Etude de la corrosion localisée par piqures des aciers inoxydables 304L et 430

Abstract

Stainless steels are very resistant to uniform corrosion grace to the presence of oxide film on the surface, very thin and very protective. They are susceptible to various types of localized corrosion, and particularly to pitting which appears under certain conditions when the material is used in contact with a chloride medium. The objective of our work is the study of the influence of the deformation by traction and rolling on corrosion in NaCl 3% of the stainless steels 304L and 430, by taking in considerations various rates of lengthening. Techniques used in this study are polarization and electronic microscopy, which allowed us, to separately analyze the various stages of development of pitting (starting, propagation, repassivation) and to analyze the effect of the deformation on the cited parameters. Obtained results show that the repassivation potential of 304L stainless steel decrease when the rate of deformation by rolling increase; it is the same with the potential of corrosion, implying a greater susceptibility to corrosion, especially by pitting. It should be noted that the various rates of deformation applied to the 304L, do not have large influences on the pitting potentials, which remain practically identical. Relatively to corrosion behavior of materials in NaCl 3% after traction tests at various lengthening rates, let us note that the repassivation potential does not depend directly on the rate of lengthening in the case of steel 430, which is not the case of 304L steel. Concerning 304L and 430 steels, noblest corrosion potential corresponds to the weakest lengthening rate. In the case of A % = 2.18, corrosion potential of 304L steel is nobler compared to the other lengthening rates and in the case of 430 steel,the noblest corrosion potential was recorded for the lengthening rate A % = 1.82. Finally, a comparative study of the behavior of steel 304L and Ti6Al4V alloy in 30g/l solution showed that Ti6Al4V is more resistant than 304L stainless steel under the conditions considered.