La passivation de l’acier inoxydable AISI 321 en milieu sulfurique normal

Influence de la présence d’ions de l’iode

Comparative study of the 321 austenitic stainless steel passivation in a normal sulfuric acid solution

Laboratoire des matériaux, ISITEM, Université de Nantes

Abstract

This work is established to study the AISI 321 austenitic stainless steel passivation in a normal acide sulfuric solution with pH = 0 in the presence or not of the iodine ions (I^–). Three other steels were also studied as reference.

The effect of the presence of 0,1 KI molar in solution, is the passivation peak disappearance and the zero current potential transfer to more noble potentials, this showing the inhibitor effect of iodine ions. The profitable effect of iodine ions on the 321 steel type corrosion resistance was particularly confirmed during the repassivation experiment of the depassivated tensile stressed sample. The obtained results showed that the repassivation speed of the passive film damaged by the tensile strength experiment of the 321 steel type was quicker in the iodine ions presence. The electrochemical behaviour of the same steel, in the presence of the others halides ions, was also studied.

The Auger spectroscopy analysis, the weight loss mesurement, and the scanning acoustic microscopy of a 321 steel sample anodised at the potential corresponding to + 550 mV/ECS, showed the existence of a preferential dissolution at the grain boundary.