Volume 04 - Heat Treating Part 12 ppsx

Fig. 18 Effect of austenitizing temperature and tempering conditions on hardness of M2 high-speed tool steel Tempering at too low a temperature or for too short a time, or both, may not adequately condition the 20 to 30% retained austenite present after initial quenching, and the steel will still retain abnormally large quantities of austenite after cooling from the initial temper. This austenite will not transform until the steel is cooled from the second temper, and a third temper is then required to temper the martensite so formed. It should be noted that the second temper provides a negligible increase in hardness. In order to carry these reactions as near to completion as possible, high-speed steel should always be cooled to room temperature between tempers. The beneficial effect of multiple tempering on mechanical properties of T1 high-speed steel is shown in Table 11. Table 11 Effects of single and double tempering on mechanical properties of T1 Time at tempering temperature Hardness, HRC Bend strength, MPa (ksi) Torsion-impact strength, J (ft · lbf) Single tempering at 565 °C (1050 °F) 6 min 65.1 2150 (312) 22 (16) 1 h 65.7 1860 (270) 41 (30) 2 1 2 h 65.0 2810 (408) 65 (48) 5 h 64.5 2590 (376) 65 (48) Double tempering at 565 °C (1050 °F) 2 1 2 h + 2 1 2 h 64.5 3130 (454) 85 (63) Forced-air furnaces are generally conceded to be the most desirable for tempering high-speed steel, because the heat is transmitted from the heating elements to the work by convection; consequently, the transfer of heat is gradual, and there is little danger of the work cracking as the result of thermal shock. It is advisable to place the work in a tempering chamber maintained in the temperature range of 205 to 260 °C (400 to 500 °F) and to bring the work up to the tempering temperature slowly with the furnace. This is particularly important for large or intricate tools, because too rapid a heating rate may lead to cracking. The very rapid heating rates of molten lead or salt baths, and the attendant thermal shock, usually militate against their successful use for tempering high-speed steel tools of other than simple shape and design, unless they are preheated to about 315 °C (600 °F) before being introduced into the bath. Refrigeration treatment may be employed to transform retained austenite. The application of a refrigeration treatment is recommended for high-alloy high-speed steels such as M42, M3 (class 2), and CPM Rex 60. Best results are obtained when the refrigeration treatment is performed after the quenching operation. The hardened or hardened and tempered tool is cooled to at least -85 °C (-120 °F) and then tempered or retempered at normal tempering temperatures. Carburized surfaces will respond satisfactorily to the -85 °C (-120 °F) treatment, even when they have been tempered prior to refrigeration. Nitriding. Liquid nitriding is preferred to gas nitriding for high-speed steel cutting tools because it is capable of producing a more ductile case with a lower nitrogen content. Although any of the liquid nitriding baths or processes may be used to nitride high-speed steel, the commercial bath consisting of 60 to 70% sodium salts and 30 to 40% potassium salts is most commonly employed. The nitriding cycle for high-speed steel is of relatively short duration, seldom exceeding 1h; in all other respects, however, the procedures and equipment are similar to those used for low-alloy steels. The cyanide baths employed in liquid nitriding introduce both carbon and nitrogen into the surface layers of the nitrided case. Normally, the highest percentages of both elements are found in the first 0.025 mm (0.001 in.) surface layer. For carbon and nitrogen gradients, see the section on liquid nitriding. The effect of time in a