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Basic oxygen furnace (BOF) steel slag is a main byproduct that is produced during the converter steelmaking process. The volume instability and fast crystallization of BOF slag limits its added-value application. This article aims to understand the effect of Al2O3 on the mineralogical modification and crystallization kinetics of a high basicity BOF steel slag. Continuous cooling transformation and time–temperature–transformation curves were constructed to determine the crystallization characteristics of BOF slag. The critical cooling rate to vitrify the slag was experimentally obtained. The crystallization sequence was clarified by integrating in situ and post-mortem observations with thermodynamic calculations. The results suggest that the addition of Al2O3 can effectively remove free lime, decrease the melting point, and improve the glass formation ability of the high basicity BOF slag. Undercooling the slag is enhanced by increasing the cooling rate and/or adding Al2O3. By steering the addition of Al2O3 and the cooling rate, BOF slag can be modified to obtain a more amorphous phase, presenting an enhanced potential to be a binder for added-value applications.

Crystallization of the solid glassy mold flux film occurring in the gap between the initial shell and mold wall is important, as it determines the in-mold heat transfer and mold lubrication during the process of continuous casting. In order to study the nonisothermal crystallization behavior of the glassy mold flux film in the continuous casting mold, the continuous heating transformation diagram, crystallization mechanism, and precipitate phases were investigated using the single hot thermocouple technique, kinetic models, a scanning electron microscope, and an energy-dispersive spectrometer (EDS). The results show that the initial crystallization temperature for CaO-SiO2 based flux A ranges from [1086 K to 1147 K (813 °C to 874 °C)], which is lower than the case of CaO-Al2O3 based flux B ranging from [1205 K to 1245 K (932 °C to 972 °C)]. The crystallization kinetics for flux A are constant nucleation rate, two-dimensional growth, and control by diffusion. For flux B, they are constant nucleation rate, three-dimensional growth, and control by interface reaction. Besides, the EDS results indicate that the precipitate crystals in fluxes A and B are CaSiO3 and Ca2AlSiO4, respectively.

Different types of slags have been used to refine silicon, particularly for removing boron impurity from metallurgical grade (MG) silicon. Although a number of slags have been used for silicon refining, there is limited information about boron removal kinetics, particularly during the refining reaction with CaO-SiO2-Al2O3 slags. This article investigates the boron removal kinetics using the CaO-SiO2-Al2O3 slag systems in the temperature range 1773 K to 1873 K (1500 °C to 1600 °C). All the results obtained in the present study provide a strong indication that the rate limiting step of the slag-silicon reaction kinetics was mass transport in the liquid slag. It was also shown in the study that as the reaction temperature is increased, the mass transfer coefficient is also increased. At any particular reaction temperature, adding alumina in the CaO-SiO2 slag was shown to decrease the mass transfer coefficient, which is consistent with the substantially higher viscosity of the alumina bearing slags over the CaO-SiO2 slag. The mass transfer coefficients were determined to be between 1.23 × 10−6 and 2.82 × 10−6 ms−1, with activation energies between 64 and 109 kJ/mol, respectively.

The paper describes the dissolution mechanisms of lime into liquid and foaming slags relevant to the BOF process. Two different master slags are employed, representing two different periods of the converter process: an early stage where the FeO content is fixed to 45 wt pct, and a later stage where the FeO content is fixed to 25 wt pct. For these master slags, the ratio between CaO/SiO2 is varied to examine the effect of basicity on lime dissolution. Calcium silicates are formed and peeled off, or partially peeled off, from the interface between the lime cube and the slag in all cases. The main difference for the dissolutions in pure liquid slag and foaming slag is the controlling step for dissolution. In liquid slag, the controlling mechanism is the removal of the calcium silicate layers, while in foaming slag, the controlling mechanism is the contact area between the lime and the liquid slag phase of the foam. The strong convection in the foam enhance the dissolution process, in some cases, the lime even dissociates into small pieces.

Low-temperature reduction degradation (LTRD) of sinter has an adverse effect on blast furnace permeability, and it is mainly caused by the stress produced in the reduction process of hematite. This stress is strongly influenced by alumina dissolved in hematite crystal lattice. In this work, the experiments were conducted to investigate the effect of alumina dissolved in hematite solid solution (Hss) on LTRD by reducing Hss below 550 °C. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), and optical microscope have been used to characterize the mass change and mineral change of samples, respectively. Jade software has been used to calculate the micro strain in magnetite for quantitatively studying the change of strain in reducing process. The results show that alumina was unfavorable to the reduction of Hss on thermodynamics, and the starting reduction temperature of Hss containing 6.0 mol pct alumina was 28 °C higher than that of pure hematite. According to the calculation on kinetics, the generation rate of stress was accelerated by dissolving alumina into hematite crystal lattice. The apparent activation energy of reduction reaction lowered from 47.89 to 28.07 kJ/mol with the increase of alumina content from 0.0 to 6.0 mol pct. The addition of alumina also increased the stress in the reduction products, and this stress was released in the form of LTRD.

Quality of casting products can be significantly improved by controlling the crystal growth rate. Both dendritic and equiaxed grain structures depend strongly on crystal growth rate along the crystallographic direction. Uncontrolled solidification processes may lead to the formation of porous and columnar material with an extremely non-homogeneous composition distribution. These undesirable micro-structures can be avoided by adopting an optimal cooling rate (K/s) during the crystal growth. The present work focuses on determining suitable cooling curves to obtain desired unidirectional crystal growth rates, by implementing a semi-analytical model. Here, we defined cooling curve as the time history of temperature evolution at the cold boundary. The proposed semi-analytical heat transfer model is diffusion driven and accounts for shrinkage effect during solidification. The proposed model is found capable of predicting cooling curves for prescribed interface velocities. The model is self-sufficient in validating itself by means of solving inverse and forward problems. The cooling curve prediction by the model is validated by using it as the transient boundary condition for an existing enthalpy updating scheme-based numerical model. The proposed model is also applied to empirical data reported in literature, to validate the model against experimental results. All the validations showcased excellent fit. The proposed model will facilitate controlled unidirectional crystal growth rate by providing cooling rate (K/s) as an input for the experiments involving directional solidification.

