Metals

33 pages, 983 KiB

Open AccessReview

Stainable Utilization Strategies for Basic Oxygen Furnace Slag: Properties, Processing, and Future Directions

by Chunting Ma, Siqi Zhang, Keqing Li, Tong Zhao, Qingxin Meng, Dongshang Guan and Ao Zhang

Metals 2025, 15(5), 537; https://doi.org/10.3390/met15050537 (registering DOI) - 12 May 2025

Steel slag, being the dominant solid byproduct in steelmaking, presents global challenges in sustainable management, particularly regarding resource recovery of Basic Oxygen Furnace (BOF) slag, which accounts for over 72% of total slag generation. Through the databases of ScienceDirect, Web of Science, and [...] Read more.

Steel slag, being the dominant solid byproduct in steelmaking, presents global challenges in sustainable management, particularly regarding resource recovery of Basic Oxygen Furnace (BOF) slag, which accounts for over 72% of total slag generation. Through the databases of ScienceDirect, Web of Science, and CNKI, using relevant key words, this review systematically investigates the physicochemical properties and mineralogical composition of BOF slag, elucidating the intrinsic mechanisms underlying its low hydration reactivity and volumetric instability. Pretreatment techniques have been demonstrated to effectively modulate these properties. Furthermore, valuable components can be efficiently recovered through methods including magnetic separation and related technologies. Furthermore, this review elucidates the mechanisms and existing challenges across various resource utilization approaches for steel slag, while also identifying key research priorities for future development, thereby providing a systematic theoretical framework and technical pathways to advance utilization of steel slag. Full article

(This article belongs to the Special Issue Recent Developments in Ironmaking)

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23 pages, 7536 KiB

Open AccessReview

A Review of Studies on the Influence of Rare-Earth Elements on the Microstructures and Properties of Copper and Copper Alloys and Relevant Applications

by Jin-Song Liu, Wen-Xin Yu, Da-Yong Chen, Song-Wei Wang, Hong-Wu Song and Shi-Hong Zhang

Metals 2025, 15(5), 536; https://doi.org/10.3390/met15050536 (registering DOI) - 12 May 2025

Abstract

The rapid advancements in electronics, electric vehicles, and green technologies have imposed increasingly stringent demands on copper-based materials. These requirements include high thermal and electricity conductivity, corrosion resistance, and strength properties at both room temperature and high temperatures. Rare-earth elements are excellent microalloying [...] Read more.

The rapid advancements in electronics, electric vehicles, and green technologies have imposed increasingly stringent demands on copper-based materials. These requirements include high thermal and electricity conductivity, corrosion resistance, and strength properties at both room temperature and high temperatures. Rare-earth elements are excellent microalloying agents due to their typical metallic properties and highly active chemical characteristics; these properties and characteristics enable them to react with almost all elements except noble gases. The addition of rare-earth elements to copper and copper alloys can have several beneficial effects, such as impurity removal, purification, enhancement of the metallographic structure, and improved corrosion resistance. These effects can also raise the heat treatment temperature and enhance plastic processing, thereby further improving the overall properties of copper alloys. This review examines the influence of rare-earth elements (REEs) on copper and its alloys, along with their diverse industrial applications. It was found that elements such as La, Ce, Y, and Nd are commonly added to enhance properties like electrical conductivity, strength, corrosion resistance, purity, and hot workability in alloys such as pure copper, Cu-Ni-Si, Cu-Cr-Zr, and Cu-Fe-P. The review will lay a foundation and provide novel method for the development of advanced copper alloy. Full article

(This article belongs to the Special Issue Research on Microstructure and Performance Mechanisms of Advanced Steels and Alloys)

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18 pages, 12159 KiB

Open AccessArticle

Investigation of High-Temperature Durability and Microstructure Evolution of G115 Steel After Long-Term Aging at 650 °C

by Shaohai Ma, Shun Han, Xinyang Li, Yong Li and Chunxu Wang

Metals 2025, 15(5), 535; https://doi.org/10.3390/met15050535 (registering DOI) - 11 May 2025

Abstract

This study investigated the high-temperature tensile durability of G115 steel after aging at 650 °C for different periods of time using a high-temperature tensile testing system. The results show that with the increase in aging time, the microstructure of G115 steel changes to [...] Read more.

This study investigated the high-temperature tensile durability of G115 steel after aging at 650 °C for different periods of time using a high-temperature tensile testing system. The results show that with the increase in aging time, the microstructure of G115 steel changes to a certain extent, which shows that as the martensite lath width and HAGB increases, the dislocation density decreases and the second precipitate shows obvious growth. As the tensile test temperature increases, the tensile strength decreases from ~750 MPa to ~350 MPa. The effect of aging time on the high-temperature tensile durability of steel after a 3000 h aging process is not significant, which should be related to the relatively high microstructure thermal stability of G115 steel during the aging process. Full article

(This article belongs to the Section Metal Failure Analysis)

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17 pages, 1001 KiB

Open AccessArticle

Reducing Mesh Dependency in Dataset Generation for Machine Learning Prediction of Constitutive Parameters in Sheet Metal Forming

by Dário Mitreiro, Pedro A. Prates and António Andrade-Campos

Metals 2025, 15(5), 534; https://doi.org/10.3390/met15050534 (registering DOI) - 10 May 2025

Viewed by 44

Abstract

Given the extensive use of sheet metal-forming processes in the industry and the constant emergence of new materials, the accurate prediction of material constitutive models and their parameters is extremely important to enhance and optimise these processes. Machine learning techniques have proven to [...] Read more.

Given the extensive use of sheet metal-forming processes in the industry and the constant emergence of new materials, the accurate prediction of material constitutive models and their parameters is extremely important to enhance and optimise these processes. Machine learning techniques have proven to be highly promising for predicting these parameters using data obtained either experimentally or through numerical simulations. However, ML models are often constrained by the limited dataset coverage from numerical simulations, which restricts their predictive capability to specific finite element meshes, leading to potential dependency on the discretisation scheme. To address this challenge, a new approach is proposed that integrates ML with inter-extrapolation of strain data to a grid of points within the specimen domain, expanding the dataset coverage and reducing dependency on discrete mesh points. The current work explores this approach by interpolating and extrapolating manipulated data obtained from a Finite Element Analysis, considering a biaxial tensile test on a cruciform-shaped sample. Models are trained and evaluated for performance and robustness. The results show the high accuracy of the interpolated data, along with the excellent performance metrics and robustness of the trained models, ensuring the successful implementation of this approach. Full article

(This article belongs to the Special Issue Advances in Metal Forming and Plasticity)

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22 pages, 15679 KiB

Open AccessArticle

Achieving Superplasticity in Ultrafine-Grained Mg-9Li Alloy via Dual-Phase Microstructure Optimization

by Jiahao Xu, Xinyue Gong, Wanxiang Zhao, Chao Sun, Guibin Shan, Huan Liu and Dan Song

Metals 2025, 15(5), 533; https://doi.org/10.3390/met15050533 - 9 May 2025

Viewed by 132

Abstract

In this study, high toughness and superplastic deformability were achieved in Mg-9Li alloys through dual-phase microstructure optimization. Solid solution (SS) and equal channel angular pressing (ECAP) treatments were employed to refine the alloy’s microstructure. The effects of these treatments on room-temperature and low-temperature [...] Read more.

