US3898109A

US3898109A - Heat treatment of nickel-chromium-cobalt base alloys

Info

Publication number: US3898109A
Application number: US430111A
Authority: US
Inventors: Stuart Walter Ker Shaw
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1973-09-06
Filing date: 1974-01-02
Publication date: 1975-08-05
Anticipated expiration: 1992-08-05
Also published as: DE2442532A1; CA1015250A; GB1417474A; FR2243270A1; FR2243270B1

Abstract

A four-stage heat-treatment to improve the stress-rupture life and stress-rupture ductility at elevated temperatures of nickelchromium alloys in which a two-stage heat-treatment is used intermediate of an initial solution treatment and a final aging treatment.

Description

United States Patent 1 1 Shaw [ 1 Aug. 5, 1975 1 1 HEAT TREATMENT OF NlCKEL-CHROMlUM-COBALT BASE ALLOYS [75] lnventor: Stuart Walter Ker Shaw, Wylde Green, England [73] Assignee: The International Nickel Company,

Inc., New York,

22 Filed: Jan. 2, 1974 21 Appl.No.: 430,111

[30] Foreign Application Priority Data Sept. 6, 1973 United Kingdom 41888/73 [52] US. Cl. 148/162; 75/134 F; 75/171; 148/13; 148/32.5 [51] Int. Cl. C22c 19/00; C22f 1/10 [58] Field of Search 75/134 F, 171; 148/13, 148/32, 32.5, 162

[56] References Cited UNITED STATES PATENTS 2,766,155 10/1956 Betteridge et a1. 148/162 3,356,542 12/1967 Smith 148/162 3,459,545 8/1969 Bieber et a1. 75/171 3,479,157 11/1969 Richards et al. 75/171 3,536,542 10/1970 Murphy et a1. 148/162 3,653,987 4/1972 Boesch 148/162 3,667,938 6/1972 Boesch 148/162 3,723,107 3/1973 Richards 148/162 3,741,821 6/1973 Athey et a1. 148/162 3,748,192 7/1973 Boesch 148/162 FOREIGN PATENTS OR APPLICATIONS 731,441 6/1955 United Kingdom 75/162 715,140 9/1954 United Kingdom..... 75/162 777,703 6/1957 United Kingdom..... 75/162 1,053,109 12/1966 United Kingdom..... 75/162 1,196,714 7/1970 United Kingdom 75/162 1,333,354 10/1973 United Kingdom 75/162 Primary Examiner-C. Lovell Attorney, Agent, or Firm-Raymond J. Kenny; Ewan C. MacQueen 57 ABSTRACT A four-stage heat-treatment to improve the stressrupture life and stress-rupture ductility at elevated temperatures of nickel-chromium alloys in which a two-stage heat-treatment is used intermediate of an initial solution treatment and a final aging treatment.

8 Claims, N0 Drawings HEAT TREATMENT OF NICKEL-CHROMIUM-COBALT BASE ALLOYS The instant invention relates to the heat-treatment of nickel-chromium-cobalt base high-temperature alloys.

In my United States application No. 241,443, now abandoned, there is described and claimed castable nickel-chromium-cobalt alloys containing about 0.02 to 0.25 percent carbon, about 20 to 25 percent chromium, about 5 to 25 percent cobalt, one or both of molybdenum up to 3.5 percent and tungsten up to 5 percent in such amounts that the value 0.5 percent Mo) plus %W is from 0.5 to 5 percent, about 1.5 to 5 percent titanium and l to 5 percent aluminium, with the provisos that the sum of the aluminium and titanium (i) be from 4 to 7 percent and (ii) in tungsten-free alloys not exceed 6 percent, and further that the (iii) ratio of titanium to aluminium be from 0.75:1 to 4:1, about 0.5 to 3 percent tantalum, up to 3 percent niobium, about 0.005 to 1 percent zirconium and up to 2 percent hafnium, with the proviso that the value of percent Zr 0.5 (percent Hf) be from 0.01 to 1 percent, about 0.001 to 0.05 percent boron, and up to 0.2 percent in total of yttrium or lanthanum or both, the balance, apart from impurities, being nickel in an amount of at least 30 percent.

In order to develop a high level of stress-rupture strength at elevated temperatures such as 927C (1700F) or 980C (1,800F), the alloys were to be subjected, upon casting, to a heat-treatment comprised of solution-heating and subsequent aging. Various heat-treatments of this general kind were given in my said US. Application, namely:

a. Solution-heating at 1,0501250C for 1-10 hours;

aging at 600950C for l-24 hours.

b. Solution-heating at 1,0501,250C for 1-20 hours; intermediate heating at 8001,150C for l-16 hours; aging at 600950C for 1-24 hours.

c. Solution-heating at 1,200C for 16 hours; air-cool; heat at 1,1001,150C for 2-4 hours; air-cool; age at 800C for 16 hours; air-cool.

