Formation of white etching layer on rails due to coupled thermal and mechanical actions

The formation mechanism of the white etching layer (WEL) on the rail steel material has been confirmed via two different routes; thermal-induced WEL by phase transformation and mechanical-induced WEL by severe plastic deformation. In this study, a combination of thermal and mechanical processes was performed to examine the synergistic interaction of two formation mechanisms of the WEL on rails. An experiment was conducted on the rail steel material using a Gleeble thermo-mechanical simulation system. The results confirmed that the martensitic WEL is formed by phase transformation from rapid quenching at a temperature below the critical point of material phase transformation, under 550 °C, when high hydrostatic pressure is applied. The application of combined thermal and mechanical action induced martensite with the presence of retained austenite. The microstructure of the transition zone between the WEL and the base material contains partial and full dissolution of cementite, broken pearlite lamella, and dislocation density, confirming that both thermal and mechanical processes are involved in the phase transformation of the material.