In this study, high toughness and superplastic deformability were achieved in Mg-9Li alloys through dual-phase microstructure optimization. Solid solution (SS) and equal channel angular pressing (ECAP) treatments were employed to refine the alloy’s microstructure. The effects of these treatments on room-temperature and low-temperature high-strain-rate superplasticity were systematically investigated under varying microstructural conditions. Results demonstrate that the SS-ECAP alloy exhibits outstanding superplasticity at room temperature and remarkable high-strain-rate deformation capability, achieving a maximum fracture elongation of 602.1%. Grain refinement and reduced dislocation density promote uniform void nucleation under high strain. Calculations of the strain rate sensitivity index (m-value) and activation energy (Q) reveal that the superplastic behavior in the SS-ECAP state is predominantly governed by grain boundary sliding facilitated by grain boundary diffusion. These findings provide critical insights into advancing the superplastic forming technology of Mg-9Li alloys. Full article

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37 pages, 6043 KiB

Open AccessReview

Analysis of Friction Stir Welding of Aluminum Alloys

by Ikram Feddal, Mohamed Chairi and Guido Di Bella

Metals 2025, 15(5), 532; https://doi.org/10.3390/met15050532 (registering DOI) - 9 May 2025

Viewed by 205

Abstract

Friction Stir Welding (FSW) is a solid-state joining technique that has gained widespread adoption, particularly for aluminum alloys, due to its ability to produce high-quality welds without melting base materials. This comprehensive review focuses on the influence of process parameters on weld characteristics [...] Read more.

Friction Stir Welding (FSW) is a solid-state joining technique that has gained widespread adoption, particularly for aluminum alloys, due to its ability to produce high-quality welds without melting base materials. This comprehensive review focuses on the influence of process parameters on weld characteristics and performance. Compared to conventional fusion welding methods, FSW offers notable advantages, including superior mechanical properties, fewer defects, enhanced corrosion resistance, and lower environmental impact. The review also addresses key challenges such as tool wear, precise process control, and complications arising from welding dissimilar alloys. By synthesizing recent developments and case studies, this work outlines current limitations and proposes future directions for optimizing the FSW process to expand its applicability in critical engineering sectors. Full article

(This article belongs to the Section Welding and Joining)

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27 pages, 937 KiB

Open AccessReview

Use of Hydrogen Peroxide as Oxidizing Agent in Chalcopyrite Leaching: A Review

by Danny J. Flores, Teófilo A. Graber, Alejandro H. Angel-Castillo, Pía C. Hernández and María E. Taboada

Metals 2025, 15(5), 531; https://doi.org/10.3390/met15050531 - 8 May 2025

Viewed by 150

Abstract

Leaching represents a significant challenge for the mining industry due to its slow and incomplete kinetics under ambient conditions (20 °C, 1 atm) and its increased prevalence in global ore deposits. In this context, the use of hydrogen peroxide (H₂O₂ [...] Read more.

Leaching represents a significant challenge for the mining industry due to its slow and incomplete kinetics under ambient conditions (20 °C, 1 atm) and its increased prevalence in global ore deposits. In this context, the use of hydrogen peroxide (H₂O₂) has proved to be a promising oxidizing agent for improving process efficiency. This article reviews the most recent breakthroughs in the use of H₂O₂ for chalcopyrite leaching, analyzing the experimental conditions that maximize copper extraction, including combinations with novel leachants such as organic systems, inorganic salts, and amino acids. In addition, the main challenges associated with the use of H₂O₂, such as its catalytic decomposition and thermal stability, are highlighted, along with strategies to overcome these limitations. Perspectives and challenges for its application are presented, emphasizing the need for hybrid and optimized approaches to integrate this oxidizing agent in sustainable hydrometallurgical processes. The objective of this paper is to make an exhaustive review of what has been published on chalcopyrite leaching in order to find ways to leach it in large quantities and in a simple way. Full article

(This article belongs to the Special Issue Recent Advances in the Recycling and Reuse of Metallurgical Wastes and By-Products)

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14 pages, 5818 KiB

Open AccessArticle

Impact of Heat Treatment on Microstructure Evolution in Grey Cast Iron EN-GJL-300

by Peter Petruš, Igor Barényi, Jozef Majerík, Michal Krbata, Marcel Kohutiar, Ingrid Kovaříková and Martin Bilka

Metals 2025, 15(5), 530; https://doi.org/10.3390/met15050530 - 8 May 2025

Viewed by 154

Abstract

This work investigated changes in the microstructure and local mechanical properties after the application of selected heat treatments to EN-GJL-300 grey cast iron. The main goal was to optimize heat treatment to achieve increased mechanical properties and subsequently wear resistance. The heat and [...] Read more.

This work investigated changes in the microstructure and local mechanical properties after the application of selected heat treatments to EN-GJL-300 grey cast iron. The main goal was to optimize heat treatment to achieve increased mechanical properties and subsequently wear resistance. The heat and heat–mechanical treatment were investigated by using a dilatometer as a physical simulator of treatment on real samples. Continuous cooling with three different rates and two other non-continuous treatments (austempering and ausforming) were used to treat the experimental samples. The research was focused on modification of the matrix microstructure, initially pearlitic. No change in the shape or morphology of the graphitic lamellae was required to preserve the damping properties. The results showed that, in terms of the specified conditions, heat treatment with continuous cooling at a rate of 10 °C s⁻¹ appeared to be optimal. This variant showed the presence of bainite and martensite in the microstructure with high hardness measured by nanoindentation as well as the optimal value of general Brinell hardness. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metallic Materials Under Heat Treatment)

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14 pages, 7353 KiB

Open AccessArticle

Grain Rotation and Deformation Behavior in Cube-Textured Ni Polycrystalline Alloy Studied via In-Situ Tensile Testing and EBSD

by Yaotang Ji, Hongli Suo, Zhen Ma, Baoxu Huang, Jianhua Liu, Lei Wang, Zili Zhang and Qiuliang Wang

Metals 2025, 15(5), 529; https://doi.org/10.3390/met15050529 - 8 May 2025

Viewed by 149

Abstract

The cube texture in alloys shows deterioration under plastic deformation. To further observe the evolution of orientation in individual grains during deformation, in-situ tensile testing was coupled with electron backscattered diffraction (EBSD). We found that the rotation of an individual grain is not [...] Read more.

