中文摘要：

青藏铁路等低温地区铁路的建设与维护，对钢轨钢材的低温冷脆性能与低温下服役的安全性研究提出了迫切的要求。本文采用三点弯曲试样，对我国铁路建设中两种常用的钢轨钢材U71Mn和U75V，在20℃、0℃、-20℃、-40℃、-60℃五个温度点下进行了断裂韧度KIC的评定试验。通过试验数据计算得到了上述两种钢轨钢材在不同温度下的CTOD与J积分值，结果表明，钢轨钢材的δC和JIC值随温度的降低而减小。并对两种钢轨钢材在低温下的断裂韧度进行了系统分析和总结，为工程设计中两种钢轨的断裂韧度取值提供了借鉴数据。

英文摘要：

Researches on brittle fracture properties and security required for constructions and repairs of railways in cold regions （such of rail steels at low temperature are as Qinghai-Tibet Railway,etc. ）. The fracture toughness KIC of U71 Mn and U75 V rail steels at low temperature （ 20℃, 0℃, - 20℃, - 40℃ and - 60℃ ） were tested by three-point bend specimens. Fracture toughness δC and JIC of the two typical rail steels at different low temperatures were calculated. The results indicate that δC and JIC reduce as the temperature declines. Fracture toughness of the two rail steels obtained by tests and analysis provides references to engineering designs.