Surface modified stainless steel

Abstract

A stainless steel, which after nitriding exhibits a hardened surface layer with a hardness of at least 1200 Hv is disclosed. The stainless steel can be in the form of wire, plate, strip, tube and pipe and other geometries, especially complex geometries, particularly useful in applications with high demands on a combination of high strength and/or toughness and wear resistance and as a substrate for coating.

1 . A stainless steel comprising a composition (in weight-%):  
     
       
         
               
               
               
             
                   
                   
               
                   
                   
               
                   
                 Carbon 
                 max 0.1 
               
                   
                 Nitrogen 
                 max 0.1 
               
                   
                 Copper 
                 0.5-4 
               
                   
                 Chromium 
                 10-14 
               
                   
                 Molybdenum 
                 0.5-6 
               
                   
                 Nickel 
                 7-11 
               
                   
                 Cobalt 
                 0-9 
               
                   
                 Tantalum 
                 max 0.1 
               
                   
                 Niobium 
                 max 0.1 
               
                   
                 Vanadium 
                 max 0.1 
               
                   
                 Tungsten 
                 max 0.1 
               
                   
                 Aluminum 
                 0.05-0.6 
               
                   
                 Titanium 
                 0.4-1.4 
               
                   
                 Silicon 
                 max 0.7 
               
                   
                 Manganese 
                 ≦1.0 
               
                   
                   
               
                   
                   
               
           
              
              
             
             
              
              
              
              
              
              
              
              
              
              
              
              
              
              
              
              
              
             
          
         
       
       Iron balance and 
 normally occurring usual steelmaking additions and impurities, wherein said stainless steel after nitriding exhibits a hardened surface layer with a hardness of at least 1200 Hv.  
 
     
   
   
       2 - 5 . (canceled)  
   
   
       6 . The stainless steel according to  claim 1 , wherein the stainless steel includes quasicrystalline particles in a martensitic microstructure.  
   
   
       7 . The stainless steel according to  claim 6 , wherein the quasicrystalline particles in the martensitic microstructure are a result of a precipitation hardening process.  
   
   
       8 . The stainless steel according to  claim 1 , wherein a hardness at a surface of the stainless steel is at least twice that of a hardness of at 0.5 mm into a matrix of the stainless steel.  
   
   
       9 . The stainless steel according to  claim 1 , wherein the hardened surface layer has a thickness of about 0.5 mm.  
   
   
       10 . The stainless steel according to  claim 1 , wherein the stainless steel is formed into one or more of a wire, a plate, a strip, tube and a pipe.  
   
   
       11 . The stainless steel according to  claim 1 , wherein the stainless steel is formed into a complex geometry for use in an application with a high demand on a combination of high strength and/or toughness and wear resistance.  
   
   
       12 . The stainless steel according to  claim 11 , wherein the complex geometry is a wear part of an engine, an engine component, or an impact load.  
   
   
       13 . The stainless steel according to  claim 11 , wherein the complex geometry is a cam follower, a cam follower pad, a valve stem, a valve stem guide, a piston pin, a piston shaft, a hydraulic piston, an ejector pin, a safety protection plate, a lock cylinder and other locking devices, a blocking element, or a thief-proof equipment  
   
   
       14 . A material comprising a wear resistant coating deposited on the stainless steel according to  claim 1 .  
   
   
       15 . A method for making a surface modified stainless steel, the method comprising: 
 subjecting a stainless steel to a nitriding process at a temperature of 450 to 580° C. for a time period of 1 to 40 hours in a plasma nitriding atmosphere, the stainless steel having a composition comprising:                                                Carbon   max 0.1         Nitrogen   max 0.1         Copper   0.5 to 4         Chromium   10 to 14         Molybdenum   0.5 to 6         Nickel   7 to 11         Cobalt   0 to 9         Tantalum   max 0.1         Niobium   max 0.1         Vanadium   max 0.1         Tungsten   max 0.1         Aluminum   0.05 to 0.6         Titanium   0.4 to 1.4         Silicon   max 0.7         Manganese   ≦1.0                                                           Iron balance and    normally occurring usual steelmaking additions and impurities.    
   
   
       16 . The method according to  claim 15 , wherein said stainless steel after nitriding exhibits a hardened surface layer with a hardness of at least 1200 Hv.  
   
   
       17 . The method according to  claim 15 , wherein the surface modified stainless steel does not change dimension from the nitriding process.