Another grain boundary corrosion process in sensitized stainless steel

This work investigates the intergranular corrosion of a sensitized Type 430 stainless steel in 1 N H sub 2 SO sub 4 . Once the grain boundary groove is formed by dissolution of the Cr-depleted material, a second form of localized corrosion commences within minutes and replaces the Cr-depletion mechanism. The second mechanism attacks both the bulk grains (of normal Cr content) and the Cr-depleted alloy. This is shown by groove widths that are much larger than the Cr-depleted zone widths. Gas bubbles, deduced to be hydrogen, egress from the grain boundary grooves, indicating a sizable potential drop within the grooves and the likelihood that the second corrosion process is caused by the IR phenomenon recently 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.