中文摘要：

通过量为150MGT的货运U75V重轨服役状态表面出现明显的磨损、裂纹、剥离掉块等损伤。硬度测试显示钢轨表层由于塑性变形已产生较大的形变强化。XRD测试和显微结构观察显示，在接触疲劳应力作用下，钢轨表层及近表层产生严重的塑性变形，表现为晶粒细化。内部生成的微裂纹和夹杂相互作用连接在一起形成扩展裂纹，裂纹扩展主要是穿晶形式。裂纹发展至某一阶段可能以纵向大角度向内扩展，导致钢轨断裂。

英文摘要：

Under the passing tonnage about 150 MGT, U75V rail steel was heavily damaged with the features of wear, cracking and spalling. Mechanical property test, X-ray diffraction inspection and microstructure observations showed that the surface hardness of U75 V steel rose, the surface and subsurface of structures were highly deformed under the touched fatigue stress, the grains were fined. The tiny internal cracks acted with the inclusions to propagate the cracks further by transgranular mode, the crack might extend vertical inward, leading to rail breakage.