The injection of CO2 during the Rheinstahl–Heraeus (RH) refining process as a lifting gas is a new attempt for the steel industry, and can promote refining effect and realize the utilization of CO2 as a resource. In the present study, the thermodynamic equilibrium of the RH refining process through CO2 injection instead of Ar was calculated using FactSage software. A selective oxidation sequence of [C] and [Al] with CO2 was studied and analyzed under the RH refining temperature and vacuum degree. In addition, the oxidation zones of carbon and aluminum were both defined. Industrial trials were preliminarily conducted to verify the above theory. The results show that CO2 has the potential to be used to refine low-carbon steel in RH, but its refining effect is affected by the [Al] content in steel. By reducing the additive amount of aluminum alloy in the ladle furnace and replenishing the aluminum during the late stage of the RH refining process, CO2 injection can achieve a lower temperature drop of molten steel and a better refining effect than Ar during the RH degassing process.

The free surface of aluminum melt, during stirring under different rotation speeds in unbaffled and baffled crucibles, was simulated numerically using a RANS turbulence model coupled with a particle-tracking method. The effect of mechanical stirring of Al melts containing 0.3, 0.7, and 4.5 wt pct Mg in unbaffled and baffled crucibles on the rate of elimination of bifilms from the melt was also investigated using a reduced pressure test. The results showed that the stirring increased the rate of removal of bifilms from the melt due to an increase in the rate of formation of cracks on the bifilms. Using baffles in the crucible accelerated the rate of removal of bifilms by changing the pattern of movement of bifilms in the melt. The critical stirring speeds, above which the oxide layer on the Al melt could submerge into the bulk liquid, were determined by the simulation. It was confirmed by the experimental results to be about 158 and 420 RPM for the unbaffled and baffled crucibles, respectively.

Partial isothermal sections of the Bi-Fe-Ti system at 700 °C and 900 °C were constructed to investigate the reactivity of Fe with Bi-Ti liquid alloy. In the ternary system, three-phase equilibria such as liquid-Fe-Fe2Ti, liquid-Fe2Ti-Bi2FeTi4, and liquid-Bi9Ti8-Bi2FeTi4 were confirmed at both temperatures. The solubility of Fe in liquid Bi at these temperatures is negligibly small. On the other hand, it is notable that the solubility of Fe in liquid Bi containing Ti at 900 °C is much larger and reaches 2.3 mol pct. Then, we measured the electromotive force (emf) between Bi-20 mol pct Ti alloy and pure Ti at 700 °C in equimolar NaCl-KCl where 1 mol pct TiCl2 was added. From the result, the interaction parameter of the liquid phase in the Bi-Ti system and the standard molar Gibbs energies of formation of Bi9Ti8 and Bi2FeTi4 at 700 °C were estimated.

Carbothermic smelting of ores to produce metals or alloys in alternating current open/semiclosed and closed submerged arc furnaces, or in closed direct current furnaces, results in large volumes of CO-rich off-gas being generated. Most of the CO-rich off-gas is cleaned and flared on stacks, since the storing of large volumes is problematic due to the associated toxic and explosive risks. Flaring of CO-rich off-gas results in significant wastage of energy. In this study, an alternative method to partially capture the thermal energy associated with off-gas combustion, in the form of silicon carbide (SiC) generated from waste materials (quartz and anthracite fines), is proposed. SiC can partially replace conventional carbonaceous reductants used to produce alloys such as ferrochromium. The influences of quartz and anthracite particle size, treatment temperature, and gaseous atmosphere (nitrogen or air) on SiC formation were investigated. A quartz-anthracite mixture with 90 pct of the particles

Ti-alloyed steels have severe nozzle clogging problems, which are detrimental to the steel production process. However, little research on the Al-Ti-Ca-O complex inclusion in molten steel has been carried out. Based on that, experiments with different calcium additions were carried out in an Al2O3 crucible at 1873 K to investigate the variation of inclusions in Ti-bearing Al-killed steel in the current article. It was found that calcium treatment significantly influenced the morphology, composition distribution, and size of oxides in Ti-bearing Al-killed steel. Inclusions with a higher CaO or TiOx content were liquid at 1873 K (1600 °C), indicating that the inclusions in Ti-contained steel can be modified to liquid ones through the proper calcium treatment process. The appropriate amount of calcium should be added to the steel depending upon the aluminum and titanium contents. Thermodynamics of the inclusions in the Al-Ti-Ca-O molten steel system at high temperature and during the solidification process were comprehensively calculated, including all types of inclusions such as calcium oxide, aluminum oxide, titanium oxide, calcium aluminate, calcium titanate, and liquid inclusion. The thermodynamic calculations agree well with the experimental results and can precisely predict the formation of the inclusions in Al-Ti-Ca deoxidized steel.

The slag composition plays a critical role in the formation of inclusions and the cleanliness of steel. In this study, the effects of FeO content and the C/A (CaO/Al2O3) ratio in the slag on the formation of inclusions were investigated based on a 10-minute slag–steel reaction in a MgO crucible. The FeO content in the top slag was shown to have a significant effect on the formation of MgO·Al2O3 spinel inclusions, and critical content exists; when the initial FeO content in the slag was less than 2 pct, MgO·Al2O3 spinel inclusions formed, and the T.O (total oxygen) was 20 ppm; when the initial FeO content in the slag was more than 4 pct, only Al2O3 inclusions were observed and the T.O was 50 ppm. It was clarified that the main source of Mg for the MgO·Al2O3 spinel inclusion formation was the top slag rather than the MgO crucible. In addition, the cleanliness of the steel increased as the initial FeO content in the top slag decreased. As regards the effects of the C/A ratio, the MgO amount in the observed inclusions gradually increased, whereas the T.O content decreased gradually with the increasing C/A ratio. Slag with a composition close to the CaO-saturated region had the best effect on the inclusion absorption.

