US3077397A - Low alloy-air hardening die steel - Google Patents

Description

Feb 12, 1963 P. R. BORNEMAN Low ALLOY-AIR HARDENING DIE STEEL 2 Sheets-Sheet 1 Filed May 9, 1961 Fig Fig.4

Im mm 6 Feb.- 12, 1963 P. R. BORNEMAN 3,077,397

LOW ALLOY-AIR HARDENING DIE STEEL Filed May 9, l1961 2 Sheets-Sheet 2 10005 l l 'l l 200 400 600 SOO |000 |200 TEMPERING TEMPERATURE- F 3,077,397 Patented Feb. 12, 19163 3,077,397 LQW ALLGY-All HARDENNG DEE STEEL Paul R. Borneman, Natrona Heights, Pa., assigner to Allegheny Ludlum Steel Corporation, Breckenridge, Pa., a corporation of Pennsylvania Filed May 9, 1961, Ser. No. 103,869 4 Claims. (Cl. 75126) This invention relates to improvements in die steels, and relates in particular to a new and novel low alloyair hardening die steel.

The low alloy-air hardening die steel to which the present invention is directed, is conventionally used for tools and dies having a design that prohibits the use of water hardening steels because of the hazard of distortion or cracking during hardening. The oil hardening steels generally hold their dimensions less closely than the air hardening compositions. rEhe requirements of such steels are a combination or a balance of deep hardening characteristics, a Wide hardening range, good impact resistance and good machinability in addition to dimensional stability during heat treatment. The aforementioned optimum properties are desired and required, particularly for the manufacture of dies used in punching, coining, piercing, blanking, stamping and trimming of metals and are also useful in the manufacture of hubs, bushings .and master tools where high dimensional tolerances are of importance. The low alloy-air hardenable `steels now available commercially satisfy several of the aforementioned properties; however, none satisfies all of the property requirements in good balance.

A die or tool steel has now been discovered which exhibits deep hardening characteristics, a wide hardening "range, good impact resistance, and is easily machined in addition to exhibiting unusually goed dimensional stability.

' In general, the present invention is directed to .a steel containing more than about .80% but less than .90% carbon, from 1.85% to 2.15% manganese, .25% to .50% silicon, .75% to 1.l% chromium, from 1.20% to 1.40% .molybdenum and from about .45% to .85% vanadium, the balance being essentially all iron. The carbon content preferably falls within the range of from about .83%

to .87%, and sulfur is optionally present within the range of rrom about .08% to .10% to impart improved machinability.

Consequently, it is an obiect of the present invention to provide a low alloy-air hardenable die or tool steel that exhibits good deepz hardening characteristics, a wide hardening range, good impact resistance, good machinability in the annealed condition and good dimensional stability during heat treatment.

It is also an object of the present invention to provide a die or tool steel which exhibits superior dimensional stability during heat treatment to prior known low alloy deep hardening compositions.

It is a further object of the present invention to provide a die or tool steel which exhibits a wider hardening `range than the prior known low alloy deep hardening compositions.

Other objects and advantageous features of the present invention will be obvious from the following description and the accompanying drawings wherein:

FIGURE l is a graphical representation of the dimensional distortion which occurs in the steel of the present invention .as compared with similar prior known compositions;

FIG. 2 is a graphical representation of the comparative dimensional stability properties of analyses that constitute another embodiment of the present invention; and

FIGS. 3 and 4 are cross-sectional views of 4" and 6"' cubes, respectively, showing hardness measurements taken from the center to the edge which illustrate the hardenability of the alloy of the present invention. In quenching and tempering low alloy-air hardening compositions, it has been determined that the dimensional changes take place upon phase transformation and the dimensional changes are particularly noticeable during subsequent tempering heat treatments. The parts or dies are conventionally machined in the softer annealed condition and are then heated andquenched to effect maximum hardness for their ultimate use which demands such properties. During heating, transformation of the structure of the material to a phase known as austenite is .accompanied by a decrease in size. Upon quenching the austenite is transformed to martensite; however, some of the austenite fails to transform and is referred to as retained austenite. Tempering is conducted in order to complete the transformation of retained austenite into martensite or bainite and to relieve stresses that may result in subsequent cracking. This transformation is known to generally result in an expansion of the metal and unless the shrinkage which occurs during heating is equivalent to such expansion, .a distortion of the die or tool occurs. The resulting die or tool steel part which has been shaped to close tolerances, is frequently found to be unacceptable. The tempering temperatures Vary from room temperature to 1000 F., but generally occur between the temperature range of from about 400 F. to 650 F.

