Rust formation and corrosion performance of Si- and Al-bearing ultrafine grained weathering steel

Abstract

A high Si, Al type ultrafine-grained (UFG) weathering steel was produced by the multi-pass warm rolling method, and its corrosion resistance was estimated by a cyclic wet/dry corrosion test using chloride ions. The Si- and Al-bearing UFG steel exhibited excellent corrosion resistance in comparison with Si–Mn carbon steel (SM). EPMA and TEM analyses showed that Si and Al mainly exist in nano-scale iron complex oxides in the inner rust layer formed on the developed steel. The Al K X-ray spectrum of Al 2O 3 and metallic Al had different peak positions due to chemical shifts, and that of the test sample was the same as that of Al 2O 3 in the EPMA analysis. This result suggested that Al was present in the complex oxides as Al 3+. In the same way, Si was identified as an intermediate state such as Si 2+ in the complex oxides of the inner rust. EIS (electrochemical impedance spectroscopy) measurement of the corrosion test samples revealed that the rust resistance ( R rust) and corrosion reaction resistance ( R t) of the developed steel were much larger than those of SM. It was found that nano-scale complex iron oxides formed in the lower layer of iron rust in the developed steel, resulting in increased R rust and R t, and finally suppressing corrosion.