EFFECT OF IRRADIATION IN HFIR ON TENSILE PROPERTIES OF CR-MO STEELS

Tensile specimens of tempered martensitic 9Cr-1MoVNb and 12Cr-1MoVW steels with and without additions of 2% Ni were irradiated in the High Flux Isotope Reactor (HFIR) at 400 and 600-degrees-C to displacement-damage levels of up to 72 dpa. Nickel was added to the steels to produce transmutation helium, and up to 700 appm He was produced in the steels with 2% Ni. Irradiation at 400-degrees-C caused an increase in strength and a decrease in ductility, while irradiation at 600-degrees-C caused a decrease in strength and an increase in ductility. Results at 400-degrees-C were similar to data from previous tests on steel irradiated to approximately 11 dpa (up to 110 appm He), where it was concluded that helium caused a strength increase in addition to the hardening caused by displacement damage alone. The present results indicate that the helium-enhanced strengthening at 400-degrees-C saturates with increasing helium concentration, similar to the saturation (at a lower strength level) with displacement-damage dose found in the absence of helium.