Effect of silicon content on the corrosion properties of calcium-modified weathering steel in a chloride environment

The effect of Si on the corrosion properties of Ca-modified weathering steel was evaluated with respect to the formation behavior of complex inclusions in the steel and the dissolution behavior of the inclusions in thin water film by pH measurement and electrochemical impedance spectroscopy (EIS): To understand the Long-term effect of Si, a cyclic corrosion test and an actual atmospheric exposure test were performed in a marine environment. Ca-modified weathering steel with a Si content up to 0.4% did not form complex inclusions containing silicon dioxide (SiO2), and no harmful effect of Si on the corrosion resistance was observed. Although the short-term results of pH measurement and EIS testing showed that high Si content (0.62%) indicated an adverse effect on the corrosion resistance, the long-term test results of cyclic corrosion and atmospheric exposure revealed that Ca-modified weathering steel containing 0.62% Si had the best corrosion resistance and the highest hardness value of the rust layers that formed on the steel surface, among all other steel specimens. Si content up to 0.62% in Ca-modified weathering steel can provide beneficial effects on the corrosion resistance as a result of additional modifications of the rust structure, rather than any harmful effect as speculated.