Formation of white-etching layers on rail treads

Two corrugated rail samples with different load have been investigated using a profilometer, nanoindentation technique and scanning electron microscopy. The crystal refinement and the development of the microstructure are investigated by X-ray diffraction and transmission electron microscopy. Friction tests on the crests and troughs of the corrugated rail have indicated that the crests are more resistant by better than a factor 2. On both rail samples white etching layers with a high hardness and a nanocrystalline structure are observed. Temperature calculations indicate that classic martensitic transformation during the rail-wheel contact is improbable and therefore to explain the high hardness, quantitative estimates of 5 possible hardening mechanisms are performed. This analysis implies that the transformation may be assisted or even produced by high thermal stresses. In order to support the modeling, mechanical ball milling has been used to produce steel powders with comparable mechanical behaviors.