Metallurgical and Materials Transactions B最新文献

For decades, the fixed-grid method (FGM) has undergone extensive development and widespread application in addressing phase change problems. Nonetheless, comparative studies on various FGMs in convective regime are considerably scarce. Moreover, it has been proven that two-dimensional (2D) numerical simulations can cause large deviations from experimental observations. Therefore, this study, based on a reference experiment involving gallium melting, seeks to comprehensively and quantitatively compare three prevalent FGMs: enthalpy method (EM), total enthalpy method (TEM), and heat source method (HSM). The TEM validates overestimation of temperature at low Péclet numbers, as the heat dissipation induced by non-uniform thermal properties in solid and liquid phases is not accounted for. To address this issue, a revised TEM has been introduced. The three FGMs were implemented within the OpenFOAM software, with over 150 simulations conducted on 3D meshes. The comparison focused on evaluating the numerical robustness, accuracy and stability of these FGMs, along with exploring their similarities and differences in flow patterns and velocities. Results obtained reveal that EM offers accuracy but lacks robustness, TEM manifests relatively large errors and instability due to oscillation with variations in grid size and time step, while HSM excels in robustness, accuracy, and stability. Under an identical discretization scheme, all FGMs predict similar melt front shapes, vortex structures, and velocity magnitudes. However, with the upwind scheme, the velocity magnitude of the secondary flow is approximately 50 pct of that with high-order schemes, yet it tends to overestimate the melting rate. The reason lies in the limited capacity of the slow secondary flow to effectively disrupt the stable and persistent vortex in the primary flow direction, consequently enhancing heat transfer efficiency in this direction.

The titanium distribution ratio (({L}_{Ti})) between ferrosilicon (FeSi) melt and the CaO-SiO₂-Al₂O₃ slag was measured at 1773 K (1500 °C). FeSi-slag equilibration was carried out using various slag compositions. The ({L}_{Ti}) was presented against the Vee ratio (pct CaO/pct SiO₂ = C/S) between 0.3 and 1.2, and Al₂O₃ content from 5 to 20 mass pct. The ({L}_{Ti}) exhibited minima at about C/S=0.7(±0.1) at a fixed Al₂O₃ content. In a C/S < 0.7 regime, i.e., relatively acidic melts, Ti⁴⁺ ions were considered as network forming [TiO₄]-tetrahedron unit in the aluminosilicate framework. However, in a C/S > 0.7 regime, i.e., relatively basic melts, Ti⁴⁺ ions were considered to form the [TiO₅]-pyramid structure unit compensated by Ca²⁺. When adding Al₂O₃ into the basic melts over 10 mass pct, [AlO₄]-tetrahedrons take Ca²⁺ ions for charge compensation, resulting in a decrease of stability of [TiO₅] unit because of Ca²⁺ depletion. At a greater than 10 mass pct Al₂O₃ content in the basic melts, Ti⁴⁺ replaced Al³⁺ to form the [TiO₄]-tetrahedron unit, decreasing the activity coefficient of TiO₂ in the slag.

In this paper, the hydrogen direct reduction of iron ore fines is numerically studied by using the Dense Discrete Phase Model (DDPM) in the fluidized bed. The fluidization behavior at different inlet gas velocities (U_g) as well as the influence of U_g and hydrogen concentration on reduction degree (RD) are comprehensively investigated. The result indicates the increase of time-averaged solids volume fraction for the same cross-sectional heights with increasing U_g when the bed height (H) exceeds 0.06 m. Furthermore, the reduction rate of mineral powder increases with higher U_g value, and the RD reaches almost 100 pct after 4000 seconds of reduction time with U_g ranging from 0.35 to 0.65 m/s. The reduction rate increases noticeably with the increase of hydrogen concentration in the range of 10 to 100 pct, and Fe₂O₃ can be completely converted to Fe under condition of 65 pct H₂ concentration after 4000 seconds. Moreover, higher H₂ concentration leads to faster rate of Fe₂O₃ consumption and Fe production. The mass fraction peak values of Fe₃O₄ and FeO are in the range of 0.29 to 0.34 and 0.21 to 0.24 under different H₂ concentrations, respectively.

Feeding strip significantly enhances continuous cast slab quality. To clarify its impact on inclusion distribution, a mathematical model coupling flow, solidification and inclusion motion have been developed. The upper recirculation, lower recirculation, and unformed recirculation flow occur during continuous casting. Under the resultant forces of drag, virtual mass, pressure gradient, Saffman, gravity, buoyancy, etc., the inclusion motion can be divided into two stages: Injection and Split flow. Feeding strip mainly affects inclusion motion by altering the drag, virtual mass, pressure gradient, and Saffman forces, which are closely related to the molten steel flow. After feeding strip, the lower recirculation on the strip feeding side is compressed, while it on the no-feeding side is expanded. The unformed recirculation flow on strip feeding side squeezes the flow below lower recirculation on no-feeding side. A higher strip feeding speed promotes downward inclusion motion, increasing the chance of being captured between the slab edge and strip. Unformed recirculation flow guides inclusions on the no-feeding side toward the slab edge, while expanded flow directs them toward the center. Consequently, inclusions on strip feeding side gradually gather between slab edge and quarter, while inclusions on no-feeding side first gather toward center and then toward edge of slab with increased strip feeding speed.

