Use of a duplex stainless steel alloy

Abstract

A method of providing corrosion resistance, structural stability, mechanical strength and workability in applications with aggressive environments such as chloride-containing environments, are realized by providing at least one article formed from a composition which includes (in weight- %) up to 0.03% C, up to 0.5% Si, 24.0-30.0% Cr, 4.9-10.0% Ni, 3.0-5.0% Mo, 0.28-0.5% N, 0-3.0% Mn, 0-0.0030% B, up to 0.010%, 0-0.03% Al, 0-0.010% Ca, 0-3.0% W, 0-2.0% Cu, 0-3.5% Co, 0-0.3% Ru, balance Fe and inevitable impurities. The ferrite content is 40 to 65 volume % and a PRE number of at least between 46 and 50 in both the austenite and ferrite phase, and with an optimum ratio or relationship between PRE austenite and PRE ferrite in the range of 0.90 to 1.15; preferably between 0.9 and 1.05.

We claim:  
     
         1 . A method of providing corrosion resistance, structural stability, mechanical strength and workability in applications with aggressive environments, such as in oil refining processes and hydro metallurgical processes, the method comprising incorporating an article made at least in part form a ferritic-austenitic duplex stainless steel alloy in the process.  
     
     
         2 . The method according to  claim 1 , wherein the alloy comprises, in weight %:  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   C 
                   max 0.03% 
                 
                     
                   Si 
                   max 0.5% 
                 
                     
                   Mn 
                     0-3.0% 
                 
                     
                   Cr 
                   24.0-30.0% 
                 
                     
                   Ni 
                    4.9-10.0% 
                 
                     
                   Mo 
                    3.0-5.0% 
                 
                     
                   N 
                   0.28-0.5% 
                 
                     
                   B 
                     0-0.0030% 
                 
                     
                   S 
                   max 0.010% 
                 
                     
                   Co 
                     0-3.5% 
                 
                     
                   W 
                     0-3.0% 
                 
                     
                   Cu 
                     0-2.0% 
                 
                     
                   Ru 
                     0-0.3% 
                 
                     
                   Al 
                     0-0.03% 
                 
                     
                   Ca 
                     0-0.010% 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       and the balance Fe and normal occurring impurities and additions, whereby the content of ferrite is 40-65 volume- %.  
     
     
         3 . The method according to  claim 2 , wherein the ferrite content is 42-60 volume %.  
     
     
         4 . The method according to  claim 2 , wherein the ferrite content is 45-55 volume %.  
     
     
         5 . The method according to  claim 2 , wherein the PRE or PREW value for both the ferrite and austenite phase is higher than 45 and the PRE or PREW value for the total composition of the alloy is higher than 46.  
     
     
         6 . The method according to  claim 2 , wherein the ratio between PRE(W) value for austenite phase and PRE(W) value for the ferrite phase is 0.90 to 1.15.  
     
     
         7 . The method of  claim 6 , wherein the ratio is 0.9-1.05.  
     
     
         8 . The method according to  claim 2 , further comprising providing the article in the form of at least one of: plate, strip, welding wire, and constructive parts.