Bearing steels

Abstract

There is provided a novel bearing steel composition and a method of forming a bearing. The bearing steel composition comprises: Carbon 0.4 to 0.8 wt %; Nitrogen 0.1 to 0.2 wt %; Chromium 12 to 18 wt %; Molybdenum 0.7 to 1.3 wt %; Silicon 0.3 to 1 wt %; Manganese 0.2 to 0.8 wt %; and Iron 78 to 86.3 wt %.

1 . A bearing steel composition comprising: 
       
         
           
                 
                 
                 
               
                     
                 
                     
                   Carbon 
                   0.4 to 0.8 wt %; 
                 
                     
                   Nitrogen 
                   0.1 to 0.2 wt %; 
                 
                     
                   Chromium 
                   12 to 18 wt %; 
                 
                     
                   Molybdenum 
                   0.7 to 1.3 wt %; 
                 
                     
                   Silicon 
                   0.3 to 1 wt %; 
                 
                     
                   Manganese 
                   0.2 to 0.8 wt %; and 
                 
                     
                   Iron 
                   78 to 86.3 wt %. 
                 
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         2 . A bearing steel composition according to  claim 1 , wherein the combined carbon and nitrogen content is from 0.5 to 0.7 wt % of the total composition. 
     
     
         3 . A bearing steel composition according to  claim 1 , wherein the steel composition comprises at least one of the elements in an amount of: 
       
         
           
                 
                 
                 
               
                     
                 
                     
                   Carbon 
                   0.45 to 0.7 w %; 
                 
                     
                   Nitrogen 
                   0.11 to 0.18 wt %; 
                 
                     
                   Chromium 
                   14 to 17 wt %; 
                 
                     
                   Molybdenum 
                   0.9 to 1.1 wt °70; 
                 
                     
                   Silicon 
                   0.5 to 0.9 wt %; and 
                 
                     
                   Manganese 
                   0.3 to 0.6 wt %. 
                 
                     
                 
             
                
               
               
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         4 . A bearing steel composition according to  claim 1 , wherein the steel composition comprises: 
       
         
           
                 
                 
                 
               
                     
                 
                     
                   Carbon 
                   0.45 to 0.6 wt %; 
                 
                     
                   Nitrogen 
                   0.13 to 0.17 wt %; 
                 
                     
                   Chromium 
                   15 to 16.5 wt %; 
                 
                     
                   Molybdenum 
                   0.9 to 1.1 wt %; 
                 
                     
                   Silicon 
                   0.5 to 0.9 wt %; and 
                 
                     
                   Manganese 
                   0.3 to 0.6 wt % and 
                 
                     
                 
             
                
               
               
                
                
                
                
                
                
                
               
            
           
         
       
       the balance iron and unavoidable impurities. 
     
     
         5 . A bearing steel composition according to  claim 1  and having a microstructure comprising martensite, retained austenite and precipitated carbides and/or carbonitrides. 
     
     
         6 . A bearing component formed from a composition according to  claim 1 . 
     
     
         7 . A bearing component according to  claim 6  which is at least one of a rolling element, an inner ring, and an outer ring. 
     
     
         8 . A bearing comprising a bearing component as claimed in  claim 6 . 
     
     
         9 . A method of forming a bearing component comprising:
 a) providing a powdered steel composition according to  claim 1 ; and   b) subjecting the powdered steel composition to hot isostatic pressing to form said component.   
     
     
         10 . A method according to  claim 9 , wherein the powdered steel composition is provided by atomising a molten steel composition by contacting it with at least one jet of gas. 
     
     
         11 . A method according to  claim 9 , wherein the step of hot isostatic pressing is conducted at a temperature of from 1000° C. to 1400° C. and a pressure of up to 200 MPa. 
     
     
         12 . A method according to  claim 9 , wherein the step of hot isostatic pressing is conducted under an inert atmosphere. 
     
     
         13 . A method according to  claim 9 , further comprising a step of:
 a) case hardening;   b) tempering; and/or   c) finishing.