Study of short-term corrosion behavior of Q345 steel in marine atmospheric environment

Abstract

This work studied the corrosion behavior law of Q345 steel exposed to 120 days in Qingdao marine atmospheric environment and the differences in corrosion behavior between the sunlit and shaded sides. The corrosion behavior law of Q345 steel was studied in detail by using weight loss method, electrochemical test, SEM, XRD and ultra-depth microscope. We found that the weight loss curve of Q345 steel under short exposure time still conforms to the power function form, and the corrosion rate increases in the early stage (15 d, 30 d) and decreases in the later stage. The change trend of polarization resistance (Rp) and corrosion current density (Icorr) obtained by electrochemical test corresponds to it. There are significant differences in the morphology and phase composition of the corrosion products of Q345 steel sunlit and shaded sides. On the one hand, the color of the rust layer is not the same, and the rust layer of the shaded side is loose and easy to fall off, and the corrosion is more serious. The three-dimensional morphology map after rust removal showed that Q345 steel had obvious local corrosion in the early stage of corrosion, and the depth of the corrosion pit on the shaded side was greater than that on the sunlit side. On the other hand, the ratio of (β + s)/γ * on the shaded side was greater than that on the sunlit side, and the protection ability of the rust layer on the shaded side was weak. The corrosion characteristics of Q345 steel are different between the sunlit side and the shaded side, and the corrosion of the shaded side is more serious. In engineering applications, we should consider the consequences of this phenomenon.