Abstract Inclusions in non-oriented electrical steels were automatically measured using Explorer 4 and extracted with a non-aqueous solution electrolytic method to observe their three-dimension morphology. Extracted inclusions were collected and prepared for micro-XRD test, which is performed to identify the crystal structure of inclusions. Inclusions mainly consist of AlN with P63mc structure, MnS with Fm-3m structure and Al2O3 with R-3c structure, and calculated lattice parameters of inclusions almost agree with that listed in standard PDF cards.

Abstract Effects of slag composition and alloy content as well as temperature on the deoxidation and desulfurization of Inconel 718 superalloy by CaF2-CaO-Al2O3-MgO-TiO2 ESR-type slag without the addition of a deoxidizer were systematically investigated by laboratory-scale experiments and the developed mass transfer model. The model predictions were verified through comparison with experimental results in a double-layer crucible. The results showed that the oxygen content decreased with an increase of CaO, MgO and CaF2 content in the slag at 1773 K, and CaO has a great influence on the deoxidation of Inconel 718 alloy compared with MgO and CaF2 in slag, which was responsible for the decrease in equilibrium content of sulfur in the Inconel 718 alloy. The total oxygen and sulfur content decreased from 33.2 and 20 ppm in master alloys to about 10 and 6 ppm in alloy ingots at 1773 K, respectively. Properly increasing the Al and Ti content only lowered the oxygen and sulfur content in the nickel-based alloy to a limited extent when satisfying the mechanical properties of the Inconel 718 alloy. The interfacial oxygen content increased with increasing temperature, giving rise to a decrease in the desulfurization ratio \( \left( {{{[{\text{pct S}}]_{t = t} } \mathord{\left/ {\vphantom {{[{\text{pct S}}]_{t = t} } {[{\text{pct S}}]_{t = 0} }}} \right. \kern-0pt} {[{\text{pct S}}]_{t = 0} }}} \right) \). These results show that the lower temperature favored desulfurization of the nickel-based alloy.

Abstract Acids such as aqua regia, a 3:1 mixture of hydrochloric acid (HCl) and nitric acid, that contain strong oxidizing agents are used in the dissolution-based recovery of platinum group metals (PGMs). However, nitrate-nitrogen emission has become subject to increasingly strict environmental regulations in recent years. Accordingly, we herein propose a dissolution process for PGMs via the formation of complex oxides using HCl alone. We prepared complex oxides of alkali metals and rhodium (Rh), which is particularly hard to dissolve, and investigated their dissolution behaviors in HCl. Rh-containing complex oxides were prepared by calcining Rh powder and alkali metal salts in air, and dissolution tests using HCl were conducted on the complex oxides obtained. It was found that Rh-containing complex oxides were completely dissolved under appropriate calcination and dissolution conditions.

In aluminium reduction cells, an electrochemical reaction occurs between the molten electrolyte film below the aluminium pad and the carbon cathode blocks, leading to the formation of an Al4C3 layer on the cathode blocks. The properties and role of this Al4C3 layer are therefore important for the aluminium production industry, as they could help increase the life expectancy of electrolysis cells and impact the resistive voltage losses. The purpose of this study is to gain a better understanding of the formation, growth and mechanical stability of the aluminium carbide layer formed on top of the cathode block. A reliable scenario describing both the mechanical and electrochemical behaviours of the Al4C3 layer is proposed. For different industrial graphitized cathode grades, a series of experiments were carried out in a bench-scale Hall-Héroult electrolysis cell and the Al4C3 layer formed on top of the cathode was characterized. Thereafter, the CALPHAD method was combined with density functional theory simulations to estimate the electrical and physical properties of Al4C3 together with the phase equilibria occurring at the interface between the carbide layer and the aluminium pad and the cathode blocks respectively. From these calculations, a scenario for carbide layer growth and mechanical stability was established.

The behavior of dual-phase (MnO-SiO2-Al2O3) + (SiO2) inclusions in saw wire steels during hot rolling and cold drawing was investigated in detail. It was found that the inclusion matrix (glassy MnO-SiO2-Al2O3 (silicate)) manifested rheological properties and the precipitated SiO2 experienced poor deformation in hot rolling. After multi-pass hot rolling, these two phases gradually became separated from each other. The former was elongated into a thin strip, whereas the shape of the latter was deformed from spherical to ellipsoid. Despite their distinctive deformability during hot rolling, MnO-SiO2-Al2O3 and SiO2 were both crushed into smaller pieces during cold drawing. With the proceeding of drawing, shattered pieces became tiny and their interspaces were enlarged, thus causing a reduction in filament breakage. Based on these findings, inclusions were categorized by their melting points and Young’s moduli. Hence, the effects of inclusions on saw wires fabricated by hot rolling and cold drawing were more quantitatively evaluated, and the obtained results were found to be in good agreement with industrial findings.

The effects of hydrogen gas on the reduction rate of ore and reactivity of coke were estimated by using the Boris type movable reaction furnace shaft inner reaction simulator (SIS). The temperature profile was controlled to reproduce the shaft region in the actual blast furnace, and the gas composition was self-controlled inside the reaction tube. The apparent gas utilization ratio was also affected by carbon activity.

Monitoring the meniscus velocities of molten steel in continuous casting molds is critical for revealing the velocity field in the whole mold and consequently for process control and final product quality, however, the realization of contactless online measurement in an actual metallurgy environment is a highly challenging task. In this paper, we develop a special Lorentz force velocimetry (LFV) device to measure the local meniscus velocities of molten steel flow, and this device can adapt to harsh environments with high temperature, opaque liquid metal and surrounding complex electromagnetic noise. A series of laboratory experiments and calibrations were conducted to provide support for a follow-up in-plant test. The LFV device exhibits capability and feasibility for measuring the meniscus velocity in continuous casting molds during plant tests. On this basis, the velocity field and turbulent flow in a wide slab continuous casting mold are analyzed. The measured meniscus velocity is on the order of ~ 10−1 m/s, which is consistent with the results obtained via the nail-board approach.

The compositions and crystal orientations of complex nuclei in an industrial Ti and Nb stabilized ferritic stainless steel (FSS) with a high equiaxed zone ratio were investigated to evaluate the nucleation efficiency of (Ti,Nb)(CN) on the surface of oxides. Although the thermodynamic analysis showed that the equilibrium oxide is Ti2O3, two other types of oxides mainly composed of MgAl2O4 were found in the complex nucleus. In addition, the oxide with the lowest melting temperature was found to have the smallest size. The crystal orientation relationships among MgAl2O4, Ti2O3 and (Ti,Nb)(CN) were revealed by the application of micro-area EBSD measurement after argon ion polishing (AIP) treatment. The crystal planes and crystal orientations of the MgAl2O4 are found to be completely parallel to (Ti,Nb)(CN). In the complex nucleus dominated by Ti2O3, it was found that {001}Ti2O3 is parallel to {111}(Ti,Nb)(CN) and {100}Ti2O3 is parallel to {110}(Ti,Nb)(CN). According to these orientation relationships, Ti2O3 was calculated to have a much lower disregistry with (Ti,Nb)(CN) than MgAl2O4. In addition, it was also revealed by orientation relationships that (Ti,Nb)(CN) has great potential for the nucleation of δ-Fe.

