INTRODUCTION
AISI 304 SS are well known for their good resistance to corrosion phenomena until the passive film is homogeneously present on their surface. If the material is exposed to thermal treatment in the range of temperature 500-700°C precipitation of carbides (type Cr23C6) appears, which weakens the passivity and allows intergranular corrosion to occur.
Understanding the correlation between carbide precipitation and grain boundary (GB) structure may provide a method of preventing localised corrosion. Several studies [Y Zhou, K.T. Aust, U. Erb, G. Palumbo. Scripta Materialia 45 (2001) 49, U. Erb, H. Gleiter, G. Shwitzgebel. Acta Met. 30 (1982) 1377] demonstrated that boundaries associated with low ? coincident site lattices (CSLs) show reduced susceptibility to impurity segregation and higher resistance to intergranular corrosion.
Electrochemical techniques are able to give important information since the pioneering works of Pednekar [S. Pednekar and S. Smielowska, Corrosion 36, 565 (1980)] and Cihal [V. Cihal, Intergranular Corrosion of Steels and Alloys, Materials Science Monographs no. 18, Elsevier, N.Y. (1984)] have been developed.