Microstructural investigation on a rail fracture failure associated with squat defects

•Squat-induced rail fracture was investigated to determine the root causes of squat initiation, transverse defects cracking development, and fracture failure.•Squats initiation was related to rolling contact fatigue and the existence of White Etching layers on the rail surface.•The martensitic defects at the rail subsurface triggered rapid crack development, facilitated the transverse cracking, and ultimately resulted in rail fracture failure.