Abstract: The solution-treated welded joints of 2205 duplex stainless steel welded by shielded metal arc welding were treated by aging treatment at 850℃ for 30,180 and 360 min,respectively.The microstructure evolution and the precipitation of σ phase were analyzed by OM,XRD,EDS and ferrite scope detector.The results indicate that in each region of the aged joints,σ phase precipitates at γ/α or α/α grain boundaries and grows into ferrite phase.The formation mechanism is a eutectoid reaction of α→σ+γ₂.The increase of aging time leads to a decrease in ferrite phase and an increase in σ phase.σ phase morphology changes from spotted→reticular→schistic state.Compared to the base metal and HAZ,the weld metal with the most precipitation rate of σ phase is more sensitive to the aging treatment,in which the ferrite almost completely transforms into austenite and σ phase after aging for 360 min.