U75V热轧钢轨铺设在曲线地段使用超过3 a(年),其中一支钢轨发生断裂,部分钢轨出现剥离掉块。当查找断裂原因,对断裂钢轨进行了理化检验。结果表明: 轮轨接触应力过大，超过了钢轨接触疲劳强度,由于疲劳裂纹萌生和扩展的速率大于磨耗速率,在钢轨塑性变形层表面萌生并形成了疲劳裂纹，并沿变形流线方向疲劳扩展，在轮轨接触圆角处距表面2 mm处形成了疲劳核伤,在车轮的反复作用下发生了断裂。

The U75V hot-rolled rails laid on the curving line had been used more than three years, one of them had fractured, and some other had fatigue damage of desquamation. The physical and chemical inspection was carried out to find the fracture reason. The results indicated that the contact stress of rail and wheel was too excessive and exceeded the yield strength of rail. Because the fatigue crack expansion rate exceeded the wearing speed rate, the fatigue crack generated on the surface of the rail’s plastic deformation field, and the crack extended along the deformation streamline, then the nucleus of crack caused in the round under the contact surface of rail and wheel about 2 mm. Finally, the rail had fractured in the wheel rolled repeatedly.