Austenitic heat resistant alloy, heat resistant pressure member comprising the alloy, and method for manufacturing the same member

A method for manufacturing a heat resistant pressure member excellent in creep resistance and structural stability in a high temperature range which is made from an austenitic heat resistant alloy comprising, by mass percent, C:

• more than 0.02% to not more than 0.15%, Si:
• 2% or less, Mn:
• 3% or less, P:
• 0.03% or less, S:
• 0.01% or less, Cr:
• more than 30% to 38%, Ni:
• more than 40% to not more than 60%, Co:
• 7.2 to 20%, W:
• more than 3% to not more than 15%, Ti:
• 0.53 to 1.0%, Zr:
• 0.005 to 0.2%, Al:
• 0.01 to 0.3%, N:
• 0.02% or less, and Mo:
• less than 0.5%, with the balance being Fe and impurities, in which the following formulas (1), (3) and (4) are satisfied:
• P≦3/{200(Ti+8.5×Zr)} (1),
• Al≧1.5×Zr (3),
• 1.35×Cr≦Ni+Co≦1.85×Cr (4);
• wherein each element symbol in the formulas (1), (3) and (4) represents the content by mass % of the element concerned, and
• wherein the austenitic heat resistant alloy is treated in sequence by the following steps (i), (ii) and (iii):
• step (i):
• heating to 1050 to 1250° C. at least once before final hot or cold working;
• step (ii):
• carrying out a final hot or cold plastic working such that a reduction of area is 10% or more;
• step (iii):
• carrying out a final heat treatment in which cooling is performed after heating and holding at a temperature in the range of 1100 to 1250° C.