Delayed Fracture Analysis on NIV Type Parallel Double Torsion Springs

About 0.7% NIV type parallel double torsion springs fractured during the assembling process or after assembling, and means such as macro analysis, SEM observation, and process analysis were used to analyze the fracture reason of the springs. The results show that the fracture of the springs was hydrogen induced delay cracking, and high stress concentration formed around the inclusions of the base metal and incomplete dehydrogenization after electroplating were main reasons for the fracture.