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In the present work we compared the corrosion susceptibility of AISI 316L stainless steel without any treatment and surface ion nitrided with two different processing times: 30 minutes and 6 hours. In the first case we have found the development of the phase S or expanded austenite (ãN) with a thickness of ~5 µm and a micro-hardness of 1300 - 1400 HV0,025. In the second case, the expanded austenite was totally replaced by iron and chromium nitrides. To evaluate the corrosion resistance in each case (bare and ion nitrided samples), anodic potentiodynamic polarization curves were performed, as well as immersion tests for 60 days, using as electrolyte in the tests 1M NaCl solution at room temperature. Though the nitriding process generally deteriorates the corrosion resistance of steels, in this work we have found that the corrosion resistance is well different for the expanded austenite case than for the iron nitrides one. Samples nitrided for half an hour have developed a much better resistance to pitting corrosion close to that observed in the untreated samples- than those nitrided for 6 hours. The surface of samples nitrided for half an hour showed high roughness (Ra=0.13µm) probably due to the presence of sliding bands developed in the expanded austenite phase. Indeed, these sliding bands can be the responsible of the observed partial loose of the resistance to corrosion natural of the bare stainless steel, by providing appropriate sites for the development of the pitting process. The samples ion nitrided for 6 hours instead, have shown a severe and massive surface damages due to corrosion. Also, the expanded austenite developed under short time of ion nitriding, have shown a surface hardness higher by a factor 6.5 than the one observed for the bare material. Ion nitriding of AISI316L stainless steel for short periods of time (30 minutes in our case) can be an interesting surface treatment process compared with long terms one, because this type of treatment, through the development of expanded austenite, induces an important increase in the surface microhardness with a small reduction of the corrosion resistance to NaCl solution.