Hydrogen uptake into steels used in corrosive or hydrogen-containingenvironment may cause degradation of material property leading topremature fracture under load bearing condition. Hydrogenembrittlement effect can appear in many forms of fracture behavior ofsteels including ductile and brittle fracture. It is well observed that highstrength steels exhibit intergranular or quasi-cleavage fracture. Whilethe hydrogen enhanced localized plasticity (HELP) and the hydrogenenhanced strain induced vacancy (HESIV) are considered as strongfactors for ductile fracture, hydrogen affected intergranular fracture isoften explained by the hydrogen enhanced decohesion (HEDE)mechanism. However, trace of plastic deformation is usually observedin the fracture surface, implying that hydrogen intergranular fracture isnot a simple decohesion behavior. On the other hand, the governingmechanism is still unclear for quasi-cleavage fracture while it is oftenobserved in high strength steels. Carbon containing martensitic steelexhibit quasi-cleavage fracture and cracks often show crystallographicrelationship with BCC or BCT lattice. In this paper we try to elucidate agoverning mechanism for intergranular and quasi-cleavage fracture bythe means of atomistic simulation.
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