Surface treated steel material

Abstract

A steel material suitable, e.g., for an engineering component such as a bearing component, has an alloy composition that includes at least 0.3 wt % of copper. The surface carbon content of the steel material is greater than the core carbon content and/or the surface nitrogen content of the steel material is greater than the core nitrogen content.

1 . A steel material having an alloy composition that comprises at least 0.3 wt % of copper (Cu),
 wherein the steel material has:
 a first carbon content at a surface of the steel material, 
 a second carbon content in a core of the steel material, 
 a first nitrogen content at the surface of the steel material, 
 a second nitrogen content in the core of the steel material, and 
   wherein at least one of the following conditions is satisfied:
 the first carbon content is greater than the second carbon content, and/or 
 the first nitrogen content is greater than the second nitrogen content. 
   
     
     
         2 . The steel material according to  claim 1 , wherein the core is at least 2 millimeters from the surface of the steel material. 
     
     
         3 . The steel material according to  claim 1 , wherein the first carbon content is at least 100% greater than the second carbon content. 
     
     
         4 . The steel material according to  claim 1 , wherein the first carbon content is at least 700% greater than the second carbon content. 
     
     
         5 . The steel material according to  claim 1 , wherein the first nitrogen content is at least 100% greater than the second nitrogen content. 
     
     
         6 . The steel material according to  claim 1 , wherein the first nitrogen content is at least 700% greater than the second nitrogen content. 
     
     
         7 . The steel material according to  claim 1 , wherein the first carbon content is at least 0.58 wt %. 
     
     
         8 . The steel material according to  claim 1 , wherein the first carbon content is at least 0.7 wt %. 
     
     
         9 . The steel material according to  claim 1 , wherein the first nitrogen content is at least 0.1 wt %. 
     
     
         10 . The steel material according to  claim 1 , wherein the first nitrogen content is at least 0.2 wt %. 
     
     
         11 . The steel material according to  claim 1 , wherein the alloy composition of the core of the steel material comprises (in wt %): 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Cu 
                   0.3-1.75, 
                 
                     
                   C 
                   <0.3, 
                 
                     
                   Si 
                   <0.4, 
                 
                     
                   Mn 
                   0.4-1.5, 
                 
                     
                   Cr 
                   0.4-1.8, 
                 
                     
                   Ni 
                   0.2-3.75, 
                 
                     
                   Mo 
                   <0.65, 
                 
                     
                   Al 
                   0.01-0.05, 
                 
                     
                   Nb 
                   <0.03, 
                 
                     
                   V 
                   <0.08, 
                 
                     
                   Ti 
                   <0.03, 
                 
                     
                   B 
                   <0.004, 
                 
                     
                   N 
                   <0.015, 
                 
                     
                   P 
                   <0.025, and 
                 
                     
                   S 
                   <0.015, 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       the balance being iron (and unavoidable impurities). 
     
     
         12 . The steel material according to  claim 1 , wherein the alloy composition of the core of the steel material consists of (in wt %): 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Cu 
                   0.3-1.75, 
                 
                     
                   C 
                   <0.3, 
                 
                     
                   Si 
                   <0.4, 
                 
                     
                   Mn 
                   0.4-1.5, 
                 
                     
                   Cr 
                   0.4-1.8, 
                 
                     
                   Ni 
                   0.2-3.75, 
                 
                     
                   Mo 
                   <0.65, 
                 
                     
                   Al 
                   0.01-0.05, 
                 
                     
                   Nb 
                   <0.03, 
                 
                     
                   V 
                   <0.08, 
                 
                     
                   Ti 
                   <0.03, 
                 
                     
                   B 
                   <0.004, 
                 
                     
                   N 
                   <0.015, 
                 
                     
                   P 
                   <0.025, and 
                 
                     
                   S 
                   <0.015, 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       the balance being iron and unavoidable impurities. 
     
     
         13 . The steel material according to  claim 12 , wherein the core is at least 2 millimeters from the surface of the steel material. 
     
     
         14 . The steel material according to  claim 13 , wherein the first carbon content is at least 400% greater than the second carbon content. 
     
     
         15 . The steel material according to  claim 14 , wherein the first carbon content is at least 0.7 wt %. 
     
     
         16 . The steel material according to  claim 15 , wherein the alloy composition consists of (in wt %) 0.093 C, 0.2 Si, 1.11 Mn, 0.036 Al, 0.001 Nb, 0.012 V, 0.028 Ti, 0.4 Cu, 1.12 Cr, 0.2 Ni, 0.007 Mo, and 0.002 B, the balance being iron and unavoidable impurities. 
     
     
         17 . The steel material according to  claim 13 , wherein:
 the first nitrogen content is at least 700% greater than the second nitrogen content, and   the first nitrogen content is at least 0.2 wt %.   
     
     
         18 . A bearing component comprising the steel material according to  claim 1 . 
     
     
         19 . A method of manufacturing an engineering component, comprising:
 forming a steel material into a rough geometry of the engineering component, wherein the steel material has an alloy composition comprising at least 0.3 wt % of copper, and   thereafter, subjecting the steel material to a thermochemical surface enrichment treatment selected from the group consisting of carbonitriding, nitriding, case carburizing and nitrocarburizing until the steel material has a higher surface carbon content than its core carbon content and/or a higher surface nitrogen content than its core nitrogen carbon content.   
     
     
         20 . The method according to  claim 19 , wherein subjecting the steel material to a thermochemical surface enrichment treatment comprises:
 carburizing the steel material for a predetermined period of time at a temperature of at least 850° C. at a carbon potential of at least 0.8%;   ramping down the carbon potential;   ramping down the temperature to <800° C.; and   direct quenching the steel material.