Study of the Mechanical Property Changes of Irradiation Embrittled Pressure Vessel Steels and Their Response to Annealing Treatments

摘要

Isochronal and isothermal heat treatments have been used to study the recovery of hardness of an irradiated pressure vessel steel forging for purposes of planning and realizing IAR (Irradiated-Annealed-Reirradiated) experiments. Charpy V notch tests have been performed to assess the toughness of the material irradiated to various fluences up to a maximum of 5x10 sup 19 n/cm sup 2 , E > 1 MeV at 290 degrees C with and without an intermediate annealing treatment at 450Cx168h. The effect of the intermediate annealing was evident. The recovery of the upper shelf energies was strongly enhanced by a thermal aging effect due to the annealing treatment for all fluence levels investigated compared to the irradiated condition. The transition temperature shifts exhibited a less straight forward behaviour due to the mentioned aging effect which opposed the recovery process for this property leading to a net shift increase at lower and to a net recovery benefit at higher fluence levels. A phenomenological model description for the IAR embrittlement-recovery path is suggested. For this material and these irradiation conditions a plant life extension (PLEX) may be brought about if a specific annealing treatment is applied at a fluence level that is half the anticipated target fluence F for PLEX. In this case it was found that F > 1.6x10 sup 19 n/cm sup 2 . (ERA citation 12:041298)