Effect of gas atoms and displacement damage on mechanical properties and microstructures of F82H

Effects of displacement damage and gas atoms on microstructures and mechanical properties of F82H steel were examined by some various different methods. The hardness of F82H was increased by triple beams, dual beams and single beam at 270 °C to 20 dpa and 360 °C to 50 dpa, and the increment of hardness by irradiation at 360 °C was larger than that at 270 °C. The increment of hardness due to triple, dual and single beams depended on the irradiation temperatures. The peak temperature of swelling induced by dual ion beams to 50 dpa was about 430 °C at temperatures from 360 to 600 °C and the value of swelling was about 0.6%. Strength of F82H-std steel tested at 600 and 700 °C by small punch (SP) was increased by about 84 appm helium implantation at 120 °C, and no degradation in ductility was observed. In a 0.18DCT fracture toughness test performed at 300 °C of ductile properties, the strength of F82H with helium production was rapidly decreased as compared to that with no helium production beyond a maximum strength in ductile temperature region. The cause is related to the occurrence of sub-boundary, such as lath boundaries and packed boundaries, cracking due to helium migration to sub-boundaries. From these results, the design window of safety zone of F82H steel for operation of nuclear environment systems may be modified.