The CaTiO3 phase is the intermediate phase at the cathode in the preparation of titanium metal through the direct electrochemical deoxidization of titania in molten CaCl2. The formation mechanism of CaTiO3 in the cathode and the releasing of Cl2 from the anode were studied during deoxidation of TiO2 by FFC Cambridge process. Experiments were conducted, where a preformed TiO2 cylindrical pellet was dipped into molten CaCl2 at 900 °C under high-purity Ar to evaluate the formation of CaTiO3 from the hydrolysis of molten CaCl2. Partial electrolysis experiments were also used to confirm the formation of CaTiO3 in molten CaCl2, particularly short-time electrolysis (1, 5, 10, 20, and 30 minutes). In addition, Cl− was observed to discharge at the anode. The results show that the behaviors of both electrodes are closely related to current–time curve. After the turning point on the current–time curve, Cl2 will no longer be released, maybe no CaTiO3 will be formed.

Niobium is a strategic resource because it is useful in a wide number of applications and its global distribution is uneven. It has been reported that kaolin clay from the bottom of the Xuanwei Formation, the Late Permian sequences in southwest China, contains Nb. In this paper, the major, trace, and mineral compositions of kaolin clay were characterized using XRF, ICP-MS, and XRD. The results show that it is mainly composed of kaolinite, anatase, and rutile, with a chemical composition of Al2O3 34.38 pct, SiO2 39.97 pct, TiO2 8.79 pct, Fe2O3 3.24 pct, and Nb 491 μg/g. A process including calcination treatment and acid–alkali leaching with HCl and NaOH was employed to separate Al, Fe, and Si in a leaching solution and to enrich Nb and Ti in the residue. The experimental results indicated that the reaction temperature played a vital role for Al and Fe extractions from acid leaching, while the concentration of alkali was the key factor for Si extraction. Under the optimal conditions, the contents of Nb and Ti in the final product were 4280 μg/g and 80.5 pct, respectively.

We investigated the effect of direct reduced iron (DRI) addition on dephosphorization of molten steel by electric arc furnace (EAF) slag at 1823 K (1550 °C). Various phenomena such as CO gas evolution and slagmaking by gangue oxides in DRI were experimentally observed at each reaction step. Thermodynamic behaviors of phosphorus, oxygen, and carbon were strongly dependent on DRI content. Basicity, which is the thermodynamic driving force of dephosphorization, decreased with the increasing DRI content because SiO2 concentration in the slag was proportional to DRI addition. The excess free energy of P2O5 increased with the increasing SiO2 content in slag. A higher DRI content made dephosphorization difficult by decreasing the basicity and stability of P2O5 in the slag. Therefore, when using DRI in EAF process, it is very important to control the basicity of slag.

The evolution of CaO-Al2O3-MgO-(SiO2) inclusions associated with CaS during electroslag rapid remelting (ESRR) of the tool steel with ultra low oxygen (8 ppm) under protective atmosphere was investigated. Thermodynamic calculation was performed to evaluate the oxygen level of liquid steel and the inclusion evolution during ESRR with the help of FactSage software (CON2 database). The results demonstrated that the reoxidation of liquid steel took place during industrial ESRR, resulting in the oxygen pickup of approximately double content. The oxygen level in the steel was determined by [Al]-[O] equilibrium during ESRR, whereas FeO in the slag transferred oxygen into the liquid steel, as indicated by the significant oxygen pickup. The inclusions in the steel electrode are oxide–sulfide type of CaO-Al2O3-MgO partially wrapped with CaS. The original oxide inclusions that had not been removed in ESRR process were transformed to liquid CaO-Al2O3-SiO2-MgO inclusions through reacting with the dissolved oxygen supplied from the reoxidation of liquid steel and concerned elements in liquid steel during ESRR. These CaO-Al2O3-SiO2-MgO inclusions were invariably associated with patch-type or shell-type CaS, which hold different formation mechanisms. The inclusions ranging from 2 to 4 µm take up a dominant proportion (a little more than 50 pct of the total inclusions) in the remelted ingots, and those larger than 8 µm account for about 3 pct. Melting rates of ESRR not only exerted a negligible effect on the steel cleanliness and the removal efficiency of oxide inclusions, but also on the inclusion size distribution.

In this study, desulfurization from liquid iron by Ar and (10 to 40 pct)H2 + Ar plasma arc melting (HPAM) was examined. The experimental results show that the rate of desulfurization increases as hydrogen is added proportionally to plasma gas. The thermodynamic analysis suggests that the interaction of activated atomic hydrogen and dissolved sulfur in liquid iron, $$ \left[ {\text{S}} \right] + 2{\text{H}} = {\text{H}}_{ 2} {\text{S}}, $$ could be taking place. The kinetic analysis confirms that the desulfurization from liquid iron obeys a first-order rate law.

A microsegregation model coupled with inclusion precipitation, variable partition coefficient, and diffusion coefficient of the solute was developed to investigate solute microsegregation for high-sulfur steel solidification. The effects of the solidification path and phase transition on solute microsegregation were explored. The results showed that the solute concentration predicted by the variable partition coefficient was quite different from the solute concentration predicted by the constant partition coefficient, and the percentage differences of solutes Si, P, and S were − 35.5, − 25.0, and 43.0 pct, respectively. For high-sulfur steel solidification, the concentrations of solutes Mn and S would be reduced by 88.3 and 74.9 pct, respectively, due to the precipitation of MnS. The solidification path and phase transition has a significant effect on the solute partition coefficient and microsegregation. With the increase in C content, the fraction of δ-phase decreased while the fraction of the γ-phase increased, and the microsegregation ratio of solutes C and Si decreased while the microsegregation ratio of solute P increased. To predict microsegregation more accurately, all influencing factors of the partition coefficient, inclusion precipitation, and phase transition should be comprehensively considered.

