Heat-resistant austenitic steel having high resistance to stress relaxation cracking

Abstract

An austenitic steel not susceptible to relaxation cracking, with composition comprising, in percentages by weight: 0.019% ≦C ≦0.030%, 0.5% ≦Mn ≦2%, 0.1% ≦Si ≦0.75%, Al >0.25%, 18% ≦Cr ≦25%, 12% ≦Ni ≦20%, 1.5% ≦Mo ≦3%, 0.001 % <B ≦0.008%, 0.25% ≦V ≦0.35%, 0.23% ≦N ≦0.27%, the balance being iron and unavoidable impurities wherein: Ni(eq.) ≧1.11 Cr(eq.) −8.24, wherein: Cr(eq)=Cr+Mo+1.5 Si+5V+3AI+0.02, Ni(eq)=Ni+30C+x(N−0.045)+0.87 wherein: x=30 for N≦0.2, x=22 for 0.2<N≦0.25, x=20 for 0.25<N≦0.35.

1 . An austenitic steel not susceptible to relaxation cracking, with composition comprising, in percentages by weight:
 0.019% ≦C≦0.030%     0 . 5 % ≦Mn ≦3%   0.1≦Si ≦0.75%   AI ≦0.25%   18% ≦Cr ≦25%   12% ≦Ni ≦20%   1.5% ≦Mo ≦3%   0.001% ≦B ≦0.008%   0.25% ≦V ≦0.35%   0.23% ≦N ≦0.27%   the balance being iron and unavoidable impurities, and wherein:   Ni(eq.) ≧1.11 Cr(eq.) −8.24, wherein:   Cr(eq)=Cr+Mo+1.5Si+5V+3AI+0.02   Ni(eq)=Ni+30C+x(N−0.045)+0.87 wherein:
 x=22 for 0.23% ≦N≦0.25% 
 x=20 for 0.25% <N≦0.27% 
   
     
     
         2 . A steel according to  claim 1 , wherein:
 14% ≦Ni ≦17%   
     
     
         3 . A steel product with composition according to any of  claim 1  or  2 , wherein the elongation is higher than 30% at the temperature of 750° C. 
     
     
         4 . A steel product with composition according to any of  claims 1  to  3 , wherein the lifetime under 36 MPa at 750° C. is higher than 0.5×10 5  h 
     
     
         5 . Use of a steel product having a composition according to any of  claims 1  or  2 , or of steel product according to  claim 3  or  4 , for the fabrication of reactor vessels, forgings and pipelines