Effect and Mechanism of Ca2+ on the Corrosion of Hot-Rolled Strip in Turbid Ring Water Containing Cl− and SO2- 4

Abstract

After the hot-rolled strip is cooled by laminar flow, Cl−, SO2- 4 and Ca2+ in turbid ring water will remain on the surface of the steel plate, which makes the steel plate corrode during storage in a humid environment. In order to clarify the effect and mechanism of residual Ca2+ on the corrosion of strip, simulations were carried out by setting different Ca2+ concentrations in solutions containing Cl− and SO2- 4 with different times of alternate immersion. Through the analyses of corrosion pit morphology, corrosion rate, electrochemical characteristics and corrosion products, it was found that the corrosion rate increased first and then decreased regardless of the Ca2+ concentration. When the Ca2+ concentration is 50~300 mg/L, the increase of Ca2+ concentration will increase the adsorption rate of the matrix and increase the corrosion pits. In addition, the corrosion rate decreases, the depth of corrosion pit becomes shallow and the polarization resistance increases due to the inhibition of the calcium salt layer, and the increase of Ca2+ concentration will enhance the inhibition of corrosion. When the Ca2+ concentration is 1000 mg/L, the denseness of the calcium salt layer is easily destroyed and the corrosion is intensified due to the large amount of adsorption of ions by the matrix.