STRUCTURE AND PROPERTIES OF ULTRAHIGH-STRENGTH STEELS A symposium sponsored by the METALLURGICAL SOCIETY OF AIME and the AMERICAN SOCIETY FOR TESTING AND MATERIALS Cleveland, Ohio, Oct 22, 1963 Reg U S Pat Off ASTM Special Technical Publication No 370 Price $11.00; to Members $7.70 Published by the AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race St., Philadelphia 3, Pa Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproduc © by American Society for Testing and Materials 1965 Printed in Baltimore, Md March, 1965 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproducti FOREWORD The papers in this volume were presented at a Symposium on Steels With Yield Strengths Over 200,000 psi sponsored by the Panel on Structural Materials for Airframes and Missiles of the ASTM-ASME Joint Committee on Effect of Temperature on the Properties of Metals, and the Structural Materials Committee, Institute of Metals, Metallurgical Society of AIME The Symposium was held on Oct 22, 1963, in Cleveland, Ohio F M Richmond, of Universal-Cyclops Steel Corp., and J W Welty, of Solar Aircraft Co., were the chairmen of the morning session E E Reynolds, of Allegheny Ludlum Steel Corp., and J J Heger, of U S Steel Corp., presided over the afternoon session Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reprodu iii NOTE—The Society is not responsible, as a body, for the statements and opinions advanced in this publication Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproduc CONTENTS Introduction Relationships Between Microstructure and Toughness in Quenched and Tempered Ultrahigh-Strength Steels—A J Baker, F J Lauta, and R P Wei Discussion Relationships Between Structure and Properties in the 9Ni-4Co Alloy System— J S Pascover and S J Matas Discussion High-Strength Stainless Steels by Deformation at Room Temperature—S Floreen and C R Mayne An Evaluation of the 18Ni-9Co-5Mo Maraging Steel Sheet—D L Corn The Metallurgy and Properties of Cold-Rolled Am-350 and Am-355 Steels—T H McCunn, G N Aggen, and R A Lula Discussion Fracture Micromechanics in High-Strength Steels—Bani R Banerjee Discussion The Effect of Solidification Practice on the Properties of High-Strength Steels— C M Carman, R W Strachan, D F Armiento, and H Markus Discussion High-Strength Steel Forgings—H J Henning Ausform Fabrication and Properties of High-Strength Alloy Steel—W W Gerberich, A J Williams, C F Martin, and R E Heise Thermomechanical Treatments Applied to Ultrahigh-Strength Bainites—D Kalish, S A Kulin, and M Cohen Discussion Ultrahigh-Strength Steel Fasteners—A C Hood and R L Sproat Discussion PAGE 23 30 45 47 54 78 93 94 116 121 143 147 154 172 205 208 220 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No f V RELATED ASTM PUBLICATIONS Properties of Basic Oxygen and Open Hearth Steels, STP 364 (1963) Stress Corrosion Cracking of Austenitic Chromium-Nickel Stainless Steels, STP 264 (1960) Chemical Composition and Rupture Strengths of Super-Strength Alloys, STP 170-C (1964) Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproduction vi STRUCTURE AND PROPERTIES OF ULTRAHIGH-STRENGTH STEELS INTRODUCTION The increasing demands of the military for improved performance of structural materials for space, land, and deep ocean environments has resulted in an intensive activity in the development, evaluation, and prototype testing of a broad range of materials including oxides, carbides, aluminum, titanium, and even gold A significant portion of this activity has been devoted to high-strength steels Recognizing the scope of this activity and the need to assemble into one seminar the more recent advances in the development and application of highstrength steels, the Panel on Structural Materials for Airframes and Missiles of the Joint Committee of ASTM and ASME, and the Structural Materials Committee of the Institute of Metals Division of the Metallurgical Society of AIME, organized this Symposium on Steels With Yield Strengths Over 200,000 psi Until recently, steels having yield strengths in excess of 200,000 psi were not considered suitable as materials of construction, because fabrication and inspection techniques were not sufficiently sophisticated to permit full utilization of these high strengths, which at that time were accompanied by low ductility and low toughness Recently, however, major developments have occurred not only in alloy development, which has permitted the achievement of higher levels of ductility and toughness, but also in inspection and fabrication techniques that