Investigation of white etching area at non-carbides origin in M50 bearing steel under rolling contact fatigue

White etching areas (WEAs) were originated in regions free of carbides or non-metallic inclusions under rolling contact fatigue (RCF) in M50 bearing steel. Two types of WEAs with largely sheared and compact morphologies were observed. They were investigated using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The results show that WEAs involve martensite-to-austenite phase transformation and amorphization, in contrast to the butterfly-winged WEAs consisting of only ferrite nanocrystallines. It is suggested that the nanocrystallines are the result of recrystallization. The high micro shear strain of 0.9–1.1 drives phase transformation. The solid-state amorphization occurs due to accumulation of high dislocation density. The dislocation density in the compact WEA is much higher than that in the sheared WEA.