In this work, the possibility of the direct removal of oxygen species from metallic Ti through the formation of rare-earth oxyfluorides has been investigated from a thermodynamic viewpoint. The deoxidation limit of β-Ti using rare-earth metals (M: Y, La, Ce, and Nd) as deoxidants was evaluated. It was found that Ti metal with an oxygen concentration of 200 mass ppm or less could be theoretically obtained under the M/MOF/MF3 equilibrium at 1300 K (1027 °C), which suggested a possibility of reducing the oxygen content in Ti below 500 mass ppm utilizing a fluoride-based molten salt. Furthermore, a new deoxidation process, in which oxygen was removed in the form of MOF compounds using Mg deoxidant, was discussed as well. The obtained results revealed that the oxygen content in β-Ti could be theoretically reduced to a level below 1000 mass ppm using a MF3-containing molten salt equilibrated with Mg. Rare-earth metals and their alloys are usually produced by the electrolysis in a fluoride-based molten salt; hence, the modern industrial electrolysis techniques can be potentially utilized for deoxidizing Ti scrap.

A mathematical model was developed to predict the carbon concentration during RH refining process. Three reaction sites such as the free surface, inner sites of the molten steel in vacuum chamber, and the bubble surface were considered. The decarburization at inner sites of the molten steel in vacuum chamber was dominant at the initial stage, and then subsequently, it was dominated by the free surface and bubble surface. The decarburization rate constant was also evaluated.

Direct reduction of TiO2 powder has been attempted for decades by researchers in an effort to decrease titanium (Ti) metal production costs. The main objective has been to avoid energy-intensive steps involved in production of primary Ti by the Kroll process. The emerging hydrogen-assisted magnesiothermic reduction process, which uses Mg to directly reduce TiO2 powder under a H2 atmosphere, has been shown to have the potential to compete directly with the Kroll process. The present studies represent an effort to understand the reduction reaction mechanisms of this process. Phase transformations and the reaction pathways are examined by SEM/EDX analysis of partially reduced powder cross-sectional, X-ray diffraction, and other analytical techniques. The results show important morphological changes, the prominent intermediate and final phases under the H2 atmosphere, as well as the local deposition behavior of the MgO byproduct. The effect of the specific surface areas of the initial particles is also discussed.

During ISA copper smelting process, ISASMELT furnace discharges a large amount of matte and slag mixture and the separation of them has an important influence on the recovery of valuable metals. This paper presented a reduction-sulfurization sedimentation process for recovering copper and cobalt from the matte–slag mixture of ISA furnace. Firstly, matte–slag mixture and traditional static sedimentation slag are characterized to determine their mineral composition and occurrence state. It indicates that Cu is primarily lost in slag in the form of sulfide, while Co is mostly lost in the form of oxide. With coke and pyrite as the reducing agent and vulcanizing agent, an orthogonal laboratory experiment was conducted to determine the effects of the smelting temperature and additive dosage on the recovery process. The optimum slag cleaning conditions were found to be: a coke dosage of 2 pct, a pyrite dosage of 2 pct, and a smelting temperature of 1260 °C lasting for 2 hours. In order to improve on the low utilization ratio of additives associated with the industrial sedimentation process, an innovative additive introducing method was put forward which enables the additives to mix and react with slag more adequately. A powder injection device was purpose-made to inject additives into molten slag in dispersion state, and a laboratory experiment was carried out to simulate this process. By injecting 2 pct coke and 2 pct pyrite, the contents of Cu and Co in cleaned slag decreased to 0.46 and 0.01 pct, respectively. It proves that the injection of additives into molten slag is an effective method to recover Cu and Co from the matte–slag mixture of ISA furnace.

The dissolution of metallic elements from Fe and steel materials into pure liquid Mg was investigated with the aim of improving control of impurities in Mg during processes such as Mg-alloy production and Ti smelting. Pure Mg was melted between 1073 and 1323 K (800 and 1050 °C) for 24 to 96 hours in closed crucibles made of pure Fe, low-carbon steel, or austenitic stainless steel SUS316. From the experiments using the pure Fe crucible, the relationship between the solubility of Fe in liquid Mg [Csol,Fe (mass pct)] and temperature [T (K)] was determined to be log(Csol,Fe) = − 3.67 × 103/T + 2.48 (± 0.06), from which the standard Gibbs energy of Fe dissolution in liquid Mg was evaluated. The amount of Fe dissolved from low-carbon steel was the same as that from pure Fe. From SUS316, not only Fe but also Cr and Ni dissolved into liquid Mg; the Fe and Cr concentrations in liquid Mg did not change significantly over time, whereas the Ni concentration increased monotonically. Preferential Ni dissolution resulted in a Ni-poor layer on the SUS316 surface. Finally, using the experimental data of Fe dissolution from low-carbon steel, the Fe contamination route in the current Ti smelting process, where a large amount of Mg is used as a reducing agent, is discussed.

To understand the mechanism for the entrapment of non-metallic inclusions by curved hooks beneath the surface of continuous casting slabs, the etching of the slab, the observation of hooks and the detection of inclusions on sections vertical and parallel to the slab surface were performed. The location of inclusions and hooks was revealed, and forces acting on the inclusion below a hook were analyzed. Inclusions gathered more below the curved hook than in the overflow zone above the hook. From the observation of hooks and inclusions on sections vertical to the slab surface, the number density of 3 to 5 μm inclusions in the hook zone and no-hook zone was very close, while the number density of > 10 μm inclusions in the hook zone was larger than that in the no-hook zone. From the observation on sections parallel to the slab surface, > 20 μm inclusions were located near the hook line more than in other regions, and the number density of inclusions in the hook zone was more than that in the no-hook zone. The apparent friction coefficient dominated the critical capturing size of inclusions from the solidification front, and the deflection angle, flow velocity, sulfur content and solidification velocity had influences on the size range.

