High alloyed duplex stainless steels, referred to as super duplex, are being used increasingly for applications in corrosive environments. The higher Cr and Mo contents of these materials can lead to susceptibility toσ-phase precipitation, even during short time exposures to high temperatures. The 800°C aging of a high alloyed duplex stainless steel was investigated. Optical microscopy with image analysis, X-ray diffraction, and SEM were used to determine theσ-phase and to estimate the amount. Mechanical properties such as tensile strength, impact strength and hardness were investigated. It was found that the impact strength is most sensitive to aging at 800°C. Theσ-phase transformation is discussed and the microstructural aspects are described.