Enhancement of irradiation hardening by nickel addition in the reduced-activation 9Cr-2W martensitic steel

Reduced-activation martensitic (RAM) steels with and without an addition of 1% Ni were irradiated in a so called multisection-multidivision controlled irradiation capsule in the JMTR at 220 degrees C up to 0.15 dpa. The 1/4 power dependence of the irradiation hardening on neutron dose was observed for the specimens irradiated in the controlled capsule. A part of the specimens were simultaneously irradiated in the capsule out of the reactor core where the irradiation temperature was considered to be lower than 170 degrees C. The out of-reactor core irradiation induced a tremendous irradiation hardening as much as 350 MPa in the Ni added RAM steel but only 120 MPa of the hardening in the unadded RAM steel. The tremendous irradiation hardening was never observed following the irradiation at 220 degrees C. As for the results of positron annihilation measurements, no significant effect of the Ni addition was observed in the life time spectrum. Post-irradiation annealing studies indicate that the irradiation hardening observed in the Ni added RAM steel begins to recover at 190 degrees C and diminishes after the annealing at 250 degrees C. (C) 1998 Elsevier Science B.V. All rights reserved.