An investigation on the formation and hardening mechanisms of white etching layer in hypoeutectoid rail surface

The stress distribution in a hypoeutectoid U71Mn rail surface due to the wheel-rail contact was simulated via finite element, and the microstructure and hardening of the after-service rail surface were comparatively studied with heat treated (holding at 850°C for 30min and cooling at 15°C/s) samples under atmospheric pressure (AP-850) and under hydrostatic pressure of 1GPa (HP-850), respectively. The rail surface experiences 3-dimensional stress-state of 1GPa and large shear stress. A white etching layer (WEL) was formed, showing martensite-type microstructure with spherical cementite particles and a hardness of 1101HV. The phase composition and hardening show great resemblance to those of the HP-850 sample, but differ significantly from those of AP-850 sample. High pressure martensitic transformation is proposed to interpret the formation of WEL and the hardening is analyzed according to the structural cause.