Metallurgical and Materials Transactions B最新文献

Direct reduction, with reducing gases containing CO and H₂, is becoming an increasingly important process for reduction of iron ore to iron. There is a need for understanding reduction and carburization mechanisms for CO + H₂ gases in shaft-like conditions. The experimental setup includes a column of pellets, where ingoing gas of 40 pct CO and 60 pct H₂ and known temperature enters at the bottom and exits at the top. Experiments are carried out at 600 °C, 700 °C, 800 °C, and 900 °C for 1, 2.5, or 5 hours with gas flow rate of 4 or 6 nL/min. After reduction, pellets are removed, taking note of vertical position, and analyzed for reduction degree, total carbon, and cementite content. Results show that there is a gradient in reduction and carburization over the column height, which decreases with increasing time. Comparison of thermodynamic calculations with experimental results shows that kinetic factors have a strong influence on reduction and carburization. Consumption of gas by reduction or carburization reactions limits gas suitability at the local reaction sites. It could therefore be of interest to design the shaft process so that reduction and carburization take place in two steps.

The crystallization behaviors of CaF₂–CaO–Al₂O₃–MgO–B₂O₃ slag for electroslag remelting of B-containing rack steel was investigated through a series of non-isothermal and isothermal crystallization experiments. The techniques employed for this determination included differential scanning calorimetry, X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and FactSage 8.2. The results indicated that an increase in B₂O₃ content suppressed the crystallization of CaF₂–CaO–Al₂O₃–MgO slag. The crystallization temperature decreased as the B₂O₃ content in the slag increased from 2 to 7 mass pct. In the slag containing 2 mass pct B₂O₃, spherical CaF₂ precipitates first, followed by reticulate Ca₁₂Al₁₄F₂O₃₂ phase. Increasing B₂O₃ addition promoted the formation of Ca₅(BO₃)₃F and calcium aluminate (Ca₁₂Al₁₄O₃₃ or CaAl₄O₇), and decreased the crystallization of Ca₁₂Al₁₄F₂O₃₂ phase. The crystallization sequence transformed into CaF₂ → CaAl₄O₇ → MgAl₂O₄ + Ca₅(BO₃)₃F in the case of 7 mass pct B₂O₃. B₂O₃ addition inhibits the crystallization of the dominated phase CaF₂, which would improving the lubrication and heat transfer performance of ESR-type CaF₂–CaO–Al₂O₃–MgO slags.

Quantifying the degree of element transfer within the droplet zone during submerged arc welding (SAW) remains challenging due to the coverage of the droplet zone by fluxes and the presence of arc plasma, which are characterized by exceedingly high temperatures and short lifetime. This present study has investigated element transfer behaviors within the droplet zone during SAW by employing fused CaO–SiO₂–MnO fluxes with varying MnO contents and welding current intensities. An apparatus designed for capturing droplets in SAW was employed. The results indicate that, as the welding current increases from 200 to 400 A, the average transfer levels of Si, Mn, and O in the fluxes to the droplet increase by 1.81, 2.52, and 1.42 times, respectively. As the MnO content increases from 10 to 60 wt pct, the average transfer levels of Si, Mn, and O in the fluxes to the droplet increase by 24.97, 3.01, and 2.22 times, respectively. Our current findings may facilitate elucidating the influence of arc plasma on element transfer within the droplet zone, thereby establishing a theoretical framework for comprehensively understanding the contribution of individual reaction zones during SAW.

