Use of a duplex stainless steel object

Abstract

The present disclosure relates to the use of a solution-annealed object comprising a duplex stainless steel, having the following composition in weight % (wt %): C less than or equal to 0.03; Si less than or equal to 0.5; Mn less than or equal to 1.0; Ni 5.0 to 7.0; Cr 22.0 to 26.0; Mo 2.5 to 4.5; N 0.1 to 0.2; P less than or equal to 0.03; S less than or equal to 0.03; Cu less than or equal to 0.3; Al less than or equal to 0.10; the balance being Fe and inevitable impurities; wherein the duplex stainless steel fulfills the equation of Cr+50N≤35; and wherein the duplex stainless steel has a ferrite phase content in the range of from 40% to 60% by volume and an austenite phase content in the range of 40 to 60% by volume; in sea water applications.

1 . A method of improving resistance to hydrogen induced stress corrosion of a solution-annealed object, the method comprising:
 making the object from a duplex stainless steel consisting of a composition in weight % (wt %):   
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   C 
                   less than or equal to 0.03; 
                 
                     
                   Si 
                   less than or equal to 0.5; 
                 
                     
                   Mn 
                   less than or equal to 1.0; 
                 
                     
                   Ni 
                    5.0 to 7.0; 
                 
                     
                   Cr 
                   22.0 to 26.0; 
                 
                     
                   Mo 
                    2.5 to 4.5; 
                 
                     
                   N 
                    0.1 to 0.2; 
                 
                     
                   P 
                   less than or equal to 0.03; 
                 
                     
                   S 
                   less than or equal to 0.03; 
                 
                     
                   Cu 
                   less than or equal to 0.3; 
                 
                     
                   Al 
                   less than or equal to 0.10; 
                 
                 
                 
               
                     
                   the balance being Fe and inevitable impurities; 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
               
            
             
                
                
               
            
           
         
         wherein the duplex stainless steel fulfills the equation of Cr+50N≤35, and 
         wherein the duplex stainless steel has a ferrite phase content in the range of from 40% to 60% by volume and an austenite phase content in the range of 40 to 60% by volume, and 
         wherein the object is used in sea water applications. 
       
     
     
         2 . The method stool according to  claim 1 , wherein the content of Cr is of from 23.0 to 24.0 wt %. 
     
     
         3 . The method according to  claim 1 , wherein the content of Ni is of from 6.0 to 7.0 wt %. 
     
     
         4 . The method according to  claim 1 , wherein the content of N is of from 0.12 to 0.20 wt %. 
     
     
         5 . The method according to  claim 1 , wherein the content of Mo is of from 2.8 to 4.0 wt %. 
     
     
         6 . The method according to  claim 1 , wherein the content of Cu is less than or equal to 0.2 wt %. 
     
     
         7 . The method according to  claim 1 , wherein the duplex stainless steel fulfills the equation of Cr+50N≤34. 
     
     
         8 . The method according to  claim 1 , wherein the duplex stainless steel fulfills the equation of Cr+50N≤33. 
     
     
         9 . The method according to  claim 1 , wherein the object is in the form of; a bar, a tube, a seamless or a welded tube, a constructive part, a plate, a sheet, a strip or a wire. 
     
     
         10 . The method according to  claim 1 , wherein making the object from a duplex stainless steel includes manufacturing by a process comprising the following steps:
 a. melting;   b. casting;   c. hot working;   d. cold working;   e. solution annealing and wherein the solution annealing is performed at a temperature above the recristallisation temperature of said duplex stainless steel.   
     
     
         11 . The method according to  claim 10 , wherein the solution annealing is performed in a temperature of from in the range of from 1030-1150° C. 
     
     
         12 . The method according to  claim 1 , wherein the sea water application is as a cathode.