Austenitic Stainless Steel Material

Abstract

There is provided an austenitic stainless steel material having a consistent high-strength across the overall length of the steel material, which has a chemical composition consisting of, in mass percent: C: 0.10% or less, Si: 1.0% or less, Mn: 3 to 8%, P: 0.05% or less, S: 0.03% or less, Ni: 10 to 20%, Cr: 15 to 30%, N: 0.20 to 0.70%, with the balance being Fe and impurities, the austenitic stainless steel material having a grain size number of 6.0 or greater, the grain size number conforming to ASTM E 112 tensile strength of the austenitic stainless steel material is 800 MPa or more, and the difference between the maximum value and the minimum value of the tensile strength is 50 MPa or smaller. The number of alloy carbo-nitrides having a circle equivalent diameter of larger than 1000 nm in the steel is 10/mm 2 or more.

1 . An austenitic stainless steel material comprising:
 a chemical composition consisting of, in mass percent:   C: 0.10% or less;   Si: 1.0% or less;   Mn: 3 to 8%;   P: 0.05% or less;   S: 0.03% or less;   Ni: 10 to 20%;   Cr: 15 to 30%;   N: 0.20 to 0.70%;   Mo: 0 to 5.0%;   V: 0 to 0.5%; and   Nb: 0 to 0.5%, with the balance being Fe and impurities,   wherein a grain size number conforming to ASTM E 112 is 6.0 or greater, a tensile strength is 800 MPa or more, a difference between a maximum value and a minimum value of the tensile strength is 50 MPa or less, and a number of alloy carbo-nitrides with circle equivalent diameters of larger than 1000 nm in steel is 10/mm 2  or more.   
     
     
         2 . The austenitic stainless steel material according to  claim 1 , wherein the chemical composition contains one, or two or more elements selected from the group consisting of:
 Mo: 1.5 to 5.0%;   V: 0.1 to 0.5%; and   Nb: 0.1 to 0.5%.   
     
     
         3 . The austenitic stainless steel material according to  claim 1 , wherein a difference between a maximum value and a minimum value of the grain size number is 1.5 or smaller. 
     
     
         4 . The austenitic stainless steel material according to  claim 1 , wherein the austenitic stainless steel material is one of a steel pipe, a steel bar, and a wire rod. 
     
     
         5 . The austenitic stainless steel material according to  claim 2 , wherein a difference between a maximum value and a minimum value of the grain size number is 1.5 or smaller. 
     
     
         6 . The austenitic stainless steel material according to  claim 2 , wherein the austenitic stainless steel material is one of a steel pipe, a steel bar, and a wire rod. 
     
     
         7 . The austenitic stainless steel material according to  claim 3 , wherein the austenitic stainless steel material is one of a steel pipe, a steel bar, and a wire rod. 
     
     
         8 . The austenitic stainless steel material according to  claim 4 , wherein the austenitic stainless steel material is one of a steel pipe, a steel bar, and a wire rod.