Irradiation-induced grain-boundary solute segregation and its effect on ductile-to-brittle transition temperature in reactor pressure vessel steels

Nishiyama, Yutaka ; Yamaguchi, Masatake   ; Onizawa, Kunio ; Iwase, Akihiro*; Matsuzawa, Hiroshi*

A study on grain-boundary segregation and embrittlement in terms of the Charpy ductile-to-brittle transition temperature (DBTT) has been performed for the neutron-irradiated A533B steels with a typical contents of impurities of Japanese reactor pressure vessel ones. The neutron irradiation was conducted at 563K to a fluence of 1.3 10 n/m (E1MeV) using Materials Testing Reactors. The neutron irradiation induced the phosphorus (P) and nickel (Ni) segregation and the reduction of segregated carbon (C) in some cases at grain-boundaries. The increase in the P segregation at high fluences (5 10 n/m, E1MeV) was less than 0.15 in monolayer coverage for the steels with the bulk content of P not exceeding 0.02 wt.%. The hardening more strongly affected the DBTT shift than the P segregation for those steels. The reduction of segregated C that enhances the grain-boundary cohesion by neutron fluence is not large enough to cause the DBTT shift.