Effect of tensile orientation on stress corrosion cracking in SUS 304 steel single crystals.

The susceptibility to stress corrosion cracking (SCC) and its oriented crack plane in boiling 42% MgCl2 solution at 416K were examined in SUS 304 steel single crystals with the tensile axes in five orientations.The threshold stress to SCC initiation which depended on the tensile axis orientation decreased with increasing Schmid factors in the primary slip system. The threshold stress corresponded to nearly 80% of the 0.2% yield strength (or critical resolved shear stress) in oil at 416K. Many cracks initiated at slip-steps induced by the plastic deformation.The morphology of fracture also depended on the tensile axis orientation: The single crystals in all orientations except the region near ‹100› tensile axis were characteristic of river-like pattern, which was formed by the crack growth along ‹110› direction on {110} plane. However, the single crystal near ‹100› orientation was characteristic of fan-shaped pattern formed mostly by {100}-‹110› crack growth.The above results imply that the SCC propagation occurs by the active dissolution of Lomer-Cottrell sessile dislocation in corrosive environment.