The cube texture in alloys shows deterioration under plastic deformation. To further observe the evolution of orientation in individual grains during deformation, in-situ tensile testing was coupled with electron backscattered diffraction (EBSD). We found that the rotation of an individual grain is not only determined by its Schmid factor and size, but also by the condition of the adjacent grains. We demonstrated the interactions between grains using the EBSD data in different models, including the crystal orientation, the kernel average misorientation, the Schmid factor, the inverse pole figure, and the grain reference orientation deviation. A systematic three-factor coupled model involving the Schmid factor, grain size, and neighboring grain states is proposed. Furthermore, the mechanism by which small-sized grains induce the splitting of adjacent larger grains through the pinning effect has not been reported in highly textured polycrystalline materials to date. This characterization allows us to better understand the changes in grain shape and crystal lattice rotation, which can be used to characterize other polycrystalline alloys. Full article

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10 pages, 2090 KiB

Open AccessArticle

Augmenting Fatigue Datasets for Improved Multiaxial Fatigue Strength Prediction with Neural Networks

by Napon Opasanon, Leon Josef Stahr, Lukas Suchy and Alexander Hasse

Metals 2025, 15(5), 528; https://doi.org/10.3390/met15050528 - 7 May 2025

Viewed by 122

Abstract

Accurate fatigue prediction is essential for ensuring the reliability and durability of engineering systems. Suitable predictive performance was achieved by artificial neural networks trained on the FatLim dataset; however, further improvements are needed due to its small sample size. This study explored the [...] Read more.

Accurate fatigue prediction is essential for ensuring the reliability and durability of engineering systems. Suitable predictive performance was achieved by artificial neural networks trained on the FatLim dataset; however, further improvements are needed due to its small sample size. This study explored the impact of dataset augmentation on model performance by exemplarily expanding the FatLim dataset from 294 to 1732 cases and comparing results against the original dataset. The dataset was augmented by generating additional uniaxial stress scenarios and applying tensor transformations to simulate varied stress orientations. Neural network models were trained separately on the original and expanded datasets, and their predictive performance was evaluated. The results demonstrate that the model trained on the augmented dataset achieved better accuracy, with the mean prediction error decreasing from 0.95% to 0.31% when tested on the original dataset, confirming the effectiveness of dataset expansion in improving fatigue prediction. This research underscores the potential of data augmentation techniques to enhance machine learning models for fatigue analysis. Full article

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17 pages, 10899 KiB

Open AccessArticle

Keyhole Depth Prediction in Laser Deep Penetration Welding of Titanium Alloy Based on Spectral Information

by Yunqian Li, Yanfeng Gao, Hao Pan, Donglin Tao and Hua Zhang

Metals 2025, 15(5), 527; https://doi.org/10.3390/met15050527 - 7 May 2025

Viewed by 58

Abstract

Laser deep penetration welding has been widely applied in industrial fields. However, keyhole depth during the welding process significantly affects the service performance of final products. Based on the spectral signals generated in the laser welding process, this study employs a Long Short-Term [...] Read more.

Laser deep penetration welding has been widely applied in industrial fields. However, keyhole depth during the welding process significantly affects the service performance of final products. Based on the spectral signals generated in the laser welding process, this study employs a Long Short-Term Memory (LSTM) neural network to predict keyhole depth in titanium alloy welding. A coaxial plasma optical information acquisition system is established to collect spectral signals emitted from the welding plasma and analyze the relationship between keyhole depth and plasma spectral features. By analyzing the spectral signals and calculating the plasma temperature, the mapping model between the plasma temperature and keyhole depth is built. The LSTM network prediction results show that the average relative error between the predicted and actual values is 2.31%, which demonstrates that the method proposed in this study has high accuracy for predicting keyhole depth in laser deep penetration welding. Full article

(This article belongs to the Section Welding and Joining)

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14 pages, 9035 KiB

Open AccessArticle

Efficient Regulation of Oxygen Vacancies in β-MnO₂ Nanostructures for High-Loading Zinc-Ion Batteries

by Jian-Chun Wu, Yaoyu Yin, Haitao Zhou, Xicheng Shen, Hongquan Gao, Xiaowei Li, Zhiyong Liu, Yihong Deng and Yanxin Qiao

Metals 2025, 15(5), 526; https://doi.org/10.3390/met15050526 - 7 May 2025

Viewed by 86

Abstract

Manganese-based oxides, particularly β-MnO₂, have emerged as promising cathode materials for aqueous zinc-ion batteries (ZIBs) due to their high theoretical capacity, low cost, and intrinsic safety. However, their sluggish reaction kinetics, limited active sites, and poor conductivity often lead to suboptimal [...] Read more.

Manganese-based oxides, particularly β-MnO₂, have emerged as promising cathode materials for aqueous zinc-ion batteries (ZIBs) due to their high theoretical capacity, low cost, and intrinsic safety. However, their sluggish reaction kinetics, limited active sites, and poor conductivity often lead to suboptimal electrochemical performance. To address these limitations, we propose a facile ethanol-mediated hydrothermal strategy to engineer rod-like β-MnO₂ nanostructures with tailored oxygen vacancies. By precisely adjusting ethanol addition (3–5 mL) during synthesis, oxygen vacancy concentrations were optimized to enhance electronic conductivity and active site exposure. The experimental results demonstrate that β-MnOx-2-5 synthesized with 5 mL of ethanol delivers an exceptional areal capacity of 4.87 mAh cm⁻² (348 mAh g⁻¹, 469.8 Wh kg⁻¹) at 200 mA cm⁻² under a high mass loading of 14 mg cm⁻². Further, a hybrid electrode combining oxygen-deficient β-MnO₂-x-3 (air-calcined) and structurally stable β-Mn₅O₈-y-3 (Ar-calcined) achieves a retained capacity of 3.9 mAh cm⁻² with stable cycling performance, achieving an optimal equilibrium between high capacity and long-term operational durability. Systematic characterizations (XPS, ESR, XANES, FT-EXAFS) confirm vacancy-induced electronic structure modulation, accelerating ion diffusion and redox kinetics. This scalable vacancy engineering approach, requiring only ethanol dosage control, presents a viable pathway toward industrial-scale ZIB applications. Full article

(This article belongs to the Section Metallic Functional Materials)

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6 pages, 168 KiB

Open AccessEditorial

Challenges and Trends in Additive Manufacturing for Metallic Applications: Toward Optimized Processes and Performance

by Petru Berce and Rǎzvan Pǎcurar

Metals 2025, 15(5), 525; https://doi.org/10.3390/met15050525 - 7 May 2025

Viewed by 53

Abstract

Additive Manufacturing (AM) for metallic applications continues to redefine how complex, high-performance components are designed and fabricated across a wide range of sectors, including the aerospace, biomedical, and automotive fields, etc [...] Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications (2nd Edition))

22 pages, 11628 KiB

Open AccessReview

Advances in Heavy Metal Extraction Using Organophosphorus Compounds: A Comprehensive Review

by Meriem Essakhraoui, Aziz Boukhair, Fouad Bentiss, Hamid Mazouz, Redouane Beniazza and Nils Haneklaus

Metals 2025, 15(5), 524; https://doi.org/10.3390/met15050524 - 6 May 2025

Viewed by 207

Abstract

Organophosphorus compounds (OPC) are a large class of organic compounds that provide a wide range of applications, and their importance has grown steadily in recent years. In each category and family, these compounds have similarities and differences. Due to their immense variety, these [...] Read more.

