US3512963A

US3512963A - Process for improving elevated temperature strength and ductility of nickel-base alloys

Info

Publication number: US3512963A
Application number: US567400A
Authority: US
Inventors: Jacob Schramm; John H Olson; Clarence G Bieber
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1966-07-25
Filing date: 1966-07-25
Publication date: 1970-05-19
Anticipated expiration: 1987-05-19
Also published as: GB1180974A; BE701793A; AT282211B; DE1608172A1; SE340702B

Description

United States Patent 3,512,963 PROCESS FOR IMPROVING ELEVATED TEMPERA- TURE STRENGTH AND DUCTILITY OF NICKEL- BASE ALLOYS Jacob Schramm, Ringwood, and John H. Olson, Franklin Lakes, N.J., and Clarence G. Bieber, Sulfern, N.Y., assignors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed July 25, 1966, Ser. No. 567,400 Int. Cl. C22c 19/00, 1/02 US. Cl. 75-171 ABSTRACT OF THE DISCLOSURE The elevated temperature properties and hot workability of nickel-base alloys such as nickel-chromium alloys is markedly improved by a melting practice involving vacuum treatment followed by an addition of magnesium under a non-reactive gas atmosphere.

The present invention is directed to a method for inlproving the properties of nickel-base alloys and, more particularly, to a method for improving the elevated temperature strength and ductility thereof.

The beneficial effects which flow from vacuum melting and vacum treatment of molten nickel-base alloys from the viewpoint of improving the properties thereof are now well known. In fact, for the melting of many alloys which are required to have high strength and reproducible properties at elevated temperatures this is a standard practice. The use of high purity charges and improved vacuum melting techniques has resulted in very low impurity 6 Claims ice reducing the rate of magnesium volatilization, providing practical control of final magnesium content, etc., a nonreactive gas such as argon, helium or nitrogen having a partial pressure in the amount of at least about one-third atmosphere up to about one atmosphere is placed over the melt upon completion of the vacuum melting cycle,

magnesium is then introduced into the melt, and the magnesium-containing melt is thereafter cast. Magnesium may conveniently be introduced into the melt in the form of a master alloy containing about 4% to about magnesium, e.g., about 12% to 14% magnesium, and the balance essentially nickel. The nonreactive gas can be led directly into the vacuum melting chamber or vacuum melted metal can be carried in a ladle from the vacuum melting chamber through a vacuum lock into an inert-gas chamber for the magnesium addition.

Alloys susceptible to treatment in accordance with the invention may contain, by weight, up to chromium, e.g., about 10% to about 22% chromium, up to cobalt, e.g., about 8% to about 22% cobalt, up to about 15% molybdenum, e.g., about 2% to about 12% molybdenum, up to 5% titanium, e.g., about 0.25% to about 5% titanium, up to 7% aluminum, e.g., about 0.25% to about 7% aluminum, up to about 15% tungsten, up to 0.2% carbon, e.g., about 0.02% to about 0.2% carbon, up to about 10% columbium, e.g., about 0.5% to about 8% columbium, up to about iron, up to about 0.1% boron, up to about 0.25 zirconium, up to about 2% manganese, up to about 2% silicon, and the balance essentially nickel. The sulfur content of the alloys should be as low as possible. Compositions of various alloys susceptible to treatment in accordance with the invention are set forth in the following Table I.

Bal. ess.- Bala11 ce essentially, including minor amounts of manganese, silicon, borozirconium, impurities, etc.

levels in vacuum melted products. Thus, sulfur levels not exceeding about 0.005% in vacuum melted alloys is common.

We have now discovered a method wherein vacuum melting is employed and wherein the properties of nickelbase alloys treated in accordance with the method are improved as compared to alloys prepared by vacuum melting and/or vacuum treating alone.

It is an object of the present invention to provide a process for improving the elevated temperature strength and ductility of nickel-base alloys.

It is a further object of the invention to provide a process for improving the hot workability of nickel-base alloys.

Other objects and advantages of the invention will be- 7 It is found that processing in accordance with the invention to provide a controlled retained magnesium content in vacuum melted alloys even though contents of sulfur and other impurities are very low provides markedly improved rupture life and rupture ductility in the treated alloys, e.g., nickel-chromium alloys. Furthermore, hot workability of the treated alloys is greatly improved.

