An object comprising a duplex stainless steel and the use thereof

Abstract

The present disclosure relates to an object comprising a duplex stainless steel, in particular the object is suitable for use in spring applications. The duplex stainless steel has the following composition, in weight %:—C less than or equal to 0.040;—Si less than or equal to 0.60;—Mn 0.80-10.0;—Cr 21.0-28.0;—Ni 4.0-9.0;—Mo 0.9-4.5;—N 0.10-0.45;—Cu less than or equal to 0.50;—V less than or equal to 0.10;—P less than or equal to 0.010;—s less than or equal to 0.006; balance Fe and unavoidable impurities. The present disclosure also relates to a method of producing the object comprising said duplex stainless steel.

1 . An object manufactured from a duplex stainless steel, wherein the duplex stainless steel comprises the following composition, in weight %: 
       
         
           
                 
                 
                 
               
                     
                 
                     
                   C 
                   less than or equal to 0.040; 
                 
                     
                   Si 
                   less than or equal to 0.60; 
                 
                     
                   Mn 
                   0.80-10.0; 
                 
                     
                   Cr 
                   21.0-28.0; 
                 
                     
                   Ni 
                    4.0-9.0; 
                 
                     
                   Mo 
                    0.9-4.5; 
                 
                     
                   N 
                   0.10-0.45; 
                 
                     
                   Cu 
                   less than or equal to 0.50; 
                 
                     
                   V 
                   less than or equal to 0.10; 
                 
                     
                   P 
                   less than or equal to 0.010; 
                 
                     
                   S 
                   less than or equal to 0.006; 
                 
                 
               
                   balance Fe and unavoidable impurities, 
                 
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
               
            
             
                
                
               
            
           
         
       
       and
 wherein the duplex stainless steel consists of 55-75 vol % austenite phase and 25-45 vol % ferrite phase, and 
 wherein the object has alternating layers of ferrite phase and austenite phase, said alternating layers are essentially parallel with the plane of the object and said alternating layers have an average layer thickness less than or equal to about 4.5 μm. 
 
     
     
         2 . The object according to  claim 1 , wherein the duplex stainless steel has a PRE greater than 28 and wherein PRE is defined as PRE=Cr+3.3Mo+16N. 
     
     
         3 . The object according to  claim 1 , wherein the duplex stainless steel consists of 55-70 vol % austenite phase and 30-45 vol % ferrite phase. 
     
     
         4 . The object according to  claim 1 , wherein the average ferrite or austenite thickness is between about 0.01 to about 4.5 μm . 
     
     
         5 . The object according to  claim 1 , wherein the content of Mn in the duplex stainless steel is in the range of from 2 to 5 wt %. 
     
     
         6 . The object according to  claim 1 , wherein the content of N in the duplex stainless steel is in the range of from 0.3 to 0.42 wt %. 
     
     
         7 . The object according to  claim 1 , wherein the content of Mo in the duplex stainless steel is in the range of from 2 to 4 wt %. 
     
     
         8 . The object according to  claim 1 , wherein the content of Cr in the duplex stainless steel is in the range of from 24 to 28 wt %, such as 26 to 28 wt %. 
     
     
         9 . The object according to  claim 1 , wherein the content of Ni in the duplex stainless steel is in the range of from 7.0 to 9.0 wt %. 
     
     
         10 . The object according to  claim 1 , wherein said object is a sheet or a strip or a wire. 
     
     
         11 . A spring comprising the object according to  claim 1 . 
     
     
         12 . A method for manufacturing an object according to  claim 1 , comprising the steps of:
 providing a body of the duplex stainless steel as defined in  claim 1 ;   one or more hot working processes to transform the body to a workpiece, wherein the hot working processes are performed at a temperature of about 1050 to about 1300° C.;   one or more cold working processes to transform the workpiece into the object,   wherein the final step of said method must be a cold working process.   
     
     
         13 . The method according to  claim 12 , wherein the hot working process is hot rolling. 
     
     
         14 . The method according to  claim 12 , wherein the cold working process is cold rolling. 
     
     
         15 . The method according to  claim 12 , wherein the method also comprises one or more heat treatment steps, wherein the one or more heat treatment step is annealing which is performed at a temperature of above 1000 to 1250° C. 
     
     
         16 . The method according to  claim 12 , comprising a further step of aging the object for 0.25 to 4 hours at a temperature of from 400 to 450° C., wherein the aging is performed after the final cold working step. 
     
     
         17 . The object according to  claim 3 , wherein the duplex stainless steel consists of 65-70 vol % austenite phase and 30-35 vol % ferrite phase. 
     
     
         18 . The object according to  claim 4 , wherein the average ferrite or austenite thickness is between about 1.0 to about 4.2 μm.