liquid nitriding bath at 565 °C (1050 °F) on the nitrogen content of the first 0.025 mm (0.001 in.) surface layer of a T1 high-speed steel is shown in Table 12. A nitrogen content of 0.06% was obtained in the first 3 min at temperature, and it gradually increased to 1.09% at the end of a 6-h cycle at this temperature. Table 12 Effect of nitriding time on surface nitrogen content of T1 high-speed tool steel Nitrogen content of first 0.025 mm (0.001 in.) layer Time at 565 °C (1050 °F) Nitrogen, % 3 min 0.06 10 min 0.093 30 min 0.15 90 min 0.26 3 h 0.58 6 h 1.09 As shown in Table 13, carbon also was absorbed by the steel, at nitriding temperatures as low as 455 °C (850 °F). In a 30- min nitriding cycle, the carbon content of the first 0.025 mm (0.001 in.) surface layer increased with an increase in the nitriding temperature. However, it was reported that only a portion of the carbon was absorbed by the steel, most of the carbon being mechanically attached to the surface, filling microscopic pits. (This pitting is not dangerous under normal conditions, because the pits are shallower than ordinary grinding or machining marks.) Table 13 Carbon content of nitrided T1 high-speed tool steel Carbon content of the first 0.025 mm (0.001 in.) surface layer of steel originally containing 0.705% C. Some of the carbon was in pits on the surface, rather than diffused into the steel. Nitriding Temperature °C °F Time, min Surface carbon, % 455 850 30 0.85 510 950 30 0.99 565 1050 30 1.18 High-speed steel tools that are nitrided in fresh baths or for short times show steep nitrogen and hardness gradients. To avoid these steep gradients, which are believed responsible for the brittleness of the case after such treatments, the use of longer immersion time, higher temperature, or a thoroughly aged bath is recommended. To avoid brittleness of case when relatively short immersion times are used, the cyanate content of the bath should exceed 6%. These conditions often will lower the surface hardness as well as the hardness gradient. Figure 19 compares the hardness gradients obtained on specimens of T1 high-speed steel nitrided at 565 °C (1050 °F) for 90 min in a new bath and for various lengths of time in an aged bath. Fig. 19 Effect of bath condition and immersion time on hardness gradients in type T1 high- speed steel specimens nitrided at 565 °C (1050 °F) Nitriding of decarburized high-speed steel tools should be avoided, because it results in a brittle surface condition. For those surfaces that have been softened from grinding, nitriding is frequently employed as an offsetting corrective measure. Liquid nitriding provides high-speed steel tools with high hardness and wear resistance and a low coefficient of friction. These properties enhance tool life in two somewhat related ways. The high hardness and wear resistance lower the abrading action of chips and work on the tool, and the low frictional characteristics serve to create less heat at and behind the tool point, in addition to assisting in the prevention of chip pickup (see the article "Wrought Tool Steels" in Volume 1 of ASM Handbook, formerly 10th Edition Metals Handbook). Plasma nitriding (also known as ion nitriding, glow-discharge nitriding, and the glow-discharge deposition process) is a heat treatment that uses a large electrical potential to ionize (break down) a treatment gas into ions which are attracted to the surface of the workpiece. When the reaction is properly controlled, the hardened case obtained is similar to a liquid nitride case. Detailed information is available in the article "Plasma (Ion) Nitriding" in this Volume. Steam treating produces a nonuniform, soft layer of iron oxide on the surface of finished high-speed steel tools. This layer, approximately 0.005 mm (0.0002 in.) thick, has