The dynamic J-lntegral toughness and associated strength changes in solution-treated Type 321 stainless steel have been characterized following fast reactor irradiation to displacement doses in the range 20 to 54 dpa (displacements per atom) at mean temperatures of ~230 and ~400°C, using instrumented impact test procedures.

Irradiation induces significant but not deleterious toughness degradation. Both the dose and test temperature dependence of the toughness changes are controlled by the irradiation temperature. Maximum toughness loss occurs at doses below 20 dpa for both irradiation temperatures; however, 400°C irradiation is associated with subsequent saturation of the toughness loss, whereas the 230°C irradiation condition exhibits further toughness degradation up to 54 dpa. The toughness response is consistent with fractographic observations that demonstrate that a predominantly ductile fracture mode is maintained after irradiation, but with significant changes in the scale of microvoid coalescence.