Steel rolling elements in bearings are known to undergo premature failure due to brittle flaking or what is also known as white structure flaking. This failure mode is associated with the formation of white etching cracks (WEC) and white etching areas (WEA). Literature findings point out to the mechanism resulting in early brittle flaking as a form of hydrogen-assisted fatigue; hence, the term hydrogen assisted rolling contact fatigue (HARCF) was coined. Understanding the factors affecting the diffusion and subsurface accumulation of hydrogen in bearing steel is crucial to developing measures to mitigate or even eliminate its detrimental effect.

Within the DFG-project “CoLifeHi”, finite element simulation models of a cylindrical roller thrust bearing (CRTB) will be developed. The simulation models will enable studying the diffusion of hydrogen and obtaining qualitative information pertaining to stress-assisted diffusion in tribological loading under the influence of predefined physical quantities. Preliminary work has revealed rather insignificant hydrogen accumulation due to stress-assisted diffusion in comparison to concentration gradient driven diffusion. On the other hand, residual stresses had an evident influence on the subsurface accumulation of hydrogen. The overlap between regions undergoing high stresses and those showing high concentrations of accumulated hydrogen pointed out to the triggering mechanism of HARCF.

This ongoing research work will particularly investigate the influence of residual stresses, trap densities and trap energies on the diffusion and accumulation of hydrogen in bearing steel. In parallel, the effect of hydrogen concentration on the mechanical behavior of steel will be investigated. The validated experimental data will be incorporated into the simulation models to provide information as to why premature failure of bearings occurs. The aim is to correlate the results of the simulations with full bearing tests to obtain lifetime predictions of bearings suffering premature failure.