Advanced Processes in Metallurgical Technologies

1. Introduction and Scope

The production of metals and their alloys will continue to increase in the coming years, mainly due to the growing demand for these products. Currently, the production of metals is a very important field of research, especially given their high prices and enormous demand. This field needs to be looked at from both the economic side, i.e., developing technologies that need less energy, and the ecological one, i.e., developing technologies that emit fewer pollutants and, at the same time, promote green technologies. The aim of this collection of articles is to contribute to the development of metallurgy and materials engineering from the point of view of a multidisciplinary approach, taking into account the issues of environmental protection, generated waste, disposal options, and energy savings.

2. Contributions to This Topic

The papers included in this Topic present trends in advancements in the fields of metallurgy and engineering materials. Thirty-eight manuscripts were accepted for publication in this Topic. The contributions are listed below:

• Castro-Cedeno, E.-I.; Jourdan, J.; Martens, J.; Bellot, J.-P.; Jardy, A. Study of Assimilation of Cored Wire into Liquid Steel Baths. Metals 2024, 14, 462. https://doi.org/10.3390/met14040462.
• Zhu, K.; Jia, H.; Huang, J.; Zhang, J. The Integrated Preparation of Porous Tungsten Gradient Materials with a Wide Porosity Range. Metals 2024, 14, 427. https://doi.org/10.3390/met14040427.
• Yu, P.; Song, H.; Tian, Y.; Dong, J.; Xu, G.; Zhao, M.; Gu, X. The On-Line Identification and Location of Welding Interference Based on CEEMD. Metals 2024, 14, 396. https://doi.org/10.3390/met14040396.
• Liu, Y.; Xiong, S. Research Progress on Thermal Conductivity of High-Pressure Die-Cast Aluminum Alloys. Metals 2024, 14, 370. https://doi.org/10.3390/met14040370.
• Xu, L.; Zhao, B. A Fundamental Study on the Preparation of Sodium Tungstate from Wolframite via the Smelting Process. Metals 2024, 14, 299. https://doi.org/10.3390/met14030299.
• Peng, H.; Zhao, Y.; Fu, W.; Chen, Z.; Zhang, M.; Liu, J.; Tan, X. Comparative Study of Anti-Corrosion Properties of Different Types of Press-Hardened Steels. Materials 2024, 17, 1022. https://doi.org/10.3390/ma17051022.
• Eom, D.; Yi, S.; Letzig, D.; Park, N.-J. Effects of Zn Addition and Twin Roll Casting Process on the Microstructure, Texture, and Mechanical Properties of the Mg-Al-Mn-Ca Sheet. Metals 2024, 14, 261. https://doi.org/10.3390/met14030261.
• Folstad, M.B.; Einarsrud, K.E.; Tangstad, M. Dissolution of CaO in SiO₂-CaO-Al₂O₃ Slag in Si Production. Metals 2024, 14, 243. https://doi.org/10.3390/met14020243.
• Shabanov, Y.; Makhambetov, Y.; Saulebek, Z.; Toleukadyr, R.; Baisanov, S.; Nurgali, N.; Shotanov, A.; Dossekenov, M.; Zhumagaliyev, Y. Pilot Tests of Pre-Reduction in Chromium Raw Materials from Donskoy Ore Mining and Processing Plant and Melting of High-Carbon Ferrochromium. Metals 2024, 14, 202. https://doi.org/10.3390/met14020202.
• González, R.; Barrueto, Y.; Jiménez, Y.P. Thermodynamic Modeling of the Drowning-Out Crystallization Process for LiOH and CHLiO₂. Metals 2024, 14, 78. https://doi.org/10.3390/met14010078.
• Lisińska, M.; Wojtal, T.; Saternus, M.; Willner, J.; Rzelewska-Piekut, M.; Nowacki, K. Two-Stage Leaching of PCBs Using Sulfuric and Nitric Acid with the Addition of Hydrogen Peroxide and Ozone. Materials 2024, 17, 219. https://doi.org/10.3390/ma17010219.
• Dudchenko, N.; Ponomar, V.; Ovsiienko, V.; Cherevko, Y.; Perelshtein, I. Mineral Magnetic Modification of Fine Iron Ore Tailings and Their Beneficiation in Alternating Magnetic Fields. Metals 2024, 14, 26. https://doi.org/10.3390/met14010026.
• Long, X.; Luo, W.; Li, X.; Long, S.; Ma, H.; Luo, D.; Zheng, C. Structure and Heat Transfer Characteristic Evolution of CaO-SiO₂-CaF₂-Based Solid Mold Flux Film upon Solidification. Metals 2024, 14, 1. https://doi.org/10.3390/met14010001.
• Seo, S.; Park, J. Annealing Heat Treatment for Homogenizing the Microstructure and Mechanical Properties of Electron-Beam-Welded Thick Plate of Ti-6Al-4V Alloy. Materials 2023, 16, 7423. https://doi.org/10.3390/ma16237423.
• Türkmen, M.; Tanouz, A.M.; Akgün, M.; Erden, M.A. The Effect of Mn and Ti Ratio on Microstructure and Mechanical and Machinability Properties of 316 L Stainless Steel Used in Biomedical Applications. Metals 2023, 13, 1804. https://doi.org/10.3390/met13111804.
• Syafei, D.I.; Chiang, M.-T.; Chuang, T.-H. Formation of Cu Nanotwins on Silicon Carbide Wafers with Cr Adhesive Layer under Various Substrate Bias. Metals 2023, 13, 1747. https://doi.org/10.3390/met13101747.
