wrought plate and nine steel castings. The plate members of the frame construction are translucent in the figure in order to show more clearly the component parts of the unit. Two wrought plates A were formed into a box section and welded together. The two mounting arms B consist of four plates of identical form, and the other lettered items are steel castings welded into these plates. 168 DESIGN The idea of composite fabrication can be carried to wide limits both as to size of the part and the number of parts combined. Figure 265 illustrates the combining of steel castings, a stamping, tubing, and plate steel to form a finished assembly by welding. However, when the number of pieces required is so great that it complicates the jigs and fixtures necessary for quantity production, a steel casting often will simplify the jig and fixture problem and reduce the cost. STAMPING CASTING CASTING TUSING PLATE CASTING PLATE TUBING FINISHED ASSEMBLY Fig. 265—Composite fabrication consisting of steel castings, plate, stamping and tubing. Steel Castings Versus Competitive Structures A steel casting design is preferable to competitive structures under the following circumstances : (a) When a steel casting can replace a complicated or difficult forging; (b) When a single steel casting can replace a bolted or welded assembly of wrought steel parts; (c) When relatively small numbers of a steel component are required and where the cost of dies for forging and fixtures for weldments would be excessive; (d) When a casting design can eliminate weight; (e) When compactness is required and when a light-alloy forging, stamping or pressing would have excessive bulk for the desired strength; (f) When, in a component of complex design, the necessary fatigue strength cannot be given by a light alloy (aluminum or mag- nesium) casting or cast iron; (g) When the necessary toughness, resistance to shock, and modulus of elasticity or rigidity cannot be given by malleable iron, cast iron or nodular (ductile) iron. DES I GN 169 SECTION VI Evaluation of the Steel Casting Design The casting design can be evaluated by making a stress analysis of the first casting produced. Often a foundry will make a pilot casting so as to check on casting dimensions and tolerances, surface charac- teristics, and internal soundness. The pilot casting, if not destroyed by sectioning for observation, can then be submitted to the customer for design evaluation by stress analysis studies. Some steel foundries have stress analysis laboratories and are able to make these studies as an accommodation for their customers. There are several methods of carrying on stress analysis, such as by: (1) calculations, (2) photoelastic studies, (3) X-ray diffraction, (4) stress coat with brittle lacquers, and (5) strain gage analysis. The stress coat and the strain gage methods are the only ones that are of practical value for stress analysis of steel castings. Of course, the mathematical approach is used by the designer in planning the design, and has its advantages when properly applied. Stress Calculations ... The following is an example of the manner in which a change in casting design can be brought about through a mathe- matical approach to the problem. Figure 266(a) is the cross section of a riding ring which is supported by two rollers. A shell rests inside of the riding ring so that the load of the shell is always downward on the riding ring. As the riding ring revolves it is stressed from com- pression to tension twice in each revolution. A mathematical stress analysis of the riding ring as designed showed that the calculated bending stress was 25,000 psi. This stress was considered too high, so 21 24 Rit 락 ​- 209.5 DIA. k 84 84 -28 (a) OLD DESIGN BENDING STRESS 25,000 psi Fig. 266—Cross section of a riding ring casting. Old and new design based on mathematical stress anal. ysis. 224 4 -211.25DIA. K747 k 734 (6) NEW DESIGN BENDING STRESS 19,000 psi 170 DESIGN that fatigue failure could possibly occur. The shape of the riding ring was then changed to that shown in Figure 266(b). The new design decreased the calculated bending stress to 19,000 psi which was con- sidered satisfactory. Brittle Lacquer Stress Analysis ... The surface of the casting to be studied and tested by brittle lacquer must be absolutely clean and free from loose scale, grease and paint. The strain indicating coating is selected from commercially available lacquers for the conditions that will prevail at time of test. The coating is then sprayed on the casting uniformly and, at the same time, the calibration strips are coated. The part is assembled into the test setup and allowed to dry at 90 degrees or more for twelve hours in the testing room. The air in the room is brought under control to conform to the conditions for the selected coating. Calibration of the coating is made by applying a known strain to the strips, and the strips are then placed in the strain indicating scale where the coating sensitivity value is read. Loads simulating those which will be encountered under actual service conditions are then applied to the casting. An example of loading a coupler casting for freight cars is shown in the tension fixture of Figure 267. Cracking of the brittle coating forms fine hair-like patterns at right angles to the maximum principal tensile strain such as shown in Figure 268 for the coupler tested as illustrated in Figure 267. To 312-2 오 ​i . 1 1 Fig. 268—Cracking of the brittle coating into hair-like patterns. (Coupler casting of Figure 267.) Fig. 267—Loading a freight car coupler in tension after coating with brittle lacquer. DESIGN 171 Fig. 269_Coupler casting with strain gages in place. Detecting the formation of the first strain pattern in the coating and calibration of the coating at the time of testing is important if accurate quantitative values are to be obtained. The strain patterns formed on the casting are then matched with the known patterns on the calibration strip and values read from the strain scale. Stress values are then computed by multiplying the values of strain by the tension modulus of elasticity of the casting. Stress may be computed from the strain lines with an accuracy of about 15 percent. However, brittle lacquer techniques clearly indi- cate the location and orientation points for resistance wire strain gages which have an accuracy of 2 percent. When actual quantitative infor- mation is required, brittle lacquer analysis is essential but should be followed by a strain gage survey as is illustrated in Figure 269, which shows strain gages in place on a railroad coupler casting. > The application of stress analysis using brittle lacquer is illus- trated by an example, selected from many, of a spring equalizer casting which was over-stressed and of excessive weight. The original design of the spring equalizer casting is shown in the drawing of Figure 270 (a). A 2,000 pound load was placed on the steel casting first in tension and then in compression, and the areas of lacquer cracking are shown on the drawings. The maximum stress was 13,100 psi in tension, and 12,400 psi in compression. The casting was then redesigned, as shown in Figure 270(b). Section thickness was increased at the highly stressed area and metal was eliminated at the low stressed area to reduce the casting weight. Also, fillet radii were made more generous. 172 DESIGN ORIGINAL DESIGN REDESIGN TENSION STRESSES AT 2000 LB. LOAD AREA 1 :13,100 psi. :10,900'psi. 2 : 2 TENSION STRESSES AT 2000 LB. LOAD AREA 1 : 10,900 psi. 2: 8.500 psi. TENSION COMPRESSION STRESSES AT 2000 LB LOAD AREA 1 : 9,600 psi. COMPRESSION STRESSES AT 2000 LB. LOAD (AREA 1 : 12,400 psi. Fig. 2704(a) Spring equalizer casting, original design showing areas of stress concentration. Fig. 270—(b) Redesigned casting on the basis of brittle lacquer analysis. Stress concentration reduced 17 percent with a weight savings of 1242 percent. The redesigned casting was 1212 percent lighter than the original and the brittle lacquer analysis showed that the maximum stress in tension was 10,900 psi, or a drop in stress concentration of 17 percent, while effecting a 121/2 percent savings in weight at the same time. Strain Gage Measurements ... General stress distribution patterns give an overall picture of service stress conditions, and the possible improvement in the design of a component usually becomes apparent. Strain gage studies prove whether the design of the part is adequate to carry the loads and assure the design engineer that a proposed design will meet service requirements. If not, the results of the experimental stress analysis will indicate the action necessary to improve the stress distribution. This is done by adding or removing metal adjacent to the highly stressed areas. The test procedure is repeated when modifica- tions in the design have been effected and the optimum design is developed, based on facts instead of opinions. Modifications are made and evaluated by stress analysis until the design is acceptable. Altera- tions to the pattern equipment are not difficult. Sections can be built up or radii can be increased with sculptor's clay, or sections can be made lighter by removing pattern stock, and a new test casting can be easily and quickly prepared. No other process lends itself so easily to redesign as does the casting process. An example of what can be done in steel casting redesign by strain gage measurements is the spring lockout beam illustrated in Figure 271 (a), which constitutes the original design. This part was first pro- duced as a malleable iron casting, but it was converted to a steel casting in the same design because of service failures. This design did not lend itself to the production of high-quality steel castings, and service DESIGN 173 Fig. 271–a) Truck-spring lockout beam, original design. Weight 55 lbs. Fig. 271—(b) Modified design by strain gage analysis. failures resulted although the foundry did not believe that the quality alone was responsible for the failures. An experimental stress analysis of the part was undertaken with a strain gage setup, as illustrated in Figure 272. The test studies revealed the stresses to be too high and the ribs to be stress raisers. The beam casting was redesigned, Figure 271(b), and tested by strain gage technique. It was found that the critical stress was reduced by 57.5 percent, strength increased by 235 percent, and weight reduced by 3.2 pounds. The redesign was compatible with good foundry practice and enabled the foundry to consistently produce castings to meet the high standards required. All service failures were eliminated by the modified design. Fig. 272—Test ar- rangement for stress analysis by strain gage of the beam casting. 174 1 DESIGN SECTION VII Correlation of Destructive Testing of Steel Castings with Stress Analysis, and Mechanical Properties The importance of hidden flaws, or non-homogeneous sections in castings is a subject of some disagreement. Minor discontinuities, as revealed by radiography, are often classed as serious imperfections and subject to casting rejection or extensive welding repairs, very fre- quently out of proportion to their intrinsic real effect. Materials engineers may point with alarm to differences found in ductility values from specimens taken from separately cast test coupons and from various sections of castings, even though they know that ductility does not enter into design calculations. Its only consideration is its incorporation in safety factors. If ductility exceeds 5 percent, the material is considered ductile instead of brittle. A decrease in casting yield strength or ductility or the presence of small discontinuities often have been blamed for service failures when the true culprit was inadequate design, resulting in stress concentration. It is a difficult task indeed to persuade a customer that his design is at fault, but factual information has shown that over 95 percent of all service failures are directly attributable to stress concentration resulting from improper design. A number of studies have been made in connection with the correla- tion of casting and design qualities. Several of these studies are reported in the next few pages so that the design engineer may be cognizant of developments and the engineering possibilities resulting therefrom. The steel castings to be discussed were obtained from steel foundries which were producing them in numbers to meet normal customer requirements and all test work was carried on by professors of an engi- neering university interested in machine design, materials and metal- lurgical engineering. Six production steel castings were studied and tested. A drawing of the casting is shown with test bar locations indicated. Discontinuities observed on the casting surface or below the surface by X-ray are indicated as to type by letters while the degree of severity is estimated in numerals of 1 to 5 with No. 1 as the least severe indication. This determination of discontinuities is in accordance with the ASTM Speci- fication E71, Industrial Radiographic Standards for Steel Castings, Classes 1 to 5. The discontinuities are also as listed in E71, namely: A- Porosity B— Sand or slag inclusions C- Internal shrinkage D — Internal tears 1 DESIGN 175 0 Crankshaft The crankshaft castings, illustrated in Figure 273, were submitted in the fully machined condition. Test bars were taken from two locations in the castings and test results compared to those obtained from test bars machined from a separately cast coupon (control test). The sections are thin and it will be observed that the properties CRANKSHAFT КАН II Fig. 273—Steel crankshaft. Casting tested as to properties and to failure. Test Specimen Locations and Types Tested Casting-Arrow Showing Failure Tensile and Impact Data Control I II Breakdown Data Tensile (1000 psi) 84 88 88 Yield (1000 psi) 63 64 64 Service Torque (In. Lbs) 500 Elongation (%) 28.6 20.7 27.5 25000 70°F Charpy Static Torque to Fail (In. Lbs) 3000 V-Notch (Ft Lbs) Fatigue Limit (In. Lbs) 46 34 50 Trans Temp (°F) 170 Trans Energy (Ft Lbs) 62 of the test bars machined from the castings gave properties similar to those from the control separately cast coupon. Testing to destruction resulted in failure at a junction of the shaft and a throw which is a position of stress concentration because of a machined-in notch. How- ever, the part was designed on the basis of 500 in. lbs. service torque and the casting failed at 25,000 in. lbs. or a safety factor of 50. In other words, the casting was 50 times over-designed. The castings showed no discontinuities upon nondestructive testing. Hook . .. Some engineers have a prejudice against steel castings as crane or sling hook applications. The steel hook casting shown in Figure 274 is designed for 5-ton loads and is used in this and other sizes by many industries. Test bars were machined from four locations in the hook and com- pared against the properties of a separately cast coupon. A tensile strength of 128,000 psi was reported for the control bar with a 43 ft.- lbs. Charpy V-notch impact value, which are very good values, indeed. Specimens taken at locations II, III and IV showed slightly lesser values, about 90 percent of the control values, which is normal for the increased mass and design effects. The test specimen for location I came from an area that showed the presence of shrinkage on nondestructive test- ing. The strength properties fell off considerably and the ductility 176 DESIGN HOOK C-3 a ce D A-1 Fig. 274—Steel hook casting tested as to properties and to failure. Tested Casting Showing Stress Coat Pattern and Failure Breakdown Data Test Specimen Locations and Types and Locations of Defects Tensile and Impact Data Control 1 II III IV Tensile (1000 psi) 128 85 117 117 Yield (1000 psi) 103 71 96 Elongation (%) 15.4 2.9 9.7 10.4 70°F Charpy V-Notch (Ft Lbs) 43 42 Trans Temp (°F) 30 50 Trans Energy (Ft Lbs) 41 96 Service Load (Tons) Load to Yield (Tons) Load to Fail (Tons) 5 53 56 40 properties were very low indeed. The hook was given a stress analysis and tested to destruction. Failure took place where the brittle lacquer indications indicated a position of stress concentration. It will be observed that the load to failure was 11 times greater than the designed service load. Furthermore, failure did not occur in the area of recorded shrinkage and low mechanical properties. These tests show that tests taken from the center of sections may give poor values but it is the part or the entire section that must be tested in order to determine the true properties of a steel casting. It is not the properties along the centerline of a section that are important, but the character of the stresses and their concentration that is of major importance. Suspension Yoke ... The steel casting drawing shown in Figure 275 is a suspension yoke for an automotive truck. Only one position in the casting permitted a test bar to be machined from it, and the strength properties of this bar were very close to the control test bar taken from a separately cast coupon. The test casting is shown with strain gages attached. The casting was designed to a load of 4.5 tons but required an application of 60 tons to produce failure, indicating an inordinate degree of overdesign; in fact, a safety factor of 12. A more realistic design factor would be less than half this figure. DESIGN 177 SUSPENSION YOKE 0 Fig. 275—Suspension yoke casting tested as properties and to failure. Tested Casting Arrow Showing Failure Test Specimen Locations and Types and Locations of Defects Tensile and Impact Data Control I Tensile (1000 psi) 111 107 Yield (1000 psi) 88 86 Elongation (%) 19.7 14.3 70°F Charpy V-Notch (Ft Lbs) 42 30 Breakdown Data Service Load (Tons) Load to Fail (Tons) 4.5 60 . Lifting Arm ... The steel casting illustrated in Figure 276 is a lifting arm to raise and tilt a load in the operation of construction equipment. The part is a solid piece construction with cored opening at the tiedown bosses. Test specimens were taken from the uniformly thick plate. A cross section of the arm is shown at the section which failed during destructive testing. The casting test bar values are about 85 to 90 per- cent of the strength properties of the coupon properties, but the ductility is only 8 percent as compared to 31 percent given by the control test bar. Shrinkage areas were found in the plate and rim section, and the casting test bars show the influence of these conditions on the properties. The test-to-failure data indicates that while the service load was from 5 to 8 tons, the load-to-failure was 106 tons. Again, it may be seen that the properties from test bars machined from the casting bore no relation to the failure load of the casting. The casting failed finally at the design point of stress concentration. The casting apparently was overdesigned by a factor of 13. Load Equalizer ... The load equalizer casting shown in Figure 277 is a tandem trailer part. The casting consisted of uniform sections with the plate wing sections, the location of Specimen II, as the heaviest section. The design is such that the casting is difficult to produce at commercial prices without some centerline shrinkage. The drawing 178 DESIGN LIFTING ARM D-3 & C-1 09 A-1 Fig. 276—Steel lifting arm casting tested as to properties and to failure. Test Specimen Locations and Tested Casting Showing Fracture Types and Locations of Defects Surface and Failure Tensile and Impact Data Control I II Breakdown Data Tensile (1000 psi) 90 80 Yield (1000 psi) 71 59 Service Load (Tons) 8 Elongation (%) 31.4 8.0 Load to Yield (Tons) 101 70°F Charpy Load to Fail (Tons) 106 V-Notch (Ft Lbs) 47 26 Trans Temp (°F) 120 200 Trans Energy (Ft Lbs) 53 49 -- LOAD EQUALIZER C-1 C:1 C-1 C-2 피 ​C-2 C-5 Fig. 277—Load equalizer steel casting tested as to properties and to failure. Tested Casting-Arrow Showing Failure Breakdown Data II 94 Test Specimen Locations and Types and Locations of Defects Tensile and Impact Data Control I Tensile (1000 psi) 101 88 Yield (1000 psi) 61 Elongation (%) 23.6 9.7 70°F Charpy V-Notch (Ft Lbs) 30 18 Trans Temp (°F) 190 Trans Energy (Ft Lbs) 73 64 Service Load (Tons) Load to Fail (Tons) 9* 33 21.5 24 * And infrequent Impact Loads 45 --- 1 DESIGN 179 in Figure 277 shows that several areas in the casting contained center- line shrinkage as determined by X-ray testing. The shrinkage was slight except in one area of the tubular section where it was rather severe. A test specimen that was machined from this general area produced strength properties of 83 to 88 percent of the separately cast control test coupon with ductility values of only 41 percent. The plate section of specimen location II, produced more favorable test values. The service dynamic loads to which the casting was subjected were 9 tons with additional infrequent impact loading. However, the casting failed by buckling in the side plates in the area near the tubular section and the positions marked C-1 and C-2. The load at the time of buckling was 33 tons or 312 times the service loads. This was the area of design weakness, and the shrinkage of area C-5 with the lower property values showed no indications of the effect of the high loads. Again, this casting failed because of design weaknesses and not because of mechani- cal properties of specimens taken from the casting, or because of the presence of discontinuities. The casting far exceeded the load require- ments, and modification by the foundry to change the production methods to eliminate the discontinuities would only have added to the costs without improving its serviceability. Spring Bracket ... The steel casting is a part of the front axle of a truck and is illustrated in Figure 278. It is a thin-walled casting which is difficult to produce absolutely free from discontinuities. The drawing indicates areas of porosity, shrinkage, and sand inclusions; neverthe- less, the mechanical properties of the casting were nearly equal to those of the control coupon specimen. The required service load is 1.7 tons yet the casting supported a 50-ton loading before it buckled in the side walls near the flanges. Even on the basis of 6 tons dynamic loading the casting far exceeded its requirements. The examples of steel castings tested to failure show that all the castings failed at loads far in excess of the service loads and that failure was related to design and not to sub-standard properties as indicated from test specimens taken from the casting or from possible discon- tinuities within the casting. Several of the examples showed that the safety factors used in the design were abnormally high and could have been reduced at significant cost advantage to the purchaser. 180 DESIGN SPRING BRACKET A-3 C-2 C-4-7 B- C-4 Ext. Sink *** B- B-1 Fig. 278—Spring bracket casting tested as to properties and to failure. Tested Casting-Arrow Showing Failure Breakdown Data Test Specimen Locations and Types and Locations of Defects Tensile and Impact Data Control I Tensile (1000 psi) 79 75 Yield (1000 psi) 50 43 Elongation (%) 25.5 31.5 70°F Charpy V-Notch (Ft Lbs) 18 Service Load (Tons) Maximum Load (Tons) 1.7* 50 * And 3 to 4 Tons Dynamic Safety Factors Magnitude of Design Factors ... The preceding information clearly indicates that unreasonably large safety factors are frequently applied in the preparation of steel casting designs. Also, it is indicated that excessive compensation is provided for the variation in strength prop- erties between the coupon and the casting. The working stresses used in the designing of machines and struc- tures are called allowable unit stresses. The ratio of the ultimate stress to the allowable stress is known as the factor of safety. Since the stress at the yield point frequently limits the allowable unit stress, the factor of safety is sometimes defined as the ratio of the stress at the yield point to the allowable unit stress. The magnitude of the factor of safety depends upon: 1—The knowledge the engineer has of the service application; 2-Effect of design, particularly with regard to stress concentration; 3—Experience of the designer with the material of construction. Each of these three requirements may be broken down into their several elements, such as: DESIGN 181 1-Service load requirements a-Effect of initial stresses; b-Effect of possible temperature changes; C-Type of loads: steady stress (static); variable stresses (dynamic); shock (dynamic); d-Assumptions on which the computations are based, such as new design where loads can be only an intelligent guess. 2-Design a—Effect of stress concentration resulting from notches, sharp fillets and holes; bMaintaining rigidity of structures, resistance to bending and torsional stresses. 3-Materials of Construction а—Туре; b—Variations in the material, and inaccuracies of workmanship; C—Discontinuities in the material; d-Ductile vs. brittle types. Static Stress Design ... Items 1c and 3c are usually combined in the procedures for determining allowable stresses. In other words, the type of load and whether the material is ductile or brittle determines the factor of safety. For example, steel being a ductile material, (over 5 percent ductility constitutes a ductile material) the working stress for static loading is equal to 1/2 of the strength (yield or ultimate), or a factor of 2. For brittle materials a factor of 6 is used. > . Dynamic Stress Design ... Variable stresses or cyclic loading are usu- ally figured on the basis of endurance limit. A 13 value of the endurance limit is taken for cast or wrought steel to determine the allowable unit stress, or a factor of safety of 3. If the endurance limit of notched- bar fatigue curves is available, a safety factor of 2 can be employed. Shock loads are at times shown in tables of factors of safety with higher factors than those given for variable loading, as impact loadings may cause stresses twice as high as steady loads of a given value. Materials of no impact resistance, which is certainly the category of cast iron and nodular iron, have factors of safety upward of 20. Ignorance Factor ... The effect of design, or the design engineer's ignorance factor, as it is often facetiously called, may be of any value, 182 DESIGN depending on his experience. The type of material, whether it is a steel casting or a wrought steel product, does not enter this factor. Unfamiliar Material of Construction ... Design engineers who are not familiar with the material of construction employ additional factors of safety. This is understandable because they are not certain of the quality of the material, and additional factors of 0.5 to 5.0 are often applied for this purpose. Thus it is that many designers who are not familiar with the reliability of steel castings use added safety factors of 2 to 5 and even greater for this item. It is for this reason that there are such wide differences in the design and yield loads listed in the 6 casting illustrations given in the preceding section. Steel Casting Design Factors ... A design engineer who is familiar with steel casting design, such as for example, the engineers who design steel castings for railroad service where dynamic stresses are involved, would use a total factor of safety of 3.6 on the endurance limit. This is composed of a factor of 3 because of dynamic stress; no factor for design because of the designer's familiarity of railroad component requirements; and a factor of 0.6 for the material of construction. This latter is ample to cover the differences possible between coupon proper- ties and casting properties. A steel of 90,000 psi tensile strength and 43,000 psi endurance strength with a factor of 3.6 means an allowable unit stress of 12,000 psi. An inexperienced designer may use a factor of 9 consisting of the factor of 3 for dynamic stress, a factor of 2 for design, and a factor of 4 for the material of construction (steel castings). A factor of 9 of 43,000 psi permits only an allowable unit stress of 4,800 psi. This would call for a cross section 2.5 times greater than the design made by the experienced engineer. SECTION VIII Design of Steel Castings vs. Steel Weldments Design and materials engineers are called upon to design and recom- mend the form the engineered part shall assume in the finished machine. There is always the question of whether the design should be made as a casting, or by other methods of shaping and fabrication. The decision is not always one of design, as certain economical features must be given consideration. Such items as final cost, including machining, availability, and delivery schedules, often dictate the final selection. Even more important than these is the familiarity and knowledge which the engineer has concerning the type of construction and the quality that may be expected from the various structures in question. An example of this dilemma can be cited. A design engineer who is unfamiliar with steel castings may employ, in his design of a casting, much higher factors of safety and quality than he would normally use for the medium of construction with which he is well acquainted. This DES I GN 183 can result in over-design to such an extent that the casting would not be economical from the standpoint of final weight and cost considera- tions. Another engineer, with considerable background and experience in the field of steel castings, would apply realistic safety and quality factors which would bring the casting weight and cost into proper focus. It is accordingly evident that there is a definite need for trust- worthy information comparing the different engineering structures. However, such comparisons are not easily obtained because the testing of complete and integral structures is difficult. Large testing machines of high capacity are necessary to apply loads of sufficient magnitude to provide reliable data and all variables must be properly reconciled. The following sub-section relates to exhaustive research conducted by the Steel Founders' Society of America in this particular field. Testing of Comparable Cast and Fabricated Structures... All engineer- ing structures contain joining sections and these sections are, in effect, characteristic of the methods employed in their manufacture. The L section and the box section are found in numerous engineering struc- tures. These joining sections are produced as a continuing member in castings but often they are joined together by a weld in a weldment. In such cases the design and the quality of the weld or the casting could have considerable bearing on the load carrying abilities of these members when incorporated into a unit structure. These sections were produced as commercial steel castings and as commercial weldments. The steels used for their manufacture were of a similar range but they were not of the same strength. This is not a detriment to the studies because a commercial weldment and a com- mercial casting, in practically all cases of procurement, would not be of the same strength level. Furthermore, it was more important to show the designer what could be expected if he were comparing typical com- mercial weldments with typical structural grades of steel castings. It should be noted here that the weldment designs were checked with welding fabricators, and modifications which they made in the design were adopted prior to their fabrication. Also, the two major weldment designs tested are approved by the American Welding Society as corner designs for fatigue service. The weldment designs (L and box), as compared to the casting designs, are shown in Figure 279. The section width was 5/8 inch. The weldments and castings were produced in large components and then cut into 1-inch slices for test specimens. It will be observed that the outside dimensions of casting and weldment designs 1 and 2 are the same. These designs are preferred by fabricators for both static and dynamic loading, and full strength is obtained for all loadings. Weldment design 5, the single fillet welded joint, is used in product design because 184 DESIGN 56 5.W ( WELD WELD 56" La nó WELD inló into ū 10 20 5/" C G CF I-W jo tivo 5/5 " 2-W 30 4C Fig. 279—Sketch illustrating corner type designs for cast steel specimens and fabrication techniques employed in producing the weldment corner joints. fabricators can weld the structure only from the outside. The use of this design is on the basis of low-cost construction. Many parts in dynamic loading have been observed with the single fillet welded joint of type 5, because the part is so constructed that welding is only possible from one side. The box design castings were produced with all corners alike. This was not possible in the case of the welded box designs, which were made by producing type 1 or type 2 corners and then welding the two L plates together with type 5 design. The weldments were produced from ASTM A285 grade C wrought steel plate, which is the normal grade for commercial weldments. They were prepared by both machine and hand welding using a LH-70 rod for DESIGN 185 hand welding and a L-30 rod for machine welding. Some weldments were stress relieved at 1100 degrees F, others were tested in the as- welded condition. The steel castings were produced to ASTM A27 class 70-36, which is a normal grade of commercial structural steel castings. All were given a normalizing heat treatment. Stress Concentration Factors ... Each of the 5 different corner designs has a different stress concentration factor. The data in Table 7 are significant because the factors determined by photoelasticity are idealized, since they duplicate the drawing exactly, whereas the strain measurements are made on actual parts containing deviations from the drawing design as well as surface imperfections. The two stress concentration factors agree remarkably well for the steel castings, but the photoelastic method greatly underestimates the strain measurement determined factor for the weldments. The major reason for this deviation is the inevitable departure of the fillet geometry from that shown by the idealized drawings. The drawing of Figure 279 shows a fillet of weld metal to a geometrical radius and smooth blending to the legs of the joining sections. However, the Table 7-Stress Concentration Factors for the L and Box Designs Factors determined by: Corner Photo- Strain Design Process elasticity Measurementt 1-L 2-L 3-L 4-L Casting Casting Casting Casting Weldment Weldment Weldment 1.21 1.23 1.36 1.58 1.17 1.22 1.33 1-L 2-L 5-L 1.21 1.23 1.52 1.64 1.92 1.37 - 1 Box 2 Box 3 Box 4 Box Casting Casting Casting Casting Weldment Weldment Weldment 1.21 1.23 1.36 1.58 1.40 1 Box 2 Box 5 Box 1.21 1.23 1.52 2.13 2.10 $ Average of from 4 to 10 test measurements actual welds, produced commercially, have flat surfaces (see Figure 280), and the fillet is commonly unsymmetrical. Such uncontrolled departure from the drawing not only adds to the stress concentration, > 186 DESIGN : Fig. 280—Weld fillet geometry for corner designs 1 and 5 in the box section. but increases its variability. Since the flat fillet is normal in welding, its effect must be carefully considered by designers, unless they wish to request the rather expensive step of contouring the weld by grinding. Steel castings, however, can be easily contoured and streamlined closely to any shape desired. Static Tests ... The L and box sections of both castings and weldments were tested statically to failure with the yield loads determined (Table 8). The steel castings yield at a significantly higher load, of about 33 percent, than the corresponding weldment. However, the commercial cast steel had a 30 percent higher yield strength than the steel plate normally used for commercial weldments. Table 8 merely reflects the yield strength of the two materials. Table 8--Yield Load of Equivalent Casting and Weldment Designs Yield loads, lbs. Casting Weldment Design L Corner 1 L Corner 2 Box Corner 1 Box Corner 2 2100 2100 10900 10000 (approx.) 1690 1610 7480 7410 Fatigue Limit ... A limited number of fatigue tests were made to establish S-N curves for certain designs. Casting designs 1 and 3 are shown in Figure 281. Design 2 data fall between the two curves as shown. Only design 2 weldments were studied (Figure 282), and a comparison of welding procedures was made. The S-N curves indicate that procedure is not one of too much importance. A comparison of Figures 281 and 282 indicates casting superiority. DESIGN 187 60,000 S-N CURVE-CYCLES OF STRESS VS COMPUTED STRESS 50,000 X 40,000+ X CALCULATED STRESS AT POINT OF FRACTURE 30,000 *** 20,000 10,000 PSI X. 1.BC DESIGN 0 - 3-BC DESIGN 105 2x104 106 107 NUMBER OF CYCLES Fig. 281--S-N curve for the box casting designs 1.BC and 3-BC. 60,000 S-N CURVE - CYCLES OF STRESS VS COMPUTED STRESS 50,000 40,000 CALCULATED STRESS AT POINT OF FRACTURE 30,000 x Х 20,000 10,000 PSI X. 2.BW HAND WELDED, STRESS RELIEVED O2BW MACH. WELDED, STRESS RELIEVED 105 10? 2x104 106 NUMBER OF CYCLES Fig. 282—S-N curves of the box weldment; design 2-BW comparing the hand weldments with machine weldments. All weldr.ents were stress relieved at 1100 degrees F. Limited Life Fatigue Tests . . Limited life fatigue tests are more than significant and of greater utility to the design engineer than the S-N curves, because machines and equipment are not always designed to last indefinitely. The limited life fatigue test is a thorough study of the sloping portion of the familiar S-N curve and supplies the answer to the question of what number of cycles of stress the part will stand under given stress conditions. Of course, the answer depends on what probability of fracture is accepted as realistic. The designer decides that 1, 5 or 10 percent of the parts can fail in service, and then uses these distributions to determine the life of the part, knowing the load which will apply. The different loads for the L section were 1170 and 1300 pounds, and for the box section they were 5,000 and 7,000 pounds. Figure 283 188 DESIGN compares the values for castings and weldments at one load from the extensive studies which have been made. The weldment curves are listed as a band, because the variables of hand welding vs. machine welding and stress relief vs. as-welded specimens for designs 1 and 2, were insufficient to produce any large variations in the limited life fatigue tests. Outside geometry of the weld surface, plus the unsym- metrical welded corner, overshadowed any effects which welding proce- dure, or heat treatment has on fatigue life. The graph shows conclusively that cast corners 1, 2 and 3 are definitely superior to any welded corner design. The box section life tests show similar results, as indicated in Figure 284 and again the steel casting box sections have a fatigue life that is much superior to the steel weldments. 102 CASTING 1-2 10? 1-BC LOAD O TO 1300 LBS. R2-4 CASTING 3-6 3-BC 106 1106 CYCLES CASTING 4-6 CYCLES WELDMENTS 1-BW AND 2-BW 105 105 WELDMENTS I-L AND 2-2 LOAD O TO 5000 LBS. 1 1 1 1 4x104 1 11 1 3x10 10 20 30 40 50 60 70 80 90 100 % FAILURES IN LIMITED LIFE STUDY 10 20 30 40 50 60 70 80 90 100 % FAILURE IN LIMITED LIFE STUDY Fig. 283—Percent of failure in limited life tests at loads of 0-1300 pounds comparing L design of castings and weldments. Fig. 284—Percent of failure in limited life tests at loads of 0 to 5000 pounds com- paring the box design of castings and weldments. The chart of Figure 285 illustrates the corner designs as produced as steel castings and weldments that were tested in fatigue at a con- stant preload of 1170 pounds. These tests show that the number of cycles before failure for the steel casting designs far exceeded those of commercial weldments. Sharp radii and metal buildup are pri- marily responsible for the low values. DESIGN 189 10.000000 1,000,000 CYCLES TO FAILURE - 1170 POUND PRELOAD 100,000 4 4 4 10,000 |S |S ( ৬ L | 1 2 3 4 2 1 HAND MACHINE CASTINGS WELDMENTS Fig. 285—Limited life fatigue tests of steel castings and steel weldments at a constant preload of 1170 pounds. Recommendation on Steel Castings vs. Weldments ... The following conclusions can be drawn from the studies on the joining sections of steel castings and steel weldments: 1- Normal structural parts, as produced in steel castings, are stronger under static loading than commercial weldments for a given design because of the higher carbon, manganese and silicon contents in steel castings and, therefore, the generally higher tensile strength steel employed for castings. 2-Steel castings generally have better fatigue properties than weldments for the corner designs studied. 3—The corner designs produced as steel castings resulted in lower stress concentration than existed in comparable designs as pro- duced by fabrication welding. 4-Stress concentration factors for welded corners are dependent upon the particular shape attained by the weld fillet. Actual values are higher than those found by photoelastic examination of idealized shapes. 5—The corner designs listed in order of increasing stress concentra- tion factors are: Types 1, 2, 3, 4 and 5. Some casting corners of type 3 design perform as well as designs 1 and 2 under fatigue loading, but the greater variability shown in design 3 is a dis- advantage. The weldments show no clear evidence of superiority between types 1 and 2. 6-Corner designs, types 1 and 2 gave the greatest fatigue life and are recommended from the standpoint of castings and weld- ments used in fatigue service. 190 DESIGN 7-There appears to be no consistent difference between hand and machine welded corner design specimens or between as-welded and stress relieved corner design specimens when they are subjected to comparable limited fatigue life tests. REFERENCES 1-Briggs, C. W., Gezelius, R. A., and Donaldson, A., “Steel Casting Design for the Engineer and the Foundryman” Journal, Am. Soc. Naval Engineers, May 1938. Also Trans. American Foundrymen's Society, Vol. XLVI, 1938, P. 605. > > 2—Commission Technique de la Metallurgie des Aciers, Guide Pratique du Trace des Pieces en Acier Moule, 1948. 3— Rassenfoss, J. A., “Engineering Uses for Steel Castings”, Steel, December 15, 1947, pp. 90-92, 102-104. 4Briggs, C. W., "Good Steel Casting Design Improves Quality and Reduces Cost”, Materials and Methods, Feb. 1951, pp. 68-72. 5-Felt, J., “Design-Production Teamwork is Key to Steel Foundry Gains", American Foundryman, September 1952, pp. 65-68. 6—Franck, R. J., “Evaluating Cast Design”, Machine Design, March 1953, pp. 104-108. 7-Franck, R.J., “A Practical Approach to Casting Design”, Product Engineer, ing, July 1953, pp. 192-195. 8—Hall, J., “Cast-Weld Construction", Foundry, March 1954, pp. 114-119. 9—Gibson, G., “Designing Cast-Weld Construction for Stainless Steel”, American Foundryman, June 1955, pp. 82-84. 10—Davidson, T., “What Design Engineers Look for in Castings”, American Foundryman, May 1955, pp. 118-122. 11-Blanc, G., and Joumain, M., "Cooperation between Engineer and Foundryman on Casting Design”, Foundry Trade Journal, Jan. 19, 1956, pp. 63-74. 12—Sloane, D., “Developing the One-Piece Cast Steel Frame”, Die Casting Engineer, June 1958. 13—Caine, J. B., “What Foundrymen Should Know About Casting Design", Foundry, Jan. 1959, pp. 74-79. 14—Caine, J. B., “Interrelation Between Stress Concentration and Castability”, Modern Castings, Feb. 1959, pp. 101-104. 15—Henry, J., “Aid for the Design Engineer", Modern Castings, March 1959, p. 53-60. 16—Caine, J. B., “Dynamic Loading Its Effect on Casting Design”, Foundry, April 1959, pp. 166-176; May 1959, pp. 92-95. 17—Caine, J. B., “Design Properties of Four Streamlined Cast Sections", Foundry, July 1959, pp. 91-97. 18—Caine, J. B., “Interrelation Between Stress Concentration and Castability”, Modern Castings, Feb. 1959, pp. 101-104. 19—Roark, Hatenberg, and Williams, “Influence of Form and Scale on Strength”, Engineering Experiment Station Bulletin, University of Wisconsin, 1938. 20—Marek, C. E., “Fundamentals in the Production and Design of Castings”, John Wiley & Sons Co., New York, 1950. 21—Nara, H. R., Wright, D. K. and Briggs, C. W., "Studies of the Design of Steel Castings and Steel Weldments as Related to Methods of Their Manufac- ture", Machine Design Div. Trans. ASME, 1960. Paper No. 60-SA2. - CHAPTER V PATTERNS FOR STEEL CASTINGS The pattern provides the essential link between a design drawing and a useful steel casting, since it gives its shape to the refractory mold cavity where the molten steel solidifies to the desired contour and dimensions. In most cases core boxes comprise a part of pattern equipment. These give form to the refractory inserts, which are placed in the mold cavity to provide voids in the casting to satisfy design requirements. It follows that the first step in the manufacture of steel castings is to procure the necessary pattern equipment for production of a mold cavity to suit the design, regardless of the number of castings to be made. It will be obvious to the reader that a casting cannot be more accurate than the pattern equipment from which the mold is made, and it is generally regarded as fact that the quality of the casting goes hand in hand with the quality of the pattern. Patterns are expensive to produce. The money spent for them may make up a considerable portion of the cost of the castings if only a few are required. Accordingly, the foundry engineer should give serious thought to the type of pattern equipment necessary and adequate to produce the desired number of castings at a minimum pattern cost. It is unwise to go too far in economizing on pattern costs. Inade- quate and unsuitable patterns greatly increase the time required to produce molds. They also may cause poor molds and the resulting castings will require extra processing time in the cleaning room or machine shop. Money saved by cheap pattern construction may be spent many times over in the foundry operations. A cheap, flimsy pattern is only justified when a single casting is to be made, with loose requirements as to surface accuracy. At the same time, it is not always advisable to procure the best possible pattern. Expensive pat- tern equipment or elaborate rigging is not normally justified for the production of only a few castings, provided the resultant equipment is adequate to produce the desired casting dimensional tolerances. In any case, the additional pattern cost must be balanced against molding and finishing economies, and the possibility of future orders for the same casting. Pattern Costs The cost of the pattern and core box equipment for a particular casting can vary several hundred percent, depending upon the type of equipment selected, the kind of material used in constructing the pat- 192 PATTERNS tern, and the accuracy and finish required. The decision as to the type of pattern equipment to make depends on several fundamental factors, such as: 1~Number of castings to be produced; 2–Molding process to be employed; 3—Dimensional tolerances required; 4-Disposition of the pattern after completion of the order; 5—Type and size of the molding machine; 6- Size of the available flasks; 7—Casting design, and intricacy of shape and size. Those casting purchasers who supply their own pattern equipment should give consideration to the foundry's requirements. The most appropriate pattern equipment for each casting is best selected through the cooperative efforts of the customer and the foundry engineer. Such a customer should know the classes of pattern equipment in order to select that pattern construction which will give satisfactory pattern life, and a satisfactory casting at an economical cost. The pattern equipment has, in many instances, become more elaborate and costly as mechanization has increased in the foundry industry. This is particularly true when a large number of castings is to be made from one pattern. Elaborate patterns can be produced at lower costs by the adaptation of new pattern material, such as plastics. < Pattern Rigging and Production Costs ...A consultation with the patternmaker and foundry engineer is advisable before the casting purchaser produces the pattern for a new design. Such a consultation will often result in substantial savings in production costs. Considera- tion should be given, in designing new pattern equipment, to the follow- ing general principles : 1- Location of the parting line so that the smallest possible portion of the pattern is located in the cope; 2–Use of full cores is more economical than half cores that must be joined together; 3—Use of patterns with offset partings can often reduce or elimi- nate cores; 4-Use of multiple patterns in a mold; 5—Location of risers for proper feeding; 6—Large pockets of sand in the cope should be avoided. A flat back pattern with only the risers and sprue in the cope is the ideal parting, as this eliminates any possibility of mismatch between cope and drag. The conventional pattern design of a pulley wheel usually has the web in the center of its face. An alternate design is illustrated by the . PATTERNS 193 de- Fig. 286—Simplified flat back pa sign for easier casting production. pattern shown in Figure 286 in which the center web is moved to the cope side. This results in a lower cost flat back pattern that is readily matched and easily risered to produce a sound casting. The pattern illustrated in Figure 287 shows proper feeding facilities for a gate valve wedge casting. The pads at the top are heavy enough to permit feeding through this point. 618 CRUISER Fig. 287–Use of pads on pattern to facilitate proper feeding. An illustration of the manner in which pattern quality and design can contribute to over-all casting quality is shown in Figure 288. The casting must have flat surfaces and the sides must be at right angles to each other with a tolerance of + 1/16 inch. The pattern was parted 194 PATTERNS Fig. 288—Illustration of parting to eliminate pattern draft. across corners and tilted to allow sufficient draft on the closed end, thus taper on the casting for draft was eliminated. This made it possible to meet and maintain the required + 1/16 inch tolerances. The method of gaging and checking the casting is also illustrated. The use of interchangeable loose pieces can result in considerable saving in the cost of pattern equipment. This principle is illustrated by Figure 289 which shows a hardwood pattern mounted on cope and drag pine boards. The equipment produces both the right and lefthand castings by interchanging loose pieces shown in the photograph. How- ever, loose change pieces are not practical for high production pat- tern equipment. Fig. 289—Pattern cost re- duced when the use of loose pieces permits pro- duction of right and left castings. Fig. 290—Parting an alu- minum match plate pattern to eliminate a core box. Drag face only of pattern is shown. The use of an irregular parting of the pattern, as shown in Figure 290, results in lower over-all pattern cost from core box elimination. If a straight parting were used, then a core would be required under the arm which displays the pattern number (see Figure 290). It is usually less expensive, in the case of small castings, to part patterns as shown, than to construct core boxes. The pattern equipment shown in Figure 291 illustrates redesign to eliminate the outside core box. This pattern was originally parted on line X-X with a core box as indicated by the solid lines. Splitting the pattern through the center, as shown in Figure 291, eliminated the core boxes, and provided for improved foundry production. The foundry cannot do very much to the pattern once the design has been established. However, when the purchaser permits the found- ry engineer to suggest alterations in line with good foundry practice before the design is released, the pattern may be constructed accord- ingly. Such procedure will yield significant returns in both casting quality and cost. Fig. 291-Redesigned pat- tern resulted in a reduced pattern and molding cost. Fig. 292— Illus- tration of a flim- sy pattern for a single casting. Note knotty pine construction. > The quality of a casting is affected by the type, quality and con- struction of the pattern equipment. Pattern equipment such as sweeps and loose patterns normally results in castings of indifferent accuracy. Also, molding, cleaning and finishing costs are higher; thus, both cast- ing quality and cost are affected: costs are higher and quality down- graded. Poorly constructed patterns, which may distort or warp while in storage or during molding, can produce distorted castings. Patterns of poor quality, while doubtless cheaper in initial cost, may be most expensive as far as end cost, quality and accuracy of the actual castings are concerned. Good patterns and core boxes may be somewhat more expensive, but they almost invariably reverse this picture. Pattern and Core Box Equipment Patterns may range from light construction, such as Figure 292, designed to produce a single casting, as shown in Figure 293, which will never require reproduction, to precision-machined metal patterns and contingent equipment costing many thousands of dollars, such as Figure 294, which is designed for semi-automatic production of large quantities of close tolerance castings at low unit cost. Classes of Pattern Equipment ... Patterns are classified in a number of ways: (1) the material of construction, e.g., softwood, hardwood, plastics, metals; (2) the method of mounting, such as a "loose" pattern or one mounted in a permanent manner; (3) solid or split patterns; and (4) form, such as a full pattern, or a sweep pattern. Many castings require cores of some type to form passages in the im man 69-ZM-34353-6 Fig. 293— Auto motive die cast- ing weighing 6620 pounds, pat- tern equipment shown in Fig. 292. PATTERNS 197 Upper: cope of Fig. 294—Example of pattern equipment costing several thousand dollars. pattern coupler, Lower: drag of pattern coupler. casting, to control the casting contour or, in some instances, by assembly to form the entire mold. Therefore, core boxes are generally required as an essential part of pattern equipment. Materials Used to Make Patterns ... The material used for pattern and core box construction will depend primarily on the number of cast- ings required, the dimensional tolerances needed, and the possible num- ber contemplated for future orders. In some cases, the type of molding process to be used governs the selection of pattern material. For example, patierns for shell molding must be made of metal that can be heated to over 450 degrees F. It is not necessary that patterns or core boxes be entirely con- structed of a i one material. For example, wood patterns will have metal or plastic inserts in areas of wear. In Figure 295 the shape of the spokes a I loose pieces are of plastic; and in Figure 296 the outer core box shell is of aluminum and the shape of the casting is of a plastic material. Wood Patterns ... Pine and mahogany are most commonly used to make working patterns, as well as master patterns from which metal working patterns are made. Softwood (pine) patterns are the least expensive, but can be used only for limited production. Fig. 295–Pattern equipment using different con- struction materials. Wood patterns, particularly those constructed of pine, are some- what prone to warpage. This is because of the shrinkage or swelling which occurs in wood as a result of changes in moisture content. The 1. PBB Com Fig. 296—Two halves of a blower core box. Plastic poured inside aluminum frames. PATTERNS 199 chart shown in Figure 297 shows the volumetric changes resulting from changes in the moisture content of sugar pine, northern pine, and mahogany, and the effect of humidity on the equilibrium moisture content of these three woods. It can be observed from the chart that 41 NORTHERN WHITE PINE SUGAR PINE PERCENT EXPANSION IDEAL MOISTURE CONTENT AS HONDURAS MAHOGANY RECEIVED 0 10% 10 15% 30 40 50 60 70 80 % PERCENT HUMIDITY IN THE ATMOSPHERE N PERCENT SHRINKAGE * THE EQUILIBRIUM MOISTURE CONTENT IS THE ULTIMATE MOISTURE CONTENT THAT LUMBER WILL ATTAIN WHEN SUBJECTED TO A GIVEN HUMIDITY CONDITION Fig. 297—Effect of: moisture content of pine and mahogany wood on the resulting changes. Reference point - size with 5 percent moisture content. a change of 5 percent in the moisture content of mahogany or northern pine results in a 11/2 percent volumetric change, which can be respon- sible for an appreciable change in the dimensions of a pattern. Thus, radical changes in humidity can result not only in warpage of the pat- tern, but in dimensional variation as well. Patterns shipped from a foundry in an area of high humidity to a relatively dry area may warp as a result of the wood drying out. Hardwood patterns must be well made, using bolts, screw and glued construction instead of nailing, in order to withstand the longer expected service life, and to resist during their longer life, the cyclic stresses set up by contraction and expansion of the wood. The volumetric changes caused by atmospheric conditions can be minimized by the use of moisture retardant pattern coatings. Three coats of lacquer are about 80 percent effective against moisture being absorbed under normal conditions. Metal Patterns ... Metal patterns are particularly well adapted to long production runs, sand slinger operations, and other molding methods where abrasion and hard usage may be encountered. They may be made of aluminum, cast iron, or cast steel. The latter are often case- hardened to provide maximum life on jobs where close tolerance is imperative. Metal core boxes usually are made of aluminum or cast iron. Aluminum core boxes which have a constricted area may not be satisfactory for high production runs because of excessive wear in these areas. In such cases, bushings and other inserts of steel are used to resist wear and prolong service life. Cast iron core boxes give much better service life than aluminum, and when weight is not a governing factor, cast iron core boxes are used for core blowing operations. Table 9 is given only as a guide to the use of wood or metal as construction material for patterns. 200 PATTERNS Table 9—Construction Materials for Patterns and Life Guide Number of Castings (before repairs) Material Pattern 500 2000 6000 200 1000 Small castings under 24 inches largest dimension Core Box 300 Softwood patterns and core box. 2000 Hardwood, metal faced patterns and core boxes. 6000 Aluminum patterns and core boxes. Plastic match plate patterns. Medium castings—up to 72 inches largest dimension 100 Softwood patterns and core boxes. 750 Hardwood patterns and core boxes with wearing surfaces metal faced. 3000 Aluminum patterns and core boxes. Large Castings-over 6 feet largest dimension 50 Softwood patterns and core boxes. 150 Softwood patterns exposed projections, metal faced. Boxes are to be of softwood, metal faced. 500 Hardwood patterns, metal reinforced. Hardwood core boxes, metal faced. 3000 50 200 500 Plastic Patterns ... The steady rise in costs and the shortage of skilled man-power have long stimulated the steel casting industry to explore new ideas and materials for producing patterns and core boxes. The industry's interest in plastic patterns was reborn with the introduction of the epoxy resins. Epoxy resins have proved very adaptable because of their ability to bond to other materials, and their high strength as pattern material. They have the following charac- teristics: (1) dimensional stability, (2) high compressive strength, (3) excellent adhesive qualities, (4) impact resistance greater than wood, (5) wetting ability, (6) chemical resistance, (7) high flexural strength, (8) high abrasive resistance, and (9) easy release from molding sand. > Epoxy plastic patterns are used with success on core blowers and sand slingers. Double shrinkage patterns are eliminated and any single shrink pattern can be reproduced exactly without costly finishing. The use of plastic patterns and core boxes can reduce the cost of new equipment for production work. However, plastics will not show to great advantage where simple shapes and block patterns are concerned, but the more intricate the contours become, the more advantageous be- comes the use of plastics. Fig. 298—Single, loose, wood valve body pat- terns. The foundry engineer must evaluate plastic materials for their application in his plant. The purchaser of steel castings should consult with the patternmaker and the foundry engineer before purchasing spe- cial types of plastic pattern equipment. Pattern Types ... Loose patterns, either wood or metal, are used only for very limited production. They are most suitable when an experi- mental piece of apparatus is being constructed or only a few castings are required from a pattern. Both wood and metal patterns, when loose, have the disadvantage that excessive molding time and a high de- gree of molding skill are required. This materially affects the cost of producing castings with loose patterns, and often may cause a variation in the quality of the castings. Examples of loose, softwood pattern equipment are shown in Figures 298 and 299. Figure 300 shows a hardwood pattern split for loose or matching setup. Mounted patterns usually cost but little more than loose patterns and the small additional cost almost invariably will be far outweighed by reduced molding and finishing charges. This is particularly true in regard to intricate designs where dimensional accuracy is important. The useful life of either soft or hardwood patterns can be materially jung Fig. 299–Loose, soft wood pattern equipment (10 molds). ***** 202 PATTERNS increased by mounting the pattern. Figure 301 is an example of a mounted softwood pattern. The expected service life of the mounted softwood pattern is 250 molds for slinger operation and 500 molds for a squeezer operation, while the mounted hardwood pattern would have a service life of 2000 molds. The mounted aluminum pattern shown in Fig. 300—Hardwood split pattern for loose or matching set-up (50 to 100 molds). Figure 302 has an expected life of 6000 molds, if molds are rammed with a sand slinger. However, the life would be doubled if a jolt-squeeze molding machine was used. Thus, it can be seen that the molding oper- ation has a definite effect on pattern life. A single-piece pattern with a flat parting on one surface, or a two- piece pattern that is split on a flat parting can be readily mounted to Fig. 301-Mounted soft wood pattern. Expected service life 500 molds with squeezer operation and 250 with sand slinger. Fig. 302—Mounted alumi- num pattern with lite ex. pectancy of at least 12,000 molds on a jolt squeeze molding machine. make a match plate. Figure 303 shows an aluminum flat back match plate and Figure 304 shows the two halves of a split aluminum pattern mounted on opposite sides of a no-shift aluminum match plate. Cope and 232332 Fig. 303—Aluminum flat back match-plate pattern. • drag views are shown in Figure 304 (b) and (c). Match plate pattern equipment is used on a molding machine and simplifies the molding operation. Often a match plate has two or more patterns on the board, thereby increasing the number of castings per mold. Castings requiring an irregular parting (see Figure 305) can be easily made as a one-piece matching plate. A cope and drag setup generally is used when the pattern and flask equipment is too large for a molding machine operator to handle safely, 204 PATTERNS a) side view of pattern equipment b) cope view of pattern c) drag view of pattern Fig. 304—Cope and drag mounted on single cast aluminum waffle board. D a) side view showing irregular part b) cope view of pattern c) drag view of pattern Fig. 305—Pattern mounted on a wood offset board, (irregular part). PATTERNS 205 or when production requirements warrant a multiple-casting mold. The cope portion of the pattern is mounted on one board (Figure 306a) and the drag on another board (Figure 306b). pania (a) view of cope board (b) view of drag board Fig. 306—Cope and drag set of aluminum patterns. Expected production 20,000 molds. Figure 307 illustrates the use of multiple castings on a cope board. The six metal patterns shown are case-hardened cast steel patterns. The base and stripper plates are also cast steel, but the gates and small prints on joints are of aluminum. This type of pattern equipment will make 100,000 molds (600,000 castings). Fig. 307–Multiple patterns mounted on a cope plate. Fig. 308—Medium size pat- tern of solid construction. C) Full patterns that form the entire outline of the piece are the simplest type, but often are expensive. A solid pattern is illustrated in Figure 308. Note that the parting plane is through the casting, but is irregular. Making a solid pattern similar to the one shown in Figure 309 requires considerable experience. The parting plane coincides with one surface of this pattern, thereby eliminating the parting seam in close tolerance areas, thus affording freedom from shift. The core box is shown directly back of the pattern. The patterns for large castings need not be a complete replica. The molds for certain types of castings may be shaped by a template-type of pattern called a sweep. Figure 310 illustrates a sweep for molding a ring gear. Box No. 1 is the ring gear section core box, and Box No. 2 the gear section cover core box. The mold is produced by rotating the 120 PS Fig. 309-Large size pattern of solid construc- tion. Note large core box directly back of pattern. Contour of pat- tern sculptured by hand. is We BA Fig. 310—Sweep molding pattern equipment for molding large ring gear. 1 2 sweep around the axis to produce the mold surface. Special types of pattern equipment, such as sweeps, should be considered by the pur- chaser of steel castings only after consultation with the foundry engi- neer and the patternmaker. Core Box Construction and Durability Cores are used to form the internal cavities or shape of a casting, and in some cases to shape a complex external portion. The most com- monly used material for general practice in making core boxes is wood. Both soft and hard woods are used. Pine is often used for constructing the main framework, and hardwood or metal is used for facings, bosses, and flanges which are subjected to severe wear. The metals which are used for repetitive work are usually aluminum (cast or rolled), brass, and cast iron. Cast iron is sometimes preferred in the case where the core blowing of a large number of cores is involved. Also, the epoxy resins, with glass fibre or mat as reinforcement, are finding increased use in the industry. Fig. 311–Full split hard- wood box which elimi- nates pasting of core Expected life - 1,200 cores. Figure 312— Aluminum corę box for 2'' gate valve body. Whole cores made on bench. Production 8,000 cores before major repairs. Cores which are symmetrical can be made with only one box for half the core. The identical core halves are then pasted together to make the complete core. Core pasting is costly and time consuming and its elimination is advisable on production runs. The core box setup shown in Figure 311 illustrates a full split core box which eliminates pasting. The aluminum core box illustrated in Figure 312 also produces complete cores. Figure 313 shows a split aluminum box for core blower use, equipped with rubber seals to eliminate blow-bys. The rubber seal shown in the joint face of the core box replaces the steel facing normally used, and a substantial increase in service life is gained by this method. This Fig. 313—(a) Split aluminum blow core box with rubber seals. Fig. 313—(b) Aluminum core drier. PATTERNS 209 Fig. 314—Core box without usual steel facing. core blowing equipment, with normal maintenance, should make upward of 100,000 cores. Core driers for the core are also shown in Figure 313. Shell cores, which normally are produced in cast iron core boxes, do not require core driers or a baking operation. The hardwood core box shown in Figure 314 is for limited produc- tion as it does not have a steel facing. This type of equipment will pro- duce very few accurate cores because of wear on the strike-off face. Facing with steel will eliminate this problem, and several thousand cores of reasonable accuracy can be made, if production requirements warrant the additional expense. Resins (plastics) play an important part in duplicating complicated prototype patterns and core boxes. The ease and speed with which plastic pattern equipment can be reproduced assist the foundry in meeting customer schedule requirements more readily than is the case when pro- ducing metal pattern equipment. The use of plastic lined core boxes is advantageous because it is not necessary to rap the core box to eject the sand core. This feature alone is highly desirable since it aids in dimensional control. Core Box Cost vs. Service Life ... The number of cores that can be made from a core box is dependent on the materials used in its construc- tion, the design of the core box and the method of producing the cores. In Figure 315 is shown a series of softwood core boxes from which 200 to 300 satisfactory cores could be made. If the core boxes were hard- wood, then 2,000 cores might be made and, if the inside and top were metal faced, 5,000 cores could be made, with periodic repairs. A solid Joy Fig. 315-Series of core boxes. Softwood 200-300 cores Hardwood 2000 cores Metal faced 5000 cores Solid aluminum 50,000 and up. aluminum core box would produce possibly as many as 50,000 cores, with periodic maintenance. Listed in Table 10 are individual data on the actual cost and esti- mated production runs of different core blow boxes, which were con- structed of aluminum, wood, or plastic, as well as plastic-lined wood or metal boxes. Figures 316 through 321 illustrate the construction and designs of the core boxes. The core box illustrated in Figure 316 was originally made of cherry wood at a cost of $700.00. The plastic lined core box cost approximately 312 times as much, but the production figure expected with normal handling would be five fold, except under conditions stated in footnote (1) Table 10. The direct costs of the core box illustrated in Figure 318, as made in aluminum or aluminum-plastic, are given in Table 10. Fig. 316—Plastic lined cherry wood blow core box. PATTERNS 211 Table 10—Comparative Cost and Estimated Production of Different Blow Core Boxes Life of Box - No. of Cores Original Cost Before Repairs Production Construction in Dollars of Resin Facing Expected Remarks Cherry Wood 700 700 10,000 & up (1) Cherry Wood Plastic Lined 2,000 7,000 50,000 & up (1) See Fig. 316 Aluminum Plastic Coated 4,000 3,000 50,000 & up (1) See Fig. 317 Aluminum 10,000 25-30,000 50,000 & up (1) See Fig. 318 Aluminum- Plastic Coated (2) 5,000 19,800 50,000 & up (1) See Fig 318 See Fig. 319 Plastic - Main Resurfacing 1/3 Body Core Box 500 30,000 (3) 50,000 & up cost of box Plastic Gate Core Box - Side Frame 750 30,000 50,000 & up See Fig. 320 Plastic- Resurfacing 1/5 Core - Draft Gear 500 30,000 50,000 & up cost of core box Plastic Gate Core - Knuckle 200 30,000 (3) 50,000 & up See Fig. 321 (1) The life of a cherry wood, aluminum or plastic coated aluminum core box, with an aluminum bottom board reinforced, as shown in Figures 317, 318, and 319, should exceed 200,000 units whenever all the following conditions are observed: (1) the blow ports on the blower are placed so that the sand does not strike the walls of the core box, (2) a pre-fill blower technique is employed, and (3) proper maintenance is given to the equipment. (2) Replacement of the aluminum pattern. (3) Minor repairs due to accidents. Cost differentials in relation to metals and plastics are difficult to define. The savings attained by the use of plastics increases in propor- tion to the complexity of the pattern equipment. This is primarily due to the elimination of machining, templates, and reduced handwork. - - WWW Xos Fig. 317—Metal blow core box, plastic lined. Fig. 318–Alumi- num blow core box. - Cost $10,000. An intricate plastic core box designed for core-blower production, is shown in Figure 319. The original cope and drag boxes were made of cast iron with brass inserts and required over 700 manhours to com- plete. The plastic multiple cavity core box required only 175 manhours. -Wear Resistant Materials ... Erosion of pattern equipment caused by the velocity of sand in foundry sandslinging and core blowing operations is a major concern of the industry. There is a continuous search for abrasion resistant materials for use in pattern construction. It is gen- erally acknowledged that hard-chrome plated patterns exhibit the least wear of any material in the production of long-run castings. The application of hard-chrome-plated liners to plastic patterns is less expensive than metal patterns because it is a relatively simple matter to cut, fit, and set hard-chrome-plated liners at any indicated wear sections of the pattern before laminating with fibre glass and epoxy resins. The relatively new epoxy-polyurethane castor oil base materials appear to possess abrasion resistant properties that surpass hard- Fig. 319–Plastic blow core box - Cost $500. PATTERNS 213 94 Fig. 320–Plastic blow core box for side frame-Cost $750. chrome-plating and it behooves both the foundry engineer, pattern- maker, and casting purchaser to keep abreast of the new developments in plastic abrasion resistant material. Patternmaker's Shrinkage Allowance . . . Shrinkage allowance is the correction on the pattern which must be made to compensate for the contraction of the casting as it cools in the mold from the metal freezing temperature to room temperature. (See section on Volume Changes, Chapter VIII). This contraction which takes place is commonly known in the foundry as patternmaker's shrinkage. The pattern is made larger by the amount of shrinkage of the particular metal used to compensate for the contraction effect. . Fig. 321–Plastic blow core box for knuckles—Cost $200. 214 PATTERNS a The amount of contraction varies with the type of steel used (Chap- ter VIII). The contraction also varies with the casting design, where the resistance of the mold to the normal contraction of the casting may be materially influenced by the shape. It is therefore possible to have sev- eral different shrinkage allowances in one pattern. Molding methods may also require certain changes in shrinkage allowances. The methods employed by two different foundries may be so unlike that somewhat different shrinkage allowances will be required by each for the same pattern. It is strongly urged that buyers of castings have their patterns made at the foundry where the castings are to be produced, which will minimize difficulties arising from a lack of knowledge of shrinkage requirements. It has been stated that the contraction characteristics of a casting depend to a considerable degree upon its design. A simple illustration will suffice: if a cylindrical bar pattern illustrated in Figure 322 were molded, and the mold cavity poured with a 0.35 percent carbon steel, the steel bar, when cold, would have a length 2.40 percent shorter than the pattern. This means that the bar would have contracted freely in accord- ance with the physical cooling characteristics of the metal. The mold or the design would have had no influence upon the bar to hinder or pre- vent the normal contraction from taking place. The patternmaker's shrinkage value that must be applied is 0.288 inch (approximately 9/32 inch) per foot. The bar is now changed (Figure 322b) by placing a large knob on each end. If this bar is molded and poured, after cooling it is found to have contracted only 1.64 percent. This means that the bar was re- strained in its contraction, and contracted in accordance with curve 3 of Figure 323. These curves show that when the casting is at room tem- perature in the mold, it is under a load of approximately 2650 pounds per square inch. The reason for this is that the bar, in its attempt to contract, is restricted by the sand that lies between the two knobs. The sand offers considerable resistance and consequently a stress is built up resulting from the hindered contraction. In other words, the casting is stretched and elongated during cooling. In this particular case the bar contracted only 0.196 inch per foot, which is slightly over 3/16 inch per foot. The ratio of 3/16 inch per foot is the usual figure used for pattern- maker's shrinkage. The fact that it has been considered a normal figure is misleading as will be shown. Buyers of castings who make their own patterns often find that the castings do not come within the proper tol- erances primarily because they have adopted the usual figure of 3/16 inch per foot for patternmaker's shrinkage without considering the de- sign of the casting and the possibility of hindered contraction within the mold. PATTERNS 215 SAND: MOLD BAR А SAND MOLD BAR WITH KNOBS B SAND MOLD BAR WITH FLANGES : Ć Fig. 322—Patternmaker's shrinkage and hindered contraction: (A) straight bar (B) Bar with knobs (C) Bar with flanges. The difficulty of this situation lies in trying to explain to the buyer that the pattern is at fault and that the figure 3/16 inch per foot cannot be used. The explanation of this point may be illustrated by referring again to the bar of Figure 322 (c) whose design is again slightly altered so that prominent flanges appear on both ends. In this case, it is found that after the casting has been produced it has contracted only 0.92 per- 216 PATTERNS 2.0 2,830 42716 contraction of plain carbon steels Bars restrained by a light Spring 12,602 5 1.5 12,538 3 .. 2,421 1. b08% Carbon 2. 6.14% 3. 6.35% 4. 6.45% 5. 6.55% 6. 6.90% 4 12,310 . Percent 2,182 12,045 pounds per sq. in at smallest diameter of bor. 1.0 11.895 2 1,750 11,594 14,418 1,259 0.5 4,075 2 1889 44.5 688 6 472 232 1200 1600 2912 1400 2552 1000 1832 800 1472 600 1112 400 752 200 342 °C. 32 °F 2192 Fig. 323--Contraction of plain carbon steel restrained by a light spring (Briggs and Gezelius)". cent of the pattern length. This means that the bar was restrained from contracting to an even greater degree than it was under design conditions of Figure 322 (b). It also shows that it contracted similarly to those conditions of curve 3 of Figure 324 wherein a 0.35 percent carbon steel contracted against a medium strong spring. It may be observed from this curve that a stress equivalent to 6500 pounds per square inch was acting on the casting while in the mold, because of hindered contraction. The power of the sand mold to hinder contraction is greater in this case than in that of the bar with knobs because a greater volume of sand is inter- posed between the end protuberances, and the shape of the casting is such that it will displace the sand less readily. PATTERNS 217 18.106 Contraction of plain carbon steels Restrained by a medium heavy G spring 7601 1.0 7,040 5 6,475 .. 1. 0.09% Carbon 2. 0.14% 3. 0.35 % 4. 6.45% 5. 0.55% 6, 62.90 % 15,850 Percent. Pounds per sq.in at the smallest diameter of the bar. 5,197 4,527 0.5 3811 3,043 2,275 4 1,532 1-2 724 400 200 o °C. 1600 2912 1400 2552 1200 2192 1000 1852 800 1472 600 1172 752 392 32 °F. Fig. 324–Contraction of plain carbon steel restrained by a medium-strong spring (Briggs and Gezelius). The patternmaker's shrinkage under the above conditions would be equivalent to 0.110 inch per foot, or approximately 7/64 inch per foot. This is a decided change over the patternmaker's shrinkage required by the bar with knobs. The value of 7/64 is not the smallest value that can be obtained since, under certain conditions of mold design and molding procedure, it is possible to obtain a solid contraction of only 0.50 percent, or approximately 1/16 inch per foot patternmaker's shrinkage. Casting shape and mold conditions causing high hindered contrac- tion are responsible for this low figure, with the result that very high stresses, in the neighborhood of 10,000 pounds per square inch, are acting upon the casting as it cools to room temperature. Such stresses and even those of lesser magnitude, often introduce production difficul- ties. Certain special molding techniques are reasonably effective in curing such a situation, but redesign is the surest remedy. The purchaser of steel castings who builds his own patterns should be very careful in the use of tables purporting to give patternmaker's shrinkage. The best policy is to discuss the question of patternmaker's shrinkage values with the foundry that is to make the castings or, better still, to allow the foundry to construct the pattern. 218 P A T T E RNS 多 ​Pattern Distortion Allowances... Occasionally, castings produced from a pattern are found distorted from the desired shape and do not conform to the lines of the pattern; these castings include those having large flat areas, or those of U-shape and circular design. Casting distortion is caused by high hindered contraction stresses resulting from irregu- larity of design. Minor distortions found in castings are corrected by mechanical means but, if the distortions are consistent and prominent, it is necessary that changes be made in the pattern dimensions and shape in order to counteract the distortions which arise during the cooling of the casting. When patterns are to be so changed, it is important that there be a consultation between the engineer or the buyer and the foundry supply- ing the casting, to discuss future casting production, dimensional toler- ances, and other items which may be effective in reducing the expense of pattern equipment or casting production. Machine Finish Allowances Sufficient excess metal should be pro- vided on all surfaces requiring finish machining. The necessary allow- ance, commonly called finish, depends upon: (a) the class of steel, (b) the shape of the casting and the surface to be machined, (c) the size of the casting, (d) the pouring position, (e) the tendency to warp, and (f) the machining method and setup. Standard finish allowances for steel castings have not been formu- lated since it has been found that each casting design is a problem peculiar to itself. Allowances that would be acceptable for one casting would not be sufficient for a different one. In general, allowances vary from almost nothing to 34 inch, depending upon the variables listed above. This subject is discussed in detail in Chapter VI on Tolerances for Steel Castings. Casting Finish Tolerances ... Many steel castings are produced with sufficient accuracy so that machining operations are not necessary in order to fit them as integral parts into machines and equipment. This is especially true when steel castings are purchased in such quantities as will justify the foundry's use of gages, templates, and coining operations. A single set of tolerances as to finish size without machine surfaces cannot be established for steel castings. Each steel casting design is a problem in itself and, as an individual problem, tolerance characteristics must be considered from the standpoint of casting design and applica- tion. The subject of steel casting tolerances is fully discussed in Chapter VI and the reader is referred to that chapter for pertinent data on this subject. PATTERNS 219 Draft ... Draft is the taper which must be allowed on all vertical faces of a pattern to permit its removal from the sand mold without tearing the mold walls (Figure 325). Regardless of the type of pattern equip- ment used, draft must be considered in all casting designs. In cases where the amount of draft may affect the subsequent use of the casting, the drawing should specify whether this draft is to be added to or sub- tracted from the casting dimensions as given. DRAFT Fig. 325—Draft or taper allowances. The necessary amount of draft depends upon the size of the casting, the method of production, and whether molding is by hand or machine. Machine molding will require a minimum amount of draft, Interior sur- faces in green sand molding usually require more draft than exterior surfaces. The amount of draft recommended under normal conditions is from 1/16 to 1/8 inch per foot, and this allowance normally would be added to design dimensions. Draft can be eliminated, in some cases, through special techniques. These situations should be discussed with the foundry engineer. Location Points ... Layout points to be used as benchmarks by the ma- chine shop are important items frequently neglected until after the casting is made. When possible, they should be indicated on the drawing so that castings may be checked from the same reference point by the pattern shop, the foundry, and the machine shop. An effort should be made to place them on the same side of the parting line, and they should be located so that they will not be easily influenced by a shift of a core, the cope, or the drag. Points should be as far apart as the size of the casting permits, as this will insure the most accurate results. Dimen- sions which have no finish allowances and are to be held to close limits, should be considered as the proper place from which to start develop- ment of tooling fixtures. Gating and Risering ... Pattern equipment which is designed for one cast metal (e.g., cast iron) should not be employed to produce castings of another metal (e.g., steel) because certain changes are necessary in pattern design to secure acceptable castings. Gating and risering arrangements for one type of metal usually are not satisfactory for 220 PATTERNS another. Pattern equipment for iron castings should be reviewed by the steel foundryman before the pattern is used for steel. A pattern that is initially constructed for another metal cannot normally be used for steel without some alterations to compensate for differences in metal shrinkage. Gating and feeding constitute two of the most important features incident to the production of a casting, and they should be fully consid- ered in the construction of the pattern. The location of risers and gates depends greatly upon the knowledge and experience of the foundry engi- neer, which is a further reason why patterns should be constructed preferably at the foundry where the castings are to be produced or under the authorization of the foundry at the customer's or independent pat- tern shops. Patterns for Special Molding and Coremaking Techniques ... The pro- duction of core boxes and patterns for shell molding techniques must meet high standards. Shell patterns made of cast iron or brass are diffi- cult to produce, and are expensive. Each casting design made by the shell process is an individual problem, and its pattern equipment should not be made without the cooperation of the foundry producing the cast- ing. The maker of shell mold patterns needs all the detailed information the foundry and buyer can furnish on such subjects as: shell molding equipment to be used; gating and risering techniques; location of ejector pins, mold contact area for cementing the two halves together, draft allowances, and parting surfaces. All are significant data which the patternmaker needs in the construction of shell patterns. The customer should indicate the areas of the casting which are not critical and where, if any, maximum tolerances can be allowed. Both the buyer and the producing foundry of shell castings must realize that this type of pattern equipment is a precision job. Therefore, ample time should be allowed for the pattern shop to make such equipment. Shell core boxes may be made of several metals such as iron, alumi- num, steel and bronze; but gray iron seems to be the metal generally used. Pattern Storage The storage of customers' pattern equipment is often a major problem to the foundry, since no foundry has enough pattern storage area. Four factors govern the space requirements for pattern storage, namely: (1) quantity and volume of equipment on hand, (2) rate of acquisition of new patterns for storage, (3) general rate of obsolescence of patterns on hand, and (4) type of pattern equipment. PATTERNS 221 It is the last two items that tend to overcrowd pattern storages and, only when an agreement is reached between the customer and the foundry concerning a procedure on returning non-productive equipment or the destruction of the old and obsolete patterns, can the foundry main- tain adequate pattern storage space. REFERENCES 1. Briggs, C. W. and Gezelius, R., “Studies on Solidification and Contraction of Cast Carbon Steel”, Trans. American Foundrymen's Society, Vol. 43, 1935, pp. 449-476. > 2. Briggs, C. W., "The Metallurgy of Steel Castings", McGraw-Hill, New York, 1946. 3. Gray Iron Castings Handbook, Gray Iron Founders' Society, Inc., 1957 Edition. 4. Cast Metals Handbook, American Foundrymen's Society, 1957 Edition. 5. Hall, John Howe, “Patterns and Molding Methods for Steel Castings”, Foundry, November 1948, December 1948, January 1949, February 1949 and March 1949. 6. United States Gypsum, "Epoxical Plastic Tooling Resin”, Bulletin No. 400, Chicago 6, Illinois. 7. Blake, Elmer, “Design of Core Boxes and Driers", The Foundry, June 1951, p. 114, 1951. 8. Nass, Chester V., “What the Foundry Expects of the Pattern Shop”, The Foundry, May 1950, pp. 132-134, 306. 9. Siebert, W. H., "Practical Suggestions for Building of Wood Patterns”, Ameri- can Foundryman, April 1952, pp. 132-134. 10. von Colditz, Paul and Burton, H. A., “Plastics in Patternmaking”, The Foundry, December 1956, pp. 98-103. 11. McAfee, E. J., “Epoxy Resin Patterns”, Modern Castings, May 1956, pp. 70-75. 12. “Tentative Standard Pattern Colors for New Patterns", Modern Castings, December 1958, p. 32. 13. Burton, H. A., “The Practical Application of Reinforced Epoxy Resins for Foundry Use", The British Foundryman, March 1959, pp. 127-136. 14. Turney, J.W., "Epoxy Patterns and Core Boxes”, The Foundry, December 1957, pp. 86-90. 15. Geary, E. A., "Pattern Standards for Practical Foundry Usage", Modern Castings, October 1958, p. 556. 16. Graham, C. R., “Newest Way to Save with Plastics”, Plant Administration, May 1959, pp. 60-61. 17. Kobee, Frank, “Plastic Patterns, New Tools and Materials”, Modern Castings, May 1960, p. 139. 18. Leaman, J. M. and Morrison, P. L., “Cast Epoxy Core Driers”, The Foundry, March 1958, pp. 84-87. 19. Olson, Ray, “Shell Pattern Equipment”, The Foundry, April 1958, pp. 104-106. 20. Stock, J. E., “Core Boxes for Shell Cores", Modern Castings, July 1959, pp. 71-72. CHAPTER VI TOLERANCES IN STEEL CASTINGS Steel castings, like all other manufactured products, are subject to surface and dimensional variations. It is important, therefore, that design engineers and purchasers of steel castings have a clear understanding of the factors which influence tolerances and a working knowledge of the dimensional variations that may be normally expect- ed in a production run of castings. An improper restriction of toler- ances may significantly affect the cost and delivery of a casting. Di- mensional tolerance requirements which are too stringent result in a need for special manufacturing techniques, higher finishing costs, and an increased rejection rate. Tolerance limits which are not sufficiently stringent may result in an increase in machining by the purchaser of a casting, as well as the addition of unnecessary weight. The use of realistic tolerances is of critical importance if ultimate cost of the casting, ready for service application, is to be held to a practical minimum. Dimensional tolerances to which steel castings can be held are primarily functions of: (1) design, and (2) variables in the steel casting manufacturing process. Before the designer and casting manufacturer can correctly and accurately set tolerance limitations on casting dimensions, a comprehensive study of these variables must be made. It is essential for such a study that the fundamentals of design - as set forth in Chapter IV of this Handbook - be thoroughly understood. This will provide common ground for intelligent discus- sion and mutual agreement between designer and steel casting pro- ducer regarding dimensional limits. SECTION I Design Influences Casting Tolerances Casting Shape ... Casting shape and complexity of design determine the contraction behavior of cast steel from the solidifying temperature to room temperature which, in turn, largely governs the tolerances that can be commercially obtained. Shape and complexity introduce the factor of hindered contraction which has been fully discussed in Chapter V (see pages 214-217). The more complex the casting design, the greater the hindered contraction and the less predictable its final dimensions. Contraction may range from as much as 9/32 inch per foot to practically zero. Hindered contraction can also result in warpage and distortion which will increase the dimensional varia- tions. TOLERANCES 223 A secondary effect of casting design on hindered contraction is that of hindered contraction by gates and risers, since casting design dictates the number and location of these gates and risers. Although gating and risering are not the designer's problem, the designer should have some awareness of the fact that the location and number of gates and risers can influence dimensions and affect tolerances. Parting . The design of a casting determines the manner in which the mold will be parted and, thus, affects dimensions across the mold parting. Tolerances must always be greater on dimensions across the parting because of the fact that the cope and drag flasks, and the cope and drag parting surfaces of the sand mold, will not close together precisely at all points from mold to mold. The same situation exists in forgings where a die closure tolerance is made for deviations in thickness dimensions across a die parting. Casting design plays an important role in the determination of the type of pattern and core box equipment to be used, as well as the material from which it will be made. Patterns and core boxes bear an important relation to tolerances, and they will be discussed in detail in the following section of this chapter. Draft and Openings ... Draft, or the pattern taper that must be al- lowed on all vertical faces to permit the pattern to be removed from the sand without tearing the mold walls, is another factor that must be considered in casting design. Regardless of the type of pattern equip- ment to be used, draft has to be considered in all casting designs. The necessary amount of draft depends on the size of the casting, the method of production, and the type of pattern and core equipment used. Actual draft requirements may be found in Chapter V, page 219. Physical size and weight of a casting influence the ability of the molding medium to contain the molten metal to its requisite shape. Heavy sections will increase the stress placed on mold walls and thus increase deformation of the mold, causing greater variations in thickness than would be encountered in light sections. As a result, larger tolerances must be allowed for thick sections. Similarly, the accuracy and precision of cored passage dimensions may be limited by the ability to make cores which will not bow or sag as a result of their size or shape. The minimum diameter core which can be used successfully in steel castings is dependent upon three factors: (1) the thickness of the metal section surrounding the cores, (2) the length of the core, and (3) the special precautions and proce- dures used by the foundry. The first two of these factors are functions of the design, and must be given consideration by the design engineer when the casting drawings are developed (see Chapter IV, page 138). 224 TOLERANCES The use for which a casting is intended should play a very impor- tant role in establishing realistic tolerance limitations. If a casting is to be machined, the tolerances need not be as stringent as they would be were the casting to be used in the unmachined condition. Certain castings may have only a few critical dimensions which require close tolerances. To place tight limitations on dimensions that are not critical merely increases the final casting cost without benefit to the purchaser. a Dimensional Variations in Production Castings The Steel Founders' Society of America initiated, in 1958, a comprehensive study of dimensional tolerances obtained in routine production of a wide variety of steel castings embracing the major fields of application. The foundries that contributed to this study were requested to measure and record detailed dimensions of at least 25 castings of a production lot, processed in normal fashion and selected at random. These data covered 88 individual designs ranging from simple to complex, and small to large, thus providing an ideal background for thorough appraisal and authoritative summary. A detailed analysis of the results has been made for each individual design by employment of the following basic concepts relating to tolerance: Design dimension and tolerance, if specified; Maximum positive and negative deviations from design dimension; Most probable positive and negative deviations from de- sign dimension. (Where less than 25 castings were measured, the average deviations were used. Such in- stances were entirely confined to large castings); Average casting weight; Maximum positive and negative deviations from average weight; Type of pattern equipment. This Handbook is not the proper place to reproduce the data re- lating to all of the 88 designs which were analyzed in this manner, but Figures 326 through 335 provide representative examples. The com- plete data were used, however, in preparation of the section of this chapter on “Recommendations on Steel Casting Tolerances.” А F, &-531 -00 E BC, E, Fig. 326—Classification: Agricultural Equipment. Casting: Shaft Bearing Pattern: Aluminum Mounted Drag Board Casting %* %t Maximum Most Frequent Specified Dimension Deviation Deviation Tolerances Inches (Inches) (Inches) (Inches) (+) (-) (+) (-) (+) (-) A-8-29/32 100 24 1/32 1/16 0 1/32 3/32 5/64 B-6 100 56 1/64 0 0 0 3/32 5/64 D(a)-3-4/32 100 64 1/16 1/32 0 0 2/32 0 D(a)—26/32 100 44 1/32 0 1/64 0 1/32 0 E-3 100 40 1/32 0 1/64 0 2/32 3/64 F-7 100 52 1/32 1/32 1/64 0 3/32 5/64 Weight: Average 22.1 lbs. Maximum Deviation (+) 2.6% (-) 2.6% * Percent of castings within the specified tolerances. (a) Cored opening. † Percent of castings with the measured dimension identical to the blueprint. - Casting: Chain Link Pattern: Hardwood Mounted Matchplate Casting %* %+ Maximum Most Frequent Specified Dimension Deviation Deviation Tolerances Inches (Inches) (Inches) (Inches) (+) (-) (+) (-) (+) (-) B(b)-1 100 43 1/32 1/32 1/64 0 3/64 1/32 C-5-4/32 100 14 0 2/32 0 3/64 0 2/32 D—12-30/32 100 2/32 0 3/64 0 7/64 3/32 G(a)—1-8/32 57 0 3/32 0 2/32 0 3/64 1/32 Weight: Average 9.5 lbs. Maximum Deviation (+) 0.63% (-) 5.2% * Percent of castings within the specified tolerances. † Percent of castings with the measured dimension identical to the blueprint. (a) Cored opening. (b) Dimension across parting line. Fig. 327—Classification: Mining and Crushing Machinery. 