Corrosion behavior of ion nitrided AISI 316L stainless steel

NOSEI, L; FARINA, S; AVALOS, M; NACHEZ, L; GOMEZ, B J; FEUGEAS, J N

THIN SOLID FILMS

Elsevier

Año: 2008 vol. 516 p. 1044 - 1050

0040-6090

In the present work the corrosion susceptibility of ion nitrided AISI 316L stainless steel was investigated for two different nitriding times andcompared with the corrosion susceptibility of the untreated material. Plasma nitriding for short times (30 min) produced the “S” phase or expandedaustenite (γN), with a thickness of ∼5 μm and a micro-hardness of 1300–1400 HV0.025 (6.5 times higher than the untreated material). Plasmanitriding for long times (6 h) resulted in the precipitation of iron and chromium nitrides.To evaluate the corrosion resistance of both untreated and nitrided samples, anodic potentiodynamic polarization curves and immersion testswere performed in 1 M NaCl at room temperature. It was found that the corrosion resistance depends on the nitriding time. Samples nitrided forhalf an hour developed a much better corrosion resistance – close to that observed in the untreated samples – than those nitrided for 6 h. Samplesnitrided for half an hour showed high roughness probably due to the presence of sliding bands developed in the expanded austenite phase. Thesesliding bands provide appropriate sites for the developing of the corrosion process. This would explain the results obtained in the corrosion tests.Samples ion nitrided for 6 h showed a severe and massive surface damage due to corrosion.Ion nitriding of AISI 316L stainless steel for short periods of time (30 min in the present case) may be an interesting surface treatment processthat efficiently improves the surface hardness of the steel with some reduction in its corrosion resistance.