• Li, H.; Qi, T.; Zhang, Y. Effect of Furnace Structure on Burden Distribution and Gas Flow in Sinter Vertical Cooling Furnace. Appl. Sci. 2023, 13, 11268. https://doi.org/10.3390/app132011268.
• Chanouian, S.; Larsson, H.; Ersson, M. The Importance of Mixing Time in Intensely Stirred Metallurgical Reactors: Applied on Decarburization Reactions. Metals 2023, 13, 1694. https://doi.org/10.3390/met13101694.
• Rajulwar, V.V.; Shyrokykh, T.; Stirling, R.; Jarnerud, T.; Korobeinikov, Y.; Bose, S.; Bhattacharya, B.; Bhattacharjee, D.; Sridhar, S. Steel, Aluminum, and FRP-Composites: The Race to Zero Carbon Emissions. Energies 2023, 16, 6904. https://doi.org/10.3390/en16196904.
• Han, Z.; Wang, E.; Zhai, Z.; Wang, Z. An Experiment on Surface Fluctuation of Ga-In-Sn Alloy with a Permanent Magnet Flow Control Mold. Metals 2023, 13, 1662. https://doi.org/10.3390/met13101662.
• Tan, K.; Li, Z.; Han, Y.; Qi, X.; Wang, W. Research and Application of Coupled Mechanism and Data-Driven Prediction of Blast Furnace Permeability Index. Appl. Sci. 2023, 13, 9556. https://doi.org/10.3390/app13179556.
• Bazhenov, V.E.; Sannikov, A.V.; Kovyshkina, E.P.; Koltygin, A.V.; Bazlov, A.I.; Belov, V.D.; Dmitriev, D.N. The Influence of Injection Temperature and Pressure on Pattern Wax Fluidity. J. Manuf. Mater. Process. 2023, 7, 141. https://doi.org/10.3390/jmmp7040141.
• Meng, F.; Lang, L.; Xiao, Y. Comparative Analysis of the Hot Isostatic Pressing Densification Behavior of Uniform and Non-Uniform Distributed Powder. Metals 2023, 13, 1319. https://doi.org/10.3390/met13071319.
• Cegarra, S.A.; Pijuan, J.; Riera, M.D. Cooling Rate Modeling and Evaluation during Centrifugal Atomization Process. J. Manuf. Mater. Process. 2023, 7, 112. https://doi.org/10.3390/jmmp7030112.
• Tang, K.; Rasouli, A.; Safarian, J.; Ma, X.; Tranell, G. Magnesiothermic Reduction of Silica: A Machine Learning Study. Materials 2023, 16, 4098. https://doi.org/10.3390/ma16114098.
• Macias, R.; Garnica, P.; Fernandez-Salvador, C.; Olmos, L.; Jimenez, O.; Arroyo-Albiter, M.; Guevara-Martinez, S.; Cabezas-Villa, J.L. Analyzing the Sintering Kinetics of Ti12.5Ta12.5Nb Alloy Produced by Powder Metallurgy. Metals 2023, 13, 1026. https://doi.org/10.3390/met13061026.
• Grimm, T.; Mears, L. Heat Treatment of AA7075 by Electropulsing and DC Current Application. J. Manuf. Mater. Process. 2023, 7, 73. https://doi.org/10.3390/jmmp7020073.
• Suliga, M.; Wartacz, R.; Kostrzewa, J.; Hawryluk, M. Assessment of the Possibility of Reducing Energy Consumption and Environmental Pollution in the Steel Wire Manufacturing Process. Materials 2023, 16, 1940. https://doi.org/10.3390/ma16051940.
• Dwulat, R.; Janerka, K. Evaluation of the Metallurgical Quality of Nodular Cast Iron in the Production Conditions of a Foundry. J. Manuf. Mater. Process. 2023, 7, 18. https://doi.org/10.3390/jmmp7010018.
• Wang, J.; Li, Q. Microhardness Distribution of Long Magnesium Block Processed through Powder Metallurgy. J. Manuf. Mater. Process. 2023, 7, 5. https://doi.org/10.3390/jmmp7010005.
• Bernasowski, M.; Stachura, R.; Klimczyk, A. Fuel Consumption Dependence on a Share of Reduction Processes in Imperial Smelting Furnace. Energies 2022, 15, 9259. https://doi.org/10.3390/en15239259.
• Torresani, E.; Ischia, G.; Molinari, A. Localized Defects in Cold Die-Compacted Metal Powders. J. Manuf. Mater. Process. 2022, 6, 155. https://doi.org/10.3390/jmmp6060155.
• Kukharova, T.V.; Ilyushin, Y.V.; Asadulagi, M.-A.M. Investigation of the OA-300M Electrolysis Cell Temperature Field of Metallurgical Production. Energies 2022, 15, 9001. https://doi.org/10.3390/en15239001.
• Kong, H.; Cheng, X.; Huang, S.; Qiu, Y. Inclusion Characteristics in Steel with CeO₂ Nanoparticle Addition. Metals 2022, 12, 1994. https://doi.org/10.3390/met12111994.
• Smalcerz, A.; Ptak, S.; Łabaj, J.; Półka, M.; Kula, A.; Blacha, L. Analysis of Using Soot Application in the Processing of Zinc-Bearing Waste Materials. Energies 2022, 15, 7969. https://doi.org/10.3390/en15217969.
• Yang, S.; Liu, S.; Guo, S.; Zhang, T.; Li, J. Fusion Separation of Vanadium-Titanium Magnetite and Enrichment Test of Ti Element in Slag. Materials 2022, 15, 6795. https://doi.org/10.3390/ma15196795.
• Xie, L.; Shi, W.; Wu, T.; Gong, M.; Cai, D.; Han, S.; He, K. Effect of Dynamic Preheating on the Thermal Behavior and Mechanical Properties of Laser-Welded Joints. Materials 2022, 15, 6159. https://doi.org/10.3390/ma15176159.
• Liu, K.; Li, W.; Ding, R.; Liu, C. Microstructural Evolution of the TLP Joints of RAFM Steel during Aging and Creep. Metals 2022, 12, 1333. https://doi.org/10.3390/met12081333.