28 - F T C A B D 2002 E D 0 00 D C A Fig. 328–Classification: Railroad. Casting: Center Filler Pattern: Mounted Wood.on Cope and Drag Boards Casting %* %+ Maximum Most Frequent Specified Dimension Deviation Deviation Tolerances Inches (Inches) (Inches) (Inches) (+) (-) (+) (-) (+) (-) A—17-4/32 100 40 1/32 1/32 0 1/64 2/32 2/32 B—13-24/32 100 80 1/32 0 0 0 3/32 1/32 C(a)—2-4/32 56 0 4/32 0 2/32 0 3/32 0 D(b)—15-3/32 100 100 0 0 0 0 2/32 0 E-12-28/32 100 100 0 0 0 0 1/32 2/32 Weight: Average - 333 lbs. Maximum Deviation (+) 2.70% (-) 1.67% * Percent of castings within the specified tolerances. † Percent of castings with the measured dimension identical to the blueprint. (a) Cored opening. (b) Dimension across parting line. 3 %* Casting: Cement Mixer Truck Drum Head Pattern: Hardwood Mounted on Cope and Drag Boards. Casting %+ Maximum Most Frequent Specified Dimension Deviation Deviation Tolerances Inches (Inches) (Inches) (Inches) (+) (-) (+) (-) (+) (-) A—70-28/32 94.5 9.0 8/32 14/32 0 6/32 0 24/32 B-10 100 47 4/32 6/32 0 2/32 4/32 4/32 Weight: Average 1517 lbs. Maximum Deviation (+) 2.50% (-) 2.44% * Percent of castings within the specified tolerances. † Percent of castings with the measured dimension identical to the blueprint. - Fig. 329—Classification: Construction Machinery and Equipment. A B Hvis KA vull Х. SECTION X-X Fig. 330—Classification: Construction Machinery and Equipment. Casting: Transmission Housing Pattern: Hardwood Mounted on Boards Casting %* %+ Maximum Most Frequent Specified Dimension Deviation Deviation Tolerances Inches (Inches) (Inches) (Inches) (+) (-) (+) (-) (+) (-) A—15-4/32 100 40 1/32 2/32 1/64 0 2/32 2/32 B(a)-7-16/32 72 20 4/32 1/32 2/32 1/64 2/32 2/32 C—42-6/33 28 20 0 6/32 0 3/32 2/32 2/32 D—16 100 36 2/32 2/32 0 1/32 2/32 2/32 E-1-8/32 76 0 4/32 4/32 2/32 0 2/32 2/32 F-18/32 68 36 4/32 0 2/32 0 2/32 2/32 Weight: Average 408.2 lbs. Maximum Deviation (+) 1.44% (-) 1.03% * Percent of castings within the specified tolerances. (a) Cored opening. † Percent of castings with the measured dimension identical to the blueprint. Casting: Steam Turbine Lever Pattern: Hardwood Mounted on Boards Casting %* %t Maximum Most Frequent Specified Dimension Deviation Deviation Tolerances Inches (Inches) (Inches) (Inches) (+) (-) (+) (-) (+) (-) A-28-4/32 100 0 8/32 0 6/32 0 9/64 7/64 F-3 100 60 2/32 2/32 0 0 3/32 2/32 J(b)—3-3/32 50 0 1/32 3/32 0 2/32 3/32 2/32 K-7-16/32 40 0 0 10/32 0 9/64 8/64 8/64 Weight: Average - 135.2 lbs. Maximum Deviation (+) 2.07% (-) 2.36% * Percent of castings within specified tolerances. (b) Dimension across parting. † Percent of castings with the measured dimension identical to the blueprint. Fig. 331–Classification: Electrical Machinery Equipment. TIE-BAR -N & FO # ! THE ED B G w SECTION X-X Fig. 332—Classification: Oil, Gas Field, Valves and Piping. Casting: Valve Body Pattern: Hardwood Mounted on Cope and Drag Boards Casting %* %† Maximum Most Frequent Specified Dimension Deviation Deviation Tolerances Inches (Inches) (Inches) (Inches) (+) (-) (+) (-) (+) (-) A (b)—9-16/32 66 0 5/32 3/32 1/32 1/32 2/32 2/32 B(b)—6-12/32 72 0 3/32 1/32 2/32 0 2/32 2/32 C(a)—3 100 0 1/32 1/32 1/32 1/32 2/32 2/32 D—14-20/32 30 0 0 5/32 0 3/32 2/32 2/32 H(a)—4-22/32 94 0 3/32 1/32 0 1/32 2/32 2/32 Weight: Average - 67 lbs. Maximum Deviation (+) 4.48% (-) 2.95% * Percent of castings within the specified tolerances. † Percent of castings with the measured dimension identical to the blueprint. (a) Cored opening. (b) Dimension across parting line. Casting: Coupling Box Pattern: Pine Matched on Cope and Drag Board Casting %* %+ Maximum Most Frequent Specified Dimension Deviation Deviation Tolerances Inches (Inches) (Inches) (Inches) (+) (-) (+) (+) (-) A (b)—22-16/32 100 20 4/32 0 2/32 0 9/64 7/64 B—18 100 0 4/32 2/32 2/32 2/32 9/64 7/64 C(a)—13-28/32 80 40 3/32 0 3/64 0 2/32 0 D(a)—5-8/32 40 40 4/32 0 2/32 0 0 2/32 E—14-16/32 100 40 2/32 2/32 1/32 1/64 4/32 5/64 Weight: Average - 905 lbs. Maximum Deviation (+) 0.56% (-) 0.44% * Percent of castings within the specified tolerances. † Percent of castings with the measured dimension identical to the blueprint. (a) Cored opening. (b) Dimension across parting line. - Fig. 333—Classification: Rolling Mill. B ADI с heubly 972 D 0 TE B E Fig. 334—Classification: Material Handling. Casting: Link Belt Pattern: Metal Matchplate Casting %* %+ Maximum Most Frequent Specified Dimension Deviation Deviation Tolerances Inches (Inches) (Inches) (Inches) (+) (-) (+) (-) (+) (-) A-3-7/32 93 0 0 3/32 0 2/32 0 2/32 B—3-10/32 100 1/32 1/32 1/64 1/64 2/32 0 C—14-8/32 100 27 1/32 0 1/32 0 7/64 5/64 D—8-8/32 100 2/32 1/32 1/32 0 3/32 3/64 H—3-30/32 100 73 1/32 1/32 0 0 1/32 1/32 Weight: Average 23.9 lbs. Maximum Deviation (+) 0.42% (-) 1.6% * Percent of castings within the specified tolerances. † Percent of castings with the measured dimension identical to the blueprint. 40 27 Casting: Spring Bracket for Truck Trailer Pattern: Aluminum Matchplate Casting %* %+ Maximum Most Frequent Specified Dimension Deviation Deviation Tolerances Inches (Inches) (Inches) (Inches) (+) (-) (+) (-) (+) (-) A—4-12/32 20.0 0.0 4/32 0 2/32 0 2/32 2/32 B-2-16/32 20.8 1.3 6/32 0 2/32 0 2/32 2/32 D Bottom- 5-28/32 100.0 0.0 4/32 0 3/32 0 4/32 4/32 E—3-4/32 100.0 1.3 0 2/32 0 2/32 4/32 4/32 F(a)—1-3/32 1.3 1.3 1/32 0 1/32 0 0 1/32 Weight: Average 9.0 lbs. * Percent of castings within the specified tolerances. (a) Cored opening. † Percent of castings with the measured dimension identical to the blueprint. Fig. 335—Classification: Motor Vehicle. E G 7 ВА D 230 TOLERANCES The 10 illustrations of tolerance variations of commercial steel castings were selected to show examples in the various major end use classifications. Also, the castings were selected on the basis of size, from small to large; and on the basis of design, from simple to complex. The maximum deviation value should be considered with the percent of the castings falling within the specified tolerances. On this basis it will be observed that in most cases values upward to 100 per- cent are recorded. This indicates that the tolerances are realistic for commercial castings. Also, it indicates that only one or two castings out of the number tested were outside the specified tolerance. Per- centage values of less than 50 indicate that either the tolerance is unrealistic or that additional processing is necessary to meet the specified tolerance. In some cases tolerances are set on dimensions that are not critical and the customer accepts castings outside the tolerance limits. This practice should be discouraged as it leads to a lack of concern with production procedures and manufacturing costs. SECTION II Process Methods Influence Tolerances Normal variations in foundry processes and practices must also be considered in establishing dimensional tolerances, in addition to the previously discussed factors of design. It would be well, however, be- fore considering the effect of process variables, to consider briefly the nature of variations in steel castings, and to make a distinction between variations from casting to casting within a lot as opposed to thé deviation of actual casting dimensions from specified blueprint dimensions. Figure 336 shows normal distribution curves of devia- tions which occurred on a particular casting dimension. Curves 1 and 2 are identical except that curve number 2 is shifted one unit to the right. In other words, the deviation ranges of both lots of castings for this particular dimension are the same, but the lot depicted by curve number 2 does not adhere to design dimensions. Curve 3 illustrates a wider distribution than that obtained by curves 1 and 2. While the variation from casting to casting within this lot was greater, the adherence to blueprint dimension was much better than the lot de- picted by curve number 2, but not as good as in the lot described by curve 1. Curve 3 indicates that the proper value of hindered con- traction has been applied to the pattern but that variables in the process are greater than in the case of curves 1 and 2. The distinction between adherence to blueprint dimension and variation from cast- ing to casting within a lot should be kept in mind. TOLERANCES 231 2 Kw FREQUENCY A : -4 -3 -2 -1 0 +1 +2 +3 +4 DEVIATION FROM BLUE PRINT DIMENSION Fig. 336—Hypothetical curves showing different distributions of dimensional variations which may be obtained on a particular casting dimension. > Pattern and Core Box Equipment ... Adherence to design dimensions is determined, to a marked degree, by the pattern; specifically, by whether or not the proper hindered contraction value (patternmakers' shrink rule) is applied, as well as proper compensation for warpage. (See Chapter V for a complete discussion of hindered contraction.) These are the major factors involved in the determination of the posi- tion of the mode of the distribution curve with respect to design dimen- sions. Another factor which must be considered is the situation of castings produced from the same pattern by different foundries. In this case the conditions which may be constant within one foundry may be constant but are very probably different in another foundry. For example, the resistance to contraction of cores at one foundry can be constant, but may vary from one foundry to the next. The same is true of the degree of compaction of molding sands which affects the ability of mold walls to resist deformation. The amount of hindered contraction to be applied to any par- ticular casting is only an experienced estimate. However, a pattern can be adjusted after a pilot casting is made so that close tolerances can be secured for castings made on production runs. As in any metal forming process, short runs afford limited opportunity for adequate pilot work. Only on long runs, repetitive jobs, is there time and money to make necessary adjustment and changes in tooling and rig- ging. Therefore, it is recommended that the foundry selected to make a particular casting should also make or control the construction of the pattern so that the long experience of the personnel in the foundry with hindered contraction and shrink rules will help to minimize pat- tern alterations and costs. .232 TOLERANCES The expected length of production run has a secondary effect on tolerance since the length of run usually determines the type of ma- terial from which a pattern will be made. The dimension variations from casting to casting within a lot will be greater with wooden pat- terns than with metal or plastic patterns, since wood is sensitive to changes in moisture. Below is a list of various types of pattern equip- ment in order of decreasing variations which may be expected from casting to casting within a lot, as well as decreasing deviation from the design dimension. 1-Loose wood pattern 2—Pine pattern mounted on cope and drag boards 3—Hardwood pattern mounted on cope and drag boards 4Plastic pattern mounted on cope and drag boards 5—Metal pattern mounted on cope and drag boards 6—Wood matchplate 7-Metal matchplate Specific examples of variations obtained with two of the above types of pattern equipment are given in Figures 337 and 339. A com- 30 DIMENSION 8:9/4" o: 0.0546". 20 FREQUENCY (PERCENT) 0 9%29% 9,9% 922 944 9%29%169% ACTUAZ ČAŠTING DIMENSION (INCHES) Fig. 337—Histogram and statistically determined distribution curve of actual casting dimensions held on dimension B of the bearing retainer of Figure 338. The pattern was pine mounted on cope and drag boards. B Fig. 338—Bearing retainer casting. Length 14 inches. 136 pounds. Dimension B - 944 inches. Weight . TOLERANCES 233 40 DIMENSION G : 8%8" o: 0.0296 30 FREQUENCY (PERCENT) 20 10 i 0 898% 88% 872 ACTUAL CASTING DIMENSION (INCHES) Fig. 339—Histogram and distribution curve of actual casting dimensions obtained on dimension G of the valve body of Figure 340. The casting was made from an aluminum pattern mounted on cope and drag boards. Fig. 340—Valve body. Dimension G - 878 inches. Weight 129 pounds. parison of the curves for approximately the same linear design dimen- sion reveals two significant facts: (1) the distribution of measure- ments for the pine pattern is much broader (o=0.0546 inch) than that obtained with the metal equipment (o=0.0296 inch); and (2) the mode of the distribution corresponds much more closely to design dimen- sion in the case of the metal pattern. The displacement of the mode from design dimension was 0.0406 inch for the wood pattern as opposed to 0.0232 inch for the metal pattern. The type of core box equipment plays an important role in de- termining the casting tolerances that may be expected on dimensions produced by cores. Core box materials behave in the same manner as pattern materials, and all of the above comments on patterns also apply for core boxes. In addition, it will be found that joined cores are less accurate than one piece cores, owing to variations in the joining process. 234 TOLERANCES Dimension Variations as Influenced by Production Techniques . A study of dimension variations resulting from differences in production techniques throughout the steel casting industry was undertaken by the steel casting industry. Eight identical aluminum patterns were constructed for a casting designed by the Technical and Oper- ating Committee of Steel Founders' Society. Subsequently, 115 cast- ings were produced from these patterns by 97 steel foundries through- out the United States and Canada. Figures 341 and 342 show the pattern and a typical casting produced from it. 8 Fig. 341–Aluminum pattern equipment used in the production of castings for the study of dimensional variations due to production techniques. Fig. 342—Typical casting produced from the pattern shown in Figure 341. TOLERANCES 235 Molds were made by several different processes including pneu- matic hand ramming equipment, sand slinger, jolt machine molding, and jolt-squeeze machine molding. One casting was made in a mold produced on a diaphragm molding unit. The various molding sands used included green sand, skin dried green sand, washed and skin dried green sand, dry sand, oil sand, and sodium silicate-CO2 sand. Cores were made from sands bonded in the following different ways: oil, phenolic resin, sodium silicate, cold-setting oil, and sugar base binders. Green sand cores were also used. The castings were given a normaliz- ing heat treatment. All castings made were produced under normal production pro- cedures in each foundry. It should be pointed out that it was impossible for any individual foundry to take special measures to assure accurate dimensions. This possibility was precluded by supplying only the pattern. No drawing showing desired casting dimensions was fur- nished, and even the knowledge of what dimensions were critical was withheld. Variations in both weight and surface smoothness were also checked in this survey. Dimensional Variations ... Figure 343 shows a drawing of the test casting indicating the dimensions which were studied. All measure- ments were made at one laboratory as a precaution for uniformity. Twenty-three positions were identified for measurement, as shown by the letter series in Figure 343. Variations were tabulated and histo- grams constructed for the determination of distribution curves by statistical methods. It is not advisable to show all the histograms in this Handbook. Four curves are shown in Figures 344 to 347 as ex- amples of dimensions covering casting length, width and thickness as well as cored opening and across the parting. Three of the curves are of normal deviation whereas one is skewed. Also, the deviations vary from small to large, depending on the dimension studied. A point of major interest revealed by the curves is that the range of deviations is wider, in most cases, than that found for comparable castings made by a single foundry, examples of which were presented in the preceding section of this chapter. The reason for this is the introduction of variables from foundry to foundry which will be more constant within a single foundry. For example, mold hardness, a constant within a foundry on a particular job, varies greatly from foundry to foundry. Other salient points brought out by the study are: (1) the dis- persion of the variations increases as the linear dimension increases ; (2) mold wall deformation during the pouring of the casting, as a result of mold properties, depends on the molding methods em- ployed; (3) hindered contraction, resulting from mold construction, 236 TOLERANCES М. on N₂ N E +88+ A ܐܬ 24 23: Nz Y 1 N1,2,3 T K, к k 02 SECTION X-X SECTION Y-Y Fig. 343–Drawing of the test casting shown in Figure 342 showing dimensions on which measurements were taken. DEVIATION (INCHES) -0,10 -0.05 0 +0.05 +0.10 -0.15 DEVIATION (INCHES) -0,10 -0.05 o +005 +0.10 +0.15 0.20 -0.15 50 50 DIMENSION 0?0.0312.A :6" DIMENSION C: 21" o: 0.73/" 40 FREQUENCY (PERCENT) FREQUENCY (PERCENT) 10 10 -4 -3 -2 -1 0 +1 +2 +3 DEVIATION 1/32 INCH -5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5 +6 DEVIATION 732 INCH Fig. 344–Histogram and dis- tribution curve for variations found in dimension A. Dis- tribution normal. Fig. 345—Histogram and distribution curve for variations found in dimen- sion C. Distribution normal. DEVIATION (INCHES) -0.10 -0.05 0 +0.05 +0.10 +0.15 DEVIATION (INCHES) -0.05 0 +0.05 +0.10 50 50 DIMENSION F: 5'6" DIMENSION L,:2" o: 0.0312 40 40 FREQUENCY (PERCENT) FREQUENCY (PERCENT) 0 -3 -2 -1 0 +1 +2 +3 +4 +5 DEVIATION 1/32 INCH Fig. 346—Histogram and distri- bution curve for variations found in dimension F. Distribution pos- itively skewed. 0 -2 -1 0 +1 +2 +3 DEVIATION 22 INCH Fig. 347—Histogram and distribution curve for variations found in dimension Li. Distribu- tion normal. TOLERANCES 237 produces a skewed distribution; and (4) the removal and grinding of risers and ingate areas result in wide tolerance variations because of the difficulty in determining the exact casting face during the metal removal operations. Items 2, 3 and 4 can be considered as variable constants since they would be constant for a run of castings in one foundry; but they can be considered variable when a particular cast- ing is made in a number of foundries, resulting from differences in molding sands, ramming techniques, molding equipment, pouring and cleaning methods. A wide range distribution, as well as a positively skewed dis- tribution, usually results when the producing foundry does not know the exact desired dimensions. The study reported above indicates that if reasonably close tolerances are required, a foundry cannot be simply given a pattern and asked to produce castings. A blueprint must also be furnished, showing dimensions and tolerances which are to be kept within control. Deviations from Average Casting Weight ... Figure 348 shows the distribution of weights obtained for the 115 castings produced by the 97 foundries, to the design of Figure 343. Average casting weight was found to be 41.7 pounds with the range of deviations from the average weight being normal. The standard deviation was found to be 1.09 pounds. This deviation is nearly as narrow as would be expected from a single foundry. 24 AVERAGE WEIGHT: 41.7LBŞ. O :1.09 LBS. 20 FREQUENCY (PERCENT) 4 0 38 39 40 41 42 43 CASTING WEIGHT (POUNDS) 44 45 Fig. 348—Histogram and distribution curve for casting weights. 94.88 percent of the distribution is within + 5% of the average casting weight. 238 TOLERANCES SECTION III Recommended Tolerances for Steel Castings Comparison of Molding Methods ... Table 11 gives a general com- parison of various molding methods used to produce average, light- weight steel castings, as well as the attributes of the castings expected from each production technique. Specific data on tolerances are listed throughout the remainder of this chapter. For accurate information on other items in Table 11, it is suggested that a contemplated design be submitted to a foundry engineer for comments. Table 11–General Comparison of Casting Methods Casting Requirements Sand CO2 Shell Ceramic Investment Surface Smoothness Fair Fair Good Very Good Excellent 1/4 3/16 5/32 3/32 1/16 +0.0312 +0.020 +0.008 +0.006 +0.005 Minimum Metal Section (Inches) Base Tolerances Inches per inch Added Tolerance Across Parting Intricacy Metal Limitations +0.0312 +0.020 Fair Good +0.010 +0.010 No Parting Very Good Extra Good Excellent Low Carbon None None Steel None None Most Most Least Least Finish Allowances Size Adaptability No Limit Slight Limit Average Small Castings Up to 250 lbs. Small Castings Up to 100 lbs. Small Castings Up to 50 lbs. Pattern Costs Low Low High Long Average Short High Longest Lead Time Shortest Shortest Steel Casting Tolerances (Sand Mold) Analysis of the data given for the 88 steel castings discussed in Section I of this chapter, covering the "Dimensional Variations in Production Castings" resulted in the values shown in Table 12, which are recommended as economically realistic tolerances for steel castings made in sand molds. Note that this table shows the normally expected range of deviations from design di- mensions. Variations encountered from casting to casting within a production run are highly dependent upon design. For this reason, con- sultation with the foundry engineer on acceptable tolerances is strongly recommended. As indicated by Table 12, the higher the quality of the pattern equipment employed, the narrower become the tolerance ranges. It also should be pointed out that these ranges probably can be reduced TOLERANCES 239 Table 12—Dimensional Tolerances for Steel Castingst Normally Expected Deviation of Linear Casting Dimensions from Design Dimensions (1/32 inch) for Steel Castings in Quantity Blueprint Dimension (Inches) 3.1 - 7.0 7.1 - 20.0 0 - 3.0 20.1 - 100.0 - +1 -1 +3 -2 +4 -2 +4 -4 Pattern Type Metal Matchplate Metal Pattern Mounted on Cope and Drag Boards Hardwood Pattern Mounted on Cope and Drag Boards +2 -2 +3 -3 +4 -3 +7 -4 +3 - 2 +4 -3 +4 -3 +8 -5 † Surfaces that are not to be machined considerably if alterations of pattern equipment are made after pilot castings have been checked as to tolerances obtained. This condition also applies to variations from casting to casting, as well as those deviations from design dimension which may be expected from cored passages. Table 13 gives data relative to deviation from blueprint dimensions for cored openings. Table 13—Normally Expected Deviation of Cored Opening Dimensions from Design Dimensions (1/32 inch) for Steel Castings in Quantity Blueprint Dimension (Inches) 0 - 2.0 2.1 - 10.0 +2 -1 - +4 -3 The tolerance limitations placed on a steel casting must include an allowance for dimensions across the mold parting: i. e., dimen- sions not completely defined by surfaces contained in one-half of a mold. Recommended values are given in Table 14, and are to be added to the normally expected deviation set forth in Table 12. Such allow- ances are necessary, regardless of the type of pattern equipment, since they are dependent upon the size and type of flask equipment employed. These additional variations may be expected from casting to casting within a lot, as well as in deviations from blueprint dimensions. Table 14—Mold Parting Allowance to be Added to Normally Expected Deviations from Blueprint Dimensions Design Dimension (Inches) Mold Parting Allowance (Inches) . 0 - 3.0 3.1 7.0 7.1 20.0 20.1 and up +1/64 +1/32 +3/64 +1/16 240 TOLERANCES . Weight Tolerances . . . Allowance must be made for variations in weight from casting to casting within a lot. Table 15 gives the recom- mended allowable deviations from average casting weight. It should be noted that these deviations do not give values for casting weight as calculated from a design drawing. In cases of complex design and irregular contours it is very difficult to calculate casting weight with accuracy and actual weight will often differ somewhat from such estimates. Table 15-Allowable Deviations from Average Casting Weight (Percent) Casting Weight Positive Deviation Negative Deviation Up to 100 lbs. 10 to 500 lbs. 500 to 10,000 lbs. 10,000 lbs. and up 5.0 4.0 3.0 2.5 5.0 3.0 2.5 2.0 † Deviations do not apply to weights as calculated from a design drawing. Machine Finish Allowances The dimensional allowance to be added to the casting section for machining purposes will depend entirely on the design of the casting. Certain faces of a casting may require larger allowances than others, as a result of their position in the mold, and the possible hindered contraction stresses that may be acting on the castings. For example, the cope side of a large casting may require 5/8-inch allowance whereas on the drag and side walls 3/8-inch may be ample. Sufficient excess metal should be allowed to satisfactorily accom- plish the necessary machining operations. One very good rule is to allow enough “finish" so that the first cut remains in its entirety below the cast surface of the metal by at least 1/32 of an inch. Definite values of machine finish allowances cannot be established for all casting designs, but certain guides can be suggested to design- ers. Such guides have been prepared and are given in Table 16 which lists machine finish allowances for gears, wheels and other circular shaped castings. Minimum Tolerances by Controlled Techniques ... Increased dimen- sional accuracy may be obtained in steel castings through the use of special production techniques. Certain critical dimensions can be held to tolerances of lesser deviation than those shown in Table 12 without resorting to the more expensive molding processes identified in Table 11. This is done in local areas of a casting by employment of special rigging or coring, pressing or grinding to gate templates. The extra TOLERANCES 241 Table 16—A Guide to Machine Finish Allowancest Circular Shapes Machine Allowance on the Outside Radius, Inches Rings, Spoked Wheels, Spoked Gears, Circular Shaped Castings Casting Diameter Inches Up to 18 18 to 36 36 to 48 48 to 72 72 to 108 108 and up 1/4 5/16 3/8 1/2 5/8 3/4 Bores Bore diameter Inches Machine allowance on bore radius - Inches - Up to 1 2 to 7 7 to 12 12 to 20 Cast solid 1/4 3/8 1/2 Flat Shapes Greatest dimension of the Casting Inches Machine Allowances Inches Up to 12 12 to 24 24 to 48 48 to 96 3/16 1/4 5/16 3/8 1/2 96 and up † These allowances apply to short orders, and may be reduced to some degree on production runs which permit adequate pilot work to be done. They also in- dicate that a flat surface is more easily produced than a true circle. Machine allowances for castings of very large size, such as greater than 15 feet, should be determined through consultation with the foundry that is to produce them. operating costs necessary to carry out these operations may be less than the pattern equipment and process costs of a casting technique permitting closer tolerances. The cost of pattern equipment and proc- essing is fairly high for castings made by the shell, ceramic, and in- vestment methods, and the economics of producing a particular design to exacting tolerances must be carefully considered to make certain that any greater casting costs will be offset by savings in machining, assembly, or other areas. 242 TOLER ANCES Very close tolerances can be held on small steel castings which can be produced by precision investment molding. Tolerances on such finished castings (blast-cleaned and buffed) will vary somewhat from part to part, depending on factors of metal, size, and configuration. A general rule of thumb, however, can be applied with reasonable accuracy, particularly in the smaller sizes. This general rule is ex- pressed in Table 17. Table 17—Investment Casting Tolerances (1) Finished Tolerance Dimension Tolerance (Inches) General Tolerance Dimension Tolerance (Inches) (Inches) Up to 1 Over 1 +0.005 inch +0.005 in/in Under 2 2 4 4 6 Over 6 +1/64 +1/32 +3/64 +1/16 - Tolerances of +0.003 inch for dimensions of 0.250 inch and under and +0.004 inch for dimensions from 0.251 to 0.500 inch can be held to meet special requirements. Such tolerances should not be specified unless necessary, since exceptionally close tolerances will ma- terially increase the production cost. Tolerances applied to nonfunc- tional areas should be as generous as possible to insure economical production of the casting. For an extended discussion of investment casting tolerances the reader is referred to “How to Buy and Design Investment Castings."(1) Other methods for producing close tolerance castings are ceramic molding and shell molding. Ceramic molding is quite similar to invest- ment molding with the exception that molds are made in halves em- ploying a reusable pattern such as is used in conventional sand molding instead of an expendable wax or frozen mercury pattern. The molding slurries are approximately the same. Ceramic molded casting toler- Table 18—Dimensional Tolerances for Shell Molded Steel Castings Dimension in Inches Tolerance(a) in Inches Less than 2 2 to 8 8 to 16 16 to 32 Across the parting, additive Draft Hole Diameter +0.005 +0.006 +0.010 +0.015 +0.005 0.0020 inches per in. +0.010 in./in. (a) Between unmachined surfaces TOLERANCES 243 ances approach those obtainable by the investment process, but addi- tional allowances must be made on dimensions across the parting line. Between ceramic molding and sand molding lies the realm of shell molding. Excellent tolerances may be held on shell molded cast- ings primarily because of the nature of shell pattern equipment, which is normally made from cast iron and completely machined. Tolerances held on five shell molded castings may be found in Table 18. Since all of the methods for the production of close tolerance steel castings are rather complex and highly dependent upon design, con- sultation with the foundry engineer of the producing foundry is strongly recommended concerning tolerances which can be held on a particular design. Comparison of Wrought and Cast Steel Tolerances ... Table 19 shows AISI tolerances for three wrought shapes which one might typically find as cast steel sections. Comparison of the table with Table 12 reveals the fact that steel castings having sections comparable to the wrought steel sections listed may be expected to have equally good dimensional accuracy. On a long production run which economically justifies alterations of pattern equipment, even closer tolerances may be expected. It should be pointed out that steel casting tolerances are not tabulated on a basis of design shape as are wrought steel values. This means that tolerances given in Table 12 also apply to dimensions of shapes much more complex than wrought structural shapes. Table 19—Typical Dimension Tolerances for Rolled Steel Products (2,3) Low-Alloy Steel Tolerance, inches Thickness +1/16 - 0.01 Hot Rolled Plate Width to 36 in. Thickness 2-3 in. Bar Size Channel Sizes to 142 in. Section Depth Flange Width +1/32 +1/32 Bar Size Tees Sizes 114 to 2 in. Width or depth +3/64 A study of tabulated values, published by the Drop Forging Association, “Standard Practices and Tolerances for Impression Die Forgings” shows casting tolerances to be much narrower than forging tolerances. For example, a 6-inch length or width dimension on a section of a forging formed within a single die requires a total toler- ance (shrinkage plus die wear) of + 1/8 inch on a 50-pound "Commer- cial Standard” forging. "Close standard” tolerances on the same forg- 244 TOLERANCES ing allow + 1/16 inch. The same dimension on a 100-pound "Com- mercial Standard" forging requires + 0.335 inch or nearly 11/32 inch! Tolerances for the same dimension on a commercial steel casting, as shown by Table 12, would be no greater than + 1/8, -3/32 inch regardless of casting weight and would be as low as + 3/32, -1/16 if a metal matchplate pattern were used. Similarly, steel casting tolerances for dimensions across a parting plane are much narrower than those required on forging dimensions across a die parting. Tolerances for thickness dimensions across a die parting are quoted in terms of the forging weight and are inde- pendent of section thickness. For a 100-pound "Commercial Standard” forging a thickness dimension, be it 1/2 inch or 3 inches, requires a tolerance of +0.174, -0.058 or approximately +11/64, -3/64. Com- parable tolerance values for a steel casting dimension would be+3/64, -1/32 for a casting made from a metal matchplate pattern. Excellent dimensional accuracy of sand molded steel castings may be maintained in production runs made from good pattern equip- ment. Still narrower tolerances may be held with special molding techniques, such as shell molding, and dimensional accuracy of pre- cision investment castings is excelled only by machined parts. REFERENCES 1-"How to Design and Buy Investment Castings”, edited by Robert H. Herrmann, Investment Casting Institute, Chicago, Illinois. 2—“Alloy Steel Plates”, AISI Steel Products Manual, September 1958. 3—“High Strength Low-Alloy Steel”, AISI Steel Products Manual, December 1958. > CHAPTER VII NORMAL VARIATIONS IN THE PROPERTIES OF CAST STEEL Certain conditions which exist relative to testing should be exam- ined before entering into any discussion concerning the mechanical properties of cast steel. The shape of the test coupon or the design of the casting are inherent qualities which have an effect on the me- chanical properties of cast steel. Other influences, such as mass effect, size characteristics, position of attached coupons, and location of test specimens machined from castings must be considered in order that the numerical values obtained from testing may be understood and full significance be given to the extent of their usefulness, as well as to their limitations. Experienced engineers realize that by the mechanical testing of materials it is possible to obtain numerical values indicative of the properties of the material under test but not necessarily conclusive as to the properties of the material in its commercial forms. The fact that mechanical test values represent the properties of the material rather than those of the composite structure as a whole is not peculiar to any other material or metal but is common to all. A typical example is the leather that is used to make part of a shoe. If it is tested in tension a definite numerical value is obtained; but no one would expect to obtain this same value if the entire shoe were test- ed in tension. The reason for this, of course, is that the composite structure contains certain parts of different characteristics, therefore of different tension values. In the case of a shoe, the individual char- acteristics are the different types of leather and the quality of the sewing A test bar from any metal provides a means of measuring strength and ductility properties of the metal under standard and comparable conditions. Any perceptible variation from the standard test bar will cause a corresponding variation. An 8-inch gage length does not give the same percent elongation as a 2-inch gage length. If a V-notch is cut around a tensile test bar, the bar will break without appreciable deformation. In neither case is the actual ductility of the metal or any other property affected. Only the figures are changed. Such a condi- tion exists in all ductile metals and in all of the commercial forms that metals may take. Thus, for example, any type of casting, as given to the foundry by the designer, may contain sharp changes in contour comparable to the V-shaped notch in the test specimen. Under destruc- tive testing of the casting, these design features would be responsible 246 NORMAL VARIATIONS for lower values than would be obtained if only a representative sample of the metal were tested. Separately cast test bars indicate only the quality of the metal from which the casting is made. They do not give the actual proper- ties of the steel casting; neither are they a quantitative measure of the quality of the casting, nor are they truly representative of the final casting. Sometimes a sample may give misleading information. For exam- ple, the tensile properties of wrought steel products are generally tested and reported for specimens taken from bars or plate in the direction of rolling. Working of steel in one direction, such as rolling, produces directionality and the properties of the steel are found to be different in different directions. The properties transverse to the direction of roll- ing are always less than the longitudinal properties, and the differ- ence can be significant. The mechanical properties of a metal as determined by the testing of a standard tensile test specimen thus refer to values that are char- acteristic of the metal and the limitations of specimen preparation. Be- fore consideration is given to the differences that may exist due to variations in metal characteristics, it is necessary that attention be given to the test specimen. Test specimens which are not carefully prepared will not reveal true property values. The specimen must conform to the prescribed dimensions within the established limits of tolerance. The final surfaces should be smooth and true, as the values obtained vary somewhat with the character of the finish. Also, when any test specimen shows dis- continuity of metal during its final stages of preparation, it should not be used for test purposes, since it must be remembered that the test is designed for the purpose of recording the true metal characteristics and not those of a metal specimen in which notches exist which normally are responsible for low values. a The measurable quality of any manufactured product varies by a certain amount owing to chance as well as to known causes. For exam- ple, the diameter of a machined shaft will show chance variations from piece to piece as well as a slight increase caused by tool wear. number of shaft pieces are inspected and a suitable allowance made for known causes of variations, then it is possible to prepare a histogram of frequency vs. quality which will show chance variations. If a A material is controlled when it is possible to predict within reason- able and practical limits how the material will vary in the future. Nat- urally, an element of chance enters into all forms of prediction and, in nature, constant systems of chance do exist. NORMAL VARIATIONS 247 Assignable causes of variations may be found, and by eliminating them, the manufacturer establishes reasonable limits in assuring a uni- form quality. Uniform quality may still have variations caused by chance or unknown causes such that the limits of acceptability may be very wide. An example of this is illustrated in Figure 349, where 1304 specimens were prepared and tested from clear, green Sitka spruce. 10g 80| 60 Number 20 3000 4000 5000 6000 7000 8000 9000 10000 Modulus of Rupture in Pounds per Square Inch Fig. 349—Variability in modulus of rupture of clear specimens of green Sitka spruce. The variability that existed in the modulus of rupture of the spruce specimens is shown by the distribution curve in Figure 349. The wide spread in the modulus values can be partially explained by examining the structure of the material (Figure 350) which consists of concen- tric rings of chance distribution. The photomicrograph of a carbon steel shown in Figure 351 further illustrates the statistical nature of materials as it can easily be seen that Fig. 350—Macrostructure of Sitka spruce (US Forest Products Laboratory). 248 NORM AL V A RIATIONS Fig. 351–Microstructure of carbon steel (1000X) (Vilella). the material is not isotropic. Such an arrangement is apparently pro- duced by chance and the effect of such heterogeneity upon a mechani- cal property, such as tensile strength of a test specimen machined from a coupon attached to a casting, is some function of a chance distribution. SECTION I Variations in Elements as Affected by Commercial Manufacturing Process In the manufacture of any material such as a particular grade of steel, it is not possible to duplicate, day after day, its identical chemical composition. There will be slight variations between the desired anal- ysis and the analysis reported for the produced material. These var- iations, though slight, are in some degree responsible for minor fluctu- ations in the mechanical values obtained. These variations are not peculiar to the manufacture of steel, but are common to all types of manufacturing. The steel casting industry is subject to the same variables as those of any other metal industry. NORMAL VARIATIONS 249 2 Thus, if emphasis is placed upon steel castings during this discussion, it is not because the manufacturer of steel castings requires any greater attention or is burdened with more variations, but merely because it is the subject under consideration. Variables of Chemical Analysis of Carbon Steel ... The extent to which variations in the chemical content normally occur in the commer- cial production of carbon and low-alloy steel castings is illustrated in Figures 352 through 355. These curves indicate that the frequency distribution of the chemical values is fairly normal. The peak of the distribution curve, or the mode, is more significant than the arithmetical ARITHMETICAL MEAN! 0.435%- MEDIAN 0.438 % MEDIAN 0.295 % IK ARITHMETICAL MEAN 0.298 % 35 CURVE NO. 2 20 CURVE NO 15 10 MODE 0.294 % Fig. 352—Distribution of percentage carbon in cast steels. Curve No. 1 - Grade B cast steel, 600 heats. Curve No. 2 . 0.45 carbon cast steel, 516 heats. MOOC 0.438 % 0.20 0.24 0.28 032 0.36 0.40 0.44 PERCENT CARBON 0.48 MEDIAN 0.428% KARITHMETICAL MEAN 0.430 % 45 40 35 MEDIAN 0.746 %- - ARITHMETICAL MEAN 0.747% FREQUENCY (PERCENT) N A CURVE NO. CURVE NO. 2-> : MODE 0.743% MODE a425% : 0.60 0.66 0.72 0.78 0.84 0.30 Q40 050 060 0.60 PERCENT MANGANESE PERCENT SILICON Fig. 353—Distribution of percentage manganese (Curve No. 1) and silicon (Curve No. 2) in carbon cast steel - manganese 1 percent max., 500 heats - ARITHMETICAL MEAN a onsi % ARITNMETICAL MEAN a 0256 % MEDIAN 0.0258% 25 MEDIAN DOIS % MEDIAN 0.0136 % ARITNMETICAL MEAN 0.0137 % MEDIAN ARITHMETICAL MEAN .0195% -0.0194% CURVE NGA CURVE NO. 2 IM CURVE NA CURVE NO. 2 MODE 0.0152 % MODE 0.0252% MODE 20134% MODE .0192% .004 .008 012 016 020 024 028 032.036 PERCENT SULFUR Fig. 354—Distribution of percentage sulfur in cast steel. Curve No. 1 . Basic alloy cast steel, 640 heats. Curve No. 2 - Basic Grade B cast steel, 600 heats. .004 .008.012 .016 .020 .024 .028 .032 PERCENT PHOSPHORUS Fig. 355 — Distribution of percentage phosphorus. Curve No. 1 - Alloy steel; 840 heats. Curve No. 2 - Grade B carbon steel, 600 heats. 250 NORMAL VARIATIONS mean values, as it indicates the value most frequently obtained, and normally expected in the manufacture of a material. The frequency distribution curves shown in Figure 352 are plotted from data on steel castings produced to a desired 0.30 and 0.45 percent carbon. The difference in the width of the base of the curves is an indication of the degree of control employed. The AAR-M-201 Speci- fication does not call for any specific range in the carbon content of the casting, hence the control is not as rigid as in the case of the castings produced to a definite carbon limitation such as the 0.45 percent car- bon cast steel. The width of the curve or spread is measured by the statistical yardstick called "Standard Deviation" and is an appraisal of the con- trol employed. It is observed that 99 percent of the 0.30 percent carbon heats fall within a carbon range of 0.14 percent carbon (+0.07) and the 0.45 carbon heats fall within a range of 0.10 percent carbon (+0.05). Two distribution curves for sulfur, and one for phosphorus, are given in Figures 354 and 355. The sulfur content for the steel of curve 1 was kept particularly low because of low temperature impact require- ments. Curve No. 2 represents data based on the sulfur content for Grade B carbon cast steels. The sulfur and phosphorus content of acid steels have frequency distributions similar to those shown in Figures 354 and 355, except that they are somewhat higher. The spread is generally in the range of 14 to 20 points and the values are dependent on the quality of the scrap. Variables in Chemical Analysis of Alloy Steels ... The most popular alloying additions to cast steels are the elements nickel, molybdenum, manganese, and chromium. Chemical limits for these elements are varied, and their assigned limits are based chiefly on the mechanical properties desired, as well as the service application of the castings. Typical examples of the frequency distribution of these alloys, in sey- eral common ranges used in the production of steel castings, are given in Figures 356 through 360. Cast steels containing nickel and molyb- 35 MEDIAN 2.258 % ARITHMETICAL MEAN 2.262 % MEDIAN 0.53% 35 ARITHMETICAL MEAN 0.548 % FREQUENCY (PERCENT) FREQUENCY (PERCENT) · MIN. SPECIFICATION 0.30 15 A 1 MODE 2.253 % MODE 0.502% 2.18 2.22 2.26 2.30 2.34 2.38 PERCENT NICKEL Fig. 356 — Distribution of percentage nickel in 2 percent nickel cast steel 200 heats. .31.37 43 49.55 0.67 0.79 0.91 PERCENT NICKEL Fig. 357—Distribution of percentage nickel in Ni-Cr-Mo cast alloy steel - 150 heats. NORMAL VARIATIONS 251 MEDIAN 0.349% MEDIAN 0.540% ARITHMETICAL MEAN 0.594 % 35 30 ARITHMETICAL MEAN 0.35 % CURVE NO. 2 CURVE NO. / w 10 MODE 0.346% MODE 0.505 96 0.30 0.34 0.38 0.42 0.46 0.50 0.54 0.58 0.62 PERCENT MOLYBDENUM Fig. 358—Distribution of percentage molybdenum in alloy cast steel. Curve No. 1 - specification limit 0.30 - 0.40 (Mn-Mo steel), 140 heats. Curve No. 2 - specification limit 0.45 - 0.60 (Ni-Cr-Mo), 250 heats. . denum have normal distribution curves (Figures 356, 357 and 358) and the spread is within specification limits. The elements which are not ox- idized from the bath during melting, such as nickel and molybdenum, are easily controlled, and the specification limits can be narrow if required. Alloys which are oxidized from the bath, such as manganese and chromium, are more difficult to control as is indicated by the frequency distribution curves (Figures 359 and 360). Manganese and chromium 25 ARITHMETICAL MEAN 1.665 % 25 MEDIAN 1.681 % ARITHMETICAL MEAN 0.548 % MEDIAN -0.568 % 20 20 15 LAA . MODE 1.686 % MODE 0.512% 1.30 1.40 7.50 1.60 1.70 1.80 1.90 PERCENT MANGANESE Fig. 359—Distribution of percentage manga. nese in alloy cast steel. Manganese specifi- cation 1.30 - 1.80, 345 heats. 0.30 0.38 0.46 0.54 0.62 0.70 0.78 0.86 PERCENT CHROMIUM Fig. 360—Distribution of percentage chromium in cast steels. Specification 0.35 · 0.80. percent, 250 heats. have skewed distribution curves and the ranges are wide. Specifications should permit wide limits; and it is further suggested that only a mini- mum value be specified when any alloy is needed, since the mechanical property requirements will dictate the alloy range most suited for design values. Variations Between Heat Analysis and Casting Analysis ... There are no appreciable differences between the heat (ladle) analysis and the actual analysis of the individual castings as may be seen by a review of Table 20. 252 NORMAL VARIATIONS Table 20—Chemical Analysis of Castings vs. Corresponding Heat Analysis С Mn P Ni Cr Mo S Si Percent 0.36 0.36 0.91 0.93 0.028 0.024 0.043 0.043 0.47 0.52 0.13 0.14 0.11 0.12 0.03 0.03 Heat Analysis Casting Analysis Heat Analysis Casting Analysis Heat Analysis Casting Analysis-1 Casting Analysis-2 0.34 0.34 0.89 0.89 0.025 0.029 0.040 0.042 0.46 0.46 0.10 0.08 0.06 0.05 0.03 0.02 0.26 0.27 0.28 0.76 0.78 0.79 0.015 0.018 0.018 0.027 0.027 0.027 0.43 0.40 0.40 An analysis of the data for 300 heats of Ni-Cr-Mo and Ni-Mo heats (Table 21) shows that there is no appreciable difference between the alloy content of the casting and the alloy content reported as the ladle analysis. Although the manganese can vary as much as 0.10 percent, the most probable deviation is 0.05 percent or less. Table 21—Variations in Ladle Analysis and Casting Analysis for 300 Heats Alloy Elements Max. Variation Specification Between Casting Limits in Analysis and Percent Heat Analysis Type of Steel Mn-Ni-Mo 1.05 - 1.25 0.25 . 0.45 0.10 - 0.18 + 0.10 + 0.03 + 0.03 Mn-Cr-Ni-Mo Manganese Nickel Molybdenum Manganese Chromium Nickel Molybdenum 0.90 1.20 0.70 . 1.20 0.80 - 1.20 0.40 - 0.60 + 0.10 + 0.05 + 0.03 + 0.03 Effect of Variations of the Elements on Cast Steel Properties ... The distribution curves for the various elements in cast steels indicate that the total deviation which may be expected in 95 percent frequency would be as follows: Carbon Manganese Silicon Nickel 0.10 percent 0.30 percent 0.20 percent 0.30 percent Chromium 0.30 percent Molybdenum 0.30 percent Phosphorus 0.02 percent Sulfur 0.02 percent The variation of 0.10 percent carbon has an effect on the strength, hardness and hardenability of the steel. The effects on properties for NORMAL VARIATIONS 253 the total 0.10 percent carbon (+0.05 percent) are as follows: Normalize Quench Tensile Strength, psi 12,000 (+6000) 12,000 (+6000) Yield Strength, psi 7,000 (+3500) 11,000 (+5500) Elongation in 2 in. % 4 (+2) 3 (+1.5) Reduction of Area % 8 (+4) 8 (+4) Brinell Hardness (BHN) 24 (+12) 32 (+16) Impact, Charpy V-Notch Ft. lbs. 10 (+5) 15† (+7) Hardenability (1/2 in. from Surface) Rc 7 7 † Tempered at 1200 degrees F Variations in manganese, silicon, nickel, chromium and molybde- num in the values listed above would not have any effect on the tensile and impact strength of either normalized cast steels or on quenched and tempered cast steels. The values are too small to affect the air harden- ing abilities to produce a perceptible change in the hardness of air hard- ening steels. The variations, however, do produce slight changes in hardenability. For example, a steel of 0.70 percent chromium would show a greater hardness at 1/2 inch from the surface than a 0.40 percent chromium steel, all other elements being constant. The difference would be small: only 2 points Rockwell C hardness. Phosphorus and sulfur in variations of 0.02 percent have no effect on tensile properties but they lower impact and ductility properties. The effect of variations in the sulfur content of a cast 0.23 carbon- manganese-molybdenum steel on the low temperature Charpy V-notch impact values is graphically illustrated in Figure 361.(2) The data 50 40 Fig. 361–Relation between sulfur content and Charpy V-notch values at -40 degrees F, phosphorus content - 0.020 percent. Bri- nell hardness 265-269. CHARPY V-NOTCH IMPACT FT. LBS. 30 20 10 0 0.010 0.020 0.030 0.040 0.050 0.060 SULFUR CONTENT, PERCENT published show improved mechanical properties with sulfur reduc- tion. Good tensile and impact values may be attainable in cast steel with high sulfur and phosphorus contents, but the reduction of both sulfur and phosphorus is conducive to improvement of these proper- ties. Figure 361 indicates that at a hardness level of 270 Brinell, a re- duction of 0.010 in the sulfur increases the impact values from 7 to 9 ft-lbs. 254 NORMAL VARIATIONS The nitrogen content of cast steels of normal expected property values varies from 0.004 to 0.015 weight percent. In these percentages nitrogen is of little significance in the properties, providing the residual aluminum content of the steel is not of a high value. Hydrogen has been established as a cause of loss in ductility in steel.(3) Such losses can be corrected and ductility regained by an aging treatment. The amount of hydrogen which must be present to give a specified loss of ductility depends on the structure, cleanliness and history of the steel. A hydrogen content below 0.5 ppm (parts per million) has little critical effect on tensile ductility. However, the ductility of a steel containing 1.0 to 1.5 ppm of hydrogen may be 85 to 80 percent of that of hydrogen-free steel. Practically no tensile specimens containing 3.5 to 4.5 ppm can be expected to show more than 15 to 30 percent of the normal ductility value. The effect of hydrogen on the percent elongation of cast steel is shown in Figure 362. 28 26 24 22 20 • POSITION (CENTER) I POSITION (SIDE) A POSITION (CORNER) 4"x4" BARS NORMALIZED DATA FROM 6-HEATS ELONGATION • PER CENT IN 2" 10 2 3 6 7 8 10 4 5 HYDROGEN IN PPM Fig. 362-Effect of hydrogen content of cast steel on percent elongation. Research studies have shown that an aging treatment, applied to steels of low ductility resulting from the presence of hydrogen, will increase ductility and reduce the hydrogen content. This phenomenon takes place at room temperature but is accelerated at elevated temper- atures. Temperatures upward of 700 degrees F have been used, but the temperature usually suggested is about 400 degrees F. One hour at this latter temperature is equivalent to 10 days at room temperature of 70 degrees F. The relation of aging time at 400 degrees F is pro- portional to section thickness (1 inch equals 20 hours). Equal im- provement in ductility is ultimately attained at both temperatures as may be seen in Figure 363. Therefore, steel castings need not be given an accelerated aging treatment since by the time the castings have been integrated into a machine or structure and placed in service, a suffi- ciently long period will have transpired to obviate any necessity for accelerated aging. NORMAL V A R I ATIONS 255 TIME · MOURS O 32 60 COUPONS AGED AT 400 F. RCO. OF ARCA CLONGATION o DUCTILITY.” o ° COUPONS AGCO AT ROOM TEMPERATURE END VALUE OBTAINED X IN ACCELERATED AGING 30 REDUCTION OF ARCA EXO VALUE OBTAINED I IN ACCELERATED AGING 20 ELONGATION 10 3 yo AS to sto CO SO $75 NORMALIZCO TIME • DAYS Fig. 363—Change in ductility with time for 1 in. coupons aged at room temperature and at 400 degrees F. Values plotted are average of three tests. Also, research studies (3) indicate that there is no appreciable decline of impact values with changing hydrogen content such as is experienced for ductility. Figure 364 is a plot of the hydrogen content of a steel and the corresponding room temperature Charpy V-notch impact and reduction of area values. These curves show no positive correlation with the hydrogen content of the steel after aging. 70-4 CARBON CAST STEEL 50 NORMALIZED BARS TEST SPECIMENS 60 6"X 6" X 12" LOCATION OF REDUCTION OF AREA IMPACT CENTER O SIDE CORNER A 50- 40 IMPACT PERCENT REDUCTION OF AREA %a8%,见​四 ​40 CHARPY V-NOTCH IMPACT VALUES IMPACT Fig. 364—Comparative changes in impact and duc- tility with variations in the hydrogen content. 30 REDUCTION OF AREA is .. 204 - -0- 0.4 .8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 HYDROGEN IN ppm It is considered by engineers that the notched bar impact test is a critically sensitive test and indicative of the ability of metal to withstand sudden shock. In view of the results of impact testing, a loss in ductility resulting from the presence of hydrogen is not as important a considera- tion of structural design as may have been previously considered, espe- cially since ductility is seldom taken into consideration in the design of engineering structures. 256 NORM AL V ARIATIONS SECTION II Variations in Mechanical Properties as Affected by Commercial Manufacturing Process Variations in Carbon Steel-Grade B... The variations in mechanical properties which normally occur in the production of commercial carbon steel castings are shown in Figures 365 through 367. The frequency distribution illustrated is based on 513 observations of 0.25 carbon steel produced to comply with the American Association of Railroads specifi- cation M-201 Grade B. This steel called for the following minimum acceptance limits : Tensile Strength 70,000 psi Yield Point 38,000 psi Elongation in 2 inches 24 percent Reduction of Area 36 percent 35 MEDIAN 46,000 psi ARITHMETICAL MEAN 46,100 psi MEDIAN ARITHMETICAL MEANTIK 79,900 psi 79,800 psi 20 АЛ a 15 A MODE 45,900 psi MODE 80,400psi 37 39 41 43 45 47 49 51 53 55 57 70 72 74 76 78 80 82 84 86 88 YIELD STRENGTH IN 1000 psi TENSILE STRENGTH IN 1000 psi Fig. 365—Distribution of tensile and yield strength values for 577 heats of Grade B. carbon cast steel. ARITHMETICAL MEAN 29.7 % MEDIAN 29.8 % 25 25 ARITHMETICAL MEAN 48.8 % - MEDIAN 49.4 % 20 20 1 1 MODE 30.3 % MODE 50.7% 48 22 24 26 28 30 32 34 36 PERCENTAGE ELONGATION IN 2 INCHES 64 36 40 44 52 56 60 PERCENTAGE REDUCTION OF AREA Fig. 366—Distribution of percentage elonga- tion values for 377 heats of Grade B carbon cast steel. Fig. 367—Distribution of percentage reduc- tion of area values for 577 heats of carbon cast steel. NORMAL VARIATIONS 257 The tensile strength and yield values are normally distributed but there is a slight skew in the distribution of the percent elongation. The distribution in the reduction of area is definitely skewed to the left. However, it is interesting to note that all of the mechanical values are above the specification minimum values set forth in the specification. A comparison of the distribution curve of the tensile strength of carbon cast steel (Figure 365) with the modulus of rupture curve of Sitka spruce (Figure 349) shows that the cast steel is a controlled product and not subject to the chance variations that exist in a natural product. The distribution curve of the spruce covers from 3,000 to 10,000 pounds per square inch, or a tolerance range of over three times the lowest value. The cast steel, however, shows a variation from 70,000 to 90,000 pounds per square inch, or only 1.3 times the lowest acceptable figure. This latter figure is very much in line with variations existing in other man- ufactured products. Variations in Alloy Cast Steels ... Figure 368 illustrates the frequency distribution of the tensile strength of 0.45 percent carbon cast steel to ASTM Specification A-148 Class 80-40. The data were obtained from separately cast coupons which were normalized from 1650 degrees F. Figures 369, 370 and 371 illustrate the frequency distribution for the yield point, percent elongation and percent reduction of area. Figures 372 through 375 illustrate the distribution of the tensile properties of alloy cast steels heat treated to a Brinell hardness range of 268 - 321. These data were obtained from three different alloy cast steels. The chemical requirements of the alloy steels are given in Tablo 22. ARITHMETICAL MEAN 56,300 psi MEDIAN -56,300 psi 25 ARITHMETICAL MEAN 94.4 psi MEDIAN 99.6 psi 25 20 A 不 ​MODE MODE 101.8 psi 57,400 psi. 82 llo 114 40 68 86 90 94 98 102 106 TENSILE STRENGTH IN 1000 psi 44 48 52 56 60 64 YIELD STRENGTH IN 1000 psi Fig. 368—Distribution of tensile strength values of 0.45 carbon steel - (meets ASTM A148 - Ch 80-40), 513 heats. Fig. 369—Distribution of yield strength values of normalized 0.45 carbon cast steel. 258 NORM AL VARIATIONS MEDIAN 22.8% ARITHMETICAL MEAN 22.8 % 30 ARITHMETICAL MEAN 52.4 % 25 MEDIAN 52.6% 25 15 1 MODE 22.7% MODE 55.9 % 25 31 37 43 49 55 61 PERCENT REDUCTION OF AREA 67 18 20 22 24 26 28 30 PERCENT ELONGATION Fig. 370—Distribution of percentage elonga- tion of normalized 0.45 carbon cast steel. Fig. 371-Distribution of the percentage re- duction of area of normalized 0.45 carbon cast steel. 25 MEDIAN. 140,800 psi ARITHMETICAL MEAN 140, 800 psi 20 25 MEDIAN 124,200 psi ARITHMETICAL MEAN 124, Yoo psi BRINELL RANGE 270-321 A A i A 10 MODE 138,500 psi MODE 122,800 psi 104 120 128 136 144 152 160 168 TENSILE STRENGTH IN 1000 psi Fig. 372–Distribution of tensile strength for alloy cast steel heat treated to a Brinell hardness range of 268-321 (120,000 psi min- imum). 96 112 120 128 136 144 152 YIELD STRENGTH IN 1000 psi Fig. 373—Distribution of yield strength for alloy cast steel with a tensile range of 120,000 to 160,000 psi. 25 MEDIAN 42.4 % ARITHMETICAL MEAN 42.4 % MEDIAN 16.7% ARITHMETICAL MEAN 16.8 % 20 FREQUENCY (PERCENT) 35 30 25 20 15 10 FREQUENCY (PERCENT) 人 ​MOPE 16.9% MODE 39.8 % 8 10 12 14 16 18 20 22 24 26 PERCENT ELONGATION Fig. 374—Distribution of percentage elonga- tion in alloy cast steel with a tensile strength range of 120,000 to 160,000 psi. 24 32 40 48 56 62 70 PERCENT REDUCTION IN AREA Fig. 375—Distribution of percentage reduc- tion of area for alloy cast steel with a tensile strength range of 120,000 to 160,000 psi. NORMAL VARIATIONS 259 Table 22—Chemical Specifications Alloy Steel Mn-Mo Cr-Mo Mn-Cr-Mo Percent Carbon Manganese Molybdenum Chromium No. of Heats 0.25 0.33 1.30 - 1.60 0.30 0.40 0.25 - 0.30 1.30 - 1.70 0.40 0.60 0.60 - 0.90 60 0.17 - 0.25 0.60 - 0.90 0.60 - 0.80 2.40 - 3.10 100 100 All three steels were water quenched and tempered to meet the required hardness. The distribution curves are similar to those pre- viously shown for lower strength steels. The data for the foregoing frequency distribution curves are based on values obtained from cast coupons. Perhaps the most important point which these curves illustrate is the fact that the specifications for steel castings have been carefully studied, well prepared and that the tolerance limits selected are justifi- able from both the producers' point of view and consumers' require- ments. Although many of the distribution curves lie above the minimum requirements, this does not mean the specification values are too low, as the lower values of the distribution curves approach the minimum specification values. Through improved melting and heat treating practices, the industry is able to produce medium carbon and alloy steel castings that will consistently meet the minimum test bar specification requirements. When the specification limits are too high, a large per- centage of the heats will be rejected; thus making it necessary to: (1) employ special manufacturing methods, (2) use different classes of steel, or (3) employ more extensive heat treatments, all of which would be reflected in an increased cost of the product. A tolerance range should be as small as necessary and practicable. However, if it is too small, rejections become excessive. Therefore, a balance must be maintained between the value of establishing a narrow tolerance range and the cost increase resulting from the exacting quality control required in holding a manufacturing process within rather narrow limits. The determination of an economic tolerance range requires con- siderable study, much statistical information and common sense; hence the preparation of a specification is an exacting undertaking in which buyers and producers should collaborate. Specification control can be obtained only when the normal expected value and the standard deviation are known. 260 NORM AL VARIATIONS The proper creation of a specification is much more time-consuming than is usually supposed. There may be some who believe that by averaging the results of a few tensile tests, it is possible to arrive at a proper specification. Others may believe that even this is not necessary, but that all one needs to do is to thumb through the pages of handbooks and select the average values of a carbon or alloy cast steel and adopt it as a specification limit. The charts herein presented indicate the fallacy of such ideas. Why, then, are the average, or the mode, property values of carbon and alloy steels set forth in periodicals and books of reference for the design engineer? It is because that is the only means by which the approximate characteristics of a steel may be illustrated. Normal expected properties (the mode of a distribution curve) act as reference points to help the designer and purchaser of steel cast- ings to select the proper steel for the required application. It gives an indication of how the steel reacts to various heat treatments and records the relation of one property to another property. Thus, there is a de- cided need for the normal expected properties shown in Chapters IX, X, XI and XII. The designer selects the desired properties on the basis of their normal expected values as fulfilling his requirements. He then considers the property values from a specification point of view so as to provide the proper acceptance limits well suited to the consumers' needs and in line with reasonable manufacturing latitude. The best manner in which this may be accomplished is to place the normal expected values into one of the nationally recognized specifications listed for steel cast- ings, such as the specifications of the American Society for Testing Materials which contain many grades or classes into which may be fitted almost all property requirements. The specifications of the ASTM are familiar to most designers and engineers with the result that they select the design values directly from the minimum specification properties without the necessity of resorting to an investigation of the normal expected properties. It may be added that the present tendency of all purchasers, producers, and engineering groups is to discard private specifications and replace them with specifications prepared by nationally known specification writing bodies. This movement has promoted better under- standing by all interested parties and better results have been obtained because the specifications are prepared as a cooperative effort by pur- chasers and manufacturers. It is true that in the testing of any material the normal expected values are somewhat higher than the specification minimum values and NORM AL VARIATIONS 261 it is quite natural for the purchaser or design engineer to look longingly at the normal expected values with the thought of using them in design calculations instead of the minimum values. However, he should not use this value, if safety factor values are not employed, since this value does not take into consideration the characteristic variations of steel manufacturing. The variations and limitations found in the manufacture of steel and their effect upon mechanical properties should not be of too much concern to the designing engineer in viewing his own problems in design which, in a way, may be looked upon as tolerance limitations of design. From the design viewpoint, factors of safety of 3 or 4 are commonly employed based upon the tensile strength, or 2 or 3 based upon the endurance limit, for steel structures under dynamic loading. These values are applied to the design of sections because of unknown stress concentrations and magnitudes. This latitude or tolerance range, used more or less arbitrarily by engineers, is much greater than the devia- tions that exist in the mechanical properties resulting from the varia- tions in the manufacture of steel. Standard deviation values, which are about one-third of the maximum deviations encountered, are so small, as compared to the variations in the factor of safety, that the difference between the normal expected values and the specification minimum limits is not of sufficient importance to make an issue of which set of figures should be used. The fact that designers are using normal expected values as the basis for design figures when factors of safety are used illustrates the fact that the deviation existing between the tolerance limits and the normally expected values is overshadowed by the application of safety factors. Distribution of Charpy Impact and Brinell Hardness ... The varia- tions in the impact resistance of cast steels are not entirely a matter of pure chance. Wide variations may be caused by dimensional inaccura- cies in the test specimen itself, e.g., the squareness of the specimen, the radius of the notch, the depth of the notch, and testing procedures. The physical dimensions of the test specimen can and must be controlled to the specific limits established. Comparative Charpy V-notch impact test data on identical steels are given in Table 23. Three steels representing three different hard- ness levels were tested. The dimensional accuracy of the specimens. was carefully checked. It can be observed that the variation from the average values in all cases except one was less than + 1 ft-lb. These results show that when identical impact specimens are tested, the varia- tions in the impact values can be small. Many steel castings are purchased to a minimum Charpy V-notch 262 NORMAL VARIATIONS Table 23—Comparative Charpy V-Notch Impact Tests Max. Deviation Average from Average BHN Impact - Ft-lb. -40°F 46.2 46.8 285 285 321 400 48.0 47.0 45.5 22.2 46.6 47.0 44.8 23.5 47.5 49.0 44.5 23.4 47.1 47.5 45.3 23.3 +0.9, -0.9 +1.5, -0.5 +0.9, -0.8 +0.7, -0.9 46.4 24.0 T impact value at a definite hardness level. Large variations exist in the impact values of different heats of the same alloy steel which have been heat treated to the same hardness level. In Figure 376, the range of the Charpy V-notch impact values at -40 degrees F for water quenched and tempered steel is shown at various hardness levels. The minimum value, & 90 80 TYPICAL ANALYSIS KEY C -0.30 T &HIGHEST VALUE Ni - 0.70 RANGE * Manganese ... Manganese in cast steel functions in three ways: it combines with sulfur in the liquid steel as non-harmful manganese sulfide, thus preventing the formation of harmful iron sulfides; it acts as a mild deoxidizer, contributing to soundness; and it has a moderate effect in increasing the strength of cast steel. All cast steels usually contain at least 0.50 percent manganese. An upper limit of 1.20 per- cent manganese is allowed by one specification (ASTM A27 Grade 70 - 40), while others have set various limits of 0.60 to 1.00 percent manganese. Specifications for cast steels for welding grades are largely responsible for the various maximum manganese restrictions, even though it is known that manganese is not as important as carbon content from the standpoint of weldability. High manganese contents can be used if carbon content is low. The carbon content and the manganese content are usually linked together in welding grade specifications by allowing for each 0.01 percent carbon drop below the carbon specifica- tion limit a 0.04 percent manganese increase above the manganese limit. Some specifications allow a manganese content of 1.25 to 1.40 percent on the basis of this carbon-manganese trade-off. The manganese content of castings is frequently not specified and in this case manufacturers usually prefer a manganese content of from 0.65 to 0.85 percent. In amounts over 1.00 percent, manganese is con- sidered as an alloying element in cast steel and as an alloying element, it increases the strength of cast steel. However, its effect in increasing strength in normalized carbon cast steels is comparatively small, CARBON 317 STEEL and then only at the higher amounts—upwards of 0.80 to 1.00 percent manganese. Additions of manganese above 1.00 percent assist in developing increased strength especially when the cast steels are water quenched. Silicon ... Silicon is a deoxidizer of molten steel and ordinarily is used for this purpose alone. It effectively stops the reaction between carbon and iron oxide, and gas evolution ceases. Silicon is commonly said to “kill” the steel and thereby contributes to the soundness of castings. The silicon content of steel castings is usually not specified by purchasers. Some specifications place a maximum of either 0.60 or 0.80 percent silicon, but in general, foundrymen should be permitted to vary the silicon content in accordance with the best interest of the product under manufacture. Silicon contents above 0.80 percent are considered as alloy additions and the resulting steels are not usually classed as carbon cast steels. The lower limit of silicon content has been established by foundry- men as 0.25 percent to provide that cast steel be killed properly. In amounts above those which are necessary for purposes of deoxidation, silicon is associated with iron and forms a solid solution of iron and silicon. In normal amounts silicon has little apparent effect upon the tensile properties of steel at room temperature; however, in quantities of from about 0.50 to 0.80 percent and above, it increases the harden- ability of cast steel since it strengthens the ferrite. Sulfur ... The specification for sulfur is usually about 0.060 percent maximum. Sulfur in cast steel has the tendency of segregating into the grain boundaries and it is for this reason that sulfur is tied up with manganese in the form of manganese sulfide so that brittleness may not occur. Phosphorus ... The phosphorus content in carbon cast steel is usually held by specification to a 0.050 percent maximum. Low phosphorus is generally recommended as a means of safeguarding against brittleness. Phosphorus combines with iron to form a solid solution of iron and phosphorus called steadite. Steadite tends to segregate into the grain boundaries and impairs the impact resistance of steels. This impair- ment is most in evidence at ambient and lower temperatures. Residual Elements ... Copper, nickel, chromium, tin, vanadium, tung- sten and molybdenum exist in carbon cast steel in small quantities. They are not added but exist in the scrap steel used as melting stock. Most carbon steel specifications do not specify limits on these elements. A few specifications covering welding grades of cast steel specify maximums of 0.25 to 0.50 percent for copper and 0.40 to 1.00 percent 318 STEEL CARBON for nickel. These maximums are specified to limit the effects of these elements on hardenability. Aluminum, titanium or calcium frequently are added to cast steel in very small quantities as deoxidizers. Their presence is beneficial in assuring soundness and providing improved mechanical properties, as a result of their effect on refining the grain size of cast steel. SECTION II Tensile Properties The mechanical properties recorded in this chapter are those ob- tained from coupons, either attached to the steel casting, or cast sepa- rately. Therefore, it must be understood that the properties are those resulting from representative testing and are subject to the same limita- tions of use and interpretation as in the case of similar data for other structural materials. The values listed in the tables and shown graphically on the charts are those normally expected in the production of low carbon steels. These values are obtained from distribution curves, similar to those illustrated in Chapter VII. Values for the various mechanical properties set forth in this and subsequent chapters are obtained from cast coupons after heat treat- ment. It is from such coupons that the test specimens are carefully prepared. The values reported consequently do not show the influence of the mass of the casting, the properties of the cast sections, or other variables. Information on these subjects may be obtained by referring to Chapter VII. The property values shown in the charts and graphs in this chapter are included as guides to these properties. They should not be applied as minimum values in specifications, but they do represent normally ex- pected values as found by the testing of machined specimens prepared from coupons. The properties presented in this section were obtained on cast carbon steels as normally manufactured for commercial use. Heat treatments given to the castings and coupons are those used commercially unless otherwise noted. Figures 410 and 411 show the variation of tensile properties with carbon content for cast carbon steels given various heat treat- ments. Tensile strength and yield strength increase with increasing carbon content while elongation and reduction of area values decrease. The standard heat treatment for most carbon steel castings is a normalizing or a normalizing-temper treatment. Heat treatment is CARBON 319 STEEL 3 TENSILE STRENGTH, 1000 psi. 150 140 130 27 120 110 100 90 80 70 1 - WATER QUENCHED AND TEMPERED · 1200 °F 60 2 - NORMALIZED Fig. 410—Tensile strength and 50 3- NORMALIZED AND reduction of area vs. carbon TEMPERED · 1200°F content for carbon cast steels. 4. ANNEALED 60 50 40 30 20 10 0 0.0 0.10 0.20 030 0.40 050 060 0.70 0.80 0.90 1.0 PERCENT CARBON beneficial in removing residual casting stresses and must be employed for all castings whose design is such that high stresses are introduced by hindered contraction or temperature differentials during solidifica- % REDUCT. OF AREA 3 2100 YIELD STRENGTH, 1000 psi. a. Fig. 411-Yield strength and elongation vs. carbon content for carbon cast steels. 90 80 3 70 60 50 40 30 1 • WATER QUENCHED AND 20 TEMPERED -1200 °F 2. NORMALIZED 3 · NORMALIZED AND 40 TEMPERED - 1200 °F 35 4. ANNEALED 30 25 20 15 10 5 0 0.0 0.10 0.20 0.30 0.40 0.50 060 0.70 0.80 0.90 1.0 PERCENT CARBON % ELONGATION 3 2 320 STEEL CARBON 280 260 1 240 220 - 2* .............. 200 *4 BRINELL HARDNESS NUMBER 180 - 160 140 1. WATER QUENCHED AND TEMPERED · 1200 °F 2 - NORMALIZED 3 - NORMALIZED AND TEMPERED - 1200°F 4- ANNEALED 120 11 11 1 1 100 00 00 0.20 0.30 0.40 0.50 060 0.70 0.80 090 LO PERCENT CARBON Fig. 412~Hardness vs. carbon content for carbon cast steels. tion and cooling to room temperature. Some standard, well-designed, low carbon steel castings are used in the as-cast condition. This practice is only followed where service criteria do not warrant the cost of heat treatment, and where no distortion can be tolerated or properly corrected subsequent to heat treatment. 240 220 - 200 / 180 Fig. 413—Hardness vs. carbon content for normalized carbon cast steel tempered at various temperatures for 2 hours. BRINELL HARDNESS NUMBER 160 140 1. 1050 °F 2 1200 °F 3 · 1300 °F 120 1 100 0.0 0.1 0.2 0.3 0.4 0.5 0.6 PERCENT CARBON 0.7 CARBON 321 STE E L Water quenching is employed as a heat treatment for carbon cast steels of carbon content less than 0.35 percent to improve their tough- ness (resistance to service stresses of shock loading). The curves shown for water quenched and tempered carbon steel probably represent mini- mum values for thin walled carbon steel castings since the tensile speci- mens were taken from the center of one-inch thick test coupons and carbon steel will not completely harden through a one-inch section. Figure 412 shows the variation of hardness with carbon content for cast carbon steels of various standard heat treatments. Hardness increases with increasing carbon content and is seen to vary consider- ably with heat treatment for the medium-to-high carbon steels. Figure 413 illustrates the effect of tempering temperature on hardness. The higher the tempering temperature, the lower the resulting hardness. Variation in the time of holding at a particular tempering temperature also affects the hardness but not to as great an extent as temperature variations. Hardness can conveniently be used as an indication of tensile properties. The data of Figures 410, 411 and 412 have been employed in 130 120 110 T. S., 1000 psi. 110 100 90 80 70 60 50 70 60 YIELD STR., 1000 psi. TENSILE STR., 1000 psi. 75 65 70 60 Y. S., 1000 psi. NORMALIZED - WATER QUENCHED AND TEMPERED - 1200°F 65 % RED. OF AREA 60 50 40 30 20 % RED. OF AREA 25 35 30 CAST AND NORMALIZED HOT - ROLLED 45 % ELONGATION 20 15 % ELONGATION 15 120 140 160 180 200 220 240 260 280 BRINELL HARDNESS NUMBER 0.0 0.1 0.2 0.3 0.4 0.5 0.6 PERCENT CARBON Fig. 415—Comparison of tensile properties of cast and hot-rolled carbon steels. Fig. 414—Tensile properties of carbon cast steel as a function of hardness. 322 STEEL CARBON plotting the graph shown in Figure 414. This graph shows the tensile properties that may be expected at the various commonly used hardness levels. Such values are very useful commercially because of the com- parative simplicity and economy of hardness testing over tensile testing. Figure 415 is a comparison of the tensile properties of cast and hot-rolled carbon steels. The cast carbon steel is seen to possess higher yield and tensile strength and slightly less ductility than the rolled steel. The curves for the hot-rolled steel are for tensile tests made in the rolling direction. Tensile tests made in the transverse direction are of somewhat lower value as was shown by data presented in Chapter I (see Figures 22 and 24). The cast steel, being isotropic, illustrates the same tensile properties in any direction and thus may be strained equally in any direction without premature failure. Carbon Steel Microstructures ... The tensile properties of cast carbon steels are closely related to microstructure. This relationship is so close that an experienced metallurgist can usually predict the mechanical properties of carbon steel just from observing its microstructure. For example, he would determine the carbon content by noting the relative amounts of ferrite and pearlite; the grain size will usually show whether it has been annealed or normalized, and the appearance of martensite will indicate whether or not it has been quenched. This knowledge, along with the data presented in this chapter, will enable a close approx- imation of the tensile properties to be made. Photomicrographs of a low-carbon steel are shown in Figure 416. Photomicrographs (a), (b), and (c) each contain approximately 23 percent pearlite (dark areas), and 77 percent ferrite (light areas). Photomicrograph (a) shows as-cast blocky and Widmanstatten ferrite in a pearlite matrix. > Photomicrograph (b) shows the effect of annealing on micro- structure. Annealing is seen to coalesce the ferrite. No evidence of a Widmanstatten structure is present because the cooling rate was not rapid enough to allow the ferrite to nucleate in preferential crystallo- graphic directions. The normalized structure is shown in photomicrograph (c). The cooling rate, which is more rapid than that of the as-cast and annealed specimens, results in smaller, more evenly dispersed particles of ferrite in a matrix of fine pearlite. Photomicrograph (d) illustrates an altogther different type of microstructure. The rapid quench transformed the austenite directly to martensite resulting in a structure entirely devoid of pearlite. CARBON 323 STEEL A с B D Fig. 416—Photomicrographs of a low carbon (0.18%) cast steel. (a) as cast (100%); (b) an- nealed (100%); (c) normalized (100X); (d) water quenched and tempered at 750 degrees F (500X). Figure 417 shows microstructures of a medium (0.28 percent) carbon cast steel. The structures are similar to those of the low-carbon steel, the only difference being that there is now 35 percent pearlite and 65 percent ferrite present in photomicrographs (a), (b), and (c). There is a general relation between the microstructure of carbon cast steel and the mechanical properties of the steel. Figure 418 shows the effect of miscrostructure on the mechanical properties of a 0.30 carbon cast steel. It will be observed that the maximum ductility is obtained with a random blocky ferrite plus pearlite; but the best com- bination of strength, ductility and toughness is obtained with a com- bination structure of Widmanstatten ferrite and blocky ferrite plus 324 STEEL CARBON А с B D Fig. 417—Photomicrographs of a medium carbon (0.28%) cast steel (a) as cast (100X); (b) annealed (100X); (c) normalized (100%); (d) water quenched and tempered at 750 degrees F (500X). pearlite. This subject is discussed in further detail in Chapter X; see page 348. Microstructures of a high (0.67 percent) carbon cast steel in the as-cast, and the annealed condition, are shown in Figure 419. These microstructures contain 85 percent pearlite and 15 percent ferrite. The as-cast structure for the high-carbon steel is seen to be different than for the lower carbon levels. The ferrite in high-carbon steels tends to form preferentially in the prior austenite grain boundaries, resulting in the structure shown. CARBON 325 STEEL 40 35 30 A Reduction of Area % a o 25 20 10 E do 25 AA la 20 A 15 ܘ̄ ܘ FI-Lb Charpy Elongation % Fig. 418—Efect of structure on the properties of a 0.30 percent carbon steel. (C 0.30, Mn 0.66, Si 0.37, P 0.048, S 0.036 percent) 15 10 110 100 90 3° per min. -8° per min. -2500° per min. Yield Strength ,1000 psi - 80 70 Key --Random blocky ferrite plus pearlite 0-Martensite 0 -Blocky and Widmanstätten ferrite plus pearlite 60 50 40 AA 80 1 1 90 100 TIO 120 Tensile Strength, 1000 psi 130 A B Fig. 419–Photomicrographs of a high carbon (0.67%) cast steel. (a) as cast (500X); (b) annealed (500X). 326 STEEL CARBON SECTION III Impact Properties The term “toughness” as related to steel has been used and ex- plained in a number of ways. It can be defined as the property determ- ining the amount of energy absorbed before fracture, and may be represented by the area under a stress-strain curve, therefore involving both ductility and strength. Formulae expressing toughness have been devised, based on tensile strength and ductility values. However, it is recognized that a test specimen containing a notch will give precise information regarding the nature of brittle fracture of a metal. There are a number of tests which employ a notch to measure toughness, including procedures apply- ing a bending or axial tensile load as slowly as in the standard tension test to those of high speed impacts as developed by explosive loading. Increasing the rate of load application, however, increases the temper- ature of transition from ductile to brittle fracture; therefore, the tem- perature at which the notch test is conducted is most important. A steel is tough or brittle depending on the temperature at which transition from a ductile to a brittle fracture occurs. Most authorities agree that the notched-bar impact properties of the steel are the best criteria. The notch enables the specimen to fracture exactly as it would under service conditions, i.e., by notch propagation of a crack. Impact properties of a steel vary, depending on strength, hardness, composition, steelmaking, deoxidation and heat treating variables, and the temperature of the test. Impact data for carbon steel at very low temperatures are not readily available. This is primarily because of the inherently poor im- pact resistance of wrought and cast carbon steels at low temperatures. In any case, applications requiring high impact resistance at low tem- peratures would specify the use of a low alloy steel rather than a carbon steel. Notched-bar impact values for low alloy steels can be found in Chapter X. Figure 420 shows the variation of impact properties of carbon cast steels with carbon content. Normalized carbon steels are seen to have lower impact resistance than quenched and tempered carbon steel of the same carbon content. This is because tempered martensite in the quenched and tempered carbon steel will absorb a greater impact than the ferrite and pearlite constituents of the normalized carbon steel. Annealed carbon steel has even lower impact resistance than the nor- malized carbon steel for the same carbon content. The curves shown in Figure 420 represent the normally expected impact values of a cast carbon steel given the heat treatment shown. Impact resistance is ex- CARBON 327 STEEL 80 NORMALIZED 70 QUENCHED AND TEMPERED 60 50 CHARPY IMPACT, FT. - 18. 40 Fig. 420--Room temperature Charpy V- notch values vs. carbon content for carbon cast steel in the normalized and quenched and tempered condition. Tempering temp- erature 1200 degrees F. 30 20 10 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 PERCENT CARBON tremely sensitive to inclusion distribution, microporosity, and sulfur, phosphorus and in some cases, nitrogen content, hence wide variation between similar steels is not entirely uncommon. This fact should be kept in mind when interpreting the data in this section. Figures 421 and 422 show the variation of impact resistance with testing temperature for a low carbon and medium carbon cast steel, respectively. This graph again illustrates the variation of impact properties with carbon content and heat treatment. The poor low temperature impact properties of carbon steel are clearly seen. Alloy additions move the transition curves to the left, hence increasing the impact properties at low temperatures. This explains why low alloy steels should be used for applications requiring high toughness at low temperature levels. 90 80 1 - NORMALIZED 2 - ANNEALED 3• AS CAST 1 70 60 50 1 CHARPY IMPACT, FT. - LB. Fig. 421-Charpy V-notch im pact values vs. testing temp erature for a 0.16% carbon cast steel (Jackson)'. 30 3 . 20 - 10 0 1 -60 -40 -20 0 +20 +40 +60 +80 +100 +120 TESTING TEMPERATURE, OF 328 STEEL CARBON 90 80 1. QUENCHED AND TEMPERED 2 - NORMALIZED 3 • ANNEALED 70 60 50 Fig. 422—Charpy V-notch impact values vs. testing temperature for a 0.30% carbon cast steel. CHARPY IMPACT, FT. -LB. 40 30 3 20 10 0 -60 -40 -20 0 +20 +40 +60 +80 +100 +120 TESTING TEMPERATURE, of Impact resistance of cast carbon steels is closely related to their hardness as well as carbon contents. Data for cast carbon steel are presented in Figure 423. Quenched and tempered carbon steel gives higher notched-bar impact values than normalized carbon steel at any given hardness level. This is attributable to the fact that a tempered martensite structure is tougher than a microstructure of pearlite and ferrite. 90 80 70 NORMALIZED QUENCHED AND TEMPERED 60 50 - Fig. 423—Room tempera: tore Charpy V-notch value vs. BHN for carbon cast steel. CHARPY IMPACT, FT. -LB 40 30 20 1 10 0 120 140 160 180 200 220 240 260 280 300 320 340 BRINELL HARDNESS NUMBER CARBON 329 STEEL EXPLOSIVE BULGE TEST METHOD Fig. 424—Bulge test method. Crack Propagation Test ... Another test used to determine impact resistance is the crack propagation test. It is generally recognized that the most severe stress conditions to be met in service are developed by sharp cleavage cracks. If a metal resists brittle fracture to the lowest service temperature in the presence of such cracks, it may be deemed to be immune to brittle fracture. The test method entails placing a brittle weld, of the type which is ordinarily used for hard surfacing, on the surface of a 14 x 14 x 34- inch test plate. The high energy required to deform such a thick plate is obtained by explosive loading. Figure 424 illustrates the general features of the method. The test plate is placed over a circular die cavity and the explosive is positioned at a preset distance above the plate by means of an expendable cardboard box. The intense gas pres- sure produced by the explosion serves the dual purpose of clamping the plate to the shoulders of the die and forcing the development of a bulge in the portion of the plate which is not supported by the die. Tests are conducted at any desired temperature by heating or refrigerating the plates in controlled temperature boxes prior to positioning on the die. The energy delivered by the explosion is adjusted to develop a deforma- tion of approximately a one-inch deep bulge if fracture does not result. 330 STEEL CARBON ROLLED MILD STEEL 160 (TEMP OF) CLASS "B" CAST STEEL Fig. 425—Crack starter tests of rolled and cast steels of equal Charpy V-notch toughness, illustrating similarity of fracture characteristics. Numbers refer to test temperature, degrees F. (Pellini, Brandt and Layne)'. Figure 425 illustrates the result of crack starter tests conducted over a series of temperatures. The upper series represents a commercial rolled structural steel of average quality, and the lower series represents a commercial Class B cast steel also of average quality. It is apparent from the nature and extent of cracking at the various temperatures that the performances of the two steels are similar. It may be observed from Figure 425 that the test plates remained essentially flat when tested at 20 degrees F. At higher temperatures definite bulging was developed prior to fracturing. This behavior is significant in that it indicates that at 20 degrees F the steels fracture in a brittle manner immediately upon the development of the sharp cleavage crack. At temperatures above 20 degrees F, the presence of the sharp flaw developed by the brittle weld was not sufficiently critical to prevent continued deformation prior to cracking. CARBON STEEL 331 80 CRACK STARTER TESTS TYPICAL CLASS "B" CAST STEEL 26%C 62%MN -45% SI 70 60 140°F 50 1000F 8097 ENERGY-FT. LBS. 60°F 30H CHARPY "V" 40°F 204 2007 0°F 10) 26 100 120 140 160 60 80 TEMPERATURE-"F Fig. 426—Correlation of fracture characteristics of carbon cast steel with Charpy V-notch transition data. (Pellini, Brandt and Layne). The relation of a typical Class B fracture series to the Charpy V-notch transition curve is illustrated in Figure 426. It is observed that brittle fracture is not developed at temperatures which are related to the upper shelf portion of the Charpy curve. Fractures which re- quire extensive deformation for initiation and propagate with difficulty, as observed from the limited extent of fracture, are developed at inter- mediate and high portions of the curve. Fractures which are highly brittle, as denoted by the complete break-up of the test plate and flatness of the broken pieces, are developed at temperatures related to the lower portion of the curve. The latter type represents the highly brittle fractures which are developed in the failure of common engineering structures. SECTION IV Fatigue Properties The service requirements of steel castings are usually very exact- ing. Steel castings are often parts operating in moving equipment. Also, many are highly stressed under conditions of elevated or low tem- peratures. These castings must withstand an indefinitely large number of cycles of stress application. 332 STEEL CARBON 3 ins " öker ök, 23 ساہ 16 481" 100- " DIA. 20NC TAPPED HOLE į DEEP -.015 RELIEF 220" 97" TAPER I "7.005" PER FT. RAD. BLEND $": RAD. 3 THE ola win سیاہ " .220"NOTCH DIA. 481" -001 DIA 20 NC TAPPĒD HOLE 골 ​DEEP .2907 .015 RELIEF TAPER NOTCH 60° ANGLE 0.015 R AT BASE X0.035 DEEP, 7.005" PER FT 3 9 RAD. 8 BLEND_RAD. Fig. 427–Fatigue test specimens for rotating beam fatigue testing. Design engineers are currently giving greater consideration to en- durance properties than ever before. Entire parts are being subjected to fatigue testing whenever possible. Stress analysis on structures as loaded in service presents information on stress concentration and in- dicates the importance and necessity of reducing or repositioning stress raisers. Thus it is that fatigue studies on specimens containing severe notches can be used in engineering design and are of interest to de- signers. Fundamentals of Fatigue Testing ... The results of fatigue testing are plotted on graphs as stress versus number of cycles. This plot is often referred to as an "S-N” curve, where "S" stands for the stress and "N" for the number of cycles at a stress “S” to cause failure. The data for constructing an S-N curve are obtained by preparing a number of specimens (see Figure 427) of a particular steel, testing in rotating beam or bending beam fixture machines under conditions of repeatedly applied cyclic stress of known intensity to each specimen until fracture occurs. The number of cycles of stress required to cause failure is recorded. Naturally, as the stress decreases, the number of cycles required to cause failure increases. Finally the stress is lowered to a value that does not cause failure regardless of the number of cycles of stress applied. This stress is referred to as the endurance limit of CARBON 333 STEEL the particular material. For steel, a life cycle of ten million (107) is considered reasonable assurance that the endurance limit has been reached. Figure 428 illustrates typical S-N curves for cast carbon steel in the normalized and tempered condition. 55 NORMALIZED AND TEMPERED 350 45 0.30% CARBON % STRESS, 1000 psi. 35 0.20% CARBON NO FAILURE 30 104 105 106 CYCLES TO FAILURE 10? Fig. 428—The S-N fatigue curves for carbon cast steel in the normalized and tempered condi- tion. (Evans, Ebert, and Briggs)'. The term endurance ratio should also be mentioned here. The endurance ratio is the ratio of endurance limit to the tensile strength of the steel. This ratio is usually about 0.45 for carbon steels in normal strength ranges. Variables Affecting Fatigue Properties ... The major variable affect- ing the fatigue properties of a given steel is its tensile strength. Factors such as chemical composition and heat treatment only affect fatigue properties through altering the tensile strength. External notches of one type or another are nearly always present in commercial steel parts because of design requirements, machining methods or surface conditions. The presence of a notch affects the fatigue properties of steel more than any other single factor. This applies to both cast and wrought steels regardless of heat treatment. Figures 429 and 430 clearly illustrate this fact. The notched fatigue curves for both cast and wrought materials exhibit the same general shape of curve as recorded for the smooth specimens, i.e., a continuously decreasing stress with increasing number of cycles to failure and with no sharp discontinuities evident. The data indicate very little scatter in either cast or wrought steels. The en- durance limit of the notched cast steel is about the same as that of the comparable wrought steel — in fact, the fatigue curves are nearly super- imposed upon one another. 334 CARBON STEEL 50 WROUGHT CAST 45 à 40 UNNOTCHED Fig. 429—S-N fatigue curves for full annealed cast and wrought 1040 steels. The tensile strengths are: wrought · 81,400 psi; cast - 83,500 psi. (Evans, Ebert, and Briggs). STRESS, 1000 psi. 35 30 NOTCHED 25 ANNEALED 0.40 % CARBON NO FAILURE 20 104 106 CYCLES TO FAILURE 105 107 55 WROUGHT CAST 50 445 STRESS, 1000 psi . 104 106 Fig. 430—S-N fatigue curves UNNOTCHED for normalized and tempered 40 1040 cast and wrought steels. The tensile strengths are: wrought · 90,000 psi; cast 35 94,200 psi. (Evans, Ebert, and NO FAILURE Briggs)'. NOTCHED 30 NORMALIZED AND TEMPERED -0.40% CARBON 25 105 107 CYCLES TO FAILURE The relative flatness of the band for the notched specimens in Figure 431 indicates less is gained by using higher strength steels when a notch is involved. For example, Figure 431 shows that in- dividual notched fatigue points in the band for steels of tensile strength of approximately 100,000 psi are similar to, or slightly lower than, the individual values shown for the steels in the range of 121,000 to 127,000 tensile strength. The smooth-bar fatigue values, on the other hand, are considerably higher. Therefore the increase in fatigue values (en- durance limit) by increasing tensile values is dependent on the notch severity and the stress concentration. CARBON STEEL 335 100 90 O WROUGHT STEELS • CAST STEELS 80 70 UNNOTCHED WROUGHTS 60 277 UNNOT 50 LIMITesloo0 PSI END.RATIO=.5 40 NOTCHED. CAST. WROUGHT. 30 ENDURANCE 20 10 O 60 70 80 90 100 110 120 130 140 150 160 170 180 TENSILE STRENGTHCS 1000 PSI Fig. 431—Variation of endurance limit with tensile strength for comparable cast and wrought steels. Data include both carbon and low alloy seel values. (Evans, Ebert, and Briggs)'. Severe stress raisers (notch effect) often introduce a difficulty that cannot be remedied by changing to a higher tensile strength steel. As several authorities point out, there is little, if anything, to be gained by raising the tensile strength above 125,000 to 150,000 as the increased endurance limit on smooth bars is neutralized by the increased notch sensitivity. In practical terms this means that if the design is based on fatigue, the high strength steels offer little or no advantage, and to obtain much benefit from high strength steels, stress concentration should be reduced by careful design. Steel components subjected to fatigue service seldom meet the pol- ished surface condition of the laboratory test specimens. The design engineer should consider the damaging effect of surface finish roughness on fatigue properties. This does not necessarily mean that a fine polished surface is always to be applied to all surfaces, as in many cases a relatively rougher surface finish may be adequate. When the endur- ance limits for polished and as-cast finishes are compared, it is found that an as-cast finish lowers the endurance limit about 30 percent. A comparable finish for a wrought steel, for example, a hot-rolled or as- forged finish, is known to decrease the endurance limit about 50 percent at a tensile strength level of about 110,000 psi.