Effects of Cerium on the Inclusions and Pitting Corrosion Behavior of 434 Ferritic Stainless Steel

The effects of Ce addition on the inclusions and the pitting corrosion behavior of ferritic stainless steel were investigated. The results showed that Ce2O3 center dot SiO2 and Ce2O2S inclusions were mainly found in 434 ferritic stainless steel containing 0.011% or 0.023 wt% Ce, which is the most appropriate addition of Ce that could contribute to produce the dispersive and fine rare earth inclusions. According to the thermodynamic analysis, Ce inclusions could be produced by rare earth elements combining with oxygen, sulfur, or preexisting SiO2. While the kinetic analysis and mechanism for formation of inclusions suggested that the area ratio of the pure SiO2 inclusion decreased with Ce increasing, and the difference of [Ce] concentration between the original inclusion interface and the SiO2 solid unreacted nuclear interface is the main reason to cause the different process of inclusion modification. Meanwhile, when the content of Ce was 0.011% or 0.023%, the resistance to pitting corrosion increased with the interface areas between the inclusions and the steel matrix decreasing. However, the excessive Ce addition resulted in the increase of size and quantity of inclusions, which would reduce the resistance to pitting corrosion.