Corrosion of austenitic stainless steels in hot concentrated aqueous NaOH solutions

When austenitic stainless steel is exposed to a hot concentrated aqueous NaOH solution, two corrosion products are formed at the surface: (i) nickel, building up as a superficial metallic layer, and (ii) mixed oxide of the type NaMO₂, finely dispersed in the underlying austenite. The electrochemical and crystallographic factors which govern the growth of these products have been studied. The thermodynamics and kinetics of their formation are discussed. The morphology of the mixed oxide small crystals and their orientation relationships with the metallic matrix are such that they may be liable to initiate cracks. This possibility of crack initiation by the corrosion products is presented as a working hypothesis for the extension of this study.