Microstructural characterization of white etching cracks in bearings after long-term operation in wind turbines

White etching cracks and other microstructural features have been investigated in two 100Cr6 steel bearings failed after several years of service in wind turbines. It is found that cracks in these bearings propagate predominantly through prior austenite grains in the tempered martensite structure. Both sharp and gradual transitions between the tempered martensite structure and white etching matter adjacent to the cracks are observed. Furthermore, it is suggested that structural refinement of carbide particles present in the microstructure of the wind turbine bearings occurred at a late stage of white etching matter formation.