Corrosion behaviour of Al-containing high Cr ferritic oxide dispersion strengthened steel in nitric acid environment

Higher chromium containing 17Cr oxide dispersion strengthened (ODS) steel (Fe-16.78Cr-4.46Al-0.5Ti-0.45Y2O3-0.36Y) with the ferritic structure are a prospective applicant fuel cladding materials for the high operating temperatures of future advanced nuclear reactors system. In this study, the microstructure, passive oxide composition and corrosion resistance of the Al-containing 17Cr ODS steel in different concentrations of nitric acid were investigated by means of SEM, TEM, XPS and electrochemical methods. The corrosion result shows that with increasing concentration of 3 M–11.5 M HNO3, open circuit potential revealed nobler potential and the potentiodynamic polarization plots exhibited a shift in corrosion potential toward transpassive region. The boiling nitric acid test after 240 h exposed in 3 M–11.5 M HNO3 showed desirable corrosion rate of ∼0.075–0.25 mm/y. As the nitric acid concentration increased, the corrosion morphology varied from smaller pits to enlarged pits with groove-like features. The improved corrosion resistance of the ODS alloy is attributed to the alloy composition, nature of dispersed oxide and passive film nature, where Al2O3 is prominently enriched. The corrosion mechanisms of ODS steel is further discussed. •The ennoblement of corrosion potential with an increase in nitric acid concentration.•17Cr ODS with 4.5 wt % Al exhibited lower corrosion rate in boiling nitric acid test.•XPS passive film analyses showed enrichment of Al2O3 in the passive layer.•Dispersed particles act as the pit initiation site.•The ODS steel corrosion mechanisms is discussed.