Deformation-induced amorphization and austenitization in white etching area of a martensite bearing steel under rolling contact fatigue

The paper investigated the composition and the formation mechanism of white etching areas (WEAs) generated in rolling contact fatigue (RCF) of a bearing steel using scanning electron microscopy (SEM) transmission electron microscopy (TEM). It is generally accepted that WEA consists of nano ferrites. However, the current study revealed that nano ferrite is not the final product of the WEA. Instead, it involves phase transformation and amorphization. TEM inspection showed the WEA exhibits an amorphous phase with martensite, austenite and carbides embedded interior. The amount of austenite is greatly increased in the WEA, indicating a phase transformation from martensite to austenite. The analysis showed that both the amorphization and the austenitization are proceeded under a shear-induced mechanism. As a result of partial amorphization, nanocrystallites and amorphous phase coexist. Various morphologies are present in the WEA.