Investigation on butterfly white etching area formation mechanism and crack source at different stages in M50 bearing steel.

Rolling contact fatigue tests with different stresses and cycles have been conducted to study the formation mechanism and crack source of butterfly white etching area (WEA) in different stages of M50 bearing steel. The results suggest that the structural transformation is prior to cracks. The initial microstructure is the nanocrystalline α-Fe formed by dislocation assisted carbon migration. With the extension of cycles, unlike the previous studies, the butterfly-origin carbide is refined into Mo 2 C and M 7 C 3 nanocrystalline by the accumulated dislocation clusters. Subsequently, the increase of interfacial energy drives the metal elements diffusion and thus the formation of amorphous structures. A new mechanism called diffusion-assisted dislocation has been proposed for butterfly WEA formation. [Display omitted] • The evolution of butterfly WEA in M50 bearing steel has been studied under different stresses and cycles. • A new detailed formation mechanism of butterfly WEA is proposed. • The structural transformation of butterfly WEA is prior to cracks. • M 2 C carbides are more likely to cause butterfly WEA and cracks. [ABSTRACT FROM AUTHOR]