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 microst ructure are investigated by X-ray diffraction and transmission electro n microscopy. Friction tests on the crests and troughs of the corrugat ed rail have indicated that the crests are more resistant by better th an a factor 2. On both rail samples white etching layers with a high h ardness and a nanocrystalline structure are observed. Temperature calc ulations indicate that classic martensitic transformation during the r ail-wheel contact is improbable and therefore to explain the high hard ness, quantitative estimates of 5 possible hardening mechanisms are pe rformed. This analysis implies that the transformation may be assisted or even produced by high thermal stresses. In order to support the mo deling, mechanical ball milling has been used to produce steel powders with comparable mechanical behaviors.