Corrosion Mechanism of Q235A under 3.5% NaCl Salt Spray

Abstract

Low-carbon steel Q235A is the main material used in marine construction, but it experiences corrosion because of salt spray and seawater exposure. In this study, we investigated the corrosion performance of Q235A in the presence of 3.5% NaCl salt spray. We characterized the microstructure of the material using electron backscattered diffraction, scanning electron microscopy, and specimen weight loss. The phases and morphologies of the corrosion products were then analyzed after salt-fog corrosion testing. The degree of coverage and compactness of surface corrosion products gradually increased from the 24 to 96 hours in the salt spray environment. Under short-term corrosive conditions, surface corrosion products were primarily composed of a loose, porous layer of flocculent γ-FeOOH. With increasing time, the corrosion products gradually changed to a lump-like and block-like dense structure of β-FeOOH and α-FeOOH. The results of electrochemical polarization tests of the corroded steel samples showed that the γ-FeOOH might accelerate corrosion, and that β-FeOOH and α-FeOOH inhibit corrosion.

Fig. 6 Corrosion micrograph of Q235A steel, the corrosion time of (a), (b), (c), (d) were 24, 48, 72 and 96 h, respectively.