Browsing by Author "Neubert, Lukas"

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GRK 2802: Densities, Surface Tensions, and Viscosities of Molten High-Silicon Electrical Steels with Different Silicon Contents
(Technische Universität Bergakademie Freiberg, 2025-10-24) Neubert, Lukas; Bellé, Matheus Roberto; Yamamoto, Taisei; Nishi, Tsuyoshi; Yamano, Hidemasa; Ahrenhold, Frank; Volkova, Olena
Density, surface tension, and viscosity of various liquid electrical steels are measured at different temperatures, varying in their silicon content between 3 and 6mass%. Density and surface tension are determined using the maximum bubble pressure method, while viscosity is investigated comparatively using a vibrating finger viscometer and an oscillating crucible viscometer. The results are compared with models known from the literature. Based on this, the density of the steel [ρ] = kgm 3 and the surface tension [σ] =Nm 1 can be described as a function of temperature [θ] = °C and silicon content [Si] =mass% using the equations: ρðθ, SiÞ ¼ 1.28 θ 104.18 Si þ 9081.8, σðθ, SiÞ ¼ 10 4 ½ 0.00903 θ2 1.21494 Si2 þ 29.268 θ 1.987 Si 22334 . There is a lack of experimental data in the literature for high-temperature thermophysical properties for electrical steels. This underlines once again the novelty and significance of this study, as the determined thermophysical properties are essential for a wide range of applications. For instance, they are crucial in the production of metallic powders for additive manufacturing by atomization to adjust the properties of the powders precisely. The findings are also important for steelmaking itself, as the corrosion behavior of refractory material can be better determined.
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GRK 2802: Effect of Oxygen on Thermophysical Properties of Molten High-Silicon Electrical Steels and Its Impact on Bubble Formation Behavior
(Technische Universität Bergakademie Freiberg, 2025-10-24) Neubert, Lukas; Bellé, Matheus Roberto; Seetharaman, Sridhar; Volkova, Olena
The presence of oxygen in liquid steels has a considerable influence on their properties. Higher oxygen concentrations are typical for unkilled melts, after tapping from the basic oxygen furnace (BOF) or during secondary metallurgy. This influences thermophysical properties, for instance, surface tension, due to the surface activity of dissolved oxygen. Processes in secondary metallurgy or the interaction of the melt with the refractory material will be different. In this study, density and surface tension of molten high-silicon electrical steels are analyzed dependent of different oxygen contents, which are comparable to industrial melts during secondary metallurgy. The maximum bubble pressure method was used, and total oxygen contents between 77 and 300 ppm were taken into consideration. The silicon content of the steels is varied between 3 and 6 mass-pct. The effect of oxygen on the bubble formation behavior during decarburization in a liquid steel melt is also discussed. The results make it possible to calculate the size of bubbles that form in a melt. These findings are transferred to the processing of electrical steels, to vacuum treatments like the RH or VOD process. Reactions such as decarburization and the dissolution behavior of alloying agents are described more precisely based on these insights.
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GRK 2802: Extraction of Vanadium from CaO–SiO2–MgO–Al2O3 Slags Based on Vaporization of Vanadium Pentoxide
(Technische Universität Bergakademie Freiberg, 2025-10-24) Neubert, Lukas; Shyrokykh, Tetiana; Tinkova, Nataliia; Seetharaman, Sridhar; Volkova, Olena
Vanadium is an important micro-alloying element for various steel grades. Consequently, it is also present in the slags used in the production of those grades. During steelmaking, the vanadium vaporization from the slag is not desirable, as it increases vanadium consumption and at the same time releases toxic vapors of its higher oxides. However, the recovery of vanadium from the slag after the processing is worthwhile. In oxidic form as vanadium pentoxide (V2O5), vanadium can be extracted from the slag. In this research, the vaporization behavior of vanadium from CaO–SiO2–MgO–Al2O3 industrial slag is investigated at 1873 K. The effect of different process parameters, e.g., the pressure in the furnace chamber, the duration of the oxygen treatment of the slag, and the oxygen flow rate, is considered. The effect of P2O5 and Fe2O3 addition on the extraction of vanadium is studied. It is possible to induce formation of V2O5 gas bubbles in the slag due to the oxidation of vanadium. Thus, vanadium respectively V2O5 is extracted from the slag.
