US2453598A - Ferrous alloys and rotor forgings for gas turbines - Google Patents

Description

Patented Nov. 9, 1948 UNITED ,STATES PATENT ALLOYS AND ROTOR FORGINGS FOR GAS TURBINES FERROUS F F l C E Adolph 0. Schaefer, Whitpain Township, Montgomery County, Pa., assignor to The Midvale Company, Philadelphia, Pa., a corporation of Delaware No Drawing.

, 1 Rotorforgings for gas turbines of jet propulsion units of airplanes and for other gas turbine application must be made of material possessing the characteristics of weldability, of machin characteristics as sensitivenessto small variations in manufacture, which frequently occur in the same technique; or they are inclined to show both external and internal defects in ingots as well as in the forgin s made from them, which may not appear on the surface at any stage of manufacture and can only bediscovered by skiagraphic or supersonic test; or they may be difficultly forgeable; or may lack hot strength or ductility at operating temperature.

V In several of the alloys some of the chemical elements apparently have a tendency to form areas of local enrichment instead of entering uniformly into the general alloy. Such nonhomogeneous areas have the eifect of embrittling .the article in which they exist, so that on overspeed bursting tests there may be Wide variations in the speed at which failure occurs. These compositions are also prone to surface defects entail ing a highpercentage of loss in forging.

With the object of producing a ferrous alloy which would be more readily fabricated, would be free from the defects above mentioned, would have suflicient strength at working teperatures,

and possess such improved ductility and soundness as would give more uniform performance in operation, many thousandsof dollars have been expended under my direction in testing a wide variety ofcompositions, which have covered the range of elements in general use for such ferrous alloys, in an effort to determine Whether any combination of them would exhibit thev desired characteristics. This involved a determination of what alloys are essential, which are non-essential or objectionable, and the limitswithin which the absolute and relative proportions of the selected elements should be present. I finally found that an alloy of the following composition would achieve the desired result, besides having other desirable and important characteristics:

Application August 29,1945, Serial No. 613,423

4 Claims. (c1. 75 -12s) As is well understood by those skilled in the art, it is generally not possible to secure an exact composition, and that in the endeavor to obtain my preferred composition the result is likely to vary within approximately the following limits:

Percent C 1 to 15 Mn 4 to 6 Si 4 to 6 Ni 11 to i 12 Cr 18. '75 to 19.75 W 3 to 3. 5 Cb l to 1.5 N2 About 15 Fe 62 to Deviations from the above percentages, although within rather limited ranges, are permissible withoutseriously impairing the qualities of the alloyed steel. Such qualities are retained, with but moderate impairment in degree, in compositions not within the above limited ranges but within the following broader ranges:

Percent C 05 to 3 Mn 3 to 1. 0 Si 3 to l. 0 Ni 9 to 15 Cr 15 to 25 W 2 to 5 Cb 5 to 2 N2 05 to 3 Fe (balance) 52 to '72 While the minimum of chromium and the maximum of nickel within the above broader ranges are approximately the same, the percentage of chromium in any given composition should substantially exceed the percentage of nickel.

Similarly, while the minimum of tungsten approximates the maximum of columbium within the above broader ranges, the percentage of tungsten in any given composition should substantially exceed the percentage of columbium.

Ferrous alloys embodying my invention will not be entirely free from impurities such as phosphorous and sulphur, but the percentage of these impurities should be kept low and preferably should not exceed about .03% of either.

While a composition embodying my invention does not necessitate the absolute exclusion of any alloying ingredient in addition to those named, I am aware of no other element that can be added that will improve the composition, and the addition of any one of most common alloys of steel in any substantial proportion will, I believe, appreciably impair the desirable qualities of the specified composition. For example, the addition of molybdenum in any percentage approaching that of the prescribed percentage of tungsten is dis- The presence of a slight D rcientageof tantalum whether introduced in the f-errocolumbium or in-' tentionally, is without utility, as.wou1d also be the addition of titanium, of which the-presence iniany substantial proportion is detrimental. Therefore, aside from the elements specified, the remainder of the composition is preferably nearly all iron.

A ferrous alloy embodying my invention is readily fabricated without undue loss in casting or forging operations. The material hasbeencast in a number of induction furnaces, and in one large arc furnace, heats with excellent results and airsoduction of sound forgings several times that secured in another composition used for the same purpose with Which 1 have had several years experience.

Investigation of cut-up Wheel forgings made of known suitable ferrous-alloys offer-valuable advantages -for this material.

Another quality of my improved alloy which is of great importance is the remarkable uniformity in physical properties of the forgings made from it. This is in striking contrastto the results obtained from such compositions as are sensitive to slight variations in manufacturing technique.

if improved ,ferrous alloy is readily fabricated and the product extremely uniform in quality, as stated. Five 18 /2" diameter wheels of this material have been overspeeded until they "burst, and the range of bursting speed wa only afrom 22,610 R. P. M. to 23,350 R. P. M.

My claims with regard to this alloy are thatit has:

11. Sufficient strength at the temperature range of operation of gas turbines.

2. Greater flexibility in fabrication both :in casting and forging, than the ferrous alloys now in use for this purpose.

manufacture of rotorforgings for gas turbines, said alloy containing carbon .05 to less than .3 per cent, manganese over .3 and less than one per cent., silicon over .3 and less than one per cent., nicke1,0Ver.-'9't0' less than per cent,. chromium over 15, to less than 25 per cent., tungsten over 2 .to less than 5 per cent., columbium over .5 to less "than-.2 per. cent and nitrogen over .05 to less than ..-.3.per cent., with a maximum of phosphorus and sulphur not over. 103'per cent. each, substantially all of the remainder being iron which comprises the majorproportion of the alloy, the percentage Considerable savings in material, labourand equipment as a result of the decreased: loss 0 forgings in process.

Higher ductility than materials heretofore used, which permitsan automatic distributioniof stresses to a greater degree than is possible in materials of equal strength and less ductility.

' 5. Greater uniformity of product because of the :less sensitive nature of the alloy. 1

6. More uniform properties in parts of-widely of chromium substantially exceeding the percentage of nickel and the percentage of tungsten substantially exceeding the percentage of columbium; said composition being characterized by great ease in casting andiorging, adequatestrength at the temperature rangeof operation of gasturbines, high ductility permitting of maximum automatic distribution of stresses, and uniformity of product particularly in parts of widely different thicknesses.

2. A ferrous alloy containing carbon .10 to .15

per cent.,- manganese .4 to .6 per cent., silicon .4 to .6-per cent., nickel 11,to 13'per cent., chromium 18.5 to' 19.75 per cent.,, tungsten 3. to'3.5 per cent., columbium .8 to 1.5 per cent., nitrogen .10 to .20 per. cent., with a maximum of phosphorous and sulphur not over .03 per cent. each, substantially all of the-remainder, about 62 to 65 per cent,'beon, the percentage of chromium substantially exceeding the percentage-of nickel and the percentage of tungsten substantially exceeding the percentage of columbium; said c-ompositionbein characterized by great ease in casting and forging, adequate strength at the temperature range of operation of gas turbines, high ductility permitting of maximum automatic distribution of stresses, and uniformity of product particularly inparts of Widely different thicknesses.

'3. A-rotor forging for gas turbines having the composition specified in claim 1.

"4. A rotor forging for gas turbines having the composition specified in claim 2.

ADOLPH O. SCHAEFER.

"REFERENCES CITED The following. reference s areofv record. in the .file of this patent:

OTHER, REFERENCES Eifects of Special Alloy Additions to'Stainless Steel. Franks; published in October 1938 by the Electro' Metallurgical'C-o, New York city.