Effect of Cobalt Addition on Austenite Formation and Corrosion Behavior in Pulsed Nd:YAG Laser-Welded Super Duplex Stainless Steel UNS S32750

Abstract This study evaluates cobalt addition by electrodeposition on the microstructure and corrosion behavior of pulsed Nd:YAG laser-welded UNS S32750 SDSS. Four conditions Co_1, Co_2, Co_3 and Co_4, containing 3.3, 5.0, 7.5, and 11.0 wt% Co on the weld surface were analyzed by SEM/EDS, and cyclic polarization was performed in 3.5 wt% NaCl at 25 °C and 70 °C. Increasing Co promoted austenite formation in the fusion zone, and Co3 (7.5 wt% Co) showed the phase balance closest to the base metal, whereas the HAZ remained predominantly ferritic in all cases. At 25 °C, the curves exhibited a similar passive plateau and a highly restrictive hysteresis loop, with no measurable differences in localized corrosion resistance within the experimental scatter. At 70 °C, all welded conditions showed poor repassivation, with $$\:{E}_{\text{r}\text{e}\text{p}\text{a}\text{s}\text{s}\text{i}\text{v}\text{a}\text{t}\text{i}\text{o}\text{n}}$$ close to $${E}_{\text{c}\text{o}\text{r}\text{r}}$$ , indicating the weld as the critical site for localized corrosion and a secondary Co effect. EDS line scans showed a systematic decrease in the detected Cr and Mo signals with increasing Co, with Co_4 presenting the lowest intensities.