Heat treatment for nickel-base alloys

Details Heat treatment for nickel-base alloys Heat treatment for nickel-base alloys

2000-03-02

2001-11-13

Sheehan, John (Department: 1742)

Metal treatment

Process of modifying or maintaining internal physical...

Heating or cooling of solid metal

C148S677000

Reexamination Certificate

active

06315846

ABSTRACT:

TECHNICAL FIELD
The instant invention relates to corrosion resistant nickel-base alloys in general, and more particularly, to a heat treatment that encourages gamma prime and double gamma prime precipitation and relatively high yield strengths on the order of 156-172 ksi (1076-1186 MPa) as well as low temperature fracture toughness and ductility.
BACKGROUND ART
In physically and chemically demanding environments, such as oil patch and gas turbine applications, there is a need for higher strength nickel-base alloys having corrosion resistance greater than the workhorse 3% molybdenum precipitation hardened alloys—INCONEL® alloy 718 (UNS N07718) and INCOLOY® alloy 925 (UNS N09925). In particular, a yield strength in the range of about 140-170 ksi (965-1172 MPa) combined with superior corrosion resistance is desired by fabricators and component manufacturers. The “UNS” prefix and the “UNS” numbers set forth herein refer to the alloy compositions in the well-known “Unified Numbering System” established by SAE HS-1086 and ASTM DS-566.
Oil patch applications include subsurface and well head completions and drill components. High strength and corrosion resistant containment rings and associated components on gas turbine engines require lightweight but robust construction.
Age hardenable alloys based upon nickel and containing precipitation hardening amounts of titanium, niobium and/or aluminum have been known and used for many years. Various heat treatment techniques have been employed to obtain desired physical and chemical characteristics. See, for example, U.S. Pat. No. 3,871,928.
More particularly, component fabricators and designers have identified the following characteristics and targets as desirable for specific oil/gas and turbine applications:
(1) Age-hardenable yield strength ≧140 ksi (968 MPa);
(2) Low temperature Charpy V-notch impact strength at −75° F. (−58° C.)=25 ft-lbs (111 N-m);
(3) Pitting resistance superior to alloy 718 (UNS N07718) and alloy 925 (UNS N09925);
(4) Resistance to hydrogen embrittlement per NACE TM-0177 test;
(5) Stress corrosion cracking resistance to moderately sour oil field environments at temperatures from 250° to 350° F. (121° to 177° C.);
(6) Fracture energy as expressed by tensile strength elongation greater than exhibited by alloy 718 (UNS N07718); and
(7) High temperature strength greater than exhibited by alloy 625 (UNS N07716).
The typical commercial compositions of alloy 725 (UNS N07725) and alloy 625 (UNS N07716) are given in Table 1 below:
TABLE 1
Chemical Composition (wt. %)
Alloy 725
Alloy 625
(UNS N07725)
(UNS N07716)
Nickel
55.0-59.0
57.0-63.0
Chromium
19.0-22.5
19.0-22.0
Molybdenum
7.0-9.5
7.0-9.5
Niobium
2.75-4.0
2.75-4.0
Titanium
1.0-1.7
1.0-1.6
Aluminum
0.35 max.
0.35 max.
Carbon
0.03 max.
0.20 max.
Manganese
0.35 max.
0.20 max.
Silicon
0.20 max.
0.20 max.
Phosphorus
0.0l5 max.
0.0l5 max.
Sulfur
0.0l0 max.
0.0l0 max.
Commercial Impurities
Trace
Trace
Iron
Remainder
Remainder
Alloy 725 (UNS N07725) is strengthened by precipitation of double gamma prime phase during an aging treatment. Before aging, the alloy is currently solution annealed at 1900° F. (1040° C.) and air cooled or water quenched. For sour gas applications, the published recommended aging treatment is 1350° F. (730° C.)/8hours, furnace cooled and then air cooling.
In summary, in order to obtain the published high yield strength for, say, age hardened rounds (133 ksi (917 MPa)) or strip (143 ksi (992 MPa)), the current practice is to anneal, cold work and then age.
In order to exceed the properties of alloys 718 and 925, it was contemplated that a new heat treatment paradigm would be necessary.
SUMMARY OF THE INVENTION
Accordingly, there is provided a heat treatment for 725 type alloys (alloys N07725 and N07716).
In contrast to current practice, the heat treatment is performed directly on hot or cold worked material, hereinafter referred to as “worked material”.
The heat treatment of the present invention consists of an initial anneal on the worked material of about 1825° F. (996 ° C.)±25° F. (14° C.) for at least about 1.5 to 4.0 hours, followed by age hardening at about 1400° F. (760° C.)±50° F. (28° C.) for about 3.0 to 10.5 hours, followed by furnace cooling at about 50° F. (28° C.)±25° F. (14° C.) per hour to about 100° F. (56° C.)±25 ° F. (14° C.) per hour and finally heat treating the alloy at about 1200° F. (649° C.)±50° F. (28° C.) for about 4.0 to 12.5 hours.
The resultant room temperature 0.2% yield strength of the alloy is in excess of about 140 ksi (986 MPa), preferably above 150 ksi (1042 MPa); and more preferably in excess of 155 ksi (1069 MPa). The low temperature impact strength properties at −75° F. (−58° C.) are dramatically improved by the heat treatment of the present invention, exhibiting Charpy V-notch values greater than 25 ft-lbs (111 N-m).


REFERENCES:
patent: 3046108 (1962-07-01), Eiselstein
patent: 3871928 (1975-03-01), Smith, Jr. et al.
patent: 4750950 (1988-06-01), Clatworthy et al.
patent: 4788036 (1988-11-01), Eiselstein et al.
patent: 4979995 (1990-12-01), Hattori et al.
patent: 5059257 (1991-10-01), Wanner et al.
patent: 5244515 (1993-09-01), Miglin
patent: 5556594 (1996-09-01), Frank et al.
patent: 2202331 (1997-10-01), None
Alloy Digest, “Custom Age 625 Plus Alloy,” Jul. 1988, 1 p.
Alloy Digest, “Inconel Alloy 725,” Jan. 1994, 3 pp.

Affiliated with

Also associated with

Rating

Heat treatment for nickel-base alloys does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Heat treatment for nickel-base alloys, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat treatment for nickel-base alloys will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2595524