42CrMo合金钢螺栓的断裂失效分析

Analysis on Fracture Failure of 42CrMo Alloy Steel Bolt

通过宏观和微观断口形貌观察、化学成分分析、力学性能检测、金相观察、渗氮层检查等方法对42CrMo合金钢的螺栓断裂原因进行分析。结果表明:螺栓断裂属于大应力集中高应力双向弯曲疲劳断裂,裂纹起源于螺栓退刀槽靠近螺杆端圆角处;由于表面渗氮硬度高,韧性和抗疲劳性能下降,承载大冲击载荷能力减弱,引起螺栓断裂失效。改进工艺后,螺栓圆角处不做渗氮强化,螺栓没有发生断裂失效。

The failure reasons of 42 CrMo alloy bolt were analyzed by observing macrograph and micrograph, chemical composition analysis, mechnical properties testing, metallography observation,carburized layer inspection and so on. The results show that the fracture is high stress bidirectional bending fatigue fracture with large stress concentration, and the crack initiates in the rounding chamfer of tool withdrawal groove near the screw stem. Because of high hardness of surface nitriding layer, the toughness and fatigue resisitance decrease, the ability to withstand large impact loadshas weakened, which causes the bolt fracture failure. The bolts do not break when the rounding chamfer is not nitrided under the improved technology.