Passive film properties and corrosion resistance of AISI 304L stainless steel

The passive film properties and resistance to general and different types of localised corrosion of the AISI 304L stainless steel were analysed. The properties and behaviour of two microstructural states, the as-received and sensitisation-annealed, are comparatively analysed by electrochemical methods (linear sweep voltammetry-LSV, Mott–Schottky, electrochemical impedance spectroscopy-EIS and electrochemical potentiokinetic reactivation method with double loop-DL-EPR) and surface analytical techniques (scanning electron microscope-SEM/EDS and X-ray photoelectron spectroscopy-XPS). XPS analysis showed the presence of Fe 2+ , Fe 3+ and Cr 3+ oxides and hydroxides, and a higher Cr:Fe ratio in the passive layer for the sensitised than as-received specimens. Sensitised stainless steel shows a lower defect density and higher protective stability of the passive layer, and a higher resistance to general corrosion, than the as-received one. However, during LSV measurements, at higher electrode potentials, sensitised stainless steel showed lower passive film stability, due to the metastable pits formation and transformation in the stable pits.