Austenitic stainless steel and method of manufacturing austenitic stainless steel

An austenitic stainless steel having a chemical composition of, in mass %:

• 0.005 to 0.060% C;
• 0.20 to 1.20% Si;
• 4.0 to 8.0% Mn;
• 12.0 to 15.0% Ni;
• 19.0 to 24.0% Cr;
• 1.0 to 4.0% Mo;
• 0.05 to 0.40% Nb;
• 0.05 to 0.40% V;
• 0.20 to 0.50% N;
• up to 0.050% Al;
• 0 to 3.0% Cu;
• 0 to 0.50% Co;
• 0 to 0.0050% Ca;
• 0 to 0.0050% B;
• 0 to 0.10% W;
• 0 to 0.10% Ta;
• and
• balance Fe and impurities,
• the impurities including:
• up to 0.030% P;
• up to 0.010% S;
• and
• up to 0.015% O,
• a tensile strength being not lower than 800 MPa,
• a braking elongation being not lower than 35%,
• an amount of Nb determined through analysis of an electrolytic extraction residue satisfying expression (1) below,
• the amount of Nb determined through analysis of the electrolytic extraction residue and a crystal grain size satisfying expression (2) below:
• 0.7
• ×
• Nb
• ≤
• [
• Nb
• ]
• ≤
• 0.3
• ,
• (
• 1
• )
• and
• 20
• ×
• [
• Nb
• ]
• /
• D
• ≥
• 0
• .
• 0
• ⁢
• 50
• ,
• (
• 2
• )
• in expressions (1) and (2), the Nb content in the chemical composition represented in mass %, the amount of Nb determined through analysis of the electrolytic extraction residue represented in mass %, and the crystal grain size represented in μm are substituted for “Nb”, “[Nb]”, and “D”, respectively.