Pitting Resistance of Pure Fe-17%Cr Alloys : Consequences for Localized Corrosion Modeling

Abstract
Pitting corrosion was observed on a high purity Fe-17Cr alloy in 0.02M NaCl solution of pH 6.6 at high anodic potential (+ 550 mV/SCE). Potentiostatic electrochemical noise measurements were performed, revealing the presence of a characteristic current noise below stable pitting, differing strongly from that observed on a series of AISI 430 type 17% Cr stainless steels, with respect to the frequency of occurrence and shape of the metastable events. These rather small, infrequent and long-lived events exhibit a sudden increase followed by a slow decrease with a decay time ≈ 100 s. Arguments are given in favor of a pit initiation process occurring at some weak points of the passive film, distinct from scratches. In the light of the present study, analysis of previous results obtained on some AISI 430 type inclusions containing industrial stainless steels reveal that, after a certain polarization time, pitting may also occur by local breakdown of the passive film.