US3508912A - Tool steel containing chromium and cobalt - Google Patents

Description

April 28, 1970 v. K. CHANDHOK ETAL 3,

TOOL STEEL CONTAINING CHROMIUM AND COBALT 5 Sheets-Sheet 1 iled May 26, 1969 I000 Quench Quench and Refrigerate t wmme kmm Tampering Temperature, "F.

I P I000 5 4 4 t mwm PS Quench Quench and Refrigerate Temper/n9 Temperature, "F.

INVENTORS V/JAY K. CHANDHOK and AUGUST KASAK y 2 Attorney A ril 28;, 1970 v. K. CHANDHOK ETAL 3,508,912

TOOL STEEL CONTAINING CHROMIUM AND COBALT Filed May 26, 1969 5 Sheets Sheet 2 S & =2 50o- I I Room Temperature 275- Tensile Strength 0 S 250-" Q Room Temperature 9 225 Yield Strength q i I75- it l50= AV/N H00 F Tens/7e Strength //00F. Y/e/d Strength l l I L 1 l 1 l 0 2 3 4 5 6 7 8 9 l0 l2 Chromium, Weight Percent Q Q E 3 w Q Q: k k & v? I I I I Q 60- 60 I Q k a "a 5 -4 e 5 55 s a 3 50- -50 g a I 45 -45 Q 3 0- -40 K g s: g: g as- E & Tempered a) Hardness g A o 5- -H0rdness /400 Q 0 E Decrease c 500 I 20- t 0 I200F o I I l l l l l l l l I J 3 4 7 8 .9 l0 l2 [3 I4 [5 l6 5 6 Mo/yb denum, Weight Percent Attorney A ril 28, 1970 Filed May 26, 1969 Strength, l000 psi Strength, I000 psi v. K. CHANDHOK ETAL 3,508,912

TOOL STEEL CONTAINING CHROMIUM AND COBALT 5 Sheets-Sheet 5 Room Temperature W Tensile Strength o---- Room Temperature Yield Strength //00 F. Tensile Strength //00F. Yield Strength I l l I J l l l l I I00 Proportion of Tungsten, Percent Ferr/tea Delta Free Ferrite g steels Room Temperature Contain/n9 Q Tensile Strength Steels Room Temperature Yield Strength ll00 Ff Tensile Strength ll00l-'. Yield Strength l I I l I l 1 l Cobalt, Weight Percent INVENTORS. V/JAY K. CHA/VDHOK and AUGUST KASAK Attorney A ril 28, 1970 V. K. CHANDHOK ET Al Flled May 26, 1969 H's. E

Hardness, R 4\ Hardness, R 0| /000F. //00F. /200F.

I I v 5 SheetsSheet 4.

High Speed Steel A/S/ Type M2 Steel 64374 30 I l l l l l l I I l Temper/n9 Parameter P= 7/20 +109 f)X/0' I I I I 1 -1 TILE-.- 1D

A/S/ Type H/9 A/S/ Type H// A/S/ Type H/O INVENTORS. I/IJA) K. CHANDHOK and AUGUST KASAK AI forney April 28, 1970 v. K. CHANDHOK ET AL 3,508,912

TOOL STEEL CONTAINING CHROMYLUM AND COBAL'J' Filed May 26, 1969 .5 Sheets-Sheet R r f f P- m M m m m n T .m w w 0 m H M-m Gk:

-n kwkm a H I l 0 n w Bunk} M 5 P 4 G M E F -um 198:: 9 1 2 W /J! vwsi -u a .D wt: -9 m 7 M85 6 Room Temperature Tensile Strength Room Temperature Yield Strength //00/-'. Tensile Strength //00/-'. Yield Strength INVENTORS. V/JAY K. CHAA/DHO/r and AUGUST KASAK B) p 87a Attorney wmnwmmwmnm QQSE 26533.

United States Patent Int. Cl. C22c 39/20 US. Cl. 75-128 2 Claims ABSTRACT OF THE DZSCLOSURE This invention relates to a tool steel that may be machined in the austenitized and quenched condition and then age-hardened. The composition, in percent, is carbon+nitrogen up to .08, chromium 2.5 to 6, molybdenum 3 to 12, cobalt 8 to 15, nickel up to 4, cobalt+nickel 10 to 18, manganese up to 1, balance iron.

This application is a continuation-in-part of our copending application Ser. No. 514,076, filed Dec. 15, 1965.

Traditionally, tool steels of the prior art, hot work steels as well as cutting tool steels, depends, by and large, upon the presence in the steel microstructure of simple or complex carbides to provide the necessary strength and wear resistance.

However, the presence of substantial amounts of carbon in the alloy, and the consequent presence of microstructural carbides, in the useful condition of heat treatment of the steel, causes serious difiiculties in the processing and use of conventional prior art tool steels. Thus, carbon and carbides tend to become severely segregated during the solidification of ingots, and this segregation leads to inhomogeneities in the tool steel products made from such ingots, even after large amounts of working. The result is inconsistent tool performance and more or less severe embrittlement and consequent breakage in use. Moreover, carbon-containing tool steels are subject to loss of carbon under the decarburizing environmental conditions often encountered during mill processing, heat treatment, and tool manufacture and service use. As is Well known, decarburization detracts considerably from the usefulness of the steel in tool steel applications and may, indeed, necessitate the use of other, more expensive and otherwise less satisfactory alloys in many instances.