Organophosphorus compounds (OPC) are a large class of organic compounds that provide a wide range of applications, and their importance has grown steadily in recent years. In each category and family, these compounds have similarities and differences. Due to their immense variety, these chemicals have various properties and, therefore, various applications. In fact, various works have been published recently that present the main applications of OPC, especially in metal extraction. Despite their extemsive range of use, optimizing their performance as extractant agents remains a challenge due to their structural variability and sensitivity to process parameters. This review provides a critical analysis of pentavalent OPCs, focusing on how their chemical nature influences heavy metal extraction efficiency. For the first time, we present a novel classification system for OPCs based on phosphorus valency and heteroatom coordination, offering a framework to guide future research. Our findings reveal that the direct coordination of the phosphorus to heteroatoms such as oxygen, sulfur, and nitrogen has a great influence on the physicochemical characteristics of the extractant and the metal extraction efficiency. This observation is in line with Pearson’s Hard and Soft Acids and Bases (HSAB) theory in the sense that it demonstrates that altering the heteroatom alters the metal affinity of the ligand. As a result, these structural modifications can improve the extraction performance by up to 40% for some heavy metals, highlighting the potential for optimized molecular designs to maximize industrial applications. In the future, this work offers a solid foundation for future studies on the rational design of organophosphorus-based extractants. Using HSAB theory and our novel classification system, researchers can rationally design OPCs for their target metal with unparalleled precision. These results have transformative impacts on metal recovery efficiency-intensive sectors like mining, waste recycling, and clean energy technologies. Full article

(This article belongs to the Special Issue Separation, Purification and Extraction of Metals from Primary and Secondary Resources)

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12 pages, 2631 KiB

Open AccessArticle

Alkaloid Extract from Chimarrhis cymosa as a Corrosion Inhibitor for C38 Steel in 1M Hydrochloric Acid: Electrochemical and XPS Studies

by Mahado Said-Ahmed and Mounim Lebrini

Metals 2025, 15(5), 523; https://doi.org/10.3390/met15050523 - 6 May 2025

Viewed by 137

Abstract

The inhibitory effect of the alkaloid extract from Chimarrhis cymosa on C38 steel corrosion in 1M HCl was examined through electrochemical investigations. An inhibition efficiency of 90% was achieved with 200 mg/L of the alkaloid extract from Chimarrhis cymosa at 25 °C. Potentiodynamic [...] Read more.

The inhibitory effect of the alkaloid extract from Chimarrhis cymosa on C38 steel corrosion in 1M HCl was examined through electrochemical investigations. An inhibition efficiency of 90% was achieved with 200 mg/L of the alkaloid extract from Chimarrhis cymosa at 25 °C. Potentiodynamic polarization revealed that the extract acts as a mixed-type inhibitor. Nyquist plots showed that an increase in the concentration of the alkaloid extract from Chimarrhis cymosa led to an increase in charge-transfer resistance and a decrease in double-layer capacitance, resulting in enhanced inhibition efficiency. The adsorption of inhibitor molecules followed the Langmuir adsorption isotherm. XPS analysis confirmed the formation of an inhibitor layer on the steel surface containing the Chimarrhis cymosa alkaloidic extract. Full article

(This article belongs to the Special Issue Feature Paper Collection of “Current Challenges in Corrosion Research" (2nd Edition))

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16 pages, 20819 KiB

Open AccessArticle

Production of ZnO Nanofibers from Zinc Galvanizing Flue Dust

by Klaudia Kundráková, Jana Pirošková, Jarmila Trpčevská and Erika Múdra

Metals 2025, 15(5), 522; https://doi.org/10.3390/met15050522 - 6 May 2025

Viewed by 118

Abstract

This work focuses on the production of ceramic nanofibers from waste materials, which represents a significant contribution to the sustainable use of resources and innovative solutions in the field of nanotechnology. The research builds on existing knowledge of nanofiber production, with a specific [...] Read more.

This work focuses on the production of ceramic nanofibers from waste materials, which represents a significant contribution to the sustainable use of resources and innovative solutions in the field of nanotechnology. The research builds on existing knowledge of nanofiber production, with a specific focus on the use of zinc galvanizing flue dust. The main objective of the study is to explore the possibilities of converting zinc-containing waste materials into ceramic nanofibers, introducing a new direction in nanotechnology. Laboratory experiments involved leaching processes and electrostatic spinning processes of zinc solutions. From the obtained results, it can be concluded that ZnO ceramic nanofibers produced from both synthetic and real solutions exhibit similar fiber structures. Therefore, it can be stated that both acids (HCl and H₂SO₄) are suitable for preparation. Among them, 0.5 M HCl is the most ideal, resulting in oval fibers with a rough and coarse surface, while 0.5 M H₂SO₄ produces fibers with a different morphology in the form of hollow ribbons, which are presumed to have a higher specific surface area. Thus, it can be concluded that the production of ceramic nanofibers from zinc galvanizing flue dust is feasible and effective, with electrostatic spinning proving to be a low-waste technology. The study also examines the influence of contaminants from real waste solutions on the production of ceramic nanofibers and compares their properties with nanofibers obtained from synthetic solutions. Experimental results suggest that contaminants in real solutions did not have a negative impact on the morphology of the prepared ZnO nanofibers. In conclusion, the production of ZnO ceramic nanofibers from waste offers a promising approach for the future development of nanotechnology, combining innovation with sustainability and efficient resource utilization. Full article

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15 pages, 4813 KiB

Open AccessFeature PaperArticle

Double-Flush Riveting for Hybrid Busbar Assembly

by Rui F. V. Sampaio, João P. M. Pragana, Miguel P. Figueiredo, Ivo M. F. Bragança, Carlos M. A. Silva and Paulo A. F. Martins

Metals 2025, 15(5), 521; https://doi.org/10.3390/met15050521 - 5 May 2025

Viewed by 148

Abstract

This paper explores a novel double-flush riveting process for assembling hybrid busbars made from aluminum and copper sheets. The process involves drilling and forging countersunk holes with controlled geometry in both materials followed by compression of cylindrical rivets into the holes to create [...] Read more.