In order to understand the reaction mechanism of Al-killed medium-Mn steel with glazed MgO refractory, some laboratory experiments were conducted at [1873 K (1600 °C)]. The refractory rods were glazed by four different basicity slags, and inserted into liquid steel (Mn:5.5 mass pct) for different times. The results show that MgO refractory can react with medium-Mn steel to generate (Mn, Mg)O solid solution with even (Mn, Mg)O-Al2O3 spinel at the boundary of the refractory. When a glaze layer is formed at the edge of a MgO refractory, the glaze layer will supply inclusions into liquid steel and may act as a protection layer for the refractory. Although the glaze could also react with dissolved Mn in steel to generate MnO in both the glaze and refractory, the MnO contents in both the glaze and refractory are evidently lower than that without glaze. The reaction between glazed MgO refractory and liquid steel is influenced by the basicity of the glaze layer. High-basicity slag would hinder the generation of MnO in both the glaze and refractory. Therefore, lower-basicity glaze needs to be avoided for the steelmaking process of medium-Mn steel grades.

Previous studies on inclusions behavior at the front of the solidifying steel shell have mainly focused on low-carbon steels. However, with the increasing applications of high-carbon steel in recent years because of its superior properties, it is crucial to understand this behavior in high-carbon steel. Most of the high-carbon steels are deoxidized by silicon, calcium treated, and contain higher sulfur percentage. Also, higher carbon content has a determining influence on the viscosity and surface tension, which will affect the inclusion behavior. In this study, we have investigated the engulfment behaviors of inclusions in front of the solidifying interface in high-carbon steels using concentric solidification method. The critical velocity of the growing shell, at which the particle is engulfed in the solidifying shell, instead of being pushed by this shell, was determined. The inclusion identified in this study is a bi-component form of CaO-SiO2-based oxide and CaS. It was revealed that engulfment behavior is strongly affected by convection of liquid steel that originates from carbon push out in high-carbon steels. This study provides new crucial information to produce high-carbon steel with fewer inclusions, which opens new application pathways for this emerging grade of steel.

This study provides the thermodynamic properties of the Mg-B binary alloys. Experiments were performed to measure the electromotive force (emf) as a function of temperature (773 K to 873 K) using a solid-state electrochemical cells that can be represented as $$ ( - ){\text{Pt}},{\text{Ar}}/\{ {\text{Mg}} + {\text{CaF}}_{2} \cdot{\text{MgF}}_{2} \} \left\| {{\text{CaF}}_{2} } \right\|\{ {\text{Mg}}({\text{alloy}}) + {\text{CaF}}_{2} \cdot{\text{MgF}}_{2} \} /{\text{Ar}}, {\text{Pt}}( + ) $$ The activities of Mg in Mg-B alloys were calculated from the experimental emf data. The activity coefficients of Mg in Mg-B alloys were also determined. The integral Gibbs energies of formation (∆G f ° ) of alloys were calculated from the activities of the Mg using tangent rule. The integral Gibbs energies of formation (∆G f ° ) of MgB2, MgB4, and MgB7 are − 15.48, − 22.03, and − 15.89 kJ/mol-atoms at 873 K.

Copper slag, a by-product of copper pyrometallurgy, inevitably contains a certain amount of copper. Oxygen-enriched smelting technologies increase the copper content in slag indirectly because of the production of higher-grade matte. The effect of iron phase evolution on the copper content in slag during the slag cleaning process in an electric furnace was investigated using the method of combining theory with experiments. Based on the analysis, the main factors that impede the separation of slag and copper/matte were determined. Subsequently, the properties of slag were analyzed after decreasing the magnetite content within the slag. The experimental results showed that decreases in magnetite content were beneficial for the separation of copper and slag because of the decrease of slag viscosity. Nevertheless, Cu-Fe alloys formed when magnetite was completely reduced to metallic iron, and the foaming slag was formed at 1250 °C. Furthermore, the distribution of copper in the reduced slags was studied in detail.

A hybrid laser-tungsten inert gas (LasTIG) welding system was applied for 3-mm-thick S460MC and S700MC high-strength low-alloy steel sheet butt welding with the aim to reduce the cooling rate compared with laser welding. The effect of the electric current was evaluated. Increasing arc current led to the increase of fused metal and heat-affected-zone (HAZ) dimensions. Fused metal grains were larger whereas the microhardness increase toward the base metal was lower at higher currents in this region. Microhardness peaks corresponding to the coarse-grained HAZ were reduced at higher currents for S460MC but were almost not affected in S700MC. The tensile strength of both the laser weld and LasTIG welds was comparable to the base metal for both alloys.

Copper smelting slag contains less than 2 mass pct of Cu oxide and 30–50 mass pct of FexO. Each year, the grade of copper ore decreases, while the amount of slag generated in the copper smelting process increases. In this study, a coupled reaction model to simulate the reaction between multicomponent slag and FeS-based matte was developed using reported thermodynamic data and double-film theory for the recycling of copper smelting slag. The activity coefficients of oxides in the multicomponent slag were calculated using a regular solution. The activity coefficients of Cu2O in the slag and those of FeS, Cu2S, and CaS in the FeS-based matte used previously reported data. The behaviors of Cu in slag and matte were confirmed by comparing the simulated results and the reported solubility of Cu in the slag in the temperatures ranging from 1473 K to 1573 K. In addition, the effect of the input amount of FeS on the copper content of the slag was verified by comparing the results of reaction model to experimental results. Using the reaction model, the influences of the initial ratio of FeO/SiO2 of the slag, temperature, and matte composition on the behaviors of Cu in the slag and matte were investigated.

The effect of MgO on crystallization and heat transfer of fluoride-free mold fluxes was studied using single/double-hot thermocouple technique (SHTT/DHTT) and infrared emitter technique (IET), respectively. SHTT experiments demonstrated that the increase of MgO concentration promoted the crystallization tendency of mold fluxes. XRD analysis showed that the dominant phases changed from CaSiO3 to CaSiO3/Ca2MgSi2O7/Ca11Si4B2O22, and to Ca2MgSi2O7 as the MgO content was increased. The heat flux across mold flux disks was reduced from 671 to 615 kW/m2 in IET experiments when MgO concentration was increased from 0.9 to 4.9 mass pct.

