某铁道线路进行大修换轨铺设新轨时,一支采用闪光焊接工艺焊接的长500 m的钢轨在中部位置的焊缝附近发生横向断裂，采用宏观检验、化学成分分析，断口分析及微观组织分析等方法对钢轨断裂的原因进行了分析。结果表明：钢轨的冶金质量良好,钢轨发生断裂主要是因为其轨头踏面表层形成的马氏体组织在铺轨时的弯曲拉应力作用下，产生裂纹并快速扩展，导致钢轨发生脆性断裂;钢轨焊接时出现了高接头,为保证焊接钢轨的平直度对其进行了打磨,但打磨工艺控制不良，从而导致钢轨轨头踏面局部产生高温,发生马氏体组织转变。

A 500 m welding rail fractured transversely at the middle position during installing process. Macro examination,chemical compositions analysis,fracture analysis,microstructure examination were introduced to study the fracture reason of the rail. The results indicate that metallurgical quality of the rail was good and it was the martensite microstructure at the rail tread surface that resulted in the fracture under the action of bending pulling stress. The rail was ground to make sure its straightness and then the martensite structure was formed at the rail tread surface because of the local high temperature caused by the improper grinding.