Fractographic Approach to the Mechanism of Hydrogen Embrittlement

In high strength steel, for example, the embrittlement increases proportionally to an increase in the strength and the amount of absorbed hydrogen. Also, from a mechanical point of view, it makes the surface strain conditions more embrittling than that of surface stress. At this time, the fracture mechanism and why it becomes so susceptible to an increase in hydrogen presence are not quite understood. Recently, however, two theories have been getting increased attention. According to Troiano lattice embrittlement, hydrogen loosens the intermolecular bonding forces, and this idea was further developed by Oriani et al. The other theory as explained by Beachem focuses on hydrogen assisted fracture. In the case of iron, there are not many fractographic investigations, although Fe-Si single crystals have been investigated by Tetelman et al. in the past. Vehoff et al. used Fe-2.6% Si crystal at 10 mPa to 100 Kpa and investigated embrittlement mechanism as illustrated with numerous photographs from other researchers. Lynch has conducted fractography on many metals and has shown that hydrogen embrittlement fracture and liquid metal embrittlement fracture surfaces are almost the same. Gerberich has used acoustic emission (AE) for Fe-3% Si and 101 KPa hydrogen with tensile orientation along [100] and failure surface of (100). Details of other research works are given for fractures in Ni multi O crystal along {111} planes, as well as those for commercial and pure iron.