Technische Universität Bergakademie Freiberg

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Browsing Technische Universität Bergakademie Freiberg by Author "Bellé, Matheus Roberto"

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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: 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.