Synergistic effects of chromium depletion and ohmic potential drop on the susceptibility to intergranular corrosion and hydrogen embrittlement of sensitized stainless steel

This paper explores the consequences and analyzes the kinetics of the intergranular corrosion of the Cr-depleted zones in sensitized stainless steel. The corrosive attack of the Cr-depleted zones generates occluded grooves along the grain boundaries (g.b.) which are unable to passivate under the prevailing potential. The g.b. grooves deepen and branch beneath the surface until they eventually perforate the steel membrane. Furthermore, the resulting local electrode potentials within the g.b. grooves allow for hydrogen evolution even though the outer surfaces of the steel are held at much more oxidizing electrode potentials which prohibit this reaction. Using a Devanathan-Stachurski cell it was found that part of this ohmic (IR)-produced hydrogen dissolves into the steel. The results are explained by the IR potential shift mechanism. Similarities and differences between this anodic charging and the conventional cathodic hydrogen charging experiments are also presented. (C) 1997 Acta Metallurgica Inc.