Showing papers in "Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science in 2020"

Effect of Cerium Content on Inclusions in an Ultra-Low-Carbon Aluminum-Killed Steel

Abstract: The effect of cerium on inclusions in an ultra-low-carbon Al-killed steel was studied at 1873 K (1600 °C) using laboratory experiments. The content of cerium in the steel varied from 0 to 0.028 wt pct. The contents of the total oxygen (T.O), total nitrogen (T.N), total sulfur (T.S), total cerium (T.Ce) and dissolved aluminum ([Al]) in the steel samples 1, 5, 10 and 30 minutes after adding cerium were measured, and inclusions were characterized using an automatic scanning electron microscope. It was found that a cerium-concentrated zone formed after the cerium alloy was added to the molten steel. Many inclusions were generated in the cerium-concentrated zone and then disappeared with the decrease of the cerium content. The variation of the inclusion composition was Al2O3 → CeAlO3 → Ce2O2S → Ce2O2S + CeS with the increasing cerium content in the steel, which agreed well with the thermodynamic analysis. The value of T.Ce/T.O was able to evaluate and predict the type of inclusions. A prediction model of the composition of inclusions was established based on thermodynamic calculation and mass balance and was validated by experimental data. When the value of T.Ce/(T.S + T.O) was ≥ 4.4, the average composition of inclusions changed little since most inclusions were fully modified.

Computational Thermodynamic Calculations: FactSage from CALPHAD Thermodynamic Database to Virtual Process Simulation

Abstract: The CALPHAD-type computational thermodynamic databases have been developed since 1970. Several commercial computational thermodynamic software equipped with comprehensive and accurate thermodynamic databases and fast Gibbs energy minimization routine are widely used in the design of new materials and the optimization of materials processing. In this study, the FactSage software, which is the most frequently accessed software in high temperature materials processing, is briefly overviewed. The current databases and on-going directions of the thermodynamic database development are discussed. Application examples of FactSage thermodynamics databases to steel processing from the iron ore sintering process to the final metallic coating process are presented. Lastly, the most recent and future application of the FactSage thermodynamic databases to virtual steelmaking process simulations for the so-called industry 4.0 (smart factory) is highlighted.

Recovery of Noble Metals from Spent Catalysts: A Review

Abstract: In the past several decades, many technologies to recover platinum group metals (PGMs) and rhenium (Re) from electronic waste and spent catalysts have been developed and published. The reasons for the rising interest in this area are: (1) The abundance of these elements in the earth’s crust is 590 tons; (3) electronics and catalyst industries consume > 90 pct of precious metals (about 65 pct of Pd, 45 pct of Pt and 84 pct of Rh are used in catalytic converters); (4) properties of PGMs and Re (resistance to corrosion and oxidation, high melting temperatures, electrical conductivity and catalytic activity) are of great commercial interest. Even though several comprehensive reviews on the recovery of precious metals from spent catalysts have recently been published, several developments were not focused by the scientific community. The reviews divide the technologies into hydro- and pyrometallurgical ones. However, the variety of different approaches requires a more detailed classification. This article is an overview of the recently reported works and a comparison of different technologies in terms of extraction efficiency, environmental friendliness, and capital and operational expenditures. A new electrochemical method, which is now under development, is also presented.

Recent Progress in Titanium Extraction and Recycling

Abstract: This paper presents a brief review of the history of titanium smelting and the current trends in related research and development. Presently, both electrolytic and metallothermic reduction processes utilizing various feed materials such as titanium oxide are widely studied. However, many challenges remain to be addressed before realizing the practical application of smelting processes utilizing oxide feed. To make titanium a “common metal”, a new reduction process that is high speed, energy-efficient, low cost, and of low environmental impact is required. The current status of titanium recycling is likewise outlined, and the development of the recycling process is discussed. Low-grade titanium scraps heavily contaminated by oxygen and iron are currently used for producing additive alloys (ferro-titanium) in the steel industry. In the near future, if the demand for titanium metal increases dramatically, there could be an oversupply of low-grade titanium scraps in the market. Therefore, the development of anti-contamination and efficient removal processes for oxygen and iron is essential for the efficient utilization of titanium. The development of these technologies is vital for expanding the titanium industry through innovation in both titanium smelting and recycling technologies.

