Abstract: 2205 duplex stainless steel was solid-solution treated at 1050 ℃ and 1350 ℃ for 30 min, and then aged at 650-1000 ℃ for 0.5-1440 min. The microstructure and σ phase were characterized by optical microscope (OM) and scanning electron microscope (SEM). The results show that the precipitation of σ phase in the 2205 duplex stainless steel after solid solution treatment at 1050 ℃ occurs during aging treatment at 650-850 ℃. At 850 ℃, the precipitation of σ phase is the fastest, and the precipitation rate decreases when the aging temperature deviates from 850 ℃. After solid solution treatment at 1350 ℃, the precipitation temperature of σ phase rises in overall, and its range is wider. The σ phase coarsens quickly after precipitation and the volume fraction reaches 0.25%-0.75% within 3 h, then the growth rate of σ phase decreases with the increase of aging time. The σ phase precipitates at the phase boundary between ferrite and austenite with the morphology of quasi-spherical particles less than 1 μm, then it grows in the narrow region of several microns along the width of ferrite phase. The aging temperature affects the precipitation behavior of 2205 duplex stainless steel, and the aging temperature should be away from 850 ℃ to avoid the precipitation and growth of σ phase.

Key words: 2205 duplex stainless steel, aging process, σ phase, precipitation