Metallurgical and Materials Transactions B最新文献

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.

Materials like metallic iron and its alloys are essential to daily living and industrial production. The benefits of using electrolysis technology to prepare iron and its alloys are great efficiency, controllability, and environmental protection. This study focuses on the feasibility of the electrochemical method for the direct preparation of metallic iron and Si–Fe alloys in iron ores with high fluoride content. The electrochemical behavior of Fe(II) and Fe(III) in molten SiO₂–CaO–CaF₂ slag on tungsten electrodes was investigated by using cyclic voltammetry and square wave voltammetry methods. It was determined that the reduction of Fe(II) ions follows a one-step two-electron transfer process: Fe(II) + 2e⁻ → Fe(0). The reduction of Fe(III) involves a two-step electron transfer process: Fe(III) + e⁻ → Fe(II) and Fe(II) + 2e⁻ → Fe(0), respectively. The Fe(II)/Fe(0) process is an irreversible reaction controlled by diffusion. The diffusion coefficient of Fe(II) is D_Fe(II) = 1.5 × 10⁻⁶ cm² s⁻¹. The cathodic deposits of iron were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS). The findings indicate that the production of Fe₂Si alloy through electrolysis is more favorable when Fe(II) is present in the slag, while the production of metallic iron is more favorable when Fe(III) is present in the slag. This work provides a basis for the electrochemical direct preparation of Fe–Si alloy and metallic iron in high fluorine iron ore.

To enhance the quality of vacuum arc remelting (VAR) ingots in enterprises, a remelting model and cracking criterion was developed based on simulation and a series of designed experiments to predict the segregation behavior, shrinkage cavity, thermal stress, and cracking tendency of VAR ingot. The remelting model was established by MeltFlow-VAR and Abaqus software. As MeltFlow-VAR cannot calculate the stress, through the secondary development program, the thermal stress of VAR ingot was calculated by introducing the temperature field of VAR process into Abaqus. This model was verified by longitudinal dissection of a 406 kg IN718 alloy VAR ingot. The simulated evolution of molten pool, shrinkage cavity, freckle formation probability and secondary dendrite arm spacing (SDAS) align consistently with the ingot microstructure and experimental results. Combined with thermal stress, the alloy strength at different temperature during cooling and solidification, and failure criterion, a crack criterion was constructed to predict the cracking tendency. Calculating the complete solidification time and cracking tendency of the VAR ingot after melting allows for the determination of the safe demolding time without cracks. This method can be used to explore the effect of different melting parameters, optimize VAR process and improve the quality of VAR production.

An experimental investigation was conducted to elucidate the impact of cooling rate on the microstructure evolution of boron-containing steel 22MnB5 by in-situ observation using the confocal laser scanning microscope (CLSM). The observations manifested distinct multi-phase formation of reconstructive grain boundary allotriomorphic ferrite (GBA) and pearlite (P) to sympathetic intergranular acicular ferrite (IAF) and bainite (B), as well as the displacive martensite (M) under different predefined cooling rates (1, 10, and 20 °C/s). Notably, as the cooling rate escalated from 1 to 10 or 20 °C/s, the starting and finishing phase transition temperature decreased significantly. For the 22MnB5 steel cooled at 1 °C/s, the solid phase transition sequence followed γ→GBA→P→IAF, while for the steel cooled at 10 and 20 °C/s, the transition sequence shifted to γ→B→M. Additionally, in the sample cooled at 20 °C/s, the bainite lath spacing reduced and more small size martensite appeared as the mechanical stabilization of austenite. Simultaneously, the dislocation density increased compared to the slow cooled samples, primarily due to the elevated nucleation rate from austenite to ferrite and larger internal stress induced by the enhancing cooling intensity.

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