Effects of neutron-irradiation induced intergranular phosphorus segregation and hardening on embrittlement in reactor pressure vessel steels

Nishiyama, Yutaka ; Onizawa, Kunio ; Suzuki, Masahide; Nagai, Yasuyoshi*; Toyama, Takeshi*; Hasegawa, Masayuki*; Kameda, Jun*

The effects of intergranular P segregation and hardening on the ductile-to-brittle transition temperature (DBTT) in several neutron-irradiated reactor pressure vessel steels with different bulk contents of P and Cu have been investigated using a scanning Auger microbe, a local electrode atom probe and positron annihilation spectroscopy. Increasing the neutron fluence at 563 K promotes intergranular P segregation. The content of P significantly affects irradiation hardening due to distinct formation of P-rich precipitates arising from the stabilization of vacancies. Analyzing the correlations between the P segregation, hardening, fraction of intergranular fracture and DBTT, it is found neutron irradiation mitigates an embrittling effect of segregated P, and therefore the hardening more strongly affects the DBTT shift than the P segregation.