Post-irradiation fatigue test of 2 1/4Cr-1Mo steel for the pressure vessel material of the HTTR

Low cycle fatigue tests of the irradiated 2 1/4Cr-1Mo steel for the pressure vessel material of the High Temperature Engineering Test Reactor (HTTR) were performed to examine the neutron irradiation effect on fatigue properties, i.e., fatigue life and cyclic softening behavior. These tests were performed at 450degC in a vacuum of ∼10-4 Pa using a servo-hydraulic fatigue testing machine installed in a hot cell of the Hot Laboratory of the Oarai Research Establishment. Axial strain rate was controlled at 0.1%/sec with total strain ranges of 0.75, 0.8, 1.0, 1.2 and 1.5%. Main results are summarized as follows: 1) Maximum stress at the initial stage of the cyclic fatigue testing of the specimens irradiated to a neutron fluence over 2x1019 n/cm2 (>1MeV) increased in comparison with the unirradiated specimens. 2) No significant difference was found in the cyclic softening behavior between the irradiated and unirradiated specimens. 3) Fatigue life of the irradiated specimen whose ductility was reduced by the neutron irradiation decreased slightly in comparison with the unirradiated specimen. 4) It is considered that there is no effect of the neutron irradiation on the fatigue life and the cyclic softening behavior at the total fluence expected in the lifetime of the HTTR pressure vessel. (author)