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Coefficient B values determining influence of main alloying elements on hardenability according to Moser and Legat.
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The presented work was aimed at evaluating influence of boron on hardenability of steel quantitatively and evaluating this effect during complex use of boron with other alloying additives like chromium, vanadium and titanium. For this purpose, eight melts with variable chemical compositions were prepared. From the ingots, cylindrical specimens with...
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... Furthermore, increasing the tempering temperature above 450°C promotes the diffusion of atoms, the carbon dissolved in the crystalline matrix during hardening precipitates in the form of iron carbides which reduces the hardness [23,19] and significant increase in elongation. The increase in the percentage of addition elements such as Mn (0.81%) and Cr (1.06%) justifies the notable increase in the hardness of the material in the untreated state [24,25]. The fracture of the samples is ductile, characterized by the presence of macroscopic plastic deformation, and therefore by the slow propagation of cracks with high energy consumption. ...
Understanding the mechanical properties of steel is crucial to ensuring the proper functioning of industrial mechanical systems. This study focuses on the tensile behavior and specific mechanical properties of low-alloy steel AISI 4041. It combines practical experiments and numerical simulations using Abaqus software. The experiments involve fabricating 18 standard-sized tensile specimens, followed by a heat treatment including oil quenching and various tempering temperatures (ranging from 350°C to 650°C) to create a range of hardness levels. Tensile tests provided experimental data, subsequently validated by numerical analyses using the eXtended Finite Element Method (XFEM). The results indicate a maximum hardness of 522 HV, maximum tensile load and a maximum tensile strength of 1680 MPa with tempering at 350°C. This approach significantly improved the results, with errors generally below 0.06% for maximum strain and stress. This study provides valuable insights for designing and optimizing low-alloy steel structures suitable for high-temperature environments.
... %, which lies within this solubility range. Bialobrzeska (2021) reported that a hardenability increase can be provided by a boron addition of only 5 ppm (0.0005 wt. %) if a low-alloyed Cr steel is the case. ...
A new kind of boron-added cast austenitic steel which also contained chromium, molybdenum and manganese was manufactured via vacuum induction melting followed by casting procedure. Solution annealing heat treatment was performed at three different temperatures for three different times to dissolve eutectic M2C carbides in austenitic matrix. All of the samples were rapid-cooled in oil medium after the solution annealing heat treatment. Aging treatments were carried out after solution annealing heat treatment performed at 1250 °C for 24 hours. Hardness value was decreased after solution annealing performed at 1250 °C for 24 hours. Transformation of M2C carbide with a hexagonal lattice into Fe-rich M6C carbide with a face-centered cubic lattice and formation of precipitates occurred as a result of aging performed at 700 and 800 °C. Sub-micron sized Cr23C6 carbides and Mo2BC precipitates were formed and hardness value was increased after aging performed at 700 °C. Nano-sized Cr23C6 carbides, Mo2B borides and Cr7BC4 precipitates were formed and hardness value was higher after aging performed at 800 °C. An optical light microscope was utilized to characterize solution annealing treatments and to perform grain size measurements. A scanning electron microscope was used to identify carbide types and carbide transformation during aging.
... Therefore, in the presented article, an attempt was made to correlate the results obtained from tribological tests with selected mechanical properties of the analyzed materials in order to replicate the experiment of Sundström et al. [9] (limited to low-alloy steels only). Limiting the experiment to low-alloy steels only is a novelty of this study, especially since some of the analyzed cast steels contained micro-addition of boron, which puts the analyzed materials in the group of modern boron steels with higher abrasion resistance which come from various manufacturers such as ThyssenKrupp Steel Europe AG (steels XAR and TBL), Dillinger Hütte GTS (steels Dillidur), Grobblech GmbH (Durostat), AcelorMittal (Usibor), TATA Steel Group (Abrazo), TITUS Steel (Endura), SUMITOMO Metal (Sumihard) and JFE EVERHARD Corporation (JFE-EH) [2,20,21]. These steels are commonly used by industry in various wear-related applications which also makes the motivation for this study practical. ...
