Effects of Helium Production and Heat Treatment on Neutron Irradiation Hardening of F82H Steels Irradiated with Neutrons

The influcence of addition of 10B and 11B on radiation hardening as a function of irradiation temperature was examined in reduced-activation martensitic F82H+B steels (8Cr-2W-0.2V-0.04Ta-0.1C-0.006B). Specimens used were 10B doped, 10B+11B doped and 11B doped F82H steels. Helium concentration produced in the specimens through 10B(n, α)7Li reaction was measured from about 15 to about 330 appm. Radiation hardening of the specimens irradiated at 300°C to 2.3 dpa and 150°C to 1.9 dpa was observed. Increment of radiation hardening possibly due to helium in the specimen irradiated at 300°C tended to increase slightly with increasing helium production in tensile test at 20°C, but it was not observed for 150°C irradiation. Therefore, it can be mentioned that the enhancement of radiation hardening in the 10B(11B) doped steels depends on irradiation temperature. The dependence of radiation hardening on tempering time was also examined for F82H-std irradiated at 150°C to 1.9 dpa. Increment of yield strength of F82H-std tended to increase with increasing tempering time. The relation between the shift of DBTT and the increment of yield strength due to irradiation suggest that the extension of tempering time or the increase of tempering temperature would be beneficial for mechanical properties of F82H-std.