Effects of thermal aging on fracture toughness and charpy-impact strength of stainless steel pipe welds.

Abstract

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 temperature 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 decreased by 50-80 J/cm 2 . The decrease in fracture toughness J-R curve or J IC is relatively small. Thermal aging had little or no effect on the tensile strength of the welds. Fracture properties 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 fracture properties of the welds. Differences in fracture resistance of the welds arise from differences 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 establish minimum expected fracture properties for SS welds.

Crack growth rates and fracture toughness of irradiated austenitic stainless steels in BWR environments.

“…For thermal embrittlement of cast SSs the fracture toughness of CF-8M steel represents the worst-case scenario. 28,30 It thus might represent a bounding case also for the synergistic effects of irradiation and thermal aging.…”

“…[28][29][30] strength, hardness, and Charpy-impact transition temperature, and it decreases the ductility, fracture toughness, and impact strength. The extent of mechanical-property degradation is essentially determined by the chemical composition of the steel, the casting process used to construct the component, the ferrite content and ferrite morphology of the steel, and the time and temperature of service for the component.…”

“…Formation of Cr-rich ∃% phase in the ferrite is the primary mechanism for thermal embrittlement of cast austenitic SSs; [28][29][30][31][32][33][34][35][36] thermal aging has little or no effect on the austenite phase. Embrittlement of ferrite phase from neutron irradiation occurs at lower fluences than does embrittlement of the austenite phase.…”

“…27 Another issue that has been a concern for reactor core internal components is the possibility of a synergistic interaction between irradiation and thermal embrittlement of cast austenitic SSs and SS weld metals. [28][29][30][31][32] Although wrought SSs are typically completely austenitic, welded and cast SSs have a duplex microstructure consisting of austenite and ferrite phases. The ferrite phase increases the tensile strength and improves resistance to SCC, but it is susceptible to thermal embrittlement after extended service at reactor operating temperatures.…”

Microscopic analysis of the stainless steel weld metal after long-term thermal exposition in the primary circuit of the nuclear power plant

“…The embrittlement behavior that has been observed in stainless steels led the researchers to the investigation of the influence of low-temperature thermal aging on stainless steels weld joints [50][51][52][53][54][55][56][57][58][59][60]. The results of the experimental investigations have shown that the low-temperature decomposition of the ferrite → (α + α ) reduces both corrosion resistance and mechanical properties of the corrosion resistant steels and their welds and weld metals.…”