The excellent water-cooling structure contributes to achieve efficient and reasonable heat transfer in the mold, which is essential for achieving the ultra-large beam blank continuous casting (ULBBCC). Therefore, this work designed different ultra-large beam blank mold (ULBBM) which were composed of three wide face copper plates with different water-cooling structures and two narrow face copper plates with different water-cooling structures, on the basis of which a three-dimensional heat transfer model of the copper plate coupling with the cooling water flow in the water-cooling structure was developed with the consideration of fluid-solid coupling interaction. Then, the accuracy of the model was verified by comparing the model-predicted and measured water temperatures. Finally, the focus is comparing the heat transfer behavior of the mold under different water-cooling structures, as well as the temperature and flow evolution of the cooling water, and the most optimal water-cooling structure was proposed. The results show that the water-cooling structure of water slots with semicircular roots (Mold II) contributes the narrow face copper plate of ULBBM to obtain excellent temperature uniformity and achieve homogenization of heat transfer. The water-cooling structure of small hole water channel with a diameter of 10 mm (Mold III) decreases the maximum temperature at the fillet of wide face copper plate of ULBBM to 582.9 K and the maximum circumferential temperature difference near the meniscus to 103.3 K, and which contributes the wide face copper plate to obtain higher temperature uniformity and lower fillet temperature, and achieve homogenization of heat transfer.

This study investigates the influence of spinel crystallization characteristics on vanadium extraction during the converter vanadium slag-cooling process through thermodynamic calculations and experimental investigations. The phase evolution and micro-morphology variations of V-containing slag at different quenching temperatures are characterized via X-ray diffraction and scanning electron microscopy-energy dispersive X-ray spectroscopy, and the grain size of spinel phases is measured using an image processing software. Results indicate that the crystallization sequence in V-containing slag during the cooling process is V-spinel → Ti-spinel → olivine → rhodonite. When the temperature is reduced from 1400 °C to 1000 °C, the grain sizes of spinel exhibit a log-normal distribution, with the mean diameter and leaching rate of vanadium increasing from 15.11 to 27.27 μm and from 82.65 pct to 92.06 pct, respectively. The restrictive step in the crystallization process is the interfacial reaction. When cooled from 1000 °C to 25 °C, Ostwald ripening-type grain size distribution is observed, and the mean diameter increased to 41.9 μm. The vanadium leaching rate decreased to 85 pct due to the encapsulation of V-spinel by Ti-spinel and olivine, and the crystallization process is observed to be controlled by diffusion.

The bottom blowing element is critical for ensuring the effectiveness of top and bottom blowing in converter steelmaking process. Investigating the influence of different bottom blowing elements on the stirring properties of molten bath contributes to the optimization of the bottom blowing system. The effects of structural variations in dispersive, circular seam and straight cylinder types of bottom blowing elements on molten bath fluid dynamics, turbulent kinetic energy and multiphase flow properties of gas-slag-metal were investigated through numerical simulations. In addition, physical simulations were used to measure the mixing time of molten bath, observe changes in the flow field, and validate and analyze the results of the numerical simulations. The results show that the dispersive type element has a wider dispersion range of the flow jets, while the straight cylinder type has the smallest dispersion range. When the bottom blowing intensity is below 0.05 Nm³/t·min, the dispersive type has the longest mixing time, while the circular seam type has the shortest mixing time. Conversely, at more than 0.08 Nm³/t·min, the dispersive type shows the shortest mixing time and the straight cylinder type shows the longest. The dispersive type significantly influences the bottom flow field and disperses tracers from the interior of molten bath. The circular seam type mainly affects the middle flow field and directs tracers along the central area. The straight cylinder type, on the other hand, has a significant influence on the surface flow field and directs tracers along the pool surface.

40Cr10Si2Mo steel is widely utilized because of its excellent mechanical properties, with grain size being a critical factor determining subsequent phase transformation processes and material microstructure performance. This paper reports the use of high-temperature laser scanning confocal microscopy (HT-LSCM) for in situ observation experiments to systematically investigate the growth of austenite grains and the martensitic phase transformation mechanism in 40Cr10Si2Mo steel during an 1800-second isothermal hold at temperatures ranging from 900 °C to 1250 °C. A dynamic model of austenite grain growth is established to optimize the parameters of the austenitic process. The results indicate that the austenite grain size increases continuously with increasing temperature and prolonged time. The Dong model predicts grain sizes that align well with experimental values. Austenite grains grow through grain boundary migration and grain annexation, whereas the precipitation and dissolution of M(Cr, Mo)₂₃C₆ affect grain growth. With prolonged time, some grain boundaries extend into new boundaries through subgrain rotation. The fine grains at lower temperatures reduce the initial temperature of the martensite transition (M_s), and the primary martensite nucleates along the grain boundaries of the prior austenite. The secondary martensite is attached to the primary martensite nucleus at a certain angle and grows in parallel while inhibiting the phase transition of the surrounding untransformed austenite.