High-speed continuous casting of steel billets entails considerable turbulence in the liquid core, which results in significant slag entrapment unless high viscosity slags are used. It has been suggested that such slags remain glassy or crystallize slightly under the prevailing mold cooling, temperature and residence time conditions. Slags whose composition lead to formation of melilite minerals (i.e., to formation of calcium sodium magnesium aluminum iron disilicates), as the main crystalline phase, possess viscosities > 0.5 Pa/s at 1573 K (1300 °C), are low or do not contain F, and incorporate transition metal oxides (e.g., FeO, MnO and TiO) to absorb infrared radiation and soften steel shell-to-mold heat transfer. In this work, a commercial melilite mold powder, for casting medium carbon steels round billets, is selected to carry out detailed analysis of the kinetics of precipitation of crystalline phases from glassy—devitrification—and super-cooled liquid slags—crystallization—under non-isothermal and isothermal conditions. High-temperature confocal laser scanning microscopy is used in both cases and differential scanning calorimetry just in non-isothermal ones. Assessment of amorphous and crystalline phases in treated samples is done by quantitative X-ray powder diffraction analysis. It is found that even after prolonged treatment (» 36,000 seconds) at 1248 K (975 °C) approximately 13 wt pct of the slag remains amorphous. Additionally, the results indicate that nucleation of crystalline phases in super-cooled liquid and glassy slags occurs on the surface. Thus, it is found that crystallization kinetics is strongly influenced by the topography of the surface with which the super-cooled liquid is in contact, as well as, by shearing actions imposed on the liquid slag surface, which contribute by developing nucleation sites. Devitrification tends to be stronger on surfaces contacting foreign walls and over cracks. Moreover, it is found that predictions of the kinetic model, developed for estimating time–temperature–transformation diagrams from non-isothermal differential scanning calorimetry data, portray reasonably well experimental results of crystallization, as well as devitrification of consolidated samples.

An innovative electroslag remelting furnace with a water-cooled electrode was introduced to recycle the rejected electrolytic manganese metal (EMM) scrap. To clarify the desulfurization process in the rejected EMM scrap, a transient three-dimensional comprehensive numerical model was elaborated. Using the magnetic potential vector approach, the respective electromagnetic fields were calculated via the Maxwell equations. The Lorentz force and the Joule heating fields were derived as phase distribution functions and interrelated via the momentum and energy conservation equations as source terms, respectively. The molten manganese metal droplet motion, as well as the fluctuation of the slag–metal interface, was described by the volume-of-fluid (VOF) approach. Besides, the solidification was modeled via the enthalpy-based technique. A thermodynamic module was established to estimate the sulfur mass transfer rate between the molten manganese metal and the molten slag. Furthermore, a factor related to the magnitude and frequency of the alternating current and the physical properties of the melt was introduced to include the electro-emulsification phenomenon. An experiment has been carried out with a commercial-scale ESR device. The predicted values of the slag temperature and sulfur content in the final manganese ingot were found to agree reasonably with the corresponding measured data. Under continuous melting of the rejected EMM scrap, molten manganese metal droplets are formed at the domain inlet, grow, and fall down. Highly conductive molten manganese metal droplets significantly change distributions of the current streamline, the Joule heating, and the Lorentz force around and within it. Moreover, droplets are inclined to rotate and move inside the mold. With the renewal of the slag–manganese interface, sulfur in the molten manganese metal is constantly transferred to the molten slag. With the applied current ranging from 3000 to 4000 A, the average sulfur content of the manganese ingot dropped from 0.0447 to 0.0291 pct, and thus, the desulfurization rate rose from 55.3 to 70.9 pct.

To predict the behavior of an alumina inclusion in front of the solid–liquid interface during solidification, the interfacial tension between SPFH590 micro-alloyed steel and alumina was experimentally determined. The surface tension of the micro-alloyed steel was measured by the constrained drop method, and the contact angle between the micro-alloyed steel and alumina was investigated by the sessile drop method. Temperature was controlled within the range of 1823 K to 1873 K, and the sulfur concentration in the steel was set in the range of 11 to 94 ppm. With increasing temperature, the surface tensions of steel samples decreased. Further, with increasing temperature, the contact angles of the samples containing 11 to 72 ppm sulfur decreased whereas that of the sample containing 94 ppm sulfur increased. The experimental data were then used to calculate the interfacial tension between the micro-alloyed steel and alumina according to Young’s equation. With increasing temperature, the interfacial tensions of the samples containing 11 to 72 ppm sulfur decreased whereas that of the sample containing 94 ppm sulfur increased. The behavior of an alumina inclusion in front of the solid–liquid interface in the SPFH590 steel was predicted using the calculated interfacial tension values. It was estimated that an increase in the sulfur concentration from 5 to 10 ppm caused a transition of the inclusion from being in an entrapped state to being pushed away from solid–liquid interface.

Abstract To increase the utilization fraction of vanadium titano-magnetite in the blast furnace burden to > 80 pct, a new slag zone with high MgO was found. The effect of the TiO2 content and MgO/CaO mass ratio on the viscosity and liquidus temperature of the high TiO2-bearing blast furnace slag was investigated in the present work. The results indicated that at a fixed CaO/SiO2 ratio of 1.1, the viscosity decreases with increasing TiO2 content at a range of 20 to 34 mass pct. Conversely, increasing the MgO/CaO ratio from 0.32 to 0.65 causes a slight increase in the slag viscosity. The activation energy may show a concomitant variation corresponding to the viscosity of slag. The liquidus temperature first increases and then slightly decreases with TiO2 content. However, the liquidus temperature first decreases and then increases with the MgO/CaO ratio, similar to the variation of the thermodynamic calculation using FactSage software. Various viscosity models were employed to predict the viscosity, and Yan’s model was found to be the most reliable in predicting the viscosity in the present study. In addition, the iso-viscosity distribution diagram was obtained using Yan’s model calculation. It may have potential for application in the blast furnace ironmaking process with super-high (> 80 pct) vanadium titano-magnetite. A suitable slag composition was found to satisfy the smelting process in a blast furnace with super-high TiO2 content at low temperature by using more MgO and less CaO content.

Abstract Deoxidation methods of titanium (Ti) scrap and Ti powder have become increasingly important in recent years. Some rare earth (RE) metals with strong deoxidizing capabilities, including Y, La, Ce, and Ho, are candidate agents for the development of a new deoxidation technology. In this study, a new method was developed to directly remove oxygen (O) from Ti using the Y/YOCl/YCl3 equilibrium. According to the calculation based on available thermodynamic data in the literature, the O concentration in β-Ti can be reduced to less than 10 ppm O at 1300 K (1027 °C) in the Y/YOCl/YCl3 equilibrium. To demonstrate the effectiveness of this method using the Y/YOCl/YCl3 equilibrium, the deoxidation limits of Ti samples using Y metal in YCl3 (l) or in YCl3-NaCl-KCl (l) at 1300 K (1027 °C) were experimentally investigated in this study. As a result, the O concentrations in the Ti samples were from 30 to 60 ppm O in YCl3 (l). This result revealed that Ti with extremely low O concentration can be reliably obtained using the RE/REOCl/RECl3 equilibrium for the first time. The establishment of this process will realize efficient recycling of Ti scrap and production of low O concentration Ti powder, which contribute to the large-scale use of Ti products.

The major challenge while using sintering models for simulation of densification in multi-component alloys is finding the correct transport parameters, which are affected by not only temperature but also chemical composition and phase dispersion. A novel approach for determining the effective self-diffusivity and hence modeling the densification of engineering alloys during sintering is proposed. The approach integrates computational thermodynamics and simulation of diffusion-controlled transformations in multi-component alloys together with a low-order model for solid-state sintering. Computational thermodynamics, using the CALPHAD method, is used to predict microstructural phase stability, which is then used by diffusion simulation models to evaluate the effective transport properties for the sintering model. The modeling approach is validated by comparing results for densification of precipitation-hardened and austenitic stainless-steel alloys during an iso-rate sintering schedule with data from the literature. It is shown that the model can capture experimental observations very well. The modeling approach can thus be used in the development of an efficient search methodology for particulate materials within the context of an integrated computational materials engineering (ICME) frameworks.

