Materials

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21 pages, 6534 KiB

Open AccessArticle

High-Precision Instance Segmentation Detection of Micrometer-Scale Primary Carbonitrides in Nickel-Based Superalloys for Industrial Applications

by Jie Zhang, Haibin Zheng, Chengwei Zeng and Changlong Gu

Materials 2024, 17(19), 4679; https://doi.org/10.3390/ma17194679 - 24 Sep 2024

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Abstract

In industrial production, the identification and characterization of micron-sized second phases, such as carbonitrides in alloys, hold significant importance for optimizing alloy compositions and processes. However, conventional methods based on threshold segmentation suffer from drawbacks, including low accuracy, inefficiency, and subjectivity. Addressing these [...] Read more.

In industrial production, the identification and characterization of micron-sized second phases, such as carbonitrides in alloys, hold significant importance for optimizing alloy compositions and processes. However, conventional methods based on threshold segmentation suffer from drawbacks, including low accuracy, inefficiency, and subjectivity. Addressing these limitations, this study introduced a carbonitride instance segmentation model tailored for various nickel-based superalloys. The model enhanced the YOLOv8n network structure by integrating the SPDConv module and the P2 small target detection layer, thereby augmenting feature fusion capability and small target detection performance. Experimental findings demonstrated notable improvements: the mAP50 (Box) value increased from 0.676 to 0.828, and the mAP50 (Mask) value from 0.471 to 0.644 for the enhanced YOLOv8n model. The proposed model for carbonitride detection surpassed traditional threshold segmentation methods, meeting requirements for precise, rapid, and batch-automated detection in industrial settings. Furthermore, to assess the carbonitride distribution homogeneity, a method for quantifying dispersion uniformity was proposed and integrated into a data processing framework for seamless automation from prediction to analysis. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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14 pages, 9055 KiB

Open AccessArticle

Ultra-High Strength in FCC+BCC High-Entropy Alloy via Different Gradual Morphology

by Ziheng Ding, Chaogang Ding, Zhiqin Yang, Hao Zhang, Fanghui Wang, Hushan Li, Jie Xu, Debin Shan and Bin Guo

Materials 2024, 17(18), 4535; https://doi.org/10.3390/ma17184535 - 15 Sep 2024

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Abstract

In this study, high-pressure torsion (HPT) processing is applied to the as-cast Al_0.5CoCrFeNi high-entropy alloy (HEA) for 1, 3, and 5 turns. Microstructural observations reveal a significant refinement of the second phase after HPT processing. This refinement effect is influenced by [...] Read more.

In this study, high-pressure torsion (HPT) processing is applied to the as-cast Al_0.5CoCrFeNi high-entropy alloy (HEA) for 1, 3, and 5 turns. Microstructural observations reveal a significant refinement of the second phase after HPT processing. This refinement effect is influenced by the number of processing turns and the distance of the processing position from the center. As the number of processing turns or the distance of the processing position from the center increases, the fragmentation effect on the second phase becomes more pronounced. The hardness of the alloy is greatly enhanced after HPT processing, but there is an upper limit to this enhancement. After increasing the number of processing turns to 5, the increase in hardness at the edge becomes less significant, while the overall hardness becomes more uniform. Additionally, the strength of the processed alloy is significantly enhanced, while its ductility undergoes a noticeable decrease. With an increase in the number of processing turns, the second phase is further refined, resulting in improvement of strength and ductility. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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19 pages, 18403 KiB

Open AccessArticle

Preparation of Metallized Pellets for Steelmaking by Hydrogen Cooling Reduction with Different Cooling Rates

by Guanwen Luo, Zhiwei Peng, Kangle Gao, Wanlong Fan, Ran Tian, Lingyun Yi and Mingjun Rao

Materials 2024, 17(17), 4362; https://doi.org/10.3390/ma17174362 - 3 Sep 2024

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Abstract

To utilize the sensible heat of hot roasted iron ore pellets with no CO₂ emission in the production of metallized pellets for direct steelmaking, the pellets were reduced in H₂ during their cooling process with variable cooling rates. When the cooling [...] Read more.