A common approach in the processing of Al-killed steels is the modification of alumina inclusions by calcium treatment. A model for this process has already been developed by the current authors and validated by means of plant data. Often, magnesium aluminate spinels are also present and transformed to magnesium calcium aluminate inclusions during calcium treatment. In the current study, a fundamental kinetic model is proposed for modification of spinel inclusions considering mass transfer of solute through the boundary layer to the inclusion and diffusion within the product layer. Sensitivity analysis has been carried out to determine rate-controlling step for spinel modification. The rate of transformation of spinel inclusions is compared with alumina inclusions reported in the current authors’ prior model.

Inclusions in Al-killed steel with [S] of about 0.0060 to 0.0070 mass pct were characterized and discussed, evaluating the combined effects of basic slag refining and Ca treatment in ladle, together with reoxidation of liquid steel in casting tundish. Inclusions were changed from Al2O3 to MgO-Al2O3 spinel and then to MgO-Al2O3-CaO during basic slag refining. After Ca treatment, many (MgO-Al2O3) + CaS inclusions were formed, featuring the coexistence of MgO-Al2O3 and CaS to form a dual-phased structure. In the following Ar blowing, the number density of (MgO-Al2O3) + CaS inclusions and pure CaS increased obviously, which implied that [Ca] preferentially reacted with [S] rather than [O] in steel. Reoxidation in casting tundish caused the pickup of oxygen in steel, and the rise of total oxygen (T.O) was 0.0002 mass pct; even 55t steel has been poured. As a result, the content of CaO in inclusions increased and MgO-Al2O3-CaO inclusions were formed again. Thermodynamic calculations revealed that the driving force was strong for the formation of CaS-based inclusions. Higher carbon content in steel would help to reduce oxygen content while enhancing the activity of [S] in steel, which further stabilized the existence of CaS-based inclusions. Therefore, inclusions were mostly the solid (MgO-Al2O3) + CaS dual-phase ones, without the formation of liquid calcium aluminates. Contents of CaS and CaO in inclusions were affected by the [mass pct S]/[mass pct O] ratio, which was calculated as about 4.58 K and 5.34 K at 1873 K and 1823 K, respectively. This finding implied that lower oxygen was not favorable to prevent the solid inclusions in the calcium treatment of high carbon special steel.

Converter copper slag can be viewed as an important secondary resource for valuable metals, considering its high commercial value. The current research investigates the recycling of copper by a combination of theoretical and experimental methods. Based on a modified Stokes equation, it was determined that copper droplets in the molten slag exhibited a low terminal settling velocity of 2.140 × 10−6 m/s. The copper particles will collide with each other during settling, resulting in particle growth. The results from high temperature experimentation, scanning electron microscopy, and energy-dispersive spectroscopy confirm that in the absence of reducing agents, copper droplets are encased in magnetite to form composite ‘Cu droplet–magnetite’ particles. Other copper droplets adhere to magnetite particles which are suspended in the slag in a short-range-ordered array. The study also confirms that in the presence of increasing amounts of anthracite as a reducing agent, the magnetite content of the slag is progressively decreased and the recovery of copper from the slag is significantly improved. Based on the findings from this work, a new processing route is proposed to treat copper slag for the recovery of copper.

In order to reduce ironmaking-related CO2 emissions, hydrogen-enriched blast furnace (BF) operation is currently under development. In hydrogen-enriched BF operation, coke layer thickness can be decreased to reduce CO2 emissions. However, BFs operating with thin coke layers may experience instability or discontinuous phenomena such as particle slip and gas channeling problems, so it is important to optimize the particle diameter and coke layer thickness for optimal BF operation. In this study, the effects of particle diameter and coke layer thickness on the solid flow and stress distribution in a BF were analyzed using a three-dimensional discrete element method. Furthermore, the effects of particle diameter and coke layer thickness on the burden layer stabilities, particle velocities, and particle stress distributions have been investigated. The results show that decreasing the coke layer thickness caused instability owing to the mixing of the coke and ore layers in the BF-cohesive zone and slight increases in both the average particle velocities and the average normal particle stress magnitudes. In addition, the average particle velocities and average normal particle stresses were higher for the smaller particles than for the larger ones during the simulations.

Reduction of a low-grade nickel laterite ore with carbon monoxide to produce Fe-Ni alloy was investigated using a thermo-gravimetric analysis (TGA) method. Non-isothermal reduction tests with a fixed heating rate of 10 °C/min from room temperature to 1200 °C were carried out to determine the different reduction stages and reaction products in each state. Combining measured mass losses with theoretically calculated values together with X-ray diffraction analysis, the products of different reduction stages were identified and a reaction path was established. Isothermal reduction tests with temperatures ranging from 500 °C to 1100 °C were performed to evaluate the temperature dependence of the reduction kinetics. Various kinetic models were fitted to the experimental data to further determine the rate-controlling step in the isothermal tests. Then, two groups of TG experiments were carried out to study the effect of CO flow rate and sample mass on the rate of reaction. The results indicated that the reduction rate increases with the increase of the reduction temperature from 500 °C to 1100 °C. More alloy products are formed and the apparent activation energies increase from 8.6 to 14.7 kJ/mol with the increase of the reduction temperature from 700 °C to 1100 °C. Accordingly, it was proposed that diffusion of CO in the gas bulk and through the pores of the laterite ore sample bed are the rate limiting steps.

For an oxygen bottom blowing converter, a high-temperature fire spot zone forms above the tuyere owing to oxygen reaction. The bottom blowing tuyere and surrounding brick are simultaneously heated by high-temperature fire spot and flowing molten steel. High-speed fluids flowing in the inner tube and the annular gap of the tuyere can remove part of the heat transferred from the fire spot zone and molten steel, playing a vital role in cooling the tuyere. To determine the temperature distributions of the tuyere and surrounding brick under the condition of oxygen bottom blowing, a fluid–solid coupling heat transfer numerical model that considers both the radiation of the fire spot and convection of the molten steel was established in this study. The simulation results agree well with previous experimental results; thus, the numerical model was validated. Utilizing the validated model, the influences of the tuyere inner tube material and fire spot zone temperature on the tuyere temperature distribution were studied in detail. Along with an increase in the material thermal conductivity, the maximum temperature of the inner tube at the hot face decreased, verifying the superiority of copper as the inner tube. More importantly, it was found that reducing the fire spot zone temperature by mixing CO2 in the bottom blowing oxygen fundamentally alleviated the burning loss of the tuyere and the surrounding brick.