Element Transfer Behaviors of Fused CaF 2 -SiO 2 Fluxes Subject to High Heat Input Submerged Arc Welding

Abstract: 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.

Element Transfer Behaviors of Fused CaF 2 -TiO 2 Fluxes in EH36 Shipbuilding Steel During High Heat Input Submerged Arc Welding

Abstract: Fused CaF2-TiO2 fluxes are developed and applied on EH36 shipbuilding plates under high heat input submerged arc welding. Transfer behaviors of O and major alloying elements are systematically investigated. TiO2 contributes to O gain in the weld pool, but leads to concurrent losses of Si, Mn, and C via deoxidation and decarburization reactions. Transfer of Ti to the weld metal is suppressed due to improved flux O potential and chemical interaction between CaF2 and TiO2.

Kinetic Modeling of Nonmetallic Inclusions Behavior in Molten Steel: A Review

Abstract: The kinetic modeling for the nucleation, size growth, and compositional evolution of nonmetallic inclusions in steel was extensively reviewed in the present article. The nucleation and initial growth of inclusion in molten steel during deoxidation as well as the collision growth, motion, removal, and entrapment of inclusions in the molten steel in continuous casting (CC) tundish and strand were discussed. Moreover, the recent studies on the prediction of inclusion composition in CC semiproducts were introduced. Since the 1990s, the development of thermodynamic model and relevant databases for inclusion engineering has been initiated by the steel industry. Later, the commercial software FACTSAGE employing the FACT database was widely used to predict the gas (atmosphere/bubble)–liquid (steel/slag/inclusion)–solid (refractory/slag/steel/inclusion) multiphase equilibria. With the help of the comprehensive thermodynamic database and solution models in conjunction with the development of user-friendly computing packages, the kinetics of inclusion evolution in molten steel can be successfully predicted based on several kinetic models such as the coupled reaction (CR) model, reaction zone model, and tank series recirculation (TSR) model. However, some parameters are needed to represent the real processes according to the model employed at different operational or experimental conditions. The effect of reoxidation on the evolution of inclusions in the ladle and tundish, which was experimentally confirmed, can be simulated by the effective equilibrium reaction zone (EERZ) model. The complex slag–steel interfacial reaction phenomena have been successfully explained by the interfacial kinetic model based on the dynamic interfacial tension and oxygen adsorption/desorption characteristics at the slag-steel interface.

Three-Dimensional Modeling of an Ironmaking Blast Furnace with a Layered Cohesive Zone

Abstract: 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.

Element Transfer Behaviors of Fused CaF 2 -SiO 2 -MnO Fluxes Under High Heat Input Submerged Arc Welding

Abstract: Submerged arc welding is conducted employing CaF2-SiO2-MnO fluxes with varying MnO content under high heat input of 60 kJ/cm using EH36 shipbuilding steel. Transfer of elements between slags and weld metals is quantified. Mn and O transferred from slag to weld metal increase with MnO addition, whereas the transfer of Si seems to be independent of MnO content. Factors that govern the transfer of elements between slag and weld metal are evaluated.

CFD Investigation of Effect of Multi-hole Ceramic Filter on Inclusion Removal in a Two-Strand Tundish

Abstract: 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.

Agglomeration Characteristics of Various Inclusions in Al-killed Molten Steel Containing Rare Earth Element

Abstract: The nozzle-clogging problem is closely related to the agglomeration behavior of inclusions in steel-containing rare earth (RE). The present study first optimized the thermodynamic model by supplementing thermodynamic data of the RE compound to study the formation of various inclusions in the Ce-Al-O-S system. Based on that, laboratory-scale experiments with different Ce and Al contents were designed to obtain samples containing a single type of inclusions, viz., Al2O3, Ce-Al-O, Ce2O3, and Ce-O-S, respectively. Additionally, the agglomeration behavior of inclusions was observed in situ by confocal laser scanning microscopy (CLSM), and the calculated attractive forces were used to compare the agglomeration tendency of the four inclusions. The results show that the agglomeration of Al2O3 inclusions is attributed to the strongest attractive force (1.0 × 10−15N to 3.0 × 10−14N) among the four kinds of inclusions. Although Ce-Al-O and Ce2O3 inclusions have the weaker attractive forces (1.3 × 10−16N to 2.0 × 10−14N), they can also agglomerate together and form large-sized clusters. The attractive forces between Ce-O-S inclusions are the weakest (2.1 × 10−18N to 6.0 × 10−16N), that is, this kind of inclusion is more difficult to agglomerate than other inclusions. The study can provide theoretical support for improving the nozzle-clogging problem of RE-containing steel from the inclusion-controlling perspective.

