Low temperature aging embrittlement of CF-8 stainless steel

Cast stainless steels such as CF-8 are used for several components such as pump and valve casings, elbows, fittings and primary coolant pipes in nuclear power plants. CF-8 stainless steel has a duplex microstructure consisting of austenite and about 15–20% δ-ferrite. Long-term exposure at the reactor operating temperatures results in aging-induced embrittlement of the material due to spinodal decomposition of the ferrite phase. In this paper, we report the effects of low temperature aging (673 K) up to 18 months on the mechanical and fracture properties of cast CF-8 stainless steel in the range of 173–423 K. These studies have been carried out using non-destructive ball indentation tests. Standard Charpy and tensile tests were also carried out to complement the ball indentation data. Increase in strength and decrease in toughness have been observed following aging. These changes in the properties tend to saturate on aging for more than 12 months.