Investigation of Intergranular Corrosion Propagation Promoted by Interactions between Sensitized Grain Boundaries using Closely Packed Electrode Arrays

Intergranular corrosion (IGC) can be defined as the phenomena in which the corrosion rate of the grain boundary is higher than that of the bulk grain body. Austenitic stainless steels can become “sensitized” to this type of corrosion when the bulk metal experiences a temperature excursion above that necessary to make chromium carbides dissolve. As the metal cools, chromium carbide preferentially precipitates at the grain boundaries causing the local Cr concentration adjacent to the grain boundary to decrease relative to the Cr concentration in the bulk of the grain (Figure 1). This relative drop in Cr concentration adjacent to the grain boundary is called sensitization. A single loop electrochemical potentiokinetic reactivation (SLEPR) method, originally developed for the nuclear industry and now an ASTM Standard, will be used to quantitatively measure the DOS of material in each array. A modification of this test can be made to show that IGC could occur in sensitized stainless steel adjacent to pits that grow by the acid-pitting mechanism.