Duplex stainless steel alloy and use of this alloy

Abstract

The present invention relates to a duplex stainless steel alloy containing in weight-%: C max 0.03%, Si<0.30%, Mn 0-3.0%, P max 0.030%, S max 0.050%, Cr 25-29%, Ni 5-9%, Mo 4.5-8%, W 0-3%, Cu 0-2%, Co 0-3%, Ti 0-2%, Al 0-0.05%, B 0-0.01%, Ca 0-0.01%, and N 0.35-0.60%, balance Fe and normal occurring impurities, wherein the ferrite content is 30-70 volume-%, and wherein each weight-% of Mo above may optionally be replaced by two (2) weight-% W.

1 . A duplex stainless steel alloy, comprising, in weight-%: 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   C 
                   max 0.03% 
                 
                     
                   Si 
                   <0.30% 
                 
                     
                   Mn 
                     0-3.0% 
                 
                     
                   P 
                   max 0.030% 
                 
                     
                   S 
                   max 0.050% 
                 
                     
                   Cr 
                   25-29% 
                 
                     
                   Ni 
                   5-9% 
                 
                     
                   Mo 
                   4.5-8%   
                 
                     
                   W 
                   0-3% 
                 
                     
                   Cu 
                   0-2% 
                 
                     
                   Co 
                   0-3% 
                 
                     
                   Ti 
                   0-2% 
                 
                     
                   Al 
                     0-0.05% 
                 
                     
                   B 
                     0-0.01% 
                 
                     
                   Ca 
                     0-0.01% 
                 
                     
                   N 
                   0.35-0.60% 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
         balance Fe and normal occurring impurities, 
         wherein the ferrite content is 30-70 volume-%, and 
         wherein each weight-% of Mo may optionally be replaced by two weight-% W. 
       
     
     
         2 . Alloy according to  claim 1 , wherein the content of Si is max 0.25 weight-%. 
     
     
         3 . Alloy according to  claim 1 , wherein the content of Si is max 0.23 weight-%. 
     
     
         4 . Alloy according to  claim 1 , wherein the content of Mo is a weight-% and the content of W is b weight-%, wherein a+b/2>5.0. 
     
     
         5 . Alloy according to  claim 4 , wherein a >5.0. 
     
     
         6 . Alloy according to  claim 4 , wherein a+b/2≦8. 
     
     
         7 . Alloy according to  claim 1 , wherein the content of Co is 0-0.010 weight-%. 
     
     
         8 . Alloy according to  claim 1 , wherein the content of Cr is 25.5-28 weight-%. 
     
     
         9 . Alloy according to  claim 1 , wherein the content of Ni is 6-8 weight-%. 
     
     
         10 . Alloy according to  claim 1 , wherein the content of N is 0.35-0.45 weight-%. 
     
     
         11 . Alloy according to  claim 1 , wherein the content of ferrite is 40-60 volume-%. 
     
     
         12 . Alloy according to  claim 1 , wherein an average PRE- or PREW-value of the two phases of the alloy exceeds 44, where PRE=% Cr+3.3% Mo+16% N and PREW=% Cr+3.3(% Mo+0.5% W)+16% N, and where % is weight-%. 
     
     
         13 . Alloy according to  claim 12 , wherein a PRE- or PREW-value for both the ferrite and the austenite phase is higher than 47 and that said average PRE- or PREW-value is higher than 48. 
     
     
         14 . Alloy according to  claim 12 , wherein a ratio between PRE(W)-value for the austenite phase and PRE(W)-value for the ferrite phase lies between 0.90 and 1.15. 
     
     
         15 . Use of an alloy according to  claim 1  in chloride containing environments in product forms such as bars, tubes, such as welded and seamless tubes, plate, strip, wire, welding wire, constructive parts, such as for example pumps, valves, flanges and couplings. 
     
     
         16 . A method to improve corrosion resistance in a product exposed to a chloride containing environment, the method comprising forming the product from an alloy according to  claim 1 . 
     
     
         17 . The method of  claim 16 , wherein the product is a bar, a welded tube, a seamless tube, a plate, a strip, a wire, a welding wire, a pump, a valve, a flange or a coupling. 
     
     
         18 . Alloy according to  claim 13 , wherein the PRE- or PREW-value for both the ferrite and the austenite phase is higher than 48.5 
     
     
         19 . Alloy according to  claim 13 , wherein the average PRE- or PREW-value is higher than 49. 
     
     
         20 . Alloy according to  claim 14  wherein the ratio between PRE(W)-value for the austenite phase and PRE(W)-value for the ferrite phase lies between 0.95 and 1.05.