US2206847A - Alloy steel - Google Patents

Description

Patented July 2, 1940 UNITED STATES 2,206,847 ALLOY STEEL Clarence H. Lorig, Columbus, Ohio, assignmto Battelle Memorial Institute, Columbus, Ohio, a

corporation of Ohio No Drawing. Original application Serial No. 218,633. Divided and July 11, 1938, this application March 13. 1940, Serial No. 323,791

4 Claims.

My invention relates to an alloy steel. It relates more particularly to a steel which has a high sensitivity to work-hardening.

One of the objects of this invention is the provision of an alloy steel which may be used for producing wrought andcast articles having a high capacity for work-hardening.

A further object of this invention is the provision of an alloy steel used for producing articles having a high sensitivity to work-hardening that possesses great strength and toughness.

Still another object of this invention is the provision of a work-hardenable alloy steel product havinggreat strength and toughness.

Other objects and advantages of my invention will become apparent from the following description and claims. 1

This application is a division of my co-pending application Serial No. 218,633, filed July 11, 1938. I have found that the manganese content of the 11 to 14 per cent manganese work-hardening steel canbe substantially reduced by alloying with copper and molybdenum and that the stabilization of the austenite structure of this type of workhardening steel can be accomplishe y employing much lower manganesecontents w en both copper and molybdenum are present. The composition range in which the tages were found is as follows:

Carbon 0.50 to 1.7 per cent, manganese 2.0 to

specified advan-.

1.5 per cent silicon may be present in the steel. Some chromium may be used to further increase the wear resistance and-to raise the yield and tensile strengths of the steel. For this purpose, however, less than 3 per cent of chromium is satisfactory.

I have discovered the combining of manganese, copper, molybdenum, and carbon in the proportions indicated makes steel very sluggish to allotropic changes, so that in the condition or after cooling in the austenitic state. However, the changes are not too sluggish, so that cold-working will cause the worked surface of the steel to transform from soft austenite to extremely hard martensite. High sensitivity to Work-hardening is obtained when the transformation of austenite to martensite by cold working is rapid. In applications where my steel is subjected to combined pounding or impact and abrasion, the transformation is rapid and the steel resists wear to a remarkable degree. New, hard surfaces form as rapidly as quickly in air it stays the earlier martensitic surfaces are removed by' wear.

The following table lists the hardness of a number'of steels after diiferent heat treatments and shows the relative work-hardenability of the steels by the difference in Rockwell C hardness of the unworked surface and the hardness at the 9.0 per cent, copper 1 to 5 per cent, molybdenum bottom of a Brinell impression where the metal traces to 3.0 per cent, the remainder being men is worked.

Hardness after various heat treatments 1,650 F. water quenched 1,650 F. air cooled 1,650" F. furnace cooled O, Mn, Cu, Mo, 1 steel percent percent percent percent Rockwell "0" Rockwell 0 Rockwell 0" Brinell Brinell Brinell hardness Sup Bottom of hardness Bottom of hardness Sup Bottom of f Brinell Surface Brinell face Brinell a impression impression impression 0.5 1.5 3.0 0. 578 61 87 549 55 60 361 1.2 3.0 3.0 .5 200 24 43 210 24 43 477 1.2 3.0 3.0 3.0 232 32 46 241 29 .44 531 1. 2 2. 0 5. 0 1. 0 245 35 56 285 39 52 477 1. 25 2.0 3.0 0.5 255 33 50 401 42 52 409 39 44 1.25 4.0 i 4.0 .5 224 19 242 20 39 513 49 54 1. 5. 0 3. 0 5 217 14 28 228 15 36 454 38 49 l. 25 5. 0 3. 0 75 229 23 232 18 41 429 43 50 1. 25 6.0 3.0 Trace 221 22 38 225 20 42 404 41 47 1. 25 7. 0 3.0 Trace 228 24 40 246 24 46 385 38 46 1.25 7.0 3.0 .50 229 23 39 229 18 40 378 40 54 1. 25 7. 0 1. 5 50 224 18 38 241 18 42 398 39 55 1. 25 4.0 1.0 .50 226 20 256 21 43 e 518 54 1. 25 4.0. i 2. 0 1.00 229 20 34 232 16 40 560 52 58 1. 50 3. 0 3. 0 5 269 28 43, 354 33 46 499 49 54 1.00 3.0 3.0 .5 215 27 42 205 20 i 44 518 50 54 0.75 3.0 3.0 .5 477 54 60 435 50 56 514 52 54 1. 25 5. 0 3. 0 25 224 18 39 234 16 41 441 42 51 together with the usual amounts of silicon, sulfur, and phosphorus normally in steel. From traces up to 0.15 per centphosphorus, from traces up to 0.10 per cent sulfur, and from traces up to As compared with the above steels, a 14 per cent manganese, 1.25 per cent carbon steel after quenching in water from 1900 F. had a Brinell hardness of 175, a Rockwell C hardness of 13 water-quenched on the 'unworked surface, and a Rockwell "C" hardness of 40 on the bottom of a Brinell impression.

