Duplex stainless steel alloy

Abstract

A duplex stainless steel alloy with ferritic-austenitic matrix and with high resistance to corrosion in combination with good structural stability and hot workability, with a content of ferrite of 40-65% and a well balanced composition that imparts corrosion resistance properties, which makes it is more suitable for use in chloride-containing environments than earlier been considered being possible. The total PRE or PREW number exceeds 44. The ratio of PRE(W) value for the austenite phase to PRE(W) value for the ferrite phase lies between 0.90 and 1.15. One preferred composition 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.

We claim:  
     
         1 . A ferritic-austenitic duplex stainless steel alloy, comprising 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% 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       balance Fe and normal occurring impurities and additions, wherein the alloy has a content of ferrite of 40-65 volume %.  
     
     
         2 . The alloy according to  claim 1 , wherein the content of Mn is 0.5 to 1.2 weight %.  
     
     
         3 . The alloy according to  claim 1 , wherein the content of Cr is between 27.0 to 29.0 weight %.  
     
     
         4 . The alloy according to  claim 1 , wherein the content of Ni is 5.0 to 8.0 weight %.  
     
     
         5 . The alloy according to  claim 1 , wherein the content of Mo is between 3.6 and 4.7 weight %.  
     
     
         6 . The alloy according to  claim 1 , wherein the content of N is 0.35 to 0.45 weight %.  
     
     
         7 . The alloy according to  claim 1 , wherein the content of Ru is 0 to 0.3 weight %.  
     
     
         8 . The alloy according to  claim 7 , wherein the content of Ru is greater than 0 and up to 0.1 weight %.  
     
     
         9 . The alloy according to  claim 1 , wherein the content of Co is 0.5 to 3.5 weight %.  
     
     
         10 . The alloy according to  claim 9 , wherein the content of Co is 1.5-3.5 weight %.  
     
     
         11 . The alloy according to  claim 1 , wherein the content of Cu lies between 0.5 and 2.0 weight %.  
     
     
         12 . The alloy according to  claim 11 , wherein the content of Cu is 1.0-1.5 weight %.  
     
     
         13 . The alloy according to  claim 1 , wherein the content of ferrite is 42 to 60 volume %.  
     
     
         14 . The alloy according to  claim 13 , wherein the content of ferrite is 45-55 volume %.  
     
     
         15 . The alloy according to  claim 1 , wherein the total PRE or PREW value of the alloy exceeds 44, whereby PRE=% Cr+3.3% Mo+16N and PREW=% Cr+3.3(% Mo+0.05% W)+6N, wherein % corresponds to weight %.  
     
     
         16 . The alloy according to  claim 1 , wherein the PRE or PREW value for both ferrite and austenite phases is higher than 45 and PRE or PREW value for the total composition of the alloy is higher than 46.  
     
     
         17 . The alloy according to  claim 16 , wherein the PRE or PREW value for both ferrite and austenite phases is 47 to 49.  
     
     
         18 . The alloy according to  claim 15 , wherein the ratio of PRE(W) value for austenite phase to PRE(W) value for the ferrite phase is 0.90 to 1.15.  
     
     
         19 . The alloy according to  claim 18 , wherein the ratio is 0.9-1.05.  
     
     
         20 . An article for use in chloride-containing environments, the article in a form chosen from: bars, tubes, plate, strip, wire, welding wire, constructive parts, valves, flanges and couplings, the article comprising the alloy of  claim 1.