Effect of Various Metallurgical Microstructures on the Response of the Nickel-Molybdenum-Chromium BH 70 Steel to Neutron Irradiation at 285°C

Radiation hardening and embrittlement of the BH 70 steel heat treated to different microstructures (tempered martensite, tempered bainite, and tempered mixed ferrite-perlite, bainite, and martensite after neutron irradiation about 7 × 10²³ n/m² > 1 MeV at 285°C) were compared with commercial heat treatment conditions. Only moderate radiation hardening, with small differences for individual conditions, was measured in all four heat treatment conditions (by 29 to 48%). Roughly the same radiation embrittlement ΔTT_4IJ = 137 to 148°C) was found in all heat treatment conditions used. The initial (unirradiated) and resultant (irradiated) Charpy-V 41-J transition temperature of the BH 70 steel, however, can be altered appreciably through heat treatment practices, resulting in different microstructure. Initial transition temperatures (TT_4IJ) of individual heat treatments were found in the range from −73 to −143°C.