Metallurgical and Materials Transactions B最新文献

The present study integrated the multiphase flow of molten steel, desulfurizer dispersion, and desulfurization kinetics to explore the impact of injection amount, injection speed, and lance position on desulfurizer injection desulfurization. This investigation employed a coupled k-ε model, Volume of Fraction (VOF) model, Discrete Phase Model (DPM), user-defined scalar equation (UDS), and unreacted core desulfurization kinetic model. The sulfur content measured in the actual desulfurization process was utilized to validate the mathematical model. Most of the finer powder particles with a diameter of 3 mm tended to stay at the steel surface in the vacuum chamber, with only a fraction being carried by the steel flow into the ladle and then rising to the steel surface. As the increasing of the total desulfurizer amount, the average sulfur content in the molten steel initially increased, but then remained unchanged. However, reducing the total desulfurizer amount from 1200 to 400 kg decreased desulfurization efficiency by 13 pct while the reduction in sulfur content per unit weight of desulfurizer at 400 kg was 2.5 times greater than that achieved at 1200 kg. An increase in the injection speed of desulfurizer resulted in a decrease in average sulfur content, while reducing the injection speed from 200 to 100 kg/min decreased desulfurization efficiency by 19.66 pct. Increasing the position of the desulfurizer injection lance elevated the average sulfur content in the molten steel. Lowering the high lance position of 3.2 m to the low lance position of 2.0 m increased the desulfurization efficiency at the endpoint by 7.45 pct. Additionally, the highest average desulfurization rate increased from 0.0477 to 0.0542 ppm/s. The relationship between the sulfur content in the molten steel and the injection amount, injection speed, and injection lance position can be described by the equation ({text{ln}}left( {left[ {{text{pctS}}} right]/{{left[ {{text{pctS}}} right]}_0}} right) = 1.841 times {10^{ - 6}}cdot{m_{{text{de}}}}^{0.2}cdot{I^{1.5}}cdot{H^{ - 1.2}}t) This equation holds significant practical relevance for powder injection desulfurization during the RH refining process.

Thermodynamic data is of great significance to investigate the formation and control mechanisms of solidification defects during the casting process of H13 steel which is high in Si, Cr, Mo, and V elements. It has been proven that the conventional Ueshima model based on the equilibrium phase diagrams of Fe-X (X = C, Si, Mn, P, S, Cr, Mo, and V) binary alloys cannot accurately predict the phase transition in the solidification of H13 steel with multi components. So, the pseudo-binary phase diagrams of Fe-X alloys at different initial concentrations were calculated via Thermo-Calc software. And, the datasets of liquidus and δ/γ phase transition temperatures were obtained. Then, a backpropagation (BP) neural network model was developed to predict the δ/γ phase transition temperature. While, the slopes of liquidus lines were fitted. These updates were implanted into the Ueshima model. And, the BP-Ueshima model was validated with the phase transition temperatures measured via the differential scanning calorimetry (DSC) test. Subsequently, the phase transition and solute micro-segregation behaviors in the solidification of H13 steel were analyzed as well as the influences of solute elements. The results show that the predicted liquidus temperature (T_L) and solidus temperature (T_S) of H13 steel via BP-Ueshima model agree with the experimental results. As the cooling rate increases from 10 to 20 °C/min, the phase transition temperatures change slightly. Both the solidus and liquidus temperatures decrease with increase of the initial contents of solute elements. Increasing the initial contents of C and Mn can enhance T_P and T_δ (the vanishing temperature of δ phase), whereas the trend is reversed for the other solute elements. Changes of the phase transition temperatures depends on the segregation behaviors of solute elements. The micro-segregation ratios of solute elements in the liquid phase at the end of solidification decreases in the order of S, P, Si, Mo, C, V, Mn, and Cr, respectively. It is determined by the redistributive capacity at the solid/liquid interface and the back diffusion in the solid phase of solute elements.

