US3416916A - Ductile cobalt-base alloy - Google Patents

Description

United States Patent 3,416,916 DUCTILE COBALT-BASE ALLOY Robert B. Herchenroeder, Kokomo, Ind., assignor to gniokn Carbide Corporation, a corporation of New or No Drawing. Filed July 7, 1966, Ser. No. 563,371 3 Claims. (Cl. 75-171) This invention relates to cobalt-base alloys and more specifically to high-strength, heat-resistant cobalt-base alloys with superior ductility after aging.

Various cobalt-base alloys containing chromium have been extensively used in the past under conditions of high stresses at high temperatures and it is well known that alloys of this class generally tend to lose ductility after prolonged exposure at high temperature. Many attempts have been made to improve cobalt-base alloys in this respect to thereby reduce or eliminate embrittlement after aging and it can be said that, up to the present, this problem has not been completely solved.

It is an object of this invention therefore to provide a cobalt-base alloy that will remain ductile after prolonged exposure in the temperature range between about 1400 F. and 1900 1?.

Another object of this invention is to provide a superior oxidation-resistant cobalt-base alloy in the form of wrought products.

A further object of this invention is to provide cobaltbase alloys that have an optimum combination of high strength and resistance to embrittlement and oxidation. These and other objects were satisfied by the alloy in accordance with the present invention which COnsistS essentially of about: 18 to 25 percent chromium, 11 to 15 percent tungsten, 1 6 to 25 percent nickel, 0.05 to 0.5 percent carbon, 0.001 to 0.025 percent boron balance cobalt and incidental impurities. The alloy of this invention may contain the usual impurities found in commercial alloys of this class, i.e. up to, about percent iron, about 1.5 percent molybdenum, about 1 percent manganese, about 0.75 percent silicon; and about 0.15 percent total phosphorous, sulfur, hydrogen, oxygen, and nitrogen. Table 1 shows alloy ranges and specific compositions in accordance with the present invention.

TABLE 1.ALLOYS OF THIS INVENTION [Composition, in Weight Percent] 3,416,!) l 6 Patented Dec. 1 7, 1 968 ICC There are many alloys commercially available and well known in the art that contain cobalt, chromium, tungsten, and/or molybdenum, nickel and iron and some of these alloys are shown in Table 2.

These alloys, often called superalloys are especially suitable for service at high temperature except that they tend to embrittle after prolonged use at temperatures above about 1400" F. Furthermore, while each alloy has certain outstanding individual characteristics, none by itself has the advantage of combined optimum characteristics of high strength, oxidation resistance and resistance to embrittlement. For example, Alloy 1 is known to have outstanding, high temperature strength but its oxidation resistance is lower than that of Alloy 2. Alloy 2 has outstanding oxidation resistance but its high temperature strength is lower than that of Alloy 1. Up to the present such limitations had to be tolerated in the application of these superalloys.

The alloys of this invention on the other hand provide an optimum combination of all the advantageous properties generally associated with this class of superalloys. As shown hereinbelow, the alloys of this invention have strengths equal to or higher than Alloy 1 and also have oxidation resistance characteristics approaching that of Alloy 2.

Although the exact mechanism of the strengthening effects of the elements proportioned within the scope of this invention is not completely understood, it is thought at this time to be a combination of solid solution and carbide dispersion hardening.

In accordance with the present invention, chromium, within the ranges shown in Table 1, provides oxidation resistance and contributes to high temperature strength; chromium contents below the indicated range are not sufiicient to provide adequate oxidation resistance while chromium contents above the indicated range tend to yield alloys of decreased dutility at room temperature.

Typical Examples Broad Range Preferred Range Alloy A Alloy E Alloy G Alloy H (-238) (-51) (71-2 (65-81-1) Chromium- 18 to 25 18.5 to 22 18. 9 19. 62 19. 88 21. 89 Tungsten 11 to 15- 11 to 14 11. 4 11.77 13.0 14. 02 Carbon .05 to .50-.-" .05 to .35 .25 .15 .30 .11 NickeL 19. 5 19. 2 19. 48 Manganeseto 1 46 64 .64 Boron .001 to .025- .001 to 0.02- 008 008 .018 O15 Cobalt and (9 Incidental Impurities.

1 Balance.

Tungsten is present in the alloy, within the indicated ranges, as a carbide former and in a solid solution matrix to provide high strength. Molybdenum is not substitutable for tungsten in the alloy of this invention, although molybdenum may be present as an unavoidable impurity up to not more than 1.5 percent by weight in the total alloy as previously noted.