In the composition of the present invention, manganese, chromium and molybdenum are present as hardening agents Within the usual and known ranges which are relatively critical in providing optimum deep hardening characteristics and impact resistance. The carbon content is also present as an essential hardening agent, since carbon, .as is well known, is a necessary material for the formation of martensite which is the primary hardening phase. ln the composition of the present invention, however, the carbon is present within critical limitations in that the amount of carbon present must exceed .80% (about .83%) in order to impart the necessary hardening and hardenable characteristics, While 4it must be below .90% (about .87%) in order to retain the excellent stability of the steel. Vanadium also must be within the critical range limitations of from about .45% to .85%. The function of the vanadium over and above .about .20%, which is dissolved in the steel and acts as a hardening agent, is beieved to be in combining with the carbon. lf excessive amounts of vanadium are used, the effects are identical to that of insufficient amounts of carbon, in that insuicient amounts of available carbon caused either by excessive vanadium or too little carbon in the composition would result in insuicient hardening properties. On the other hand, the vanadium carbide precipitates at grain boundary junctions, and having a high solution temperature, controls grain growth and contributes to a wide hardening temperature range. This same vanadium carbide in some Way appears to contribute to the dimensional stability, probably by controlling the amount of carbon which can be taken into solution during austenitizing. Consequently, if the vanadium is too low or below the critical range set forth, the dimensional stability properties are not obtained. i

TABLE I Designation C Mn Si Cr Mo V S T 2.14 36 1.06 1.35 .03 XT-OZSEZ 2.02 24 1.02 1. 22 .02 .081

The superior dimensional stability of applicants alloys as compared to the prior known similar compositions is particularly illustrated by the data shown by the following Tables II, III and IV and FIGS. 1 and 2 of the drawings. In Table II, there are shown the dimensional changes effected on 3%: inch round X 2.000 long specimens of the material designated in Table I as .AL-123, Airloy and XT-O28 when the material is hardened and hardened plus tempered at temperatures ranging up to 1000 F. Each of the commercial grades was hardened by air quenching from the temperature recommended for the specific grade to secure optimum mechanical properties and applicants composition was quenched from 1525 F., which is within 25 F. of the quenching temperature of the other materials and which temperature gave applicants composition equivalent or superior mechanical properties as well as superior dimensional properties. The dimensional changes were determined by measuring the length of the bars before and after heat treatment. The data of Table II is plotted graphically in FIG. 1 to more clearly show the advanages of applicants analysis. In FIG. l dimensional changes are plotted against tempering temperatures and curve 1 represents applicants alloy, while curve 2 shows the dimensional stability of the XT-028 analysis and the curve 3 the Airloy composition. The line 0 represents no dimensional change and the initial plots indicate the dimensional change occurring upon quenching.

TABLE II Dimensional Stability [Average change inches/inch of length 0i" round x 2.0000" I'As hardened, change from the finish machined size. NOTE 1.-- l- Denotes expansion, denotes contraction.

NOTE 2.-XT028-Hardened at 1550F. for 8 minutes TAT-Air Quench. AL-123-Hardened at 1525F for 8 minutes TAT-Air Quench. Airloy-Hardened at 1500F for 8 minutes TAT-Air Quench.

It may be readily observed from either Table II or d FIG. 1 that applicants alloy exhibits less dimensional change either as quenched or as quenched and tempered at any tempering treatment up to l000 F. Although greater dimensional change is experienced by all three alloys in the 450 F.600 F. temperature range, applicants alloy exhibits the least change or deviation from the original dimensions of the bars.

Table III shows the dimensional properties of 1A round samples of the same materials employed to obtain the data shown by Table II and FIG. l. This data confirms the data of Table II in that in nearly every instance, applicants alloy shows far greater dimensional stability than the other grades.

TABLE III [y round x 2.0000 long samples- Heat treatment identical to 3/4" rd. samples] Temper- XT-028 .AL-123 Airloy ing oteFmp.,

+. 00005 00005 00050 (l) 00018 00005 -i-Y 00048 200 00051 .00005 l. 00037 300 00066 .00008 +.00020 400 00083 +.00020 .00000 500 00007 +.00051 +.00080 600 00060 .00012 00110 700 00081 00031 -l-.00090 800 00089 00045 00070 900 00103 00055 -f-.00060 1,000

1 As hardened.

In Table lV and FIG. 2, there is shown dimensional stability of applicants alloy AL-123EZ for diierent quenching temperatures. FIG. 2 and Table lV also show the comparative dimensional stability of a similar grade identified as XT-028EZ (see Table I). These analyses contain sulfur that has been added to improve machinability. %-inch round x 2.000 long samples were hardened at the recommended temperatures for the respective materials and at temperatures 50 F. above and 50 F. below these temperatures for 8 minutes and air quenched. The specimens were measured (lengthwise) to the fourth decimal place before hardening, after hardening and after each temper. The results were as follows:

TABLE IV Dimensional Stability Average Change [Inches/inch of length 27g round x 2.000" long samples] AL-123EZ XT-OZSEZ Austenitizing temperatures, F.

