Keywords: steel, reactor pressure vessel, RPV embrittlement, neutron embrittlement, structural defects, positron annihilation, Mossbauer spectroscopy, nuclear reactors, thermal treatment, hardness measurement, thermal embrittlement, transmission electron microscopy, microstructure
Microstructural study of thermally treated reactor pressure vessel steels using spectroscopic methods
Positron annihilation spectroscopy (lifetime and Doppler broadening techniques), transmission Mössbauer spectroscopy, integral low-energy electron Mössbauer spectroscopy and transmission electron microscopy were applied to examine thermally treated reactor pressure vessel steels (RPV). The results of these methods obtained for different types of steels are discussed and correlated with hardness measurements on thermally treated 15Kh2MFA and 15Kh2NMFA RPV steels prepared under laboratory conditions simulating the heat-affected zone, which is the most discussed and sensitive part of RPV from the thermal and neutron embrittlement point of view. Positron-annihilation lifetime measurements on the heat-affected zone specimens, annealed at successively higher temperatures, show the drastic increase in the vacancy-type defect formation in the temperature region 525 to 600°C. Therefore, these specimens were selected for a further detailed study by transmission electron microscopy.