Method for producing austenitic heat resistant steel

A method for producing an austenitic steel in which a difference between a content of Nb and an amount of Nb analyzed as extraction residues satisfies Formula (i) shown below, the method comprising:

• a forming step of machining and forming a steel into a product shape, the steel including a chemical composition consisting of, in mass %:
• C:
• 0.04 to 0.12%,
• Si:
• 0.01 to 0.30%,
• Mn:
• 0.50 to 1.50%,
• P:
• 0.001 to 0.040%,
• S:
• 0.0050% or less,
• Cu:
• 2.2 to 3.8%,
• Ni:
• 8.0 to 11.0%,
• Cr:
• 17.7 to 19.3%,
• Mo:
• 0.01 to 0.55%,
• Nb:
• 0.400 to 0.650%,
• B:
• 0.0010 to 0.0060%,
• N:
• 0.050 to 0.160%,
• Al:
• 0.025% or less,
• O:
• 0.020% or less,
• Co:
• 0 to 1.00%,
• W:
• 0 to 1.00%,
• Ti:
• 0 to 0.40%,
• V:
• 0 to 0.40%,
• Ta:
• 0 to 0.40%,
• Sn:
• 0 to 0.0300%,
• Ca:
• 0 to 0.0100%,
• Mg:
• 0 to 0.0100%, and
• REM:
• 0 to 0.0800%,
• with the balance:
• Fe and impurities;
• a solution heat treatment step of performing, after the forming step, heat treatment under conditions including a heat treatment temperature satisfying Formula (ii) shown below and a soaking time satisfying Formula (iii) shown below;
• and
• a cooling step of performing cooling after the solution heat treatment step:
• 0.17
• ≤
• Nb
• -
• Nb
• ER
• ≤
• 0.48
• (
• i
• )
• -
• 250
• ⁢
• Nb
• +
• 1200
• ≤
• T
• ≤
• -
• 100
• ⁢
• Nb
• +
• 1290
• (
• ii
• )
• 405
• -
• 0.3
• T
• ≤
• t
• ≤
• 2475
• -
• 1.5
• T
• (
• iii
• )
• where a symbol of an element in the formulas indicates a content (mass %) of the element contained in the steel, and symbols in the formulas are defined as follows:
• NbER (mass %):
• amount of Nb analyzed as extraction residues
• T (° C.):
• heat treatment temperature
• t (sec):
• soaking time.