Currently available correlations for the effects of specimen size on the upper shelf energy (USE) were developed for relatively ductile steels and do not serve as well when the steels become embrittled. Size effects correlations were developed recently for the impact properties of less ductile HT9 to be applied to other initially more ductile steels as they lose their ductility during irradiation. These new correlations successfully predict the ductile brittle transition temperature (DBTT) and USE of full-size Charpy specimens based on subsize specimen data. The new DBTT and the USE correlations were tested against published experimental data on other ferritic steels and shown to perform successfully at lower USE, particularly when both notched and precracked specimens as well as notched-only specimens were employed.

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Hardness measurements were used to determine the post-irradiation annealing response of A533B class 1 plate steel irradiated to a fluence of 1 x 1019 n/cm2 (E>1 MeV) at 150°C. Rockwell hardness measurements indicated that the material had hardened by 6.6 points on the B scale after irradiation. The irradiation induced hardness increase was associated with a decrease in upper shelf energy from 63.4 J to 5-1.8 J and a temperature shift in the Charpy curve at the 41 J level from 115°C to 215°C. Specimens were annealed after irradiation at temperatures of 343°C (650°F), 399°C (750°F), and 454°C (850°F) for durations of up to one week (168 h). Hardness measurements were made to chart recovery of hardness as a function of time and temperature. Specimens annealed at the highest temperature 454°C recovered the fastest, fully recovering within 144 h. Specimens annealed at 399°C recovered completely within 168 h. Specimens annealed at the lowest temperature, 343°C recovered only ∼70% after 168 h of annealing. After neutron irradiation, a new feature of black spot damage was found to be superimposed on the unirradiated microstructure. The density of black spots was found to vary from 2.3 x 1015/cm3 to 1.1 x 1016/cm3 with an average diameter of 2.85 nm. Following annealing at 454°C for 24 h the black spot damage was completely annealed out. It was concluded that the black spot damage was responsible for 70% of the irradiation-induced hardness.