The microscopic process of void formation and propagation has been investigated in hydrogen embrittlement of iron. Specimens of pure iron in bamboo structure as well as polycrystalline specimens were tested in tension under cathodic hydrogen charging in 3%NaCl aq. at a current density of 100 A/m². Origins of fractographic features of hydrogen embrittlement were analyzed and interpreted by making correspondence to the structures developed within the specimens. Main results are as follows:
(1) Initiation and propagation of voids take place along deformation bands of which orientations coincide with the traces of slip planes. Microvoids in array were observed within dislocation cell bands and along cell walls.
(2) Units of fracture surface are areas bordered by deformation bands. Fine patterns on the fracture surface result from multiple slip band clusters.
The above features have been discussed and a kinematic model has been proposed for hydrogen embrittlement of iron. It has been shown that hydrogen transported by dislocations can produce sufficient supersaturation at deformation bands, where glide of dislocations on primary slip planes is blocked, and can stabilize elastic microcracks which will successively extend plastically and link together.