Mechanical White Etching Layer Formation Kinetics in Pearlitic Steels: A Phenomenological Model Based on Microstructural Characterization

In order to predict the lifetime of railtrack components, numerical models are required to better describe the apparition of microstructural defects that lead to material failure. In pearlitic steels, the severe mechanical loading or/and the local temperature increase result in the formation of a hard and brittle phase that is prone to cracking, which is called White Etching Layer (WEL). The current study proposes a phenomenological model, based on the microstructural evolution, to describe the mechanically-induced-WEL kinetics of formation. First, a detailed multiscale microstructural characterization was performed in order to identify suitable microstructural indicators for the WEL formation. The grain size, orientation and morphology, and internal disorientation were characterized for different steps of mechanical WEL formation. This could be achieved thanks to the use of a dedicated test bench that allows to monitor the wheel-rail contact condition (sliding, number of cycles, and contact pressure) independently. The proposed model was validated using tests performed in extreme load and sliding conditions. The numerical and experimental results indicate that the most severe conditions (contact pressure and sliding ratio) catalyze WEL formation, and that the same deformation state can be achieved through different loading paths.