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/sigma 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.