Fracture Analysis of 30CrMnSiA Self-Locking Nut

The test fractures of 30CrMnSiA self-locking nut were inspected by the macro-observation, scanning electronic microscope (SEM) observation and energy spectrum analysis. Then, an overall analysis by synthesis method was conducted in combination with process tests. Finally, the results show that: the root cause for test fractures is liquid-metal embrittlement which may be occured when the zinc-plated nut fitted with a cadmium-plated test bolt is loaded and heated to test locking properties at 300˚C, and similar test fractures on the nut can be avoided effectively by mating with a zinc-plated test bolt.