This paper explores a novel double-flush riveting process for assembling hybrid busbars made from aluminum and copper sheets. The process involves drilling and forging countersunk holes with controlled geometry in both materials followed by compression of cylindrical rivets into the holes to create strong, form- and force-closed mechanical joints. Experimental and numerical analyses are combined to examine material flow, quantify the required forces, and assess the structural integrity of the joints through destructive testing. Additionally, the electrical resistance of these novel joints is evaluated and compared with that of ideal and conventional fastened hybrid busbar joints in order to assess their performance and reliability in real-world electrical service conditions. The results indicate that the novel double-flush riveting process is a viable alternative to other conventional joining processes, such as fastening, delivering good structural integrity and enhanced electrical conductivity for hybrid busbar applications. Full article

(This article belongs to the Special Issue Numerical Modelling of Metal-Forming Processes)

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14 pages, 5864 KiB

Open AccessArticle

Reducing Residual Stresses in Synthetic Cast Iron by Ti Microalloying

by Peter Futas, Janette Brezinová, Miroslav Pástor and Alena Pribulova

Metals 2025, 15(5), 520; https://doi.org/10.3390/met15050520 - 5 May 2025

Viewed by 114

Abstract

During solidification and cooling of the castings, residual stresses are produced in the material. In technical practice, residual stresses are very important because, in addition to the operational loading, they can lead to material failure and, consequently, to equipment or structural failures. The [...] Read more.

During solidification and cooling of the castings, residual stresses are produced in the material. In technical practice, residual stresses are very important because, in addition to the operational loading, they can lead to material failure and, consequently, to equipment or structural failures. The accurate determination of residual stresses by numerical simulations presents a significant challenge due to the number of variables involved in modelling technological processes. Consequently, in many cases, residual stress levels are typically obtained using experimental measurements. Where possible, these measurements are complemented by monitoring and evaluating parameter changes that occur due to changes in the input conditions. In this paper, findings from experimental measurements of residual stresses in castings made from synthetic cast iron are reported, with a specific focus on the effect of titanium (Ti) microalloying on these residual stress levels. Comparison of the experimental results obtained from castings composed of grey cast iron shows that microalloying with titanium metal effectively reduces the residual stresses while maintaining the same tensile strength and Brinell hardness (HB). This highlights the potential benefits of microalloying in enhancing the benefits and reliability of cast iron materials. Full article

(This article belongs to the Special Issue Recent Advances in Residual Stress Research in Metallic Materials)

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17 pages, 4514 KiB

Open AccessArticle

Statistical Modeling and Characterization of Laser Marking on AISI 301LN Stainless Steel Using Short-Pulsed Fiber Laser

by Mohammad Rezayat, Mojtaba Karamimoghadam, Nicola Contuzzi, Giuseppe Casalino and Antonio Mateo

Metals 2025, 15(5), 519; https://doi.org/10.3390/met15050519 - 4 May 2025

Viewed by 254

Abstract

This study explores the effects of nanosecond short-pulsed fiber laser processing on AISI 301LN stainless steel, focusing on optimizing surface characteristics through precise parameter control. Using a Design of Experiments (DOE) approach combined with response surface methodology (RSM), the influence of laser power [...] Read more.

This study explores the effects of nanosecond short-pulsed fiber laser processing on AISI 301LN stainless steel, focusing on optimizing surface characteristics through precise parameter control. Using a Design of Experiments (DOE) approach combined with response surface methodology (RSM), the influence of laser power (30–60 W) and the number of laser passes (5–15 times) was systematically investigated. The results demonstrate that increasing the laser power and passes significantly affected the surface properties. The highest surface roughness of 16.8 µm and engraving width of 51 µm were achieved with 60 W power and 15 passes, whereas the lowest roughness of 13.8 µm and width of 35 µm were observed with 30 W power and 5 passes. Wettability measurements revealed an inverse correlation with roughness, with contact angles ranging from 86.4° for rougher surfaces to 92.4° for smoother textures. The findings demonstrate the capability of short-pulsed fiber laser processing to tailor surface properties effectively, with potential applications in manufacturing and surface engineering where controlled roughness and wettability are critical. Full article

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24 pages, 23216 KiB

Open AccessArticle

Effect of Aging at Different Temperatures on Microstructure Evolution of 347H Heat-Resistant Steel-Welded Joints

by Jun Xiao, Geng Tian, Di Wang, Kuo Cao and Aimin Zhao

Metals 2025, 15(5), 518; https://doi.org/10.3390/met15050518 - 4 May 2025

Viewed by 267

Abstract

This study used 347H heat-resistant steel as the base material and systematically investigated the microstructural evolution and second-phase precipitation in typical regions during welding and aging processes. The results showed that the weld metal consisted of austenitic dendrites and inter-dendritic ferrite in a [...] Read more.

This study used 347H heat-resistant steel as the base material and systematically investigated the microstructural evolution and second-phase precipitation in typical regions during welding and aging processes. The results showed that the weld metal consisted of austenitic dendrites and inter-dendritic ferrite in a lath-like form. In the welded samples, the HAZ (Heat-Affected Zone) and BM (Base Material) regions were composed of equiaxed crystals. The microhardness of the HAZ was lower, mainly due to the coarser grain size and fewer second-phase particles. After aging at 700 °C, the hardness of all regions of the welded joint increased significantly due to the precipitation of M₂₃C₆ and MX phases. When the aging temperature increased to above 800 °C, the stability of the M₂₃C₆ phase decreased, and the diffusion rate of Nb in the matrix accelerated, promoting the preferential growth and stable presence of the MX phase. As the MX phase competes with the M₂₃C₆ phase for carbon during its formation, its generation suppresses the further precipitation of the M₂₃C₆ phase. Under 800 °C aging conditions, the γ/δ interface exhibited high interfacial energy, and the Nb content in the ferrite was higher, which facilitated the formation of the MX phase along this interface. As the aging temperature continued to rise, the hardness of the HAZ and BM regions initially increased and then decreased. After aging at 800 °C, the hardness decreased because the M₂₃C₆ phase no longer precipitated. After aging at 900 °C, the hardness of the HAZ and BM regions significantly increased, mainly due to the large precipitation of the MX phase. The hardness of the W (Weld Zone) and FZ (Fusion Zone) regions gradually decreased with the increase in aging temperature, mainly due to the reduction of inter-dendritic ferrite content, coarsening of second-phase particles, weakening of the pinning effect, and grain growth. In the 900 °C aging samples, the MX phase particle size from largest to smallest was as follows: W > HAZ > BM. The Nb-enriched ferrite provided the chemical driving force for the precipitation of the MX phase, while the δ/γ interface provided favorable conditions for its nucleation and growth; thus, the MX phase particles were the largest in the W region. The HAZ region, due to residual stress and smaller grain boundary area, had MX phase particle size second only to the W region. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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10 pages, 7420 KiB

