Studies on Electrochemical Corrosion Behaviors and 316NG Stainless Steel in Boron-Lithium Solutions

The electrochemical behaviors of 316NG stainless steel in the boron-lithium solutions (pH=5~8) at 300℃ were studied by using electrochemical polarization curves and the electrochemical impedance spectroscopy(EIS), and the experimental E-pH diagram at the same environment was graphed. The results indicated that the polarization current in the passivation region decreased sharply, especially in the region close to the secondary transpassivation point, and there were three passivation domains when pH was 7~8, The polarization resistance of 316NG stainless steel in the alkaline solution was apparently higher than that in the acidic solution or in the neutral solution, which was found by using electrochemical impedance spectroscopy, showing the oxide film at alkaline environment had a better protective effect. The oxide film was consisted of Cr₂O₃ and Fe₂O₃ in the acidic solution; When pH=6~8, a multilayered oxide film occurred: the outer Fe-rich layer consisted of Fe₃O₄ while NiFe₂O₄ occurred as the depth of layer increased, and the inner Cr-rich layer was composed of FeCr₂O₄. R_sol and the polarization resistance significantly decreased as the conductivity of the solution increased. The E-pH diagram based on the polarization curves was consistent with the inference.