lubricant-retaining and antigalling properties, and in some applications will improve tool life by reducing tool-edge buildup. The oxide layer is removed from the tool after a short interval of operation; during this interval, the cutting surfaces of the tool develop a burnished surface that adds further to antigalling characteristics. Steam treatment requires a special furnace with a sealed retort from which all air can be displaced by steam, which is admitted at controlled rates. The presence of excessive levels of moisture in the furnace prior to the admission of the steam will cause rusting and an unsatisfactory surface finish. A typical processing cycle involves placing the work in the special furnace, heating to approximately 370 °C (700 °F), and equalizing. After a suitable equalizing time, which depends on the load, the steam is admitted at controlled rates for approximately h. The furnace is then partly sealed to develop positive steam pressure, and the temperature is raised to 525 °C (975 °F). The steam can then be shut off and the work removed from the furnace and cooled normally. The treatment produces a blue-black film whose appearance is improved by subsequent dipping in oil. This treatment may sometimes be combined with normal tempering treatments, because the type of film produced is relatively insensitive to temperature up to approximately 580 °C (1075 °F). Steam treating offers an additional advantage for tools hardened in salt baths, because it effectively reduces the pitting that can result from adhering salt. Carburizing is not recommended for high-speed steel cutting tools because of the extreme brittleness of the case so produced. However, it is suitable for applications requiring extreme wear resistance in the absence of impact or highly concentrated loading, such as are encountered with certain types of cold-work dies made from high-speed steel. At the same level of hardness, the carburized layer does not have the heat resistance of normal high-speed steel because carbides in the microstructure are predominantly Fe 3 C, rather than the complex alloy carbides characteristic of high-speed steel. Carburizing cycles for high-speed steel consist of packing in a carburizing medium, heating to approximately 1040 to 1065 °C (1900 to 1950 °F) long enough to develop the depth of case desired, and air cooling. The usual holding time at carburizing temperature is from 10 to 60 min, to produce a case 0.05 to 0.25 mm (0.002 to 0.010 in.) deep. Deeper cases should be avoided because of the extreme brittleness which develops. This treatment carburizes the surface and serves as the austenitizing treatment for hardening the entire piece. The carburized layer will harden to 65 to 70 HRC at the surface. Hardening of Specific Machine Tools High-speed tool steels are used extensively as materials for broaches, chasers, milling cutters, drills, taps, reamers, form tools, hobs, thread rolling dies, threading dies, tool bits, and bearing components. Broaches require maximum edge hardness because of the continuous cutting action and light chip load to which they are subjected. This indicates a minimum hardness of 65 HRC for the standard grades and 66 HRC for the premium grades of high-speed steel. Broaches should be suspended vertically in the hardening furnace to avoid undue distortion, and should be quenched under controlled and uniform cooling conditions. Broaches should be straightened while still warm from the hardening operation, and should be cooled to at least 65 °C (150 °F) before tempering. These precautions are particularly important for large diameters. Chasers, because they usually are quite small, present no particular problem in hardening with regard to straightness or residual stress. Hardness recommendations for chasers depend largely