Contribution 1 presents results on the laboratory-scale in which the kinetics of assimilation of cored wire in liquid steel baths were studied. A dataset of positions of the wire/melt interface of cored wire as a function of time and steel bath temperature was obtained. The dataset was compared against simulations made with a transient 1D (radial) thermal model of the assimilation of cored wire. This dataset is a valuable resource for the validation of future developments in the field of modeling of the assimilation of cored wires in liquid metal baths. With proper inputs, these kinds of models are used for producing guidelines for the optimization of the process of the injection of cored wire. Some potential applications of interest are the individual adjustment of wire feeding speeds depending on the type of trimming addition performed in the steel ladle, the optimization of cored wire injection practice for the calcium treatment of steel to decrease reactivity and increase calcium recovery, and the optimization of cored injection practices in shallow vessels such as tundishes for continuous casting and shallow ladles for alloy modification in cast iron and copper foundries.

Contribution 2 combines tape casting and dealloying methods to achieve the integrated preparation of porous tungsten gradient materials with a wide range of controllable porosity. The focus was on the phase composition and microstructure evolution during the preparation of porous tungsten gradient materials. As a result, the authors claim that it is possible to obtain the precise and controllable thickness of each layer of the porous tungsten materials and uniform composition structure, while the stepwise dealloying of Fe and Ti enables a wide range of controllable porosity for these materials. Compounds generated by the W-Fe-C interfacial reaction can play a role in bonding the matrix particles, which in turn promotes the low-temperature sintering densification of the precursor and maintains the stability of the skeleton structure during the dealloying process.

The main objective of Contribution 3 is the identification and localization of two types of welding disturbances, namely, an insufficient amount of shielding gas and an unremoved oxidation film on the surface of the base metal, in the process of welding aluminum alloys using the Pulse Multi-Control Gas Metal Arc Welding (PMC GMAW) method. The welding current signal during the PMC GMAW process was measured using a Hall sensor. The Complementary Ensemble Empirical Mode Decomposition (CEEMD) method was used to decompose the recorded welding current signal. The characteristic frequency spectrum of the Intrinsic Mode Function (IMF) was analyzed in both time and frequency domains. As a result of this research, it was found that for a stable welding process, the frequency of the characteristic IMF is concentrated within a narrow range, with a specific dominant frequency, and by analyzing the frequency spectrum of the characteristic IMF, disturbances such as an insufficient amount of shielding gas can be detected, and a surface of the base metal with an oxidizing layer may be identified and located.

Contribution 4 reviews the research progress on the thermal conductivity of HPDC aluminum alloys. This article discusses the general mechanism of heat transport in aluminum alloys, including electrical transport and phonon transport, several popular systems of die-cast aluminum alloys used in heat dissipating elements, e.g., the Al-Si alloy system and silicon-free aluminum alloy systems, and the effect of process parameters on the conductivity heat transfer of HPDC aluminum alloys. Some heat treatment strategies to increase the thermal conductivity of die-cast aluminum alloys are also discussed. In addition, the authors present a summary of theoretical models used to calculate the thermal conductivity of die-cast aluminum alloys, and on this basis, they conclude that a single model cannot describe the complex microstructure formed in many stages of the die-casting process. Ultimately, the authors highlight the need to build a new model for calculating the thermal conductivity of die-cast alloys in order to comprehensively understand the relationship between their microstructure and thermal conductivity.

Contribution 5 presents a simple and cheap process for the production of sodium tungstate through the high-temperature treatment of wolframite with high efficiency. The high-density sodium tungstate could be easily separated from the immiscible slag which contained impurities such as wolframite, flux, excess sodium oxide, and dissolved tungsten oxide. The influence of the Na₂CO₃/ore and SiO₂/ore ratios, temperature, and reaction time on the direct and total recovery of tungsten and WO₃ from sodium tungstate was investigated. It was found that the total tungsten recovery increases with increasing Na₂CO₃/ore ratio, decreases slightly with increasing temperature, and is almost independent of reaction time above 30 min. The compositions of WO₃-containing slags and sodium tungstate presented in this article fill the knowledge gap in the tungsten thermodynamic database.

Contribution 6 presents a new technology that is widely used in the production of advanced high-strength steel parts for automotive applications, i.e., hot stamping (press hardening). The authors [1] performed electrochemical measurements (potentiodynamic polarization and electrochemical impedance spectroscopy), as well as accelerated corrosion tests (neutral salt spray testing and periodic immersion testing) on press-hardened samples made of uncoated strips and press-hardened steels with Al-Si coating to explain their distinct anti-corrosion mechanisms. Based on the test results, it was found that the corrosion resistance of press-hardened steel with an Al-Si coating significantly decreased after the hot stamping process due to the presence of microcracks and increased iron content in the coating after austenitizing heat treatment. This led to the conclusion that, given the high performance and energy efficiency of press-hardened hot-rolled steel, it can replace cold-rolled steel and even aluminum–silicon-coated press-hardened steel in car manufacturing.

