高强度螺栓材料为20MnTiB钢，服役时间约24 h发生断裂。利用光学显微镜、扫描电子显微镜、直读光谱仪、能谱分析仪和显微硬度机等手段，对断裂螺栓进行了宏观、化学成分、氢含量、硬度、金相、能谱和开裂面电子显微形貌分析后，得出该螺栓断裂的主要原因是在使用前已经存在裂纹，造成应力集中，在拉应力的作用下，材料中的氢原子向裂纹尖端移动、富集，使局部氢浓度升高，螺栓发生了氢致延迟脆性断裂。
20MnTiB high strength bolt was fractured after 24 hours service. The analysis on optical microscopr, SEM, EDAX, hardometer and chemincal composition were carried out on the cracked bolt. The comprehensive analysis results showed that the bolt existed cracks before using.The primary cracks led to stress concentration,so the hydrogen in material moved to the crack top and enriched. With local incerease in hydrogen content there occured hydrogen ductilebrittle fracture in bolt.
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