permit the full utilization of higher strengths that are now obtainable The papers presented at this symposium included descriptions of new steels (or new concepts for making steels) having yield strengths in excess of 200,000 psi, and good ductility and toughness Specifically mentioned are the new maraging steels, higher strength and higher toughness martensitic steels, steels strengthened by thermomechanical treatments, and steels strengthened by cryogenic treatments Progress has been made in the understanding of the illusive property known as toughness, and two papers are presented summarizing the state of art in this area Also the effect of melting and processing on high strength properties, the characteristics of specific products—namely, forgings and fasteners—and the fabrication of the new high-strength steels are discussed in detail In reviewing the information contained in this Symposium, the reader is reminded that steels having the high yield strengths discussed herein will not always be confined to military applications The American economy demands that such steels eventually will be used for pressure vessels as well as for structural members in such prosaic applications as buildings and bridges, and perhaps even for the structural members of the transportation vehicles that the reader will be using as a personal means of conveyance within the next 10 years This page intentionally left blank Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions aut RELATIONSHIPS BETWEEN MICROSTRUCTURE AND TOUGHNESS IN QUENCHED AND TEMPERED ULTRAH1GH-STRENGTH STEELS BY A J BAKER,1 F J LAUTA,1 AND R P WEI1 SYNOPSIS An investigation was made of a number of 0.30 and 0.40 per cent carbon alloy steels to determine the relationships between their fracture toughness properties and their internal microstructures The plane-strain fracture toughness of the steels was measured after tempering quenched material in the temperature range 300 to HOOF A thin section transmission electron microscopy study was carried out on the tempered materials From the fracture toughness studies it was concluded that all the materials behaved similarly and that alloying elements (carbon and silicon) had little influence on the general relationship between tensile strength and toughness in these fully hardenable steels It was found that the fracture toughness remained low at low tempering temperatures but improved rapidly once a critical tempering temperature, characteristic of the particular steel, was reached The microscopy study showed that major microstructural changes occurred in the tempering range where the rapid increase in toughness was observed At low tempering temperatures the defect structure of the as-quenched martensite remained unchanged, and continuous films of carbide were formed in the boundaries of the martensite In the critical tempering range the carbide films were spheroidized and the defect structure of the matrix removed or modified by recovery processes On the basis of these observations, it was concluded that the low fracture toughness of the steels in a lightly tempered condition was due to their high defect densities and the presence of carbide films at boundaries Only when these features were removed or modified did toughness increase In recent years there has been a growing demand for materials of very high strength for aerospace applications such as rocket motor casings This demand has stimulated research aimed at the development of ultrahigh-strength steels, that is, steels with useable yield strengths of more, than 200,000 psi; and an important part of this research has been the study of quenched and tempered low-al- loy steels with carbon contents in the range of 0.3 to 0.5 per cent Quenched and tempered low-alloy steels already have many uses both as structural materials and, at higher strength levels, as machine parts When their yield strengths are raised to the strength level mentioned, there is the major problem of maintaining an adequate level of toughness that will meet the design require- i Technologists, U S Steel Corp., Applied Research Laboratory, Monroeville, Pa mentS Pkced UP°n them' The present investigation was carried HOOD AND SPROAT ON ULTRAHIGH-STRENGTH STEEL FASTENERS FIG 1—A Twelve-Point External Wrenching Aircraft Bolt Thread exposure of f-20, 200,000-psi bolts measured from shank thread runout to point of thread engagement 209 The bolt is subjected not only to high tension loads, but to shear, bending, and fatigue Depending on the