Industrial trials were performed to study the effect of calcium treatment on inclusions in non-oriented electrical steels. The evolution and characterization of inclusions in both molten steel and rolled steel were investigated, including a thermodynamic analysis using FactSage 7.1. In the Ca-treated steel, alumina inclusions were transformed into Al2O3-CaO-CaS, with a mass fraction of CaO that increased with increasing the Ca/S ratio. Inclusions of Al2O3-CaO-CaS were classified into wrapping and adhesion type according to their morphologies. Adhesion-type Al2O3-CaO-CaS inclusions were observed only in the steel with Ca/S > 0.84. The two types of Al2O3-CaO-CaS inclusions were transformed into Al2O3-CaS with distinctive morphologies. The mass fraction of Al2O3 and CaS in the inclusions was experimentally found to depend on the Ca/S ratio of the steel and confirmed by thermodynamic analysis. The two types of Al2O3-CaS inclusions could hardly be deformed during the hot-rolling process of the steel but showed different deformation behavior during the cold-rolling process of the steel. The component of CaS in the adhesion-type Al2O3-CaS inclusions was more easily separated from Al2O3 and formed a tail along the rolling direction of the steel, while only a little part of the CaS component broke off from the wrapping-type Al2O3-CaS inclusions.

In situ studies of two separate events of the peritectic phase transition during continuous casting, the peritectic reaction and the peritectic transformation, were performed using high-temperature confocal scanning laser microscopy (HTCSLM). The interface migration velocities during the peritectic transformation at different cooling rates were analyzed in situ by measuring the migration distance of the interface vs time. Moreover, the solute distributions near the moving liquid/solid interface during the peritectic reaction and the peritectic transformation were predicted using the commercial software package diffusion-controlled transformation. The results revealed that the images of HTCSLM clearly recorded these two separate events: the peritectic reaction (L + δ → γ) and the peritectic transformation (L → γ and δ → γ). In the initial stage of the peritectic reaction, the austenite (γ) phase was observed to nucleate at the liquid/δ-ferrite (L/δ) interface and then grow along the periphery of primary δ phases. Upon further cooling, these emerging γ phases gradually isolated the liquid and primary δ phases. Subsequently, the laterally growth of the γ phase was regarded as the peritectic transformation. The growth rate of the γ phase was governed by the liquid to γ and δ to γ phase transformations. As the cooling rate increased, the peritectic reaction was observed to occur at lower temperature. Higher cooling rates enhanced the migration rates of the L/γ and γ/δ interfaces during the peritectic transformation. Meanwhile, an interesting massive transformation of δ into γ phase was observed to occur at a cooling rate of 60 °C/min. All primary δ phases were quickly covered by wrinkled γ phases in a short time. Based on the assumption of the solute incomplete diffusion in the liquid phase, the predicted results revealed that the enrichment of carbon near the L/δ, L/γ, and γ/δ interfaces increased as the cooling rate increased. An increase in the cooling rate exacerbated the carbon segregation of the interface during continuous solidification, causing a nucleation suppression of the γ phase. In turn, the increasing carbon enrichment accelerated the interface migration with the diffusion of large amounts of solute across the interface, causing an increase in the driving force for the peritectic transformation.

A series of fused CaF2-SiO2 binary fluxes have been developed to investigate element transfer behaviors under high heat input submerged arc welding. Transfer of elements is quantified by Δ quantities, which demonstrate respective contributions from the flux to the weld metal. Effects of SiO2 contents on the transfer of Si, Mn, and O have been thoroughly evaluated. Thermodynamic considerations have been attempted for constraining chemical reactions and mechanisms involved in welding.

The effect of iron oxide concentration on the conductive behavior of a molten oxide electrolyte has been investigated at 1823 K using stepped linear scan voltammetry. To maximize the current flow through the electrolyte the ohmic drop in the cell was minimized by shortening the electrode distance. The acquired current was then interpreted by means of an ohmic drop correction, taking into account the conductivity of the alumina-silicate electrolyte and the geometrical form factor of the cell. Via this methodology, a mass transfer limitation in dependence of the iron oxide concentration was identified. This mass transfer limitation vanishes above 7 wt pct of iron oxide where charge transfer starts to be limited solely by electrochemical reaction kinetics. In the analyzed range of concentration, an impact of iron oxide on electronic conduction was not measurable. In addition to these findings, the faradaic yield of the anode half-reaction was determined by the life-measure of O2-production. Hereby, a domain of an anodic yield close to 100 pct for various iron oxide concentrations was identified. Based on these findings, suitable conditions for the electrochemical production of liquid iron were determined.

The ironmaking processes that directly use iron ore fines as raw material are under development and receiving more and more attention. In a flash reduction process, both the thermal decomposition reaction and the reduction reaction of ore fines are extremely fast and cause loss of oxygen from iron oxides. However, it is difficult to distinguish between the thermal decomposition and reduction during the conversion from hematite to magnetite. In this work, the thermal decomposition behavior of hematite ore fines with different particle sizes is investigated by using a thermogravimetric analyzer (TGA). The kinetic parameters are calculated based on the Coats–Redfern method and then verified by the Satava–Sestak method. The F2 model is identified as the most probable mechanism function under the present experimental conditions. The average values of activation energy and the pre-exponential factor are 1256 kJ mol−1 and 1.94 × 1041 s−1, respectively. The internal morphology of the fine hematite particle with partial decomposition is observed to further investigate the reaction mechanism. Moreover, the relative contribution of the two kinds of chemical reactions (thermal decomposition and gaseous reduction) to the overall conversion process from hematite to magnetite is investigated by kinetic calculations based on the obtained reaction rate equations.

A three-dimensional (3D) parallel process model simulating ironmaking blast furnaces (BFs) has been developed using computational fluid dynamics (CFD). It explicitly describes the layered burden and cohesive zone (CZ), gas and liquid re-distribution near raceways, trickling liquid flow in the CZ and dripping zone, and stockline variation. The applicability of the model is confirmed by the reasonable agreement between predicted and measured in-furnace states and global performance under experimental and industrial conditions. Using this model, the 3D characteristics of in-furnace states for a 5000 m3 commercial BF with 40 tuyeres are revealed. Also, it is used to assess the commonly used slot, axisymmetric, sector and full 3D models, which may treat burden distribution as well as gas and liquid flows around raceways differently. The results reveal that the sector and full 3D models are nearly the same; the slot model over-predicts the coke rate up to 13 kg/tHM, and the axisymmetric model gives slightly higher productivity and liquid temperature. These differences are clarified by analyzing model simplifications and their impacts on in-furnace states.

A typical high-sulfur microalloyed steel was investigated by a sub-rapid solidification process for grain refinement of the as-cast microstructure. The size and distribution characteristics of the MnS precipitates were analyzed. The variations in the dendrite morphology and secondary dendrite arm spacing (SDAS) under different cooling rates have been studied, which strongly influence the precipitation behavior of MnS. The 3D-morphology of MnS precipitates was revealed by a novel saturated picric acid deep-etching method. Most MnS precipitates with a length smaller than 5 μm were columnar or equiaxed in the corresponding dendrite zones under sub-rapid solidification conditions at cooling rates of 261 to 2484 K/s. Furthermore, an area scan analysis of the precipitates showed the number of small MnS per square millimeter with lengths lower than 3 μm decrease from 200,537 to 110,067. The percentage of large MnS with a length over 5 μm increased from 2.6 to 6.2 pct as the solidification condition changed from sub-rapid to air cooling. In addition, the size of MnS precipitate was found to depend linearly on the SDAS.