Contribution 7 focuses on the microstructure and texture of the Mg-1.0Al-xZn-0.2Mn-0.5Ca (AMX100) and Mg-1.0Al-1.0Zn-0.2Mn-0.5Ca (AZMX1100) alloys. The authors considered the influence of sheets obtained by the conventional casting process or the twin roll casting method (TRC) on the microstructure and mechanical properties of the analyzed alloys, and also analyzed their relationship with the mechanical properties of the sheet to the final thickness. Based on the test results, it was found that there is no significant difference in texture between sheets produced by casting and TRC. The influence of Zn addition on the microstructure, texture, and mechanical properties of the sheets was also investigated. It turned out that the highest yield strength was achieved by the AZMX1100 sheet produced using the TRC process, and all the tested sheets showed mechanical anisotropy consistent with their texture.

The effect of dissolving CaO in SiO₂-CaO-Al₂O₃ slag compositions relevant for Si production is investigated in Contribution 8. The dissolution and the dissolution rate of CaO into three different compositions of slags with a CaO content of 15–21% were investigated through experiments up to 1600 °C. During the dissolution process, a layer containing 35–42% CaO was formed between CaO and the slag, which corresponded to the CaO·Al₂O₃·2SiO₂ or 2CaO·Al₂O₃·SiO₂ phases. The authors used two models to determine the slag dissolution rate. The first model assumes that the rate is controlled by the rate of the chemical reaction. The second model assumes that the rate is controlled by mass transport and depends on the rate of CaO diffusion through the boundary layer on the CaO surface. As a result of the tests carried out, it was concluded that both models provided a similar accuracy of experimental values, and a proportional relationship between rate constants and viscosities was obtained.

Contribution 9 presents the results of research carried out as part of a pilot study on the initial reduction of chromium raw materials using the innovative Hoganas technology in a tunnel furnace. The authors demonstrate that the pre-reduction process scheme is more effective in reducing the overall energy consumption for melting high-carbon ferrochrome compared to the feed heating and sintering schemes. The use of pre-reduction reduces the total energy consumption in the melting process. The pilot studies carried out showed the possibility of achieving a chromium reduction level above 60%, and, moreover, this technology can ensure a high uniformity of the chromium reduction rate, which will have a good impact on the subsequent melting process. The authors also state that it is necessary to develop solutions that will prevent the material from sticking to the crucible walls and the segregation of charge materials during initial reduction.

Contribution 10 concentrated on the thermodynamic modeling of crystallization (by means of the drowning process) of lithium salts like lithium hydroxide and lithium format. Such modeling includes the use of thermodynamic properties (activity, osmotic, and solubility coefficients) within the ternary systems LiOH + co-solvent + water and CHLiO₂ + co-solvent + water, as well as their respective binary systems [2]. The authors chose ethanol as the co-solvent for both salts, which facilitates comparative analysis. In the case of lithium format, due to the generally scarce information available in the literature, the authors supplemented the gaps in this area based on the research conducted. A modified Pitzer model was used for modeling, in which parameters for both systems were successfully obtained with a deviation of less than 1%. Additionally, a mass and energy balance of the drowning-out crystallization process of both salts was carried out.

Contribution 11 focuses on the very current topic of metal recovery from printed circuit boards (PCBs) of used mobile phones using the hydrometallurgical method [3]. The authors proposed a two-stage leaching of metals such as Cu(II), Fe(III), Sn(IV), Zn(II), Ni(II), and Pb(II) using the acids H₂SO₄ (2 and 5 M) and HNO₃ (2 M), with the addition of H₂O₂ (10 and 30%) and O₃ (9 or 15 g/h). The oxidants used (hydrogen peroxide and ozone) allowed for the acceleration of the process and did not generate too many waste solutions. The variable parameters were as follows: process temperature from 313 to 353 K, process time from 60 to 300 min, type and concentration of the leaching agent, type and concentration of the oxidant, and the solid–liquid ratio (S/L). Two leaching stages allowed the researchers to maintain the selectivity, separation, and recovery of metals: in the first stage, Fe(III) and Sn(IV), and in the second stage, the remaining tested metal ions. The authors found that the removal of Fe from the tested PCBs at the initial stage eliminates the need to use magnetic methods, which are associated with high operating costs. Moreover, they report that the best degree of leaching of all tested metal ions (100% Fe(III), Cu(II), Sn(IV), Zn(II), Ni(II), and 90% Pb(II)) was obtained when 2 M H₂SO₄ (T = 353 K) was used in the first stage of the study, and 2 M HNO₃ and 9 g/h O₃ at room temperature in the second leaching stage.

Contribution 12 focuses on the properties, mineral magnetic modification, and beneficiation of waste from the central mining and processing plant in Kryvyi Rih, Ukraine. The authors conducted a series of studies of the collected samples, including X-ray diffraction, X-ray fluorescence, microscopy, and magnetization measurements. They used the beneficiation of concentrates by means of magnetizing roasting with carbon monoxide, and proposed a new approach to magnetic separation of fine magnetically modified wastes based on a combination of constant and alternating magnetic fields, which consequently allowed to increase the mass magnetization from 0.3–1.5 Am²/kg to 11–62 Am²/kg. Magnetic separation allowed the researchers to obtain concentrates with a composition almost entirely of magnetite with an iron content reaching 68.5–70.2 wt.%, and the non-magnetic residues contained mainly quartz. The authors conclude that the waste can be effectively upgraded by magnetic roasting and magnetic separation, thus obtaining two valuable products: iron concentrate and quartz powder.