design and characteristics of surrounding structural materials, it often must carry loads in excess of those imparted to the adjacent structure Being made of steel, it is subject to all the problems inherent in steel, such as corrosion, heat treat FIG 2—Effect of Thread Engagement on Bolt Tensile Strength The stress required to achieve 65,000-cycle fatigue life for bolts with rolled threads after heat treatment peaks is slightly below 200,000 psi tensile strength to assemble the high-strength steels into variables, hydrogen embrittlement, and notch sensitivity useful structures The design of a bolt tends to make it Fortunately, the bolt may be tested difficult to utilize the full strength in its entirety, without resorting to the potential of materials Basically, the method of testing metal specimens to bolt is a bar with a series of notches at predict the properties of the bolt one end, a non-uniform cross-section, a The combination of stresses imposed diameter change at the other end, and on of a boltEST under Copyright by ASTM Int'l (all rights reserved); localized Mon Decareas 13:15:25 2015load is sharpDownloaded/printed fillet in-between,by as shown in Fig so complex that the material property University of Washington (University of Washington) pursuant to License Agreement No further re STRUCTURE AND PROPERTIES OF ULTRAHIGH-STRENGTH STEELS 210 approach offers little guide to bolt properties Bolts are therefore tested as specimens to provide tensile, shear, fatigue, and even impact data TENSILE STRENGTH The tensile strength of the base material is the initial criterion for its use in a fastener The tensile strength of a bolt made from a material must be as near as possible to the strength of the ASTM specimen in order to merit further consideration While it is desirable to utilize a maTABLE 1—HIGH-STRENGTH BOLTING MATERIALS Material at Various Tensile Strengths, psi 220,000 260,000 300,000 H-ll" H-ll" Vasco MIL-S-7108A0 4340° A-2860 Inconel 718 15-7 Mo Waspaloy Mar aging Steel, 300 AFC 77 Maraging Steel, 325 Ausformed H-ll Currently used as bolting MA" Jet engagement of internal and external threads Another factor affecting the tensile strength of a bolt is the number of threads exposed between the runout thread and the point where the first nut thread is engaged In Fig the tensile strength drops as a function of the number of threads exposed (I).2 In aircraft bolting, where thread length is generally short, the tensile strength is measured at three exposed threads A number of comparative studies have been made of material and bolt strength, in an effort to establish an empirical method for calculation of thread area (2—4) The resulting bolt area has been chosen from these investigations and further reference to bolt tensile strength will be on this basis SELECTION or BOLTING MATERIALS High-strength bolting has been categorized into tensile strength levels of 220,000, 260,000, and 300,000 psi Table shows ultrahigh-strength alloys which are capable of achieving bolt strengths of these magnitudes Their selection as a bolting material, however, is not governed by strength alone Other factors affecting the selection of a high-strength material include thread tensile strength, fatigue endurance, range of temperature stability, fabricability, susceptibility to hydrogen embrittlement, and resistance to corrosion and stress-corrosion The important aspect of the above, however, is that the selection be made on the basis of bolt properties and not limitations imposed by material data To cite a specific example, note in Table the properties of both material and notch strength It is not until the tension-tension fatigue life of bolts made from both materials can be compared that a separation can be made terial of high yield strength, the term bolt yield strength has little meaning, since there is no reference either to uniform cross section or fixed gage length For this reason, subsequent discussion of ultrahigh-strength steel fasteners will be in terms of bolt ultimate tensile strength The tensile strength of a bolt cannot be accurately predicted from the notch properties of the base material, although these values often serve as a guide in the screening of high-strength steels The stress-concentration factor of a multiple-notched specimen may be calculated, but it is not the same as the The2015boldface numbers in parentheses refer Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST condition which exists in the loaded to the list of references appended to