Abstract Springs are susceptible to fatigue fracture due to wear and stress concentration in dynamic impact, cyclic loading and harsh environments. In this study, the fracture failure mechanism of a defense-related spring 65Si2MnWA was investigated. The microstructure, micro defects, elemental compositions and fracture morphologies of the failed spring were characterized by light microscopy (OM), scanning electron microscopy (SEM) and inductively coupled plasma mass spectrometry (ICP), and the n