某汽车发动机前制动软管螺栓发生断裂现象，采用宏观观察、化学成分分析、扫描电镜分析、金相检验、硬度测试等方法分析了螺栓断裂的原因。结果表明：未对螺栓进行热处理，导致冷作硬化没有消除；在酸洗电镀工序中，氢离子浸入螺栓的根部，使螺栓根部发生氢致延迟断裂。

The bolt of front brake hose of an automobile engine was broken. The causes of bolt fracture were analyzed by means of macroscopic observation, chemical composition analysis, scanning electron microscope analysis, metallographic examination and hardness test. The results show that the bolt was not heat treated, resulting in cold hardening was not eliminated. In the pickling and electroplating process, hydrogen ions were immersed in the root of the bolt, causing hydrogen induced delayed fracture at the root of the bolt.