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GRK 2802: Interactions between Molten High-Silicon Electrical Steels and Carbon-Bonded MgO Refractories Based on Recyclates
(Technische Universität Bergakademie Freiberg, 2026-05-29) Neubert, Lukas; Bellé, Matheus Roberto; Yehorov, Anton; Mospan, Anhelina; Stadtmüller, Till M. J.; Sridhar, Seetharaman; Aneziris, Christos G.; Volkova, Olena
In the present study a comprehensive investigation of the interactions between different molten high-silicon electrical steels (3 to 6 mass-% silicon) in aluminum killed condition with conventional and recycled MgO–C refractories is conducted. Immersion tests are carried out in accordance with the standards for testing and assessment of corrosion of refractories by liquids (DIN CEN/TS 15 418). Various mechanisms are defined and described which determine the corrosion of the refractory material in addition to infiltration. Scanning electron microscopy including energy dispersive X-ray spectroscopy (EDX analysis) is conducted to identify wear reactions, material transfers and reaction products at the contact zones and in the infiltration layers. The theoretically possible infiltration length is calculated and the limited applicability of the equations known from the literature is discussed. The formation of calcium sulfides and on other crucible reactions that take place are considered. These provide information and at the same time they influence the interactions between refractory materials and liquid steel.
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GRK 2802: Phosphorus Partition Between Liquid Crude Steel and High-Basicity Basic Oxygen Furnace Slags Containing V2O5
(Technische Universität Bergakademie Freiberg, 2025-10-24) Neubert, Lukas; Kovtun, Oleksandr; Kreschel, Thilo; Volkova, Olena
The influence of V2O5 on the phosphorus partition between liquid crude steel and heterogenous basic oxygen furnace (BOF) slag with CaO/SiO2 = 4.2 was investigated at a temperature of 1600 C in a middle frequency induction furnace. Thereby the phosphorus transfer from ‘‘steel to slag’’ as well as from ‘‘slag to steel’’ was studied over a holding time of 60 minutes. The measured results were shown as phosphorus partition and phosphorus capacity and compared with the experimental values from the literature. It was found that V2O5 in highly basic BOF slags decreases phosphorus partition and phosphorus capacity. In addition, the resulting slags were investigated using a scanning electron microscope (SEM).
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GRK 2802: Population of Nonmetallic Inclusions in Liquid High-Silicon Electrical Steel in Contact With MgO–C Refractories Based on Recyclates and Environmentally Friendly Binders
(Technische Universität Bergakademie Freiberg, 2026-05-29) Neubert, Lukas; Bellé, Matheus Roberto; Kerber, Florian; Gunasekar, Dinesh Kumar; Weddige, Hans-Jörn; Aneziris, Christos G.; Volkova, Olena
Nonmetallic inclusions (NMIs) are integral constituents of ferrous materials, but almost always have a negative impact on their properties. Therefore, it is best to implement strategies during production to avoid NMIs as much as possible or at least control their formation. To gain a better understanding of these mechanisms, this study investigated the population of nonmetallic inclusions in liquid high-silicon electrical steel (Si 3 mass-%) depending on the contact with different MgO–C refractories. Both conventional refractory materials and those containing MgO–C recyclate and environmentally friendly binder systems, such as collagen, fructose, and lignin, were considered. Immersion tests were carried out for 30min at a temperature of 1600°C in accordance with DIN CEN/TS 15418. Surface phenomena, diffusions reactions, and corrosion mechanisms occurring in the refractory materials were characterized after the tests using SEM and EDX analyses. The change in the chemical composition of the steels was determined using spark spectroscopy, and the NMI population was evaluated after the tests using an automated feature analysis (AFA).
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GRK 2802: Vaporization of Vanadium Pentoxide from Iron and Steel-Making Slags
(Technische Universität Bergakademie Freiberg, 2025-10-24) Neubert, Lukas; Volkova, Olena
Vanadium is present in increased amounts in slag because of the production of certain steel grades and manufacturing technologies. In terms of circular economy, vanadium should be recovered from the slag, to use it again as an alloying element. Only a few studies on the extraction of vanadium have been carried out with synthetic slags. The core of this study is the characterisation of the extraction behaviour of vanadium by evaporation of its oxides from real iron and steel-making slags. The effect of various influencing factors on the evaporation behaviour of the slags should be demonstrated. The evaluation of the results should also take crucible wear into account. In addition, the phases formed in the slag are to be analysed. For this purpose, several melting tests are carried out with different blast furnace slags. To determine the vaporised components, the slags are analysed by an X-ray fluorescence spectrometer.
