The effect of high-temperature thermomechanical treatment (HTMT) with plastic deformation by rolling in austenitic region on the microstructure and mechanical properties of 12% chromium ferritic-martensitic steel EP-823 is investigated. The features of the grain and defect microstructure of steel are studied by Scanning Electron Microscopy with Electron Back-Scatter Diffraction (SEM EBSD) and Transmission Electron Microscopy (TEM). It is shown that HTMT leads to the formation of pancake structure with grains extended in the rolling direction and flattened in the rolling plane. The average sizes of martensitic packets and ferrite grains are approximately 1.5–2 times smaller compared to the corresponding values after traditional heat treatment (THT, which consists of normalization and tempering). The maximum grain size in the section parallel to the rolling plane increases up to more than 80 µm. HTMT leads to the formation of new sub-boundaries and a higher dislocation density. The fraction of low-angle misorientation boundaries reaches up to ≈68%, which exceeds the corresponding value after HTMT (55%). HTMT does not practically affect the carbide subsystem of steel. The mechanical properties are investigated by tensile tests in the temperature range 20–700 °C. It is shown that the values of the yield strength in this temperature range after HTMT increase relative to the corresponding values after THT. As a result of HTMT, the elongation decreases. A significant decrease is observed in the area of dynamic strain aging (DSA). The mechanisms of plastic deformation and strengthening of ferritic-martensitic steel under the high-temperature thermomechanical treatments are also discussed.

In this work, we study the effect of high-temperature thermomechanical treatment (HTMT) with deformation in the austenite region on the microstructure, tensile properties, impact toughness, and fracture features of advanced low-activation 12% chromium ferritic-martensitic reactor steel EK-181. HTMT more significantly modifies the steel structural-phase state than the traditional heat treatment (THT). As a result of HTMT, the hierarchically organized structure of steel is refined. The forming grains and subgrains are elongated in the rolling direction and flattened in the rolling plane (so-called pancake structure) and have a high density of dislocations pinned by stable nanosized particles of the MX type. This microstructure provides a simultaneous increase, relative to THT, in the yield strength and impact toughness of steel EK-181 and does not practically change its ductile-brittle transition temperature. The most important reasons for the increase in impact toughness are a decrease in the effective grain size of steel (martensite blocks and ferrite grains) and the appearance of a crack-arrester type delamination perpendicular to the main crack propagation direction. This causes branching of the main crack and an increase in the absorbed impact energy.

Using X-ray diffraction, scanning and transmission electron microscopy, the microstructure of a new low-activation chromium-manganese austenitic steel with a high content of manganese and strong carbide-forming elements is studied. Its structure, dislocation character and particle composition are detailed. The processes taking place in the steel under cold-rolling deformation are described. It is shown that the mechanical properties of the new high-manganese steel revealed by testing at 20 and 650 °C are comparable with those of well-known analogs or exceed them. Relying on the structural studies, this is attributed to the dispersion and substructural strengthening. Better plastic properties of the steel are associated with the twinning-induced plasticity effect. It is shown that the steel fracture after tension at the test temperatures is mainly ductile dimple transcrystalline with the elements of ductile intercrystalline fracture (at 20 °C), while at 650 °C the signs of the latter disappear. The low-activation chromium-manganese austenitic steels characterized by increased austenite stability are thought to be promising structural materials for nuclear power engineering.

A new low-activation austenitic steel with a modified composition and high austenite stability is proposed. The features of its microstructure after solution treatment (ST) and cold rolling (CR) are studied. The mechanical properties and features of the fracture behavior of this steel under tensile tests in the temperature range of 20–750 °C are discussed. After ST, an austenitic structure with stacking faults and dispersed carbide particles of the MC and M₂₃C₆ types is observed in the steel. After CR, the grains are refined, and the average grain size decreases from 41.4 µm (after ST) to 33.9 µm. High-density microtwin packets form in the material, and the dislocation density increases relative to that after ST. As the test temperature increases from 20 to 750 °C, the yield strength of the steel decreases by approximately two times, from ≈300 to 150 MPa (for ST) and from ≈700 to 370 MPa (for CR). In the studied temperature range, the steel demonstrates up to 2.6 times higher values of elongation to failure, ≈40–80% (for ST) and ≈13–27% (for CR), compared to steels of similar compositions and lower manganese content. Mechanical twinning contributes to the high steel ductility up to 300 °C. Signs of discontinuous flow in the tensile curves after ST in the temperature range of 500–600 °C and a decrease in the elongation to failure in the close temperature range indicate dynamic strain aging (DSA). Steel fracture after tension at all test temperatures mainly occurs via a ductile dimple transcrystalline mechanism with elements of ductile intercrystalline fracture. It is shown that cracks nucleate on clusters of dispersed second-phase particles. The mechanisms of plastic deformation, fracture, and strengthening of the proposed modified low-activation austenitic steel are discussed.