The micro structural study of 15Kh2MFA and 15Kh2NMFA reactor pressure vessel steels using positron-annihilation spectroscopy, mössbauer spectroscopy and transmission electron microscopy

The micro structure of the non-irradiated low-alloyed steels (15Kh2MFA and 15Kh2NMFA) was studied using different spectroscopic methods as the positron annihilation lifetime and Doppler broadening techniques, the Mössbauer spectroscopy, and the Integral low-energy electron Mössbauer spectroscopy as well as the Transmission electron microscopy. Differences in the microstructural parameters of these types of RPV steels are well detectable using all methods. It was confirmed that the heat-affected zone of these steels is the most sensitive place for thermal embrittlement in the reactor. Positron-annihilation lifetime measurements on the successive annealed specimens (XTA, YTA), which simulated the heat-affected zone, showed the rapid increase in the vacancy-type defects formation in the temperature region 525–600°C. Therefore these specimens were studied using Transmission electron microscopy in more detail.