Effect of Crystal Grain Size on Corrosion Resistance of Weathering Steels in Atmosphere

The atmospheric corrosion resistance of four types of weathering steels with mean grain sizes of 6, 10, 19 μm, and 60 μm were studied using accelerated industrial atmospheric corrosion test in lab. Thus the steels were subject to dry-wet cyclic immersion tests, and the morphologies and process of the rust layers were analyzed by means of optical metallography, X-ray diffraction, and electrochemical impedance spectroscopy. It was found that during the initial corrosion period when the inner rust layer was not formed, the fine-grained weathering steels had a higher corrosion rate than the coarse-grained one. During the later corrosion period when the inner rust layer had been formed, both the coarse-grained and fine-grained weathering steels had nearly the same corrosion rate. Though grain-refining helped to greatly improve the mechanical properties of the weathering steels, it had little effect on the atmospheric corrosion resistance and the compactness of the rust layers of the weathering steels.