Analysis on the Formation Cause of Spalling and Damage of the Heat-Treated Low Rail on Shuohuang Railway Curve

The performance of 5 segments of 75 kg·m-1 U75V rail on Shuohuang Railway has been inspected to analyze the performance of the damaged rail near the crack.Analyses show that the microstructures and hardness of the parent metals of U75V hot-roll rail are eligible.Whereas,both the quenching layer depth and the transect hardness of U75V heat-treated rail fail to meet the requirements of TB/T2635—2004.The results of rail micro-hardness show that there is a thin hardened layer in rail transect.The depth of the crack in the middle of the curve low rail tread is about 1.3 mm,and there are much different spalling that is related with the distribution characteristics of rail hardness.Cracks initiate from the plastic flow layer of rail head surface.There is an acute angle between the spread of crack initiation and the direction of train running.Cracks spread basically along vertical direction towards rail head when cracks are out of the plastic flow layer.When the cracks grow to certain extent,they manifest barb shape and spread approximately along the right-about with train running direction towards rail top.Finally,spalling is formed.In order to reduce the spalling of low rail at which heat-treated rail is used,and eligible heat-treated rail should be used and grinding also should be implemented at curve rail,and the transverse and longitudinal creepage force of rail should be decreased.