Blast Furnace Ironmaking Process with Super-High TiO 2 in the Slag: Viscosity and Melting Properties of the Slag

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.

Electric Current Distribution During Electromagnetic Braking in Continuous Casting

Abstract: The electromagnetic brake (EMBr) is a well-known and widely applied technology for controlling the melt flow in the continuous casting (CC) of the steel. The effect of a steady (DC) magnetic field (0.31 T) in a CC mold is numerically studied based on the GaInSn experiment. The electrical boundary conditions are varied by considering a perfectly insulating/conductive mold or the presence of a conductive solid shell, which is experimentally modeled by 0.5 mm brass plates. An intense current density (up to 350 kA/m2) is induced by the EMBr magnetic field in the form of loops. The electric current loop tends to close either inside the liquid bulk or through the conductive solid. Based on the character of the induced current loop closures, the turbulent flow is affected as follows: (i) it becomes unstable in the insulated mold, forming 2D self-inducing vortex structures aligned with the magnetic field; (ii) it is strongly damped for the conductive mold; and (iii) it exhibits transitional behavior with the presence of a solid shell. The application of the obtained results for the real CC process is discussed and validated.

X-ray Radioscopic Visualization of Bubbly Flows Injected Through a Top Submerged Lance into a Liquid Metal

Abstract: 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.

Review of Peritectic Solidification Mechanisms and Effects in Steel Casting

Abstract: Surface quality and castability of steels are controlled greatly by initial solidification. Peritectic steels suffer more from surface quality problems, including deep oscillation marks and depressions, crack formation, and breakouts than other steels. This paper reviews current understanding of the fundamental mechanisms of initial solidification of peritectic steels that lead to these problems. First, different empirical relations to identify peritectic steel grades from their alloy compositions are summarized. Peritectic steels have equivalent carbon content that takes their solidification and cooling path between the point of maximum solubility in δ-ferrite and the triple point at the peritectic temperature. Surface defects are related more to the solid-state peritectic transformation (δ-ferrite → γ-austenite) which occurs after the peritectic reaction (L + δ → γ) during initial solidification. Some researchers believe that the peritectic reaction is controlled by diffusion of solute atoms from γ phase, through the liquid, to the δ phase while others believe that γ growth along the L/δ interface involves microscale heat transfer and solute mixing due to local re-melting of δ-ferrite. There is also disagreement regarding the peritectic transformation. Some believe that peritectic transformation is diffusion controlled while others believe that massive transformation is responsible for this phenomenon. Alloying elements and cooling rate greatly affect these mechanisms.

Effects of BaO on the Viscosity and Structure of a New Fluorine-Free CaO-Al2O3-TiO2-Based Mold Flux for High Titanium Steel

Abstract: Herein, the effects of BaO (i.e. 5, 10, 15 and 20 pct) on the viscosity and structures of a new fluorine-free CaO-Al2O3-TiO2-based mold flux with w(CaO pct)/w(Al2O3 pct) ratio of 1.0 are investigated using a rotary viscometer, molecular dynamics (MD) simulations, and Raman spectroscopy. The viscosity of the samples (the testing temperature is 1300 °C) decrease from 0.46 to 0.21 Pa·s as the BaO content increased from 5 to 20 pct, and the activation energy decreases from 150.7 to 119.7 kJ·mol−1, the break temperature (Tbr) decreases from 1475 K to 1429 K which are achieved as the initial testing temperature of 1300 °C decreased under the furnace cooling. With the addition of BaO, the MD simulation results suggest that the coordination numbers (CNs) of Al (Ti)-O are reduced, while Q3, Q4, and Q5 are depolymerized into Q0, Q1, and Q2. The Raman spectroscopy results illustrate that the bridge oxygens (BOs) originating from the Ti-O-Ti (Al) linkages and Q2 (Al-O−) are depolymerized into Q1 (Si-O−) and Q0 (Al-O−) as the BaO content is increased. The Raman spectroscopy results agree well with those of the MD simulation. Therefore, BaO can simplify the structure of melts and decrease the viscosity of such systems. This work not only presents a new fluorine-free CaO-Al2O3-TiO2-based mold flux, but also deepens the understandings of the role of BaO in this system.

