Application of the EBSD Method to Study the Fracture Mechanisms of Reactor Pressure Vessels Steels under Operational Factors

The mechanisms of degradation of the structure and properties of steels of pressure vessels of pressurized water reactors (PWRs) have been analyzed using еlectron backscatter diffraction (EBSD) method, whose possibilities are demonstrated by an example of materials of the pressure vessels of the VVER-440 reactors after 45 years of operation. It is shown that the long-term use of the materials of a VVER-440 pressure vessel at elevated operating temperatures (~270°C) induces the occurrence of portions with intercrystallite fracture, which was not observed previously. Fracture occurs at the boundaries of primary austenitic grains along the ferrite–bainite interface.