Exploring the Effect of Lanthanum on the Corrosion Resistance and Antimicrobial Properties of Fe–20Cr–18Ni–6Mo–0.8Cu–0.2N Stainless Steel in Seawater

This study investigates the effects of lanthanum (La) on the microstructure and corrosion resistance of Fe–20Cr–18Ni–6Mo–0.8Cu stainless steel in seawater. Microstructural analysis shows that La addition refines grain size and alters precipitated phases. X‐ray diffraction confirms austenitic structures, while transmission electron microscopy reveals the formation of Cu₅La compounds and ferrite/σ phases. Electrochemical tests indicate that the sample without La has the highest open‐circuit potential and best corrosion resistance in nonseawater conditions. However, after 16 days of seawater exposure, the 0.5 wt% La sample exhibits superior corrosion resistance with a corrosion rate of 0.0175 mm/a, while higher La contents (1.0 wt% and 1.5 wt%) leads to poor corrosion resistance and large corrosion craters. Scanning electron microscopy confirms minimal surface corrosion for the 0.5 wt% La sample. In sulfate‐reducing bacteria environments, La enhances corrosion resistance, except for pitting corrosion observed in the 1.5 wt% sample. Scanning Kelvin probe force microscopy shows minimal surface potential fluctuation (from −30 to 10 mV) for the 0 wt% La sample, indicating the best corrosion resistance. This study provides insights into the role of rare earth elements in super austenitic stainless steels.