Effect of cerium on the initiation of pitting corrosion of 444-type heat-resistant ferritic stainless steel

Abstract

AbstractThe 444-type heat-resistant ferritic stainless steel is widely utilized in automotive exhaust pipes and solid oxide fuel cells, due to its excellent properties at elevated temperature. To meet the demands of significantly harsh service environments, rare earths were added in 444-type ferritic stainless steel. For the purpose of evaluating the effect of rare earths on pitting corrosion initiation, the metastable pitting corrosion behavior in 444-type ferritic stainless steel was studied through potentiodynamic polarization and potentiostatic polarization tests. The results demonstrated that pitting corrosion was initiated at the inclusion/alloy interface. The cerium alloying in 444-type ferritic stainless steel decreased the amount of preferential dissolution sites. The beneficial effect of Ce on pitting corrosion resulted from the formation of stable cerium oxides, as well as from the reduction in the amount and size of inclusions in 444-type ferritic stainless steel. In addition, electrochemical impedance spectroscopy test results revealed that cerium alloying enhanced the polarization resistance of passive films through insignificant thickness alteration.