(3) Tests made on cast-to-shape specimens made both with and without slight centerline shrinkage showed that the endurance limit and en- durance ratio stay the same in spite of the presence of the slight center- line shrinkage. (4,5) The stress in any fiber of a specimen in bending 336 STEEL CARBON > fatigue is proportional to the distance from the neutral axis, therefore, discontinuities near the neutral axis are less likely to result in early fatigue failure than those discontinuities at or near the surface. SECTION V Hardenability Hardenability curves for cast carbon steel of various carbon con- tents are shown in Figures 432 and 433. The shaded portion of these curves represents the range within which the hardenability curve for a given carbon steel would fall. 70 HARDNESS, ROCKWELL C 8 8 8 8 8 8 8 30 20 142 2 DISTANCE FROM QUENCHED END, INCHES 242 Fig. 432—Hardenability curves for carbon cast steels. 70 60 40 HARDNESS, ROCKWELL C 30 1070 20 10 / 1% 2 DISTANCE FROM QUENCHED END, INCHES 2% Fig. 433—Hardenability curves for carbon cast steels. CARBON 337 STEEL 60 50 ANALYSIS: с : 0.21% Mn 0.75 % Si 0.40% 40 30 HARDNESS, ROCKWELL C 20 doza UNTEMPERED .900 F 1000 1100 1200 10 % 14 2 DISTANCE FROM QUENCHED END, INCHES 22 Fig. 434-Hardenability curves for a 1020 cast steel quenched and tempered at various temperatures as shown. 60 u 50 UNTEMPERED ANALYSIS : C 0.29% Mn 0.76% Si 0.48% 40 900°F 30 HARDNESS, ROCKWELL C 1000 1100 -1200 20 10 22 1% 2 DISTANCE FROM QUENCHED END, INCHES Fig. 435—Hardenability curves for a 1030 cast steel quenched and tempered at various temperatures as shown. 60 UNTEMPERED 50 ANALYSIS: C 0.42% Mn 0.71 % Si 0.45% 40 800°F 30-1000 HARDNESS, ROCKWELL C 20 1200 10 0 % 1² 2 DISTANCE FROM QUENCHED END, INCHES 242 Fig. 436—Hardenability curves for a 1040 cast steel quenched and tempered at various temperatures as shown. 338 STEEL CARBON 1 UNTEMPERED ANALYSIS: с 0.70% Mn 0.74 % Si 0.42% 40900°F HARDNESS, ROCKWELL C 8 8 8 8 8 8 1000 30 1100 201200 10 0 1 ½ 1² 2 DISTANCE FROM QUENCHED END, INCHES 24 Fig. 437—Hardenability curves for a 1070 cast steel quenched and tempered at various temperatures as shown. Carbon steels are not as hardenable as the low-alloy steels (see Chapter X) and for this reason, carbon steels would not be used in applications requiring high hardenability. Figures 434, 435, 436 and 437 show the effect of various tempering treatments upon the hardness of a 1020, 1030, 1040 and 1070 steel, respectively. These data can in turn be correlated with the curves of Section II to determine the tensile properties which may be expected at any distance from the quenched surface of a carbon steel casting. SECTION VI Applications of Various Cast Carbon Steels Low-Carbon Steel ... Some castings for the railroad industry are produced from low-carbon cast steel. Castings for the automotive in- dustry are produced from this class of steel, as are annealing boxes and hot metal ladles. Steel castings in this class are also produced for case carburizing, by which process the castings are given a hard, wear resistant exterior and a tough, ductile core. The magnetic properties of this class of steel, as illustrated in Chapter VIII, make it useful in the manufacture of electrical equipment. Free machining cast steels containing high sulfur contents (0.08 to 0.30 percent) are also produced in low-carbon grades. Medium Carbon Steel ... Over half of all steel castings manufactured are of the medium carbon grade and their field of application is ex- tensive and varied. Medium carbon steels find service in railroad and other transportation industries, in machinery and tools, equipment for rolling mills, mines, road building, quarries, and building construction plus a host of miscellaneous applications. In fact, they are to be found wherever rugged service and dependability must be obtained at reason- able cost. CARBON 339 STEEL High-Carbon Steel ... The high-carbon cast steels are principally used in the metal working industry for bending, blanking and forming dies. Rolls, machine tools and miscellaneous castings which require consider- able hardness, resistance to abrasion and high rigidity are also produced from the high carbon cast steels. REFERENCES 1. Jackson, W. J., "Some Features of the Metallurgical Properties of Steel Cast- ings", The British Foundryman, (April 1957) p. 217. 2. Pellini, W. S., Brandt, F. A., and Layne, E. E., “Performance of Cast and Rolled Steels in Relationship to the Problem of Brittle Francture", A. F. S. Transactions (1953) Vol. 61, pp. 243 - 262. > 3. Noll, G. C., and Lipon, C., "Allowable Working Stresses”, Proc. Soc. Exp. Stress Analysis, Vol. III, No. II, (1946), pp. 89 - 101. 4. Evans, E. B., Ebert, L. J., and Briggs, C. W., "Fatigue Properties of Comparable Cast and Wrought Steel”, ASTM Procedings, Vol. 56 (1956), pp. 979 - 1010. CHAPTER X ENGINEERING CAST STEELS-LOW ALLOY GRADES The low alloy cast steels are characterized in analysis by a carbon content primarily under 0.40 percent and by small proportions of alloy- ing elements. These steels are applied to meet requirements of higher strength than carbon steel with the very advantageous combination of excellent toughness. The low alloy cast steels are, as a class, more resistant to atmos- pheric corrosion than ordinary carbon cast steels and, with few exceptions, they are readily weldable. They are superior to the carbon steels in notch toughness and experience indicates that the low alloy steels are superior in fatigue and abrasion resistance. The various combinations of alloy confer on the low alloy steels a greater depth of hardenability in a section when compared to carbon steels of similar carbon content. The cost of alloy cast steels is somewhat above that of mild carbon cast steel but alloy cast steels pay off as engineering structural com- ponents of (1) longer life, (2) greater pay load, (3) lower operating costs, (4) greater safety and (5) less maintenance. It is very difficult to draw a hard and fast line separating the low alloy steel casting group from the carbon steel castings. One of the reasons for this difficulty is that as yet no adequate definition of alloy steel has been formulated. Perhaps the classifications should be extended to other aspects rather than that of chemical analysis alone. It is quite possible to differentiate on the basis of static loading or dynamic loading, or a combination of both. Resistance to hardenability or other special requirements may also provide grounds for differentia- tion. Negligible percentages of alloying elements present in the cast steel are the result of either residual accumulation or additions for the purpose of deoxidation. On the other hand, if an element such as alu- minum, boron, chromium, cobalt, copper, manganese, molybdenum, nickel, silicon, titanium, tungsten, or vanadium was intentionally added in an amount required to produce a desired improvement of properties, the resulting product would be clearly an alloy steel. Accordingly, any alloy present in low alloy steel castings would be in excess of those elements which are not removed by the melting process or are added primarily for deoxidation purposes. Cast steel LOW 341 ALLOY STE ELS containing more than the following alloy amount as a single constituent would be considered as a low alloy cast steel: Manganese Silicon Nickel Copper Chromium Molybdenum Vanadium Tungsten Aluminum Titanium Zirconium 1.00 percent 0.80 percent 0.50 percent 0.50 percent 0.25 percent 0.10 percent 0.05 percent 0.05 percent 0.10 percent 0.10 percent 0.10 percent 1 a Low alloy cast steels may have a total alloy content ranging upward to 8 percent. Cast steels with alloy content in excess of that figure are generally classed as high alloy. Chemistry is only a contributing factor in the development of the desired mechanical properties in a steel casting. The basic and essential consideration is to provide correct hardenability or depth of hardening for the specific section involved. The amount of carbon in a steel dictates the surface hardness of the steel, whereas the amount of alloy is re- sponsible for the depth to which hardness penetrates. Thus, plain carbon steels are shallow hardening and alloy additions increase the depth of hardening. However, such generalizations are not sufficient for modern- day engineering needs. Recordable hardenability values for various steels are required. Such values may be obtained by applying the “end- quench" or "Jominy” hardenability test or by sample calculations using factors for individual elements. The end-quench hardenability test has made it possible to predict the depth to which a particular steel can be hardened by applying a specific cooling rate. Fundamentally, it consists of extracting heat from a specimen of predetermined size in a prescribed manner, and sub- sequently measuring the hardness gradient developed. The reaction of each steel to the specified cooling rates produces specific structural conditions in the steel and, consequently, specific hardness values. The end-quench test is simple, easy to perform, and remarkably consistent and accurate in its results. The details of the test are specified by the American Society for Testing Materials. Various combinations of alloying elements can be used to attain the same hardenability, and hence the same mechanical properties, at a given depth in a steel casting. Heat treatment variations can, and 342 LOW ALLOY STEELS should, be used to develop a wider range of mechanical properties than variations in chemistry. The use of a quenching and tempering heat treatment will develop more fully the mechanical property potentials of a low alloy steel than will a normalizing or an annealing treatment. However, hardenability is related to the cooling rate and the higher hardenability steels will attain greater hardness in a particular section during air cooling, or will be more “air hardening” than would steels of low hardenability. SECTION I Consolidated Information Regarding Mechanical Properties Steel castings, whenever possible, are purchased to property re- quirements rather than to chemical analysis specifications. Most of the national specifications specify the tensile properties, and in some cases, hardness, impact values and hardenability bands, thereby permitting the foundry engineer to select the alloy compositions to meet the speci- fied mechanical properties. This policy is as it should be because engineers design on the basis of mechanical properties rather than on a translation of chemical composition to mechanical property values. Only in the case of steel castings for high temperature service is chemical analysis, rather than mechanical properties, paramount. The reason for this is that composi- tions for these grades must be employed which are known to prevent graphitization of steel at high temperature and have good creep re- sistance for long service life. Therefore, it is planned to present in the first part of this chapter the property values which may be expected for low alloy cast steels in general. The second part of this chapter will contain hardenability and fatigue data for a few of the most popular types of low alloy cast steel compositions. The mechanical properties presented in this chapter are those obtained from coupons, either attached to the steel casting, or cast separately. It therefore must be understood that the properties are those resulting from representative testing and are subject to the same limita- tions of use and interpretation as in the case of similar data for other materials. Mechanical properties are obtained from carefully prepared test specimens machined from uniform cast coupons after final heat treat- ment. While these values are consequently not influenced by the mass of the casting during solidification and other similar variables, the coupons during heat treatment are either placed on the casting or with a load of LOW 343 ALLOY STEELS 140 120 NORMALIZED AND TEMPERED 100 80 500 60 460 420 40 380 REDUCTION OF AREA, % ELONGATION, % VIELD STRENGTH, 1000 PSI 30 20 HO BRINELL HARDNESS NUMBER 10 300 60 260 50 220 180 30 20 140 100 60 80 10 60 80 100 120 140 160 TENSILE STRENGTH ,1000 PSI 100 120 140 160 180 200 220 240 TENSILE STRENGTH, 1000 PSI Fig. 438-Hardness vs. tensile strength for Fig. 439—Tensile properties of low alloy low alloy cast steels regardless of heat cast steels in the normalized and tempered treatment. condition. castings. They, therefore, not only represent the quality of the steel but also the quality of the heat treatment to which the castings are subjected. With this understanding as to the manner in which the mechanical properties were obtained, it is emphasized that the values shown in the charts and tables are included as guides to these properties. They should not be applied as minimum values in specifications, but they do represent normally expected values as found by the testing of specimens prepared from coupons. The properties presented in this chapter were obtained on low alloy câst steels as normally manufactured for commercial use. Heat treatments given to the coupons are those used commercially. Hardness ... It is obviously important to the engineer to be able to pre- dict the engineering properties of cast steels; but cast steels vary in composition and frequently they are used in various states of heat treatment. However, the tensile strength of cast steel when plotted against its hardness results in a straight line function. The linear rela- tion of tensile strength and Brinell hardness number is well known. Indeed, many engineers estimate tensile strength by multiplying the Brinell hardness number by 500. Modifications of this relation because of composition have been noted and recorded. These modifications have resulted in the establishment of a band or range of values, such as indicated in Figure 438. The band given in the graph represents the 344 ALLOY STE ELS LOW 220 200 QUENCHED AND TEMPERED Ö 180 160 /40 YIELD STRENGTH, 1000 PSI 120 100 80 60 ELONGATION, % de 40 30 20 10 Fig. 440—Tensile properties of low alloy cast steels in the quenched and tempered con- dition. 60 50 REDUCTION OF AREA,% 30 20 10 o 80 100 120 140 160 180 200 220 240 260 TENSILE STRENGTH, 1000 PSI normally expected range that is to be found in commercial cast steels when the Brinell hardness number is plotted as a function of tensile strength, regardless of the type of heat treatment employed. Tensile Properties ... Figure 439 illustrates the normally expected tensile properties for low alloy cast steels in the normalized and tem- pered condition. Yield strength is seen to increase as a straight-line function of tensile strength, while the elongation and reduction of area decrease with increasing tensile strength. The tensile properties of low alloy cast steels in the quenched and tempered condition are shown in Figure 440. Much higher tensile strengths are obtainable. Although the graph only shows data for tensile strengths up to 260,000 psi, specially processed cast steels of higher strengths are being produced for individual applications. Impact Properties . . . Steel castings purchased on the basis of tensile properties are frequently used under shock and embrittling conditions. LOW ALLOY 345 STE ELS 100 90 QUENCHED AND TEMPERED 80 10 60 50 + 70 °F CHARPY V-NOTCH IMPACT, FT-LB 40 -40°F 30 20 0 80 100 120 140 160 180 200 220 240 260 TENSILE STRENGTH, 1000 PSI Fig. 441-Charpy V-notch impact vs. tensile strength for low alloy cast steels in the quenched and tempered condition tested at 70 and -40 degrees F. In such cases the notched bar impact test more nearly describes the service condition than does the tensile test. It is, therefore, importanti to know generally the relation which exists between impact values and the commonly determined tensile strength. Relations of this nature are to be found in the literature indicating that the notched bar impact value is inversely proportional to strength and directly proportional to ductility. The relation is complicated in that the type of heat treatment and the resulting microstructure have considerable bearing on the re- sults. Additionally the tensile test is conducted under essentially uniaxial stress up to the moment reduction in cross section occurs, while the notched bar impact test is made under conditions of multiaxial stress. Therefore, any relation between impact values and tensile properties is empiric. Figures 441 and 442 illustrate the variation of Charpy V-notch im- pact value with tensile strength for cast low alloy steels in the quenched and tempered, and normalized and tempered conditions, respectively, It is realized that the bands are fairly wide although this can be expected as the results were from many different sources, each having a some- what different melting, deoxidation and processing procedure. It should also be pointed out that the impact bands will vary depending on the steel composition at the same hardness levels. 346 STEELS LOW ALLOY 80 70 NORMALIZED AND TEMPERED 60 50 50 QUENCHED AND TEMPERED TESTED AT - 40'F 40 30 CHARPY V-NOTCH IMPACT, FT-LB 30 +70F CHARPY V NOTCH IMPACT, FT-LB 20 10 1 200 220 240 260 280 300 320 340 360 BRINELL HARDNESS NUMBER 10 -40% o 60 80 100 120 140 160 180 TENSILE STRENGTH ,1000 PSI fig. 442-Charpy V-notch impact vs. tensile strength for low alloy cast steels in the normalized and tempered condition tested at 70 and 40 degrees F. Fig. 443—Normally expected variation of Charpy V-notch impact values with hardness for cast low alloy steels in the quenched and tempered condition tested at 40 de grees F. Quenched and tempered specimens are seen to possess better im- pact properties than normalized and tempered specimens at all strength levels. In addition, cast steel in the quenched and tempered condition exhibits good impact resistance at much lower temperatures than will cast steel in the normalized and tempered condition. Empirical data have been obtained for the impact values of cast low alloy steels as a function of hardness. The normally expected re- lationship is illustrated in Figure 443. These results compare favorably with those shown in Figure 441 when the tensile strength properties are converted to Brinell hardness. Fatigue Properties ... The endurance limit of cast steel is primarily a function of the tensile strength of the steel. This relationship is shown in Figure 444 for low alloy cast steels, using both notched and unnotched fatigue specimens. The relative flatness of the band for the notched specimens indicates little is gained by using higher strength steels when a notch is involved. Wrought low alloy steels in the notched condition offer no improvement over the cast low alloy steels in the notched condi- tion as may be seen by referring to Figure 431, Page 335. Microstructure... Many purchasers of steel castings are confused by the great variety of microstructures they observe in cast steels. Their experience with wrought steel structures indicates to them that certain of the cast steel structures they observe are not conducive to the secur- ing of maximum mechanical properties. In view of this situation, the Steel Founders' Society conducted extensive research to study the effect of microstructure on the mechanical properties of cast steels. LOW 317 ALLOY STE ELS 100 80 UNNOTCHED 60 ENDURANCE LIMIT, 1000 PSI 40 -NOTCHED 20 60 80 100 120 140 160 180 200 TENSILE STRENGTH , 1000 PSI Fig. 444—Endurance limit vs. tensile strength for low alloy cast steels in the notched and unnotched conditions regardless of heat treatment. The experimental results of the study demonstrated that while microstructure did have an important effect, other variables also in- fluence the mechanical properties of cast steel; among these are design) section size and steelmaking practices. Many heats of cast steel were studied intensively and wrought steels were likewise studied for comparison purposes. All test bars were given identical austenitizing treatments and cooled at various rates to develop different structures. The various cooling rates were obtained by employing water and oil quenching, cooling in moving and still air, cooling samples 'coated with asbestos fibers, and by furnace cooling. The cooling methods provided a range of cooling rates from less than 1 degree F per minute to more than 1000 degrees F per minute. Tension tests showed that tensile strength increased regularly with cooling rate. The tensile test data are presented graphically in Section II of this chapter for the various cast steels studied. Figure 445 represents an idealized set of curves for low alloy steels, typical of the curves shown in Section II. This curve shows the changes in other mechanical properties as related to tensile strength to give a rational basis for comparison. The highest strengths were obtained by water-quenching and the structure is tempered martensite. Oil-quenching gave structures con- sisting of Widmanstatten ferrite plus fine pearlite and tempered mar- 348 STEELS LOW ALLOY . Dendritic Random Widmanstätten ferrite,, Widmanstätten, Widmanstätten blocky blocky blocky ferrite, ferrite ferrite ferrite territe & a la pearlitela pearlite Spearlite pearlite Martensite FI-Lb Charpy Elongation % Reduction of Area % Yield Strength Tensile Strength fig. 445—Idealized diagram showing the effect of microstructure on mechanical properties of cast steel. Cooling rate increases from left to right. tensite. This structure results in a lower tensile strength but a higher ductility. With progressively less violent quenching and various types of air cooling, the Widmanstatten structures became progressively coarser and the martensite disappeared. As a result, the tensile strength decreases but the ductility levels off. The characteristic structures as obtained and noted in the key of Figure 445 are shown in Figure 446. Some interesting general conclusions were drawn from the re- search studies. There is available a wide range of cooling rates and a correspondingly wide range of tensile strengths in which satisfactory ductility can be obtained. Furthermore, better ductility can be obtained frequently with the higher strength Widmanstatten structure than with any other structure except tempered martensite. In other words, Widmanstatten ferrite structures give good all-round ductility and the appearance of Widmanstatten ferrite in a microstructure of cast steel should not cause apprehension. (a) Widmanstätten ferrite plus blocky fer- rite and pearlite. (b) Widmanstätten ferrite plus blocky fer- rite and pearlite. (c) Widmanstätten ferrite and pearlite. (d) Random blocky ferrite and pearlite. (e) Dendritic blocky ferrite and pearlite. (f) Martensite. Fig. 446—Typical microstructures obtained in low alloy cast steel (0.30 percent carbon). 350 ST E ELS LOW ALLOY The research also indicated that large differences in microstructure affect the mechanical properties of cast steel much as they do wrought steels. It is interesting to note in this connection that steels consisting of dendritic blocky ferrite, considered by some purchasers of steel castings to be an undesirable structure, produced acceptable ductility and notched bar impact properties. A dead soft anneal will produce a microstructure of dendritic blocky ferrite plus pearlite, causing the properties to fall on the low points of the curve. A faster cooling rate, as obtained by normalizing would produce the random blocky ferrite plus pearlite and develop ductility- strength ratios along the peak of the curve. It is true, however, that successively better ratios of ductility to strength are obtained when the microstructures are the result of increasing speeds of cooling. SECTION II Property Data for Various Types of Cast Steels Somewhere between 75 and 100 combinations of various alloys are being produced as low alloy cast steels by the steel casting industry, either regularly or occasionally. The reason for this large number is that the industry can manufacture special tailor-made steels in small quantities upon request of the casting buyer. However, an individual foundry will seldom be called upon to make more than 10 or 15 different steels, and of this number, only 3 or 4 normally will be produced daily. The industry regularly manufactures 15 to 20 different steels, corresponding for the most part to the AISI or SAE standard composi- tions. Buyers are familiar with these grades through wrought steel association and, in those cases where composition is specified, the more prominent compositions such as used in the wrought steel industry are favored. It is the plan in this section to discuss those cast steels which are regularly produced by the steel casting industry and are known gen- erally by users of steel products. This group of cast steels includes the following classes: Cast Steel Type Cast Steel Type 1300 8000 8400 80B00 2300 3100 4600 (Mn) (Mn-Mo) (Mn-Mo) (Mn-Mo-B) (Ni) (Ni-Cr) (Ni-Mo) 8600 (Ni-Cr-Mo) 4300 (Ni-Cr-Mo) 4000 (Mo) 5100 (Cr) 4100 (Cr-Mo) 9500 (Mn-Ni-Cr-Mo). Copper-Manganese-Silicon LOW 351 ALLOY STE ELS Cast steels do not follow exactly the composition ranges specified by the AISI for wrought steels, which in some cases cover slightly wider or different alloy ranges. In all cases the silicon content is be- tween 0.30 and 0.65 percent and the manganese content, when not specified as an alloy, will usually fall in the range of 0.50 to 1.00 percent. Most engineers and buyers are familiar with the SAE or AISI number- ing classification; therefore that numbering system is used in the follow- ing section; but the reader is requested to note that compositions may vary to some extent from the standard classification. The steels are discussed in groupings according to composition, rather than numerical sequence. Impact Properties ... Information on low temperature impact proper- ties for the various low alloy cast steels is given in Chapter XII. Such data include transition curves with +70 degrees F temperature values as a part of the curves. Therefore, the reader is directed to Chapter XII for information on impact values of low alloy cast steels at normal temperatures. Manganese Cast Steels (1300 Series) Manganese, when added to cast steel in an amount in excess of that required for deoxidation or for the conversion of the sulfur to man- ganese sulfide, is considered as an alloying element. For practical purposes a dividing line has been set at 1 percent manganese; that is, under 1 percent the steel is classified as a plain carbon steel, and over 1 percent it is classified as an alloy cast steel. Cast steel containing 1.25 to 1.75 percent manganese and 0.20 to 0.50 percent carbon has received considerable attention by engineers in the past because of the excellent properties that can be developed with but a single relatively inexpensive alloy and by a single normalizing or a normalizing and tempering heat treatment. The steels of this type are seldom used in the annealed condition because the property values obtained do not justify the cost of the alloying element. However they show excellent properties in the normal- ized condition. The normalizing treatment may or may not be followed by tempering. The effect of a high tempering treatment is to increase the ductility and impact values with a decrease in the yield point and tensile strength. The mechanical properties, both with and without the tempering treatment, are satisfactory and the choice of the treatment is dependent upon the use to which the casting is to be put. Medium manganese steels should be air cooled after tempering in order to secure the best results. Titanium or vanadium is sometimes added to medium manganese cast steel to refine the grain and to make 352 STE ELS LOW ALLO Y 65 60 - 55 Reduction of Area % 50 1 45 A A ΔΔ 40 35 30 Elongation% 25 20 45 40 Fi-Lo Charpy 35 AA Δ * 1 30 25 120 ITO E Yield Strength, 1000 psi - 370° per min.- -2° per min. 100 -2200° per min.- 90 - Кеу .-Dendritic blocky ferrite plus pearlite --Random blocky ferrite plus pearlite *-Widmanstätten ferrite plus fine pearlite 0-Martensite 80 70 90 100 TIO 120 130 140 150 Tensile Strength, 1000 psi Fig. 447—Effect of microstructure on the mechanical properties of a 1330 alloy cast steel (C 0.30, Mn 1.61, Si 0.44 percent). the steel less sensitive to critical cooling rates, thereby permitting more consistent ductility and impact resistance. The property values are not too uniform after a quenching and tempering heat treatment and the steel at times is subject to brittleness. The effect of microstructure on the mechanical properties of a 1300 cast steel is illustrated in Figure 447. These steels, after most heat treatments, have a structure showing a pronounced tendency for the ferrite to form preferentially at the austenite grain boundaries. No pure Widmanstatten ferrite was formed. The curves are of the same shape as for other alloy cast steels, except that the drop in ductility seems to come before the dendritic pattern is well developed. LOW ALLOY 353 STE ELS The end-quench hardenability of 1330 manganese cast steel is illustrated in Figure 448. The band indicates the values that can normally be expected in the testing of commercial cast steels. The wide spread in the hardenability band can be traced to variations in the 60 1330 CAST STEEL 40 HARDNESS, ROCKWELL C 1330 20 0 2/2 / / 1% 2 DISTANCE FROM QUENCHED END, INCHES Fig. 448—End-quenched hardenability of 1330 cast steel. 80 75 1330 CAST STEEL QUENCHED AND TEMPERED T.S. -122,000 PSI 65 70 60 1330 CAST STEEL NORMALIZED WD TEMPERED T.S.: 1 - 99,000 PSI 8- 97,000 PSI 65 UNNOTCHED 55 60 50 STRESS, 1000 PSI UNNOTCHED STRESS, 1000 PSI 45 40 45 NOTCHED 35 NOTCHED 40 11 30 35 NO FAILURE → 25 30 104 107 104 NO FAILURE → 105 106 CYCLES TO FAILURE 105 106 10? CYCLES TO FAILURE Fig. 449—S-N curves for cast manganese (1330) steel in the quenched and tempered condition. Tensile strength-122,000 psi. Fig. 450—S-N curves for cast manganese (1330) steel in the normalized and tempered condition. Tensile strength: A-99,000 psi; B-97,000 psi. 354 STEELS LOW ALLOY manganese and residual elements such as chromium, molybdenum, nickel, etc., not intentionally added. Fatigue data for 1330 cast steel in the quenched and tempered and normalized and tempered conditions are shown in Figures 449 and 450 respectively, tested both with and without a notch. Standard ASTM rotating beam fatigue specimens were used in all cases. Manganese-Molybdenum Cast Steels (8000, 8400 Series) Manganese-molybdenum cast steels are very popular low alloy steels of the mild air hardening type. Steels of these grades are very similar to the medium manganese steels with the added characteristic of a high yield point value at elevated temperatures, higher yield ratio at room temperature, greater freedom from temper brittleness and greater hardenability. For these reasons these steels in many cases have sup- planted medium manganese steel for certain applications. There are two general grades of manganese-molybdenum cast steels: 8000 series—Mn 1.00 to 1.35 percent, Mo 0.10 to 0.30 percent 8400 series—Mn 1.35 to 1.75 percent, Mo 0.25 to 0.55 percent The carbon content of each of these series is normally from 0.18 to 0.50 percent. 8000 Series ... The main difference between the 8000 and 8400 series is that the hardenability is greater in the 8400 series and the tensile 60 8030 CAST STEEL 40 HARDNESS , ROCKWELLC 20 8030 0 ½ 1² 2 2/2 DISTANCE FROM QUENCHED END, INCHES Fig. 451-End-quench hardenability of manganese-molybdenum (8030) cast steel. RONG LOW 357 ALLOY STEELS 60 55 50 45 40 * 30 F1-LB Charpy Elongation % Reduction of Area, % 25 20 15 * 30 25 20 * Fig. 452—Effect of struc- ture on mechanical prop- erties of a manganese- molybdenum (8030) cast steel (C 0.30, Mn 1.26, Mo 0.14, Şi 0.42 percent). 110 4000° per min. 100 - - 2° per min. 13° per min. 800° per min. 90 - 80 Yield Strength, 1000psi Key .-Dendritic blocky ferrite plus pearlite A-Random blocky ferrite plus pearlite *-Widmanstätten ferrite plus fine pearlite 0-Martensite -Martensite plus Widmanstätten ferrite D -Blocky and Widmanstätten ferrite plus pearlite 1 70 60 - 50 - 80 90 140 100 110 120 130 Tensile Strength, 1000 psi 60 8440 40 8430 HARDNESS, ROCKWELLC 84200 20 0 을 ​1² 2 2% DISTANCE FROM QUENCHED END - INCHES Fig. 453—End-quench hardenability of manganese-molybdenum (8400) series cast steels. 354 STEELS LOW ALLOY 355 d strengths are slightly higher for all types of heat treatments. :l of the 8000 series is most frequently used in the normalized pered condition. end-quench hardenability band obtained for 8030 commercial cast steel is illustrated in Figure 451. The effect of the microstructure on the mechanical properties of an 8030 cast steel cooled to room temperature at various rates and then tempered at 1000 degrees F is presented in Figure 452. 8400 Series ... The 8400 series is used in applications requiring slightly greater hardenability than is obtainable from the leaner 8000 cast steels. This greater hardenability is primarily the result of the higher molybde- num content of the 8400 steels. End-quench hardenability bands for 8420, 8430 and 8440 cast steels are given in Figure 453. Manganese-Molybdenum-Boron Cast Steels (80B00 Series) The use of boron to increase the hardenability of cast steels has become increasingly important in recent years. A shortage of the alloy- ing elements generally used to increase the hardenability of a steel has been created by their great demand and limited resources, both domestic and foreign. The most important of these strategic alloying elements are molybdenum, chromium, nickel, manganese and vanadium. Boron is another element which improves hardenability appreciably. It is very effective when added in minute amounts and can be used to re- place several hundred times its own weight of the scarce alloys. The domestic resources of this material are adequate. For these reasons, a considerable amount of research has recently been done to determine the characteristics of boron steels. These investi- gations have shown, among other things, that the effect of boron de- creases with increasing carbon content and is practically negligible in steels containing more than 0.8 percent carbon. Also, boron is ineffec- tive in normalized steels unless the carbon content is less than 0.20 per- cent. The improvement in hardenability produced by a boron treatment decreases with austenitizing temperatures above 1600 degrees F and virtually disappears at 2000 degrees F. Boron additions to liquid cast steel should be in amounts of 0.002 to 0.004 percent to attain optimum hardenability and mechanical proper- ties, and may be permitted to range upward to 0.006 percent without appreciably affecting ductility and impact values. However, boron content in excess of 0.006 percent can have an adverse effect on these properties. LOW 357 ALLOY STE ELS 60 80850 CAST STEEL 40 HARDNESS, ROCKWELLC 80B30 20 0 / 1/2 2/2 DISTANCE FROM QUENCHED END, INCHES Fig. 454—End-quench hardenability manganese-molybdenum-boron (80B30) cast steel. Boron treatment is frequently employed in the production of man- ganese-molybdenum type steels for the express purpose of increasing their hardenability. The end-quench hardenability band for 80B30 cast steel is given in Figure 454. A comparison with the previously given hardenability band for 8030 cast steel shows the increased hardenability attributable to the boron addition. The welding characteristics of boron treated cast steels can be similar to those steels without boron depending on the base alloy. Nickel Cast Steels (2300 Series) Among the oldest of alloy cast steels are those containing nickel. These steels are characterized by high tensile strength and elastic limit, good ductility and excellent resistance to impact. The nickel content in the plain nickel cast steels of the 2300 series is from 2.0 to 4.0 percent, depending on the grade required. Nickel enters principally into solid solution in iron (ferrite) and, when present in moderate amounts (0.5 to 5.0) in hypoeutectoid steels, tends to produce a fine-grained ferrite structure and to refine the struc- ture of the pearlitic areas, imparting strength, toughness and to a lesser degree hardness, without decreasing ductility proportionally. Excellent dynamic properties, i.e., resistance to impact and fatigue stresses at atmospheric and low temperatures, are obtained with these steels. Nickel retards the transformation of austenite to martensite or pearlite, thus causing a lowering of the Ar critical ranges. As a result of the retarded transformation period, nickel alloy steels are better adapted for heat treated castings of large sections than are the plain carbon .358 STEELS LOW ALLOY 60 2330 AND 2320 CAST STEEL 40 HARDNESS , ROCKWELL C 2330 20 2320 % 112 2 2/2 DISTANCE FROM QUENCHED END, INCHES Fig. 455-End-quench hardenability of nickel (2320 and 2330) cast steel. steels, because of ferrite strengthening and the differences in the critical cooling rates of the two steels. This explains why certain nickel alloy steels are particularly well adapted to large sections which cool relatively slowly and in which high strength, toughness and ductility are required. Also, as certain of these steels respond to cooling in air, the problem of obtaining excellent mechanical properties in complicated castings is simplified, for many castings cannot be quenched in oil or water without disastrous results through cracking or distortion. The end-quench hardenability bands for 2320 and 2330 cast steels are given in Figure 455. A major use of the nickel steels with low carbon content is very low temperature service applications (-75 to -150 degrees F). Of all the low alloy cast steels, only the 2300 series is not brittle at these temperatures. Information on this point is given in Chapter XII. Nickel-Chromium Cast Steels (3100 Series) The addition of chromium improves hardenability and imparts strength and hardness to a nickel steel along with ductility and tough- ness when proper heat treatment is employed. Chromium unites with carbon and the resulting carbide possesses high strength and hardness, thus contributing materially to improvement of mechanical properties. In the low carbon steels, the chromium acts as a ferrite strengthener. In addition to high strength, nickel-chromium cast steels have good elastic, fatigue and abrasive wear properties. LOW 359 ALLOY STEELS 60 3130 CAST STEEL HARDNESS, ROCKWELL C 3130 20F o 72 1² 2 2/2 DISTANCE FROM QUENCHED END, INCHES Fig. 456—End-quench hardenability of nickel-chromium (3130) cast steel. . The usual composition range of 3100 series steels is 1.10 to 1.50 percent nickel and 0.50 to 0.85 percent chromium. Nickel-chromium cast steels have been used in cast steel valves for various high temper- ature applications, including oil refineries. The chromium acts to pre- vent graphitization of carbon at high temperatures, but not as well as a combination of chromium and molybdenum. In addition to better room temperature properties, the Ni-Cr cast steels have higher resistance to 60 40 31409 HARDNESS, ROCKWELL C 20 0 ½ / 12 2 2% DISTANCE FROM QUENCHED END-INCHES Fig. 457—End-quench hardenability band for nickel-chromium (3140) cast steel. 360 ALLOY STEELS LOW creep than plain carbon cast steels at temperatures of 850 degrees F or higher. The end-quench hardenability bands for 3130 and 3140 cast steels are given in Figures 456 and 457. Endurance limits of 43,000 to 45,000 psi for normalized and tempered 3140 cast steel and 50,000 psi for these steels in the quenched and tempered condition have been re- ported by the industry. Nickel-Molybdenum Cast Steels (4600 Series) Molybdenum is added to nickel steels to improve their mechanical properties at normal and at elevated temperatures. The hardenability of nickel steels is greatly augmented by small quantities of molybdenum, so that excellent properties are developed by normalizing and tempering. Thus, they are adaptable to the production of large or intricate castings where a liquid quench is not feasible. Their ability to retain high strength at elevated temperatures extends their field of usefulness to high temperature applications. i The normal composition range of 4600 cast steels is 1.50 to 2.00 percent nickel and 0.20 to 0.40 percent molybdenum. End-quench hardenability bands for 4620 and 4640 cast steel are presented in Figure 458. i 60 4640 AND 4620 CAST STEEL 40 4640 HARDNESS, ROEKWELL E 20 4620 į o % 1/2 2 2½ DISTANCE FROM QUENCHED END, INCHES Fig: 458-End-quench hardenability of nickel-molybdenum (4620 and 4640) cast steel. > LOW ALLOY 361 STEELS a Nickel-Chromium-Molybdenum Cast Steels (8600, 4300 Series) The addition of molybdenum to nickel-chromium steel significantly improves hardenability, thereby developing excellent air hardening characteristics, and makes the steel relatively immune to temper-brittle- ness. The mechanical properties of the 4300 series cast steels in the normalized and tempered condition are often equivalent to those obtained by liquid quenching of some of the other cast steels. This fact is of particular significance where the shape or design of a casting is such as to prevent the use of a liquid quench. Nickel-chromium-molybdenum cast steel is particularly well adapted to the production of large castings because of its depth hardening properties. Also, the ability of steels of this type to retain high strength at elevated temperatures extends their field of usefulness to many industrial applications. The quenched and tempered strength properties of these steels are very high, and for this reason they are in great demand in applications where the need for exceptional strength is necessary. 8600 Series ... The 8600 series composition range was adopted by in- dustry during World War II and proved its worth so conclusively that it has become an important composition since that time. A number of steel foundries employ this steel for most of the low alloy steel requirements. The composition range is as follows: Nickel 0.45 to 0.80 percent Chromium 0.45 to 0.80 percent Molybdenum 0.15 to 0.30 percent The end-quench hardenability bands for 8620, 8630 and 8640 cast steel are given in Figure 459. Since boron additions are often made 60 8646 40 8630 HARDNESS, ROCKWELL C 778620 20 0 ½ / 1² 2 2% DISTANCE FROM QUENCHED END -INCHES Fig. 459—End-quench hardenability of nickel-chromium-molybdenum (8600) series cast steel. 362 STEELS LOW ALLOY 60 86B30 CAST STEEL 8630 CAST STEEL 40 86B30 HARDNESS , ROCKWELL C 8659 20 0 / / 12 2 272 DISTANCE FROM QUENCHED END, INCHES Fig. 460—End-quench hardenability of nickel-chromium-molybdenum-boron (86B30) cast steel as compared to 8630 cast steel. 90 85 8630 CAST STEEL QUENCHED AND TEMPERED T.S.- 137,500 PSI 80 75 75 70 8630 CAST STEEL NORMALIZED AND TEMPERED T.S.-110,500 PSI UNNOTCHED 70 65 65 60 UNNOTCHED 1000 PSI 55 STRESS, 1000 PSI 55 50 STRESS - 50 NOTCHED NOTCHED 45 40 1 35 1 40 NO FAILURE → 35 30 NO FAILURE- 11 105 104 107 104 107 105 106 CYCLES TO FAILURE 106 CYCLES TO FAILURE Fig. 461-S-N curves for cast nickel-chromi. um-molybdenum (8630) steel in the quenched and tempered condition. Tensile strength- 137,500 psi. Fig. 462—S-N curves for cast nickel-chrom. um-molybdenum (8630) steel in the normal. ized and tempered condition. Tensile strength -110,500 psi. LOW 363 ALLOY STEELS to this type of steel, a hardenability band for 86B30 cast steel is pre- sented in Figure 460 and compared to the 8630 cast steel so that an estimate of the effect of boron can be obtained. This shows the greater hardenability attainable with a small addition of boron to this type of steel. Fatigue data for 8630 cast steel in the quenched and tempered, and normalized and tempered conditions are presented in Figures 461 and 462, respectively. These data include values obtained from standard ASTM rotating beam fatigue specimens, both notched and unnotched. The character of the microstructure has some effect on the mechani- cal properties of the 8630 cast steel as may be seen by reviewing Figure 463. 50 45 0 25 00 Ft.Lb Chorpy Elongation% Reduction% 20 15 como 20 100 15 ** 140 1401 2500° per min. 130 -4.5.0 per min. — -18° per inin. - -900° per min.- 120 110 -OO Yield Strength, 1000 psi, 90 80 - Key .-Dendritic blocky ferrite plus pearlite *-Widmanstätten ferrite plus fine pearlite 0-Martensite • -Martensite plus Widmanstätten ferrite 0-Blocky and Widmanstätten ferrite plus pearlite 70 60 1 1 100 150 110 120 130 140 Tensile Strength, 1000 psi Fig. 463—Effect of structure on the mechanical properties of nickel-chromium-molybdenum (8630) cast steel. 364 STE ELS LOW ALLOY 4300 Series ... These are the old reliable cast steels which have gained wide acceptance and use wherever high hardenability and strength are required. The composition range of the 4300 series cast steels is as follows: Nickel Chromium Molybdenum 1.40 to 2.00 percent 0.55 to 0.90 percent 0.20 to 0.40 percent The mechanical property bands presented in Figure 464 are based on 133 heats of commercial 4335 normalized and tempered cast steels. 60 REDUCTION OF AREA 40 PERCENT 20 VELONGATION 280 112 260 BRINELL HARDNESS NUMBER 104 240 Fig. 464—Normally ex- pected properties of Ni- Cr-Mo (4335) cast steels based on 133 heats. C 0.30 - 0.40, Mn 0.65 0.85, Ni 1.60 - 2.00, Cr 0.65 0.85, Mo. 0.25 . 0.35 percent. Normal- ized and tempered (N1700, N1550, T1100 . 1200 degrees F). BRINELL, "HARDNESS. - YIELD STRENGTH 11000 p.s.i.) 96 220 YIELD STRENGTH: 80 72 90 106 1/4 122 130 134 98 TENSILE STRENGTH - 1000 p.s.i. 4300 series cast steels are more highly alloyed than the 8600 nickel-chromium-molybdenum steels and, as a result, have even greater hardenability characteristics. 4300 series cast steels are ideal for thick- walled castings requiring deep hardness. The end-quench hardenability band for 4330 cast steel is given in Figure 465. 4300 series cast steels along with 8600 cast steels can attain extremely high strength levels if properly quenched and tempered, and LOW 365 ALLOY STEELS 60 4330 40 HARDNESS, ROCKWELL C 20 0 ½ 1² 2 2% DISTANCE FROM QUENCHED END - INCHES Fig. 465—End-quench hardenability of nickel-chromium-molybdenum (4330) cast steel. ena 100 85 4355 CAST STEEL NORMALIZED AND TEMPERED TS-126,500 PSI 95 4335 CAST STEEL QUENCHED AND TEMPERED T.S-168,200 PSI 80 - 90 75 85 UNNOTCHED 70 UNNOTCHED 80 65 1 -- 75 60 - STRESS, 1000 PSI STRESS , 1000 PSI 70 55 50 65 60 45 1 NOTCHED NOTCHED 55 40 50 35 - NO FAILURE → NO FAILURE > 45 10+ 30 107 105 10 CYCLES TO FAILURE 104 107 106 105 CYCLES TO FAILURE Fig. 466-S-N curves for cast nickel-chromi- um-molybdenum (4335) steel in the quenched and tempered condition. Tensile strength- 168,200 psi. Fig. 467—S-N curves for cast nickel-chromi- um-molybdenum (4335) steel in the normal- ized and tempered condition. Tensile strength -126,500 psi. 366 STE ELS LOW ALLOY often find use in applications such as aircraft castings, where high strength-to-weight ratios are required. Fatigue data for 4335 cast steel in the quenched and tempered, and normalized and tempered conditions are presented in Figures 466 and 467, respectively, representing values for standard ASTM rotating beam fatigue specimens both notched and unnotched. The 4300 series steels possess excellent air hardening properties. Accordingly they have been used to a considerable extent in the steel casting industry with only a normalize and temper heat treat- ment when complicated casting designs are encountered, which may crack during water quenching. 1 Molybdenum Cast Steels (4000 Series) Molybdenum has the effect of increasnig the hardenability of cast steels, whether the addition be made to plain carbon or alloy composi- tions. In quantities less than one percent, molybdenum produces an increase in tensile strength while retaining satisfactory toughness. The usual molybdenum content of 4000 series steels is 0.20 to 0.50 percent. The hardenability band for 4030 cast steel is given in Figure 468 and is in the category of a low hardenable steel similar to 1300 and 2300 series cast steels. One of the outstanding characteristics of molybdenum cast steel is a satisfactory strength and yield point value at elevated temperatures upwards of 900 degrees F at low alloy costs. This characteristic is reflected in the creep tests and largely accounts for its use for the medium high temperature applications. Molybdenum cast steel is often used for castings ordinarily made from carbon steel which cannot, 1 60 1 40 HARDNESS, ROCKWELL C 4030 20 O % 12 2 272 DISTANCE FROM QUENCHED END - INCHES Fig. 468—End-quench hardenability of molybdenum (4030) cast steel. Ols ena LOW ALLOY 367 STEELS because of large size or intricate shape, be quenched to attain the desired hardness. Molybdenum cast steels can be used with just a normalizing treatment to obtain steels which afford moderate increases in strength. Chromium Cast Steels (5100 Series) The chromium content of 5100 series low alloy steels is usually in the range of 0.70 to 1.10 percent. Chromium steel castings are not in common use although as a class they are used in applications requiring moderate hardenability and moderate wear resistance. Chromium in contents of about 1 percent provides nominal improvement in resistance to heat, the high temperature mechanical properties and resistance to chemical action. a Chromium is one of the most popular alloying elements used by the steel foundries. Although it is most often used with one or more other alloying elements, quite excellent properties are obtained from a simple chromium steel. Chemically, chromium forms either a chromium carbide, which, in turn, dissolves in the cementite, or a complex carbide of chromium and iron. These carbides are very hard, and since the hardness which can be procured in steel is dependent in a large measure upon the carbides formed, the amount of carbon as well as the chromium content are important factors in determining the properties of such steel. However, chromium increases hardness not only because of the hard- ness of these chromium carbides, but because it aids in retarding the austenite transformation. On cooling from above the critical range, cementite containing chromium does not separate out to form pearlite 60 40 HARDNESS, ROCKWELL C 5130 20 0 V / 1% 2 22 DISTANCE FROM QUENCHED END - INCHES Fig. 469—End-quench hardenability of chromium (5130) cast steels. 368 ALLOY STEELS LOW as readily as does ordinary cementite. Therefore, in rapid cooling it helps to prevent the transformation of the austenite, thus increasing not only the hardness of the surface but the depth of hardening as well. The chromium cast steels have a medium hardenability and are in the same class as the 8000, 4600 and 4100 series cast steels. The end-quench hardenability band for 5130 cast steel is given in Figure 469. Chromium-Molybdenum Cast Steels (4100 Series) Chromium-molybdenum cast steels are widely used in foundries producing low alloy grades. The addition of molybdenum to chromium cast steel increases the resistance to impact and creep point attainable for any given heat treatment or strength level. Also these cast steels show excellent properties in the normalized and tempered condition. The increased hardenability imparted by chromium and molybdenum permits the advantageous use of these steels for large or intricate cast- ings which require deep hardening, but which may not be regarded as suitable for liquid quenching. The presence of molybdenum reduces the tendency toward temper brittleness exhibited by certain chromium- containing alloy steels. The composition of 4100 cast steel is 0.70 to 1.10 percent chromium and 0.15 to 0.40 percent molybdenum. End-quench hardenability bands for 4130 and 4140 cast steel are given in Figure 470. Fatigue data for 4135 cast steel in both the quenched and tempered and normalized and tempered conditions are given in Figures 471 and 60 4140 40 HAHAHAH HARDNESS, ROCKWELLC 4130 20 0 / 1늘 ​2 2%2 DISTANCE FROM QUENCHED END - INCHES Fig. 470—End-quench hardenability of chromium-molybdenum (4130 and 4140) cast steel. LOW 369 A L L'O Y STEELS 85 4135 CAST STEEL QUENCHED AND TEMPERED T. S.- 146,400 PSI 80 75 +135 CAST STEEL NORMALIZED AND TEMPERED 7.5. - 112,700 PSI 75 70 70 - 65 UNNOTCHED 65 60 STRESS, 1000 PSI UNNOTCHED 60 STRESS, 1000 PSI 55 50 50 45 1 45 -- NOTCHED 40 NOTCHED 40 35 NO FAILURE → NO FAILURE → 35 30 105 105 106 107 104 105 106 107 CYCLES TO FAILURE CYCLES TO FAILURE Fig. 471-S-N curves for cast chromium- molybdenum (4135) steel in the quenched and tempered condition. Tensile strength- 146,400 psi. Fig. 472–S-N curves for cast chromium- molybdenum (4135) steel in the normalized and tempered condition. Tensile strength- 112,700 psi. 472, respectively, representing values for standard ASTM rotating beam fatigue specimens both notched and unnotched. 3 3 Percent Cr-Mo Cast Steel ... Another, more highly alloyed, chrom- ium-molyblenum steel is also produced by steel foundries. This steel contains 2.50 to 3.50 percent chromium, 0.40 to 0.60 percent molyb- denum and 0.25 to 0.40 percent carbon. This alloy was originally de- veloped for use in cast armor and now finds wide use in applications requiring excellent impact and wear resistance. It is employed only in the water quenched and tempered condition. The end-quench hard- enability band for this steel is shown in Figure 473. Manganese-Nickel-Chromium-Molybdenum Cast Steels (9500 Series) The four alloy, 9500 series steels are produced primarily for the purpose of securing high hardenability. Sections of upwards of 5 inches in thickness will quench out and develop a complete fibrous fracture (tempered martensite) on tempering. 370 ALLOY STEELS LOW 60 40 HARDNESS, ROCKWELL C Cr-Mo CAST STEEL C-0,30 % CR-2.50 -3.50 % Mo-0.40-0,60 % 20 / 112 2 272 DISTANCE FROM QUENCHED END, INCHES Fig. 473—End-quench hardenability band for 2.50 to 3.50 percent chromium, 0.40 to 0.60 percent molybdenum cast steels. The composition range employed for the 9500 series is as follows: Manganese, percent 1.30 to 1.60 Nickel, percent 0.40 to 0.70 Chromium, percent 0.55 to 0.75 Molybdenum, percent 0.30 to 0.40 The hardenability band for 9530 cast steel is given in Figure 474. The fact that the manganese-nickel-chromium-molybdenum cast steels 60 1 95303 40 HARDNESS, ROCKWELLC 20 ½ / 12 2 272 DISTANCE FROM QUENCHED END -INCHES Fig. 474--End-quench hardenability of manganese-nickel-chromium-molybdenum (9530) cast steel. LOW ALLOY 371 STEELS react so readily to air cooling permits the employment of a high temperature tempering treatment with considerable hardness being re- tained. This allows castings to be stress relieved without a significant sacrifice of hardness. Because these steels are hardenable to consider- able depth on water quenching, they are used in structural and dynamic applications of all types where high yield, high strength steels are needed in heavy sections. The effect of structure on the mechanical properties of a 9525 cast steel is shown in Figure 475. 50 OD 40 30 O 20 o Elongation % Reduction of Area % 10 25 O O 20 O 15 . 10 O 35 30 - 4 25 a Ft-Lb Chorpy O 20 o *-*- 15 Key 90 -1per min.- per min. -10° per min.- 0_30 240° per ming 80 Yield Strength, 1000 psi OD 70 .-Dendritic blocky ferrite plus pearlite A-Random blocky ferrite plus pearlite *-Widmanstätten ferrite plus fine pearlite 0 -Blocky and Widmanstätten ferrite plus pearlite O 60 50 1 1 1 90 100 110 120 130 140 Tensile Strength, 1000 psi Fig. 475-Effect of structure on the mechanical properties of manganese-nickel-chromium-molyb denum (9525) cast steel. Copper-Manganese-Silicon Cast Steels Copper is added to steel primarily for the purpose of increasing the tensile and yield strength with only a slight decrease in ductility by a precipitation hardening heat treatment. 372 STEELS LOW ALLOY Of the various types of copper cast steel produced, the largest ton- nage has been of a copper-manganese-silicon combination. In the com- mercial production of this steel, the carbon content is kept below 0.20 percent in order that the optimum ductility for a given yield strength may be obtained. The usual composition of copper-manganese-silicon cast steel is : 0.20 Max. 1.50 to 1.80 Carbon, percent Copper, percent Manganese, percent Silicon, percent 0.90 to 1.25 0.85 to 1.10 Several outstanding advantages of copper-manganese-silicon cast steels are worth considering. Two characteristics of this type of cast steel are rather unique. These are: (1) its excellent fluidity in the Table 56—Tensile Properties of Copper-Manganese-Silicon Cast Steels for Various Heat Treatments(10) Heat Treatment Composition Cu Mn Tensile Properties T. S. Y. S. El. RA С Si 0.12 1.85 0.83 0.79 0.12 1.85 0.83 1.48 0.15 1.82 1.27 0.93 0.15 1.77 1.08 0.98 0.16 1.67 0.90 1.11 0.16 1.67 0.90 1.11 0.16 1.67 0.90 1.11 0.20 1.77 0.98 0.97 0.20 1.77 0.98 0.97 0.24 1.70 1.12 1.05 0.12 1.85 0.83 0.79 0.12 1.85 0.83 1.48 0.15 1.82 1.27 0.93 0.16 1.54 0.96 1.07 0.20 1.77 0.98 0.97 0.24 1.70 1.12 1.05 0.15 1.85 0.73 0.93 0.15 1.82 1.27 0.93 0.17 1.94 0.92 1.14 0.17 1.94 0.92 1.14 0.17 1.94 0.92 1.14 0.17 1.94 0.92 1.14 1700 AC; 930 ( 2 Hr) AC 1700 AC; 930 ( 2 Hr) AC 1700 AC; 930 ( 2 Hr) AC 1700 AC; 930 ( 2 Hr) AC 1700 AC; 930 ( 112 Hr) AC 1700 AC; 840 ( 142H r) AC 1700 AC; 840 ( 6 Hr) AC 1700 AC; 930 ( 2 Hr) AC 1700 AC; 930 ( 4 Hr) AC 1700 AC; 930 ( 2 Hr) AC 1700 AC; 1200 ( 4 Hr) AC 1700 AC; 1200 ( 4 Hr) AC 1700 AC; 1200 ( 2 Hr) AC 1700 AC; 1200 ( 4 Hr) AC 1700 AC; 1200 ( 4 Hr) AC 1700 AC; 1200 ( 4 Hr) AC 1700 AC 1700 AC 1650 WQ;1000 (20 Hr) AC 1650 WQ; 900 (20 Hr) AC 1650 WQ; 800 ( Hr) AC 1650 WQ; 650 (14 Hr) AC 100,000 82,000 106,000 86,000 104,000 86,500 108,000 90,000 110,000 86,500 103,000 79,500 110,000 87,500 114,500 87,500 118,000 89,500 117,500 90,000 77,000 61,000 83,000 63,000 87,000 68,000 79,000 60,000 86,500 62,500 90,000 63,500 87,000 71,000 95,000 75,500 116,500 102,000 122,000 106,000 155,000 138,000 156,000 145,000 24 24 20 20 21 22 20 16 18 15 32 31 25 34 25 57 57 37 40 36 38 36 29 38 26 67 66 48 66 45 24 41 27 23 17 20 16 14 50 42 40 42 32 32 AC=Air Cooled WQ=Water Quenched LOW 373 ALLOY STEELS molten state, and (2) its ability to be precipitation hardened. In addi- tion, copper increases the yield and tensile strength and yield ratio of the steels to which it is added. The basis for precipitation hardening of copper steels lies in the fact that ferrite can dissolve about 1.5 percent copper at 1530 degrees F but below 1200 degrees F, only about 0.35 percent is soluble. Copper- bearing steels, cooled above a certain critical rate, maintain an excess of copper in super-saturated solution from which the copper will precipitate in a more or less finely divided state throughout the steel, after a tempering heat treatment. Copper steels are different from other precipitation hardening systems in their ability to increase in strength and hardness without serious loss in ductility, provided the carbon content is of a low value. Impact resistance is reduced somewhat, however. Figure 476 shows the tensile properties of copper-manganese-sili- con cast steel in the normalized and tempered condition and the normal- ized and precipitation hardenend condition, both as a function of copper NORMALIZED AND AGED (930°F, 2 HR.) NORMALIZED AND TEMPERED (1200 °F, 4 HR.) 110 100 TENSILE, 1000 PSI 90 80 90 80 YELD, 1000PS/ c - 17% MN - 1.21 % S - .97% 70 60 60 50 ELONGATION, % RED. OF AREA,% 40 30 20 2.00 .50 1.00 1.50 PERCENT COPPER Fig. 476—Effect of copper content on tensile properties of copper-manganese-silicon cast steels in the normalized and tempered, and normalized and precipitation hardened conditions (Taylor, Bishop, and Rominski). 374 STEELS LOW ALLOY 50 с Mr si Cu *.30 .75.41 .21 1.08 1.19 1.74 40 COPPER 30 CARBON FLUIDITY: INCHES 20 10 o 2010°F 1400°C 2730'F 1500°C 2910°F 1600°C 3090°F 1700°C POURING TEMPERATURE Fig. 477—Fluidity of copper-manganese-silicon steel as compared to carbon steel (Taylor, Rominski, and Briggs)". content. This graph shows that a definite change in properties is obtained with copper contents above about 0.75 percent, resulting from precipitation hardening. It is essential that carbon content be kept below 0.20 percent if the steel is to be precipitation hardened. It is not necessary that copper-manganese-silicon cast steel be quenched before being precipitation hardened. A super-saturated solution of copper in ferrite is obtained by even very slow cooling, and sections of six inches can be hardened throughout by low temperature age hardening after normalizing. Table 56 shows typical tensile properties of copper- 60 COPPER-MANGANESE-SILICON CAST STEEL 0.20% CARBON 1.50-1.80 % CU 0.90-1.25 % MN 0.85-1,10 % SI 40 HARDNESS, ROCKWELL C 20 12 , 142 2 272 DISTANCE FROM QUENCHED END, INCHES Fig. 478—End-quench hardenability of copper-manganese-silicon cast steel. LOW ALLOY 375 STEELS manganese-silicon cast steels for various heat treatments. Optimum mechanical properties are obtained by a normalizing treatment followed by an “aging" treatment at approximately 930 degrees F for 2 hours. Figure 477 shows the relative fluidity of copper-manganese-silicon cast steel as compared to a 0.30 percent carbon cast steel. A significant improvement is noted. This improvement is the result of the combined effects of the copper and the high silicon content. The increased fluidity is an important feature of the Cu-Mn-Si cast steel, resulting in its suc- cessful use in the production of long rangy steel castings of thin section. The end-quench hardenability band for copper-manganese-silicon cast steel is shown in Figure 478. Copper improves the hardenability over that of a carbon steel. Steel castings of copper-manganese-silicon composition have exten- sive applications, being used in the logging and excavating industries for logging yarders, boom yarders, tractor bulldozers and steam shovel booms. They also find application in gears to be case hardened, gear hoist housings, machine frames, cradle car castings and long shafting, and for many other types of long rangy castings. REFERENCES 9 1. Evans, E. B., Ebert, L. J., and Briggs, C. W., "Fatigue Properties of Comparable Cast and Wrought Steels”, ASTM Proceedings, Vol. 56 (1956), pp. 979-1010. 2. Grange, R. A., and Garvey, J. M., “Factors Affecting the Hardenability of Boron Treated Steels”, ASM Transactions, Vol. 37 (1946), pp. 136-191. 3. Grange, R. A., Seens, W. B., Holt, W. S., and Garvey, J. M., “Effect of Boron and Kind of Boron Additions Upon the Properties of Steel”, ASM Transactions, Vol. 42 (1950), p. 75. 4. Briggs, C. W., “Recent Developments Concerning the Properties of Cast Steels”, Trans. ASME, Vol. 70 (1948), pp. 37-48. 5. Hawkes, M. F., “Mechanical Properties of Cast Low Alloy Steels”, Trans. ASM, Vol. 39 (1947), pp. 1-40. 6. Metals Handbook, American Society for Metals, 1948 Edition, pp. 523-526. 7. Hoyt, S. L., “Metal Data”, Reinhold, (1952), pp. 255-269. 8. Archer, R. S., Briggs, J. Z., and Loeb, C. M., “Molybdenum Steels, Irons, Alloys”, Climax Molybdenum Company, (1948), pp. 221-256. 9. “Nickel Alloy Steels”, International Nickel Company (1947), Section 3. 10. Taylor, H. F., Bishop, H. F., and Rominski, E. A.—“Summary Report of Low Alloy Copper Cast Steel", NRL Report No. M1935 (September 1942). 11. Taylor, H. F., Bishop, H. F., and Wayne, R. C., “Copper and the Steel Casting", AFA Transactions, Vol. 54 (1946), pp. 213-224. 12. Taylor, H. F., Rominski, E. A., and Briggs, C. W.—“The Fluidity of Ingot Iron and Carbon and Alloy Cast Steels”, AFA Transactions, Vol. 49 (1941) pp. 1-83. > CHAPTER XI CAST STEELS FOR WEAR RESISTANCE Introduction Steel castings are used in a great many applications requiring resistance to wear. Such castings have special properties not usually necessary for cast steels used only in structural applications. This chapter will show what factors determine the steel's ability to resist wear, the types of steels the industry is now using for wear-resisting applications, the methods used to produce wear resistant cast steels and data relating to salient properties. It will also cover the production and processing of austenitic manganese steel castings, including information on the unique properties which recommend this alloy for certain types of service. Wear may be defined as the unintentional removal of material from the surfaces of bodies moving in contact with one another. Wear resistance cannot be considered as a single inherent property of a metal, but must be determined in conjunction with the specific conditions of service. a > Wear occurs by the displacement and detachment of metallic parti- cles from a metallic surface. This process may be caused by contact with another metal (metallic wear), by contact with either a métallic or a nonmetallic abrasive (abrasion), or by contact with flowing liquids or gases (erosion). Erosion is frequently combined with some form of corrosion, whereas metallic wear and abrasion may or may not be. A subcommittee of the American Society of Metals(2) has classified wear depending on the nature of the contacting surfaces as follows: I. Metal against metal (Metallic Wear) A. Sliding friction 1. Lubricated (shaft in bearing) 2. Nonlubricated (brake shoe against wheel) B. Rolling friction 1. Lubricated (gears) 2. Nonlubricated (wheel on track) II. Metal against nonmetal or abrasive (Abrasion) A. Sliding friction WE ARRESIST ANCE 377 1. Wet (conveyor screws for wet sand) 2. Dry (plowshares) B. Rolling friction 1. Wet (ball and rod mills) 2. Dry (jaw crushers, crushing rolls) C. Impact of loose abrasives 1. Wet (impellers) 2. Dry (sand and shot blast) III. Metal against liquids or vapors (Erosion) A. Wet steam (turbines) B. Combustion gases (gas turbines) Metal-to-metal wear involves two surfaces moving in contact with some of the projections of one interlocking with projections of the other or gouging into the surface of the other to such an extent that the pro- jections are deformed and torn off or grooves are made. Under such conditions hardness, toughness and surface smoothness are necessary for wear resistance-hardness to resist initial indentation, toughness to resist the dislodgement of metallic particles, and surface smoothness to eliminate the projections. Abrasive wear results when the abrading particles first penetrate the steel and then cause the tearing off of the metallic particles. The rate of wear of the steel depends primarily on the hardness of the steel since the degree of hardness determines the ease with which the abrad- ing particles may dig into the surface. Erosion implies an actual disintegration or displacement of the material being eroded. Eroding mediums need not be of high hardness as is illustrated by the erosion of steam turbine blades by drops of water. Erosion is frequently combined with some form of corrosion, whereas abrasion and gouging usually are not. SECTION I Factors Affecting the Wear Resistance of Cast Steel The chief factors governing the resistance of steel to various types of wear are hardness, carbon content and other chemical components, toughness, heat treatment and microstructure. Service variables such as contacting materials, pressure, speed, temperature, surface finish, corrosion and lubrication also have an important bearing on the prob- lem. A general appraisal of each of these factors is difficult. Among 378 WE AR RESISTANCE many of them, a more or less rigid but still unclarified inter-relationship exists. Thus, to state that a certain composition is the most wear resist- ant is obviously impossible without considering many of the other factors associated with the metal, as well as the conditions of service. Two materials, one of which is definitely superior to the other in a particular service, may suffer a reversal in position by a slight change in the conditions of service. Resistance to wear does not increase directly with any of the aforementioned factors. High hardness tends to improve wear resistance by making the steel resistant to penetration, scratching, and deforma- tion. A correlation between hardness and wear resistance that has been suggested is given in Figure 479. Wear resistance tends to increase with increasing hardness as long as extreme brittleness and chipping or spalling of the surface does not take place. There is no universal wear test, because there are many different types of wear and a material that is advantageous in one application may be unsatisfactory in another. Equipment for wear testing should be designed to simulate actual service conditions. The rating of materials obtained by any one test cannot be applied, ordinarily, to a different type of wear. These principles should be kept in mind when interpreting data on wear testing. 0.14 0.12 HARDENED WEAR, GRAMS 0.10 NORMALIZED 0.08 4 0.06 0 200 400 600 800 BRINELL HARDNESS NUMBER Fig. 479—Relation between hardness and abrasive wear of carbon steels (wear type II A2). Illinois glass sand passed through sieve of 0.297 mm opening. Pressure of rotating disc - 10 kg. Length of test - 60 meters travel of disc (Rosenberg)'. WE AR RESISTANCE 379 The effect of carbon content and heat treatment on the wear resistance of carbon steels is shown in Figure 480. The data show that wear resistance of carbon steels is markedly changed by heat treatment, and that it is desirable to keep the carbon content of the steel over 0.40 percent to obtain good resistance to this type of wear. These data should not be interpreted to mean that a hardened steel is best in all applications. The brittleness of high carbon, high hardness steel often renders it unsuitable for many purposes, and in such cases, some resistance to wear must be sacrificed by further tempering or lowering the carbon content to improve toughness. The effect of tempering on abrasive wear of quenched steel is nearly a straight line function show- ing increased wear with increasing tempering temperature. If the wear is of the metal-to-metal type, tempering above 900 degrees F decreases wear resistance at an accelerated rate(2). 0.16 0.14 ANNEALED 0.12 NORMALIZED GRAMS WEIGHT LOSS, 0.10 0.08 HARDENED 0.06 o 0.20 0.40 0.60 0.80 1.00 1.20 PERCENT CARBON Fig. 480—Effect of carbon content on abrasive wear of carbon steels (wear type II A2). Illinois glass sand passed through sieve of 0.297 mm opening. Pressure of rotating disc - 10 kg. Length of test - 60 meters travel of disc (Rosenberg)'. The relationship between hardness and wear resistance presented in Figure 481 again shows that wear tends to decrease with increasing hardness, as long as extreme brittleness and chipping or spalling of the surface does not take place. Although a quenched and tempered steel is usually superior in wear resistance to a normalized steel at any given 380 WE AR RESISTANCE 3.5 0.35 C 3.0 NORMALIZED 2.5 0.60 C 2.0 WEAR , GM/105 M-KG OF WORK 0.100 1.5 - QUENCHED AND TEMPEREO 1.0 0.5 0.80 C 0.35 C 0.600 1.200 0.800 1.200 0 100 200 300 400 500 600 BRINELL HARDNESS NUMBER Fig. 481–Wear rate versus BHN for plain carbon steels (wear type 1A2 and 1B2). Amsler machine-pressure 60,000 to 70,000 psi, length of test 10,000 revolutions, speed 220 rpm, contacting specimen 0.81% C hardened steel (data from Rosenberg). > carbon level, if tempered back to too low a hardness the quenched and tempered steel will not perform as well as a normalized steel of the same hardness. It is seen from Figure 481 that in this type of wear test, normalized carbon steel of a high carbon content performs better than quenched and tempered carbon steel of a low carbon content at the same hardness level. This apparently is related to the microstructure obtained as a result of the different heat treatments. Free ferrite is known to be detrimental to wear resistance. Increasing the carbon content until a fully pearlitic structure is obtained is usually beneficial. The presence of small, well-distributed carbides is beneficial in improving wear re- sistance. A high or prolonged tempering treatment which agglomerates the carbides reduces the wear resistance of highly tempered steel. The hardness of the abrading medium is an important factor affect- ing the wear rate of cast steel. An illustration of how the hardness of the abrasive influences the wear rate of cast steel is provided in Figure 482. Data for constructing these curves were determined by noting the wear rates of cast steel grinding balls when grinding three relatively pure minerals of different hardness in a three-foot diameter pilot plant ball mill for a number of 24-hour periods. An application such as this does not require that the steel casting have impact resistance or much toughness; but high resistance to abrasion is essential. This fact is borne out by the data which shows the superiority of the harder steel. The effect of alloying elements of steel is somewhat inconsistent. In unhardened steels, alloying elements appear to affect wear resistance only insofar as they cause the formation of more pearlite and of finer WE AR RESISTANCE 381 12 QUARTZ 10 FELDSPAR PEARLITIC STEEL , 24 RC PEARLITIC STEEL, 40 RC WEAR RATE, GM/100 CM / DAY 2 CALCITE -MARTENSITIC STEEL, 61 RC - 100 700 800 200 300 400 500 600 KNOOP HARDNESS NUMBER Fig. 482—Influence of hardness of abrasive mineral on the wear rates of 0.80 percent carbon cast steel grinding balls (data from Norman)'. pearlite. The best microstructures for wear resistant applications are usually fine pearlite or a mixture of martensite, bainite and austenite, depending upon the degree of impact resistance required. The effect of alloying elements in fully hardened steels is generally less noticeable, unless they cause the formation of hard carbides which serve to decrease the rate of softening under the influence of frictional heat. Recent developments with the low-alloy steels have demonstrated that when they are properly heat treated to around 500 Brinell, they can produce excellent abrasive resistant properties for specific applications. This is especially true in the handling of extremely hard, abrasive ores. The advantage of a prehardened low alloy part is that it is hard all the way through and does not bend or distort, while still maintaining satis- factory impact resistance under the most severe conditions. Generally, the following alloys are added to wear resistant cast steels to improve the toughness and resistance to fatigue: molybdenum, nickel, chromium and manganese. Compositions employing these alloys or combinations of these alloys have found extensive use, especially in the mining industry. Section II of this chapter will show the results of an industry-wide survey to determine the compositions and properties of cast steels for wear resistant applications. However, it should be stressed that chemical composition is not particularly important in itself, except as a means to obtaining the required hardness and struc- ture. Any one of several compositions could lead to the desired results. 382 WE AR RESISTANCE SECTION II Steels Used for Wear Resistant Applications A survey was undertaken by Steel Founders' Society to determine the types of steel the industry is using for wear resistant applications. The results of this survey are shown in Tables 57 and 58 and it is interesting to note that a wide range of carbon and alloy contents are employed for many of the same applications. The survey showed that 57 percent of the casting applications requiring wear resistant steel were produced from cast steels containing between 0.30 and 0.45 percent carbon. This may be somewhat of a sur- prise to the reader in view of the fact that better wear resistance may be expected from the high carbon steels. However, the foundry engineer knows that the medium carbon cast steels provide an excellent combina- tion of hardness and toughness with greater freedom from quench cracking, which makes them ideally suited for wear resistant-high impact applications. Good wear resistance also can be obtained by employing the 12 percent austenitic manganese cast steel, provided peening or pressure application is sufficient to produce a work hardened surface. Steel castings of such steels give excellent service life in railroad crossings and in the working of gravels and rock. Fig. 483—Ball mill liners for a 7 feet diameter by 26 feet mill produced from an alloy cast steel of C 0.40, Si 1.60, CI 0.85, Ni 1.85, Mo 0.40, V 0.08 percent. WE AR RESISTANCE 383 No. 1 2 С .18 .23 .28 .28 .29 .30 .30 .30 .30 000 00000 + ++to++++++ SEEEEE FEE & 10 .30 .30 .25 11 12 .30 13 .32 Sao Bo Eo DFO 000~0OTA W 14 .33 Table 57—Steels Used by Various Foundries for Wear Resistant Applications Composition, Percent Mn Cr Ni Mo Other Heat Treatment Application .89 .69 1.52 .27 .0028 (B) Q + T Crawler shoes for power shovel .67 + Differentially Sheaves; jet circulation bits for well drilling Hardened 1.65 .80 .50 .0025 (B) Q+T Earth moving equipment 1.55 Friction casting for railroad service .86 .64 .75 .27 Dipper teeth; crawler shoes 1.15 1.10 .40 .09 (V) Teeth; liners .70 :.80 1.65 .25 Dipper teeth; rail segments for power shovel 1.40 .23 Treads; sprockets; gear teeth; crane wheels 1.50 .20 Friction shoes .75 .75 1.00 .30 Tractor and shovel castings 1.20 .05 (V) Soil digger teeth .80 1.00 1.00 .50 Dredge pumps; crusher jaws; rollers; pump shells; pinions .75 .50 .55 .20 Q+T Tractor pads; liners; crawler shoe treads; scarifier teeth 1.30 N + Differentially Shovel equipment Hardened .55 3.00 .20 Q + T Dredge pumps; crusher jaws; rollers; pump shells; pinions 1.20 .20 .0030 (B) Q+T+Differentially Dipper teeth; sprockets; shovel shoes; tank Hardened track shoes; sheaves; cable pulleys .80 .75 .45 Q+T Swing hammers for coke crushing and clay grinding mills 1.50 .40 Q+T Dredge cutter parts; rock quarry parts; digger and bucket teeth .70 .50 1.50 .30 N+T Track shoes; shovel bits .70 .75 1.75 .30 Q+T Rock crushers; sprockets; gears; wear plates; digger teeth; crawler shoes; steering knuckles; chain conveyor; liner parts .75 .85 1.85 .40 $1.60 (Si) 1.08 (V) Q+T Liner parts .87 .55 .58 .20 + T Gears; hammers 1.40 Q + T Bucket teeth; pinion gears; bull gears .80 .95 .25 Q+T Palletizing die; crawler shoes; gears; sprockets; wear plates; digger teeth .70 1.25 2.00 .25 + T Hammers for corn cob mill 1.15 .30 .35 Q+T Teeth; liners .90 .45 .55 .40 .20 (W) .60 (Co) Q + T Dipper bucket teeth 15 .35 16 .35 17 .35 18 .35 19 20 .36 .38 21 .40 22 23 .40 .40 .40 .25 24 25 26 .40 .42 .43 27 384 WE AR RESISTANCE No. С 28 29 .45 .45 30 .45 31 32 33 .45 .50 .50 34 35 36 37 .50 .55 .56 .58 .60 .60 38 39 40 41 42 .60 .60 .65 Table 57—Steels Used by Various Foundries for Wear Resistant Applications—(Continued) Composition, Percent Mn Cr Ni Μο Other Heat Treatment Application 1.60 .35 N+T Cams; pinions; gears .55 3.00 .40 Q+T Dredge pumps; crusher jaws; rollers; pump shells; pinions 1.60 N+T+Differentially Gears; pinions; crane wheels; hammer mill Hardened parts; redge pump impellers and casings 1.50 .30 .10 (V) Q+T Trunnions for rotary kiln 1.30 .50 .10 (V) Q+T Liner parts .90 .65 .20 N+T+Differentially Die blocks Hardened .70 .95 1.75 .30 N+T Dies; liners .70 2.10 .30 T Mill liners and grates .70 2.10 Mine grates; shute and bin liners .80 1.50 2.75 .53 T Pumps for sand slurry conveying .80 5.00 .50 N Cement mills; sand handling conveyor links .80 .75 .45 Q+T Taconite pellet conveying grate; wing nose for railway ballast cleaner; cutter points; scarifier points .70 2.15 .40 Liner parts .80 1.00 2.00 .60 T Crusher jaws; pug knives .90 1.50 .45 Cement mill liners and screen plates; pug mill knives .70 1.50 2.00 .35 T Liners; crushers .70 2.30 .55 T Roll crushers .90 2.10 .50 .25 .05 (V) T Ore grinding mills .70 1.50 .05. (V) T Crane wheels .70 2.10 .30 T Mill liners and grates .85 1.50 .70 .35 T Ball and rod miſl liners; screen plates; drag chain links; crusher liners and rings; pump and impeller parts .70 2.10 .35 N + T Mine mill liners and grates .60 2.50 .15 (V) Cement mills; sand handling conveyor links 16.00 Garbage disposal unit 12.50 2.00 Pulverizer hammer tips; track shoes 12.00 Hammers; mine mill; chute and bin liners; power shovel teeth; gears; grizzly bars 12.50 2.50 Hammers; liners; crusher jaws; buckets; lips; coal breaker segments; fronts; chain; railroad frogs and crossings .30 13.00 1.00 1.00 N Dies; low level impact applications 43 44 45 46 47 48 如​HR SH始​幻​8 .65 .65 .70 .70 .75 .80 ZZZZZZ ZZO ++++++ +++ 49 50 51 52 53 .85 .90 1.10. 1.20 1.20 .75 © DOZZ+ 54 1.20 55 1.75 WE AR RESISTANCE 385 Table 58—Mechanical Properties for the Steels Used for Wear Resistant Applications Brinell Tensile Hardness Strength Percent Yield Percent Red. Strength Elongation of Area No. Charpy V Charpy V at +70°F at -40°F 318 143,000 77,000 235,000 134,000 47,000 140,000 10 30 10 22 54 25 20 24 10 10 150,000 249,000 170,000 148,000 125,000 195,000 156,000 126,000 15 5.5 7 12 25 8.3 17 25 1 2 3 4 5 6 7 8 9 10 11 12 15 16 17 18 19 21 173,000 190,000 155,000 160,000 Oo oo 8 8 15 12 10 15 17 175,000 120,000 150,000 95,000 : 10 18 15 40 175,000 160,000 11 30 260,000 218,000 5 11 9 9 22 48 133,000 262,000 120,000 229,000 19 5.5 33 8.5 4 10 500 460 300 495 361 290 480 500 440 470 381 270 375 400 400 528 265-380 270 555 480 225-300 370 260 450 286 325 350 475 375 437 460 500 333 400 275 325 388 325 350 500 200 195 210 600 185,000 133,000 165,000 68,000 7 14 15 25 10 132,000 145,000 105,000 90,000 20 8 ខ 35 12 175,000 204,000 142,000 185,000 2.5 3.9 4 23 26 27 28 29 30 32 34 35 36 37 38 40 41 43 44 45 46 47 48 49 50 51 52 53 54 55 3 150,000 120,000 90,000 3 8 8 190,000 140,000 145,000 192,000 145,000 165,000 4 12 8 5 8 er oor o NA 4 16 12 5.7 12 90,000 135,000 120,000 110,000 115,000 52,000 45,000 55,000 40 30 30 35 20 24 Data not available for steels of the following numbers: 13, 14, 20, 24, 25, 31, 33, 39 and 42. Fig. 484— Liners of Figure 483 in place in the ball mill after grind ing 177,000 bar- rels of cement. SECTION III Surface Hardening of Steel Castings Many applications require that a steel casting have both a hard, wear-resistant surface and a tough, ductile core. There are a number of processes in common use for surface hardening (case hardening) steel castings. The optimum process for a given application depends upon many factors. High case hardness with sufficient depth to give reason- able service life is necessary for resistance to abrasion. The three most common processes used to case harden steel castings are local heating and quenching, carburizing, and nitriding.(4,5) Other methods are face hardening by the use of welding and by sprays, chrome plating and cyaniding. Local Heating and Quenching . . Almost any steel which contains sufficient carbon to produce a high hardness is applicable to a local heating and quenching process. Carbon content should not be too high or quench cracking may result. The usual range is about 0.35 to 0.50 percent. There are three common methods of surface hardening steel castings by a local heating and quenching process: (1) flame hardening, (2) induction hardening, (3) differential quenching. The flame hardening process embraces the use of the oxyacetylene flame to raise specific sections of the steel casting above the austenite transformation temperature, so that subsequent quenching will produce a desired hardness and microstructure. The process is limited primarily to surface heating of the casting, and a hardened surface layer can be obtained that may vary in depth from a mere skin to as much as 3/8 inch, according to the practice used and the composition of the steel treated. . Fig. 485—A typical rig for flame hardening cast steel gears. Note how closely the water quench follows the flame. Flame hardening may be a hand or machine operation but is usually the latter. In the flame hardening of large areas, multiple flame heads generally are provided with water jets and flame tips set close together. The steel is then water quenched immediately behind the flame tip. This process is used for hardening teeth on cast steel gears of all types. An illustration of a rig for flame hardening gear teeth is shown in Figure 485. Castings subject to flame hardening usually have had a previous normalizing and tempering treatment to produce the required toughness and ductility in the base sections of the casting. Induction hardening depends for its operation upon localized heat- ing produced by currents induced in a metal placed in a rapidly pulsating magnetic field. Heating results from the resistance of the steel to passage of these currents. The case obtained by induction hardening is similar to that obtained in flame hardening. Thinner cases can be obtained, however, because of greater speed of heating. Entire sections of castings as well as the surface can be hardened by the induction heat- ing method; thus, the heated portions may be hardened while maintain- ing the original properties in the unheated portions. Advantages of the process include speed of heating, minimum distortion, and freedom from scaling. Among the disadvantages are the initial cost of the equipment, a limitation on size of castings which can be handled economically, and high maintenance costs. The differential quenching process permits only certain sections of a uniformly heated casting to be subjected to a liquid quench. Differen- tial quenching is obtained by spraying, spinning, or partial immersion in the quenching medium, while the remainder of the casting air cools. Considerable ingenuity is exercised in the construction of fixtures to 388 WE AR RESIST ANCE perform these various operations. Cast steel wheels of various types are often given a differential quenching treatment, the rim face being hardened by rotating the rim portion in water or by water spraying the rim face. The quenching process requires careful attention and is often a time-quench process. . Carburizing ... Carburizing may be defined as "a process of case hardening in which carbon is introduced into a solid ferrous alloy by heating above the transformation temperature while in contact with a carbonaceous material which may be a solid, liquid or gas.” This process is primarily applied to a low carbon steel in order to transform the surface layer into high carbon steel. Carburizing is usually followed by a quenching treatment to produce a hard case. Figures 486, 487 and 488 show steel castings which have been carburized before being used in their particular application. The three most widely used methods of carburizing are pack carburizing, gas carburizing, and liquid carburiz- ing. Fig. 486—Carburized cast tooth rack and shrouded pinion used in converting mill in steel industry. Fig. 487—Carburized cast tooth hinge gears for arc bridge bucket. Fig. 488 Carburized spur and helical gears and double helical shaft pinion. Herring- bone ring and center design gear and shaft pinion used on trolley drive for large crane. Pack carburizing is practiced by placing the casting and a solid organic carburizing agent into a box, sealing the box and heating it in a suitable furnace to the required temperature, holding it at this tem- perature for a definite period depending on how deep a case is desired and slow cooling. Pack carburizing is well adapted for applications requiring heavy case depths. Several of the advantages of this process result from its simplicity. The packing material offers excellent support for sections which might warp during carburizing, and the natural slow cooling in the containers also holds warpage to a minimum. Among the disadvantages of pack carburizing is the relatively large amount of labor involved in handling the parts and the compounds. The slow heating of the boxes and sluggish heat transfer within the charge are also drawbacks. Gas carburizing depends on the case layer to be produced by carbon supplied by the furnace atmosphere. This can be accomplished with hydrocarbon gases, in particular methane (natural gas), propane, butane, or vaporized hydrocarbon fluids. Disadvantages of the process include the strict control of the gas composition required, high main- tenance costs, and the requirement of high production rates to make the process economically feasible. An important advantage of gas carburiz- ing is the fact that the composition of the gas, rate of flow and tempera- ture can be adjusted to obtain the desired carbon content and depth of case. The adaptability of the process to volume output for the mass . production foundries is realized to the fullest extent in large continuous furnace installations, but batch furnaces are also used with great success. The liquid carburizing process depends on the carbon being supplied to the steel by cyanides dissolved in various liquid salts. This solvent is 390 WE AR RESIST ANCE ... usually a salt of barium, potassium, and/or sodium. The work is loaded in baskets or suspended from racks and lowered into this liquid bath. This method is usually used for the production of cases in the range of 0.030 to 0.100 inch in depth, although deeper cases may be produced. Liquid carburizing is quite flexible since different case depths can be obtained in the same furnace by varying the carburizing cycle. Similarly, a piece can be carburized selectively by immersing only the section to be carburized. Distortion tends to be less in liquid carburizing than in other processes. The toxic nature of the cyanides, the resulting disposal problem, and the danger of explosions from wet charges are disadvan- tages of the process. Nitriding Nitriding may be defined as "a process of case hardening in which a ferrous alloy is heated in an atmosphere of ammonia or in contact with nitrogenous material to produce surface hardening by the absorption of nitrogen, without quenching." Any steel that contains nitride forming elements such as chromium, molybdenum, vanadium, tungsten, or aluminum may be nitrided. The hardness of the case, how- ever, is a function of the amount and nature of the nitride forming elements present; while the depth of case decreases with increasing alloy contents. The compositions of steels commonly nitrided are given in Table 59. Nitriding has several advantages over other methods of case hardening. Practically no distortion or warpage of the casting occurs as a result of the low temperature used in nitriding and the elimination of the quenching treatment. Nitrided cases are much harder and retain their hardness at much higher temperatures than cases formed by other methods. Disadvantages of this process include the long treatment time usually employed, the close technical control required, and the precautions which must be observed in handling ammonia gas. Table 59—Typical Compositions of Cast Steels Surface Hardened by Nitriding STEEL C Cr Mo Ni Al 1 4140 0.35 -0.45 0.15 -0.30 - - 0.75 - 1.10 0.55 - 0.80 4340 0.35 -0.45 0.20 - 0.40 1.40 - 2.00 0.20 - 0.30 0.90 - 1.40 0.15 -0.25 0.85 - 1.20 0.30 - 0.40 0.90 - 1.40 0.15-0.25 0.85 - 1.20 Nitralloy 125 H Nitralloy 135 G Nitralloy 135 M Nitralloy N Nitralloy 230 0.38 - 0.45 1.40 - 1.80 0.30 - 0.45 0.85 - 1.20 0.20 -0.27 1.00 - 1.30 0.20 - 0.30 3.20 - 3.80 0.85 - 1.20 0.25 -0.35 1.00 - 1,50 0.15-0.25 - All Steels Contain 0.60 - 1.00 Mn and 0.30-0.60 Si Fig. 489—An austenitic manganese gyratory crusher mantle. SECTION IV Austenitic Manganese Cast Steel Austenitic manganese steel is sometimes referred to as Hadfield's manganese steel (after the name of the inventor, Sir Robert A. Had- field) and is also often spoken of as “high manganese steel.” It was the first alloy steel produced on a commercial scale. The composition of austenitic manganese steel as usually produced to A. S. T. M. Standard A 128 is within the following limits : Carbon, percent — 1.00 to 1.40 Manganese, percent - 10.00 to 14.00 Silicon, percent - 0.30 to 1.00 Sulfur, percent - 0.05 maximum Phosphorus, percent -- 0.10 maximum - Some producers keep the lower limit for manganese at 11 percent instead of 10 percent, as the steels containing less than 11 percent manganese - - - - Fig. 490 Large crusher jaws of cast austenitic manga- nese steel. Fig. 491-Line of 8 cubic foot buckets for a gold dredge cast of austenitic manganese steel. are somewhat lacking in ductility and strength unless other alloys such as chromium or molybdenum are present. The tendency is also to hold the carbon content to a maximum of 1.30 percent, as heavier castings containing a higher carbon content tend to crack in heat treatment. For most uses, an austenitic manganese steel with carbon content below 1 percent has no advantage over medium manganese steel having a man- ganese content of from 1.00 to 2.00 percent. No appreciable effect on the mechanical properties is observed from variations in silicon between 0.30 and 1.00 percent. Sulfur in manganese steel is always of little consequence because it is largely removed during steel making by the formation of manganese sulfide. The phosphorus content is dependent upon the purity of the ferro-manganese used. It is generally between 0.05 and 0.09 percent. j 3 Fig. 492 5-yard dipper for channel dredging made of austenitic manga. nese steel. WE AR RESISTANCE 393 . Wear . . . Austenitic manganese steel owes its power to resist severe abrasive wear to its characteristic of hardening by cold working to an extent approached by few other ferrous metals. The Brinell hardness of the steel in the quenched condition in which it is used is only moderately high (about 180 to 200). Under cold working the metal flows, but the resistance to further flow increases with additional cold working until the worked surface shows a hardness of from 450 to 550 Brinell. The rapidity with which this metal hardens under cold working of all kinds is extraordinary and is responsible for its ability to endure severe wear conditions coupled with heavy pressure or repeated impact. However, if the conditions of wear are such that cold working is largely absent so that the surface of the casting does not become hardened, then austenitic manganese steel will not outwear other metals. In fact, under certain conditions of erosive or metallic wear action, other wear resistant type alloy steels may be better. Hence the success or failure of a manganese steel part depends upon the wear service condi- tions it is called upon to handle. The shifting of a shovel or dredge from a a location where it is digging blasted rock or coarse gravel, to one where gritty loam of fine sand is to be moved, often results in an increase in the rate of wear of the manganese castings, because the impacts of rock or heavy gravel work harden the steel and increase the resistance to wear in a manner which is not possible when such castings are subjected to abrasion only. Additions of chromium in amounts up to approximately 2.0 percent are sometimes made to austenitic manganese steel of the usual analysis. Such additions increase resistance to abrasion in certain applications. However, this improved resistance is obtained at a sacrifice in toughness a and shock absorption capacity. Wear resistance data have been obtained by field tests on a jaw- crusher. The loss in weight of the moving jaw in a machine that crushes about 800 pounds of trap rock per day was used as a criterion of abrasive wear resistance, yielding values in Table 60. Table 60-Summary of Wear in Jaw-Crusher Service (Hall)6 Wear of Jaw Surface(a) Fixed Jaws Moving Jaws Cast Steel Austenitic Mn (1.21C, 11.9Mn, percent) Carbon Steel (0.50C, percent) Cr Steel (0.50C, 0.73Cr, percent) Ni Steel (0.24C, 3.63Ni, percent) Ni Steel (0.55C, 3.29 Ni, percent) Ni-Cr Steel (0.44C, 1.38Ni, 0.44Cr, percent) 0.072 to 0.191 0.95 0.72 0.58 0.43 0.41 0.086 to 0.124 1.07 0.82 0.47 0.48 0.39 (a) Grams per square inch per 1000 pounds of stone crushed. 394 WE AR RESISTANCE Somewhat similar service is typified by stamp-mill shoes. With operating conditions that include 1550 ft-lb blows at the rate of 100 per minute for a total of 21 million times, austenitic manganese steel out- wore by 25 percent the next best of 11 cast alloy steels. (7) Comparative tests on log washer lugs indicated that the manganese steel was about 25 percent worn out with no breakage, while white iron lugs of 450 BHN in the same period wore to the point of uselessness with 14 percent breakage. Also clay-crusher rolls of chilled iron were out- worn from two to three times. Cast iron grinding-barrel liners had a life of two to three years as compared with ten years for austenitic manganese steel.(7) Work hardening is a distinct advantage in metal-to-metal contact because it confers to the steel resistance to galling. Compressive loads, rather than impact, provide the work hardening required to produce a smooth, hard surface that has good resistance to wear but does not abrade the contacting part. Sheaves, and castings for railway track- work are common applications of austenitic manganese steel. Heat Treatment ... Austenitic manganese steel in the “as cast” state is quite brittle and the structure consists of austenite with considerable free carbide both in patches and in a network between the austenitic grains. The steel is strengthened and made tough by heating it to the range of 1830 to 1940 degrees F followed by water quenching. This treatment results in all the carbide being taken into solid solution when the composition of the steel is within the correct limits, producing a uniform austenitic structure and a high degree of strength and tough- ness. However, if the metal section is too thick or the carbon content too high, some carbide precipitation may take place during the cooling period, which will result in a decrease in the strength and ductility of the steel. The quenched steel is not tempered since if it is reheated to tempera- tures above 750 degrees F, it will become exceedingly brittle because of the precipitation of the carbide and the partial transformation of austenite. > An addition of from 3.0 to 5.0 percent nickel to the standard man- ganese steel composition, coupled with a reduction in the carbon content to below 0.80 percent makes it possible to obtain an austenitic structure in thin sections with only a normalizing treatment. Also, in the case of abnormally thick sections, a nickel addition retards phase transforma- tion during quenching. The shrinkage of manganese steel is greater than that of carbon steel by approximately 1/16 inch per foot for the same application, WE AR RESIST ANCE 395 hence, it is necessary that patterns be constructed accordingly. This fact, together with the combination of high thermal expansion, low thermal conductivity, low ductility in the as cast condition, and lack of opportunity for removing stresses by a thermal treatment, make it mandatory that customers consult with the producers of manganese cast steel in the proper design of the casting and pattern construction. Mechanical Properties ... The temperature at which manganese steel is poured has a marked effect upon the structure of the castings. The normal pouring range is 2650 to 2850 degrees F. A pouring tempera- ture higher than this range produces a coarse crystalline structure which is not refined in heat treatment, and produces a tensile strength of 15,000 to 20,000 pounds per square inch lower than the fine grained steel poured at lower temperatures. Depending upon the pouring temperature and the origin of the test piece, the mechanical properties of quenched austenitic manganese cast steel are as shown in Table 61. Table 61—The Mechanical Properties of Quenched Austenitic Manganese Cast Steel (Hall) 6 Mechanical Properties Cast to Size Ground from Coupon Tensile Strength, p.s.i. 80000-100000 118000a Proportional Limit, p.s.i. 42900b Elongation in 2", % 15-35 44.la Reduction of Area, % 15-35 39.0a Brinell Hardness Number 180-220 Bend (12" x 34" on 1" pin) degrees 180 Limit of Proportionality in Compression, p.s.i. 24000 Shear Strength (single shear), p.s.i. 84000 Fatigue Limit, p.s.i. 39000c -Average of 15 tests; b-Average of 5 tests; c-Determined with H. F. Moore Machine a-- Hundreds of laboratory tests on machine ground test specimens from cast coupons gave the following property values: Tensile Strength, p.s.i. 120000-130000 Elongation 2", percent 45.0-55.0 Reduction of Area, percent 35.0-45.0 Endurance Limit 0.34 x Tensile Strength Brinell Hardness No. 185 to 210 As Quenched Brinell Hardness No. 450 to 550 Work Hardened Charpy V-Notch Impact 70°F. 90 to 200 Other physical properties which have been determined on man- ganese cast steel are as follows: 396 WEAR RESISTANCE .286 pounds 2450°F. 71 microhms per cm-cube Weight per cubic inch Melting Point Electrical Resistance Thermal Conductivity (between 0-100°C.) Coefficient of thermal expansion (0-100°C.) (100-300°F) 0.027 cgs units 0.000018 in. per in. per degree C. 0.0000102 in. per in. per degree F. Magnetic Properties ... Austenitic manganese steel is virtually non- magnetic with a permeability of about 1.03 or less (H = 24). This per- mits use of the material where a strong, tough non-magnetic metal is required, as in magnet cover plates, traveling crane collector shoes, generator and motor stator core parts, liner plates for storage bins holding materials that are handled by lifting-magnets, magnetic separa- tor parts, instrument-testing devices, and parts in the magnetic field of electric furnaces. 