To explore the feasibility of small-scale sintering pot testing, a ‘millipot’ facility (diameter of 53 mm and height of 400 mm) was established and used to examine the sintering performance of iron ores and other non-traditional ferrous materials. The sintering performance of a millipot was examined across a range of different operational conditions (coke rate and suction pressure) and compared with an industrial sinter strand operation. Tablet tests were also performed to assist in the design of the millipot experiments and identify conditions for achieving mineral composition similar to the industrial sinter. For the millipot experiments, the materials used need to be compacted to increase the bulk density, and a higher coke rate is required to compensate the high heat loss caused by wall effects. A higher suction pressure is also necessary to maintain an oxidizing atmosphere in the sinter bed. As expected, it was not possible to eliminate the wall effect, which resulted in more primary hematite at edges of the sintered column. However, the sintered material from the center of column simulates industrial sinter reasonably well. As such, millipot provides a practical way to evaluate the sintering process and material performance at laboratory scale, helping to bridge the gap between tablet sintering and large scale pot sintering, or full scale plant trial. The results of millipot testing can be used for designing larger scale experiments or commercial sintering trials.

Electrolytic reduction of dissolved iron oxide to metal iron in molten salts with an inert anode is an alternative short route for steelmaking without CO2 emissions. A novel and simple integrated yttria-stabilized zirconia (YSZ) cell was constructed from a YSZ tube with a closed end. The YSZ tube played multiple functions, including the container for the molten salts, the solid electrolyte membrane in the O2−|YSZ|Pt|O2 (air) reference electrode (RE), and the solid electrolyte membrane between the working and counter electrodes (WE and CE). Electrochemical behavior of ferric ions (Fe3+) that were formed by dissolution of 0.5 wt pct Fe2O3 in the molten CaCl2-NaCl eutectic mixture was investigated on a Pt WE at 1273 K by various electrochemical techniques including cyclic voltammetry, linear scan voltammetry, square wave voltammetry, chronopotentiometry, chronoamperometry, and potentiostatic electrolysis. Analysis of the mechanism of electrode reactions was further assisted by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Some electrochemical parameters were obtained, including the number of exchanged electrons and the diffusion coefficient of ferric ions in the mixed molten salts. The results from various electrochemical techniques are in good agreement with each other, and show that the electrochemical reduction of Fe3+ to Fe in the molten salt mixture could be a single three-electron transfer step and diffusion-controlled reaction that was also possibly reversible. This work may form the foundation for extraction of iron and alloys from molten salts and also provide a stable O2−|YSZ|Pt|O2 (air) RE with wide applicability for investigation on electrochemical properties of other electroactive metal oxides in molten salts.

The wetting behaviors of a TiO2 substrate by calcium ferrite (CF) series slags were investigated using an improved sessile drop method at 1523 K (1250 °C). The initial contact angles were in the range 35 to 50 deg, the final equilibrium apparent contact angles were

We propose a method to identify calcium aluminate inclusions in calcium-treated aluminum-killed steels (Ca12Al14O33, CaAl4O7, CaAl12O19, and Al2O3) using cathodoluminescence (CL) analysis. Such inclusions result in nozzle clogging and melting of the stopper rod during continuous casting. We obtain CL images and CL spectra of calcium aluminate inclusions in model samples of calcium-treated aluminum-killed steel. The model samples are prepared by heating mixtures of Fe powder, Al powder, and Ca shot at 1550 °C in an argon atmosphere. On the basis of the CL colors and CL spectra of the calcium aluminate inclusions, we demonstrate that it is possible to distinguish Ca12Al14O33, CaAl4O7, CaAl12O19, and Al2O3 inclusions from CaAl2O4 and Ca3Al10O18 inclusions, which do not cause nozzle clogging and melting of the stopper rod, by comparing CL images obtained using digital cameras with and without a built-in filter. The acquisition times for the CL images are less than 10 seconds. Thus, the method we present here can be applied for the rapid detection of harmful calcium aluminate inclusions during continuous casting. The CL spectra also provide basic information to specify compositions in agglomerated calcium aluminate inclusions.

Rutile (TiO2) is a vital industrial material used in pigments and in many other valuable chemicals. A new production process to synthesize rutile from natural ilmenite ore and therefore overcome the environmental problems associated with conventional rutile extraction processes was developed. Because the simple phase separation of ilmenite (FeTiO3) into Fe2O3 and TiO2 occurs due to air oxidation, extracting TiO2 by removing Fe2O3 may be possible if pseudobrookite (Fe2TiO5), known as a stable compound in the Fe2O3-TiO2 system at higher temperatures, is of unstable phase in the lower-temperature range. In order to clarify the potential of this new approach, the phase stability of pseudobrookite in the lower-temperature range is discussed. The free energy of formation of pseudobrookite from the respective pure oxides was measured at temperatures ranging from 1073 K to 1473 K by the chemical equilibrium technique using Al2O3 as the reference oxide. The observed free energy is given as a function of temperature: ∆G0 = 7715 − 7.7T (J/mol). The results indicate that pseudobrookite has an unstable phase below 929 K. This has important industrial implications as a new approach to producing synthetic rutile from ilmenite ore by oxidation at low temperatures and acid leaching.

