Hot Rolled Plate or Forging of an Austenitic Steel

Abstract

A hot rolled plate or forging of an austenitic steel not susceptible to relaxation cracking is provided. The hot rolled plate or austenitic steel includes a composition having in percentages by weight: 0.019%≤C≤0.030%, 0.5%≤Mn≤2%, 0.1%≤Si≤0.75%, Al≤0.25%, 18%≤Cr≤25%, 14%≤Ni≤17%, 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, Ni(eq.)≥1.11 Cr(eq.)−8.24, Cr(eq)=Cr+Mo+1.5Si+5V+3Al+0.02, Ni(eq)=Ni+30C+x(N−0.045)+0.87; x=30 for N≤0.2, x=22 for 0.2<N≤0.25, x=20 for 0.25<N≤0.35.

What is claimed is: 
     
         1 : A hot rolled plate or forging of an austenitic steel resistant to relaxation cracking, with composition comprising, in percentages by weight:
 0.019%≤C≤0.030%   0.5%≤Mn≤3%   0.1%≤Si≤0.75%   Al≤0.25%   18%≤Cr≤25%   14%≤Ni≤17%   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+3Al+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 hot rolled plate or forging of an austenitic steel resistant to relaxation cracking, with composition comprising, in percentages by weight:
 0.019%≤C≤0.030%   0.5%≤Mn≤3%   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, and wherein:
 Ni(eq.)≥1.11 Cr(eq.)−8.24, wherein: 
 Cr(eq)=Cr+Mo+1.5Si+5V+3Al+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%; and 
 a microstructure consisting of austenite. 
 
     
     
         3 . The hot rolled plate or forging with composition according to  claim 1 , wherein the hot rolled plate or forging is resistant to stress relaxation cracking at temperatures from 500 to 900° C. 
     
     
         4 . The hot rolled plate or forging with composition according to  claim 1 , wherein the hot rolled plate or forging is resistant to stress relaxation cracking at temperatures from 550 to 750° C. 
     
     
         5 : The hot rolled plate or forging with composition according to  claim 1 , wherein an elongation is higher than 30% at the temperature of 750° C. 
     
     
         6 : The hot rolled plate or forging with composition according to  claim 1 , wherein a creep rupture lifetime under 36 MPa at 750° C. is higher than 0.5×10 5  h. 
     
     
         7 : Reactor vessels, forgings or pipelines comprising:
 the hot rolled plate or forging with composition as recited in  claim 1 .   
     
     
         8 : The hot rolled plate or forging of the steel according to  claim 1 , wherein a microstructure of the steel consists of austenite. 
     
     
         9 : The hot rolled plate or forging of the steel according to  claim 1 , wherein the hot rolled plate has a thickness from 5 to 100 mm. 
     
     
         10 : The hot rolled plate or forging of the steel according to  claim 1 , wherein the steel has a Charpy V fracture energy greater than 100 Joules. 
     
     
         11 : The hot rolled plate or forging with composition according to  claim 1 , wherein the hot rolled plate or forging is resistant to stress relaxation cracking at temperatures from 500 to 900° C. 
     
     
         12 : The hot rolled plate or forging with composition according to  claim 1 , wherein the hot rolled plate or forging is resistant to stress relaxation cracking at temperatures from 550 to 750° C. 
     
     
         13 : The hot rolled plate or forging with composition according to  claim 1 , wherein an elongation is higher than 30% at the temperature of 750° C. 
     
     
         14 : The hot rolled plate or forging with composition according to  claim 1 , wherein a creep rupture lifetime under 36 MPa at 750° C. is higher than 0.5×10 5  h. 
     
     
         15 : Reactor vessels, forgings or pipelines comprising:
 the hot rolled plate or forging with composition as recited in  claim 1 .   
     
     
         16 : The hot rolled plate or forging of the steel according to  claim 1 , wherein 14%≤Ni≤17%. 
     
     
         17 : The hot rolled plate or forging of the steel according to  claim 1 , wherein the hot rolled plate has a thickness from 5 to 100 mm. 
     
     
         18 : The hot rolled plate or forging of the steel according to  claim 1 , wherein the steel has a Charpy V fracture energy greater than 100 Joules. 
     
     
         19 : A hot rolled plate or forging of an austenitic steel resistant to relaxation cracking, with composition comprising, in percentages by weight:
 0.019%≤C≤0.030%   0.5%≤Mn≤3%   0.1%≤Si≤0.75%   Al≤0.25%   18%≤Cr≤25%   14%≤Ni≤17%   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+3Al+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%; and 
 
       the hot rolled plate or forging being resistant to stress relaxation cracking at temperatures from 550 to 750° C.