2 Cast manganese steel is probably the most economical and strongest material for non-magnetic parts. The cost of production and a max- imum operating temperature of 500 degrees F should be considered in its selection. A modification of the nominal composition of high manganese steel for use in non-magnetic service, where machinability is desired, is a low carbon, lower manganese-nickel steel of the following composition: Carbon, percent Manganese, percent Nickel, percent 0.20 10.0 7.0 Machining ... Largely because it hardens under and in front of the tool, austenitic manganese steel is difficult to machine. Even the small- est amount of chatter of the tool on the casting results in the building up of extreme hardness at the point of contact, and in the dulling and rapid wear of the tool, with little effect on the casting. Machining must be carried on with cemented carbide tools, using heavy, rigid equipment and slow, steady feed. A well-equipped manganese steel machine shop, with a variety of specially adapted machines, is able to perform with grinding wheels a large part of the precision work which is done on more easily worked metals with ordinary machines and cutting tools. Boring, planing, keyway-cutting and similar operations are done efficiently by grinding. WE AR RESISTANCE 397 Welding ... The use of a welding rod of a composition identical to the austenitic manganese casting has never been satisfactory because the weld metal, when cold, is not fully austenitic but contains free carbide distributed through it. In addition, a weak zone is developed at the weld-cast metal interface because of grain coarsening. Austenitic manganese-nickel steel rod with a less than normal car- bon content will, with proper arc-welding technique, produce weld metal of an austenitic structure similar to that of the parent metal. The weld-rod contains from 3 to 5 percent nickel and 10 to 15 percent man- ganese, with carbon generally from 0.60 to 0.80 percent. Table 62 presents information on the welding of austenitic manganese steels. Table 62—Suitable Current Values for Welding Austenitic Manganese Steel (Avery and Day) 7 Diam. of Rod. In Bare Rod D.C. Amps Coated Rod D.C. Amps A.C. Amps - 1/8 5/32 3/16 1/4 80 - 100 80 - 125 110 - 150 135 - 160 75 - 90 85 - 110 100 - 130 110 - 140 80 - 100 90 - 125 110 - 150 135 - 160 - The adoption of the high manganese-nickel rods has resulted in making the fusion welding of austenitic manganese steel commercially successful and many difficult welds of worn and cracked parts are now giving satisfactory results in severe service. Pre-Peening and Explosive Hardening . . Manganese steel develops its full resistance to wear only after the surface layers have been de- formed by pressure, and therefore for some applications it is advanta- geous to perform this deformation artificially. This is especially desir- able when it is important that the initial shape of the piece be main- tained (for example in railway trackwork). In such cases, the part is finished to a little above the desired final dimensions by cold working and then ground to final size and the casting can be shipped in condition to give the best resistance to wear from the beginning of its installation, without becoming distorted in shape before developing its work hard- ened condition. Austenitic manganese steel, until recently, was always work hard- ened either by hammer action or pressing. A new process utilizing a a sheet explosive for work hardening is now also used. In this process, a shock wave generated from the detonation of a sheet explosive taped to the surface is passed through the casting at great speed. The pressure at the casting face and the stress set up in the casting work harden the surface, thus hardening it in the same manner as would hammering 398 WE AR RESISTANCE 48 44 40 D 36 HARDNESS , RC 32 28 B 24 A 114 1 20 12 3/4 142 2 DEPTH , INCHES Fig. 493—Hardness curves for explosive hardened austenitic manganese steel show pro gressively deeper hardening from A to D as single charges become heavier. Multiple shots will give steeper curves (increased surface hardness) without affecting depth of hardness (Harper)". or pressing. Several different hardness patterns are possible, as shown in Figure 493, depending upon the depth and degree of hardness desired. The two insert crossings shown in Figure 494 have been hardened with four different patterns, the areas subjected to the most severe field service having higher hardness and at greater depth. The darkest areas are dried adhesive which was not burned by the last explosion. Fig. 494 — Two insert crossings which have been explosive hard. ened. WE AR RESISTANCE 399 Applications of Austenitic Manganese Steel ... Castings of austenitic manganese steel are manufactured in all weights, from a few ounces to over 25,000 pounds. One of the large applications for manganese steel castings is in railroad equipment such as trackwork crossings, frogs, switches, guard rails and the like. The greatly lessened maintenance cost of high manganese steel castings in trackwork has been thoroughly proven in comparison with built-up rail members, and the toughness of the metal practically eliminates the hazard of sudden fracture. Austenitic manganese steel castings have long been standard for applications involving resistance to wear and breakage in the dredging, excavating, pulverizing and crushing industries where impact is en- countered. They are likewise used around blast furnaces, coke ovens, steel plants, cement mills, oils wells, and equipment for clay products, coal mining, foundry, glass, logging, and metal mining, sand pit, stone quarry and many other industries. REFERENCES > 1. Rosenberg, S. J., "The Resistance of Steel to Abrasion by Sand”, Trans. ASST, No. 18 (1930), p. 1093. 2. Rosenberg, S. J., “The Resistance to Wear of Carbon Steels”, Trans. ASST, No. 19 (1932), p. 247. 3. Norman, T. E., “Factors Influencing the Resistance of Steel Castings to High Stress Abrasion”, AFS Transactions, Vol. 66 (1958), pp. 187 - 196. 4. Bever, M. B., and Floe, C. F., “Case Hardening of Steel by Nitriding”, Surface Protection Against Wear and Corrosion (Chapter 8), ASM (1954). 5. Metals Handbook, American Society for Metals, 1948 Edition, pp. 647 - 651, 677 - 702. 6. Hall, J. H., “Wearing Tests on 12 Percent Manganese Steel”, Proc. ASTM 28, Part 2, pp. 326 - 331. 7. Avery, H. S., and Day, M. J., "Austenitic Manganese Steel”, Metals Handbook, 1948 Edition, American Society for Metals, pp. 526 - 534. 8. Harper, W. A., “Controlled Explosive Blasts Hardness Into Steel", Product Engineering (April 1959), pp. 62-63. CHAPTER XII CAST STEELS FOR LOW TEMPERATURE APPLICATION 1 Introduction Steel castings are often used in equipment subjected to temperatures below those considered normal. Such steels require certain properties not usually found in cast steel employed at atmospheric temperatures. Some mechanical properties of steel such as tensile strength, yield strength, and modulus of elasticity, increase as temperature decreases; therefore, these properties introduce no problems in most designs for low temperature service. Toughness, however, is often adversely af- fected by low temperatures. Certain types of wrought or cast steels possess high toughness values at extremely low temperatures, whereas other steels exhibit a brittle fracture at temperatures even above room temperature. The term "toughness” has been used and explained in a number of ways. It can be defined as the property determining the amount of en- ergy absorbed before fracture, and it thus involves both strength and ductility: Formulae expressing toughness have been devised which are based on tensile strength and ductility values. It is generally recognized that a test specimen containing a notch will give precise information regarding the fracture of steel. Among the number of tests which em- ploy a notch to determine toughness, the most widely used is the Charpy V-notch impact test.(1) Other reliable tests are the crack propagation test (discussed in Chapter IX) and the drop weight test.(2) This chapter will be presented in two parts. Section I will discuss the various factors influencing the low temperature impact resistance of cast steels. Section II will present low temperature test data for many of the cast steels commonly produced. The steel grades will not be limited merely to those cast steels which are classified by the American Society for Testing Materials as “suitable for pressure containing parts for low temperature," but will also include carbon and other alloy steels. The reader should be cautioned as to his interpretation of the test data since they are not meant to convey the idea that the type of steel with the lowest transition temperature is the best for any particular low temperature application. There are many other mechanical and economic variables which must be considered in the production of steel castings. The customer should be aware of the fact that low temperature properties can be met with any of several types of steels and, in the interest of economy, the steel casting producer should be free to choose the grade which will meet the specified mechanical properties. LOW TEMPERATURE USE 401 SECTION I Factors Affecting Low Temperature Impact Resistance Tensile testing has proven inadequate in determining the service characteristics of steel castings at low temperatures. For this reason, low temperature impact tests have been devised to simulate actual serv- ice conditions under which fracture may occur. It is well known that all metals show some loss of ductility at low temperatures. Metals which crystallize in body-centered cubic systems, such as ferritic, pearlitic and martensitic materials, possess what is referred to as a transition tem- perature illustrated by Figure 495. Above the transition temperature range, the test fractures are essentially ductile; below this narrow range of temperatures, they are brittle. Tough Transition Zone Energy Absorbed in Rupture Brittle Temperature Fig. 495—Typical curve of impact value vs. testing temperature for steel, showing transition zone between brittle and ductile fracture. The transition zone varies in different steels, or even in the same steel, between temperatures as low as ---350 degrees F and as high as 150 degrees F. Many factors influence the position of the transition zone; and the major ones are severity and type of notch, heat treatment, chemical analysis, melting and deoxidation practice. Each of these basic factors will be discussed further. Effect of Notch Type ... In recent years, it has been determined that the principal feature of the impact test is the presence of the notch. Studies on the mode of brittle test fracture(2,3,4,5) have shown that the actual failure of structural steel at low temperatures is intimately re- lated to the presence of a notch which initiates and propagates a crack. The ability of a steel to resist crack propagation or to absorb impact in the presence of a notch, without failure, is termed the "notch toughness” of the steel. 402 LOW TEMPERATURE USE The sharpness of the notch is of prime importance in determining the toughness of the steel. A sharp notch will result in cleavage rather than in a shear type of fracture below the transition temperature. The effect of notch sharpness is shown in Figure 496. Since cleavage 120 80 Rodius: 01 .025 .03.05 .009 .O 28° 40 0 Fig. 496 Elfect of notch sharpness on the impact properties of a carbon steel (top) and a nickel steel (bottom). (Armstrong and Gag nebinje Chorny mooct, F.Iba 120147 80 Rodius: 18 .025 .033) .Q25.018 1.009" 3/16 40 11 0 -310-280 -240 -200 -80 -40 0 -160 -120 Temperature, F. cracks rather than shear cracks are of major concern in brittle failure, the Charpy V-notch (0.010-inch radius) impact specimen is a more sensitive test than the keyhole notch specimen for determining the low temperature toughness and transition temperature. These two types of specimens are illustrated in Figure 497. 2.165": 0.010 L * L SAW CUT SIKK OR LESS 0.39407 +0.001 * * 0.079" T 0.197" * 0.001 K. + CHARPY IMPACT SPECIMEN KEYHOLE NOTCH 0.394": 0.001 2.165": 0.010 L L 45° 1° -0.010 RADIUS 0.394" +0.001 T 0.315" : 0.001 CHARPY IMPACT SPECIMEN "V" NOTCH 0.3947 0.001 Fig. 497—Charpy keyhole notch and Charpy V-notch test specimens. LOW TEMPERATURE USE 403 50 KEYHOLE NOTCH 80 '1015 V-NOTCH KEYHOLE NOTCH 70 1030 60 - 1040 30 - CHARPY IMPACT, F1.- Los. CHARPY KEYHOLE IMPACT, Ft.-LBS. QUENCHED AND TEMPERED HO 30 20 10 NORMALIZED AND TEMPERED 10 A 1650 N1650 T.1275 WQ1550 T./100 OSSION T1275 100 -200 -150 -100 - 50 + 50 TEMPERATURE, F HEAT TREATMENT Fig. 498—Transition curves for a Cr-Mo cast steel showing the effect of the type of specimen used. Fig. 499—Effect of heat treatment on Charpy impact values of carbon cast steels at room temperature. The transition curve obtained with the V-notch impact specimen illustrates a much more clearly defined transition zone than that obtain- able with the keyhole specimen. In general, the V-notch specimen gives slightly lower impact values at lower temperatures, and higher values at higher temperatures. No valid conversion between the two types of test values is possible. Figure 498 illustrates the transition curve ob- tained with each type of specimen in the low temperature testing of a chromium-molybdenum cast steel. This is typical of the relationship between the two test methods. The sharper the notch, the greater the stress concentration factors. Some current specifications require the keyhole specimen, others the V-notch; but it appears likely that the future will see a change to an exclusive use of the V-notch. Accordingly, V-notch data will be presented except when they are not available to illustrate a particular point. Effect of Heat Treatment ... Heat treatment plays just as important a part in obtaining toughness and low transition temperatures as it does in tensile testing. Any given steel develops its highest toughness when in the quenched and tempered condition. A normalize and temper treatment, while giving lower values than obtained with a quench and temper heat treatment, gives higher impact values than an annealing treatment. Figure 499 shows this variation of Charpy keyhole im- 404 LOW TEMPERATURE USE pact values with heat treatment for three carbon steels. These data are typical of the heat treatment results which would be obtained with any other carbon or low-alloy steel. Care must be used in the selection of a tempering temperature in order to avoid temper brittleness. Most steels have a temper embrittle- ment range somewhere between 500 to 950 degrees F, depending upon the steel's composition. Tempering at embrittling temperatures will move the steel's transition zone to a higher temperature, thus reducing its toughness. The effect of heat treatment will be further illustrated for various steels in Section II of this chapter. Effect of Steel Composition ... The chemical content is a major vari- able in the control of the low temperature impact resistance of steel castings. The alloying elements in steel exert their influence on low temperature impact properties primarily through their effect on the properties of the ferrite matrix. In general, the low-alloy steels of suitable heat treatment have lower transition temperatures than the carbon steels and are, therefore, more suitable for low temperature applications. The general effect of the common alloying elements on the transition temperature of a low carbon steel is shown in Figure 500. Carbon and silicon are seen to have an adverse effect upon low temperature impact properties while chromium, nickel, and manga- nese are beneficial in the range shown. 6 1 Carbon, more than any other element, exerts an adverse effect upon low temperature impact resistance, raising the transition temperature +300 C +200 Si +100 CHANGE IN TRANSITION TEMPERATURE, o С. -100 No MN -200 1.5 0.5 1.0 PERCENT ALLOYING ELEMENT Fig. 500–General effect of various alloying elements on the V-notch transition temperature of low carbon steel. LOW TEMPERATURE USE 405 3 nearly 4 degrees F for each 0.01 percent increase in carbon content. Other things being equal therefore, the lower the carbon content, the lower the transition temperature. Silicon is beneficial in quantities less than 0.30 percent; in larger quantities, however, it is detrimental to low temperature impact properties. Moderately low chromium contents (below about 4 percent) have only a slightly beneficial effect. Ferritic chromium steels of 4 to 6 percent chromium are rapidly embrittled riti decreasing temperatures. The simultaneous presence of high nickel will tend to form stable austenitic structures which are not embrittled. Manganese, in contents up to about 1.5 percent, has a highly beneficial effect on the transition temperature. However, manganese contents greater than 1.5 percent are detrimental to low temperature impact properties. Nickel is the alloying element which is most generally used to control low temperature impact resistance. When the nickel content of steel exceeds about 3 percent, room temperature toughness is slightly diminished; but low temperature toughness continues to increase. The effect of nickel content on the low temperature impact resistance of low carbon steels is shown in Figure 501. Temperature - Degrees Centigrade -150 -100 -50 -200 70 0 60 50 40 Charpy Impact - Ft. Lb. 13% Ni. 30 872% Ni. 20 ♡ 2% Ni. 0% Ni. 5% Ni. 312% Ni. 10 -300 -200 -100 0 +100 Temperature - Degrees Fahrenheit Fig. 501-Effect of nickel content on impact resistance of normalized low carbon steels (key. hole notch). All steels contain 0.10 percent carbon except the 0 percent Ni and 2.0 percent Ni which contain 0.20 and 0.15 percent C respectively. (Nickel Alloy Steels)? 406 LOW TEMPERATURE USE ! Other elements, in addition to those mentioned above, are usually present in the steel as residual elements. These would include sulfur, phosphorus, copper, aluminum, vanadium, titanium, molybdenum and dissolved gases such as oxygen, nitrogen and hydrogen. Sulfur and phosphorus in excess of 0.025 percent, and the dissolved gases are highly deleterious to low temperature toughness. The other elements are not harmful if present in small amounts, for some of them refine the grain size and deoxidize the steel, and are purposely added. However, in larger amounts they may be detrimental. Effect of Deoxidation Practice ... Deoxidation of cast steel improves low temperature impact resistance in three ways: (1) by tying up the free oxygen and thus preventing porosity; (2) by promoting a globular, or crystalline, type rather than the stringer type of sulfide inclusion; (3) by refining the grain size. Figure 502 shows the effect of deoxida- tion practice on the low temperature impact resistance of a quenched and tempered Mn-Mo cast steel. The results are typical of those which would be obtained for almost any steel. Aluminum deoxidation is at present the practice most widely em- ployed (manganese and silicon are added to the melt prior to the alu- minum in most cases). Aluminum, when added in the proper quantities, will promote the formation of angular crystalline type inclusions, thus enhancing toughness at all temperatures. An excess amount of alumi- num, especially in the presence of high nitrogen, results in very low impact properties because of the formation of aluminum nitrides in the 35 30 DEOX I DATION ; 1-de, 2 Lo/TON 2- NONE 3- Ab, 6 Lo/TON 80 1030 CARSON CAST STEEL 25 20 CHARPY V-NOTCH IMPACT, Ft-los 2 CHARPY V-Norcm IMPACT, FT.-Lo. 1 1 - 75 + 75 100 + 100 - 200 - 150 - 100 - 50 o + 50 TEMPERATURE, :F Fig. 502—Effect of deoxidation on the V. notch impact resistance of a quenched and tempered Mn-Mo cast steel. (C 0.33, Mn 1.38, Mo 0.29) -50 - 25 + 25 +50 TESTING TEMPERATURE , 'F Fig. 503—Charpy V-notch impact vs. testing temperature for a carbon cast steel given various heat treatments (Q + T = quenched and tempered, N = normalized, A = nealed). LOW TEMPERATURE USE 407 grain boundaries which, in turn, lead to intergranular or “rock candy" fractures. Other Factors Affecting Low Temperature Impact ... The low temper- ature impact resistance of steel is also affected by such factors as grain size, hardness, and section size. Finer grained steels are tougher in low temperature service than are the coarse grained steels. Aluminum is a grain refiner and its use as a deoxidizer usually assures a fine grained structure. There is a relationship between hardness (tensile strength) and impact resistance, as may be seen in Figures 441 and 442 (see Chapter X). In general, high hardness results in lower impact resist- ance for a given composition and heat treatment, but related factors such as micro-structure and deoxidation tend to obscure this relation- ship. Section size has an indirect effect on low temperature impact re- sistance due to its effect upon hardenability. A larger section size makes it more difficult to attain a fully martensitic structure or heat treat- ment; hence toughness is impaired. Additional alloys, such as manga- nese, chromium, nickel, molybdenum or boron are required to produce a fully hardened section as the section increases in thickness. . SECTION II Low Temperature Impact Data for Various Cast Steels Present specifications(8) for steel castings for use at low tempera- tures are inadequate in many respects. Steel casting specifications are often restrictive because chemical requirements are included in addition to mechanical properties. This is an unfortunate situation for both the customer and the manufacturer, which ultimately results in higher costs. Most specified mechanical properties can be met by a number of the compositions produced daily in steel foundries throughout the country without special analysis requirements being necessary. This section will present low temperature impact data, as deter- mined from fully hardened test bars, for the cast steels which are most commonly produced in steel foundries. The reader should use discretion in his interpretation of these data. The data for the various steels should not be interpreted to mean that any specific type of steel is better than any other for all low temperature applications. Figure 503 presents data for a 1030 carbon cast steel. In general, plain carbon steels are not used in applications requiring a high degree of impact resistance. Data for three steels containing only one alloying element are presented in Figure 504. Note the improvement over plain carbon steels which is obtainable by the addition of an alloying element. 408 LOW TEMPERATURE USE 60 50 MEDIUM MANGANESE (1330) CAST STEEL 40 Q-T N+T 30 20 10 50 NICKEL (2330) CAST STEEL 40 CHARPY. V-NOTCH IMPACT, F7.-18. 30 Q+7 20 Net N - 50 40 MOLYBDENUM (4030) CAST STEEL 30 Q+T N+T 20 10 - 0 - 200 - 100 0 +100 TESTING TEMPERATURE , °F Fig. 504—Charpy V-notch impact vs. testing temperature for three single alloy cast steels IQ + T = quenched and tempered, N + 1 = normalized and tempered, N = normalized). LOW TEMPERATURE USE 409 a Data for a Ni-Mo (4630) and a Cr-Ni (3130) cast steel are presented in Figures 505 and 506, respectively. Figure 507 illustrates low tem- perature impact data for two popular Cr-Mo cast steels. The Cr-Mo steel of the lower graph has found wide use in the production of armor castings tested at -40 degrees F. Figure 508 presents impact data for two Mn-Mo cast steels. 50 50 Ni-Mo (4630) CAST STEEL Cr-Ni (3730) CAST STEEL 40 40 30 QrT CHARPY V-NOTCH IMPACT, Fr.-LB. Q-T CHARPY V-NOTCH IMPACT, Fr.-Le. N-T 10 10 N+T 0 +100 + 100 - 200 -100 TESTING TEMPERATURE, F -200 -100 TESTING TEMPERATURE , °F Fig. 505—Charpy V-notch impact vs. testing temperature for Ni-Mo (4630) cast steel (Q + T = quenched and tempered, N + T normalized and tempered). Fig. 506-Charpy V-notch impact vs. testing temperature for Cr-Ni (3130) cast steel (Q + T = quenched and tempered, N + T normalized and tempered). 80 CR-MO (4130) CAST STEEL 70 ;;! 60 Q+T 50 40 30 - N+T CHARPY V- Notch IMPACT, Ft.-Le. 20H Fig. 507 Charpy V-notch impact vs. testing tempera- ture for two Cr-Mo (4130 and 3.0% Cr, 0.50% Mo) cast steels (Q + T quenched and tempered, N + T : normalized and tempered, N normalized). 70 60 Cr-Mo (0.30 % C) CAST STEEL CR : 3.0 % Mo :0.50 % QrT BHN- 250 -250 50 Q-T BHN = 300 40 30 +100 - 200 -100 o TESTING TEMPERATURE, °F 410 LOW TEMPERATURE USE Fig. 508 Charpy V-notch impact vs. testing tempera- ture for two Mn-Mo cast steels (Q + T = quenched and tempered, N + T normalized and tempered). CHARPY V-NOTCH IMPACT, FT. -Le 80 70 MN - MO (8023) CAST STEEL 60 50 Q+T 40 30 N+T 20 10 0 60 MN-MO (8430) CAST STEEL 50 MN : 1.35 - 1.75 % 40 MO : 0.25 - 0.55 % 30 Q+T- 20 RN+T 10 0 -250 -200 -150 -100 -50 0 +50 +100 TESTING TEMPERATURE, OF 40 Ni - CR-MO (4330) CAST STEEL 30 20 Q+T RN+T 9 CHARPY V-NOTCH IMPACT, FT.-18. 50 Ni-CR-MO (8640) CAST STEEL Fig. 509 Charpy V-notch impact vs. testing tempera- ture for two Ni-Cr-Mo cast steels (Q + T = quenched and tempered, N + T normalized and tempered). 40 30 -Q+T 20 *N+T 10 0 -250-200 -150 -100 -50 0 +50 +100 TESTING TEMPERATURE, OF LOW TEMPERATURE USE 411 Transition curves for three popular three-way low-alloy cast steels are shown in Figures 509 and 510. Impact data for a four-way Mn- Ni-Cr-Mo steel are shown in Figure 511. Figure 512 illustrates data for copper containing cast steels. Cop- per as an alloying element is seen to have virtually no effect on low temperature impact resistance. 50 40 MN - CR -MO CAST STEEL C:.31% MN: 1.61% CR: .59% MO: .56% RQ + T BHN: 250 30 CHARPY V•NOTCH IMPACT, FT.-28. 20 10 N+T -200 -100 0 +100 TESTING TEMPERATURE, OF Fig. 510_Charpy V-notch impact vs. testing temperature for Mn-Cr-Mo cast steels (Q + T = quenched and tempered, N + T normalized and tempered). 80 70 60 1 MN - Ni - CR -MO CAST STEEL C: .27 % MN: 1.00 % KBHN-220 Ni : 1.00% CR : 1,12 % MO :..48% QUENCHED AND TEMPERED KBHN - 250 50 I CHARPY V•NOTCH IMPACT, FT.-28. 40 - Fig. 511 Charpy V-notch impact vs. testing tempera. ture for Mn-Ni-Cr-Mo cast steel in the quenched and tempered condition. 30 KBHN-320 20 10 0 -200 -100 0 TESTING TEMPERATURE, OF +100 412 LOW TEMPERATURE USE 40 Cu-MN-SI CAST STEEL C: 0.20 % Cu: 1,80 % MN:1.00 % Si:1.00 % 30 CHARPY V-NOTCH IMPACT, FT.-L8. N+T 10 N+A . 1 1 0 -150 -100 -50 o +50 +100 TESTING TEMPERATURE, F Fig. 512—Charpy V-notch impact vs. testing temperature for Cu-Mn-Si cast steel (Q + T quenched and tempered; N + T = normalized and tempered, N + A = normalized and aged). High-alloy steels, because of their austenitic structures, find wide use in applications requiring high impact resistance at extremely low temperatures. Figure 513 shows data for a relatively new type of high-alloy cast steel. The microstructure of this 9 percent nickel steel is a mixture of ferrite and austenite which provides good toughness 80 70 9.00 % Ni CAST STEEL AIR COOLED 60 0.15%C 50 CHARPY V-NOTCH IMPACT, FT.-LB. 40 30 R 0.15%C 0.30% MO 20 0 -300 -200 -100 0 +100 TESTING TEMPERATURE, OF Fig. 513—Charpy V-notch impact vs. testing temperature for 9. percent nickel cast steel. (Elman and Diran) LOW TEMPERATURE USE 413 180 AUSTENITIC 18.8 CR - Ni 160 CAST STEEL (CF-8) HEAT TREATMENT : 140 2050 °F, W.Q. 120 -V: NOTCH $100 - CHARPY IMPACT, FT. •LB. 80 60 40 - -KEYHOLE NOTCH 20 0 -400 -300 -200 -100 0 +100 TESTING TEMPERATURE, OF Fig. 514_Charpy V-notch and keyhole impact vs. testing temperature for CF-8 austenitic 18-8 Cr-Ni cast steel. Carbon 0.08 percent maximum. properties. Figure 514 presents data for CF-8 Cr-Ni high alloy steel. This steel, when water quenched, is characterized by an austenitic structure which permits it to retain high impact resistance at extremely low temperatures. im Fig. 515 — Com- pressor made from steel cast- ings for produc- ing ethylene by low temperature, high pressure fractionation. 414 LOW TEMPERATURE USE APPLICATIONS Steel castings for low temperature applications are used by the oil refining and chemical industries under various pressure conditions, which may range from extremely high to nominal. The castings most commonly employed in this service include valves, flanges, fittings and 30 NOS 72 DD 343 -12 INCHES Fig. 516—Valve body suitable for handling liquids at -50 degrees F. RENESA Fig. 517—The top halves of two different size casings which are a part of a six stage pressure pump for handling liquids at operating temperatures below minus 100 degrees F. LOW TEMPERATURE USE 415 pumps. Figures 515 through 517 show typical castings which are regularly produced and in daily use under low temperature operating conditions. Also, steel castings are employed in equipment that operates in cold climates and cold environments such as castings in aircraft, ordnance equipment, hydroelectric and mining equipment, railroad and ship cast- ings, and components for low temperature test equipment. REFERENCES 1. ASTM, “Notched Bar Impact Testing of Metallic Materials”, ASTM Standards, (1958). 2. Pellini, W. S., Brandt, F. A., and Layne, E. E., "Performance of Cast and Rolled Steels in Relationship to the Problem of Brittle Fracture", AFS Transac- tions, Vol. 61 (1953) pp. 243-262. 3. Pellini, W. S., “Evaluation of the Significance of Charpy Tests”, ASTM Special Technical Publication No. 158 (1954), pp. 216-258. 4. Puzak, P. P., Babecki, A. J., and Pellini, W. S., “Correlations of Brittle-Fracture Service Failures with Laboratory Notch-Ductility Tests”, Welding Research Supplement (September, 1958), pp. 391-410. 5. Puzak, P. P., Schuster, M. E., and Pellini, W. S., “Crack-Starter Tests of Ship Fracture and Project Steels”, Welding Research Supplement (October, 1954), pp. 481-495. 6. Armstrong, T. N. and Gagnebin, A. P., "Impact Properties of Some Low Alloy Nickel Steels at Temperatures Down to 200 degrees Fahr.”, ASM Transactions, Vol. 28 (1940), pp. 1-20. 7. Nickel Alloy Steels, International Nickel Co., New York (1949). 8. ASTM Specification A352-58T, Tentative Specifications for Ferritic Steel Cast- ings for Pressure Containing Parts Suitable for Low Temperature Service. 9. Elman, I. B. and Diran, L. M., “Cast Nine Percent Nickel High Strength Steel for Low Temperature Service", International Nickel Company, Technical Paper 246 (1957). CHAPTER XIII CAST STEELS FOR HIGH TEMPERATURE AND HEAT RESISTANT APPLICATIONS 1 Steel castings have an extensive field of application in equipment designed for high temperature service. Steels for such castings are, for the most part, of alloy compositions and properties differing from the grades presented in Chapter X, since it is imperative that they possess excellent resistance to creep, coupled with high strength prop- erties at service temperatures. Additionally, they must resist scaling and formation of graphite flakes, which often develop in standard compositions upon continuous use at elevated temperatures. The cast steels under consideration in this chapter are divided into two groups: cast steels for service up to 1150 degrees F, and cast steels for service above 1150 degrees F. The first group will include the low-alloy, ferritic grades, and the second will include only the high-alloy grades. > SECTION I Cast Steels for Service up to 1150 Degrees F Composition ... The American Society for Testing Materials has form- ulated three sets of specifications covering basic types of ferritic cast steels suitable for pressure-containing parts operating at elevated temperatures. These grades, along with their chemical requirements, are listed in Table 63. Selection of the proper grade will depend on design and service conditions as related to mechanical properties, and the high temperature and corrosion resistant characteristics. Large tonnages of these steels are in commercial use, operating under stress at elevated temperatures where creep is involved. The creep strength of plain carbon steel can be greatly improved by the addition of certain alloying elements which increase the recrystalliza- tion temperature and form stable carbides or intermetallic compounds. Molybdenum is the most potent alloying element now in use for im- proving the creep resistance of cast steel; and its effect is shown in Figure 518. Small additions of chromium do not appear to improve the creep strength of plain molybdenum steels, and higher additions actually decrease the strength. Notwithstanding, chromium is needed for surface protection, and protection against graphite formation, at temperatures of around 900 degrees F and higher. HIGH TEMPERATURE USE 417 Table 63—Chemical Requirements for Standard Ferritic Heat Resistant Grades of Cast Steel Chemical Analysis, Percent Specifi- С cation Grade Max. P S Si Max. Max. Max. Mn Ni Cr Mo V - A217- 59T .70-1.10 .60-1.00 WC1 0.25 .50-.80 0.05 0.06 0.60 WC4 0.20 .50-.80 0.05 0.06 0.60 WC5 0.20 .40-.70 0.05 0.06 0.60 WC6 0.20 .50-.80 0.05 0.06 0.60 WC9 0.18 .40-.70 0.05 0.06 0.60 C5 0.20 .40-.70 0.05 0.06 0.75 C12 0.20 .35-.65 0.05 0.06 1.00 .45- .65 .50- .80 .45- .65 .50- .90 .90-1.20 1.00- 1.50 .45- .65 2.00- 2.75 .90-1.20 4.00- 6.50 .45- .65 8.00-10.00 .90-1.20 A356- 58T .15-.25 1 2 3 4 5 6 7 8 9 10 0.35 0.70 0.05 0.05 0.60 0.25 0.70 0.05 0.05 0.60 0.25 .50-.80 0.05 0.05 0.60 0.20 .50-.80 0.05 0.05 0.60 0.25 0.70 0.05 0.05 0.60 0.20 .50-.80 0.05 0.05 0.60 0.20 .50-.80 0.05 0.05 0.60 0.25 .50-.80 0.05 0.05 0.60 0.20 .50-.80 0.05 0.05 0.60 0.20 .50-.80 0.05 0.05 0.60 .40- .60 .90-1.20 .90-1.20 .40- .70 .40- .60 1.00- 1.50 40- .60 1.00- 1.50 40- .60 1.00- 1.50 .90-1.20 1.00- 1.50 .90-1.20 2.00- 2.75 .90-1.20 .15-.25 .15-.25 A389- 59T C23 0.20 .30-.80 0.05 C24 0.20 .30-.80 0.05 0.06 0.60 0.06 0.60 1.00- 1.50 .45- .65 .15-.25 .80- 1.25 .90-1.20 .15-.25 20 NORMALIZED 15 CREEP STRENGTH, 1000.psi 10 NORMALIZED AND TEMPERED 55 2.5 0.5 1.0 1.5 2.0 MOLYBDENUM CONTENT, % Fig. 518—Effect of Molybdenum content on creep strength (stress for a creep rate of 1 percent per 10,000 hours) of molybdenum steel at 1000 degrees F. (Weaver)' 418 HIGH TEMPERATURE USE Carbon is beneficial in amounts up to about 0.15 or 0.20 percent; above this amount, increase of the carbon content results in a decrease in creep strength. Vanadium, when used in small quantities, acts in a manner similar to molybdenum. Tungsten, titanium, and columbium are moderately beneficial in improving high-temperature strength. although they are not widely used in this country. The influence of manganese, nickel, copper, and silicon is mild while aluminum de- creases creep strength. Mechanical Properties ... Table 64 shows the tensile requirements for the standard grades listed in Table 63. Creep... Creep data for cast steels are widely dispersed throughout the literature, and Table 66 is a compilation of all the data available on the standard grades at this time. Table 65 is a compilation of creep data for various other types of cast steels. The creep resistance of cast and wrought steels of corresponding composition and grain size is similar and, in the absence of creep data for cast steel, wrought steel data may be used. A comparison Table 64—Tensile Requirements for Standard Ferritic Heat Resistant Grades of Cast Steel Tensile Requirements Tensile Yield Strength Strength Elongation Red. of Area psi min. psi min. % min. % min. Specification Grade A217-59T 35 35 35 35 35 35 A356-58T WC1 WC4 WC5 WC6 WC9 C5 C12 1 2 3 4 5 6 7 8 9 10 C23 C24 65,000 70,000 70,000 70,000 70,000 90,000 90,000 70,000 65,000 80,000 90,000 70,000 70,000 70,000 80,000 95,000 85,030 70,000 80,000 35,000 40,000 40,000 40,000 40,000 60,000 60,000 36,000 35,000 50,000 60,000 40,000 45,000 40,000 50,000 60,000 55,000 40,000 50,000 24 20 20 20 20 18 18 20 22 18 16 22 22 22 18 15 20 18 15 35 35 35 35 35 35 35 35 35 35 35 35 35 A389-59T HIGH TEMPERATURE USE 419 Table 65—Creep Data for Various Types of Cast Steels. (Data from various sources) Alloying Elements Room Temperature Properties Creep Strength Cr С % Ni % Mn % Μο % T.S. psi Y.S. psi Elong. % R.A. % Stress in psi for 0.1% Elong. - 1000 Hr Heat 800°F. 900°F. 1000°F. 1200°F. Treatment % 3,200 0.66 97,000 59,000 26 56 2.08 2.03 1.77 2.11 2.00 1.15 7,000 9,500 15,000 15,000 17,000 18,000 28,000 0.77 0.66 0.65 0.80 112,000 106,000 95,000 84,000 72,000 65,000 19 20 22 45 42 0.40 0.28 0.40 0.35 0.28 0.32 0.32 0.28 0.24 0.31 0.23 0.35 0.28 0.31 0.34 0.30 0.28 0.12 8,000 7,000 7,000 9,500 6,000 9,200 15,000 12,500 51,000 36,000 40,000 32,000 49,000 52,000 23,000 20,000 19,000 0.82 0.92 0.35 0.32 0.45 0.35 0.43 0.31 0.43 0.58 0.50 0.53 0.50 0.40 0.50 1.50 1.35 1.10 1.38 1.20 1.01 89,000 72,000 Ann. N-D 1275 N-D 1300 N-D N-D N-D N-D N-D 1000 ? ? ? ? ? N-D 1300 Ann. ? ? ? | | | ខ ន ន | | ន ទ | | ទ ន ន ន ន 51,000 40,000 22 30 一​加​一一​归​纪​田​一一​团​红​一二​组​%如​如 ​31 41 1.13 2.00 4.86 5,400 7,100 10,000 1,300 118,000 84,000 105,000 85,000 80,000 17 26 21 2.00 90,000 41,000 75,000 60,000 50,000 0.80 2.00 9.00 35,700 16,000 18,000 16,000 10,700 16,000 24,700 44 38 40 40 50 28,500 17,900 16,800 4,700 7,100 5,800 1,000 1,350 1,600 I 1 25 1 0 1 At 850° F. · Values for these steels are for .01% elongation in 1000 hours. 2 420 HIGH TEMPERATURE USE Table 66—Creep Properties of Standard Ferritic Heat Resistant Grades of Cast Steel (Data from various sources) Specification Grade A 217-59T WC 1 Stress Required For 1% Elongation in 10,000 Hr. 1000°F. 14,300 psi 1% Elongation in 100,000 Hr. 1000°F. 7,100 psi WC 4 .01%. Elongation in 1000 Hr. 800°F. 15,500 psi 900°F. 9,400 psi 1000°F. 3,600 psi 1200°F 450 psi 1% Elongation in 10,000 Hr. 900°F. 32,000 psi 950°F. 25,000 psi 1000°F. 12,400 psi 0.1% Elongation in 10,000 Hr. 1050°F. 6,000 psi 1100°F. 4,800 psi 1% Elongation in 10,000 Hr. 1000°F. 10,000 psi 1200°F. 2,000 psi 1% Elongation in 100,000 Hr. 900°F. 22,000 psi 950°F. 10,000 psi 1000°F. 5,000 psi WC 5 WC 6 WC 9 C 5 1% Elongation in 100,000 Hr. 1000°F. 7,300 psi 1050°F. 4,500 psi 1200°F. 1,000 psi 1% Elongation in 10,000 Hr. 1000°F. 12,000 psi 1100°F. 7,600 psi 0.1% Elongation in 10,000 Hr. 900°F. 14,000 psi 1000°F. 6,700 psi 1100°F. 3,100 psi 1200°F. 1,500 psi 1% Elongation in 10,000 Hr. 950°F. 30,500 psi 1100°F. 9,000 psi 1200°F. 3,700 psi 0.1% Elongation in 1000 Hr. 850°F. 45,000 psi 1000°F. 14,200 psi .01% Elongation in 1000 Hr. 800°F. 21,000 psi 900°F. 14,700 psi 1000°F. 6,100 psi 1200°F. 1,100 psi 0.1% Elongation in 10,000 Hr. 900°F. 24,000 psi 1000°F. 8,500 psi 1100°F. 3,700 psi 1200°F. 1,600 psi 1% Elongation in 10,000 Hr. 850°F. 35,000 psi 1000°F. 16,000 psi C 12 1% Elongation in 100,000 Hr. 950°F. 14,000 psi 1100°F. 3,800 psi 1200°F. 2,000 psi HIGH TEMPERATURE 421 USE Table 66—(Continued) Specification Grade A 356-58T 1 Stress Required For 0.1% Elongation in 10.000 Hr. 8'0°F. 12,000 psi 000°F. 4,500 psi 1000°F. 1,800 psi 1% Elongation in 10 000 Hr. 800°F. 16 000 psi 000°F. 6,000 psi 1000°F. 5,200 psi .01% Elongation in 1000 Hr. 800°F. 9,350 psi 000°F. 4,600 psi 1000°F. 2,200 psi 1200°F. 400 psi Same as WC 1 .01% Elongation in 1000 Hr. 800°F. 21,000 psi 900°F. 12,000 psi 2 3 1% Elongation in 1000 Hr. 900°F. 43,000 psi 4 0.1% Elongation in 1000 Hr. 800°F. 28,000 psi 900°F. 20,800 psi 1000°F. 11,200 psi 1% Elongation in 100,000 Hr. 850°F. 11,000 psi 1000°F. 3,000 psi 1% Elongation in 100,000 Hr. 17,000 psi 1000°F. 5,000 psi 5 900°F. 6 7 0.1% Elongation in 100,000 Hr. 850°F. 8,000 psi 1000°F. 1,000 psi 0.1% Elongation in 100,000 Hr. 900°F. 15,000 psi 1000°F. 8,000 psi Same as WC 6 1% Elongation in 10,000 Hr. 800°F. 44,000 psi 1000°F. 20,000 psi 1100°F. 10,000 psi 1200°F. 3,000 psi 1% Elongation in 1000 Hr. 1000°F. 28,000 psi 1% Elongation in 1000 Hr. 1050°F. 33,000 psi 1% Elongation in 100,000 Hr. 800°F. 26,000 psi 1000°F. 10,000 psi 1100°F. 5,000 psi 1200°F. 2,300 psi 9 1% Elongation in 10,000 Hr. 1050°F. 27,000 psi 10 Same as WC 9 A 389-59T C 23 Same as 7 C 24 Same as 9 422 HIGH TEMPERATURE USE 800°F 10,000 LBS. PER SQ. IN. 0.0010 CAST NI/NI FORGED 0 0.0120 (1.2%) 800°F 20,000 LBS. PER. SQ. IN. Fig. 519–Creep-time curves for 0.29 percent carbon cast steel. Comparison of full annealed cast steel with full annealed forged steel of a split heat. CREEP STRAIN, 0.0080 (0.8%) CAST FORGED 0.0040 (0.4%) 04 0 40 10 20 30 TIME, DAYS 240 480 720 TIME, HOURS 0 960 between the creep properties of a cast and a wrought steel is shown in Figure 519. Tests were made on a split heat of 0.20 percent carbon cast steel, part of which was tested full annealed, the other part being forged and full annealed. Heat Treatment ... Steel castings for service at elevated temperatures are generally used as normalized or normalized and tempered, since creep resistance is highest in steels in this condition. High temperature properties are closely related to the microstructure. The microstruc- ture obtained by normalizing and tempering (i.e., pearlite or bainite) is more resistant to coalescence of the carbides than is the martensitic microstructure obtained by quenching and tempering. ASTM Specifi- cation A217-59 permits the heat treatment to be at the discretion of the manufacturer unless otherwise agreed upon. ASTM Specifications A356-58T and A389-59T require a normalize and temper heat treat- ment. Service Temperatures ... Maximum service temperature for the var- ious grades will depend somewhat upon their application rather than entirely upon properties. Such factors as applied stress, allowable surface oxidation, and duration of use at temperature, will influence the selection of the proper composition. The steels listed under ASTM Specification A217-59T are the only grades for which allowable stresses at elevated temperatures HIGH TEMPERATURE USE 423 have been determined. These can be found in the ASME Boiler and Pressure Vessel Code, and the ASME Code for Pressure Piping. Al- though allowable stresses are listed as high as 1100 degrees F for grades WC 1, WC 4, and WC 5 and up to 1200 degrees F for grades WC 6, WC 9, C5, and C12, somewhat lower maximum temperatures are usually prescribed by the manufacturers. Recommended maxi- mum service temperature for each of the cast steels listed under ASTM A217-59T is generally as follows: Grade Max. Service Temp., °F 850 850 850 WC 1 WC 4 WC 5 WC 6 WC 9 C5 C12 950 1050 1100 1150 Steels with less than one percent chromium ordinarily should not be used above 850 degrees F because of graphitization which takes place. Graphitization has a marked deleterious effect upon creep and mechanical properties. Unfortunately, the ASME Code does not list allowable stress values for the newer ASTM A356 or A389 steels. A leading manufacturer of large steam turbines, for which the A356 steels are generally used, reports that they are concerned with 1 Fig. 520 Turbire, first stage shroud segment ko'der castings. Operating temperature 1000 degrees F. Cast steel: C 0.18, Ni 0.75, Cr 0.70, Mo 1.00 per- cent grade WC5 ASTM A217. Casting weight 25 Founds. yen28&ez Fig. 521 Combustion chamber cap casting. Operating temperature 700 degrees F. Cast steel: C 0.17, Cr 1.30, Mo 0.50, V.0.20 ASTM A-356, Class 7. by graphitization in steels with less than one percent chromium for applications above 850 degrees F. Also, they are concerned about ferritic steels with chromium contents less than three percent for applications above 1050 degrees F, mainly because of oxidation resist- ance above this temperature. The two grades of ASTM A389 have not been recognized by the Boiler Code or Pipe Code nor have they come into .wide usage. Piping of this type has been used to some extent for turbine piping, but interest in it has diminished because of the critical controls of compo- sition and heat treatment required. Applications ... The cast steels described in this section are used for such applications as valves, flanges, fittings, cylinders (shells), valve chests, throttle valves, steam turbines, and other pressure containing parts operated at elevated temperatures. Grades C5 and C12 of ASTM A217-59T are also popular for use in handling corrosive gases in oil refinery service. The corrosion resistance of these grades at elevated temperatures is the result of their high chromium content. Several castings for service at elevated temperatures were illustrated in Chapter II, and also are shown in Figures 520 and 521. SECTION II Cast Steels for Service Above 1150 Degrees F Steels must contain a total alloy content in excess of about 12 percent to be effective for service above 1150 degrees F. This is neces- sary if they are to provide effective resistance to oxidation (scaling) or to corrosive gases. Heat resistant compositions, as a group, are higher in alloy content than the corrosion resistant grades. High chromium content is distinctive in improving abrasion, oxidation, and sulfidation resistance. The addition of nickel, in quantity, improves HIGH TEMPERATURE USE 425 high temperature creep strength, resistance to thermal shock, and cor- rosion resistance. The primary requirements for heat resistant castings in elevated temperature service are: (1) that the alloy be resistant to the atmos- phere encountered, and (2) that the alloy retain its mechanical prop- erties without excessive change over a long period of time. The atmos- pheres to which heat resistant alloys are most frequently exposed are air and flue gases. The latter may be either oxidizing or reducing (or fluctuating from one to the other), and may contain sulfur in varying amounts. In selecting high-alloy compositions, the following are among the factors that should be considered: 1—normal operating temperature; 2-maximum and minimum temperatures; 3-period and frequency of temperature cycles, if cyclic service; 4-presence of thermal gradients in the casting; 5—thermal expansion characteristics of the alloy; 6—applied load; 7-manner of loading and supporting; 8/required life of the casting 9—atmosphere present. Consultation with experienced alloy foundrymen is recommended before selection of allowable working stress for design purposes. Composition Heat resistant cast high-alloy steels fall under three general composition classifications: Class I–Iron-chromium alloy castings containing 8 to 30 percent chromium. These alloys are used chiefly for resistance to oxidation since they possess relatively low strength at elevated temperatures. The chromium content is increased as the service temperatures are increased (see Figure 522). These alloys are ferritic and magnetic. Class 11–Iron-chromium-nickel alloy castings containing 18 to 32 percent chromium and 8 to 22 percent nickel, with chromium always exceeding nickel content. These alloys are partially or fully austenitic, and have greater strength and ductility in service than the iron- chromium group. These alloys can be used in sulfurous, oxidizing, and reducing atmospheres. Class III-Iron-nickel-chromium alloy castings containing 33 to 68 percent nickel and 10 to 21 percent chromium. These alloys are 426 HIGH TEMPERATURE USE 28 24 - 20 16 CHROMIUM CONTENT, % 12 8 00 4 0 1 1000 1200 1800 2000 1400 1600 TEMPERATURE, OF Fig. 522—Maximum chromium content necessary for freedom from scaling at temperatures from 1000 to 2000 degrees F. (U. S. Steel) fully austenitic and nonmagnetic, and have high strengths at elevated temperatures. Although the high nickel content makes Class III alloys unsuitable for use in the presence of appreciable sulfur, they give excellent service in chemically reactive media and, also, under con- ditions involving thermal shock. The chemical compositions of the standard heat resistant high- alloy grades are given in the Engineering Tables in the Appendix, and are similar to, but not identical with, those of the wrought grades. The cast high-alloy compositions are balanced so as to provide both castability and heat resistance. Characteristics of the Standard Grades4 . Iron-Chromium Group The Alloy Casting Institute lists three standard types in this class of heat resistant high alloys: HA, HC, and HD. The HA grade corresponds to the C-12 grade under ASTM Specification A217-59T and was discussed in Section I of this chapter. It has limited application because of its low strength at high temper- atures. Types HC (26-30 Cr, 4 max. Ni) and HD (26-30 Cr., 4-7 Ni) can be used for load bearing applications up to 1,200 degrees F, and where only light loads are involved, up to 1,900 degrees F. Type HD has a somewhat greater strength at elevated temperatures because of its high nickel content. The HC alloy is supplied in two carbon ranges: up to 0.50 percent for normal high temperature service, and up to 3.0 percent where an abrasion resistant material is required. Types HC and HD are used in ore roasting furnaces for parts such as rabble arms and blades. They are also used for salt pots, grate bars, and high sulfur atmosphere applications not requiring high strengths. HIGH TEMPERATURE USE 427 Iron-Chromium-Nickel Group ... These alloys, types HE, HF, HH, - HI, HK and HL, are partially or completely austenitic and, accord- ingly, have greater high temperature strength and ductility than the iron-chromium alloys. They can be used in either oxidizing or re- ducing atmospheres. Type HF alloy (19-23 Cr, 9-12 Ni) is similar in composition to the 18-8 stainless steels employed for corrosion resist- ance, except that carbon content is higher. This alloy can be used at temperatures up to 1,600 degrees F. Type HF castings operate in the 1,200 to 1,600 degrees F temperature range in oil refineries as tube supports and beams, in cement mill parts, ore roasting furnace parts, and in heat treating furnaces. Type HE (26-30 Cr, 8-11 Ni) has a higher chromium content than type HF, which makes it suitable for service up to 2,000 degrees F. This alloy has excellent corrosion resistance at high temperatures. It is stronger and more ductile than the straight chromium types at room temperature, and at elevated temperatures it retains good ductility and moderate strength. Its relatively low nickel content makes it readily applicable for use in high sulfur atmospheres where some strength is required. Typical applications are in ore roasting furnaces, and in steel mill furnaces. Type HH (24-28 Cr, 11-14 Ni) exhibits high strength and excellent resistance to oxidation at temperatures up to 2,000 degrees F. Since these properties make it a very useful alloy, it accounts for about one- third of the production of all heat resistant castings. Depending on the exact composition, the alloy may range from partially ferritic to fully austenitic. The selection of a type HH alloy must be tailored to the applica- tion. The partially ferritic alloy has lower creep strength and higher ductility at elevated temperatures than the austenitic alloy. However, between 1,200 and 1,600 degrees F the ferritic alloy may develop a weak intermediate structure phase called sigma; thus, the austenitic type should be used if operation will be in this temperature range. Either of the compositions can be used for service above 1,600 degrees Fig. 523—Heat resistant fittings of 29% Cr, 9% Ni cast steel (HE) for a pulp digester. Fig. 524—A rotary- hearth assembly of heat resistant cast. ings of 26% Cr, 12% Ni (HH) cast steel. F. The HH type of alloys finds typical application in heat treating furnace parts. They are not generally recommended for service where severe temperature cycles are encountered, such as in quenching fixtures. Type HI (26-30 Cr, 14-18 Ni), with higher nickel and chromium content than type HH, is more resistant to oxidation and can be used up to 2,150 degrees F. Although similar to the HH alloys in mechani- cal properties and composition sensitivity, it is more likely to be austenitic. Cast retorts for magnesium production have been the major application for this grade. Type HK (24-28 Cr, 18-22Ni) with still higher nickel content than type HI is similar to a fully austenitic HH alloy. This alloy has high strength at temperatures above 1,900 degrees F, and can be used in structural applications up to 2,100 degrees F. Type HK resists hot gas corrosion somewhat better than type HH. It is not recom- mended for high sulfur atmospheres, or where severe thermal shock is a factor, but is widely used for parts where high creep strength is needed, such as jet engines, gas turbines, furnace parts and chains. Type HL (28-32 Cr, 18-22 Ni) is similar to type HK but with higher chromium content. Because this alloy is the most resistant of the group to corrosion in high sulfur atmospheres up to 1,800 degrees F, it is used where higher strength is required than obtainable with straight chromium alloys. Typical uses are for gas dissociation equipment fixtures. HIGH TEMPERATURE USE 429 Iron-Nickel-Chromium Group The high-nickel group normally constitutes about 40 percent of the total production of heat resistant castings. These alloys, types HT, HU, HW, and HX, employ nickel either as the predominant alloying element, or actually as the base metal. As a result, these alloys have a stable austenitic structure and are not as sensitive to variations in composition as the high chromium grades. They can be used for almost all applications up to 2,100 degrees F, and give excellent service life where subject to rapid heat- ing and cooling. Because of their high nickel content, however, they are not recommended for use in high sulfur atmospheres. In selecting alloys from this group, the following factors are important: 1—Increasing nickel content increases resistance to carburization and thermal shock but decreases hot strength. 2-Increasing chromium content increases resistance to corrosion and oxidation. 3—Increasing carbon content increases hot strength. 4-Increasing silicon content increases resistance to carburiza- tion, but decreases strength. Type HT (33-37 Ni, 13-17 Cr) can be used satisfactorily at tem- peratures up to 2,100 degrees F in oxidizing atmospheres, and 2,000 degrees F in reducing atmospheres. Where carburization must be held to a minimum, silicon should be not less than 1.25 percent. Type HT alloy is widely used for heat treating furnace parts such as rails, rolls, disks, chains, boxes, pots, and fixtures subject to cyclic heating. It is also used for glass rolls, enameling racks, and radiant heater tubes. Type HT (37-41 Ni, 17-21 Cr) is recommended for severe service conditions because of its high hot-strength. The higher chromium content also increases resistance to corrosive attack. Fig. 525 — Heat ex- change castings. HK steel: 26% Cr, 20% Ni. re Fig. 526 Conveyor shaft and wheels from bar forming furnace, HN steel: 25% Ni, 20% Cr. Type HW (58-62 Ni, 10-14 Cr) is used in oxidizing atmospheres up to 2,050 degrees F, and in reducing atmospheres up to 1,900 degrees F. It finds extensive applications for parts that require resistance to oxidation, carburization, nitriding, and thermal shock. Its high elec- trical resistivity makes it suitable for cast electrical heating elements. It is not recommended for exposure to high sulfur hot gases. Typical castings are for severe service at high temperatures involving cyclic heating or thermal shock. Usual applications are hearths, muffles, retorts, trays, boxes, burner parts, enameling fixtures, quenching fix- tures, and containers for molten lead. . Type HX (64-68 Ni, 15-19 Cr) is more resistant to corrosion at elevated temperatures than type HW, because of its higher nickel and chromium content. It is considerably better than type HW in resistance to reducing gases containing sulfur at 1,800 degrees F. Both HW and HX alloys are highly resistant to carburization when in contact with tempering and cyaniding salts. They are not recom- mended for use with neutral salts, or salts used in hardening high speed steels. Type HX is used for the same applications as type HW where improved resistance to hot gas corrosion is required. Heat Treatment High-alloy heat resistant castings are generally used without heat treatment unless otherwise specified by the pur- chaser. Type HA is often annealed, or normalized and tempered, to improve its high temperature properties. Types HF, HH, and HT, when used in applications where they are repeatedly heated and cooled, may be improved by heating to 1900 degrees F and furnace cooling. Mechanical Properties ... The minimum allowable tensile properties for high-alloy steel castings, as prescribed under ASTM Specification A297-59, are given in Table 67. Representative (not maximum nor minimum) mechanical property data for heat resistant alloys are HIGH TEMPERATURE USE 431 Table 67—Minimum Allowable Tensile Properties for High Alloy Heat Resistant Castings (Properties Prescribed in ASTM Specification A297-59) Tensile Strength Min., psi Yield Strength Min., psi Elongation Min., % ACI Grade 60,000 18** 90,000 55,000 9 HA* HC HD HE HF HH HI HK HL HN HT HU HW HX 85,000 70,000 70,000 70,000 75,000 40,000 35,000 35,000 35,000 35,000 10 10 10 ន - I 1 + | 65,000 65,000 60,000 60,000 * ASTM Specification A217-59T applies. ** Reduction of area of 35% also required. given in Tables 68 and 69. The elevated temperature data in Table 69 are valid for constant temperature operation, but must be modified downward if the alloys are exposed to cyclic temperatures. Thus, values of stress used for design calculations must take into account not only normal and maximum temperatures of service, but also the frequency and speed of temperature fluctuations. Furthermore, con- Table 68—Typical Mechanical Properties at Room Temperature (Representative Values NOT Minimum Specification Values) Tensile Strength psi Yield Strength psi Elon- Brinell gation Hardness % No. Heat Treatment ACI Grade 21 2 16 HA HC HD HE HF HH HI HK HL HN HT HU HW HX 107,000 70,000 85,000 95,000 85,000 80,000 80,000 75,000 82,050 68,000 70,000 70,000 68,000 65,000 81,000 65,000 48,000 45,000 45,000 50,000 45,000 50,000 52,000 38,000 40,000 40,000 36,000 36,000 20 35 25 12 17 19 17 10 9 4 9 220 190 190 200 165 185 180 170 192 160 180 170 185 176 N-T 1250 °F As Cast As Cast As Cast As Cast As Cast As Cast As Cast As Cast As Cast As Cast As Cast As Cast As Cast 432 HIGH TEMPERATURE USE Table 69—Limiting Creep Stress at Various Temperatures for Standard Heat Resistant Grades (ACI Data Sheets)* Grade Limiting Creep Stress, psi (rate 0.0001%/hr.) 1200°F 1400°F 1600°F 1800°F 2000°F 2150°F 3,100 360 900 1,400 13,000 HA HC HD HE HF HH HI HK HL HN HT HU HW HX 1,300 3,500 4,000 6,000 3,000 6,600 6,800 7,000 750 1,900 2,400 3,200 1,700 3,600 4,200 4,300 6,300 4,500 5,000 3,000 3,200 300 800 1,000 150 200 11,700 1,100 1,900 2,700 2,200 3,100 2,000 2,200 1,400 1,600 -- 900 500 600 150 8,000 8,500 6,000 6,400 600 sideration must be given to the rate at which a metal section will decrease because of surface or sub-surface corrosion. In the determi- nation of design stresses, no single set of data can wholly represent the safe working strength of an alloy at high temperatures under all service conditions unless the worst possible conditions are assumed. In the average case this would result in an extravagant use of alloys. In view of the numerous factors that can influence high-alloy casting behavior at elevated temperature, prospective heat resistant casting users should seek advice from an experienced high-alloy steel casting manufacturer at the inception of their plans in order to assure satisfactory design and service. It is most important to understand that mechanical property data such as those given in Tables 68 and 69 can be translated into design stress values only after consideration of all the peculiarities of the expected application and then only by those familiar with similar installations. Processing Recommendations ... The Alloy Casting Institute's recom- mended machining methods for the standard grades of high-alloy heat resistant steel castings are given in Table 70. All of the cast high-alloy steels can be welded satisfactorily. Electric-arc welding is generally employed, but gas welding is also successfully used. The Alloy Casting Institute's recommended welding procedures for the standard grades of high-alloy heat resistant steel castings are given in Table 71. HIGH TEMPERATURE USE 433 Table 70–Recommended Machining Methods for High Alloy Heat Resistant Steel Castings (Alloy Casting Institute)" ALLOY MACHINING PROCEDURE HA Chips are tough and stringy. Use chip curlers and breakers. Rough-turn at 40-50 sfm and feed at 0.010-0.030 ipr. Finish-cut with 0.005-0.010 ipr feeds. Drill at 35-70 sfm and tap at 10-25 sfm. Rough-turn at 40-50 sfm with 0.025-0.035 ipr feeds. Finish- cut at feeds of 0.010-0.015 ipr. Drill at 40-60 sfm and tap at 10-25 sfm. Chips are tough and stringy. Use chip curlers and breakers. HC HD Same as HC HE HF Chips are tough and stringy. Rough-turn at 30-40 sfm with 0.020-0.025 ipr feeds. Finish cut feeds of 0.005-0.010 ipr. Drill at 30-60 sfm and tap at 10-25 sfm. Chips are tough and stringy. Use chip curlers and breakers. Rough-turn at 25-35 sfm. Feed at 0.020-0.25 ipr. Finish- cut with feeds of 0.005-0.010 ipr. Drill at 20-40 sfm and tap at 10-20 sfm. Use chip curlers. Chips are tough and stringy. Rough-turn at 25-35 sfm, feed at 0.015-0.020 ipr. Finish-turn at double the above speeds at feeds of 0.005-0.010 ipr. Drill at 20-40 sfm, tap at 10-20 sfm. Same as for HH. HH HI HK Same as for HF. HL Same as for HE. HN HT Chips are rough and stringy. Use chip curlers and breakers. Rough-turn at 35-45 sfm, feed at 0.020-0.025 ipr. Finish- turn with 0.005-0.010 ipr feeds. Drill at 40-60 sfm and tap at 5-15 sfm. Chips are rough and stringy. Use chip curlers and breakers. Rough-turn at 40-45 sfm with 0.025-0.035 ipr feeds. Finish cut with feeds of 0.005-0.010 ipr. Drill at 40-60 sfm and tap at 5-15 sfm. Like HT, but finish-cut at 0.010-0.015 ipr. Like HT, but finish-cut at 0.010-0.015 ipr. Like HT, but finish-cut at 0.010-0.015 ipr. HU HW HX Fig. 527—Rolls for armor plate harden. ing furnace. HT steels 35% Ni, 15% Cr. Table 71—Recommended Welding Procedures for High Alloy Heat Resistant Steel Castings (Alloy Casting Institute) ALLOY WELDING PROCEDURE HA HC HD HE HF HH HI Heat castings to between 450 and 550 F before welding. After welding, heat to from 1200-1300 F, depending on original tempering heat. Let heat become uniform through- out, then air-cool rapidly. Preheat castings to from 600-1000F. Peen each bead before depositing the next one. After welding, heat to 1550 F, let heat spread uniformly, then air-cool rapidly. Preweld heat treating is not needed, except to relieve stresses. No heat treating is required. No heat treatment is necessary. Metal-arc welding is best. For gas welding, use Type 309 bare rods and a slightly rich flame. No heat treatment. Same as for HH. Metal-arc is best. Gas weld with Type 310 bare rod and a medium rich flame. Arc-weld downhand for high temperature service. No heat treatment is needed. Gas weld with a medium rich flame and Type 310 bare rod. Omit heat treatments. Metal-arc welding is best. Same as for HT. For high temperature service, use gas welding. Use a very rich flame and Type 330 bare rod. Omit heat treatments. Same as for HT. Gas welding is best for high temperature service. Use Inconel bare rods and fluxes for stainless steels. The flame should be very rich. No heat treatments are needed. Same as for HW. HK HL HN HT HU HW HX - Fig. 528 Heat resistant castings: electric furnace hearth plates of type HU (40% Cr), pusher trays for continuous heat treating turnace of type HT (35% Ni, 15% Cr), and hangers for continuous furnace, type HH (26% Cr, 12% Ni). WALI WAND Applications Figures 523 through 528 illustrate some of the typical high-alloy castings produced for heat resistance applications. The following list of applications is intended as a general guide in the selection of com- positions for specific applications, and the recommendations of experi- enced foundrymen should be relied upon in the manufacture of heat resistant steel castings. Alloy Type HA HC Typical Applications Valves, flanges, fittings where light stresses at high temperatures are applied. Ore-roasting furnaces, rabble arms, blades, etc.; salt pots, grate bars; service in high sulfur atmos- pheres not requiring high strength. Similar to HC. Used where improved strength is required. Used in high sulfur atmospheres where moderate strength is required; ore-roasting furnaces, steel mill furnaces, carrier blades, etc. HD HE 436 HIGH TEMPERATURE USE HF HH HI HK > HL Uses similar to HH but in temperature range 1200-1600 degrees F : oil refinery castings, cement mill and heat treating furnace parts. Tube supports, beams, etc., oil refineries; cement mill parts; ore-roasting, furnace parts; heat treat- ing furnace parts: rails, rolls, pots, etc. Similar to HH. Used for retorts and furnace parts up to 2150 degrees F. Used up to 2100 degrees F, where severe thermal shock is not a factor, for furnace parts, chain, gas turbines, jet engines, and parts where high creep strength is needed. Similar to HK. Used at high temperature in high sulfur atmospheres where strength is required. Heat treating furnace parts: rails, rolls, discs, chains, boxes, pots, and fixtures subject to cyclic heating. Also glass rolls, enameling racks, and radiant heater tubes. Not recommended for high sulfur atmospheres. Similar to HT. Used where improved resistance to hot gas corrosion is required. Severe service at high temperatures involving cyclic heating or thermal shock; used in hearths, muffles, retorts, trays, boxes, burner parts, enamel- ing fixtures, etc. HW used where improved resist- ance to hot gas corrosion is required. HT HU HW & HX REFERENCES 1-Weaver, S. H., “The Effect of Carbide Spheroidization Upon Creep Strength of Carbon-Molybdenum Steel”, Proceedings, ASTM, Vol. 41 (1941), pp. 608-627. 2_United States Steel Corporation, “The Making, Shaping and Treating of Steel", Seventh Edition, 1957. 3_Lockwood, C. K., “Cast High Alloys-Properties of the Heat Resistant Grades”, Reprint from Product Engineering (February 1955). 4Alloy Casting Institute, Data Sheets, issued March, 1957. 5—Alloy Casting Institute, “How to Cut, Weld and Heat Treat Cast Stainless Steels”, Reprint from Metalworking (November 1957). 6—Creep Data A Compilation of High Temperature Creep Characteristics of Metals and Alloys; published jointly by ASTM and ASME, 1938. 7-ASTM Special Technical Publication No. 151, “Report on the Elevated-Tempera- ture Properties of Chromium-Molybdenum Steels” (1953). 8-ASTM Special Technical Publication No. 37, “Compilation of Available High- Temperature Creep Characteristics of Metals and Alloys” (1938). 9—Hoyt, S. L., “Metal Data”, Reinhold Publishing Corporation, New York, 1952. 10—Schoefer, E. A., “A Selection Guide to Heat-Resistant Cast High Alloys," Machine Design (April 2, 1959), pp. 118-125. > CHAPTER XIV, CAST STEELS FOR CORROSION RESISTING SERVICE Introduction Castings are classified as corrosion-resistant if they are capable of sustained operation when exposed to attack by corrosive agents at service temperatures. Ferrous alloy castings for such service fall into the following groups: iron-chromium ("straight chromium” alloys), iron-chromium-nickel (chromium in excess of nickel), and iron-nickel- chromium (nickel in excess of chromium). This chapter will cover corrosion resistant cast alloys which are used in mild to severe corro- sion service, as well as some of the alloy cast steels (less than 12 percent total alloy content) used in very mild corrosion service. > The high-alloy ferrous base compositions are usually given the name "steel", although this use has been questioned. However, certain of the high allbys, such as 12 percent chromium steel, exhibit many of the familiar physical characteristics of carbon and low alloy steel ; and some of their mechanical properties such as hardness and tensile strength can be altered by suitable heat treatment. The alloys of high chromium (20 to 30 percent) and chromium-nickel do not show the changes in phase observed in ordinary steel when heated or cooled in the range from room temperature up to the melting point. Conse- quently, the materials are non-hardenable and their mechanical prop- erties depend upon their composition rather than on heat treatment. This is not to say that the materials may not be affected by exposure to certain temperatures, but rather to point out that such mechanism differs from that known in carbon and low alloy steel. The high alloy steels differ from carbon and low-alloy steels in other respects, such as in their production and properties. Consider- ation must be given to each grade with respect to casting design and foundry practice. Minor elements such as carbon, silicon, molybdenum and columbium may exert a profound influence on the ultimate struc- ture of these complex alloys, so that balancing of the alloy composi- tions is frequently required, if a satisfactory product is to be obtained. The balance among the major and minor elements also may affect the castability of the metal. Hence, chemical ranges useful in the man- ufacture of wrought stainless alloys may not be applicable to casting production since a different balance must be achieved to provide both castability and the desired corrosion resistance. Corrosion resistance of an alloy is a relative term, dependent upon the particular environment to which a specific alloy is exposed, there- 438 CORROSION RESISTANCE fore it is misleading rather than helpful to list the comparative corrosion rates of different alloys when exposed to the same corroding medium. Alloy casting users will find it helpful to rely on the experi- ence of the foundry engineer in selecting alloys and, in this connection, they should recognize that complete information about the proposed application is essential if reliable judgment is to be obtained. Among the factors that must be considered are: 1. The principal corrosive agent. 2. Its concentration. 3. Known or suspected impurities. 4. Operating temperature. 5. Presence of oxygen or other gases in solution. 6. Whether the equipment will operate continuously or inter- mittently. 7. Velocity of flow. Discretion is required in determining the relative corrosion rates of various steels because of the uncertainties of the actual service condi- tions. Corrosion rates determined in controlled laboratory tests should be applied cautiously when considering actual service. Two major crite- ria used for determining the corrosion resistance of an alloy are loss in weight, and maximum depth of pitting. Both criteria furnish bases for comparison of materials, but in a somewhat different manner. The loss in weight and average penetration, as calculated from the loss in weight, indicate the general trend of corrosion. The maximum penetration as measured on the corroded specimens indicates the trend of the material toward a local perforation. Each of these measurements is important, but in a different way. For example, in pipelines or other liquid or gas carrying vessels, the maximum pit depth after a given exposure period is of a major importance, since this will indicate the tendency toward local perforation and the sub- sequent loss of the transported commodity. On the other hand, for underground structures that are primarily load bearing, such as piling, the maximum penetration is of less interest than the overall weight loss or average penetration. SECTION I Corrosion of Carbon and Low Alloy Cast Steels Iron and steel, unless shielded by a protective coating, will corrode in the presence of water and oxygen, and hence corrosion in steel will take place when exposed to moist air. The rate at which corrosion CORROSION RESISTANCE 439 proceeds in the atmosphere depends upon the conditions existing in the particular locality in which the material is in use, as well as upon the means which have been taken to prevent corrosion. It also depends upon the corroding medium, its movement, velocity and conditions of electro-potential. It increases with a rise in temperature. The rate of corrosion is also dependent upon the character of the steel as de- termined by its chemical composition and heat treatment. The prob- able rate of corrosion of a material in any environment can generally be estimated only from long-time tests. Cast steel and wrought steel of similar analysis and heat treat- ment exhibit about the same corrosion resistance in the same environ- ments. Plain carbon steel and certain of the low alloy steels do not resist drastic corrosive conditions. In order to greatly increase the corrosion resistance of steel, it is necessary to resort to high alloying. Small amounts of copper slightly improve the resistance of steel to Table 72—Comparative Rates of Corrosion of Cast, Bessemer & Open-Hearth Steels and Gray Cast Iron in Several Different Soils (U. S. Bureau of Standards) Loss in Ounces per Square Foot per Year Soil No. Years Buried Wrought Open- Wrought Gray Hearth Bessemer Cast Steel Steel Iron Electric Years Cast Buried Steel Soil Type 2.33 2.12 1.90 0.20 0.21 0.11 1.94 1.92 2.86 2.16 2.09 1.99 1.20 1.57 2.45 13 Alkali Soil 2.29 1.30 1.93 (Carbonates) 24 Merrimac Gravelly 2.69 0.26 1.32 Sandy Loam 28 Montezuma Clay 1.64 2.49 1.64 Adobe 29 Muck- 2.11 2.07 1.96 New Orleans 42 Susquehanna 2.08 1.41 1.98 Clay 43 Tidal 2.78 0.92 1.29 Marsh 45 Alkali Soil 2.60 0.44 1.18 Sulphates Average Loss In Seven Soils 1.125 Chemical Composition, % С Mn P 1.70 1.80 0.91 0.81 1.22 1.36 1.478 1.561 1.652 S Si 1.55 0.37 Gray Cast Iron Carbon Cast Steel Open-Hearth Steel Bessemer Steel 3.45 0.27 0.12 0.09 0.56 0.68 0.41 0.39 0.05 0.03 0.04 0.08 0.07 0.03 0.04 0.04 440 CORROSION RESISTANCE atmospheric attack, while appreciably larger amounts of other ele- ments such as chromium or nickel greatly improve it. Steels of this latter type are considered in Section II. Table 72 shows the comparative rates of corrosion of cast and wrought steel and gray iron in different soils under mild corrosive conditions. In general, there is little difference in the corrosion resist- ance of steel and gray or ductile iron. Table 73 shows the resistance of cast steels to petroleum corrosion, while Table 74 supplies similar data relating to water and acid attack. Table 73—Corrosion Resistance of Cast Steels-Petroleum Corrosion* Corroding Medium: Petroleum vapor under 175 lbs. pressure for 1000 hrs. at 650°F, Material Wt. loss (mg/sq. in.) Cast Carbon Steel 196.0 Cast Steel (0.75 Cr-2.00 Ni) 153.0 Seamless Tubing (5.00 Cr) 99.2 Cast Steel (5.00 Cr-1.00W) 61.5 Cast Steel (5.00 Cr-0.50 Mo) 47.0 Cast Steel (12.00 Cr) 6.4 Stainless Steel (18 Cr-8 Ni) 2.1 * Data from "Book of Stainless Steels.” Table 74-Water and Acid Corrosion of Cast Steels Corroding Media No. of Months Exposure Analysis C 0.29 Mn 0.39 Si 0.14 Analysis C 0.32 Mn 0.36 Cr 1.12 Corrosion Factor Analysis C 0.11 Mn 0.11 Cr 3.58 Tap Water 2 6 100 100 100 100 100 100 100 100 100 100 85 73 60 80 93 109 71 89 223 100 Sea Water Wet and Dry 2 6 2 6 2 6 2 1 58 61 26 40 30 25 68 102 61 -64 0.05% H2SO4 0.50% H2SO, Hot Water Acid Corrosion of Carbon vs. Chromium Steel Analysis of Steel C Cr Wt. loss in 5 hrs. 5% HCI 5% H2SO. 5% HNO3 (%) (%) 0.31 0.30 (grams/sq. cm.) 0.00270 0.00490 (grams/sq. cm.) 0.00210 0.00541 (grams/sq. cm.) : 0.08079 0.04736 2.42 CORROSION RESISTANCE 441 Several low and high alloy cast steels have been studied as to their corrosion resistance to high temperature steam. Test specimens six inches long and 12 inch in diameter were machined from test coupons and were then exposed to steam at 1200 degrees F for 570 hours. The steel compositions and test results are given in Table 75. These data, just as those of Tables 74 and 75 show the essential value of higher chromium content for improved corrosion resistance. High chromium contents are imperative in castings for use under highly corrosive conditions. Table 75-Corrosion of Cast Steels at 1200°F for 570 Hours (Hawkins and Potter)? Chemical Analysis Percent Spec- imen No. Average Penetration Inches С Cr Ni Mo N 1 2 3 4 5 6 7 8 9 10 Type of Cast Steel Carbon Carbon Carbon-Moly Carbon-Moly Ni-Cr-Moly Ni-Cr-Moly 5 Cr-Moly 5 Cr-Moly 7 Cr-Moly* 9 Cr-1.5 Moly 0.24 0.25 0.21 0.20 0.35 0.28 0.22 0.27 0.11 0.23 2.13 2.25 0.64 0.73 5.07 5.49 7.33 9.09 0.49 0.49 0.26 0.26 0.47 0.43 0.59 1.56 .012 .011 .012 .010 .010 .010 .004 .004 .002 .001 * Not a cast steel Atmospheric Corrosion ... A research program is presently being conducted by Steel Founders' Society to compare the corrosion resist- ance of nine cast steels in marine and industrial atmospheres. A report on the results of three years exposure at the International Nickel Company site at Kure Beach, North Carolina and at the ASTM industrial atmosphere site at East Chicago, Indiana is pre- sented herein. However, it should be pointed out that the exposure tests are continuing as this Handbook goes to press. The cast steel specimens are 4 by 6 by 1/2-inch specimens of the chemical compositions shown in Table 76. The surfaces of half of the specimens were machined. Specimens of each composition and surface condition were divided into three groups and exposed in marine atmos- pheres 80 and 800 feet from the ocean, and in an industrial atmosphere. The loss in weight of the specimens was converted to corrosion rates in terms of inches per year (ipy) or mils per year. A summary of these rates is shown in Figure 529. The conclusions that can be 442 CORROSION RESISTANCE Table 76—Chemical Composition of Steels Tested in Figure 529 С Mn Si Ni Cr P s Other 0.017 0.021 0.19 0.60 2.26 0.56 0.94 Cu 1.08 0.15 Mo 0.07 V 0.17 0.26 0.28 0.27 0.37 0.14 0.37 0.25 0.33 0.77 0.80 0.87 1.70 1.36 0.61 1.42 0.65 1.48 0.65 0.44 0.42 0.42 0.34 0.41 0.38 0.51 0.40 0.09 V 0.10 0.21 0.020 0.016 0.027 0.011 0.031 0.016 0.023 0.026 0.022 0.021 0.038 0.025 0.05 Ti Cost and machined steel specimens exposed for 3 years Kure Beach Eost Chicago - - Medium-carbon steels with: 0.77 Mn - 2.26 Ni - 0.19 Cu 0.80 Mn - 0.56 Ni - 0.60 Cr 0.87 Mn - 0.94 Cu - 0.07 V 1.70 Mn - 1.08 Ni 1.36 Mn 0.09 V 0.61 Mn - 0.IONI - 0.21 Cr 1.42 Mn 0.65 Mn 1.48 Mn I As cast Machined O 0.5 1.5 1.5 2.0 80 f1 from ocoan 800 f1 from ocoon 1.0 2.0 0 0.5 1.0 Average corrosion rato, mils per yr Fig. 529—Corrosion rates of steel castings exposed to mild atmospheric corrosion at two different localities. drawn from the data collected after one and three years of exposure are as follows: ! 1. Machining the surfaces of cast steel specimens of the nine compositions included in this investigation has no significant effect on their corrosion resistance when exposed to any of the test environ- ments. There is no basis for the assumption that an as-cast surface retards corrosion. 2. Cast steels containing nickel, manganese and chromium as alloy elements have corrosion resistance superior to cast steels con- taining manganese alone when exposed in any of the test environments. 3. Increasing the chromium and nickel contents of cast steels containing manganese increases the corrosion resistance in all three test environments. 4. Cast steels containing only nickel and manganese do not exhibit as favorable corrosion resistance as do cast steels containing chromium with reduced amounts of nickel and manganese. CORROSION RESISTANCE 443 • CORROSION RATE 16. X-X WT. LOSS 415 IPY 14 14 GRAMS 1 12 ot T 13 10 -12 CORROSION RATE WT. LOSS x 6 . 10 3 EXPOSURE YEARS Fig. 530—A comparison of the corrosion rate and total weight loss as a function of time for cast steel in atmospheric corrosion. SURES 5. A small amount of copper apparently increases the corrosion resistance of cast steels containing manganese alone or manganese and vanadium. However, the data are not sufficient to justify the establishment of a definite trend. 6. All of the cast steels included in this investigation corroded at a slower rate in the marine atmosphere 800 feet from the ocean than in the other two test environments. The fastest corrosion rate occurred in the marine atmosphere 80 feet from the ocean. A comparison of the corrosion rate and total weight loss as a function of time, showing the protective nature of the scale and rust coating for cast steel, is shown in Figure 530. The rate of corrosion decreases as the thickness of rust and scale increases, and the product of corrosive action acts somewhat as a protective coating. SECTION II Corrosion Resistant Alloy Cast Steels Certain high alloy steels are far more resistant to rusting and staining than are plain carbon and low alloy steels. Although elements such as copper, aluminum, silicon, nickel, and molybdenum increase the corrosion resistance of steel somewhat, they are limited in their results. The superior corrosion resistance of high alloy steels is 444 CORROSION RESISTANCE 0.7 52 MONTHS 0.6 0.5 WEIGHT LOSS, GRAMS PER SQUARE INCH. 0.4 0.3 4 6 8 10 12 14 16 CHROMIUM, PER CENT. Fig. 531—The influence of chromium on the atmospheric corrosion of low carbon steel (Binder and Brown)'. brought about primarily by the addition of the element chromium to steel. For this reason, discussion will be confined to the iron-chromium and iron-chromium-nickel steels. The most common of these higher alloy steels manufactured for corrosion resistance are those containing approximately 12 percent chromium, and those of 18 percent chrom- ium - 8 percent nickel. For maximum resistance, it is necessary that both alloy types be heat treated in such a manner as to leave the carbides in solution. Figure 531 gives some indication of the effect of chromium content on the atmospheric corrosion of steel. Only slight variations from this behavior may be expected in different atmospheres. The standard corrosion resistant grades and chemical composi- tion ranges are listed in the Appendix, page 657. Chemical composi- tions of the corresponding wrought grades are slightly different. These slight differences in chemistry are metallurgically important to provide workability on the one hand and castability on the other. Table 77 gives the minimum tensile properties of corrosion resistant grades prescribed by the ASTM specifications, where applicable. Characteristics of the Standard Grades Chromium Alloy Steels ... The iron-chromium alloys are generally highly resistant to strong oxidizing solutions and find considerable application in chemical plants processing nitric acid and nitrates. Deaerated or reducing conditions are unfavorable for these alloys. The degree to which they become passive in oxidizing media in general increases with increasing chromium content. CORROSION RESISTANCE 445 The CA-15 (12 percent Cr) steel can be classed as mildly corro- sion resistant. This composition finds many uses in the chemical and petroleum industries, also in power plants. Typical applications are valve and pump parts for use at normal and superheated steam tem- peratures, and for handling of hot oil in refineries. Good service life can be expected in mildly abrasive uses such as coke and coal handling equipment. The CA-40 (12 percent Cr) alloy has the same general properties as CA-15. Because of the additional carbon, greater hardness is pos- sible. Uses are similar to applications mentioned for CA-15, especially where greater hardness is required. Table 77—Minimum Allowable Tensile Properties for High Alloy Corrosion Resistant Steel Castings (Properties Prescribed in ASTM Specification A296-59) ACI Type Tensile Strength Min. psi Yield Strength Min. psi Elongation Min. % Reduction of Area Min. % 65,000 65,000 30,000 18 18 90,000 90,000 65,000 55,000 30 30 80,000 40,000 10 35 70,000* 70,000 28,000 30,000 30 CA-15 CA-40 CB-30 CC-50 CD-4M Cu CE-30 CF-3 CF-8 CF-20 CF-3M CF-8M CF-12M CF-8C CF-16F CG-8M CH-20 CK-20 CN-7M 70,000 30,000 30 70,000 70,000 30,000 30,000 30 25 70,000* 65,000 30,000 28,000 30 30 * A tensile strength of 65,000 psi, min., is permitted when the carbon content is 0.06 percent max. or the silicon content is 1.00 percent max., or both. The CB-30 (20 percent Cr) alloy has greater resistance to most corrosive environments than the CA type, but the material is only slightly hardenable by heat treatment. These castings are used for valve bodies and trim in general chemical production, containers for nitric acid, and pumps, valves and impellers in acetate rayon and nitrogen production. When used in contact with nitric acid, the carbon content of the alloy is usually limited to 0.20 - 0.30 percent. As the carbon content is increased above this level, corrosion resistance may 446 CORROSION RESISTANCE 0 12 INCHES Fig. 532—Volute casings used in the chemical industry, cast in CN-7M steel. 26% Ni, 20% Cı. be impaired. In recent years the CF type (19 percent Cr, 9 percent Ni) has replaced the CB grade in many applications. The CC-50 (28 percent Cr) alloys are resistant to oxidizing cor- rodents and are used extensively in contact with acid mine waters, alkaline liquors and in nitrocellulose production. Castings can be used without heat treatment. In the CC type of alloy containing more than 2 percent Ni, strength and ductility are improved by increasing the nitrogen content to 0.15 percent or more. Chromium-Nickel Alloy Steels ... These alloys, having higher chrom- ium than nickel, find service mainly in acid solutions which are strongly oxidizing. They are also passive in solutions of dilute acids containing strong oxidizing salts such as ferric and cupric sulfates. An increase in temperature of the corrodent will increase the corro- sion rate of the alloy, particularly if accompanied by a lowering of the oxidizing capacity of the acid solution. These materials have excellent resistance to nitric acid, which is a strong oxidizing agent under most conditions of temperature and concentration. Sulfuric and sulfurous acid solutions may or may not be corrosive to the austenitic types depending on the concentration, temperature and oxidizing power of the solution. Molybdenum and/or copper additions to the alloys may greatly improve their resistance to such solutions. These alloys are passive in almost all concentrations of acetic acid at temperatures up to boiling. However, hot acetic acid vapors are highly corrosive and additions of molybdenum improve the corrosion resistance under such service conditions. Both weak and concentrated alkaline solutions are successfully handled by the austenitic cast alloys. Salt solutions other than those com- Fig. 533— Pump casing for land-based, mercial atomic power plant, cast in CF8 steel. 18% Cr, 8% Ni. Weight 25,000 pounds. Require- ments for acceptance: 100% dye penetrant, 100% radiography. containing acid chloride, do not corrode these alloys. Corrosion can be expected when the alloys come in contact with oxidizing acid chloride salts, fluorides and bromides. They resist corrosion in sea water where oxygen is available to the metal surface. The non-aqueous products of the oil industry and many other commercially important non-aqueous liquid and gaseous corrodents are successfully resisted by the austenitic alloys. Moist chlorine and hydrochloric acid gases seriously attack these alloys yet, if dry, they pose no problem. Sulfur dioxide and hydrogen sulfiide are also corro- sive if moist, and higher alloyed materials are required to properly cope with such gaseous corroding media. The CE-30 (30 percent Cr, 10 percent Ni) alloy composition has been used with notable success for digester fittings, pumps, and valves in sulfite service in the paper industry. Because of its relative non- susceptibility to intergranular attack, it can be used where heat treat- ment is not feasible, as in welding large castings. Although the CE alloy is often used in the as-cast condition, the ductility and resistance to corrosion may be improved somewhat by quenching from about 2000 degrees F. The CF (19 percent Cr, 9 percent Ni) alloys constitute the most widely used group of corrosion-resistant alloys. When properly heat treated, these alloys are resistant to a great variety of corroding media, and are usually considered the best “general purpose" types. Micro-structurally, they are composed of austenite with small amounts of ferrite, which greatly enhance weldability. Thus, castings made in these grades are normally slightly magnetic. However, by proper balance of the nickel, manganese, and nitrogen contents, the alloys may be made completely nonmagnetic, but at a sacrifice of weldability. OD Fig. 534—Turbine casing for high temperature and high pressure steam service: 5000 psi at 1200 degrees F. Produced from CF8 steel. Acceptance requirements: 100% radiography. weldability tests, mechanical property tests at elevated temperatures. Note weldability test sections removed from nozzles. 12 INCHES The CF type of material is made in the lower-carbon grades for best resistance to corrosion, and designated CF-3 and CF-8, containing 0.03 and 0.08 percent carbon maximum respectively. The 0.03 percent carbon grade also provides resistance to intergranular corrosion. The medium-carbon grade, CF-20, with 0.20 percent carbon maximum is used satisfactorily under less corrosive conditions than those which require the low-carbon type. Where the intended service will involve contact with dilute sul- furic acid, the resistance of the alloy can be improved by the addition of 2 to 3 percent molybdenum, as in the CF-3M, CF-8M, and CF-12M types. Higher molybdenum content (CF-8M) is sometimes specified for special conditions of corrosion, but such alloys are less resistant to corrosion in nitric acid than the molybdenum-free material. Columbium and selenium are also used as special additions to the normal CF composition_columbium (CF-8C) as a stabilizing element to minimize intergranular attack, and selenium (CF-16F) to improve machinability. The CH (25 percent Cr, 12 percent Ni) alloy is similar to the CF composition. It is used for special applications in the chemical and paper industries including digester fittings, pumps, impellers, strainers, and valves for handling paper pulp solutions and nitric acid. The CH alloy is often made in a lower carbon grade containing 0.10 percent carbon maximum. The low carbon type is used for more severe corrodents. The CK (25 percent Cr, 20 percent Ni) alloy is used for agitators and fittings to handle sulfite liquor or cold dilute sulfuric acid. It is similar to the CE and CH compositions, but has higher nickel. 12 INCHES Fig. 535—Volute casing for use in a canned motor pump for nuclear submarine service. Weight 2700 pounds. 20% Ni, 10% Cr cast steel. Casting sub- ject to 100% radiography and dye penetrant inspection. Nickel-Chromium Alloy Steels ... The CN-7M (25 percent Ni, 20 per- cent Cr) alloys are used for resistance to various concentrations of hot sulfuric acid and for special applications of a severely corrosive nature. Within the broad ranges of nickel and chromium for this grade are several proprietary, patented alloys. The compositions contain molybdenum and copper in varying amounts. Processing and Application Recommendations Heat Treatment ... All corrosion resistant castings are required by ASTM Specification A296 to be heat treated in accordance with Table 78, unless otherwise agreed upon by the manufacturer and purchaser. Table 78—Specified Heat Treatment for High Alloy Corrosion Resistant Steel Castings (ASTM Specification A295-59) Grade Heat Treatment (1) Heat to 1750 degrees F. min., air cool and temper at 1100 degrees F. min., or CA-15, CA-40 (2) Anneal at 1450 degrees F. min. (1) Heat to 1450 degrees F. min., and air cool, or CB-30, CC-50 All other Types (2) Heat to 1450 degrees F. min., and furnace cool. As agreed upon by the manufacturer and the purchaser so as to develop the acceptable corrosion resistance. Se 19.2 Fig. 536 Stainless steel Tee casting fur- nished for the Savan- nah River Project. Steel CF8. Acceptance re quirements: 100% radiography, mass spectrometer leak test and ferroxlyl test. 12 INCHES The heat treatments specified for the straight chromium alloys CA-15, CA-40, CB-30, and CC-50 are primarily for the purpose of developing desired mechanical properties. For all other types the heat treatment is left to the descretion of the manufacturer and purchaser, since the particular treatment that will achieve acceptable corrosion resistant qualities is dependent not only on the composition, but on the casting design and prospective application. A procedure frequently employed is to heat the castings to a uniform temperature in the range 1950 to 2050 degrees F, and then rapidly to quench them in air, water or oil in order to insure the retention of carbides in solution. When castings of these grades cannot be quenched rapidly enough because of size or other circumstances, they are sometimes held at 1600 to 1800 degrees F for periods of 24 to 48 hours or longer. This treatment, Table 79—Mechanical Properties at Room Temperature (Representative Values NOT Specification Minimum Values) Tensile Yield Strength Strength psi psi Reduc- Elong- tion Brinell ation of Area Hardness % % No. Heat Treatment Degrees F. Type 60 17 - - CA-15 CA-40 CB-30 CC-50 CE-30 CF-8 CF-20 CF-8M CF-12M CF-8C CF-16F CH-20 CK-20 CN-7M - 115,000 140,000 75,000 100,000 97,000 77,000 83,000 88,000 80,000 85,000 80,000 88,000 76,000 70,000 22 14 10 13 18 55 55 50 100,000 113,000 50,000 61,000 63,000 37,000 42,000 45,000 42,000 44,000 42,000 50,000 38,000 35,000 225 267 170 207 170 140 155 160 160 150 156 190 144 140 1800 AC - 1200 T 1800 AC - 1200 T A 1450 - AC A 1650 - AC 2000 - WQ 2000 - WQ 2000 - WQ 2009 - WQ 2000 - WQ 2000 - WQ 2000 - WQ 2000 - WQ 2100 - WQ 2000 - WQ - 50 45 45 38 37 20 CORROSION RESISTANCE 451 Table 80–Recommended Machining Methods for High Alloy Corrosion Resistant Steel Castings (Alloy Casting Institute)" Alloy CA-15 CA-40 CB-30 Machining Cuts best when hardened to about 225 Brinell. Chips are stringy but not abrasive. Rough-turn at speeds of 40-50 sfm, feeds of 0.010-0.030, ipr. Finish-out at feeds between 0.003 and 0.010 ipr. Drill at 35-70 sfm and tap at 10-25 sfm. Chips are stringy. Rough-turn at 25-35 sfm and feed at 0.030-0.040 ipr. Finish-cut with 0.015-0.020 ipr feeds. Drill at 30-60 sfm, tap at 10-20 sfm. Chips are short and brittle. Rough-turn at 40-50 sfm with feeds of 0.020-0.030 ipr. Finish-turn with feeds from 0.010- 0.015 ipr. Drill at 30-60 sfm Tap at 10-25 sfm. Chips are short and brittle. Avoid local overheatng. Rough- turn at 40-50 sfm with feeds of 0.025-0.035 ipr. Finish-cut with feeds of 0.010-0.015 ipr. Drill at from 40-60 sfm. Tap at 10-25 sfm. Use, chip curlers. Rough-turn 30-40 sfm with 0.020-0.025 ipr feeds. Finish-turn at feeds of 0.005-0.010 ipr. Drill at 30-60 sfm, tap at 10-25 sfm. Use chip curlers. Chips are tough and stringy. Rough-turn at speeds of 25-35 sfm and feeds of 0.020-0.025 ipr. Finish- turn with feeds of 0.005-0.010 ipr. Drill at 20-40 sfm and tap at 10-20 sfm. Same as for CF-8. CC-50 CE-30 CF-8 CF-20 CF-8C Same as for CE-30 CF-8M CF-12M CF-16F Same as for CF-8 except for drilling speeds of between 20 and 50 sfm and tapping speeds of between 10 and 20 sfm. Rough-turn at 45-55 sfm speeds and feeds from 0.020-0.025 ipr. Finish-turn at double the above speeds, but with feeds of 0.005-0.010 ipr. Drill at 30-80 sfm and tap at 15-30 sfm. Same as for CF-8 but drill at 20-50 sfm and tap at 10-20 sfm. CH-20 CK-20 Same as for CF-8. CN-7M Same as for CF-16F, but drill at 30-60 sfm and tap at 10-25 sfm. while helpful in improving resistance to intergranular attack, does not provide resistance equivalent to properly quenched material of the same composition. For best performance, all the grades except CF-3, CF-8C, and CF-3M require heat treatment after welding for maximum protection against intergranular corrosion. Typical tensile properties for most of the standard grades, in their usual condition of heat treatment, are given in Table 79. Machining . Machining methods for most of the standard grades of high alloy corrosion resistant steel castings are given in Table 80. 452 CORROSION RESIST ANCE Table 81—Recommended Welding Procedures for High Alloy Corrosion Resistant Steel Castings (Alloy Casting Institute)" Alloy Welding Procedure CA-15 Preheat castings from 400-600 F before welding. After welding, cool to no less than 300 F, heat to from 1125-1400 F, hold until heat is uniform throughout, then air-cool. CA-40 Same as for CA-15 CB-30 Preheat castings to between 600 and 800 F before welding. After welding, cool to 150 F or lower, heat to at least 1450 F, let heat spread uniformly, then air-cool. CC-50 Preheat castings to from 350-400 F before welding. After welding, heat to 1650 F, hold until heat is uniform, then air-cool. CE-30 Same as for CF-8 except that heat treatment after welding is not necessary. CF-8 Preheating_ is not required. After welding, quench from 1950-2050 F range to restore maximum corrosion resistance. CF-20 Preheating is not necessary. After welding, quench castings from between 2000-2100 F to restore corrosion resistance. CF-8C Same as for CF-8 except that heat treatment after welding is not necessary. CF-8M CF-12M No preheating is needed. After welding, quench from a 1950-2100 F range to restore corrosion resistance. If parts are not to be used in highly corrosive conditions, post-weld heat treatments may be omitted. CF-16F Same as for CF-20 CH-20 Same as CF-20. Post-weld heat treatment can be omitted if casting is not to be exposed to highly corrosive conditions. CK-20 Preheating is not necessary. After welding, quench from the 2000-2150 F range: Post-welding heat treatments may be omitted if the castings are not going to be exposed in service to highly corrosive conditions. CN-7M Preheat castings to 400 F before welding. After welding, cool the parts slowly. Then reheat them to 2000 F and water quench. Welding . . . All of the cast high alloy steels can be welded satis- factorily. Electric arc welding is generally employed, but gas welding is also successfully used. Certain precautions are necessary when welding some of the alloy grades in order that the desired properties of the material will not be impaired. The recommended welding practices for most of the standard grades of high alloy corrosion resistant steel castings are given in Table 81. Fig. 537—Primary cool. ant pump for use in a boiling water nuclear reactor system, cast in CF8 steel. Weight 5,560 pounds. Acceptance re- quirements 100% dye penetrant and radio- graphy, mass spectro- meter leak test. Applications ... Figures 532 through 537 illustrate some of the typical castings produced for corrosion resistant applications. The following list of applications is intended as a general guide, but the recommen- dations of foundrymen experienced in the manufacture of corrosion resistant steel castings should be relied upon in the selection of alloys for specific installations. Alloy Type Typical Applications CA-15 Valves and valve trim, pump parts for power plant and oil refining equipment, sliding or wearing parts. Valve trim, abrasion and erosion resistant appli- cations. CA-40 CB-30 CC-50 Food processing, nitric acid and rayon manufac- ture, rabble blades in ore roasting furnace, nitro- gen production, pumps, valves, impellers. Nitrocellulose production, alkaline liquors, oxidizing acids, pumps for dilute sulfuric acid in mine water. Digester fittings, pumps, valves for sulfite pulp service. CE-30 CF-3 CF-8 Similar to CF-8, but also resistant to intergranular corrosion. General service; pumps, valves, etc. for chemical processing, oil refineries, textile dyeing, food ma- chinery, architectural trim. 454 CORROSION RESIST ANCE CF-20 CF-3M Similar to CF-8, but for less severe service. Similar to CF-8M, but also resistant to intergran- ular corrosion. Pumps, valves, fittings, etc., in reducing acids, paper mill equipment, process industries, sea water serv- ice. CF-8M 1 Į CF-12M CF-8C CF-16F CG-8M Similar to CF-8M, but for more severe service. Similar to CF-8, but especially useful where parts cannot be heat treated after welding. Improved machinability-useful in service similar to CF-8 or CF-20 where finished product requires extensive drilling or threading. Similar to CF-8M where chance of pitting corrosion is more severe. Paper pulp service; digester fittings, pumps, im- pellers, strainers, valves. Sulphite liquor, cold dilute sulfuric acid service, agitators, fittings. Applications requiring resistance to hot sulfuric acid. CH-20 CK-20 CN-7M REFERENCES 1-Soil Corrosion Tests, Bureau of Standards Technical Paper No. 368, Research Paper No. 95, August, 1959. 