Grinding-Induced Microstructural Variations in Pearlitic Rail Steels under Tribological Conditions

Rail grinding is widely used as a preventive maintenance technique in railway systems to remove surface defects and restore rail geometry; however, the tribological interaction between the grinding wheel and rail steel can generate significant subsurface microstructural transformations. In this study, an experimental methodology was developed to investigate the relationship between grinding parameters and microstructural evolution in pearlitic rail steels under controlled laboratory conditions. A dedicated experimental setup was designed to reproduce representative grinding conditions while allowing the systematic variation of cutting speed and depth of cut. Rail steel coupons (R260 grade) were subjected to controlled grinding tests, after which specimens were extracted from the contact region and prepared using standard metallographic procedures. Microstructural characterization was conducted using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM), complemented by microhardness measurements to evaluate mechanical changes within the modified layers. The results revealed pronounced subsurface microstructural modifications, including severe plastic deformation of the pearlitic structure and the formation of White Etching Layers (WELs) with variable morphology and thickness. The region immediately beneath the WEL interface exhibited heavily distorted lamellar pearlite, while hardness profiles showed a marked increase near the surface compared with the bulk material, indicating localized strain hardening. The observations suggest that the formation of these transformed layers is strongly associated with intense plastic deformation generated by tribological loading during grinding. Nevertheless, the potential contribution of frictional flash temperatures cannot be excluded, suggesting that WEL formation may result from a coupled thermo-mechanical mechanism. These findings highlight the importance of understanding the interaction between grinding parameters, tribological stresses, and thermal effects to optimize rail maintenance strategies and mitigate undesirable microstructural degradation.