Radiation hardening and -embrittlement due to He production in F82H steel irradiated at 250 °C in JMTR

The dependence of helium production on radiation hardening and -embrittlement has been examined in a reduced-activation martensitic F82H steel (8Cr-2W-0.2V-0.04Ta-0.1C) irradiated at 250 °C to 2.3 dpa. In this study, 10B and 11B-doped specimens were irradiated to minimize the errors from the effect of B on mechanical properties by comparing the results. The specimens used were 10B-doped, 10B + 11B-doped and 11B-doped F82H steels. The total amounts of doping boron were about 60 mass ppm. The range of helium concentration produced in the specimens was from about 5 to about 330 appm. Tensile and fracture toughness tests were performed after neutron irradiation. 50 MeV-He2+ irradiation was also performed to implant about 85 appm He atoms at 120 °C by AVF cyclotron to 0.03 dpa, and small punch testing was performed to obtain ductile-to-brittle transition temperatures (DBTT). Radiation hardening of the neutron-irradiated specimens increased slightly with increasing helium production. The 100 MPa m1/2 DBTT for the F82H + 11B, F82H + 10B + 11B, and F82H + 10B specimens were 40, 110, and 155 °C, respectively. The shifts of DBTT due to helium production were evaluated as about 70 °C by 190 appm He and 115 °C by 330 appm He. In cyclotron experiment using standard F82H, a similar DBTT shift due to He was measured. These results suggest that helium production can increase the DBTT.