Application of a Slip Dissolution-Repassivation Model for Stress Corrosion Cracking of AISI 304 Stainless Steel in a Boiling 42% MgCl₂ Solution

Dissolution-repassivation behavior of AISI 304 stainless steel (SS) in 42% MgCl₂ at 143 C was investigated using a straining electrode technique at different potentials. Dissolution current, i(t), was expressed as i(t) = J^∘⋅exp(−βt)⁠, where J^∘ is the initial dissolution current density (CD) of slip steps, β is the decay constant, and t is time. The results obtained were discussed on the basis of a film rupture model. The following equation has been formulated to give the crack propagation rate for transgranular cracking (TGC): da/dt = 2.02⋅10⁻⁶⋅J^∘/β⋅n^˙_s⋅[1−exp(−β/n^˙_s)]⁠, where n^˙_s is the formation rate of slip steps. The equation is consistent with the observed values of the crack propagation rate for TGC, which were obtained from stress corrosion cracking (SCC) tests by slow strain rate technique (SSRT) of AISI 304 SS in 42% MgCl₂ at 143 C. Furthermore, a potential (environmental factor) −n^˙_s (mechanical factor) − da/dt (SCC susceptibility) diagram was constructed.