Austenitic stainless steel material

An austenitic stainless steel material consisting of, in mass %,

• C:
• 0.030% or less,
• Si:
• 0.01 to 1.00%,
• Mn:
• 0.01 to 2.00%,
• P:
• 0.040% or less,
• S:
• 0.0100% or less,
• Ni:
• 8.00 to 18.00%,
• Cr:
• 15.00 to 25.00%,
• Mo:
• 0.10 to 5.00%,
• Nb:
• 0.20 to 1.00%,
• N:
• 0.060 to 0.250%,
• Cu:
• more than 2.00 to 4.00%,
• B:
• 0.0010 to 0.0100%,
• sol. Al:
• 0 to 0.100%,
• Co:
• 0 to 1.00%,
• W:
• 0 to 5.00%,
• V:
• 0 to 1.00%,
• Ti:
• 0 to 0.50%,
• Ta:
• 0 to 0.50%,
• Hf:
• 0 to 0.10%,
• Zr:
• 0 to 0.10%,
• Ca:
• 0 to 0.0200%,
• Mg:
• 0 to 0.0200%, and
• rare earth metal:
• 0 to 0.100%,
• with the balance being Fe and impurities,
• and satisfying Formula (1):
• Nbs×0.8>Nbb (1)
• where, in Formula (1), an average Nb concentration in percent by mass in an outer layer from a surface of the austenitic stainless steel material to a depth of 10 μm is substituted for Nbs, and an average Nb concentration in percent by mass in a region excluding the outer layer of the austenitic stainless steel material is substituted for Nbb.