Corrosion mechanism and microstructure evolution of yttrium-doped marine steel

The effects of Yttrium dosage and heat treatment process on the microstructure, inclusions, and corrosion resistance of marine steel, as well as the electrochemical parameters on corrosion behavior were studied in this work. The results show that Yttrium mainly exists in Yttrium oxide and Yttrium sulfide. In the process of the optimal heat treatment temperature (800 degrees C-5h), the movement of grain boundaries is hindered by the nailing action of Y2O3, which makes the grain size refined. Yttrium can refine the corrosion products and improve the adhesion ability between the corrosion layer and the substrate, which can effectively improve the corrosion resistance of marine steel. The electrochemical parameters mainly affect the proportion and structure of alpha-FeOOH and alpha-Fe2O3 in the corrosion layer by affecting the ion diffusion rate or oxygen content, thus affecting the corrosion resistance property. With the increase of temperature, the diffusion coefficient of oxygen in solution increases, and the limiting current density also increases, which is not conducive to the formation of dense corrosion layer and will lead to faster corrosion speed.