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GRK2802: Density, Surface Tension and Viscosity of Liquid Low-Sulphur Manganese-Boron Steel via Maximum Bubble Pressure and Oscillating Crucible Methods
(Technische Universität Bergakademie Freiberg, 2026-04-27) Bellé, Matheus Roberto; Neubert, Lukas; Sherstneva, Anastasiia; Yamamoto, Taisei; Nishi, Tsuyoshi; Yamano, Hidemasa; Weinberg, Matthias; Volkova, Olena
This study investigates the thermophysical properties of low-sulphur manganese-boron steel with varying boron and sulphur contents at different temperatures. Density and surface tension were measured between 1550-1650 °C using the Maximum Bubble Pressure (MBP) method, while viscosity was examined between 1530-1570 °C using an improved Oscillating Crucible Viscometer (OCV). The methods yielded results with low error, consistent with existing literature. The density of the base steel decreased from 7057 ± 25 kg m-3 at 1550 °C to 6843 ± 85 kg m-3 at 1650 °C. The addition of boron (up to 57 ppm) and sulphur (up to 130 ppm) did not significantly change the density. Sulphur, increasing from 39 ppm to 130 ppm, reduced the surface tension from 1416 ± 12 mN m-1 to 1302 ± 9 mN m-1 at 1650 °C. Boron’s effect on surface tension varied, possibly influenced by other elements like oxygen. Viscosity ranged from 5.74 to 6.44 mPa s, with boron and sulphur additions causing minimal changes, the largest deviation being 8%. These results provide valuable data for the simulation, modelling, control, and optimization of liquid steel processing.
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GRK2802: Effect of microporous Al2O3-MgAl2O4 content on the thermal shock resistance and molten steel purification performance of β-SiC whisker-reinforced Al2O3-MgAl2O4-C ceramic filters
(Technische Universität Bergakademie Freiberg, 2026-04-27) Song, Jinwen; Yan, Wen; Volkova, Olena; Andrä, Stefan; Bellé, Matheus Roberto; Neubert, Lukas; Tian, Can; Li, Yuanbing
This study investigates the effect of microporous Al2O3-MgAl2O4 content on the phase composition, microstructures, mechanical properties, and purification performance for molten steel of Al2O3-MgAl2O4-C filters, conducted through XRD, SEM, EDS, immersion test with molten steel, and so on. The results indicate that the microporous Al2O3-MgAl2O4 raw material significantly promotes the formation of in-situ β-SiC whiskers within the filters, which intertwine among the particles and grow within the microporous structure, working synergistically with the MgAl2O4 phase to improve the strength and thermal shock resistance. Regarding molten steel purification, on the one hand, the microporous structure of Al2O3-MgAl2O4 particles enhances the filter’s contact area with molten steel, imparting a higher physisorption efficiency to the filter. On the other hand, MgAl2O4 has a greater tendency for carbothermal reactions, generating Mg vapor that has a strong chemisorption capability for [Al], [O], and Al2O3 inclusions in the molten steel. The microporous structure and MgAl2O4 facilitate the formation of a MgAl2O4 reaction layer at the interface during immersion test, contributing to the purification of the molten steel. The filter AM60, prepared with 60 wt% microporous Al2O3-MgAl2O4 powder, not only exhibits excellent thermal shock resistance (with a cold compressive strength of 0.54 MPa and a strength of 0.59 MPa after three thermal shock tests), but also demonstrates a high purification efficiency (reducing inclusions in steel by 68%, and lowering the total oxygen content from 56.3 ppm to 13.5 ppm). Finally, the formation mechanism of in-situ β-SiC whiskers, the role of microporous Al2O3-MgAl2O4 raw material in purification function, and the comprehensive molten steel purification mechanism were proposed.