2-Hawkins, G. and Potter, A., “Corrosion of Steel and Various Alloys by High Temperature Steam”, J. Am. Soc. Engineers, Vol. 53 (November, 1941), pp. 705-723. 3—Metals Handbook, American Society for Metals, 1960 Edition. 4-Binder, W. 0. and Brown, C. M., "Atmospheric Corrosion Tests on High- Chromium Steels”, ASTM Proceedings, Vol. 46 (1946), pp. 593-608. 5—Alloy Casting Institute, “How to Cut, Weld and Heat-Treat Cast Stainless Steels”, Reprint from Metalworking, November, 1957. 6–Schoefer, E. A., “Cast High Alloys — Properties of the Corrosion Resistant Grades”, Reprint from Chemical Engineering, October, 1953. 7-Schoefer, E. A., “A Selection Guide to Corrosion Resistant Cast Alloys”, Reprint from Machine Design, December, 1954. 8—Copson, H. R., “Atmospheric Corrosion of Low Alloy Steels”, ASTM Proceedings, Vol. 52 (1952), pp. 1005-1026. 1-Angler, E. M., Dundon, W. E. and Thompson, G., "How to Weld High Alloy Castings", Welding Engineer, April, May, September, 1953. > CHAPTER XV WELDING OF STEEL CASTINGS The welding process is an important adjunct to the manufacture of steel castings. It is used in steel foundries in two ways: (1) in fabricating structures either by welding castings together (cast-weld construction) or by welding steel castings to wrought steel products (composite fabrication), and (2) in the correction of casting irregulari- ties which may occur in the course of manufacture. The user of steel castings may also employ welding in producing cast-weld or composite structures, building up worn surfaces, applying special purpose facings, and the making of repairs when necessary. The information reported in this chapter is designed to assist the casting user to determine which method and welding procedure is recommended for performance of this operation on steel castings of a definite composition. Weldability of Cast Steels... All steels are weldable, whether wrought or cast, and research studies have shown that the welding of steel cast- ings presents no more problems than the welding of wrought steels of the same composition and heat treatment. It is also important to note that some steel compositions are readily weldable and require only nominal precautions, while other compositions will call for special operational techniques to assure satisfactory and dependable results. To repeat, all steels are weldable provided welding conditions can be specified. The welding of steel castings is somewhat simpler, by way of fur- ther comparison, than welding of wrought steels because all steel cast- ings after welding are stress-relieved, tempered, or given a full heat treatment. Stress relief is also an accepted procedure when cast-weld or composite structures are produced. This eliminates all possibility of either (1) excessive hardness in the heat-affected zone or (2) severe weld stresses; both of which may exist in welded structures not sub- jected to a stress-relieving heat treatment after fabrication. Carbon and low-alloy cast steels under 0.30 percent carbon and normal amounts of manganese, sulfur, phosphorus and silicon are readily weldable, and technically do not require post heat treatment. Even so, the welds in such readily weldable steel castings are seldom left in the as-welded state. Since a heat treatment following welding is universally used in the steel casting industry, the maximum limits for a readily weldable steel requiring no preheat are: carbon 0.33 percent, manganese 456 WELDING 0.70 percent, chromium 0.20 percent, molybdenum 0.20 percent, with a 1.00 percent total maximum content of the unspecified alloying elements. For each reduction of 0.01 percent carbon under the maximum specified, an increase of 0.04 percent manganese above the maximum specified is permitted, but in no case is the manganese to exceed 1.00 percent. Castings with carbon contents above 0.33 percent are considered less readily weldable, and require special welding techniques. Such steels may develop hard, brittle areas adjacent to weld deposits, which can crack during or after the welding because of chilling the highly heated zones by the adjacent colder metal areas. The base metal is important in the welding process because many welds do not fail in the weld but fail in the immediately adjacent zone — the heat-affected zone of the parent metal. While the weld metal is being deposited, this zone is heated momentarily to melting temperature close to the weld, with the temperature decereasing with increasing distance from the weld. This heating induces structural changes especially in higher carbon and alloy compositions, forming hard, brittle areas adjacent to the weld which are prone to crack. Cracking may be prevented in carbon and low-alloy cast steels if the Vickers Brinell hardness of the weld bead does not exceed 350. This is a general figure, and the value may be exceeded where the condi- tions are such that only compressive stresses result in the welding process, and should be lowered in cases where extreme restraint is involved. a If the weld is to be used in the as-welded state, the limited hardness value is more difficult to estimate as the type of service determines the amount of ductility required next to and in the weld. A value of 200 Vickers for the weld bead and heat-affected zone is satisfactory for practically all cases, and such a steel would be considered readily weldable. Cast steels respond to the various welding tests, such as the notched- bead slow-bend test, substantially in the same degree as rolled steel, except, as shown by studies at Battelle Memorial Institute, that the average amount of underbead cracking of welded test specimens in cast steels was less than for rolled steel of a comparable carbon equivalent Mn Si (expressed as C + + -). 4 4. Welding Applications in the Steel Foundry .. There is an unlimited field for the application of steel castings as integral parts of composite welded structures. Cast steels have the same strength in one direction as in another, therefore, they are especially well qualified for use in built-up welded structures. Mechanical properties of welds joining cast steel to cast steel or welds joining cast steel to wrought steel are similar WELDING 457 to welds joining wrought steel to wrought steel. Steel castings are readily welded to steel forgings, steel plates, rolled shapes or to other steel castings. Cast-Weld Construction ... The adoption of cast-weld designs has had a gradual growth in the steel foundry industry since World War II, and there is today an increased recognition of the cast-weld construction in many types of engineering structures. Where considerations of weight, design and cost make it impossible to produce a piece as a single, quality casting, the design can be divided into more readily castable segments. These segments are welded together into a unit of perfection which would have been considered impossible a few years ago. Such cast-weld designs are being produced for all types of industry and are performing most satisfactorily. The over-all quality of the designs in most cases has been greatly improved since the small, less complex individual castings are made more advantageously from the standpoint of casta- bility. Perhaps the simplest application of cast-weld design is in the elimination of appendages which are cast separately and later welded into place. Cast-weld designs have been used increasingly, in recent years, for high-pressure and high-temperature service, for nuclear power applica- tions, as integral parts of process piping and auxiliary equipment for the refinery industry, etc. A few examples of the many hundreds of cast- weld designs which have currently been produced by steel foundries are illustrated in Figures 538 through 543. WELD Fig. 538—Cast-weld intercept valve. elbow casting. An assembly weld of a valve casting and a flanged - Fig. 539 Cast-weld rolling mill pinion housing. The use of a half pattern to cast symetrical sections for joining by welding. AU Fig. 540—Cast-weld hydraulic turbine stay ring. A difficult single piece casting to produce in one piece. The cored openings in the ends of the vanes and stubs permits single weld joints. Fig. 541 Cast-weld crawler wheel. Two simple cast structures welded together rather than produce a single casting of more diffi- cult molding and feed- ing problems. Fig. 542—Cast-weld pump. Two stainless steel half-pump castings welded to- gether using a con- sumable insert filler into the joint for an inert-gas tungsten. arc root pass and completed with an inert-gas metal arc electrode. 1 Fig. 543—Cast-weld peg roll. Identical steel castings can be welded in different positions to produce an entirely different looking single casting construction. 460 WELDING Composite Fabrication ... A wide range of products can best be pro- duced by incorporating wrought steel forgings, plate, bars, tubes and other shapes and steel castings into a final engineered structure. Examples of composite fabrication are shown in Figures 544 to 549. Steel castings, as components of weldments, are widely used because of possible cost savings. The use of steel castings is advantageous in regard to quality production, useful properties, and simplified design. G# Fig. 544—Composite fabrication of a gear case cover. other parts are plate steel. The sides are steel castings and the Fig. 545—Composite fabrication of a base for a hard board press. Cylinder castings 125 inches long, OD 51 inches, plate steel welded to form base. Fig. 546 Composite fabrication of a hoist drum. Three steel cast- ings, the two drum ends and center spider, welded to 23/4 inch rolled plate. Length, 10 feet; diameter, 5 feet. All joints pre- machined and union melt welded. Fig. 547—Composite fabrication of a gear case. (a) The three A frames are single steel castings which are (b) welded together with plate steel with the base and bottom pan plate steel. (a) (b) 10 17! Fig. 548—Composite fabrication of a locomotive gas turbine discharge cas. ing. Two steel castings assembled in welded steel plate. Fig. 549—Composite fabrication of a Diesel engine block. The seven frame bearing castings are welded into a fabricated plate steel base. Weld Build-up and Facings ... Cladding and overlay deposition of weld metal to steel castings is an acceptable procedure. Generally, the auto- matic or semiautomatic submerged arc process is used where large quantities of weld deposit are required. Figure 550 illustrates this WELDING 463 process in which an overlay of special metal is being deposited on the bottom and spout of a large cast matte ladle to prevent erosion. Fig. 550—Weld metal overlay on a steel casting matte pot to prevent erosion. Specifications for Welding Steel Castings ... Four general types of specifications for the welding of steel castings are issued by: 1. Government agencies: Army, Navy and Air Force; 2. Technical societies, such as American Welding Society, American Society for Testing Materials, and the Association of American Railroads; 3. Various steel foundries for governing welding procedures in their own plants; 4. Industrial customers of steel foundries. The welding procedures in government specifications are usually a part of a broader specification for a type of casting. This is also true of some of the technical society specifications. A list of applicable specifications for the welding of steel castings is given in Table 82. 464 WELDING Table 82—Specifications Governing the Welding of Steel Castings U. S. NAVY General specifications for inspection of material Appendix II, Metals, Part F- Radiography, Section F-1- , 1— Definitions and Radiographic Requirements Appendix VII, Welding, Part C, Section C-3 — Welding of Cast Steels 46E2— Electrodes, Welding (Covered), Molybdenum Alloy Steel 46S5 - Steel, Alloy (Special), Castings (Aircraft Use) 47E2- Electrodes, Welding (Covered or Bare), Iron and Steel FEDERAL QQ-S-6810 — Federal Specification for Steel; Castings MILITARY MIL-E-986B (Ships) — Electrodes, Welding, Mineral Covered, Low – Hydrogen, Ballistic Plating and Armor Weld Application MIL-S-870B-Steel Castings, Molybdenum Alloy MIL-S-15083 (Ships) — Steel; Castings AMERICAN WELDING SOCIETY A5.1-Mild Steel Arc-Welding Electrodes A5.5—High Tensile and Low-Alloy Steel Covered Arc-Welding Electrodes A5.4 – Corrosion-Resisting Chromium and Chromium-Nickel Steel Covered Welding Electrodes AMERICAN SOCIETY FOR TESTING MATERIALS - A27 — Mild to Medium-Strength Carbon-Steel Castings for Gen- eral Application A148 — High-Strength Steel Castings for Structural Purpose A216 — Carbon-Steel Castings Suitable for Fusion Welding for High-Temperature Service A217 — Alloy-Steel Castings for Pressure Containing Parts Suit- able for High-Temperature Service A351 — Ferritic and Austenitic Steel Castings for High-Tempera- ture Service A233 Same as AWS A5.1 A298 — Same as AWS A5.4 A316 — Same as AWS A5.5 - 1 1 . - WELDING 465 Table 82—(Continued) ASSOCIATION OF AMERICAN RAILROADS M-201 — Steel Castings - M-203 - Truck Side Frames, Cast Steel M-204 — For Purchase and Acceptance of AAR Standard "E" Cou- plers, Knuckles, Locks, and Other Parts M-206 — Purchase and Acceptance of AAR Standard Tight Lock Couplers and Coupler Parts, Radial Connections, Yokes and Attachment Parts SOCIETY OF AUTOMOTIVE ENGINEERS SAE Automotive Steel Castings, Recommended Practice Methods of Welding Cast Steels ... Manual-arc welding with coated electrodes, called "shielded metal-arc welding", has been used for many years in welding steel castings. In this method the rod coating forms a fusible flux to protect the welding zone so as to deposit sound metal. Where long welds or large volumes of weld metal are required, it is often good practice to employ “submerged-arc” welding. This practice involves the use of a bare metal electrode, with the arc submerged in a blanket of fusible material (flux) to shield the work. Inert-gas metal- arc welding, called "gas-shielded metal-arc welding”, may also be used for long welds and large volumes of deposit. This method employs a bare rod, with the welding zone protected by a localized atmosphere of inert gas, argon for example. The Welding Operation Groove Preparation ... The basic idea in the design of all types of weld preparation is to obtain fusion throughout the entire wall thickness and at the same time to keep weld shrinkage, residual stresses and distor- tion to a minimum. Proper access to the root is a prime requisite for securing full penetration, since it permits the operator to follow the welding process and to maintain control of the welding arc. The shape of the groove is also important. The dimensions of the groove are largely controlled by the size of the repair or of the casting section to be welded. All changes in contour need be fairly gradual, and all sides should slope toward the bottom of the groove. Sharp inside corners serve as points of stress concentration, which might start cracks during welding. Deep, narrow grooves make it very difficult to get complete weld penetration, and they also promote undercutting. Incomplete penetration and undercutting may lead to slag inclusions 466 WELDING or cavities at the roots and sidewalls of the welds and are not acceptable in quality welding. Figure 551 shows typical weld preparation for join- ing heavy-walled sections. 20° AR alw R BACKING STRIP 16 4 16 Fig. 551-A method of weld preparation for cast-weld or composite fabrication by metal arc welding. Groove Backup... It is best to turn the casting over, if welding must extend entirely through the section, and lay one or more sealing passes from the root side of the weld. A backing should be used wherever possible if this cannot be done. Backings can be made from refractory materials, such as firebrick, silica brick, or carbon plates. These should be thoroughly dried because water vapor produced during welding may cause cold cracking at the joint. Metals, such as copper, plain-carbon steel, or stainless steel also may be used as backing material. Ordinarily, the backup material merely acts as a dam and is not bonded to the weld metal. Backings which form integral parts of the castings gener- ally should be of the same composition as the casting. Preheat ... Four undesirable effects may occur from welding which, in order of their importance, are: cold cracking, hot cracking, permanent deformation and weld-metal porosity. The most effective step to elimi- nate or minimize these weld problems is to slow down the heating and cooling rates of the weld metal and the heat-affected zone. This is done by selecting suitable preheat temperatures, interpass temperatures and post-welding heat treatments. a Welds that have a high degree of restraint and high residual stresses are often encountered during fabrication of cast-weldments and in weld repairing. The usual contour of a casting repair weld is an elliptical cup shape and often occurs in the heaviest sections where high multiaxial stresses may be induced. The use of a preheat will eliminate or minimize any trouble from these stresses. WELDING 467 The maintenance of preheat during welding is a necessity in the successful processing of highly restrained welds. It is advantageous, also, to maintain the preheat temperature until post-weld heat treatment can be effective in eliminating stress concentrations. Preheating reduces the temperature differential between the weld and the unaffected base metal. The principal benefits of preheating are those resulting from slower cooling of the weld zone, particularly at low temperatures in the range of martensite formation. Slow cooling promotes completion of austenitic transformation at higher temperatures in this range and permits hydrogen to diffuse from the weld joint. This, in turn, eliminates a principal cause of underbead cracking. The slow cooling rates because of preheating also lower the internal stresses set up during cooling. Two types of preheat are used: a general preheat, in which the entire casting is heated, usually in a furnace; a local preheat where only the section around the wéld is heated, such as by a gas torch or electric- resistance heaters. General preheating is always preferable, since it minimizes localized stresses. Furnaces for general preheating are a standard installation in steel foundries. The preheat temperature depends on the properties of both casting and weld metal, as well as on the size and shape of the casting. There are certain general rules to follow in selecting the correct preheat tem- perature. In the first place, the preheat temperature should be as low as is practical, because with higher temperature it is more difficult to lay a weld bead without undercutting and, furthermore, adequate pro- tection for the welding operator becomes a problem. A temperature of 50 to 100 degrees F above the minimum will seldom do any harm and, therefore, a close calculation of the preheat temperature is not necessary. A good rule to apply is to preheat when in doubt and to preheat at a little higher temperature than calculated. The chemical composition of the casting is a major factor in select- ing the preheat temperature. Steels which are low in carbon and alloy contents will not quench harden excessively nor form cold cracks. They, therefore, require either no preheat, or much less preheat than needed for high-carbon, high-alloy castings. The same reasoning applies also to the deposited weld metal, particularly in multipass welds. Plain carbon and low-alloy castings with carbon contents below 0.30 percent generally do not require preheat. Preheats of 200 to 400 degrees F should be used for castings with carbon contents between 0.30 and 0.50 percent. The higher side of this range would be used with the higher carbon and alloy contents, and with increasing thickness and complexity of the casting. Where both the carbon and alloy contents are high, preheats over 400 degrees F may be necessary. 468 WELDING > The thickness and the shape of the casting also must be considered in preheating. Thicker castings have greater heat-absorbing capacities and, therefore, greater quenching powers. As a rule, the thicker the casting, the higher should be the preheat. Simple shapes with fairly uniform cross sections will cool uniformly and so require a minimum of preheat. Complex castings consisting of alternating thin and thick sections cool more rapidly in the thin sections, which may lead to severe internal stresses. In such cases a higher preheat should be used. Also, such complex casting designs should be protected from drafts during welding and should be cooled more slowly than simpler castings of the same composition. Another factor influencing the selection of a preheating tempera- ture is the size of the weld in relation to the thickness of the casting. Tack welding on a sensitive steel can be a dangerous procedure, since a small weld cools more rapidly than a large one. Casting failure has resulted from cracks started from a tack weld made without preheat. Furnaces with accurate controls are used to obtain the correct pre- heating temperature. “Tempilstiks”, which make a mark that melts when the part reaches the required temperature, are also available for a wide range of temperatures within the normal preheating tempera- ture range. Surface pyrometers are very effective if properly used. Interpass Temperature ... The control of interpass temperature, i.e., the temperature between passes in multipass welds, should be con- sidered along with preheat. In order to maintain the desirable condi- tions developed by preheat, the interpass temperature should never fall below the preheat temperature. The interpass temperature can safely exceed the preheat temperature by 100 to 200 degrees F, depending on the particular casting; higher temperatures may result in the side walls of the weld groove being severely undercut. The heat supplied by welding alone may not be enough to maintain the original preheat temperature for rangy castings, and in such cases additional heat is supplied by reheating the entire casting or locally heating the weld area. Choice of Welding Process ... The choice of welding method will de- pend on the amount of weld metal to be deposited and the repetitive nature of the welding. Gas-shielded processes will usually be uneco- nomical unless the time saved on the application makes up for the generally higher cost compared to manual electrode welding. Much greater deposition of weld metal is possible in the downhand or flat position if the castings can be positioned. Repair welds are often made by the semi-automatic submerged-arc process. Manual shielded-metal- arc welding is also used in short welds on odd shapes, nonrepetitive in nature, and on cast-weld and composite structures. Besides repair WELDING 469 • welds, the semi-automatic submerged-arc process should be considered when repetitive cast-weld or composite welding is advisable. Arc Atmosphere ... The electrode must be selected after the process has been chosen. The arc atmosphere produced by different types and sizes of electrodes can affect both the quality of a weld and the ease of welding. Different arc atmospheres will contain different amounts of hydrogen, and the amount of available hydrogen depends on the com- position of the coating which varies for the different types of electrodes. Underbead cracking in the weld heat-affected zone will be minimized by selecting types which will have arc atmospheres low in hydrogen. The gas-shielded metal-arc atmospheres contain hydrogen in rela- tively small amounts compared with the coated-electrode atmospheres. The chances for underbead cracking are further reduced when the semi- automatic and automatic processes can be used. Heat Input and Current ... Some classes of electrodes require higher welding currents than others for the same diameter. Larger diameter electrodes of a given class require more current than smaller ones, and increasing the current increases the welding heat input. This acts in a lesser degree, like preheating, to reduce temperature differences in the weld area and lower the cooling rate. Therefore, other things being equal, larger diameter (hotter) electrodes should be selected for repair welding. The continuous consumable electrodes used for the gas-shielded processes normally have small diameters, 0.040 to 3/32 inch, although larger diameters are available and are used on some applications. The welding current is much higher than for coated electrodes of the same diameter. The current for a 1/16-inch diameter electrode may range from 300 to 400 amperes. The burnoff rates are also relatively high compared with manual electrodes, and the deposited weld metal per unit time is thus higher. Manufacturers generally print the recommended current ranges for their electrodes on the containers. These ranges are usually rather wide and will vary somewhat, even for electrodes of the same class. The higher currents are for, downhand or flat welding under favorable con- ditions; while the lower currents are for situations where careful control of the weld metal is needed, such as in vertical or overhead welding, or where the preheat is high. Experienced welders can usually select the proper current, but some will tend to use higher currents than they should in order to get out more work. Poor welds may result if this is allowed. Higher welding currents will give higher welding heat inputs, which are frequently advantageous. However, for making a good weld with a 470 WELDING given size and type of electrode in a given position, great variation in welding current is not advisable. Deposition Techniques ... There are many ways of depositing a weld in a groove, but usually there are one or two ways which are best for welding certain castings. The selection depends on the size of the groove, the thickness of the section, and the properties of the casting and weld metal. The position in which the weld is to be made also must be con- sidered, as the deposition technique for position welding is different than that for downhand welding. Two basic factors which have to be considered in selecting the proper deposition technique are the speed of welding and the volume of the weld. These two factors may be varied to control the heat effects of welding. The higher the welding speed for a given size of weld bead the more rapid the cooling rate. This increases the underbead hardness and tendency to underbead cracking. On the other hand, the tendency to distortion is reduced by minimizing the volume of heat- affected base metal. The effects of slower speeds are the converse. Welding speed is not important if preheat is used, provided a sound, well-contoured bead is laid. The effects of mass of the weld are quite similar to those of speed; a small weld produces effects similar to those with high speed, because the cooling rate of the weld zone is relatively fast. Conversely, a large volume of weld metal deposited in a single pass results in considerably more heat in the weld zone. This gives a slower rate of cooling in the weld zone but higher shrinkage stresses. There are two basic types of weld beads: the string bead and the weave bead. The string bead is laid in a continuous pass in one direction. The weave bead also progresses in one direction, but has a side-to-side motion. The width of the weld bead for manual electrode welding should be limited to two or three times the electrode diameter. These bead techniques are illustrated and fully discussed in another SFSA publi- cation(1) (see Note 1). The various welding sequences which can be used with either the manual or semiautomatic welding process, as well as the techniques of multilayer welding, are discussed in this SFSA publication. NOTE 1 The SFSA publication “Recommended Practice for Repair Welding and Fabrication Welding of Steel Castings”, may be purchased from Steel Founders' Society of America, 606 Terminal Tower, Cleveland 13, Ohio, at $0.50 per copy. This publication is an excellent reference manual on the correct methods and quality control of welding of steel in relation to castings, cast-weld construction, and composite fabrication. Also, it contains an up-to-date list of electrodes as to producer, trade names, classes and properties. WELDING 471 - Any of the deposition techniques can be used for the multilayer welding of large grooves. Often it is advantageous to run one bead in one direction and the next bead in the opposite direction. Another simple procedure is to build up the weld in horizontal layers, or the weld can be built up in spiral layers around the side. Nearly all repair welds in castings can be made with string or weave beads laid from start to finish in single or multiple layers. The presence of a backing does not markedly change the required deposition technique, but particular care must be taken in laying the root passes. Where a backing is to become a part of the assembly, it is very important to see that full penetration into the backing is obtained. Where a tem- porary backing - either ceramic or ceramic-washed metal — is used, good fusion between the root pass and the side walls of the groove must be assured. The "step-pass” technique is used for the manual submerged arc welding of a circumferential butt joint in a tube having a fixed horizontal axis. This technique is extensively used to weld connections, such as flanged elbows, to large castings when the workpiece cannot be rotated for mechanized welding. The adjacent base metal temperature rises rapidly after a short weld time with manual submerged-arc welding, and it is recommended that the interpass temperature be limited to 750 degrees F to assist in the complete removal of the fused slag. Bead thickness for the step- pass and straight pass should be limited to 1/4 inch. Arc length is another factor in deposition technique which may be extremely important. Ordinarily, a good welder automatically holds a proper, or "normal" arc length. For the low-hydrogen type electrodes -AWS-ASTM classes EXX15 and EXX16—the arc required for deposit- ing high-quality weld metal is shorter than for other classes of electrodes. This is an important difference which may be overlooked even by good welders whose experience has been with the other classes of electrodes. They should be reminded frequently of this difference, until they have become thoroughly familiar with the low-hydrogen electrodes. Good deposition technique, although important, is generally not too difficult to choose. Competent operators may not all use the same technique, but with relatively little guidance, they will choose one that will do the job satisfactorily. Peening ... Distortion is sometimes minimized by peening the weld. Heavy peening after each pass will reduce distortion by “spreading out" the weld metal, thus counterbalancing its natural shrinkage. For cast- ings thick enough to resist distortion, deep peening gives a mechanical stress relief. Peening must be carefully controlled, because over-peening causes weld metal cracking and is, therefore, worse than none. 472 WELDING Peening is generally not used for castings which are to be stress relieved after welding. Where severe distortion during welding might occur, as in filling a relatively large groove in a thin rangy casting, peening may be helpful in minimizing distortion. Postwelding Heat Treatment ... The great majority of castings can be cooled to room temperature in still air after welding, but those of higher alloy content, which are more sensitive to cracking, should have retarded cooling from the welding temperature. This is primarily to give greater insurance against cold cracking. Such retarded cooling may be accom- plished by heating with a flame or burying the casting in some insulating material. However, inasmuch as crack-sensitive steels require pre- heating as well, one of the best practices is to put the castings back in the preheating furnace as soon as welded. Welded castings, except some of the low-carbon unalloyed steels, should be given a postwelding heat treatment. The minimum treatment should be a stress relief, which consists of heating to 1100 to 1250 degrees F. Such a treatment will remove practically all residual stresses and prevent subsequent cold cracking, and in addition, it will reduce the hardness of the heat-affected zone. Many castings will be given their regular final heat treatment, such as normalizing or quenching and tempering after welding. Either of these treatments will eliminate the heat-affected zone and, of course, make a stress-relieving treatment unnecessary. Though normalizing or quenching and tempering generally improve the base metal, they may reduce the weld metal properties, unless suitable electrodes are chosen. Electrodes ... Most of the commercially available electrodes used for welding plain-carbon and low-alloy castings have been classified by the American Welding Society, the American Society for Testing Materials and the Navy Department. The best known classification is that of the American Welding Society and American Society for Testing Materials. Electrodes are designated by the letter prefix “E” (“ND” in Navy Department specifications), followed by a set of four (sometimes five) digits. From left to right the first two or three) digits indicate the approximate minimum tensile strength of the as-deposited weld metal, in thousands of pounds per square inch. The last two digits indicate the type of coating. The coating, in turn, governs the position in which the electrodes can be used, and the type of current (alternating or direct) required. It should be pointed out that the American Welding Society will qualify any electrode under only one classification, although it is known that some, at least, would fulfill the requirements for other classifica- tions (for example, some Class E6013 electrodes would meet the require- ments for Class E6012; also, some of the Class E6015 electrodes would meet the requirements for Class E7015, etc.). WELDING 473 Information on electrode classification, as well as a brief description of coating types, usable welding positions, type of current and weld metal properties of the various electrode classes, is found in reference (1). Weld Metal Properties ... The selection of electrodes for the metal-arc welding of steel castings is not always simple. One reason for this is that electrode deposits are usually lower in carbon than the castings being welded. The weld metal, which is a mixture of the electrode metal and the fused base metal, is consequently lower in carbon than the parent castings. Alloying elements are added to the electrodes to com- pensate for the lower carbon content. Electrode compositions are designed to give adequate strength when welds are either left as deposited or are simply stress relieved. This simplifies the problem of selection when the castings are merely tempered or stress relieved after welding. Castings which are fully heat treated after welding result in a weaker weld metal than in the as-deposited or stress-relieved condition. Welds in castings which are to have strengths equal to the base metal should be of such composition that they will have comparable strengths after heat treatment. Since it is not always necessary that weld strengths match the strengths of the castings, the lowering of weld strength by heat treatment may not be important unless it affects some other step in the processing of the casting, such as machining. There is very little information available on the mechanical prop- erties of all-weld-metal deposits of the commercially available electrodes, after they have been heat treated. There is even less information on the heat-treated properties of weld metals formed by different electrode base-metal combinations. It is nevertheless possible to find electrodes that will deposit weld metal matching the strengths of castings after heat treatment. Many of these electrodes fall into the AWS-ASTM classifications and details are given in reference (1). In addition, there are some electrodes not in those classifications which deposit weld metal which would be sufficiently strong after heat treatment. In general, because of the subsequent heat treatment, the electrodes used for repair- ing castings should be of a higher classification than electrodes for welding wrought steels of the same composition. For example, Class E8015 or E9015 electrodes might be used for welding castings, whereas Class E7015 electrodes might be used in welding a wrought steel of the same composition. There is a notable difference in the results when depositing metal with the manual electrodes and with the gas-shielded electrodes; the gas-shielded metal arc has a much deeper penetration than the covered electrode arc, and the properties of the weld after heat treatment may be closer to matching the base metal if gas-shielded metal-arc welding is used. 474 WELDING Data on properties to aid the buyer of steel castings in the selection of electrodes for welding steel castings are given in considerable detail in the publication “Recommended Practice for Repair Welding and Fabrication Welding of Steel Castings"(1). (See Note 1, page 470). The rapid cooling of the high-temperature zone of the base metal next to the weld quench-hardens that zone; however, most castings with either construction or repair welds are given a heat treatment after welding to reduce the hardness in the heat-affected zone. Thermal Stresses ... Rapid heating and cooling during welding pro- duce thermal stresses which may be quite large. There is a rapid ex- pansion of the heated base metal around the weld during heating. If the unaffected metal surrounding the weld zone is strong enough, or if the casting is rigidly clamped, the expanding metal in the weld zone will be upset. Upon cooling, the upset section will not return to its original dimensions, and internal stresses will be set up. Shrinkage of the solidified weld metal also causes internal stresses. Internal weld stresses are not serious unless they are of sufficient magnitude to cause distortion or actual cracking. They are essentially eliminated by any of the heat treatments ordinarily given castings after welding. However, if stress is developed while the metal is at high temperatures and in a weak condition, it tears or hot cracks instead of deforming as it would at a slightly lower temperature. Hot cracks are more apt to occur in the weld metal than in the base metal. Cracking of the base metal in the heat-affected zone may occur at low temperatures if stresses build up to high proportions. This under- bead cracking is caused by a combination of: (1) the structure formed by the high cooling rates, (2) hydrogen from the arc atmosphere, and (3) internal stresses. Hydrogen is present in most arc atmospheres although the amount varies greatly with different electrode coatings and, during welding, hydrogen is dissolved in the weld and the adjacent hot base metal. Hydrogen is released as the weld cools and collects in submicroscopic voids under very high aerostatic pressures. These pressures, in addition to stresses caused by a volume change in the metal, frequently start cracks which are then propagated by the other stresses in the weld zone. At least one investigation(4) has shown that carbon steel castings are less prone to underbead cracking than wrought steels of similar composition. Weld metal also may be prone to cold cracking(14, 16). These references indicate that the ductilities of low-carbon weld metals may be lowered by quenching, and microfissures have been found in weld metals so treated. Ductilities are not affected by thermal stresses when preheats over 300 degrees F are used, and low ductilities may be W.ELDING 475 improved by postheating to temperatures around 600 degrees F. It is thought that hydrogen may be the cause of the lowering of ductility in these weld metals. The ductilities of welds in steel castings are not seriously affected by the cooling rates when castings are preheated or postheated. A serious problem sometimes encountered in welding is weld metal porosity, which is caused by entrapped gases. Gases may come from the arc atmosphere, such as by the breakdown of gas-forming com- ponents, or by decomposition of moisture picked up by the electrodes during storage. Gases also may be formed by reaction of elements in the base metal at welding temperatures and sulfur is one of the major porosity-forming elements. Porosity can be minimized by slowing down the freezing of the molten weld metal. This allows the gases to escape to the surface of the weld metal. The weld should be chipped out, and the groove rewelded whenever severe porosity is found. Recommended Welding Practice Carbon-Steel and Low-Alloy Steel Castings . Although considerable time has been spent in studying carbon equivalents and hardening properties of steels, it is not possible to satis- factorily select a method for rating castings according to the ease with which they may be welded. Recommending certain welding procedures does not imply that other methods are not acceptable. Qualified operators will not all handle a particular electrode in the same way; all electrodes of the same general class will not have identical welding characteristics; and welding machines of the same rated capacity will not all have the same electrical characteristics. Thus, it is impossible to set up rigid procedures. Good welds can be made by following definite procedures, but these procedures should not preclude a reasonable deviation for a particular application. Detailed welding procedures for each type of steel should include such items as the welding process, type of steel, electrode specifications, electrode diameter, electrical characteristics (voltage and amperage), details of welding technique, such as machine setting and welding sequence, preheat, interpass temperature and postheat. The recommended procedures listed in Table 83, are very general in nature and for further details on the welding procedure for cast steels, reference (1) is recommended. Multipass welding often requires rigid controls of the interpass temperature, especially for high alloy cast steels. For example, aus- 476 WELDING None except for SAE prohibits welding of car- over 0.40% C. All bon over 0.35% 11-1200 stress Higher C castings should be relieved cooled slowly Cool in still air; High nickel and/or carbon - stress relieve 1100- stress relieve immediately 1250 after welding or furnace cool Low C & alloy - still Low hydrogen electrodes per- air; most-cool in mit lower preheat; may stress furnace or under in relieve immediately after weld- sulation ing, 1100-1250 Insulate or furnace Full heat treatment after weld- cool, or stress relieve ing, low carbon - stress relieve after welding 1100-1250 Cool in still air, but Castings should be ultimately retard cooling fur- stress relieved 1100-1250, high- nace, cool if not er carbon steels full heat treat- stress relieved Table 83_Welding Procedures for Carbon and Alloy Cast Steels* Type of Cast Steel Electrodes Classification Diameter** in Inches Preheat Temperature in Degrees F Postheat Temperature in Degrees F COMMENTS 3/16 Carbon 0.15-0.24% Carbon 0.25-0.33% All E60XX E70XX; E80XX for higher carbons No requirements No immediate care needed 3/16 None None except for widely varying sec- tions None if EXX15 or EXX16 used, other- wise use 200-400 Carbon 0.34-0.50% E70XX, E80XX or E90XX; for Q & T omit E70XX 3/16 E70XX to E100XX Nickel 2300 2-3%; 3-3.75% 3/16 None with EXX16 to 0.35% C; other electrode: 200-400 Ni-Cr (3100) 3/16 E90XX or 100XX E120XX for high C and high alloy Use low hydrogen E100XX-120XX None for low C with EXX16 200- 400 Ni-Cr-Mo 4300 ment Cool in still air high Low hydrogen electrodes elimi- C - furnace cool or nate preheat in many cases; insulate all castings should be stress relieved 1100-1250 3/16 400-600 Ni-Cr-Mo 8600 9800 Low hydrogen E90XX; E100XX; high 3/16 C-E120XX Low carbon EXX16- none; High C 200- 400 Medium Mn 1-2% E90XX & E100XX E120XX for high C None for low C and low alloy 3/16 WELDING 477 Table 83_Welding Procedures for Carbon and Alloy Cast Steels*--(Continued) Electrodes Classification Diameter** in Inches Type of Cast Steel Preheat Temperature in Degrees F Postheat Temperature in Degrees F COMMENTS Mn-Mo Mn 1.00-1.35% Mo 0.10-0.30% 3/16 Use same welding precautions as for medium manganese steel castings 3/16 Mn-Cr-Mo Mn 1.25-1.50% Cr 0.70-0.90% Mo 0.30-0.40% E80XX to E100XX E120XX for some high C - higher alloy Low alloy - none with EXX16; others 200-400 Cr-Steel 5100 E90XX, E100XX & occasionally E120XX 3/16 use low hydrogen if possible E80XX to E100XX 3/16 Low C & low alloy, none if use EXX16; others 200-400 Low C with EXX16 Cool in still air high Castings should be ultimately C & alloy furnace stress relieved. Full heat treat- cool or immediately ment, if possible stress relieve 1100- 1200 Still air, high C & Castings should be stress re- alloy furnace cool lieved 1100-1250 or with insulation Low C still air; For heavy sectioned castings, others - F.C. or use 400 to 600 degrees F Preheat. insulation unless All castings stress relieve stress relieved after 1100-1250 degrees F. welding. Mo-Steel 4000 none - Higher C 200-400 *Fuller details are given in “Recommended Practices for Repair Welding and Fabrication Welding of Steel Castings”. **Maximum diameter for vertical and overhead welding. Otherwise use largest diameter which can be readily handled. 478 WELDING > tenitic chromium-nickel stainless steels are welded with a maximum interpass temperature of 200 degrees F, while martensitic straight- chromium stainless steel requires a minimum preheat of 600 degrees F, which must be maintained while welding. Interpass temperatures are generally governed by the minimum or maximum preheat. The indis- criminate use of preheat and postheat may lead to structures with high hardness and reduced ductility when hardenable steels are welded. It is essential, in the welding of high-carbon and medium-alloy cast steels, to establish a detailed welding procedure which will eliminate undesirable welding defects. The following facts are significant: 1. The maximum quenched hardness is dependent upon the carbon content of the base metal. 2. The postheat temperature required to maintain a given hard- ness in the heat-affected zone should increase with an increase in carbon content. 3. Postheat treatment is most advantageous in welding hardenable cast steels which are sluggish in their cooling transformation. Such steels will develop high hardness and low ductility with only a single preheat. 4. The cooling time for complete transformation of hardenable steel is increased with increases in carbon and alloy content. 5. Generally speaking, the smaller the weld bead deposited, the higher the hardness in the heat-affected zone. 6. Increasing the size of the weld bead decreases the maximum hardness in the heat-affected zone. However, in hardenable steels, it may be advisable to use smaller weld beads in order to reduce the tendency of weld metal cracking or excessive grain growth in the heat-affected zone. Welding Operators . . . It is necessary to assume that the welding operators are qualified and capable of making good welds in all positions. Tests for qualifications of welders have been established by technical societies and government agencies. Welder qualification tests are listed below: 1. MIL-STD-248 (SHIPS) Qualification Tests for Welders. 2. American Welding Society, "Standard Qualification Proce- dure", Part II, Operator Qualification. 3. American Society for Mechanical Engineers, Boiler Code, Section IX. WELDING 479 REFERENCES 1. Recommended Practice for Repair Welding and Fabrication Welding of Steel Castings”, SFSA, Cleveland 13, Ohio. 2. Welding Handbook, American Welding Society, New York, N. Y., 1950. . 3. Henry, O. H., Claussen, G. E., and Linnert, G. E., “Welding Metallurgy”, American Welding Society, New York, 1949. 4. Williams, R. D., Roach, D. B., Martic, D. C., and Voldrich, C. B., “The Weldability of Carbon-Manganese Steels”, Welding Journal, Vol. 28, No. 6, July, 1949, pp. 311-325. 5. Wilson, R. A., “How to Use Semiautomatic Submerged Arc Welding”, Welding Journal, June 1955, pp. 535-541. 6. Wilson, R. A., "A Selection Guide for Methods of Submerged Arc Welding”, Welding Journal, June 1955, pp. 549-555. 7. Smith, D. C., Rinehart, W. G., and Helton, D. C., "Properties and Applications of Low-Hydrogen Iron-Powder Electrodes", Welding Journal, April 1956, pp. 341-347. 8. Ward, A. C., “How Heat and Time Affect Welding", The Iron Age, January 17, 1957, pp. 75-77. 9. Gearhart, Samuel W., Jr., “Welding and Related Procedures Encountered in a Modern Steel Foundry”, Welding Journal, July 1957, pp. 693-702. 10. Wayman, C. M., and Stout, R. D., “Factors Affecting the Tensile Properties of Steel Weld Metal”, Welding Research Supplement, May 1957, pp. 252-262. 11. Rice, W. H., “Welding Cast Components for Nuclear-Power Applications”, Welding Journal, October 1958, pp. 971-978. 12. Chapin, N. A., Soldan, C. H., and Songer, L. W., "Welding Low-Alloy Steel Castings for High-Pressure and High-Temperature Service”, Welding Journal, October 1958, pp. 979-987. 13. Bland, J., Parrish, C. B., and Wheeler, R. C., “Casting Weldments in a Petroleum Refinery”, Welding Journal, August 1958, pp. 789-798. 14. Bland, Jay, "Effect of 'Quench Time' on Weld Metal”, Welding Journal, Vol. 28, No. 5, May 1949, pp. 216-226. 15. Pomfred, R. A., “Removal and Repair of Steel Casting Defects”, Trans. of American Foundrymen's Assn., Vol. 53, 1945, pp. 191-195. 16. Flanigan, Alan E., “An Investigation of the Influence of Hydrogen on the Ductility of Arc Welds in Mild Steel", Welding Journal, Vol. 26, No. 4, April 1947, pp. 1930-2140. > > CHAPTER XVI HEAT TREATMENT PRINCIPLES AND RECOMMENDED PRACTICES The heat treatment of steel castings involves heating and cooling operations designed to improve one or more of the properties of cast steel. The general purposes of heat treatment are to relieve internal stresses, refine the grain, or otherwise change the microstructure and thus obtain desired mechanical and physical properties. SECTION I Principles of Heat Treatment All heat treating processes involve two fundamental operations: a heating cycle, and a cooling cycle. A third factor—the element of time at one or more temperatures, and the rate at which temperature changes are effected—must be taken into consideration in devising a heat treat- ment schedule for any particular steel. The rate of temperature change is of paramount importance in the cooling cycle in establishing the de- sired microstructure and properties. The first step in the heat treatment of carbon and low-alloy cast steel is to raise the temperature of the steel from a low temperature (Figure 552) to some temperature either in or above the transforma- HOLDING UPPER TRANSFORMATION LOWER TRANSFORMATION -FULL ANNEAL TEMPERATURE Fig. 552 A generalized sketch of the steps in the heat treating of steel cast. ings. -NORMALIZE (AIR COOL) HEATING WATER QUENCH TIME HEAT TREATMENT 481 tion range, usually well above a lower limit of 1300 degrees F, in order to put the metal in the austenitic (gamma) condition. The cementite, ferrite, and other components which exist at room temperature, are thus caused to dissolve at the high temperature above the transformation point where they form a homogeneous solid solution called austenite (see Figure 553). This austenite solid solution may be considered as the raw material at high temperature out of which is built the final metal structure on subsequent cooling, or cooling plus tempering opera- tions. Certain high-alloy cast steels, such as austenitic manganese and austenitic stainless steels, are inherently austenitic. These steels, although non-hardening by accelerated cooling rates, are subjected to heating and cooling cycles for retention of certain carbide phases in the solid solution state as well as for the purpose of stress relief. OF 3000 2802°F DELTA PLUS LIQUID LIQUID DELTA 2800 IRON 2600 2552 °F 2400 AUSTENITE PLUS LIQUID DELTA PLUS AUSTENITE 2200 2000 AUSTENITE 1800 1670°F 1600 FERRITE PLUS AUSTENITE AUSTENITE PLUS CEMENTITE 7400 ALPHA FERRITE 1200 A, A 1333°F 1000 800 600 FERRITE PLUS CEMENTITE 300 0 0 0.2 0.4 0.6 0.8 1.0 1.4 PERCENT CARBON 2.0 Fig. 553—The iron-carbon diagram as used for the heat treatment of steel. 482 HEAT TRE A TMENT Heating Heating Rate ... Many heat treatment procedures and specifications for steel castings still advise the operator to heat the castings slowly and uniformly. This is an unfortunate carry-over from the early days of the steel casting industry when metallurgy was in its infancy and accurate temperature control of heat treating furnaces was unknown. Steel Founders' Society has conducted extensive research in the area of heat treatment of carbon and low-alloy cast steels. This research has shown that, for steels of these types, excessive temperature gradients are not possible even under conditions of drastic heating. Figure 554 shows typical time-temperature curves obtained at the surface and center of low-alloy steel castings by heating from a cold furnace and also by heating from furnaces initially at 1250 degrees and 1750 degrees F. It is seen that the temperature difference between the surface and the center of the steel section is small during the heating cycle, regardless of the furnace temperature at the time the casting is placed into it. Steel Founders' Society research has shown conclusively that rapid heating rates are not detrimental to carbon and low-alloy steel castings provided heat transfer to all parts of the furnace load is adequate. It is easy to understand why fast heating of castings is advisable. The rate of heat transfer through the steel casting is such that temper- ature gradients are relatively low, and low temperature gradients are not responsible for initiating high stresses to be set up in the casting. Furthermore, such stresses, if they do form, cannot reach a large magni- tude because increasing temperature in the casting results in stress relief. Stresses in castings are relieved by heating to the temperatures 1800 1800 INTO FURNACE AT 1750°F 1600) INTO FURNACE AT 1750°F 1600 INTO FURNACE AT 1250°F 47400 1400 INTO FURNACE AT 1250F INTO COLD FURNACE 1200 1200 INTO COLD FURNACE 1000 1000 TEMPERATURE - DEGREES F TEMPERATURE • DEGREES F 800 800 1 INCH SECTIONS 3 INCH SECTIONS 600 600 FAL 400 400 SURFACE CENTER SURFACE CENTER 200 200 0 20 40 60 80 100 120 140 160 180 TIME IN MINUTES 20 40 60 80 100 120 140 160 180 TIME IN MINUTES (a) 1-inch section. (b) 3-inch section. Fig. 554—Heating curves at surface and center of a low-alloy steel casting. HE ATTRE A T MENT 483 normally employed in tempering, and the higher the temperature em- ployed, the shorter the time required for relieving the stresses. There- fore, as the casting temperature rises during the fast heating cycle, the casting stresses present in the as-cast condition are relieved. There are definite advantages to rapid heating which include: (1) reduced scaling, (2) less decarburization, (3) avoidance of grain growth, and (4) increased furnace capacity and fuel economy. Maximum Temperature ... The selection of the maximum temperature is determined by the chemical composition of the steel. The higher the temperature, other things being equal, the larger the austenitic grain size, the faster the transformation, as well as speedier solution of cementite and ferrite. However, a temperature just above the upper transformation or critical temperature (A3) (1600 to 1650 degrees F) is usually recommended for carbon and low-alloy cast steels of carbon contents ranging from 0.15 to 0.85 percent. Carbon steels above about 0.80 percent carbon, are heated to a temperature between the lower transformation or critical temperature (A1) and the upper critical (Acm). Full advantage of the hardening effect of the carbon can be obtained by heating to a temperature just at, or slightly above, the Aem temperature. Attention is again directed to Figure 553 which shows the iron-carbon diagram as used to provide a metallurgical guide for the heat treatment of steel. Time at Maximum Temperature ... The length of time steel castings are held at temperature has an influence similar to that of the temper- ature employed. In any heat treating process, temperature and time must be considered simultaneously since practically all changes in metals require time and usually take place more rapidly at higher temperatures. The constitutional changes sought at the maximum temperature are comparatively rapid, which makes the element of time of less importance than the actual temperature itself. Generally speaking, a relatively small increase in temperature will have a far greater effect in accomplishing the desired change than a longer time at some lower temperature. This precludes the need for long soaking times. In addition, scaling, decar- burization, distortion, and similar surface changes are increased with time at temperature. Where these effects are to be avoided, the time factor assumes greater significance. For such reasons, as well as econom- ical ones, it is advisable to use shorter soaking times whenever possible. Cooling The next step after the steel has been heated to the predetermined time-temperature relation, is to cool it at the required rate to develop the desired structure. The temperature, on cooling, at which the transforma- 484 HE AT TREATMENT a tion of austenite to ferrite and cementite takes place (Figure 553) is dependent upon the composition and rate of cooling; and this cooling rate determines the resultant structure and, therefore, the mechanical properties. A slow cooling rate permits only a moderate undercooling to occur and the transformation of austenite takes place just slightly below the lower critical temperature (A1). The resulting structure is char- acterized by coarsely laminated pearlite of relatively low strength, low hardness, and high ductility. With slow cooling there is also a precipita- tion of ferrite in steels under about 0.80 percent carbon. The vast majority of steel castings are made from such steel and, therefore, the resulting microstructure from slow cooling consists of pearlite and ferrite. More rapid rates of cooling, such as air cooling, permit the lamellar pearlite to become progressively finer, and the precipitation of the ferrite also becomes finer and more widely dispersed throughout the matrix, resulting in a less ductile, harder, and higher strength steel. If the cooling speed is increased still further, such as in liquid quenching, the product of the austenite transformation at the lowered transformation temperatures is not pearlite and ferrite, but a new series of hard constituents called bainite or martensite. These constituents are characteristic of fully hardened steel. The cooling rate which just causes the steel to harden fully to a martensitic condition is known as the "critical cooling rate", and depends primarily upon the composition and section thickness of the steel. The martensite which is formed by quenching is very hard and brittle in the untempered condition, and in this condition steel is prone to relieve itself of internal stresses by spontaneous cracking—a fact well known to practical heat treaters. The microstructures of cast steels cooled at different rates are illus- trated in the photomicrographs shown in Section II of this chapter. The alloy content of cast steel has a pronounced effect upon the structure obtained upon cooling. Increased alloy content retards the transformation rate of the austenite, causing the finer and slightly harder lamellar structures to be formed even at relatively slow cooling rates. Further increases in alloy content cause bainite to form upon slow cooling. A so-called “air hardening" steel, therefore, is one in which the transformation rate has been so retarded by sufficient alloy- ing additions as to form the hard martensite or bainite structures even on air cooling from the austenitic condition. > The influence of section thickness must be taken into account in any consideration of the subject of heat treatment. The interior of a heavy section cools more slowly than the surface and so transformation takes place in the interior portions at a later time, with the production of a softer internal structure, than the more rapidly cooling exterior. HEAT TREATMENT 485 This gives rise to a difference in properties between the interior and ex- terior, as well as to possible distortion, non-uniform internal stress, and mixed microstructures. Tempering Tempering is carried out for relief of casting stresses, obtaining the required hardnesses, and for the recovery of toughness and ductility following a hardening treatment. The operation consists of heating at temperatures below the A, transformation temperature (see Figure 553. The stress relief and recovery of ductility are brought about primarily through precipitation of cementite from martensite, and through diffusion and coalescence of the cementite as the tempering operation proceeds. Tempering is a temperature-time operation; for example, a water quenched low-alloy cast steel tempered to the following temperatures, for corresponding holding times, gives the same hardness and properties: Tempering Temperature Holding Time BHN Charpy V-Notch Impact — 40°F °F min. ft - lbs - 1075 1135 1175 1200 300 90 30 15 322 310 310 316 40 41 38 39 Conversely, if a quenched steel is held at a definite tempering tem- perature for various holding times, the hardness values will decrease, as follows: Tempering Temperature Holding Time °F min. BHN Charpy V-Notch Impact — 40°F ft - lbs 1050 1050 1050 1050 15 30 90 320 385 365 340 310 10 18 30 41 SECTION II Transformation Diagrams and Hardenability Isothermal-Transformation Diagrams ... The iron-carbon constitu- tional diagram (Figure 559) indicates that steel at high temperatures is a solid solution, termed austenite, in which condition it is ready either for hardening or for full annealing (softening). Changes in the steel's physical condition takes place on cooling from this austenitic state. These phase changes are determined by the rate of cooling. In order that the effect of different rates of cooling be understood, it is necessary to study the time required for decomposition of austenite as it changes to other structures at individual temperatures below the normal transformation temperature. 486 HEAT TREATMENT . The transformation pattern can be determined experimentally by quenching a group of small specimens from above the transformation temperature into a bath held at a chosen constant temperature. Individ- ual specimens are then removed from the constant elevated temperature bath at different time intervals and quenched in brine. They are then examined under the microscope to ascertain the amount of decomposition of the austenite that has occurred over the particular holding time at the given temperature. A series of such tests conducted at a sufficient number of temperature levels produces the isothermal-transformation diagram (Time-Temperature-Transformation, TTT-curves). Figure 555 is a schematic diagram showing the relationship between cooling rate, microstructure, and hypothetical TTT-curve for a low-alloy cast steel. The shape of the curves, and their positions with reference to the time scale, depend markedly upon the composition and grain size of the transforming austenite. Nearly all alloying elements which Olve in austenite, when added to steel, will change the shape of the curves. These changes are characteristic, depending upon the alloying elements, and thus make it possible to classify steels according to the types of their TTT-curves. In general, an increase in alloy content or in grain size of the austenite results in a retardation of the transformation of the austen- ite; that is, the TTT-curve of Figure 555 is moved to the right in relation to the time axis. Steels whose curves lie farther to the right have greater hardenability, because of the influence of alloying or the increased grain size of the austenite. A fully martensitic structure is initially desired for quenched steel castings so as to develop high strength and toughness properties. To obtain such a structure it is necessary to adopt a cooling rate lying to the left of the knee of the TTT-curve. To determine this cooling rate it is necessary to know the position of the knee of the TTT-curve on the time scale. Thus, a knowledge of the shape of the TTT-curve of a steel is essential to intelligent heat treatment. > The isothermal transformation diagrams of most low-alloy steels are not as simple in shape as the one shown in Figure 555. Some diagrams show two knees, an upper and a lower, on the left-hand curve. In such cases the knee representing the shorter of the two time intervals for the beginning of transformation is the critical one to be considered in a hardening operation. Isothermal-transformation diagrams have been determined for several cast steels.1 TTT-curves for three cast steels are shown in Figures 556, 557 and 558. The three TTT-curves shown are for a cast steel of low hardenability (1030), medium hardenability (4130), and high hardenability (4330), respectively. HE ATTRE AT MENT 487 gu BEGINNING OF FERRITE PRECIPITATION BLOCKY FERRITE END OF FERRITE PRECIPITATION IDMANSTATTEN FERRITE Antigui TEMPERATURE TIME WIDA Random BLACKY DENDRITIC WIDMANSTATTEN FERRITE WIDMANSTATTEN + BLOCKY FERRITE FERRITE + BLOCKY FERRITE MARTENSITE + PEARLITE + PEARLITE PEARLITE + REARLITE Fig. 555—Schematic diagram showing effect of cooling rate on miscrostructure for a hypothetical low-alloy 0.30 percent carbon cast steel (Magni- fication 100 X, reduced 25 percent in reproduction). 488 HEAT TREATMENT 1400 A AF 1200! F+C 1000 A+F+0 800 TEMPERATURE , °F 690 400 1030 CAST STEEL C-0.30 GRAIN Size : 7-8 200 20 HR. I Min. IHR I 103 TIME, SECONDS 10 102 104 105 Fig. 556—TTT-curve. for 1030 plain carbon cast steel. 1400 A 1200 Fuc A+F A +F+C 1000 800 TEMPERATURE, °F F+C A+F+C 600 400 - 4130 CAST STEEL с 0.32 % CR 0.75 % мо 0.27 % GRAIN Size : 8 I MIN. - 200 I HR 20 HR. 10 T 102 103 TIME, SECONOS 104 105 Fig. 557-TTT-curve for 4130 (Cr-Mo) cast steel. HEAT TREATMENT 489 7400 1200 F+C A 1000 A+F A+F+C 800 1 A+F+C TEMPERATURE , °F F + c 600 400 - 4330 CAST STEEL C - 0.33 % CR - 0.72 % No 1.41 % Mo- 0.28 % GRAIN Size :7-8 Min. 200 HR. 20 HR. 1 10 102 104 105 103 TIME, SECONDS > Fig. 558—TTT-curve for 4330 (Cr-Ni-Mo) cast steel. These diagrams may be studied in terms of the different fields of which they are composed. These fields are designated by the following letters: A-Austenite F-Ferrite C-Cementite (Iron Carbide) The field marked “A + F" represents a region in which austenite (A) and ferrite (F) exist together. The longer the time the steel is held at a particular temperature, the greater will be the transformation and, hence, the quantity of ferrite present. Fairly accurate heat treating plans can be designed for various steels by using TTT-curves. Treatments that can be established with precision if TTT-curves of the steels or similar steels are available are: spheroidizing, normalizing, annealing, hardening and martempering. The practical heat treater will, of course, realize that quenching steel into water or oil at room temperature does not result in transformation at a constant temperature, but in transformations which occur during continuous cooling. The transformation in such cases starts at temper- atures and times that are displaced somewhat below and to the right of the TTT-curves. 490 HEAT TREATMENT Isothermal-transformation diagrams (TTT-curves) may also be used to prevent hardening. This fact is of use in certain cases, such as the welding of steel castings, where it is quite desirable that the steel surrounding the weld forms the softer, pearlitic structure rather than the harder, martensitic structure. It can be used to control shakeout temperatures so that air hardening of green castings is avoided. Considerable evidence exists that there is no difference between the TTT-curves of cast and wrought steels of the same composition. (1, 2, 3) Therefore, TTT-curves established for either cast or wrought steel of like composition can be utilized in the heat treatment of steel castings or wrought steel products. Hardenability ... The ability of steel to harden upon quenching has long been recognized as one of its most valuable properties. The hard- ness of the steel depends upon the speed of the quenching process; the more rapid quench usually results in a high hardness (at a given car- bon content). The degree of hardening which occurs with specific quenching rates is a measure of the hardenability of the particular steel. Since quenching rates decrease from the surface to the center of a steel structure, depth hardening depends upon the "hardenability" of the particular steel. The term “hardenability" as applied to any particular steel em- braces two basic principles: (1) quenching develops a maximum surface hardness; and (2) there is a limit to the section size which will be hardened completely through, upon quenching. As to the first principle, the degree of maximum hardness increases mainly with the carbon content of the steel. This maximum hardness is not significantly affected by the addition of alloy contents up to approximately 5 percent. How- ever, before maximum hardness can be imparted to a steel, three condi- tions must be fulfilled: (1) the carbon must be completely in solution in the austenite at the time of quenching; (2) the steel must be cooled at a sufficiently fast rate to result in the formation of the hard, martensitic structure; and (3) austenite must not be retained, following the quench- ing treatment. > The second principle of hardenability is understandable in light of the fact that the addition of almost any alloying element dissolved in the austenite of steel retards the transformation of the austenite upon cooling. This condition reduces the critical cooling rate of the steel, and makes it possible for the steel to be fully hardened at a lower cooling velocity. Thus, it is possible, by alloy additions, to completely harden thick sections. By the same principle it is possible to harden thinner sections by less rapid cooling methods, such as air cooling, instead of water quenching. HEAT TREATMENT 491 It has long been recognized that plain carbon steels are shallow hardening, and that alloy additions to steel increase the depth of hard- ening; but such generalizations are not sufficiently accurate for modern- day engineering needs. Measurable hardenability values for various steels are required, and such values are obtained by applying the end- quench hardenability test. This test has made it possible to predict the depth to which a particular steel can be hardened by applying a specific quenching rate. The American Society for Testing Materials and the Society of Automotive Engineers have accepted the end-quench method of deter- mining hardenability, and have published approved procedures for con- ducting the tests. The hardenability of cast steel is greatly affected by alloy contents and slightly affected by grain size. The effect of alloy content was shown by the hardenability curves for the various low-alloy steels in Chapter X. The reader is requested to refer back to that chapter for specific in- formation on this subject. Hardenability decreases with decreasing grain size. This relationship is shown in Figure 559. This curve shows the variation of ideal critical diameter with grain size for a plain carbon steel. The ideal critical diameter is the diameter of a bar which would harden just to 50 percent martensite at the center under ideal quenching conditions. The hardenability of either cast or wrought steels of the same com- position is identical. Generally, cast steels contain slightly higher amounts of silicon and manganese than comparable wrought steels and so usually have slightly greater hardenability. 0.8 PLAIN CARBON STEEL 0.7 - IDEAL CRITICAL DIAMETER , INCHES 0.6 1 0.5 0.4 3 5 7 9 GRAIN SIZE Fig. 559—Ideal diameter vs. grain size for a 0.30 percent carbon steel, aluminum killed. (Data from Kramer, Siegel, & Brooks) 492 HE ATTRE AT M E NI SECTION III Liquid Quenching The engineering value of quenching and tempering steel castings has been proven conclusively in service. The large quantity of high- tensile, high-yield strength castings, needed by the Army during World War II, introduced large scale use of quenched and tempered steel cast- ings. This wartime experience has proven valuable to the present-day steel castings design engineer, producer and purchaser. The outstanding record of wartime castings has enhanced the reputation and use of steel castings in general. Increasingly, purchasers are becoming more fully acquainted with the attractive possibilities of using high-strength, liquid-quenched castings possessing excellent toughness. A point of special emphasis is that complete hardening and temper. ing of cast steel sections produce a higher ratio of ductility to tensile strength than either full annealing, or normalizing and tempering. In addition to the increased strength and toughness obtainable, quenching and tempering can permit the use of lower alloy content, in many instances, to meet a particular specification, with attendant savings in material cost. The best combination of strength, ductility and toughness, as measured by resistance to impact, is produced in cast steels by quench- ing and tempering treatments. The section thickness must have the capacity to be sufficiently hardened by the quench which is used. In some cases complete hardening may be considered as accomplished for commercial purposes when the section has a microstructure of 50 percent martensite at the center. The factors which determine the depth to which a steel will harden are: (1) the severity of the quench, (2) the sectional thickness of the casting, and (3) the chemical composition and grain size. It should also be remembered that the maximum mechanical properties attain- able from quenching and tempering cannot be secured in central por- tions of sections which are only partially hardened. For example, if a cast steel is of such a composition that, upon quenching it will just harden throughout a one-inch section, any section larger than one inch, when similarly quenched, will have an unhardened center. The thicker the section of this particular steel, the greater will be the internal portion not completely hardened, with the result that the average mechanical properties of the section will be lower than the maximum potential properties of the steel. The metallurgical principles involved in the water quenching of steel castings are the same as those applying to the quenching of any other steel structures when complete cross sectional hardening is sought. The requisite factors are: HEAT TREATMENT 493 (1) Steel of sufficient hardenability for the section size involved; (2) A quenching bath of such capacity and circulation that the surface of the piece being quenched rapidly approaches the temperature of the quenching medium, thus providing the maximum possible cooling rate; (3) Removal of the quenched part before its temperature has dropped below the martensitic transformation (M) temper- ature. This temperature will vary, depending upon the steel composition; but for most low-alloy cast steels this temper- ature is between 250 and 350 degrees F. The risk of quench cracking is greatly increased if the temperature of the casting is allowed to drop much below the Me temperature, or to about 250 degrees F, before being tempered. The factors which must be controlled and repeated time after time in as nearly the same manner as possible are: (1) The temperature of the casting as quenched; (2) The severity of the quench: (a) liquid temperature, (b) liquid circulation; (3) The immersion or spraying time; (4) The temperature and time of tempering after quenching. Steel castings, upon removal from the heat treating furnace, must be conveyed to the quenching tanks before any austenite has trans- formed, and quenched in accordance with a precise schedule. Figure 560 shows steel castings in the process of being quenched in water. Small castings are often placed in baskets for quenching; medium-size castings are suspended from, or placed on, racks; and large castings are usually handled individually by an overhead crane or by the use of a quenching fixture. - Fig. 560 — Water quenching of medi. um size steel cast- ings. 494 HE AT TREATMENT Comparison of Quenching Processes The drastic cooling required in carbon and low-alloy steels to obtain a martensitic structure usually produces high residual stresses in the casting due to the steel's contraction on cooling. In addition, the reaction of austenite changing to martensite results in a volume expansion of approximately 4 percent. The interaction of these two factors may be so severe as to cause distortion and cracking. The ideal method for minimizing the distortion and cracking in quenching castings would be to cool the steel rapidly until it reaches the martensite formation temperature, and then cool very slowly through this range to minimize temperature gradients and reduce the high stresses which they produce. It is difficult to attain the ideal method in actual practice, but several methods have been developed that provide practical and effective solutions to the problem. Conventional Quenching ... The conventional and usual quenching and tempering method employed over the past several hundred years, is shown in Figure 561 (A). The steel casting is quenched from above the transformation temperature into a suitable liquid (water), then re- heated to the tempering temperature until the desired hardness is obtained. CONVENTIONAL A QUENCHING AND TEMPERING MAR TEMPERING B Ae, Ae, CENTER TEMPERED MARTENSITE CENTER TEMPERED MARTENSITE SURFACE SURFACE Ms Mf 70°F 70 °F LOG TIME TEMPERATURE AUSTEMPERING 15OTHERMAL QUENCHING AND TEMPERING Ae, Ae, CENTER CENTER TEMPERED MARTENSITE SURFACE SURFACE Ms Mf 70%! 70°F LOG TIME BAINITE Fig. 561—Comparison of quenching processes. (Data from United States Steel Corp.)" HEAT TREATMENT 495 a Martempering ... Quenching employing the martempering operation requires quenching the casting in a molten salt or metal bath (see Figure 561 B). The quenching bath temperature depends on the martensite transformation range of the steel being treated (see Table 84). Usually the martensite formation temperature (M) or one slightly above is selected for the bath temperature. The casting is permitted to equalize its temperature in the molten salt bath, after which it is re- moved and permitted to cool in air to room temperature. The steel cast- ing is then reheated for tempering to the required hardness. The time the casting remains for equalization in the molten bath will depend on its thickness, the temperature of the bath, and the composition of the steel. The purpose of holding the casting in the bath is to reduce the thermal gradients and produce resulting stresses of low value. This process aids materially in reducing distortion and cracking. > . Isothermal Quenching .. In the isothermal quenching method, the castings are quenched in a molten salt bath, which is just above the Me temperature. The steel casting is held in this bath until its tem- perature gradients become equalized and then it is removed from the molten salt bath and placed in the tempering furnace which is maintained at the desired tempering temperature. This practice is shown in Figure 561(C). The isothermal quenching method is often used in place of martempering if the steel being quenched has a high M, temperature. It is often difficult to get past the nose of the TTT- curve unless a lower temperature bath is used. For this reason, iso- thermal quenching is used as a compromise between marquenching and conventional quenching. Table 84—Temperature Range of Martensite Formation in Several Carbon and Alloy Cast Steels (Grange and Stewart) 5 Steel SAE No. Martensite Formations (Ms) °F. 50% Martensite Formed °F. 99% Martensite Formed °F. 1030 1065 1090 1335 2340 3140 4130 4140 4340 4640 5140 6140 8630 9440 650 530 425 650 580 635 715 650 550 650 650 620 690 625 560 425 315 560 560 550 650 570 480 570 570 560 630 540 450 300 180 450 405 430 550 440 370 480 450 450 530 405 496 HEAT TREATMENT Austempering ... Another method of quenching used for the purpose of preventing cracking and distortion is austempering. This method of heat treatment is not widely used because the castings must be small and of thin sections. High-carbon steels, in the neighborhood of 0.90 percent, are suitable for this method. The pieces are quenched in a molten salt or metal bath, the tem- perature of which is above the martensitic transformation temperature but below the nose of the TTT-curve (see Figure 561 D). For a 0.90 percent carbon steel the temperature would be about 500 to 600 degrees F. Use of the high temperature bath is necessary to insure the absence of martensite. The steel piece is held in the bath until trans- formation to bainite is complete. Thin sections are required because it would take too long to transform heavy sections. Austempering fur- nishes a method of heat treatment for excellent toughness in high hard- ness ranges where stress concentration is held to a minimum. Time Quenching and Slack Quenching ... Two modifications of the aforementioned delayed-quenching methods are time quenching and slack quenching. In the time quenching method, castings are quenched and the time is found for the thickest section to cool to about the middle of the martensite transformation range. The casting is then removed from the quenching liquid and the temperature permitted to equalize throughout the casting. The casting is then placed in the tempering furnace as soon as the casting temperature has dropped to just below the Me temperature, and it is heated to the tempering temperature. The slack quenching method permits the casting to be immersed in the quenching liquid until the surface has begun to transform to mar- tensite. The casting is then pulled out of the quench tank and held in air for a short time in order that the surface and center can approach the same temperature. It is then immersed in the liquid and quenching is completed. A tempering treatment follows. Both of these quenching methods are used primarily for the purpose of avoiding quench cracks. In this respect, the delayed quenching methods are somewhat more effective than the conventional method of quenching. However, this improved freedom from quench cracks is realized often at the expense of a mixed microstructure, mixed hardness, and mechanical properties that vary continuously from the outside to the center of the casting. SECTION IV Recommended Practice for the Heat Treatment of Carbon and Low-Alloy Steel Castings Furnace and Loading Requirements ... Controlled furnaces are re- quired in heat treating operations so that uniform temperatures and HEAT TREATMENT 497 heating rates can be maintained. For this reason, the following re- quirements must be met if optimum furnace performance is to be attained : 1-Tight-fitting doors and sand seals are required to prevent ex- cessive air filtration, convection losses of heat, and cold spots. 2—Burners must have the proper amount of air and correct gas pressure. 3–Proper burner velocities and furnace design are necessary to assure thorough circulation of hot gases without stagnant layers or pockets. 4-A sufficient number of properly located burners is necessary if thermal blind spots are to be eliminated. Care must be taken in loading the furnace. The castings should be well spaced on the truck or supported on racks. Proper spacing and stacking of the load and positioning of the castings on the furnace floor are most important for optimum circulation of the hot gases to permit rapid and economical heating of the castings (see Figure 562). Radia- tion is the most important mechanism of heat flow at austenitizing temperatures. Annealing ... Full annealing is carried out to provide maximum soft- ness and full relief of stresses, and is the only heat treatment given to many carbon steel castings. The full annealing treatment should never be given to low-alloy steel castings since it provides no mechanical property advantage to justify the use of the extra alloying elements. Full annealing serves to increase the ductility of the steel but it lowers its strength. Fig. 562—Cast cross bearer arms loaded on car for heat treatment. Note care- ful spacing for optimum heat treating results. 498 HE AT TRE AT MENT A full anneal involves heating to a temperature above the upper critical (A3), holding at this temperature for a short period of time to insure that the section is fully at temperature, and furnace cooling. The austenite which is formed at the annealing temperature breaks down into ferrite and pearlite on furnace cooling. Casting purchasers sometimes specify that carbon and low-alloy steel castings be given a homogenized treatment before annealing, or even a double anneal. Both of these procedures are superfluous and obsolete. The practice should be discontinued by economy-conscious operators. These prior treatments have no effect on the quality or the mechanical properties of properly heat treated steel castings. The rate of cooling determines the degree of softening during full annealing, and if the TTT-curve is transversed at a higher temperature by slower cooling, a softer product is formed. The rate of cooling after the transformation is complete is of little consequence, and appreciation of this fact, and a knowledge of the TTT-curve of the steel, often can save hours of furnace time. Better properties can be obtained by air cooling (normalizing) and, therefore, it is well to avoid the full annealing treatment of castings where possible. An air cool followed by a stress relief or temper also results in less furnace tie-up during heavy production periods. Normalizing... This term is applied to the method of heat treatment which consists of cooling the castings in air, after holding them for a short time at a temperature just above the upper critical. Although normalizing is not usually a drastic hardening process, variations in the rates of cooling through the transformation range will influence the resulting mechanical properties. A one-inch section will cool faster and give higher strengths than a two-inch section cooled under similar conditions. Therefore, because of these variations in cooling rate, lower strengths and hardnesses may be expected within the heavier sections of a casting that contains both light and heavy sections. Also, in batch- a type furnaces, the cooling rate is normally retarded in the central portion of the load, so the method of furnace loading must be considered care- fully if uniform results are to be obtained in air cooling treatments. It is often expedient to remove the heated castings from the furnace chamber or car to cooling stands which afford free circulation of air. This provides uniform cooling at a faster rate, with resultant improve- ment in physical properties. Additionally, furnace capacity and fuel economy are enhanced by this practice. A homogenizing treatment or a prior normalizing treatment some- times has been specified before the final normalizing. Both of these pretreatments are superfluous and do not result in any improvement in Fig. 563—Steel cast. ings being removed from the furnace after a normalizing heat treatment. casting quality or in mechanical properties. In the best interests of economics, they should not be specified. Another important point is the time the castings must be held at temperature before air cooling. Once the whole casting reaches the normalizing temperature the time can be relatively short; 15 to 30 minutes at temperature is sufficient, regard- less of section thickness. It should be understood that the time of holding is initiated when the slowest heating portion of the load reaches temperature, and not when the furnace atmosphere reaches temperature. An advisable heating temperature for normalizing is one of 50 to 100 degrees F above the Az temperature; for most cast steel, this would be 1600 to 1650 degrees F. Normalizing is often preferred to quenching, particularly for cast- ings of complex design, in order to avoid quench cracking. Cooling of thin section castings in an air blast is not considered normalizing, since this treatment produces accelerated cooling rates somewhat like those employed in conventional quenching operations. Quenching ... The casting is heated to a temperature above the upper critical (A3) and cooled rapidly by immersion in a liquid, if full harden- ing is required. The best mechanical properties are produced by quench- ing followed by tempering, and together they give an optimum combina- tion of strength, hardness, ductility and toughness to the steel. The recommended procedure for the quenching of most carbon and low-alloy steel castings is as follows: 1–Place the castings in a furnace which has been preheated to the austenitizing temperature; 500 HE AT TRE ATMENT 2-Raise load as rapidly as possible to 50 or 100 degrees F above the upper critical temperature; 3–After the entire casting reaches the austenitizing temperature, hold for 15 to 30 minutes; 4-Quench in a water bath or spray; 5—Temper. The above procedure affords the optimum mechanical properties and, at the same time, the lowest possible heat treating costs. The reader will note in the above procedures that several new con- cepts in the heat treating of carbon and low-alloy steel castings are in- troduced. Recent extensive research has shown conclusively that such practices as slow heating of castings, homogenizing or normalizing prior to quenching, long holding times, and double quenching do not result in any additional mechanical property benefits, but merely result in furnace tie-up and increased cost which cannot be justified; therefore, these practices should not be employed. Efficient quenching may be difficult to achieve because of the presence of different thicknesses within the same casting. The uneven cooling, because the heavier sections cool slower than the lighter sec- tions, may result in cracking in the lighter sections; thus a liquid quench treatment may not be suitable for some castings. Methods are available to minimize the danger, such as: differential quenching, directed spray quenching, lagging lighter sections, or protecting them with plates to prevent excessively rapid cooling. Tempering ... . The tempering treatment follows the normalizing or quenching operation. The function of the tempering after a normalizing heat treatment is primarily to relieve cooling stresses and provide the desired hardness or mechanical properties. Tempering, following a quenching treatment, acts similarly to reduce stresses and hardness, and further acts to precipitate the carbides which reduces the brittleness of the martensite present. Tempering normally decreases the tensile strength and yield point of the hardened steel, but markedly increases ductility and impact resistance. The recommended procedure for tempering carbon and low-alloy steel castings is as follows: 1-Place the castings in a recirculating type furnace which has been preheated to the tempering temperature. Attention should be given to proper casting spacing so that good heat distribution is possible to all parts of the load; HEAT TREATMENT 501 2–Heat as rapidly as possible to a tempering temperature not to exceed 1275 degrees F; 3—After the castings reach the tempering temperature, hold for such a time as to develop desired hardness levels. Wherever possible to do so, adjust temperatures for 15 to 30-minute hold times, regardless of casting thickness; 4–Air cool or quench. This procedure results in the optimum mechanical properties and, at the same time, the lowest possible costs. Such procedures as holding at tempering temperature for one hour per inch of cross section and double tempering do not benefit the usual carbon and low-alloy steel casting quality or mechanical properties and, in the interests of economy should not be practiced. Stress Relief Treatment ... If the relief of stresses is the only con- sideration, temperatures lower than 500 degrees F are of little value and temperatures higher than 1100 degrees F are not often required. Experimental work has indicated that a temperature of 750 degrees F will reduce residual stresses approximately 50 percent, and that tem- peratures of 1000 degrees F will reduce stresses more than 90 percent. The time and temperature selected depend upon the degree of stress relief desired. Increased temperatures for stress relieving of hardened steel will cause a progressive loss in strength, along with progressive improvement in ductility and impact resistance. Stress relief tem- peratures lower than 1000 degrees F will have little effect on the strength or ductility of normalized steel. Castings made from steels of high hardenability, such as many low- alloy grades, usually should be preheated before flame cutting or welding to avoid the buildup of localized high stresses. No further stress relief is necessary for hardened steels which have been tempered, since the tempering treatment serves for stress relief. Differential Hardening ... A differential hardening treatment may be employed when it is desired that only certain portions of the casting possess the qualities afforded by liquid quenching. Castings can be differentially hardened by a method which involves quenching of the entire casting following selective heating by one of several methods. The process embraces the use of oxy-acetylene flame, induction heating, or furnace heating, to raise the temperature of the surface of the steel castings at the desired locations above the Az transformation point, so that subsequent quenching will produce a desired hardness and structure. This process, along with other surface hardening procedures, is dis- cussed in more detail in Chapter XI. 502 HEAT TREATMENT REFERENCES 1–Eddy, C. F., Marcotte, R. J., and Smith, R. J., "Time Temperature Transformation Curves for Use in Heat Treatment of Cast Steel”, Transactions AIME, Vol. 162 (1945) pp. 250 - 267. 24United States Steel Corporation, “Atlas of Isothermal Transformation Dia- grams", Second Edition, 1951. 3—United States Steel Corporation, “Supplement to the Atlas of Isothermal Trans- formation Diagrams”, 1953. 4-Kramer, I. R., Siegel, S., and Brooks, J. G., "Factors for the Calculation of Hardenability", Transactions AIME, Vol. 167 " (1946) pp. 670 - 697, 5—Grange, R. A., and Stewart, N. M., “The Temperature Range of Martensite Formation", Transactions AIME, Vol. 167 (1946) pp. 467 - 501. > 1 CHAPTER XVII THE MACHINABILITY OF STEEL CASTINGS Machinability is a term used to indicate the relative ease with which a material is shaped by cutting tools in operations such as turning, drilling, milling, broaching, threading, reaming, sawing or grinding. The machining operation involves efficient metal removal in roughing operations as well as high accuracy and good finish during final machin- ing. Machinability is evaluated in several different ways depending on the objective. Machinability generally includes a concept of tool life, cutting speeds and surface finish. Therefore, it involves tool performance, surface finish, machine speeds, feed and depth of cut, design of cutting tool, cutting fluid and the quality, composition, hardness and microstructure of the steel. Machinability may be evaluated commercially by several criteria, for example, in terms of tool performance as represented by the tool life per operation under given conditions; the speed at which the material can be cut, under different conditions, while maintaining a given tool life; the force, energy or power required for the cutting; the surface finish produced or the dimensional accuracy maintained among like pieces under given conditions. Values of machinability are comparative and usually only represent the behavior of the material under the given conditions. The factors affecting machinability are as follows: 1. Material being cut—its composition, structure, shape and size. 2. The cutting speed, size and shape of cut. 3. The cutting tool—its material, quality, treatment, shape, size, surface quality and condition. 4. The condition of the machine tools on which the cutting is done, together with the process involved. 5. The cutting process—different processes may yield different ratings because of variations in the feed, speed and depth of cut. 6. Rigidity of the tool and work holding device. 