Rolling, sliding part and process for producing same

Abstract

A rolling, sliding part comprises a bearing steel, is subjected to a carburizing treatment and has a surface layer from a surface the part to a depth to which a maximum shear stress acts. The surface layer is 1.0 to 1.6 wt. % in total carbon content, has a matrix containing 0.6 to 1.0 wt. % of solid-solution carbon, and contains a precipitating carbide in an amount of 5 to 20% in area ratio, the carbide being up to 3 μm in particle size. The rolling or sliding part is improved in wear resistance, usable with a lubricant free of or less susceptible to impression by extraneous matter present in the lubricant, and less susceptible to compressive stress due to the extraneous matter, with the development of cracks suppressed.

1 . A rolling, sliding part comprising a bearing steel, subjected to a carburizing treatment and characterized in that a surface layer of the part from a surface thereof to a depth to which a maximum shear stress acts is 1.0 to 1.6 wt. % in total carbon content, the surface layer having a matrix containing 0.6 to 1.0 wt. % of solid-solution carbon, the surface layer containing a precipitating carbide in an amount of 5 to 20% in area ratio, the carbide being up to 3 μm in particle size.  
     
     
         2 . A rolling, sliding part according to  claim 1  wherein the surface layer has a surface hardness of 62 to 67 in Rockwell C hardness, contains 20 to 40 vol. % of retained austenite and has a compressive residual stress of at least 100 MPa.  
     
     
         3 . A rolling, sliding part according to  claim 1  wherein the amount of carbide is 5 to 15% in area ratio.  
     
     
         4 . A rolling, sliding part according to  claim 3  wherein the surface layer has a surface hardness of 62 to 67 in Rockwell C hardness, contains 20 to 40 vol. % of retained austenite and has a compressive residual stress of at least 100 MPa.  
     
     
         5 . A rolling, sliding part according to  claim 1  wherein the carbide is contained in an amount of 10 to 20% in area ratio and is up to 2 μm in particle size.  
     
     
         6 . A rolling, sliding part according to  claim 5  wherein the surface layer has a surface hardness of 62 to 67 in Rockwell C hardness, contains 20 to 40 vol. % of retained austenite and has a compressive residual stress of at least 100 MPa.  
     
     
         7 . An antifriction bearing comprising an inner and an outer race and rolling elements, and at least one of the inner and outer races and the rolling element comprising a part according to one of  claims 1  to  6 .  
     
     
         8 . A process for producing a rolling, sliding part characterized in that a worked blank of the part prepared from a bearing steel in a predetermined form is carburized by being heated at 840 to 870° C. for at least 3 hours in a carburizing atmosphere having a carbon potential of at least 1.2% and thereafter quenched to thereby form a surface layer of the part from a surface thereof to a depth to which a maximum shear stress acts, the surface layer being 1.0 to 1.6 wt. % in total carbon content and having a matrix containing 0.6 to 1.0 wt. % of solid-solution carbon, the surface layer containing a precipitating carbide in an amount of 5 to 15% in area ratio, the carbide being up to 3 μm in particle size.  
     
     
         9 . A process for producing a rolling, sliding part characterized in that a worked blank of the part prepared from a bearing steel in a predetermined form is heated at 930 to 970° C. for at least 1 hour in an atmosphere having a carbon potential of 0.9 to 1.1% to thereby dissolve the existing carbide in a matrix, then quenched, subsequently carburized by being heated at 840 to 870° C. for at least 3 hours in an atmosphere having a carbon potential of at least 1.2% and thereafter quenched to thereby form a surface layer of the part from a surface thereof to a depth to which a maximum shear stress acts, the surface layer being 1.0 to 1.6 wt. % in total carbon content and having a matrix containing 0.6 to 1.0 wt. % of solid-solution carbon, the surface layer containing a precipitating carbide in an amount of 10 to 20% in area ratio, the carbide being up to 2 μm in particle size.