Comparison of electrochemical behavior between coarse-grained and fine-grained AISI 430 ferritic stainless steel by Mott-Schottky analysis and EIS measurements

In this study, the electrochemical behavior of coarse-grained and fine-grained AISI 430 ferritic stainless steel in 0.1 M HNO3 solution was investigated. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements showed that grain refinement operation offer better conditions for forming the passive films. Mott-Schottky analysis revealed that the passive films behave as n-type and p-type semiconductors and grain refinement did not change the semiconductor type of the passive films. Also, according to Mott-Schottky analysis, it was found that the calculated donor and acceptor densities decreased with grain refinement. These observations were consisted with the results of the potentiodynamic polarization curves and EIS measurements, evidencing that the passivation behavior enhanced with decreasing the grain size. In conclusion, grain refinement offer better conditions for forming the passive films with higher protection behavior, due to the growth of a much thicker and less defective films.