on the type of application and the pitch of the thread. Recommended hardnesses for chasers used to cut threads in steel are listed in Table 14. Table 14 Recommended hardness values for chasers and taps used to cut threads in steel Hardness, HRC Threading tool Fine-pitch threads Coarse-pitch threads Acme threads Pipe threads Chasers 61-63 64-65 60-62 . . . Taps 63-65 63-65 62-64 62-64 For cutting cast iron or plastics, chasers should be heat treated to the maximum attainable hardness, because these materials are cut without any significant cutting force but require maximum abrasion resistance. For Acme threads, however, it is sometimes advisable to underharden. Milling Cutters. Fine-tooth cutters and those with fragile forms should be hardened to 63 to 64 HRC. Heavy-duty milling cutters and cutters for use on soft, abrasive materials should be hardened to the maximum hardness obtainable for the particular type of steel. Drills. Hardening techniques for drills vary, depending on the diameter of the drill. Straightness of these tools is extremely important. Various jigging methods are employed, but it is usually advisable to heat treat drills vertically suspended by their shanks in order to reduce distortion in the hardening operation. Straightening is best accomplished in the as-hardened condition before tempering. In tempering, the tempering furnace must not be overloaded, and all drills must receive the correct tempering temperature and time at temperature. Specific recommendations for the hardness of drills for cutting steel are as follows: • Most drills 5 mm ( 3 16 in.) in diameter and smaller are usually hardened to 63 to 65 HRC. (Drills of this size used for plastics, aluminum, or magnesium may have hardness as high as 65 HRC) • Drills over 5 mm ( 3 16 in.) in diameter, to 63 to 65 HRC • Heavy-duty drills normally use grades of high- speed steel providing hardnesses equal to or higher than those noted above. (These drills generally are designed for maximum rigidity and require maximum abrasion resistance) Taps, like drills, are slender in section and require hardening techniques that minimize distortion; this generally means hardening in the vertical position suspended in suitable jigs. Taps should be straightened in the as-hardened condition before tempering. Tempering of these tools must be carefully controlled to allow adequate heating time. Specific hardness recommendations for taps that are to be used to cut steel are listed in Table 14. Reamers encounter a minimum chip load but require maximum wear resistance. For this reason, they are always hardened to the maximum hardness attainable for each grade of steel. Form tools of all types also should have maximum hardness. In general, a minimum of 65 HRC is necessary, and for the premium grades hardnesses ranging from 68 to 70 HRC are frequently desirable. Hobs. Because of their shaving action, hobs require maximum edge hardness. They may become oval in shape if they are not placed in the hardening furnace in the vertical position. Such placement may require special fixtures. Techniques and temperatures in both hardening and tempering must be accurately controlled if tools of this type are to be produced successfully and economically. The hardness of fragile tooth forms may have to be reduced to 62 to 64 HRC to avoid breakage, although the lower hardness results in a shorter production life. Thread rolling dies are usually made of A2 or D2 steel, although dies made of high-speed steel frequently afford superior results, particularly in rolling the harder materials. For fragile thread forms, thread rolls should be hardened to 60 to 62 HRC. For heavier thread forms and those used to roll high-strength materials, hardnesses of 63 to 65 HRC are recommended; however, at these higher hardnesses, dies