Mechanical and metallurgical characteristics of steels for nuclear power plant components

The objective of the study was to compare for three different steels the values of fracture toughness obtained for large test specimens 150 mm in thickness with those obtained for small specimens consisting of fractured parts of the large specimens from different, accurately defined sites, and to compare the fracture toughness values for all tested materials. Temperature dependence was also determined of the dynamic values of fracture toughness and compared with static and with reference values. Steel 20Cr2.5MoV showed approximately a double level of static and dynamic fracture toughness and also a double cyclic life as against steel 20Mn. In components of large cross sections, the fracture toughness of the part with the lowest brittle fracture resistance is probably responsible for the level of fracture toughness. The knowledge obtained on the fatigue crack kinetics as well as the values on cyclic life agree with previously obtained results for steels of the 10Cr2.5Mo and 15Cr3Mo types. (M.S.)