Abstract: After a period of service, a 50CrVA steel spring of the aircraft hatch door broke at the thread. The fracture morphology, microstructure, hardness, hydrogen content and chemical composition of the fractured spring were tested and analyzed, respectively. The results show that the failure of the spring is hydrogen induced delayed fracture, the fracture source area is intergranular cracking, and the typical hydrogen embrittlement fracture morphology exists on the grain surface. The investigation on the manufacturing process shows that more hydrogen is introduced into the matrix of the steel spring and the thread bears the bias load, both the factors promotes the fracture of the spring during service. The former factor is caused by without dehydrogenation when the cadmium plating with defects formed in the first cadmium plating process is removed and then replated, while the latter happens when the spring is assembled. The failure mode of hydrogen-induced delayed fracture is validated in the corresponding process experiment for the 50CrVA steel spring.

Key words: 50CrVA steel, spring, hydrogen induced delayed fracture