The effect of plastic deformation temperature on the microstructure and mechanical properties of EK-164 austenitic steel
Keywords:austenitic steel, EK-164 steel, draw, cold deformation, low-temperature deformation, warm deformation, localized deformation stripes, mechanical twinning
Chromium-nickel austenitic EK-164 steel has good ductility, corrosion resistance, and effective resistance to radiation swelling in comparison with other steels of this class. Currently, due to these properties, EK-164 steel is used as one of the main materials for the production of shells of fuel elements of reactors. The construction of new fast-neutron reactors (BN-1200, etc.) requires the improvement (strength improvement) of existing nuclear power engineering materials. The paper studies the effect of plastic deformation temperature on the features of microstructure and mechanical properties of EK-164 austenitic steel. The authors proposed the technique of modification of microstructure and mechanical properties of austenitic steel using plastic deformation at various temperatures, determined the features of microstructure and mechanisms of deformation ensuring the improvement of strength properties of steel under the draw. The study showed that during cold deformation ε≈30 %, mechanical twinning (mainly by two systems) develops in the steel microstructure. The authors did not identify the formation of martensite phases in the twins’ intersections that proves the stability of austenite against the phase transformations in the process of deformation of the selected steel. Low-temperature deformation with pre-cooling in liquid nitrogen ε≈50 % leads to more intense twinning (twins by several systems) and contributes to the development of localized deformation in the micro-twin structure. In this case, the localized deformation develops mainly in places with a high density of micro-twins. In the process of warm deformation at 600 °C, ε≈60 %, the original austenite grains are fragmented with the formation of the distorted submicrocrystalline plates, which have both the low-angle and large-angle boundaries of disorientation. The structural states obtained as a result of plastic deformation provide a significant (≈2–5 times) increase in the strength properties of steel.
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