Comparison study of rust layers formed on Q420 and weathering steel after 6 years of exposure in marine atmospheres

In this study, the corrosion products formed on Q420 and weathering steel (WS) after 6 years of exposure in marine atmospheres in Pingtan, Fujian Province in China was examined. The evolution of the rust layers in terms of surface and cross-sectional morphologies were observed by SEM, while the consisted phases on the Q420 and WS were detected by XRD. The protective effect of the rust layers on the steels was studied by the electrochemical tests. The results of weight loss indicated that the Q420 had a relatively higher corrosion rate than that of the WS steel. The SEM observation showed that the WS steel could form a relative compact with fewer cracks after a long time of exposure concerning the Q420 steel. The electrochemical tests suggested the rust layer formed in the initial stage for the Q420 steel showed a better protective effect than that one formed at a later stage, whereas a better protective effect of the rust layer was formed at the later stage for the WS steels.