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Schematic representation of (a) flake and (b) spheroidal graphite and their apparent growth directions. The low and high interfacial free energy planes, as estimated from subsequent molecular dynamics simulations, are also indicated.
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Applications of cast irons, from mundane to more challenging, are decided by the morphology of free graphite in the metallic matrix. The morphology changes from flake to spheroidal, as controlled by magnesium (Mg) addition during metal castings. Though this technology dates back several decades, the exact mechanism remains debatable. This study use...
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... both flake and spheroidal graphite were orientated such that their basal direction ( 0 0 01 ) always pointed towards ferrite grains (refer schematic unit cells in Fig. 4 b and d). ( Fig. 5 b), on the other hand, grew radially from the center. Its growth is thus estimated to be along the c -direction ( 0 0 01 ). ...
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... microtexture measurements ( Fig. 4 a-d) thus provided plausible mechanism(s) for the growth of flake and spheroidal graphite from the melt, and more importantly, that their apparent growth directions differed ( Fig. 5 a,b). However, the question of why graphite grows in different shapes and directions with the addition of Mg as a spheroidizing agent remained to be addressed. ...
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... higher interfacial free energy compared to that of the prism plane of graphite, the high-energy basal plane of pure Fe-C ( L1 ), Fe-C-O-2.4Mg ( L4 ), and Fe-C-O-6.3Mg ( L5 ) propagates along its pole -resulting in the formation of spheroidal graphite (see Fig. 7 d). The graphite growth in both flake and spheroidal graphite is thus illustrated in Fig. 5 a,b. However, when the difference between the energy for basal and prism plane of graphite is relatively small, both basal and prism plane can propagate at comparable speed -resulting in the formation of intermediate graphite. This can happen when the Mg concentration at the graphite-melt interface is less than 2.4 at. % (that is, closer ...
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... continues to grow in the solid-state, below eutectic and eutectoid temperature, due to the reduced solubility of C in the solid phase. During the growth of speroidal graphite, the basal plane always faced outward (the radial direction of the spheroid being parallel to the basal direction of the hexagonal crystal structure of graphite -see Fig. 5 b). However, a steric barrier on the basal plane would always exist, preventing the migration of Mg and O atoms in the graphite phase. Similarly, O atoms would not enter from the basal pane (along the thickness of graphite flakesee Fig. 5 a) in a flake graphite. It is thus expected that Mg and O atoms would be carried along with its ...
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... of the spheroid being parallel to the basal direction of the hexagonal crystal structure of graphite -see Fig. 5 b). However, a steric barrier on the basal plane would always exist, preventing the migration of Mg and O atoms in the graphite phase. Similarly, O atoms would not enter from the basal pane (along the thickness of graphite flakesee Fig. 5 a) in a flake graphite. It is thus expected that Mg and O atoms would be carried along with its interface, during the growth of graphite in the solid-state. Thus, the concentration of Mg and O atoms at room temperature would be proportional to the temperature where these atoms were active in controlling graphite growth. As AES ...
Citations
... Adding Mg to cast iron causes graphite to grow in different directions, transforming flake graphite into spheroidal graphite [69]. The influence of Mg on carbides with the same faceted phase is mostly reflected in the following aspects. ...
In high-speed steel, carbides are essential phase constituents, which have a direct impact on engineering performance and qualities of high-speed steel. The formation, morphology, and distribution of carbides are dictated by alloying elements. In this paper, various types of carbides in high-speed steel are presented. The effects of different alloying elements such as C, W, Mo, Cr, and V on the formation of carbides in high-speed steel are discussed. Research progresses on carbide improvement by microalloying elements such as N, B, Mg, and rare earth (RE) elements are reviewed. It is reported that Cr promotes the precipitation of M2C, N enhances the formation of fibrous M2C, Mg effectively shatters the large-size carbide grid, Nb refines granular carbide MC, and rare earth elements encourage the formation of M6C, resulting in irregular M2C lamellae. The incorporation of microalloying elements improves the distribution and size of carbides and also refines the solidification structure of high-speed steel.
