Passivity breakdown on 436 ferritic stainless steel in solutions containing chloride

Passivity breakdown on 436 ferritic stainless steel (FSS) has been investigated in solutions containing different concentrations of chloride at 25 degrees C and interpreted in terms of the point defect model (PDM). The measured near-normal distributions of passivity breakdown potentials for 436 FSS under experimental conditions are in good agreement with the calculated results according to the PDM. The linear dependence of breakdown potential on the square root of potential scanning rate, which was described by the PDM, provides the estimation of the critical concentration of condensed vacancies at the metal/film interface, which leads to the passivity breakdown. This value is in good agreement with that calculated from the microstructure properties of the alloy substrate and the barrier layer of the passive film. This study demonstrates the validity of the PDM in describing the passivity breakdown on 436 FSS in NaCl solutions. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.