Optimizing GTAW parameters for superior corrosion resistance in UNS32750: A trade-off between welding current intensity and microstructural integrity

The superior corrosion resistance of super duplex stainless steel (SDSS) UNS 32750 allows it to be used in aggressive environments. However, exposure to temperatures above 280 ° C during welding can weaken its corrosion properties. This study investigates the impact of welding current on the microstructure and corrosion behavior of UNS S32750, welded using the gas tungsten arc welding (GTAW) process. The current intensities of 105, 130, 155, and 180 A were used. Increasing the welding current raises the ferrite fraction from 29.0 to 34.5 %, improving phase balance. However, this increase also promotes the formation of chromium carbides, secondary austenite, and reformed austenite, with the potential for χ-phase precipitation. Electrochemical analyses, using double-loop electrochemical potentiokinetic reactivation (DLEPR) tests, showed an increase in the degree of sensitization, from 2.49 to 10.25 % as the welding current increased. Also, critical pitting temperature (CPT) measurements indicated a decrease from 54 to 45 ° C, suggesting a reduced pitting resistance. Thus, the current range of 105–130 A, and heat input of 0.78–0.99 kJ/mm was recommended. Although the phase balance improves at high welding current intensities, the formation of these secondary phases reduces the overall corrosion resistance.