The initiation of localized corrosion of types 430 and 443J1 ferritic stainless steels was evaluated in 0.15 mol dm(-3) Na2SO4 solution. A liquid-phase ion gun (LPIG), a silver microelectrode covered with a silver chloride layer, was cathodically polarized to generate Cl- in the vicinity of the stainless steel polarized at 0.4 V-SSE. Contact of the stainless steel surface with the Cl- -concentrated environment by the LPIG operation induced a rapid increase in anodic current flow through the stainless steel electrode after the induction period t(d) and consumption of the cathodic electric charge Q(d) by the LPIG microelectrode. Numerical modeling using the LPIG microelectrode current for t(d) gave a critical Cl- concentration [Cl-](d) needed for the initiation of localized corrosion. These parameters obtained by LPIG tests showed that type 443J1 stainless steel was superior to type 430 stainless steel in localized corrosion resistance. AES depth profiling of the stainless steel surfaces after the LPIG operation revealed enrichment of Cl in the outermost oxide film as well as decreased film thickness. The mechanism of degradation of the stainless steel surface due to contact with the Cl- -concentrated solution is discussed. The adsorption of Cl- on the oxide surface is thought to be a trigger of the oxide degradation. (C) The Author(s) 2016. Published by ECS.