To utilize the sensible heat of hot roasted iron ore pellets with no CO₂ emission in the production of metallized pellets for direct steelmaking, the pellets were reduced in H₂ during their cooling process with variable cooling rates. When the cooling rate decreased from 5.2 °C/min to 2.0 °C/min, the total iron content, reduction degree, and iron metallization degree of the pellets increased continuously from 74.0 wt%, 52%, and 31.1% to 84.9 wt%, 93.4%, and 89.2%, respectively. However, the compressive strength of the pellets increased initially from 2100 N/p to 2436 N/p and then decreased considerably to 841 N/p. As the cooling rate decreased, more Fe₂O₃ was reduced to Fe with diminishing FeO and Fe₂SiO₄. The porosity of the pellets increased from 23.9% to 54.3%, with higher distribution uniformity of pores. The morphology of metallic iron particles also transited from a layered form to a spherical form and lastly to a porous reticular form. Meanwhile, the metallic iron particles in the pellets grew evidently with more uniform distributions. When the cooling rate was 3.7 °C/min, the resulting metallized pellets had the reduction degree of 74.2%, iron metallization degree of 66.9%, and the highest compressive strength of 2436 N/p, in association with the spherical morphology and relatively large size of metallic iron particles. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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22 pages, 17848 KiB

Open AccessArticle

Formability Prediction Using Machine Learning Combined with Process Design for High-Drawing-Ratio Aluminum Alloy Cups

by Yeong-Maw Hwang, Tsung-Han Ho, Yung-Fa Huang and Ching-Mu Chen

Materials 2024, 17(16), 3991; https://doi.org/10.3390/ma17163991 - 11 Aug 2024

Viewed by 768

Abstract

Deep drawing has been practiced in various manufacturing industries for many years. With the aid of stamping equipment, materials are sheared to different shapes and dimensions for users. Meanwhile, through artificial intelligence (AI) training, machines can make decisions or perform various functions. The [...] Read more.

Deep drawing has been practiced in various manufacturing industries for many years. With the aid of stamping equipment, materials are sheared to different shapes and dimensions for users. Meanwhile, through artificial intelligence (AI) training, machines can make decisions or perform various functions. The aim of this study is to discuss the geometric and process parameters for A7075 in deep drawing and derive the formable regions of sound products for different forming parameters. Four parameters—forming temperature, punch speed, blank diameter and thickness—are used to investigate their effects on the forming results. Through finite element simulation, a database is established and used for machine learning (ML) training and validation to derive an AI prediction model. Importing the forming parameters into this prediction model can obtain the forming results rapidly. To validate the formable regions of sound products, several experiments are conducted and the results are compared with the prediction results to verify the feasibility of applying ML to deep drawing processes of aluminum alloy A7075 and the reliability of the AI prediction model. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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15 pages, 14029 KiB

Open AccessArticle

Toward Metallized Pellets for Steelmaking by Hydrogen Cooling Reduction: Effect of Gas Flow Rate

by Wanlong Fan, Zhiwei Peng, Ran Tian, Guanwen Luo, Lingyun Yi and Mingjun Rao

Materials 2024, 17(16), 3896; https://doi.org/10.3390/ma17163896 - 6 Aug 2024

Cited by 1 | Viewed by 686

Abstract

This study proposed a strategy to prepare metalized pellets for direct steelmaking by hydrogen cooling reduction (HCR) of iron ore pellets with a focus on the effect of H₂ flow rate on the process. It was demonstrated that increasing H₂ flow [...] Read more.

This study proposed a strategy to prepare metalized pellets for direct steelmaking by hydrogen cooling reduction (HCR) of iron ore pellets with a focus on the effect of H₂ flow rate on the process. It was demonstrated that increasing H₂ flow rate could effectively enhance the reduction performance of iron ore pellets. However, due to the influence of the countercurrent diffusion resistance of gas molecules, too high H₂ flow rate no longer promoted the reduction of the pellets when the maximum reduction rate was reached. The reduction swelling index (RSI) of the pellets initially increased and then decreased with increasing H₂ flow rate. This change was associated with the decreased content of Fe₂SiO₄ in the metalized pellets and the changes in porosity and iron particle size. The compressive strength (CS) decreased continuously, showing a sharp decline when the H₂ flow rate reached 0.6 L/min. It was attributed to the significant increases in porosity and average pore size of the metalized pellets, with the presence of surface cracks. When the H₂ flow rate was 0.8 L/min, the metalized pellets had the optimal performance, namely, reduction degree of 91.45%, metallization degree of 84.07%, total iron content of 80.67 wt%, RSI of 4.66%, and CS of 1265 N/p. The findings demonstrated the importance of controlling the H₂ flow rate in the preparation of metallized pellets by HCR. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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10 pages, 3804 KiB

Open AccessArticle

Study on the Migration Patterns of Oxygen Elements during the Refining Process of Ti-48Al Scrap under Electromagnetic Levitation

by Xinchen Pang, Guifang Zhang, Peng Yan, Zhixiang Xiao and Xiaoliang Wang

Materials 2024, 17(15), 3709; https://doi.org/10.3390/ma17153709 - 26 Jul 2024

Viewed by 484

Abstract

This study investigated the migration patterns of oxygen in the deoxidation process of Ti-48Al alloy scrap using electromagnetic levitation (EML) technology. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to analyze the oxygen distribution patterns and migration [...] Read more.

