Rust Scale Structure and Anti-corrosion Mechanism of Unpainted Weathering Steel in Coastal Area Environment

Abstract

The corrosion thickness loss of a Ni-containing weathering steel and a common low-alloy steel Q420 was comparatively studied, by means of a dry- wet cyclic immersion test, which aims to simulate the atmospheric environment at coastal area. SEM and Raman spectroscopy were used to characterize the morphology, microstructure and phase composition of the formed rust scales. The results show that Ni has an important impact on the structure of weathering steel rust scale; the rust scale on weathering steel exhibits layered structure with an inner layer consisted mainly of α- Fe OOH, which seems to be stacked with small clusters resulting in a compact layer with good continuity and protectiveness. Besides the formed rust scale is strongly adhesive to the steel substrate so that to ensure the integrity of the rust scale during exposure in coastal environment with high salt content. In the contrast, the rust oxide scale on Q420 steel is so loose and porous with large sized grains of γ-Fe2O3 and Fe3O4hence its corrosion resistance is very poor. Furthermore, a relatively flat interface may not be favorable to the adhesion between the rust layer and Q420 steel substrate.