Electrochemical Behaviors of Rusted N80 Steel in NaCl Solution

The corrosion behaviors of rusted N80 steel in NaCl solution were studied by linear polarization, electrochemical impedance spectroscopy (EIS) and surface analysis techniques. The results indicated that the control step of the corrosion process changed from electrochemical reaction to diffusion process, the charge transfer resistance and the diffusion resistance decreased. The angles between diffusion tail in the Nyquist plot at low frequency and the real-axis decreased with the increase of immerging time of N80 steel in 0.2 mol/L NaCl solution. A physical model describing the rusted steel was used to explain the correlation of EIS characters and porosity of corrosion rust layer. The corrosion rust was found to have two layers, the outer layer was loose and porous, the inner layer was relatively compact. The Cl- was concentrated in the inner layer and the corrosion process of the substrate metal was promoted.