A further property requirement in many, if not most, tool steel applications is that the product must be shaped or finished by machining to a final desired configuration, so that machinability of the steel is important. The carboncontaining tool steels must be machined in an annealed condition due to the hardness and relative brittleness of the ferrite-carbide structure that exists at low temperatures. Following machining, a full heat treatment, consisting of austenitizing, quenching or air cooling, and tempering, is necessary to attain the optimum combination of properties for service.

The austenitizing heat treatment, as aforesaid, necessitates the use of high temperatures, e.g., about 1800 F. to 2400 F., and, as a consequence of the dimensional changes attendant upon phase transformations during such heat treatment, warpage of a finished machined tool or tool part is a frequent occurrence. This is particularly troublesome in the case of articles of complex configurations. Additionally, the required high austenitizing temperatures are productive of appreciable surface scaling and/or decarburization unless the environmental conditions are carefully controlled. Such protective procedures are, of course, time consuming and costly. Post-austenitizing corrective finishing operations are often required.

As a rule, articles fabricated from the carbon-containing, hardenable tool steels of the prior art must be tempered immediately following the austenitizing heat treatment because strain cracking of the article is otherwise likely. The mediumor high-carbon martensite resulting from the austenitizing treatment is very brittle so that cracks are prone to occur due to severe internal stresses created by non-uniform cooling rates across the article cross section, or as a result of different cooling rates of cross-sectional variations in complex article shapes.

Carbon-containing hot work too] steels of the prior art all suffer from heat checking to a greater or lesser degree. Such steels in service are exposed to relatively high surface temperatures, while a short distance beneath the surface, the temperature is much lower. Such conditions are productive of tremendous fatigue stresses which, upon repeated cycling, cause the formation of small surface cracks which, growing in size and extent, constitute the familiar heat checking condition.

Accordingly, it is an object of the present invention to provide new and improved tool steels which are substantially free of the disadvantages of prior art tool steels containing substantial amounts of carbon.

It is another object of this invention to provide tool steels which are heat hardenable by means other than carbide formation, specifically steels which are hardenable by the precipitation in the steel microstructure of intermetallic compounds, as compounds of the elements iron, molybdenum, tungsten and chromium.

It is still another object of the invention to provide new and improved steels which are readily machinable in an austenitized condition and thereafter hardenable at a relatively lower temperature to avoid high temperature dimensional changes and surface deterioration.

It is yet another object to provide new and improved hot work die steels which exhibit the aforestated objectives and which have an enhanced resistance to heat checking.

It is a further object to provide new and improved, substantially carbon-free cutting tool steels which are ha rdenable by intermetallic compound precipitation upon tempermg.

In accordance with the foregoing objects, the invention constitutes a hot work steel consisting essentially of, by Weight percent, carbon-l-nitrogen up to .08 chromium 2.5 to 6, molybdenum 3 to 10 or 12, cobalt 8 to 15, nickel up to 4, cobalt-I-nickel 10 to 18, manganese up to 1 and balance iron.

The foregoing and other objects of the invention will be more readily apparent from the following description and drawings wherein:

FIGURE 1 comprises a series of tempering curves, at various austenitizing temperatures from 1700 to 2200 F., showing the change in hardness with change in tempering temperature between 1000" F. and 1350 F., for an inventive steel particularly suited for use as a hot work die steel;

FIGURE 2 comprises a series of tempering curves similar to those of FIG. 1, for a steel of the invention particularly suitable for use as a cutting tool steel;

FIGURE 3 comprises a series of graphs relating the chromium content of experimental steels with the room temperature and elevated temperature strength properties of the steels;

FIGURE 4 is illustrative of, first, the relationship between molybdenum content of certain experimental steels and the maximum attainable tempered hardness thereof, and, second, the effect of that element upon the tempering resistance of those steels, expressed in terms of the percentage difference between the maximum hardness and the hardness observed at progressively higher tempering temperatures;

graphs constituting FIGURE constitutes a series of graphs relating the room temperature and elevated temperature strength properties to the proportion of tungsten in the total content of molybdenum plus one-half the tungsten in an approximately 0.05C-5Cr-7.5 (Mo+ /2W)-13 (Co+Ni) base do not exist, and, consequently, no special measures are needed to prevent this undesirable occurrence during mill processing, heat treatment, article manufacture, or inservice application.

A further important advantage of our new steels is that composition; 5 no high temperature (e.g., 1400-2400 F.) heat treatment FIGURE 6 constitutes a pair of graphs comparing the is required after machining of the steels in the austenitized tempering resistance of a high hardness steel of the incondition. Only a relatively low temperature aging or vention (useful as a cutting tool steel) and that of a curtempering treatment, e.g., at about 1000-l100 F., is rently commonly used high speed steel; needed after finish machining to impart to the optimum FIGURE 7 comprises a series of graphs relating the tool steel properties. Consequently, previously necessary cobalt content of experimental steels with the room temsteps in the tool manufacturing operation can be elimiperature and elevated temperature strength properties of nated and, quite importantly, difiiculties arising from the steels; dimensional distortion and scaling during final heat treat- FIGURE 8 constitutes a series of graphs relating the coment are avoided or minimized. balt content of experimental steels with the spread in The martensite formed in those low-carbon or substanhardness in the austenitized condition and in a hardened tially carbon-free steels is considerably softer and tougher condition after tempering; than that formed in hardenable mediumor high-carbon FIGURE 9 constitutes a series of graphs relating the tool steels. Consequently, these new steels retain relatively room temperature and elevated temperature strength proplow hardness values and are readily amenable to easy erties to the proportion of nickel in the total content of machining prior to subsequent age hardening to much cobalt plus nickel in an approximately 0.05 C-S Cr-7.7 higher, final hardnesses. Moreover, the new steels avoid Mo-13.5'to 15.(Co+Ni) base composition, and or minimize the tendency toward strain cracking on cool- FIGURE 10 constitutes a series of graphs illustrative of i h QQ P Q P Ie$i$t?ne of a representative When compositionally controlled as taught herein, the velftlve Stee} Wlth that of P art hot Work and heat steels of the invention are producible free and substantially l l l Stamless Steels" l 1 1 f th free of free ferrite, and accordingly exhibit a high degree th f f s 5 o e PH,or of dimensional stability and hot workability.

