焊接热循环对U71Mn铁轨钢热影响区粗晶区组织性能的影响

U71Mn铁轨钢为高碳钢，其热影响区的粗晶区是焊接接头的薄弱部位。本文利用焊接热模拟技术、金相显微镜、维氏硬度计、冲击试验机、扫描电镜，研究分析了U71Mn铁轨钢在不同热循环下的热影响区的粗晶区显微组织、显微硬度、冲击韧性和断口形貌。研究结果表明，增加冷却时间t8／5能减少组织中马氏体含量，当t8/5〉100s时，马氏体消失；第2次热循环时，由于热循环峰值温度为1000℃，位于热影响区的细晶区，第2次热循环对第1次热循环产生的粗晶组织有细化作用，能增加硬度，提高韧性。

Influence of Welding Thermal Cycle on Structure and Properties in Grain-coarsening Region of U71Mn Rail Steel

U71 Mn rail steel belongs to high-carbon steel, and it＇s coarse grain heat affected zone is the weak part of wel-ded joints. In this paper, by using welding thermal simulation technology, metaloscope, Vickers hardness tester, impact testing machine, and scanning electron microscope, microscopic constitution, micro hardness, impact ductility, and fracture morphology of coarse grain heat affected zone of U71Mn rail steel under different thermal circulation were researched. The results showed that the increase of t8/5 reduced the content of martensite in the microstructure, and the martensite disap- peared when the t8/t was longer than 100 s. Compared with single thermal cycle, the second thermal cycles can refined the grain size of CGHAZ, because the peak temperature of the second thermal cycle was 1 000 ℃, and improve hardness and toughness.