Surface modified precipitation hardened stainless steel

Abstract

The present invention relates to a surface hardened and coated stainless steel said surface showing low static friction and with improved wear resistance. Moreover, it relates to a coating of the surface of said stainless steel, in which a surface hardening is accomplished simultaneously with said coating. The resulting coated steel showing a very high hardness simultaneously as it shows improved adherence. Said steel advantageously being used in applications with high requirements regarding a combination of high strength and/or toughness and wear resistance together with low friction, such as, e.g., shock absorbers and items for combustion engines and hydraulic systems, produced with a highly cost effective process. The used precipitation hardened stainless steel substrate has the following composition (in weight-%): Carbon max about 0.1 Nitrogen max about 0.1 Copper from about 0.5 to about 4 Chromium from about 10 to about 14 Molybdenum from about 0.5 to about 6 Nickel from about 7 to about 11 Cobalt 0 up to about 9 Tantalum max about 0.1 Niobium max about 0.1 Vanadium max about 0.1 Tungsten max about 0.1 Aluminum from about 0.05 to about 0.6 Titanium from about 0.4 to about 1.4 Silicon max about 0.7 Manganese max about 1.0 Iron balance and normally occurring usual steelmaking additions and impurities.

1 . A coated, surface hardened precipitation hardened stainless steel with following composition (in weight-%):  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   Carbon 
                   max about 0.1 
                 
                     
                   Nitrogen 
                   max about 0.1 
                 
                     
                   Copper 
                   from about 0.5 
                 
                     
                     
                   to about 4 
                 
                     
                   Chromium 
                   from about 10 
                 
                     
                     
                   to about 14 
                 
                     
                   Molybdenum 
                   from about 0.5 
                 
                     
                     
                   to about 6 
                 
                     
                   Nickel 
                   from about 7 
                 
                     
                     
                   to about 11 
                 
                     
                   Cobalt 
                   0 up to about 9 
                 
                     
                   Tantalum 
                   max about 0.1 
                 
                     
                   Niobium 
                   max about 0.1 
                 
                     
                   Vanadium 
                   max about 0.1 
                 
                     
                   Tungsten 
                   max about 0.1 
                 
                     
                   Aluminum 
                   from about 0.05 
                 
                     
                     
                   to about 0.6 
                 
                     
                   Titanium 
                   from about 0.4 
                 
                     
                     
                   to about 1.4 
                 
                     
                   Silicon 
                   max about 0.7 
                 
                     
                   Manganese 
                   max about 1.0 
                 
                     
                   Iron 
                   balance 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       and normally occurring usual steelmaking additions and impurities wherein said steel is coated and surface hardened in one and the same operation, having a combination of high strength and/or toughness and wear resistance together with low friction and improved adhesiveness.  
     
     
         2 . The precipitation hardened stainless steel of  claim 1  wherein said coating is applied on a nitrided surface of said steel.  
     
     
         3 . The precipitation hardened stainless steel of  claim 1  wherein said coating consists essentially of a single layer.  
     
     
         4 . The precipitation hardened stainless steel according to  claim 1  wherein said coating consists essentially of a single layer of diamond-like carbon (DLC).  
     
     
         5 . The precipitation hardened stainless steel of  claim 1  wherein said coating consists essentially of a single layer of diamond-like carbon (DLC) with addition of tungsten carbide.  
     
     
         6 . The precipitation hardened stainless steel of  claim 1  wherein said coating consists essentially of titanium nitride.  
     
     
         7 . The precipitation hardened stainless steel of  claim 1  wherein said precipitation hardened stainless steel has been strengthened by the precipitation of quasi crystalline structured particles.  
     
     
         8 . A process for producing a stainless steel with a low static friction on a very hard and wear resistant surface, said process comprising using PVD to apply a low static friction coating in the same operation as surface hardening, said stainless steel having the following composition (in weight-%):  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   Carbon 
                   max about 0.1 
                 
                     
                   Nitrogen 
                   max about 0.1 
                 
                     
                   Copper 
                   from about 0.5 
                 
                     
                     
                   to about 4 
                 
                     
                   Chromium 
                   from about 10 
                 
                     
                     
                   to about 14 
                 
                     
                   Molybdenum 
                   from about 0.5 
                 
                     
                     
                   to about 6 
                 
                     
                   Nickel 
                   from about 7 
                 
                     
                     
                   to about 11 
                 
                     
                   Cobalt 
                   0 up to about 9 
                 
                     
                   Tantalum 
                   max about 0.1 
                 
                     
                   Niobium 
                   max about 0.1 
                 
                     
                   Vanadium 
                   max about 0.1 
                 
                     
                   Tungsten 
                   max about 0.1 
                 
                     
                   Aluminum 
                   from about 0.05 
                 
                     
                     
                   to about 0.6 
                 
                     
                   Titanium 
                   from about 0.4 
                 
                     
                     
                   to about 1.4 
                 
                     
                   Silicon 
                   max about 0.7 
                 
                     
                   Manganese 
                   max about 1.0 
                 
                     
                   Iron 
                   balance 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       and normally occurring usual steelmaking additions and impurities.  
     
     
         9 . The process of  claim 7  wherein the low static friction coating comprises one or more of diamond-like carbon (DLC), diamond-like carbon with addition of titanium nitride.  
     
     
         10 . A process for producing a stainless steel with a low static friction on a very hard and wear resistant surface, said process comprising using PVD to apply a low static friction coating onto a plasma-nitrided surface of the stainless steel in the same operation, said stainless steel having the following composition (in weight-%):  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   Carbon 
                   max about 0.1 
                 
                     
                   Nitrogen 
                   max about 0.1 
                 
                     
                   Copper 
                   from about 0.5 
                 
                     
                     
                   to about 4 
                 
                     
                   Chromium 
                   from about 10 
                 
                     
                     
                   to about 14 
                 
                     
                   Molybdenum 
                   from about 0.5 
                 
                     
                     
                   to about 6 
                 
                     
                   Nickel 
                   from about 7 
                 
                     
                     
                   to about 11 
                 
                     
                   Cobalt 
                   0 up to about 9 
                 
                     
                   Tantalum 
                   max about 0.1 
                 
                     
                   Niobium 
                   max about 0.1 
                 
                     
                   Vanadium 
                   max about 0.1 
                 
                     
                   Tungsten 
                   max about 0.1 
                 
                     
                   Aluminum 
                   from about 0.05 
                 
                     
                     
                   to about 0.6 
                 
                     
                   Titanium 
                   from about 0.4 
                 
                     
                     
                   to about 1.4 
                 
                     
                   Silicon 
                   max about 0.7 
                 
                     
                   Manganese 
                   max about 1.0 
                 
                     
                   Iron 
                   balance 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       and normally occurring usual steelmaking additions and impurities.  
     
     
         11 . The process of  claim 9  wherein the low static friction coating comprises one or more of diamond-like carbon (DLC), diamond-like carbon with addition of titanium nitride.