Passivation Behaviour of Surface-Treated 17-4PH Stainless Steel in Chloride-Containing Environment with Varying Concentrations

The influence of chloride concentration on the corrosion behaviour of SS17-4PH after surface treatment by mechanical deformation was investigated in 0.6–1 M concentration of NaCl aqueous solution through polarization study and morphology observation. The potentiodynamic polarization results revealed that the corrosion resistance of SS17-4PH decreases with increasing NaCl concentration. Unlike the SS17-4PH samples polarized in a higher concentration of NaCl (0.7 and 0.9 M concentration of NaCl) with higher corrosion current densities (1.486 and 3.085 mA/cm², respectively), the sample polarized in 0.6 M NaCl exhibited a much lower corrosion current density of 0.807 mA/cm². The lower corrosion current density value obtained signifes a better corrosion resistance and this can be accrued to the fact that increasing molarity of NaCl solution can increase the electron mobility and conductivity of solution thereby increasing the concentration of ions in the water and thus increases the corrosion rate (rate of oxidation).