Microstructural characterization of δ/γ/σ/γ2/χ phases in silver-doped 2205 duplex stainless steel under 800 °C aging

• χ and γ2 phases were observed for 1hr aging at 800 °C.
• σ phase grows up with depletion χ phase gradually.
• δ → χ + γ2 → χ + σ + γ2 phase transformations in silver-doped 2205 DSS under 800 °C aging.

In this study 0.2 wt.% Ag alloyed 2205 duplex stainless steels was selected as test material. The effect of aging time on the phase transformations of 0.2 wt.% Ag alloyed 2205 duplex stainless steel was investigated at 800 °C. Results show that the different intermetallic compounds (σ and χ) were generated when the aging time increased at 800 °C. The Mo-enriched χ phase was firstly initiated at δ/γ grain boundaries, but the Cr-enriched σ phase was precipitated with the increase of aging time. Ag particles distributed over matrix stably and do not seem to influence microstructure evidently after aging treatment. From the quantitative analysis results, the σ + χ phase volume fractions indeed would increase from 0.58% to 22.9% with the aging time in the period of 1–10 h at 800 °C. However, the σ + χ phase tended to slow down while the aging time in the period of 10–100 h, and then the σ + χ phase volume fractions rose from 22.9% to 31.33%. In addition, the δ phase volume fractions decreased and the γ + γ2 phase volume fractions increased. Aging heat treatment at 800 °C changed the δ and γ + γ2 phase volume fractions due to the δ → χ + γ2 → χ + σ + γ2 phase transformations.