Fracture behavior of thermal aged duplex cast stainless steel for nuclear power plant

The impact properties and ductile-brittle transition temperature (DBTT) as well as the fracture mechanism of Z3CN20-09M CSS made in China treated at 400 degrees C with different accelerated ageing time are investigated by instrumentation impact test and SEM. The results show that one exception is the variation of the yield force Fgy and the other characteristic values of impact force are indistinctively affected by the thermal ageing time range from 0 to 3000h. And except for the energy corresponding to yield force Wgy, all the impact energy parameters decrease with the increment of the thermal ageing time. Moreover, the impact fracture mode of Z3CN20-09M CSS changes from the microvoid coalescence and the dimpled ductile tearing to the quasi-cleavage fracture with the prolong of the thermal ageing time. The tearing ridge and the river pattern of cleavage fracture can be seen in partial areas after the ageing treatment for 3000h. In addition, DBTT of Z3CN20-09M CSS increases with the thermal ageing time. All these indicate that the thermal ageing embrittlement occurs in the Z3CN20-09M CSS.