However, for many purposes, eg for gas turbine noz zle guide vanes, rotor blades and integrally bladed rotors, for small gas turbines such as for automotive propulsion, auxiliary engines on aircraft or ships and for diesel engine turbo-blowers, it is extremely important that articles and parts cast from high-temperature alloys should not only have high stress-rupture strength at the aforementioned high temperatures of 927C or 980C, but also have a combination of high stressrupture strength and stress-rupture ductility (as measured by the elongation at fracture) at intermediate temperatures, e.g. 816C (1500F).

Given the emphasis on stress-rupture strength, ob taining an improved level of ductility has not been without difficulty. For it will be appreciated that the ductility of alloys of a given base composition at a given temperature generally decreases as the stress-rupture strength is increased by minor modifications in composition. And the results in Table ll of my prior Application reflect that the stronger alloys, i.e., those for which /2 (percent Ta) percent Nb percent Ti percent Al is between 6.7 and 7.7, generally have elongations at rupture, when tested under a stress of 276 l\l/mm (28 kgf/mm at 816C, of less than about 4 percent. The specimens had been heat-treated by solutionheating at 1,150C for 4 hours, air-cooled, aged at 850C and again air-cooled. Little improvement in duetility resulted from the interposition of an intermediate heating in between the solution-heating and aging, as in heat-treatment (b) above.

The present invention is based on the discovery that the stress-rupture ductility and the stress-rupture life at 816C for the alloys aforedescribed can be substantially improved provided there is interposed between the solution-heating and aging steps a two-stage intermediate treatment at temperatures within critical ranges.

According to the invention the alloys are given the following heat-treatment:

i. solution-heating at 1 1 C for from 2 to 16 hours (preferably at about 1150C for about 4 hours) ii. heating at-970l030C for from 2 to 10 hours (preferably at about 1,000C for about 6 hours) iii. heating at 870930C for from 8 to 48 hours (preferably at about 900C for about 24 hours) iv. aging at 600-800C for from 8 to 48 hours (preferably at about 700C for about 16 hours) The alloys may be cooled at any convenient rate after each heat-treatment stage, e.g. by air-cooling generally to room-temperature).

The improvement brought about by this four-stage heat-treatment is most surprising, particularly since 1 have determined that two prior art four-stage heattreatments (there could be others) for nickelchromium-cobalt base alloys seriously impair either the stress-rupture life or ductility at 816C.

It is well known that if the more advanced nickelchromium base alloys which possess the highest creeprupture strengths attainable at a particular chromium content contain a small excess of hardening elements, sigma phase can be formed during very long time service under stress at temperatures in the range of about 800 to 870C. This is also true for alloys of the present invention, and for such very prolonged service in this temperature range in order to eliminate the possibility of sigma phase formation (or render the amount that could be formed so small that its effect on the properties of the alloys would be negligible) (i) the value of /2 (percent Ta) percent Nb percent Ti percent Al should not exceed 7.7 percent, (ii) the chromium content should not exceed about 23.5 percent and (iii) the W /2 (percent Mo) should not be greater than about 2.5 percent.

The advantages of the heat-treatment of the invention are clearly shown by the results of tests on an alloy of the same nominal composition as Alloy No. 24 of my prior Application, namely:

23 percent Cr, 15 percent Co, 2 percent W, 1 percent Nb, 1.4 percent Ta, 3.5 percent Ti, 1.9 percent A1, 0. 15 percent C, 0.1 percent Zr, 0.01 percent B, balance (apart from impurities) Ni.

Test-pieces machined from tapered test-bar blanks cast from a vacuum-melted heat of this alloy were given various heat -treatments and then subjected to stressrupture tests at 816C under a stress of 276 N/mm and to tensile tests at 20C. The heat-treatments and tests results are set forth in Table l.

TABLE I Strcssrupturc Tensile C Heat Treatment 27(1/81(iC U.T.S.

A 411 1 150C 6h/l()()0C +24h/900C lob/700C 1572 8.8 941 3.7 B 411/1 150C 2411 900c 1290 5.2 897 1.0 +16h/7()0C 1327 5.8 903 0.8 C 4h/l 150C 6h 1000C +l6h/70()C 1358 4.4 942 2.2 D 4h/1 150C 16h/850C 1336 3.4 1010 4.3 1399 4.0 1020 2.9 E 411/1 163C 411/ 1080C +24h/927C l6h/760C 430 8.5 922 1.1 F 411/1 177C 4l1/l080C +24h/843C loll/760C 907 2.6 1030 1.2

