Fracture Toughness of Z3CN20.09M Cast Stainless Steel with Long-Term Thermal Aging

Accelerated thermal aging tests were performed at 400 A degrees C for nearly 18,000 h on Z3CN20.09M cast stainless steel which was used for primary coolant pipes of nuclear power plants. A series of Charpy impact tests were conducted on Z3CN20.09M after different long-term thermal aging time. The test results indicated that the Charpy impact energy of Z3CN20.09M cast stainless steel decreased rapidly at an early stage and then almost saturated after thermal aging of 10,000 h. Furthermore, J-resistance curves were measured for CT specimens of longitudinal and circumferential pipe orientations. It showed that there was no obvious difference in the fracture characteristics of Z3CN20.09M in different sampling directions. In addition, the observed stretch zone width (SZW) revealed that the value of initiation fracture toughness J (SZW) was significantly lower than that of fracture toughness J (IC), indicating a low actual crack initiation energy due to long-term thermal aging.