The role of size and volume fraction of carbides on hydrogen embrittlement and white etching areas formation in bearing steel under dynamic loading

Abstract

Despite of more than two decades of research in white etching areas (WEAs), this phenomenon still persists in wind turbine gearbox bearings leading to a reduction of L10 life by 90 percent. There are various drivers for WEAs formation among which hydrogen is considered one of the root causes which accelerates the microstructural degradation. Diffusible atomic hydrogen reduces the threshold for dislocation motion leading to localized strain accumulation. The tendency to form WEAs in bearing steel depends on the stability of carbide precipitates during plastic deformation and resistance to diffusible hydrogen. In this research work, the role of size and volume fraction of carbides on their relative stability against decomposition and hydrogen embrittlement is studied. The performance of bearing ball samples with different carbide sizes and distribution is tested in the presence of two different lubricants in the dynamic load pin-on-disc (PoD) test rig. The results from the study show that reducing the size of carbide precipitates improved their stability against plastic deformation leading to the stagnation of WEAs formation.