Effects of Cl- Ions on the Corrosion Behaviour of Low Alloy Steel in Deaerated Bicarbonate Solutions

The effect of Cl-ions on corrosion evolution of NiCu low alloy steel during immersion tests (up to 70 days) in deaerated 0.05 mol/L bicarbonate solutions was investigated by in-situ electrochemical measurements combined with X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) characterisations. The results showed that due to the acceleration of substrate dissolution in the presence of Cl-, corrosion of NiCu low alloy steel underwent only two stages, i.e., a quick oxidation process followed by a final metastable passive state, without the initial slow anodic dissolution as observed in the C1(-)-free bicarbonate solution. The main components of the formed rust layer in the Cl--free bicarbonate solution were alpha-FeOOH and Fe3O4, while apart from alpha-FeOOH, Fe-6(OH)(12)CO3 was found evident instead of Fe3O4 in the Cl--containing solution. Metastable pits were only found in the Cl--containing solution where Cl- accumulated after the immersion test, confirming the attack of Cl-on the substrate after penetrating the formed corrosion product layer. Copyright (C) 2016, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited. All rights reserved.