Comparative electrochemical studies of UNS S20910 and UNS S31803 stainless steels in chloride-containing media

In this study, the electrochemical behaviour and corrosion resistance of UNS S20910 austenitic and UNS S31803 austenitic/ferritic stainless steels were investigated in a 3.5 wt.% NaCl solution at different immersion times and temperatures. Cyclic voltammetry revealed susceptibility to pitting corrosion in both steels, with resistance decreasing at higher temperatures. The pitting potential shifted from ∼1.39 V to 1.30 V for UNS S20910 and from ∼1.30 V to 1.20 V for UNS S31803 as temperature increased, while repassivation potential decreased from ∼1.00 V to ∼0.950 V and ∼0.940 V, respectively. Both alloys exhibited passive behaviour, with the austenitic steel showing a wider passive region (∼1.72 V) than the duplex (∼1.60 V) at 25 °C, suggesting greater stability against localised corrosion. Long-term immersion (up to 360 h) at 25 °C confirmed the formation and stabilisation of protective oxide films. Open-circuit potential showed that UNS S20910 reached equilibrium faster (∼24 h) than UNS S31803 (∼168 h). Electrochemical impedance spectroscopy results confirmed the development of protective oxide films, with polarisation resistance increasing from ∼10 5 to 10 6 Ω·cm 2 over time for both steels. Despite faster passivation of UNS S20910, both steels achieved comparable corrosion resistance, confirming suitability for chloride-rich environments, under the studied conditions.