this paper Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 211 HOOD AND SPROAT ON ULTRAHIGH-STRENGTH STEEL FASTENERS Another possible choice at this strength level would be AISI 8740 steel Figure illustrates, however, that the fatigue resistance of this alloy peaks at a strength level slightly below 200,000 psi (5) Fatigue is not the only criterion for selection Resistance to hydrogen embrittlement would again enable a separa- chromium content and resistance to hydrogen embrittlement An advantage of H-ll steel at the 220,000 and 260,000 psi strength level is its retention of strength at elevated temperature, which enables it to be used for 900-F bolting with only a slight loss in strength at that temperature (8,9) TABLE 2—MATERIAL AND BOLT PROPERTIES OF 4330 MODIFIED, 4340, AND H-ll STEELS 4330 Modified Property H-ll 4340 BOLTS HEAT THEATED FROM 180,000 TO 200,000 PSI Material UTS, psi Material yield strength, psi Elongation in diameters, % Reduction of area, % Notch-to-smooth ratio, Kt6 Bolt UTS, psi Fatigue-cycles, maximum stress, 93,000 psi 201,100 190,200 13.5 53.0 1.2 204,300 71,000 196,000 184,000 11.9 42.3 1.4 199,000 59,500 197,700 158,200 15.5 47.7 1.4 198,000 321,100 BOLTS HEAT TREATED FBOM 220,000 TO 250,000 PSI Material UTS, psi Material yield strength, psi Elongation in diameters, % Reduction of area, % Notch-to-smooth ratio, Kt6 Bolt UTS, psi Fatigue-cycles, maximum stress, 115,000 psi 242,800 208,800 12.6 49.4 1.2 238,100 20,400 229,000 210,500 10.9 41.6 1.2 230,700 174,000 236,800 199,400 13.5 48.3 1.3 239,000 417,600 BOLTS HEAT TREATED FROM 260,000 TO 290,000 PSI Material UTS, psi Material yield strength, psi Elongation hi diameters, % Reduction of area, % Notch-to-smooth ratio, KtQ Bolt UTS, psi Fatigue-cycles, maximum stress, 135,000 psi tion to be made The data in Fig show a comparison of H-ll and 4340 steels, using notch tension specimens under a sustained load of 90 per cent of notched ultimate strength (6) All alloy steels in aircraft are plated Therefore, , the possibility of hydrogen embrittlement cannot be overlooked The above data have recently been confirmed in part by Beck and Jankowsky v(7), who note a Copyright strong relationship bybetween ASTM increased Downloaded/printed University of by Washington 289,000 229,800 9.0 29.2 1.0 290,000 24,000 288,000 243,700 12.1 41.4 1.1 288,400 700,000 A need for a high-strength, hightemperature stainless bolting material exists Alloys sometimes considered for use as high-strength bolts are A-286, Inconel 718, and Waspaloy Since heat treatment alone will not provide these strengths, the alloys are cold worked prior to aging to raise the aged material strength A combination of corrosion resistance and high cryogenic toughness Int'l (all their application rights reserved); has prompted in areas (University of Washington) Mo pursu 212 STRUCTURE AND PROPERTIES or ULTRAHIGH-STRENGTH STEELS FIG 3—Fatigue Strength Versus Bolt Strength of AISI 8740 Material Test specimens heat treated to Re 50, cadium fluoborate plated, and baked at 375 F for 23 hr were subjected to a sustained load at 90 per cent of their notched tensile strength Tension specimens had a notch stress concentration factor of Kt = 4.9 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further repro HOOD AND SPROAT ON ULTRAHIGH-STRENGTH STEEL FASTENERS 213 FIG 4—Comparison of Hydrogen Embrittlement Susceptibility of 4340 and H-ll Steels Improvement from cold working and thread form design approach endurance stress of H-ll smooth bar TABLE 3—MATERIAL AND BOLT PROPERTIES OF H-ll AND MARAGING STEEL, 300 H-ll Room Temperature Maraging Steel, 300 -320F Room Temperature -320 F 302,000 263,000 10.2 39.0 283,000 272,000 10.7 53.3 354,000 327 000 10.0 44.3 297,000 65,000 37 279,000 43,000 50 352,000 25,000 44 SPECIMEN UTS psi Yield strength psi Elongation, *% Reduction of area, % Charpy impact ft-lb° 279,000 240,000 11.5 42.0 5.0 1.5 5.7 3.4 BOLT UTS, psi Fatigue-cycles, maximum stress 135,000 psi Tension impact, ft-lb, 1-28 bolt 280,000 100,000 50 Subsize specimen per ASTM E 23, Type W such as the liquid gas section of rocket with properties developed by heat engines They have also been considered treatment alone The alloy is essentially for elevated temperature structures, an iron base, chromium-cobalt-molybwhere it is necessary to match the coeffi- denum material Limited data on bolting cients of expansion of both bolt and joint has shown it to have a nominal ultimate strength of 294,000 psi at room temmaterials A new alloy (10), AFC77, shows perature, falling off to 246,000 psi at 900 F (n) promise of providing a Int'l stainless high- reserved); Copyright by ASTM (all rights Mon Dec 13:15:25 EST 2015 The maraging steels have been used for strength bolting material useful to 900 F, Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No fu 214 STRUCTURE AND PROPERTIES OF ULTRAHIGH-STRENGTH STEELS bolts in the 260,000-psi category Although their notched strength, Kt = 6, is higher than that of H-11 at this strength level (1.5 at 276,000 psi versus 1.1 at 288,000 psi for H-11) (12), they offer no particular advantage over H-11 and actually have some disadvantages The resistance to temperature is lower for these steels as a result of a lower aging temperature Susceptibility to hydrogen embrittlement of maraging steels appears to be greater than that of H-11 Notched tension specimens, Kt = 4.9, of the maraging steel (300) were cadmiumfluoborate plated and not baked They failed during loading to 90 per cent of Steel Co., was selected The factors governing the selection of fastener materials were considered and one or another of many alloys was rejected Since the development of a 300,000psi fastener, new materials have shown promise; the comparative properties of three alloys are shown in Table A few words are necessary to describe the last two materials in more detail Maraging 325 steel is a higher titanium modification of the maraging steel series, and limited data indicate that it may be capable of achieving sufficient properties as a fastener to warrant its use in this capacity However, further research will be necessary before it is regarded as TABLE 4—ULTRAHIGH-STRENGTH BOLTING MATERIALS Property Vasco Jet MA Maraging 325 Ausformed H-11 UTS psi Yield strength, psi Elongation % Reduction of area % 311,600 252 000 84 31.7 344,000 332,000 10 48.5 371 000 305 000 12 47.0 Bolt UTS, psi 307,800 330,000 360,000 notched ultimate tensile strength H-11 suitable The ausformed H-11 data show steel under the same conditions still had thread properties only, since techniques not failed after 550 hr, when the test have not as yet been developed to fabriwas terminated cate heads on ausformed steels at this The one possible area where maraging strength level The highest thread propsteels may offer an advantage is in the erties to date, 392,000 psi, have been area of cryogenic applications Note in obtained on ausformed Vasco Jet MA Table 3, however, that fasteners of H-11 (13) It is for this reason that ultrahightested at —320 F stand up quite well strength bolting with a strength as high Only when the Charpy impact values of as 400,000 psi may be practical in the the two materials are compared, how- future To provide some perspective to ever, does the maraging steel show a the problem, however, it is necessary to superiority at the lower temperature consider that threads must be rolled It would be recommended for use at after heat treatment to achieve both' — 320 F on the basis of current knowl- tensile strength and high fatigue life in edge the bolt Quench and temper treatments The selection of a bolting material for will not produce bolts at this strength 300,000 psi narrows the choice consider- level because of high notch brittleness ably It was only after several years of Accomplishing the thread rolling on a research that Vasco Jet MA, a modified steel whose hardness is Re 63 is a large by ASTMby Int'l (all rights reserved); Dec problem 13:15:25 EST 2015 tool Copyright steel developed Vanadium Alloys Mon technical in itself Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproduction HOOD AND SPROAT ON ULTRAHIGH-STRENGTH STEEL FASTENERS 215 FIG 5—Effect of Bolt Design on Endurance Limit Stress of 220,000-psi H-ll Bolts Bolts are tested in tension-tension fatigue at loads cycling between 10 and 100 per cent of maximum load FIG 6—Endurance Limit as a Function of Bolt Tensile Strength Uncontrolled atmospheres resulting in carburization or decarburization reduces bolt fatigue life The bolts were tested in tension-tension fatigue at loads cycling between 5,250 and 52,500 psi by rolled ASTMbefore Int'l heat (all rights reserved); Mon Dec 13:15:25 EST 2015 Bolt Copyright threads were treatment Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further rep 216 STRUCTURE AND PROPERTIES or ULTRAHIGH-STRENGTH STEELS BOLT DESIGN AND PROCESSING To produce reliable bolts of the strength levels indicated above, it is the function of bolt design and processing to maintain as great a percentage of the base