Recovery of Precious Metals (Au, Ag, Pt, and Pd) from Urban Mining Through Copper Smelting

Abstract: With the aim of investigating deportments of precious metals in pyrometallurgical processing of waste electrical and electronic equipment, the distributions of selected precious metals (gold, silver, platinum, and palladium) between copper matte and three different silica-saturated slags (pure FeOx-SiO2, FeOx-SiO2-Al2O3, and FeOx-SiO2-Al2O3-CaO slag) were investigated at 1300 °C in controlled flowing CO-CO2-SO2-Ar gas atmosphere by a high-temperature isothermal equilibration technique. The phase compositions were analyzed by Electron Probe X-ray Microanalysis and Laser Ablation-High Resolution Inductively Coupled Plasma-Mass Spectrometry. It was shown that the distribution coefficients of gold, platinum, and palladium between matte and slag (Lm/s(Me) = [Me]in matte/(Me)in slag) were very high and increased with increasing matte grade. The distributions to the matte phase were increased by adding basic oxides alumina and lime into the acidic silicate slags. The experimentally measured distribution coefficients Lm/s(Me) followed the order of platinum > palladium > gold > silver. The present experimental results can be used for upgrading thermodynamic databases for the complex recycling processes through nonferrous smelting.

Behavior of Dual-Phase (MnO-SiO 2 -Al 2 O 3 ) + (SiO 2 ) Inclusions in Saw Wire Steels During Hot Rolling and Cold Drawing

Abstract: 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.

Refinement of the Solidification Structure of Austenitic Fe-Mn-C-Al TWIP Steel

Abstract: The solidification structure of austenitic Fe-22Mn-0.6C-1.6Al TWIP steel with and without Ce inoculation is compared on the macro- and microscale. The expansion of the equiaxed zone, decrease of equiaxed dendrite size and thinning of the dendrite arm are observed in Ce-inoculated TWIP steel. The refining mechanism for the expanded equiaxed zone and the decreased equiaxed dendrite size is the Ce2O3 particles acting as the heterogeneous nucleation sites. With increasing Ce content, the effective density of Ce2O3 particles of around 1 μm size increases initially and then decreases, while the total density always increases. The average diameter of Ce2O3 particles in TWIP steel increases as the amount of Ce increases. The mechanism for the thinning of the secondary dendrite arm is mainly by the solute effect, including the increase in both the undercooling in front of the dendrite tip and the drag effect on solid-liquid interface migration. In addition, the correspondence between the dendrite and grain in Fe-Mn-C-Al TWIP steel under as-cast condition is revealed. It is observed that the primary dendrite interface completely matches the austenite grain boundary. The crystallographic relationship follows 〈100〉d//〈100〉g and {100}d//{100}g (d and g represent the dendrite and grain, respectively) in both the columnar and equiaxed zones. The refinement of the equiaxed austenite grain in Fe-Mn-C-Al TWIP steel is purely the result of dendrite refining during solidification.

