Influence of Anions on the Corrosion Behavior of 9Cr-1Mo Ferritic Steel in Aqueous Media

Abstract

Modified 9Cr-1Mo steel is used as steam generator material in prototype fast breeder reactors, owing to its good corrosion resistance, creep, and thermal conductivity characteristics. In the present study, the corrosion behavior of modified 9Cr-1Mo steel in aqueous environments containing various corrosive ions at potentiodynamic polarization conditions is reported. In chloride-exposed samples, randomly distributed dense shallow pits were seen, whereas mixed anions (, Cl−, and ) in fresh water resulted in deeper pits uniformly distributed on the entire surface. Laser Raman spectroscopy studies revealed the formation of Fe-oxides/hydroxides and Cr(VI) species, except in alkaline solution. A very thin film of only Fe-oxides (Fe3O4, γ-Fe2O3, and α-Fe2O3) was identified in an OH– ion-dominated solution. X-ray photoelectron spectroscopy results confirm the corroded surfaces comprised of Fe, Cr, and Mo-oxides of varying composition and enrichment of Mo-oxides in alkaline solution. Chloride ions present in the corroded layer influenced the pitting corrosion in neutral chloride and fresh water solutions. Field emission scanning electron microscopy images revealed abundant crystalline lepidocrocite with laminar morphology and doughnut-type magnetite together with pits on the samples exposed in neutral chloride and fresh water media.