This study investigated the migration patterns of oxygen in the deoxidation process of Ti-48Al alloy scrap using electromagnetic levitation (EML) technology. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to analyze the oxygen distribution patterns and migration path during EML. The refining process resulted in three types of oxygen migration: (1) escape from the lattice and evaporation in the form of AlO, Al₂O; (2) formation of metal oxides and remaining in the alloy melt; (3) attachment to the quartz tube wall in the form of metal oxides such as Al₂O₃ and Cr₂O₃. The oxygen content of the scrap was dropped with a deoxidation ratio of 62%. It indicated that EML can greatly promote the migration and removal of oxygen elements in Ti-Al alloy scrap. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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13 pages, 8762 KiB

Open AccessArticle

Effects of Mean Normal Stress and Microstructural Properties on Deformation Properties of Ultrahigh-Strength TRIP-Aided Steels with Bainitic Ferrite and/or Martensite Matrix Structure

by Koh-ichi Sugimoto, Shoya Shioiri and Junya Kobayashi

Materials 2024, 17(14), 3554; https://doi.org/10.3390/ma17143554 - 18 Jul 2024

Cited by 1 | Viewed by 569

Abstract

The effects of mean normal stress on the deformation properties such as the strain-hardening, strain-induced martensite transformation, and micro-void initiation behaviors of low-carbon ultrahigh-strength TRIP-aided bainitic ferrite (TBF), bainitic ferrite/martensite (TBM), and martensite (TM) steels were investigated to evaluate the various cold formabilities. [...] Read more.

The effects of mean normal stress on the deformation properties such as the strain-hardening, strain-induced martensite transformation, and micro-void initiation behaviors of low-carbon ultrahigh-strength TRIP-aided bainitic ferrite (TBF), bainitic ferrite/martensite (TBM), and martensite (TM) steels were investigated to evaluate the various cold formabilities. In addition, the deformation properties were related to the microstructural properties such as the matrix structure, retained austenite characteristics, and second-phase properties. Positive mean normal stress considerably promoted strain-induced martensite transformation and micro-void initiation, with an increased strain-hardening rate in an early strain range in all steels. In TM steel, the primary martensite matrix structure suppressed the micro-void initiation through high uniformity of a primary martensite matrix structure and a low strength ratio, although the strain-induced transformation was promoted, and a large amount of martensite/austenite constituent or phase was contained. A mixed matrix structure of bainitic ferrite/primary martensite in TBM steel also suppressed the micro-void initiation because of the refined microstructure and relatively stable retained austenite. Promoted micro-void initiation of TBF steel was mainly promoted by a high strength ratio. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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18 pages, 5939 KiB

Open AccessArticle

On Strain-Hardening Behavior and Ductility of Laser Powder Bed-Fused Ti6Al4V Alloy Heat-Treated above and below the β-Transus

by Emanuela Cerri and Emanuele Ghio

Materials 2024, 17(14), 3401; https://doi.org/10.3390/ma17143401 - 9 Jul 2024

Viewed by 766

Abstract

Laser powder bed-fused Ti6Al4V alloy has numerous applications in biomedical and aerospace industries due to its high strength-to-weight ratio. The brittle α′-martensite laths confer both the highest yield and ultimate tensile strengths; however, they result in low elongation. Several post-process heat treatments must [...] Read more.

Laser powder bed-fused Ti6Al4V alloy has numerous applications in biomedical and aerospace industries due to its high strength-to-weight ratio. The brittle α′-martensite laths confer both the highest yield and ultimate tensile strengths; however, they result in low elongation. Several post-process heat treatments must be considered to improve both the ductility behavior and the work-hardening of as-built Ti6Al4V alloy, especially for aerospace applications. The present paper aims to evaluate the work-hardening behavior and the ductility of laser powder bed-fused Ti6Al4V alloy heat-treated below (704 and 740 °C) and above (1050 °C) the β-transus temperature. Microstructural analysis was carried out using an optical microscope, while the work-hardening investigations were based on the fundamentals of mechanical metallurgy. The work-hardening rate of annealed Ti6Al4V samples is higher than that observed in the solution-heat-treated alloy. The recrystallized microstructure indeed shows higher work-hardening capacity and lower dynamic recovery. The Considère criterion demonstrates that all analyzed samples reached necking instability conditions, and uniform elongations (>7.8%) increased with heat-treatment temperatures. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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14 pages, 6130 KiB

