Explanation for Initiation of Pitting Corrosion of Stainless Steels at Sulfide Inclusions

An explanation for the chemical changes which lead to high‐rate dissolution of sulfide inclusions and hence to pit initiation is found in the composition changes induced in the sulfides as the steel cools from the melting temperature of the steel to the solidification temperature of the sulfide. In this temperature regime, on cooling, substantial chromium depletion of the steel may occur around the sulfide, and metallic phases rich in iron and depleted in chromium may precipitate within the inclusion. These chromiumdepleted zones can provide the high‐rate dissolution which triggers pitting corrosion. Experimental observations on artificial inclusions are supported by thermodynamic calculations. © 2000 The Electrochemical Society. All rights reserved.