ee S o e mven are.car or contain i y A first series of experimental steels was prepared by residual amounts of carbon introduced into the steel inlevitation meltin in the form of 15 ran button in 0t cidentally to conventional steelmaking practices. The ina d th H g t th g 5 h ventive steels derive their strength and wear resistance e mgo z f 8 eat principally from the precipitation of intermetallic comeat treats (austenmze queue refngerated i f pounds upon aging (tempering) at elevated temperatures aged), and then tested for hardness. The compositions of By a proper proportioning of the Several essential alloy these steels, the heat treatment cond1 t1ons, and the harding elements, and by the use of a proper heat treatment, Hess values P? ({btamed are glven m Table In each th ne St l n b h d d to high hardnesses, as case, austenitization was carried out at 2100" F. for one 6065 Rockwell C, i.e., in the high speed steel hardness half hour. Refrigeration of each of the test specimens was range. done at l00 F. for one half hour.

TABLE I Hardness, R..-

After austenitination at 2.100 After Tempered 2+2 hours at indicated temper- Composition, weight percent for reirigtigation ature, then air cooled C Cr Mo Co V Fe quenched for 5 hour 900 F. 1,000 F 1,100 F. 1,200 F Moreover, the steels of this invention are extremely temper resistant, retaining strengths and hardnesses, at temperatures of 1100 to 1400 F. or higher, clearly supperior to other, known commercial tool steels.

Additionally, since the steels of the invention do not depend on carbon for production of the necessary property characteristics, the problems usually arising as a result of decarburization of carbon-containing tool steels The Table I data is illustrative of the unexpectedly high hardness values obtained on tempering these essentially carbon-free steels at temperatures up to 1200 F.

A further series of steels was prepared as 10-pound, induction melted heats, these heats processed to bar form, and similarly heat treated and tested for aging hardness response and tempering resistance. The compositions of this second series of steels is given in Table II.

TABLE II Composition, weight percent N Cr Me Co Ni Mn St S Fe 10. 01 13.84 0.22 0.12 0.009 Balance.

9.95 14.08 0.20 0.16 0.008 Do. 8. 91 14. 12 O. 22 0. 15 0. 009 Do. 1190 13.84 0.36 0.24 0.010 Do. 15.00 13.84 0.48 0.30 0.008 Do. 9. 04 12.09 2. 25 0.16 0.13 0. 009 Do. 9.04 13. 0.09 0.19 0.14 0.009 D0. 9. 30 13. 92 0. 09 0. l8 0. ll 0. 009 D0. 6 6. 45 9.41 9.86 4. 26 0.16 0.12 0.012 Dc. 0. 005 3. 59 7. 35 10. 96 2. 08 0. 10 0. ll 0. 015 Do.

Hardness (R Tempered Cumulatlvely at- 1,100 F. 1,200 F. 1,300 F. 1,350 F. l,400 F steels, as HWI, HWZ, HW3, HW6-HW9, are hardenable to about 57-61 R on tempering at 1100 F. after austenitizing at 2200 F. Substantial and highly useful hard- TABLE III [Results of Tempering Studies on the Table II Steels As quenched plus As rcirig erated 1,000" F.

As rolled quenched The test conditions to which the Table II steels were subjected, and the results thereof, are set forth in Table III.

Austenitizing temperature, F.

Steel 9 6 Lea 405 0 7 9 L2 3 0 0 0 6 43 3 433 333 4 3 3 3444 444 3 755429 995555 523330 505425 765555 452055 565519 88555555 5555599 65 6.5 3 544444 L 7 1 2 1 L 4 0 & 4- 4-L 752 23 M4 4 4 L8 44 4 44 4 5 4 4 555 4 4 3 4 44 44444 444443 65 25 55 55 55 155 55 595 255555 41995 555505 525 555 9955 42 a am madm n? 3 0 &7 & 007 0 55446. 55 3 1 7 a zm fee 9&M

5 44 555 54 5 5 55 5 6555 4 5555 4 5 55 444 M51 444 115555 5 862 8655 25555 5158 995555 005755 75755510 5545155 66 wm555 m6 .6 .5 55 .5 66 .55 5 .55 .55 .5 .5 .4

