How to reproduce a mechanical white etching layer (WEL) on rail surface thanks to a new experimental wheel-rail contact test bench

Abstract This study presents a successful attempt to reproduce White Etching Layer (WEL) under pure mechanical conditions, with the use of a new experimental test bench with tests conditions representative of the wheel-rail contact. The effect of the presence of a run-in or corrosive fuse layer at the rail surface has a great effect on the microstructure evolution. This layer prevents wear and allows microstructural transformation of rail steel. First, a tribological analysis of the effect of the surface preparation on material flows in the contact, hardness evolution, and formation of WEL is presented. Then a multiscale characterization approach combining optical microscopy, scanning electron microscopy and near surface EBSD characterization at the sub-μm level has been carried out to understand the formation mechanism of such mechanically formed WEL. The different scenarios of the wear behavior and microstructural transformation were drawn. The influence of the conditions of preparation of the sample surfaces, in particular of the presence of a tribological fuse layer (either a run-in layer or a corrosive layer) on the wear fatigue competition and the WEL formation, were also studied. The normal stress due to the normal force in the tests leads to the formation of a hardened layer of nanograins. When submitted to shear in the rolling with sliding tests, this layer is removed by wear if the cohesion between the surface and the bulk is too weak. The presence of a fuse layer before the shear solicitation by sliding increases this cohesion, and turns the wear behavior into progressive microstructural transformation. Therefore White Etching Layer were formed through a mechanical process with realistic operating conditions avoiding the formation of thermal WEL.