Effects of Thermal Aging on Fracture Toughness and Charpy–Impact Strength of Stainless Steel Pipe Welds

The degradation of fracture toughness, tensile, and Charpy–impact properties of Type 308 stainless steel (SS) pipe welds due to thermal aging has been characterized at room tempera-ture and 290°C. Thermal aging of SS welds results in moderate decreases in Charpy–impact strength and fracture toughness. For the various welds in this study, upper–shelf energy de-creased by 50–80 J/cm2. The decrease in fracture toughness J–R curve or JIC is relatively small. Thermal aging had little or no effect on the tensile strength of the welds. Fracture prop-erties of SS welds are controlled by the distribution and morphology of second–phase particles. Failure occurs by the formation and growth of microvoids near hard inclusions; such processes are relatively insensitive to thermal aging. The ferrite phase has little or no effect on the frac-ture properties of the welds. Differences in fracture resistance of the welds arise from differ-ences in the density and size of inclusions. Mechanical–property data from the present study are consistent with results from other investigations. The existing data have been used to es-tablish minimum expected fracture properties for SS welds. NUREG/CR–6428 iv v NUREG/CR–642