Maps of the strain tensor component εyy and profiles of the distribution of εyy along the length of the sample plotted by the method of digital image correlation are used to study the evolution of εyy and the width bb of the nucleating center, of the band nucleus and the band itself during tension of sample 1 of steel 08G2B exhibiting a high magnitude of the strain aging effect (SAE) after heating to Th = 250°C; the results are compared to the data for sample 2 (Th = 680°C) with low SAE. The experimental data obtained are used to reconstruct at the micro- (dislocation) level the process of formation and growth of the nucleating center and of the nucleus of the localized strain band emerging from it.

По картам компоненты тензора деформации εyy и профилям распределения εyy вдоль длины образца, построенных методом корреляции цифровых изображений, изучена эволюция εyy и ширины bп зародышевого центра, зародыша полосы и самой полосы в ходе растяжения образца 1 стали 08Г2Б, имеющего большую величину эффекта деформационного старения (ЭДС), после нагрева до Тн = 250 °C, а также образца 2 (Тн = 680 °C) с низким ЭДС. На основе полученных экспериментальных данных реконструирован на микро- (дислокационном) уровне процесс образования и роста зародышевого центра и выходящего из него зародыша полосы локализованной деформации.

Методом корреляции цифровых изображений определены структурно-деформационные факторы на мезо- и макроуровнях, ответственные за низкую пластичность стали 08Г2Б, проявляющей эффект деформационного старения после нагрева при 250 °C. К ним относится небольшой масштаб пластической деформации по полосовому механизму, локализованной в ~ 1/3 части образца, где на короткой площадке текучести формируются только две деформационные полосы, образующие очаг деформации при пересечении. Остальные два очага деформации возникают на линейной и степенной стадиях растяжения, когда разблокировка дислокаций происходит в ходе рассредоточенной деформации.

The short-term mechanical properties of commercial corrosion-resistant nickel alloys based on Ni-Cr (Hastelloy® G-35® or UNS N06035), Ni-Mo (Hastelloy® B-3® or UNS N10675), and Ni-Cr-Mo (VDM® Alloy C-4 or UNS N06455, VDM® Alloy 59 or UNS N06059, and KhN62M-VI) systems were analyzed in the as-received state and after long-term (up to 5000 h) aging at 500–700 °C. All alloys exhibited moderate strength and high ductility in the as-received state. Under the influence of high temperatures, these alloys showed a tendency toward the decomposition of Ni-based FCC solid solutions and a change in mechanical properties. It was shown that the difference in chromium and molybdenum content in Ni-Cr-Mo alloys leads to the formation of secondary phases of various composition and morphology, which had varied influence on the short-term mechanical properties of the materials. Grain boundary precipitates had a negligible effect on the strength properties of the investigated alloys, while intragranular precipitates embrittled nickel-based alloys, reducing their possible application at high temperatures.

Исследованы структура и механические свойства конструкционной стали 38Г2Ф после закалки и высокотемпературного изотермического отпуска различной продолжительности. На основе анализа кривых растяжения в условных и истинных координатах выявлены особенности деформационного поведения образцов на площадке текучести и равномерной стадии деформации. Проанализировано влияние распределения компоненты деформации εyy вдоль рабочей части образца на изменение прочностных и пластических характеристик стали на разных стадиях/периодах растяжения.

We study the structure and mechanical properties of 38G2F structural steel after quenching and high-temperature isothermal tempering of different durations. By analyzing the stress-strain diagrams in conventional and true coordinates, we reveal specific features of the deformation behavior of samples on the yield plateau and in the uniform stage of deformation. We also analyze the influence of the distribution of strain component εyy along the working part of the sample on the variations of strength and plastic characteristics of steel in different stages/periods of tension.

The viscoplastic properties of microalloyed medium carbon steel 38G2F specimens subjected to quenching from 900°C and tempering at 650°C followed by cooling in various media are studied by analyzing the results of tensile and impact bending tests. The parameters controlling metal embrittlement during room-temperature tests are found for the stages (periods) on stress–strain and impact bending curves. Based on the revealed correlations between the parameters of static and dynamic tests (between true stress Sf, impact toughness KCV, and relative reduction of area φf to failure and static fracture toughness a), we proposed a new approach for estimating the viscoplastic properties of steels in various structural-phase states.

The structure and mechanical properties of low- and medium-carbon steels quenched and tempered with different isothermal holding times at temperatures ranging from 250 to 650 °C are studied. It is shown that, for the steels under study, three stages can be distinguished on the curves of hardness as a function of isothermal holding at different temperatures. Hardness testing is used to determine tempering conditions leading to a comparable level of hardness. To calculate the tempering parameter, the constant C in the Hollomon–Jaffe equation is determined for the steels in question.

The morphology of structural components in hot rolled pipes made of 38G2F steel has been studied by optical metallography. It is shown that the sections elongated along the rolling direction with a morphology different from pearlite are sections of upper bainite, the hardness of which is comparable to the hardness of pearlite ( 290–300 HVμ). Plotting the thermokinetic diagrams (TKD) of the decomposition of supercooled austenite, as well as a joint analysis of the microstructure and hardness, allowed us to determine the minimum velocity Vcool 0.5°C/s at which the bainite component in the pipe wall is formed. The temperature–time parameters of the decomposition of supercooled austenite with increasing austenitization temperature from 850 to 1000°C have been determined.