Carcon is required in the alloy within the range as indicated in Table 1 as a solid solution strengthening element and as a carbide former to provide high strength and nickel must be present in the alloy within the indicated ranges to provide adequate post aging ductility, oxidation resistance, and high temperature strength. Alloys containing less than 15.5 percent nickel tend to embrittle after prolonged use at temperatures between about 1400 F. and 1900 F.

Manganese may be present in the alloy in amounts not loys 1 and 2, in addition Table 6 shows that the alloys of this invention have much better oxidation resistance than alloy 1 of the prior art.

The oxidation tests of Table 6 were identical for all alloys tested. All oxidation test samples were nominally 0.07-inch thick sheet, 0.75-inch square and were uniformly polished to a 120-grit finish. One group of samples was exposed at 2000 F. for 100 hours continuously while another group was intermittently exposed at 2000 F. for eight 3-hour periods and four 19-hour periods for a total of 100 hours as indicated in Table 6. The oxidation rates were determined and are shown on the basis of mils penetration per year (m.p.y.). It is significant that the oxidation rates of the alloys of this invention closely approach those of alloy 2 which is generally recognized as the superior wrought oxidation-resistant alloy presently available in the metals industry.

TABLE 3.COMPOSITION OF TESTED ALLOYS OF THIS INVENTION exceeding about one percent and it appears that some metallurgical benefits are provided with manganese within the range 0.2 to 0.65 percent by weight.

Incidental impurities in amounts normally found in alloys of this type, may be tolerated as previously mentioned while zirconium, columbium, titanium and tantalum, often added in alloys of this class, are not required in the alloys of this invention. The combined total content in the final alloy of zirconium, columbium, titanium and tantalum must not exceed over one percent by weight, as impurities and residuals of prior processing steps, in order that the desired combination of properties be obtained.

In the course of experimentation, a series of alloys were prepared by a process commonly used in alloys of this class; however, other consolidating techniques could be used. In the technique employed, the alloy compositions were melted in an induction furnace, cast into ingots, forged and rolled into 0.063-inch thick sheet for testing purposes. Prior to testing, the alloys were annealed at 2150 F. for 15 minutes and fan cooled. Compositions of alloys prepared and tested are given in Table 3. The alloys of this invention described in Table 3 are in the range of about 19-20% Ni, 11-14% W, 19-22% Cr and 0.l-0.3% C. and will be seen to have an excellent combination of industrially useful properties. All of the alloys of Table 3, except alloy B, are in accordance with this invention. Tensile test results of these alloys, and prior are alloys, are shown in Table 4 while creep and stress-rupture test results are shown in Table 5.

In all tests, the alloys of this invention are seen to be superior, or at least comparable to, both alloys 1 and 2 of the prior art. For example, within the range 1400 F. to 1600 F. the average tensile strengths of the alloys of this invention are about 1.5 times the strengths of al- TABLE 4.AVERAGE TENSILE PROPERTIES OF ALLOYS TESTED Yield Ultimate Strength Tensile Elongation, 0.2% Strength, Percent Offset, 1,000 1,000 p s l p.s.i.

1 Not determined, specimen broke outside of gage marks.

Total Elong, Lite,

20 percent Hours TABLE 5.CREEP AND STRESS RUPTURE DATA Initial Time for Total Elonga- Stress, Elong., tlon Percent, Hours Test Temp., F. 1,000 p.s.l. percent 1 0 Alloy A:

1 Bend not completed due to failure.

In a further test for ductility after aging, two sample specimens each of Alloy G of this invention and Alloy 1 in the form described above were exposed in air at temperatures and for time periods as vfollows:

Alloy G:

984 hours at 1600 F. 310 hours at 1500 F. Alloy 1:

26 hours at 1600 F. 140 hours at 1500 F.

The sample specimens were given a free bend test, as described above, after aging for the times and temperatures shown above. Both samples of Alloy G were successfully bent to 180 degrees angle about a radius of about inch. Both samples of Alloy 1 fractured before they were bent 90 degrees.