The effects of high undercooling and a large cooling rate can be achieved by the use of a containerless drop tube technique, which is conducive to rapid solidification and formation of a metastable phase. Here, the rapid solidification of Fe78Si13B9 (S1) and Fe78Si9B13 (S2) alloys was completed under microgravity condition. Based on theoretical calculations, a maximum undercooling of 433 K (0.29 TL) and 412 K (0.28 TL) was obtained, respectively. The microstructure evolution and the formation of an amorphous-nanocrystalline structure for the two alloys were compared and analyzed. The results show that S2 alloy has better amorphous forming ability and higher hardness. During the solidification of S1 alloy, the primary phase α-Fe grows by the manner of dendrites, and the secondary dendrite arm spacing decreases exponentially with increased undercooling. An amorphous-nanocrystalline structure is developed when the undercooling is increased up to 388 K; S2 alloy forms an amorphous-nanocrystalline structure at an undercooling of 275 K and is completely amorphized after exceeding an undercooling of 402 K. In addition, the hardness and elastic modulus are acquired by nanoindentation technology under different degrees of undercooling. The phase constitution, morphology, distribution, and grain refinement of the alloys have important effects on the micromechanical properties of these alloys.

The static and dynamic holdups of liquid slag flow in a packed coke bed were investigated at a temperature of 1723 K by using the three-dimensional combined discrete element method and a computational fluid dynamics model. Coke particles with three different diameters (8, 14, and 22 mm) were considered. The simulation results for the static holdup agreed well with previously reported experimental results and the prediction values suggested by Jang et al. The simulation results for the dynamic holdup were compared with the values predicted using several water-model-based correlations. The simulation results for the dynamic holdup were slightly lower than the values predicted using the Fukutake model and the Otake and Okada model and were significantly higher than those predicted using the model proposed by Bando et al. The summation of the static and the dynamic holdups yielded the total holdup. With the increase of the modified capillary number (or particle size), the total holdup decreased monotonically, mainly owing to the considerable decrease in the static holdup.

The oxidation kinetics of silicon hexaboride (SiB6) was studied at different partial pressures of oxygen. The specific weight gain was measured at 1173 K, 1223 K, and 1273 K for \( P_{{{\text{O}}_{2} }} \) = 0.1, 0.23, and 0.33 atm using thermogravimetric analysis. The conventional empirical expressions for oxidation were observed at all selected oxygen partial pressures and temperatures. The structural characterization of the oxidation product was characterized using XRD and FT-IR, with SiB6, SiO2, B, and amorphous B2O3 observed after oxidation for 25 hours. The oxidation surface morphology was also characterized to obtain the oxidation product size, ranging from 4.54 to 24.69 µm with increasing \( P_{{{\text{O}}_{2} }} \) and temperature. The diffusional activation energy for the oxidation process was also calculated from the empirical constant, obtained from the mathematical fitting of the specific weight gain with time. The oxidation activation energies for SiB6 are 250.72, 235.64, and 232.65 kJ/mol at \( P_{{{\text{O}}_{2} }} \) = 0.1, 0.23, and 0.33 atm, respectively.

The distribution of surface macro-inclusions is an important parameter that can directly influence the surface quality of IF steel sheets. In the present work, macro-inclusions > 100 μm within a 20-mm zone from the slab surface across the whole slab width were characterized by step machining methods, and the total analyzed area was 3,300,000 mm2. Three kinds of macro-inclusions were detected: bubbles (including single and aggregated), alumina associated with bubbles and refractory-related alumina. The three-dimensional distribution of surface macro-inclusions across the whole slab width was reconstructed, which showed macro-inclusions along the thickness direction almost concentrated 8 to 20 mm from the slab surface, corresponding to the center of the upper roll zone and stagnant zone below the submerged entry nozzle bottom according to the full-scale water mold model simulation. An inclusion stability model was established that indicated that increasing the flow velocity sharply decreased the stability degree at the solidification front because of the washing effect. The calculated results by this model agree with the fact that macro-inclusions were mainly concentrated in the slab center because of the low flow velocity at this location. The present work indicates that increasing the flow velocity at the solidification front as well as eliminating the stagnant zone is a potential way to improve the surface quality of IF steel slabs.

Direct to blister (DTB) accounts for a significant process for copper making due to its simplified process chain and the production of a single stable SO2-concentrated off-gas. In this study, the phase equilibria of iron silicate slags in the Cu-Fe-Si-S-O system at controlled atmosphere were, for the first time, experimentally investigated in the spinel primary phase field. The liquidus temperatures were quantified, including the equilibrium “Cu2O” content as well as the solid solutions in spinel.

An in situ observation technique of the TiO2 interfacial behavior in molten LiCl-KCl electrolysis was developed. The variation of the thin TiO2 electrode surface were tracked through the high-speed digital microscopy synchronized with the electrochemical measurement. Two characteristic interfacial behaviors were discovered: physical breakage of the titanium oxide and Li(l) spreading on electrode surface. These electrochemically induced interfacial behaviors affect the current-time curves due to the heterogeneity of the titanium oxide film shape.

Interfacial properties play a key role in determining the solubility of solids in liquids for both low- and high-temperature processes. In this study, the interfacial interactions between inclusions comprising TiO2 or TiN and the mold flux were investigated. The results of sessile drop tests show that the wettability of the mold flux on the TiO2 substrate was better than that on the TiN substrate when the temperature was below 1503 K. However, the contact angle on the TiN substrate decreased more than that on the TiO2 substrate when the temperature was above 1503 K due to the enhancement of the interfacial reaction. The thermodynamic calculations suggest that the reactions of TiN with O2 and SiO2 resulted in a bubbling phenomenon during the TiN sessile drop test. The scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) results show that the final products of the interfacial interaction between the mold flux and the TiO2 substrate comprised perovskites, whereas those for the TiN substrate comprised perovskites and SiTi.

Multi-hole ceramic filter is regarded as an effective and cheap method of additional flow control device in tundish. In order to evaluate the performance of the ceramic filter, a transient three-dimensional (3D) comprehensive numerical model has been developed to study the flow pattern, temperature distribution and residence time of the molten steel, as well as the elimination of inclusion in a full size two-strand tundish. One-way coupled Euler–Lagrange approach with random walk model was adopted to track the inclusion motion trajectory. The gravity, buoyancy, drag, virtual mass, lift, pressure gradient, and rebound forces were included. The inclusion Reynolds number was utilized for the judgment of the inclusion separation at the slag-steel interface and the internal surface of the filter hole. Besides, the residence time distribution curve has been analyzed for figuring out the macroscopic mixing of the molten steel. The results indicate that the ceramic filter increases the flow resistance of the molten steel in the tundish, resulting in a longer residence time and a higher temperature drop. Except removed by the covering molten slag, the inclusion could also be trapped by the filter hole when the molten steel travels through the ceramic filter. The elimination of the smaller inclusion is significantly improved. The removal ratio of the 1 μm inclusion in the tundish without ceramic filter is only 59.3 pct, while the value is improved to 65.3 pct if we apply the ceramic filter with slenderness ratio of 3 to the tundish. And with the slenderness ratio changing from 3 to 5, the removal ratio of the 1 μm inclusion increases from 65.3 to 72.0 pct. Additionally, the ceramic filter could counteract certain side effects of the increasing inclusion density on the removal, especially for the smaller inclusion. With the inclusion density increasing from 3990 to 5000 kg/m3, the removal ratio of the 1 μm inclusion decreases by 14.5 pct in the tundish without ceramic filter, and after using the ceramic filter, the removal ratio decreases by 13.0, 7.4, and 5.0 pct with the slenderness ratio varies from 3 to 5.

