Seal member and method for manufacturing same

1 . A seal member made of a γ′ precipitation-hardening alloy,

wherein the γ′ precipitation-hardening alloy has a component composition consisting of, in mass %:

Ni: from 40 to 62%;

Cr: from 13 to 20%;

Ti: from 1.5 to 2.8%;

Al: from 1.0 to 2.0% provided that Ti/Al: 2.0 or less;

Nb: 2.0% or less;

Ta: 2.0% or less provided that Nb+Ta: from 0.2 to 2.0%;

B: from 0.001 to 0.010%;

W: 3.0% or less; and

Mo: 2.0% or less provided that Mo+(½)W: from 1.0 to 2.5%, and optionally,

C: 0.08% or less;

Si: 1.0% or less;

Mn: 1.0% or less;

P: 0.02% or less;

S: 0.01% or less;

Co: 5% or less; and

Cu: from 0.1% to 3.0%,

with the balance being Fe and inevitable impurities, and

wherein the seal member has a hardness of 250 Hv or more, and has a cold-rolled microstructure where precipitates comprising a γ′ phase are dispersed in a crystal grain, and

wherein the cold-rolled microstructure maintains an area ratio of an unrecrystallized grain comprising the γ′ phase in a crystal grain at 20% or more in an observation cross-section after heating at 900° C. for 400 hours.

2 . The seal member according to claim 1 , wherein the cold-rolled microstructure comprises 0.05% or more of an inhomogeneous strain.

3 . The seal member according to claim 1 , wherein the cold-rolled microstructure maintains an area ratio of an unrecrystallized grain comprising the γ′ phase in a crystal grain at 30% or more in an observation cross-section after heating at 900° C. for 400 hours.

4 . The seal member according to claim 1 , wherein the seal member has a thickness in the range of from 0.05 mm to 0.5 mm.

5 . The seal member according to claim 1 , wherein the cold-rolled microstructure includes an inhomogeneous strain in the range of from 0.05% to 0.33%.

6 . The seal member according to claim 1 , wherein the seal member exhibits a high-temperature hardness in the range of from 170 Hv to 230 Hv at 900° C.

7 . The seal member according to claim 1 , wherein the cold-rolled microstructure is obtained without heat treatment after cold rolling, maintaining the cold-rolled microstructure in the seal member as used.