1 Dimentional changes are in inches/in.

In FIG. 2 the plots represent the actual dimensional changes as set forth in Table IV. The graph more clearly shows the advantages of applicants analyses. All plots designated A, A' or A are plots of analyses reported in Table I above (AL-IZBEZ), which are within the scope of the present invention, while al1 plots designated X,

TABLE V Hardenng and T emperng Data [Samples 2 long x 135 rd. of steel having the analysis shown by Table I, were hardened lor 5 minutes at the indicated temperature and air cooled. They were fractured and tested for hardness. The samples were then tempered cumulatively for lhour at the indicated temperatures with the Rockwell C hardness checked aft-er cach temper] t Grain size Cumulative 1-hour draw at- Hardening temp., Hardness Shepherd F as quenche( rating 300 F. 400 F 500 F. 600 F. 700 F. 800 F. 900 F. 1,000 F 1,350 26. 5 5 27 29 28 28 27 23 25 26 1,400. 52. 5 7% 54 5 l 54 53 52 52 50. 5 49 1,450- 57 9% 58 57 56 56 53. 5 l 53 5l 1,50 59. 5 l0 61 59 57 56. 5 53. 5 54. 5 54 52 1,550- 59. 5 l0 60.5 59 56 55. 5 55 56 55. 5 52 1,600 52. 5 l0 62 60 59 57 57 56 52. 5 1,65 63. 5 9% 62. 5 69. 5 57 57. 5 55. 5 56 55 54 1,70 63 10 62 60 57 56. 5 56. 5 55 55 54 1,75 63 l0 63 69. 5 58 57 56 55. 5 55 53. 5 1,80 63. 5 l0 63 62 57 57 56 55 55 54 1,8 62. 5 9 62. 5 60. 5 57. 5 57 56 55. 5 55 54 1,90 63 9 63. 5 60 57 57 55 55 56 54. 5 1,95 63 9 63 59. 5 57. 5 55. 5 56 55 55 54 2,0 02. 5 8 62. 5 59. 5 58 57 57 56 54 55 X or X are plots of the XT-028EZ material. The temperatures from which the samples were quenched varied, each material being air quenched from the temperature from which optimum die steel properties are obtained and at 50 F. above and below such optimum tempera- As may be readily seen from the data of Table IV and from FIG. 2 at any given temper applicants analysis exhibits far less distortion than the presently available compositions. This data shows that the degree of stability of applicants alloy varies to some extent in accordance with the hardening treatment, but that similar compositions also vary, -but are generally less dimensionally stable regardless of the exact head treatment given.

As may be observed from the data of Tables II-IV and FIGURES l and 2, applicants compositions exhibit a closer relation to the theoretical zero limit of dimensional change than other low alloy-air hardening die steels now being used. This holds true for both large and small sample size showing that the vanadium addition in combination with the proper level of carbon produces close dimensional stability.

FIGS. 3 and 4 demonstrate the hardening properties of applicants alloy. These figures show the results obtained when 4" and 6 cubes of applicants alloy (AL- 123) were heated to l550 F., air cooled and cnt in half, then tested for Rockwell C hardness from the edge and corner of each to the center of the former cubes. The results, as shown, clearly illustrate the good deep hardening characteristics of the material. These characteristics are known to be prevalent over la hardening range of l500 F. to 1800 F. Such a wide band of acceptable hardening temperatures is greatly advantageous to a fabricator, since he can use a variety of equipment which may be available to him for such heat treatment and, additionally, can heat treat the material for purposes of quenching with other steels of various grades.

Table V shows the wide hardening range of the .AL- 123 analysis. Samples which were air quenched at temperatures of from 1500 F. to 1800 F. are shown to pos- Table VI below, shows the Izod impact properties of the hardened and quenched AL123 analysis. These properties are shown to be equivalent or superior to those possessed by the known commercially available materials.

TABLE VI Izod Impact Tests at Room Temperature [Unnotched Izod samples 3 long x .425 square were hardened at the indie :teil temperatures and air quenched. Tempering for 1 hour at the indicatedtempcraturepreccded finish grinding to .304" squares. The samples were then tested in a it. lb. Izod machine] Hardening Tcmpering Hardness Average temp., F temp., F Rockwell C impact value, ft. lbs.

