Role of inclusion and microstructure on corrosion initiation and propagation of weathering steels in marine environment

Abstract The present research examined the effects of inclusions and microstructure on the initial marine corrosion and evolution of corrosion products in weathering steels by using first-principle modeling and various highly-sensitive analyatical techniques including in-situ scanning vibrating electrode technique (SVET), scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDS), x-ray diffraction (XRD), and electrochemical workstation. The results demonstrated that CaS in the (Al, Mg)Ox-CaS inclusion formed in both Q500qE and Q370qE steels preferentially dissolved and triggered the initial corrosion. The acidic environment created between the inclusions and the iron matrix further promoted the dissolution of the inclusions. Moreover, due to the discrepancy in corrosion tendency, galvanic couples generated between the bainite ferrite (BF) phase and martensite/residual austenite (M/A) island in the Q500qE steel as well as the ferrite phase and pearlite phase in the Q370qE steel, accelerating the initial corrosion. In addition, pearlite facilitates a faster spread rate of local corrosion compared to bainite. Furthermore, with prolonged exposure, Q500qE steel exhibited more uniform and dense structure of the corrosion products layer, demonstrating a higher corrosion resistance than Q370qE steel. Finally, the mechanistic model was established to illustrate the influence of inclusions and microstructure on corrosion initiation and propagation of weathering steels.