7. Characteristics of the cutting fluid used and its cooling prop- erties. Actual machining experience, correlated with metallurgical data, have resulted in much information on the fundamental factors which affect the machining of steel. However, factors which are confined to 504 MACHIN ABILITY the cutting operation itself are not within the scope of this chapter, and only those factors which are metallurgical in character and inherent in the steel are considered in detail. The chemical composition of a steel has a major influence on the machinability of the steel, since composition affects the properties and the structure of the steel. Carbide forming elements generally decrease machinability by in- creasing hardness. However their detrimental effect can be modified through heat treatment. Elements which form inclusions that are hard or abrasive, such as alumina or silica, or those which dissolve in ferrite have deleterious effects on the machinability of steel. Conversely, elements which form soft inclusions have a beneficial effect. Sulfur provides a specific example, and is the element most commonly used by the wrought steel industry to improve machinability. However, it is imperative that manganese also be present, in amounts at least three times the sulfur content, if significant benefits are to be realized. The large globular sulfide inclusions which result from this practice are somewhat more effective in reducing friction between the cutting tool and the metal chip, than are linear sulfide inclusions. Carbon itself has a varying effect on machinability. Very low carbon steels are difficult to machine because they are too tough. But on the other hand, cutting qualities of cast and wrought steels decrease rapidly with increase of carbon above 0.30 percent. The effect of manganese on machinability depends on the total carbon, the manganese, and sulfur content. The amount of manganese added to the steel should be more than that required to combine with the sulfur. This precludes the existence of harmful iron sulfide, and some manganese is left in the matrix to act as a steel strengthening agent. The general effect of alloying elements is to decrease the machin- ability by increasing the hardness and toughness of the steel. However, molybdenum, chromium or vanadium decrease machinability to a lesser degree than do other alloying elements, such as nickel. Additions of lead, selenium or tellurium to cast or wrought steels improve their machinability. Selenium and sometimes tellurium are added to stainless steel castings for this express purpose. The addition of lead as a uniform mixture in steel provides an automatic lubricant for heavy sliding friction at the cutting edge of the tool. The advantage of lead lies in its ability to act as a lubricant under loads up to and exceeding the ultimate strength of the steel being machined. Additions of lead to cast steels, particularly low alloy steels, are effective in permitting faster machining speeds as well as increasing the tool life. MACHIN ABILITY 505 Machining of Steel Castings Many steel castings are used in the machined condition by all types of industries. Data on the machining of various grades of cast steels with different heat treatment (different microstructure) have been obtained recently, and the significance of microstructure, hardness and tensile strength of cast steel on its machinability has been evaluated. Steel castings are often delivered to the customer in the normalized condition. This is not necessarily the heat treatment which produces optimum machining properties. Heat treatment for optimum machin- ability, because of other considerations, may not always be employed; but it may be justified when the production requirements are large enough, and the tool and time savings great enough, to offset the addi- tional heat treating cost. Furthermore, the strength requirements and applications of the casting must be considered. For example, the micro- structure for castings requiring high impact strength is not the micro- structure that might give the best machining properties. Thus machin- ability in this particular case would be necessarily sacrificed because of the strength requirements. Effect of Microstructure ... The machinability of cast steel depends not only on its chemical composition, toughness and hardness, but also on its microstructure. Free ferrite, which is present in cast steels under 0.50 percent carbon, is a soft, ductile material, which is easily cut with little tool wear. At the same time, it is tough and easily deformed-properties which allow it to be torn away from the stock leaving a rough machined surface. Pearlite, present in small amounts in low carbon cast steels, in- creases with carbon content. The laminated structure of pearlite is . quite rigid, since the soft ferrite layers prevent the hard carbide plates from breaking while the latter prevents the ferrite from deforming. Lamellar pearlite is a most favorable structure in steel for optimum machinability unless there is too much present. The ideal ratio of ferrite to pearlite in carbon cast steels is a 60:40 ratio. Machinability decreases as the percentage of pearlite rises above the ideal 60:40 ratio, due to the increase in strength from this source. An excessively high pearlite content may affect machining to a very serious degree. Machinability of cast steels that contain an unfavorable dis- tribution of ferrite and pearlite may be improved by spheroidizing the cementite (changing the form of the iron carbide) through heat treat- ment. Generally speaking, spheroidized steel provides longer tool life with high-speed tools, but is not as effective if carbide tools are employed. 506 MACHIN ABILITY Carbon cast steels up to 0.50 percent carbon are more easily machined when a lamellar pearlitic structure is present in the favorable ratio. Grain size has a significant effect on the machinability of steel, and it is generally agreed that some improvement in machining performance occurs with large grain size. Fine grain size usually produces excellent surface finish but gives less pieces for each grinding of the tool. In low carbon steel, the finer grain size affords better machinability because the microconstituents are harder and less ductile. This greater hardness and lower ductility are needed when steels have a large amount of free ferrite. In medium carbon cast steels, the finer grain steels develop more heat in machining, thus more frequent tool grinding and a sub- sequent decrease in production occur. Medium carbon steels of large grain size can have a detrimental effect on machinability because the tool must cut through the large areas of pearlite which are about 0.85 percent carbon. Although it is generally true that the larger grain size gives better machinability, this is only true up to the point where the grains become quite large and the ferrite begins to exist as thin envelopes around the coarse pearlite grains. Alloy steel castings may be purchased with fine, medium, or coarse grain size, with a variety of microstructures, and with various degrees of hardness depending on the heat treatment employed. Thus it is obvious that the structural conditions (grain size, microstructure and hardness) of an alloy steel casting will affect its machinability. Alloy steel castings are more difficult to machine than carbon steel castings because some alloying elements are carbide formers. The elements that form carbides have the same effect as higher carbon on machining properties because of the effect of the carbide forming elements on hardenability. The poorer machining properties of alloy castings are evidenced at a lower carbon content than for plain carbon cast steels. However, if the carbide is spheroidized through heat treatment, the carbide forming elements cause no particular difficulty. Alloying elements which form solid solutions toughen and strengthen the ferrite. Therefore, alloy castings alloved with such elements as manganese, nickel and chromium are more difficult to machine than straight carbon steels. Effect of Hardness and Tensile Properties ... Hardness alone is not an absolute criterion for predicting tool life in the cutting of cast steels, because such items as composition, microstructure and mechanical factors which have a bearing on machinability are not always reflected in the Brinell hardness test. However, Brinell hardness may be re- garded as a rough index of machining properties and a Brinell range of 170 to 229 usually gives the most satisfactory machining. MA C H IN A BILITY 507 Figure 564 is a plot of cutting speed for one hour tool life vs. the Brinell hardness of cast steels. The plot indicates a wide range correlation. For example, at a hardness range of 175 to 200 Brinell, the cutting speed for one hour tool life varies from 60 to 135 surface feet per minute. The plot indicates by its general direction that, as the hardness increases, the cutting speed for one hour tool life decreases. CODE 400 4340 QT A ANNEALED 400 BHN N 375 NORMALIZED NA NORMALIZED & ANNEALED 350 NN DOUBLE NORMALIZED NT NORMALIZED & TEMPERED 325 NS NORMALIZED & SPHEROIDIZED NOQ NORMALIZED & OIL QUENCHED QT QUENCHED & TEMPERED 300 275 4340 QT 250 300 BHN 4340 NS 8430 NT-1200°F 225 O 1040 NOQ -8430 NT-1275 °F 1040 N 200 K1040 NN 1330 N 175 1040 NA 4130 N 150 1330 NT 8630 A 4130 A 125 1020 N O 1020 A 100 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 CUTTING SPEED, FEET PER MINUTE Fig. 564_Cutting speed for one hour tool life vs. Brinell hardness using high-speed steel tools. 08630 N BRINELL HARDNESS 4340 NAO Free machining steels are soft, with poor ductility, and have the property of low work hardness. Tensile properties can be used to show the relationship of tensile strength to ductility. Power Requirements for Cast Steels ... The power requirements for machining various cast steels are evaluated as horsepower per cubic inch per minute. Table 85 gives an indication of machine capacity in terms of horsepower. The high-speed steel tools were checked in the speed range of 50 to 100 fpm, and the carbide tools were checked in the range of 200 to 800 fpm. The feeds per revolution were in the range of 0.005 to 0.015 inch. It will be noted that the power required by the high-speed tools generally follows the Brinell hardness of the cast steel. This is not necessarily true for carbide tools. 508 MACHIN ABILITY Table 85–Power Requirements for Machining Cast Steels Cast Steel Speed (fpm) Carbide HSS Hp/cu in/min Carbide 78B HSS Structure BHN 1020 200-500 300-800 50-100 50-100 Annealed Normalized 122 134 0.89 0.90 0.82 0.82 1040 200-500 200-500 300-500-800 300-800 50-100 50-100 50-100 50-100 Annealed Normalized Double normalized Normalized and quenched 175 190 185 225 0.77 0.74 0.87 0.78 0.84 0.82 0.94 0.93 1330 200-500 200-500 50-100 50-100 Normalized Normalized and tempered 187 160 0.83 0.92 0.79 0.89 4130 300-800 300-800 50-100 50-100 Annealed Normalized & spheroidized 175 175 0.82 0.85 0.90 1.02 བ བ བ བ 4340 200-500 300-800 200-500 200-500 50-100 50-100 50-100 50-100 Annealed Normalized & spheroidized Quenched and tempered Quenched and tempered 200 210 300 400 0.81 0.80 0.87 0.90 0.87 0.93 1.00 1.07 8430 300-800 50-100 180 0.76 0.98 Normalized & tempered, 1275°F Normalized & tempered, 1200°F 300-800 50-100 200 0.71 0.88 8630 300-800 300-800 50-100 50-100 Annealed Normalized 175 240 0.76 0.85 0.88 0.89 Estimates of power requirements for steel castings when schedul- ing and planning work for the machine shop are made by these steps: 1. Determine the rate of metal removal [(cutting speed in inches per minute) X (inches per revolution) X (depth of cut)]. 2. Select unit power requirement from Table 85. 3. Multiply unit power by rate of metal removal to obtain horse- power required at the cutting tool for a sharp cutter. 4. Normal efficiency of the machine itself, plus the added drag as the cutting tool becomes dull, will increase the power require- ment of Item 3 by approximately 50%. Accordingly, a factor of 1.5 should be used to provide a safe motor rating. The power requirement for turning a normalized 1040 tubular shaped steel casting with a carbide tool at 300 surface feet per minute, with a feed of 0.015 inch per revolution and with a depth of cut of 0.125 inch, is determined as follows: MACHIN ABILITY 509 (1) Rate of metal removal is 300 x 12 x 0.015 x 0.1256.75 in? (2) From Table 85. The power requirement per cu in/min is 0.74 Hp. (3) The power requirement for 6.75 in is 6.75 x 0.74–5 Hp. (4) Fifty percent should be added for tool dulling and machine efficiency, thus the lathe motor required will be 5 x 1.5-7.5 Hp. Machining the Surface of Steel Castings ... The skin is usually con- sidered to consist of the oxide scale as well as any base metal approxi- mately 1/8 to 14 inch below the surface which may not be chemically or structurally equivalent to the base metal. The surface scale resulting from heat treatment has a detrimental effect on machinability and must always be removed by pressure blasting prior to any machining operation. The steel casting industry strives to cast close to the final dimen- sions of a part, and, therefore, the major part of the machining is often confined to the skin. Some misconception concerning the machin- ing characteristics of cast steel has, no doubt, arisen from the fact that most commercial machining is done on the casting skin. Early studies on the machinability of cast steel indicated that for a skin cut the machining operations should be carried on at approximately one-half the cutting speed recommended for the base metal in order to obtain equivalent tool life. In Figure 580, the "cross" lines on the tool life graph indicate the results obtained in machining the casting skin. However, the machinability of the surface of 0.30 carbon cast steels which are free from scale, pits and occluded sand, is equivalent to that of the base metal. This is illustrated in Figures 565 and 50 Х SKIN 40 ./252 30 UNDER SKIN TOOL LIFE, MINUTES Fig. 565—Tool life of high-speed steel tools for 0.30 percent carbon cast steel. 20 10 0 100 125 150 175 200 CUTTING SPEED, FEET PER MINUTE 510 MACHINABILITY 566, in which tool life is plotted against cutting speeds. In both of these figures, it can be observed that the curves for a skin cut and for the base metal cut overlap each other. 60 x 50 -125" UNDER SKIN 40 SKIN TOOL LIFE, MINUTES 30 Fig. 566—Tool life of high-speed steel tools for 0.30 percent carbon steel. 20 10 .250" UNDER SKIN 0 75 100 125 150 175 CUTTING SPEED, FEET PER MINUTE Results from milling studies in the machinability of the casting skin for both high-speed steel and carbide tools are illustrated in Figures 567 and 568. Again, the machinability of the skin is about equivalent to the base metal. 120 100 . MATERIAL: CAST STEEL TOOL: HSS (18-4-1) FEED: .005 IN. /TOOTH DEPTH OF CUT: 125 INCH SKIN 0.25C (SKIN) UNDER SKIN 80 TOOL LIFE, MINUTES (SKIN) 60 0.34C (0.125" UNDER SKIN) 0.25C(0.125" UNDER SKIN) Fig. 567— Milling tests. Tool life of high-speed steel tools for 0.34 and 0.25 percent carbon steels. 40 20 0.34C(SKIN) 0 120 140 160 180 200 220 240 260 280 300 CUTTING SPEED, FEET PER MINUTE MACHINABILITY 511 120 100 80 MINUTES TOOL LIFE, MATERIAL: CAST STEEL TOOL : 78 B CARBIDE FEED: .005 IN./TOOTH DEPTH OF CUT: 125 INCH SKIN UNDER SKIN 0.34C (0.125"UNDER SKIN) 0.25C (0.125" UNDER SKIN) 60 40 0.34C (SKIN) 0.25 C (SKIN) 200.25C(SKIN) 0 200 300 400 500 600 700 800 900 1000 1100 CUTTING SPEED, FEET PER MINUTE Fig. 568—Milling tests. Tool life of carbide tools for 0.34 and 0.25 percent carbon steels. The first machining cut for steel castings should be a deep hogging cut, and the cutting speed should be less than for the lighter finishing cuts of the base metal. Deep hogging cuts are recommended because this allows the tool to cut under any surface imperfection. Also, the use of a high feed and large depth of cut allows metal to be removed most efficiently in machining, i.e., a large volume of metal can be removed per minute per horsepower. This practice may be combined with low cutting speed to give long tool life. The size of cut is the variable having the greatest influence on forces and power consumption in machining steel. There are several factors which set a limit on the maximum size cut that can be taken. These are: (1) the maximum power available from the machine tool, (2) the maximum force the cutter can take, (3) the maximum permissi- ble deflections of the machine tool and work consistent with the accuracy required, and (4) the tendency to chatter. Machining of Welded Areas ... Welding is an acceptable and integral part of the steel casting process. It is used also in the fabrication welding-cast-weld construction and composite fabrication-of steel castings. The welded areas are often machined, and they can have an adverse effect on machining operations. The effect of weld deposit on the machinability of cast steel is graphically illustrated in Figure 569. The hardness of the as-welded deposits was equal to, greater than, and less than the 0.30 carbon base metal. The maximum hardness in the heat-affected zone was 250 Brinell. This chart illustrates that regardless of the type of electrode used to make weld deposits and/or the hardness of the weld, machining 512 MACHIN ABILITY 60 50 CUTTER: HIGH-SPEED STEEL FEED/TOOTH: .004 INCH DEPTH OF CUT: .100 INCH AWS CLASS #4510 ELECTRODE 143 BHN AWS CLASS #6012 ELECTRODE 170 BHN 40 TOOL LIFE, MINUTES 8 8 8 8 8 30 Fig. 569—The effect of transverse welds on the tool life of high-speed steel tools. Cutting tool machined seven welds, four- teen heat affected zones and eight l-inch sections of the base metal (0.30C). 20 Ý BASE METAL 170 BHN 10 AWS CLASS #9016 X ELECTRODE 237 BHN 150 175 200 225 250 275 300 CUTTING SPEED, FEET PER MINUTE operations will be adversely affected if the welds are in the as-welded state. Therefore, weld deposits which are to be machined must be given a subsequent heat treatment prior to machining, because the hard areas adjacent to the weld are the underlying reason for a shorter tool life. Any heat treatment of as-welded metal will reduce the hardness of the weld, and it will not only reduce the hardness of the heat-affected zone, but will also reduce the width of the transition zone. Therefore, as-welded deposits, which match the hardness of the base metal, will become softer than the base metal, while over-matched weld deposits will approach the base metal hardness. The effect of tempering on the tool life of high-speed steel tools is given in Table 86. The microstructures of the weld, heat-affected zone and base metal are entirely different, and subsequent heat treatments will not completely obliterate the differences in microstructure. Therefore, the machining characteristics of steel containing welds will not equal the machinability of cast steel without welds. However, this condition can be markedly improved through heat treatment. Also, the presence of slag, porosity or areas lacking good fusion will adversely affect the machining char- acteristics of the casting. Table 86–High-Speed Tool Life Results on Welds at a Cutting Speed of 23-ft/min. Brinell Hardness HAZ Tool Life Minutes Test Pieces Electrodes Weld Base As-welded Tempered at 1250°F As-welded Tempered at 1250°F Base Metal 0.30 Carbon E9016 E9016 E6012 E6012 250-254 168 250 234 170 120-140 234 220-254 155-174 149 164-170 149 170 6.0 10.5 15.5 21.0 28.0 MACHINABILITY 513 Summary of the Factors Affecting the Machining of Steel Castings The data on the machinability of cast steels previously given in this chapter point to several conclusions which may be considered as guides or recommendations for machining steel castings. 1. The microstructure has a definite effect on the machinability of steel castings, and it is possible to improve machining characteristics as much as 100 to 200 percent by altering the microstructure through heat treatment. However, it may not be advisable to change the structure to improve machinability, as mechanical requirements are not always compatible with the best microstructure for machinability. 2. Hardness alone cannot be taken as the general criterion for predicting tool life in the cutting of cast steels. 3. For a given microstructure, the plain carbon steels usually possess better machining properties than the alloy steels. 4. The machinability of carbon (1040) cast steel varies as the ratio of ferrite to pearlite varies in its microstructure. The best ratio is 60:40. 5. The machinability of steel castings or any wrought product is influenced by the properties of the skin, and a hogging cut of 1/4 to 3/8 inch should be used when making the first surface cut. Machinability Ratings . Machinability Index ... Machinability indexes are prepared to show the relative machining characteristics of steels having various composi- tions and heat treatments. Index numbers give but general trends in the interpretation of the suitable cutting speeds which should be used in machining (turning). The relative ratings for the machining of steels are not necessarily the same when using high-speed steel tools as compared with carbide tools. One main disadvantage to most index systems is that they are usually applied to steels over too wide a hard- ness range. The machinability index of Table 87 for cast steels using high- speed tools is an aid in making quick relative comparisons of the machinability of cast steels. The base reference in this table is a standard wrought steel of the free machining type (B1112), machined at 180 surface feet per minute and giving a tool life of 2 to 3 hours. The HSS index number is based upon 100 for machining the standard wrought steel. 514 MACHIN ABILITY Table 87—Machinability Index for Cast Steels with High-Speed Steel Tools (Machining speed: 180 sfm with tool life of 2 to 3 hours) Machinability BHN Index Number Steel and Heat Treatment B1112 Free machining steel (wrought) 1020 Annealed 1020 Normalized 179 122 134 100 90 75 70 75 1040 Double normalized 1040 Normalized and annealed 1040 Normalized 1040 Normalized and oil quenched 185 175 190 225 65 45 1330 Normalized 1330 Normalized and tempered 187 160 40 65 4130 Annealed 4130 Normalized and spheroidized 175 175 55 50 4340 Normalized and annealed 4340 Normalized and spheroidized 4340 Quenched and tempered 4340 Quenched and tempered 200 210 300 400 35 55 25 20 8430 Normalized and tempered, 1200F 8430 Normalized and tempered, 1275F 200 180 50 60 8630 Normalized 8630 Annealed 240 175 40 65 The machinability index of Table 88 using carbide tools is based on the amount of metal removed from annealed carbon cast steel (1020) in cubic inches per tool grind using a carbide tool and a machining rate of 300 feet per minute. This condition was arbitrarily given an index number of 10. A number 4, for example, means that in the machining of this particular cast steel 40 percent as much metal will be removed per tool grind as for the base steel. A number 11 means that 10 percent more metal removal per grind can be expected. MACHIN ABILITY 515 Table 88—Machinability Index for Cast Steels Using Carbide Tools (Machining Speed 300 sfm) Cast Steel Machinability Index Number Heat Treatment BHN 10 1020 1020 Annealed Normalized 122 134 6 1040 1040 1040 1040 Annealed Normalized Double Normalized Quenched & Tempered 175 190 185 225 10 6 11 6 187 2 1330 1330 Normalized Normalized & Tempered 3 160 3 4130 4130 Annealed Normalized & Spheroidized 175 175 4 3 4340 4340 4340 4340 Annealed Quenched & Tempered Quenched & Tempered Normalized & Spheroidized 200 300 400 210 3 2 0.5 6 8430 Normalized & Tempered 180 4 5 8630 8630 Annealed Normalized 175 240 2 Speed Index Number ... The speed index numbers listed in Table 89 are the actual cutting speeds (surface feet per minute) for each cast steel which will give one hour tool life in turning. The speed index numbers for high-speed steel tools are based on the cutting speed which will give one hour tool life using a standard 18-4-1 high-speed steel tool. For carbide (78B or its equivalent) the speed index is based on the cutting speed which will give one hour tool life based on a 0.015-inch wearland. The development of speed index numbers is a new system of rating the machinability of cast steels and is based on reliable data for testing done in one hour, and no extrapolations are required. The speed number system has the significance that it gives directly the cutting speed to use to give one hour tool life, and it points out the differences resulting from using high-speed and carbide tools. However, the numbers are not percentage figures and, therefore, it is not as easy to compare one steel with another. 516 MACHIN ABILITY Table 89—Speed Index for Cast Steels Heat Treat- ment* High- Speed Car- Steel bide Speed Speed No. No. Type No. BHN Microstructure Carbon 1020 A 122 160 400 Carbon 1020 N 134 135 230 Carbon 1040 N, N 185 130 400 Carbon 1040 N, A 175 135 380 Carbon 1040 N 190 120 325 Carbon 1040 N, Q 225 80 310 Med. Mn 1330 N 187 75 140 Med. Mn 1330 N, T 160 120 230 MnMo 200 80% Blocky Ferrite + 20% Pearlite 85% Blocky & Widmanstatten Ferrite + 15% Pearlite 60% Blocky Ferrite 40% Pearlite 51% Blocky Ferrite 50% Pearlite 35% Network Ferrite 65% Pearlite 30% Widmanstatten Ferrite 70% Pearlite 40% Blocky + Widmanstatten Ferrite + 60% Pearlite 50% Dendritic Blocky Ferrite + 50% Pearlite 70% Widmanstatten + Blocky Ferrite + 30% Pearlite 80% Widmanstatten + Blocky Ferrite + 20% Pearlite 40% Blocky Ferrite + 60% Pearlite 40% Blocky Ferrite + 60% Spheroidized Carbide 40% Blocky Ferrite + 60% Pearlite 50% Blncky Ferrite + 50% Spheroidized Carbide Tempered Martensite Tempered Martensite 8n0% Widmanstatten Ferrite 20% Pearlite 50% Dendritic Blocky Ferrite + 50% Pearlite 90 NT (1200°F) N, T (1275°F) 200 MnMo 180 110 240 CrMo 4130 175 95 260 CrMo 4130 N, Sph. 175 90 200 NiCrMo 4340 NA 200 60 210 NiCrMo 4340 N, Sph. 210 290 NiCrMo NiCrMo NiCrMo 200 4340 4340 8630 Q, T Q, T 95 45 35 300 400 180 N 240 75 180 NiCrMo 8630 A 17 120 290 * A=Annealed; N=Normalized; N, N=Double Normalized; N, Q=Normalized and Quenched; N, T=Normalized and Tempered; N, Sph.=Normalized and Spheroid- ized; Q, T=Quenched and Tempered; N, A=Normalized and Annealed. Machinability Curves for Cast Steels Machinability of Cast Carbon Steels ... The data on the machining of cast carbon steels are plotted on Tool Life vs. Cutting Speed Charts. The tool life is taken as the amount of machining that can be done between tool grinds and is expressed in cubic inches of metal removed for a given MACHINABILITY 517 i tool wearland. The final tool life value for high-speed steel was de- termined by the complete breakdown of the tool nose or a wearland of 0.060 inch on the flank. The end point for carbide tools was either a flank wear of 0.015 inch or localized failure of 0.040 inch. Increasing the cutting speed decreases the amount of metal re moved for a given tool wearland. A plot of cutting time per wearland vs. cutting speed indicates how metal removal varies with the cutting speed in feet per minute. The composite machinability data for carbon cast steels (1020 and 1040) using high-speed tools are plotted in Figure 570, while Figure 571 shows the composite data for carbide cutting tools. Carbon (1020) Cast Steels ... The wide spread in the tool life obtained in machining 1020 cast steel in two different microstructural types (annealed and normalized) can be observed in Figures 570 and 571. It is possible to machine the annealed steel with carbide tools at a cutting speed 85 percent higher than the normalized steel and still obtain equivalent tool life. At 300 fpm, almost twice the metal removal can be expected for the annealed form of the steel. This difference in machining characteristics is obtained in spite of the fact that the two forms are of similar hardness, 122 to 134 BHN. Annealed 1020 steel can be machined with high-speed steel at a 25 percent higher speed than the same steel in the normalized condition. : 70 TOOL LIFE vs CUTTING SPEED VS PLAIN CARBON STEEL TOOL: HIGH SPEED STEEL 0 102/ 60 A 1040 e 50 1021 ANNEALED ន ន ន 40 METAL REMOVED, CUBIC INCHES O 1021 NORMALIZED 1040 NORM. & ANNEALED o 1040 QUENCHED AND TEMPERED 20 D 1040 NORMALIZED 10 1040 DOUBLE NORMALIZED 0 20 40 60 80 100 120 140 160 180 200 220 240 260 CUTTING SPEED, FEET PER MINUTE Fig. 570—Tool life vs. cutting speed for 1021 and 1040 cast steels using high-speed tools. 518 MACHIN ABILITY 400 350 TOOL LIFE VS CUTTING SPEED PLAIN CARBON STEEL TOOL 288 CARBIDE 0 1021 0 1040 - CUBIC INCHES 300 - 1 250 200 1021 ANNEALED 1021 NORMALIZED 1040 SINGLE NORMALIZED 1040 NORMALIZED & OIL QUENCH. 1040 DOUBLE NORMALIZED -1040 NORM& ANNEALED 150 METAL REMOVED 100 50 HIGH SPEED LUISTEEL III/ CHART AREA (SEE FIG,7) ) 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 CUTTING SPEED, FEET PER MINUTE Fig. 671—Tool life vs. cutting speed for 1021 and 1040 cast steels using carbide tools (78B). Carbon (1040) Cast Steels ... The data in Figures 570 and 571 present information on four different microstructural types for 1040 cast steel. The oil-quenched heat treatment was used to obtain the type of structure found in thin normalized sections. The double normalize heat treatment which produced a microstruc- ture of 60 percent blocky ferrite and 40 percent pearlite permits machin- ing with carbides at a speed 50 percent higher than the single normalized form, which has a structure of 35 percent network ferrite and 65 percent pearlite. This difference in machinability was observed, although the hardness of the two structures was practically the same, 185 to 190 BHN. The machinability of the four heat-treated cast steels when cut with carbide tools seems to be proportional to the ratio of ferrite to pearlite in their microstructure. The 60:40 ratio machines best; the others follow in the order of their decreasing amounts of ferrite. The machining properties of the four heat-treated cast steels with high-speed steel tools correspond closely to the Brinell hardness, the softest microstructure exhibiting the best machining characteristics. However, all of the microstructure types, with the exception of the normalized and quenched steel, machine almost alike. The latter should be machined at about 50 percent of the cutting speed of the former. Machinability of Alloy Cast Steels ... In Figure 572 composite data on tool life vs. cutting speed, using high-speed steel tools, are plotted, and in Figure 573, the composite data are plotted for various alloy cast steels when carbide tools are employed. MACHINABILITY 519 METAL REMOVED, CUBIC INCHES 80 TOOL LIFE VS CUTTING SPEED ALLOY STEELS TOOL: HIGH SPEED STEEL 1326 70 A 4335 -1326 NORMALIZED & TEMP. V 4131 60 08433 8630 ANNEALED 8630 4131 ANNEALED 50 8630 NORMALIZED 1326 NORMALIZED 4335 QUENCHED & 10 TEMP. TO 300 BHN 4335 NORM, & ANNEALED 4131 NORM. & SPHEROIDIZED -4335 NORM. & SPHEROIDIZED 4335 8433 NORM. & TEMP. AT 1275 °F 20EQUEN & 8433 NORM. & TEMP. AT 1200°F TEMP. TO 400 BHN 10 0 0 20 40 60 80 100 120 140 160 180 200 220 240 260 CUTTING SPEED, FEET PER MINUTE Fig. 572—Tool life vs. cutting speed for alloy cast steels using high-speed tools. 225 4200 175 150 TOOL LIFE VS CUTTING SPEED ALLOY STEELS TOOL: 78 B CARBIDE A 1326 O 4335 4131 ANNEALED 4131 -4131 NORM. & SPHEROIDIZED V 8433 0 8630 8630 ANNEALED 8630 SINGLE NORMALIZED 8433 NORMALIZED & TEMP. AT 1200 °F 8433 NORM. & TEMP. AT 1275 °F -4335 NORMALIZED & ANNEALED 1326 NORMALIZED 4335 NORM. & SPHEROIDIZED 4335 QUEN. & TEMP. TO 300 BHN 1326 NORM, & TEMPERED 125 METAL REMOVED, CUBIC INCHES 100 75 50 HIGH 25CHARTA SPEED STEELS TAREA (SEE FIG.9) 4335 QUEN & TEMP. TO 400 BHN 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 CUTTING SPEED, FEET PER MINUTE Fig. 573—Tool life vs. cutting speed for alloy cast steels using carbide tools (78B). 520 MACHINABILITY . Medium Manganese (1330) Cast Steel ... The machining data for the 1330 steels are based on two different heat treatments, namely, normal- ized and tempered and normalized only. In the normalized and tempered state, this steel can be machined with carbides at a speed 125 percent higher than the straight normalized steel, although there is only a difference of 27 in the Brinell hardness. When high-speed steels are used as the machining tools, the softer, tempered steels can be machined at a speed 75 percent higher than that for the steels in the normalized condition. An increase in metal removal of 300 percent can be attained at a speed of 120 fpm by tempering. Chromium Molybdenum (4130) Cast Steel ... The Cr-Mo (4130) data are for two heat treatments, annealed and normalized, and spheroidized. The hardness was the same for each heat treatment, and there is little difference in the machining regardless of the cutting tool. Nickel-Chromium-Molybdenum (4330) Cast Steel . The machining data in Figures 572 and 573 are obtained from four differently heat treated castings, i.e., (1) normalized and annealed, (2) normalized and spheroidized, (3) quenched and tempered to 300 BHN and (4) quenched and tempered to 400 BHN. The cast steel with the spheroidized microstructure displays the best machining characteristics with carbide tools. This microstructure type can be machined at approximately 65 percent greater speed than the annealed steel. As to be expected, the quenched and tempered steels machine poorly. However, at very low speeds, 175 to 200 fpm, the two steels machine almost alike; but at higher speeds, the softer steel can be machined more easily, for example, at 300 fpm, an increase in metal removal of 400 percent is obtained through heat treatment. A spheroidizing cycle produces good machining characteristics; in fact, there is considerable improvement over that shown by the annealing heat treatment. At the same time, there is a difference of only 10 hardness points between the two steels: the spheroidized steel recorded 210 BHN and the annealed, 200 BHN. Studies with high-speed steel tools showed that the 4340 steel for the four conditions of heat treatment can be more readily machined in the order of increasing hardness with the exception of the spheroidized steel which machines slightly better than the annealed steel. Manganese-Molybdenum (8430) Cast Steel . . . The machining data were obtained from specimens which were normalized, and then tem- pered at either 1200 degrees F or 1275 degrees F. It is to be noted that the high temperature tempering treatment allows an increase in cut- ting speed of 25 percent when the steel is processed with carbides. This is an appreciable improvement. > . MACHIN ABILITY 521 The high tempered cast steel (180 BHN) can be machined with high-speed steel tools at a cutting speed about 35 percent higher than the other cast steel (200 BHN). Nickel-Chromium-Molybdenum (8630) Cast Steel ... The 8630 cast steel in the annealed condition (50 percent ferrite - 50 percent pearlite) machines considerably better than the same steel with a normalized structure (80 percent Widmanstatten). This steel in the annealed con- dition can be machined with a carbide tool at a cutting speed 65 percent greater than in the normalized state. An increase in metal removal of 135 percent can be attained if the annealed 8630 steel is machined at 300 fpm. The 8630 annealed steel (175 BHN) can be machined with high- speed tools at a speed 65 percent greater than the normalized steel (240 BHN). Individual Machinability Curves ... Data on the machining of 1020, 1040, 1330, 4130, 4340, 8430 and 8630 cast steels are plotted on separate tool life vs. cutting speed charts and are presented in Figures 574 through 580. Each set of curves gives the metal removal for either high-speed steel or for general purpose (78B) carbide tools. Also in- cluded on each chart is a plot of the cutting time in minutes vs. the cutting speed. The high-speed steel tests were made with a nose radius of 0.005 inch at a depth of cut of 0.062 inch and a feed of 0.010 inch per revolu- tion, and the carbide tests were made with a nose radius of 0.040 inch at a depth of cut of 0.100 inch and a feed of 0.010 inch per revolution. The wearland for the HSS tests was 0.060 inch and for the 78B carbide tool 0.015 inch. Application of Machining Data to Machining Operations The tool life data in Figures 574 through 580 show the cubic inches of metal removed when the depth of cut is 0.100 inch and the feed is 0.010 inch for various cutting speeds. These data may be applied to practical machining operations. For example, assume that 5 cubic inches of metal per casting must be removed in a turning operation. The castings are furnished in 8630 steel, annealed, and the cutting tool is 78B carbide. According to Figure 580, the metal removed in cubic inches at 300 surface feet per minute is 200 cubic inches. Therefore, 40 castings (200/5) may be machined before the total wearland reaches 0.015 inch. 522 MACHIN ABILITY 1021 CAST STEEL 50 -40 30 METAL REMOVED, CU. IN. 400 20 O 350 10 HSS 300 120 140 160 180 200 220 240 260 280 CUTTING SPEED, FEET PER MINUTE 250 METAL REMOVED, CU. IN. 200 O ANNEALED 122 BHN O NORMALIZED 134 BHN CARBIDE HSS 150 100 CARBIDE 50 0 300 400 500 600 700 800 900 1000 1100 CUTTING SPEED, FEET PER MINUTE CUTTING SPEED, FT/MIN. 2000 1500 1000 800 600 400 300 200 es:85:6- 1 100 2 3 4 6 8 10 20 30 40 60 80 100 CUTTING TIME, MINUTES Fig. 574—Cutting speed charts for 1021 cast steel. High speed steel feed/rev: 0.010 in.; depth of cut: 0.062 in.; wearland: 0.060 in. Carbide feed/rev: 0.010 in; cut: 0.100 in; wearland: 0.015 in. M A CHIN ABILITY 523 1040 CAST STEEL 50 HSS 40 30 METAL REMOVED, CU. IN. 400 20 350 CARBIDE 300 60 80 100 120 140 160 180 200 CUTTING SPEED, FEET PER MINUTE 250 METAL REMOVED, CU. IN. 200 0 150 O DOUBLE NORMALIZED 185 BHN • NORMALIZED AND ANNEALED 175 BHN X SINGLE NORMALIZED 190 BHN O NORMALIZED AND OIL QUENCHED 225 BHN CARBIDE HSS 100 50 0 300 400 500 600 700 800 900 1000 1100 CUTTING SPEED, FEET PER MINUTE 1000 800 600 400 300 CUTTING SPEED, FEET PER MINUTE 200 SX 100 80 60 N 3 4 6 8 10 20 30 40 60 80 100 CUTTING TIME, MINUTES Fig. 575—Cutting speed charts for 1040 cast steel. High speed steel feed/rev: 0.010 in.; depth of cut: 0.062 in.; wearland: 0.060 in. Carbide feed/rev: 0.010 in.; cut: 0.100 in.; wearland: 0.015 in. 524 MACHIN ABILITY 1326 CAST STEEL HSS METAL REMOVED, CU.IN. 30 400 20 .... 350 300 250 CARBIDE 80 100 120 140 160 180 200 220 CUTTING SPEED, FEET PER MINUTE METAL REMOVED, CU. IN. 200 150H - O NORMALIZED AND TEMPERED 160 BHN NORMALIZED 187 BHN CARBIDE HSS 100H 50 0 100 200 300 400 500 600 700 800 900 1000 CUTTING SPEED, FEET PER MINUTE 1000 800 600 400 300 200 CUTTING SPEED, FT./MIN. 100 80 50 2 3 4 6 8 10 20 30 40 60 80 100 CUTTING TIME, MINUTES Fig. 576—Cutting speed charts for 1326 (medium manganese) cast steel. High speed steel feed/rev: 0.010 in.; depth of cut: 0.062 in.; wearland: 0.060 in. Carbide feed/rev: 0.010 in.; depth of cut: 0.100 in.; wearland: 0.015 in. MACHIN ABILITY 525 4131 CAST STEEL 50 -40 HSS METAL REMOVED, CU.IN. 30 400 20 350 10 300 60 80 100 120 140 160 180 200 220 CUTTING SPEED, FEET PER MINUTE 250 METAL REMOVED, CU. IN. 2001 CARBIDE 150 O ANNEALED 175 BHN NORMALIZED & SPHEROIDIZED 175 BHN CARBIDE HSS 100 1 50 0 300 400 500 600 700 800 900 1000 1100 CUTTING SPEED, FEET PER MINUTE 1000 800 600 - 400 - 300 - CUTTING SPEED, FEET PER MIN. 200 160 -O DOO 120 100) 2 3 4 6 8 10 20 30 40 60 80 100 CUTTING TIME, MINUTES Fig. 577—Cutting speed charts for 4131 cast steel. High speed steel feed/rev: 0.010 in.; depth of cut: 0.062 in.; wearland: 0.060 in. Carbide feed/rev: 0.010 in.; depth of cut: 0.100 in.; wearland: 0.015 in. 526 MACHIN ABILITY 4335 CAST STEEL 50 Х -40 30 METAL REMOVED, CU.IN. HSS 400 20 350 10 300 0 CARBIDE 20 40 60 80 100 120 140 160 CUTTING SPEED, FEET PER MINUTE 250 Х METAL REMOVED, CU. IN. 200 150 O NORMALIZED AND ANNEALED 200 BHN X NORMALIZED AND SPHEROIDIZED 210BHN O QUENCHED AND TEMPERED 300 BHN. QUENCHED AND TEMPERED 300 BHN CARBIDE HSS 100 - 50 0 100 200 300 400 500 600 700 800 900 1000 CUTTING SPEED, FEET PER MINUTE 800 600 400 300 X - CUTTING SPEED, FEET PER MINUTE X-X-X-4 Dood படடடடட -0 200 160 120 100 80 60 50 40 X 2 3 4 6 8 10 20 30 40 60 80 100 CUTTING TIME, MINUTES Fig. 578—Cutting speed charts for 4335 cast steel. High speed steel feed/rev: 0.010 in.; depth of cut: 0.062 in.; wearland: 0.060 in Carbide feed/rev: 0.010 in.; depth of cut: 0.100 in.; wearland: 0.015 in. M A CHIN ABILITY 527 8433 CAST STEEL 350 40 30 METAL REMOVED, CU. IN. 400 20 350 10 HSS 300 1 0 60 80 100 120 140 160 180 200 CUTTING SPEED, FEET PER MINUTE 250 200 METAL REMOVED, CU.IN. CARBIDE 150 NORMALIZED AND TEMPERED 180 BHN NORMALIZED AND TEMPERED 200 BHN CARBIDE HSS 100 50 0 300 400 500 600 700 800 900 1000 1100 CUTTING SPEED, FEET PER MINUTE 1000 800 600 400 300 CUTTING SPEED, FEET PER MIN. 200 160 120 100 2 3 3 4 6 8 10 20 30 40 60 80 100 CUTTING TIME, MINUTES Fig. 579—Cutting speed charts for manganese molybdenum (8433) cast steel. High speed steel feed/rev: 0.010 in.; depth of cut: 0.062 in.; wearland: 0.060 in. Carbide feed/rev: 0.010 in.; depth of cut: 0.100 in.; wearland: 0.015 in. 528 MACHIN ABILITY 8630 CAST STEEL 2:50 HSS -40 METAL REMOVED, CU. IN. 301 **** 400 20 350 10 300 0 40 60 80 100 120 140 160 180 CUTTING SPEED, FEET PER MINUTE 250 CARBIDE METAL REMOVED, CU. IN. 200 150 SINGLE NORMALIZED 240 BHN O ANNEALED 175 BHN BASE METAL WITH CARBIDE BASE METAL WITH HSS CASTING SKIN 100 50 0 300 400 500 600 700 800 900 1000 1100 CUTTING SPEED, FEET PER MINUTE 800 600 UUUU 400 300 CUTTING SPEED, FEET PER MINUTE 200 160 120 100 80 2 3 4 6 8 10 20 30 40 60 80 100 CUTTING TIME, MINUTES Fig. 580—Cutting speed charts for 8630 cast steel. High speed steel feed/rev: 0.010 in.; depth of cut: 0.062 in.; wearland: 0.060 in. Carbide feed/rev: 0.010 in.; depth of cut: 0.100 in.; wearland: 0.015 in. MACHINABILITY 529 The amount of metal removed by increasing the depth of cut to 0.150 inch at the same cutting speed (300 ft/min) is increased 50 percent or 300 cubic inches. Thus, the number of castings machined per tool grind is 300/5 or 60. However, at a cutting speed of 500 ft per minute (Figure 580), 100 cubic inches will be removed with a 0.100 inch cut and 150 cubic inches with a depth of cut of 0.150 inch. The number of castings which can be machined is 150/5 or 30. The turning operation in this hypothetical case under consideration is a roughing operation and size control is not important. Therefore, it is possible to extend the wearland to 0.030 inch instead of 0.015 inch. This would allow the number of castings machined per tool grind to be doubled and, consequently: At 300 sfm, the number of castings would equal 2 x 60, or 120 castings; At 500 sfm, the number of castings would equal 2 x 30, or 60 castings. The cutting time vs. cutting speed plot of Figure 580 shows that at 300 sfm, 55 minutes are required to machine 60 castings, or 110 minutes for 120 castings (0.030-inch wearland). This is approximately 1 casting per minute. If the loading and unloading time per casting is 1/2 minute, then the total time per casting is 11/2 minutes or the total time for the 120 castings is 180 minutes. Thus, tools would need to be changed every three hours. The cutting time for 100 cubic inches at 500 sfm is 15 minutes for 30 castings based on a wearland of 0.015 inch (Figure 580) or 60 castings, based on a wearland of 0.030 inch, would require 30 minutes per tool grind. Thus, 60 castings can be machined in one hour if 112 minute is allowed for loading and unloading. A comparison of the machining operations at 300 sfm and 500 sfm is given in Table 90. Table 90—Machining Data for 120 Ni-Cr-Mo Steel Castings sfm Machining Time Minutes Time Between Tool Changes Minutes No. of Tool Changes 300 500 180 120 180 60 1 3 At the higher speed the production rate is increased approximately 50 percent, but tool changes are required three times as frequently. The tool speed charts are very helpful in providing data to determine the optimum cutting speed that gives the best balance between produc- tion and tool cost. 530 MACHIN ABILITY Machinability of Cast Steel vs. Wrought Steel Most of the published machinability data on steels have related to wrought steels, and it was not possible to make a direct comparison of the machinability of cast and wrought steels until data on the machin- ability of cast steels became available through research undertaken by Steel Founders' Society. Table 91, page 533, gives the composition of wrought and cast steels of similar structures. The machining characteristics of these steels are compared in Figures 581 through 583. Cast vs. Wrought Cr-Mo Steel (41XX)... The machining character- istics of annealed Cr-Mo (175 BHN) cast steel and annealed (180 BHN) wrought steel are compared in Figure 581. In this state the cast and wrought steels have similar microstructure, and the machining characteristics of the cast steel prove to be superior when high-speed 4/XX CAST VS WROUGHT STEELS 50 -40 DoDooDooDooDoo 30 HSS METAL REMOVED, CU. IN. O--0-0 400 20 10 $ 350 300 AOA 80 100 120 140 160 180 200 220 240 CUTTING SPEED, FEET PER MINUTE 250 200 CARBIDE METAL REMOVED 150 A CAST: ANNEALED 175 BHN O WROUGHT: ANNEALED 180 BHN CARBIDE HSS 100 50 0 300 400 500 600 700 800 900 1000 1100 1200 1300 CUTTING SPEED, FEET PER MINUTE Fig. 581—Comparison of Cr-Mo (41XX) cast and wrought steels. High speed steel feed/rev: 0.010 in.; depth of cut: 0.062 in.; wearland: 0.060 in. Carbide feed/rev: 0.010 in.; depth of cut: 0.100 in.; wearland: 0.015 in. MACHIN ABILITY 531 tools are used. In fact (Figure 581) the cast steel can be processed at a speed 40 percent higher than the wrought steel, with equivalent tool life characteristics. The results with carbide tools (Figure 581) indicate that the wrought steels at the low speed of 300 sfm have improved machining properties. The two curves have different slopes and cross at about 450 sfm; above this speed, the cast steel shows improved machinability. The fact that the wrought steels at low speeds have better machin- ability than the cast steels indicates that the wrought steels have less carbide present. However, the carbide is not as important in tool break- down at high turning speeds as is the temperature developed at the tool interface. Cast vs. Wrought Ni-Cr-Mo Steel (43XX)... A comparison between cast and wrought Ni-Cr-Mo (4340) steel with various heat treatments 43XX CAST VS WROUGHT STEELS 50 +*• WROUGHT:ANNEALED 221 BHN **A CAST: ANNEALED 200 BHN O WROUGHT: Q. & T. 300 BHN A CAST: Q & T. 300 BHN -40 METAL REMOVED. CU.IN. 400 20 logo AQ 350 300 HSS 0 20 40 60 80 100 120 140 160 CUTTING SPEED, FEET PER MINUTE 250+ CARBIDE METAL REMOVED, CU. IN. 200 150 11挂 ​X CAST : QUEN. & TEMPERED 400 BHN O WROUGHT:Q. & T. 400 BHN WROUGHT: ANNEALED 221 BHN CAST: NORM. & ANNEALED 200 BHN 100 50 0 100 200 300 400 500 600 700 800 900 1000 1100 CUTTING SPEED, FEET. PER MINUTE Fig. 582—Comparison of Ni-Cr-Mo (43XX) cast and wrought steels. High speed steel feed/rev: 0.010 in.; depth of cut: 0.062 in.; wearland: 0.060 in. Carbide feed/rev: 0.010 in.; depth of cut: 0.100 in.; wearland: 0.015 in. 532 MACHIN ABILITY is shown in Figure 582. The heat treatments are: annealed, quenched and tempered to 300 BHN and quenched and tempered to 400 BHN. The cast and wrought steels have comparable machining character- istics when machined with high-speed steel tools at practical speeds. The results with carbide tools (Figure 582) are comparable to those obtained with high-speed tools. Cast vs. Wrought Ni-Cr-Mo Steel (86XX) ... Similar machining char- acteristics when using high-speed steel tools are observed in Figure 583, which compares 8630 cast and wrought steel in the annealed and normalized states. The curves in this Figure show that the cast steel is equivalent to a higher carbon wrought steel when their hard- nesses are similar. When machined with carbide tools, Figure 583, wrought steels show better machining properties in the lower speed range, but at approximately 425 sfm the cast steels give better results. 86XX CAST VS WROUGHT STEELS 350 140 HSS 30 METAL REMOVED, CU. IN. 400 20 350 10 ܒCAܫܘ 3005 CARBIDE 0 60 80 100 120 140 160 180 200 CUTTING SPEED, FEET PER MINUTE 250 METAL REMOVED, CU. IN. 200 150 • WROUGHT STEEL ANNEALED 170 BHN A CAST STEEL ANNEALED 175 BHN O WROUGHT STEEL NORMALIZED 250 BHN A CAST STEEL NORMALIZED 240 BHN 100. 50 0 300 400 500 600 700 800 900 1000 1100 1200 1300 CUTTING SPEED, FEET PER MINUTE Fig. 583—Comparison of Ni-Cr-Mo (86XX) cast and wrought steel. High speed steel feed/rev: 0.010 in.; depth of cut: 0.062 in.; wearland: 0.060 in. Carbide feed/rev: 0.010 in.; depth of cut: 0.100 in.; wearland: 0.015 in. MACHIN ABILITY 533 Table 91-Comparative Data of Cast and Wrought Steels with Similar Microstructures Heat Treatment Fer- rite Pearl- ite Composition - Percent Si Р S Cr Type BHN С Mn Ni Мо C* W** 40 35 5 0 60 65 95 100 0.31 0.42 0.35 0.42 0.74 0.91 0.69 0.73 0.30 0.26 0.49 0.30 0.010 0.026 0.032 0.017 0.024 0.022 0.032 0.019 1.00 0.98 0.90 0.82 0.16 0.17 1.72 1.81 0.22 0.18 0.27 0.26 Annealed Annealed Norm. & Ann. Annealed Norm. & Spher. Spheroidized Quenched & T. Quenched & T. Quenched & T. Quenched & T. Annealed Annealed Normalized Widmanstatten 175 180 200 221 210 206 300 300 400 400 175 170 240 250 W 50 50 50 0.30 0.42 50 50 50 0.74 0.91 0.48 0.24 0.036 0.017 0.029 0.021 0.66 0.54 0.55 0.52 0.18 0.22 Steel 4130 4140 4340 4340 С W С W С W С 4340 4340 8630 8640 8630 8640 С W С W * Cast ** Wrought 534 MACHIN ABILITY Comparison of Cast and Wrought Steels Using Index Numbers ... In Table 92, several cast and wrought steels are compared in the turn- ing operation, with high-speed tools. The basis of comparison is the free machining wrought steel B1112. In three of the five cases the index numbers are identical and quite similar in the other two. Thus, the wrought and cast steels of like microstructures and compositions machine alike when high-speed steel cutting tools are used. Table 92-Machinability Index Numbers of Cast and Wrought Steels of Similar Microstructure with High-Speed Tools* Machinability BHN Index Number Steel B1112 Wrought Steel 1020 Wrought Annealed 1020 Cast Annealed 4340 Wrought Annealed 4340 Cast Normalized & Annealed 4340 Wrought Spheroidized 4340 Cast Normalized & Spheroidized 4340 Wrought Quenched & Tempered 4340 Cast Quenched & Tempered 4340 Wrought Quenched & Tempered 4340 Cast Quenched & Tempered 179 115 122 221 200 206 210 300 300 400 400 100 90 90 40 35 50 55 25 25 20 20 * Machining speed 180 sfm In Table 93, a comparison of cast and wrought steels on the basis of speed index is given. This comparison is based on the cutting speed which will give one hour tool life using either an 18-4-1 high-speed tool or a 78B carbide tool or equivalent. Table 93—Speed Index Numbers for Cast and Wrought Steels of Similar Microstructure Cutting Speed Which Will Give One Hour Tool Life High-Speed Steel Speed No. Steel BHN Carbide Speed No. 11 1020 Wrought 1020 Cast 4340 Wrought Annealed 4340 Cast Normalized & Annealed 4340 Wrought Spheroidized 4340 Cast Normalized & Spheroidized 4340 Wrought Quenched & Tempered 4340 Cast Quenched & Tempered 4340 Wrought Quenched & Tempered 4340 Cast Quenched & Tempered 115 122 221 200 206 210 300 300 400 400 160 160 70 60 85 95 45 45 35 35 550 400 300 200 375 300 325 200 225 175 MACHIN ABILITY 535 It can be observed that with high-speed steel tools the comparison is favorable but that with carbide tools the cast steels machine at lower speeds. Machining of Special Cast Steels Machining Heat and Corrosion Resistant Cast Steels ... Annealed cast- ings of the CF-8 (19 percent chromium, 9 percent nickel) type can be machined at about 40 to 45 percent of the speed at which Bessemer screw stock is machined. Using this value as a basis for comparison, the other cast alloy grades are listed in Table 94 as equal, easier, or more difficult to machine. Table 94—Relative Machinability of High Alloy Cast Steels as Compared to CF-8 Classification Better Equivalent Alloy Type CA-15, CE-30, CF-8C, CF-16F, HT, HU, HW, HX CB-30, CC-50, CF-20, CF-8M, CF-12M, CG-12, CK-20, HB, HC, HE, HK, HL CH-20, HH, HI Poorer The best combination of feed and speed to be used in cutting stainless steel is to reduce the speed first, then, if necessary, the feed. The tool must advance steadily into the work. Use slow feeds, 1/16 to 1/8-inch cuts and powerful, rigid machines. The recommended cutting speeds for stainless steels are listed in Table 95 when high-speed tools are used, and it is suggested that about twice these speeds be used for carbide tools and finishing- turning. Machining Leaded Steels ... Steels containing lead are more machin- able than non-leaded steels. The improvement in machinability is re- flected in reduced machining time and tool wear as well as in faster removal of metal, because it is possible to make deeper cuts and to em- ploy faster speeds. The relative ease of machining leaded steels pays off most noticeably with steels hardened for high strengths. Non-leaded steels heat treated to hardness levels that are difficult to machine become machinable when leaded. Results of machining tests on cast steels with and without lead are given in Table 96. Cast steels incorporating lead machine similarly to comparable lead containing wrought steels, and since the preponder- ance of data for leaded steels have been presented on wrought steels, 536 MACHIN ABILITY Table 95— Recommended Machining for Heat Treated Stainless Steel with High-Speed Steel Tools29 Alloy ACI Type AISI Type of Chips Feeds (IPR) Rough Finish Speeds (sfm) Finish Drill Rough Tap 410 420 431 446 312 304 302 347 stringy, not abrasive stringy short and brittle short and brittle use chip curlers tough and stringy, use chip curlers Same as for CF-8 Same as for CE-30 0.010-0.030 0.030-0.040 0.020-0.030 0.025-0.035 0.020-0.025 0.025-0.035 0.003-0.010 0.015-0.020 0.010-0.015 0.010-0.015 0.005-0.010 0.005-0.010 40-50 25-35 40-50 40-50 30-40 25-35 CA-15 CA-40 CB-30 CC-50 CE-30 CF-8 CF-20 CF-8C CF-8M CF-12M CF-16F CH-20 CK-20 CN-7M HA 35-70 30-60 30-60 40-60 30-60 20-40 10-25 10-20 10-25 10-25 10-25 10-20 Same as CF-8 except as noted 0.020-0.025 316 303 309 310 0.005-0.010 45-55 90-110 20-50 30-80 20-50 10-20 15-30 10-20 ::: 0.010-0.030 0.005-0.010 40-50 30-60 35-70 10-25 10-25 HC 446 0.025-0.035 0.010-0.015 40-50 40-60 10-25 HD 327 0.025-0.035 0.010-0.015 40-50 40-60 10-25 HE 312 0.020-0.025 0.005-0.010 30-40 30-60 10-25 HF 302B 0.020-0.025 0.005-0.010 25-35 20-40 10-20 Same as for CF-8 except as noted Same as for CF-8 Same as for CF-16F except as noted use curlers and breakers, tough and stringy use chip curlers and breakers, tough and stringy use chip curlers and breakers, tough and stringy use chip curlers and breakers, tough and stringy use chip curlers and breakers, tough and stringy tough and stringy tough and stringy tough and stringy tough and stringy use chip curlers and breakers, rough and stringy use chip curlers and breakers chips are rough and stringy chips are rough and stringy chips are rough and stringy chips are rough and stringy 309 50-70 50-70 HH HI HK HL HN 310 0.015-0.020 0.015-0.020 0.020-0.025 0.020-0.025 0.020-0.025 0.005-0.010 0.005-0.010 0.005-0.010 0.005-0.010 0.005-0.010 25-35 25-35 25-35 30-40 35-45 20-40 20-40 20-40 30-60 40-60 10-20 10-20 10-20 10-25 5-15 HT 330 0.025-0.035 0.005-0.010 40-45 40-60 5-15 HU HW HX 0.025-0.035 0.025-0.035 0.025-0.035 0.010-0.015 0.010-0.015 0.010-0.015 40-45 40-45 40-45 40-60 40-60 40-60 5-15 5-15 5-15 MACHIN ABILITY 537 additional machining information is given in Table 97 on the machin- ing of wrought steels. Machining Alloy Steels in Excess of 500 BHN ... Turning tests for ultra-high strength alloy (514BHN) steels indicate that reasonable tool life in turning can be obtained by adhering to the following general recommendations: (1) Use a rigid machine and strong, solid tools and fixture (2) Use the proper type of carbide. For a given type of carbide, select the hardest grade that will perform without chipping (3) Use cutting speeds, feeds and tool geometries selected from turning data given in Figures 584 and 585. Table 96—Machinability Rating for Leaded and Non-Leaded Cast Steels* (Phillips) 28 Average of Five Tests Machinability Treatment BHN Rating Steel Carbon Carbon Alloy Alloy Non-leaded, Normalized Leaded, Normalized Non-leaded, Q & T Leaded, Q & T 163 165 252 252 81 118 87 116 * Machinability ratings based on performance of a C1018 steel assigned an arbitrary rating of 72. 70 70 TOOL CARBIDE 6-8 60 60 50 CARBIDE C-67 - CERAMIC A -CARBIDE C•7 CARBIDE C-8 ,CERAMIC B 50 40 40 - -.009 IN./REV. TOOL LIFE, MINUTES OL LIFE, MINUTES 30 30 20 10 0 50 100 150 200 250 300 350 CUTTING SPEED, FEET PER MINUTE Fig. 584—Turning tool life results for 4340 steel quenched and tempered to 514 BHN. Tool: carbide: mechanical chip breaker: teed/rev: 0.009 in.; depth of cut: 0.100 in.; wearland: 0.015 in. (29). 20 K015 IN./REV 10 .019 IN./REV. 0 50 100 150 200 250 300 350 CUTTING SPEED, FEET PER MINUTE Fig. 585—Turning 4340 quenched and tem. pered to 514 BHN; effect of feed; tool: C-8 carbide; mechanical chip breaker; feed: see graph; depth of cut: 0.100 in.; wearland: 0.015 in. (29). 538 MACHIN ABILITY Table 97—Machining Wrought Leaded Alloy Steels25 Feed in. Depth of cut in. Steel BHN Operation Speed Results 1/8 3/16 4137 4137 + Lead 4137 4137 + Lead 69% less time 290-330 290-330 290-330 290-330 2-3/4 rpm 6 rpm Turning Turning Tooth Cutting Tooth Cutting 1/32 1/32 0.028 0.028 35 strokes 35 strokes 1600% longer tool life, 94% less wear 4140 4140 + Lead 4140 285-302 285-302 285-302 Turning Turning Tooth Cutting 17 rpm 25 rpm 0.028 0.028 0.017 47% less time 37.5 strokes 4140 + Lead 285-302 46.5 strokes 0.024 47% less tool wear 41% less time 437% longer tool life 4150 255 275 sfm 0.016 4150 + Lead 255 475 sfm 0.021 56% less time 4150 4150 + Lead 4150 255 255 255 276 sfm 475 sfm 89 strokes 0.005 0.010 0.0237 71% less time 0.62a 4150 + Lead 255 Tooth Cutting Turning, Face Cuts Turning, Face Cuts Turning Turning Tooth Cutting Roughing Tooth Cutting Roughing Tooth Cutting Finishing Tooth Cutting Finishing Tooth Cutting Tooth Cutting 111 strokes 0.02956 0.62 21% less time 200% longer tool life 50% less tool wear 4150 255 89 strokes 0.0237 0.0306 4150 + Lead 255 111 strokes 0.0368 47% less time 187% longer tool life 46% less tool wear 1070 1070 240-260 240-260 32 rpm 40 rpm 0.048 0.076 0.69 0.69 50% less time *Roughing cut Finish cut, newly ground cutter ‘Roughing and finishing cuts M A CHI N ABILITY 539 REFERENCES 1. Metals Handbook, 1948 Edition, American Society for Metals, Cleveland, Ohio. 2. Tool Engineers Handbook, Section 17, 1949 Edition, American Society of Tool Engineers, McGraw-Hill, New York, N. Y. 3. Briggs, C. W., The Metallurgy of Steel Castings, McGraw-Hill, New York, N. Y., 1946. 4. A Treatise on Milling and Milling Machines, Cincinnati Milling Machine Com- pany, Cincinnati, Ohio. 5. Modern Steels and Their Properties, Bethlehem Steel Company, Bethlehem, Pennsylvania, Handbook No. 268. 6. Manual on Cutting of Metals, American Society of Mechanical Engineers, New York 18, N. Y., 1953. 7. Increased Production, Production Costs and Control of Materials and Machines, Vol. I, 1950, Vol. II, 1951, Curtiss-Wright Corporation, Woodridge, New Jersey. 8. Steel Handbook No. 42 for Machine Tool Users, Republic Steel Corporation, Massillon, Ohio. 9. Woldham and Gibbons, Machinability and Machining Metals, McGraw-Hill, New York, N. Y. 10. Boston, O. W., Metal Processing, Second Edition, John Wiley and Son, New York, N. Y. 11. Machinability Depends on Microstructure, Special reports from Air Force, Curtiss-Wright, Ford Motor Car Co., Metcut Research Association, American Machinist Report, Copyright McGraw-Hill, New York, N. Y., 1950. 12. Woldman, Norman E., “Good and Bad Structures in Machining Steel”, Materials and Methods, February, 1947, pp. 80-86. 13. Zlatin, N., and Nowikowski, L., "Effects of Structure on Machinability", The Iron Age, August 2, 1951, pp. 95-98. 14. Ernst, Hans, "Cutting Speed: Horizons Limited", Steel, February 9, 1953, pp. 88-90. 15. Zlatin, N., Kahles, J. F., Briggs, C. W., "The Machinability of Cast Steels”, Tool Engineer, February 1953. 16. Albrecht, A. B., "Practical Approach to Optimum Machining", The Monarch Machine Tool Co., Sidney, Ohio, 1953. A reprint of 4 articles appearing in the American Machinist, 1953. 17. “Machinability Studies Compare Cast and Wrought Steels”, The Iron Age, January 22, 1953. 18. "Machinability of Cast Steels”, American Machinist, February 2, February 6 and March 2, 1953. 19. Zlatin, N., Kahles, J. F., and Friedlander, W. H., "How do Boron Steels Compare in Machinability ?", The Iron Age, October 29, 1953, pp. 94-97. 20. “Leaded Steels Take Cut at Machining Cost”, The Iron Age, October 25, 1954, pp. 159-162. 21. Elliott, R. C., and Koffman, D. M., "A Literature Survey on Leaded Steels”, Appendix B, U. S. Department of Commerce, Office of Technical Services, PB 111, 917, July 1955. 22. Carbonaro, P.A.G., “Ceramic Cutting Tools”, Ordnance, January-February 1956, pp. 712-714. 540 MACHIN ABILITY > 23. Hays, L. C., "Free Machining Steels”, SAE Journal, November 1956, pp. 45-46. 24. Funk, C .R., “New Leaded Steels Reduce Machining of Large Gear", Materials and Methods, December 1956, pp. 94-95. 25. Unterweiser, P. M., “Machinability Testing: Science or Fiction ?”, The Iron Age, February 28, 1957, pp. 75-78. 26. Phillips, W. J., “Lead in Cast Steel: How Much Does Machinability Improve?”, The Iron Age, August 15, 1957, pp. 102-103. 27. “How to Cut, Weld and Heat-Treat Cast Stainless Steels", Metalworking, November, 1957. 28. Simon, W., "A Fresh Look at Leaded Steels”, Product Engineering, April 14, 1958, pp. 72-73. 29. Arzt, P. R., Gould, J. V., and Maranchik, J., “Air Force Program Evaluates the Machining Characteristics of AISI 4340 Low Alloy Steel”, SAE Journal, May 1959. > CHAPTER XVIII THE MANUFACTURE OF STEEL CASTINGS Steel castings are being manufactured in approximately two hundred foundries throughout the United States. These foundries range in size from those capable of producing several thousand tons a month to those which produce less than one hundred tons a month. Many steel foundries, such as those which produce railroad special- ties, are highly mechanized. Jobbing foundries, on the other hand, must have a flexible layout which is readily adaptable to the produc- tion of a wide variety of steel castings which may range from large to small and embrace a number of different analyses and heat treat- ments. Each plant is an individual entity; therefore, it would be im- practicable to explain in detail the process of manufacture at all plants or, for that matter, all of the methods employed by a single foundry. A description of the general manufacturing methods common to all steel foundries will be given. In this way, modifications and variations in practice can be touched upon to illustrate the diversity existing in the manufacture of steel castings. It is very important to realize that one method of melting steel, or a particular molding method used by one manufacturer, may or may not be duplicated by another manufacturer. This difference in manu- facturing processes has no bearing upon the quality of the product, but simply reflects the nature of the product of each plant. For example, one producer manufactures castings on a small scale of perhaps only a hundred tons a month, producing miscellaneous jobbing castings. Another manufacturer's output may be several thousand tons a month, confined largely to the production of a specific line of castings. The type of equipment, the methods of processing and materials handling may be entirely different in the two shops, yet the castings produced may very likely be required to meet similar inspection and quality tests. SECTION I Melting Practice There are several methods by which steel for castings is produced in America. These methods are listed as follows: Electric Arc (Acid and Basic) Open Hearth (Acid and Basic) Electric Induction (Acid and Basic) Oxygen Converter (Basic) 542 MANUFACTURE The manufacturing methods used by any one manufacturer depend upon certain general conditions and circumstances. The choice of the steelmaking method to be employed depends upon the policy of the organization as to: (1) the plant capacity or tonnage required, (2) the size of the castings, (3) the intricacy of the castings, (4) the grades of steel to be produced, (5) the raw materials available and the prices thereof, (6) fuel or power costs, (7) the type of operation most de- sirable (acid or basic), (8) the amount of capital to be invested, (9) type of labor available, and (10) previous experience. The open-hearth furnace is used where a large tonnage is contin- ually required, and the small electric arc furnace is preferred for steels of widely differing analyses, which often involve small lot production. Small quantities of expensive steels of special composition, such as high-alloy steel, are often produced in the high frequency induction furnace. Foundries which have access to good grades of scrap and, there- fore, do not need to reduce the phosphorus and sulfur contents of the steel to meet specifications, usually prefer to use a furnace lined with silica refractories (acid lined). Other foundries which do not have a good source of a low phosphorus and sulfur scrap, or desire steel of very low phosphorus and sulfur content use basic type refractories (magnesite, dolomite, etc.) for the furnace lining. Certain types of steels, such as the austenitic manganese steel, are normally made in a furnace with a basic lining. The same type melting furnaces employed to produce steel for castings is also used for the production of wrought steel. Although the equipment is the same, the processes are often different. Steel for wrought steels may be made as rimming, semi-killed or killed steels. Only thoroughly killed steel is used for steel castings. The method of production of the killed steel used for wrought products may differ from that used for castings, since certain properties of the steel are more important to one than to the other. For example, the steel maker in a steel foundry is very much interested in the property of steel fluidity and, therefore, he employs a procedure calculated to produce a steel with excellent casting qualities. On the other hand, the producer of wrought steel products is not as interested in fluidity since he is required to fill only ingot molds and not irregular and complicated sand molds. However, the salient features of the making of steel for castings are the same as those employed for producing dead-killed wrought steel. A detailed description of practices followed in the manufacture of steel for castings by the various melting methods would be too lengthy for reproduction herein. However, the salient features of each method MANUFACTURE 543 FUEL SUPPLY OPERATING FLAME FUEL SUPPLY, IDLE SLAG 2 MOLTEN STEEL HEARTH PREHEATED AIR WASTE GASES COLLET AIR CHECKERS CHECKERS REVERSING VALVE 2STACK Fig. 586—Cross sectional sketch of open-hearth furnace with unregenerated gas or liquid fuel. > are set forth in this chapter. Detailed descriptions are readily available from several technical sources(1), including the Steel Founders' Society, should the reader desire to pursue the matter further. It may be well at this point to discuss briefly the use of oxygen as an aid in steelmaking, since it has become available in large quanti- ties at reasonable cost. Oxygen is being increasingly used in both open-hearth and electric arc furnaces to increase the speed of melt- down, thus shortening the heat cycle. It is also widely used to accelerate refining reactions, such as carbon oxidation, by direct injection into the molten bath, with an accompanying increase in bath temperature. The use of oxygen to oxidize the carbon content of the bath has resulted in eliminating or reducing the amount of iron ore added to the charge, and during the refining period. Open-Hearth Melting ... The open-hearth process and furnace take the name from the fact that both the hearth and the charge resting on it are exposed to the direct action of the flame employed in converting the solid charge into the liquid state. The process consists essentially in melting steel scrap and some pig iron, and oxidizing carbon, silicon and manganese by means of additions of iron ore or oxygen and, finally, adjusting the composition by proper additions. A cross section sketch of an open-hearth furnace, Figure 586, shows how the flame is directed upon and over the metal Fig. 587—Charging as open-hearth furnace with steel scrap. charge which rests in the bowl-like depression of the hearth. Steel melting temperatures are attained by means of regenerators, located on each end of the furnace, which store heat from the spent gases of combustion and, upon reversal of the direction of air flow, return this heat to the incoming combustion air. Several types and combinations of fuels are used for heating open-hearth furnaces, such as natural and producer gas, coke oven gas, powdered coal and oil. No preheat is required for any of these fuels except producer gas, and the regenerators supply heat to the combustion air alone. The heated air from the regenerator, or checker chamber, as it is commonly called, is mixed with the fuel upon en- trance into the furnace. The combustion air is preheated to around 2400 degrees F, providing a very high flame temperature; and the waste gases pass out through the ports and checker chambers on the opposite end of the furnace. The direction of flow of air and combus- tion gases is reversed at regular intervals in order to maintain uni- formly high flame temperature and melting speed. The furnace hearth, side walls, and roof are lined with suitable basic or acid refractories. The acid practice employs furnaces lined with silica refractories and a siliceous slag covers the metal. Neither phosphorus nor sulfur is eliminated from the steel during steelmak- ing operations, hence the process is limited to the melting of raw ma- terials low in these two elements. Basic linings consisting of mag- nesite and dolomite, and basic slags high in lime content, facilitate the removal of phosphorus and sulfur from the steel. The open-hearth furnace is designed with doors on one side through which the charge is placed on the hearth (see Figure 587), Fig. 588—A battery of open-hearth furnaces as viewed from the charging platform. and the melting operations are controlled by additions and tests. Figure 588 shows the entire open-hearth platform for six 30-ton open- hearth furnaces. Charging boxes for steel scrap, pig iron, ferro- alloy additions, and granulated refractories for furnace hearths are shown on the platform. Figure 589 shows the pouring of a steel sample for chemical analysis and, in Figure 590, the furnace operators have just taken a temperature measurement and are removing the immersion thermocouple. The tap hole is on the opposite side of the furnace and enters at the center and bottom of the hearth. During the steelmaking period, the tap hole is closed with a refractory ma- terial which is removed when the heat is tapped (see Figure 591). Open-hearth bottoms consist of several courses of refractory brick laid on the pan. On top of this, a granulated refractory ma- terial is sintered or rammed into place and shaped to the specific contour of the furnace. If the furnace is to be basic, a dead-burned magnesium oxide clinker is used as the bottom material, and for the Fig. 589–Pouring a test sample during the re- fining period. 12018 *** w Fig. 590—Removing im- mersion thermocouple from open-hearth bath after a temperature measurement taken. Note inset showing high speed recorder for steel temperature measure. ments. acid process the bottom is rammed with a sized ganister or natural silica sand. A new furnace is thoroughly heated prior to adding the metallic charge. No molten metal is charged into the open-hearth furnaces used in the steel casting industry. Acid Open-Hearth Practice ... The usual metal charge consists of 10 to 20 percent of low phosphorus pig iron, the remainder being selected low-phosphorus and sulfur scrap, foundry returns, and about 3 percent iron ore. The aim of the melter is to prepare the charge so that after melting it will contain an appreciably higher carbon content than the desired final composition. Oxidation from the flame and ore, or from oxygen injection, removes carbon, manganese and silicon. When the desired carbon content is reached and the temperature is satisfactory, alloys and deoxidizers are added and the metal is tapped from the furnace. One of the most important advantages of the acid process is that the slag is almost self-controlled. An acid open-hearth slag will con- sist of FeO 18 to 25 percent, MnO 12 to 20 percent, Si0, 50 to 58 percent, and CaO 2 to 5 percent. There is a very slight gain in phosphorus in the metal owing to loss of iron by oxidation, and the sulfur content of the melting fuel may be reflected in some small increase of this element in the steel. High quality steel is made by this process when proper care is exer- cised in the selection of raw materials and fuel. Basic Open-Hearth Practice ... The metallic charge consists of steel scrap, including foundry returns, and pig iron. The latter will usually 30-ton open-hearth Fig. 591—Tapping a turnace. vary between 10 and 35 percent of the charge, but through the addi- tion of recarburizing material, may be eliminated altogether. It is essential that the charge be balanced so as to provide a carbon content at meltdown which is somewhat higher than the desired final analysis. This insures proper action between slag and metal to eliminate im- purities during the refining period. The slag-forming material is burned lime or limestone, which usually is placed in the furnace early in the charging cycle. When ex- pressed in available Cao it may range from 3 to 6 percent of the weight of the metal charge. It is imperative that the molten slag be highly basic in order to remove phosphorus from the steel and prevent its return during the late stages of refining. Fluorspar is employed to insure complete solution of the lime and reduce viscosity of the slag. Burned lime in varying amounts is often added during the refining period to maintain high basicity. In this manner a low phosphorus content may be insured, accompanied by a significant reduction in sulfur. The basic open-hearth is essentially an oxidizing process and the slag acts as a regulator of oxidation as well as a carrier of undesired impurities. A basic open-hearth finishing slag contains the following major constituents: CaO 40 to 50 percent, MnO 10 to 15 percent, FeO 13 to 18 percent, and SiO2 15 to 20 percent. It is possible in an average basic open-hearth heat to reduce the phosphorus from 0.20 to 0.02 percent. A certain amount of sulfur 548 MANUFACTURE elimination can also be realized, but this will vary according to bath condition and the sulfur content of the fuel. Sulfur reductions of 0.005 to 0.010 percent are easily obtained. With present day knowledge a heat containing 0.035 to 0.040 percent sulfur at meltdown can be reduced to 0.018 to 0.020 percent. Basic open-hearth steel has found wide favor because of the ability of the process to reduce phosphorus and, to a limited degree, sulfur; hence, low priced scrap with pig iron may be used to produce steels of excellent quality. Electric Arc Furnace Melting The electric furnace should not be considered as replacing the open-hearth furnace as a method of steelmaking for steel casting production. The open-hearth probably will always be used for large to age and large casting production. The electric furnace is well Electrodes Slag Zul Arc Arc Molten Steel ELECTRIC FURNACE Fig. 592–Cross sectional sketch of an electric arc furnace. - Fig. 593 Top charging a 5-ton electric arc furnace. IA adapted to limited tonnages and varied analyses. It also provides very hot metal when it is desired to run extremely thin sections; moreover, it can be run intermittently, as it is not essential to its operation that it be kept continuously hot. The electric arc furnace consists essentially of a metal shell, lined with refractories to form a melting chamber, the hearth of which . is bowl-shaped. Three electrodes carry the three-phase current into the furnace through ports in the roof. A diagrammatic sketch of a cross-section of an electric furnace is shown in Figure 592. The steel, either in the solid or molten condition, is the common conductor for the current flowing between the electrodes, which are made of carbon or graphite. Melting of the metal is achieved by heat from arcs between the electrodes and the metal charge. The steel is melted both by direct impingement of the arc, and by radiation from the roof and walls. The electrodes are controlled automatically so that an arc of the proper length may be maintained throughout the melting cycle. Modern electric furnaces have removable roofs which permit top charging, as shown in Figure 593. The tapping temperature and the fluidity of the molten steel are very important in electric-arc furnace melting, and are accurately controlled. The temperatures are often measured with an immersion thermocouple (Figure 594). The fluidity of the molten steel can be determined by means of fluidity spirals. In Figure 595, a furnace helper is pouring a test, and in Figure 596 fluidity spirals are shown. Fig. 594—Measuring temperature of steel in electric arc furnace with immersion thermo- couple. Acid-Electric Practice ... The furnace hearth of the acid electric fur- nace is composed of silica sand or ganister rammed into place. The furnace is charged with selected scrap low in phosphorus and sulfur content, as the acid process is unable to eliminate these elements. About 40 percent of the charge is usually made up of foundry re- turns such as gates and risers. The process consists of melting down the charge as quickly as possible, adding a small amount of sand to the bath from time to time during the melting period in order to form a protective slag of proper consistency. A good grade of iron ore is added, or oxygen Fig. 595 Furnace operator pouring a fluidity spiral. Fig. 596—Fluidity spirals. Left indicates cold heat. Right indicates full spirals indicating hot heat. is injected into the bath as soon as melting is complete to remove carbon, silicon, manganese, hydrogen, and nitrogen from the charge (see Figure 597). The carbon is reduced approximately 0.20 to 0.25 percent during the vigorous carbon boil. Then the boil is killed off by the addition of deoxidizers in the form of ferromanganese and ferrosilicon to the bath. The metal is then tapped into the ladle as is shown in Figure 598. It is common procedure in acid electric practice to add a specific amount of aluminum to the ladle as a final deoxidizer. The finishing slag will consist of approximately 55 to 60 percent SiO2, 12 to 16 percent MnO, 4 to 6 percent A1203, 7 to 10 percent CạQ, and 12 to 20 percent Feo. , , The acid electric process produces steel of high temperature that has excellent fluidity and high mechanical properties. However, it requires careful selection of melting scrap, since no phosphorus or sulfur is removed. Basic Electric Practice ... The basic electric furnace won a place in the industry because it enabled the steelmaker to carry the elimina- tion of phosphorus and sulfur to a point lower than that obtainable by any other steelmaking method. Its popularity is growing in the steel casting industry since scrap steel of adequately low phosphorus and sulfur content is becoming more costly and difficult to obtain. These conditions have materially increased the use of the basic electric process during the past ten years, particularly in the production of special alloy steels. The hearth of the basic electric furnace usually is composed of dead burned magnesium oxide clinker rammed into place. The charge, consisting of a known weight of purchased scrap steel and foundry returns, is melted down as quickly as possible. Small quantities of 1 Fig. 597 Oxygen lancing to reduce the carbon content of the bath. .: lime are added from time to time during the melting period to form a protective slag over the molten metal. Iron ore, or oxygen, is added to the bath just as melting is completed. The slag is now highly oxidizing and in the correct condition to take up phosphorus from the metal. The slag is removed shortly thereafter if the two-slag process is used. Complete removal of the oxidizing slag is necessary since this slag carries the phosphorus which, under reducing conditions, will revert to the steel from any portion permitted to remain. A new slag composed of lime and fluorspar is then added. Pulverized coke, carbon, ferrosilicon, or a combination of these, is spread at intervals over the surface of the melted second slag to reduce the oxides of iron and other oxidizable elements and form a calcium carbide slag, which is essential to the removal of sulfur from the metal. This refining slag has approximately the following compo- sition: CaO 45 to 55 percent, SiO, 15 to 20 percent, FeO 0.50 to 1.5 per- cent, CaF 5 to 15 percent. Adjustments are made in the carbon content of the bath by the addition of a low phosphorus pig iron. After the proper bath temper- ature is obtained, ferromanganese and ferrosilicon are added and the furnace is tapped. Aluminum generally is added to the steel in the ladle as a final deoxidizer. The basic furnace in the steel foundry is indispensable in the manufacture of 12 to 14 percent manganese steels, and the 18-8 stain- less steels. It also permits the remelting of alloy steels containing high percentages of easily oxidized elements, such as chromium; in such instances, a single reducing slag is used. - Fig. 598 — Tapping an electric arc furnace. An advantage offered by the basic electric furnace over the basic open-hearth furnace, especially in the production of alloy steels, is the conservation of alloys and the greater reduction of sulfur content. This is because an effective reducing slag can be employed in the basic electric furnace, which is not possible in the normally constructed open-hearth furnace. The refining process in the open-hearth furnace is essentially an oxidizing one because of the air introduced in the burning of the fuel. Steel of excellent mechanical properties is obtained from the basic electric process, and because of the low phosphorus and sulfur contents the impact properties are exceptionally good. Electric Induction Furnace Melting ... The high frequency induction furnace is essentially an air transformer in which the primary is a coil of water-cooled copper tubing and the secondary is the metal charge. A sketch of the furnace is shown in Figure 599. The shell of the furnace consists of fiberboard with trunnions on which the furnace pivots when pouring. A circular winding of copper tubing is placed inside the shell. Fire brick is placed on the bottom portion of the shell, and the space between that and the coil is rammed with grain refractory. The melting chamber may be a refractory crucible, or it may consist of a rammed and sintered lining. The general practice is to use ganister rammed around a steel shell which melts down with the first heat, leaving a sintered lining. Basic linings are often pre- ferred and, in this case, a rammed lining of magnesia grain or a clay- bonded magnesia crucible is used. The process consists of charging the furnace with steel scrap, and then passing a high frequency current through the primary coil, 554 MANUFACTURE ®®®®®®®®®®®®®®® Molten Metal To high frequency power supply 999999aeg Fig. 599–Cross sectional sketch of a high frequency induction furnace. thereby inducing a much heavier secondary current in the charge, which heats it to the desired temperature by electrical resistance. The charge is carefully selected from scrap and alloys of known composition so as to produce the desired analysis in the finished steel. A very close control of elements is obtained in this manner. The time of melting depends upon the size of the furnace, its burden, and power input. A very pronounced stirring action takes place as soon as a pool of metal is formed. Melting is quite rapid; so much so, that there is only a slight loss of the easily oxidized elements. Steel scrap is added during the melting-down period if a full capacity melt is required. As soon as melting is complete, the desired superheat tem- AAX Fig. 600—Battery of 3 induction furnaces. 1 MANUFACTURE 555 perature is obtained and the metal is deoxidized and tapped. Figure 600 shows a battery of three induction furnaces. No attempt is made in most cases to melt under a slag cover, since the stirring action of the bath makes it difficult to maintain a slag blanket on the metal. However, this is not necessary since oxida- tion is so slight. The induction furnace is proving valuable in the steel foundry because of its flexibility in operation, particularly in the production of small lots of castings. The requirements of certain industries are such that numerous types of steel castings containing high percentages of alloys must be produced. The quantity of castings for any one par- ticular service may be small while, at the same time, the number of alloy types desired may be large. Such production requirements are satisfactorily met by the use of the induction furnace. The fact that high alloy steels can be remelted without loss of alloy content through oxidation makes it an almost ideal melting medium. It is also valuable for melting low carbon steels because no carbon is picked up from electrodes such as may occur in the electric arc furnace practice. Induction furnaces used in the steel foundry range in capacity from 100 pounds to 10,000 pounds, with approximately half of them in the 1,000 to 2,000 pound bracket. Few foundries have furnaces where capacity exceeds one ton. . Basic Oxygen Process ... A recent evolution in the use of oxygen in steel-making is the Basic Oxygen Process which combines certain ad- vantages offered by both the basic open-hearth and the converter pro- Fig. 601-Basic oxygen steelmaking pro- cess. 556 MANUFACTURE cess, and at the same time eliminates many of their respective deficien- cies. In this process, molten iron is refined to steel in a basic-lined, solid-bottom vessel by directing a jet of nearly pure oxygen vertically on the surface of the hot metal bath. The oxygen is discharged through a retractable water cooled, copper tipped lance. The resulting steel is low in phosphorus, sulfur, and nitrogen, and of comparable quality to basic open-hearth steel. The steel scrap, which amounts to approximately 30 percent of the metallic charge, is added into the melting unit, and the molten iron is immediately poured into the converter. The vessel is placed in a vertical position, the oxygen flow is started, and the lance is lowered and clamped into position when it reaches the proper distance above the bath. The desired quantities of lime, fluorspar, and scale (iron oxide) are added about one minute after the blow begins. The oxygen is shut off when the blow end point is reached, the lance is retracted, the slag decanted, and the temperature of the steel taken with an immersion thermocouple. Any necessary correc- tions as to carbon content and temperature are made before the steel is tapped. Figure 601 is a photograph of a melting unit used in the Basic Oxygen Process during the “Blow.” As of the year 1960, only one foundry is pouring castings with steel made by this process, but there are indications that the process will enjoy expanded use in the steel casting field. Vacuum Degassing ... In the 1950's a German steel manufacturer succeeded in applying vacuum degassing techniques, first to the pro- duction of ingots, and later to steel castings. The process reduces Fig. 602—View of vacuum chambers with furnace ladle pouring into pony ladle. MANUFACTURE 557 gas content and nonmetallic inclusions to a minimum. The practice has found favor in the United States, particularly in the production of ingots for heavy forgings. Additionally, two steel foundries are now using vacuum degassing in their production of heavy castings for highly specialized applications. In the vacuum degassing process illustrated in Figure 602, the steel from the furnace ladle is poured into a 15-ton pony ladle. The steel from the pony ladle enters the vacuum chamber and flows into another ladle. Hydrogen and other gases are removed from the pour- ing stream as the metal enters the vacuum. The vacuum chamber is brought to atmospheric pressure after the heat is degassed, the ladle in the vacuum chamber is removed, and the castings are poured in the usual manner. It may be of interest to note that vaccum degassing was perfected at the same German plant which, sometime prior to 1851, produced some of the earliest steel castings of record. SECTION II Molding and Coremaking Steel castings are produced by pouring molten steel into refrac- tory molds where it solidifies to the desired shape and contour. A wide variety of refractory materials is available for molding with the choice of a particular material governed by such factors as the size and section of the castings, the number required, the design of the casting, the facilities available in the foundry, the tolerances re- quired, and the economics of the process. Molding Materials ... Fundamentally, the making of a mold for a casting is the shaping of a suitable plastic refractory material into the desired form so that a liquid metal introduced into it will, after solidification, retain the shape predicated by the mold and can be sep- arated from it. This sounds very easy, but when the material to be cast is molten steel, certain very definite characteristics are demanded of the mold. These characteristics are: (a) The mold must be strong enough in its construction to sustain the weight of the metal. (b) It must be so constructed as to permit any gases formed within it to permeate through the body of the mold rather than to penetrate the metal itself. (c) It must resist the erosive action of a rapidly-moving stream of intensely hot metal during the pouring, and not be de- 558 MANUFACTURE stroyed by the high temperature metal (2850 to 3000 de- grees F) until the casting is solid. (d) It must be weak enough to permit the steel to contract without undue hinderance after solidification. (e) It must be of such material as will cleanly strip away from the casting after cooling. (f) It must be economical since large amounts are used. These stipulations so narrow the field of possibilities that, at present, the most economical material that can successfully qualify is a bonded granulated refractory-silica sand. More expensive gran- ulated refractories such as zircon sand, olivine sand, sillimanite and mullite are used for special applications or processes. Graphite is employed as a permanent mold material for steel castings, but its use is presently limited to the production of steel car wheels in which pressure pouring techniques are employed. There are various types of sand used for molds depending upon special requirements, such as the shape, size, weight or intricacy of the proposed casting. Economy may dictate the use of sands found locally. They may be somewhat different from those found in deposits elsewhere, but techniques can be devised to make them fulfill the requirements of a good molding material. Natural bonded sands are not employed in the production of steel castings because of the variable properties of these sands. Synthetic bonded sands are usually prepared by adding clays, such as western bentonite and/or high-grade fire 'clay, as well as various types of organic binders such as cereals, resins, lignin, oils, etc., to high-grade silica sand, in order to develop good molding quali- ties. Other binders sometimes used, besides clays, to produce molding sands are Portland cement, ethyl silicate, sodium silicate (cured with carbon dioxide), phenol formaldehyde resins, etc. Such sands are em- ployed for either a particular process such as shell molding, ceramic molding, cement-bonded molding (Randupson Process) or to specific types of castings which are adaptable to one of these special tech- niques. A synthetic molding material produced from calcined aluminous clay grog is used occasionally in steel foundries. This material is called "Chamotte." It is graded to size classifications and mixed with about 10 percent raw clay and 6 percent water to form a molding mixture. - Fig. 603 Automatic sand preparation equip ment. 17 Close control of moisture and binders is of utmost importance, as these materials do much to determine the molding properties of the sand mixture at both room and elevated temperatures. Steel foundry molding sands are prepared in mulling machines in which the sand, bond and water are intimately mixed and mulled. No one combina- tion of sand and bonding agents fulfills all molding requirements; therefore, facing sands, backup sands, and core sands must be specially mixed. Different combinations of new sand, old sand, binders and other additives are required. These materials are accurately weighed for each batch of molding sand so that the molding properties will be similar from batch to batch. Moisture control is especially im- portant and often is done automatically through instrumentation. > 02 SEE * IN Fig. 604—Main control panel for auto- matic sand preparation system. Fig. 605—Sand storage hoppers for prepared sand mixes. Prepared mixes are distributed to mold area on con- veyor belts. 1 2 3 INE Casting quality readily reflects the quality of the molding sand used in the manufacturing process, and for this reason every foundry strives toward consistent and close control of the sand mixes. An aid in attaining this goal is automatic sand preparation, an example of which is illustrated in Figure 603 with the main control panel shown in Figure 604. The molding sand coming from the mullers is sampled and tested to ascertain whether or not the desired sand properties are attained. Sand testing equipment is standard apparatus used in a routine manner in steel foundries. The prepared sand is delivered to the molding floor by various means such as: overhead cranes using buckets, belt or pneumatic conveyors, or by lift trucks with bucket attachments. In some cases, the prepared sand is stored in hoppers, such as shown in Figure 605, and from these hoppers the sand is dis- tributed to the various molding and coremaking areas. Conventional Molding Operations ... Molding equipment differs from foundry to foundry. The reasons for this are twofold: (1) no two steel foundries have the same plant layout, and (2) the equipment varies in its construction in accordance with the type of castings regularly produced. The installation shown in Figure 606 is an auto- matic molding set up. On the other hand, a jobbing foundry which, along with miscellaneous work, specializes in producing gears, for example, will have some mechanical molding equipment to aid in the production of their specialty. Small jobbing foundries, in contrast to the so-called production foundries, may have little mechanized mold- ing equipment. Mass production plants may employ sand slinger ramming units with roll-over draw molding machines, Figure 607. The jobbing Fig. 606 Automatic molding machine. 111 foundry, making specialties, may find that jolt roll-over draw ma- chines are the most adaptable equipment. The small foundry may employ only the jolt squeeze type of molding machine which is illus- trated in Figure 608. Thus, a pattern constructed for the mass pro- duction plant may not be adaptable to the equipment of the jobbing foundry without alteration. If the same pattern were placed with a small foundry, it might require complete rebuilding so that it could be used on the machines available at that foundry. The substance of this discussion is to clarify for the engineer and purchaser of steel castings the fact that if a pattern is sent from one shop to another, and if requests are received for pattern alteration, it is not a question of whether the foundry knows how to make the job, but simply the necessity of adapting the pattern to their particular Fig. 607—Sand slinger and jolt rollover mold. ing. Fig. 608—Jolt squeeze molding. type of molding equipment. In the past this point has not been gen- erally appreciated and has occasionally given rise to some misunder- standing. A mold is made by placing the pattern in the flask (a metal or wood box) and then compressing the molding sand around it by various methods. In many cases a specially prepared layer of sand is placed against the face of the pattern, after which the flask is filled with the regular molding sand. The specially prepared layer of sand is called facing sand, while the balance required to fill the flask is known as backing sand. Patterns of simple design with one or more flat surfaces may be molded in one piece. Other patterns may be split into two or more parts for the purpose of facilitating the molding operation. In the case of large or complicated castings there may be dozens of parts to the pattern. The pattern part to be molded is so placed in the flask that after the sand has been rammed around it, the pattern can be removed from the sand without disturbing the impression left in the sand. The mold may be rammed in one, two, or more parts. In Figure 609, the "drag" half of the mold, which is the portion formed in the lower flask, has just been lifted from the pattern. The upper portion of the mold is called the "cope." Intricate pattern designs sometimes require intermediate flasks known as "cheeks." The mold can be made manually, using hand or pneumatic ram- mers, but mechanical means are in universal use today. These may be: jolt machines, squeezers, jolt-squeeze-strip machines, jolt roll- over-draw machines, or sand-slinger ramming units with the roll-over- Fig. 609–Molding operation. draw machine. These various molding operations are shown in Figures 607, 608, 609 and 610. Other methods aimed toward improved economy and quality are in limited use or in various stages of development. Shell Molding ... Not all molds are produced by ramming sand about the pattern. Within the last decade a new concept in producing sand molds, called shell molding, has gained increasing favor. This process was developed in Germany and brought to this country after World War II. It is a method of producing small to medium size close-toler- ance castings with excellent surfaces. In the late 50's this process be- came adaptable to the production of carbon and low-alloy steel cast- ings. Fig. 610–Molding with the of sand slinger. use a UC Fig. 611 Shell mold being ejected from pat- tern after curing cycle. 