AFM study of the early corrosion of a high strength steel in a diluted sodium chloride solution

The high strength steels employed as reinforcement in pre-stressed concrete structures are drawn wire steels of eutectoid composition with a pearlitic microstructure. This work is focused on the study, by atomic force microscopy, of the early stages of the corrosion of such steels as a consequence of their exposition to a sodium chloride solution. The obtained images show the pearlitic microstructure of the steel, with a preferential attack of the ferrite phase and the cementite acting as a cathode. The corrosion rate was determined by calculating the amount of material lost from a roughness analysis. The obtained results are in good agreement with the predictions of Galvelel's theory, according to which the corrosion rate slows down as the pit depth increases.