I. Yu. Litovchenko

Evolution of Structural and Phase States at Large Plastic Deformations of an Austenitic Steel 17Cr-14Ni-2Mo

We present the results of the investigation of the evolution of the defect substructure and phase transformations in the process of deformation by rolling and high-pressure torsion of a chromium-nickel steel 17Cr-14Ni-2Mo. Experimental evidences have been found in favor of the occurrence of γ → α(α′) → γ transformations as one of the mechanisms of plastic deformation and reorientation of the crystal lattice at large plastic deformations of the steel under study. It has been shown that the nanostructured states are formed in the process of interaction of localized deformation bands with microbanded twin structures. Mechanisms of deformation and reorientation of the crystal lattice upon the formation of the above-indicated states and possible mechanisms of phase transformations in the process of large plastic deformations of this steel have been discussed.

Microstructure of EK-181 ferritic-martensitic steel after heat treatment under various conditions

The effect of heat treatment conditions on the microstructure and phase composition of a lowactivated high-temperature ferritic-martensitic EK-181 steel (Fe-12Cr-2W-V-Ta-Ba) is studied. Additional thermal cycling about the austenite-martensite phase transition temperature between quenching and tempering hinders the formation of fine interstitial phases, decreases the phase transformation-induced hardening intensity, retards the formation of a substructure with continuous misorientations, and decreases the brittle-ductile transition temperature.

Crystal-lattice distortions during mechanical twinning of the B2 phase of titanium nickelide via the mechanism of local reversible martensitic transformations

Tensor of distortions upon the formation of a {113} deformation twin by the mechanism of a combined (forward-plus-reverse) (occurring on an alternative transformation system) martensitic transformation in the B2 phase of titanium nickelide has been analyzed theoretically in the approximation of small deformations using the model of martensitic transformations based on the concept of “freezing” of cooperative thermal vibrations of atoms in close-packed atomic planes in metals. It is shown that this mechanism satisfactorily describes not only the reorientation angle but also the habit plane of the twin.

Thermal stability of the microstructure of 12% chromium ferritic–martensitic steels after long-term aging at high temperatures

The structure of EK-181 (RUSFER-EK-181, low-activation) and ChS-139 12% Cr ferritic–martensitic steels is investigated and their mechanical properties are tested after long-term (13500 h) aging at 450 and 620°C. The microstructure of the steels exhibits a high thermal stability, which provides the retention of their initial short-term mechanical properties at test temperatures.

Structure–phase transformations and physical properties of ferritic–martensitic 12% chromium steels EK-181 and ChS-139

The thermophysical properties (specific heat, thermal diffusivity, thermal conductivity, linear thermal expansion coefficient, density) of 12% chromium ferritic–martensitic steels EK-181 (RUSFER-EK-181) and ChS-139 and the structure–phase transformations that occur in them upon heating and cooling in the temperature range 20–1100°C are studied. The temperatures of the start and finish of the α → γ and γ → α transformations in these steels and the Curie temperature are determined by differential scanning calorimetry. Peaks in the temperature dependence of the specific heat and jumplike changes in the linear thermal expansion coefficient and the density and the minimum of thermal diffusivity are detected in the α → γ transformation range. Specific heat peaks, thermal conductivity minima, and inflection points in thermal diffusivity curves are also observed near the Curie temperature.

Martensitic transformations and the evolution of the defect microstructure of metastable austenitic steel during severe plastic deformation by high-pressure torsion

It has been shown that, in metastable austenitic Fe–18Cr–10Ni–Ti steel, under conditions of torsion under pressure, local reversible (forward plus reverse) (γ → α′ → γ) martensitic transformations can occur, which are one of the mechanisms of the formation of nanostructured states. An increase in the rotation rate, which leads to an increase in the deformation temperature, stimulates the reverse (α′ → γ) transformation. The evolution of the structural and phase states is represented as the following sequence: (1) mechanical twinning; (2) nucleation of martensitic plates in the microtwinned structure of the austenite with the formation of two-phase (γ + α′) structures, packet α′ martensite, and structural states with a high curvature of the crystal lattice; (3) reverse (α′ → γ)-transformations; and (4) the fragmentation of nanosized crystals via the formation of a nanotwinned structure in the austenite and of a nanoscale banded structure of the ε martensite in the α′ martensite.

Crystal-lattice distortions upon the formation of localized-deformation bands via combined forward-plus-reverse martensitic transformations

The model of plastic flow as a combined forward-plus-reverse (on an alternative flow system) martensitic fcc → bcc → fcc transformation was used to theoretically investigate transformation-related distortions on the example of localized-deformation bands with a 60°〈110〉 crystal-lattice reorientation that are formed as a result of such a transformation upon rolling of austenitic steels. An analysis of the relative contributions of various modes of deformation and crystal reorientation to the total transformation distortion has been performed.

Effect of high-temperature thermomechanical treatment in the austenite region on microstructure and mechanical properties of low-activated 12% chromium ferritic-martensitic steel EK-181

The effect of high-temperature thermomechanical treatment with deformation in the austenite region on the microstructure and mechanical properties in low-activated 12% chromium ferritic-martensitic steel EK-181 (Fe–12Cr–2W–V–Ta–B) has been investigated. This treatment leads to a significant increase (compared to traditional regime of treatment) in the density of dislocations, dispersity, and volume fraction of nanosized particles V(C,N) and, as a consequence, to an increase in the yield strength while maintaining a sufficient reserve of ductility.

EFFECT OF TEMPERING TEMPERATURE ON THE PHASE TRANSFORMATIONS IN THE FERRITIC-MARTENSITIC 12% CHROMIUM STEEL EK-181

Институт физики прочности и материаловедения Сибирского отделения РАН, Томск, Россия Национальный исследовательский Томский государственный университет, Сибирский физико-технический институт им. В.Д. Кузнецова, Томск, Россия Высокотехнологический научно-исследовательский институт неорганических материалов имени академика А.А. Бочвара, Москва, Россия Национальный исследовательский ядерный университет «МИФИ», Москва, Россия