Impact of chloride concentrations on the electrochemical performance and corrosion resistance of austenitic and ferritic stainless steels in acidic chloride media

This study evaluates the electrochemical behavior and corrosion resistance of 304 austenitic stainless steel (304SS), atlas F20S ferritic stainless steel (F20S), and 316L austenitic stainless steel (316SS) in 2 M H2SO4 containing 0-3.25% NaCl. Techniques including potentiodynamic polarization, potentiostatic analysis, open circuit potential (OCP) measurements, and optical microscopy were used to elucidate corrosion mechanisms and material performance. Results showed varying corrosion resistance influenced by Cl- concentration and metallurgical properties. Potentiodynamic polarization revealed 304SS exhibited the highest corrosion rates due to Cl--induced destabilization of its passive Cr2O3 layer, with anodic dissolution reflected by more negative corrosion potentials. F20S displayed intermediate resistance, with corrosion rates peaking at 1.75% NaCl before declining. Conversely, 316SS had the lowest corrosion rates (0.0066-0.0094 mm/y at 1.25-3.25% NaCl), attributed to its robust passive oxide layer resisting Cl- attack. Potentiostatic data highlighted pitting resistance and passivation. For 304SS, increasing Cl- shifted passivation potential negatively, signaling localized corrosion susceptibility, though its passivation range suggested pitting resistance. F20S showed fluctuating passivation and reduced resistance beyond 1.75% NaCl, with lower passivation range values compared to 304SS. 316SS maintained high passivation potentials and delayed pitting, reflecting stable passive film properties. OCP analysis confirmed alloy composition's role in corrosion behavior. Higher NaCl concentrations yielded more electronegative OCPs for 304SS and F20S, indicating increased susceptibility. In contrast, 316SS showed electropositive potentials, suggesting a pseudo-passive state and resistance to Cl- degradation. Optical microscopy revealed distinct corrosion morphologies. 304SS showed surface deterioration and pitting at higher Cl- levels. F20S exhibited localized corrosion with increased pit density and size. 316SS maintained structural integrity, reflecting superior resistance to pitting and general corrosion.