Abstract: 2205 duplex stainless steel (DSS) joints welded by manual arc welding are subjected to solution treatment at 1 050 ℃ and aging treatment at 850 ℃ for various holding time. The microstructure evolutions and the distribution of σ phase in each joint region are observed by optical microscope. Hardometer, tensile and impact testers are used to evaluate the mechanical properties of the welded joints. Meanwhile, the impact fractographs and fracture mechanism are analyzed through scanning electronic microscope. The results show that the solution treatment at 1 050 ℃ for 2205 DSS welded joint can effectively improve the microstructure and properties. After aging at 850 ℃, σ phase precipitated at the γ/α interface can be found in all the joint regions, including base metal, weld metal and heat affected zone (HAZ). With increasing aging time, σ phase grows into the adjacent ferrite grains and the amount of σ phase increases. The weld metal is more sensitive to σ phase precipitation. The hardness in the base and weld metal markedly increases due to the σ phase formation, and the increment rate is faster in the weld region. Furthermore, the extent to which brittle σ phase improves the ultimate strength is found to be in evidence, being more pronounced in reducing the ductility and impact toughness. The fracture mechanism of impact fracture is a transformation from the mixed rupture as-solution treated to the brittle fracture after aging at 850℃, characterized by cleavage crack.

Key words: Aging, Duplex stainless steel, Mechanical properties, Solution treatment, Welding