US2212495A - Alloy steel - Google Patents

Description

Patented Aug. 27. 1940 UNITED STATES PATENT OFFICE Allegheny Ludlum Steel Corporation,

Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application January 10, 1939, Serial No. 250,187

3 Claims.

My invention relates to alloy steels which substantially maintain their hardness when repeatedly heated to temperatures of the order of 1200 to 1600 F., and air cooled. It also relates to steels quantities as will not substantially impair the characteristic properties of the alloy. For ex.- ample, silicon, a usual ingredient in steel, may be present up to about 0.75%. Additions of cowhich are characterized by high hardness and balt do not in any way affect that outstanding 5 high strength at elevated temperatures. characteristic of my alloy which is its ability sub- One of the objects of my invention is to prostantially to maintain its hardness upon repeated vide an alloy steel which, while adapted for genheating to and air cooling from temperatures of eral use, is particularly suited for those applicathe order of 1200 to 1600 F. But cobalt in quantions where resistance to scaling combined-with tities of from about 0.25% to about 2.50% does 10 high strength and hardness at elevated temperaincrease, in degree, the maintainable hardness, tures are required characteristics; and where such and is therefore use ul for hot d e p p s s a strength and hardness are not substantially also for poppet valve applications. Phosphorus afi'ected by repeated heating and cooling. Such and sulphur may be present in the usual small steels are espec1ally adapted for use in poppet quantities, and the content thereof may even be 15 valves of internal combustion engines, hot work raised to as high as about 0.15%, in which case ales and 5111111 artlcles Whlch may be elther the phosphorus increases the hardness obtainable. forged or Where phosphorus is present in more than the The essential alloylng elements in my steel and usual maximum f about 094%, Small quantities h Fpprommate percentage ranges' by Welght, of selenium, up to about 0.20%, may be added to 20 within which they must be used to accomplish .3 the foregoin objects are about a f n improve the machineabihty 01 the alloy.

g S 0 In the table below, I have set forth for com- Percent parative purposes a number of alloy steels each m C 50110 containing carbon, chromium and manganese 25 gi 0 to 26-00 within the limits of my invention above set forth,

N to together with their hardness in the as forged cong 2 dition, their hardness when air cooled from temance peratures of the order of 12000 F. to 1600 F.,

In addition to the foregoing, other elements and their hardness after reheating and air cool- 30 may, of course, be incorporated in such small ing from temperatures of this order.

Analysis Cone Rockwell hardness N- AS Air cooled from g g g g zg 0 Cr Mn N 00 P Se iorged 1200 F. 1400 F. 1600 F. 1200 F. 1400 F. 1500 F.

. 5.19 34 35 43 42 33 42 42 40 4.52 40 41 42 42 43 40 4o 43 4. 78 43 44 40 40 40 3s 39 4o 5.36 34 33 37 37 34 35 34 5.12 34 3o 29 30 30 3o 20 0.10 35 32 32 33 32 32 33 5.70 29 22 22 25 24 24 26 45 4.00 41 3s 43 41 42 37 40 24.51 3.13 33 35 33 34 27 23 27 25.07 3.12 36 31 22 27 21 19 22 23.37 4.15 33 39 40 41 34 35 37 22.67 4.46 as 33 4o 39 30 33 32 23.26 4.96 43 46 4s 4s 43 42 40 24.02 3.16 37 44 46 37 42 39 43 25.17 2.63 43 43 45 44 43 36 46 50 24.05 5.22 24 24 23 24 23 21 24 22.13 4.72 40 32 33 35 25 27 32 23.26 4.50 37 3o 32 33 27 .24 32 25.00 2.32 2o 13 13 13 1s 1s 13 25.34 5.10 27 25 23 23 22 22 23 By comparison of melts S 31, S-32 and S-7'7,

it will be noted that the chromium and manganese contents are as nearly alike as can be melted, but that the nitrogen content in these specimens is 0.16%, 0.26% and 0.33%, respectively. Each of these steels, when heated and cooled from 1200 F., 1400 F. and 1600 F., and again heated and cooled from these temperatures, maintains a hardness in the neighborhood of 35 to 45 Cone Rockwell. Specimen S-31 containing the lowest quantity of nitrogen maintains the lowest hardness. Specimen S-32, although less hard than specimen S-31 in the as forged condition, becomes harder upon heating and cooling, and maintains a higher hardness upon reheating and cooling, than specimen S--31, while S-7'7 which contains .33%of nitrogen together with slightly higher carbon than the other two specimens, maintains the highest hardness.

