Influence of Copper Content of the Base Steel on the Corrosion Behavior of Nickel-coated Steel Sheets

Influence of copper content in a base steel on corrosion resistance of a nickel-coated steel sheet in solutions as strongly corrosive high-acid beverage has been studied, and the following facts were revealed: Copper addition to the base steel greatly improves the corrosion resistance of the nickel-coated steel sheet in the citric acid and sodium chloride solution. This improvement is resulted from a reduction in the couple current between the nickel and the base steel in the pinholes formed in the nickel coating layer. The reduction in the couple current is considered to arise from shifting corrosion potential of the copper-added steel to the noble direction and increasing in anodic polarization. The enrichment of copper on the corroded steel surface is considered to bring about great changes in electrochemical properties. The decrease in the couple current between the nickel and the base steel is also obtained under the variation of an area ratio of anode to cathode. Copper addition to the base steel also gives high corrosion resistance to the nickel-coated steel sheet in the simulated beverages, such as those containing citric acid, citric acid and sodium chloride, malic acid and, lactic acid except containing phosphoric acid.