Thermodynamic analysis of the formation of tetragonal bainite in steels

Mirzayev, D. A.; Мирзоев, А. А.; Buldashev, I. V.; Okishev, K. Yu.

doi:10.1134/s0031918x17060060

Cited by 7 publications

(13 citation statements)

References 14 publications

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“…Some recent calculations based on the theory of Zener and Khachaturyan show that carbide suppression can lead to tetragonality. An increase of 40% to 60% of carbon solubility in BCT compared to the BCC structure was highlighted [26]. The localization of retained austenite in the microstructure can give valuable information regarding the nature of the surrounding phases.…”

Section: Feature Characteristicsmentioning

confidence: 99%

Microstructure Evolution and Competitive Reactions during Quenching and Partitioning of a Model Fe–C–Mn–Si Alloy

Aoued

Danoix

Allain

et al. 2020

Metals

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The mechanisms behind the carbon enrichment of austenite during quenching and partitioning are still a matter of debate. This work investigates the microstructural evolution during the quenching and partitioning of a model Fe–C–Mn–Si alloy by means of in situ high energy X-ray diffraction (HEXRD) atom probe tomography, and image analysis. The ultra-fast time-resolved quantitative information about phase transformations coupled with image analysis highlights the formation of carbide-free BCT bainite, which is formed within a very short range during the reheating and partitioning step. Its transformation rate, which is a better indicator than the intrinsic volume fraction, depends on the quenching temperature (QT). It is shown to decrease with decreasing QT, from 45% at QT = 260 °C to 20% at QT = 200 °C. As a consequence, a significant part of the carbon enrichment observed in austenite can be attributed to bainite transformation. Furthermore, a large part of carbon was shown to be trapped into martensite. Both the formation of Fe2.6C iron carbides and the segregation of carbon on lath boundaries in martensite were highlighted by atom probe tomography. The energy for carbon segregation was determined to be 0.20 eV, and the carbon concentration on the lath boundaries was obtained to be around 25 at %. Therefore, the carbon enrichment of austenite is the result of competitive reactions such as carbon partitioning from martensite, bainite transformation, and carbon trapping in martensite.

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Section: Feature Characteristicsmentioning

confidence: 99%

Microstructure Evolution and Competitive Reactions during Quenching and Partitioning of a Model Fe–C–Mn–Si Alloy

Aoued

Danoix

Allain

et al. 2020

Metals

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“…The primary results from the ultra-rapid quenching experiments were published as graphs, exemplified by the reproduction in Figure 1 for some Fe-C alloys. [5] For the three low C alloys in Figure 1, it is evident that lath martensite did not have sufficient time to form a detectable amount above the M P s line during cooling at a rate above a critical cooling rate, v 0 cr , which was the basis of the conclusion of similarity to isothermal martensite. However, there was another critical cooling rate, v 0 cr , below which plate martensite cannot form.…”

Section: Critical Time For Complete Formation Of Lath Martensitementioning

confidence: 96%

“…The two kinds of critical cooling rates were evaluated from similar graphs for the remaining 30 binary or ternary Fe alloys, [5][6][7][8][9][10][11][12] utilizing the first experimental point on the M P s line for v 0 cr and the last experimental point on the M L s line for v 00 cr . The values were read off a scanned copy of Figure 1 and the other graphs using the Plotdigitizer software.…”

Section: Critical Time For Complete Formation Of Lath Martensitementioning

confidence: 99%

“…Exceptions have been classified as isothermal martensite. [1][2][3][4] A Russian group [5][6][7][8][9][10][11][12] instead applied ultra-rapid quenching on steels that could then form both lath and plate martensite. They found that the formation of lath martensite can be suppressed by very high cooling rates, and the rate of formation should, thus, be limited although at a very high level.…”

Section: Introductionmentioning

confidence: 99%

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Evaluation and Modeling of the Rate of Formation of Lath Martensite in Fe-C Alloys, Extracted from Ultra-Rapid Quenching Experiments

