动车转向架六角头螺栓断裂失效分析

通过宏观形貌分析、扫描电镜及能谱分析、金相组织检测、力学性能检测、化学成分检测对六角头螺栓断裂原因进行分析。结果表明， 失效螺栓的化学成分、表心硬度、显微组织、晶粒度等指标均无异常。断口宏观形貌显示，约1/2断面区域呈黑色。经能谱扫描表明，黑色区域氧化严重，该区域可能经历过高温氧化。断口微观可见明显的沿晶断裂形貌，晶粒粗大。结合螺栓制造工艺，推断红打工序加热炉存在“跑温”情况导致样品发生过烧。因此，判断螺栓失效模式为过烧引起的过载断裂。

Fracture failure analysis of a hexagon head bolt on the bogie for motor cars

The failure reason of the hexagon head bolt was studied by macroscopic morphology analysis， scanning electron microscope and energy dispersive spectrometer analysis， metallographic microstructure detection， mechanical properties detection and chemical composition analysis. The results showed that the chemical composition， surface and core hardness， microstructures， grain size of the bolt were all qualified. The macroscopic appearance showed that about half of the area was black. The data of energy dispersive spectrometer showed that the black region was oxidized severely， and the region may have experienced high temperature oxidation. There was intercrystalline fracture morphology on the section， and the grain was coarse. Combined with the bolt manufacturing process， it was concluded that there was a running temperature in the red heating furnace， which resulted in overburn. Therefore， the failure mode of the bolt was the overload fracture caused by overburn.