Contribution 13 focuses on the study of two commercially used fluxes for molds based on CaO-SiO₂-CaF₂. The immersion of the improved copper probe, which was cooled by water, in the molten fluxes for different probe immersion times and molten slag temperatures allowed the researchers to determine the solid slag layers of the two fluxes. The authors measured the layer thickness, closed porosity, and surface roughness of the layer in contact with the copper probe. Moreover, the structure and overall evolution of the thermal conductivity of the slag layers were determined, also taking into account the contact thermal resistance between the slag layer and the copper wall. Based on the conducted studies, it was found that the heat flux through the low-basicity foils showed large fluctuations due to the evolution of fusion cracks in the glass layer compared to the heat flux through the high-basicity foils. The high-basicity mold fluxes resulted in higher film thickness, growth rate, surface roughness, and devitrification rate. It was further found that the total thermal conductivity of high-basicity and low-basicity layers ranged from 0.63 to 0.91 and from 0.62 to 0.81 W/(mK), respectively. The results obtained provide a new method for analyzing the potential influence of structural factors of slag layers on heat transfer control and controlling the heat transfer behavior of slag layers.

Contribution 14 focuses on the problem of significant stress concentration in the base material (BM) under the influence of tensile stress in the application of Ti-6Al-4V for structural components of the aerospace industry, during the welding of thick plates with a thickness close to the thickness of the components. The authors decided to solve this problem by post-weld heat treatment, and consequently performed heat treatment at temperatures both below (mill annealing, MA) and above the beta-transus temperature (beta annealing, BA) on electron-beam-welded Ti-6Al-4V plates with a thickness of 18 mm [4]. The microstructure and hardness were analyzed at different depths from the top surface and areas (fuzion zone (FZ), heat-affected zone (HAZ), and BM), and the tensile properties were also measured at different depths. The authors found that the observed differences in the FZ and HAZ zone were resolved by both mill annealing and beta annealing. Especially in the latter, the microstructural gradient completely disappeared, and, as a result, the tensile strength was higher than that of the freshly welded and MA heat-treated plates.

In Contribution 15, the authors focus on the introduction of titanium (Ti) and manganese (Mn) powders in the amounts of 0.35–0.75 and 1.5 wt.% into a 316 L stainless steel matrix using powder metallurgy (PM) technology, either singly or in pairs. The samples were obtained by cold pressing and then sintered in a tube furnace at 1250 °C for two hours in an argon atmosphere. The authors investigated the microstructure and mechanical properties of the produced steels using an optical microscope, SEM, EDS, tensile test, and hardness test. Based on the obtained results, the stainless steel samples with the addition of 0.35 Ti and Mn to the 316 L stainless steel had the highest yield strength, tensile strength, and hardness. This sample was also characterized by the best surface quality. The authors further indicated that the addition of 0.75–1.5 Ti, 0.75–1.5 Mn, and 0.75–1.5 wt.% to the steel caused a decrease in mechanical properties.

Contribution 16 presents research related to the analysis of nano-twinned copper (Cu) layers deposited by magnetron sputtering on silicon carbide (SiC) chips. The authors used a chromium (Cr) adhesive layer combined with variable bias conditions for this study. The aim of this research was to comprehensively investigate the influence of the adhesive layer and negative bias voltages to better understand the joining technologies for advanced applications. The authors assumed that the formation of nano-twinned structure and (111) surface orientation can be properly controlled by the applied substrate bias. On this basis, they conducted research considering the introduction of high-density nano-twinned structures to Cu layers sputtered on SiC substrates with 82.3% of (111) orientation ratio at 150 V, much higher than the Cu layer sputtered with a different substrate bias. The authors conclude on this basis that the sputtered Cu nanofiber layer formed with a bias voltage of 150 V has the potential to be used as an intermediate layer for direct bonding at low temperature.

Contribution 17 focuses on the process of sinter sensible heat recovery using a vertical cooling furnace. The problem is the escape of a large amount of cooling gas from the short-circuit channel of the vertical cooling furnace, which consequently affects the uniform gas–solid heat transfer in the furnace. To solve this problem, the authors proposed the use of a vertical Venturi type cooling furnace. Using a single silo of the vertical cooling furnace in Meishan Steel, they developed a slot model, and the effect of improving the Venturi furnace structure on the charge distribution and gas flow was studied using the DEM–CFD coupling method. Based on the conducted research, they found that in comparison with the existing type of furnace, the inclined wall of the Venturi furnace changed the channel direction from vertical to inclined-vertical; the minimum and average values of voids in the shrinkage part of the section increased, which caused the distribution of voids to change from U-shaped to W-shaped along the longitudinal direction; and the gas flow direction changed from vertical upward to vertical inclined upward, which increased the gas–solid contact. In addition, the authors found that in the variable diameter section, the high-velocity gas channel disappeared, the uniformity of the gas velocity distribution significantly improved, and the gas pressure drop increased from 4140 Pa to 6410 Pa (an increase of 54.83%). Therefore, when designing a Venturi type of furnace, it is necessary to take into account the improvement in the gas velocity distribution and the increase in the pressure drop. The research results presented in this article [5] can be valuable tips for optimizing the design of a vertical cooling furnace for sintering.

Contribution 18 uses numerical modeling to understand the complexity of the processes occurring in metallurgical converters. The authors proposed a practical model combining fluid dynamics and chemical reactions to investigate the effect of mixing time on decarburization. For this purpose, they used computational fluid dynamics (CFD) and an arbitrary metallurgical reactor with continuous oxygen supply, focusing on the Fe-C-O system. They assumed that the model uses local equilibrium, a turbulence limiter, and a finite volume method for mass, momentum, and energy transfer. They found that tracer injection points in the rising region of the gas plume exhibit faster mixing, and a comparison of reaction cases reveals different decarburization rates based on the oxygen injection distribution and the effect of turbulence on the reactions. Based on the conducted studies, they concluded that although mixing time is important, this system is primarily governed by thermodynamics and oxygen supply.