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GRK2802: Effect of Surface-active Elements on the Wetting Behavior and Surface Tension of Steels: Assessing Sessile Drop and Maximum Bubble Pressure Techniques
(Technische Universität Bergakademie Freiberg, 2026-04-29) Bellé, Matheus Roberto; Neubert, Lukas; Baraka, Abdelrahman A.; Angelini, Alberto; Song, Jinwen; Volkova, Olena
This study investigates the influence of surface-active elements (Si, S, and B) on the surface tension (σ) and wetting behavior of molten steels and provides a direct comparison between the Maximum Bubble Pressure (MBP) and Sessile Drop (SD) measurement techniques. High-silicon electrical steels (ES) (3 - 6 wt% Si) and Mn-B steels (WS) with controlled B and S contents were examined at 1500 - 1650 °C. The results show that the increasing Si content decreases both σ and contact angle, enhancing the wettability on MgO. ES steels exhibit a characteristic parabolic temperature (T) dependence of σ, attributed to Si-O interactions and surface oxidation effects. In WS steels, S reduces σ, and the T coefficient becomes increasingly positive with rising S content. B displays an ambiguous effect: MBP measurements show a slight σ reduction with increasing B, whereas SD measurements indicate the opposite trend. Steel infiltration into porous MgO affects the contact line, causing reduced wetting angles and deviations in SD σ values. Across all compositions and temperatures, SD consistently yields higher σ values than MBP. This discrepancy is primarily linked to surface depletion of volatile species (Mn and S) during SD experiments, while the continuous surface renewal in MBP minimizes compositional changes. The findings demonstrate that both alloy chemistry and measurement technique significantly influence the determined interfacial properties. Overall, this work provides a comprehensive assessment of how surface-active elements govern wetting and σ in steel-MgO systems and highlights methodological considerations essential for interpreting high-temperature interfacial measurements in steelmaking research.
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GRK2802: Enhanced strength and high reactivity of Al2O3-MgAl2O4-C ceramic filters with in-situ β-SiC whiskers: Role of nano-Al2O3
(Technische Universität Bergakademie Freiberg, 2026-04-27) Song, Jinwen; Yan, Wen; Volkova, Olena; Cheng, Zhenyu; Neubert, Lukas; Angelini, Alberto; Bellé, Matheus Roberto; Li, Yuanbing
The role of nano-Al2O3 content on the phase composition, microstructure, mechanical properties, and purification performance for molten steel of Al2O3-MgAl2O4-C ceramic filters was investigated through XRD, SEM, EDS, as well as immersion test with molten steel. Results indicate that nano-Al2O3 firstly improves slurry retention performance, increases filter strut thickness, and ensures uniform distribution without cracks. Furthermore, during the sintering process, nano-Al2O3 accelerates the mass transfer (Mg2+ and Al3+) between microporous Al2O3-MgAl2O4 particle and nano-Al2O3 due to its high sintering reactivity, which promotes the development and growth of neck connections among the microporous Al2O3-MgAl2O4 particles, resulting in a substantial improvement in the mechanical properties. Regarding molten steel purification, on the one hand, its high reactivity significantly promoted the carbothermal reduction reaction, generating reductive gases that interact with and adsorb [Al], [O], and Al2O3 inclusions in the molten steel, quickly forming a continuous and uniform Al2O3-MgAl2O4 reaction layer at the interface. On the other hand, high mechanical strength also improves filter’s resistance to molten steel erosion and avoids contamination of the molten steel. Together, these two effects synergistically contribute to the purification of molten steel. The filter N5, with 5 wt% nano-Al2O3, not only exhibits excellent mechanical properties with a cold compressive strength of 1.41 MPa and 1.21 MPa after three thermal shock tests, but also demonstrates high purification efficiency, reducing inclusions by 44% and lowering the total oxygen content from 56.3 ppm to 26.1 ppm. Finally, the role of nano-Al2O3 in sintering behavior and purification function, as well as the comprehensive molten steel purification mechanism were proposed.
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GRK2802: Interaction Between Molten Al-Killed Mn-B Steel and Carbon-Bonded MgO Refractories Based on Recyclates
(Technische Universität Bergakademie Freiberg, 2026-04-29) Bellé, Matheus Roberto; Neubert, Lukas; Yehorov, Anton; Stadtmüller, Till Manon Jannis; Aneziris, Christos Georgios; Volkova, Olena
This work investigates the high-temperature interactions between low-sulfur Al-killed Mn-B steel and carbon-bonded magnesia (MgO-C) refractories containing 0 wt% and 50 wt% recycled material (recyclates). Finger immersion tests (FIT) were conducted at 1600 °C under an argon atmosphere, with variations in boron (B) and sulfur (S) content. Microstructural and chemical analyses via SEM/EDX revealed the formation of protective MgO and CaS layers at the steel-refractory interface, alongside spinel (MgAl2O4) and calcium silicate phases. B and S jointly influenced wetting and infiltration behavior, while increased S promoted thicker CaS layers. Recyclates introduced microstructural heterogeneity (distributed dissolution sites) but did not significantly alter the interfacial reaction mechanisms. Both refractories exhibited comparable performance in forming protective layers, suggesting that recyclate-containing MgO-C materials can serve as sustainable alternatives without compromising thermochemical stability or steel cleanliness. These findings support the use of recycled materials in refractory manufacturing, contributing to waste reduction and circular economy practice in steelmaking.