1 Shell molding utilizes a heated metal pattern and a dry resin- sand mixture as the mold material. Heat from the pattern softens the resin sufficiently to create a thin shell over the pattern surface. This shell is permitted to cure or harden on the pattern for a period of a minute or less, and is then stripped off by pins, as shown in Figure 611. The bonding resin is a phenol formaldehyde type, and can be used with silica, zircon, and olivine sands. Numerous shell molding machines have been developed. In Figure 612 one type of machine is illustrated, and the operator is in the process of removing the cured shell mold. > Not all castings can be produced by the shell process, as overall dimensions and section thickness are limiting factors. Patterns are costly and limit the use of this method to mass-produced items. The process is adaptable to castings of either simple or extremely intri- cate design which require close tolerances. Fig. 612—Shell molding machine. MANUFACTURE 565 Ceramic Molding ... The ethyl silicate process of slurry molding is another recent development which does not utilize ramming as a means of producing a mold. This process is sometimes called ceramic molding and is also known by such names as the Shaw Process, the Osburn-Shaw Process, Ceramicast Process, etc. a The ethyl silicate process employs a mixture of graded refractory fillers, hydrolyzed ethyl silicate, and a liquid catalyst which are blended to a slurry consistency. Various refractory materials, such as sillimanite, mullite, zircon flour, silica flour, and calcined fire clay may be used as filler material. The slurry is poured over a pattern (Figure 613) and sets in a few minutes, first to form a gel, and finally a rigid mold. During the gel stage, the mold is moderately flexible which facilitates stripping from the pattern at this time. The mold is then heated to a high temperature as is normally done in making ceramic materials. Molds can be poured with steel when they are hot, or after cooling. The process has limited application, but is particularly adaptable to small intricate castings such as jet engine manifolds, blades, brake backing plates, as well as blades and vanes for gas turbines, etc. Castings up to 500 pounds have been produced in ceramic molds. Investment Molding ... Steel castings weighing from a few ounces to several pounds are being produced by investment molding (“lost wax” process). A master mold must be prepared of the part to be cast. This mold is usually made from a low-melting temperature alloy. The duplicate dispensable pattern used for each casting is made by pouring or extruding wax, or a low-temperature plastic, into the master mold. After the wax pattern is made it is surrounded 0 Fig. 613–Producing a mold by the slurry process. B. 3007 566 MANUFACTURE or covered by an investment refractory material. The molds are vibrated thus allowing the investment to pack uniformly. Investments vary widely in composition but all consist of a fine particle size refractory aggregate (such as silica flour) and binders. The investment produces a hard, dense, smooth surface mold. The mold is heated, and the dispensable pattern is melted and poured out of the mold. The mold is fired and is then ready for filling with steel or any other metal. Sometimes the mold is placed in a cen- trifugal casting machine or air-pressure casting machine for pouring. Castings so made reproduce the pattern with excellent precision (see Figure 614). Tolerances of plus or minus .005 inch have been reported. Fig. 614-A precsion steel casting. Sodium Silicate Molding ... The production of steel castings by this method was initiated in the steel casting industry in the late 50's. The practical use is limited in molding because of the high cost of sodium silicate bonded sands. Generally, this method of molding consists of cope and drag matched boxes. The molds are produced in the same manner as green sand molds such as squeeze molds, jolt squeeze, etc. The pat- tern is faced with the sodium silicate sand and backed with a coarser sand containing a small percentage of sodium silicate. The green molds are immediately hardened by impregnating with carbon dioxide and then are stripped from the box. The copes and drags are pasted and then paste dried before pouring the mold. Types of Molds ... The mold is transferred to the core assembly station or to the drying oven, depending upon whether the casting is to be poured in a green mold or a dried mold. A green sand mold is Fig. 615—A large pit mold. one which may be poured as soon as produced, whereas a dry sand mold requires the removal of all the moisture by a process of heating or drying. There are modifications of these two main types: namely, air- dried, skin-dried, and the previously discussed carbon dioxide hard- ened molds. Air-dried molds are green sand molds which are allowed to stand several hours, overnight, or for several days, and in so doing lose moisture to the atmosphere. Skin-dried molds are prepared by torch drying the mold cavity. Mold drying temperatures generally used in dry sand molding practice are upward of 600 degrees F. Molds are dried in ovens that are heated by gas, oil, coal or electricity. When the mold is too large for the available drying ovens, portable gas or oil fired driers are at- tached to the mold by means of special hoods and fixtures. Molding Fig. 616—Cope and drag molds of castings before assembly. Fig. 617—Core mold -After molding pit is prepared the cores are then set. Workmen are set- ting first series of cores. sands that are to be dried are seldom the same as those that are used in the green state, in that the quantity and kind of bonding materials are usually different, and the moisture content may be higher. Decision as to the type of mold should be left to the experienced foundry engineer, whose choice will be based upon a working knowl- edge of the method that will produce the best castings at the lowest cost. An intricate casting may be made in green sand, since mold resistance to the normal contraction is less than would be experienced in a dried sand mold. A dry sand mold would probably be used if the casting is large and heavy, because a dry sand mold has high strength properties and can better withstand the metal weight and pouring erosion. These and other factors influence the choice of mold types to be employed (Figures 615, 616, 617, 618 and 619). Fig. 618 Same mold as shown in Figure 617. Work- men are now setting the last cores. Fig. 619-Sweep mold for ball ring gear. 180 inches O.D. and 24 inch face. Metal mold inserts are of great value in the production of cast structures which might otherwise be extremely difficult to manu- facture. They are often used as separately cast or preformed parts to be incorporated into the casting design, such as blades for a nozzle diaphragm, or as pipe inserts to form passages which are impractical to core, or too expensive to machine. They also find wide usage as external or internal chills, which compensate for local hot spots and promote directional solidification. In Figure 620 the cope and drag of a shell mold and the core ring with preformed inserted blades are illustrated. The completed shell mold and blade assembly is shown in Figure 621. Engineers and purchasers of steel castings should attach no sig- nificance to any statement that quality castings may only be produced by the use of one particular molding method. Quality castings are being produced every day by any and all of the processes described herein. Accordingly, a specific process need only be of general interest to the purchaser. His prime concern is whether the delivered castings meet the tolerance requirements and designated specifications. The Importance of Risers ... In various other sections of this hand- book the fact is mentioned that steel, upon solidifying, contracts in volume. A casting solidifies from the outside face toward the center of the section and, since the center of the section is the last portion to solidify, reservoirs of molten metal are placed at suitable locations on the casting to provide liquid steel to maintain casting solidity as the steel contracts. These reservoirs, which are not a part of the casting but are essential to its integrity, are spoken of as risers. The risers are removed when the casting is cleaned, and the casting is finished smooth to the casting contour. 570 MANUFACTURE Fig. 620-Shell mold halves and core ring with inserted rolled blades. om Fig. 621-Complete shell mold and blade assembly ready for casting. Certain steel castings may be so designed that it is impossible to provide risers to feed particular sections. These sections may be pro- duced sound by rapidly solidifying the section through the use of metal chills placed in the mold walls or within the mold cavity. Each casting design must be studied by the production staff of the foundry in order to place the risers where they will function properly. The size of the risers is carefully calculated by the foundry engineer so that they will solidify later than the sections which they are to feed and will contain sufficient metal to compensate for shrink- age requirements. Core Sand and Coremaking ... Cores are component parts of a mold which form internal passages and contours which are required by MANUFACTURE 571 the casting design, but cannot be made by the pattern alone. The fol- lowing simple example will serve to clarify: if one wished to cast a hollow metal cylinder, a solid pattern would be used which would produce a mold with a cylindrical-shaped cavity. Then a sand core would be placed in the center of the cavity to form the inside contour. Spacers used to assure proper placement of cores are known as chap- lets. Cores are usually made of baked sand and the requirements for a good core are as exacting as those for a good mold. The core ma- terial must be very refractory, since in some cases metal will nearly surround it. The core must be sufficiently strong to withstand normal handling, yet not so strong as to prevent the metal surrounding it from contracting normally. A good core should break down or crumble as soon as it has completed its primary purpose of displacing the molten metal, in accordance with the design features. A core should be so constructed as to permit the gas which is formed at molten metal temperature to pass through vents in its body to the outside atmosphere. A core must be constructed so that it may be easily removed from the casting after the casting has been produced. Cores in the steel foundry are made of a fine grain sand bonded with a variety of liquid and solid binders of oil, resin, and cereal, to mention a few. The bonding materials are thoroughly mixed with the sand in a muller. The mulled core sand is distributed to the coremaker and cores are produced either by hand ramming or by machine, depending upon the size of the core and the number of cores to be made. In many ways, the production of cores is similar to that of molds, and they $R& Fig. 622 Producing cores with core shooter (left) and core blower (right). *24 Fig. 623—Modern tower type of core oven. are often made in two or more parts and pasted together. Figure 622 illustrates the production of cores on coremaking machines. In many cases the modern foundry employs either core blowers, core shooters, or both, which pneumatically transport and pack the sand into the core boxes. The operation which follows the making of the core is one of drying or baking. Newly made, or green, cores are placed on plates or metal core dryers shaped to the core contour and placed in ovens (Figure 623) where they are baked at temperatures of 350 to 450 degrees F for the time interval which will insure the strength or collapsibility properties desired. After the cores have cooled, those that have been made in two or more parts are pasted together with Fig. 624 - Dielectric - core oven. 1883 Fig. 625—Production of bench cores by the sodium silicate-carbon dioxide process. Note regulators and one. minute timers. an organic binder. This operation may necessitate rebaking the cores to develop sufficient strength at the joint to hold them together. All cores require careful checking as to dimensions and pattern con- formity before they are sent to the mold assembly floor. Special con- sideration is given to the venting of cores so that gas formed by the heat of the molten metal will not be trapped in the casting. A development in the production of small cores substitutes synthetic resin for core oil and employs dielectric heat for drying. Figure 624 shows a modern dielectric core oven. The high frequency current creates molecular friction and heat at all points within the core instantaneously, and uniform heating results. The sodium silicate-carbon dioxide process for bonding sands is also used for the production of cores. Lower costs are possible and baking is eliminated, thus reducing production time. Sand is mixed with sodium silicate and certain additives, and the core is produced in the usual manner. Carbon dioxide gas is then passed through the core and as a result of the chemical reaction be- tween carbon dioxide and sodium silicate, the sand mass hardens. Figure 625 shows a production setup for producing cores by this method. After gassing, the core is stripped from the corebox and is ready for use. The process is not limited to the production of small cores. In Figure 626 a large core made by this process is being set in the drag half of a mold. Cold setting core binders are used in many jobbing foundries to replace conventional core oil. The binder plus an accelerator (oxidiz- ing agent) is added to cool, dry sand and mixed in a sand muller. The mulled sand has no green strength and is so flowable that it can be poured into the corebox and packed by hand, thus eliminating conventional ramming. The core is allowed to stand for a period varying from a few minutes to several hours until oxidation has Fig. 626 — Setting drag half of core in mold. Core carbon dioxide cured. proceeded so that it can be stripped from the box without damage to the core. Cores are oven cured at a temperature between 400 and 425 degrees F. The core shown in Figure 627 was produced by the cold set process. Shell coremaking has proved to be an important and economical process for the steel casting industry. The shell core is made in the same manner as is the shell mold. Figure 628 shows a manually operated shell core machine with an electrically heated plate to which the corebox is attached. There are many modifications of coremaking procedures depend- ing on how and where the cores are to be used. In some cases, cores are Fig. 627—300-pound core made by cold set process. Fig. 628—Manually operated shell core machine. made of green sand and are air dried; in other cases, the bottom half of the core may consist of a baked oil sand and the top half of green sand, or a shell core used in a green sand mold. It is not necessary that all the cores in a mold be produced from core sand using one type of binder. It is entirely possible that the large cores could be made with a cold setting binder, while the other smaller cores could be carbon dioxide hardened, oil or resin baked, or even shell cores. How cores shall be made depends upon the foundry operating staff. Their study of the blueprints of the casting and construction of the pattern, combined with their experience and knowledge of the exacting conditions imposed by the molten metal upon the cores, are the determining factors regarding the selection of core materials and methods. The cores, having reached the molding assembly floor, are set in their proper places within the mold cavity. The small cores are - Fig. 629 Setting the core in a mold for a hydroelectric turbine spiral casting. do Fig. 630— Mold inspec tion checking core positions. placed by hand while large ones may require mechanical equipment and a crew of men to set them in place as shown in Figure 629. Other mold and core assemblies are exhibited in Figure 630. In some cases the entire mold cavity is formed using cores (Fig. ures 32 and 33). This practice is used when the casting design is such that the pattern, because of surface irregularities, cannot be drawn from the sand. Large molds are often produced by the practice of assembling cores in a pit. Fig. 631-Bottom pouring railway treight car truck bolsters. 0 - Fig. 632 Pouring a large casting with three bottom pour ladles. A Mold Inspection and Pouring ... The entire mold is inspected and checked after the cores are set to determine that the proper clearances have been provided, metal sections maintained, and that the cores are properly placed. The sections of the mold are then put together and the entire assembly is securely bolted or clamped together. The mold is now ready for delivery to the pouring floor. For obvious reasons pit molds and other molds of extreme size are assembled directly on the pouring floor. The metal is transported from the furnace to the pouring floor in ladles. Bottom pour ladles are generally used to pour large molds. In Figure 631 a large number of castings are being poured from a 30-ton bottom pour ladle, and in Figure 632, three bottom pour ladles are simultaneously pouring one large mold. Teapot or lip-pour ladles are generally used when the heats are not very large. The teapot ladle combines features of both top and bottom pouring methods in Fig. 633—Pouring small castings with a teapot ladle. 12 Fig. 634—Pouring ced- trifugally cast pipe. that it draws the steel from the bottom of the ladle, thus separating the slag from the metal, while the stream of metal flows over the lip of the ladle. Lip pour ladles are generally placed on stands on the pouring floor, and the metal is transferred into hand shank ladles which are carried manually or by monorail equipment to the molds, and poured. Figure 633 illustrates the method of pouring molds by shanking. Molds for certain castings are also mounted in centrifugal ma- chines. Such machines are operated, depending on the type of casting, at 100 to 1000 revolutions per minute. Metal is poured into a central opening while the mold is revolving and the centrifugal force throws the metal out to the exterior of the mold cavities. Molds may be re- volved vertically or horizontally. In some cases metal molds are used and internal passages are formed by sand cores. In Figure 634 cast pipe is being poured centrifugally. The pouring operation is one requiring considerable experience and diligent supervision. The metal temperatures are closely watched, - Fig. 635 Pressure pouring railway car wheels. MANUFACTURE 579 pouring speeds are carefully controlled, and mold relieving operations are so correlated that they proceed with precise timing after the pouring of the mold. Pressure pouring was originally developed as a method of con- trolled pouring to be utilized in the production of steel car wheels from permanent graphite molds. However, it is now being used to some extent with molds made of silica sand. Pressure pouring is accomplished by forcing molten steel through a refractory tube and into the bottom of a mold cavity by means of compressed air. The height to which the metal is raised is dependent upon the air pressure applied, and the rate of pouring is determined by the inside diameter of the pouring tube and by the rate of increase of air pressure. Figure 635 is a close-up of the actual pouring. SECTION III Finishing Operations The flasks containing the solidified and cooled castings are usually transferred to vibratory shakeout machines (Figure 636) where the sand is jarred loose from the castings (Figure 637). Removal of Gates and Risers ... The castings are delivered from the shakeout to the cleaning room where the risers and gates are removed (Figure 638) either by: (1) sledging, (2) shearing, (3) cold sawing, or (4) torch burning (Figures 639 and 640). Research in riser design has resulted in the shaping of the riser so that a thin sand core is frequently used to separate most of the Fig. 636—Vibrating shakeout machine. Fig. 637 — Steel casting after being stripped from the mold and adherent sand. Fig. 638—Casting on conveyor after shakeout. Fig. 639—Cleaning room operator remov. ing gates and risers from casting by torch burning. Fig. 640—Removing risers by cold sawing. riser from the casting, the connection resulting in a small neck. This neck can be broken fairly easily by sledging, after the casting has cooled. Snagging ... The removal of fins and other extraneous metal, includ- ing pads, added for the purpose of making the design castable, is an operation known as snagging. Tools used in this operation consist of electric and air operated grinders, pneumatic chipping hammers fitted with many varieties of chisels, scarfing torches, and carbon-arc equip- ment. Good judgment on the part of the workman is essential in producing well-finished castings. Considerable physical labor is ex- pended in the removal of metal by chipping and great care must be taken to grind or chip to the casting contour. Grinding operations, if performed, generally follow the chipping and blasting operations. In Figure 641 swing grinders, are shown in operation, and in Figure 642 Fig. 641--Swing grind- ers in operation, meren Som 582 MANUFACTURE an air operated hand grinder is being used to grind a riser pad to the casting's contour. The relatively recent adoption of carbon-arc equipment by the steel casting industry for removal of excess metal, has been most rapid. In fact, in some steel foundries it has now replaced all grinding and chipping operations. It has become popular by virtue of its high Fig. 642—Grinding riser pads with hand grinder. rate of metal removal at considerable savings. The carbon-arc method consists of using a high amperage electric arc with a carbon electrode, together with a special holder that blows a stream of compressed air at the tip of the electrode which oxidizes and removes the molten metal as quickly as it is formed. Both the carbon-arc and the flame washing processes, with either propane or natural gas, are rapidly supplanting the use of the chipping hammer in the cleaning room. Figure 643 shows excess metal being Fig. 643—Removing ex. cess metal by torch scarfing. Fig. 644—Flame wash. ing riser pads with oxygen-natural gas torch. removed by scarfing with an oxy-acetylene torch while Figures 644 and 645 illustrate the removal of riser pads with a natural gas torch and carbon-arc equipment. Blast Cleaning ... Pressure blasting is used to clean castings of adhering sand, to remove cores, to improve the casting appearance, and to prepare the castings for inspection, painting, machining or as- sembling. The operations are often fully mechanized and various types of machines are available to handle castings of all sizes. Methods utilize abrasive pressure blasting, hydraulic cleaning, and tumbling. Scale produced during the heat treating operation, adher- ing sand, and other foreign matter are removed from the castings by these operations. Abrasives consist of sharp sand, and iron or steel grit and shot, which are propelled through nozzles at high velocity by means of compressed air, high-pressure water or centrifugal force - Fig. 645 — Removal of riser contacts, fins, etc., by the carbon elec- trode-air process. This eliminates necessity of chipping or grinding. Fig. 646 — Centrifugal tumble blast equipment for cleaning steel cast. ings. (Figure 646). The stream of abrasive strikes the castings with suf- ficient force to effectively remove the foreign material from the sur- faces. The cleaning operations are carried on in cabinets or an en- closure (Figures 647 and 648). The cabinet may contain a revolving table on which small castings may be placed, the blast being so arranged that all casting faces are reached. Checking ... One of the important finishing operations is checking the castings to see that they conform to the customer's required dimensions. Occasionally, rangy castings, or those which have a con- siderable number of varying cross-sectional members, may require some straightening of the casting to dimensions. This is often neces- sary following heat treating operations, since the relief of casting stresses may result in some distortion of casting members. The oper- 1 i Fig. 647—Large casting after room blast clean- ing. MANUFACTURE 585 Fig. 648—Continuous shot blast cleaning of railway couplers. ation of straightening to dimensions is usually carried on under power presses using templates as gages. High strength members are usually pressed hot. Figure 649 shows a cross bearer arm being checked in a jig after pressing for dimensional accuracy. Each casting is required to fit perfectly in the jig with the pin gages lined up without forcing. These castings are used without machining and illustrate the accuracy with which steel castings can be made. The hopper car body bolster of Figure 650 must be dimensionally accurate in every respect. This large and rangy casting is transferred directly from the normalizing furnace to a cooling jig where weights 'T Fig. 649—Jig testing of a straightened casting. 586 MANUFACTURE are applied. Figure 651 shows the casting mounted in an inspection fixture for final checking prior to shipment to the car builder. 1 Fig. 650—Hopper car body bolster casting. Fig. 651—Final check of hopper car body bolster in an inspection fixture to insure accurate assembly. Welding ... Welding operations occupy a normal place in the pro- duction of steel castings where they are used to correct minor depar- tures encountered in the manufacturing process, and also in the fab- rication of composite structures. Welding progress in the steel foun- dry has kept pace with new welding developments (Figure 652). Welders qualified to exacting codes are employed, and careful control over welding techniques and procedures is practiced (Figure 653). . MANUFACTURE 587 Fig. 652–Carbon dioxide welding equipment and the welding of a casting. Steel castings are as readily weldable as wrought steel of similar composition, and the mechanical properties obtained from the juncture of weld metal and cast steel are completely satisfactory. The reader is referred to Chapter XV for further information on the welding of steel castings. SECTION IV Heat Treating Facilities and Operations The generally accepted practice in the steel casting industry is to heat treat all castings following the preliminary cleaning which includes any necessary welding. (See Chapter XVI–Heat Treating Principles and Recommended Practice). A number of different types of heat treating furnaces are used by the steel casting industry. Design of the furnaces, and the method - Fig. 653 — Electric arc welding of steel cast. ings. INT Fig. 654—Large annealer (24 x 30 x 13 feet) and quench tank (24 x 24 x 14 feet). 1 . 1 1 1 1 in which they are used depends largely upon the size, shape, and composition of the castings requiring heat treatment. Large castings are heat treated in car bottom type furnaces such as shown in Figures 654 and 655. Continuous heat treating furnaces are designed primarily for heat treating high production run castings. A majority used in the industry are of the pusher type, and employ 3 to 5 heating zones. Also, pit type furnaces with removable tops are used to some extent by the industry. Figure 656 illustrates a modern heat treating department in a steel foundry, showing a direct gas fired car-type heat treating furnace with a quench load being removed from the car and quenched in a 7129 Fig. 655 Removing heat treated castings trom car type furnace. Fig. 656—Modern heat treating facilities in a steel foundry. Note fur. nace (hardening and tempering) in back- ground and on side. 12 x 12 x 12-foot water tank. The castings are lowered into the quenching tank and removed from the water after a predetermined holding time. Three propeller type agitators circulate the water, and pumps move it through cooling towers to maintain water temperatures between 65 and 95 degrees F. Castings are then transferred to the tempering furnace for final heat treatment and requenching. A modern automatic quenching setup is illustrated in Figure 657. Steel castings are given a full anneal, a normalize, a normalize and temper treatment, or a quench and temper treatment, depending on the type of steel and on the properties desired. Details concerning heat treating procedures are given in Chapter XVI. Heat treating temperatures are effectively maintained by the use of thermocouples Fig. 657—Modern auto- matic quenching tank and hardening furnace and recirculating air type tempering furnace. 590 MANUFACTURE and recording pyrometers. Controlled atmosphere furnaces, or salt bath furnaces, are used to prevent oxidation and scale formation when the product so dictates. It should be mentioned that pickling of steel castings for the purpose of removing scale formed during heat treatment is not recom- mended. The action of the acid solution frequently results in the for- mation of hairline surface cracks on the castings. Scale should be removed by pressure blasting. Differential Hardening ... Castings are differentially hardened either by a quenching operation, or by the flame or induction hardening method. Standard heat treating furnaces are used in the differential quench method, and the castings are heated uniformly to about 1550 degrees F, and specific areas quenched. Only a portion of each casting is immersed in the liquid while the remainder of the casting cools in air. For example, the rim of a wheel would be run through water, and the hub and spokes cooled in air. Some casting designs are such that differential quenching methods cannot be used owing to possible crack formation. The flame hardening process has wide application, especially in the heat treatment of gears. In order to avoid hardening too deeply it is sometimes necessary to establish a steep temperature gradient at the instant of quenching. This means that heating must be very rapid, and the quench applied almost immediately after the surface comes to temperature. The flame temperature is high in order to establish a steep gradient. The process is one in which an oxyacety- lene flame is played upon the surface to be hardened and immediately thereafter a water spray applied. A modification of the process em- ploys electric induction to heat the casting part to be hardened, and then the entire casting is water-quenched. Steel castings are produced for carburizing, nitriding or cyaniding treatment. The typical batch-type carburizing furnaces and nitriding equipment are used, while cyaniding is carried on in the usual type of commercial cyanide bath. The most popular quenching medium used in steel foundries is water, although some oil quenching is done on the higher carbon steels. In general, the liquid quench is used to improve toughness of the cast steel, as well as to increase the hardness; and castings are tempered at temperatures between 1000 and 1250 degrees F. Tempering is done in car or hearth furnaces, usually of the indirect- fired, recirculating type. MANUFACTURE 591 SECTION V Inspection and Testing Castings are pressure blasted following the heat treating oper- ation and prior to final inspection. This facilitates the careful exami- nation given to all steel castings before they are shipped from the foundry. Steel foundries maintain complete inspection departments, not only for the detection and correction of imperfect material and workmanship in their own product, but also for materials and equip- ment purchased by the foundry. All castings are given a visual examination to ascertain if the casting surface fulfills the requirements of the customer (Figure 658). The casting is also checked as to dimensional tolerances, including wall thickness. Cored areas are studied and templates are used to check these areas against the drawing requirements. Castings requir- ing machining are checked for finish requirements and dimensions on layout tables (Figure 659). The character and extent of the inspection depends upon the service requirements of the casting, and the purchaser may specify one or more inspection tests. For example, a small pulley might require only visual inspection, whereas a turbine casting may require visual examination, a determination of the mechanical properties and the chemical analysis of the steel, radiographic and magnetic particle 055 Fig. 658—Inspector making visual inspection of side frames. 1 H AYO INS Fig. 659—Layout table. Inspector checking casti.g for dimensional accuracy. testing, and certain pressure tests. In some instances these tests are witnessed by inspectors who represent the purchaser. Mechanical Property Tests ... The inspection department carries on the tests as to chemical composition and mechanical properties so as to ascertain whether they meet specification requirements. (See Chap- ter VII for detailed information on these points). Standard coupons of ASTM design which are either attached to the casting, or cast separately at the time the casting is poured, are machined into stand- ard tensile test specimens. When required, bend and impact specimens are prepared. Testing of standard specimens is performed on calibrated ma- chines. The tensile strength, yield point (yield strength), percent elongation, and percent reduction of area are determined. The hard- ness of the castings is often required; and in the steel casting industry it is usually reported in terms of Brinell numbers unless face hard- Fig. 660—Typical me chanical testing labor. atory. 00000000 Fig. 661-Spectrometer equipment for rapid chemical analysis of steel. ened castings are specified. Figure 660 illustrates the usual mechani- cal testing equipment normally required in a steel foundry. Special tests, such as torsion, fatigue, or corrosion are performed when requested. Also, the microstructure of the steel may be studied as to grain size, inclusion content, and the structure changes brought about by the heat treating. An ever increasing number of steel foundries are installing spec- trometers (Figure 661) and other equipment such as: carbon-an- alyzers, sulfur determinators, and automatic balances for rapid and accurate chemical analysis of the steel. These instruments can provide analyses for most common elements in a few minutes. Pilot castings are made when castings are ordered in quantities, so that changes can be made to pattern equipment and molding tech- niques to insure correct dimensions and to cure "imperfections. De- tailed measurement of the sample casting provides dimensional infor- mation, while design tests, strain-gage studies, sectioning or nonde- structive tests, quickly reveal imperfections. In many instances several pilot castings are analyzed before quantity production is started. Steel castings are purchased in large quantities from various foundries by the railroads and other industries, and it follows that pilot casting analysis and production gaging procedure must be very thorough to assure interchangeability and dependable service. Gaging truck bolsters for dimensional requirements to insure proper fit and oper- ation is illustrated in Figure 662. Design tests are also required on certain castings, where specifi- cation limits the deflection of the casting under specified loads. The ultimate strength is also specified on some castings, requiring special 9 Fig. 662—Gaging truck bolsters for dimensional requirements to insure proper tit. tests to destruction. If the design meets the required specifications, subsequent castings made from the same pattern are accepted on the basis of chemical and mechanical properties. The static testing of a truck side frame (railroad casting) in a one million pound testing machine is illustrated in Figure 663. Various readings are recorded, such as deflection, permanent set, stresses at critical locations, and ultimate breaking load. The machine illustrated previously in Figure 391 is a dynamic testing machine which is arranged to apply various and simultaneous loadings to a railway car truck side frame. Service conditions are reproduced in the test and the frame is given practically every identi- fiable load encountered in actual use. Destructive Tests Destructive tests are sometimes required on the first casting from a pattern. Generally, the casting is sectioned . . Fig. $3—Testing castings in 1,000,000 pound machine. TA MANUFACTURE 595 by sawing, and a visual inspection of critical areas is made, thus indicating the internal conditions of the casting at various locations. . Occasionally the customer specifies that a casting, or several castings of a new design, is to be tested to destruction in a large static testing machine (Figure 663), or by dropping a heavy metal ball on the casting. The broken sections are then examined. It should be pointed out, however, that castings will tend to break at points where the section is vulnerable to the applied load, and stress con- centration through notch effect is important. Nondestructive Testing ... Testing to destruction is not an economical inspection procedure for miscellaneous castings. Nondestructive test- ing has generally supplanted destructive testing in the steel casting industry and is used in some form in practically all steel foundries. There are five types of nondestructive tests generally employed in the steel casting industry: (1) radiography with either gamma- rays or X-rays, (2) magnetic particle testing, (3) dye or fluorescent penetrant inspection, (4) ultrasonic testing, and (5) various simulated service tests, such as pressure testing. It is quite possible that, in certain cases, there would be a need for using three of the tests on a single steel casting. Through radiographic inspection it is possible to examine the interior of the casting by photographic, or fluorscopic means. Magnetic particle testing and dye or fluorescent penetrants reveal hairline surface discontinuities not discernible to the naked eye or by radiographic methods. Practically all castings for pressure services are tested under compressed air, oil, or hydrostatic pressure. This is often the case, even though the casting has received radio- graphic inspection since, in the case of large castings, it is not eco- nomical to inspect every portion by radiographic means. Radiographic Testing ... Steel castings are being used at greater speeds, higher pressures, and at higher and lower temperatures. As a result of the more critical applications, much attention is being directed to the internal and external integrity of steel castings. Thus, nondestructive testing by radiography has become increasingly sig- nificant in the inspection of steel castings. The use of radium radiography has rapidly been supplanted by radioactive isotopes such as cobalt 60 and iridium 192. These sources of radiation are obtained from suppliers licensed by the Atomic Energy Commission. Iridium 192 is used primarily for sections under 112 inches while cobalt 60 is generally employed for section thicknesses of 1 to 8 inches. The majority of steel foundries purchase radioactive isotopes in the range of 12 to 10 curies. However, sources up to 1000 Fig. 864— Radiograph- ing a casting with 750 curie of Cose. curies are available. Special handling equipment and facilities are necessary for large radiographic sources (see Figure 664). Radioactive isotope (gamma ray) radiography is used by the steel casting industry to a greater extent than X-ray radiography. The reason for this is that radium or an isotope is portable; it is its own power plant, and can be used any place in or out of the foundry. Also, gamma ray radiography has great latitude. It can produce acceptable radiographs at positions of changes in section which are often critical stress points in metal structures. In the steel foundry X-ray finds its best application with 400 Kv or million volt units, although units ranging from 250 to 2000 Ky are in use. These Fig. 665—X-ray radiography with a 1,000,000 volt X-ray machine. Fig. 666—Inspecting a casting for internal soundness with a 22. million volt betatron. are rather expensive installations, whereas radioactive isotopes can be purchased at a nominal figure. Figure 665 illustrates X-ray radi- ography with a one million volt X-ray machine. Seven steel foundries have installed betatrons (22 million volt X-ray units) to examine the internal soundness of thick section cast- ings for atomic energy power application and ordnance castings. Figure 666 shows a typical radiographic inspection of a large casting by the use of a betatron. The American Society for Testing Materials has prepared refer- ence radiographs (E-71) of various degrees of soundness that must be met in order to pass radiographic acceptance tests, as well as a specification covering radiographic procedure (E-94). These methods are available to engineers, buyers, and producers. Each casting has different service requirements and, therefore, imperfections which may be injurious in some castings may not be serious in others and may even be advantageous in certain circumstances. Castings should be regarded as structural units rather than as materials of construc- tion. That they have been so regarded is illustrated by the way in which radiographic inspection tests are usually handled. If imper- fections are revealed, they are considered from the standpoint of known stress distribution or other conditions of service. Magnetic Particle Testing ... The magnetic particle method of non- destructive testing is useful to determine discontinuities on, or close to, the surface. When an article is magnetized, discontinuities, if present, give rise to localized leakage fields, which are revealed by attraction and adherence of finely divided magnetic particles. - Fig. 667 Magnetic particle testing using the prod method. The American Society for Testing Materials has prepared stand- ard reference photographs of acceptance for magnetic particle indi- cations (E-125), and it has standardized the methods of testing (E-109 and E-138). These testing methods are available to engineers, buyers, and producers of steel castings. . Two methods of magnetization are used: (1) the overall method, and (2) the prod method. In the overall method an entire casting is magnetized by wrapping the conductor around the casting. The prod method consists of magnetizing an area or portion of a casting by attaching two prod type conductors to the casting about 6 to 8 inches apart. These tests are adapted to production methods in that they may be carried on quite rapidly. A casting in process of magnetic particle testing is shown in Figure 667. The prod method, employing dry powder, is used by the steel foundries in most cases. A fe foundries and their customers use the wet method by which the fine magnetic particles are suspended in a liquid in which the magnetized casting is immersed. The suspended magnetic particles are attracted and cling to any surface discontinuity. Fluorescent Penetrant Inspection ... The inspection of steel castings with fluorescent, or dye, penetrants involves spraying, brushing, or dipping to coat the casting with the penetrant. The surface coating is then washed or wiped off and a developer is applied to help draw the penetrant from the depths of any discontinuity and spread it on the surface of the casting for a short distance on each side of the discontinuity. When viewed under black light, fluorescent penetrants reveal discontinuities not visible to the eye. Dye penetrant indications Fig. 668 — Wet fluores- cent magnetic- particle test setup. Casting viewed under black light. are viewed under normal light. A method for liquid penetrant in- spection has been prepared by ASTM (A-165). The penetrant techniques are used mostly on nonmagnetic steels, although they are used to some extent on magnetic steel castings. Typical fluorescent penetrant inspection setups are shown in Figures 668 (for magnetic steel castings) and 669 (nonmagnetic steel cast- ings). Ultrasonic Testing ... Discontinuities can be detected in steel sections that extend from 1 inch to 28 feet by sending ultrasonic impulses (inaudible high-frequency sound waves of 0.5 to 11 megacycles) into the steel, and measuring the time required for these impulses to pen- etrate the material and be reflected from the opposite side or from the discontinuity, and return to the sending point. One test method uses a quartz crystal to dispatch the sound waves. The vibrating crystal is moved over the surface to be inspected, using a liquid film between the crystal and the work in order to obtain transmission of the sound energy. The ASTM has prepared a recommended practice Fig. 669—Inspection of stainless steel castings by means of a fluores- cent penetrant viewed under black light. 600 M ANUFACTURE 1 - Fig. 670- Testing a cast steel roll for metallurgical soundness using ultrasonic equipment. for ultrasonic testing (E-114). The casting surface must be fairly smooth although a ground surface is not necessary. Application of ultrasonic testing has been limited somewhat to the study of rolls in the steel casting industry, although it can be performed on large and small castings alike, and application on castings will find more extensive use during the next 10 years. The testing of a large ma- chined steel roll casting for metallurgical soundness by ultrasonic methods is illustrated in Figure 670. Pressure Testing ... The strict demands of high temperature, high pressure and corrosion resistant service have necessitated many changes in the testing procedures for pressure-containing steel cast- ings. However, hydrostatic or air testing, with visual leak detection still remains the most widely used test method. Almost all steam or fluid containing equipment castings receive this inspection. Cast- ings are set up with all ports and openings blanked off, and the casting filled with water, oil, or compressed air. Pressure is applied until the test pressure is reached. This is maintained for the specified time, and the outside surface of the casting is very closely studied for leaks. A two-hole return bend casting undergoing hydrostatic testing is shown in Figure 671. MANUFACTURE 601 Fig. 671-Hydrostatic testing of a two-hole return bend steel casting. Numerous other test methods such as high pressure air or nitro- gen, freon, helium, steam, and high vacuum, are being specified in certain instances. Pressure tests are required in order to: (1) test the pressure (or vacuum) holding ability of the casting or assembly, and (2) prove the strength of the casting or assembly. . Repair of Discontinuities Revealed by Nondestructive Testing ... Harmful but reparable discontinuities found during the nondestruc- tive inspection of a casting are explored by carbon arc, chipping, grinding, or other metal removal techniques, and corrected by weld- ing. Castings developing leaks during pressure testing are radio- graphed in the area of the leak to insure complete removal of the discontinuity prior to the welding operation. These welds are made using recommended procedures with approved welding electrodes (see Chapter XV). Following such correction and reheat treatment, the casting is again subjected to thorough inspection and test prior to shipment. REFERENCES 1-Briggs, C. W., "The Metallurgy of Steel Castings”, McGraw-Hill Publishing Co., New York, 1946. CHAPTER XIX STEEL CASTINGS: YESTERDAY, TODAY AND TOMORROW SECTION I History of the Steel Casting Industry Steel castings, by their very nature, require molten steel in their process of manufacture. Molten steel was unknown prior to the year 1750. True enough, steel was well-known centuries earlier, as the Damascus and Toledo blades of legendary fame will testify, but this steel was forged from pasty masses of iron produced in the Catalan forge. In the year 1750, in England, Huntsman originated the Cru- cible process, which first produced steel that could be poured as a liquid. This method of steel making came into wide favor but its use was confined to the production of small ingots which were in turn worked into the desired shape. 1 It was not until 1845 that steel castings, i.e., steel cast to final shape, appeared on the scene. On July 14 of that year, Johann Conrad Fischer, the Swiss metallurgist, exhibited various small castings pro- duced from crucible steel.(1) On July 23, 1845, Fischer applied to the British Patent Office for priority rights to a "new way of making horseshoes” which consisted of casting steel in sand molds. Steel castings are also supposed to have been discovered by Jacob Mayer, Technical Director of the Bochumer Verein, Bochum, Germany, some time before 1851. Records of the Bochumer Verein Company, which is still engaged in producing steel castings, indicate that cast steel church bells were produced in 1851. Some of these bells weighed as much as 17 tons. In all probability much smaller steel castings were made prior to the casting of the bells for it is difficult to be- lieve that such an important undertaking would be made without considerable previous "know-how” and experience. The steel church bell castings were displayed at various Expo- sitions throughout Europe and created quite a sensation because of their fine, clear tones and the fact that their selling price was about half that of the bronze bells formerly in general use. In a park outside of Bochum, one of the early steel church bells is enshrined (Figure 672 as a marker of steel casting history. It even successfully escaped the desperate needs of Germany for scrap steel during World War II. The steel for these early castings was made in crucible furnaces and poured in loam molds. Gegossen v. Bochumer Vereinina Fig. 672 Steel cast ing church bell. Poured by Bochumer Verein in 1867. Finished in 1867 for the World Fair in Paris. Weight 15,000 Kg (16.5 tons). Diameter -3.13 meters (10 feet). Angefertigt im Jolie 182 fir die Weltgusstellung Gewicht is Durchmer Whether Mayer or Fischer originated the first commercial steel castings is a matter for possible further research. The record indi- cates, however, that the steel casting industry is only a little over a century old. The history of steel castings in the United States begins with the Buffalo Steel Company, Buffalo, New York, now owned and operated by the Pratt and Letchworth Division of the Dayton Malleable Iron Company, Inc. The foundry was built in 1860, and in 1861 produced the first crucible steel made in the district. The records indicate that these first crucible steel castings were for railroad applications. Some of the first commercial steel castings produced in the United States are believed to have been made by the William Butcher Steel Works later the Midvale Company) near Philadelphia in July, 1867. These castings are said to have been crucible steel crossing frogs and car wheels, probably for the Philadelphia & Reading Railway. In 1870 William Hainsworth of Pittsburgh, one of the most suc- cessful steel men of his day, began the manufacture of cast steel cut- ting parts for agricultural implements, using a 2-pot coke fired cru- cible furnace. In 1871 Mr. Hainsworth founded the Pittsburgh Steel Casting Company, reputed to have been the first steel company in the 604 HISTORY Table 98—A Partial List of Early Steel Foundries in the United States with Dates of Organization Date of Incorporation Original Name Location Company now known as: Buffalo Steel Company Buffalo, N. Y. 1861 Wm. Butcher Steel Works Pittsburgh Steel Casting Co. Chester Steel Casting Co. Otis Iron & Steel Co. Isaac G. Johnson & Co. Eureka Steel Castings Co. Hainsworth Steel Co. Old Fort Pitt Foundry Solid Steel Casting Co. Nicetown, Penna. Pittsburgh, Penna. Chester, Penna. Cleveland, Ohio Spuyten Duyvil, N. Y. Chester, Penna. Pittsburgh, Penna. Pittsburgh, Penna. Alliance, Ohio July 1866 March 1871 1872 Circa 1874 Circa 1850+ 1877 Circa 1880 Circa 1881 Pratt & Letchworth Div. of Dayton Mall. Iron Co. Discontinued Operations Discontinued Operations Discontinued Operations Discontinued Operations Discontinued Operations Discontinued Operations Discontinued Operations Mackintosh-Hemphill Co. American Steel Foundries Alliance Works General Steel Castings Corp. Lorain Div., Carnegie-Illinois Steel Corp. Discontinued Operations Discontinued Operations Discontinued Operations Discontinued Operations August 1882 Circa 1882 Standard Steel Castings Co. Johnson Steel Street Ry. Co. Thurlow, Penna. Johnstown, Penna. March 1883 1884 1882 . 1885 Pacific Rolling Mills Co. S. G. Flagg & Company Cowing Steel Castings Co. Sharon Steel Casting Co. San Francisco, Cal. Philadelphia, Penna. Cleveland, Ohio Sharon, Penna. 1882 • 1885 Feb. 1887 † First started making steel castings in 1880. country which devoted itself exclusively to the manufacture of steel castings. Therefore, it can be concluded from the above that the first steel castings business, conducted as a commercial enterprise, was at Phila- delphia (1867); and the first company organized to manufacture steel castings, exclusively, was at Pittsburgh (1871). Table 98 consists of a tabulation of the names of some of the early steel foundries estab- lished in this country prior to 1890. The First Open-Hearths ... The first open-hearth furnace used in the steel casting industry was a 31/2-ton unit installed at the William Butcher Steel Works from which the first heat was poured on January 21, 1871. After 92 heats had been run, the furnace, which had not proved very satisfactory, was shut down and discarded. The Pittsburgh Steel Casting Company installed an open-hearth furnace in 1874 which was used for the production of steel castings in 1875. Meanwhile, the Midvale Steel Works, which was the new name of the William Butcher Steel Works, had built another open-hearth furnace, there being a record of their having poured two hammer dies and a hammer head weighing over a ton, in April and May, 1876. HISTORY 605 Isaac G. Johnson & Company, Spuyten Duyvil, New York, erected an 8-ton open-hearth furnace in 1882 for the manufacture of steel castings. The first open-hearths on the Pacific Coast were built at the plant of the Pacific Rolling Mills Company, San Francisco, California. These furnaces were of 18-ton and 5-ton capacities and were used for castings as well as for ingots. Steel castings for the battleship Oregon were made during the fall of 1884. In the early days of the Steel Foundry Industry all open-hearth charging was by hand using peels and shovels, sometimes requiring four or five men three or four hours to charge a 10 - or 15-ton furnace. In contrast, our large open-hearth plants today can charge a 50-ton heat by machine in less than one hour. It was common for the pouring ladle to be hoisted by a jib crane located at the side of the furnace. The molds, arranged in a semi- circle, were poured by swinging the crane from mold to mold (see Figure 673. Modern overhead cranes, a considerable percentage of the weight of which consists of cast steel parts, have revolutionized the handling of the molten steel. Geared safety ladles were designed and built by James Nasmythe in 1867. Prior to this, bull ladles were tipped by a number of men applying leverage on large horizontal arms. Hand shank ladles made their appearance about the same time as the geared-tilt ladles. The Bessemer & Tropenas Converters ... The first use of the Bessemer converter to produce steel for castings is said to have been made by William Hainsworth as early as 1881. The first Bessemer used ex- clusively for steel castings was a 7-ton converter installed by the Hainsworth Steel Company, Pittsburgh, in 1884. The Bessemer never became popular as a source of steel for castings. The Tropenas type converter came about a decade later. The first installation in the United States, of which there is an authentic record, was at the plant of the George H. Smith Steel Castings Com- pany, now Grede Foundries, Inc., Milwaukee, Wisconsin, the first converter steel being poured in April, 1899. Two converters designed by Selden Deemer of New Castle, Dela- ware, were installed at least as early as 1900 at the plant of the Chester Steel Casting Company, Chester, Pennsylvania. However, the converters were only in service a few days when E. W. Dwight, then President of the Chester Steel Casting Company, visited the plant. Observing the sparks leaving the mouths of the converters, he im- mediately ordered them shut down and taken out of the plant. This was done and the converters were never used thereafter. 1 606 HISTORY JANUARY 21, 1888.) FRANK LESLIE'S ILLUSTRATED NEWSPAPER. 383 OOOO PENNSYLVANIA - CASTING THE GREAT STEEL GUN FOR THE GOVERNMENT, AT THE WORKS OF THE PITTSBURG STEEL CASTING COMPANY, JANUARY 11TE - POURING THE METAL INTO THE MOLD hox BRETCE BY JORY W. BLATTI - BEE PAGE 388 Fig. 673—Reproduction of a newspaper illustration of a scene in a steel foundry in the late eighties, showing the pouring of a cast steel gun barrel for the United States Government. HISTORY 607 Other early Tropenas converter installations were: American Brake Shoe & Foundry Company, Chicago Heights, Illinois (April, 1900); American Hoist & Derrick Company, St. Paul, Minnesota (July, 1900); Brylgon Steel Casting Company, Reading, Pennsylvania (Book- walter converter) (May, 1901); William Wharton, Jr. & Company, Philadelphia, Pennsylvania (June, 1901) (later absorbed by Taylor Wharton Iron & Steel Company, Highbridge, New Jersey). Many other Tropenas installations followed within the next few years. > Mechanical blowers, which had been available to foundries since 1850, made possible the use of the converters as melting furnaces. The First Electric Arc Furnace ... The first electric arc furnace steel for commercial castings was poured at Treadwell Engineering Com- pany, Eaton, Pennsylvania, on November 15, 1911. The furnace was one of several Heroult furnaces built in this country shortly prior to that date. A duplicate of the Treadwell furnace was installed later at the Warman Steel Casting Company (now the Los Angeles Steel Castings Company) then located at Redondo Beach, California. National Malleable & Steel Castings Company, Sharon, Pennsyl- vania, was among the first steel foundries to install an electric arc furnace for the production of steel for castings, pouring the first heat from a six-ton Heroult furnace in July, 1912. However, this company poured steel at its Sharon plant from an experimental electric arc furnace of 300 pounds capacity, as early as July, 1910. There is a record of the making of electric furnace steel in a Stassano furnace during the first quarter of 1912 at the Buchanan Electric Steel Company, Buchanan, Michigan, now the Clark Equip- ment Company. Crucible Steel Casting Company, Milwaukee, Wiscon- sin, installed a 1-ton single phase Snyder electric furnace late in 1912, which was successfully operated for many years. Electric Induction Furnaces ... The first low frequency electric induc- tion furnace for melting steel for castings was a Roechling-Roden- hauser furnace installed by the Crucible Steel Casting Company, Lansdowne, Pennsylvania, from which the first heat was poured on April 4, 1913. Some use of the high frequency electric induction furnace for melting alloy steel for castings was carried on beginning in January, 1927, by the Midvale Company, Nicetown, Pennsylvania, but the first installation of such equipment for the regular melting of steel for commercial castings was at Lebanon Steel Foundry, Lebanon, Penn- sylvania, where the initial heat from their first Ajax furnace was poured in October, 1930. 608 HISTORY Molding in the Early Days ... Along with the development of melting furnaces used in producing steel for castings, similar progress in the improvement of molding and other foundry processes and equipment was steadily being made. The earliest molds for steel castings, of which there is a record, were made of ground brick and fire clay. Later, William Hainsworth of Pittsburgh patented a molding sand mix (about 1877) which was composed of sand, fine ground coke, small amounts of loam, flour and Welch mountain clay, moistened with molasses, glue and clay water, the mixture being milled from 10 to 15 minutes. However, George Cowing of Cleveland is credited with first making a mold for steel castings composed of nearly pure silica sand bonded with glue water and molasses. In the early days all molds were dried in ovens. The art of using green or undried sand molds was invented and patented by James G. McRoberts, in St. Louis, in 1891-1893. Discovery of the art came about in the following manner: Previously the unused metal from a heat was poured into dry sand pig molds. One day, Mr. McRoberts, finding no pig molds available, had a green sand ingot mold quickly prepared and amid predictions of dire calamity, himself poured the steel into this mold. To the amazement of all, the metal lay quietly in the green sand and a new era in steel founding was born. Several St. Louis foundries were among the first to use the new method. The First Molding Machines . A dependable molding machine of the jarring type was put on the market in 1837 by Jarvis Adams. The name of Hainsworth again appears in the early history of the development of molding machines. Hainsworth patented a jarring machine in 1869. Jarvis Adams with a series of patents in 1878 sim- plified his machine and brought the art to a higher level even though his machines, by modern standards, were very crude. Early experi- ments with crude molding machines included one fitted with a rubber diaphragm that was supposed to be inflated to press the sand uniformly around the pattern. The idea was ingenious, but the diaphragm in- variably burst! Today the industry is successfully using the dia- phragm principle in producing molds for steel castings. In the 1880's practical equipment was originated, such as the stripping machine, by Charles Herman. The first machines were hand and mechanically operated. With the advent and broadening com- mercial use of compressed air and electricity, power machines were placed on the market (1891). Harris Tabor, Elizabeth, New Jersey, and Henry E. Pridmore, were pioneers in the molding machine industry. While the so-called HISTORY 609 Pridmore Drop Machines had been used earlier for other types of castings, their first use for steel casting molds was about 1902 at what is now the Sharon Plant of National Malleable & Steel Castings Com- pany. Successive improvements in molding machines have been made, until today all steel foundries have a number of fully mechanized molding machines. The introduction of molding machines has eliminated molding which was previously done by hand. Men who were active in foundry work back in the early days declare that the molders of the period, through necessity, had developed the art to an extremely high degree. Precision mechanical molding aids have lessened the dependence upon manual skill. The machines which prepared the molding material in early days were essentially mills to pulverize brick and clay for additions to the sand. About 1870, machines were developed for mixing sand. These were fundamentally paddle mixers. The revolving pan mill with web- foot muller was introduced about 1900. The muller employing indi- vidually mounted revolving mullers made its appearance in 1912. By the 1880's core production had accelerated and boys at numer- ous benches made almost all cores. Cores were racked and dried in kilns and then placed on racks to be carried to the foundry. Tray type core ovens for drying small cores were produced by Millett in 1887. At the turn of the century there was no electric welding in the foundry, heat treatment was still relatively primitive, burning torches were unknown and sandblasting equipment had not been devised. Early Heat Treating Methods . . . Such heat treatment of steel cast- ings as was done consisted of simple annealing, usually in pit-type furnaces in which it was almost impossible, even with expert firing, to produce uniform heating. Steel castings produced in the period 1860 to 1880 were not heat treated but castings in the '80's were usually annealed from two to three weeks. Vast strides have since been made in that department of the foundry, heat treating today being an exact science with temperatures accurately controlled by pyrometer-act- uated regulators in carefully designed furnaces, using cycles and proc- esses based on extensive research. Early Cleaning Methods ... Whereas it was necessary in the old days to break off, with hand sledges or drop-hammers, gates, fins and risers, today the steel foundry has the gas or electric torch and fast cutoff saws. The electric welder is one of the modern steel foundry pro- duction tools. Indeed, the steel foundries were among the first to use acetylene and arc welding, and to maintain staffs of high-grade welders. . 610 HISTORY The tumbling mill developed by W. W. Sly between 1880 and 1887 was an advancement in the preparation of castings for market. The latter part of the 1890's brought the pneumatic chisel into the foundry. One of the greatest innovations, in the opinion of some men who have been connected with the industry since its infancy, was the in- troduction of sandblast cleaning of castings. This proved to be of tremendous practical value to steel foundrymen, providing an inspec- tion tool, and improving the quality and surface finish of their castings. Sandblast equipment was first put on the market around 1900, the earliest known installation being one set up in that year at the plant of the Logan Manufacturing Company at Phoenixville, Pennsyl- vania. Not many years after that the first complete installation, con- sisting of six fully equipped blast rooms, was erected at the foundry of Buckeye Steel Castings Company, Columbus, Ohio. Today all steel foundries have blast cleaning equipment of improved design capable of producing almost any degree of surface smoothness desired. Vari- ous types of metal shotblasting and water-blasting are now commonly used. They render blast cleaning of castings less potentially hazardous to workmen. Centrifugal Casting of Steel ... Railway car wheels were probably the first foundry products in the United States to be centrifugally cast. The idea of centrifugal casting of car wheels was first conceived by James C. Davis in 1898. The first wheels produced using this practice were made at the East St. Louis Works of American Steel Foundries in 1902. The production of centrifugally cast wheels was later trans- ferred to the Granite City Works of this Company where centrifugal casting was carried on until the year 1930. In the early years, in the production of wheels using the centrif- ugal pouring process, ground manganese was introduced into the first metal going into the mold, the centrifugal action causing this metal to be thrown to the outside of the mold forming the rim and flange, while the plate and hub sections of the mold were formed of the milder steel. This was later superseded by the casting of one grade of metal for the entire wheel. The centrifugal casting of tubes and jackets for the 75 mm field gun was the goal of experiments con- ducted at The Buckeye Steel Castings Company during World War I. These experiments provided a fine pyrotechnic display but fell short of the desired results. Later on, extensive research and development was carried on at Watertown Arsenal under the direction of Dr. F. C. Langenberg, re- sulting in the successful and practical application of centrifugal cast- ing in this field. William D. Sargent, New York City, pioneered in the field of centrifugal casting and of late years the Ford Motor Com- HISTORY 611 pany, Detroit, Michigan, and American Cast Iron Pipe Company have brought the process to a high degree of perfection. A number of com- mercial steel foundries are now using this process. Contrasting the facilities, equipment, and product of a modern steel foundry with that of the best foundry of even ten or fifteen years ago, is like comparing the modern streamlined motorcar with the creditable but primitive horseless carriages of 1900 and 1910. New devices and technological improvements are being developed so rapidly that it is safe to conclude that the steel foundry of today will be antiquated and obsolete within another decade. Steel foundrymen in charge of production are ever alert to these new developments, proc- esses and equipment quickly adopting the latest production tools as they are put on the market and prove their merit in actual operation. Steel Castings in the Railroad Field ... As previously noted some of the first steel castings produced in this country were made during and shortly after the Civil War and are said to have been railroad cross- ings, switch frogs and car wheels. This marked the beginning of a parallel growth of both railroads and steel foundries which has been a continuous record of progress. At times, railroad developments forced improvements in steel castings, while at other times the Steel Casting Industry pointed the way toward safer, faster, and more eco- nomical rail transport. The invention of the automatic car coupler and the air brake lent great impetus to the development of both industries. In the early days of rail transport all freight and passenger cars were coupled together with so-called link-and-pin draw bars. This method of coupling was responsible for many serious accidents to trains, crews and passengers, and many substitutes were tried in efforts to overcome this costly weakness. The Automatic Coupler and the Air Brake ... The present standard coupler has been an evolution from the invention of Eli Janney in 1873. He contrived the first coupler with a hook pivoted on a vertical pin and a gathering arm to guide the approaching coupler into engage- ment. Further developments followed so that by 1876 the coupler was applied to some 150 cars, with successful service performance. The first couplers were produced from crucible steel, but as demand in- creased they were made mostly of malleable iron. These couplers achieved immediate popularity and, by an act of Congress, they were made mandatory on all cars after January 1, 1898. However, during the period of their introduction the complete success of the air brake was attained, which so greatly increased train lengths that by 1900 the railroads were turning from malleable iron to cast steel automatic couplers for additional strength and shock resistance. 612 HISTORY A large number of cast steel coupler designs appeared on the market, but since their parts were not interchangeable, it necessitated carrying many different parts in stock. This was overcome by the development of the standard coupler about 1916 - a joint achieve- ment of the coupler manufacturers and the Master Car Builders Association, now known as the Mechanical Division of the Association of American Railroads. That standard design continued in use up until 1931, when a more modern “E” Type Coupler was evolved. In late years a Type F coupler has been developed for freight cars, and a Type H for passenger equipment. Both designs incorporate the feature of interlock as an added safety measure. Contrasting the coupler of the late '90's with the present type E, F, or H cast steel couplers indicates some of the engineering prog- ress made in a few decades. Whereas the old type coupler was re- quired to pull around 150,000 pounds, the modern cast steel coupler will withstand a load of well over 500,000 pounds. Throughout this period of development many other parts of cars and locomotives were converted to cast steel construction until today between sixteen and eighteen percent of the modern freight car is comprised of steel castings. The Integral Cast Steel Truck Side Frame ... The integral cast steel truck side frame of the freight car is an achievement deserving special mention. Replacing the old arch bar construction which required 27 separate parts, it has become standard equipment required by order of the Association of American Railroads for all cars used in interchange with other roads. The integral cast steel side frames are unsprung and must withstand the pounding shocks of traversing rail joints, crossovers and switches. Moreover, they must resist side thrust and other transverse stresses. The almost universal use of integral cast steel side frames has materially reduced train wrecks, a large number of which were for- merly traceable to the inherent weakness of the built-up arch bar as- sembly (Figure 674). The integral cast steel truck frame design which replaced the arch bar assembly is shown in Figure 675. The more modern designs have previously been shown in Figure 55. Inte- grally cast steel structures have eliminated 99 freight car parts which were formerly separate components. Moreover, maintenance costs , have been practically eliminated. Considerable space has been devoted to a description of steel castings for railroad service because the railroads were the steel foundries' first substantial customers and continue to be the indus- HISTORY 613 7384 Fig. 674-Arch bar construction railroad car side frame. Fig. 675—The integral cast steel side frame which replaced the arch bar construction. try's largest buyers. Coincident with the developments in this field steel castings have constantly broadened their scope of application. To chronicle the history of steel castings in the hundred other industries in which they are now used would simply trace the prog- ress made by practically every American industry during the past century. The outstanding advances made by the steel casting industry during recent years are well exemplified by the cast armor develop- ments of World War II, and the Korean War. Prior to the year 1940 there was no significant commercial production of cast armor for armored vehicles; however, during the years 1932 to 1935, Watertown Arsenal produced a limited quantity of small armor castings to satisfy tank-building needs of Rock Island Arsenal. The advantages of cast armor became immediately apparent to the Ordnance Department of the U. S. Army, since it afforded the widest possible latitude in design and construction to give protection against enemy gun-fire. In cast armor the obvious virtues of proper contour, varying thickness, unit construction, etc., could be utilized 614 HISTORY to the fullest extent. However, extensive ballistic testing was neces- sary and progress was slow, with only a few steel foundries in limited production during the period immediately preceding World War II. A Committee known as the Metallurgical Advisory Committee on Cast Armor was organized by Army Ordnance in September of 1940 and consisted of technical representatives of producer companies, and representatives of the Ordnance Department of the Army and Navy, for the purpose of developing cast armor. Only seven industrial com- panies were represented at the start. The membership increased as new producers entered the field, until in 1943 the maximum member- ship consisted of representatives of thirty-three industrial producers of cast armor, eighteen military establishments, one industrial facility of an allied country, and three military agencies of allied governments. Under this Committee, the technical knowledge and production "know- how” were pooled among the producers of cast armor. This greatly aided the newer companies in the production of cast armor since ad- vice and data were obtained from the older producers and from the test studies made by the military establishments. Problems mounted upon problems as the high quantity production of cast armor was extended. More and more castings were used and as ballistic information became available, many were redesigned as to contour and thickness. A particular problem was the shortage of critical alloys. This resulted in numerous changes in chemical compo- sition and reductions in alloy content, while full production was maintained. Furthermore, specification requirements were increased, and heavier armor was developed concurrently with the alloy restric- tions. Refinements were made in the processing procedures in order to speed critical deliveries. The industry did an outstanding job on cast armor, both as to production and quality, with producer companies working harmoni- ously together in close cooperation with the military to supply their requirements. This close cooperation continues to be active and well-organized, with constant attention to improvements in design, metallurgy, produc- tion methods, and potential capacity against any national emergency which may arise. SECTION II The Steel Casting Industry of Today There are about 240 commercial steel foundries in the United States, and 33 in Canada, exclusive of those companies which are solely engaged in the production of investment molded castings. Some HISTORY 615 30 companies operate foundries that use the entire output in the manufacture of their own line of finished machinery, or as repair and replacement parts for their production equipment. In this group, a number are connected with steel mills and automobile plants. The steel foundries in the United States have a potential maxi- mum annual capacity of nearly 212 million net tons of steel castings. Table 99—Analysis of Steel Casting Capacity 1960 Total Capacity Castings for sale Captive tonnage 2,480,000 tons annually 1,880,000 tons annually 600,000 tons annually 1,735,000 tons annually 55,000 tons annually 125,000 tons annually Carbon Steel Castings All Types Low-Alloy Steel Castings All Types High-Alloy Castings All Types High Manganese 70,000 tons High Alloy - 55,000 tons Railway Specialties Rolling Mill Rolls 465,000 tons annually 100,000 tons annually Total 2,480,000 tons annually They are located in 32 different states with points of maximum con- centration in and near Philadelphia, Buffalo, Pittsburgh, Columbus, Chicago, Milwaukee, St. Louis, Los Angeles, and Seattle. An analysis of the steel casting capacity is given in Table 99. The peak demand for steel castings since 1951 has increased about 38 percent. The production of steel castings over the past 30 years is shown in Figure 676. The years 1938 and 1939 were depression years, and the years of 1941 through 1945 were World War II years. The postwar production years covered the period of 1946 through 1948. Another high production period was reached during the period of the Korean incident (1951 - 1953). This was followed by poor years (1954, 1958, 1959) and good years (1956, 1957) with an average production of 1,500,000 tons of steel castings. The steel casting production for the post World War II years indicates that the average per capita consumption is about 20 pounds of steel castings, which should rep- resent a production of 2,500,000 tons by 1970. The total shipments of steel castings is made up of: (1) carbon and low-alloy castings, (2) high-alloy castings, and (3) captive ton- nage. The total shipments of steel castings falling in these three cate- gories for the period 1946 through 1959 is shown in Figure 677. 616 HISTORY 3,000 2,500 2,000 1,500 THOUSANDS OF TONS 1,000 500 1940 1945 1950 1955 0 Fig. 676—Production of steel castings in the United States for the years 1938 through 1959. 1938 - 1943—-U. S. Bureau of Census–Production steel castings for sale. 1944 - 1945—U. S. Bureau of Census—Total production, steel castings. 1946 - 1959—U. S. Bureau of Census—Total shipments, steel castings. THOUSANDS OF TONS THOUSANDS OF TONS 2400 2400 2200 2200 2000 1800 TOTAL SHIPMENTS OF STEEL CASTINGS IN U.S. 2000 HAIGH 1800 1600 CAPTIVE ALLOY CASTINGS TONNAGE 1600 1400 1200 1000 1400 1200 1000 800 600 400 200 CARBON AND LOW ALLOY CASTINGS (FOR SALE) SHIPPED 800 600 400 200 0 1956 1957 1958 1959 0 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 Fig. 677—Shipments of steel castings. Net tons of all castings shipped by types indicated. Years 1946 - 1959. HISTORY 617 STEEL CASTINGS SALES GROSS NATIONAL PRODUCT (MILLIONS OF DOLLARS) AND DURABLE GOODS SALES (BILLIONS OF DOLLARS) 10,000 1000 8000 800 6000 600 GROSS NATIONAL PRODUCT 4000 400 3000 300 2000 200 1500 150 1000 100 MANUFACTURERS' 800 80 DURABLE GOODS SALES 600 60 500 50 400 40 300 30 200 20 NET VALUE OF STEEL CASTINGS SHIPPED 100 10 1946 47 48 49 50 51 52 53 54 55 56 57 58 59 Fig. 678—Steel casting sales compared to gross National Product and Manufacturers' Durable Goods Sales (years 1946 - 1959). Source-SFSA Yearly Survey and U. S. Dept. of Commerce. The semi-logarithmic chart of Figure 678 gives information on steel castings sales in comparison to the gross national product and to the sales of durable goods. These curves demonstrate the ex- treme cyclical nature of the steel casting industry as compared to general industrial activity. The steel castings sales figures are net sales value of steel castings shipped by members of Steel Founders' Society, but do not include captive foundry sales. PERCENT OF TOTAL VALUE 100 78% 77% 77% 70% 6.6% 76% 18.5% 73% 70% 7.3% MALLEABLE IRON CASTINGS STEEL CASTINGS 80 119.0%||17.1% 120.9% 23.5 119.3% 119.0% 12352||24.0% 20.5% 60119.3% 24.0% 124.8% (27.0% 1277% 21.6% 21.3% 21.8% 23.6% 23.0% IRON AND STEEL FORGINGS 40 20F53.9% 51.27] 46.6% 42.5% 436% 51.5% 51.2% 474% 45.42 49.23 GRAY IRON CASTINGS 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 Fig. 679—Value of shipments. Malleable iron castings, steel castings, iron and steel forgings and gray iron castings industries. Source-U. S. Dept. of Commerce, Annual Survey of Manu- facturers and Census of Manufacturers. 618 HISTORY The value of steel casting shipments in dollars as a percent of the total sales value of the four competing industries (malleable iron, steel castings, steel forgings and cast iron) is illustrated in Figure 679. These values are derived from comparable sources of the U. S. Department of Commerce. The chart indicates steel castings and steel forgings are about equal in annual sales. Table 100 presents information on the shipments of steel cast- ings in accordance with the end use of steel castings. This informa- tion is based on a survey made by Steel Founders' Society, and is an average for the years 1957 and 1958 which are representative since 1957 shipments were higher than average, and 1958 shipments were lower than average. The major classes are illustrated in a chart (see Figure 50, Chapter II). The chart shows that today all the major construction industries build with steel castings. A measurement on the basis of tons may not be entirely the correct criterion in the com- parison of one industry's use of castings with that of another or, for that matter, in the comparison of one year with another, such as 1949 with 1959. The reason for this is that there has been a general shift to higher strength materials and to closer tolerances; and one industry's requirements may be different in this respect than in another. The total steel castings in use today is difficult to determine. Some steel castings, such as steel castings in bridges, are expected to last in their applications for 100 years or more. Others may be limited to a one-time performance, such as those in rockets or missiles. How- ever, the amount of steel castings in use is gaining each year. An ex- ample, as a basis of estimate, is railroad equipment which is expected to be functional for 30 years. On the basis of 15,000 pounds of steel castings for each freight car, there are over 15 million tons of steel castings in this use today. This is equivalent to about 10 years of normal production for the entire industry. Also, there are 41/2 million tons of steel castings in Diesel locomotives, on the basis of 30,000 pounds of steel castings for each locomotive. Since the above esti- mates account for about 30 percent of the total market, a safe esti- mate would indicate that over 50 million tons of steel castings are in use at the present time, which is equivalent to about 30 years of pro- duction. Production Method Changes ... Changes are taking place every day in production methods. An example of this is the interest in closer tolerances, afforded by investment and shell molded steel castings, as is shown by the production curves in Figure 680. The Steel Found- ers' Society's 1950 - 1954 surveys showed very minor production in these fields whereas the 1958 survey indicated a major change. It is true that HISTORY 619 TABLE 100. SHIPMENTS OF STEEL CASTINGS - Distribution by General End Use Classifications (Adopted in 1959) Average 1957 - 1958 Average Shipments 1957 - 1958 Percent Tong of Total A. AGRICULTURAL EQUIPMENT 12 Agricultural Machinery & Equipment Castings, Including Farm Tractors & Conveyors 10,479 1.00 B. MOTOR VEHICLE 14 Motor Vehicle Castings, Including Trailer & Semi-Trailer (On Highway Type Only). 40,088 3.83 C. .74 CONSTRUCTION MACHINERY & EQUIPMENT 18 Bucket & Dipper Castings (For Power Shovels & Trenchers) 27 Hoist & Derrick Castings (Electric, Hydraulic, Air, Gasoline or Steam Power) 40 Power Shovel, Dragline & Locomotive Crane Castings 48 R Building, Construction Machinery & Off Highway Trı Castings (Except Tra & Crushing Machinery) 55 Tractor Castings (Except Agricultural) 7,783 3,031 82,768 .29 7.90 30,567 37,738 2.92 3.60 161,887 15.45 D. CONSTRUCTION (STRUCTURAL COMPONENTS) 17 Bridge Castings. 30 Lock & Dam Castings 4,068 2,131 .39 .20 6,199 .59 E. MINING & CRUSHING MACHINERY 21 Crushing & Pulverizing Machinery 34 Mining Machinery & Equipment Castings 72 Cement Mill Castings 27,257 27,753 8,371 2.60 2.65 .80 63,381 6.05 F. METAL SHAPING, FINISHING & FORMING 32 Machine Tool Castings 33 Metal Working & Metal Processing Machinery Castings 41 Press (Geared Power) Castings, Press Castings (Hydraulic, Air, Steam or Electric) 83 Die & Fixture Castings 4,825 18,270 8,719 1,419 .46 1.74 .83 .14 33,233 3.17 .89 G. ELECTRICAL MACHINERY & EQUIPMENT 23 Electrical Machinery & Equipment Castings 28 Hydroelectric Power Plant Castings 53 Steam Generator Castings, Steam Turbine Castings 9,312 9,522 26,675 .91 2.55 45,509 4.35 H. RUBBER MILL CASTINGS 51 Rubber Mill Castings, Rubber Mill Press Castings (Hydraulic, Air, Steam or Electric or Vulcanizing or Curing Press) 5,577 .53 1. OIL, GAS FIELD, VALVES & PIPING 35 Oil, Gas Field, Pipeline & Refinery Castings 56 Valve & Piping Castings 30,117 43,388 2.88 4.14 73,505 7.02 J. MILITARY 36 Ordnance Cast Armor Castings 37 Ordnance, Quartermaster Corps, Engineer Corps, Air Corps (But not including Castings for Aircraft) Chemical Warfare Service and Signal Corps (U.S. Army) Castings.... 12,056 1.15 12,201 1.17 24,257 2.32 620 HISTORY TABLE 100-SHIPMENTS OF STEEL CASTINGS (Continued) Average Shipments 1957 - 1958 Percent Tons of Total K. RAILROAD 43 Railroad Specialties 44 Railroad Locomotive Castings 45 Other Railroad (Standard Gauge) Castings 257,815 19,791 47,438 24.62 1.89 4.53 325,044 31.04 L. ROLLING MILL 19 Coke Oven Equipment 46 Refractory, Brickyard and Ceramic Machinery & Equipment Castings 49 Rolling Mill Rolls. 50 Other Rolling Mill, Blast Furnace & Steel Plant Castings 1,237 970 58,632 79,876 .12 .09 5.60 7.63 140,715 13.44 M. SHIP & MARINE 22 Dredge Castings 52 Ship & Marine Castings 5,233 10,668 .50 1.02 15,901 1.52 N. MATERIAL HANDLING 20 Conveyor & Material Handling Equipment Castings, Including: Sprockets & Chain Wheels 29 Industrial Tractor & Truck Castings (In-plant & Yard type Operation) 38 Overhead Power Operated Crane (Traveling) & Charging Machine Castings 7,102 7,148 3,854 .68 .68 .37 18,104 1.73 3,965 762 2,627 1,623 .38 .07 .25 .16 O. SPECIAL MACHINERY, PRODUCTS & COMPONENTS 11 Aeronautical & Air Field Castings, Jet Engine Components, Missiles, & Ground Support Equipment 13 Atomic & Nuclear Energy Castings 15 Bearing Housing Castings 16 Boiler, Tank & Piping Castings 24 Engine (Diesel) Castings, Engine (Oil, Gas, Steam Gasoline) Castings, Including Gas Turbine 25 Foundry Machinery & Equipment Castings 31 Logging, Lumber Machinery & Sawmill Castings 39 Paper & Pulp Machinery Castings 42 Pump & Compressor Castings (Air & Gas, Except Refrigeration Compressors) 47 Refrigeration & Air Conditioning Machinery Castings (Including Refrigeration Compres- sors 54 Sugar Mill Castings 57 Wire Manufacturing & Fabricating Machinery Castings, Wire Rope & Cable Accessory Castings 58 Food Processing & Handling, Meat Packing, Chemical, Bottling and Glass Machinery 59 Heat Treating & Industrial Furnace Equipment 71 Safe & Vault Castings 82 Textile & Dyeing Machinery Castings 5,596 7,843 2,456 4,407 9,811 .54 .75 .24 .42 .94 1,437 1,371 .14 .13 1,694 2,636 3,708 588 589 .16 .25 .35 .06 .06 51,113 4.90 P. GEAR, PINION & WORM CASTINGS 26 Gear, Pinion & Worm Castings 13,965 1.33 Q. UNCLASSIFIED 63 All Others (Miscellaneous classifications not listed above and not substantial enough, ton- nage-wise to list separately) 18,147 1.73 GRAND TOTAL 1,047,104 100.00 HISTORY 62) 5000 4000 3000 TONS SHELL MOLD STEEL CASTINGS 2000 1000 INVESTMENT STEEL CASTINGS 1950 1951 1952 1953 1954 1955 1956 1957 1958 Fig. 680—Shipments of investment and shell mold castings. Steel Founders' Society of America Survey. this amount represents only 0.6 percent of the total shipment of steel castings, in the case of shell mold, and 0.2 percent for investment molded steel castings. Nevertheless, the 1960 shipment values will probably indicate more than 15,000 tons for shell mold steel castings. Other changes are being made today in production methods so as to improve casting quality and reduce casting costs. Much consider- ation has been given to casting inspection methods. Nondestructive testing methods are familiar to the industry and are extensively em- ployed. All steel foundries have isotopes or X-ray equipment avail- able for radiography, or they are readily available to them. Also, magnetic particle testing equipment or liquid penetrant equipment is at hand for inspecting casting surfaces. In some cases, ultrasonic testing equipment is available for special applications of testing cast- ings. Several foundries are equipped with expensive Betatron installa- tions to examine heavy section castings for high-temperature service. Much consideration is being given today to surface characteristics of castings, and to producing castings to closer tolerances than ever before. Processes have been developed to reduce machining to a min- imum or to eliminate it completely, namely: shell, ceramic, or invest- ment molding techniques. Even the machining of steel castings has improved through new techniques, and the further knowledge of tech- nical requirements. Quality control through statistical sampling methods is being adopted by the modern steel foundry for casting improvement and 622 HISTORY uniformity. Certain steel foundries have set up stress analysis oper- ations to assist customers in developing efficiently designed castings for improved service performance. Recent Technical Developments ... Considerable attention is being given by steel foundry companies to the technical education of per- sonnel to assure that they keep abreast of research developments in- cluding new methods and techniques. The operating executives and technical men in the ste:I casting industry are organized, through the Steel Founders' Society, for cooperative effort toward improve- ment of the quality of steel castings, and increasing their usefulness. Eight geographical groups of technical and operating men from steel foundries in the area meet monthly for the purpose of improving the manufacture of steel castings through exchange of information on the practical application of new materials and techniques. These monthly meetings culminate in an annual three-day con- ference, devoted entirely to the technical and operating phases of steel casting manufacture. Carefully selected papers are presented, covering the latest developments in the field of steel castings, and at- tendance includes industry representatives from every corner of our country. Steel Casting Research ... The Steel Founders' Society of America has been conducting a cooperative research program for many years. This research program starts with the individual foundries and culmi- nates in work that is done in the major research laboratories and en- gineering colleges of the United States under the supervision of the Technical and Research Director of the Society. The results of this program, incorporated in everyday practice, have resulted in tre- mendous improvements in the quality of cast-to-shape metal products, and in the development of cost reducing techniques. Two general classes of research projects are maintained by the Steel Founders' Society: (1) Fundamental studies on the properties of cast steel and steel castings, and (2) Product and methods research. Class (1) type of projects are studied to increase fundamental knowl- edge of cast steels and their properties, thus providing basic informa- tion to purchaser, engineer, student and foundryman as to the true capabilities and advantages of steel castings. Class (2) type of proj- ects are formulated with the plan of continuously improving the quality of steel castings, and assisting the steel foundryman with pro- duction problems. Both lead to higher quality, lower costs, and more intelligent application of steel castings. The results from research studies of class (1) projects are pub- lished by Steel Founders' Society and by the various technical societies HISTORY 623 of the United States, and appear in their published transactions. The research findings of class (2) projects are disseminated to Society members and are occasionally submitted for publication to other technical societies. The Steel Casting Industry of Tomorrow ... It is most certain that there will be many improvements made in the production of steel castings during the next 10 years. Current development of the oxygen converter may be extended to the steel casting industry, so that con- tinuous pouring of steel castings will be possible in any foundry re- gardless of size. This will permit molds to be poured with molten steel as soon as they are made. Continuous pouring techniques will require extensive changes in mold and casting handling mechanisms, with molds moving to and away from the continuous pouring area. Greater emphasis will be placed on casting surface during the next 10 years than on any other production feature, in order to im- prove surface appearance and casting dimensional tolerances and machinability. The production of castings to ultra-high tensile strengths will be a normal requirement rather than the unusual accomplishment of to- day. Thinner walled steel castings will also come into general use. Automation of all equipment used in the foundry will be the quest of steel foundry operators and equipment builders, to satisfy a desire to reduce man hours, lower costs, and improve process capabilities and casting quality. Changes in molding methods will take place to produce molds of uniform hardness and other properties. Most all cores employed will be of the shell variety and many of them will be made of inorganic mixtures. The new short cycle heat treatment will be universally adopted both by producers and customers in order to take advantage of cost savings and to minimize surface decarburization and scale. Extensive industry and government research into the many facets of the steel casting process can open the door to increased fundamental knowledge. This will provide all industries with steel castings of ever- improving quality with an even wider scope of utility and application than is available today. REFERENCES > 1.—Graeff, A. D. “A History of Steel Castings”, The Kutztown Publishing Co., Pa. 2.—Simpson, B. L. “Development of the Metal Casting Industry”, American Foundrymen's Society, 1948, p. 246. GLOSSARY OF FOUNDRY TERMS A general understanding of the meaning of the following terms as used in the Handbook and in the foundry industry may be helpful to engineers and purchasers in discussing casting problems with steel foundrymen. . Acid Bottom and Lining ... In a melting furnace, the inner bottom and lining composed of refractory materials that have an acid reaction in the melting process. The materials may be silica sand, siliceous sand, or silica brick. Acid Steel ... Steel melted in a furnace with an acid bottom and lining and under a slag containing an excess of an acid substance, such as silica. . . . Aerator A machine for fluffing or decreasing density of, and cooling sand by admixture of air. Age Hardening ... The gradual hardening of a metal caused by precipitation of a constituent from a supersaturated solid solution. Air Hardening ... The process of hardening steel and alloy steel by cooling in air from a temperature higher than the transformation range. Alloy ... A substance having metallic properties and composed of two or more chemical elements of which at least one is a metal. Alloying Elements ... Elements added to adapt the various properties of a steel to suit the desired end-use and service. Alpha Iron ... The magnetic form of iron that is stable below the critical temperature (1663 degrees F for pure iron) and characterized by a body-centered cubic crystal structure. Annealing ... A heat treatment which consists of heating the steel to a temperature above the critical temperature, holding it for a proper time, followed by slow cooling generally in the furnace. Arbor ... (1) A structural metal shape imbedded in green sand or dry sand cores to support the sand or the applied load during casting. (2) A shaft or bar used for holding a cutting tool or workpiece. Arc Furnace ... A furnace in which steel is melted either directly by an electric arc between an electrode and itself, or indirectly by an arc between electrodes above the steel. Arc Melting ... Melting steel in an arc furnace. GLOSSARY 625 Arc Welding ... Welding accomplished by using an electric arc that may be formed between the electrode and the metal being welded. Arithmetical Average (Arithmetical Mean) ... An average value. The sum of the values constituting the data divided by the number of values. See also Mean. As Cast Condition ... Cast steel as removed from the mold without subsequent heat treatment. Atmospheric Riser ... A blind riser with a pencil core extending into its top to permit atmospheric pressure to be exerted on the liquid metal interior after the exterior has solidified. . Austempering ... A trade name given to a heat treating process that consists of quenching steel from a temperature above the trans- formation range, in a medium having a rate of heat abstraction sufficiently high to prevent the formation of high-temperature trans- formation products; and in maintaining the steel, until transformation is complete, at a temperature below that of pearlite formation and above that of martensite formation. Austenite ... Solid solution of carbon in the face-centered cubic lattice of iron or an alloy of iron. Austenitizing ... Process of forming austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing). Avcrage Deviation ... The arithmetical mean of the absolute devia- tions X) of the values from the average of the total sum of values. See also Standard Deviation. Back Draft ... A reverse taper on a pattern which prevents its removal from the mold. Backing Sand ... Sand used to fill the flask after facing sand has been put on the pattern. Also referred to as heap sand. Basic Bottom and Lining . The inner bottom and lining of a melting furnace consisting of materials such as crushed burnt dolomite, magnesite, magnesite bricks, or basic slag that give a basic reaction at the operating temperature. Basic Steel ... Steel melted in a furnace with a basic bottom and lining and under a slag containing an excess of a basic substance, such as magnesia or lime. Baume ... A scale for measuring the specific gravity of liquids using a hygrometer. 