As part of ongoing work to develop a low fuel consumption smelting process for comprehensive utilization of Hongge vanadium titanomagnetite (HVTM), the influence mechanism of SiO2 on the oxidation behavior and induration process of HVTM pellets (HVTMP) was investigated in this study. Results showed that as the amount of added SiO2 increased, the oxidation degree and compressive strength of HVTMP decreased rapidly while porosity increased. SiO2 had little effect on phase composition; however, it greatly influenced the microstructural evolution of HVTMP. Moreover, the Si-rich phases that precipitated at the grain boundary reduced grain migration, eventually suppressed grain growth, and affected the induration process. A schematic based on the experimental results was proposed to discuss the induration mechanism of HVTMP with different SiO2 additions. The results could provide theoretical and technical foundations for the comprehensive utilization of HVTM.

The use of physical agents when casting aluminum alloys has proven to be an effective route for grain refinement and avoids the inconvenience of residual impurities left in the material when chemical agents are used. The application of ultrasonic waves to the molten metal before casting generates acoustic cavitation, which promotes extensive heterogeneous nucleation and contributes to degassing of the metal. In addition, the application of mechanical vibration during solidification has been proven to promote dendrite fragmentation, and therefore, grain refinement. The aim of this work is to evaluate microstructural refinement due to cavitation produced by ultrasonic melt treatment (UST) of Al5Si5Zn alloy (Al-5wt pctSi-5wt pctZn) and to compare the resulting microstructure with that achieved with and without simple mechanical vibration (MV) during casting so that the best manufacturing procedure for refining aluminum silicon feedstock for subsequent thixoforming can be identified. After casting, the alloy produced under each condition was partially melted to a 0.45 solid fraction to obtain a primary phase with a spheroidized microstructure. The rheological behavior of each semisolid slurry was also evaluated. Microstructural characterization was performed using optical and scanning electron microscopy. Mechanical performance was evaluated by means of tensile tests and hardness measurements. The use of ultrasonic stirring for 30 seconds resulted in slightly better mechanical performance than the other casting conditions. However, because of the short life expectancy of the sonotrodes, mechanical vibration can be considered a simpler, superior solution for feedstock production.

The equation 1 “1 − ϕ” should be “1 − ϕ2”.

Because of interfacial and surface tension, micron-sized liquid oxide droplets are expected to change from spherical (when fully immersed in liquid steel) to lens shape on top of steel. Inclusion sizes were measured by automated analysis of polished sections of calcium-treated aluminum-killed steel. A sample of the same steel was remelted and observed using confocal scanning laser microscopy. Droplets on the steel surface appear to have approximately twice the diameter of fully immersed spherical inclusions.

Many inherent issues, such as the detrimental residual stress, columnar grains with anisotropy, and weak mechanical properties, have severely impeded the adoption of metal additive manufacturing (AM) techniques including powder bed fusion and directed energy deposition (DED) processes. In this study, a hybrid AM process that consists of layer-wise laser metal deposition (i.e., a DED process) and in-situ ultrasonic impact peening (UIP) was applied to obtain Inconel 718 superalloy workpieces. Also, for further property enhancement, a post-heat treatment was applied to the deposited material obtained by the hybrid AM process. Scanning electron microscopy and transmission electron microscope were used to investigate the microstructure morphology and reveal the underlying strengthening mechanism. Electron backscatter diffraction was employed to quantitatively study the microstructure resulted from the hybrid AM process and the post-heat treatment. The profile of residual stress along the depth direction was obtained through X-ray diffraction. The results demonstrate that this hybrid AM process is capable of producing high-quality metal parts with significantly refined microstructure, and beneficial compressive residual stress along the depth into surface. Severe plastic strains are introduced by UIP, and the resulted mechanical twinning and dynamic recrystallization play an important role in refining microstructure. The material microstructure is further refined down to 100 µm, and the texture anisotropy is significantly diminished after solution treatment at 980 °C for 1 hour. Under the as-built condition, in-situ ultrasonic peening alters the residual stress component from a tensile state to an overall compressive state with a maximum value of − 190 MPa within the range of measurement depth.

The concentration and chemical bonding state of carbon in direct-reduced iron (DRI) might affect DRI melting temperature and rate. The effects of carbon bonding state and concentration were evaluated with high-temperature confocal microscopy, differential scanning calorimetry, and by monitoring the carbon monoxide generation rate from reaction between DRI pellets and a laboratory slag-steel melt. In industrial steelmaking, DRI melting is likely controlled by heat transfer; the concentration and bonding state of carbon play secondary roles.

Modeling of the basic oxygen furnace (BOF) process, both for online monitoring and fundamental research, has gained importance in steelmaking industry over the past few decades. Especially models integrating fundamental physicochemical relations are appealing. Even though a vast amount of these kind of models and submodels can be found in the literature, no recent review paper is available which thoroughly discusses the most up-to-date BOF modeling methods. This study aims to do so. In the introductory chapters, an overview is given on the assumptions and models for underlying BOF phenomena, which are frequently used in the BOF models and submodels. Focus was put on six models with emphasis on the chemical aspect of the BOF process. For each model, its assumptions are given and subsequently evaluated, highlighting both their strengths and limitations. The six different models are also compared with each other. Finally, opportunities for future research are discussed.

This article elucidates the quantitative relationship between viscosity and structure in a basic slag system of CaO-SiO2-MgO-Al2O3 and focuses on the role of Al2O3. Slag viscosity was measured by the rotating cylinder method, and structural information was obtained using Fourier transformation infrared, Raman and magic angular spinning nuclear magnetic resonance (MAS-NMR) techniques. The results show that, as the Al2O3 content increased, slag viscosity increased initially and decreased afterwards, directly indicating that Al2O3 had an amphoteric effect on slag viscosity. The Raman spectra verified that with increasing Al2O3 content, the concentrations of Q0(Si) and Q2(Si) decreased first and then increased, while that of Q1(Si) kept increasing and that of Q3(Si) increased first and then decreased. The 27Al MAS-NMR spectra proved that the mole ratios of AlO5 and AlO6 to AlO4 kept increasing with the increase of Al2O3 content, and, overall, Al2O3 changed from a network former to a network modifier. The relationship between the viscosity and structure of the molten slags was further analyzed quantitatively based on the modified (NBO/T), denoted as (NBO/T)′, and we found a fine linear correlation between the logarithm of viscosity and (NBO/T)′. Moreover, the variations of thermodynamic properties of this system also indirectly supported the present experimental results.

The softening and melting properties of iron-bearing materials play a decisive role in the formation of the cohesive zone, which greatly affects blast furnace gas flow distribution and heat-transfer efficiency. To improve the understanding regarding the evolution of condensed phases during reduction, softening, and melting, a thermodynamic model has been developed using FactSage™ thermodynamic software and macro-processing. The model was constructed using a series of equilibrium stages and splitters to determine flow directions of streams and to consider kinetic inhibitions. For all iron-bearing materials studied, the methodology proposed for modeling was capable of obtaining reduction degrees in very good agreement to its experimental data. The evolution of solid phases was qualitatively comparable to the available literature, with Fayalite, Kirschsteinite, Melilite, and FeO as the main solid phases in equilibrium before slag formation. The comparison between the profiles of the calculated slag mass fraction and the experimental pressure drop showed a close relation between these properties. Moreover, the level of heterogeneity of each raw material may play a significant role in the interpretation of its results.

