White etching crack (WEC) investigation by serial sectioning, focused ion beam and 3-D crack modelling

White structure flaking (WSF) as a premature wear failure mode in steel rolling element bearings is caused by white etching cracks (WECs) that form in the 1 mm zone beneath the contact surface. Hydrogen diffusion into raceways and transient operating conditions have been suggested as drivers of WSF. The initiation and propagation mechanisms for WEC formation are not well understood. This study elucidates WEC initiation processes in hydrogen charged 100Cr6 bearing steel by carrying out two-roller RCF testing. The application of serial sectioning enabled mapping and modelling of entire independent WECs and revealed critical information about initiators. The application of FIB tomography verified initiation mechanisms. The results show strong evidence for subsurface initiation of WECs from inclusions.