Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/056—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 10% but less than 20%

Definitions

• Ballston Lake, N.Y. assignors to--General Electric Company, a corporation of New York ICC able that the alloys used in the gas turbine hot stages be able to withstand mechanical stress over long periods of time. It is accordingly a primary object of this invention to produce such alloys of the above nickel-base type which not only are resistant to surface degradation at No Drawing. Filed May 31, 1968, Ser. No. 733,259 5 elevated temperatures, but which are further characterized Int. Cl. C21d 1/00 by much improved life at such temperatures under the 143-162 5 C ai stress-rupture conditions to which they are subjected in actual use.
• alloys of ABSTRACT OF THE DISCLOSURE the nickel-base type set forth are subjected to a heat treat-
• the elevated temperature stress-rupture life of nickelment which compl'isoa treating at a temperature of about base alloys containing as major constituents nickel, cobalt, 2100 to 2200 tot about tWo to eight hours, P chromium, aluminum, titanium, and molybdenum, which y about 2125 about 4 hours followed y fast are also characterized by good oxidation and hot corro- Cooling, treating at a temperature of about 1975 sion resistance at elevated temperature, is improved by a about two to eight hours, Preferably four hours followed special heat treatment.
• the heat treating method comy fast cooling, treating at a temperature of about 17003 prises treating the alloy to a temperature of from about from about 12 hours to 48 hours, Preferably about 2100 F. to 2200 F. for from aboutZto 8 hours followed 24 hours followed y fast cooling, and finally treating by fast cooling, treating at a temperature of about 1975 at a temperature of about 1400 R for about 3 to 25 F.
• ductility as represented by elongation and reduction in area, and the like.
• Thi invention relates to a new d f l h treat- Those features of the invention which are believed to ment for alloys. More particularly, it relates to a new heat be novel are set forth With particularity in the Claims P- treatment for nickel-base, high temperature oxidationpended hofoto- The invention Will, however, be better and corrosion-resistant alloys which substantially imunderstood and further. advantages and j a o proves their stress-rupture life at elevated temperatures. appreclated from a conslderatwn of the followmg p- The use of nickel base alloys in equipment such as gas tionturbines which operate at elevated temperatures is well Amon the nickel-base alloys Which are considered to known. These materials are designed particularly to withbe particularly suitable to the new heat treatment are stand extreme stress for long periods of time, as well as those shown in Table I below.
• the alloy is first heated at a temperature of from about 2100 to 2250 F. for from about 2 to 8 hours, and preferably at 2125 F. for about 4 hours and fast cooled as by a gasquench, such as by introducing cold inert gas into the furnace or by Withdrawing the alloy into the open air.
• a gasquench such as by introducing cold inert gas into the furnace or by Withdrawing the alloy into the open air.
• the purpose of this heat treatment step is to solutionize the alloys. Temperatures above about 2250 F. would tend to cause incipient melting of the alloy and defeat the purpose of the heat treating step.
• M C often has the composition Cr Mo C are placed in solution leaving only the continuous alloy matrix, and MC carbides (where a composition such as (Ti,Mo)C is often experienced) as such.
• a temperature of the least 2100 F. must be used because at lower temperatures certain of these phases will tend to percipitate in an uncontrolled fashion, and, as pointed out above, temperatures above about 2250 F. will produce incipient melting of the alloy. Treatment times of less than about 2 hours can not be expected to produce full solution, and treatment for more than about 8 hours for 2125 F. would be uneconomical. After this treatment the alloy is fast cooled as above.
• the alloy is held at a temperature of about 1975 F. for from about 2 to 8 hours and preferably for about 4 hours.
• the object of this treatment is to initiate precipitation of the 'y strengthening phase, which is distributed generally as a finely divided particulate precipitate. This initiation of precipitation at this temperature results in the development of optimum size 7' particles upon subsequent aging, which contributes to the achievement of maximum strengthening. Treatment in this temperature regime for less than about 2 hours results in inadequate precipitation, and again more than about 8 hours treatment would be unnecessary and uneconomical.
• the alloy at the end of this treatment is fast cooled as described above.
• the third step in the present heat treatment is critical, is the essence of this discover, and is the major single variant from prior art practice.
• This treatment first of all, causes the 7' particles precipitated as described above to grow to an approximate optimum size for the generation of maximum strengthening.
• this treatment precipitates M C carbides at grain boundaries through a solid state reaction which is believed to be as follows:
• the M C compound percipitates as discrete carbide particles which are of optimum size at the grain boundaries, strengthening these boundaries and locking or fixing them to prevent or delay undesirable slippage.
• An important part of this heat treatment is believed to reside in the fact that the 'y' degeneration product develops as a continuous envelope around the M C carbides precipitated at the grain boundaries.
• This englovement or surrounding of M C particles by prevents subsequent precipitation of deleterious cell-like M C at the grain boundaries during actual service of the alloy, an experience found in the past which can cause failure of parts in service.
• This englovement also acts as a strong ductile cushion inhibiting the onset of alloy fracture and promoting long rupture life.
• the alloy is heated at 1400 F. for 16 hours and fast cooled as above.
• This final treatment causes a further precipitation of the 7' phase and may also bring a small additional amount of M out of solution. As a general proposition it tends to stabilize the alloy as a whole.
• the time of treatment can be varied from about 8 to 24 hours.
• alloys having been heat treated as shown in Table I above for alloy A having been heat treated as shown in Table I above for alloy A, the time and temperature of treatments being those indicated above as preferred. This improvement is expressed as the ratio of the stress rupture life for the new treatment as opposed to that for the old treatment.
• said alloy contains as major essential constituents in percent by weight, cobalt about 14.25 to 15.75, chromium about 14.00 to 15.25, aluminum about 4.00 to 4.60, titanium about 3.00 to 3.70, molybdenum about 3.90 to 4.50, boron about 0.012 to 0.020, zirconium about 0.04 max, carbon about 0.05 to 0.09, with the remainder nickel.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)

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Cited By (11)

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Citations (6)

• 1968
  • 1968-05-31 US US733259A patent/US3536542A/en not_active Expired - Lifetime
• 1969
  • 1969-02-12 GB GB7690/69A patent/GB1248492A/en not_active Expired
  • 1969-05-02 DE DE19691922314 patent/DE1922314A1/de active Pending
  • 1969-05-05 CH CH685769A patent/CH523329A/de not_active IP Right Cessation

Patent Citations (6)

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