Effect of aging treatments on microstructure and impact properties of tungsten substituted 2205 duplex stainless steel

The effects of partial substitution of tungsten for molybdenum on the microstructure and impact properties in 22Cr-5Ni-3Mo (wt-%) duplex stainless steel (DSS) have been investigated following aging heat treatments in the temperature range 600-1000°C. During aging the intermetallic σ and χ phases were precipitated, and the impact toughness was significantly decreased with an increase in the σ phase content. The χ phase had been precipitated on the α/γ boundary in the early stages of aging. Ferrite and χ phases in tungsten substituted duplex stainless steel contain a large amount of tungsten, and their decomposition rates are much lower compared with those in steel containing only molybdenum. Consequently, the precipitation of the σ phase is retarded in tungsten substituted DSSs, which results in high impact toughness. However, after aging for a long time, the α and χ phases transformed to the σ and austenite phases in the tungsten substituted steels, and the steels showed low impact toughness.