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| Cause analysis of bolt fracture |
| ZHU Jiao1,ZHONG Zhenqian1,YU Xueliang1,LI Jie2 |
1. National Analysis Center for Iron and Steel, Beijing 100081, China；
2. University of Science and Technology Beijing, Beijing 100083, China |
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Abstract The material trademark of one bolt was 0Cr17Ni4Cu4Nb (17-4PH). The surface of bolt was coated with zinc after quenching and tempering heat treatment. Then it was installed on the equipment and the fastening stress was applied. In the next year, the equipment was shipped and put into marine environment. The fracture of bolt was observed after service for two and half years. The mechanical properties, microstructure, hardness, fracture morphology and chemical composition of the bolt materials were analyzed and tested. The results showed that the hydrogen content in surface coating was high. The high material strength and sensitivity to hydrogen embrittlement were the main reason to cause hydrogen embrittlement fracture of the bolt. In the process of service, the fastening force was applied onto the surface of the thread segment, which resulted in the diffusion and enrichment of hydrogen in the bolt surface coating to the nearby root of the thread. When the local hydrogen content reached the critical concentration of hydrogeninduced cracking, the hydrogen embrittlement fracture occurred in the bolt.
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Received: 18 November 2020
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2022, Vol. 40 