In Contribution 19, the authors hypothesized that the competitiveness of steel products in the market will vary depending on the ability of individual manufacturers to reduce CO₂ emissions measured by cradle-to-gate life-cycle analysis (LCA). They proved this thesis by using a life-cycle analysis and cost estimates to compare CO₂ emissions and additional production costs of different decarbonized materials used in sheets for automotive applications using a mass reduction factor based on bending stiffness, taking 2019 as a reference point. In this article [6], the authors discussed future cost scenarios based on carbon taxes and hydrogen costs, and assessed decarbonization pathways for steel and alternative materials such as aluminum and reinforced polymer composites. For these materials, they calculated normalized global warming potential (nGWP) and found that secondary aluminum and 100% recycled scrap for steelmaking have the lowest nGWP. They then located the direct reduced iron-arc furnace (DRI-EAF) natural gas route with carbon capture and the blast furnace–oxygen furnace (BF-BOF) route with carbon capture. They also found that, taking into account costs, the currently cheapest decarbonized production route is the DRI-EAF natural gas route with carbon capture and storage. The authors also included a renewable electricity grid option (50% solar cells and 50% wind) in their study, and for this option, the lowest nGWP was found for steelmaking with 100% scrap and secondary aluminum recycling, followed by the DRI-EAF hydrogen route and the DRI-EAF natural gas route with carbon capture.

Contribution 20 presents a new type of combined permanent magnet flow control braking system (PMFC-Mold), the main advantage of which is that this device can control the flow of molten steel in the mold without additional energy. The authors recorded the surface fluctuations using a laser level meter and a camera. The influence of different casting speeds and permanent magnet locations on the surface fluctuations was studied at a distance of 7, 18, and 36 mm from the narrow mold surface. The authors proposed three types of permanent magnet locations by setting the differences between the center of the permanent magnet height and the free surface in the plate mold (0, 25, and 75 mm). Based on the obtained results, with the acceleration of the casting speed, the average height and standard deviation of the surface fluctuations at the measurement point increased, but the surface fluctuation pattern remained. The least reasonable solution for the permanent magnet location was a distance of 75 mm, and then the fluctuations were observed to intensify.

Contribution 21 focuses on the issues of monitoring the parameters of the blast furnace smelting process, such as the gas permeability index, which directly reflects the performance of the blast furnace in actual production. The authors undertook the task of predicting the trend of the gas permeability index of the blast furnace by developing an intelligent prediction model and using a data-driven approach to monitor the gas permeability index and ensure the stable operation of the blast furnace. In order to detect and eliminate the outliers in the original data, they applied the isolated forest algorithm based on the actual production data of the blast furnace. Then, they analyzed the coupling mechanism between the blast furnace permeability and the gas flow, as well as the Spearman correlation analysis and the maximum information coefficient MIC analysis, which allowed them to screen out the key parameters as feature variables from the data-driven set [7]. Finally, they used the wavelet neural network algorithm to construct an intelligent prediction model of the gas permeability index of the blast furnace. The developed model was applied to the actual production of a blast furnace, and the analysis of the results showed that the predicted value of the blast furnace permeability index is highly consistent with the actual value of the blast furnace production in real time.

Contribution 22 focuses on issues related to precision casting processes and, in particular, on the problem of filling the mold with modeling wax. The authors investigated the fluidity of three commercial modeling waxes using a newly developed injection fluidity test. Based on the obtained results, the fluidity of the waxes increased with the increase of injection temperature and pressure, and the simultaneous increase in temperature and pressure resulted in a significant improvement in fluidity compared to single changes in temperature or pressure. In addition, the authors investigated the rheological behavior of the waxes at different temperatures using a rotational viscometer and determined the temperature dependence of the dynamic viscosity of the waxes. They found that the viscosity of the wax increased more than tenfold with the decrease in temperature from 90 to 60 °C [8]. In addition, the authors show that the main factor dependent on the fluidity of the wax is its viscosity, which changes significantly in the range of tested temperatures and shear rates. Thus, waxes exhibit different behavior than metal alloys, for which the main parameters influencing fluidity are the freezing range and the heat released during solidification.

Contribution 23 focuses on the issue related to hot isostatic pressing (HIP) technology, and especially on the numerical modeling of the relative powder density distribution, which in reality, even with the use of additional tools, such as vibrating tables, is not uniform, which in consequence can cause the uneven shrinkage of the powder and capsule after HIP. The authors therefore developed a numerical model for HIP of Ti-6Al-4V powder in order to improve the prediction by comparing the uniform and non-uniform initial powder distribution. The analysis of the numerical simulation results and their comparison with the experimental results allowed the researchers to state that taking into account the non-uniform powder distribution inside the capsule is crucial for improving the numerical results and obtaining shape components close to the net. The maximum simulation error taking into account the non-uniform initial powder distribution is 3.16%, compared to the usual error of the initial setting of the relative density at the level of 65%, which is 4.2%.