Open AccessArticle

Effect of Heat Treatment on the Corrosion Behavior of Selective Laser Melted CX Stainless Steel

by Shaoqian Wu, Shuo Wu, Shilong Xing, Tianshu Wang, Jiabin Hou, Yuantao Zhao, Zongan Li and Yanbo Liu

Metals 2025, 15(5), 517; https://doi.org/10.3390/met15050517 - 3 May 2025

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Abstract

The effects of different heat treatment regimes on the microstructure and corrosion behavior of selectively laser melted (SLM) Corrax (CX) stainless steel were systematically investigated. Three distinct thermal processing approaches solution treatment (ST), aging treatment (AT), and combined solution aging treatment (ST + [...] Read more.

The effects of different heat treatment regimes on the microstructure and corrosion behavior of selectively laser melted (SLM) Corrax (CX) stainless steel were systematically investigated. Three distinct thermal processing approaches solution treatment (ST), aging treatment (AT), and combined solution aging treatment (ST + AT) were comparatively examined to assess their microstructural evolution and corrosion performance. The results demonstrated that the SLM-processed CX sample initially consisted of martensite and retained austenite. After solution treatment at 900 °C for 0.5 h, microsegregation was eliminated, and the retained austenite fully transformed into martensite. During direct aging at 525 °C for 3 h (AT), a portion of the martensite reverted to austenite, accompanied by grain refinement that reduced the average grain size to 1.79 μm. When the CX was solution-aged at 900 °C for 0.5 h and then 525 °C for 4 h (ST + AT), the retained austenite transformed completely into martensite. The results of potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) revealed that the aged specimen demonstrated comparatively superior corrosion resistance with reduced surface accumulation of corrosion products relative to both ST and ST + AT specimens. The electrochemical test results indicate that the selection of heat treatment parameters has a significant impact on the corrosion resistance of SLM-formed CX samples. Compared to ST and ST + AT, the corrosion performance of AT-treated samples is improved to a certain extent, with the highest E_pit (322 mV) and the largest ΔE (742). The corrosion potential is relatively high (E_corr, −414 mV vs. SCE), and the corrosion current density is relatively low (I_corr, 0.405 μA·cm⁻²). This indicates that the AT samples exhibit good corrosion resistance. Full article

(This article belongs to the Special Issue Mechanical Properties and Corrosion Behavior of Metals after Surface Modification)

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17 pages, 25857 KiB

Open AccessArticle

Dynamic Response of WMoZrNiFe Energetic Structural Material Based on SHPB

by Guiyan Pei, Zhe Peng, Xiaolu Bi, Qingjie Jiao, Rui Liu and Jianxin Nie

Metals 2025, 15(5), 516; https://doi.org/10.3390/met15050516 - 2 May 2025

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Abstract

Energetic structural materials (ESMs) are widely studied due to their high energy density, which enhances their potential in various industrial and engineering applications, such as in energy absorption systems, safety devices, and structural components that need to withstand dynamic loading. A high-strength WMoZrNiFe [...] Read more.

Energetic structural materials (ESMs) are widely studied due to their high energy density, which enhances their potential in various industrial and engineering applications, such as in energy absorption systems, safety devices, and structural components that need to withstand dynamic loading. A high-strength WMoZrNiFe energetic structural material was prepared, and its mechanical properties and ignition behavior under dynamic loading were studied. Using the split-Hopkinson pressure bar (SHPB) experimental device, samples with different initial tilt angles of 0°, 30°, and 45° were dynamically loaded. The influence of the sample tilt angle on the ignition threshold was analyzed. The dynamic mechanical properties, failure modes, and ignition threshold based on the energy absorption of the WMoZrNiFe energetic structural material during the dynamic loading process were obtained. The results show that the material has a strain rate effect in the range of 1000 s⁻¹~3000 s⁻¹. The yield strength of the sample with a tilt angle of 0° increased from 1468 MPa to 1837 MPa, that of the sample with a tilt angle of 30° increased from 982 MPa to 1053 MPa, and that of the sample with an inclination angle of 45° increased from 420 MPa to 812 MPa. Through EDS elemental analysis, the ignition reaction mechanism of the WMoZrNiFe energetic structural material under dynamic compression was obtained. The violent reaction of the material occurred after the material fractured, and the active elements reacted with oxygen in the air. Full article

(This article belongs to the Special Issue Properties, Microstructure and Forming of Intermetallics)

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14 pages, 36719 KiB

Open AccessArticle

Gradient Dual-Phase Structure Design in Brass: A New Strategy for Balancing Mechanical and Tribological Properties

by Jing Han, Tao Zhang, Bin Zhang, Jing Zhang and Jiyun Zhao

Metals 2025, 15(5), 515; https://doi.org/10.3390/met15050515 - 1 May 2025

Viewed by 148

Abstract

This study introduces a novel gradient dual-phase structure design in brass, achieved through ultrasonic severe surface rolling (USSR) processing, which enables an unconventional asymmetric bilayer structure—comprising a hardened surface layer (>1 mm thick) and a ductile substrate—distinct from conventional hard-soft-hard sandwich configurations in [...] Read more.

This study introduces a novel gradient dual-phase structure design in brass, achieved through ultrasonic severe surface rolling (USSR) processing, which enables an unconventional asymmetric bilayer structure—comprising a hardened surface layer (>1 mm thick) and a ductile substrate—distinct from conventional hard-soft-hard sandwich configurations in gradient nanostructured materials. Microstructural characterization reveals a gradient dual-phase (α + β′) structure in the hardened layer, progressively transitioning into a homogenized dual-phase structure in the substrate. This unique architecture endows the USSR brass with exceptional mechanical properties, including a yield strength of 582.4 ± 31.0 MPa, ultimate tensile strength of 775.3 ± 33.9 MPa, and retained ductility (9.3 ± 1.0%), demonstrating an outstanding strength-ductility synergy. The USSR brass also demonstrates superior wear resistance with a 42.32% reduction in wear volume and 40.82% decrease in coefficient of friction compared to its as-received counterpart under oil lubrication. This architectural paradigm establishes a robust framework for engineering high-performance brass that simultaneously achieve an exceptional strength-ductility balance and enhanced wear resistance. Full article

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16 pages, 3462 KiB

Open AccessArticle

Plasma–Chemical Low-Temperature Reduction of Aluminum with Methane Activated in Microwave Plasma Discharge

by Alexander Logunov, Andrey Vorotyntsev, Igor Prokhorov, Alexey Maslov, Artem Belousov, Ivan Zanozin, Evgeniya Logunova, Sergei Zelentsov, Anton Petukhov and Sergey Suvorov

Metals 2025, 15(5), 514; https://doi.org/10.3390/met15050514 - 1 May 2025

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Abstract

High-purity aluminum is widely used in metallurgy, microelectronics and chemical synthesis. In this work, the method of carbothermic reduction of aluminum powder in a microwave plasma discharge with the formation of valuable organic products such as synthesis gas, acetylene and benzene was used. [...] Read more.

