Generation Process Observation Of Micro-Structural Change In Rolling Contact Fatigue By Hydrogen-Charged Specimens

Rolling contact fatigue tests on hydrogen-charged bearing steel and the micro-structural observations under the tracks were performed. Needle-like cracks were observed as precursor of WEA(White Etching Area) generation. It seems that hydrogen caused the localized plastic deformation and subsequent needle-like crack generation. A model was proposed, where the needle-like cracks forms micro-cracks and WEA was subsequently generated in the specific area along the micro-crack. Although WEA was also caused by localized plastic deformation, it was estimated that the micro-crack kink caused the localization. A stress analysis demonstrated that WEA was generated in a hydrostatic compressive region formed by the micro-crack kink. Although the hydrostatic stress does not contribute to the plastic deformation, it was supposed that the hydrostatic compressive stress assisted the accumulation of the plastic strain, because compressive stress suppressed new generation and propagation of the micro-cracks.