Mechanical properties of neutron-irradiated nickel-containing martensitic steels: I. Experimental study

Tensile and Charpy specimens of 9Cr-1MoVNb (modified 9Cr-1Mo) and 12Cr-1MoVW (Sandvik HT9) steels and these steels doped with 2% Ni were irradiated at 300 and 400 degrees C in the High Flux Isotope Reactor (HFIR) up to 12 dpa and at 393 degrees C in the Fast Flux Test Facility (FFTF) to approximate to 15 dpa. In HFIR, a mixed-spectrum reactor, (n, alpha) reactions of thermal neutrons with Ni-58 produce helium in the steels. Little helium is produced during irradiation in FFTF. After HFIR irradiation, the yield stress of all steels increased, with the largest increases occurring for nickel-doped steels. The ductile-brittle transition temperature (DBTT) increased up to two times and 1.7 times more in steels with 2% Ni than in those without the nickel addition after HFIR irradiation at 300 and 400 degrees C, respectively. Much smaller differences occurred between these steels after irradiation in FFTF. The DBTT increases for steels with 2% Ni after HFIR irradiation were 2-4 times greater than after FFTF irradiation. Results indicated there was hardening due to helium in addition to hardening by displacement damage and irradiation-induced precipitation. (c) 2006 Elsevier B.V. All rights reserved.