Fracture Failure of Zinc-Plated Hub Bolts by Hydrogen Embrittlement

In this work, the failure behavior of a batch of zinc-plated hub bolts with high strength was detected and analyzed to determine the failure mechanism. The fracture failure occurred at the head-to-shank transition. The initial region of the crack was at the external edge of the bolts. Brittle fractures containing intergranular and transgranular features were observed using a scanning electron microscope. Yawning grain boundaries as well as micropores on the grain surfaces were observed at many areas of the fracture surfaces. According to the analysis results, hydrogen embrittlement is considered as the probable mechanism of the failed specimens. Poor baking treatment may be the reason leading to the incomplete removal of hydrogen.