High-purity aluminum is widely used in metallurgy, microelectronics and chemical synthesis. In this work, the method of carbothermic reduction of aluminum powder in a microwave plasma discharge with the formation of valuable organic products such as synthesis gas, acetylene and benzene was used. Al powder was studied by inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The yield of by-products was studied by gas chromatography equipped with a mass spectrometer, as well as optical emission spectroscopy of plasma discharge. High-purity aluminum powder reduced with the plasma was used to synthesize oxygen-free trimethylaluminum (TMA). For the first time, TMA was synthesized in one vacuum cycle without the system depressurizing to improve the purity of the final product. Trimethylaluminum was analyzed by gas chromatography, which confirmed that the main substance is ≥99.99% pure. Gas chromatography with a mass spectrometer was used to determine by-products and residual reaction products. Additionally, ICP-MS was used to confirm trace metal concentrations, achieving the 7N standard for ultra-high-purity materials. Full article

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28 pages, 24038 KiB

Open AccessArticle

Advanced Porosity Control of CP780 Galvanized Steel During Gas Metal Arc Welding with Pulsed Arc

by Carlos Adrián García Ochoa, Jorge Alejandro Verduzco Martínez, Francisco Fernando Curiel-López, Víctor Hugo López-Morelos, José Jaime Taha-Tijerina, Ariosto Medina Flores and Maleni García Gómez

Metals 2025, 15(5), 513; https://doi.org/10.3390/met15050513 - 1 May 2025

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Abstract

This study investigated the control of porosity during gas metal arc welding with pulsed arc (GMAW-P) of complex-phase 780 (CP780) galvanized steel. Due to the Zn coating on this type of steel, porosity forms during welding as a result of Zn vaporization. The [...] Read more.

This study investigated the control of porosity during gas metal arc welding with pulsed arc (GMAW-P) of complex-phase 780 (CP780) galvanized steel. Due to the Zn coating on this type of steel, porosity forms during welding as a result of Zn vaporization. The objective was to optimize the welding parameters to minimize porosity with a design of experiments using an L9 orthogonal array to analyze the effects of peak current (I_p), pulse time (t_p), and pulse frequency (f) in high-speed welding conditions. The results showed that porosity was significantly reduced with a peak current of 313 A, a frequency of 10 Hz, and a pulse time of 10 ms, achieving ~0% porosity in the validation welding trials. A microstructural analysis identified allotriomorphic ferrite, Widmanstätten ferrite, acicular ferrite, bainite, and martensite in the heat-affected zone (HAZ). A predictive model to anticipate the percentage of porosity with an R² of 99.97% was developed, and an ANOVA determined the peak current as the most critical factor in porosity formation. Full article

(This article belongs to the Special Issue Intelligent and Sustainable Welding: State of the Art, Challenges and Prospects)

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23 pages, 7979 KiB

Open AccessArticle

Constitutive Model for Hot Deformation Behavior of Fe-Mn-Cr-Based Alloys: Physical Model, ANN Model, Model Optimization, Parameter Evaluation and Calibration

by Jie Xu, Chaoyang Sun, Huijun Liang, Lingyun Qian and Chunhui Wang

Metals 2025, 15(5), 512; https://doi.org/10.3390/met15050512 - 1 May 2025

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Abstract

The development and validation of constitutive models for high-temperature deformation are critical for bridging microstructure evolution with macroscopic mechanical behavior in materials. In this study, we systematically analyzed the hot deformation behavior of Fe-Mn-Cr-based alloys, compared the modeling processes of physical, phenomenological, and [...] Read more.

The development and validation of constitutive models for high-temperature deformation are critical for bridging microstructure evolution with macroscopic mechanical behavior in materials. In this study, we systematically analyzed the hot deformation behavior of Fe-Mn-Cr-based alloys, compared the modeling processes of physical, phenomenological, and data-driven approaches in detail, and optimized their structural and predictive properties. First, the advantages, disadvantages, and applicability of three traditional models, namely the physical Arrhenius model, the phenomenological Johnson–Cook model, and the artificial neural network (ANN) model, are compared for flow stress prediction. Subsequently, traditional mathematical derivations and numerical optimization methods are evaluated. The parameters and architecture of the ANN model are then systematically optimized using optimization algorithms to enhance training efficiency and prediction accuracy. Finally, sensitivity analysis integrated with Bayesian posterior probability density functions enables the calibration of physical model parameters and uncertainty quantification. The results demonstrate that the ANN with optimized parameters and architecture achieves superior prediction accuracy (R² = 0.9985, AARE = 3.01%) compared to traditional methods. Bayesian inference-based quantification of parameter uncertainty significantly enhances the reliability and interpretability of constitutive model parameters. This study not only reveals the strain–temperature coupling effects in the hot deformation behavior of Fe-Mn-Cr-based alloys but also provides systematic methodological support for constitutive modeling of high-performance alloys and a theoretical foundation for material processing technology design. Full article

(This article belongs to the Special Issue Modeling, Simulation and Experimental Studies in Metal Forming)

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15 pages, 8046 KiB

Open AccessArticle

Mechanical and Microstructural Properties of High-Speed Friction Stir Welding of AA 7020 Aluminum Alloy Using Multi-Pin Tool

by Ramin Delir Nazarlou, Samita Salim, Michael Wiegand, Christian Wolf and Stefan Böhm

Metals 2025, 15(5), 511; https://doi.org/10.3390/met15050511 - 30 Apr 2025

Viewed by 218

Abstract

High-speed friction stir welding (HSFSW) has emerged as a promising technique for improving the manufacturing efficiency of aluminum alloy structures by enabling faster welding while maintaining the quality of welded joints. This study investigates the mechanical properties and microstructural characteristics of AA 7020-T651 [...] Read more.

