中文摘要：

包括青藏铁路在内的北方大部分铁路钢轨在使用过程中常常经历比较低的温度环境，对于钢轨钢材的低温断裂性能有更严格的要求，有必要对钢轨钢材低温下断裂性能进行系统研究。通过对青藏铁路常用的钢轨钢材U71Mn和U75V三点弯曲试样断口的宏观形貌进行观察，并对所制备断口的微观形貌进行了电镜扫描分析，对这两类钢轨钢材在低温下的断裂特性进行了分析与讨论。最后，对这2种钢轨钢材断裂性能的研究方法以及化学成分的断裂性能的影响进行了进一步讨论，得出U71Mn较U75V更适合于在低温下作为钢轨钢材。

英文摘要：

Most steel rails in north China are always exposed under low temperature conditions including Qinghai - Tibet Railway, and stricter demand on fracture toughness of rails steel under low temperatures should be made. Fracture surface from threepoint bending test specimens in two typical rails steel material U71Mn and U75V in Qinghai- Tibet Railway were observed, and an analysis from the pictures of scanning electron microscope was given. Studies on fracture properties of these two kinds of rails steel under low temperature conditions were made based on fracture surface shapes and patterns. Finally, research methods for the two types of rails steel and the influences of chemical composition on fracture properties were discussed furthermore. U71Mn rails steel is more appropriate than U75V rails steel for cold situation.