Frontier Materials & TechnologiesFrontier Materials & TechnologiesFrontier Materials & Technologies2782-40392782-6074Togliatti State University111110.18323/2782-4039-2025-3-73-4ArticlesСтатьиResearch ArticleMicrostructure, properties and strengthening mechanisms of low-carbon steel subjected to equal-channel angular pressingМикроструктура, свойства и механизмы упрочнения низкоуглеродистой стали, подвергнутой равноканальному угловому прессованиюhttps://orcid.org/0000-0003-1185-5648MalininAndrey V.МалининАндрей Владимирович
Russian Federation

PhD (Engineering), Deputy General Director for Research

кандидат технических наук, заместитель генерального директора по исследованиям

MalininAV@bnipi.rosneft.ruhttps://orcid.org/0000-0002-9948-1099SitdikovVil D.СитдиковВиль Даянович
Russian Federation

Doctor of Sciences (Physics and Mathematics), senior expert

доктор физико-математических наук, старший эксперт

SitdikovVD@bnipi.rosneft.ruLebedevYuri A.ЛебедевЮрий Анатольевич
Russian Federation

PhD (Physics and Mathematics), senior researcher

кандидат физико-математических наук, старший научный сотрудник

lebedev@anrb.ruLLC RN-BashNIPIneftООО «РН-БашНИПИнефть»Institute of Physics of Molecules and Crystals of Ufa Federal Research Center of RASИнститут физики молекул и кристаллов Уфимского федерального исследовательского центра РАН300920253516530092025Copyright ©; 2025, Malinin A.V., Sitdikov V.D., Lebedev Yu.A.Copyright ©; 2025, Малинин А.В., Ситдиков В.Д., Лебедев Ю.А.2025Malinin A.V., Sitdikov V.D., Lebedev Yu.A.Малинин А.В., Ситдиков В.Д., Лебедев Ю.А.https://creativecommons.org/licenses/by/4.0https://vektornaukitech.ru/jour/article/view/1111

In the work, an ultrafine-grained (UFG) state was formed in a low-carbon steel by equal-channel angular pressing (ECAP) (8 passes, 200 °С), demonstrating high mechanical properties (yield strength is 1021 MPa, tensile strength is 1072 MPa, ductility is 10.7 %) along with satisfactory corrosion resistance (0.345 mm/year). To explain the reasons for improvement of strength properties and changes in corrosion properties, UFG steel microstructure was analysed using electron microscopy and X-ray scattering methods. Specifically, electron microscopy methods revealed structural refinement of ECAP-processed steel, resulting in the formation of equiaxed grains averaged ~240 nm in size. Modified Williamson–Hall and Warren–Averbach X-ray procedures were applied to find the patterns of changes in coherent scattering domains size, density ρ and fraction fs of screw-type dislocations, effective outer cut-off radius Re of dislocations and some other parameters of low-carbon steel depending on a number of ECAP passes (degree of deformation). X-ray diffraction analysis and small-angle X-ray scattering methods were used to determine evolution trends of mass fraction, size and morphology of various precipitates depending on the number of ECAP passes. Based on the obtained data, a model of microstructure transformation during UFG state formation in steel was proposed. Furthermore, strengthening mechanisms of both coarse-grained and UFG steels were discussed. It was found that in initial state, steel strength was primarily ensured by grain-boundary strengthening and precipitation of small Ме23С6 and Ме3С2 precipitates. It was shown that during UFG structure formation, steel strength increases due to grain-boundary strengthening and dislocation density increase. The contribution of precipitates in the UFG state to the strengthening decreases and this is due to their growth during ECAP processing. It was found that an increase in corrosion rate of UFG steel results from a decrease in ferrite grain size, an increase in grain-boundary dislocations density and a cellular structure formation.

В работе методом равноканального углового прессования (РКУП) (8 проходов, 200 °С) сформировано ультрамелкозернистое (УМЗ) состояние в низкоуглеродистой стали, демонстрирующее высокие механические свойства (предел текучести 1021 МПа, предел прочности 1072 МПа, пластичность 10,7 %) наряду с удовлетворительной коррозионной стойкостью (0,345 мм/год). Для объяснения причин повышения прочностных и изменения коррозионных свойств проанализирована микроструктура УМЗ стали методами электронной микроскопии и рентгеновского рассеяния. В частности, методами электронной микроскопии установлено измельчение структуры подвергнутой РКУП стали, в результате которого формируются равноосные зерна со средним размером ~240 нм. Модифицированные рентгеновские методики Вильямсона – Холла и Уоррена – Авербаха применены для получения закономерностей изменения размера областей когерентного рассеяния, плотности ρ и доли fs дислокаций винтового типа, внешнего эффективного радиуса Re сечения дислокаций и ряда других параметров в низкоуглеродистой стали в зависимости от числа проходов (степени деформации) РКУП. Методами рентгенофазового анализа и малоуглового рентгеновского рассеяния найдены закономерности изменения массовой доли, размера и морфологии различных преципитатов от числа проходов РКУП. На основе полученных данных предложена модель трансформации микроструктуры стали при формировании в ней УМЗ состояния. Обсуждаются механизмы упрочнения крупнокристаллической и УМЗ стали. Обнаружено, что в исходном состоянии прочность стали в основном обеспечивается за счет зернограничного упрочнения и выпадения преципитатов Ме23С6 и Ме3С2 малого размера. Показано, что при формировании УМЗ структуры стали прочность возрастает в результате зернограничного упрочнения и роста плотности дислокаций. Вклад в упрочнение преципитатов в УМЗ состоянии понижается, и это обусловлено их ростом при обработке РКУП. Выявлено, что увеличение скорости коррозии УМЗ стали объясняется уменьшением размера ферритных зерен, повышением плотности зернограничных дислокаций и формированием ячеистой структуры.

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