High-speed friction stir welding (HSFSW) has emerged as a promising technique for improving the manufacturing efficiency of aluminum alloy structures by enabling faster welding while maintaining the quality of welded joints. This study investigates the mechanical properties and microstructural characteristics of AA 7020-T651 aluminum alloy joints welded using a novel multi-pin tool at high feed rates ranging from 2500 to 6000 mm/min under a constant rotational speed of 4000 rpm. Defect-free welds were successfully fabricated, as confirmed by metallographic analysis and micro-computed tomography (µ-CT). The multi-pin tool facilitated consistent material flow and heat distribution, which contributed to reliable joint formation across all feed rates. At the highest feed rate, the tensile strength reached 76% of the base material. A consistent softening in the nugget zone (NZ) was observed, and electron backscatter diffraction (EBSD) analysis showed a more than 70% grain size reduction in this zone, averaging ~3 µm, due to dynamic recrystallization. These findings underscore the suitability of HSFSW with multi-pin tools for high-speed industrial applications, offering enhanced productivity without compromising structural integrity. Full article

(This article belongs to the Section Welding and Joining)

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23 pages, 6623 KiB

Open AccessArticle

Enhanced Corrosion Resistance of Carbon Steel Rebar in Chloride-Containing Water Solutions: The Role of Lotus Extract in Corrosion Inhibition

by Dan Song, Juhang Wang, Hao Guan, Sijie Zhang, Zhou Zhou and Shuguang Zhang

Metals 2025, 15(5), 510; https://doi.org/10.3390/met15050510 - 30 Apr 2025

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Abstract

Corrosion inhibitors play a crucial role in the corrosion protection of rebars in reinforced concrete structures under harsh service conditions. However, conventional corrosion inhibitors often suffer from low efficiency and environmental concerns. This study investigates a low-cost and environmentally friendly lotus leaf extract [...] Read more.

Corrosion inhibitors play a crucial role in the corrosion protection of rebars in reinforced concrete structures under harsh service conditions. However, conventional corrosion inhibitors often suffer from low efficiency and environmental concerns. This study investigates a low-cost and environmentally friendly lotus leaf extract (LLE) as a corrosion inhibitor and examines its effects on carbon steel rebar corrosion under various conditions. The structure and composition of LLE were characterized using SEM, FTIR, and LC-MS. The effects of LLE on rebar corrosion behavior under different environmental conditions were investigated using electrochemical tests, Mott–Schottky analysis, and XPS. The main findings indicate that LLE is rich in polar chemical bonds and functional groups, which facilitate adsorption and film formation on the rebar surface. In a 3.5% NaCl solution, rebar corrosion is primarily influenced by the solution pH, and low concentrations of LLE exhibit effective corrosion inhibition. In a simulated concrete pore solution, higher concentrations of LLE promote the formation of a passivation film in a chloride-alkaline environment. Studies on pre-passivated rebar indicate that LLE effectively protects the passivation film, with the optimal LLE concentration for passivation film protection and adsorption film quality being 0.5 wt%. This study contributes to the application and development of novel LLE-based corrosion inhibition technology for carbon steel rebar. Full article

(This article belongs to the Special Issue Corrosion Behavior of Alloys in Water Environments)

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19 pages, 7500 KiB

Open AccessArticle

The Effect of Quenching and Partitioning (Q&P) Processing on the Microstructure, Hardness, and Corrosion Resistance of SAE 9254 Spring Steel

by Alisson Denis Carros Nizes, Silvano Leal dos Santos and Renato Altobelli Antunes

Metals 2025, 15(5), 509; https://doi.org/10.3390/met15050509 - 30 Apr 2025

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Abstract

In the present work, the effect of quenching and partitioning cycles on the microstructure, hardness, and corrosion behavior of SAE 9254 spring steel was investigated. Initially, the critical phase transformation temperatures were analyzed by dilatometry. The samples were then treated by four routes [...] Read more.

In the present work, the effect of quenching and partitioning cycles on the microstructure, hardness, and corrosion behavior of SAE 9254 spring steel was investigated. Initially, the critical phase transformation temperatures were analyzed by dilatometry. The samples were then treated by four routes of quenching and partitioning in a dilatometer with quenching stop temperatures of 250 and 220 °C. The partitioning temperatures were 300 and 400 °C. The partitioning time was 480 s. Quantitative characterization of austenite and martensite volume fractions was carried out by X-ray diffraction. Qualitative characterization was carried out by optical microscopy and scanning electron microscopy in addition to quantitative assessments of the chemical composition of segregations by EDS. The formation of martensite, retained austenite, and bainite was observed. The dilatometric curves displayed the occurrence of volumetric expansion in the partitioning step, indicating the formation of secondary martensite (fresh martensite) during the final cooling process (final quenching). The mechanical properties were evaluated by Vickers microhardness and nanoindentation tests. There was heterogeneity of hardness inside and outside the banding regions. The electrochemical properties were evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization tests in a 0.1 M H₂SO₄ solution. The best corrosion resistance was achieved for samples quenched at 250 °C and partitioned at 400 °C due to the higher volume fraction of retained austenite when compared to the other heat treatment conditions. Full article

(This article belongs to the Special Issue Advances in Corrosion and Protection of Materials (Third Edition))

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12 pages, 17360 KiB

Open AccessArticle

Study of the Behavior and Mechanism of Sponge Iron Oxidation

by Pingguo Jiang, Chen Zhang, Xionggang Lu and Wangjun Peng

Metals 2025, 15(5), 508; https://doi.org/10.3390/met15050508 - 30 Apr 2025

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Abstract

This paper investigates the kinetic characteristics of sponge iron powder reoxidation under two different oxidation atmospheres by examining the reoxidation process from thermodynamic, microstructural, and kinetic perspectives. It reveals the changes in the surface microstructure and oxide content of sponge iron under different [...] Read more.

This paper investigates the kinetic characteristics of sponge iron powder reoxidation under two different oxidation atmospheres by examining the reoxidation process from thermodynamic, microstructural, and kinetic perspectives. It reveals the changes in the surface microstructure and oxide content of sponge iron under different oxidation conditions. The results indicate that the thermodynamic conditions for the formation of Fe₂O₃ were more relaxed than those for Fe₃O₄. As the oxidation time increased, the surface microstructure of the sponge iron transitioned from a porous granular form (Fe) to a dense blocky structure (Fe₃O₄), eventually forming a rod-like product (Fe₂O₃). Under an atmosphere of O₂/Ar = 21/79, the oxide content was significantly higher compared to an atmosphere of O₂/Ar = 11/89. Under an atmosphere of O₂/Ar = 11/89, the oxidation rate index (n) remained at 0.68 throughout all stages, indicating a consistently higher oxidation rate. Conversely, under an atmosphere of O₂/Ar = 21/79, the initial oxidation rate index (n₁) was 1.17, reflecting a slower initial oxidation rate, while in the final stage, the oxidation rate index (n₂) dripped to 0.33, indicating a substantial increase in the oxidation rate. The research results provide basic research ideas and references for an in-depth study of the antioxidant storage of sponge iron. Full article

(This article belongs to the Section Extractive Metallurgy)

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