are more susceptible to breakage. Threading Dies. Most threading dies are made of carbon steel; however, button and acorn dies justify the use of high- speed steel. The relation between hardness and thread form for threading dies is the same as that recommended for taps and chasers. Tool Bits. Standard tool bits, as well as cheeking tools, offset-head bits, and other special types, all require maximum hardness. Standard-duty tool bits should be hardened to 65 to 66 HRC, whereas tool bits made from the higher-alloy high- speed steels should be hardened to 67 to 69 HRC when possible. Bearing Components. The heat treatment of M50 high-speed steel bearing components for aerospace applications must be capable of producing a part with high hardness, uniformly fine grain size, and dimensional stability over a wide temperature range. M50 steel has a nominal composition of 0.83C-4.0Cr-4.0Mo-1.0V with a M s temperature of approximately 163 to 166 °C (325 to 330 °F). The time-temperature transformation (TTT) diagram for M50 is illustrated in Fig. 20. Fig. 20 TTT diagram for M50 steel Virtually any cooling rate capable of cooling the austenitized part to 205 °C (400 °F) or below in 15 min will produce high hardness. To minimize distortion, residual stress and crack susceptibility, a cooling similar to the idealized rate shown in Fig. 20 is desirable. The following practices and procedures are recommended for heat treating M50 bearing components to provide optimum bearing properties: • M50 can be satisfactorily heat treated in vacuum or protecti ve atmosphere furnace. However, most bearing manufacturers prefer to heat treat these bearing components in a neutral molten salt bath or baths • Parts should be preheated prior to the austenitizing cycle to minimize the required soak time at the high auste nitizing temperature. If a single preheat is employed, a bath temperature of 815 to 870 °C (1500 to 1600 °F) with a cycle of 5 to 15 min is recommended. If multiple preheat baths are available, recommended bath temperatures and cycles are listed in Table 15. • The high- temperature bath cycle is the most critical operation in heat treating M50 steel. Following preheating, p arts should be austenitized at 1105 to 1120 °C (2025 to 2050 °F) for 3 to 10 min, depending on cross section and gross load weight. Optimum cycles in the austenitizing bath may be established empirically by varying the soak cycle in the high-temperature bath in 1 2 - min increments and evaluating resultant grain size and hardness. Grain size is more easily measured on as- quenched samples; however, hardness should be checked on parts subsequent to final tempering operations. Ideally, th e cycle will be as short as possible to minimize grain growth while producing desired hardness • Following austenitizing, parts should be quenched in 540 to 595 °C (1000 to 1100 °F) molten salt for 5 to 10 min. The quench minimizes internal stresses and the core-to- surface thermal differential prior to subsequent air cooling and martempering operations • Parts should be subjected to a 175 to 190 °C (350 to 375 °F) martemper bath for 5 to 15 min following quench or quench/air cool operations. The martemper bat h, which operates between 15 and 30 °C (25 and 50 °F) above the M s temperature for M50, equalizes core-to- surface thermal differentials and facilitates subsequent transformation of austenite into martensite with minimal residual stress, distortion, or crac king potential. To avoid undesirable intermediate transformation products, the interval between austenitizing and martempering should not exceed 15 min • Following martempering, parts should be air cooled to room temperature prior to washing, tempering, or subzero treatment. The air- cooling equipment and conditions should provide uniform cooling