Method for making seamless tubing with a stable elastic limit at high application temperatures

Abstract

The invention relates to a process for producing seamless line pipes within the quality grade range X 52 to X 90, with a stable yield strength up to a temperature of use of 200° C., and with an essentially constant stress-strain characteristic, by hot-rolling a pipe blank made from a steel which contains the following alloying elements (% by weight): C 0.06-0.18% Si max. 0.40% Mn 0.80-1.40% P max. 0.025% S max. 0.010% Al 0.010-0.060% Mo max. 0.50% V max. 0.10% Nb max. 0.10% N max. 0.015% W >0.30-1.00% remainder iron and usual impurities, in which process the hot rolling is followed by reheating of the cooled pipes to above AC 3 , after which the pipes are quenched to below 100° C. at a cooling rate of at least 15° C./s and are then tempered within the temperature range from 500 to 700° C.

1 . A process for producing seamless line pipes within the quality grade range X 52 to X 90, with a stable yield strength up to a temperature of use of 200° C., and with an essentially constant stress-strain characteristic, by hot-rolling a pipe blank made from a steel which contains the following alloying elements (% by weight):  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   C 
                   0.06-0.18% 
                 
                     
                   Si 
                   max. 0.40% 
                 
                     
                   Mn 
                   0.80-1.40% 
                 
                     
                   P 
                   max. 0.025% 
                 
                     
                   S 
                   max. 0.010% 
                 
                     
                   Al 
                   0.010-0.060% 
                 
                     
                   Mo 
                   max. 0.50% 
                 
                     
                   V 
                   max. 0.10% 
                 
                     
                   Nb 
                   max. 0.10% 
                 
                     
                   N 
                   max. 0.015% 
                 
                     
                   W 
                   >0.30-1.00% 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
         remainder iron and usual impurities, in which process the hot rolling is followed by reheating of the cooled pipes to above AC 3 , after which the pipes are quenched to below 100° C. at a cooling rate of at least 15° C./s and are then tempered within the temperature range from 500 to 700° C.  
       
     
     
         2 . The process as claimed in  claim 1 , wherein up to 0.050% Ti is added to the steel which is to be used, for fixation of nitrogen.  
     
     
         3 . The process as claimed in one of  claims 1  to  2 , wherein the steel which is to be used contains from 0.35 to 0.70%, in particular from 0.35 to 0.40%, W.  
     
     
         4 . The process as claimed in one of  claims 1  to  3 , wherein the steel which is to be used contains from 0.05 to 0.40%, in particular from 0.10 to 0.25%, Mo.  
     
     
         5 . The process as claimed in one of  claims 1  to  4 , wherein the steel which is to be used contains at least 0.04% V.