Influence of Microstructure on Corrosion Behavior of Bridge Steels in Simulated Ocean Tide Zone

Bridge steels with different heat treatment processes were used for polarization curve measurement in 3.5% NaCl solution and alternate immersion accelerated corrosion testing in artificial seawater. The corrosion evolution of bridge steels was studied by weight-loss method and corrosion product analysis. The results showed that the microstructure of the bridge steels was changed from non-equilibrium granular bainite to equilibrium temper sorbite after drawing temper. Because of the grain refinement and uniformity of structure, the corrosion resistance of temper sorbite microstructure was better than that of granular bainite microstructure in simulated ocean tide zone. As carbide grains were dispersive and fine, the seawater corrosion resistance of the sample tempered at 640 ℃ was the best in simulated ocean tide zone. The rust layer formed through alternated immersion test provided protection for the substrate steels, but α/γ in the outer rust layer FeOOH of hot rolled sample with granular bainite microstructure was relatively low and the percentage of α-Fe in inner rust layer was relatively high, resulting in fairly poor protection capability of the rust layer.