The paper reports on a transmission electron microscopy analysis of the dislocation structure of normalized 09G2S steel with strain aging. The analysis shows that in a steel specimen deformed to its yield stress, the dislocation density peaks at the center of a strain localization band (in its active zone) and decreases by about an order of magnitude at its sides. The structure of these band zones, which are in different strain hardening stages, is examined and the Burgers vector of dislocations of the primary slip system is determined. The ends of such dislocations form ordered planar dipole walls, leading to polygonization by dislocation slip. Also considered is the specimen structure at the yield and ultimate stresses.

The effect of rolling modes and cooling conditions on the structure and mechanical properties medium-carbon manganese low-alloy steels of type 38G2F is investigated. The critical temperatures Ac 1 and Ac 3 are determined. The characteristics of the ferrite, pearlite and bainite structural components (the content and the morphology) and the sizes of the initial austenite grains in pipes with different wall thicknesses are determined. Tensile mechanical tests are performed. It is shown that the high level of mechanical properties (σ 0.2 > 650 MPa, σ r > 900 MPa) of the pipes with wall thickness 16.0 mm is a result of the presence of bainitic component in the structure. It is suggested that the temperature of heating of the pipe billet for rolling should be reduced from 1230 – 1260°C to 1170 – 1180°C for manufacturing pipes with a size of ∅93.2 × 13.0 mm and ∅127 × 16.0 mm. The combination of their mechanical properties matches the E strength group.

The evolution of the structure and mechanical properties of medium-carbon microalloyed steel after quenching and tempering at 650оС of various durations has been studied. It is shown that the change in the microstructure and softening of steel with an increase in the duration from 2 to 3000 minutes falls on two stages of martensite tempering: medium (stage II) and high-temperature (stage III). Intensive drop of strength properties ~ 100 MPa/min at stage II is replaced by a very inert softening ~ 0.1 MPa/min at stage III. Using TEM, EBSD and X-ray diffraction analysis the evolution of the microstructure was observed and a quantitative estimation of the strengthening components and their relative contribution to the yield strength at different stages of tempering was performed.

A transmission electron microscopy study was carried out to examine the dislocation structure of normalized steel 09G2S that exhibits a strain aging effect. In a specimen stretched to the yield point, the maximum dislocation density is observed in the center (active zone) of the localized deformation band and decreases by about an order of magnitude at the band edges. The structure of these band regions, which are at different stages of strain hardening, is analyzed. The Burgers vector of dislocations of the primary slip system is determined; the dislocation ends form ordered flat dipole walls, leading to slip polygonization. The relationship between the specimen structure at the yield point and at the ultimate load is considered.

The features of Lüders deformation in the normalized 09G2S steel are studied by the methods of digital image correlation, topography, and scanning electron microscopy of specimen faces. The paper studies the appearance, growth, structure, and location of deformation bands, as well as plastic strain in them.

The article is devoted to studying the rheological properties of metals and alloys in a cold state based on the results of tensile tests of cylindrical specimens. The aim of this study is to apply the method for optical measuring the neck profile for determining the hardening curve and to evaluate the accuracy of the data obtained using reverse simulation of the test process. For the study, the specimen of aluminum was used, which is characterized by increased plasticity and a continuous stage of deformation concentrated in the neck. The experimental data were processed using the Bridgman, Davidenkov-Spiridonova, and Ostsemin models. The results of the reverse simulation that performed using the hardening curve based on the Ostsemin model have the greatest convergence with the laboratory experiment in terms of tensile force and convergence at the level of other models in terms of neck shape change.

Изучено влияние режимов проката и условий охлаждения на структуру и механические свойства среднеуглеродистых марганцовистых микролегированных сталей типа 38Г2Ф. Определены критические температуры (Ac1, Ac3), характеристики структурных составляющих - феррита, перлита, бейнита (количество и морфология), а также размеры бывшего аустенитного зерна в трубах разной толщины. Проведены механические испытания на растяжение. Показано, что высокий уровень прочностных характеристик (σ0,2 650 МПа, σв 900 МПа) труб с толщиной стенки 16,0 мм обусловлен наличием бейнитной составляющей в структуре. Предложено снизить температуру нагрева трубной заготовки перед прокаткой от 1230 - 1260 °C до 1170 - 1180 °C для получения труб размерами Ø93,2 × 13,0 мм и Ø127 × 16,0 мм с комплексом механических свойств, соответствующим требованиям группы прочности Е.

The influence of crystallographic texture of low-carbon, low-alloyed pipe steel (06Mn2MoNb) after thermo-mechanical controlled processing on fracture deformation has been studied by means of tensile testing and electron backscatter diffraction (EBSD) method. The paper demonstrates that fracture in textured metallic materials is characterized by anisotropy, while its characteristics are orientation-dependent.