In order to give those skilled in the art a better understanding and appreciation of the advantages of the invention, the following illustrative examples are given.

EXAMPLE I A series of age-hardenable alloys containing nominally about 21.5% chromium, about 13.5% cobalt, about 4% molybdenum, about 2% columbium, about 2.5% titanium, about 0.20% aluminum, about 0.05% carbon, not more than 0.005% sulfur, and the balance essentially nickel were prepared by vacuum melting under a pressure not exceeding 10 microns of mercury. In each instance, the molten metal was treated with about 0.05% carbon, and held in vacuum about 30 minutes at 2900" F. to remove oxygen and other gasses prior to magnesium treat ment. The alloys were worked from the ingot stage to %-ll1Ch diameter hot rolled rod using the same hot working procedure in each instance. The hot rolled rod material was annealed for one hour at 1800 F. followed by air cooling and a 24 hour aging at 1400 F. It was found that the alloys to which no magnesium had been added had rupture lives when tested at 1200 F. under a stress of 100,000 pounds per square inch (p.s.i.) in the range from about 122 hours to about 188 hours with elongations in the range of 9.5% to 17% and reductions in area in the range of about 11% to 30%. Other vacuum melted alloys in the series to which magnesium was added under a partial pressure of about one-half atmosphere of argon in accordance with the invention had magnesium contents, and when tested under the same stress rupture conditions, had rupture lives and ductility values as set forth in the following Table II.

TABLE II Magnesium Rupture Reduction in content, life, Elongation, area, percent hours percent percent EXAMPLE II A number of vacuum melted ingots were prepared from an alloy containing nominally about 0.05% carbon, about 15% chromium, about 3% molybdenum, about 3% tungsten, about 3% columbium, about 7% iron, about 0.4% aluminum, about 0.5% titanium, not more than about 0.004% sulfur, and the balance essentially nickel. A vacuum not exceeding about 10 microms of mercury was employed in each instance for melting. In each instance, the molten metal was treated with about 0.05% carbon and held in vacuum for about 30 minutes at 2900 F. to remove oxygen and other gases prior to magnesium treatment. One of the ingots was cast without a magnesium addition. Another melt was treated with magnesium under vacuum and contained only 0.005% magnesium. Magnesium additions were made to the remainder of the vacuum melts under argon as in Example I and magnesium was recovered therein in amounts up to 0.035%. The alloys contained about 0.005% boron and about 0.02% zirconium. The resulting ingots were converted to hot rolled square bar 0.64 inch square using the same procedure in each instance. Material from each of the bars was annealed at 1800 F. for one hour, air cooled and subjected to stress rupture at 1200 F. and 70,000 psi. with the results set forth in the following Table III.

TABLE III Magnesium con- Rupture Elonga- Reduction Alloy tent, life, tion, in area, Hot No. percent hours percent percent workability 6 185 30 32 Very poor.

I 0.005 277 26 24 Good.

O. 017 660 58 65 D0. 0.022 299 60 69 Do. 0. 026 530 45 69 D0. 0.035 1, 015 33 70 Do.

It is to be noted that recovery of magnesium in the material produced a substantial increase of rupture life together with marked improvement in ductility values. It is further to be noted that even treated with magnesium under vacuum wherein only 0.005 magnesium Was recovered in the alloy improved rupture life and hot workability. Alloy No. 6 to which on magnesium was added contained 1 part per million (p.p.m.) hydrogen, 6 p.p.m. oxygen, and less than 5 p.p.m. nitrogen. The gas contents of Alloy No. 11, which contained 0.035% magnesium, were 1.1 p.p.m. hydrogen, 6 p.p.m. oxygen, and less than 5 p.p.m. nitrogen, i.e., were almost axactly the same as for Alloy No 6. Microexamination of the stress-rupture specimens of Alloys Nos. 6 and 7 showed that grain 4 boundary microcracking occurred therein with little grain deformation whereas in Alloys Nos. 8 to 11 considerable grain deformation occurred before grain boundary cracking took place.

The invention is applicable to the production of castings as well as to the production of wrought products.