of parts from the 175 to 190 °C (350 to 375 °F) martempering bath to room temperature within 30 to 60 min. Shorter cooling rates may result in increased residual str ess, distortion, or susceptibility to stress cracking • M50 steel requires multiple tempers to provide maximum toughness and dimensional stability. Parts should be subjected to a minimum of three tempers of 540 to 550 °C (1000 to 1025 °F) for 2 to 4 h, with cooling to room temperature between each temper. Failure to cool to below 40 °C (100 °F) between tempers may result in retained austenite. Tempering may be performed either in neutral molten salts or in atmosphere or air furnaces • Subjection to subzero te mperatures prior to and/or after initial tempering enhances transformation of retained austenite to martensite. Common deep-freeze cycles for M50 are -70 to -85 °C (-90 to - 120 °F) for 2 to 4 h. Use of lower temperatures provides little if any added benefit. The deep- freeze cycle provides maximum benefit when employed before tempering; however, it is not recommended for parts not subjected to martempering or parts susceptible to cracking. When parts are subzero treated before tempering, caution should be ex ercised to ensure that the total elapsed time between martempering and tempering does not exceed 5 h. Use of prior stress-relief cycles reduces effectiveness of deep- freeze operation. When equipment, time constraints, or part design are unfavorable for per forming deep freezing prior to tempering, the parts should be subjected to deep freeze between the first and second tempering operations • Parts requiring re- treating should be annealed prior to rehardening to minimize susceptibility to developing duplex/nonuniform grain Table 15 Recommended bath temperatures and cycle times for preheated M50 bearing steel Temperature Cycles °C °F Time (a) , min Two preheat baths 1 675-730 1250-1350 10-15 2 815-870 1500-1600 5-15 Three preheat baths 1 675-730 1250-1350 10-15 2 815-870 1500-1600 5-15 3 955-1010 1750-1850 5-10 (a) Time predicated on relative load size/bath capacity Low-Alloy Special-Purpose Tool Steels Nominal compositions of the low-alloy special-purpose tool steels are given in Table 1 of the article entitled "Introduction to Heat Treating of Tool Steels" in this Volume. These steels are similar in composition to the water-hardening tool steels, except that the addition of chromium and other elements provides the L steels with greater wear resistance and hardenability. Types L1, L3, L4, and L7 are similar to the production steel 52100 and are used for similar applications. Because of their relatively low austenitizing temperatures, the L steels are easily heat treated. Recommended heat-treating practices are summarized in Table 16. Table 16 Recommended heat-treating practices for low-alloy special-purpose tool steels Annealing Hardening Normalizing temperature (a) Temperature (b) Cooling rate (c) Austenitizing temperature (d) Steel °C °F °C °F °C/h °F/h Annealed hardness, HB °C °F Holding time, min Quenching medium Quenched hardness, HRC (e) L1 900 1650 775- 800 1425- 1475 22 40 179-207 790- 845 1450- 1550 10-30 O, W 64 L2 870- 900 1600- 1650 760- 790 1400- 1450 22 40 163-197 790- 845 1450- 1550 10-30 W 63 845- 925 1550- 1700 10-30 O 63 775- 815 1425- 1500 10-30 W 64 L3 900 1650 790- 815 1450- 1500 22 40 174-201 815- 870 1500- 1600 10-30 O 64 L6 870 1600 760- 790 1400- 1450 22 40 183-212 790- 845 1450- 1550 10-30 O 62 L7 900 1650 790- 815 1450- 1500 22 40 183-212 815- 870 1500- 1600 10-30 O 64 (a) Holding time, after uniform through heating, varies from about 15 min, for small sections, to about 1 h, for large sections. Work is cooled from temperature in still air. (b) Lower limit of range should be used for small sections, upper limit for large sections. Holding time