This paper focuses on relationship between the mechanical properties and abrasive wear resistance, expressed by the Kb index, using an example of low-alloy cast steels. In order to achieve the aim of this work, eight cast steels of varying chemical composition were designed, cast and then heat treated. The heat treatment involved quenching and tempering at 200, 400 and 600 °C. Structural changes caused by tempering are demonstrated by the different morphologies of the carbide phases in the ferritic matrix. In the first part of this paper, the present state of knowledge about the influence of structure and hardness on the tribological properties of steels is discussed. This research involved the evaluation of a material’s structure, as well as its tribological and mechanical properties. Microstructural observations were performed using a light microscope and a scanning electron microscope. Next, tribological tests were carried-out with the use of a dry sand/rubber wheel tester. To determine the mechanical properties, Brinell hardness measurements and a static tensile test were carried out. The relationship between the determined mechanical properties and abrasive wear resistance was then investigated. The analyses also provided information regarding the heat treatment states of the analyzed material in the as-cast and as-quenched states. It was found that the abrasive wear resistance, expressed by the index Kb, was most strongly correlated with hardness and yield point. In addition, observations of the wear surfaces indicated that the main wear mechanisms were microcutting and microplowing.
... Boron, due to its atomic magnitude (the smallest substitutional element or the largest interstitial element), inter alia, tends towards segregation on the former austenite grain boundaries, which delays the initiation of phase transformations. Moreover, in order to ensure the highest hardenability, an appropriate combination of the boron content with the remaining elements, i.e., manganese, chromium, and vanadium, whose effects delay diffusion transformations (illustrated with corresponding curves on the TTT diagram), is necessary [5]. Thus, it is possible to obtain a uniform martensitic structure on the cross section of a sheet with a considerable thickness of even up to 130 mm. ...
This paper presents the results of wear tests of three types of commercial abrasion-resistant steels. The samples, cut from commercially available sheets of metal, were subjected to wear tests to a total friction path of 20,000 m. The tests were provided using the “rotating bowl” method in three types of natural soil masses. The soil moisture and test parameters were kept constant. The tests were carried out in six replications for each material. The testing results indicate that hardness does not determine the resistance to abrasive wear, which is supported by the weight loss results for particular materials. Hardox 600 steel, which is not characterized by the highest hardness, exhibited the lowest weight loss value compared to the other materials in all test soils. For the light soil, the weight loss for Hardox 600 was approx. 1.3 times lower than for Hardox 500 steel and approx. 1.6 times higher than for Hardox Extreme steel. With regards to the medium and heavy soil, the weight losses for Hardox 600 in relation to Hardox 500 steel were approx. 1.7 and 1.6 times lower, respectively, while in relation to Hardox Extreme steel the weight losses were 1.5 and 1.7 times higher, respectively.
... For decades carbon and low alloy steels have been a crucial structural material due to their excellent combination of ductility and strength resulting from a heat treatment [1,2], specialized alloying additives [3,4] or specialized thermomechanical influencing on steel microstructure refinement [5,6]. One of the most popular steel utilized for forged components is low-alloy grade 42CrMo4 (AISI 4140). ...
For decades, steel has been a crucial structural material. Mainly low-alloy steel grade 42CrMo4 is utilized for
manufacturing forgings. This paper investigates the microstructure and hardness development of the 42CrMo4
steel hollow component with an outer flange. The component has been formed via cold forging in combination
with extrusion and upsetting technologies. Prior to forming, the workpiece was annealed to obtain hardness at the
level of 181±9 HV0.3. The FEM analysis reveals the areas that undergo higher stress and strain. The flow lines
macrostructure and microstructure of hollow parts were investigated using light optical microscopy (LOM) and
scanning electron microscopy (SEM) equipped with EDS. Vickers hardness allows identifying the work hardening
of the crucial element areas. The microstructure consists of ferrite matrix and semispherical carbides. Laboratory
studies confirm appropriate flow lines arrangement, which corresponds well to those shown by FEM computer
simulations. The highest hardness at the level of 293±7 HV0.3 was identified in the flange area, where the material
shows a higher distribution of effective strain revealed by FEM. Cold metal forming results in work-hardening of
the steel. The work hardening ranges up to 1.62 of the initial 42CrMo4 steel hardness. The metal forming process
did not affect the microstructural uniformity of the flanged hollow part. The final outer flange component presents
high quality and is free from plastic deformation nonuniformities.
... Adding 10-30 wt ppm boron could produce a hardening effect comparable to that obtained by adding 0.6 wt% Mn, 0.7 wt% Cr, 0.5 wt% Mo or 1.5 wt% Ni [2]. The beneficial effect of boron on hardenability is believed resulting from the segregation of boron atoms at austenite grain boundaries to lower the grain boundary energy and retard the nucleation of ferrite and bainite [3][4][5][6][7][8][9][10][11]. However, boron can easily react with carbides and nitrogen to form metal borocarbides and boron nitrides in steels during high-temperature processing [12]. ...
