Formation of Platelike Carbides during Rolling Contact Fatigue in High-carbon Chromium Bearing Steel

Abstract

Rolling fatigue behaviors of high-carbon-chromium bearing steel were investigated on the thrust-type fatigue tester. Platelike carbides, dark and white etching constituents were found immediately underneath the rolling surfaces.
Microscopic observation o f an area right below the flaking has demonstrated that the Platelike carbides are, among others, blamed for the flaking. The Platelike carbides consist of Fe₃C or ε-Fe_2-3(C, N) with a hardness up to Hv 1300. They are harder than martensite and can be the cause of the flaking. The Platelike carbides are precipitates of C and N in the martensite, diffused by a rolling stress and caught in the stress concentrated area between oxide inclusions near the rolling surfaces.
It is, therefore, necessary for an improvement in fatigue strength of high carbon-chromium bearing steel that oxides be reduced in the steel and carbon content in the martensite be lowered to reduce the formation of the Platelike carbides as long as a hardness required of a rolling element is maintained.