关键词: 40Cr 钢；定位销；氢致延迟断裂；非金属夹杂物；电镀

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