Failure cause analysis of surface burn on high-speed railway U75VG rails

Purpose To conduct a systematic failure analysis on the typical surface rail burn defects of U75VG rail steel in the straight section of a passenger dedicated line, and clarify the evolution law and failure mechanism of the damage. Design/methodology/approach Macroscopic morphology observation, scanning electron microscopy microanalysis, metallographic structure characterization, as well as comprehensive tests on chemical composition and mechanical properties were adopted to carry out the research. Findings The damage is a type of rail head tread burn dominated by rolling contact fatigue. The instantaneous high temperature caused by wheel-rail relative sliding during train braking converts the pearlite structure in the rail head surface layer into a hard and brittle martensitic white layer with a maximum thickness of 2.5 mm. Cracks initiate on the tread surface, propagate inward at an inclination angle of about 80°, bifurcate and change the propagation direction when reaching the martensite-matrix interface, and finally lead to spalling or transverse fatigue fracture. Originality/value A zoned differentiated maintenance strategy is proposed based on the failure mechanism, which provides a theoretical basis for the precise prevention and control of rail burn in high-speed railways.