Metallurgical and Materials Transactions B最新文献

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.

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.