The heterogenous distribution of white etching matter (WEM) around subsurface cracks in bearing steels

White etching cracks (WECs) initiate subsurface in bearings and can propagate to cause premature failure. These cracks are bordered by an altered microstructure known as white etching matter (WEM), which is thought to form via a crack-rubbing mechanism. However, WEM is often observed bordering a single side of a meandering crack. In search of a microstructural difference to justify the observed WEM asymmetry, regions of untransformed material, adjacent to cracking in a bearing inner ring, which had undergone hydrogen charging prior to testing, were studied using correlative electron microscopy (EM), electron backscattered diffraction (EBSD), electron probe microanalysis (EPMA) and nano-indentation techniques. The investigations found no significant differences between the untransformed material neighbouring the cracks and the parent material; both were found to have similar: grain size and shape; crystallographic texture; carbon concentration; carbide population and hardness, which questions why only one rubbed surface of the crack has formed WEM. The initiation of WEM ahead of the crack is suggested, however more investigations are needed to build another WEM formation model. EPMA characterisation revealed evidence of carbide dissolution in the WEM. Despite this, significant variation in the carbon concentration of the WEM was found; ranging from +13% enrichment to 42% depletion (in counts), relative to the parent material. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd.