IRRADIATION-INDUCED MICROSTRUCTURAL CHANGES, AND HARDENING MECHANISMS, IN MODEL PWR REACTOR PRESSURE-VESSEL STEELS

A series of model steels and commercial alloys from the IAEA Phase 3 irradiation programme was irradiated to a dose of 14 mdpa (similar to 9 X 10(22) n m(-2) (E > 1 MeV)) at 290 degrees C. The steels were examined using small angle neutron scattering and a range of transmission electron microscope techniques. Measured yield stress and hardness changes were interpreted in terms of the irradiation-induced microstructural developments. The irradiation of Cu-containing steels produced Cu-rich precipitates of similar to 2 nm diameter which were alloyed with Mn and Ni. The Ni content of the precipitates increased markedly for bulk Ni contents > 0.7 wt%. The volume fractions of precipitate increased with increasing bulk Cu content and, also, with increasing bulk Ni content > 0.7 wt%. The precipitate-induced strengthening and hardening varied according to the square root of the volume fraction of precipitate. Yield stress changes in low-Cu steels were consistent with data from the IAEA Phase 2 irradiation programme.