Metallurgical and Materials Transactions B最新文献

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.

Graphical Abstract

The design and optimization of blast furnace (BF) profiles generally rely on limited empirical knowledge and experience. Such exercise can now be improved by means of process modeling and optimization. In this work, the effect of furnace profile on BF performance is numerically investigated across a wide range of furnace volumes (500 to 6000 m³), focusing on the ratio of effective height to belly diameter (H/D ratio). This is done based on the recently developed 3D multi-fluid BF process model. The results indicate that the optimized H/D ratio under different furnace volumes can be determined by minimizing the total energy consumption, namely, the summation of chemical and physical energy consumptions. Comparative analysis indicates that the industrial data on the variation of H/D ratio with furnace volume, collected over years, can be reproduced quantitatively by the current model. The increase in BF size or volume results in high thermal energy efficiency and low coke rate, primarily attributed to the reduced heat dissipation from the top gas and furnace wall. But there exists a size threshold between small and large BFs, approximately 2000 m³ under the conditions considered. Beyond this threshold, the BF performance and in-furnace states do not change significantly. Optimum BF profile needs to consider the coupled effect of H/D ratio and effective furnace volume.

To investigate the qualitative and quantitative effects of flow rate on fluid dynamics within a tundish using channel induction heating, a mathematical model was developed to reflect the macroscopic transport phenomena. The simulation results show that as inlet velocities increased from 0.3 to 0.9, the ratios of plug zone volume to total volume, dead zone volume to total volume, plug zone to dead zone, and plug zone to mixed zone consistently fell within the ranges of 0.257 to 0.263, 0.118 to 0.119, 2.152 to 2.231, and 0.412 to 0.427. Concurrently, the inclusion removal rate in the tundish's dead zone under channel induction heating increased with the inlet velocity. Additionally, analysis of the mean characteristics in the tundish system reveals that the mean residence time linearly decreases with increasing mean flow temperature and linearly increases with the inlet velocity. Furthermore, the inclusion removal rate linearly increases with the inlet velocity. This work enables precise quantitative and qualitative predictions and analyses of physical parameters in the electromagnetic induction heating tundish at various casting speeds, providing an efficient method for evaluating and optimizing the multi-physical fields within the metallurgical container.

In the current study, a three-dimensional mathematical model that integrated the large eddy simulation (LES) turbulent model, volume of fluid (VOF) multiphase model, and the dynamic mesh model, was developed to investigate the influence of the mold oscillation on the steel, slag, and air multiphase flow and the slag entrainment in a slab continuous casting mold. The results indicated that the mold oscillation led to an increase of about 0.35 m/s in the speed of molten steel at the impact point of the upper and lower circulation on the narrow surface. However, it reduced about 0.047 m/s in the maximum speed of the meniscus at 1/4 width of the mold. The Fast Fourier Transform (FFT) analysis revealed that the characteristic frequency of the speed fluctuation in the gravity direction of the meniscus near the narrow surface was 1.27 Hz without the consideration of the mold oscillation. Upon the application of the mold oscillation, a new characteristic frequency of 3 Hz, matching the mold oscillation frequency, emerged with twice the intensity of the original 1.27 Hz frequency. Moreover, the mold oscillation had little effect on the characteristic frequency of the speed fluctuation on the meniscus far away from the narrow surface. A user-defined function (UDF) was employed to quantify the number, size, and spatial distribution of entrained slag droplets. The net slag entrainment rate was reduced from 0.0152 to 0.0113 kg/s after the consideration of the mold oscillation, and the number of entrained slag droplets was also decreased. The effect of mold oscillation on the size distribution of entrained slag droplets and the occurrence location of the slag entrainment on the meniscus were not significant.

The effects of the Al₂O₃ content and MgO/Al₂O₃ ratios on the structure and viscosity of CaO–SiO₂–MgO–Al₂O₃ silicate-based slag were studied by the rotating cylinder method. The evolution of the silicate structure was analyzed by Fourier transform infrared spectroscopy. The results show that when the CaO/SiO₂ ratio is 1.20 and the MgO content is 10 mass pct, the Si–O–Al structure and [AlO₄]⁵⁻ tetrahedron structure of the slag increase with increasing Al₂O₃ content (17 to 22 pct), which increases the viscosity, break-point temperature, and activation energy of the slag. In addition, when the CaO/SiO₂ ratio is 1.20 and the Al₂O₃ content is 18, 20, and 22 mass pct, respectively, with the increase of MgO/Al₂O₃ ratio in the range of 0.4 to 0.7, the viscosity, break-point temperature, and activation energy of slag decrease. The analysis of the Raman spectra in the 800 to 1200 cm⁻¹ range indicates that complex silicate structures ([Si₂O₅]²⁻, [Si₂O₆]⁴⁻) disaggregate into simpler structures ([Si₂O₇]⁶⁻ and [SiO₄]⁴⁻) with the MgO/Al₂O₃ ratio increase. The proportion of structural units Q³ and Q² decreases, the proportion of Q¹ and Q⁰ increases, and the proportion of silicate structural units (Q⁰ + Q¹)/(Q² + Q³) increases, which indicates that the non-bridging oxygen content in the slag increases, resulting in a decrease in slag polymerization.

Production of direct reduced iron (DRI), particularly with green hydrogen, is a key pathway to the decarbonization of the iron and steel industry. However, the sticking tendency during the production of DRI creates serious operational issues and limits production outputs. Coating inert materials on the surface of iron ores can act as a barrier to effectively prevent the bonding between newly formed iron surfaces, and can interfere with the formation of iron whiskers. However, the principle of coating has not been systematically studied. This review covers the mechanism of sticking in both shaft furnaces and fluidized bed-based gaseous DRI production. The factors that influence the reduction kinetics and morphology, including physical and chemical ore properties, pellet induration conditions, and reduction conditions are summarized as well. Understanding the relationship between these factors and morphology change is critical to eliminating the sticking issues of DRI. Findings from this study suggest that coating with inert additives (e.g., metal oxides) can successfully prevent sticking in both shaft furnaces and fluidized bed processes. The types of additives and coating methods, the stage of reduction where the coating is applied, and reduction temperature will dramatically affect the coating performance. The outlook is discussed as well given the need for further work to improve the performance of coating (methods, timing, and cheaper alternatives), to further de-risk DRI technologies.