Phenomenological wear model of case-hardened 20MnCr5 under cyclic line rolling contact

Tribo-machineries employ machine elements, such as discs and gears, which are frequently subjected to Hertzian loads that cause their mechanical failure. Case hardening is a popular method that ensures better productivity and performance of such elements compared to its untreated variants. This paper presents a wear and fatigue model for case hardened steels under Hertzian loads in line contact. Steel discs with different case hardening depths were tested using a three-disc testing machine, and the samples were analyzed using optical microscopy, SEM and a portable X-ray diffractometer. The influence of type of contact, case hardening depths, normal force (contact stress) and slip conditions on the damage process are investigated in detail. It was found that the hardening layer should be adapted to the load, since a too large hardening depth means a shorter service life due to higher residual stresses gradients. The transferability of results to increase the service life of real-life components is an essential component of this work.