THE EFFECTS OF CHROMIUM AND MOLYBDENUM ON THE CORROSION BEHAVIOR OF FERRITIC STAINLESS-STEELS IN BOILING ACETIC-ACID SOLUTIONS

The corrosion behavior of type 410L, 430, 434, 444 and XM27 ferritic stainless steels in boiling acetic acid solutions was investigated by corrosion tests and physicochemical measurements. Corrosion rates of type 434, 444 and XM27 stainless steels containing more than 16% chromium and a small percentage of molybdenum were far smaller (near zero) in aqueous acetic acid solutions in comparison with those of type 410L and 430 stainless steels, but in the non-aqueous acetic acid solution their corrosion rates were very high. Electrochemical measurements revealed that type 434, 444 and XM27 ferritic steels are more stable than type 410L and 430 steels in aqueous solutions since increasing chromium and molybdenum enhance the passivity. Types 434, 444 and XM27 stainless steels were corroded in the non-aqueous solution, because of no passivation. Surface analysis revealed that the corrosion of type 434, 444 and XM27 stainless steels was inhibited by passivation in the aqueous solution, while they were corroded in the non-aqueous solution.