US2423738A - Forgeable alloy for hightemperature use - Google Patents

Description

Patented July 8, 1947 ronoaanm ALLOY FOR mon- TEMPERATURE USE Rudolf H. Tliielemann, Schenectady, N. -Y., assignor to General Electric Company, a corporation of New York No Drawing. Application March 1, 1941, Serial No. 381,377

The present invention relates to alloys, and more particularly to alloys which are readily forgeable, which have high creep and rupture strengths at elevated temperatures and are suitable for use at temperatures up to about 1400 F.

In the design and manufacture of certain types of high temperature equipment, it is desirable to employ alloys which have good high temperature properties and at the same time are readily forgeable and machinable. Commercially available alloys which can be worked in this manner are not strong enough to meet the high temperature requirements. On the other hand, commercial alloys which have high strength at the temperatures involved either cannot be forged readily, as in drop forging operations, or they do not have the necessary oxidation and corrosion resistance.

It is an object of the present invention to provide an alloy which is readily forgeable in large sections and easily machinable which resists scaling when subjected to exhaust gases from airplane engines and the like, which maintains its metallurgical stability at operating temperatures up to 1400 F., and which has high long time load carrying ability at temperatures up to but not materially in excess of 1400 F.

A further object of the invention is to provide an alloy which is particularly desirable for use as forged parts in both gas and supercharger turbines. v In a gas turbine such parts include wheels, rotors, brackets, nozzles and valves. In supercharger turbines, the particular application for the present alloy is the turbine wheel. Such 8 Claims. (Cl. 75-128) wheels generally are forged in a contour forging die, and therefore require a material which has exceptional high temperature properties ancl with good forgeability and machinability has the following composition:

- Per cent Carbon 0.30 to 0.50 Manganese 0.40 to 0.60 Silicon 0.40 to 0.60 Chromium 14 to 16 Nickel 24 to 26 Molybdenum 4 to 6 Columblum 1.5 to 2.5

Remainder, iron.

My improved alloy can be made in either an are or induction type furnace in accordance with well known metallurgical practice. Large ingots can be forged and rolled by employing the same technique required for working chromium-nickel austenitic type alloys. The present alloy can be welded by either the electric are or atomic hydrogen processes.

To obtain the best high temperature properties the alloy is heat treated, the heat treatment varying somewhat with the particular application. Generally the alloy is precipitation hardened by heating at about 1050" C. to 1250 C. preferably about 1200 C. for about two hours, quenching in oil or water and then drawing at about 600 to 800 C. preferably about 700 C. for about two hours after which it may be air cooled. The

drawing temperature employed will depend some- ,what upon the properties required in the alloy. The alloy, heat treated in this manner will maintain its metallurgical stability up to a temperature of about 1400 F.

If desired bar stock may be heated to forging temperature, for example about 1150 C., and forged to within about 10% of the required finished size. The partly forged alloy is then heated at about 1050 to 1250 C. for about two hours and quenched in oil or water. The alloy is then heated to a temperature of about 650 C. forged to the desired finished size andthereaf-ter given a draw at about 650 to 850 C. preferably for about two hours. The cold working from 650 C. results in a more complete'precipitation hardening reaction and improved properties in the alloy.

As hereinbefore set forth, the alloy may be forged readily and when drop forged or upset it has high resistance to cracking and bursting.

commercial 3 For an alloy of this type it is readily machinable and has excellent resistance to oxidation and scaling at temperatures up to 1800 F. In the form of iorged turbine wheels, the alloy, after heat treating has a short time tensile strength at 1500 F. of about 55,000 pounds per square inch. In the form of small drop forged turbine buckets which have been cold finished and heat treated, both as hereinbefore set forth-the short time tensile strength at 1500 F. is about 65,000 pounds per square inch.

The long time rupture properties of the alloy at 1200 F. and 1300 F. in the quenched and drawn condition are as follows:

M At 1300 F Time for Time for Stress stress -lsq. iii. iflgf ib./sq i, tig s e,

The stress for 1% of creep after a given period of time can be calculated approximately by dividing the corresponding rupture stress by about 1.5.

Small gas turbine wheels operate at speeds up to 30,000 revolutions per minute. The tempera- 1 is particularly suitable for use as such wheels not only because of its excellent high temperature properties but because its cost is not excessive and it has excellent working as well as high temperature properties. Prior to the present invention these turbine wheels generally have been machined out of relatively large pancake blocks of material. However, since the present alloy is readily forgeable in contour dies it is possible to effect a saving of material and time in the fabrication of such wheels.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A forgeable alloy containing about 0.30% to 0.60% carbon, about 0.30% to 1.50% manganese, about 0.40% to 0.60% silicon, about 12% to 18% chromium, about 20% to 40% nickel, about 2% to 8% molybdenum, about 1% to columbium with the remainder substantially all iron.

2. A forgeable alloy containing about 0.30% to 0.50% carbon, 0.40% to 0.60% manganese, 0.4% to 0.60% silicon, about 14%,to 16% chromium, about 24% to 26% nickel, about 5% of molybdenum, about 2% columbium'with the remainder substantially all iron.

3. A forgeable alloy which is characterized by good oxidation resistance at temperatures up to 1800 F. by its metallurgical stability at temper atures up to 1400 F. and by its high rupture strength and resistance to creep at temperatures about 1000 F., said alloy containing a plurality of ingredients of which the following in the proportions stated are the only ones necessary to attain said characteristics:

Per cent Carbon .30 to .60 Chromium "1..---- 12to 18 Nickel 20 to 40 Molybdenum 2to 8 columbium lto 5 Remainder, substantially all iron.

4. A forgeable precipitation hardened alloy containing about 0.30% to 0.60% carbon, about 0.30% to 1.50% manganese, about 0.40% to 0.50% silicon, about 12% to 18% chromium, about 20% to 40% nickel, about 2% to 8% molybdenum, about 1% to 5% columbium with the remainder substantially all iron.

5. A forgeable precipitation hardened alloy containing about 0.30% to 0.60% carbon, 0.40% to 0.60% manganese, 0.40% to 0.60% silicon, about 14% to 16% chromium, about 24% to 26% nickel, about 5% of molybdenum, about 2% columbium with the remainder substantially all iron.

6. The method of hardening an alloy containing about .30% to .60% carbon, about .50% to .80% manganese, about .40% to .60% silicon, about 12% to 18% chromium, 20% to 40% nickel, 2% to 8% molybdenum, 1% to 5% columbium with the remainder substantially all iron, which comprises heating the alloy for about two hours at a temperature of 1050" to 1250 C., quenching the alloy and then drawing it at a temperature of about 650 to 750 C. for about two hours.

7. The method for improving the properties of an alloy containing about .30 to .60% carbon, about .30 to 1.50% manganese, about .40 to .60% silicon, about 12 to 18% chromium, about 20 to 40% nickel, about 2 to 8% molybdenum, about 1 to 5% columbium with the remainder substantially all iron which comprises heating the alloy to a' forging temperature, forging the alloy to within about 10% of the desired finished siz'e,

' heating the alloy to a temperature sufllcient to produce a condition of solution in the alloy,

quenching the alloy, cold working it to finished REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Number Country Date 374,541 Great Britain June 16, 1932 375,777 Great Britain June 30,1932

OTHER REFERENCES U. S; S. Carilloy Steels, page 199, published in 1938.