Contribution 24 focuses on the issues related to centrifugal atomization and, in particular, on the temperature evolution of metal particles produced by this technique. The authors investigated the cooling rate of centrifugally sprayed Al-4%Cu using mathematical modeling and experimental validation. In order to achieve the intended results, they implemented a heat transfer model, and the value of the convective heat transfer coefficient was obtained from the semi-empirical Whitaker correlation, taking into account three cases of studying the thermophysical properties of the gas. To assess the validity of the Whitaker correlation, a cooling rate measurement based on the Secondary Dendrite Arm Spacing (SDAS) technique was used [9]. The results of mathematical calculations showed the best agreement with the experimental results at a cooling rate of 10⁵ Ks⁻¹ for powders < 32.5 m sprayed in a helium atmosphere.

Contribution 25 deals with the research related to the magnesiothermal reduction of silica with different Mg/SiO₂ molar ratios in the temperature range from 1073 to 1373 K at different reaction times (10–240 min). The authors applied a machine learning approach using hybrid datasets to describe complex magnesiothermal reductions. In order to obtain correct results, experimental laboratory data, equilibrium relations calculated by the thermochemical database, and the developed Gaussian Process Machine (GPM) were used [10]. The authors show that training a physics-based Gaussian Process Machine (GPM) using the hybrid dataset resulted in a regression score of 0.9665, and the GPM itself was used to predict the effects of Mg-SiO₂ mixtures, temperatures, and reaction times on the magnesiothermal reduction products, which were not covered by the experiments.

Contribution 26 focuses on the analysis of the sintering kinetics of the Ti12.5Ta12.5Nb alloy using the dilatometry method. The material for the study was a mixture of Ti, Ta, and Nb powders, which were axially compacted, and the sintering process was carried out at a temperature of 1260 °C using different heating rates. Using X-ray diffraction and scanning electron microscopy, the authors determined the microstructure of the tested material. Based on the obtained results, densification was achieved by solid-state diffusion and the relative density increased when the heating rate was low. The authors determined the activation energy based on the densification rate and found that two main diffusion mechanisms, grain boundary and lattice self-diffusion, are dominant. Furthermore, the heating rate plays a major role in the diffusion of Ta and Nb during sintering, influencing the resulting microstructure.

Contribution 27 uses electrical resistivity to estimate the relative precipitate density in AA7075. The authors subjected various test parameters to the differences between pulse and DC currents [11], and found that resistive heating could be effectively used to perform the rapid regression heat treatment of these alloys and that holding time at temperature was not necessary. The results obtained allowed the authors to conclude that there was no difference between DC and pulse/transient electrical conditions, suggesting that an electroplastic effect is not needed to explain the results of this test; rather, the results can be clearly attributed to Joule heating.

Contribution 28 presents research on the influence of the technology of galvanized steel wire production on the energy and force parameters of the drawing process, energy consumption, and zinc inputs. In the first part of the article, the authors calculated that the use of the optimal wire drawing technology makes it possible to reduce energy consumption by 37%, and consequently save 13 TJ within one year and reduce CO₂ emissions by tons and ecological costs by about EUR 0.5 million [12]. They also found that the drawing technology has a significant influence on zinc coating losses and CO₂ emissions. Obtaining a 100% thicker zinc coating is possible by properly selecting the parameters of the wire drawing technology, which, in the case of reduced CO₂ emissions, are as follows: the use of hydrodynamic strands, a drawing reduction zone angle of 5, and a drawing speed of 15 m/s.

Contribution 29 is concerned with determining the factors influencing the metallurgical quality of cast iron during the serial production of castings using campaign cast iron and a holding furnace. It was found that the stage of proper preparation of cast iron is the only way to obtain castings without shrinkage defects. Therefore, in this article, the authors conducted research on the physicochemical and mechanical properties, microstructure, and shrinkage tendency of ductile cast iron depending on the input materials used, the amount of Mg used during spheroidization, and the type of final modifiers. Based on the conducted research, increasing the share of pig iron at the expense of steel increases the minimum eutectic solidification temperature and therefore increases the potential for graphite nucleation in cast iron. The latter can be obtained by adding anthracite, FeSi, and SiC [13]. Moreover, it is also important to limit the length of the core wire containing Mg, which is a carbide-forming element, during spheroidization. Additionally, the authors found that the lower the initial sulfur level, the greater the possibility of reducing the amount of core wire, and that the most advantageous final modifiers from the point of view of obtaining the best microstructural parameters and plastic properties of cast iron are modifiers containing Ce and Bi.

Contribution 30 deals with powder metallurgy issues. The authors synthesized long blocks of magnesium, with a ratio of about 2.8 between the sample height and the side length of the sample under three uniaxial and two biaxial conditions [14]. After obtaining the samples, they tested them for hardness on the outer surface and the middle plane to investigate the microhardness distribution. Based on the results, the modified analytical expression indicates that the normal pressure decreases exponentially along the compression direction, which is consistent with the hardness distribution trend, and that more metallic bonds are formed after sintering. Furthermore, it was found that the sidewall pressure increases the surface hardness during the first pressing, while during secondary compression, the hardness of the bottom and the core is mainly improved due to the change in the orientation and position of the powders.

Contribution 31 presents the application of new modeling techniques taken from iron smelting in the pyrometallurgical process of zinc production. The authors first performed a thermochemical analysis to determine the boundary conditions of reduction processes occurring in the working volume of the Imperial Smelting Furnace (ISF) [15]. Based on this analysis and using Ramm’s rules regarding the optimal share of direct and indirect reduction, they built a model of minimizing fuel consumption, assuming that the leading role of the model is to minimize coke consumption in the ISF while maintaining the thermal state of the furnace at an appropriate level. The model was verified in real conditions at the Miasteczko Śląskie plant, and the results indicate coke savings of about 30 kg per ton of raw zinc.