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GRK2802: Non-metallic Inclusion Evolution in Interaction of Al-killed Mn-B Steel with Desulfurization Slag and MgO-C Refractories Containing Environmentally Friendly Binders and Recyclates
(Technische Universität Bergakademie Freiberg, 2026-05-20) Bellé, Matheus Roberto; Neubert, Lukas; Yehorov, Anton; Kerber, Florian; Gunasekar, Dinesh Kumar; Salpagarov, Eldar; Aneziris, Christos G.; Volkova, Olena
The high-temperature interaction between Al-killed Mn-B steel, desulfurization slag, and carbon-bonded magnesia refractories containing conventional, environmentally friendly binders and recyclate systems was systematically investigated using finger immersion testing at 1600 °C for 30 minutes. Chemical analysis of steel and slag, combined with SEM/EDX characterization of refractory/steel/slag interfaces and non-metallic inclusions (NMIs), was performed to interpret reaction mechanisms and the evolution of inclusions. Significant slag modification occurred during testing, characterized by MgO enrichment, CaO and Al2O3 depletion, and the formation of Fe- and Mn-bearing oxides. In the steel, pronounced decarburization, sulfur increase, boron depletion, and enhanced oxygen and nitrogen contents were observed, indicating reoxidation and interfacial reactions. Independent of refractory condition, MgAl2O4 spinel and Ca2SiO4 phases were detected in the infiltrated refractory zone. Refractories containing recyclates and alternative binders chemically modified the inclusion population and significantly increased NMI number density, particularly Mn-Si-Ti-based inclusions. The results demonstrate that refractory composition strongly influences slag chemistry, inclusion characteristics, and steel cleanliness. These findings provide a new understanding of refractory-slag-steel interactions during secondary metallurgy and highlight the need for optimized slag/refractory formulations to ensure inclusion control and steel quality under increasingly sustainable material strategies.
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GRK2802: Wetting behavior and interfacial reactions of molten steel in contact with the Al2O3-MgAl2O4-C substrate: Effect of porous Al2O3-MgAl2O4 raw material
(Technische Universität Bergakademie Freiberg, 2026-04-27) Song, Jinwen; Wen, Yan; Volkova, Olena; Wang, Qinghu; Bellé, Matheus Roberto; Neubert, Lukas; Andrä, Stefan
This paper investigates the wetting behaviors of molten steel in contact with the Al2O3-MgAl2O4-C (Abbreviated as AM) and Al2O3-C (Abbreviated as A) substrates respectively by the sessile drop wetting method, and thoroughly discusses the interfacial reaction mechanism. In the initial stage of the wetting experiment, the initial contact angle between the molten steel and substrate AM (121°) was significantly smaller than that with substrate A (129°). As the carbothermal reactions proceeded in the substrate, gaseous products accumulated in the micropores of substrate AM, rose into the molten steel and were subsequently expelled. This process caused the molten steel droplet to shake and move on the surface of substrate AM, leading to instability in the contact angle, which fluctuated with time but exhibited an overall increasing trend. In contrast, the contact angle between the molten steel and substrate A remained relatively stable, with no significant gas expulsion observed. During this period, the reducing gases generated by the carbothermal reactions in substrates rose and formed distinct reaction layers at the molten steel/substrate interfaces gradually. A MgAl2O4 layer was observed at the interface between the molten steel and substrate AM. Notably, this reaction layer exhibited a dense and continuous structure in the middle area but became porous and discontinuous in the edge area. By comparison, an Al2O3-Al6Si2O13 layer was detected at the interface between the molten steel and substrate A. Following the formation of reaction layers, the contact angle between the molten steel and substrate AM gradually increased and eventually stabilized at 139°, which was higher than the final stable contact angle (130°) between the molten steel and substrate A. Finally, the comprehensive wetting behavior and the interfacial reaction mechanism were proposed.