Tensile properties of ferritic/martensitic steels irradiated in HFIR, and comparison with spallation irradiation data

Tensile properties of four ferritic/martensitic steels, 9Cr–1MoVNb, 9Cr–1MoVNb–2Ni, 9Cr–2WV, and 9Cr–2WVTa, and two bainitic steels, 3Cr–3WV and A533B, were measured after irradiation to doses up to 1.2 dpa at temperatures in the range 60–100 °C in the High Flux Isotope Reactor and compared with two ferritic/martensitic (F/M) steels irradiated with 800 MeV protons and spallation neutrons in the LANSCE facility at 60–164 °C. Irradiation hardening in the steels was strong, and all of them displayed plastic instability shortly after yield for irradiations of 0.054 dpa and higher. Despite large loses in elongation, all failures occurred in a ductile manner. The dose dependencies of the increases in the yield strength with dpa were similar for all six steels, and contained a pronounced change at about 0.05 dpa. Below 0.05 dpa, the hardening exponent was 0.5–0.6, consistent with a barrier hardening mechanism. Above 0.05 dpa, the exponent was reduced to 0.1–0.2, which is speculated to be due to intervention by dislocation channeling. A trend curve for correlating changes in yield strengths of F/M steels with dose at irradiation temperatures below 160 °C is offered.