Abstract: The positioning pin made of 40Cr steel suddenly broke several times during operation, based on this, chemical composition, microstructure and fracture morphology are analyzed, the results show that the failure is caused by hydrogen-induced delayed fracture. Mainly because of class D non-metallic inclusions in materials and producing internal stress after surface quenching, the positioning pin absorb hydrogen in following processes of pickling and electroplating and break down in under the action of alternating stress. It is suggested to improve the metallurgical quality of materials, add the process of stress relief annealing after surface quenching, and it is more important to add the process of removal of hydrogen after electroplating.

Key words: 40Cr steel; Positioning pin; Hydrogen-induced delayed fracture; Non-metallic inclusions; Electroplating

摘要： 由 40Cr 钢制成的定位销在工作过程中多次突然断裂，基于此，文章分析了定位销的化 学成分、显微组织、断口形貌等。结果表明，此次断裂为氢致延迟断裂，主要是由于原材料 内存在 D 类非金属夹杂物，同时表面淬火后产生内应力，后续生产过程中的酸洗及电镀工艺 致使定位销吸氢，最终在交变应力的作用下发生断裂。改善原材料的冶金质量，表面淬火后 增加去应力退火工艺，电镀后增加除氢工序，可有效解决该断裂问题。

关键词: 40Cr 钢；定位销；氢致延迟断裂；非金属夹杂物；电镀