Corrosion behavior of new Q550qENH weathering bridge steel in marine atmospheric environment

Complex corrosion environments such as strong irradiation, variable climate and high temperature high humidity high salt condition in marine areas impose higher requirements on high-performance weathering bridge steel.A new low C+(Cu-Cr-Ni) alloyed Q550qENH weathering steel was taken as the research object while ordinary Q355B carbon steel served as the reference steel to investigate corrosion behavior in simulated marine atmospheric environment. Cyclic immersion test, scanning electron microscope(SEM), X-ray diffractometer(XRD) and electrochemical test were employed to study corrosion weight loss and rust layer evolution of Q550qENH steel in 3.5% NaCl solution at different corrosion cycles(72, 168, 360, 576 h). The results show that during 72 h to 360 h of corrosion, the surface rust layer of Q550qENH steel transforms from partial coverage to full coverage, and the corrosion weight loss rate increases rapidly with time extension. X-ray diffractometer analysis of corrosion products indicates that corrosion products of the experimental steel at different cycles consist of α-FeOOH, γ-FeOOH and Fe₃O₄, among which α-FeOOH accounts for the highest proportion, followed by Fe₃O₄ and γ-FeOOH. When corrosion time extends to 576 h, the corrosion weight loss rate of the experimental steel increased slightly, the corrosion products are mainly α-FeOOH, and the content of γ-FeOOH decreases. Electrochemical test results demonstrate that as corrosion time extends from 72 h to 576 h, the polarization curves of Q550qENH steel all shift to the right, and corrosion current density shows a trend of first increasing and then decreasing. This phenomenon means that, with the progress of corrosion the rust layer on Q550qENH steel surface gradually thickens and its compactness enhances. Compared with ordinary Q355B carbon steel, the weight loss rates of Q550qENH steel at different corrosion cycles are 53.56%, 67.38%, 96.45% and 74.85% of those of Q355B, respectively. In the later stage of corrosion, the content of α-FeOOH in corrosion products of Q550qENH steel is significantly higher than that of Q355B steel, and the rust layer is denser.This effectively inhibits the penetration of corrosive media into the matrix, thus endowing Q550qENH steel with better corrosion resistance than Q355B steel.