Corrosion Behavior of Austenitic and Duplex Stainless Steel Weldings in Aqueous Lithium Bromide Solution

The corrosion behavior of three stainless steels UNS 14311, UNS 14429 (austenitic stainless steels [SS]), UNS 14462 (duplex SS) and their corresponding filler metals (alloys in form of wire) for welding was studied in a commercial lithium bromide (LiBr) solution (850 g/L LiBr solution and 4.3 g/L lithium chromate [Li₂CrO₄] in their welded and nonwelded conditions at 25°C). Metallographic examination was carried out to characterize the microstructure of the samples. Potentiodynamic curves were obtained to analyze the general corrosion behavior of the alloys. The inhibitor influence of chromate on the corrosion resistance was analyzed. Localized corrosion resistance was studied by cyclic potentiodynamic curves. Open-circuit potentials and corrosion potentials shifted toward more negative values in the welded condition compared to the parent metal, and their values were established between the potentials of the base and filler metals. The most resistant alloy to general corrosion was the UNS 14462 because it had the lowest corrosion current for all conditions. Duplex structure contributes to the best corrosion resistance. In all the cases, corrosion current increases in the filler metal. Resistance to pitting corrosion was analyzed in terms of pitting potential, passivation current, and repassivation potential. Pitting corrosion resistance is improved with the UNS 14462, which has the highest pitting potential and the lowest passivation current for welded and nonwelded conditions, and it also has the most corrosion-resistant filler metal. The duplex alloy does not have the best repassivation behavior (in terms of the broadest difference between corrosion potential and pitting potential), although it repassivates in all conditions (welded and non-welded). Temperature influence during the welding process is very significant on the passivation current of UNS 14462; by contrast, the passivation current of UNS 14311 and UNS 14429 highly decreases when welded. With respect to the austenitic SS (UNS 14311 and UNS 14429), the higher nickel and molybdenum contents of the UNS 14429 alloy makes the material more resistant to general and localized corrosion.