Steel and steel tube for high- temperature use

Abstract

The invention concerns steel for high temperature use containing by weight: 0.06 to 0.20% of C, 0.10 to 1.00% of Si, 0.10 to 1.00% of Mn, not more than 0.010% of S, 10.00 to 13.00% of Cr, not more than 1.00% of Ni, 1.00 to 1.80% of W, Mo such that (W/2+Mo) is not more than 1.50%, 0.50 to 2.00% of Co, 0.15 to 0.35% of V, 0.040 to 0.150% of Nb, 0.030 to 0.12% of N, 0.0010 to 0.0100% of B and optionally up to 0.0100% of Ca, the rest of the chemical composition consisting of iron and impurities or residues resulting from or required for preparation processes or steel casting. The chemical constituent contents preferably verify a relationship such that the steel after normalizing heat treatment between 1050 and 1080° C. and tempering has a tempered martensite structure free or practically free of δ ferrite.

1 . A steel for seamless tubular products intended for high temperature use, characterized in that it contains, by weight:  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   C 
                   0.06% to 0.20% 
                 
                     
                   Si 
                   0.10% to 1.00% 
                 
                     
                   Mn 
                   0.10% to 1.00% 
                 
                     
                   S 
                   0.010% or less 
                 
                     
                   Cr 
                   10.00% to 13.00% 
                 
                     
                   Ni 
                   1.00% or less 
                 
                     
                   W 
                   1.00% to 1.80% 
                 
                     
                   Mo 
                   such that (W/2 + Mo) is 1.50% or less 
                 
                     
                   CO 
                   0.50% to 2.00% 
                 
                     
                   V 
                   0.15% to 0.35% 
                 
                     
                   Nb 
                   0.030% to 0.150% 
                 
                     
                   N 
                   0.030% to 0.120% 
                 
                     
                   B 
                   0.0010% to 0.0100% 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       and optionally, at most 0.050% by weight of al and at most 0.0100% by weight of Ca; the remainder of the chemical composition being constituted by iron and impurities or residual elements resulting from or necessary to steelmaking or casting:  
     
     
         2 . A steel according to  claim 1 , characterized in that the amounts of the constituents of the chemical composition are linked by a relationship such that after normalization heat treatment between 1050° C. and 1080° C. and tempering, the steel has a tempered martensitic structure that is free of or almost free of δ ferrite.  
     
     
         3 . A steel according to  claim 1  or  claim 2 , characterized in that its Cr content is in the range 11.00% to 13%.  
     
     
         4 . A steel according to any one of  claims 1  to  3 , characterized in that its Si content is in the range 0.20% to 0.60%.  
     
     
         5 . A steel according to any one of  claims 1  to  4 , characterized in that its C content is in the range 0.10% to 0.15%.  
     
     
         6 . A steel according to any one of  claims 1  to  5 , characterized in that its Co content is in the range 1.00% to 1.50%.  
     
     
         7 . A steel according to any one of  claims 1  to  6 , characterized in that its Mo content is 0.50% or less.  
     
     
         8 . A steel according to any one of  claims 1  to  7 , characterized in that its Mn content is in the range 0.10% to 0.40%.  
     
     
         9 . A steel according to any one of  claims 1  to  8 , characterized in that its Ni content is 0.50% or less.  
     
     
         10 . A steel according to any one of  claims 1  to  9 , characterized in that the residual elements are controlled so that the Cu content in the steel is 0.25% or less and preferably 0.10% or less.  
     
     
         11 . A steel according to any one of  claims 1  to  10 , characterized in that its S content is 0.005% or less, and preferably 0.003% or less.