Water-quenched specimens of steel coming within the range of composition which I previously specified will have a Brinell hardness in excess of 210. In the range of composition centering around 1.00 to 1.5 per cent carbon, 3 to '7 per cent manganese. 1 to 4 per cent copper, and from traces to 1.00 per cent molybdenum, which is my preferred range, Brinell hardnesses of waterquenched specimens are from 210 to about 260, or values that are substantially above the value for the 14 per cent manganese steel. The higher hardness is also associated with higher tensile strength. In this range of preferred composition, the steel transforms very rapidly at the surface from soft austenite to extremely hard martensite on cold working, as shown by the difference in Rockwell C hardness of the unworked surface and of the bottom of the Brinell impression of water-quenched material. The air-cooled steel in the same range of composition is also austenitic and also transforms to mar-1 tensite on cold-working. After furnace cooling, the steel is partially or fully martensitic and hard.

Below the preferred range of carbon and alloy contents, it is more difficult to obtain the steel in the austenitic state and thus make it workhardenable without an extremely drastic quenching from high temperatures.

Carbon has a very powerful influence on stabilizing austenite and in making the steel suitable for work-hardening. With carbon contents below 1.0 per cent, it becomes increasingly difficult to develop work-hardening properties in the steel. A suitable carbon range is quite narrow, as I have found that with carbon contents above 1.50 per cent the steel not only becomes harder in the quenched state but becomes less satisfactory for work-hardening. Carbon is, therefore, an important element which must be kept within close limits in my steel.

Copper and molybdenum augment carbon and manganese in retaining austenite. Both copper and molybdenum retard the rate of transformation of gamma iron to alpha iron, and particularly so in the presence of manganese and carbon. Consequently, I have found it possible to reduce the manganese in austenitic work-hardening steel as much as 75 per cent by alloying with copper and molybdenum. 1 to 5 per cent copper and from traces to 3 per cent molybdenum make possible a reduction inthe amount of manganese of from 1 to 3 times the total percentage of copper and molybdenum added. Too high a molybdenum content like too high a carbon content tends to harden the steel when waterquenched, making it less susceptible to workhardening. For that reason, I prefer to limit its use below 3 .per cent. Excellent results are obtained with 0.25 per cent to 0.50 per cent molybdenum.

In addition to its influence on stabilizing austenite, copper increases the strength of the steel. In the range of composition in which the steel is machinable, copper also aids the machinabili'ty.

An important advantage of my alloy steel over the high-manganese steel is that in the range of composition of about 2 to 4 per cent of copper, 5 to '7 per cent of manganese, traces to 0.50 per cent of molybdenum, and 1.00 to 1.50 per cent of carbon the steel is machinable with ordinary carbon and high-speed steel tools. The machinability of the steel in this range of composition constitutes quite an advance in the art, as the high-manganese steel can be machined only with the greatest difiiculty by special carbide tools or by grinding. To efiect'machinability, the steel is cooled slowly as, for example, in a well-insulated furnace. The following table shows the maximum permissible machining speed for a number of compositions after they were cooled slowly in a furnace from 1650 F. Cuts were made on a lathe using a high-speed tool at a. feed of A -inch per revolution. A specimen %-inch square was reduced to %-inch round in one cut.

After machining, the steel can be made workhardenable by heat-treating and liquid or airquenching.

The higher quenching temperatures up to a certain maximum were found to improve the duetility of the steel considerably. A quenching temperature above 1800 F. was found to be most satisfactory, although it is possible to quench from lower temperatures.

Mechanical properties of the steel in the preferred range of composition are excellent. Its toughness was demonstrated with key-hoie notched Charpy specimens water-quenched and tested for impact in a machine of 120 ft.-lb. capacity. The specimens absorbed the full 120 ft.-lb. of energy of the machine with a single blow without breaking. Any steel coming within the range of composition specified hereinbefore will have an impact strength in excess of 30 ft.-lbs.

The alloy steel is suitable for services requiring high resistance to the combination of repeated blows or impact and abrasion. Articles such as plates for jaw crushers, ball mill liners, roll shells, dipper teeth, caterpillar shoes, etc., can be made from my alloy.

Having thus described my invention, what I claim is:

"1. An alloy steel consisting of 0.50 to- 1.7 per cent carbon, 2.0 to 9.0 per cent manganese, 1 to 5 percent copper, traces to 3 per cent molybdenum, traces to 0.15 per cent phosphorus, traces to 0.10 per cent sulfur, traces to 1.5 per cent silicon, up to 3.0 per cent chromium, and the remainder substantially all iron, said alloy steel being austenitic after quenching from a high temperature.

2. An alloy steel containing 0.50 to 1.7 per cent carbon, 2.0 to 9 per cent manganese, 1 to 5 per cent copper, traces to 3 per cent molybdenum, traces to 0.15 per cent phosphorus, traces to 0.10 per cent sulfur, traces to 1.5 per cent silicon, up to 3.0 per cent chromium, the remainder being substantially iron, said steel being austenitic and work-hardenable after quenching from a high temperature and having a Brinell hardness in excess of 210 and an impact strength in excess of 30 ft.-lbs.

3. An alloy steel containing 1.00 to 1.5 per cent carbon, 3 to 7 per cent manganese, 1 to 4 per cent copper, traces to 1.00 per cent molyb- 4. An alloy steel consisting of 1.00 to 1.5 per cent carbon, 3 to 7 per cent manganese, 1 to 4 per cent copper, traces to 1.00 per cent molybdenum, traces to 0.15 per cent phosphorus, traces to 0.10 per cent sulfur, traces to 1.5 per cent 5 silicon, up to 3.0 per cent chromium, and the remainder substantially all iron.

CLARENCE H. LORIG.