Effects of passivation on the corrosion resistance of 420 stainless steel in 3.5% NaCl solution

In this study, effects of three methods of chemical, electrochemical and electrochemical - chemical passivation on corrosion behavior of martensitic stainless steel type 420 in 3.5% NaCl have been evaluated by d.c. potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and analysis of Cr and Fe content in passivation solutions by Induction Coupled Plasma (ICP). The results showed that the impedance of surface was depend upon Fe/Cr ratio in passivation's solutions, inner and outer layers thickness of passive film and homogeneity of inner and outer layers. Also,The result indicated that electrochemical - chemical passivation provided the best performance in terms of increase corrosion resistance and the passive film formed by chemical and electrochemical passivation methods had the same functional. The result also suggested that the passive film formed with all three methods had higher corrosion resistance to passive film formed naturally (formed in moist air).