Complex heat treatment operations and advanced manufacturing processes such as laser or electron-beam welding will see the metallic workpiece experience a considerable range of temperatures and heating/cooling rates. These intrinsic conditions will have a significant bearing upon the microstructure of the material, and in turn upon the thermo-mechanical properties. In this work, a diffusion-based approach to model the growth and shrinkage of precipitates in the alpha + beta field of the common titanium alloy Ti-6Al-4V is established. Further, the numerical model is extended using a JMA-type approach to explore the dependency of the beta-transus temperature on extremely high heating rates, whereby dissolution alone is too slow to accurately describe the alpha to beta-phase transformation. Experimental heat treatments at rates of 5, 50, and 500 °C/s were performed, and metallographic analysis of the samples was used to validate the numerical modeling framework predictions for lamellar shrinkage, while data from the literature has been used to evaluate the numerical modeling framework for the growth of equiaxed microstructures. The agreement between measurements and numerical predictions was found to be good.

To provide fundamental information on the phases and microstructures formed during sintering, a liquid with a bulk composition within the silico ferrite of calcium (SFC) primary phase field in the ternary “Fe2O3”-CaO-SiO2 system in air was solidified at a controlled rate. Samples of a bulk composition with a CaO/SiO2 ratio of 4.00 and 69.24 wt pct Fe2O3, were cooled from 1623 K (1350 °C) at 2 K/s, with samples quenched at temperatures between 1513 K (1240 °C) to 1453 K (1180 °C). The silico ferrite of calcium and aluminium I (SFCA-I) and Ca7.2Fe 0.8 2+ Fe303+O53 phases were observed to form an intergrowth (‘SFC-I’) rather than the anticipated SFC phase. Solidification was found to occur in three stages, Liquid + ‘SFC-I’, Liquid + ‘SFC-I’ + C2S + CF2, and C2S + CF2 + CF, where C2S denotes dicalcium silicate, CF denotes calcium ferrite and CF2 denotes calcium diferrite. The phases formed and the solidification sequence differ from those predicted under equilibrium and Scheil–Gulliver Cooling. Although not directly applicable to industrial operations, this research clearly shows that the formation of both the SFCA and SFCA-I phase in iron ore sinters is controlled by kinetic processes rather than equilibrium conditions.

The origin of the solubility minimum of oxide (\( {M}_x\text{O}_y\)) in liquid Fe-M-O alloy was investigated, and the minimum was predicted based on thermodynamic calculations. Due to the characteristic property of activities of M and O in the liquid, a maximum exists in the product between the two activities if the affinity of M to O is significantly high, as most deoxidizing elements are. A critical activity product is defined, which is an indicator of the solubility minimum of the \( {M}_x\text{O}_y\) in the liquid Fe-M-O alloy according to the following relationship: \({{\text{max}}}(a_M^x \times a_{\underline{{{\text{O}}}}}^y) = {K_{M_x{{\text{O}}}_y}\times a_{M_x{{\text{O}}}_y}}\), where the \(a_{M_x{{\text{O}}}_y}\) is unity if the alloy is in equilibrium with the pure \(M_x{{\text{O}}}_y\). The origin of the solubility minimum was explained using the change of the activity product by composition. Available CALPHAD assessments for several binary Fe-M liquid alloys and Wagner’s solvation shell model were combined to calculate the activity product in the Fe-M-O alloy, which can be used to predict the solubility minimum of \( {M}_x\text{O}_y\). A favorable agreement was obtained when \(M = {\text{Al}}\), B, Cr, Mn, Nb, Si, Ta, Ti, V, and Zr. The Gibbs energy of dissolution of O in pure liquid M (\(\Delta g^\circ _{\underline{{{\text{O}}}}(M)}\)) and the Gibbs energy of the formation of \( {M}_x\text{O}_y\) per mole of atoms (\(\Delta g^\circ _{M_x{{\text{O}}}_y}/(x+y)\)) play important roles in determining the solubility minimum, as long as an interaction between Fe and M is less significant than the interaction between metal (Fe and M) and O. Predictions of the solubility minima of CaO and MgO were not satisfactory, requiring further improvement of the present analysis.

The Compound casting method was used to produce an Al/Ni bimetal composite. The mechanisms of formation of the reinforcing intermetallic phases were studied and the produced bimetal composite’s microstructure was then characterized. The results showed that the Al/Ni interface consisted of two intermetallic layers including Al3Ni2 and Al3Ni. It is suggested that the Al3Ni reinforcing particles of the composite originated from two sources. (1) Some Al3Ni particles detached from the Al3Ni layer formed at the interface between the Ni core and the Al melt and dispersed in the liquid Al and (2) Al-Al3Ni eutectic phase, which formed during the solidification process. The increase in the temperature led to the formation of more reinforcing particles and extended the depth of dispersion of the particles in the Al matrix.

The effects of cooling rate on acicular ferrite (AF) nucleation, growth, and inclusion characteristics in Ti-Zr deoxidation steel were studied by utilizing the high temperature confocal laser scanning microscope (HT-CLSM). The results indicated that with the increase of cooling rate, the ferrite start nucleation temperature decreased, and the difference of first nucleation temperature between AF and ferrite side plate (FSP) reduced. When the cooling rate increased to 10.0 °C/s, AF and FSP simultaneously nucleated at 564.5 °C. In addition, the AF actual growth rate rose with the increase of cooling rate and reached 30.13 µm/s at 10.0 °C/s cooling rate. The AF ratio in microstructure increased first and then decreased with the cooling rate increase and was up to the maximum 45.83 pct at 1.0 °C/s cooling rate. For inclusion characteristics, cooling rates had no obvious effect on inclusion types, but had a great influence on inclusions size distribution. With the cooling rate increase, the inclusion average diameter reduced, and diminished to 1.39 µm at 10.0 °C/s cooling rate. Finally, the AF nucleation on the Ti-Zr-Mn-O-S + TiN inclusion could be explained by the low lattice misfit between ferrite and TiN that precipitated on the Ti-Zr-Mn-O-S inclusion surface.

A review of two-dimensional (2D) analytical models of skin and proximity effects in large industrial furnaces with three electrodes arranged in an equilateral triangle is given. The models cover three different cases: one electrode only, three electrodes where two are approximated by line currents, and induced shell currents where all electrodes are approximated by line currents. The first two models show how the skin and proximity effects depend on electrode material properties and size, and the distance between the electrodes. The third model shows how the strength of the induced shell currents will depend on electrode position and furnace size. These models are compared to numerical studies including distributed electrodes and shell currents. The analytical models are accurate when induced shell currents can be disregarded. However, strong shell currents may have a significant impact on the current distribution within the electrodes. This electrode-shell proximity effect competes with the electrode-electrode proximity effect. Finally, the 2D models have been compared with three-dimensional (3D) case studies of large industrial furnaces. In 3D, the shell currents are significantly smaller than what are predicted by the 2D models, but they are sufficiently strong to cause a significant correction of the electrode current density.