55550 555851 588539 55555 Run/ 555 520755 556515 90585535 5353155 1 953 231M 5 0 5 4 3 L& 1 2 L98 L 2 98 3 8 9 6 1 2 3 84 6555 666 5 6 5 6665 5 6 655 6 5 55 5 4 5 5 5 5 5 44 565109 554350 865555 554532 055055 551045 155557 5555552 4466577 .4 .443 .44 .4 4 .4 .44 5 .5 .443 4 .3 333 14M M3333 .33 M 4 66 1 5 2 3 19 99 32 7 1198 690 7 4 44 4 4 44 4 4 4.4 44 44 3 44.33 334 3 251509 552211 755205 022355 015590 25955 005987 65575535 5565 58 4 .4 43 4 .4444 4 44 4444 54 4 .3 44 .333 3 .3 4 M 6 M 80 4 3 M 44 3 44. 4. 4 33 4 33 4A. 4 3 3 3 h h u n u u u u .1

u n m n n m n m m o 2 4 0 0 0 0 c c o c w m m C A. 4 C 4 1 1 4 0 m 1 m M 0 0 1 0 I I. .1 I .0 0 0 O m m M m. 1 M M M m 9 p e p T. r P T. C r r r C C C O C 0 C G C 5 e 4 e 5 e 0 0 0 c o c c G o 3 0 0 0 0 0 0 0 9- 0 J J l J J l D 0 0 0 0 0 O 0 0 0 r 1 2 3 4 5 0 7 9 w W W W W W W W W W H H H H H H H H H mpering F., thereby showing the perature geous propwhere the 1 Specimens austenitized at the indicated temperature, oil quenched, retrigerated at 100 F. for 3%; hour, and cumulatively tempered at successively higher indicated temperatures for 2+2 hours.

It will be seen from the Table HI test results that nesses, e.g., about 40-45 R are retained to te the experimental steels there studied are hardenable from temperatures as high as 1350" relatively low quenched (or quenched and refrigerated) extreme temper resistance and useful high tern applicability of these steels. These advanta erties are graphically illustrated in FIG. 1 Table II data for Steel HW3 are plotted as a series of tempering curves showing the change in hardness of hardnesses on the order of 37-40 R (1700 F. austenitizing temperature) or 34-50 R (2200 F. austenitizing temperature) to much higher tempered or aged hardness levels. For example, the lower (710%) molybdenum that steel with tempering temperatures between 1000 F. and 1350 or 1400 F. for each of the Table 11 anstenitization temperatures from 1700 to 2200 F. As will be seen from FIG. 1, peak hardness occurs, in each instance, at a tempering temperature of about 1000- 1100 F., and maximum hardness, about 60 R is obtained at the highest austenitizing temperature, 2200 F. Such steels find particular application as hot work steels.

Similarly, the higher (12-15%) molybdenum steels, I-IW4 and HWS, are hardenable from quenched hardnesses of about 43-50 R after a 2200 F. austenitizing treatment, to very high aged hardnesses of about 63-65 R In these steels, hardnesses of about 46-53 R are retained after tempering at temperatures as high as 1350 F. Illustratively, the Table II data for Steel HW4 is graphically shown in FIG. 2, wherein the similarity to the FIG. 1 steels is seen together with the higher peak hardnesses which particularly suit these steels for cutting applications.

A third series of steels was also prepared, as -pound heats, processed to bar form, and subjected to extensive investigation of hardness, room temperature and elevated temperature strength properties, impact strength, and ductility. The compositions of these latter steels are given in Table IV.

Characteristically, the inventive steels are essentially carbon-free, but it is realized that a certain carbon content is necessary to make the steels satisfactorily producible by conventional steelmaking practices. Test results show that an increase in carbon above 0.08% (Steels HW12, l3, and 15, Table V) resulted in a gradual drop in both the room-temperature and elevated-temperature strength properties. Hence, carbon or carbon-i-nitrogen may be present in amounts up to 0.08%.

Since the steel is intended for use at elevated temperatures in an essentially air atmosphere, some chromium is desirable to provide satisfactory oxidation (scaling) resistance. Also, test results show that the tempering resistance is somewhat increased by 2.5 or 6% chromium (HW17 and 12 vs. HWl4, Table V). At the 11.1% level (HW19, Table V), 20% delta (free) ferrite formed in the microstructure upon austenitizing at 1800" F. and the room-temperature and elevated-temperature strength properties and ductility (elongation, reduction of area, and impact value) declined. Hence, chromium is present within the range of 2.5 to 6%.

Molybdenum is an important strengthening agent in the steel. The tempering resistance is steadily increased with increasing molybdenum content, but the ductility is lowered. At 10% molybdenum (HW21, Table V), some free (delta) ferrite is formed upon austenitizing at 1 800 F.

TABLE IV Composition, weight percent Heat No. Bar No. C N Cr W Mo Co Ni Mn Si S Fe Steel No.2

HW12 1140 63 309 0. 036 0. 01 5. 19 7. 11. 16 2. 15 0. 03 0. 013 Balance 1141 63-310 0. 095 0.01 5.15 D0. 1142 63-311 0. 049 0. 01 0. 40 D0. 1143 63-312 0.161 0. 01 5. 33 D0. 1144 63-313 0. 0-51 0.01 2. 68 D0. 1145 63-314 0. 053 0. 01 2. Do. 1146 63-315 0. 037 0. 02 5. 78 D0. 1147 63-316 0. 052 O. 03 11. 14 Do. 1148 63-317 0. 047 0. O2 5. 46 Do. 1149 63-318 0.049 0. 02 5. 17 Do. 1150 63-319 0. 036 0. 02 5. 30 Do. 1151 63-320 0. 046 0. O2 5. 37 D0. 1152 63-321 0. 051 0.02 5. 39 D0. 1153 63-322 0. 053 0. 02 5. 42 0. D0. 1154 63-323 0. 043 0. 01 5. 53 Do. 1155 63-324 0. 042 0. 01 5. 32 0. Do. 1156 63-325 0.047 0. 02 5. 27 3. 11. 38 2. 16 0. 07 0.011 Do. 1157 63-326 0. 046 0. 01 5. 11 11. 41 1. 21 0. 02 0. 02 0. 009 Do. 1267 64-46 0. 080 5. 31 7. 49 17. 66 0. 20 0.06 Do.