Impact of the Electromagnetic Brake Position on the Flow Structure in a Slab Continuous Casting Mold: An Experimental Parameter Study

Abstract: Flow measurements are performed in a slab model for continuous casting of steel under the influence of a ruler type Electromagnetic Brake (EMBr). The Mini-LIMMCAST facility utilizes the low melting GaInSn alloy for flow modeling. Two-dimensional velocity distributions in the center plane of the rectangular mold with a cross section of $$300 \times 35\,\hbox {mm}^{2}$$ are determined by means of the ultrasound Doppler velocimetry. This study especially focuses on the influence of the vertical position of the EMBr and its magnetic flux density as well as the effect of different immersion depths of the submerged entry nozzle. The horizontal flow velocity just below the free surface can effectively be reduced by choosing an optimal position of the EMBr, while an improper positioning even increases the near-surface velocity compared to the case without activated brake. A general braking effect of the EMBr on the submerged jet is not observed. The decisive mechanism for controlling the near-surface flow results from a modification of the jet geometry and a reorganization of the flow field. In terms of an effective flow control an appropriate positioning of the EMBr has at least the same significance as the regulation of the magnetic field strength.

Cathodoluminescence Analysis of Nonmetallic Inclusions in Steel Deoxidized and Desulfurized by Rare-Earth Metals (La, Ce, Nd)

Abstract: The injection of misch metal, which primarily consists of La, Ce, and Nd, into molten steel can reduce the size of nonmetallic inclusions, suppress the formation of harmful nonmetallic inclusions, and reduce the content of oxygen and sulfur in steel. To investigate the impact of misch metal on these effects, we propose a method for identifying inclusions in steel that has been deoxidized and desulfurized by misch metal using cathodoluminescence (CL) analysis within 1 minute. Based on the CL images and spectra of model steel samples that were deoxidized and desulfurized by La, Ce, or Nd metal, we demonstrate that La2O3, La2O2S, CeO2, Ce2O2S, Nd2O3, and Nd2O2S inclusions can be identified by the emitted luminescence color using cameras with sensitivity ranges of 420 to 680 and 350 to 1000 nm. La2O3, La2O2S, CeO2, Ce2O2S, Nd2O3, and Nd2O2S inclusions emitted blue-green, yellow-orange, yellow-orange, violet, blue-violet, and red luminescence, respectively when observed by a camera with a sensitivity range of 420 to 680 nm. CeO2 and Nd2O3 inclusions emitted red-orange and red-violet luminescence, respectively when observed by a camera with a sensitivity range of 350 to 1000 nm.

Model for Inclusion Precipitation Kinetics During Solidification of Steel Applications in MnS and TiN Inclusions

Abstract: A simulation model for inclusion precipitation kinetics during solidification of steel was proposed in this work. With the aim to calculate the inclusion size distribution during solidification of steel, the microsegregation calculation combined with the Kampmann–Wagner numerical (KWN) model for nucleation and growth of inclusion was incorporated into the present simulation model for calculating the evolution of inclusion size distribution during solidification of steel. The inclusion agglomeration due to Brownian collisions was also taken into account. The present simulation model was first applied in simulating precipitation of MnS during steel solidification and validated by the experimental data available in the literature. The effects of cooling rates and sulfur concentrations on the precipitation of MnS were investigated by the model calculations. Then, the present simulation model was applied in simulating the precipitation of TiN inclusions during steel solidification. The calculated mean size was found to be in good agreement with data available in the literature. Finally, the model was employed for studying the effects of interfacial tension between TiN and steel due to sulfur concentration change and cooling rates on the inclusion precipitation kinetics. It was found that interfacial tension between TiN and steel has a crucial influence on the precipitation of TiN. With an increase of the cooling rate, the size distribution of TiN transforms from the lognormal distribution to the bimodal distribution.

Effect of Electromagnetic Stirrer Position on Mold Metallurgical Behavior in a Continuously Cast Bloom

Abstract: The multiphase flow, initial solidification and solute diffusion and their interactions in a mold region of 380 × 280 mm2 casting bloom under different installation positions of in-mold electromagnetic stirring (M-EMS) were analyzed and compared by a multi-physical model. The results showed that the simulated electromagnetic field and solute carbon distribution in initial solidified shell are basically consistent with measurements. As the distance from EMS center to the meniscus increases (from 0.32 to 0.62 m), the level fluctuation decrease from 7.2 to 4.5 mm, while the volume of turbulent zone clearly expands. Additionally, the solidified shell thickness at the mold outlets increase from 12.90 to 16.32 mm and from 26.41 to 28.97 mm at outlets of computational domain as EMS center moves down, while the surface temperature decreases. The maximum negative segregation deteriorates from 0.95 to 0.83 at the bloom corner while increasing from 0.84 to 0.92 in the thickness direction, and the difference between the minimum and maximum carbon concentrations at center of computational outlets is only about 0.0029 pct. The EMS should be installed around 0.42 m below the meniscus, by which the disqualified rate of non-metallic inclusions and the level fluctuations are within a low level.

