Formation process of white etching area under rolling contact in bearing steel

The formation process of White Etching Area (WEA) under rolling contact was investigated to characterize the WEA formation mechanism using radial type rolling fatigue test machine. The examination was carried out under rapid acceleration and deceleration of rotating speed. From observation of test pieces by Scanning Ion Microscope (SIM) and Transmission Electron Microscope (TEM), it was found that acicular structures were formed before forming WEA. The length and width of acicular structures were about 20 μm and about 2 μm respectively. Acicular structures were formed separately from each other and fine granular structures formed from martensite. It was considered that acicular structures were formed by locally microstructural change of martensite due to rolling contact fatigue. The distance from surface to acicular structures were concerned with the location of maximum value of shear stress under rolling contact. An angle between rolling contact surface and acicular structures wasn't consistent with the analytical shear stress angle. It suggested that the stress to govern the forming the acicular structure was not only shear stress under rolling contact but also secondary dynamic stress.