The microstructures of porous magnetite formed on gaseous reduction of dense hematite have been examined using high-resolution scanning electron microscopy. It has been shown that cellular pores are formed on reduction in the temperature range 573 K to 973 K (300 °C to 700 °C). Dendritic shaped gas pores are formed on reduction at temperatures between 1073 K and 1273 K (800 °C and 1000 °C). The apparent chemical reaction rate constant for the reduction of hematite to magnetite in CO/CO2 gas mixtures has been derived from measurements of product thickness against reaction time; the rate constant is described by the relation φCO = 0.232exp(76,000/RT) µm s−1 atm−1.

Modeling of equiaxed solidification is vital for understanding the solidification process of metallic alloys. In this work, an extended literature review is given for the models currently used for equiaxed solidification simulations. Based on this analysis, we present a three-phase multiscale equiaxed solidification model in which some approximations regarding solute transport at microscopic scale are put together in a new way and incorporated into macroscopic transport equations. For the latter, a term relating to the momentum exchange between the two phases is revised, and a modification for the grain packing algorithm is proposed. A modernized model for equiaxed dendrite growth is tested using a case of solidification of Sn-5 wt pct Pb alloy in a parallelepiped cavity that mimics the Hebditch–Hunt experiment. The results obtained using two approaches to calculate diffusion length are presented and compared both with each other and with numerical results from elsewhere. It is demonstrated that diffusion length has a crucial effect on the final segregation pattern.

The principal chemical components in iron ore sintering are Fe2O3, CaO, and SiO2. This sintering process consists of three key steps: heating, holding at peak temperature, and cooling. During the cooling stage, a liquid oxide solidifies to form the final sinter microstructures. To investigate the fundamental processes taking place during the cooling of sinters, a new experimental technique has been developed that allows the stages of solidification to be determined in isolation, rather than inferred from the final microstructures. Fe2O3-CaO-SiO2 oxide samples of a bulk composition having a CaO/SiO2 mass ratio of 3.46 and 73.2 wt pct Fe2O3 were cooled in air from 1623 K (1350 °C) at 2 K/s, quenched at 5 K temperature intervals from 1533 K to 1453 K (1260 °C to 1180 °C), and analyzed using Electron Probe Micro X-Ray Analysis (EPMA). During cooling, four distinct stages were observed, consisting of the phase assemblages Liquid + Hematite (I), Liquid + Hematite + C2S(II), Liquid + C2S + CF2(III), and C2S + CF2 + CF (IV). This solidification sequence differs from that predicted under equilibrium and Scheil–Gulliver Cooling. Importantly, no Silico-Ferrite of Calcium (SFC) phase was observed to form on solidification of the liquid. Based on the microstructures formed and liquid compositions, measured by EPMA, it was demonstrated that kinetic factors play a major role in determining the phases and microstructures formed under the conditions investigated.

Al-4.4Cu/TiB2 composites were fabricated with and without post-in-situ reaction ultrasonic melt treatment. The structural and mechanical behaviors of the composites in both the as-cast (F) and T6—peak-aged conditions were analyzed and compared with the base alloy Al-4.4Cu. The microstructural result reveals that the ultrasonic-assisted processing enhanced the dispersion of nano-sized TiB2 particles. The ultrasonic treatment-assisted fabrication has improved the yield strength of Al-4.4Cu/2TiB2 composite about ~ 2 times over the monolithic Al-4.4Cu alloy in both the as-cast and peak-aged condition while retaining > 90 pct ductility of the matrix alloy. The various strengthening mechanisms operating in the materials, namely, base alloy, micro- and nanocomposite were discussed and the theoretical yield strength was estimated using appropriate equations. The theoretical yield strength estimates were found to correlate well with the experimental observations.

Reuse of steelmaking slags is important for the effective use of natural resources. Free magnesia (f-MgO) in steelmaking slag may cause serious problems because of a hydration reaction followed by expansion when it is reused for road construction. We present a promising method to identify f-MgO that causes volume expansion rapidly by investigating cathodoluminescence (CL) images and spectra of a steelmaking slag sample. f-MgO emitted red–orange luminescence from a peak at 755 nm. The mineral phases, 3CaO·SiO2 and 2CaO·SiO2, emitted red and yellow luminescence from peaks at 720 and 590 nm, respectively. No luminescence of FeO and 2CaO·Fe2O3 was detected. f-MgO changed its composition in the slag sample that was immersed in hot (70 °C) water for a week. f-MgO that was responsible for the volume expansion (combined content of FeO and MnO below 30 mass pct) retained a red–orange luminescence, whereas the other f-MgO lost luminescence. The CL intensity of the f-MgO that retained luminescence was more than 10 times larger than that of 3CaO·SiO2 and 2CaO·SiO2. Therefore, we can distinguish f-MgO that causes volume expansion by detecting the intense red–orange luminescence from the peak at 755 nm in the CL image within a few seconds.

We present an experimental study on the formation and behavior of a liquid metal bubbly flow arising from a downward gas injection through a top submerged lance (TSL). A visualization of the bubble dynamics was achieved by the X-ray radiography combined with high-speed imaging. The experiments were carried out in a parallelepiped container (144 × 144 × 12 mm3) using GaInSn, a ternary alloy that is liquid at room temperature. The gas flow rate Qgas was adjusted in a range between 0.033 and 0.1 L/s. Three different injection positions were considered with respect to the submergence depth L. X-ray images allow for a characterization of the flow regimes and provide the properties of the individual bubbles such as size, shape, and trajectory. Formation and entrainment of smaller gas bubbles are observed at the free surface. These small bubbles can be trapped in the fluid for a long time by recirculation vortices. Bubble size distributions are determined for different Qgas. The bubble detachment frequency is measured as a function of Qgas and L. The results are compared with previously published data for water. The X-ray radiography offers an effective method for determining the local void fraction and allows for an estimation of the bubble volume.

Main modeling challenges for vacuum arc remelting (VAR) are briefly highlighted concerning various involving phenomena during the process such as formation and movement of cathode spots on the surface of electrode, the vacuum plasma, side-arcing, the thermal radiation in the vacuum region, magnetohydrodynamics (MHD) in the molten pool, melting of the electrode, and solidification of the ingot. A numerical model is proposed to investigate the influence of several decisive parameters such as arc mode (diffusive or constricted), amount of side-arcing, and gas cooling of shrinkage gap at mold–ingot interface on the solidification behavior of a Titanium-based (Ti-6Al-4V) VAR ingot. The electromagnetic and thermal fields are solved in the entire system including the electrode, vacuum plasma, ingot, and mold. The flow field in the molten pool and the solidification pool profile are computed. The depth of molten pool decreases as the radius of arc increases. With the decreasing amount of side-arcing, the depth of the molten pool increases. Furthermore, gas cooling fairly improves the internal quality of ingot (shallow pool depth) without affecting hydrodynamics in the molten pool. Modeling results are validated against an experiment.

Details of the desulfurization for molten Ni-base superalloys containing Al using solid CaO have been investigated, and the formula that explains the reaction rate has been developed. A cylindrical CaO rod was inserted into 500 g molten Ni-base superalloy TMS-1700 (MGA1700) containing 200 ppm S and held for a certain period at 1600 °C in each experiment. Sulfur content in the melt decreased with the increasing holding time of the CaO rod. Results of electron probe microanalysis show that Ca, O, S, and Al distribute in the same part of the melt/CaO interface as well as the particle boundaries of the CaO rods. The distribution of these elements suggests that CaO reacted with S in the melt to generate CaS, and Al reacted with O and CaO to form calcium aluminate slag. The desulfurization rate formula was obtained by the assumption that the rate-controlling process of the desulfurization is S diffusion through the generated layer composed of CaS and calcium aluminate slag. This formula expresses the amount of S in the melt by the diffusion term with the effective diffusion coefficient, which was obtained from the experimental results. Moreover, the time required for the desulfurization of 2 kg molten Ni-base superalloy PWA1484 using a CaO crucible, was calculated by this desulfurization rate formula which resulted in fair agreement with the actual result.

