ABSTRACT
Based on the fractographic evidence that HSC produced fracture surfaces showing 100% microvoid coalescence (dimples) [15] and the observation of shallow dimples (microdimpling) in the Hat cleavage facets at magnification higher than 5000X in some steels [6], it has been proposed that hydrogen enhances the processes of plastic How associated with the propagation of fracture by making dislocations move at reduced stresses at the crack tips. The movement of screw dislocations is generally considered to be favored. Further, it has been suggested that hydrogen is subsequently transported by dislocations to the regions ahead of cracks. If appreciable reductions or ftow stress due to dissolved hydrogen were localized to regions just ahead of crack tips, then embrittlement due to strain localization would be expected.
