Dark etching regions under rolling contact fatigue: a review

Bearing performance depends on the ability of steel to cope with a large number of stress cycles. Long bearing lives are possible because the microstructure of bearing steel has excellent resistance to Rolling Contact Fatigue (RCF). Nevertheless, it is observed that the microstructure suffers changes in the region where the maximum Hertzian contact stress occurs. Here we give an overview of the present knowledge in the area of the formation of dark etching regions (DERs) during RCF. Factors that influence the formation of DERs, various types of characterisation techniques, and the observations made in the literature are discussed. In addition, the applicability of several proposed simulation models of the formation of DERs is discussed.