Supersonic jet characteristics of oxygen lance nozzles have a significant influence on smelting; however, presently, little research has been carried out to investigate the influence of wear on the jet characteristics at the nozzle exit. A numerical model and aerodynamic testing platform were developed to analyze supersonic jet characteristics under different inlet pressures and wear levels at the nozzle exit. The numerical model was first validated by comparing the numerical results with the measured data of the aerodynamic testing experiment. Then, the effects of the inlet pressure and nozzle exit wear on the jet velocity and degree of aggregation were studied. An increase in the nozzle inlet pressure is conducive to an increase in jet velocity but also causes earlier jet convergence. An increase in the nozzle exit wear results in the faster attenuation of jet velocity, not only reducing the jet velocity but also leading to an earlier convergence point for each jet. The results of this study can provide theoretical support for the design of an oxygen lance nozzle and process optimization of smelting in industrial application.

Experiments were performed using a range of test conditions to elucidate the rate controlling step during the reaction of liquid iron-carbon droplets and slags containing manganese oxide. Four conditions were tested in the system: initial MnO content in the slag (5, 10, and 15 wt pct), initial carbon content of the metal (1, 2.5, 4.3 wt pct), initial droplet mass (0.5, 1.0, and 1.5 g), and reaction temperature (1823 K [1550 °C], 1873 K [1600 °C], and 1923 K [1650 °C]). Data were collected using the Constant Volume Pressure Increase (CVPI) technique which tracked the continuous pressure increase in the sealed furnace over time. Samples were quenched at the end of each experiment and chemistry was checked using LECO Carbon Analysis and ICP (Inductively Coupled Plasma) for manganese. The rate of reaction can be broken into a faster initial period related to internal CO formation, and a slower second reaction controlled by a complex mechanism involving transport of oxygen from slag to metal via CO2 and decomposition of the CO2 at the gas–metal interface.

Numerical simulation is the primary approach to evaluate the complex solidification behavior for the continuous casting (CC) process, in which the methods based on the mesh and topology technique have been widely used to solve field variables. For the traditional techniques, such as the finite difference, finite element, and boundary element methods, it is arduous or even impossible to deal with complicated problems that involve multiphase coupling, interface tracking/reconstruction, and self-adaptation due to the inherent weaknesses in the grid structure and mesh dependence. Hence, the present work explores a meshless calculation method for the two-dimensional unsteady heat-transfer problem and proposes an element-free Galerkin (EFG) model for solving heat transfer inside the CC mold based on the moving least-squares approximation. The temperature functions are approximated and constructed by a linear basis and cubic spline weight function over a set of rectangular supporting domain; then, the discrete heat-transfer governing equation based on the EFG method is deduced. The heat flux measured in the real casting process is set as the boundary condition to calculate the nonuniform solidification of the round billet. The calculated results demonstrate that the shell thickness is consistent with that obtained by the square root law of solidification. In addition, the high heat flux region near the meniscus directly determines the growth characteristics of the initial billet shell, which ultimately results in the overall nonuniformity of the shell. The EFG method has the characteristics of fast convergence, high computational accuracy, and great discrete flexibility; it also provides a novel and effective approach for subsequent thermomechanical coupling and crack propagation analysis in the CC process.

In this study, a numerical model was developed of the electromagnetic levitation system based on the actual structure and size of the levitation coil. The model was then used to investigate the effects of the induced magnetic field, the electric field, and the magnetic force on the lateral drift and irregular deformation of different sized copper droplets. In addition, several tests were conducted in order to verify the conclusions obtained from the numerical simulation analysis.

Fluid flow inside a beam blank mold fed through a three-port SEN (two lateral ports and one bottom port), positioned at the center of the mold, has been investigated. Literature survey shows that this kind of configuration is not frequently used. It had been shown that it is possible to get a symmetrical flow with this configuration. The downward inclination of the ports should influence the transient fluid flow. The greater the downward inclination, the greater is the instability of the jet and of the interface between the immiscible fluids that simulate the slag/metal behavior. The flow characterization was made by dye dispersion, PIV technique, measurement of the meniscus oscillation using ultrasonic sensors, and CFD simulations. The slag/metal behavior was simulated using water and oils with different physical properties. The results from PIV as well as from observations of the water–oil interface have been used to validate the CFD simulations. Oils with density close to water resulted in more instability at the interface with entrainment starting from fluid flow rate of 125 L/min (equivalent to casting speed of 1 m/min). Decreasing the viscosity of slag (oils) and increasing the casting velocity (water flow rate) result in reduction of the interfacial stability.

Phase equilibria of the ternary CaO-ZnO-SiO2 system have been investigated at 1170 °C to 1691 °C for oxide liquid in equilibrium with air and solid oxide phases: tridymite or cristobalite SiO2 (up to two immiscible liquids), pseudowollastonite (CS) CaSiO3, rankinite (C3S2) Ca3Si2O7, dicalcium silicate (C2S) (Ca, Zn)2SiO4, tricalcium silicate (C3S) (Ca, Zn)3SiO5, lime (Ca, Zn)O, zincite (Zn, Ca)O, willemite Zn2SiO4 and hardystonite (melilite) Ca2ZnSi2O7, covering the ranges of concentrations not studied before. High-temperature equilibration on primary phase (silica) or inert metal (platinum) substrates followed by quenching and direct measurement of the Ca, Zn and Si concentrations in the phases with the electron probe X-ray microanalysis (EPMA) has been used to accurately characterize the system. Liquidus phase equilibrium data of the present authors for the CaO-ZnO-SiO2 system are essential to obtain a self-consistent set of parameters of thermodynamic models for all phases.

CaO-Al2O3-based mold fluxes, which are under development for the continuous casting of high-Al steel, contain fluxing compounds, such as Na2O and B2O3. The reaction between [Al] and the fluxing agents in mold fluxes leads to an increase in Al2O3 and a decrease in B2O3 and Na2O concentrations, changing the properties of mold fluxes. The effect of the Al2O3/(B2O3 + Na2O) ratio on the melting properties, viscosity, heat transfer, and structure of the CaO-Al2O3-based mold fluxes is presented in this work. The increase of the Al2O3/(B2O3 + Na2O) ratio in the fluxes raised the melting temperature and high-temperature viscosity of mold fluxes but decreased the heat transfer rate across the flux disks. It also enhanced the degree of polymerization by promoting the formation of 3-D aluminate structure, which accounted for the change of the viscous behavior.

A mathematical model has been developed to predict the decarburization rate within individual droplets in the emulsion zone. All the chronological events pertaining to the life cycle of a metal droplet in the emulsion zone like oxygen supply (from slag), external and internal decarburization have been modeled dynamically and validated against experimental data available in open literature. The bloating behavior of metal droplets in the emulsion was represented theoretically by incorporating an escape function dependent on internal CO gas generation. The model is able to predict the onset of bloating and the residence time of metal droplets in the emulsion zone. The residence time of droplet containing 2.6 wt pct C and 0.007 wt pct S is in the range of 10 to 13 seconds. The contribution of decarburization rate in the emulsion zone to the overall decarburization rate is studied using the industrial data reported by Cicutti et al. The model predicts 5 to 75 pct of total decarburization takes place in the emulsion zone. It is found that the extent of decarburization of a metal droplet depends on its initial carbon content rather than its oxygen content for slag containing FeO greater than 10 wt pct.