ROLLING, SLIDING PART AND PROCESS FOR PRODUCING SAME
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 process for producing a rolling, sliding part, comprising carburizing a worked blank of the part, prepared from a high carbon chromium bearing JIS SUJ 2 steel, in a predetermined form, by a single carburizing step of heating the steel at 840 to 870° C., for at least 3 hours, in a carburizing atmosphere having a carbon potential of at least 1.2% as the only carburizing step of the process, and thereafter quenching, 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 contains 20 to 40 vol. % of retained austenite, and 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, and further, the surface layer has a surface hardness of 62 to 67 in Rockwell C hardness and has a compressive residual stress of 100 to 178 MPa.
2 . The process of claim 1 , wherein the single carburizing step of heating the steel at 840 to 870° C., for at least 3 hours, in a carburizing atmosphere having a carbon potential of at least 1.2% permits adjusting area ratio and particle size of the carbide to be precipitated in the surface layer and amount of retained austenite in the surface layer.
3 . The process of claim 1 , wherein the single carburizing step is performed for a period of from 3.5 to 5 hours.