Five turbulence inhibitor (TI) designs are evaluated to define the highest performance to float non-metallic inclusions through the turbulence length scale analysis. The flow structures in the flow mushrooms, formed by the entry jet and its impact with a TI, generate coherent structures in the boundary layers’ walls of this device. The second invariant of the velocity gradient, Q, analyzes these structures. In the mushroom region, the inhibitor yielding the largest magnitudes of this second invariant has the most significant efficiency to float inclusions. Other criteria like the wall shear stress, the turbulent viscosity ratio, and the kinetic energy/friction velocity ratio are proved to be as valuable as the Q criterion to assess the performance of a given TI to float inclusions. This theory was tested numerically through the dynamics of amine particles in a tundish water model to simulate the dynamics of the non-metallic inclusions in steel and with amine powder injection experiments. The mass of powder escaping through the strand decreased as the absolute magnitudes of these criteria rose.

The kinetics of the dissolution of oxide particles in metallurgical slags is simulated by means of a sharp-interface finite difference model where multi-component diffusion is considered. The effect of convective fluxes on the dissolution kinetics is being considered by a constrained boundary layer thickness. The thickness of this boundary layer can be estimated from theory and is used together with the interdiffusivity matrix to predict the dissolution kinetics of spherical alumina particles in various CaO–SiO₂–Al₂O₃ slags. The numerical results are compared to experimental observations using High-Temperature Confocal Scanning Laser Microscopy (HT-CSLM). The results imply that the processes controlling the dissolution kinetics are multi-component diffusion with density-driven convective fluxes in the liquid slag gaining more influence in the later stages of the dissolution process

The equilibrium segregation coefficient of impurities in materials is the theoretical basis for its purification. This study used the high-temperature chemical equilibration technique to determine the solid solubility and the approximate equilibrium segregation coefficients of Fe, Mn, Al, Cu, and Ni impurities in TiSi₂. The results showed that the solid solubilities of Al, Fe, Mn, Ni, and Cu in TiSi₂ were in the range of 1.0 to 1.5 wt pct, and their equilibrium segregation coefficients were less than 1.

In response to the imperative for sustainable iron production with reduced CO₂ emissions, this study delves into the intricate role of TiO₂ in the direct reduction of iron oxide pellets. The TiO₂-dependent reducibility of iron oxide pellets utilizing H₂ and CO gas across varied temperatures and gas compositions is thoroughly investigated. Our findings unveil the nuanced nature of the TiO₂ effect, underscored by its concentration-dependent behavior, revealing an optimal range between 1 and 1.5 pct TiO₂, where a neutral or positive impact on reduction kinetics and diffusion coefficient is observed. Notably, the synergistic interplay of CO and H₂ at 1000 °C emerges as particularly efficacious, suggesting complementary effects on the reduction process. The introduction of H₂ into the reducing atmosphere regulated by CO not only extends the transition range but also markedly expedites the rate of reduction. Furthermore, our study highlights the temperature sensitivity of the TiO₂ effect, with higher TiO₂ content correlating with prolonged reduction time in a 100 pct H₂ atmosphere at 900 °C. In a 100 pct H₂ atmosphere, the non-contributory role of TiO₂ stems from the water-gas shift reaction. Conversely, introducing H₂ into a CO-controlled reducing atmosphere with TiO₂ enhances the transition range and expedites the reduction rate. Additionally, our findings underscore the role of total iron content, revealing a direct correlation with the reduction process.

Bentonite is an essential binder in the iron ore pelletization process. However, limited research has been conducted on the correlation between the physical and chemical properties of bentonite and its pelletizing performances, while the evaluation criteria for pelletizing bentonite have not been standardized. To optimize the current evaluation methods, this study tested the physical and chemical properties of five representative bentonites, as well as their green balling performance after pelletizing. Additionally, a multiple regression model was constructed using R. Stepwise regression and relative weight analysis were used to optimize and evaluate the indicators of bentonite. The results showed that the raw ball performance was mainly affected by water absorption (WA), swelling index (SI), and swelling capacity (SC). The dry ball performance was mainly affected more by methylene blue index (MBI) and cation exchange capacity (CEC). The following stepwise regression analysis revealed that WA, CEC, and SC were significant predictors for green ball drop strength; WA and SI for green ball compressive strength; and WA, MBI, and SC for dry ball compressive strength. The multiple regression model developed in this study exhibits high goodness of fit and accuracy, making it a valuable way for assessing the impact of different quality bentonites on pelletizing performance as well as optimizing the evaluation methodology of bentonite’s performance in iron ore pelletization.

In addressing the retrofitting issues of conventional non-induction heating tundish, a novel butterfly-type induction heating tundish model was devised. A three-dimensional coupled mathematical model of magnetic, thermal, and fluid fields was established to investigate the temperature distribution, flow characteristics, and temperature rise curves within the butterfly-type tundish. The model for inclusion motion and removal, based on Large Eddy Simulation (LES), was devised, integrating factors such as normal critical velocity, coefficient of restitution, and critical incident angle at the wall boundary conditions to provide a more precise depiction of the reflection and adsorption processes of inclusions on the tundish wall. The findings suggest that induction heating can effectively offset the temperature loss of the molten steel and enhance the removal rate of inclusions, particularly those of large size. The outlet temperature increases by − 15 K, 7 K, 15 K, and 26 K, and the total removal rate of inclusions reaches 69.18, 83.37, 87.69, and 92.01 pct at 0, 600, 800, and 1000 kW, respectively. The channel serves as the primary site for inclusion removal when employing induction heating. Among these, the removal rates within the channel and at the slag layer exhibit a positive correlation with the inclusion diameter, while the remaining wall removal rates show a negative correlation. The implementation of induction heating technology leads to a notable decrease in the entry of large-sized inclusions into the mold.