material properties as pos- fatigue tests are normally run with the load varying between a maximum stress and 10 per cent of that maximum stress This choice parallels as nearly as possible the worst condition of bolt fatigue, namely, a loose bolt and nut For con- FIG 7—Fatigue Life of AISI 4037 Steel Bolts as a Function of Carbon Content of Heat Treating Atmosphere Failure occurred in 30 sible Bolts must be designed to minimize stress raisers, such as sharp notches and abrupt changes in cross sectional areas Processing should be controlled to prevent metallurgical damage and to create beneficial residual stresses in critical areas Since bolts are subjected to tensiontension fatigue in application, bolt tests are conducted Copyright to by simulate ASTM this Int'l condition (all rights In order to test under uniform conditions, Downloaded/printed by University of Washington (University venience, only the maximum stress is usually reported The development of maximum endurance limit stress in bolting has been going on for several years A history of this development can be considered for the 220,000-psi bolt The tension-tension fatigue endurance limit for a smooth bar of H-ll is estimated at 130,000 psi The endurance bolt made of reserved); Mon limit Dec for7 a 13:15:25 EST the same material with a standard of Washington) pursuant to License 2015 Agreement No HOOD AND SPROAT ON ULTRAHIGH-STRENGTH STEEL FASTENERS 217 thread rolled before heat treatment is vestiges of carburization or decarburiza20,000 psi The S-N curves of Fig tion, but also to remove surface imperillustrate what has been necessary to fections present in the raw material, restore a large proportion of this fatigue establish finished dimension, and create life Stressing of the thread roots by a smooth surface finish Grinding of rolling threads after heat treatment hardened steel can result in grinding nearly tripled the fatigue endurance stress Increasing of thread root radius added another increment to reach 85,000 psi (14) This is the fatigue level of the existing 220,000 psi bolting on the market today Recent research on minimizing stress concentration peaks in the engaged thread has resulted in a high fatigue thread form which has raised the endurance stress to 105,000 psi Needless to say, it has been necessary to cold work the head-to-shank fillet area as well, since this became the critical point of failure as soon as threads were rolled after heat treatment The ultimate goal continues to be that of restoring all the fatigue endurance lost when the transition was made from a smooth bar to a bolt Another means of increasing fatigue endurance has been to increase bolt strength as shown in Fig The result is that the 300,000-psi bolt has an endurance stress of 125,000 psi It should be pointed out, however, that this result has been achieved only with the largeradius thread form and rolling of threads after heat treatment The manufacture of ultrahigh-strength FIG 8—Stress-Alloy Cracking of a Cadmium bolts must be closely controlled in order Plated Bolt Exposed to 700 F and a Stress Equal that the properties anticipated by design to 90 Per Cent of the Ultimate Strength of the are retained in the final product The Bolt influence of surface carbon on tension tension fatigue can be appreciable, as burns and high tension stresses or cracks shown in Fig (10), and both carburized The high tension stresses alone can proand decarburized surfaces must be duce premature fatigue failure or reduced tolerance for hydrogen A standeliminated In spite of raw-material control and ard practice therefore is to temper all heat-treat atmosphere vigilance, the bolt blanks after grinding at a temperabody, underhead, and thread roll di- ture of 25 F below the original tempering ameter are all ground after heat treat- temperature PlatingMonfor Dec corrosion protection ment This isbynotASTM only to any reserved); Copyright Int'lremove (all rights 13:15:25 EST is2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No fur 218 STRUCTURE AND PROPERTIES OF ULTRAHIGH-STRENGTH STEELS common in high-strength bolting Cadmium is the normal plate, but aluminum has been used on occasion Although cadmium fiuoborate plating followed by baking for 23 hr at 375 F is currently used on 220,000-psi bolting, the proposed military 220,000-psi bolt requires vacuum cadmium plating This is an added precaution in spite of the reduced It can be seen that ultrahigh-strength bolts are made under conditions predicated by bolt properties and not