Specimens 8-59, 8-97, S-98, S-99, S- and S-l01 contain no nitrogen. It will be noted that some of these specimens have a hardness in the as forged condition which is comparable to that of the three specimens above discussed.

This hardness is not maintained when the steel is reheated and cooled from the test temperatures, thus showing that the as forged hardness is only incidental and has no relation to the property of maintainable hardness. Specimen 8-98, for example, having a forged hardness of 40 drops to a hardness of 25 when reheated and air cooled from 1200 F., and specimen S-99 having a forged hardnessof 37 drops to a hardness of 24 when reheated to 1400 F. and air cooled.

That-the ranges of chromium and manganese within which my results are attained are quite critical will be apparent from a consideration of the above table. For example, specimens S-55 and S-58 with both chromium and manganese near the maximum claimed limits show that the maintained hardness is rather low with carbon in the lower portion of its range. On'the other hard, specimens S-31, S-77, 8-78 and S79,sh0w that the maintained hardness increases with a decrease in the chromium, an increase in the carbon, a decrease in the manganese or by a combination of these modifications. Specimen S-79 with chromium near the upper limit, manganese near the lower limit and carbon and nitrogen in about the middle of their respective ranges maintains its hardness quite consistently upon heating and cooling.

It has often been found that steels which have a relatively high hardness when tested at room temperatures do not have relatively high strength or hardness when tested at elevated temperatures. The steel of my invention which has a high maintainable hardness in the temperature range of 1200 to 1600 F., has however, both high hardness and high strength at heat, the strength at a temperature of 1500 F. running consistently from 25000 to 35000 pounds per square inch. Such high strengths are usually found only in steels where high melting point and expensive elements such as molybdenum,.

tungsten or tantalum are used in fairly large proportions or where, in addition to the chromium, at least 10% to 20% of iron is replaced by nickel or manganese so that the alloy content approximates about 50% of the total composition. In my steel, however, the alloy content does not exceed from about onefourth.to one-third of the total weight of the steel.

My preferred quantities of chromium and manganese fall in about the middle of the ranges of these elements above specified, with carbon at least ten to fifteen points above the minimum, and nitrogen around 0.25% or more. Within these preferred ranges the alloy maintains hardness even when cooled slowly from high temperatures.

From the foregoing tests, it also seems preferable when chromium is present in the extreme upper portion of its range, that both carbon and nitrogen should also be well above the minimums specified, and the manganese should be in the lower portion of its range.

Steels which show a good order of maintainable hardness in the ranges of 1200 to 1600 F., are sometimes worthless for commercial purposes because of lack of ductilityat room temperature. This'is not the case with my alloy. Specimen 8-77, for example, which haIdens to 48 Cone Rockwell, has a bend of 5 with great strength when tested at room temperature.

What I claim is:

1. An alloy steel characterized by the substantial maintenance of hardness upon repeated heating to temperatures of the order of 1200 to 1600 F. and air cooling; saidsteel containing a plurality of ingredients of which the following, in the proportions stated are the only elements necessary to attain said characteristic, carbon from 0.50% to 1.25%, chromium from 20% to 26%, manganese from 2% to 6%, nitrogen from 0.10% to 0.50%, and thebalance iron.

2. An alloy steel characterized by the substantial maintenance of hardness upon repeated heating to temperatures of the order of 1200 to 1600 F. and air cooling; said steel containing a plurality of ingredients of which the following, in the proportions stated, are the only elements necessary to attain said characteristic, carbon from 0.60% to 1.25%, chromium from 21.5% to 24.5%, manganese from 2.5% to 4.5%, nitrogen from 0.25% to 0.50%, and the balance iron.

3. An alloy steel characterized by the substantial maintenance of hardness upon repeated heating to temperatures of the order of 1200 to 1600 ,F. and air cooling; said steel containing a plurality of ingredients of which the following, in the proportions stated, are the only elements necessary to attain said characteristic, carbon from 0.60% to 1.25%, chromium from 24% to 26%, manganese from 2% to 4%, nitrogen from 0.25% to 0.50%, and the balance iron.

RALPH P. DE VRIES.