Fluidity of Alloys Under High-Pressure Die Casting Conditions: Flow-Choking Mechanisms

Abstract: Theories on fluidity of alloys based on the solidification mode are not satisfactory in describing fluidity of alloys under high-pressure die casting (HPDC) conditions. To understand the flow-choking mechanisms under HPDC conditions, microstructure in the fluidity test coupons made using a 125-ton HPDC machine was characterized. Pre-solidified dendrites (PSDs), or externally solidified crystals (ESCs), which were formed in the shot sleeve, were found in the runners as well as in the fluidity casting. Surprisingly, a large amount of PSDs are collected in the runner adjacent to the in-gate, forming a PSD core with a thin layer of PSD-less or PSD-free region near the surfaces of the runner due to Magnus effect. Analytical calculations were performed to estimate the pressure drop for molten aluminum flowing through the mushy PSD zone. The results indicate that the pressure drop is comparable to the maximum pressure that was used for injecting molten metal to fill the casting. When the pressure drop is equal to the pressure driving the mold filling, the metal ceases to flow. Thus, it is the PSDs that are responsible for the choking of mold filling either mechanically at the in-gate or providing a pressure drop high enough to resistant fluid flow.

A Review of Steel Processing Considerations for Oxide Cleanliness

Abstract: Control of non-metallic inclusions is essential for the production of high-quality steel. This review summarizes processes that change inclusion compositions and concentrations during secondary steelmaking—slower changes are limited by reaction between bulk steel and slag or refractory, and faster changes involve direct additions to the steel bath. An example of the former is conversion of alumina inclusions to spinels during ladle treatment, while reoxidation and calcium treatment are typical exemplars of the fast changes. For the slower changes, inclusions approach equilibrium with the liquid steel and conceptually simple kinetic models correctly describe inclusion evolution during ladle treatment. Disequilibrium from faster changes persists for several minutes under typical ladle conditions, with small-scale inhomogeneity in the steel. Fast scanning electron microscopy with microanalysis has facilitated detailed study of these inclusion evolution processes by providing information on inclusion composition, size, and shape. Machine learning methods are likely to be increasingly important in analysis of the results. Such methods have already shown promise to improve classification of inclusions and recognizing inclusion clusters, from analyses of polished sections. Several unresolved issues that require future study are noted.

Effect of Slag Composition on the Deoxidation and Desulfurization of Inconel 718 Superalloy by ESR Type Slag Without Deoxidizer Addition

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.

Reduction Kinetics of Oxidized New Zealand Ironsand Pellets in H2 at Temperatures up to 1443 K

Abstract: Direct reduction of iron ore pellets using hydrogen gas has the potential to significantly reduce CO2 emissions from the ironmaking process. In this work, green pellets of titanomagnetite ironsand from New Zealand were oxidatively sintered to form titanohematite. These sintered pellets were then reduced by H2 gas at temperatures ≥ 1043 K, and a maximum reduction degree of ~ 97 pct was achieved. Fully reduced pellets contained metallic Fe as the main product phase, but several different (Fe, Ti) oxides were also present as minor inclusions. The phase distribution of these oxides depended on the reduction temperature. With increasing temperature, the relative proportion of pseudobrookite in the final product increased, while the proportion of residual ilmenite and rutile decreased. The reduction kinetics were found to be well described by a pellet-scale single-interface shrinking core model, for reduction degrees up to 90 pct. At temperatures above 1143 K, the rate-limiting step was found to be solely an interfacial chemical reaction process, with a calculated apparent activation energy of 31.3 kJ/mol. For pellet sizes from 5.5 to 8.5 mm, the reaction rate was observed to increase linearly with decreasing pellet diameter, and this linear correlation extrapolated to intercept the axis at a pellet diameter of 2.5 mm. This is interpreted as the minimum length required for a shrinking core interface to develop within the pellet.

