La corrosion par piqûres d'aciers inoxydables austéno-ferritiques dans l'eau de mer synthétique

Influence de la composition chimique et de la teneur inclusionnaire

Influence of chemical composition and inclusion contents on pitting resistance of duplex stainless steels in synthetic sea water

¹ Laboratoire de Mécanique et Matériaux, ESST, Tunis (Tunisie)
² Laboratoire de Microstructure et Mécanique des Matériaux, ENSAM, Paris

Abstract

Duplex stainless steels crevice and pitting corrosion resistance in synthetic sea water is studied. Conventional electrochemical tests and image analysis techniques are used. Three commercial steels are examined. The forged material has the best behaviour, whereas cast materials, in spite of their high nitrogen contents, have a lower corrosion resistance. Micrographic studies show a good correlation between pittings distribution and inclusions distribution and reveal that gamma phase behaviour is more affected by inclusions. The metallurgic purity of products seems to be the most important parameter in this type of corrosion. Consequently, the PREN index is questionable in pitting corrosion grading of these steels because it does not take into acount the inclusions effect.