In this study, the reduction kinetics of ilmenite concentrate from a domestic mine (Kahnuj, Kerman, Iran) in pure hydrogen in the temperature range of 500 °C to 1100 °C was investigated. From the non-isothermal reduction results corresponding kinetic parameters for the as-received and pre-oxidized concentrates were calculated using the Coats-Redfern method. The reduction process in both raw and pre-oxidized ilmenite, at 800 °C was controlled by diffusion through the product layer. The kinetic analysis for ilmenite pre-oxidized at 1000 °C indicated that the reduction process followed a chemical reaction and nucleation and growth mechanism. The samples pre-oxidized at 800 °C and 1000 °C exhibited higher mass loss values and reduction degrees compared to the raw ilmenite. The promoting effect of pre-oxidation on the reduction of ilmenite is attributed to the phase changes in pre-oxidized ilmenite and the porous structure created during the reduction process after the pre-oxidation process. X-ray diffraction (XRD) patterns confirmed the presence of pseudorutile, rutile, and hematite after oxidation at 800 °C, and pseudobrookite and rutile were stable phases after oxidation at 1000 °C.

Understanding the agglomeration behavior between inclusions during steelmaking is crucial to control steel quality and cleanliness. This work reviews the state-of-the-art lateral capillary interaction between inclusions attached to the gas/steel or slag/steel interfaces, which is an essential aspect of inclusion agglomeration. The origin of the lateral capillary force, the methodologies to measure the force, and the development of the capillary theory are discussed. High-temperature confocal scanning laser microscopy (CSLM) has been intensively used for the in situ observation of inclusion agglomeration at the gas/steel or slag/steel interfaces. To calculate the lateral capillary force between inclusions from a series of 2D CSLM images, the particle mass, the inter-particle distance, and the drag force on the inclusions are the main input parameters. We compared the capillary force between two ellipsoidal particles obtained from different particle radius approximations (long and short radii, arithmetic mean, equivalent and effective radius, and equivalent volume), separation distances (inter-center and inter-surface), and capillary models (Yin’s, Chan’s, Mu’s, K–P, and sub-particle models). The results highlight the importance of consistency in the parameters used in the force calculation from CSLM images and capillary models.

As the demand for titanium (Ti) continues to grow, so too does the use of Ti scrap, underscoring the need for innovative techniques for the efficient removal of oxygen (O) impurities from Ti scrap. Despite the immense challenge of directly removing oxygen from Ti–O solid solutions and the current lack of industrially applicable deoxidation methods, the current work explores a groundbreaking approach to address this issue. The thermodynamic analysis of a new technique for eliminating oxygen dissolved in solid Ti was conducted, leveraging the deoxidation properties of rare earth metals (REMs) such as Sc, Y, and La. This cutting-edge method relies on the in-situ production of REMs through the metallothermic reduction of REM halides. It was shown that Sc or Y metal can be synthesized via the reduction of ScCl₃ by Mg or YCl₃ by Li or Na, respectively. Ti with oxygen concentrations below 100 mass ppm can be obtained by leveraging the deoxidation properties of the Sc and Y metals produced in situ during the metallothermic reduction process, which contribute to deoxidation through their subsequent oxychloride-forming reactions. Employing REM halides in tandem with Li, Na, and Mg enables the efficient removal of oxygen impurities from Ti, even though these reactive metals have only weak deoxidation properties for Ti on their own. Remarkably, the proposed technique achieves oxygen concentrations significantly lower than those obtained using Ca metal as a deoxidant. In the future, this pioneering deoxidation method could be used to reduce CO₂ emissions and energy consumption during Ti production while promoting resource circulation as a key technology for Ti recycling.