Contribution 32 focuses on issues related to powder metallurgy. The authors modeled powder particles and their contacts using balls made of pure copper in order to demonstrate the influence of uniaxial cold densification on the stress state of the material. These balls were densified in a die at different pressures to better analyze the response of the system to the degree of deformation and thus the influence on the material behavior during sintering [16]. The authors measured the microhardness in different zones of the balls and correlated it with the dislocation concentration using the model for the identification of the cavity size. It was found that the balls after densification were more deformed along the longitudinal than the transverse direction. Moreover, differences in the dislocation density were observed between undeformed and deformed balls, and, in the case of the densified ball, between the contact surface along the longitudinal and transverse directions.

Contribution 33 investigates issues related to the issues of increasing the economic efficiency of the Soderbergh electrolysis cell. The temperature fields of the electrolysis cell were analyzed to determine the overheating points, which allowed the authors to determine the points of subsequent damage to the bottom of the furnace, causing the failure of the electrolysis cell [17]. They carried out mathematical modeling of the temperature fields using a spatially distributed mathematical model, and, at the same time, experimental studies were carried out to measure the temperature field of the electrolysis cell OA-300M bottom. The authors analyzed the possibilities of the experimental determination of internal damage to the bottom of the furnace.

Contribution 34 focuses on the application of Ce oxides in oxide metallurgy, and especially on the addition of a mixture of CeO₂ and Si nanoparticles to molten steel. An improved wettability between CeO₂ and molten steel was found with the help of Si powder, and the authors suggested that when the amount of CeO₂ is kept constant, its efficiency should increase with the increase of the added amount of Si. The authors confirmed this by a higher percentage of Ce-containing oxides in the total number of oxides and a higher average Ce content in Ce-containing oxides after normalization. Additionally, based on the statistical results, it was found that, compared to the blank sample, the oxides in the CeO₂-modified samples were refined and their dispersion uniformity was improved.

Contribution 35 deals with the process of removing zinc from waste by reduction and evaporation, but instead of coke, the authors propose more ecological solutions. Specifically, they analyzed the possibility of using soot in the process of reducing the zinc content in deposited metallurgical waste, considering the problem of fire and explosion safety [18]. Based on this research, soot and anthracite can be an alternative safe reducing agent in pyrometallurgical processes.

Contribution 36 deals with the enrichment and migration of the Ti element in vanadium–titanium magnetite slag during the melting process. The authors used XRD, SEM, and EDS analysis to investigate the effects of melting temperature, basicity, and carbon content on the Ti phase in the slag. Based on the obtained results, increasing the basicity and melting temperature is beneficial for Ti enrichment, but, at the same time, it can lead to the formation of pyroxene, diopside, and magnesium–aluminum spinel, which affects Ti enrichment [19]. In the case of carbon, its increase can cause the appearance of Ti in the slag in the form of titanium oxides, such as TiO, TiO₂, Ti₂O₃, and Ti₃O₅, but its excessive content leads to the excessive reduction of Ti compounds to TiCN and TiC.

Contribution 37 focuses on issues related to excessive thermal stresses or cracks in welds caused by the rapid heating and cooling properties of laser welding (LW). In order to solve this problem, the authors used a dynamic preheating method, which uses hybrid laser arc welding to add an auxiliary heat source (arc) to the LW [20]. A finite element model was used to investigate the effect of dynamic preheating on the thermal behavior of the LW, and the calculations were experimentally verified. The authors conducted tests of the hardness and tensile strength of the welds, on which basis they found that the use of an appropriate current leads to a significantly reduced cooling rate and temperature gradient, which is conducive to improving the hardness and mechanical properties of the welds. This led to the conclusion that the use of dynamic preheating to reduce the temperature gradient is helpful in reducing the thermal stresses and improving the tensile properties of the welds.

Contribution 38 focuses on the application of temporary liquid phase bonding (TLP) to obtain a reliable connection of reduced activation ferritic-martensitic steel (RAFM) with amorphous Fe-Si-B foil. In order to investigate the microstructural evolution during the service process, the authors conducted aging tests and creep tests of TLP joints at a temperature of 550 °C. The investigated effect of stress loading on the microstructural evolution of the TLP joint allowed them to state that creep cracks in TLP joints occur in the base material, and the main factors influencing the creep parameters of TLP joints are the recovery of substructures and the thickening and deformation of martensitic laths. In addition, the authors noted that the microstructure of the weld zone changed from large-sized ferrite to a mixed, fine microstructure of ferrite and martensite, which increased the heat resistance of TLP joints.

3. Conclusions

In the presented Topic of “Advanced Processes in Metallurgical Technologies”, a total of 38 articles were published, including 19 in Metals, 7 in Materials, 6 in the Journal of Manufacturing and Materials Processing, 4 in Energies, and 2 in Applied Sciences. These articles concern very broadly understood metallurgical processes from ore preparation and enrichment, to ore and concentrate processing in both hydrometallurgical and pyrometallurgical processes, metal refining, welding, and joining of materials, as well as the recycling and recovery of metals from various waste materials. In these articles, various materials were studied, from iron ores to various types of steel, through tungsten, manganese, tantalum, niobium, zinc, titanium, chromium, copper, aluminum alloys, magnesium alloys, cerium oxides, silicon, FeCr, lithium salts, and waste materials such as PCB, Fe tailing, zinc waste, and fluxes.

The Topic “Advanced Processes in Metallurgical Technologies” and the 38 scientific articles collected therein present interesting examples of the most important challenges and, at the same time, solutions that metallurgy faces today. We hope that these articles will be an inspiration for scientists, researchers, and technologists in this very broad field, and that the presented articles will help them in new research, debates, and discussions.