U.T,S. Ultimate Tensile Stress In each case the specimens were air-cooled to roomnominal composition: 22.7 percent Cr, 19 percent Co, temperature between successive stages of the heat- 2 percent W, 1 percent Nb, 1.4 percent Ta, 3.7 percent treatment. Ti, 1.9 percent Al, 0.15 percent C, 0.1 percent Zr, 0.01 Of the six heat-treatments in Table I, only Treatment 20 percent B, Ni balance (apart from impurities). This A is in accordance with the invention. In each of Treatll i stronger i stress-rupture than the alloy used in ments B and C On f th t intermediate heating the tests reported in Table l, and accordingly the stresssteps was mitted, th s being examples of the rupture tests at 816C were carried out under the Stage heat-treatment of y Prlor pp higher stress of 310 N/mm The results of stress- Tfeatmem D represents a Prlor Preferred twostage rupture tests at 927C under a stress of 120 N/mm are treatment. E and F are two prior art fourstage treatalso given ments described in U.K. specification No. 1,248,492.

TABLE I1 Stress-rupture Tensile 20C Heat Treatment 70 U.T.S.

N/mm C Life h. Elong. N/mm Elong.

A 411/1 150C 6h/l000C 310 816 1101 9.4 950 3.0 +24h/900C Sh/700C 120 927 800 8.0 965 3.8 1 D 4h/1150C+ lob/850C 310 816 915 2.8 846 0.5 120 927 817 8.1 875 0.7

It will be seen that Treatment A gives the best combi- These data reflect that the stress-rupture life and nation of rupture life and ductility and tensile ductility, 40 d ilit t 816C and the tensile ductility at roomthe stress'rupture ductility being more than twicfi that temperature are again substantially increased by Treatgiven -by the tw -Stag Tr a D with the Stfe$5 ment A compared with Treatment D, while the stressrupture life being some 20 percent greater. Treatments rupture properties t 927C are substantially un- B and C both afford some improvement in stressh d rupture ductility, but Offer no signififlam Change It is thought that the heat-treatment according to the stress-rupture life, and both treatments impaired tensile 'lnventlon may also advantageously be applled to the dummy Pompared Treatment alloys in the wrought form. Moreover, it is considered The prior art four-stage Treatments and F bgth that the special sequence of heating steps herein deriously detracted from stress-rupture life at 816 C and scribed is applicable to other nlckel chromlum high I i a ll f t compared z j g A (211805)) temperature superalloys, particularly those hardenable d It 39 J fi L fz stress'm? ure by at least from 3 percent to 12 percent of titanium plus uctl i is was assoc? 6 W1 very poor 8 ress' aluminium, and/or matrix hardenable by one or more rurture l f h l n m l t d herein of niobium, tantalum, molybdenum and tungsten, with n terms 0 morp o a Oys co emp a 6 elements such as cobalt, zirconium, boron, carbon and upon being subjected to the four-stage sequence of heating have a structure characterized by the presence in the grain boundaries of small, discrete M C -type carbide particles without significant extra precipitation or denudation of gamma prime precipitates in adjacent areas.

particularly good reSults are obtained with alloys consisting essentially of about 0.02 to about 0.25 carhaving compositions within the following ranges: 22.2 about 20 to about 25 Percent Chromium, about 5 to 22 8 percent C t 19,5 percent Co 8 t 22 percent to about 25 percent cobalt, at least one metal percent W, 0.9 to 1.1 percent Nb, 1.3 to 1.5 percent from the group of molybdenum up to 3.5 percent and Ta, 3.6 to 3.8 percent Ti, 1.8 to 2.0 percent Al, 0.13 to 6 tungsten up to 5 percent in amounts such that 0.5 per- 0.17 percent C, 0.04 to 0.12 percent Zr, 0.004 to 0.012 ccnt Mo plus percent W is from 0.5 to 5 percent, about percent B, balance Ni. In Table ll are set forth the rc- 1.5 to about 5 percent titanium, about 1 to about 5 per- Sults of tests on an alloy within this range having the cent aluminium, the sum of the Ti and A] being from hafnium being optionally present.

1 claim:

1. A heat treating process for improving properties of nickel-chromium alloys at elevated temperatures on the order of '8 1 5C which comprises subjecting an alloy about 4 to about 7 percent and not more than about 6 percent in tungsten free alloys, and the ratio of titanium to aluminium being about 0.75:l::4:l, about 0.5 to 3 percent tantalum, up to 3 percent niobium, about 0.005 to 1 percent zirconium, up to 2 percent hafnium, the sum of the Zr 0.5 Hf being from 0.0l to l percent about 0.001 to 0.05% boron, the balance being essentially nickel, the nickel being at least about 30 percent, to the following sequence of heat treating operations:

a. heating at about 1,1 20 to about 1, l 80C for about 2 to about 16 hours; b. heating at about 970 to about 1.030C for about 2 to about hours; c. heating at about 870 to 930for about 8 to about 48 hours; and d. heating at about 600 to about 800C for about 8 to about 48 hours. 2. The process in claim 1 in which heating (a) is for about 4 hours at about ll50C.