varies from about 1 h, for light sections and small furnace charges, to about 4 h, for heavy sections and large charges; for pack annealing, hold for 1 h per inch of pack cross section. (c) Maximum. Rate is not critical after cooling to below 540 °C (1000 °F). (d) These steels are seldom preheated. (e) Typical average values; subject to variations depending on austenitizing temperature and quenching medium Normalizing should follow forging or any other operation in which the steel has been exposed to temperatures substantially above the transformation range. For the L steels, normalizing consists of through heating to 870 to 900 °C (1600 to 1650 °F) and cooling in still air. The use of a protective atmosphere is recommended. Annealing must follow normalizing and precede any rehardening operation. Recommended annealing temperatures and cooling rates, as well as expected as-annealed hardness values, are given in Table 16. Stress relieving prior to hardening may be advantageous for complex tools to minimize distortion during hardening. A common practice for complex tools is to rough machine, heat to 620 to 650 °C (1150 to 1200 °F) for 1 h per inch of cross section, cool in air, and then finish machine prior to hardening. Austenitizing temperatures recommended for hardening the L steels are listed in Table 16; preheating is seldom employed for steels in this group. Salt or lead baths and atmosphere furnaces are all satisfactory for austenitizing these steels. A neutral salt, such as No. 3 in Table 1 of the article entitled "Processes and Furnace Equipment for Heat Treating of Tool Steels," is recommended. This salt may be deoxidized, for control of decarburization, by the method indicated in the section on rectification of salt baths in the article "Processes and Furnace Equipment for Heat Treating of Tool Steels" in this Volume. Quenching. Oil is the quenching medium most commonly used for the L steels. Water or brine may be used for simple shapes, or for large sections that do not attain full hardness by oil quenching. Rolling-mill rolls made of L7 are an example of parts for which water or brine quenching is used. These steels respond well to martempering. Tempering. Tools made of the L steels should be quenched only to a temperature at which they can be handled with bare hands, about 50 °C (125 °F), and should be tempered immediately thereafter; otherwise, cracking is likely to occur. The tempering characteristics of these steels are plotted in Fig. 21. For most applications, the S steels are used at near- maximum hardness. It is recommended that tools made of any of these low-alloy steels be tempered at a minimum of 120 °C (250 °F), even though maximum hardness is desired. Double tempering also is recommended. [...]... 73 0-9 00 135 0-1 650 22 40 8 1-1 01 90 0-9 25 165 0-1 700 79 0-8 00 145 0-1 470 15 W, B 6 2-6 4 P2 Not req 73 0-8 15 135 0-1 500 22 40 10 3-1 23 90 0-9 25 165 0-1 700 83 0-8 45 153 0-1 550 15 O 6 2-6 5 P3 Not req 73 0-8 15 135 0-1 500 22 40 10 9-1 37 90 0-9 25 165 0-1 700 80 0-8 30 147 0-1 530 15 O 6 2-6 4 P4 Not req 87 0-9 00 160 0-1 650 14 25 11 6-1 28 97 0-9 95 178 0-1 820 97 0-9 95 178 0-1 820 15 A 6 2-6 5 P5 Not req 84 5-8 70 155 0-1 600 22 40 10 5-1 16 90 0-9 25... 178 0-1 820 15 A 6 2-6 5 P5 Not req 84 5-8 70 155 0-1 600 22 40 10 5-1 16 90 0-9 25 165 0-1 700 84 5-8 70 155 0-1 600 15 O, W 6 2-6 5 P6 Not req 845 1550 8 15 18 3-2 17 90 0-9 25 165 0-1 700 79 0-8 815 145 0-1 500 15 A, O 6 0-6 2 P20 900 1650 76 0-7 90 140 0-1 450 22 40 14 9-1 79 87 0-9 00(d) 160 0-1 650(d) 81 5-8 70 150 0-1 600 15 O 5 8-6 4 P21 900 1650 Not rec Hardened by solution treating and aging(e) W, water; B, brine; O, oil; A, air; Not rec, not... 8.010.0 0 .045 0.03 303 S30300 0.15 2.00 1.00 17.019.0 8.010.0 0.20 0.15 min 0.6 Mo(b) 303Se S30323 0.15 2.00 1.00 17.019.0 8.010.0 0.20 0.06 0.15 min Se 304 S 3040 0 0.08 2.00 1.00 18.020.0 8.010.5 0 .045 0.03 304H S 3040 9 0 .040 .10 2.00 1.00 18.020.0 8.010.5 0 .045 0.03 304L S 3040 3 0.03 2.00 1.00 18.020.0 8. 012. 0 0 .045 0.03 304LN S 3045 3 0.03 2.00 1.00 18.020.0 8. 012. 0 0 .045 0.03 0.1 0-0 .16 N 302Cu S 3043 0... 10.7 10.6(c) 12. 9 14.0 14.2 5.96 5.91(c) 7.2 7.8 7.9 A6 7.84 0.283 11.5 12. 4 13.5 13.9 14.2 6.4 6.9 7.5 7.7 7.9 A7 7.66 0.277 12. 4 12. 9 13.5 6.9 7.2 7.5 A8 7.87 0.284 12. 0 12. 4 12. 6 6.7 6.9 7.0 A9 7.78 0.281 12. 0 12. 4 12. 6 6.7 6.9 7.0 D2 7.70 0.278 10.4 10.3 11.9 12. 2 12. 2 5.8 5.7 6.6 6.8 6.8 D3 7.70 0.278 12. 0 11.7 12. 9 13.1 13.5 6.7 6.5 7.2 7.3 7.5 D4 7.70 0.278 12. 4 6.9... 6.9 D5 12. 0 6.7 H10 7.81 0.281 12. 2 13.3 13.7 6.8 7.4 7.6 H11 7.75 0.280 11.9 12. 4 12. 8 12. 9 13.3 6.6 6.9 7.1 7.2 7.4 H13 7.76 0.280 10.4 11.5 12. 2 12. 4 13.1 5.8 6.4 6.8 6.9 7.3 H14 7.89 0.285 11.0 6.1 H19 7.98 0.288 11.0 11.0 12. 0 12. 4 12. 9 6.1 6.1 6.7 6.9 7.2 H21 8.28 0.299 12. 4 12. 6 12. 9 13.5 13.9 6.9 7.0 7.2 7.5 7.7 H22 8.36 0.302 11.0 11.5 12. 0 12. 4 6.1 6.4 6.7... Hardness of low-alloy special-purpose tool steels after tempering for 2 h Carbon-Tungsten Special-Purpose Tool Steels Nominal compositions of carbon-tungsten special-purpose tool steels are given in Table 1 of the article entitled "Introduction to Heat Treating of Tool Steels" in this Volume Recommended heat- treating practices for these steels are summarized in Table 17 Table 17 Recommended heat- treating. .. 17.019.0 8.010.0 0 .045 0.03 3. 0-4 .0 Cu 304N S 3045 1 0.08 2.00 1.00 18.020.0 8.010.5 0 .045 0.03 0.1 0-0 .16 N 305 S30500 0 .12 2.00 1.00 17.019.0 10.513.0 0 .045 0.03 308 S30800 0.08 2.00 1.00 19.021.0 10. 012. 0 0 .045 0.03 Type UNS designation Composition(a), % C Mn Si Cr Ni P S Other 309 S30900 0.20 2.00 1.00 22.024.0 12. 015.0 0 .045 0.03 309S S30908 0.08 2.00 1.00 22.024.0 12. 015.0 0 .045 0.03 310 S31000... S43400 0 .12 1.00 1.00 16. 0- 0 .04 0.03 0.7 5-1 .25 Mo Ferritic Type UNS designation Composition(a), % C Mn Si Cr Ni P S Other 18.0 436 S43600 0 .12 1.00 1.00 16.018.0 0 .04 0.03 0.7 5-1 .25 Mo; 5 × %C min - 0.70 max Nb 439 S43035 0.07 1.00 1.00 17.019.0 0.50 0 .04 0.03 0.15 Al; 12 × %C min - 1.10 Ti 442 S44200 0.20 1.00 1.00 18.023.0 0 .04 0.03 444 S44400 0.025 1.00 1.00 17.519.5 1.0 0 .04 0.03 1.7 5-2 .50 Mo;... %C min - 1.0 max Nb; 0.10 Ta 384 S38400 0.08 2.00 1.00 15.017.0 17.019.0 0 .045 0.03 405 S40500 0.08 1.00 1.00 11.514.5 0 .04 0.03 0.1 0-0 .30 Al 409 S40900 0.08 1.00 1.00 10.511.75 0.50 0 .045 0 .045 6 × %C min - 0.75 max Ti 429 S42900 0 .12 1.00 1.00 14.016.0 0 .04 0.03 430 S43000 0 .12 1.00 1.00 16.018.0 0 .04 0.03 430F S43020 0 .12 1.25 1.00 16.018.0 0.06 0.15 min 0.6 Mo(b) 430FSe S43023 0 .12 1.25... 10.014.0 0 .045 0.03 2. 0-3 .0 Mo; 0.1 0-0 .16 N 316N S31651 0.08 2.00 1.00 16.018.0 10.014.0 0 .045 0.03 2. 0-3 .0 Mo; 0.1 0-0 .16 N 317 S31700 0.08 2.00 1.00 18.020.0 11.015.0 0 .045 0.03 3. 0-4 .0 Mo 317L S31703 0.03 2.00 1.00 18.020.0 11.015.0 0 .045 0.03 3. 0-4 .0 Mo 321 S32100 0.08 2.00 1.00 17.019.0 9. 012. 0 0 .045 0.03 5 × %C min Ti Type UNS designation Composition(a), % C Mn Si Cr Ni P S Other 321H S32109 0 .040 .10 . req 73 0-9 00 135 0-1 650 22 40 8 1-1 01 90 0-9 25 165 0-1 700 79 0-8 00 145 0-1 470 15 W, B 6 2-6 4 P2 Not req 73 0-8 15 135 0-1 500 22 40 10 3-1 23 90 0-9 25 165 0-1 700 83 0-8 45 153 0-1 550 15 O 6 2-6 5 P3. req 73 0-8 15 135 0-1 500 22 40 10 9-1 37 90 0-9 25 165 0-1 700 80 0-8 30 147 0-1 530 15 O 6 2-6 4 P4 Not req 87 0-9 00 160 0-1 650 14 25 11 6-1 28 97 0-9 95 178 0-1 820 97 0-9 95 178 0-1 820 15 A 6 2-6 5 P5. 1650 77 5- 800 142 5- 1475 22 40 17 9-2 07 79 0- 845 145 0- 1550 1 0-3 0 O, W 64 L2 87 0- 900 160 0- 1650 76 0- 790 140 0- 1450 22 40 16 3-1 97 79 0- 845 145 0- 1550 1 0-3 0 W 63 84 5- 925 155 0- 1700