necessarily by material or design characteristics utilized for other structures In addition, environmental conditions can affect bolt fatigue just as they affect material fatigue The endurance limit stress in 90 per cent moisture has been FIG 9—Effect of Protective Coating on the Fatigue Life of 220,000 psi H-11 Bolts in 90 Per Cent Moisture Environment susceptibility of H-11 steel to hydrogen reduced from 85,000 psi to 80,000 psi, embrittlement Steel bolting at 260,000 as shown in Fig Studies of this phepsi and 300,000 psi is vacuum cadmium nomenon have resulted in the developplated as a standard practice Elevated- ment of a protective coating The coattemperature exposure of cadmium-plated ing has not only restored fatigue life to bolts under load at a temperature at or its original level but increased the enclose to the melting point of cadmium durance stress to 120,000 psi (610 F) has resulted in stress-alloy crackWith all that can be provided in the ing, as shown in Fig This has neces- ultrahigh-strength steel bolt, its life in sitated the use of a nickel-cadmium the structure is also affected by joint diffused plate for high-temperature design and proper tightening Utilization bolts Aluminum has been used for the of this hardware requires a proper underDec 13:15:25 EST 2015 sameCopyright purpose.by ASTM Int'l (all rights reserved); Mon standing of these factors Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions HOOD AND SPROAT ON ULTRAHIGH-STRENGTH STEEL FASTENERS 219 REFERENCES (1) W Schlicting, "Effect of Tensile Strength vs Thread Engagement of Socket Head Cap Screws," SPS Lab Report No 707, November 10, 1961 (2) Gregory W Gries, "Area Determination for Tensile Strength of Socket Head Cap Screws; Sizes #0-80, #1-72, #2-56, #348, #4-40, and #5-40," SPS Lab Report No 796, March 27, 1962 (3) Gregory W Gries, "Area Determination for Tensile Strength of Socket Head Cap Screws with Threads Rolled Before and After Heat Treat; Sizes #6-40, #10-32, and ^-20 at Strength Levels of 160,000, 180,000, and 200,000 psi," SPS Lab Report No 835, July 10, 1962 (4) Gregory W Gries, "Area Determination for Tensile Strength of Socket Head Cap Screws; Sizes #6-40 and #10-32 with HiLife, HiR 75%, and HiR 55% Thread Forms, Rolled Thread Before and After Heat Treat," SPS Lab Report No 858, August 23, 1962 (5) Thomas C Baumgartner, "Basic Design and Manufacturing of Aircraft Fasteners for Use Up to 1600°F," SPS Lab Report No 2300, December 17, 1958 (6) J Laurilliard, "Hydrogen Embrittlement of 4340 Material Compared to SPS-M-107 Material," SPS Lab Note No 581, November 28, 1961 (7) W Beck and E Jankowsky, "Delayed Brittle Failure in Cadmium Plated Steels," Metals Progress, Vol 84, No 2, August, 1963 (8) Thomas C Baumgartner, "EWB TM9 External Wrenching Bolt, EWN TM9 Flexloc Locknut," SPS Lab Report No 86, May 7, 1957 (9) A W Dickens, "Evaluation of SPS EWB 926 Bolts and SPS FN926 Locknuts," SPS Lab Report No 283, June 8, 1960 (10) A Kasak, V K Chandhok, J H Moll, and E J Dulis, "Development of HighStrength Elevated-Temperature CorrosionResistant Steel," Crucible Steel Company of America, ASD Contract No AF33(657)8458, November 1, 1962 (11) J Glackin, "Bolt and Material Evaluation of AFC 77 Material to 1200°F," SPS Lab Note No 822, April 22, 1963 (12) D E McGarrigan, "Susceptibility of Vasco Max 300 to Hydrogen Embrittlement." SPS Lab Note No 845, June 17, 1963 (13) J Glackin, "Progress Report on Ausformed Material from Ford Motor Company," SPS Lab Report No 759, February 21, 1962 (14) E Gowen, Jr., "Test Data of 220,000 and 260,000 psi SPS Hi-Life Bolts," SPS Lab Report No 998, May, 1963 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized DISCUSSION A R JOHNSON1—It was a pleasure to J T BiNGHAM2—The authors' data read the history behind the development on 19 per cent maraging steel, indicating of ultrahigh-strength fasteners, since it fatigue life lower than H-ll, and their clearly shows how persistent efforts to data on cadmium plate embrittlement optimize processing and design can with the same results, are open to quesachieve maximum performance from tion Extensive testing of various sizes ultrahigh-strength materials like Vasco- of bolts made from several heats of Jet 1000 and Vascojet M-A In this materials by our company have shown connection, Figs and 6, showing the more favorable results Successful proincremental gains in fatigue strength duction of parts does require close and with improvements in design and proc- precise control of forming and processing essing, are particularly interesting as mentioned by the authors It is encouraging to note that the E J DuNN3—In bolting applications, authors see some promise in the new are transverse properties important? 