Most gas-based DRI (Direct Reduced Iron) furnaces use reformed natural gas as reductant which is richer in H₂ than CO. The present study deals with the Midrex DRI plant at JSW Steel Ltd., Vijayanagar where the reducing gas is derived from the COREX furnace top gas which is richer in CO than H₂. The thermo-kinetic behavior of the DRI furnace operated with COREX gas has been modeled. A mathematical framework was developed combining the heat and mass transfer equations with kinetic data for the gas-based reduction of pellets in a DRI furnace. Using the open-source CFD software, OpenFOAM, the equations were coupled and solved for steady state inside an axisymmetric 3D wedge. The model visualizes and quantifies the burden profiles, the gas composition, solid and gas temperatures for different operating conditions. The performance of the model was validated against plant scale-operating conditions and the process curves generated for different production rates. The obtained process curves highlighted lesser specific gas consumption at lower production rates and the importance of top gas CO₂ pct and top gas temperature as indicators of metallization inside the furnace.

The evolution of the microstructure, the dissolution kinetics of (Fe,Cr)₂W Laves phase and the microhardness of Cr–W–Co heat-resistant steel with different Ce concentrations during homogenization were investigated. The mechanism of the influence of Ce on the Cr–W–Co heat-resistant steel during homogenization process was clarified. The homogenization kinetic equation considering lattice parameters and specimen thickness correction was established. The activation energy for Laves phase dissolution in the steel with 0, 0.01 and 0.03 mass pct Ce is determined based on Johnson–Mehl–Avrami–Kolmogorov model to be 302.12, 293.26 and 278.43 kJ/mol, respectively. The activation energy for the dissolution of Laves phase decreases with increasing the Ce content, leading to an increase in the volume fraction of dissolved Laves phase in the steel with the increase in the Ce content from 0 to 0.03 mass pct after the soaking for 7 hours. The homogenization degree of alloying elements Cr, W, V and Nb increases with the Ce content in steel increases after homogenization treatment. The reduction in the standard deviation of microhardness of the steel after homogenization reflects a decrease in the microsegregation degree of alloying elements.

EH36-shipbuilding steel has been welded by CaF₂-ZrO₂ fluxes with designed ZrO₂ additions. Possible chemical and electrochemical reactions have been postulated to analyze alloying element transfer behaviors. The decomposition of ZrO₂ during SAW has been validated by applying the gas–slag–metal equilibrium model and the O supply capacity of ZrO₂ has been quantified. For the entire compositional range, O content has been controlled within a well-maintained range from 220 to 400 ppm, and the transferred quantity of Zr content reaches to the maximum value of 120 ppm. It is further demonstrated that ZrO₂ addition incurs appreciable Si loss within the weld metal.

The production of organic silicon (Si) monomer from metallurgical-grade silicon (MG–Si) is hindered by CaSi₂, leading to a decreased yield of (CH₃)₂SiCl₂. Therefore, strict control of CaSi₂ content is essential. However, the existing MG–Si oxidation refining process fails to prevent the precipitation of FeSi₂ and the reduction of Si₈Al₆Fe₄Ca content, while simultaneously decreasing CaSi₂ content. To address this issue, a novel method of adjusting aluminum (Al) content in MG–Si to reduce CaSi₂ content and increase Si₂Al₂Ca or Si₈Al₆Fe₄Ca content was proposed. The results indicated that the impurity ratio in MG–Si directly influenced the type of precipitating intermetallics. Specifically, when m(Al/Ca) < 1.35, CaSi₂, FeSi₂, and Si₂Al₂Ca were present. When 1.35 < m(Al/Ca) < 1.35 + 0.48 m(Fe/Ca), FeSi₂, Si₂Al₂Ca, and Si₈Al₆Fe₄Ca were encountered. Additionally, when the Al content m(Al/Ca) > 1.35 + 0.48 m(Fe/Ca), only Si₂Al₂Ca and Si₈Al₆Fe₄Ca were observed. Upon adjusting the Al content in high-Ca MG–Si to m(Al/Ca) > 1.35, CaSi₂ was effectively eliminated. Furthermore, within the experimental range, the average content of Si₈Al₆Fe₄Ca precipitates increased from 12.84 to 37.94 wt pct after adjusting the Al content in the melt, representing a maximum increase of ~ 2.95 times. This study successfully elucidated the regulation of calcium (Ca)-containing intermetallics in high-Ca MG–Si, paving the way for the production of high-quality MG–Si raw materials for silicone monomer synthesis.

