CORROSION BEHAVIOR OF DUPLEX STAINLESS-STEELS CONTAINING MINOR RUTHENIUM ADDITIONS IN REDUCING ACID-MEDIA

The dissolution behaviour, as well as the time, potential and concentr ation dependence of HSO4-/SO42- and Cl- accumulations measured by an i n situ radiotracer method on surface oxide-layers of duplex stainless steels containing various amounts of ruthenium as additive are present ed and discussed. Several independent techniques, such as mass loss te sts, potentiodynamic responses, radiotracer and ICP methods, were used to characterize the complex features of the passivation phenomena of steels modified with ruthenium. The experimental results reveal that t he interaction of bisulfate/sulfate ions with passive oxide layer is s tronger than those of chloride ions on the stainless steels studied. B oth the extent and the strong character of bisulfate/sulfate accumulat ion are more likely related to the redistribution of the main alloying components (Cr, Ni, Mo) as well as the Ru in the surface oxide-film f ormed on steels passivated spontaneously in dilute HCl and H2SO4. It i s found that the ruthenium additions to the base duplex stainless stee l significantly increase the corrosion resistance in reducing acid env ironments, There is evidence of anodic inhibition and this seems to be responsible for the observed increased corrosion resistance of the du plex stainless steels with small ruthenium additions.