... Austempering dapat meningkatkan sifat mekanik material mulai dari kekerasan, kekuatan impak, ketahanan aus dan keuletan material [8] . Selain itu material besi cor dapat ditingkatkan sifat mekaniknya dengan cara ditambahkan unsur paduan, diantaranya nikel [9][10][11] . Nikel ditambahkan untuk meningkatkan kekuatan tarik dan kekerasan dengan metode solid solution strenghtening [12] . ...
Effect of austempering temperature on microstructure and mechanical properties gray cast iron with 10%wt nickel for boiler combustion application has been studied. Cast iron with the JIS FCD 45 standard with a minimum tensile strength of 414 MPa and a hardness of 187 HB is commonly used for this application. To improve its mechanical properties such as strength and hardness, austempering heat treatment usually applied. Austempering was carried out at 250°C, 300°C, 350°C, 400°C, and 450°C for 1 hour, with the same austenization temperature of 850°C for 1 hour. The highest increase in hardness was found at the austempering temperature of 250°C. The hardness was 321.80 HB or 19.30% of the initial hardness of 259.70 HB. In terms of strength, the highest increase occurred at the austempering temperature of 250°C which was 257 MPa or 31.52% of the initial strength of 176 MPa.
... Graphite is also considered an excellent conductor of [81,82] heat and electricity and exhibits high rigidity and excellent regular resistance. It is able to maintain its firmness and strength above 3600 C [83,84]. Two types of graphite are generally identified: natural and synthetic. ...
In modern society, technological advances are inherently driving the high demand for efficient processes in various fields. In this light, carbon-based nanomaterials have been introduced as efficacious approaches to revolutionize the energy and materials industries, which provide more ecological and economic benefits in multiple domains. This chapter is intended to provide an overview of the history and ongoing research on various carbon nanomaterials and their synthesis approaches, specifications, functionalization, as well as implementation in high-tech end uses. Carbon nanostructures are nanosized materials that have attracted the attention of many researchers over the years. They offer the potential for functionalization by copolymerization, surface modification, or combination with metals. This improves their overall performance and promotes their involvement in catalysis, water treatment, composites, electronics, biochemical sensors, etc. This literature assessment examines the diverse published outcomes regarding the historical involvement of different classes of carbon nanostructures, their characteristics, and their processing and performance in specific application areas. Our aim is to design a consequential relationship between the potential of structural modifications of carbon-based nanomaterials and their attributes, as well as to highlight futuristic perspectives and strategies to improve their valorization, and to describe the possibilities of large-scale production and industrial beatification.
... Besi cor memiliki berbagai jenis dengan salah satu pembedanya adalah bentuk grafitnya. Di antara bentuk grafit yang ada antara lain lamelar [1], nodular [2], dan vermikular (compacted graphite) [3]- [5]. Perubahan bentuk grafit dipengaruhi oleh banyak faktor misalnya unsur silikon, tembaga [6], molibdenum, dan lain-lain. ...
... Silikon pada besi cor kelabu dalam proses inokulasi berfungsi untuk mendorong terjadinya grafit [9]. Grafit berubah bentuk dengan mekanisme tertentu misalnya adanya pengaruh penambahan unsur pengubah bentuk grafit [5], selain itu ukuran grafit juga mempengaruhi karaktersitik besi cor [12]. Bagian dalam grafit berubah blok-blok yang bertumpuk-tumpuk antara satu dan lainnya [13]. ...