Table V sets forth the nominal compositions of the Table IV steels, rearranged in groups having an approximately constant base composition and wherein one or a pair of elements is varied in amount or proportion (such variable elements being italicized in Table V). The test conditions and observed property characteristics are also shown in Table V, Column 9.

Many of the standard tensile test specimens of the Table IV steels were prepared by machining in the as-austenitized condition. Machine fixtures and dies have also been similarly produced from the inventive steels.

The foregoing experimental data, especially that of Table V, shows that the steels of this invention possess high aged hardness, a considerable spread between quenched and aged hardness (thus permitting machining in the autenitized condition and subsequent age hardening), high resistance to softening upon exposure to elevated temperatures, high strength over a Wide temperature range, and reasonably good ductility-all desirable characteristics of superior materials for hot work tool and high-performance cutting tool applications.

Above 10% (HW21, Table V), the free ferrite content becomes excessive and leads to an unduly low impact value at room temperature (1 ft.-lb.). A 3 to 10 or 12% molybdenum content is provided in the steel.

Cobalt is an essential alloy ingredient to ensure proper microstructural balance in the steel, because cobalt acts as an austenite former at higher temperatures but has only a small effect on the austenite-to-martensite transformation temperature (the Ms temperature). Thus the proper amount of cobalt allows the steel to be hardened and, at the same time, essentially or completely free from delta ferrite. Moreover, cobalt increases the effectiveness of the precipitation of intermetallic compounds in strengthening the steels.

If no nickel is present, a minimum of about 10% cobalt is advantageous for the avoidance of unduly large amounts of delta ferrite in the microstructure (see Steels HW23, 24, and 25, Table V). The test results also show that the tempering resistance as Well as the room-temperature and elevated-temperature strengths increase with increasing cobalt content up about 15% (HWZS, Table V).

