PNNL

Abstract

Cast stainless steels are widely used in the primary coolant systems of nuclear power plants because of their high strength, toughness, and corrosion resistance. Mechanical property degradation in the steels, primarily due to a thermally-embrittled ferrite, is of major concern in an extended-term operation. To investigate the aging-induced loss of fracture resistance in cast stainless steels, static fracture resistance (J-R) testing was performed for three different CF8 cast stainless steels with significantly different d-ferrite contents. The materials were thermally-aged at 290-400°C for up to 10kh and fracture-tested at 25-400°C. It was found that the fracture toughness in high-ferrite materials generally decreased with thermal aging while the relationship between aging and fracture toughness in low-ferrite materials was rather complicated, showing non-monotonic variation with the degree of aging. While significant degradation was observed for the highly-aged high-ferrite materials, no material was observed having a K0.2mm less than 100 MPavm.