ABSTRAK Pengecoran besi cor kelabu membutuhkan proses inokulasi untuk lebih banyak membentuk grafit pada benda cor. Grafit yang terbentuk akan berpengaruh pada sifat mekanik benda cor baik kekuatan tarik, kekerasan, dan lainnya. Proses inokulasi dapat dilakukan di tanur peleburan atau di ladel penampung cairan logam. Cara penambahan inokulan ke dalam cairan juga dapat dilakukan dengan beberapa metode. Tujuan penelitian ini adalah untuk mempelajari pengaruh metode inokulasi pada proses pengecoran besi cor kelabu terhadap komposisi kimia dan kekerasan benda cor. Metode inokulasi dilakukan dengan tiga cara yakni inokulan dibungkus, dicurah, dan campuran sebagian dibungkus serta sebagian dicurah. Pengamatan hasil pada benda cor meliputi komposisi kimia yang terjadi dan kekerasan yang diperoleh. Pengecoran besi cor kelabu FC 250 dilakukan penuangan ke cetakan pada suhu 1434 ºС dengan menggunakan cetakan green sand. Hasil uji komposisi menunjukkan kadar karbon besi cor pada inokulasi dengan inokulan dibungkus sebesar 2,40 % atau 0,01% lebih rendah dibandingkan dengan yang dicurah dan campuran antara curah dan bungkus. Kekerasan Brinel pada besi cor dengan metode inokulan dibungkus sebesar 2,32 % atau 0,05 lebih rendah dibandingkan dengan metode inokulasi dengan dicurah dan campuran antara curah serta bungkus. Kekerasan Brinell benda cor yang dibuat dengan cara inokulan dibungkus, dicurah, dan campuran antara bungkus dan curah berturut-turut sebesar 217, 229, dan 223 HB. Hal ini menunjukkan bahwa karbon yang berubah menjadi grafit dan silikon yang membantu proses penggrafitan akan mendorong penurunan kekerasan benda cor.
ABSTRACT Gray iron casting requires an inoculation process to form more graphite in the product. The graphite formed will affect the mechanical properties of casting such as tensile strength, hardness, and others. The inoculation process can be carried out in a smelting furnace or in a handling ladle. How to add inoculant to the liquid can also be done by several methods. The purpose of this study was to study the effect of the inoculation method in the casting process of gray iron casting on the chemical composition and hardness of the product The inoculation method was carried out in three ways, namely the inoculant was packaged, bulk, and the mixture was partially packaged and partially bulk. Observation of results on product includes the chemical composition and the hardness. Ferro casting (FC) 250 gray cast iron was poured into the mold at 1434 ºС using a green sand mold. The results of the composition test showed that the carbon content of cast iron in inoculation with packaged inoculants was 2.40% or 0.01% lower than that of bulk and a mixture of bulk and packaged. The Brinel hardness of cast iron using the packaged inoculant method was 2.32% or 0.05 lower than that of the inoculation method using bulk and a mixture of bulk and packing. The Brinell hardness of casts made by inoculant packing, bulk, and a mixture of packing and bulk was 217, 229, and 223 HB, respectively. This shows that carbon which turns into graphite and silicon which assists the graphing process will lead to a decrease in the hardness of the casting.
... Different growth rates of graphite along [1010] (a-axis) and [0001] (c-axis) determine the morphology of graphite. When the growth rate of the a-axis is much faster than that of the c-axis, it is easy to grow into flake graphite; when the growth rate of the a-axis is close to that of the c-axis, it is easier to grow into spherical graphite; while vermicular graphite is in between [30]. Therefore, if several simplified graphite models with topological equivalence [31,32] are established according to the 2-D and 3-D morphological characteristics of three types of graphite and the ratio of the a-axis and c-axis, it is believed that the real vermicular graphite will be included. ...
... Therefore, graphite preferentially grows along the a-axis to flake graphite without adding spheroidized elements. With the increase in spheroidized elements, graphite morphology gradually transforms into a spherical shape [30]. Our previous work [39] also confirmed the direct interaction between the adding spheroidized elements and graphite phase during growth process by combining first-principles calculation and TEM analysis. ...
To provide the basis for thermal conductivity regulation of vermicular graphite cast iron (VGI), a new theoretical method consisting of shape interpolation, unit cell model and numerical calculation was proposed. Considering the influence of the graphite anisotropy and interfacial contact thermal conductivity (ICTC), the effective thermal conductivity of a series of unit cell models was calculated by numerical calculation based on finite difference. The effects of micro-structure on effective thermal conductivity of VGI were studied by shape interpolation. The experimental results were in good agreement with the calculated ones. The effective thermal conductivity of VGI increases in power function with the decrease in graphite shape parameter, and increases linearly with the increase in graphite volume fraction and thermal conductivity of matrix. When the graphite volume fraction increases by 1%, the thermal conductivity of nodular cast iron increases by about 0.18 W/(m·K), while that of gray cast iron increases by about 3 W/(m·K). The thermal conductivity of cast iron has the same sensitivity to the thermal conductivity of matrix regardless of the graphite shape parameter. The thermal conductivity of matrix increased by 15 W/(m·K) and the thermal conductivity of cast iron increased by about 12 W/(m·K). Moreover, the more the graphite shape deviates from the sphere, the greater the enhancement effect of graphite anisotropy on thermal conductivity than the hindrance effect of interface between graphite and matrix. This work can provide guidance for the development of high thermal conductivity VGI and the study of thermal conductivity of composites containing anisotropic dispersed phase particles with complex shapes.
