Effect of bicarbonate concentration on corrosion of high strength steel

This research evaluates the passivation process, in relation to the anodic and cathodic reactions, in deoxygenated solutions of different bicarbonate concentrations. Two types of API-X100 steel microstructures were examined. They are similar to near fusion heat affected zones (HAZs) which were produced by special thermal cycles. By monitoring the open circuit potentials, the passivation process exhibited electrochemical signs that it forms faster with higher bicarbonate concentration. During cyclic voltammetry, bicarbonate in concentrations less than 0·1M impedes the passivation, by catalysing the anodic dissolution. In higher concentrations, bicarbonate seemed more protective in facilitating the development of thicker passive films, from an electrochemical perspective that encourages corresponding physicochemical investigations in the future. The transpassivation seemed to depend more on the chemistry of the passive film than on the formation of FeCO₃. Cooling down the HAZs at high rates could make them more corrosion resistant, but probably of less protective corrosion products.