Kumpati,

Hillert,

Borgenstam

2024

Metall Mater Trans A

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Isothermal information is rarely available for the formation of martensite in Fe or Fe alloys due to a very high rate of transformation compared to the rate of heat conduction. Such information has now been extracted for lath martensite in some sets of Fe alloys from available information on ultra-rapid quenching but only at a single temperature for each alloy, related to its two MS temperatures. The temperature dependence could, thus, be studied only on binary sets of alloys. Those results have been applied to mathematical models based on the Arrhenius equation and illustrated with Arrhenius plots. For three sets of binary Fe alloys, a large group of rates came close to the rate of an almost pure and carbon-free Fe-C alloy. It illustrated that Cr, Ni, and Ru in low contents have relatively small effects on the rate of formation of lath martensite in Fe. It also demonstrated that the present measurements have considerable reproducibility. In contrast, a set of Fe-C alloys did not give a straight line in the Arrhenius plot. Using a new mathematical model based on the concept of the Arrhenius equation to express the effect of carbon, it was possible to predict the rate of formation of lath martensite for Fe-C alloys with fixed C content and their temperature dependencies which are not available experimentally due to the very high rate of formation.

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“…Тем самым уменьшаются величины искажений у сопряженных атомных z-рядов, содержащих углерод и свободных от него. По-видимому, именно энергетика этого эффекта лежит в основе теории Зинера -Хачатуряна [14,15].…”

Section: расположение атомов и октаэдрических пор типа Z в решетке оцunclassified

Analysis of the Tetragonality of the Crystal Lattice of Martensite of Fe–c Alloys in the Hard-Sphere Model

Mirzaev¹,

Okishev²,

Mirzoev³

et al. 2018

MET

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Модель укладки твердых атомов-сфер использована в статье для выяснения ряда вопросов, затрагивающих мартенситное превращение в углеродистых сталях. Рассмотрена деформация, которая возникает, когда сферический атом углерода с радиусом 0,77 Å помещают в октаэдрическую пору z-подрешетки внедрения железа. Показано, что смещения атомов железа, лежащих на оси oz, оказывается столь значительными, что они блокируют от возможного заполнения две ближайшие следующие октаэдрические поры. Они будут деблокированы только в том случае, когда четыре атома углерода займут аналогичные поры на ребрах элементарной ячейки и вновь удалят атомы железа от заблокированных пор. Был сделан расчет количества атомов углерода в элементарной ячейке в зависимости от содержания углерода в стали. Оказалось, что количество атомов углерода в ячейке равное 0,5 достигается при концентрации углерода 5,13 масс. %. Следовательно, практически у всех закаленных конструкционных и инструментальных сталей в среднем не происходит заполнения даже одной октаэдрической поры в центре грани. В рамках данной модели рассчитаны параметры решетки a и c, которые сопоставлены с экспериментальными данными, полученными академиком Г.В. Курдюмовым. Показано их очень хорошее согласие для параметра c и менее точное -для параметра a, что, с нашей точки зрения, обусловлено отсутствием информации о коэффициенте Пуассона для процессов в атомном масштабе. Разработан метод определения параметров решётки идеального мартенсита, у которого все z-поры заняты атомами углерода.Ключевые слова: тетрагональность, октаэдрические поры, атомы углерода, атомные радиусы.

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Thermodynamic analysis of the formation of tetragonal bainite in steels

Cited by 7 publications

References 14 publications

Microstructure Evolution and Competitive Reactions during Quenching and Partitioning of a Model Fe–C–Mn–Si Alloy

Microstructure Evolution and Competitive Reactions during Quenching and Partitioning of a Model Fe–C–Mn–Si Alloy

Evaluation and Modeling of the Rate of Formation of Lath Martensite in Fe-C Alloys, Extracted from Ultra-Rapid Quenching Experiments

Analysis of the Tetragonality of the Crystal Lattice of Martensite of Fe–c Alloys in the Hard-Sphere Model

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