... Despite of great research effort s made in the past decades, theories that can rigorously explain the morphology modification effect of the trace element additions on eutectic Si and graphite remain elusive [ 80 , 104 , 105 ], and no well-accepted principle-based model/criterion is available to guide the new modifying element searching. Recently, Tewary et al. [106] applied Molecular Dynamic (MD) simulation to well predict their characterization results that the morphology modification of graphite in cast iron with trace Mg addition was accompanied by a change in the preferential growth direction and atomic-scale segregation of Mg at the interface. The MD simulation results indicate that the high energy interface of graphite changed from the prismatic plane to the basal plane, owing to the combination of oxygen (O) atoms migration and Mg-O interactions in the prismatic-and basal-oriented graphite, respectively. ...
Casting aluminum (Al) alloys have been widely used in the automotive industry to improve fuel economy as well as to reduce greenhouse gas (GHG) emissions in the vehicle use phase. However, the casting Al alloys used for load-bearing body and chassis components today are mostly made from primary Al with a low impurity Fe content typically less than 0.2 wt.%, owing to the requirements for high ductility and adequate fatigue strength. Primary Al is made directly from alumina which was refined from aluminum ore (bauxite), using an electrolytic process which consumes a lot of energy and produces GHG emissions that are much higher than those from steel making. The objective of this paper is to present a Unified Casting (UniCast) Al alloy concept as a sustainable materials solution for vehicle lightweighting. The UniCast alloy chemistry is intentionally designed to be more tolerant of Fe impurity. This chemistry can not only satisfy the requirements on castability, but also deliver mechanical properties needed for a variety of thin-walled and thick-walled automotive structural components that are produced by various casting processes. The UniCast alloy concept will contribute to the establishment of a closed-loop recycling system in the future as the shredded scrap obtained from the disposed end-of-life vehicles can be directly recycled back into UniCast alloy ingot with a more efficient sorting process. In addition, by setting the upper limit of Fe content in the UniCast alloy to a higher level, it will become possible to use a high fraction of post-consumer scraps to produce this alloy. To demonstrate the feasibility of this concept, an exemplary UniCast alloy chemistry has been elaborated in this article. Furthermore, challenges and future research opportunities related to the realization of UniCast alloy concept in the automotive industry are discussed. It is hoped that this article will be of great implication to industrial researchers and academicians for making concerted efforts to establish closed-loop recycling of Al castings for the automotive and other transportation industry segments.
... Modern diesel engine cylinder blocks due to the development of high horsepower demand, so the grey cast iron block is required to withstand higher temperature and pressure in the process, and the five basic elements (C, Si, Mn, S, P) based on the low-grade grey cast iron parts are difficult to meet the requirements. To ensure the performance and stability of the product, it is often necessary to add a small amount of Cu, Cr, Sn, Ni, Mo and other alloying elements to achieve the improvement of mechanical properties [1][2][3][4][5][6][7][8][9]. These elements control the mechanical properties of grey cast iron by affecting the microstructure of grey cast iron. ...
Alloying elements (Ni, Mo) were added to grey cast iron, and the effect of Ni, Mo on microstructure and mechanical properties were analysed in this study. When Ni was added alone, the precipitation of graphite was inhibited at the early stage of solidification, and part of graphite was formed between the dendrites, resulted in an uneven distribution of graphite. Ni played a role of solution strengthening and reduced the pearlite interlammer spacing, improved the mechanical properties. The addition of Mo refined the austenite dendrites and made the carbon unevenly distributed, which led to the abnormal growth of graphite. Mo increased the eutectoid supercooling degree, reduced the pearlite interlammer spacing and improved tensile strength. When Ni and Mo were added together, the elements beneficial to strength (Mo, Sn) were not uniformly distributed, and the influence on graphite size and pearlite interlammer spacing was not obvious, resulted in poor mechanical properties.
