Austenitic Stainless Steel and Method of Manufacturing Austenitic Stainless Steel

Abstract

An austenitic stainless steel with improved strength, ductility and weldability is provided. An austenitic stainless steel has a chemical composition of, in mass %: 0.005 to 0.07% C; 0.1 to 1.2% Si; 3.2 to 6.5% Mn; 9 to 14% Ni; a total of not less than 0.005% and less than 3% of at least one of Cu and Co; 19 to 24% Cr; 1 to 4% Mo; 0.05 to 0.4% Nb; 0.15 to 0.50% N; up to 0.05% Al; up to 0.03% P; up to 0.002% S; up to 0.02% O; 0 to 0.5% V; 0 to 0.5% Ti; 0 to 0.01% B; 0 to 0.05% Ca; 0 to 0.05% Mg; 0 to 0.5% REM; and the balance being Fe and impurities, where the amount of Nb analyzed as residues after electrolytic extraction is 0.01 to 0.3 mass %.

1 . An austenitic stainless steel having a chemical composition of, in mass %:
 0.005 to 0.07% C;   0.1 to 1.2% Si;   3.2 to 6.5% Mn;   9 to 14% Ni;   a total of not less than 0.005% and less than 3% of at least one of Cu and Co;   19 to 24% Cr;   1 to 4% Mo;   0.05 to 0.4% Nb;   0.15 to 0.50% N;   up to 0.05% Al;   up to 0.03% P;   up to 0.002% S;   up to 0.02% O;   0 to 0.5% V;   0 to 0.5% Ti;   0 to 0.01% B;   0 to 0.05% Ca;   0 to 0.05% Mg;   0 to 0.5% REM; and   the balance being Fe and impurities,   where an amount of Nb analyzed as a residue after electrolytic extraction is 0.01 to 0.3 mass %.   
     
     
         2 . The austenitic stainless steel according to  claim 1 , wherein the chemical composition includes one or more elements selected from the group consisting of, in mass %:
 0.001 to 0.5% V;   0.001 to 0.5% Ti;   0.0001 to 0.01% B;   0.0001 to 0.05% Ca;   0.0001 to 0.05% Mg; and   0.001 to 0.5% REM.   
     
     
         3 . The austenitic stainless steel according to  claim 1 , wherein the austenitic stainless steel has a tensile strength not lower than 690 MPa and a breaking elongation not less than 35% at room temperature. 
     
     
         4 . The austenitic stainless steel according to  claim 1 , wherein the austenitic stainless steel is used in high-pressure hydrogen-gas equipment or in liquid-hydrogen equipment. 
     
     
         5 . A method of manufacturing the austenitic stainless steel according to  claim 1 , comprising the steps of:
 preparing a raw material having a chemical composition of, in mass %: 0.005 to 0.07% C; 0.1 to 1.2% Si; 3.2 to 6.5% Mn; 9 to 14% Ni; a total of not less than 0.005% and less than 3% of at least one of Cu and Co; 19 to 24% Cr; 1 to 4% Mo; 0.05 to 0.4% Nb; 0.15 to 0.50% N; up to 0.05% Al; up to 0.03% P; up to 0.002% S; up to 0.02% O; 0 to 0.5% V; 0 to 0.5% Ti; 0 to 0.01% B; 0 to 0.05% Ca; 0 to 0.05% Mg; 0 to 0.5% REM; and the balance being Fe and impurities;   performing hot working on the raw material; and   performing solution heat treatment on the raw material after the hot working at a solution heat treatment temperature of 950 to 1300° C. under a condition satisfying the formula provided below, (1),   wherein cold working is not performed between the hot working and the solution heat treatment,
   40×[% Nb]+100 ≤T ×log(1.2 +t/ 60)≤−200×[% Nb]+700  (1),
 
   In formula (1), the Nb content in the raw material in mass % is substituted for [% Nb], the solution heat treatment temperature in ° C. is substituted for T, and the solution heat treatment time in minutes is substituted for t.