Influence of calcination of stainless steel OC4004 covered with alumina or ceria carrier layers on their passive state in different acid media

A comparative investigation has been carried out on the corrosion behaviour of thermally treated stainless steel (SS) OC4004 covered with Al 2 O 3 or Ce 2 O 3 -CeO 2 layers (systems Al 2 O 3 /SS (t.t.) and Ce 2 O 3 -CeO 2 /SS (t.t.) ) electrodeposited on in solutions of 0.1 N HN0 3 and 0.1 N H 2 SO 4 . It has been established that in N03- containing medium SS (t.t.) tends to self-passivation. The thermal treatment of the system Al 2 O 3 /SS eliminates the protective effect of the electrodeposited Al 2 O 3 layer in the corrosion media investigated due to its mechanical cracking and the formation of galvanic Al 2 O 3 /Fe pairs. Electrodeposited ceria strongly enhances the corrosion resistance of the system Ce 2 O 3 -CeO 2 /SS both before and after thermal treatment. The protective effect of the Ce 2 O 3 -CeO 2 layers is found to be due to the enrichment of Cr in the passive film provoked by these layers as well as to effective cathodes causing a shift of the steady state potential in the system Ce 2 O 3 -CeO 2 /SS (t.t.) in a positive direction.