Re-investigation of dark etching regions and white etching bands in SAE 52100 bearing steel due to rolling contact fatigue

Microstructural alterations such as dark etching regions (DERs) and white etching bands (WEBs) have been known to manifest in the subsurface of steel bearings due to rolling contact fatigue (RCF) under medium-high stress cycles. Even though such manifestations have been reported substantially in literature for decades, their formation and their evolution mechanisms are not fully understood. As part of the re-investigation of DERs and WEBs, this paper presents the results from characterization of DER and WEBs, including both low angle bands (LABs) and high angle bands (HABs), formed in SAE 52100 bearings at different stages of bearing life. Angular contact ball bearings (ACBBs), subjected to RCF testing under different contact pressure, stress cycles and steel cleanliness, have been examined to reveal new information related to the microstructural alteration processes, e.g. the 3-D structure of the WEBs and their growth pattern. Contrary to some of the literature results, the experimental results have shown that the mean depths and density of WEBs (LABs and HABs), as opposed to DER, are correlated with the position and distribution of the principle shear stress. The results also show that HABs form as a consequence of LABs especially in densed LAB areas in the ACBBs studied here.