000050 05 00 005.6 005000 0000050 05 5500 -2305 550. 0005053 0005000 050200 05050 5000 00 050050 0 0000 05 055230 0 00 00 000050 05 00m 0055 0000 00 05 000000 505 00 00 0 505 05 50 5000.5 0.5 0505020 0005 50.0053 00050005 0005 5 32500000 500 -050 53 50500 5.505 00 0 0 05 050503 0 00005 0 050.50 550205 05. 5500050 5555 55 5? 55055 55n55o0 00 0000 0505020 05500 A0550 -0500 05 055: 053 05500 00050 00 005000 03050000 05 0503 000005 0502052000 25550500 0000 505 05 5000 050050 05.2. 0305 05 5500500 on 050500 0505200502 000 .5050 05 00 0 50050 0 000 0 050550 05 0050 5 505000 00 000 5 000 000 0 00005 5 0350000 000050000 05 0000 0 5000 00 52 50500 00050 50 55 50050 002 0 505 0002 550: 0050500 0 0000 205052096 052. 025005 05 002 5020 00 0: 000000502 0.3 0 005 0002 0003 0 000.0 0 0 050500 000500505 05 50000 5 020000 50 5 00500 000 0550050 25502 0 00 00500 00 05 500055 0 H0 05 020 00 505 250.00% 05 55 000050000 52 50500 505 00 0050000 000 050050 0005 5000.55 000 0 00. 3 0 505 0050500 0000050025 02000 05 5250509 0000500 5 5502505 00 55050 05 0053 5000 05 05050 00 0005 00 5:050 52. A 3 .2. 00 0 0032 2 08 005 0 005 500050 0005500 00 20500 0 00 0000 00. 05 0000055. 20 0 05 5 50005 03 05 200205 0w 8 2; 650m 0000000 02 5.05050 05. 5000 0 00 005 500500. 00 200 050 0500050 0:00 05 0.0 0050250 0 50 000 50 5000 00 0 0 05 00:00 8 0 0098 05 00205 000000 5 000: 2 00000 0025 0050005 :0 555. no 0 00 0 250 000 005 Cw 0 0.2. 0 02302 2 2 5 000 0 m: 0 2 5 5 5.2. A 5 .2. 00 000 00 @2505 020000 000500 00 000: 0a 000 2002052 0550 0:0 50 500005 05.65 9. 00: 050m 00 0 5 00302 0 55 53 0 0 5 $02 0 5 .2052: 5 0:03. 000080 05 55 050 05 50050 5000 05 50 5000 0 5 0000005 50050050 00505 00 0 0 00 Cw 3 .2. 2352 2 2 2 0002 5 0.55.. 5 0 5 5 00 00 002 002 m 00 00 00 0 00 0 0 0 2 0 2 0 2 2 0 00 0 0052 E 00 05 02 w 00 00 mm 0 0 m0 0 0 0 0 0 2 0 0 0 0 0 0 00 0 0032 00 00 002 00 0H 00 2 00 00 S 0 0 0 0 0 0 0 0 0 0 S 0 .0 2 00 v0 03 2 0 0m 00 00 E E 0 0 0 0 0 0 0 0 0 0 0 0 50032 00 00 002 05 0 00 00 0 0 00 0 0 0 0 0 2 0 0 0 0 0 0 0 2 00 00 05 002 E E 00 G 00 0 0 0 2 0 0. 0 0 B 0 2 2 00 00 $2 0 2 m 02 00 00 00 00 0 0 0 3 0 0 0 0 00 0 0032 00 00 002 002 0 0m 00 m0 m0 5 0V 0V 1.... 0 2 0 0 0 0 00 0 082 00 00 02 02 m 00 2 2 mm 02 00 2 0 0 0 0 0 00 0 5032 um c0 22 m2 0 3 a 0m 0m mm o o 0 0 0 2 N. 0 0 n we 0 235 0 00 SH 002 0 0m 3 5 mm mm 0V 0 H 0 e m 0 0 m 0 0 0 c i. 003m 2 02 02 002 H 2 00 .00 00 00 00 00 0 0 2 2 :2 0 0 00 0 2032 00 02 0 02 002 m 00 0* 00 00 2 02 02 02 0 0 0 2 0 5 0 0 00 0 0032 00 00 002 02 0 00 00 0 00 00 0 0 0 0 0 2 0 0 0 *0 0 0 2 S 0 0 02 00 02 00 00 m0 0m 0 0 2 0 0 2 0 0 0 0 0 0 0 532 5 3 002 02 0 2 0 mm 00 2 00 00 0 0 0 2 0 0 2 2 00 0 0 2 00 00 05 02 0 00 00 0 0 00 00 0 0 0 0 0 2 0 0 0 0 0 0 0 02.52 00 00 02 02 0 2 02 0 0 00 00 0 0 0 0 0 02 0 0 0 0 00 0 055 00 00 002 002 0 0w 5 00 00 .5 0 0 0 0 0 5 0 0 0 0 00 0 552 0 0 0 3 00 3 0m 0 0 0 0 0 02 ms 00 0 232 0 0 0 0 0 5 002 0 0m 00 2 00 5 0 0 2 0 2 2 0 0 0 0 .5 0 532 an 00 m3 202 a 0m 3 00 mm o a c 0 0 0 3 w 0 0 m 2 0 02am an 00 03 m2 m 00 2 2 0 an an o o 0 0 0 2 0 0 0 n 3 0 .2 0 HH 500.60 500.60 5.0.0 5.0.0 2 5 50500 50200 5 5.0.0 2 0000 5 0000 2 5 0000 2 5 005 2 2 0000 2 2 2 0000 2 5 0000 2 02 O 3 5 O O 2 2 80 0 5 80 2 80 2 08 5 4 5 0 5 80 2 000 2 2 5 w m 2 5 m m 1 00 5 0+0 05000500 .650 Add 00005 02 00 500.60 500000 5803 505000500 ll 12 which excessive grain growth is most pronounced. For steel HW30 the substitution being complete. FIG. this purpose, carbon is usefully present on the high side of graphically illustrates the Table V data on the tensile its contemplated range. This further advantage is illusstrength properties of these three steels, and it will be trated by the results of a further series of tests of steels seen from that figure that both room temperature and having compositions as given in the following Table VI: 1100 F. tensile properties, both yield strength and ulti- TABLE VI Composition, weight percent C Cr Mo 00 Ni Mn Si Cb Fe The steels of Table VI were austenitized at 2200 F. for mate tensile strength, are substantially unaffected by this minutes, oil quenched, the grain size determined, and substitution. However, it will be further noted from the the steels were then tempered at 1000 F. (2+2 h r Table V data, that the ductility values of the higher tungfor Steel HS 11M, 2+2+4 hours for s l 115-11), d stem steels are generally lower than those of the steels tested for impact strength. The results of such tests are having a greater Proportion of m y For this given in T bl VII; reason, as well as because of the higher cost of tungsten and the larger amounts required to achieve the proper- TAB LE VII ties obtainable with smaller amounts of the less expensive Tempered 0; Charm Onotch molybdenum, the latter element is preferred to tungsten hardness, size impact strength 25 1I1 our Steels fooirpolmds A further experimental steel, Steel No. 64374 was pre- Steel No.2 pared having the following composition:

-linz:::::::::::: 2? i3 2 Steel 64-374:

C 0.06 It will be seen from Table VII that the colu-rnbi-um-con- Cr 4.57 taining steel had a significantly smaller grain size and M0 11.34 higher impact strength than the columbium-free steel, Co 14.69 Somewhat greater amounts of carbide-formers, consist- Ni 20 cut with maintenance of a delta ferrite-free structure, may Mn 0.7-0 be used to further enhance this desirable effect, Si 0.11 As aforesaid, the steels of the invention are har F Bal. and Strengthened y Precipitation of intermelallic This steel, by reason of proper balance of ferriteand Pounds p aging Molybdenum is all important element austenite-formers, contained no free ferrite after austenitin this regard, and is believed to combine with iron to i i at 2200 F although it contained 11.34% molybform compounds, as an Fe Mo-type Laves phase, and with denurn. Upon quenching and tempering at 1000 F. for