1, 500 (l) 13 51.75 1, 500 300 42 62 1, 500 400 39 -flO 71 1,500 500 42 82 1. 500 600 40 1, 600 (1) h3 27. 50 1, 600 300 6l -62 55 1, 600 400 59 68. 25 1 500 500 50. 557 5 S2 1, 0 600 55 -50 76.50 1,800 (1) b2 -63 23. 25 1,800 300 t0 -01 57.25 1,800 400 5S -59 89.50 1,800 500 5o -57 (2) 1,800 000 54 -50 (2 1 As quenched. 2 Beyond capacity of machine.

From FIGS. 3 and 4 and Tables V and VI, it is shown that applicants alloy exhibits good deep hardening characteristics (FIGS. 3 and 4 and Table V) and good impact resistance (Table VI), in addition to unusually good dimensional stability (FIGS. l and 2 and Tables II, III and IV).

The following data shown by Table VII also illustrates the wide hardening range and line grain size of the alloy of the present invention. The material tested had the analysis reported as AL*123(2) in Table I above.

Samples 2 long were cut from 1" round annealed bar stock. They were hardened by holding for 5 minutes at the indicated temperatures and air cooling. Samples were fractured and Shepherd fracture grain size ratings obtained. Hardness measurements were yobtained as quenched and after tempering cumulatively at tempera- 7 tlires of 300 F., 400 lF., 500 F., 600 F., 700 F., 800 F., 900 F. and 1000 `F. Results are tabulated below:

ability in the annealed condition and good dimensional stability during heat treatment.

TABLE VII Hardness, Rockwell C Hardeningtempera- Shepherd ture, F. fracture Tempering temperatures grain size As Quenched 300c F 400 F. 500 F 600 F. 700 F. 800 F. 900 F 1,0)0 F.

3 25.5 2 .5 26.5 25 25 24 23 22 21 8 53 53. 5 53 5l 51 48. 5 45 44 41 8% 59 59 57 50 53 50 47 42 9% 61 61 59 56 54 5l 47 47. 5 46 9% 63 G3 60. 5 58 57 54 52 50 47. 5

The above specific examples are given to illustrate the properties of applicants novel composition and in no way limit the scope of applicants invention or claims to the exact analyses set forth.

I claim:

1. An iron base alloy consisting essentially of greater than .80% and less than .90% carbon, 1.85% to 2.15% manganese, .25% to .50% silicon, .75% to 1.10% chromium, 1.20% to 1.40% molybdenum, .45 to .85% vanadium, the balance iron plus incidental impurities, said alloy Ibeing characterized by good deep hardening characteristics, awide hardening range, good impact resistance, good machinability in the annealed condition and good dimensional stability during heat treatment.

2. An `iron base alloy consisting of greater than .80% and less than .90% carbon, 1.85% to 2.15 manganese, .25% to .50% silicon, .75% to 1.10% chromium, 1.20% to 1.40% molybdenum, .45% to .85 vanadium, the balance iron plus incidental impurities, said alloy being characterized by good deep hardening characteristics, a wide hardening range, good impact resistance, good machin- 3. An iron base alloy consisting essentially of .83% to .87% carbon, 1.85% to 2.15% manganese, .25% to .50% silicon, .75% to 1.10% chromium, 1.20% to 1.40% molybdenum, .45% to .85% Vanadium, the balance iron plus incidental impurities, said alloy Ibeing characterized by good deep hardening characteristics, a Wide hardening range, good impact resistance, good machinability in the annealed condition and good dimensional stability during heat treatment.

4. An iron base alloy consisting of .83% to .87% car-` bon, 1.85% to 2.15% manganese, .25% to .50% silicon, .75 to 1.10% chromium, 1.20% to 1.40% molybdenum, .45% to .85% vanadium, the balance iron plus incidental impurities, said alloy being characterized by good deep hardening characteristics, a Wide hardening range, good impact resistance, good machinability in the annealed condition and good dimensional stability during heat treatment.

References Cited in the le of this patent UNITED STATES PATENTS 1,972,524 Kinzel Sept. 4, 1934

Claims (1)

1. AN IRON BASE ALLOY CONSISTING ESSENTIALLY OF GREATER THAN 80% AND LESS THAN .90% CARBON, 1.85% TO 2.15% MANGANESE, .25% TO .50% SILICON, .75% TO 1.10% CHROMIUM, 1.20% TO 1.40% MOLYBDENUM, .45% TO .85% VANADIUM, THE BALANCE IRON PLUS INCIDENTAL IMPURITIES, SAID ALLOY BEING CHARACTERIZED BY GOOD DEEP HARDENING CHARACTERISTICS, A WIDE HARDENING RANGE, GOOD IMPACT RESISTANCE, GOOD MACHINABILITY IN THE ANNEALED CONDITION AND GOOD DIMENSIONAL STABILITY DURING HEAT TREATMENT.

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