Usually the assessment of the irradiation sensitivity and annealing behavior of reactor pressure vessel (RPV) steels is performed by means of destructive test methods, mainly impact and tension tests. In this paper a new kind of search for an efficient temperature-time regime for postirradiation thermal heat treatment is presented using nondestructive test methods like positron annihilation (Doppler broadening pararneter S) and hardness (Vickers hardness HV 10).
Samples of Cr-Mo-V RPV steels (Soviet type 15Kh2MFA) were irradiated to different fluence levels of fast neutrons at temperatures T < 156°C in a test reactor (base metal) and T = 265°C in a pressurized water reactor (base as well as weld metal). From isochronal and isothermal annealing curves of HV 10 and S, favorable temperature-time regimes for each type of irradiated material were estimated. The data obtained from tension and impact tests indicate that sufficiently large recoveries took place by application of these regimes.
The new approach presented is especially useful in such cases where only the smallest amounts of irradiated materials are available—a case often met for RPV surveillance specimens.