iron and chromium to form a chi phase. Tungsten is simi- 2+2+4 hours, this steel exhibited a hardness of 67 R larly useful, probably forming similar intermetallic com- Moreover, the steel also exhibited a highly superior repounds, as Fe W, and accordingly, molybdenum in the sistauce of softening, as illustrated by the graphs of FIG. new steels may in general be substituted, in whole or in 6, wherein Graph E represents the tempering resistance part, by tungsten, on a basis of 2 parts by weight of of Steel 64-374, an Graph F that of a commonly used tungsten to one part by weight of substituted molybdenum, g Speed SW61, A151 yp -L containing 035% due to the greater atomic weight of tungsten. M11, 030% C 1.95% V, 6.40% W, Graph A of FIG. 4 is illustrative of the effect of molyb- M0, balance essentially The tempering P denum content upon the maximum attainable hardness eter used in 4 is the common Larsen-Miner P upon tempering (at 1050 F.). From that graph, it will 50 filer be seen that maximum hardness is achieved at a molyb- )X denum content of about 10 to 12%. Hardnesses of 50 h i to R are readily obtainable when molybdenum is T=temperature, R, and

present in amounts of 7 to 8%. t=time, hours.

Molybdenum also is productive of temper resistance 55 in the new steels, this property increasing with increasingly larger quantities of that element. Graphs B, C and D of FIG. 4 are illustrative of this eiiect of molybdenum, wherein the molybdenum content is related to the percentage difierence in the maximum attainable tempered 6O hardness (1050 F. temper) and the hardness retained after progressively higher tempering temperatures. This spfied Steel eifect is particularly evident at the more rigorous condi- Steel 64-374 was further compared Wlth respect to tions of R and 13000 R illustrated by Graphs B cutting tool life, to commercial high speed tool steel of and C, respectively. In both instances, the hardness loss 65 the YP P t n(0.85% C, 0.30% on tempering reduces to a relatively low, constant per- 030% 445% F 195% Q cemage level in the molybdenum range of The M0, balance Fe), and with the same composition having U h h h l b t, 0 a higher (0.96%) carbon content. The workpiece was fi t e rr i per i g t e ip eratfir e. ange 1S e88 a mp at the 1 commercial AISI H-13 hot work steel (0.40% C, 0.40%

The substitutability of tungsten for molybdenum is il- M11, 530% 110% balance lustrated by the Table v data for Steels HW12, 29 and Fe) hardened to 28-30 c- The cutting tools were p- It will be seen from these two graphs that Steel 64-374, at practically all parameter values, is equivalent or superior, in tempering resistance, to the M-2 steel, and at parameters above about 34, representing more rigorous conditions of time and temperature, the experimental steel is markedly superior in this regard to the prior art high 30. In the latter two steels, tungsten was substituted for If y l/l-inch Square y 11/2 iIlChES n ngth- Cutmolybdenum, in steel HW29 the substitution being on a ting Was done :3, the depth of f WES 0062 1 0b and 48% basis (considering the combined effective amount feed was 0.010 inch per revolution. The tool geometry of these two elements as percent Mo+ /2% W), and in 75 was 3, 6, 10, 10, 10, 10 and the nose radius was 0.030 inch. The results of such tests are set out in the following Table VIII.

TABLE VIII Average Average tool life,

tool minutes plus tuming hardness,

1 Figure in parentheses is the number of test cuts. a Second figure is the standard deviation of the tests conducted.

pound precipitation (also facilitated, as noted, by the cobalt addition). For this purpose, a large spread between quenched (or quenched and refrigerated) hardness and maximum attainable tempered hardness is desirable. FIG. 8 illustrates the effect of cobalt on this property. Thus, the three graphs, G, H and I, there appearing relate the percentage of cobalt in the four steels HW23, 24, and 41, with the difference (Rockwell C points) between the untempered hardness and the tempered hardness at, respectively, 1050 F., 1100 F. and 1200 F. Maximum hardness spread is seen from these graphs to occur, in each instance, at cobalt values of about 14 to 15.5%.

TAB LE IX Hardness Total Hardness, R, at indicated tempering temperatures loss, Percent Percent percent 1,0501,400 cobalt nickel Co+Ni 1,050 F. 1,100 F. 1,200 F. 1,300 F. 1,400 F. F., percent It will be seen from the Table VIH data that, under the stated test conditions, the age-hardened steel No. 64374 tools out about twice as long as the 0.85% carbon M-2 high speed steel tools, and about equally as long as did the 0.96% M-2 tools.

The eflfect of cobalt upon tensile properties is graphically illustrated by FIG. 7, erected upon the data of Table V. From FIG. 7, it will be seen that maximum room temperature yield and ultimate tensile strengths are obtained by the inclusion in the contemplated steels of about 15% to 16% cobalt. Similarly, maximum values of these TABLE X Composition, weight percent BarNo. C Mn P S Si Cr Mo V Ni 00 Fe Steel:

HWL 241 0.058 0.06 0.08 4.64 7.52 1.93 11.30 Balance. H-l3 63-496 0.39 0.37 0.016 0. 016 1.11 5.06 1.38 1.07 0.20 Do. H131)(lowresid- 65-171 0.39 0.07 0.006 0.016 0.18 4.93 1.35 1.17 Do.

properties at elevated temperatures, e.g., 1100 F., are

obtained at about the 15% cobalt level. Usefully high strength properties, at both room temperature and 1100" F., are obtained at cobalt levels of 10 or 11% upwardly to the aforesaid maximum value.

The aforementioned test set also shows the appearance, in the tested nominally 0.05% C-5.4% Cr-7.5% Mo base composition, of a substantial proportion (30-40 volume percent) of delta ferrite at the 8% cobalt'level. Traces of this phase still remained at the 11% cobalt level.

