E. G. Astafurova

Influence of equal-channel angular pressing on the structure and mechanical properties of low-carbon steel 10G2FT

Results are presented of the investigation of mechanical properties, microstructure, and phase composition of low-carbon steel 10G2FT (Fe-1.12Mn-0.08V-0.07Ti-0.1C) before and after equal-channel angular pressing (ECAP). It has been established that the ECAP of steel 10G2FT at T = 200°C in the case of the ferritic-pearlitic state and at T = 400°C in the case of the martensitic state leads to the formation of a predominantly submicrocrystalline structure with an average size of structural elements of approximately 0.3 μm, causes an increase in the strength properties, a decrease in the plasticity, and the localization of plastic flow. It has been experimentally shown that the initially martensitic structure after ECAP causes higher strength properties in comparison with the ferritic-pearlitic structure.

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.

The influence of temperature on microstructure and microhardness in high-pressure torsion of low-carbon steel

The ultrafine-grained structures produced by cold (20 ?C) and warm (450 ?C) high- pressure torsion in low-carbon steel were studied using transmission electron microscopy and X-ray analysis. After cold high-pressure torsion, the size of fragments is smaller (100 nm) and structure is more homogeneous in comparison with warm deformation (120 nm). As a result of high-pressure torsion, the microhardness of steel investigated has been increased up to 600 HV and 570 HV after cold and warm deformation respectively.

Microstructural Characterization of Low-Carbon Steel Processed by High Pressure Torsion and Annealing

Ultrafine grained low carbon steel processed by high pressure torsion (HPT) has been investigated. Depending on initial state (ferritic-pearlitic state after normalization at 950°C, or martensitic ones after quenching from 950°C and 1180°C), the evolution of the microstructure and the mechanical properties was investigated after HPT and annealing at 400-600°C using transmission electron microscopy and X-ray analysis. It has been shown that HPT of martensitic low carbon steel provides a finer structure then that for ferritic-pearlitic initial state, and the initial martensitic morphology and phase composition is strongly dependent on the temperature of quenching. The initial structure was refined by HPT to 95nm in ferritic-pearlitic state and up to 65 and 50 nm in martensitic ones (after quenching from 950°C and 1180°C, respectively). Such ultrafine grained structures demonstrate substantial mechanical properties and possess a high thermal stability up to 500°C in all investigated states. Annealing for 1 h at 500°C results in grain growth up to 860nm for ferritic-pearlitic initial state and 150-450 nm for martensitic ones.

Effect of high-temperature annealing on the microstructure and mechanical properties of ferritic-pearlitic steel 10G2FT subjected to equal-channel angular pressing

Results are given of the investigation of mechanical properties, microstructure, and phase composition of low-carbon ferritic-pearlitic steel 10G2FT (Fe-1.12Mn-0.08V-0.07Ti-0.1C) after equal-channel angular pressing and subsequent high-temperature annealing at temperatures of 500–700°C. It has been shown that the predominantly submicrocrystalline structure formed during the equal-channel angular pressing possesses high thermostability up to a temperature of 500°C. The contribution of age hardening to the strengthening of steel 10G2FT during the equal-channel angular pressing and to the stabilization of the submicrocrystalline structure to high annealing temperatures is discussed.

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.

Strain localization in single crystals of Hadfield steel under compressive load

A study of strain localization under compression of Hadfield steel single crystals at room temperature was done by light and transmission electron microscopy. At <1%, macro shear bands (MSB) form that have non-crystallographic and complex non-linear habit planes and are the results of the interaction of dislocation slip on conjugate slip planes. Mechanical twinning was experimentally found inside the MSB. After the stage of MSBs formation, deformation develops with high strain hardening coefficient and corresponds to interaction of slip and twinning inside as well as outside the MSBs.

The microstructural stability of low-activation 12%-chromium ferritic-martensitic steel EK-181 during thermal aging

The results of structural investigations and mechanical tests of low-activation 12%-chromium ferritic-martensitic steel EK-181 after long-term (13500 h) aging at 450°C and 620°C are presented. It is shown that the high thermal stability of steel microstructure ensures that its original short-term mechanical properties are maintained at T ≤ 620°C.

Thermal stability of nanostructured Hadfield steel produced by high-pressure torsion

The influence of annealing (400°C–800°C, 1 h) on the phase composition, microstructure and microhardness of Hadfield steel single crystals processed by high-pressure torsion at room temperature has been investigated. After the high-pressure torsion, the high microhardness values of Hadfield steel (690–750 HV) remain under annealing up to the temperature of 500°C. The mechanisms responsible for the high thermal stability are the formation of ultrafine α′-phase and retaining of a high-strength state of the austenite associated with stability of deformation-induced twin boundaries.

Structural features and mechanical properties of austenitic Hadfield steel after high-pressure torsion and subsequent high-temperature annealing

Mechanisms of structure fragmentation and strengthening of single crystals of a Hadfield steel after warm torsion under high-pressure torsion (HPT) and subsequent annealing in a temperature range of 400–800°C have been studied. Multiple twinning and formation of ultrafine carbides upon HPT at 400°C (P = 5 GPa) promote rapid fragmentation of the microstructure. They are responsible for the high mechanical properties of the steel after HPT and the thermal stability of the microstructure up to an annealing temperature of 500°C.