Method for manufacturing Ni-based alloy member
Provided is a method for manufacturing an Ni-based alloy member in which the equilibrium amount of γ′ phase precipitation at 700° C. is from 30 to 70 volume %. The method includes the steps of preparing an Ni-based alloy powder having a predetermined chemical composition; forming a precursor body wherein an average grain diameter of the γ phase grains is 50 μm or less, by using the Ni-based alloy powder; and heating the precursor body to a temperature at least the γ′ phase solvus temperature and subsequently slow-cooling the heated precursor body from the temperature to a temperature at least 100° C. lower than the γ′ phase solvus temperature at a cooling rate of 100° C./h or lower. There is obtained a softened body in that the γ′ phase particles of at least 20 volume % precipitate between/among the γ phase grains having an average grain diameter of 50 μm or less.
1. A method for manufacturing an Ni-based alloy member, the Ni-based alloy member having a chemical composition comprising:
5 mass % to 25 mass % of Cr,
more than 0 mass % to 30 mass % of Co,
1 mass % to 8 mass % of Al,
1 mass % to 10 mass % of Ti, Nb and Ta in total,
10 mass % or less of Fe,
10 mass % or less of Mo,
8 mass % or less of W,
0.1 mass % or less of Zr,
0.1 mass % or less of B,
0.2 mass % or less of C,
2 mass % or less of Hf,
5 mass % or less of Re,
0.003 mass % to 0.05 mass % of O, and
the balance being Ni and unavoidable impurities,
in which an equilibrium amount of precipitation of a γ′ phase precipitating in a γ phase made up of γ phase grains as a matrix at 700° C. is 30 volume % or more and 80 volume % or less,
the manufacturing method consisting of:
an alloy powder preparation step of preparing an Ni-based alloy powder having the chemical composition;
a precursor body formation step of forming a precursor body in which an average grain diameter of the γ phase grains is 50 μm or less, by using the Ni-based alloy powder;
a softening heat treatment step of heating the precursor body to a heating temperature equal to or higher than a solvus temperature of the γ′ phase but lower than a melting temperature of the γ phase in order to dissolve the γ′ phase into the γ phase, and then slow-cooling the heated precursor body from the heating temperature to a temperature at least 50° C. lower than the γ′ phase solvus temperature at a cooling rate of 100° C./h or lower, thereby fabricating a softened body in that precipitated particles of the γ′ phase on grain boundaries of the γ phase grains make up at least 20 volume %, and the γ phase grains have an average grain diameter of 50 μm or less;
a forming step of forming a shaped workpiece with a desired shape by subjecting the softened body to hot working, warm working, cold working, or machining; and
a solution and aging heat treatment step of subjecting the shaped workpiece to a solution heat treatment to thereby decrease the precipitation amount of the γ′ phase on the grain boundaries of the γ phase grains to at most 10 volume %, and of subjecting subsequently the shaped workpiece to an aging heat treatment to thereby precipitate particles of the γ′ phase of at least 30 volume % within the γ phase grains.
2. The manufacturing method according to claim 1 , wherein the Ni-based alloy powder has an average particle diameter from 5 μm to 250 μm.
3. The manufacturing method according to claim 1 , wherein
the alloy powder preparation step is an atomization step of forming the Ni-based alloy powder.
4. The manufacturing method according to claim 1 , wherein the precursor body formation step is a hot isostatic press process using the Ni-based alloy powder.
5. The manufacturing method according to claim 1 , wherein
the γ′ phase solvus temperature is 1110° C. or higher.
6. The manufacturing method according to claim 1 , wherein
the softened body has a Vickers hardness of 370 Hv or less at a room temperature.
7. The manufacturing method according to claim 1 , wherein
the cooling rate in the softening heat treatment step is 10° C./h or lower.
8. The manufacturing method according to claim 1 , wherein
the cooling rate in the softening heat treatment step is 50° C./h or lower.
9. The manufacturing method according to claim 3 , wherein the alloy powder preparation step is an atomization step of forming the Ni-based alloy powder.
10. The manufacturing method according to claim 5 , wherein
the Ni-based alloy member has the chemical composition in which the equilibrium amount of precipitation of the γ′ phase at 700° C. is 45 volume % or more and 80 volume % or less.
11. The manufacturing method according to claim 10 , wherein the precursor body formation step is a hot isostatic press process using the Ni-based alloy powder.
12. The manufacturing method according to claim 9 , wherein
the γ′ phase solvus temperature is 1110° C. or higher.
13. The manufacturing method according to claim 9 , wherein
the Ni-based alloy member has the chemical composition in which the equilibrium amount of precipitation of the γ′ phase at 700° C. is 45 volume % or more and 80 volume % or less.
14. The manufacturing method according to claim 9 , wherein
the softened body has a Vickers hardness of 370 Hv or less at a room temperature.