Optimize Ni, Cu, Mo element of low Cr-steel rebars in tropical marine atmosphere environment through two years of corrosion monitoring

To optimize Ni, Cu, Mo element content of low Cr steel rebars in tropical marine atmosphere environment, five newly steel rebars were exposed in Dalat to carry out the outdoor exposure tests including weight loss method, surface characterization method and electrochemical test. The results show that when 0.15 wt% Mo is added in the steel rebar, the corrosion resistance is 31.8% higher than that of the steel rebar with 0.3 wt% Cu. The corrosion resistance of 0.3 wt% Cr added steel rebar is 63.4% higher than that of 0.2 wt% Ni added steel rebar. With the addition of 0.3 wt% Cu and 0.3 wt% Cr, the corrosion resistance is 46.3% higher than that of the steel rebar with 0.2 wt% Ni and 0.15 wt% Mo. Mo and Cr are the main elements to improve the protection of steel rebar rust layer. The corrosion products of the five steel rebars are composed of alpha-FeOOH, gamma-FeOOH and Fe2O3 or Fe3O4. The higher the content of Cr is, the higher the ratio of alpha - FeOOH to gamma-FeOOH (alpha/gamma) in the rust layer becomes. The protective layer composed of CaMoO4 and Fe-2(MoO4)(3), formed by molybdate in alkaline environment hinders the further corrosion of steel rebars. Cr(OH)3 produced by hydrolysis of Cr in low alloy steel inhibits the growth of FeOOH in rust, resulting in the decrease of FeOOH particle size and the rust layer more compact. On the whole, the newly designed low alloy steel rebar with a little of 1.6Cr-0.15Mo elements can be well used in tropical marine atmospheric environment.