18 per cent nickel maraging steels as A C HOOD AND R L SPROAT (authors1 ultrahigh-strength fasteners There are closure)—A R Johnson's comments are some very definite advantages inherent indeed appreciated With regard to his in these steels; for example, their tough- question on Charpy impact values shown ness at cryogenic temperatures, which in Table 3, the original paper showed the authors have pointed out In addi- Charpy values for a subsize specimen tion, however, the simplest heat treat- per ASTM E 23, Type W Subsequent ment, hr age at 900 F, and relatively tests, shown below, indicate values essensmall dimensional change on aging, tially the same as those noted by John—0.0004 in./in., should be helpful from son: a manufacturing standpoint I would H-ll Maraging Steel 300 like to point out that Charpy V-notch Room -320° F Room -320° F impact tests run at the Vanadium-Alloys Steel Company laboratory on a cali- Charpy Imbrated impact tester have shown conpact, full size 13.5 16.6 10.7 siderably higher impact strength for the maraging (300) steel than those reported The authors are grateful to J T by the authors in Table 3—18 ft-lb at Bingham for commenting on the work room temperature and 10 ft-lb at —320 of his company in the area of highF On the basis of these test results, the strength bolts Numerous attempts at maraging steel might be expected to SPS to achieve a fatigue life in the show substantially greater resistance to maraging steel bolt comparable-to H-ll shock loadingbythan other steels Copyright ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 bolts of the same strength level and Downloaded/printed by University Washington (University ofSteel Washington)Hipursuant to License Agreement Shear Corp., Torrance, Calif No further reproductions Manager ofof research, Vanadium-Alloys Westinghouse Corp., Blairsville, Pa Co., Latrobe, Pa 220 DISCUSSION ON ULTRAHIGH-STRENGTH STEEL FASTENERS design were not successful This was based on tests run with threads rolled after heat treatment, customary for high-strength bolting In addition, rotating-beam fatigue tests of H-ll and maraging steels run by Vanadium Alloys Steel Co.4 resulted in a lower endurance limit stress for the maraging steel The tests on hydrogen embrittlement of maraging steel notched specimens, Kt = 4.9, was not intended to indicate that maraging steel fasteners could not be electroplated Rather, it was an experiment to establish whether the maraging steels are susceptible to hydrogen, and if so, to what degree Numerous bolt products are made everyday which are cadmium plated, and the results are Private communication with D Yates, Vanadium Steel Co 221 satisfactory, providing proper precautions are taken with respect to hydrogen It is the authors' contention that steels of the strength level of which the maraging steels are capable should be vacuumcadmium plated to avoid the pick-up of hydrogen completely It is generally accepted that susceptibility to hydrogen embrittlement increases with increase in tensile strength Generally speaking, the transverse properties of a material are not the major factor affecting the properties of a bolt Longitudinal material properties control the properties of bolting However, bolt manufacturing operations, such as upsetting and thread rolling, are affected by the transverse properties of the raw material Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions au tHIS PUBLICATION IS ONE OF MANY issued by the American Society for Testing and Materials in connection with its work of promoting knowledge of the properties of materials and developing standard specifications and tests for materials Much of the data result from the voluntary contributions of many of the country's leading technical authorities from industry, scientific agencies, and government Over the years the Society has published many technical symposiums, reports, and special books These may consist of a series of technical papers, reports by the ASTM technical committees, or compilations of data developed in special Society groups with many organizations cooperating A list of ASTM publications and information on the work of the Society will be furnished on request Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:15:25 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized