Role of Temperature in Stress Corrosion Cratking of Iron in Nitrate Solutions

Abstract

Stress corrosion cracking (SCC) of Armco iron has been examined in 5 M NH₄NO₃ at 25–100°c under open-circuit conditions and also at controlled potentials and pH corresponding to the thermodynamic stability of Fe₃O₄ and Fe₂O₃. Potential and pH measurements under open-circuit conditions have indicated that the Fe₂O₃ film formed quickly on the corroding surface at high temperatures, but did not form at 25°c. At controlled potentials and pH the sec rate was high in the presence of the Fe₂O₃ film, even at room temperature, whereas in the presence of the Fe₃O₄ film it was, at a given temperature, lower by up to three orders of magnitude. The high SCC rate at high temperatures under open-circuit conditions was ascribed primarily to the rapid formation of the passivating γ–Fe₂O₃ film.