The present work discusses the numerical simulation of the tapping process to validate the earlier postulates related to the influence of BOF vessel shape on vortex formation. Numerical experiments were conducted by varying the initial filling flow rates (FR 40 and 20 lpm), dwell times (DT 90 and 30 seconds), nozzle diameters (ND 2.14 and 1.04 cm), and initial liquid height (LH 14 and 11 cm). It was earlier reported that the vortex formation is mainly dependent on the nozzle diameter and the stability of the vortex relay on the residual motion in the draining liquids. The present numerical study provides insight into the vortex stability and elucidates the role of residual motion in the draining liquids under different process conditions. The delay in vortex formation for the case of higher residual motion is due to a delay in acceleration and alignment of angular momentum at the nozzle axis vicinity. Further, it is also observed from the numerical experiments that the vertical velocity component’s magnitude exceeds the curl velocity’s horizontal velocity component to establish the stable vortex. The findings of simulated results are in good agreement with the experimental results reported earlier. It also supports the theory of controlling the vortex formation in BOF vessels (by tilting front/back) without using an external device, such as a dart, a device to arrest the slag entering the ladle at the tapping end.

Calcium (Ca) additions during secondary steelmaking are a well-adopted practice to transform solid oxide non-metallic inclusions (NMIs) into globular-shaped liquid oxides. The claimed hypothesis that liquid NMIs reduce SEN clogging has been proven in the past by researchers. However, the exact quantity of Ca needed to transform the physical state of NMIs during steelmaking remains uncertain. Operators in the steel plant use a consistent quantity of Ca additions for specific steel grades, but this approach does not account for the varying physical states and evolving dynamics of NMIs characteristics in each ‘heat’. To overcome this, a study was conducted to explore the impact of varying Ca additions on the transformation and behavior of NMIs in low-alloyed Ca-treated steel grades. The aim was to establish a more reliable and responsive approach to Ca treatment, potentially leading to more effective control in preventing submerged entry nozzle (SEN) clogging. The proposed methodology involved online monitoring of NMIs state coupled with controlled variations in Ca addition, deviating from fixed quantity, to observe its effects on NMIs state transformations. Through careful analysis of collected data and the implementation of a data-driven optimizer, this study reports the practical implications of using optimal amounts of Ca during secondary steelmaking. The resulting change due to dynamic calcium silicide (CaSi)-cored wire additions and their impact on SEN clogging were evaluated. The findings reveal the significant role of optimal CaSi wire additions, leading to improved steel castability and a notable 30 pct reduction in SEN clogging tendencies. The results obtained after the implementation of the data-driven optimizer ‘ClogCalc’ have significant implications for steel manufacturers, offering new insights into enhancing Ca treatment efficiency.

Varying proportions of H₂O-CO₂ atmospheres were introduced into the softening-melting-dripping detector to reduce iron ores under a high-temperature load after applying lump ores to a hydrogen-rich blast furnace. Research was carried out on the metallurgical properties of lump ores and the deterioration behavior of cokes. The primary findings were as follows. The softening rate of lump ores increased and dripping temperature decreased under an H₂O-containing atmosphere compared to a CO₂ atmosphere, with significant amounts of Fe₂SiO₄ and FeO in droplets. Moreover, the softening temperature of lump ores decreased while the melting temperature increased with the increased H₂O content. Consequently, the permeability of material columns and the liquid permeability of coke layers improved. The optimal permeability of material columns was observed at 18.75 pct H₂O content, although the Fe content in reduction products was the lowest. Increasing the H₂O content led to more surface reactions on cokes and greater difficulties in separating ores from cokes; however, it slowed the reduction in coke strength. Additionally, H₂O was found to have a weaker effect on coke graphitization compared to CO₂.