Formation mechanism and influence of white etching area on contact fatigue spalling of M50 bearing steel

Abstract

Contact fatigue spalling failure ocurred in the M50 steel bearings during test due to the formation of white etching area (WEA). In this paper, characteristics, formation mechanism, influence on contact fatigue spalling failure and control methods of the WEA were obtained by examining loctaions and morphological characteristics, composition analysis, hardness test and microstructure analysis of the WEA in the two failure bearing and the other three bearing which are not failure. The results show that the WEAs origin from the boundary between matrix and primary carbides or inclusions which located in the subsurface of raceway, show irregular block shape morphologies, have length direction of about 30°-50° degrees to the rolling direction and microstructure of body centered cubic ferrite nanocrystalline. There is no obvious difference between the WEA and matrix in chemical compositions, while hardness of the WEA is higher than that of the matrix. Formation mechanism of WEA is phase transformation driven by accumulation of plastic deformation induced by high stress in micro region. The smaller the distance between WEA and the raceway surface, the faster of WEA growth rate are reached. And WEA is more likely to cause contact fatigue spalling of the bearing as the deformation coordination between WEA and matrix is poor. The initiation and propagation of WEA can be controlled by reducing the material defects and avoiding the bearing from high working stress.