AbstractAn investigation has been undertaken to determine the magnitude of any reduction in properties that may occur in cast duplex stainless steels and weldments during long term exposure to reactor operating conditions. Test panels were fabricated in CF3 stainless steel using a manual metal arc (MMA) process and 19.9.L consumables. The mechanical properties of the parent material and weldments were measured following accelerated aging at 375 and 400°C for up to 20 000 h. Following aging at temperatures up to 400°C, reductions in both the Charpy impact and J integral–crack growth resistance R (J–R) fracture toughness of CF3 cast austenitic steel and 19.9.L austenitic weld metal were observed. For conditions equivalent to the proposed end of life for UK pressurised water reactors, the J–R fracture toughness at 300°C of both cast steel and MMA weld metal was reduced by ~30% for crack extensions of≥1 mm. Hence, it is important that these reductions in weld metal toughness are taken into account during the development of safety cases and structural integrity assessments for any component in the primary loop that contains MMA stainless steel weldments.MST/1198