On irradiation embrittlement and recovery annealing mechanisms of Cr-Mo-V type pressure vessel steels

Surveillance specimens of 15Kh2MFA reactor pressure vessel (RPV) steel and Sv-10KhMFT weld metal were investigated using internal friction, electrical resistivity and Mössbauer spectroscopy measurements in order to obtain information on their irradiation embrittlement and recovery annealing mechanisms. Internal friction measurements showed that carbon becomes trapped by irradiation-induced defects (fluence=4.1×1019 n/cm2, E>1 MeV, T=265 °C). During the recovery annealing (450 and 475 °C/1 h) carbon does not redissolve into the solid solution. Although irradiation usually increases the electrical resistivity of the RPV steels, in this study irradiation decreased the electrical resistivity of both the base and the weld metals. This can be due to a decrease in the dislocation density or precipitation under irradiation. The annealing temperature range for recovery was 300–600 °C for the base and the weld metals according to the electrical resistivity measurements. Some evidence of irradiation-induced carbide formation was achieved by the Mössbauer spectroscopy measurements.