Effect of inclusion/matrix interface cavities on internal-fracture-type rolling contact fatigue life

Flaking failure in rolling contact fatigue (RCF) of hardened bearing steels under well-controlled lubrication is known to originate from the non-metallic inclusion present in the material’s subsurface region. Many researchers stress the importance of the inclusion size as an important factor in RCF life. The RCF performance of steels has been improved through the development of a steelmaking technology that allows reducing the inclusion size. However, due to the limits in visualization of crack initiation and propagation during RCF testing, the issue regarding the number of factors involved in the process remains unsolved. In our prior research, we observed and analyzed cracks initiating from internal defects. The obtained results suggested that the inclusion/matrix interface condition might play an important role in RCF life. In this study, we investigated the effect of inclusion/matrix interface cavities on RCF life through close observation of fatigue cracks. Hot Isostatic Pressing (HIP) treatment was conducted in order to close the cavities and it was found that closing the inclusion/matrix cavities is a very valuable technique for improving RCF life of bearing steels.