动车组夹钳螺栓断裂原因分析

动车组制动夹钳紧固螺栓在安装过程中发生断裂。采用扫描电子显微镜、光学显微镜、电感耦合等离子体光谱仪等对断裂螺栓进行断口形貌、显微组织及化学成分检测与分析。结果表明:断裂螺栓化学成分、显微组织均未见明显异常；螺栓断面可见明显高温氧化痕迹和粗大晶粒轮廓，且局部晶界熔化，在圆角处与表面连通；原奥氏体晶粒内部和螺栓其他部位可见细小晶粒，结合螺栓制作工艺，可以推断该螺栓在热镦过程中因加热温度控制不当导致局部过烧。通过不同温度热镦试验，提出合理的工艺改进建议。

Analysis on Reason of Fracture of Clamp Bolt in Multiple Units

The fracture morphology, microstructure and chemical composition of fracture bolts were detected and analyzed by scanning electron microscope, optical microscope and inductively coupled plasma spectrometer. The results show that the chemical composition and microstructure of the broken bolt are not abnormal. The bolt section shows obvious high temperature oxidation traces and coarse grain profiles, and the melt local grain boundaries that connected with the surface at the rounded corners. Fine grains can be seen inside the original austenite grain and other parts of the bolt. Combined with the bolt making process, it can be inferred that the local over-burning of the bolt is caused by improper heating temperature control during the hot heading process. Through the hot upsetting test at different temperatures, reasonable suggestions for technological improvement are put forward.