The influence of copper content and phosphorus content on notch ductility recovery by 399°C postirradiation heat treatment was explored for A 533-B and A 302-B pressure vessel steels. Charpy-V (C_v) specimens for the investigation were obtained from ten plates produced from four (4-way split) laboratory melts. The plates were 15.2 mm thick but were heat treated to reproduce the microstructure of 150-mm and thicker A 302-B plates at the quarter-thickness location.

The C_v specimens were irradiated in two assemblies at 288°C (550°F) to a fluence of ∼2.5 × 10¹⁹ n/cm² in a light-water-cooled and moderated test reactor. Notch ductility properties in the as-irradiated and 399°C, 168 h postirradiation-annealed conditions were determined. In addition, separate sets of specimens were thermally conditioned at 288°C and at 288°C followed by 399°C to benchmark the effects of temperature in the absence of irradiation.

The results indicate that copper has a significant influence on the magnitude of residual embrittlement after annealing. In contrast, phosphorus contents in the range of 0.002 to 0.025% were found not to have an effect on residual embrittlement either in high or low copper steels. Essentially full recovery in 41-J transition temperature was observed for high phosphorus, low copper content steels. Effects of nickel alloying on recovery behavior were also investigated through data comparisons for A 302-B versus A 533-B plates.