An explanation for the chemical changes which lead to high-rats 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 thr steel to the solidification temperature of the sulfide, In this temperature regime, on cooling, substantial chromium depiction of the steel may occur around the sulfide, and metallic phases rich in iron and depicted in chromium may precipitate within the inclusion. These chromium-depleted zones can provide the high-rate dissolution which triggers pitting corrosion. Experimental observations on artificial inclusions are supported by thermodynamic calculations.