Effect of heat treatment on structure and properties of GTAW and laser beam welded super-duplex stainless steel joints

Duplex stainless steel, consisting of ferrite and austenite, has good corrosion resistance and is often used in harsh marine environments. In this paper, welding on SAF2507 duplex stainless steel with 5 mm thickness was finished by laser beam welding (LBW) and gas tungsten arc welding (GTAW). The post-weld solid solution treatment was also conducted at temperature of $1050^{\circ }$C followed with cooling by water after 1 h. The results showed that both LBW and GTAW could produce well-produced welds. The microstructures of the welds were composed of ferrite and austenite phases. After solid solution treatment at $1050^{\circ }$C, the two-phase structure of LBW joint became uniform, while $\sigma$ phase was produced in GTAW joint. The impact test of welded joints at room-temperature was carried out. After solid solution treatment at $1050^{\circ }$C, the impact toughness of LBW joints obviously increased, but the impact toughness of GTAW joint decreased with the fracture morphology of brittle mode. The electrochemical experiments on the welded joints showed that the pitting corrosion resistance of LBW joints improved after solid solution treatment, while the pitting corrosion resistance of GTAW joints decreased.