Case-hardening steel for bearings having excellent rolling contact fatigue properties and manufacturing method thereof

摘要

PROBLEM TO BE SOLVED: To propose a case hardened steel having improved rolling fatigue life under an environment where hydrogen enters and suitable for bearing steel especially.SOLUTION: A case hardened steel by carburization hardening or carburization nitrogen hardening steel having a component composition containing, C:over 0.1% to 0.30%, Si:0.15 to less than 1.0%, Mn:0.2 to 1.2%, Cr:6.0% to less than 10.5%, P:0.025% or less, S:0.02% or less, Al:0.05% or less, N:0.0100% or less and O:0.0030% or less and the balance Fe with inevitable impurities, a surface area from the surface to at least 200 μm depth has hardness of Hv 670 or more, an area percentage of carbide existing in the surface area is 5 to 30%, an average diameter of the carbide is 0.40 to 0.70 μm, an average aspect ratio (major diameter/minor diameter) is 2.0 or less and a retained austenite amount in the surface area is 40% or less.SELECTED DRAWING: None