Abstract: Cooling process of the U76CrRE steel rail during heat treatment was optimized, and the abnormal upper bainite microstructure in the decarburization layer of the steel rail was therefore eliminated. The causes of abnormal microstructure were analyzed, and the best heat treatment process of U76CrRE steel rail was put forward. During the stage cooling process, the forced cooling intervention temperature of U76CrRE steel rail is 568 ℃. The temperature condition for the abnormal upper bainite microstructure is that the latent heat of phase transformation inside the rail and the extremely cold surface layer easily form an isothermal layer in the decarburization layer of the rail. Simultaneously, severe decarburization at the grain boundary near surface of the rail provides the condition of chemical composition for the formation of upper bainite structure. The optimum heat treatment process of the U76CrRE steel rail consists of quenching cooling starting temperature of 780 ℃, quenching time of 120 s (20 s+100 s), quenching final cooling temperature of 410 ℃ and back temperature of 540 ℃.

Key words: U76CrRE steel rail, heat treatment, microstructure control, decarburization layer