Influence of Thermal Ageing and Specimen Size on Fracture Toughness of Z3CN20-09M Casting Duplex Stainless Steels

To assess the thermal aging embrittleness of the primary coolant pipes in pressurized water reactor (PWR), the fracture toughness test is conducted for Z3CN20-09M CDSSs thermally aged at 400 degrees C for 10,000 h and the fracture morphologies of the virgin and the aged specimen are analyzed based on SEM technique. The influence of the specimen thickness and thermal ageing time on the fracture toughness of the material is discussed in details. The results show that with increasing thermal ageing time, the J(IC) of Z3CN20-09M CDSSs significantly decreases and the fracture mechanism transits from the ductile microvoid coalescence fracture to the cleavage fracture in ferrite and the quasi-cleavage fracture in austenite. Moreover, the theoretical expression between the fracture toughness K-C and the specimen thickness t of Z3CN20-09M CDSSs is established, which can be used to estimate the fracture toughness with different specimen thickness.