Comparison of Corrosion Behavior between Fine-Grained and Coarse-grained Fe-18.5% Cr Ferritic Stainless Steel in 0.01 M NaOH Solution

This paper investigates the influence of grain size reduction, from 120 to 5 µm, on the electrochemical response of Fe-18.5% Cr ferritic stainless steel in 0.01 M NaOH alkaline solution. To analyze the electrochemical characteristics of the material, the potentiodynamic polarization, open circuit potential measurement, cyclic voltammetry, electrochemical impedance spectroscopy, and Mott-Schottky analysis were carried out. Open circuit potential analysis demonstrated that the passive layer developed on a coarse-grained sample is more stable than a fine-grained one. Based on electrochemical impedance spectroscopy measurements, it was concluded that grain refinement reduces the thickness of the passive protective layer and degrades the corrosion resistance of material. Polarization measurements showed that refinement of grain structure reduces the corrosion resistance of the investigated ferritic stainless steel exposed to NaOH solution. The Mott-Schottky analysis demonstrated that the protected layer formed on the surface of the fine-grained sample has donor and acceptor densities (2.43×1021, and 0.4×1021 cm-3, respectively) higher than that formed on the surface of the coarse-grained counterpart (2.29×1021, and 0.36×1021 cm-3, respectively).