Numerical Study of the Influence of Burden Batch Weight on Blast Furnace Performance

Abstract: Burden batch weight is a critical operating parameter in the blast furnace (BF) system. It directly affects solid distribution such as coke-layer and ore-layer thickness and thus gas permeability and thermal–chemical conditions inside a BF. However, in the open literature, few quantitative studies have been reported on the influence of burden batch weight on BF performance, such as cohesive zone (CZ) shape and location, reducing gas evolution, and iron oxide reduction behaviors. In this study, a multi-fluid BF model is used to investigate the BF performance with different burden batch weights systematically. This model features the layered burden structure with respective chemical reactions in respective coke and ore layers and a burden batch weight sub-model. The results show that, under the given simulation conditions, with the increased burden batch weight from 112 to 140 tons, the average gas velocity in central regions is significantly suppressed by ~ 1 m/s; the average gas and solid temperatures are decreased by ~ 160 K and the position of CZ decreased by ~ 7 m near the BF center; moreover, the gas utilization efficiency is improved by ~ 2.5 pct; the reduction load of the BF becomes heavier, particularly by ~ 0.05 near the BF center; the fuel rate is decreased by ~ 2.5 kg/thm, meaning a higher furnace efficiency. This study provides theoretical support for batch weight selection and optimization in BF ironmaking practice.

Calcium Modification of Inclusions via Slag/Metal Reactions

Abstract: This paper examines the consistency between experiments and thermodynamic predictions of the modification of non-metallic inclusions by dissolved Ca in liquid Fe-Al alloys. Current thermodynamic predictions made with FactSage (version 7.2) were found to overestimate the amount of dissolved Ca and the Ca in non-metallic inclusions. This was demonstrated in two ways. First, Al-deoxidized Fe was held in CaO-3 pct ZrO2 crucibles for 100-136 minutes at 1873 K (1600 °C) and then reoxidized to precipitate dissolved Ca as oxide inclusions. The amount of Ca in the inclusions after reoxidation was quantified and considered equal to the dissolved Ca in the liquid Fe prior to reoxidation. Although experimental data were limited, the results suggested that the dissolved Ca was low and that the thermodynamic behavior of Ca could be best described by excluding Ca-O interaction. The assumption of no Ca-O interaction was compared with the associate solution model employed in FactSage by simulating the evolution of inclusion compositions in Fe—2, 1, 0.5, 0.1 wt pct Al alloys exposed to CaO (sat.)-MgO (sat.)-Al2O3 slags. The assumption of no Ca-O interaction led to predictions that were much closer to experimental results. More work is needed to ensure dissolved Ca behavior is accurately described and to ensure the sources for Ca modification of inclusions in industrial samples are properly identified.

Modeling the Effect of Combined Electromagnetic Stirring Modes on Macrosegregation in Continuous Casting Blooms

Abstract: Macrosegregation is one of the most frequently observed defects in continuous casting blooms, which causes nonconformity in ultrasonic flaw detection of rolled products. To investigate the influence of combined EMS modes (M-EMS + F-EMS) on macrosegregation, a 3D multiphase solidification model based on the volume-averaged Eulerian approach was established to simulate the electromagnetic field, fluid flow, microstructural evolution, and solute transport of heavy-rail steel blooms subjected to different EMS processes. In this model, a hybrid model of the mushy zone and a back-diffusion model were introduced into the momentum and solute conservation equations to realize the calculation of microstructural evolution and solute transport with electromagnetic stirring. The predicted magnetic induction intensity, macrostructure, and macrosegregation were verified with Tesla meter measurements, etched macrostructure analysis, and infrared carbon-sulfur analysis. The calculation results showed that M-EMS had little effect on the improvement of the positive centerline segregation, whereas F-EMS effectively reduced the positive centerline segregation. Moreover, a combination of these EMS modes could further reduce the positive centerline segregation in continuous casting blooms. The change in solute concentration caused by M-EMS could be inherited by the position of F-EMS, which could enhance the metallurgical effects of F-EMS. These results were also verified through an industrial application.