Effect of aging on the microstructure and properties of ASTM A890 3A duplex stainless steel

Exposure of duplex stainless steels to high temperatures could result in microstructure changes generating precipitated phases and significantly affecting material properties. In this paper, the effects of aging at 450-850 & DEG;C on the microstructure and properties of ASTM A890 3A duplex stainless steel were studied. The microstructures were different after aging at different temperatures: only & gamma;2 was precipitated after aging at 450 and 550 & DEG;C, & gamma;2, M23C6, and & sigma; phases were observed at 650 & DEG;C, and an additional phase of & chi; was found at 750 & DEG;C. Aging at 450 & DEG;C increased the strength of duplex stainless steel while aging at other temperatures negligibly affected strength. Aging at 450 & DEG;C and 650-850 & DEG;C significantly decreased the impact toughness. Correspond-ingly, the fracture was partially or completely transformed from a ductile fracture mode before aging to a brittle fracture mode after aging. Aging deteriorated the corrosion resistance of duplex stainless steel. Aging at 750 & DEG;C had the most significant effect: the breakdown potential decreased by 28%, and the membrane resistance decreased by 81.9% relative to those without aging. The above changes in properties were closely related to the embrittlement of duplex stainless steel at 475 & DEG;C and the precipitation of the & sigma;-phase and & chi;-phase.