DFT study on the mechanism of inclusion-induced initial pitting corrosion of Al-Ti-Ca complex deoxidized steel with Ce treatment

The mechanism of inclusion-induced initial pitting corrosion of Al-Ti-Ca complex deoxidized steel with Ce treatment was studied by the experimental investigation and theoretical calculation. To figure out which phases of complex inclusion containing different components induced initial pitting corrosion, the scanning electron microscope (SEM) analysis, the continuous immersion experiments and density functional theory (DFT) calculation were conducted. Two types of inclusions and different pit morphologies were observed. The pit initially occurred at the sulfide inclusions (MnS and Ce2O2S) rather than the steel matrix due to the lower the electronic work function (EWF) of this compound compare to the steel matrix and other phases. In addition, the Ce-rich inclusion possessed the higher pitting corrosion resistance than the same type of inclusions. Finally, a schematic diagram was established to explain the mechanism of the different inclusions in initiating and proceeding pitting corrosion.