It is to be understood that by the term vacuum melting as employed herein, melting under a vacuum not exceeding about 10 microns of mercury pressure is intended. Satisfactory results are also achieved in accordance with the invention when air melted metal is subjected to a vacuum treatment for at least about 5 minutes at a pressure not exceeding 10 microns of mercury pressure followed by magnesium treatment under a nonreactive gas at a pressure of about one-third to about one atmosphere.

It is further to be understood that the processing according to the invention is particularly applicable to the processing of alloys containing about 14% to 16% chromium, about 2.75 to 3.25 columbium (plus tantalum), about 2.75% to 3.25 tungsten, about 2.75 to 3.25% molybdenum, about 5% to about 9% iron, up to about 0.08% carbon, about 0.3% to about 0.6% aluminum, about 0.4% to about 0.7% titanium, about 0.003% to about 0.008% boron, about 0.01% to about 0.05% zirconium, up to about 0.05 magnesium, up to about 0.75% manganese, up to about 0.4% silicon, with the balance nickel, and of age-hardenable alloys containing about 20% to about 22% chromium, about 1.5% to 2.5% columbium (plus tantalum), about 3.5% to 4.5% molybdenum, up to about 2% iron, up to about 0.07% carbon, about 0.2% to about 0.3% aluminum, about 2.3% to 3% titanium, about 0.002% to 0.008% boron, about 0.02% to about 0.08% zirconium, up to about 0.05 magnesium, up to about 0.25% manganese, up to about 0.15% silicon, with the balance essentially nickel.

We claim:

1. The process for improving the rupture life and ductility of nickel-chromium alloys which comprises subjecting said alloy in the molten condition to a vacuum treatment to reduce the impurity contents thereof to low levels and thereafter introducing magnesium into the vacuum treated melt such that the magnesium introduction step is carried out under a nonreactive gas atmosphere having a partial pressure of about one-third to about one atmosphere and casting the thus-treated alloy containing at least about 0.005 and up to about 0.1% magnesium.

2. The process according to claim 1 wherein the nonreactive gas is selected from the group consisting of argon, helium and nitrogen.

3. The process according to claim 1 wherein at least about 0.015% magnesium is retained in the treated alloy.

4. The process according to claim 1 wherein the alloy contains about 10% to about 25% chromium, up to about 15% molybdenum, up to about 15% tungsten, up to about 8% columbium, up to about 7% aluminum, up to about 7% titanium, up to about cobalt, up to about 0.1% boron, up to about 0.25 zirconium, up to about iron, not more than 0.005% sulfur, and the balance essentially nickel.

5. The process according to claim 1 wherein the alloy contains about 14% to about 16% chromium, about 2.75% to 3.25% columbium, about 2.75% to 3.25% tungsten, about 2.75% to 3.25 molybdenum, about 5% to 9% iron, up to about 0.08% carbon, about 0.3% to 0.6% aluminum, about 0.4% to 0.7% titanium, about 0.003% to about 0.008% boron, about 0.01% to about 0.05% zirconium, up to about 0.75% manganese, up to about 0.4% silicon, not more than 0.005% sulfur, and the balance essentially nickel.

6. The process according to claim 1 wherein the alloy contains about 20% to 22% chromium, about 1.5% to about 2.5% columbium, about 3.5% to 4.5% molybdenum, up to about 2% iron, up to about 0.07% carbon, about 0.2% to 03% aluminum, about 2.3% to 3% titanium, about 0.002% to 0.008% boron, about 0.02% to about 0.08% zirconium, up to about 0.25% manganese, up to about 0.15% silicon, not more than 0.005% sulfur, and the balance essentially nickel.

References Cited UNITED STATES PATENTS 2,570,193 10/1951 Bieber et al. 75171 6 3,160,500 12/1964 Eiselstein et al; 75-171 3,304,176 2/1967 Wlodek 75-171 3,383,204 5/1968 Hagel 75-170 US. Cl. X.R.

Patent No. 315121953 Dated i 1970 Inventor (a) a It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 2, line 46, in the 6th Column of Table I, last number,

change "2.08" to -2.8-. In the footnote of Table I, for

"boro-" read "boron,".

Col. 3, after Table III, insert the footnote 'Held in vacuum after addition of 0.06% magnesium-. Same column, line 65, for

"treated" read --treatment-. Also, line 68, for "on" read Signed and sealed this 29th day of June 1971.

(SEAL) Attest:

EDWARD M.FLETGHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents