Results are presented for the corrosion process of low carbon steel, under the influence of the combined action of chloride and sulfate ions. The rust composition, the corrosion rates, and the corrosion potential of the rust layers are analyzed. An increase of the relative magnetite content as the corrosion rate increases was found for the long-term corrosion. The corrosion potential can be used to distinguish between lower and higher corrosion rates; more importantly, a concentration (SO2—4 = 10—4 M and Cl— = 1.5 × 10—3 M) of the pollutants where a decrease of the corrosion rate is significant was found.