Microstructural Alterations in Bearing Steels under Rolling Contact Fatigue: Part 2-Diffusion-Based Modeling Approach

The microstructure of rolling element bearings can experience significant transformation when subjected to repetitive contact cycling. In Part 1 of this article, a detailed overview of the known microstructure alteration phenomena was presented and the different mechanisms for describing them proposed by various investigators were critically reviewed. It is agreed generally that the primary path of these structural changes is the decay of martensite due to carbon diffusion, leading to the formation of ferrite and lenticular carbides. Furthermore, these altered regions in the material microstructure can be stress concentration regions leading to crack initiation and propagation. In this article, a J2-based elastic-plastic Voronoi finite element model (previously developed by the authors) is coupled with a carbon diffusion-based model. Using Fick's law for stress-assisted diffusion, the dispersion of carbon in the bearing microstructure is evaluated. A backward Euler finite difference scheme is employed to solve the partial differential equations. The model can accurately predict the onset of martensitic decay and formation of the white etching bands along with their distinctive orientation. A comparison of the numerical results shows good corroboration with experimental observations.