Influence of the evolution of near-surface rail wheel microstructure on crack initiation by micro-bending investigations

Severe mechanical and thermal loadings, as well as the corrosive environment change the near-surface microstructure of rail wheels during service. Resulting severely plastically deformed (SPD) and corrosion affected microstructures are prone to influence crack initiation along the wheel tread. To evaluate the crack initiation and fracture behaviour, the in-situ micro-bending method is first applied on rail wheel samples from field within this work. Results reveal detailed insights in material behaviour of SPD microstructures, where the conducted micro-bending investigations point out predominant plastic behaviour without cracks initiated at the artificial notch of the micro-cantilevers during bending. In contrast, micro-bending investigations in microstructural regions with increased oxygen and silicon composition show crack initiation, fracture, and low maximum stress levels (approximately one seventh of the SPD microstructure). The presented study underlines the increased risk of crack initiation in corrosion affected regions by a novel testing method in this field with high spatial resolution and acknowledge the importance of periodic reprofiling of the rail wheels in service.