US2370395A - Alloys for high temperature service use - Google Patents

Description

Patented Feb. 27, 1945 ALLOYS FOR HIGH TEMPERATURE SERVICE USE Hugh S. Cooper, Cleveland, Ohio No Drawing. Application March 1'7, 1942,

Serial No. 435,009

2 Claims.

This invention relates to metallurgy and more particularly to a substantially non-ferrous alloy composition suitable for use in the manufacture of valves for automotive and aviation engines, oil cracking tubes, steam boiler tubes, turbine.

blades, and the like articles, where high temperature oxidation, corrosion and erosion resistance combined with high hardness and with high tensile strength and a low creepv value at high temperatures are essential properties desired in ad-.

dition to suflicient ductility at a hot working temperature to permit the mechanical deformation of the alloy to the desired size, shape and configuration.

One of the objects of the present invention is to provide an alloy possessing all of the properties defined above.

Another object is to provide an alloy suitable for use in the articles defined above.

Still another object is to provide a high temperature oxidation, corrosion and erosion resistant alloy possessing a relatively high tensile strength and low creep value at elevated temperatures and a high hardness value at said elevated temperatures.

Other objects and advantages will be apparent as the invention is more fully hereinafter disclosed.

In accordance with these objects I have disremaining alloy composition appears to result.

In general, I prefer maintaining the Cr content within the range to and the iron content at approximately the minimum within the range of 10 to that will dissolve the Ta or Cb and the carbon, while the Mn content is maintained as low as is possible'to obtain a substantially deoxidized alloy.

It may be seen, therefore, that with any given Ta or Cb and carbon content within the ranges specified, the minimum solutioning Fe content therefor, the physical properties of the alloy may be widely varied by varying the relative proportioning of the metals Ni and Co comprising the base while maintaining the Cr content substantially constant within the range 15 to 20%.

As one specific example, the combination of I elements giving the maximum hot forgeability with high tensile strength will be described. This alloy contains at least one of the metals Cb and Ta about 3.0%, carbon about .50%, Fe about 15%, Mnabout 1.5% and Cr about 15%, the remainder consisting of Co and Ni in the ratio of about two (2) parts Ni to one (1) part Co and in total amount constituting about 65% of the alloy. This alloy shows a tensile strength at about 1500 F. of about 69,000 pounds persquare inch and at 1800| F. shows a tensile strength of about 33,000

pounds per square inch. The hardness of the alloy at atmospheric temperatures approximates 275-300 Brinell.

The tensile strength of this alloy is materially increased by lowering the nickel content of the base which results in a material loss in ductility at temperatures within the range 1800-2200 F.

interfering with mechanical deformation, and

tensile strength at temperatures within the range 1500-4800 F., excellent oxidation, corrosion and erosion resistance at all temperatures up to 1800" F. and a relatively high hardness which persists to elevated temperatures approximating 1800 F. and requiring the use of forging temperof the remainder. the maximum workability forany given remaining alloy composition appears to result. When the nickel content of the remainder is lowered to small fractional percentages, the maximum tensile strength for any given also in a loss in machinability. The ductility of the alloy at forging temperature and the machinability may also be markedly improved by raising the iron content of the alloy somewhat. For example, with Ni under 10% the Fe should be raised to 25% to obtain equivalent ductility at the forging temperature and equivalent machinability in the higher tensile strength alloy. In this respect, Fe and Ni are equivalents. However, with respect to the solutioning of the Ta and Cb carbides present, Fe and Ni are not substantial equivalents, and it appears necessary to maintain at least a 15% Fe content in the alloy for this purpose.

Where greater hardness is desired to improve either the erosion resisting properties or the creep strength of the alloy at elevated temperatures. the Ta and Cb carbide content of the alloy may be increased within the ranges given, said inthe Co is in excess to the Ni.

crease being made at the expense of the remainder base (Co and Ni). For most purposes, however, from 2 to 3% of at least one of the elements Ta and Cb appear adequate to impart a satisfactory creep strength and hardness giving a reasonably consistent long life under the usual service conditions experienced in the several fields of use contemplated for the alloy.

The. corrosion and high temperature oxidation resistance of the alloy appears adequately taken care of by the chromium content of to particularly in those alloy compositions wherein As the Ni content approaches the same percentage as the Co, the Cr content preferably should .be maintained as close to 20% as practicable.

Valves for internal combustion engines, particularly aviation engines, are subjected to severe erosion and corrosion at relatively high temperatures besides repeated deformation stresses incident to the seating of the valve on the seat.

Valves comprised of the alloy of the present invention have been found to be greatly superior to other alloys heretofore employed and to give a much longer service life.

Oil cracking tubes made from the alloy of the present invention may be used safely at temperatures and pressures not heretofore possible with other alloys. Steam boiler tubes, particularly steam superheater tubes, made from the alloy of the present invention also may be used at temperatures and pressures not heretofore possible with other alloys.

Turbine blades made from the alloy composition of the present invention, such as in turbines operating the superchargers of aviation engines are stronger and more durable than blades comprised of any other alloy heretofore proposed.

Having hereinabove described the present invention generically and specifically and given one specific embodiment thereof with several contemplated modifications thereof, it is believed that it is apparent that the same may be widely varied without essential departure therefrom and all such are contemplated as may fall within the scope of the following claims.

What I claim is:

1. An alloy composition characterized by high temperature oxidation resistance, corrosion and erosion resistance with high hardness and with high tensile strength as well as low creep value at high temperatures, said alloy consisting of Cr 15 to 20%, Fe 10-25%, at least one of the metals Ta and Cb l5%, Mn .50-2.0%, carbon .35.75% with the balance of the alloy consisting of Ni and Co, the Ni content of said balance being within the range from small fractional percentages up to 60% of said balance and the said iron content within the range 10 to 25% being at least sufficient to effect substantially complete solution of the carbide compounds of Ta and Cb present in the said alloy.

2. A high tensile strength hot forging alloy, said alloy having a Cr content approximating 15%, an Fe content approximating 15%, an amount of one of the metals Cb and Ta approximating 3%, carbon approximating Mn approximating 1.5% with the balance of the alloy consisting of Ni and Co in the ratio of two parts Ni to one part Co, said alloy being characterized by a hardness at atmospheric temperatures approximating 275-300 Brinell.

HUGH S. COOPER.