... Cast iron offers high castability and good machining properties, as well as interesting mechanical properties [1][2]. Due to the economic benefits it offers, cast iron is used for many applications such as water pipes [3][4][5], machine building, in the automotive industry and in metal fabrication and processing [2]. ...
... Due to the economic benefits it offers, cast iron is used for many applications such as water pipes [3][4][5], machine building, in the automotive industry and in metal fabrication and processing [2]. Until today, cast iron still constitutes the majority (≈70%) of metal castings [1,6]. In addition, specific cast irons are the material of choice for seawater pump casings, rolling mill rolls and earthmoving machinery parts [2,[6][7][8]. ...
In the present study, a modified duplex melting process was set up so as to be able to produce an EN-GJL-150 gray cast iron from a local manganese-rich pig iron. A descriptive statistics showed an average Mn and Si content in raw material such that: Mn % = 2.457±0.133 and Si % = 0.682±0.088. The demanganization process was run and monitored in a cascade of two industrial-scale furnaces: a rotary kiln and an electric arc furnace. The performed experiments indicated that: 1) the manganese content decreased from 2.45 % to 0.94 %, 2) the manganese oxidation obeys the first order kinetic model, 3) Brinell and Rockwell hardness’s decreased by 38.83% and 27.81% respectively, and 4) the produced cast iron has a pearlitic microstructure with a small fraction of ferrite (1 to 5%) in the matrix and traces of cementite. All results showed that the produced castings comply with the standards in force for EN-GJL-150 cast irons, similar to gray cast iron ASTM A48 Class 20.
... Spheroidal graphite reduces stress concentrations in nodular cast iron, thereby significantly increasing toughness and ductility. Evolution from flake to spheroidal during casting is controlled by Mg [10]. Nodularity increased with the increasing percentage of Mg content. ...
Nodular cast iron is usually used for components that require good mechanical properties such as strength, toughness, and ductility. Heat treatment is applied to the components made from the nodular cast iron to improve their mechanical properties. This study aimed to investigate the influence of tempering time on the microstructure, hardness, and wear rate of nodular cast iron. The heat treatment was performed by austenitizing to 850 °C with a holding time of 1 hour and quenched in the oil medium. After quenching, it was tempered at a temperature of 450 °C by varying the tempering time to 15, 30, 45, and 60 min. The investigation consists of microstructure observation, hardness, and wear rate measurements. The results show that the highest hardness was 55.3 HRC at a tempering time of 15 min, and the lowest hardness was 54 HRC at a tempering time of 60 min. The lowest wear rate was 0.00476 g/min at a tempering time of 15 min, and the highest wear rate was 0.00574 g/min at a tempering time of 60 min. It can be concluded that the longer the holding time of tempering, the lower the hardness and the higher the wear rate.
... The microstructure of CI depends on the chemical composition, cooling rate conditions, and subsequent heat treatments [2]. Properly controlling the carbon and silicon contents and the cooling rate, the graphite crystallizes directly from the melt [3,4]. Then, the mechanical properties will strongly depend on the shape, size and distribution of the graphite particles in the metallic matrix. ...
This work is a continuation of the studies presented in a recent paper by the authors, where a methodology to obtain different nodule quality categories in spheroidal graphite cast iron, was proposed. In this study, an exhaustive analysis of the highest-quality graphite nodules was performed. The experimental methodology involves X-ray micro-computed tomography analysis and digital image post-processing of the high-quality graphite nodule population. Furthermore, different subpopulations were selected, following a nodular size criterion. The procedure involves the evaluation and comparison of the sphericity and compactness distributions and the distances between neighbouring nodules by using ad-hoc image processing software. The results reveal the complementary nature of the sphericity and compactness parameters, which allow classifying, with great accuracy, different nodular quality categories of spheroidal graphite cast iron. Additionally, new viewpoints about the nodular morphology study and the distribution of quality nodules in the metallic matrix was provided, which could be extended to other heterogeneous materials.