Open AccessArticle

Numerical Simulation of Electromagnetic–Thermal–Fluid Coupling for the Deformation Behavior of Titanium–Aluminum Alloy under Electromagnetic Levitation

by Xiaoliang Wang, Guifang Zhang, Peng Yan, Xinchen Pang and Zhixiang Xiao

Materials 2024, 17(13), 3338; https://doi.org/10.3390/ma17133338 - 5 Jul 2024

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Abstract

Electromagnetic levitation (EML) is a good method for high-temperature processing of reactive materials such as titanium–aluminum (Ti–Al) alloys. In this study, the oscillation and deformation processes of Ti-48Al-2Cr alloy specimens at different high-frequency currents during the EML process were simulated using the Finite [...] Read more.

Electromagnetic levitation (EML) is a good method for high-temperature processing of reactive materials such as titanium–aluminum (Ti–Al) alloys. In this study, the oscillation and deformation processes of Ti-48Al-2Cr alloy specimens at different high-frequency currents during the EML process were simulated using the Finite Element Method and Arbitrary Lagrangian–Eulerian (ALE) methods. The data of oscillation, stabilization time, deformation, and distribution of electromagnetic–thermal–fluid fields were finally obtained. The accuracy of the simulation results was verified by EML experiments. The results show the following: the strength and distribution of the induced magnetic field inside the molten droplet are determined by the high-frequency current; under the coupling effect of the electromagnetic field, thermal field, and fluid field, the temperature rise of electromagnetic heating is rapid, and accompanied by strong stirring, resulting in a uniform distribution of the internal temperature and a small temperature difference. Under the joint action of gravity and Lorentz force, the molten droplets are first within a damped oscillation and then tend to stabilize with time, and finally maintain the “near rhombus” shape. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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17 pages, 64643 KiB

Open AccessArticle

Hot Deformation Constitutive Analysis and Processing Maps of Ultrasonic Melt Treated A5052 Alloy

by Sun-Ki Kim, Seung-Hyun Koo, Hoon Cho and Seong-Ho Ha

Materials 2024, 17(13), 3182; https://doi.org/10.3390/ma17133182 - 28 Jun 2024

Viewed by 532

Abstract

Hot deformation constitutive analysis and processing maps of ultrasonic melt treated (UST) A5052 alloy were carried out based on a hot torsion test in this study. The addition of the Al–Ti master alloy as a grain refiner with no UST produced a finer [...] Read more.

Hot deformation constitutive analysis and processing maps of ultrasonic melt treated (UST) A5052 alloy were carried out based on a hot torsion test in this study. The addition of the Al–Ti master alloy as a grain refiner with no UST produced a finer grain size than the UST and pure Ti sonotrode. The Al3Ti phase particles in the case of the Al–10Ti master alloy acted as a nucleus for grain refinement, while the Ti atoms dissolved in the melt from the sonotrode were considered to have less of a grain refinement effect, even under UST conditions, than the Al3Ti phase particles in the Al–Ti master alloy. The constitutive equations for each experimental condition by torsion test were derived. In the processing maps examined in this study, the flow instability region was not present under UST in the as-cast condition, but it existed under the no UST condition. The effects of UST examined in this study are considered as (i) the uniform distribution of Ti solutes from the sonotrode and (ii) the reduction of pores by the degassing effect. After the homogenization heat treatment, most instability regions disappeared because the microstructures became uniform following the decomposition of intermetallic compounds and distribution of solute elements. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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19 pages, 6207 KiB

Open AccessArticle

Research on the Influence of Cold Drawing and Aging Heat Treatment on the Structure and Mechanical Properties of GH3625 Alloy

by Ji Li, Yujie Wo, Zhigang Wang, Wenhao Ren, Wei Zhang, Jie Zhang and Yang Zhou

Materials 2024, 17(11), 2754; https://doi.org/10.3390/ma17112754 - 5 Jun 2024

Viewed by 609

Abstract

With the development of the petroleum industry, the demand for materials for oilfield equipment is becoming increasingly stringent. The strength increase brought about by time strengthening is limited in meeting the needs of equipment development. The GH3625 alloy with different strength levels can [...] Read more.

