Corrosion behaviour of superferritic stainless steels cathodically modified with minor additions of ruthenium in sulphuric and hydrochloric acids

Cathodic modification of stainless steels with minor additions of noble metals and platinum group metals has proved to be an effective approach for improving their corrosion resistance in many reducing environments. In the present work, the effect of ruthenium on the corrosion behaviour of superferritic stainless steel containing approximately 0.05 and 0.2 wt% ruthenium in H2SO4 and HCl were studied using potentiodynamic polarization techniques. An improvement of the corrosion resistance in both media was observed with increasing ruthenium contents. The degree of corrosion resistance was higher in sulphuric acid. Increasing the amounts of ruthenium additions shifted the corrosion potential to a more positive value and caused a reduction in the active to passive transition, the reduction being substantial with 0.20 wt% Ru.