In the current study, the multiphase fluid flow in argon-stirred steel ladles is simulated using an Eulerian–Lagrangian two-phase approach. The momentum source and the turbulent kinetic energy source due to the motion of the bubble are considered for the liquid phase. Argon bubbles are treated as discrete phase particles, and the interfacial forces between the bubbles and the liquid phase; the dependence of the gas density and the bubble diameter on the temperature and the static pressure; and the bubble size distribution are considered. When the fluid flow reaches the quasi-steady state, the ferroalloy melting and mixing phenomena is also modeled. The melting time and the trajectory length of each ferroalloy particle are recorded using a user-defined function (UDF). Local mixing time is predicted in the entire computational domain by checking the mixing criteria in every cell. The effects of gas flow rate, porous plug location, and separation angle of two porous plugs on the fluid flow and the mixing phenomena are investigated. The results show that the flow intensity increases, and the mixing time decreases with the increasing gas flow rate. The optimal porous plug’s radial position with one porous plug is 0.50R for its best mixing condition. When two porous plugs are adopted, the separation angle of 90 deg is recommended to improve the flow field and mixing phenomena.

This article describes the influence of temperature profile on the morphology and impurity distributions of magnesium vapor condensation during silicothermic reduction of calcined dolomite. The formation of magnesium crystals was comprehensively analyzed by optical microscopy, scanning electron microscopy (SEM), and inductively coupled plasma (ICP). The results showed that the temperature changed the morphology and purity of condensation products in the condenser. When the temperature of the condenser zone was lower than 250 °C, the magnesium vapor condensation was fine and noncompacted. The crystal growth of magnesium occurred in the range of 250 °C and 380 °C. It was found that crystal magnesium became coarser and denser at higher temperatures. Based on the analysis of crystallized magnesium, the impurity distributions decreased at temperatures higher than those of the condenser. Furthermore, this indicates that the impurity contents with less than 0.04 pct were distributed randomly through the condenser.

In the current study, steel samples were etched and hooks on several successive layers of longitudinal and transverse slab sections were obtained to investigate the three-dimensional (3-D) distribution of hooks in low-carbon continuous casting slabs. The data from industrial trials and numerical calculation were used to explain the variation in the distribution and morphology of hooks. Around the slab perimeter, the mean depth of hooks at the center and edge of the wide face and the edge of the narrow face was larger than that of other locations. The 3-D hook demonstrated a varied characteristic on different layers, as the observed surface changed in the longitudinal direction. By several layers of the transverse section being polished off, hooks in the transverse direction below the slab surface were obtained, in which the truncated hook and the joint hook between the wide face and narrow face were observed at the slab corner. The same oscillation mark could show as hook type and depression type, depending on the occurrence of the overflow between the solidified meniscus and the copper plate. Industrial trials and the numerical calculation illustrated that the transient variation of hooks in the 3-D space was related to the level fluctuation of molten steel in the mold and temperature fluctuation with casting time and the fluid flow and temperature near the meniscus. Finally, the influence area and volume of hooks on the capture of inclusions and bubbles were discussed.

To investigate the effects of the quench cooling rate on corrosion resistance of Al-Cu-Mg alloy, an end-quenching test was conducted and the microstructures at different cooling rates were observed by SEM and TEM. Additionally, the corrosion resistance was characterized by an intergranular corrosion test and electrochemical test. Moreover, the finite element method was applied to simulate the end quenching process. The results indicate that the actual end quenching process can be approximated as one-dimensional heat transfer, and the cooling rate varies at different cooling distances. By affecting the microstructures, decreasing the cooling rate leads to a decline in the corrosion properties. Low cooling rates coarsen the constituent particles and grain boundary particles, resulting in a wide precipitation-free zone and an increase in the intensity of corrosion reactions. A high cooling rate concentrates on the intragranular precipitant, which can reduce the pitting depth and represents a conversion from localized corrosion to general corrosion.

The gasification properties of feed coke and tuyere coke were investigated by non-isothermal thermogravimetric method under CO2 atmosphere. The physical and chemical structure features were also systematically tested, as well as the mineral composition. The pore characteristics, graphitization degree of carbon matrix, and ash content were the main factors determining the reactivity of coke. Higher Lc decreases the reactivity of tuyere coke in low temperature, while larger porosity increases the reactivity in high temperature, forming an intersection with the gasification process of the feed coke. The high content of Fe2O3 in 25 to 20 mm tuyere coke made a rapid gasification reaction. The SiC produced in the tuyere area increased the porosity of coke especially the 5 to 1 mm coke at the edge of BF, which promoted the gasification process of coke in the area.

This study establishes a volume-averaged model for transport phenomena to study V-shaped segregation in continuous casting blooms with different superheating and cooling rates by coupling fluid flow, macro-scale heat transfer, and solute transport. The results demonstrate that the modified Won–Thomas model considering back diffusion in the solid phase corresponds well with the measured carbon segregation. V-shaped segregation decreases with decreasing superheating and increases slightly with decreases in the cooling rate. The results of original position statistical distribution analysis correspond well with the simulation results. This phenomenon can be exploited to improve the quality of bloom.

Low-grade bauxite ores are not favorable in the conventional Bayer process for alumina production, as they are producing more bauxite residue (red mud) and accompanying lower alumina yield than high-grade ores. In the current study, the thermodynamics and characterization of calcium-aluminate slags and pig iron produced from smelting reduction of high iron- and silica-containing bauxites are studied. Coke and limestone are used to reduce the iron oxide and adjust the basicity of slag during smelting. There is evidence that complete iron separation from bauxite is feasible through smelting-reduction process, and up to 99.9 pct of iron can be eliminated. Moreover, it is shown that the partial separation of silicon, titanium, and other elements from the Al2O3-containing slag occurs. The phase compositions and the distribution of elements between the metal and slag phases provide information about the high-temperature behavior of the bauxite components during smelting reduction. Employing electron microscopy analysis, it is indicated that the morphologies of CaO·Al2O3, 12CaO·7Al2O3, 2CaO·Al2O3·SiO2, and CaO·Al2O3·SiO2 phases in the slag, as well as the complex oxides of Ca-Al-Si-Ti in the slag behave differently as the mass ratio of Al2O3/(Fe2O3 + SiO2) in the bauxite changes. It is also shown that the phases of slag produced from smelting-reduction below 5 K s−1 of cooling rate are proper for further leaching process.