3. The process in claim 1 in which heating (b) is for about 6 hours at about 1000C.

4. The process in claim 1 in which heating (c) is for about 24 hours at about 900C.

5. The process in claim 1 in which heating (d) is for about l6 hours at about 700C.

6. The process in claim 1 in which the alloy treated contains about 0.13 to about 0.17 percent carbon, about 22.2 to about 22.8 percent chromium, about 18.5 to about 19.5 percent cobalt, about 1.8 to about 2.2 percent tungsten, about 1.3 to about 1.5 percent tantalum, about 0.9 to about 1.1 percent niobium, about 3.6 to about 3.8 percent titanium, about 1.8 to 2 percent aluminium, about 0.04 to 0.12 percent zirconium, about 0.004 to 0.012 percent boron, and the balance essentially nickel.

7. The process in claim 1 in which a. /2 percent Ta percent Nb percent Ti percent Al is not greater than 7.7 percent;

b. the chromium content does not exceed about 23.5

percent; and

c. /2 percent Mo percent W is not greater than about 2.5 percent.

8. The alloy produced by the process of claim I having a structure characterized by the presence in the grain boundaries of small, discrete M C -type carbide particles without significant extra precipitation of gamma prime precipitate in adjacent areas.

Claims

1. A HEAT TREATING PROCESS FOR IMPROVING PROPERTIES OF NICKEL-CHROMIUM ALLOYS AT ELEVATED TEMPERATURES ON THE ORDER OF 815*C WHICH COMPRISES SUBJECTING AN ALLOY CONSISTING ESSENTIALLY OF ABOUT 0.02 TO ABOUT 0.25 CARBON, ABOUT 20 TO ABOUT 25 PERCENT CHROMIUM, ABOUT 5 PERCENT TO ABOUT 25 PERCENT COBALT, AT LEAST ONE METAL FROM THE GROUP OF MOLYBDENUM UP TO 3.5 PERCENT AND TUNGSTEN UP TO 5 PERCENT IN AMOUNTS SUCH THAT 0.5 PERCENT MO PLUS PERCENT W IS FROM 0.5 TO 5 PERCENT, ABOUT 1.5 TO ABOUT 5 PERCENT TITANIUM, ABOUT 1 TO ABOUT 5 PERCENT ALUMINIUM, THE SUM OF THE TI AND AL BEING FROM ABOUT 4 TO ABOUT 7 PERCENT AND NOT MORE THAN ABOUT 6 PERCENT IN TUNGSTEN FREE ALLOYS, AND THE RATIO OF TITANIUM TO ALUMINIUM BEING ABOUT 0.75:1::4:1, ABOUT 0.5 TO 3 PERCENT TANTALUM, UP TO 3 PERCENT NIOBIUM, ABOUT 0.005 TO 1 PERCENT ZIRCONIUM, UP TO 2 PERCENT HAFNIUM, THE SUM OF THE ZR+0.5 % HF BEING FROM 0.01 TO 1 PERCENT ABOUT 0.001 TO 0.05% BORON, THE BALANCE BEING ESSENTIALLY NICKEL, THE NICKEL BEING AT LEAST ABOUT 30 PERCENT, TO THE FOLLOWING SEQUENCE OF HEAT TREATING OPERATION: A. HEATING AT ABOUT 1,120* TO ABOUT 1,180*C FOR ABOUT 2 TO ABOUT 16 HOURS, B. HEATING AT ABOUT 970* TO ABOUT 1.030*C FOR ABOUT 2 TO ABOUT 10 HOURS, C. HEATING AT ABOUT 870* TO 930* FOR ABOUT 8 TO ABOUT 48 HOURS, AND D. HEATING AT ABOUT 600 TO ABOUT 800*C FOR ABOUT 8 TO ABOUT 48 HOURS.

2. The process in claim 1 in which heating (a) is for about 4 hours at about 1150*C.

3. The process in claim 1 in which heating (b) is for about 6 hours at about 1000*C.

4. The process in claim 1 in which heating (c) is for about 24 hours at about 900*C.

5. The process in claim 1 in which heating (d) is for about 16 hours at about 700*C.

7. The process in claim 1 in which a. 1/2 percent Ta + percent Nb + percent Ti + percent Al is not greater than 7.7 percent; b. the chromium content does not exceed about 23.5 percent; and c. 1/2 percent Mo + percent W is not greater than about 2.5 percent.

8. The alloy produced by the process of claim 1 having a structure characterized by the presence in the grain boundaries of small, discrete M23C6-type carbide particles without significant extra precipitation of gamma prime precipitate in adjacent areas.