Comparison of pulsed and continuous current gas tungsten arc welding in dissimilar welding between UNS S32750 and AISI 321 in optimized condition

Abstract

In this research, mechanical and corrosion properties of dissimilar joint between duplex stainless steel UNS S32750 duplex stainless steel and AISI 321 austenite stainless steel welded by pulsed current gas tungsten arc welding (PCGTAW) and continuous current gas tungsten arc welding (CCGTAW) were compared. The welding parameters and the filler metal were the same in both methods. Microstructural characterization of joint was determined by optical and scanning electron microscope. The pitting potential was evaluated by potentiodynamic polarization test in 3.5 wt.% NaCl solution at room temperature. Mechanical properties of optimal joint were investigated by impact test and vickers microhardness. Microstructural evaluation shows that the equal amounts of ferrite and austenite were obtained in PCGTAW weldment, while in CCGTAW weldment fraction of phases changed to 40% ferrite and 60% austenite. TiN precipitations were formed in fusion line of CCGTAW weldment on the side of AISI 321 austenite stainless steel. The average values of hardness in PCGTAW and CCGTAW weld zone were 241 and 225 HV0.2, respectively. The higher amount of ferrite in PCGTAW weldment in comparison with CCGTAW weldment was the reason of higher hardness average. The toughness of PCGTAW and CCGTAW was 106 and 102 J, respectively. Based on cyclic polarization test, pitting potential of weldment welded with PCGTAW and CCGTAW was 1.03 and 0.8 V, respectively, which is a proof of better pitting corrosion resistance of the weld zone in PCGTAW method.