As previously mentioned, the steels of the invention, in large part due to the aforementioned part played by the cobalt addition, are machinable in the austenitized condition and thereafter hardenable by intermetallic com- The heat check test consisted of a 4-second immersion of the test specimens (mounted on a rod-like spindle) into a molten lead bath at a temperature of 1225 to 1250 F., followed by a 1.5 second quench in a to F. water bath, after which the specimens were dried above the lead bath for 5 seconds. This test cycle was repeated at a rate of about 3 cycles per minute.

Each test specimen was in the form of a circular body having a centrally apertured hub and circumferential flange extending from the midline of the hub. The flange hand an outside diameter of 2.000 inches and a thickness of 0.075 inch, while the hub hand had an outside diameter of 1.500 inches, a thickness of 0.350 inch and a hub aperture of inch.

Prior to testing, the specimens were heat treated as shown in Table XI.

The results of the heat check tests are given in Table conditions due to the high temperature differentials so XII. produced.

TABLE XII Heat check index, H at indicated number of heat check cycles 12, 500 15, 000 17, 500 Hard- 10,000 cycles cycles cycles cycles 25,000 cycles Specimen ness, Steel No Position 1 R N 2 L HO 4 N L HO N L HO N L HG N L I HG HWlZ 241-A 3 52. 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 HW12 24l-B 7 53. 0 0 0 0 0 0 0 0 0 0 (J 0 0 0 0 0 AISI H-l3- 5 63-496-4 2 44.4 1 6 6 5 28 63 13 56 202 18 84 356 a F F F AISI H-l3 63496-5 6 44.2 2 5 7 5 30 67 13 53 191 15 68 283 F F F AISI-Hl3 (10W 65-171-1 4 46 3 0 0 0 2 16 23 5 40 89 ll 88 292 F F F residual) 65-171-2 9 46.9 0 0 0 0 0 0 3 22 38 7 56 148 F F F 1 Indicated number is position of test specimen (a total of 9 Specimens were used) on the holding spindle, from left to right as viewed from the front of the test apparatus.

2 N=total number of cracks in Specimen flange. 8 L=surn of the lengths of all cracks in Specimen flange.

4 HC=Heat Check Index=L/N.

5 Specimen Nos. 63-496-4, 5 Were inserted after 1,000 cycles had been accumulated on other flable IX specimens. 5 F, indicates specimen heat checking so extensive as to be considered to have completely failed beyond usefulness in any conceivable die casting end use, prior to indicated number of cycles.

From the results of Table XII, it is seen that heat checking of A151 Type H-13 (Specimen Nos. 63-496-4, 5) hot work steel as initiated at about 10,000 cycles, whereas, in the case of the low-residual H-13 steel, heat checking commenced between 12,500 and 15,000 cycles. After 17,500 cycles, both prior art steels had exhibited complete failure. On the other hand, the inventive steel HW-l2 had not even started to show heat check cracks at 25,000 cycles when the test was discontinued.

It was further observed that the flange surfaces of the conventional and the modified (low-residual) prior art steels had eroded considerably, by scaling and decal-burization, during the test, whereas the inventive steel was essentially uneroded and was readily cleaned to present the original smooth surface appearance.

Such properties confer on the new steels a high degree of utility in application to elevated temperature end uses, as in the forging of high temperature materials, in the extrusion of brass, in the construction of spreaders and cores in aluminum castings-where the metal is subjected to the full impact of an injected stream of aluminum, in the construction of turbine buckets, blades, etc. Indeed, the new steels are useful in most hot work applications wherein very high surface temperatures, e.g. 1200-1700 F. are encountered. Water cooling can be used in such applications with relative immunity from the cracking usually exhibited by prior art hot work steels under such What is claimed is: 1. A hot Work steel consisting essentially, by weight percent, of about Carbon nitrogen Up to 0.0.8.

Chromium 2.5 to 6.

Molybdenum 3 to 12.

Cobalt 8 to 15.

Nickel Up to 4.

Cobalt nickel 10 to 18.

Manganese Up to 1.

Iron Balance, except for incidental steelmaking impurities.

2. The steel of claim 1 wherein up to of the molybdenum content is replaced by tungsten on a 2 to 1 weight basis.

References Cited UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3:5 :9 Dated April 97 Inventor) ViJay K. Chandhok and August Kasak It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column line 10, after "impart", delete --to--;

Table II, column 3, under- "C" line 2, cha e "0.006" to --0.096--; same Table, column 4, under "Cr last line, change Table III, column 1, under "Steel", line 1, change "Hwl, 0.100- 6Cr-l0Mo-l lCo t0 --HW1 0. 10C -5Cr-l0Mo-l lCo Table I1, column 12, line 17 under 1,100F, change "59" to --55-- same Table, column 13, line 19 under 1,200F, change 40" to --49--' same Table, column 15, line 5 under 1,400F, change Column 10, middle paragraph, last line, change "purpose" to --purposeful3 Column 12, line &3, change "of" (first occurrence) to --to--,'

Column l t, line 3 change "H-l2" to --H-13--;

Column 14, line 61, after "hub" delete --hand--.

SIGNED AND SEALED SE-AL) SEP 29 1970 Ed Fl id! o wmxm E. squirm, .m.

Comissioner of Patents Aneatingofficer F ORM PO-IOSO (10-69) USCOMM-DC BOSYQ-PQO a us covumnm nnmmc ornct: nu o-au-su

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