Boron is an important trace element and intentionally added for hardenability of low-alloy steels. The forms of B presence in microstructure are believed to be crucial for success or failure of boron steel production. This research addresses atomistic distribution of boron responsible for quench cracking of a boron steel. Boron steel sheets (6 mm thick) with/without quench cracking are carefully characterized with transmission electron mi-
croscopy and atom probe tomography to reveal B distribution and to understand quench cracking mechanisms. The quench cracking is brittle intergranular fracture along prior austenite grain boundaries (PAGBs). The PAGBs are decorated with boron-containing Fe 3 (C, B) precipitates in the cracked steel, but segregated with boron in the uncracked steel. Without the segregation of B at PAGBs, the formation of ferrite and massive acicular-shaped Fe 3 C during quenching makes cracks easy to initiate and propagate in the steel with deteriorated mechanical properties. Processing parameters important for engineering the distribution of boron are discussed.
... The research material constituted 8 melts of different chemical compositions. Their technological process is accurately shown and described in research [40]. The chemical composition of particular ingots was determined with the use of an emission spectrometer with spark excitation ARL NA. ...
... Etched, light microscopy and SEM. Based on own research and reference[40]. ...
... Hardness of the analysed melts after quenching. Based on own research and reference[40]. ...
The paper attempts to determine the influence of boron in the presence of chromium, vanadium and titanium on abrasion resistance and wear mechanisms using low-alloy steels as an example. The obtained tribological properties were correlated with the hardness, carbon content and prior austenite grain size. Tribological tests – the dry sand-rubber wheel test – were conducted in the presence of loose abradant, and the major wear mechanisms were then determined using scanning electron microscopy. The results indicate that the improvement of resistance to abrasion may be supported by the combined addition of chromium, boron and vanadium. For unalloyed or chromium steels, a micro-addition of boron provides no benefits in terms of improving tribological properties.
... When the cooling rate is high, boron is adsorbed on grain boundaries in atomic state, which can inhibit and delay ferrite transformation and thus improve hardenability [4]. With decreasing cooling rate, boron can be precipitated as boron phase, which leads to non-spontaneous nucleation and a sharp decrease in hardenability [5]. Consequently, the prediction of hardenability of boron steel is usually complicated [6]. ...
... relationship between the hardness value and the selected features can be described by Eq.(5). So, each data set contains 12 input variables whose attributes are numeric. ...
Boron steel is one of the most valuable lightweight steels for automobile due to its high strength after hot stamping and low cost. In order to ensure service performance of automobile parts, the steel is required to have good hardenability. A novel data-driven machine learning (ML) model has been established by using relevant material descriptors, including chemical composition and distance along the Jominy bar, to predict the hardenability curve of boron steel. By evaluating and comparing prediction results of different ML methods on training and test sets, random forest is found to be the optimal model with high correlation coefficient and low error. Moreover, the ML model performs better than JMatPro and empirical formula in terms of prediction accuracy and variation trend of hardenability curve. The optimal ML model combined with orthogonal design is employed to successfully design a press-hardening steel with good hardenability, i.e., 0.04% V-added boron steel. Therefore, this study demonstrates that ML can predict accurately and efficiently the hardenability curve of boron steel and guide the material design and heat treatment process of advanced boron steel.
Graphical abstract
... Accuracy can reflect the ability of a classification model to judge the whole sample, as shown in Equation (7), where TP is true positive, FP is false positive, FN is false negative, and TN is true negative. The F1-score can be regarded as the weighted average of accuracy and recall rate, as shown in Equation (8). Higher values of accuracy and F1-score indicate better discriminability of the model. ...
Hardenability is one of the most basic criteria influencing the formulation of the heat treatment process and steel selection. Therefore, it is of great engineering value to calculate the hardenability curves rapidly and accurately without resorting to any laborious and costly experiments. However, generating a high-precision computational model for steels with different hardenability remains a challenge. In this study, a combined machine learning (CML) model including k-nearest neighbor and random forest is established to predict the hardenability curves of non-boron steels solely on the basis of chemical compositions: (i) random forest is first applied to classify steel into low- and high-hardenability steel; (ii) k-nearest neighbor and random forest models are then developed to predict the hardenability of low- and high-hardenability steel. Model validation is carried out by calculating and comparing the hardenability curves of five steels using different models. The results reveal that the CML model works well for its distinguished prediction performance with precise classification accuracy (100%), high correlation coefficient (≥0.981), and low mean absolute errors (≤3.6 HRC) and root-mean-square errors (≤3.9 HRC); it performs better than JMatPro and empirical formulas including the ideal critical diameter method and modified nonlinear equation. Therefore, this study demonstrates that the CML model combining material informatics and data-driven machine learning can rapidly and efficiently predict the hardenability curves of non-boron steel, with high prediction accuracy and a wide application range. It can guide process design and machine part selection, reducing the cost of trial and error and accelerating the development of new materials.
