Nonmetallic inclusion bonding in bearing steel and the initiation of white-etching cracks

The presence of nonmetallic inclusions in bearing steel is well described as well as the occurrence of white-etching cracks starting at the inclusions. In this paper, the role of interfacial strength in the initiation of small cracks at nonmetallic inclusion-steel interfaces that lead to white-etching crack systems is discussed. The effect of rolling contact fatigue on the steel-inclusion interface will be described to explain the early crack initiation, with a focus on manganese sulfide and complex aluminum oxide inclusions. The factors of size and shape both play an important role in the behavior of inclusions, as well as that of interfacial bonding, which will be shown to be decisive in the strength of a bearing steel. Experimental methods to determine inclusion-steel interface properties are applied, such as advanced tensile tests combined with digital image correlation, in order to show the level of bonding of nonmetallic inclusions. The experimental results contribute to the verification of inclusion modeling in rolling contact fatigue simulations.