The microstructural evolution and mechanical properties of WWER 440 steam generator steel GOST 22K after long-term operation were thoroughly examined in this study. The samples were taken directly from a steam generator using the small punch test method. The uniqueness of these samples lies in the fact that they were real operating materials used in a nuclear power plant with different years of operation. The microstructure was characterized using optical microscopy and transmission electron microscopy supplemented by selective electron diffraction and semi-quantitative chemical microanalysis. It was found that with the prolongation of the operation time of the steam generator, the density of carbides increased slightly, which was reflected in a decrease in the mean distance between particles, but these differences were very small, which indicates the microstructural stability of GOST 22K steel. The stability of this steel was also confirmed by measuring its mechanical properties, which changed only minimally depending on the years of operation. The tensile strength values were in the range of 508 to 579 MPa. In the case of the ductile-to-brittle transition temperature (DBTT), a slight increase was found after 6 years of operation. The DBTT did not change significantly with subsequent operation.

From the point of view of the safety of nuclear power plants, it is necessary to determine the properties of the manufactured material used. One of the possible risks is the use of inappropriate turning on the material, whose subsequent surface and thus corrosion properties in such an extreme environment are significantly stricken. In this work, high cutting speed (596 m⋅min ⁻¹ ) was used for turning austenitic stainless steel 08Ch18N10T using a CBN cutting tool. Such a high cutting speed significantly affected surface integrity and surface properties such as residual stresses, roughness, hardness and surface toughness (metallographically determined and analysed using X-ray tensometry and acoustic emission). The area that was turned contained deformed grains, which contained deformation twins and slip bands. All these factors can affect stress corrosion cracking susceptibility and corrosion resistance. For this reason, the sample was exposed in a MgCl2 solution according to the ASTM G36, while the surface crack density and the crack lengths or depths were determined. The effect of residual stresses on the direction and propagation of surface cracks has been proven. DL-EPR test recorded sensitization that did not occur at the grain boundaries but in the turning direction where pitting lines appeared. Exposure in a simulated primary circuit environment was performed in an autoclave, where no signs of stress corrosion cracking were confirmed.