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To determine whether large sudden pH and Cl− concentration changes occur during the crevice corrosion of Fe-16Cr, as in the case of Fe-18Cr-10Ni-5.4 Mn, simultaneous measurement of the pH and Cl− concentration was performed in 0.01 M NaCl (pH 3.0). The corrosivity of the crevice solution was different before and after crevice corrosion initiation, and the sudden changes in the pH and Cl− concentration inside the crevice were the same as those for Fe-18Cr-10Ni-5.4 Mn. The incubation period was characterized by weak acidification (pH 1.6− 2.0) and a small accumulation of Cl−(0.1− 0.3 M). The growth period was characterized by strong acidification (pH≤ 1.0) and a large accumulation of Cl−(≥ 1.0 M). At the crevice corrosion initiation site, a metastable pit was observed and a S signal was detected from the residual in the pit. It can be concluded that the crevice corrosion of Type 430 stainless steels is …