Fracture Failure Analysis of U75V Pearlitic Rail on Sharp Radius Curved Track

A transverse fracture occurred in U75V pearlitic rail after 5 months of service on a sharp radius curved track of mixed passenger-freight railway. Systematic tests including chemical composition analysis, mechanical properties testing, macroscopic fracture inspection, metallographic observation and microscopic morphology characterization were conducted on the failed rail sample. The results indicate that the rail base metal has qualified metallurgical quality. Its chemical composition, fundamental mechanical properties and microstructure fully meet the requirements of Chinese railway standard TB/T 2344.1-2020. The failure mode is identified as instantaneous brittle fracture. Severe mechanical extrusion and impact cause prominent plastic deformation on the rail foot, leading to surface plastic flow and further triggering micro-crack initiation. Under continuous cyclic stress induced by train loads, the micro-crack tips undergo repeated tearing and closing. Severe stress concentration accelerates the formation of transgranular cracks, which propagate rapidly and unstably toward the rail interior, eventually resulting in catastrophic transverse fracture. Standardized procedures in rail transportation, hoisting and laying are essential to avoid mechanical damage, while regular line inspection and timely replacement of damaged rails should be strictly enforced.