With the development of the petroleum industry, the demand for materials for oilfield equipment is becoming increasingly stringent. The strength increase brought about by time strengthening is limited in meeting the needs of equipment development. The GH3625 alloy with different strength levels can be obtained through cold deformation and heat treatment processes. A study should be carried out to further develop the potential mechanical properties of GH3625. In this study, the GH3625 alloy was cold drawn with different reductions in area (0–30%) and heat treated, and its mechanical properties were tested. The microstructure of the alloy during deformation and heat treatment was characterized by methods such as optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) based on the principles of physical metallurgy. The strength increase caused by dislocation strengthening was calculated from the dislocation density, tested by X-ray diffraction (XRD). The calculated value was compared to the measured value, elucidating the strengthening effect of cold deformation and heat treatment. The results showed that the yield strength and yield ratio of the cold-drawn alloy significantly reduced after aging at 650 °C and 760 °C. Heat treatment can make a cold-deformed material recover, ablate dislocations, and greatly reduce the dislocation density in the microstructure of the GH3625 alloy, which was the main factor in the decrease in yield strength. The work-hardening gradient of the cold-drawn material varied greatly with different reductions in area. When the reduction in area was small (10%), the hardness gradient was obvious. When it increased to 30%, the alloy was uniformly strengthened as the deformation was transmitted to the axis. This study can provide more mechanical performance options for GH3625 alloy structural components in the petrochemical industry. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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15 pages, 10406 KiB

Open AccessArticle

Enhanced Mechanical Properties of Ti/Mg Laminated Composites Using a Differential Temperature Rolling Process under a Protective Atmosphere

by Zichen Qi, Zhengchi Jia, Xiaoqing Wen, Hong Xiao, Xiao Liu, Dawei Gu, Bo Chen and Xujian Jiang

Materials 2024, 17(11), 2753; https://doi.org/10.3390/ma17112753 - 5 Jun 2024

Viewed by 590

Abstract

Addressing the issue of low bonding strength in Ti/Mg laminated composites due to interfacial oxidation, this study employs a differential temperature rolling method using longitudinal induction heating to fabricate Ti/Mg composite plates. The entire process is conducted under an argon gas protective atmosphere, [...] Read more.

Addressing the issue of low bonding strength in Ti/Mg laminated composites due to interfacial oxidation, this study employs a differential temperature rolling method using longitudinal induction heating to fabricate Ti/Mg composite plates. The entire process is conducted under an argon gas protective atmosphere, which prevents interfacial oxidation while achieving uniform deformation. The effects of reduction on the mechanical properties and microstructure of the composite plates are thoroughly investigated. Results indicate that as the reduction increases, the bonding strength gradually increases, mainly attributed to the increased mechanical interlocking area and a broader element diffusion layer. This corresponds to a transition from a brittle to a ductile fracture at the microscopic tensile–shear fracture surface. When the reduction reaches 47.5%, the Ti/Mg interfacial strength reaches 63 MPa, which is approximately a 20% improvement compared to the bonded strength with previous oxidation at the interface. Notably, at a low reduction of 17.5%, the bonding strength is significantly enhanced by about one time. Additionally, it was found that a strong bonded interface at a high reduction is beneficial in hindering the propagation of interfacial cracks during tensile testing, enhancing the ability of the Ti/Mg composite plates to resist interfacial delamination. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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18 pages, 8620 KiB

Open AccessArticle

Numerical Simulation of Segregation in Slabs under Different Secondary Cooling Electromagnetic Stirring Modes

by Daiwei Liu, Guifang Zhang, Jianhua Zeng and Xin Xie

Materials 2024, 17(11), 2721; https://doi.org/10.3390/ma17112721 - 3 Jun 2024

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Abstract

Secondary cooling electromagnetic stirring (S-EMS) significantly impacts the internal quality of continuous casting slabs. In order to investigate the effects of S-EMS modes on segregation in slabs, a three-dimensional numerical model of the full-scale flow field, solidification, and mass transfer was established. A [...] Read more.

Secondary cooling electromagnetic stirring (S-EMS) significantly impacts the internal quality of continuous casting slabs. In order to investigate the effects of S-EMS modes on segregation in slabs, a three-dimensional numerical model of the full-scale flow field, solidification, and mass transfer was established. A comparative analysis was conducted between continuous electromagnetic stirring and alternate stirring modes regarding their impacts on steel flow, solidification, and carbon segregation. The results indicated that adopting the alternate stirring mode was more advantageous for achieving uniform flow fields and reducing the disparity in solidification endpoints, thus mitigating carbon segregation. Specifically, the central carbon segregation index under continuous stirring at 320 A was 1.236, with an average of 1.247, while under alternate stirring, the central carbon segregation index decreased to 1.222 with an average of 1.227. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Microstructure, Forming and Heat Treatment (Second Edition))

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