... The alloying of steels by boron is widely applied because this element suppresses the ferrite formation, and the resulting overcooling provides the driving force of martensitic transformation [1][2][3][4][5]. Such enhanced hardenability is ascribed to boron segregations in narrow zones at austenite grain boundaries [6 -12] which presumably hinder rearrangements of atoms required for the phase transformation [13,14]. ...
... To find out and quantify physical factors responsible for an abnormal dependence of DR threshold strain on the hot strain rate of steel B1500 is beyond the scope of the present experimental study. At the same time, when keeping in mind segregations of dissolved boron atoms at austenite grain boundaries [3,4], a related qualitative explanation deserves discussion as follows. ...
According to literature data confirmed by our experiments on various steels, the strain degree that triggers the dynamic recrystallization of austenite in high-temperature deformation increases with the strain rate. However, as shown in the present work, micro-alloying of medium carbon steel by boron results in the opposite dependence in the strain rate range of 1 to 100 s −1. The corresponding features of stress-strain diagrams comply with the former austenite structures revealed by chemical etching. A specific effect of boron is discussed with allowance for its segregations at grain boundaries where the recrystallization embryos form. Such segregations hinder rearrangement of atoms involved in the grain boundary migration and hence decelerate their bulging necessary to nucleate recrystallization origins. Similar to the known "yield tooth" effect, very strong strain hardening of the steel with boron eventually enables the boundaries to free from the segregated atoms and begin the dynamic recrystallization at relatively low strain degrees. The obtained results indicate that the considered phenomenon is not due to the ultimate strain rate as such but results from its combination with the boron alloying. The revealed regularities gain in significance for evident reasons. First, they enhance ductility of high-strength steels hot deformed with very high strain rates as, for instance, in case of hammering. Second, such treatments notably refine the austenite structure and, correspondingly, improve the transformed structure and final mechanical properties after steel quenching. Аномальное влияние скорости деформации на динамическую рекристаллизацию аустенита в борсодержащей среднеуглеродистой стали Князюк Т. В. † , Зисман А. А. Национальный Исследовательский Центр «Курчатовский Институт»-Центральный Научно-исследовательский Институт Конструкционных Материалов «Прометей», Санкт-Петербург, 191015, Россия Согласно многочисленным литературным данным, подтвержденным дополнительными экспериментами на раз-личных сталях, с ростом скорости деформирования при высоких температурах увеличивается пороговая дефор-мация, при которой начинается динамическая рекристаллизация аустенита. В то же время, как показано в данном исследовании, микролегирование среднеуглеродистой стали бором приводит к противоположной зависимости в диапазоне скоростей от 1 до 100 с −1. Соответствующие особенности диаграмм деформирования согласуются с исходными структурами аустенита, выявленными с помощью химического травления. Специфический эффект растворенного в стали бора обсуждается с учетом его сегрегаций на границах зерен, где формируются зародыши рекристаллизации. Такие сегрегации препятствуют атомным перестроениям, обеспечивающим миграционную подвижность этих границ, замедляя их выгибание на локальных участках, с которыми связано зарождение рекристаллизации. Напоминая известный эффект «зуба текучести», сильное деформационное упрочнение стали с бором позволяет границам освободиться от сегрегаций и начать рекристаллизацию при относительно малых степенях деформации. Согласно полученным результатам, высокая скорость деформации сама по себе не вызывает рассматриваемую аномалию; ее необходимым условием также является легирование стали бором. Выявленные закономерности обладают практической значимостью по следующим очевидным причинам. Во-первых, быстрая динамическая рекристаллизация улучшает пластичность высокопрочных сталей при горячей деформации с предельно высокими скоростями как, например, при ковке на молотах. Во-вторых, подобная обработка существенно измельчает зерна аустенита и, соответственно, предопределяет благоприятную превращенную структуру и высокий уровень финальных механических свойств стали после закалки. Ключевые слова: аустенит, горячая деформация, динамическая рекристаллизация, бор, скорость деформации. 72 Kniaziuk et al. / Letters on Materials 12 (1), 2022 pp. 71-75
