Method for manufacturing Ni-based super-heat-resistant alloy
A method for manufacturing a Ni-based super-heat-resistant alloy includes: a first cold working step for cold working a Ni-based super-heat-resistant alloy ingot, which has a composition in which the γ′ mole ratio is at least 40%, at a working ratio of 5% to less than 30%; and a first heat treatment step for heat-treating the cold worked material, on which the first cold working was performed, at a temperature exceeding the γ′ solid solution temperature. It is preferable that the manufacturing method also includes a second cold working step for performing, after the first heat treatment step, a second cold working on the heat-treated material at a working ratio of at least 20%, and a second heat treatment step for heat-treating the second cold worked material, on which the second cold working has been performed, at less than the γ′ solvus temperature.
1. A method for producing a Ni-based heat-resistant super alloy, comprising:
preparing an ingot of the Ni-based heat-resistant super alloy having such a composition that the alloy includes not less than 40 mol % of a gamma prime (γ′) phase;
a first cold work step of cold-working the ingot at a working ratio of not less than 5% but less than 30%; and
a first heat treatment step of heat-treating the first-cold-worked material at a temperature exceeding a solid solution temperature of the gamma prime phase.
2. The method according to claim 1 , wherein the first heat treatment is conducted at a temperature not higher than the gamma prime solid solution temperature plus 40° C. and lower than a solidus temperature of the alloy.
3. The method according to claim 1 , wherein the first cold work is conducted by forging, elongation working, or injection working, or a combination thereof.
4. The method according to claim 1 , wherein the alloy comprises, by mass:
0.001 to 0.250% C,
8.0 to 22.0% Cr,
not more than 28.0% Co,
2.0 to 7.0% Mo,
not more than 6.0% W,
2.0 to 8.0% Al,
0.5 to 7.0% Ti,
not more than 4.0% Nb,
not more than 3.0% Ta,
not more than 10.0% Fe,
not more than 1.2% V,
not more than 1.0% Hf,
0.001 to 0.300% B,
0.001 to 0.300% Zr, and
the balance of Ni and inevitable impurities.
5. The method according to claim 1 , further comprising:
a second cold work step of cold-working the first-heat-treated material at a working ratio of not less than 20%; and
a second heat treatment step of heat-treating the second-cold-worked material at a temperature lower than the gamma prime solid solution temperature.
6. The method according to claim 5 , wherein the second heat treatment is conducted at a temperature not lower than the gamma prime solid solution temperature minus 80° C.
7. The method according to claim 5 , wherein the first cold working or the second cold working is conducted by forging, elongation working, or injection working, or a combination thereof.