What is claimed is:

1. A cobalt base alloy characterized by high temperah, oxidation resistance and resistance to em- DATA [.063-inch thick sheet] Load at Cup Depth, Cup Depth,

Rupture, inch mm. 1, 000 p.s.i.

substantially the Le. within about he mini- F. Samples of Alloy A and described in Table 3, were processed under similar except that the Alloy To obtain best results with the present invention, it

In a series of further tests it was found that t mcvr w e i e a m .m m dhmm u hm a n m c mo u o m ma... 0. N a 6 R tSB 6 00 00 00000 m wmwn mnnnnn monnnn S a w mm m m .1 f s eanm b Mm mmme B 6 06 )\I m mun m d H .m H WA VAMA sAwWVAVA/UQ .w.l w m m B In S mao nk h S Vdet S w r m 0 0 hr. P p A... W W WQ O to e no 1 11 lllllm O OI d mi temd wD i a B .m.. msW.a n n n n H e 1 0.1 S. F o m o n u rim O0 0 n n H n 1t 0 1 ddr 6 S S .5 en e S S r. S S r. 92632 83083 978 4291 098463 29793 /3 flmw W M m u 0 u u 0 :0 M l ffl %UW%M mmfl u% BE %HHHBM U$QM W E 6 A h M B h M 1 11. 1 2 2 1 6 1122 a C M]. m 5 O 0 5 0 0 m2 5 1 m2 5 1 O l. 1 5 0 Afiwq o u 4 7 0 0 677 6608 436513 1... S pmF e 1 A A H nA B HMM m m 1 UB%H% m w 739 04609 4608M 52 m 350 m m2 m mum Wm Ad l e man Mean win mm mm "a a. u o a c h u m mw 554 5916A. 2121 68" 604 "2 Y M S dr. R O n keh 505 895004 7482 02. 917 4 P 3 5 3 1 S e 62 1.23 1 11 0. 2 o 8. C p 1 1. 0 t 1 124 32 .7 .l m M p n ma B2345 4 M I w m 3 6 7 4780 8776M 400m 15 m m s u 1% WE SM %M3 7 53 9295 2 0.. 7M3 M T M M me m u A R m Wmome 267 61054 4 418 51 990" G W D m m ah C LaZL taaaL e151. 00 3 7 1: "7 N n a Y r m m u i 1 a wave; i .1 316 5 u n u M x PWW N 00 0 W00 NOW m %0 M B E W w 10 8 000 00 0 0 000 0 0 0 000m 0 T e mm WnT vmm r. 55 5 O w e 1233313 m W B n m. I M mm 5222232 n C 3A 0 T 0 U I C O dm P 76 700 6 A 18 d D t n an no mann um amm nmnn an 12 1 mamm w X Ve W .D o n .mh G u sho m. u h n n u "n 6 n n EUIEWW n u h n l mi E th I L n u A t r wh F u y 21 0 m unk" I m m "u" oe .o uflmwmm .m 1 T m w m m 0 0 0 0 0 0 0 0 0 00 H n .1 a vM.l 1 m m we who. n w we I m m 1 1 1 1Y1 1Y1 LLYLL. L11 e 6 1 m m m I" HmaVHO l l A A A m 1 2 c D mmmmwo mum content of nickel must exceed about 16 percent in the alloy in order to retain the desired ductility after pronickel content of Alloy B is outside the range of the present invention; Alloy A contains 19.68 percent nickel and Alloy B contains 15.52 percent nickel. The respective al- 7 ture strengt TABLE 7.-ROOM-TEMPERATURE ERICKSEN CUP TEST appears that the nickel content should be same amount by weight as chromium, 5 percent.

longed exposure at 1500 Alloy B,

lar conditions. The two alloys are simi brittlement after exposure to elevated temperatures, said alloy consisting essentially of about:

Percent Chromium 18-25 Tungsten -2 11-15 Carbon 0.050.5 Nickel 16-25 Boron 0.001-0.025

balance cobalt and incidental impurities.

2. An alloy in accordance with claim 1 wherein:

Is about, percent 3. An alloy in accordance with claim 1 wherein:

Is about, percent Chromium 19-22 Tungsten 11-14 Carbon 0.103 Boron 0.0050.018 Nickel 19-20 References Cited UNITED STATES PATENTS 2,744,010 5/1956 Callaway 75-17l 2,746,860 5/1956 Binder ct al. 75l71 2,996,379 8/1961 Faulkner 75171 3,362,816 1/1968 Winter et al. 75-171 RICHARD O. DEAN, Primary Examiner.

US. Cl. X.R. 14832.5

Claims (1)

1. A COBALT BASE ALLOY CHARACTERIZED BY HIGH TEMPERATURE STRENGTH, OXIDATION RESISTANCE AND RESISTANCE TO EMBRITTLEMENT AFTER EXPOSURE TO ELEVATED TEMPERATURES, SAID ALLOY CONSISTING ESSENTIALLY OF ABOUT: