Materials Processing Fundamentals 2019

Most submerged arc furnaces used for the production of ferroalloys run on three-phase alternating current. This affects the electrical operation of the furnace and thus it is of interest to study alternating current distributions in the system. This work presents computations of alternating electric current distributions inside an industrial submerged arc furnace for silicon production. A 3D model has been developed in ANSYS Maxwell using the eddy current solver. In each phase, electrode, central arc, crater, crater wall and side arcs that connect electrode and crater wall are taken into account. In this paper, the dynamic current distributions in different parts of the furnace, as well as skin and proximity effects in and between electrodes are presented. Moreover, active and reactive power distributions in various components of the furnace are quantified.

In the current study, a three-dimensional mold model was established by Fluent software to investigate the fluid flow of three phases (steel–slag–air) in the mold. A quarter of the mold was simulated through the k-ε model, volume of fluid (VOF) model, solidification model and continuum surface force (CFS) method. The interfacial tension between liquid steel and liquid slag and the oscillation of the mold were added into the model to show the 3D steel–slag interface. The liquid steel exiting from the submerged entry nozzle (SEN) existed as the upper backflow and lower backflow, and flowed towards the wide face and the SEN. The largest speed on the steel–slag interface was located at approximately 0.25 m from the narrow face, which was approximately 0.15 m/s. Under the influence of the upper backflow and the movement of the shell, the slag on the steel–slag interface moved from the narrow face to the SEN, and infiltrated into the gap, which affected the lubrication in the gap.

Mold level fluctuations caused by unsteady bulging of the solidifying shell affect the quality of the steel and stable operation of the continuous steel casting process. A dynamic bulging model, which captures the behavior of the 2-D longitudinal domain through interpolation of multiple 1-D moving slices, is used to calculate the transient bulging profile, volume changes caused by unsteady bulging, and the accompanying level fluctuations in the mold. The liquid steel flow rate through the SEN into the tundish is calculated with a stopper-position-based model. These two models are combined to investigate mold level fluctuations in a thin-slab caster under real casting conditions. The model is verified by comparing the simulation results with transient measurements in a commercial thin-slab caster.

The stability of flow field in the mold has a great effect on the quality of the final continuous casting product. In the current study, the multiphase flow in a slab continuous casting strand was systematically studied using a full scale numerical simulation via Euler–Euler approach, and the effect of the operational parameters including casting speed, gas flow rate, and the submergence depth of the submerged entry nozzle (SEN) was investigated. The study showed that the lower casting speed tended to generate more single roll flow in the strand. With the decrease in the gas flow rate, the flow pattern was evolved from a single roll to a complex flow and then to a double roll. For a fixed gas flow rate and a fixed casting speed, the deeper submergence depth generated more double roll pattern in the strand.

The global flow pattern of liquid metal in the slab mold of a continuous caster is difficult to control, as it cannot be measured in real-time by conventional methods. Contactless inductive flow tomography (CIFT) can easily provide real-time information about the flow structure (double or single roll) and the angle of the jet coming out of the submerged entry nozzle (SEN) just from the raw sensor data. Furthermore, by solving the underlying linear inverse problem, the full velocity field can be reconstructed. This paper discusses the possibility of applying CIFT for flow pattern recognition in continuous casting, which is then used for setting an electromagnetic brake in order to control the angle of the fluid jet. The control loop will be implemented and developed for the Mini-LIMMCAST model of a continuous caster at Helmholtz-Zentrum Dresden-Rossendorf (HZDR).

Ultrahigh casting speed is an important tendency to improve the efficiency of continuous casting. A three-dimensional mathematical model and a hydraulic physical model on the billet mold with 160 × 160 mm cross section were established to investigate the flow behavior of molten steel with different SEN conditions and optimize the parameters of SEN at the casting speed of 6.0 m/min. Results indicate that when the immersion depth and the inner diameter of the SEN are 180 and 50 mm, respectively, the flow field and the surface velocity distribution in the mold are the most appropriate that the penetration depth of the stream is about 700 mm and the maximum surface velocity is 0.05 m/s. With the optimum parameters of SEN, the slag covers uniformly and keeps appropriately active, and no slag entrainment happens. Moreover, the differences are very slight between the results of the numerical and physical simulation, which can verify each other.

This contribution proposes a new alloy in which a small volume fraction of austenite particles is used to pin ferrite grain growth at high temperatures. During the reheating process, when the temperature is higher than 1200 ℃, the coarsening of austenite particles is driven by volume-diffusion-controlled behaviour and ferrite grain growth is dominated by the pinning effect of austenite particles. At low temperature (<1280 ℃), grain growth occurred at a rate which is proportional to the particle coarsening rate; while at high temperature (>1280 ℃), grain growth is much lower than that expected without pinning. During the solidification process, austenite particles nucleate along ferrite grain boundaries and retard grain growth. Grain growth can be completely arrested with more austenite particle precipitates. This new alloy can be applied to control grain coarsening in the thin slab casting direct rolling process, grain size control in the HAZ of welds and grain growth resistance at high temperature.

One of the most common surface defects in sand casting of grey cast iron is caused by metal penetration into the sand mould. Metal penetration is a surface condition in which metal or metal oxides have filled the voids between sand grains to various depth without displacing them, thus yielding a phase of sand grains surrounded by metal and frequently by mould–metal reaction products. The penetration is often so severe that casting components are beyond the point of economical rework and must be scrapped. This experimental work has focused on reducing metal penetration on casting component on a production scale. The casting component produced has strongly affected by sand sintering metal penetration. A series of simulations were performed with the casting simulation program MagmaSoft^® in order to investigate the solidification characteristics as well as the porosity formation in the casting component.

In this comparative study, the carbides of TBM cutter ring steel at different tempering temperatures of 530 and 560 °C, were studied using ASPEX inclusion automatic analyzer and EPMA, respectively. The results show that the number of carbides increased by about 180% at the tempering temperature of 530 °C. The inclusions of test steels were characterized through the carbides and carbides with the core of Al₂O₃. The thermodynamics results indicate that Al₂O₃ inclusions were generated in the liquid phase, and carbides started to form in the solid–liquid two-phase region. Al₂O₃ inclusion promoted the formation of carbides through serving as preferred nucleation sites. A lower temperature in the solid phase increases the difference value of actual solubility product and equilibrium solubility product, thus it is beneficial to the formation of carbide. The thermodynamic calculations are in accordance with the experimental results.

By means of the anhydrous solution electrolysis, large inclusions in crankshaft steel samples are non-destructively extracted. Through optical microscopy and scanning electron microscopy, the three-dimensional morphology, composition, size distribution and quantity density of the large inclusions in the refining, teeming and steel ingot were revealed. The size of the inclusions obtained is 50–200 μm. The results showed that the main components of inclusions in ladle furnace (LF) sample, the heated billet and the rolled products were Al₂O₃ and SiO₂. After LF and Ruhrstahl Hereaeus (RH) refining, the main components were Al₂O₃, SiO₂, CaO, and a small amount of MgO. It is found that the secondary oxidation during the pouring process is the main source for large inclusions. The shapes are mostly irregular blocks. There are more inclusions at the top of rolled products, and more inclusions in head and less inclusions in tails. During the pouring process, the molten steel in the ingot mold circulates, and the molten steel near the wall of the ingot mold flows downward and entangled in the protective slag, then captured by the solidified shell near the wall of the ingot mold, which is also the reason why large inclusions are distributed on the surface layer.

The double cold reduction (DCR) process of ultra-thin plate rolling, which is seldom based on the model calculation is generally carried out by manual input rolling instruction parameters. The L2 process control model plays an important role in any process control system. In this paper, the DCR process control of continuous annealing is taken as the study object, and the control principle and function of each control module in L2 control models are studied, and the significance of L2 model to process control and technology application is analyzed. Some suggestions for the improvement of the control model application are proposed, which can provide effective guidance for the high automatic control of the double cold reduction of the ultra-thin strip steel.

The double cold reduction (DCR) process of tin plate has the characteristics of thin entry thickness and small reduction compared with conventional cold rolling. In this case, the hypothesis of circular roll profile is no longer reasonable, and non-circular arc theory is adopted to ensure the rolling model accuracy. In this paper, the rolling model is carried out using non-circular arc theory, based on the actual process data of tin plate rolling. The effects of thickness, reduction ratio, tensile stress, entry temperature of strip, and work-roll radius on the roll force were studied, which described the various trends and changes of the roll force with strip thickness, tensile stress, roll radius and other technological parameters under different simulation conditions. The research results provide an effective guidance for developing rolling strategy of tin plate DCR process.

Laser metal deposition technique was used for the fabrication of Ti–Al–Cu coating on Ti–6Al–4V Alloy. The microstructure and elemental and phase composition of coatings were studied. The SEM images showed the homogeneous distribution of Cu addition in Ti–10Al–9Cu at scanning speed of 1.0 m/min. Strong metallurgical bond without pores and cracks were observed between the coating and the substrate. Grain refinement was observed within the microstructure as the grains grew in a columnar and dendritic pattern in a counter direction to heat flow. However, the cross-section microstructures of Ti–10Al–6Cu and Ti–10Al–3Cu at 0.8 and 1.0 m/min scanning speed and laser power of 1000 and 1100 W showed minute pores and cracks. The existence of amorphous phase revealed via XRD was also observed in the coatings. The microstructure of these alloys is highly influenced by processes involving plastic deformation and thermal treatments which, in effect, determines the mechanical properties adhering to desired properties. The microhardness testing results indicated that the fabricated coatings had enhanced by 61.9% as compared to the micro-hardness of the Ti–6Al–4V alloy substrate.

Mechanical properties of ultrafine grained 5052 Al alloy processed through multi-directional forging were investigated in the present work. The as-received 5052 Al alloy was solution-treated (ST) at temperature 540 ℃ for two hours and subjected to multi axial forging at room temperature as well as liquid N₂ temperature to a cumulative true strain of 4.2. The cryo-forged samples have exhibited a significant improvement in strength (380 MPa) and hardness (130 Hv) with 7.1% ductility, as compared to other conditions. Similarly, the high-cycle fatigue behaviour of the cryo-forged samples is found to be 80 MPa, which is better than other conditions. It was due to the formation of ultrafine grained microstructure with an average grain size of 230 nm in the cryo-forged samples. The formation of nanoshear bands in the cryo-forged samples, which accommodates the applied strain during cyclic loading is also responsible for dislocation accumulation along with broken/deformed impurity phase particles. The microstructure of the samples was characterized by optical microscopy, X-ray diffraction, and TEM to substantiate the mechanisms of grain refinement and its influence on the mechanical properties. Fractography of the tensile, as well as fatigue, tested samples were carried out using a Scanning Electron Microscope (SEM) to reveal the type of fracture.

Cu–15%Ni–8%Sn alloy was prepared by continuous unidirectional solidification (CUS) processing and the as-cast CUS Cu–15%Ni–8%Sn alloy was homogenized. The evolution of microstructure and composition distribution of as-cast and annealed CUS Cu–15%Ni–8%Sn alloy was analyzed. The results show that the microstructure of as-cast CUS Cu–15%Ni–8%Sn is mainly composed of coarse columnar grains and there exist segregation phenomenon in the grain boundaries. After annealing at temperature of 850°C for 30 min, it was found that the composition of the alloy began to become uniform and the solutes gathered at the grain boundaries diffused into the columnar grains.

Electromagnetic levitation experiments provide a powerful tool that allows for the study of homogeneous nucleation, solidification and growth in a containerless processing environment. However, in these experiments it is important to understand the magnetohydrodynamic flow within the sample and the effects that this fluid flow has on the experiment. A recent solidification study found that aluminum-nickel alloy samples have an unusual growth response to the degree of undercooling. These aluminum-nickel alloys experienced a decrease in the growth velocity as the initial undercooling deepened instead of the expected increase in solidification velocity with deepening undercoolings. Current work is exploring several different theories to explain this phenomenon. Distinguishing between several of these theories requires a comprehensive understanding of the behavior of the internal fluid flow. USTIP has done flow modeling to support this and multiple other collaborators on ISS-EML. The fluid flow models presented provide critical insights into the nature of the flow within the aluminum-nickel alloy experiments conducted in the ISS-EML facility. These models have found that for this sample the RNG k-ε model should be used with this sample at temperatures greater than 1800 K and the laminar flow model should be used at temperatures lower than 1600 K.

A new technology suggests breaking oxide films into small fragments or particles to play the role of a grain refiner. A high-shear mixer (HSM) with a rotor-stator impeller can produce mechanical breakage. Physical modelling with powders demonstrates the defragmentation potency of HSM. Optimisation methods are considered and a new design of HSM is proposed according to the experimental findings. This design improves the uniformity of mixing in the pseudo-cavern volume and exhibits the dispersion efficiency better than the design previously used. The understanding and development of high shear technology for processing of liquid metals is of great interest to the industry.

A molten LiCl-KCl (40.8:59.2, mol%) eutectic salt was used as an electrolyte due to its relatively low melting point. The molar ratio of fluoride ions and titanium ([F⁻]/[Tiⁿ⁺] ratio) was employed as a parameter to illustrate the influence of fluoride anions on the electrochemical behaviors of Ti(III), and KF was used as a source of fluoride ions. A study on the electrochemical properties of Ti(III) was carried out in molten LiCl-KCl-KF. Results suggest that there are two steps for reducing Ti(III) in molten LiCl-KCl: Ti(III) → Ti(II) and Ti(II) → Ti. Ti(III) can be reduced directly to Ti in one step when KF was added in the melt in increasing amount. Metallic titanium was produced when [F⁻]/[Tiⁿ⁺] equals to 10, and it is dendrites with a layer structure. The oxygen contents in the titanium crystal are 1200 ppm.

Metallurgical slag of laterite nickel ore contains valuable Al and Si that can be recycled by alkali roasting and water leaching process. The leaching solution was further treated to make zeolite materials as a high-value-added by-product. In this work, the contents of silicon and aluminum in the filtered liquor after water leaching was determined by ICP, and the solid residue was characterized by the laser particle-size distribution analyzer and SEM. The results showed that the contents of Al and Si in the filtered liquor increased by 44 and 65%, respectively, by using ultrasound; and the leaching residue was even more fine and uniform, and its grain size was reduced from 100 to 10 μm. This demonstrates that ultrasound can enhance the leaching efficiency of Al and Si for better recycling of the valuable metals and improving the quality of zeolite materials.

Phase equilibria in the ZnS–Ag₂GeS₃–Ge–GeS₂ part of the Ag–Zn–Ge–S system were investigated using differential thermal analysis, X-ray diffraction, and EMF methods. The data was used to model Ag₂GeS₃–ZnS polythermal section. Further, the mechanism of formation and thermal stability of the Ag₂ZnGeS₄ compound were established. The results suggest the presence of another quaternary phase Ag₄ZnGe₂S₇ in the temperature range of 695–853 K. The determined phase relations were used to express the chemical reactions. Based on the electromotive force versus temperature measurements, experimental thermodynamic data of the Ag₂ZnGeS₄ quaternary phase were derived for the first time. The calculated Gibbs energy, enthalpy and entropy values of the Ag₂ZnGeS₄ compound in both phase regions are consistent, which indicates that Ag₂ZnGeS₄ has stoichiometric composition.

Several recent studies have shown the potential of oxy-fuel combustion to reduce NO_x(gas) and SO₂(gas) emissions. However, the mechanisms through which SO₂(gas) reduction takes place has yet to be fully understood. Therefore, the development of oxy-sulfate thermodynamic database for a better understanding and control of SO₂(gas) emission during oxy-fuel combustion processes is essential. The focus of this research is on the thermodynamic modelling of the iron oxide–sulfate system with the FactSage 7.2 software package. Thermodynamic properties of selected phases in the FeO_x–FeSO₄–Fe₂(SO₄)₃ system were critically reviewed, compiled and assessed over a wide temperature range (298–2000 K) to obtain accurate thermodynamic description of the system at different temperatures. New C_p functions, which include the recent experimental data, were optimized. The obtained results are presented and discussed.

The effect of heat treatment to FePt/Fe₂O₃ and FePt/Cu magnetic performance was examined in this paper. To obtain desired phase transformations for high magnetic storage media, a self-assembled layer of FePt nanoparticles was placed between two layers of Fe₂O₃ nanoparticles using surfactants on Si and Cu substrates to minimize aggregation during heat treatment. To eliminate the surfactant, a sample made by simply mixing FePt and Cu nanoparticles in hexane was deposited on a Cu substrate. Vacuum furnace annealing at 600 °C (1 h) or laser heat treatment at 20, 40, 80 W at a speed of 1–1.5 m/s were carried out on the samples. The coercivity of FePt/Fe₂O₃-layered samples increased from 148 Oe to 366 Oe and 246 Oe for furnace annealed samples on Si and Cu substrates, respectively; while, it remained almost unchanged in laser heat-treated samples on Cu substrate and slightly higher magnetization at 40 W compared to 20 W laser heat treatment of samples on Si substrate. The FePt/Cu nanoparticles mixer layer on Cu substrate was subjected to laser heat treatment at 40 and 80 W. The coercivity at both laser powers did not show any significant change. During the 80 W laser heat treatment, most of the particles escaped from the surface indicating a high temperature process. The results indicate that the furnace annealing at 600 °C brings the desired magnetic phase transformation in all cases, while the laser heat treatment even at high power does not bring the phase transformation due to very short time period for processing.

Evaporation of perovskite was studied by high-temperature Knudsen effusion mass spectrometric method at 1700–2200 K. Vapor species typical for simple oxides and a small amount of CaTiO₃ complex gaseous oxide were identified in the gas phase over perovskite. For the first time, the partial pressure of vapor species in the gas phase over perovskite are compared with those corresponding to simple oxides, showing the predominant effect of the calcium component of perovskite on evaporation character.

Electrolytic production of copper powders is a process with a high power consumption. This study establishes a power consumption model for copper powder electrolysis using the response surface methodology (RSM) under laboratory conditions, which provides the basis for reducing power consumption. First, seven process parameters were screened out using the Plackett–Burman design (PBD) experiments. The results show that the factors that have a significant effect on the power consumption of copper powder electrolysis are electrolyte temperature, Cu²⁺ concentration, H₂SO₄ concentration, inter-electrode spacing, and current density. A quadratic mathematical model of significant factors and power consumption was then developed using the Box–Behnken design (BBD) of RSM. Finally, the model was used to optimize the most energy-efficient process conditions. In addition, scanning electron microscopy (SEM) analysis indicates that the morphologies of electrolytic copper powders deposited under the optimized conditions generally have dendritic structure and the agglomerated copper particles are almost globular.

Magnesium alloy AM60 matrix-based composite reinforced with 35 vol. % of Al₂O₃ fibers were fabricated by preform infiltration and squeeze casting technique under an applied pressure of 90 MPa. For the purpose of comparison, the matrix alloy without reinforcement was also squeeze cast under the same process conditions. Examination of microstructures by both optical microscopy (OM) and scanning electron microscopy (SEM) revealed that alumina fibers were distributed uniformly in the preform. The mechanical properties of the composite were evaluated in comparison with those of the matrix alloy AM60. The Rockwell hardness (HRB) hardness increased from 5.12 to 84.94 as the fiber volume fraction rose from 0 to 35%. The results of tensile testing indicated that the addition of Al₂O₃ fibres to magnesium alloy AM60 led to a significant improvement in mechanical properties. In particular, the modulus of the composite increased to116 GPA by almost three times over that (40 GPa) of the alloy, while the ultimate tensile strength (UTS) rose from 171.36 to 202.56 MPa by 18%. However, the notable increase in both the modulus and strength was at sacrifice in elongation.