626 GLOSSARY Bench Molding ... The process of making small molds on a molder's bench. Usually a hand operation. Bend Test ... The testing of metal bars of a rectangular cross-section 1 x 11/2 inch by bending. The specimen is bent cold around a pin 1 inch in diameter to a specified angle without cracking on the outside of the bent portion. Bentonite ... A colloidal clay-like substance derived from the decom- position of volcanic ash composed chiefly of the minerals of the montmorillonite family. Western bentonite is slightly alkaline; southern bentonite is usually slightly acidic. Binder ... Material to hold the grains of sand together in molds or cores. May be cereal, oil, clay, resin, pitch, etc. Blast Cleaning ... The removal of sand or oxide scale from castings by means of the abrasive action of sand or metal shot or grit projected under air or water pressure, or by mechanical means. Blind Riser ... An internal riser which does not reach to the exterior of the mold. Blow-By ... In core blowing, the passing of the sand particles between the plate and core box, the abrasive action of which erodes the core box. Boss ... A relatively heavy, but short, projection on a casting. Bottom Board ... A flat base for holding the flask in making sand molds. Bottom Gate ... For filling of the mold cavity from gates located at the bottom of the mold cavity. Bridging ... (1) Premature solidification of steel across a mold section before the metal below or beyond solidifies. (2) Welding or mechanical locking of the charge in a down-feed melting furnace. Brinell Hardness Testing ... A method of measuring the indentation hardness of steel by measuring the diameter of the impression made by a ball of given diameter applied under a known load. Carbon Steel ... Steel which owes its properties chiefly to various percentages of carbon without substantial amounts of other alloying elements; also known as common steel or straight carbon steel. Carburizing ... Adding carbon to the surface of iron-base alloys by heating the metal below its melting point while in contact with carbonaceous solids, liquids or gases. Case Hardening ... A process of hardening a ferrous al oy so that the surface layer or case is made substantially harder than the interior . or core. GLOSSARY 627 Cast Steel ... Commercial iron-carbon alloy under 1.70 percent carbon used for castings. Most tonnage is under 0.40 percent carbon, and is melted in open hearth or electric furnaces. Alloying elements to high percentages may be added for special properties. Cast Structure ... The internal physical structure of a casting as evidenced by the shape and orientation of crystals and segregation of impurities. Cast-Weld Assembly ... The joining of one casting to another by welding to form an integrated assembly. Casting Strains ... Strains resulting from internal stresses created during the cooling of a casting. Casting Stresses ... Stresses set up in a casting because of geometry and casting shrinkage. Casting Yield ... The weight of casting or castings divided by the total weight of metal poured into the mold, expressed as a percent. Cement Sand ... A synthetic sand used for molds, bonded with Port- land cement. Cementite ... A hard, brittle, intermetallic compound essentially composed of iron and carbon, known as iron carbide, having the approximate chemical formula Fe3C. Centrifugal Casting ... A process of filling molds by (1) pouring the metal into a sand or permanent mold that is revolving about either its horizontal or its vertical axis; or (2) pouring the metal into a mold that is subsequently revolved before solidification of the metal is complete. Centrifuge Casting ... A casting technique in which mold cavities are spaced symmetrically about a vertical axial common downgate. The whole assembly is rotated about that axis during pouring and solidification. Cereal ... An organic binder, usually corn flour. Chamotte ... A molding aggregate crushed, ground and sized from a fired refractory ceramic material. Chaplets ... Metal supports or spacers used in molds to maintain cores, or parts of the mold which are not self-supporting in their proper positions during the casting process. They become a permanent part of the casting. . Charpy Test ... A pendulum type of impact test in which a specimen, supported at both ends as a simple beam, is broken by the impact of 628 GLOSSARY the swinging pendulum. The energy absorbed in breaking the speci- men, as determined by the decreased rise of the pendulum, is a measure of the impact strength of the metal. Cheek ... The intermediate section of a flask that is used between the cope and the drag when molding a shape which requires more than one parting plane. Chill ... A metal insert imbedded in the surface of a sand mold or core, or placed in a mold cavity to increase the cooling rate at that point. Chipping ... The process of removing extraneous metal from a casting with pneumatically operated chisels. Choke ... A narrowing at the ingate of a mold to restrict metal flow. Clay ... An earthy or stony mineral aggregate consisting essentially of hydrous silicates of alumina, plastic when sufficiently pulverized and wetted, rigid when dry, and vitreous when fired at a sufficiently high temperature. Clay minerals most commonly used in the foundry are montmorillonites and kaolinites. Closing ... The final assembling, before pouring, of the several parts of the mold including cope, drag and cores. CO, Process ... A rapid, room temperature process for setting sand cores or molds, employing CO2 gas to form a silica gel binder by reaction with liquid sodium silicate. Collapsibility ... The property of a sand mixture which causes it to break down or lose strength after the mold is poured. This property is essential in relieving casting stresses due to mold expansion or metal contraction. Composite Fabrication ... The joining by welding of a steel casting to a rolled or forged steel object to form an integrated assembly. Conductivity (Thermal) ... The property of a sand mold or metal casting to conduct heat, the rate being measured in BTU/sq. ft./sec./ in./degrees F, or in gram-cal./sq. cm./sec./cm./degrees C. This prop- erty controls the rate of heat loss from the casting, and hence the rate of solidification. Continuous Casting ... A casting technique in which an ingot, billet, tube, or other shape, is continuously solidified while it is being poured, and the length is not determined by mold dimensions. Converter Steel ... Steel made by the converter process which consists of blowing air through molten pig iron or cupola metal contained in a cylindrically shaped vessel, thus removing unwanted amounts of alloyed elements by oxidation. GLOSSARY 629 Cope The upper or topmost section of a flask, mold, or pattern. Core ... A preformed sand aggregate inserted into a mold to shape the interior of the casting or that part of a casting which cannot be shaped by the pattern. Core Blower ... A machine for making cores by blowing sand into the core box, by means of compressed air. The air escapes from the core box through finely grated openings called vents. Core Box ... Wood, metal, or plastic structure containing a shaped cavity into which sand is packed, making a core. Core Driers ... Supports used to hold cores in shape while being baked. Core Oil ... A binder for core sands, made chiefly of linseed oil, which sets when baked. Core Oven A furnace or oven for baking cores. Core Paste ... A prepared adhesive for joining sections of cores. Core Plates ... Heat resistant plates used to support cores during baking. Core Print ... Projections attached to a pattern in order to form recesses in the mold at points where cores are to be supported. Core Rod ... Iron or steel in rod form used to stiffen or support a core internally. Core Set Binder ... A bonding material, usually for core sand mixes, which permits cores to harden at room temperature by internal oxidation. Core Wash ... A suspension of a fine refractory applied to cores by brushing, dipping or spraying to improve the surface of the cored portion of the casting. Coupon ... See Test Coupons. Critical (Temperature) Range Critical Points .. Temperatures at which changes in the phase of a metal take place, and are determined by liberation of heat when the metal is cooled (alpha iron forming from gamma iron), and by the absorption of heat when the metal is heated (gamma iron forming from alpha iron), resulting in halts or arrests on cooling and heating curves. Crucible ... A vessel or pot, made of a refractory substance or of a metal with a high melting point, used for melting metals. Crucible Steel ... Steel made by the crucible process which consists of melting steel or wrought iron in refractory crucibles with additions of carbon and other alloys if desired. 1 . 630 GLOSSARY Cutting Off ... The process of removing extraneous metal from a casting, such as gates, risers and pads by torch flame, by a thin abrasive wheel or by metal sawing. Cyaniding ... Surface hardening by carbon or nitrogen absorption by an iron-base alloy brought about by heating at a suitable temperature in contact with a cyanide salt, followed by quenching. Damping Capacity ... Ability of a metal to absorb vibration, changing the mechanical energy into heat. . Decarburization ... Loss of carbon from the surface of a ferrous alloy, as a result of heating in a medium containing oxygen that reacts with the carbon. Deformation (Sand) ... Change in a linear dimension of a sand mixture subjected to an applied stress. Degasificr ... A substance that can be added to molten metal to remove soluble gases which might otherwise be occluded or entrapped in the metal during solidification. See also Deoxidizer. Delta Iron ... A form of iron identical with alpha iron. The crystal structure of delta iron is body-centered cubic and its range of stability when pure is from 1400 degrees C to the melting point at 1535 degrees C. Dendritic Structure ... A structure of crystals formed during the solidification of a metal or alloy characterized by a branching struc- ture like that of a fir tree. Deoxidizer ... A metal or alloy used to remove oxygen or oxides from molten metal. . Destructive Testing . ... The breaking, fracturing or sectioning of a casting by sledge, dropball, torch cutting or sawing for the purpose of ascertaining the internal integrity of the cross sectional members by visual observation. Deviation ... See Average Deviation and Standard Deviation. Dielectric Core Baking Heating cores to baking temperatures by means of high-frequency equipment. This process is particularly well adopted to thermosetting resin core binders. Differential Hardening ... Hardening conducted in such a way that various portions of an object are hardened to varying degrees. For example, the quenching of a portion of a casting and allowing the other portion to air cool. Dilatometer ... An instrument for measuring expansion or contraction GLOSSARY 631 caused in a metal or sand sample by changes in temperature or structure. . Directional Solidification ... The solidification of molten metal in a casting in such a manner that feed metal is always available for that portion that is just solidifying. Distribution Curve ... The graphic representation of a frequency distribution. Draft ... The taper on the sides of a pattern which allows the pattern to be withdrawn from the mold without breaking the edges of the mold. Drag ... The bottom section of a flask, mold or pattern. Draw Bar ... A bar used for lifting the pattern from the sand of the mold. Dross The scum that forms on the surface of molten metals due largely to oxidation, but sometimes to the rising of impurities to the surface. Dry Sand Mold ... A mold made of prepared molding sand which is thoroughly dried before it is filled with liquid steel. Dry Strength ... The maximum strength of a molded sand specimen that has been thoroughly dried at 220 - 230 degrees F and cooled to room temperature. Also known as baked strength. Ductility ... The property permitting permanent deformation by stress in tension without rupture. Elastic Deformation ... Temporary changes in dimensions caused by stress. The material returns to the original dimensions after removal of the load. Elastic Limit ... The maximum stress that a material will withstand without permanent deformation. Electric Steel ... Steel made liquid by using electrical energy as a source of heat. . Electrode, Graphite or Carbon ... Graphite or carbon compressed under high pressure into solid cylinders or rods of various diameters and lengths and used to maintain the arc in electric arc furnaces, etc. Electrode, Welding ... A metal or alloy in rod or wire form used in electric arc welding to maintain the arc and at the same time supply molten metal or alloy at the point where the weld is to be accomplished. Elongation ... In a tension test, elongation is the total amount of permanent extension of the gage length, measured after the specimen 632 GLOSSARY has fractured, and is expressed as a percentage increase of the original gage length. . Endurance Limit ... A limiting stress below which the metal will withstand, without rupture, an indefinitely large number of cycles of stress. Endurance Ratio ... The ratio of endurance limit to ultimate strength. Eutectic ... (1) Isothermal reversible reaction of a liquid that forms two different solid phases (in a binary alloy system) during cooling. (2) The alloy composition that freezes at constant temperature, under- going the eutectic reaction completely. (3) The alloy structure of two or more solid phases formed eutectically from the liquid. Eutectoid ... The composition and temperature at which two new solid phases are formed during cooling in the solid state. Expansion (Sand) ... Maximum dimensional increase which a mass of sand undergoes when heated to a given temperature. Facing ... Specially prepared molding sand placed against a pattern to improve the surface quality of the casting. Fatigue Tendency of a metal to break, under conditions of re- peated cyclic stressing, at levels considerably below the tensile strength. Fatigue Testing ... A method of subjecting material to a large num- . ber of reversing stress cycles to measure its endurance. Feed Head ... See Riser. Ferrite . . . An essentially carbon-free, solid solution in which alpha iron is the solvent, and which is characterized by a body-centered cubic crystal structure. Ferro-Alloys ... Alloys consisting of certain elements combined with iron, used to increase the amount of such elements in molten steel. Fillet ... (1) In a casting, the concave surface joining two other sur- faces which make an angle with each other. (2) In pattern-making, the material used on a pattern, or that portion of a pattern or core box, rounding out the internal corners formed by the intersection of two surfaces; may be made of wax, plastic, leather, or wood. Fines ... (1) The product that passes through the finest screen in sorting crushed or ground material. (2) Sand grains that are sub- stantially smaller than the predominating size in a batch or lot of foundry sand. Finish Allowance Amount of stock left on the surface of a casting for machining. GLOSSARY 633 . . Flame Hardening ... Process of hardening a casting surface by heat- ing it above the transformation range with a high temperature flame followed by rapid cooling. Flask ... Metal or wood frame, without a top and without a fixed bottom, used to hold the sand of which a mold is formed; usually consists of two parts, the cope (top) and drag (bottom). Flask Pins ... Guides to assure proper alignment of the cope and drag of the mold after the pattern is withdrawn. Flowability . A characteristic of a foundry sand mixture which enables it to move under pressure so that it makes intimate contact with all surfaces of the pattern or core box. Fluidity ... The ability of liquid metal to run into and fill a mold cavity. Fluorescent Penetrant Inspection ... A non-destructive testing method (zyglo) wherein a penetrating type of oil or other liquid which has been combined with fluorescent material particles is applied over a surface and flowed into cracks, crevices, or other surface defects or irregularities, the excess removed and the article examined under ultra-violet light, thus revealing discontinuities. Fluorspar ... The commercial grade of calcium fluoride used in con- trolling basic slag viscosity. Flux ... A material used in melting to provide a protective covering for the molten metal. Also aids in the removal of such undesirable substances as sand, slag, ash or dirt from the molten metal. Follow Board ... A board which conforms to the form of the pattern and defines the parting surface of the drag. Frequency The ratio of the number of values falling within a single class to the total number of values classified. Full Annealing ... Heating of a ferrous alloy by austenitizing and then cooling slowly through the transformation range. Gaggers ... Metal pieces of irregular shape used to reinforce and support sand in deep pockets of molds. Gamma Iron ... One of the allotropic forms of iron being of face centered cubic lattice structure. It is stable in the range of temper- ature between 910 degrees and 1400 degrees Centigrade (1670 degrees F and 2550 degrees F). Gamma Ray Inspection ... See Radiography. Ganister ... A highly siliceous quartzite used as a molded refractory for monolithic acid linings in furnaces and ladles. O . . 634 : GLOSSARY Gating ... ... Employed as a general term to indicate the entire assem- bly, or system of connected channels for conveying molten metal from the point where metal enters the mold to the part forming the casting proper. Terminology for specific portions of the gating system in- clude: (1) Down sprue or down gate which is the vertical member where metal initially enters. (2) Runner or ingate which is usually essentially horizontal and channels metal directly into mold cavity or into a riser adjacent to mold cavity. Gilsonite ... Similar to pitch and finds application in foundry sand mixtures as a carbonaceous additive to improve surface finish. Grain Growth ... The phenomenon of growth of the crystal when metal is held for prolonged periods of time at temperatures above the critical transformation temperature. Grain Refiner ... Any material added to a liquid metal for producing a finer grain size in the subsequent casting, Grain Size Inspection ... An examination and estimation of the aus- tenitic grain size of steel by microscopic or macroscopic methods. Standard grain classes have been set by the American Society for Testing Materials to act as references and as a scale. See A.S.T.M. Designation E19-46. Grains ... (1) Crystals in metals. (2) Individual or component aggre- gates when referring to core or molding sands. Grcen Casting ... A casting which has been shaken out of the mold and un-heat treated. Green Sand Mold ... A mold made of prepared molding sand in the as mixed (moist) condition. See also Dry Sand Mold and Skin-Dried Mold. Green Strength Strength ... Strength of a tempered sand mixture at room tem- perature. Grit, Abrasive ... Crushed ferrous metal in various mesh sizes which is used in pressure blasting equipment for cleaning of castings. Hadfield Manganese Steel ... Essentially a high alloy containing 1 to 11/22 percent carbon and 10 - 14 percent manganese capable of being cold work hardened. Hand-Shank ... A small pot ladle to hold molten steel, which can be - carried and poured by one or two men. Hardcnability Testing ... Testing to determine the relative distribu- tion of metal hardness with respect to depth under heat treatment con- GLOSSARY 635 ditions. The test consists of water quenching one end of a specially ma- chined cylindrical steel test specimen and determining by hardness measurements to what extent from the quenched end the steel hard- ens. This standard test is referred to as the Jominy End Quench Test for hardenability of steel. See American Society for Testing Ma- terials specification, A.S.T.M. Designation A255-48T. Hardness ... Defined in terms of method of measurement; usually the resistance to indentation. Hardness Testing ... See Brinell, Scleroscope, Rockwell and Vickers Hardness Testing. Head ... See Riser. Heap Sand ... See Backing Sand. Heat Treatment ... An operation, or combination of operations, involv- ing the heating and cooling of a metal or alloy in the solid state for the purpose of obtaining certain desirable conditions or properties. Hindered Contraction ... The prevention of the free contraction of steel by mold conditions or casting design. Histogram ... A graphical representation of a frequency distribution by a series of rectangles which have for one dimension a distance pro- portional to a definite range of frequencies and for the other dimension a distance proportional to the number of frequencies appearing within . the range. Hollow Drill Testing (Trepanning) ... The removal of a cylindrical sample from a metal section or structure to determine soundness of the section. Homogenization ... A prolonged heating of steel at austenitizing tem- peratures for the purpose of obtaining a uniform distribution of the constituents. Hot Spots ... Localized areas of a mold or casting where higher tem- peratures are reached or where high temperature is maintained for an extended period of time. Hot Top ... A reservoir thermally insulated or heated to hold molten metal on top of a mold to feed the ingot or casting as it contracts on solidifying to avoid having pipe or voids. Hypereutectoid ... An alloy containing more than eutectoid composi- tion (for a carbon steel, more than about 0.80 percent C). Hypoeutectoid ... An alloy containing less than eutectoid composi- tion. 636 GLOSSARY . Hysteresis Loss ... Energy lost when a magnetic material is subjected to a complete cycle of magnetism. Immersion Pyrometer .. An instrument for determining molten steel temperature and normally consisting of a platinum-platinum rhodium bimetal thermocouple junction and a recording device for transposing the millivoltage into degrees of temperature. Impact Test ... A test in which one or more blows are suddenly ap- plied to a specimen. The results are usually expressed in terms of energy absorbed or number of blows (of a given intensity) required to break the specimen. Izod and Charpy impact tests are the common methods of studying the impact resistance of steel. Inclusions ... Particles of impurities (usually oxides, sulfides, sili- cates and such) that are held mechanically, or are formed during so- lidification or by subsequent reaction, within the solid metal. Induction Furnace ... A melting unit wherein the metal charge is A melted electrically by induction. Induction Hardening ... Process of hardening the surface of a casting by heating it above the transformation range by electrical induction, followed by rapid cooling. Ingate ... See Gating. Inserts Parts formed from a second material, usually a metal, which are placed in the mold and appear as integral structural parts of the final casting. Intensifier An addition such as boron made to low carbon or low alloy steels to complement the end result of alloying elements added for the purpose of increasing the over-all hardenability of the alloy. Investment Casting ... (1) Casting metal into a mold produced by ) surrounding (investing) an expendable pattern with a refractory slurry that sets at room temperature after which the wax, plastic, or frozen mercury pattern is removed through the use of heat. Also called precision casting or lost wax process. (2) A casting made by the process. Investment Compound ... A refractory used for molds formed around wax or plastic patterns. Isothermal Heat Treatment ... A method of hardening steel by quench- ing from the austenitizing temperature into a bath which is main- tained at a constant temperature level in the transformation range (approximately 450 to 1300 degrees F). The part is held for a time sufficient to permit transformation and then is transferred to some higher temperature level for tempering and cooling in air. . . GLOSSARY 637 Izod Impact Testing ... The testing of a metal by the sudden applica- tion of a blow or impact to an Izod or cantilever beam, notched bar test specimen approximately 3 inches long and 0.394 inch square containing a V notch. Jacket, Mold ... A wooden or metal form, which is slipped over a mold made in a snap or slip flask, to support the four sides of the mold during pouring. Jolt Machine ... A molding machine relying on the principle of jolting to ram the sand against the pattern. Jominy Test ... See Hardenability Testing. Keel Block ... A test casting for the preparation of mechanical test specimens. Killed Steel ... Steel deoxidized with a strong deoxidizing agent such as silicon or aluminum in order to reduce the oxygen content to such a level that no reaction occurs between carbon and oxygen during solidification. Knock-Out ... Operation of removing sand cores from castings. Knoop Hardness ... Microhardness determined from resistance of the metal or individual microconstituents to indentation by a diamond indenter. Ladle ... A refractory lined metal vessel used for holding, transport- ing and pouring molten metal. Loam ... A molding material consisting of sand, silt, and clay used over brickwork or other structural back-up material for making mas- sive castings. Liquid Contraction ... The shrinkage or contraction that takes place in molten metal as it cools from one temperature to another while in the liquid state. Liquidus ... The temperature at which solidification of steel begins on cooling and the temperature at which the last portion of solid steel becomes liquid on heating under equilibrium conditions. Loose Piece ... Part of a pattern or core box so attached that it re- mains in the mold or core and is then removed after the pattern or core box is drawn. Lost Wax Process ... An investment casting process in which a wax pattern is used. Machinability ... Index or rate of metal removal by various methods with machine tools, usually expressed in terms of feet per minute, depth of cut, etc. 638 GLOSSARY Macrostructure ... Structure of metals as revealed by the eye or at a magnification of less than ten diameters. Magnaflux Testing ... See Magnetic Particle Testing. . Magnesia ... Magnesium oxide, a basic refractory. Magnetic Particle Testing ... A nondestructive testing method of in- specting areas on or near the surface of ferrous metals. The metals are magnetized and then sprinkled with iron powder to locate dis- continuities such as hair-line cracks, etc. Martempering ... Quenching an austenitized ferrous alloy in a medium at a temperature in the upper part of the martensite range, or slightly above the range, and holding in the medium until the temperature of the alloy is substantially uniform. Martensite ... A microconstituent or structure in quenched steel characterized by an acicular or needle-like pattern. It has the maxi- mum hardness of any of the decomposition products of austenite. Master Alloy ... An alloy, rich in one or more desired addition ele- ments, that can be added to a melt to raise the percentage of a desired constituent to the intended level. Master Pattern ... A pattern that is used for making castings that are to become production patterns. Matchplate ... A metal or other plate on which patterns, split along the parting line, are mounted back to back with gating systems to form an integral piece. Mean ... A value in a set of data midway between the two extremes; obtained by adding together the minimum and maximum values and dividing that sum by 2. See also Mode and Median. Mechanical Properties (Less properly, physical properties) ... The properties of a metal which upon the application of force reveal the elastic and inelastic reaction, or involve the relationship between stress and strain. See also Physical Properties. Median ... The middlemost value in a set of data, or that value which divides the data into two equal portions, one with values higher than the median, the other with values lower than the median. See also Mean and Mode. > l Melting Loss ... Loss of metal in the charge during the melting and pouring operations. Metallography . The science of the nature and structure of metals and alloys as revealed by the microscope. GLOSSARY 639 Micron ... A unit of length equal to 0.001 millimeter. Mode ... The mode of a set of data is that value which occurs most frequently. See also Mean and Median. Modulus of Elasticity ... The ratio of tensile stress to the correspond- ing strain within the limit of elasticity of a material. Modulus of Rupture ... The ultimate strength or the breaking load per unit area of a specimen tested in torsion or in bending. This corre- a sponds to the tensile strength in tension. Mold ... The form, usually sand, containing the cavity into which molten metal is poured to make the casting. An ingot mold is a metal form. Mold Wash ... A slurry of refractory material, such as graphite and silica flour, used in coating the surface of the mold cavity to provide an improved casting surface. Mold Weights ... Weights placed on the tops of molds while pouring, to offset internal pressure. Molding Machines ... Hand or pneumatically operated machines on which molds are made, which ram the sand by squeezing or jolting or both. See also Sandslinger, Jolt Machine and Squeeze Molding. Moment of Inertia (of an area) ... With respect to a given axis, it is the limit of the sum of the products of the elementary areas into which the area may be conceived to be divided and the square of their distance from the axis in question. Mulling ... The process of mixing mold and sand core ingredients under the action of rubbing, stirring, rolling or grinding. Mullite See Sillimanite. Nitriding ... Adding nitrogen to iron-base alloys by heating the metal in contact with ammonia gas or other sources of atomic nitrogen. . Normal Expected Value ... The mode obtained from a distribution curve. Normalizing... Heating a ferrous alloy to a suitable temperature above the transformation range, and then cooling in still air to room temperature. Notch Sensitivity ... The reduction in the impact, endurance, or static strength of a metal that is caused by the presence of stress concen- tration as a result of scratches, pits or other stress raisers on the sur- 640 GLOSSARY face; usually expressed as the ratio of the notched to the unnotched strength. Notched Fatigue Factor ... The reduction in fatigue strength caused by the presence of a sharp notch in the stressed section. Open Hearth Steel ... Steel made by the open-hearth process which consists of melting steel scrap or scrap and pig iron in a shallow rec- tangular bath furnace and refining to produce the desired grade of steel. Optical Pyrometer ... An instrument for measuring the temperature of heated material by comparing the intensity of light emitted with a known intensity of an incandescent lamp filament. Padding ... The application of tapered layers of metal to uniform sections of a mold to permit controlled directional solidification of the casting Particle Size ... The controlling linear dimension of an individual particle as determined by analysis with screens or other suitable instruments. Parting ... Where sections of a mold are separated. Parting Compound ... Finely ground sand and/or other materials for the dusting of surfaces that are to be separated in making a sand mold. Pattern ... Model of wood, metal, plaster, plastic or other material around which molding material is placed to shape a mold for casting metals. Patternmaker's Shrinkage ... Contraction allowance made on patterns to compensate for the decrease in dimensions as the solidified casting cools in the mold from the freezing temperature of the metal to room temperature. The pattern is made larger by the amount of contrac- tion that is characteristic of the particular metal to be used. Pearlite ... The lamellar aggregate of ferrite and carbide resulting from the equilibrium transformation on cooling of austenite at Arl on the Iron-Carbon Diagram. Permanent Mold ... A long life mold usually constructed of metal into which liquid metals are cast repeatedly. Permeability ... (1) Magnetic permeability of a substance is the ratio of the magnetic induction in the substance to the magnetizing field to which it is subjected. (2) Permeability in prepared sand is that property which permits the passage of gases through it. Photomicrograph ... A photographic reproduction of any object mag- nified more than ten diameters. GLOSSARY 641 Physical Properties ... Those properties familiarly discussed in phys- ics exclusive of those described under mechanical properties. For example, density, electrical conductivity, coefficient of thermal ex- pansion, etc. Pickling ... The removal of oxide scale and sand from metal objects by treating in an acid bath, usually a 10 percent solution of sulfuric acid. Not recommended for carbon and low alloy steel castings. Pig Iron ... (1) High carbon iron made by reduction of iron ore in the blast furnace. (2) Cast iron in the form of pigs. Pipe cation. A cavity formed by the contraction of metal during solidifi- Pit Molding ... The construction of molds in pits below the level of the foundry floor. Pouring Basin ... A basin on top of a mold to receive the molten metal before it enters the sprue or downgate. Precipitation Hardening ...A process of hardening an alloy in which a constituent precipitates from a supersaturated solid solution. Precision Casting ... A metal casting of reproducible accurate dimen- sions regardless of how it is made. Pressure Casting (1) Making castings with pressure upon the mol- ten or plastic metal, as in centrifugal casting. (2) A casting made . with pressure applied to the molten or plastic metal. Pressure Testing ... The inspection of castings by the application of oil, water, steam or air pressure to internal chambers for the purpose of disclosing leaks between one chamber and another or between the inside and outside surface. Pressure Tight ... A condition existing such that a casting containing a fluid will not leak even though subjected to pressure. Proportional Limit ... The greatest stress that a material is capable of sustaining without a deviation from the law of proportionality of stress to strain. Pyrometer ... An instrument used to determine elevated temper- atures. See also Immersion Pyrometer and Optical Pyrometer. Quench Hardening ... Process of hardening a ferrous alloy of suitable composition by heating within or above the transformation range and cooling at a rate sufficient to increase the hardness substantially. The process usually involves the formation of martensite. . a 642 GLOSSARY . Quenching ... A process of rapid cooling from an elevated temper- ature, in contact with liquids, gases or solids. Radiography ... A non-destructive method of internal examination in which metal objects are exposed to a beam of X-ray or gamma ra- diation. Differences in thickness, density, or absorption, caused by internal defects or inclusions are apparent in the shadow image either on a fluorescent screen or on photographic film placed behind the object. Ramming ... Packing sand, refractory, or other material into a com- pact mass. Range The difference between the highest and lowest values in a set of data. Recarburizer ... Any carbonaceous material or pig iron (cast iron) or alloy which is added to molten steel for the purpose of increasing the carbon content of the steel. . . . Reduction of Area ... The difference between the original cross sec- tional area of a tensile test bar and that of the smallest area at the point of rupture. It is usually expressed as a percentage of the origi- nal area. Refractory ... A heat resistant material, usually non-metallic, which is used for furnace and ladle linings. Residual Induction The magnetic induction remaining in a mag- netized material when the magnetizing force has been removed. Residual Stress ... Microscopic stresses that are set up within a metal as the result of non-uniform plastic deformation. This deformation may be caused by working or by drastic gradients of temperature from quenching or welding. Resistivity .. The resistance of a material to the transmission of electrical energy. It is measured by the resistance of a body of the material of unit cross section and unit length. Ribs (1) Sections joining various parts of a casting to impart greater rigidity or stiffness. (2) The bars in the cope of a tight flask to support the sand. Riddle ... A sieve used to separate foundry sand or other granular materials into various particle-size grades or to free such a material of undesirable foreign matter. Riser . . . A reservoir of molten metal provided to compensate for the contraction of steel as it solidifies, thus preventing voids in the cast- ing. Also known as a feed head. . GLOSSARY 643 . Rockwell Hardness Testing ... A method of measuring the indentation hardness by measuring the depth of residual penetration by a steel ball or a diamond cone. Rod ... A heavy wire or bar in a sand core used for reinforcing. Runner ... (1) The channel of a gating system through which molten metal flows from the sprue to the castings and risers. (2) That part of the pattern which forms the runner. See also Gating. Runner Box ... A distribution box that divides the molten metal into several streams before it enters the mold cavity. Sand Control ... Procedure whereby various properties of foundry sand, such as fineness, permeability, green strength, moisture con- tent, are adjusted to obtain satisfactory castings. Sand Muller ... A machine for the mixing and bonding of sand by kneading and squeezing action. Sand Segregation ... Separation and concentration of different size sand particles brought about by methods of handling. Sandslinger ... A molding machine which impels sand by centrifugal force into a flask or core box. Saturation Magnetization ... The magnetic condition of a body when an increase in the magnetizing force produces practically no change in the intensity of magnetization. Scleroscope Hardness Testing .. A method of measuring hardness by the drop and rebound of a tup. Screen Analysis . . . Size distribution of sand grains expressed in terms of the percentage by weight retained on each of a series of standard screens decreasing in mesh size, and the percentage passed through the screen of the finest mesh. Section Modulus ... The value of l/c, where c is the distance from the axis about which the moment of inertia is taken to the fiber or portion of the section carrying maximum stress. I is the moment of inertia of the cross section. Self Hardening Steel ... A steel containing sufficient carbon or alloy- ing elements or both to form martensite either through air hardening, or as in welding or induction hardening through rapid removal of heat from a locally heated portion by conduction into the surrounding cold metal. Semikilled Steel ... Steel that is incompletely deoxidized and con- tains sufficient dissolved oxygen to react with the carbon to form carbon monoxide to offset solidification shrinkage. 644 GLOSSAR Y Semisteel ... A misnomer. The term refers to a gray iron, the melting charge for which contains a percentage of steel scrap. Shakeout ... The operation of removing castings from the mold. Shell Core ... A sand core made by shell molding. Shell Molding Forming a mold from thermosetting resin-bonded sand mixtures brought in contact with preheated (300 - 500 degrees F) metal patterns, resulting in a firm shell with a cavity corresponding to the outline of the pattern. Also called Croning Process. Shielded Arc Welding ... Electric arc welding in which the metal is protected from the air atmosphere by an inert gas. Shot ... Small spherical particles of metal. Shotting ... The production of shot by pouring molten metal in finely divided streams. Solidified spherical particles are formed during the fall and are cooled in a tank of water. Shrinkage Rule ... A measuring ruler used in making patterns for A castings on which the graduations are expanded to account for thermo and solidification contraction of a metal being cast. Silica Flour ... A sand additive, containing about 99.5 percent silica, commonly produced by pulverizing quartz sand in large ball mills to a mesh size 80 to 325. Sillimanite ... A refractory mineral (A1,03 . Si02) used in ceramic molding; forms mullite (3 A1203.2SiO2) on heating to 2785 degrees F. Skeleton Pattern ... A pattern made in outline form. Skimmer ... (1) A tool used for pulling slag off molten metal. (2) A core in the gating system for trapping slag. Skin-Dried Mold ... Green sand mold, the mold cavity of which has been dried by a torch flame just prior to casting. Skull ... A layer of solidified metal or dross on the walls of a pouring vessel after the metal has been poured. Slag A fused non-metallic substance which is used in steel making to protect the molten steel and extract certain impurities. Snagging ... The process of rough cleaning castings by grinding. Snap Flask ... A foundry flask, hinged on one corner so that it can be opened and removed from the mold for reuse before the metal is poured. Solid Contraction ... The shrinkage or contraction that takes place in steel as it cools from the solidifying temperature to room temperature. a GLOSSARY 645 Solidification Contraction ... The shrinkage or contraction that takes place as steel solidifies. Solidus ... The temperature at which freezing ends during cooling, or melting begins during heating, under equilibrium conditions. Solution Heat Treating ... Heating a material to a suitable temper- ature, holding it at that temperature long enough to allow one or more constituents to enter into solid solution and then cooling rapidly enough to hold the constituents in solution. Spectrograph ... An optical instrument for determining the presence or concentration of minor metallic constituents in a material by in- dicating the presence and intensity of specific wave lengths or radia- tion when the material is thermally or electrically excited. Spheroidizing . ... A long annealing at a temperature below but near the critical point, causing the cementite to spheroidize. Spray Quenching Quenching in a spray of liquid. Sprue (1) The vertical channel that connects the pouring basin with the runner. (2) That part of the pattern which forms the sprue in the mold. (3) Sometimes used to mean all gates, risers, runners and similar scrap returned to the melting unit for remelting. Squeeze Molding ... That part of the machine molding cycle in which the top of the mold is compressed by use of air or a hydraulic acti- vated device. . Stack Molding ... A molding method by which a number of identical mold sections are placed one above the other and poured through a common sprue. Standard Deviation The square root of the average value of the squares of the deviations of the values from the arithmetical mean or average. See also Average Deviation. . Stopper ... A fired refractory product consisting of clay usually im- pregnated with graphite. Serves as a means for opening and closing the nozzle in a bottom pour ladle. Strain ... The change in unit length during elongation or contraction of a casting or test specimen. Strainer ... Usually used as a ceramic disc formed with numerous holes for inserting in a gating system for separation of slag particles from the steel. Stress ... The load per unit of area. 646 GLOSSARY Stress Raisers ... Factors such as sharp changes in contour or surface defects which locally concentrate stresses. Stress Relieving . . . Heating to a suitable sub-critical temperature, holding long enough to reduce residual stresses and then cooling slowly enough to minimize the development of new residual stresses. Strip ... To draw a pattern from a mold or a core from a core box. Submerged Arc Welding ... Electric arc welding in which the metal is protected from the air atmosphere by a covering of slag-forming materials. Supercooling ... Cooling below the temperature at which an equilib- rium phase transformation takes place without obtaining the change. Superheating ... Raising the temperature of molten metal above the normal casting temperature for more complete refining, greater fluid- ity, or other reasons. Not analogous to supercooling. Sweep ... A form or template used for shaping sand molds or cores by hand. Sweep Molding ... The forming of a mold or core cavity by scraping the sand with a form (sweep pattern) having the desired profile. Swirl Gate ... A device in the gating system for trapping slag and dross before it gets to the mold cavity. Tapping ... Removing molten steel from the melting furnace and allowing the molten steel to run out into the ladle. Teapot Ladle ... A ladle arranged so steel is delivered from the bot- tom of the ladle through a vertical pouring spout to enable pouring metal free of slag. Teeming . Pouring molten metal from a ladle into ingot molds. Tempering ... (1) Reheating a quench hardened or normalized ferrous alloy to a temperature below the transformation range and then cool- ing at any rate desired. (2) Adding water to a mold or core sand. Template ... A guide, gage or pattern for the purpose of checking casting dimensions. Tensile Strength ... The maximum stress in tension which a material will withstand prior to fracture. It is calculated from the maximum load applied during the tensile test divided by the original cross- sectional area of the sample. Test Bars ... Bars cast to a standard shape and size for use in de- termining the mechanical and chemical properties of the metal. GLOSSARY .647 Test Coupons ... Special, well-fed castings from which tensile or bend test specimens are cut and subsequently machined. Steel which is cast or machined to shape for me- Test Specimens chanical testing. Thermal Stresses ... Stresses in metal resulting from the non-uniform distribution of temperature. Thermit Welding ... The welding of two ferrous metal parts by a thermit chemical reaction of metallic oxide and aluminum powder These materials are mixed and ignited. They react exothermically to produce a superheated mass of metal and a slag of molten aluminum oxide. Thermocouple ... A device for measuring temperatures by the use of two dissimilar metals in contact. A junction of these metals gives rise to a measurable electric potential with changes in temperature. . Thermoplastic Resin ... A resin which can be repeatedly softened on heating and will reharden on cooling. Thermosetting Resin ... A resin capable of being softened and formed on application of heat, which will subsequently permanently harden. Time Quenching ... Interrupted quenching in which the duration of holding in the quenching medium is controlled. Tolerance ... Permissible variation from a standard or set dimension. . Toughness . . . Ability of a metal to absorb energy without failure. May be expressed as the total area under the stress-strain curve. Tukon Hardness Testing ... A method of determining microhardness by using a Knopp diamond indentor or Vickers square base pyramid indentor. Ultrasonic Inspection ... A non-destructive testing method of locating internal dcfects in a part by sending ultrasonic impulses (inaudible high-frequency sound waves of 0.5 to 11 megacycles) into the part and measuring the time required for these impulses to penetrate the ma- terial, be reflected from the opposite side or from the defect and re- turn to the sending point. Vacuum Melting ... Melting in a vacuum to prevent contamination due to air, as well as to remove gases already dissolved in the metal; the solidification may also be carried out in vacuum or at low pressure. Vent ... A small opening or passage in a mold or core to facilitate the escape of gases when the mold is poured. 648 GLOSSARY Vickers Hardness Testing ... The determination of the degree of hard- ness of a metal by measuring the ratio of the imposed load to the area of the resulting indentation. Wood Flour ... A pulverized wood product to furnish a reducing at- mosphere in the mold, help overcome sand expansion, increase flow- ability, improve casting finish, and provide easier shakeout. Work Hardening ... Hardness developed in metal resulting from mechanical working, particularly cold working. X-Ray Inspection ... See Radiography. Yield Point ... The load per unit of original cross section at which a marked increase in deformation occurs without increase in load. Yield Strength ... The stress at which a material exhibits a specified limit of permanent strain; often the maximum unit load with a 0.2 percent deviation from a proportional stress-strain relation. Zircon Sand ... A very refractory mineral, composed chiefly of zir- conium silicate of extreme fineness, having low thermal expansion and high thermal conductivity. . ENGINEERING TABLES 649 APPENDIX ENGINEERING TABLES Page Compositions of Standard Wrought Steels 650 . Compositions of Standard Wrought Stainless and Heat Resisting Steels 654 Alloy Casting Institute Standard Compositions for Heat and Corrosion Resistant Castings 656 Summary of Steel Casting Specifications 658 650 ENGINEERING TABLES CHEMICAL COMPOSITIONS OF STANDARD WROUGHT STEELS CARBON STEELS S.A.E. & AISI Number Carbon Range Manganese Range S.A.E. & AISI Number Carbon Range Manganese Range 1010 1008 1012 1015 1016 1019 1020 1022 1023 1024 1025 1027 1030 1035 .08/.13 .10 Max. .10/.15 .13/.18 .13/.18 .15/.20 .18/.23 .18/.23 .207.25 .19/.25 .22/.28 .22/.29 .28/.34 .327.38 .307.60 .25/.50 .307.60 .307.60 .607.90 .70/1.00 .30/.60 .70/1.00 .307.60 1.35/1.65 .30/.60 1.20/1.50 .607.90 .607.90 1040 1036 1041 1043 1045 1052 1055 1060 1070 1078 1080 1085 1086 1095 .37/.44 .30/.37 .36/.44 .40/.47 .437.50 .477.55 .507.60 .557.65 .65/.75 .727.85 .75/.88 .80/.93 .80/.93 .90/1.03 .607.90 1.20/1.50 1.35/1.65 .70/1.00 .607.90 1.20/1.50 .60/.90 .607.90 .60f1.90 .307.60 .607.90 .70/1.00 .307.50 .30/.50 Phosphorus is 0.040 percent maximum and sulfur is 0.050 percent maximum. MANGANESE STEELS* S.A.E. & AISI Number Carbon Range Manganese Range 1330 1335 1340 1345 .28/.33 .22/.38 .38/.43 .43/.48 1.60/1.90 1.60/1.90 1.60/1.90 1.60/1.90 NICKEL STEELS* S.A.E. & AISI Number Carbon Range Manganese Range Nickel Range 2330 2517 .28/.33 .15/.20 .607.80 .45/.60 3.25/3.75 4.75/5.25 NITRIDING STEEL Carbon Range Manganese Range Silicon Range Aluminum Range Chromium Range Molybdenum Range .38/.43 .50/.70 .207.40 .95/1.30 1.40/1.80 .30/.40 * Phosphorus and sulfur are 0.040 percent maximum and silicon is 0.20/0.35. ENGINEERING TABLES 651 NICKEL-CHROMIUM STEELS S.A.E. & AISI Number Carbon Range Manganese Range Nickel Range Chromium Range 3140 3310 .38/.43 .08/.13 .707.90 .45/.60 1.10/1.40 3.25/3.75 .55/.75 1.40/1.75 Phosphorus and sulfur are 0.040 percent maximum for 3140, and 0.025 percent maximum for 3310. Silicon is 0.20/0.35. MOLYBDENUM STEELS S.A.E. & AISI Number Carbon Range Manganese Range Molybdenum Range Sulfur Max. 4012 4024 4028 4037 4042 4047 4063 .09/.14 .237.25 .25/.30 .35/.40 .407.45 .45/.50 .607.67 .75/1.00 .707.90 .707.90 .707.90 .707.90 .707.90 .75/1.00 .15/.25 .20/.30 .207.30 .20/.30 .20/.30 .207.30 .20/.30 .040 .035/.050 .035/.050 .040 .040 .040 .040 Phosphorus is 0.040 percent maximum and silicon is 0.20/0.35. CHROMIUM STEELS* S.A.E. & AISI Number Carbon Range Manganese Range Chromium Range 5015 5046 5120 5130 5140 5147 5150 5160 .12/.17 .437.50 .171.22 .28/.33 .38/.43 .45/.52 .487.53 .557.65 .307.50 .75/1.00 .707.90 .707.90 .70/.90 .70!.95 .707.90 .75/1.00 .307.50 .20/.35 .707.90 .80/1.10 .70/.90 .85/1.15 .707.90 .707.90 CHROMIUM-VANADIUM STEELS* S.A.E. & AISI Number Carbon Range Manganese Range Chromium Range Vanadi Range 6118 6120 6150 .167.21 .171.22 .48/.53 .50/.70 .707.90 .70/.90 .50/.70 .70/.90 .80/1.10 .107.15 .10 Min. .15 Min. * Phosphorus and sulfur are 0.040 percent maximum and silicon is 0.20/0.35. 652 ENGINEERING TABLES CHROMIUM-MOLYDENUM STEELS* * S.A.E. & AISI Number Carbon Range Manganese Range Molybdenum Range 4118 4130 4137 4140 4145 4150 .18/.23 .28/.33 .35/.40 .387.43 .43/.48 .48/.53 .707.90 .40/.60 .707.90 .75/1.00 .75/1.00 .75/1.00 .08/.15 .15/.25 .15/.25 .15/.25 .15/.25 .15/.25 NICKEL-CHROMIUM-MOLYBDENUM STEELS* S.A.E. & AISI Number Carbon Range Manganese Range Chromium Molybdenum Range Range 4320 4340 4718 4720 8115 8615 8620 8625 8630 8640 8645 8720 8735 8740 8822 9840 .177.22 .38/.43 .16/.21 .17/.22 .13/.18 .13/.18 .18/.23 .23/.28 .28/.33 .38/.43 .43/.48 .18/.23 .33/.38 .38/.43 .20/.25 .38/.43 .45/.65 .60/.80 .707.90 .50/.70 .70/.90 .707.90 .70/.90 .707.90 .70/.90 .75/1.00 .75/1.00 .70/.90 .75/1.00 .75/1.00 .75/1.00 .707.90 .20/.30 .20/.30 .30/.40 .15/.25 .08/.15 .15/.25 .15/.25 .15/.25 .15/.25 .15/.25 .15/.25 .20/.30 .20/.30 .20/.30 .30/.40 .207.30 NICKEL-MOLYBDENUM STEELS* S.A.E. & AISI Number Carbon Range Manganese Range Molybdenum Range 4615 4620 .13/.18 .177.22 .13/.18 .18/.23 .45/.65 .45/.65 .40/.60 .50/.70 Chromium Range .40/.60 .80/1.10 .80/1.10 .80/1.10 .80/1.10 .80/1.10 Nickel Range 1.65/2.00 1.65/2.00 .90/1.20 .90/1.20 .20/.40 .40/.70 .40/.70 .40/.70 .407.70 .407.70 .40/.70 .407.70 .407.70 .40/.70 .40/.70 .85/1.15 .40/.60 .707.90 .35/.55 .35/.55 .30/.50 .40/.60 .40/.60 .40/.60 .40/.60 .40/.60 .40/.60 .40/.60 .40/.60 .40/.60 .40/.60 .707.90 Nickel Range 1.65/2.00 1.65/2.00 3.25/3.75 3.25/3.75 .207.30 .20/.30 .207.30 .207.30 4815 4820 * Phosphorus and sulfur are 0.040 percent maximum and silicon is 0.20/0.35. ENGINEERING TABLES 653 SILICON STEELS S.A.E. & AISI Number Carbon Range Manganese Range Silicon Range Chromium Range 9255 9260 9262 .50/.60 .55/.65 .557.65 .707.95 .70/1.00 .75/1.00 1.80/2.20 1.80/2.20 1.80/2.20 .25/.40 Phosphorus and sulfur are 0.040 percent maximum. BORON STEELS These steels can be expected to have 0.0005 percent minimum boron content. S.A.E. & AISI Number Carbon Range Manganese Range Nickel Range Chromium Range Molybdenum Range 50B40 50B46 50B60 51B60 81B45 86B45 94B15 94B40 .38/.43 .437.50 .55/.65 .55/.65 .437.48 .437.48 .13/.18 .38/.43 .75/1.00 .75/1.00 .75/1.00 .75/1.00 .75/1.00 .75/1.00 .75/1.00 .75/1.00 .40/.60 .20/.35 .40/.60 .707.90 .33/.55 .40/.60 .307.50 .30/.50 .20/.40 .40/.70 .307.60 .30/.60 .08/.15 .15/.25 .08/.15 .08/.15 Phosphorus and sulfur are 0.040 percent maximum and silicon is 0.20/0.35. FREE CUTTING STEELS S.A.E. & AISI Number Carbon Range Chemical Composition Limits, Percent Manganese Phosphorus Range Range Sulfur Range 1108 1111 1112 1113 1115 1116 1117 1118 1120 1132 1137 1139 1141 1144 1145 1151 .08/.13 .13 Max. .13 Max. .13 Max. .13/.18 .147.20 .147.20 .147.20 .18/.23 .27/.34 .32/.39 .35/.43 .37/.45 .407.48 .42/.49 .48/.55 .507.80 .607.90 .70/1.00 .70/1.00 .607.90 1.10/1.40 1.00/1.30 1.30/1.60 .70/1.00 1.35/1.65 1.35/1.65 1.35/1.65 1.35/1.65 1.35/1.65 .70/1.00 .70/1.00 .040 Max. .07/.12 .07/.12 .07/.12 .040 Max. .040 Max. .040 Max. .040 Max. .040 Max. .040 Max. .040 Max. .040 Max. .040 Max. .040 Max. .040 Max. .040 Max. .08/.13 .08/.15 .16/.23 .247.33 .08/.13 .16/.23 .08/.13 .08/.13 .08/.13 .08/.13 .08/.13 .127.20 .08/.13 .247.33 .04/.07 .07/.13 654 ENGINEERING TABLES STANDARD WROUGHT TYPES OF STAINLESS AND HEAT RESISTING STEELS Type Manganese Phosphorus Sulfur Max. Max. Max. Silicon Max. Chromium Range Nickel Range Other Elements Number Carbon Nitrogen .25 Max. Nitrogen .25 Max. 201 202 301 302 302B 303 0.15 Max. 0.15 Max. 0.15 Max. 0.15 Max. 0.15 Max. 0.15 Max. 5.50/7.50 7.50/10.00 2.00 2.00 2.00 2.00 .060 .060 .045 .045 .045 .20 .030 .030 .030 .030 .030 .15 Min. 1.00 1.00 1.00 1.00 2.00/3.00 1.00 16.00/18.00 17.00/19.00 16.00/18.00 17.00/19.00 17.00/19.00 17.00/19.00 3.50/5.50 4.00/6.00 6.00/8.00 8.00/10.00 8.00/10.00 8.00/10.00 Molybdenum .60* Zirconium .60* Selenium .15 Min. 303Se 304 304L 305 308 309 3095 310 3105 314 316 .15 Max. .08 Max. .03 Max. .12 Max. .08 Max. .20 Max. .08 Max. .25 Max. .08 Max. .25 Max. .08 Max. 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 .20 .045 .045 .045 .045 .045 .045 .045 .045 .045 .045 .06 .030 .030 .030 .030 .030 .030 .030 .030 .030 .030 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.50 1.50 1.50/3.00 1.00 17.00/19.00 18.00/20.00 18.00/20.00 17.00/19.00 19.00/21.00 22.00/24.00 22.00/24.00 24.00/26.00 24.00/26.00 23.00/26.00 16.00/18.00 8.00/10.00 8.00/12.00 8.00/12.00 10.00/13.00 10.00/12.00 12.00/15.00 12.00/15.00 19.00/22.00 19.00/22.00 19.00/22.00 10.00/14.00 316L .03 Max. 2.00 .045 .030 1.00 16.00/18.00 10.00/14.00 317 .08 Max. 2.00 .045 .030 1.00 18.00/20.00 11.00/15.00 Molybdenum 2.00/3.00 Molybdenum 2.00/3.00 Molybdenum 3.00/4.00 Titanium 5xC Min. Cb-Ta: 10xC Min. Cb-Ta: 10xC Min. Ta: .10 Max. 321 .08 Max. 2.00 .045 .030 1.00 17.00/19.00 9.00/12.00 347 348 .08 Max. .08 Max. 2.00 2.00 .045 .045 .030 .030 1.00 1.00 17.00/19.00 17.00/19.00 9.00/13.00 9.00/13.00 ENGINEERING TABLES 655 STAINLESS AND HEAT RESISTING STEELS (Continued) Type Number Manganese Phosphorus Sulfur Max. Max. Max. Silicon Max. Chromium Range Nickel Range Other Elements Carbon 403 405 .15 Max. .08 Max. 1.00 1.00 .040 .040 .030 .030 .50 1.00 11.50/13.00 11.50/14.50 Aluminum .107.30 410 414 416 .15 Max. .15 Max. .15 Max. 1.00 1.00 1.25 .040 .040 .06 .030 .030 .15 Min. 1.00 1.00 1.00 11.50/13.50 11.50/13.50 12.03/14.00 Mo:.60* Max. Zr: .60* Max. Selenium .15 Min. 416 Se 420 430 430F .15 Max. Over .15 .12 Max. .12 Max. 1.25 1.00 1.00 1.25 .06 .040 .040 .06 .06 .030 .030 .15 Min. 1.00 1.00 1.00 1.00 12.00/ 14.00 12.00/14.00 14.00/18.00 14.00/18.00 Mo: .60* Max. Zr: .60* Max. Selenium .15 Min. 430F Se 431 440A .12 Max. .20 Max. .60/.75 1.25 1.00 1.00 .06 .040 .040 .06 .030 .030 1.00 1.00 1.00 14.00/18.00 15.00/17.00 16.00/18.00 1.25/2.50 440B .75/.95 1.00 .040 .030 1.00 16.00/18.00 440C .95/1.20 1.00 .040 .030 1.09 16.00/18.00 Molybdenum .75 Max. Molybdenum .75 Max. Molybdenrm .75 Max. Nitrogen .25 Max. Molybdenum .407.65 Molybdenum .407.65 446 501 .20 Max. Over 10 1.50 1.00 .040 .040 .030 .030 1.00 1.00 23.00/27.00 4.00/6.07 532 .10 Max. 1.00 .040 .030 1,00 4.00/6.00 * At producer's option; reported only when intentionally added. 656 ENGINEERING TABLES ALLOY CASTING INSTITUTE STANDARD DESIGNATIONS AND CHEMICAL COMPOSITION RANGES FOR HEAT AND CORROSION RESISTANT CASTINGS COMPOSITION-PERCENT (Balance Fe) Cast Alloy Designation Wrought Alloy Type (See Note A) Mn Max. Si Max. С Cr Ni Other Elements CA-15 CA-40 CB-30 CC-50 CD-4M Cu 410 420 431 Mo 0.5 Max.t Mo 0.5 Max.* 0.15 Max. 0.20-0.40 0.30 Max. 0.50 Max. 0.040 Max. 1.00 1.00 1.00 1.00 1.00 1.50 1.50 1.00 1.00 1.00 11.5-14 11.5-14 18-22 26-30 25-27 1 Max. 1 Max. 2 Max. 4 Max. 4.75-6.00 446 Mo 1.75-2.25, Cu 2.75-3.25 Mo 1.5 Max., Se 0.20-0.35 Mo 3.0-4.0 CE-30 CF-3 CF-8 CF-20 304L 304 302 0.30 Max. 0.03 Max. 0.08 Max. 0.20 Max. 1.50 1.50 1.50 1.50 2.00 2.00 2.00 2.00 26-30 17-21 18-21 18-21 8-11 8-12 8-11 8-11 CF-3M CF-8M CF-12M CF-8C 316L 316 316 347 0.03 Max. 0.08 Max. 0.12 Max. 0.08 Max. 1.50 1.50 1.50 1.50 1.50 1.50 1.50 2.00 17-21 18-21 18-21 18-21 9-13 9-12 9-12 9-12 Mo 2.0-3.0 Mo 2.0-3.0 Mo 2.0-3.0 Cb 8xC Min., 1.0 Max., or Cb-Ta 10xC Min., 1.35 Max. 1CF-16F CG-8M CH-20 CK-20 CN-7M 303 317 309 310 0.16 Max. 0.08 Max. 0.20 Max. 0.20 Max. 0.07 Max. 1.50 1.50 1.50 1.50 1.50 2.00 1.50 2.00 2.00 18-21 18-21 22-26 23-27 18-22 9-12 9-13 12-15 19-22 21-31 * Mo-Cu* ENGINEERING TABLES 657 ALLOY CASTING INSTITUTE STANDARD DESIGNATIONS AND CHEMICAL COMPOSITION RANGES FOR HEAT AND CORROSION RESISTANT CASTINGS—(Continued) Cast Alloy Designation COMPOSITION-PERCENT (Balance Fe) Wrought Alloy Type Mn Max. Si Max. (See Note A) С Cr Ni Other Elements 302B 309 HF HH HI HK 0.20-0.40 0.20-0.50 0.20-0.50 0.20-0.60 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 19-23 24-28 26-30 24-28 9-12 11-14 14-18 18-22 Mo 0.5 Max.t Mo 0.5 Max.† N 0.2 Max. Mo 0.5 Max.f Mo 0.5 Max.f 310 HL HN HT HU 0.20-0.60 0.20-0.50 0.35-0.75 0.35-0.75 2.00 2.00 2.00 2.00 2.00 2.00 2.50 2.50 28-32 19-23 13-17 17-21 18-22 23-27 33-37 37-41 Mo 0.5 Max. Mo 0.5 Max.f Mo 0.5 Max. Mo 0.5 Max.t 330 HA HC HD HE 446 327 0.20 Max. 0.50 Max. 0.50 Max. 0.20-0.50 0.35-0.65 1.00 1.50 2.00 1.00 2.00 2.00 2.00 8-10 26-30 26-30 26-30 4 Max. 4-7 8-11 Mo 0.90-1.20 Mo 0.5 Max.ft Mo 0.5 Max. Mo 0.5 Max. HW HX 0.35-0.75 0.35-0.75 2.00 2.00 2.50 2.50 10-14 15-19 58-62 64-68 Mo 0.5 Max. Mo 0.5 Max. Phosphorus and sulfur are 0.04 percent maximum except where footnoted otherwise. 1 Phosphorus is 0.17 percent maximum. +Molybdenum not intentionally added. *There are several proprietary alloy compositions falling within the stated chromium and nickel ranges, and containing varying amounts of silicon, molybdenum and copper. NOTE A-Wrought alloy type numbers are listed for the determination of corresponding wrought and cast grades, as the chemical composition ranges are not the same. See previous table for compositions of wrought alloy types. 658 SPECIFICATIONS CARBON AND LOW ALLOY CAST STEELS A 27-58 Mild to Medium-Strength Carbon-Steel Castings for General A.S.T.M. A 356-58 T Heavy Walled Carbon and Low Alloy Steel Castings for Steam Application. Turbines (Tentative). A 148-58 High-Strength Steel Castings for Structural Purposes. A.S.T.M. 389-59 T Alloy Steel Castings Specially Heat Treated for Pressure Containing Parts Suitable for High Temperature Service. A 216-59 T Carbon Steel Castings Suitable for Fusion Welding for High S.A.E. Temperature Service (Tentative). 1956 Automotive Steel Castings. A.A.R. M 201-53 Steel Castings. A 217-59 T Alloy Steel Castings for Pressure Containing Parts Suitable for A.R.E.A. Specifications for Steel Railway Bridges: Steel Castings. High Temperature Service. A.B.S. Am. Bur. Shipping. Steel Castings-1957 Rules Edition Machinery and Hull A 352-59 T Ferritic Steel Castings for Pressure Containing Parts Suitable for Castings. Low Temperature Service. Lloyd's Register of Shipping 1957 - Steel Castings. CHEMICAL COMPOSITION %-MAXIMUM Red. Other Tests: Specification Class of Bend, Impact Treatment p.s.i. % Area % Hardnesst с Mn Si PSS Cu Ni C: Other Elements E 25 (2) 35 (2) .80 .80 .30 .30. .20 (4) .20 (4) Mo .20 Mo .20 75 (2) 60 (2) 1.00 75 (2) .60 (2) 25 (2) 30 (2) 80 .80 .30 .30 .05 .05 .05 .05 .05 .05 .05 .05 .05 20 (4) .20 (4) .06 .06 06 .06 .06 06 .06 06 .06 Mo .20 Mo 20 30,000 30,000 30,000 35.000 (1) 36,000 40,000 22 24 20 24 22 22 .70 (2) .80 .30 .SO .30 (2) 35 (2) 25 (2) 20 (4) 20 (4) 70 (2) 1.20 Mo .20 Mo 20 និន៩៩៩ ៩៩៩៩៩T 1 .80 38 38 381|1llllll 35 NT or QT 80,000 40,000 NT or QT 80,000 50,000 NT or QT 90,000 60,000 NT or QT| 105,000 85,000 or QT 120.000 95,000 or QT 150,000 125,000 NT or QT 175,000 145,000 18 22 20 17 14 9 6 8888888 881111|1|||||||| 35 .OS .05 .05 .05 .05 .OS .OS .06 .06 .06 .06 .06 .06 .06 liiilii IIIIIII IIII!!! Bend-Degrees 25 (5) 30 (5) 70 (5) 1.00 (5) 05 .06 .05.06 .60 60 .50 (11) .50 (11) .50 (11) .50 (11) 25 (11) 25 (11) Mo+W 25 (11) Mo+W 25 (11) 35 (6) ASTM A 217-59T WCI WC4 WC5 WC6 WC9 A or NT A or NT A or NT A or NT A or NT A or NT A or NT 65,000 70,000 70,000 70,000 70.000 90,000 90,000 35,000 40,000 40,000 40,000 40,000 60,000 60,000 24 20 20 20 20 18 18 .25 20 .20 .20 .18 .20 .20 50-.80 50-.80 40-.70 .50-.80 .40-.70 .40-70 .35-.65 .05 05 .05 .05 .05 .05 05 .06 .06 .06 06 .06 .06 .06 60 60 60 60 .60 .75 1.00 .50 (6) .50 (6) 50 (6) .50 (6) .50 (6) 50 (6) 50 (6) .50 (6) .70-1.10 .60-1.00 .50 (6) 50 (6) .SO (6) .50 (6) Mo .45-65 SO .80 Mo .45-65 .50- .90 Mo .90-1.20 1.00 1.50 Mo .45- .65 2.00 2.75 Mo .90-1.20 4.00- 6.50 Mo .45 .65 8.00-10.00 Mo .90-1.20 C5 C12 A.S.T.M. A.S.T.M. A.S.T.M. A.S.T.M. A.S.T.M. SPECIFICATION & HEAT TREATMENT MECHANICAL PROPERTIES-MINIMUM Tensile Yield Elong. Strength Point Heat in 2" p.s.i. ASTM A 27-58 A or N or NT or QT A or N NT or QT N-1 N-2 N-3 U-60-30 60-30 65-30 65-35 70-36 70-40 ΖΖΖΖΖ | ZZ A or N or NT or QT A or NT or QT or QT A or or QT A or NT or QT 60,000 60,000 65,000 65,000 70.000 70,000 ASTM A 148-58 80-40 A 80-50 90-60 105-85 120-95 150-125 A or 175-145 A or N ASTM A 216-59T WCA WCB A or NT A or NT 60,000 70,000 30,000 36,000 24 22 35 35 1901 ASTM A 352-59T LCB LCI LC2 Nor NT (or QT) N or NT (or QT) N or NT (or QT) N or NT (or QT) 65,000 65,000 65,000 65,000 35,000 35,000 40,000 40,000 24 24 24 24 35 35 Impact-Ft.-Lbs. 15 (7) 15 (7) 15 (7) 15 (7) .30 .25 25 .15 1.00 .50-80 .50-.80 .50-.80 05 .05 .05 .05 .06 .06 .05 .05 60 60 60 .60 III Mo .45.65 2.00-3.00 3.00-.400 ודוד 11 ASTM A 356-58T (13) .70 .70 (2) 2 3 NT NT NT NT NT 1111 5 6 3333333333 ÖvoaWN 70,000 36,000 65,000 35,000 80,000 50,000 90.000 60,000 70.000 40.000 70,000 45,000 70,000 40,000 80,000 50,000 95,000 60,000 85,000 55,000 20 22 18 16 22 22 22 18 15 20 Illlllllll .35 (2) 25 (2) 25 20 25 (2) .20 20 25 20 20 .05 .05 .05 .05 05 .05 .OS .05 .05 .05 .50-.80 50-.80 70 (2) .50-80 .50-.80 .50-.80 .50-.80 .50-80 .05 .05 .OS .05 05 .05 .05 .05 .05 .05 .60 .60 .60 60 .60 60 .60 .60 60 60 |||||||lll Illlllllll V (8) Mo .40-60+ V (9) Mo .90-1.20 Mo .90-1.20 + V .15-25 40 70 Mo 40-60 1.00- 1.50 Mo 40:60 1.00 1.50 Mo .40-.60+ V 15.25 1.00 1.50 Mo .90-1.20 1.00 1.50 Mo .90-1.20 + V .15.25 2.00- 2.75 Mo .90-1.20 9 10 NT NT NT 35 35 SPECIFICATIONS 659 A 389-59T C23 70,000 40,000 18 35 20 .30-.80 .05 06 60 C24 1850 N, 1250 T (Min) Ihr/in 1850 N. 1250 T (Min) 12 hr 80,000 50,000 1.00- 1.50 Mo 45-65 V 15- 25 80- 1 20 Mo 90-120 V 15. .25 15 35 20 30-.80 05 06 60 BHN .50 (3) .50 (3) 12-22 30 (2) 40-50 40-50 .25 (3) 50-90 70 (2) 50-90 .50-90 60 60 20-60 20-60 2570 W.10 SAE Automotive 0022 0030 0050 0050 080 090 0105 0120 0150* 0175 10 A or N or NT A or N or NT or QT Nor NT QT A or N or NT or QT NT or NOT NOT NOT NQT NOT 65,000 85,000 100,000 80,000 90,000 105,000 120,000 150,000 175,000 35,000 45,000 70,000 40,000 60,000 85,000 100,000 125,000 145,000 1862887496 131 170 207 163 187 217 248 311 363 20 05 05 05 05 OS 05 05 05 05 .05 | | | | | | ఈరో 06 06 06 06 06 06 .06 .06 .06 .06 35 30 דודודוד 111111 12 "Illlllllllllll AAR M 201-53 Unannealed A or N A or N NT or QT QT QT 60,000 30,000 60,000 30,000 70,000 38.000 90,000 60,000 105,000 85,000 120,000 $100,000 22 26 24 22 17 14 85 .85 85 IIITT (10) .35 OS 05 OS .05 OS .OS Basic 05 Acid .06 II!!!! III!!! III!!! 35 30 !! A.B.S. 1 12 Hull A or NT A or NT A or NT 60,000 70,000 60,000 30,000 36,000 30,000 24 22 24 35 30 35 Bend-Degrees 120 90 120 111 Till II!! Tiili Lloyds A 20 120 - 62,720 to 78,400 EXPLANATION OF SYMBOLS ( ) Permitted only if agreed upon by purchaser. # Heat Treatment: A--Full Annealed; N-Normalized; T-Tempered, Q-Liquid Quenched. Hardenability requirements when specified. † Hardness tests when specified in contract or order. [ ] Figures in brackets are expected values only. No test required unless specified in order. (1) II full anneal specified, 33,000 psi yield required. (2) For each reduction of .01%C below the maximum specified, an increase of .04%Mn above the maximum specified will be permitted to a maximum of 1.0%Mn. (1.40 max- imum for grade 70-40, A27.) (3) Total maximum content of undesirable elements is 1.0%. For each .10% below the specified maximum alloy content of 1.0%, an increase of .02% in the Cr plus Mo content and .06% in the Ni and Cu contents above the specified maximum will be permitted. (4) For each reduction of 0.01% carbon under the maximum specified, an increase of 0.04% chromium above the maximum specified will be permitted, but in no case will the chromium exceed 0.40%. No change is recommended on the other chemistry or the carbon-manganese relationship. (5) Total maximum content of undesirable elements is 1.0%. (6) Restrictions on unspecified alloy elements: W 10% for all grades; total maximum con- tent of unspecified elements 1.0% for all grades except WC4 and WC5 where total maximum is 60% (7) Charpy keyhole notch impact test required at temperature specified by customer. Test temperatures and grades are: -50°F, LCB; -75°F, LCI; -100°F, LC2, -150°F, LC3. (8) Vanadium 0.01% minimum may be specified, or up to 0.05% permitted. (9) Vanadium 0.05% minimum may be specified. (10) Hardenability requirement of Rc=40 maximum at 10/16". (11) For each reduction of .01% below the specified maximum C content, an increase of .04%Mn above the specified maximum will be permitted up to a maximum of 1.1%. (13) The use of aluminum is prohibited in the making of all steels except grade 1. MISCELLANEOUS REQUIREMENTS Radiographic Inspection-ASTM: A27,A 148, A216, A217, A352; and SAE required whe: specified. Magnetic Particle Testing-ASTM: A27, A148, A216, A217, A352; and SAE required when specified. ABS required for stern trames. Hydrostatic Tests--ASTM: A216, A217, A352 required for all castings; A216 required when specified. Destructive Tests---ASTM: A216, A217, A352 required when specified. Welding-Major defects over 20% of wall thickness repaired with consent of purchaser by welding with approved process: ASTM: A27, A148, A216, A217, A352; SAE; AAR M201, 660 SPECIFICATIONS LOW ALLOY CAST STEELS (Government Specifications) FEDERAL QQ-S-681c (8-18-1960) Steel, Castings. MILITARY MIL-S-15083 (Ships) April 1950 Steel; Castings. Superseding 1951 (Ships). MILITARY MIL-S-870B (Ships) September 1951 Steel Castings, Alloy, Molybdenum Alloy. (Amended 7-7-53). MILITARY MIL-S-15464B (Ships) December 1950 Stool. Alloy. Chromium-Molybdenum; Castings. Revised June 1953. MECHANICAL PROPERTIES-MINIMUM CHEMICAL COMPOSITION %-MAXIMUM Tensile Yield Strength Point p.s.i. p.s.i. Elong. Red. in 2" of % Area % Other Tests: Bend, Impact Hardness с Mn P S si Cu Ni Cr Other Elements Bend--Degrees .30 (1) .30 (1) .70 (1) 1.00 .80 0.30 (2) 0.50 (2) .50 (2) .50 (2) .35 (2) .35 (2) Mo-.20 (2) (3) Mo-.20 (2) (3) 0.90 0.90 A or N or NT or QT 65,000 35,000 70-36 A or N or NT or QT 70,000 36,000 80-40 A or N or NT or QT 80,000 40,000 0050A A or N or NT or QT 85,000 45,000 0050B QT(4) 100,000 70,000 80-50 A or N or NT or QT 80,000 50,000 90-60 A or N or NT or QT 90,000 60,000 105-85 A or N or NT or QT| 105,000 85,000 120-95 A or N or NT or QT 126,000 95,000 150-125A or or NT or QT 150,000 125,000 175-145 A or N NT or QT| 175,000 145,000 24 22 17 16 10 22 20 17 14 9 6 35 30 25 24 15 35 40 35 30 22 12 ខុខុឌខុទុ ! | | | | | .05 .05 .05 .05 .05 .05 .05 .05 .05 .05 .05 .06 .06 .06 .06 .06 .06 .06 .06 .06 .06 .06 ខុទុឧឧឧ | \ \ \ \ | lllllllll IIlllllll ༄༅ | | | | | | | | | I!!! .06 .30 (1) .30 (1) .35 .70 (1) .60 (1) .20-60 .30 (6) .50 (6) .20 (6) Mo .20 (6) MILITARY CW MIL-S-15083 B A (SHIPS) A-70 A-80 A-90 A-100 ooooo QT QT QT QT or QT 55,000 60,000 70,000 80,000 90,000 100,000 27,000 30,000 35,000 40,000 55,000 60,000 15 24 22 18 18 15 25 35 30 30 30 30 Illll 111 881111 .07 .05 .05 .05 .05 .05 I!!! A 35,000 20 30 120 ($) .25 (1) .50-.75 .05 .05 .20-.60 .30 (6) 1.00 (6) .20 (8,?) Mo .40-.60 40,000 35 .20 .50-.80 .05 .05 .20-.60 .50 (8) .50 (6) 1.00 1.50 Mo .40-.60 CARBON AND (Amended 11-1-1950). SPECIFICATION & HEAT TREATMENT Specification Class Heat Treatment FEDERAL QQ-S-681c 65-35 MILITARY MIL-S-870B (SHIPS) NT or ANT 65,000 NT or ANT 70,000 MILITARY 1 MIL-S-15464B (SHIPS) NT or ANT NT or ANT 70.000 70,000 40,000 40,000 20 20 Ill .18 .18 .40-.70 .40-.70 .05 .05 .05 .06 .20-.60 .60 .50 (0) .50 (6) .50 (6) .50 (6) 2.00- 2.75 Mo .80-1.10 1.00 1.50 Mo .40-.60 +1.15.25 SPECIFICATIONS 199 EXPLANATION OF SYMBOLS IN ABOVE TABLE MISCELLANEOUS REQUIREMENTS (1) For each reduction of .01% C below the maximum specified, an increase of .04% Mo above the maximum specified will be permitted to a maximum of 1.0% Mn. (2) Total maximum content of residual elements is 1.0%. (3) Unless otherwise noted, the limits shown for Mo, Cu, Ni, and Cr are permissible residual elements and shall not be added, and shall not be reported in the ladle analysis, unless specified. (1) Casting section thicknesses should be 1 inch or less. (6) For each reduction of .01%C under the maximum specified, an increase of either .04%Mn or .04%Cr above the maximum specified will be permitted, but in no case shall the Mn content exceed 1.0% or the Cr content exceed .40%. (8) Residual maximum permitted and shall not be added. (7) For each .01%C under the maximum an increase of .04%Cr above 20% is permitted with maximum at.40%Cr. Radiographic Inspection MILITARY: MIL-S-870B, required for castings of listed services and other services when specified; MIL-S-15083 all castings for BUSHIPS only and tos other agencies when specified. MIL-S-15464B all castings; MIL-R-11471 (ORD), covers the procedure to be used in radiographic inspection of metals. Magnetic Particle Testing MILITARY: MIL-S-870B, required for castings of listed services and other services when specified; MIL-S-15083 all castings for BUSHIPS only and for other agencies when specified; MIL-S-15464B all castings; MIL-I-6868A inspection process general requirements. Welding-Major defects over 20% of wall thickness repaired with consent of purchaser by welding with approved process: FEDERAL QQ-S-681b; MILITARY: MIL-S-870B, MIL-S- 15083, MIL-S-15464B. Inspection-Military: MIL-C-6021B (ASG), inspection requirements for all metal airframe castings. Not required it reduction of area is 40% or higher. METHODS of TESTING Non-Destructive: ASTM E71-52 ASTM E109-57T ASTM E125-56T Industrial Radiographic Standards for Steel Castings • Reference standards consist of two sets of industrial radiographic negatives of detects occasionally found in carbon and alloy stoel castings which assist in classification of defects. Dry Powder Magnetic Particle Inspection. Reference Photographs for Magnetic Particle Indication on Ferrous Castings. Wet Magnetic Particle Inspection. Reference Radiographs for Steel Welds. Liquid Penetrant Inspection, Mechanical: ASTM A370-53T Mechanical Testing of Steel Products (Tentative) Procedures and definitions for the mechanical testing of wrought and cast steel products. Tension, bend, hardness, and impact tests are described. Fed. Test Method: STD-151 Metals; Test Methods of - Procedures and definitions for the mechani- cal testing of wrought and cast steel products. Tension, bend, hard- ness, and impact tests are described. MIL-STD-271 (SHIPS) Nondestructive Testing Requirements for Metals. Includes standards for radiography, magnetic particle test methods, liquid penetrant, ultrasonic, leak testing. MIL-1-6868A Inspection Process, Magnetic Particle. ASTM E138-58T ASTM E99-55T ASTM E 165-60T 662 SPECIFICATIONS HIGH ALLOY CAST STEELS ASTM A128-33 ASTM A296-60 Austenitic Manganese Steel Castings. Corrosion-Resistant Iron-Chromium and Iron-Chromium-Nickel Alloy Castings for General Application. Heat Resistant Iron-Chromium and Iron-Chromium-Nickel Alloy Castings for General Application. Ferritic and Austenitic Steel Castings for High Temp. Service (Tent.). ASTM A362-52T Iron-Chromium and Iron-Chromium-NickelAlloy Tubular Centrifugal Castings for General Applications (Tentative). ASTM B190-50 Chrom.-Nickel-Iron Alloy Castings (25-12 Class) for High-Temp. Servico. ASTM B207-50 Nickel-Chrom.-Iron Alloy Castings (35-15 Class) for High-Temp. Service. MILITARY MIL-S-16993A November 1952 Steel Castings (12 Percent Chromium) Superseding MIL-S-16993, February 1952. ASTM A297-60 ASTM A351-59T SPECIFICATION & HEAT TREATMENT MECHANICAL PROPERTIES-MINIMUM CHEMICAL COMPOSITION %-MAXIMUM Specification Class Heat Treatment Tensile Strength p.s.i. Yield Point p.s.i. Elong. in 2" % Red. of Area % Other Tosts: Bend, Impact Hardness с Mn P S Si Cu Ni Cr Other Elements ASTM A-128-33 Q - .10 .05 I Bend-Degrees 1.00-1.40 10.0(1) (150) - - BHN-241 max. .04 15 20-40 Mo -.50 Mo - .50 BHN-241 max. BHN-241 max. .04 .04 .04 10 Mo - 2.0 to 3.0 1.00 40-1.00 1.00 1.00 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 2.00 .04 1.50 .04 1.50 .04 1.00 .04 1.00 04 2.00 .04 2.00 .04 1.50 .04(4) 2.00 .04 2.00 .04 2.00 .04(2) 2.00 04 2.00 .04 1.50 .04 2.00 .04 2.00 .04 2.00 कल 1.00 1.00 2.00 4.00 8-11 8-12 9-13 8-11 9-12 9-12 9-12 8-11 9-13 10-13 12-15 19-22 11.5-14 11.5-14 18-21 26-30 26-30 17-21 17-21 18-21 18-21 18-21 18-21 18-21 18-21 20-23 22-26 23-27 .04 .04 .04 Cb(5) Mo - 2.00-3.00 Mo(2) and Se(3) IlIlll Mo - 3.0 - 4.0 .2008) Mo(8) ឧឧឧឧឧឧឧឱនឱបឪពុទះនឹងន់១ខុមុខខខ័ន III|||||||||||||||||||||||||||||||||| ಕಕ್ರಶಕ್ತಕ್ತಕ್ತಕ್ತಕ್ತಕ್ತಕ್ತಕ್ತಕಶಕ್ತಕ್ತಕ್ಕೆ ಶಕ್ತಿಶಕ್ತಕ್ತಕ್ತಕ್ತಕ್ಕೆ 04 .04 .04 .04 .04 .04 04 .04 .04 .04 .04 .04 .04 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.50 2.50 2.50 2.50 TITIIIllllllllllllllllllllllllllllllll 4.00 4-7 8-11 8-12 11-14 14-18 18-22 18-22 23-27 33-37 37-41 58-62 64-68 26-30 26-30 26-30 18-23 24-28 26-30 24-28 28-32 19-23 13-17 17-21 10-14 15-19 Mo(8) - .50 max. Mo(8) - .50 max. ..50 max. Mo(8) . .50 max. Mo(8) . .50 max. Mo(8) - .50 max. Mo(8) ..50 max. Mo(8) ..50 max. Mo(8) - .50 max. Mo(8) . .50 max. Mo(8) ..50 max. Mo(8) . .50 max. .50 max. .04 .04 Mo(8) - ASTM A296-60 (4) 18 18 NT or A NT or A N or A N or A CA-15 CA-40 CB-30 CC-50 CE-30 CF-3 CF-3M CF-8 CF-8C CF-8M CF-16F(2) CF-20 CG-8M CG-12 CH-20(3) CK-20 90,000 65,000 90,000 65,000 65,000 30,000 55,000 80,000 40,000 65,000 28,000 70,000 30,000 65,000 28,000 70,000 30,000 70,000 30,000 70,000 30,000 70,000 30,000 75,000 35,000 70,000 28,000 70,000(7) 30,000 65,000 28.000 30 35 30 30 25 30 25 35 30 30 ASTM A297-60 HC HD HE HF HH HI HK HL HN HT HU HW HX 55,000 75,000 85,000 70,000 75,000 75,000 75,000 65,000 63,000 65,000 65,000 60,000 60,000 35,000 40,000 35,000 35,000 35,000 35.000 35,000 25 15 \ TA → ០៩ ទីបី ០១ | 20-50 20-40 20-50 .20-50 20-60 20-60 20-.50 .35-.75 35-.75 35-75 .35-.75 1.00 1.50 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 ASTM A351-59T Mo -50 max. CA15 CFS CF8C CF8M CFIOMC CH20(9) CK20 CT35 CH8 222222222 90.000 70.000 70,000 70,000 70,000 70.000 65,000 65,000 65.000 65,000 28,000 30,000 30,000 30,000 30,000 28,000 28,000 28,000 18 35 30 30 20 30 30 15 30 00000000 IIIIIllll 1.00 1.50 1.50 1.50 1.50 1.50 1.50 2.00 1.50 .04 .04 .04 .04 .04 .04 .04 .04 .04 .04 04 1.50 2.00 2.00 1.50 1.50 2.00 2.00 2.50 1.50 1.00 8-11 9-12 9-12 13-16 12-15 19-22 33-37 12-15 11.5-14 18-21 18-21 18-21 15-18 22-26 23-27 13-17 22-26 Cb(5) Mo-2.00-3.00 Mo - 1.75-2.25(10) .2009) .04 04 Mo -.50 max. SPECIFICATIONS €99 Sarne as A296 or A297 Same as A296 or A297 80,000(11) 9 III 20-.45 2.50 0.010 05 05 1.75 10-14(13) 23-28 N..20 = 80,000(11) 20,000(12) Till M Perm 1.70 Rupt. 5000 psi M Perm 1.05 Rupt. 8000 psi 20- 45 2.50 05 .05 1.75 10-14(13) 23-28 N..20 65,000 4 35(14). 7550-200 04 04 80-2.50 33-37(13) 14-17 Ni + Cr-48.0 min. NT -Ź 2 NT 90,000 90,000 65.000 (15) 18 65.000 18 30 30 J5 .15 1.00 1.00 05 .05 1.50 .50 .05 .05 1.00 .65-1.0 11.5-14.00 11.5-14.0 Mo-.50 Max. Mo - .50-.70 ASTM A362 527 ASTM B190-50 I ASTM B207-50 MILITARY MIL-S - 16993A MILITARY MIL-S- 867A 1 II 000 70,000 70.000 70.000 28.000 30,000 30.000 35 30 E 08(16) 08 08 1.50 1.50 1.50 05 OS 05 .05 OS 05 2.00 2.00 2.00 II 8-11 9-12 912 18-21 18-21 18-21 Cb+Ta-1.10 Max.(17) Mo -2.00-3.00 EXPLANATION OF SYMBOLS Heat treatment as agreed upon by manufacturer and purchaser (1)-Mn - Minimum percent. (2)---For free machining properties the composition of grade CF-16F may contain suitable combinations of Se, P, and Mo (grade CF-16F) or of S and Mo (grade CF-16Fa) as follows: Selenium, phosphorus, and molybdenum: Sulfur and molybdenum: Selenium, % 20 to .35 Sulfur, % 20 to .40 Phosphorus, max., % .17 Molybdenum, % 40 to .80 Molybdenum, max., % 1.50 (3)--For more severe general corrosive conditions, and when so specified, carbon content shall not exceed 0.10% Low carbon grade shall be designated as grade CH-10. (1) Chemical analysis not normally required for P, S, and Mo, but if present in amounts over those stated may be cause for rejection. (5) Grade CF-8C shall have a columbium content of not less than eight times the carbon content and not more than 1.00%- (6)---For grade CB-30 a copper content of 0.90 to 1.20% is optional. (8) Castings having a specified molybdenum range agreed upon by the manufacturer and the purchaser may also be furnished under these specifications. (9)-By agreement, the carbon content of grade CH20 may be restricted to 0.10% maximum, The grade designation shall be CHIO. (10)-Grade CFIOMC shall have a columbium content of not less than 10 times the carbon content but not over 1.20%. (11).- Properties after aging. (12)--Short-Time High-Temperature Properties at 1600°F £ 10°F. (13)--Commercial nickel usually carries a small amount of cobalt, and within the usual limits cobalt shall be counted as nickel. (14)..Within carbon range, manufacturer and purchaser shall agree upon nominal carbon content of not less than 0.45% nor more than 0.65%. Tolerance on such specified carbon content shall be 0.10% (15)-0.2% offset. (16)_11 chromnium is over 20 percent and nickel is over 10 percent, a maximum carbon content of 0.12 will be permitted. (17)--Columbium or columbium plus tantalurn shall be not less than 10 times the carbon content and not more than 1.10 percent (tantalum shall not exceed 0.4 times the sum of the columbium and tantalumn content) or titanium content shall be not less than 6 times the carbon content and not more than 0.75 percent. 664 INDEX A 1 Acid corrosion, 440 Agricultural castings, 94-96 Air-hardening steel, 484 Allowances casting finish, 218 draft, 219 machine finish, 218, 240, 241 mold parting, 239 pattern distortion, 218 patternmaker's shrinkage, 213-217 Alloy cast steels chromium, 444-446 chromium-nickel, 446-448 effect of mass, 273 machinability of, 518-521 machining of, 537, 538 variations in composition, 250, 251 Alloying elements effect on TTT curves, 484, 486 Aluminum in heat resistant steel, 418 Anisotropy (see Directionality) Annealing, 497-498 Applications for: austenitic manganese steel, 5, 46, 399 carbon steel, 338, 339 corrosion resistant castings, 453, 454 heat resistant castings, 424, 435, 436 Arc atmosphere, welding, 469 Atmospheric corrosion, 441-443 ustemp ing, 494, 496 Austenitic manganese steel applications, 5, 46, 399 composition, 391 heat treatment, 394, 395 machining, 396 magnetic properties, 396 mechanical properties, 395, 396 welding, 397 explosive hardening, 397, 398 B Backing sand, 562 Baking of cores, 572 Basic oxygen process, 555, 556 Benefits, economic, 18-24 Bessemer converter, history of, 605-607 Binders in core sand, 558, 559, 573 Blast cleaning, 583, 584 Bosses, 131, 132 Bridge castings, 96-98 С Carbon steel acid corrosion, 440 applications, 338, 339 effect of elements, 316-318 fatigue, 331-336 hardenability, 336-338 heat treatment of, 496-501 impact, 326-328 microstructure, 322-325 tensile properties, 318-322 variations in composition, 249, 250 welding practice, 475-478 Carburizing, 388-390 Cast-weld construction, 457-459 Castability, 28 Casting finish tolerances, 218 Centrifugal casting, history of, 610 Ceramic molding, 565 Chamotte, 558 Charpy test specimens, 402 Chromium in alloy steels, 444-449 distribution in alloy steel, 251 effect on corrosion, 444 effect on transition temperature, 404 in heat resistant steel, 416, 425, 426 Chromium steel acid corrosion of, 440 Cleaning, history of, 609, 610 Cloverleaf coufon, 266 Coefficient of expansion, 299, 300 Columbium in heat resistant steel, 418 Composite fabrication, 460, 462 Construction machinery castings, 44-48 Contraction, 213-217, 3C0-304 liquid, 301, 302 solid, 303, 304 solidification, 302, 303 total, 300, 301 Converters, history of, 605-607 Core boxes cost, 210-213 effect on tolerances, 231-233 life, 211 Core sands, 570-576 Cored openings, 137-139 dimensional variations, 239 Coremaking, 570-576 Corrosion, 437-454 acid, 440 atmospheric, 441-443 of carbon and low-alloy steel, 438-443 petroleum, 440 resistance, 439-441 Corrosion resistant steel machining of, 535, 536 Cost of castings, 101-110 of patterns, 191, 192 Crack propagation test, 329-331 Capacity, steel casting, 615 Carbon distribution in carbon steel, 249 effect on transition temperature, 404 effect on weldability, 456 in heat resistant steel, 418 i INDEX 665 Creep strength effect of composition, 416-418 of heat resistant steel, 420, 421, 432 Critical cooling speed, 484 Critical diameter, ideal, 491 Cutting speed charts (see Machinability curves) Electrical properties, 308, 309 Electrical resistivity, 308, 309 Electrical steel, corrosion of, 439 Electrodes, welding, 472 Elongation (see Tensile properties and Properties, mechanical) Endurance limit low alloy steels chromium-molybdenum (4135), 369 manganese (1330) cast steel, 353 nickel-chromium-molybdenum (8630), 362 vs. tensile strength, 347 Endurance of wrought steel, 16, 334, 335 Expansion, coefficient of, 299, 300 Explosive hardening, 397, 398 D F Fatigue properties of carbon steel, 331-336 variables, 333-336 effect of mass, 274-278 Fatigue testing, 332, 333 Fluorescent penetrant inspection, 598, 599 Forgings, sales of, 617 Freezing range, 304-306 Furnaces for heat treating, 496, 497 Damping capacity, 28 Degassing, vacuum, 556, 557 Density effect of carbon, 296 effect of mass, 295 effect of temperature, 296 molten steel, 297 solid steel, 295-297 Deoxidation effect on impact properties, 406, 407 Deposition of weld metal, 470, 471 Design of castings advantages, 114, 115 for dynamic loading, 150 effect on tolerances, 222-230 flexibility, 1-12, 29-35 fundamentals, 116-139 for new castings, 105, 106 safety factors, 180 for static loading, 149, 150 for ultimate section modulus, 139-149 vs. weldments, 182-190 Destructive testing, 174-180 Destructive tests, 594, 595 Deviations (see Distribution curves, Tolerances, and Dimensional variations) Differential hardening, 501, 590 Dimensional variations, 224-230, 234-237 of cored openings, 239 Directionality of wrought steel, 13-16, 33 Distortion allowances, pattern, 218 Distribution curves of casting dimensions, 230-233, 235-237 of casting weight, 237 of chemical content, 249-251 of mechanical properties, 256-258, 262 Draft, 219, 223, 224 Dynamic tests, 288-290 G Gates, removal of, 597-581 Gears, 11, 18, 91-94 Grain size effect on TTT curves, 486 Graphite in molding, 558 Gray iron castings corrosion rate, 439 sales, 617 Grinding, 581, 582 Groove preparation for welding, 465, 466 E Elastic constants, 292-295 Electric arc furnace acid electric practice, 550-553 basic electric practice, 551-553 cross section, 548 history, 607 melting, 548-553 Electric induction furnace CTOSS section, 554 history, 607 melting, 553-555 H Hardenability of carbon steel, 336-338 effect of tempering, 337, 338 effect of grain size, 491 of low-alloy steel copper-manganese-silicon, 374 chromium (5130) cast steel, 367 chromium-molybdenum (4100), 368 manganese (1330) cast steel, 353 manganese-molybdenum (8030), 354 manganese-molybdenum (8400), 355 manganese-molybdenum-boron (80B30), 357 Mn-Ni-Cr-Mo (9530), 370 molybdenum (4030) cast steel, 366 nickel (2300) cast steel, 358 nickel-chromium (3100), 359 nickel-chromium-molybdenum (8600), 361, 362 666 INDEX 1 nickel-chromium-molybdenum (4330), 365 nickel-molybdenum (4600), 360 Hardness effect on impact resistance, 262 effect on machinability, 506, 507 effect on wear resistance, 378-381 effect of tempering temperature, 485 of low-alloy steel, 343, 344 vs. tensile strength, 343 Heat resistant cast steels, 416-436 machining of, 535, 536 for service above 1150°F, 424-436 applications, 435, 436 composition, 425-430 heat treatment, 430 machining of, 433 mechanical properties, 430-432 welding, 434 for service to 1150°F, 416-424 applications, 424 composition, 416-418 creep properties, 418-422 heat treatment, 422 service temperatures, 422-424 tensile requirements, 418 Heat treating facilities, 587-590 history, 609 Heat treatment, 480-501 of austenitic manganese steel, 394, 395 of corrosion resistant steel, 449-451 effect on impact resistance, 403, 404 effect on wear resistance, 378-380 general principles, 480-485 heating rate, 482, 483 maximum temperature, 483 cooling, 483-485 tempering, 485 of heat resistant steel, 422, 430 of weldments, 472 High temperature creep data, 419-421, 432 High temperature service (see Heat resistant cast steels) Hindered contraction, 214.217, 231 Histograms (see Distribution curves) Hydrogen effect of in steel, 254, 255 effect of in weldments, 474 low-alloy steel vs. tensile strength, 345, 346 low temperature austenitic 18-8 Cr-Ni, 413 carbon (1030) cast steel, 406 copper-manganese-silicon, 412 chromium molybdenum (4130), 409 chromium nickel (3130), 409 manganese (1330), cast steel, 408 manganese-chromium-molybdenum, 411 manganese-molybdenum (8023, 8430), 410 manganese-nickel-chromium-molybdenum, 411 molybdenum (4030) cast steel, 408 nickel (9%) cast steel, 412 nickel (2330) cast steel, 408 nickel-chromium-molybdenum (4330, 8640), 410 nickel molybdenum (4630), 409 variations, 285, 286 Inspection, fluorescent penetrant, 598, 599 Inspection of molds, 577-579 Interpass temperature, welding, 468 Investment castings shipments, 621 tolerances, 242 Investment molding, 565, 566 Iron-carbon diagram, 305, 481 Isothermal quenching, 494, 495 Isothermal-transformation diagrams, 485-490 carbon (1030) cast steel, 488 chromium-molybdenum (4130), 488 chromium-nickel-molybdenum (4330), 489 1 J Jigs, 585 Jominy hardenability (see Hardenability) K I Keel block coupon, 265 Ideal critical diameter, 491 Impact properties, effect of deoxidation on, 406, 407 Impact resistance of carbon steel, 326-331 effect of heat treatment, 327, 328 impact vs. carbon, 327 impact vs. hardness, 328 impact vs. testing temperature, 327, 328 distribution of, 261-263 effect of mass, 278-281 effect of hardness, 262 effect of hydrogen, 255 effect of sulfur, 253 L L sections, 122-126 Leaded steels, machining of, 535-537 Location points, 219 Lost wax process (see Investment molding) Low-alloy cast steel corrosion, 438-443 heat treatment, 496-501 mechanical properties, 342-350 microstructure, 346-350 types (AISI or SAE), 350-375 welding practice, 478 Low temperature impact resistance, 400-415 variables, 401-407 composition, 404-406 deoxidation practice, 406, 407 heat treatment, 403, 404 notch type, 401-403 testing temperature, 401 (See also Impact resistance, low temperature) IN DE X 667 M manganese-nickel-chromium. molybdenum (9500), 371 nickel-chromium-molybdenum (8600), 363 effect on wear resistance, 381 of low-alloy steels, 346-350 Military castings, 71-76 Mining and crushing equipment, 63-67 Modulus of elasticity, 292, 293 Modulus of rigidity, 294 Molding ceramic, 565 history of, 608 investment, 565, 566 materials, 557-560 operations, 560-563 shell, 563 564 sodium silicate, 566 Molding machines, history of, 608, 609 Molding methods, comparison of, 238 Molds, types of, 566-569 Molybdenum distribution in alloy steel, 251 effect on creep strength, 416, 417 Motor vehicle castings, 76-79 N Nickel distribution in alloy steel, 250 effect on transition temperature, 404, 405 in heat resistant steel, 425-430 Nitriding, 390 Nitrogen, effect of in steel, 254 Nondestructive testing, 595 Normal expected values, 260, 261 Normalizing, 498, 499 O Oil industry castings, 10, 20, 24, 52-56 Open-hearth furnace acid practice, 546 basic practice, 546-548 Cross section, 547 history, 604, 605 melting in, 543-548 Ordering castings, 105-110 Ovens, core, 672 Oxidizing agents (in cores), 573, 574 Oxygen in steelmaking, 555, 556 P Machinability, 503-538 of various cast metals, 28 Machinability curves alloy steel, 518-521 1020 cast steel, 517, 518 1021 cast steel, 522 1040 cast steel, 517, 518, 523 1326 cast steel, 524 4131 cast steel, 525 4335 cast steel, 526 8433 cast steel, 527 8630 cast steel, 528 Machinablity ratings, 513-516 with carbide tools, 515 with high speed tools, 514 speed index number, 515, 516 Machine finish allowances, 218 Machining, 505-513 of alloy steels, 537, 538 austenitic manganese steel, 396 corrosion resistant castings, 451 effect of hardness, 506, 507 effect of microstructure, 505, 506 of heat resistant steels, 433, 535, 536 of leaded steels, 535-537 power requirements, 507-509 of surfaces, 509, 511 of weldments, 511,512 Magnetic particle testing, 597, 598 Magnetic properties of austenitic manganese steel, 396 effect of carbon, 312 Malleable iron castings, sales, 617 Manganese distribution in alloy steel, 251 distribution in carbon steel, 249 effect of in carbon steel, 316, 317 effect on transition temperature, 404 Marine castings, 86-89 Martempering, 494, 495 Martensitic range of formation, 495 Mass effect, 269-281 alloy steels, 273 on fatigue properties, 274-278 on impact properties, 278-281 on tensile properties, 270-274 Melting in electric arc furnace, 548-553 in induction furnace, 553-555 in open-hearth furnace, 543-548 in oxygen converter, 555, 556 practice, 541-557 Microstructure of carbon steel, 322-325 effect of cooling rate on, 487 effect on machinability, 505, 506 effect on mechanical properties manganese (1300) cast steel, 352 manganese-molybdenum (8000), 355 Parting, 223 allowance, 239 Pattern distortion allowances, 218 Patternmaker's shrinkage, 213-217 Patterns costs, 191, 192 distortion allowances, 218 effect on tolerances, 231-233 668 INDEX 1 1 Properties, physical coefficient of expansion, 299, 300 density, 295-297 electrical resistivity, 308, 309 freezing range, 304-306 magnetic, 309-312 modulus of elasticity, 292, 293 modulus of rigidity, 294 Poisson's ratio, 294, 295 radiation effects, 313-315 specific heat, 307, 308 specific volume, 298-300 summary, 294 thermal conductivity, 306, 307 Properties of steel compared to other cast metals, 25-29 Purchasing of castings, 101-112 cost, 101-110 delivery and service, 103, 108, 109 patterns, 108-110 production factors, 103, 104 quality, 102, 103, 106, 107 specifications, 107, 110 lite, 200 materials, 197-201 metal, 199, 200 patternmaker's shrinkage, 213-217 plastic, 200, 201 wear resistant, 212, 213 wood, 197-199 Peening of weldments, 471, 472 Petroleum corrosion, 440 Petroleum industry castings, 10, 20, 24, 52-56 Phosphorus Quench tanks, 588, 589 Quenching, 492-496, 499, 500 Quenching process austempering, 496 comparison, 494-496 conventional, 494, 495 isothermal, 495 martempering, 495 slack, 496 time, 496 R 4 distribution in carbon steel, 249 effect of in carbon steel, 317 Pickling, 590 Pilot castings, 104 Poisson's ratio, 294, 295 Postwelding heat treatment, 472 Pouring of molds, 577-579 Preheat for welding, 466-468 Pressure pouring, 579 Pressure testing, 600, 601 Production, steel casting, 616 Properties, mechanical austenitic manganese steel, 395, 396 carbon steel, 318-322, 326-338 fatigue, 331-336 hardenability, 336-338 impact, 326-328 tensile, 318-322 corrosion resistant steel, 450 effect of hydrogen, 254, 255 effect of mass, 269-281 effect of microporosity, 275 heat resistant steel, 418, 430, 431 low-alloy steels fatigue, 346, 347 hardness, 343, 344 impact, 344-346 tensile, 343, 344 copper-manganese-silicon, 371-375 chromium (5100) cast steel, 367-368 chromium-molybdenum (4100), 368, 369 manganese (1300) cast steel, 351-354 manganese-molybdenum (8000, 8400), 354-356 manganese-molybdenum-boron (80B00), 356, 357 manganese-nickel-chromium-molybdenum (9500), 364-371 molybdenum (4000) cast steel, 366, 367 nickel (2300) cast steel, 357, 358 nickel-chromium (3100), 358-360 nickel-chromium-molybdenum (8600, 4300), 361-366 nickel-molybdenum (4600), 360 range of cast metals, 26, 27 range of steel, 17 reproducibility from coupons, 265-269 variations, 256-264 in alloy steel, 257-259 in carbon steel, 256, 257 for wear resistance, 385 Radiation effects, 313-315 Radiographic testing, 595-597 Railroad castings, 12, 20, 21, 23, 24, 35, 37-44 history of, 611-614 Randupson process, 558 Redesign bolted structures to castings, 34, 35, 164 castings to cast-weld construction, 160-162 for cost reduction, 157, 158 forgings to castings, 32-34, 162-164 for improved quality, 155-157 for reduced stress concentration, 160 riveted structures to castings, 34, 35, 164 for service life, 158, 159 for weight reduction, 158 weldments to castings, 29-32, 165-167 weldments to composite frabrication, 167, 168 Reduction of area (see Tensile properties, and Properties, mechanical) Refractories for molding, 558, 565, 566 Reinforcing members, 129-131 Resistivity, electrical, 308-310 Residual elements effect of in carbon steel, 317 INDEX 669 Risers importance of, 569, 570 removal of, 579-581 Rolling mill castings, 2, 46, 48-52 Rubber mill castings, 89-91 Sulfur distribution in carbon steel, 249 effect of in carbon steel, 317 effect on impact, 253 Surface hardening, 386-390 S T S-curves (see Isothermal transformation diagrams) Safety factors, 180-182 Sales of steel castings, 617 Section changes, 118-122 Section modulus, 139-149 Section thickness, 116-118 effect on heat treatment, 484, 492, 500 Sections applications, 147-149 properties of, 142-147 Shaw process (see Ceramic molding) Shell molded castings shipments, 621 tolerances, 242 Shell molding, 563, 564 Shipments of steel castings, 616-620 Silicon distribution in carbon steel, 249 effect of in carbon steel, 317 effect on transition temperature, 404 Slack quenching, 496 Snagging, 581-583 Sodium silicate molding, 566 Specific heat, 307-308 Specific volume, 298-300 Specifications corrosion resistant steel heat treatment, 449, 450 tensile properties, 445 heat resistant steel composition, 417 creep strength, 420, 421, 432 tensile requirements, 418, 431 for purchasing, 107, 110 for welding, 463-465, 476, 477 Standard deviation, 250 Static tests, 290 Steel for corrosion resistance, 437-454 for heat resistance, 416-436 for low temperatures, 400-415 for wear resistance, 382-385 Steel casting research, 622, 627 Stress analysis, 169-180 brittle lacquer, 170-172 calculations, 169, 170 Strain gage, 172, 173 Stress concentration, 120-124, 127, 128, 174-182, 185, 186 Stress relief, 501 of weldments, 455 T-sections, 127-132 TTT-curves (see Isothermal transformation diagrams) Tempering, 485, 500, 501 effect on hardenability, 337, 338 Tensile properties of carbon steel, 318-325 of corrosion resistant steel, 445 of copper-manganese-silicon steel, 372 effect of hydrogen, 254, 255 effect on machinability, 506, 507 effect of mass, 270-274 of heat resistant steel, 418, 430, 431 normal variations, 256-258 specimen location, 272 variations, 283-285 Test specimens cloverleaf, 266 reel block, 265 location, 270-272, 283 reproducibility of properties, 265-269 trepanned, 283 Testing of castings destructive, 594, 595 fluorescent penetrant, 598, 599 magnetic particle, 597, 598 of mechanical properties, 592-594 nondestructive, 595 pressure, 600, 601 radiographic, 595-597 ultrasonic, 599, 600 Thermal conductivity, 306-308 effect of carbon, 308 Thermal properties, 309-312 Thermal stresses in weldments, 474, 475 Time quenching, 496 Titanium in heat resistant steel, 418 Tolerances casting finish, 218 effect of core boxes on, 231-233 effect of design, 222-230 effect of foundry practice, 230-237 investment castings, 242 machine finish, 218 pattern distortion, 218 recommended, 238-244 shell molded castings, 242 weight, 240 wrought vs. cast steel, 243, 244 Tool life vs. cutting speed (see Machinability curves) Toughness (see Impact resistance) Trepanned specimens, 283 Tungsten in heat resistant steel, 418 670 INDEX U Ultrasonic testing, 595, 599, 600 Uses of steel castings (see Applications) V V-sections, 127 Vacuum degassing, 556, 557 Valve castings, 4, 31 Variations, normal in chemical composition, 248-255 in mechanical properties, 256-264 Volume changes in steel, 298-304 Vibratory shakeout machine, 579 Welding arc atmosphere, 469 of austenitic manganese steel, 397 cast-weld construction, 457-459 composite fabrication, 460-462 of corrosion resistant steel, 452 deposition of weld, 470, 471 electrodes, 472, 473 groove backup, 466 groove preparation, 465, 466 heat input, 469 of heat resistant castings, 434 interpass temperature, 468 methods, 465 peening, 471 preheat, 466-468 procedure, 476, 477 specifications, 463-465 thermal stresses, 474, 475 Weldments, machining of, 511, 512 Weldments vs. castings, 182-190 fatigue limit, 186, 187 static strength, 186 stress concentration factors, 185, 186 Wrought steel corrosion rate, 439 directionality, 13-16, 33 machinability, 530-535 tolerances, 243, 244 W X X-ray radiography, 595-597 X-sections, 133-136 Y Water corrosion, 440 Water quenching, 492, 493 Wave construction, 136, 137 Wax in molding, 565, 566 Wear of austenitic manganese steel, 392-394 classification, 376, 377 Wear resistance types of steel, 382-385 variables, 377-381 carbon content, 379 hardness, 378, 380, 381 heat treatment, 379, 380 microstructure, 381 Weight, casting deviations, 237 tolerances, 240 Weld beads, 470 Weld build-up and facings, 462, 463 Weldability of cast steel, 455, 456 rating of cast metals, 28 Y-sections, 132, 133 Yield strength (see Properties, mechanical, and Tensile properties) . 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