Fatigue Crack Growth in Neutron-Irradiated Type 304 and Type 316 Stainless Steels

Small compact-tension (½TCT) specimens of Type 304 and Type 316 stainless steels have been irradiated to a relatively low fluence level of 2 × 10²⁴ neutrons (n)/m² (E > 0.1 MeV) at a fast to thermal fluence ratio of about 1 at 823 K. Comparative constant-load-amplitude fatigue tests (aimed to link the reported data from earlier tests on high-fluence irradiated, single-edge-notch-cantilever (SENC) specimens of Type 316 and tests on low-fluence irradiated compact-tension (CT) specimens ( (V = 50 mm) of Type 304) have been performed in air with cyclic frequencies ranging from 10 Hz to 0.01 Hz at 823 K and 853 K. The trends of the crack growth curves were in good correspondence with the results from previous tests at the Naval Research Laboratory (NRL) and at the Netherlands Energy Research Foundation (ECN). The effect of the irradiation on the fatigue behavior under high-frequency loading was minor. However, the crack growth rate was significantly increased under low-frequency loading due to enhanced intergranular crack formation. Detailed comparison of present results with previous NRL data for high-fluence irradiated Type 316 showed that the fatigue crack growth rate is more affected by the low-fluence irradiation due to helium-enhanced intergranular crack growth. It is concluded that effects of testing procedures and specimen geometry are minor compared to the effects of irradiation on the fatigue crack growth rate at low cyclic frequencies.