ANOTHER GRAIN-BOUNDARY CORROSION PROCESS IN SENSITIZED STAINLESS-STEEL

This work investigates the intergranular corrosion of a sensitized Typ e 43 0 stainless steel in 1N H2SO4. Once the grain boundary groove is formed by dissolution of the Cr-depleted material, a second form of lo calized corrosion commences within minutes and replaces the Cr-depleti on mechanism. The second-mechanism attacks both the bulk grains (of no rmal Cr content) and the Cr-depleted alloy. This is shown by groove wi dths that are much larger than the Cr-depleted zone widths. Gas bubble s, deduced to be hydrogen, egress from-the grain boundary grooves, ind icating a sizable potential drop within the grooves and the likelihood that the second corrosion process is caused by the IR phenomenon rece ntly found to account for crevice corrosion in iron. The IR mechanism could also account for the observed corrosion under the lacquer at the sample edges.