Mechanism of fine granular area and white etching crack formation in AISI 52100 bearing steel

Abstract

Fine Granular Area (FGA) and White Etching Cracks (WEC) are two types of fatigue damage phenomena which are characterised by the development of cracks accompanied by a local microstructural transformation. The resulting microstructures share many properties, chiefly a strong reduction in grain size. In this study, the thickness of the transformed zones along the crack formed during FGA and WEC experiments is investigated. It is shown that in WEC, similar to earlier results on the FGA, the size of the transformed zones increases with increasing crack length. For further analysis of the more complex WEC case, an approach is presented that uses the results of a critical plane analysis for the calculation of key figures in fracture mechanics. The results are shown to be very similar to those of the FGA. Drawing on these and earlier results, it is proposed that a common mechanism of WEC and FGA formation exists. In addition, some important differences of the two phenomena are explained within the framework of the common mechanism.