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A funnel-type mold is commonly used to provide necessary clearance for the submerged entry nozzle in the thin slab casting (TSC). The partially solidified shell is subjected to the mechanical deformations, which can lead to the defects formation and, as a results, to a breakout. Traditionally, the results of the flow simulation, performed by the finite volume method (FVM), are fed to the external package for the finite element analysis of stress and strain. A coupled model was assembled using “creeping solid” approach by blending the Norton-Hoff viscoplastic stress for the solidifying shell with the Newtonian viscous stress of the liquid melt. The FVM was used to combine both liquid and solid stress models within a single solver. The iterative procedure based on the improved both side diffusion method was introduced to treat the nonlinear relation between the viscoplastic stress and the strain rate. The modeled shell thickness was verified by previously published breakout measurements and the simulation results. Temperature distribution, obtained during the TSC simulation, dominantly corresponds to the viscoplastic range. Developed numerical approach is robust and has direct industrial application.

[Display omitted] • Modified layers on composite arc cathodes are formed by material intermixing in liquid state. • Rapid solidification leads to the formation of metastable phases also including quasicrystals. • Average cooling rate estimated to 106 K/s during solidification of the modified layer. • Droplet redeposition contributes to material intermixing over larger distances. • Powder grain size in composite arc cathodes influences microstructure and phase composition. A combination of both conventional and advanced high-resolution characterization techniques was applied to study the modified layers on the surface of three composite Al-Cr arc cathodes with identical nominal composition of Al-50 at.% Cr but varying powder grain sizes. The results revealed that the modified layers consist mainly of metastable phases such as Cr solid solution, high temperature cubic Al 8 Cr 5 , supersaturated Al solid solution, and icosahedral quasicrystal. The metastable phase formation indicates that high cooling rates were involved during the solidification of molten material produced in the arc craters during cathode spot events. The average cooling rate was estimated to be 106 K/s based on secondary dendrite arm spacing measurements and supporting phase-field based simulations. The formation mechanisms of the modified layers are discussed based on the obtained results and the current literature. [ABSTRACT FROM AUTHOR]

A unidirectional solidification experiment of hypoeutectic Al-7.0 wt% Si alloy against gravity direction in a cylindrical mold with cross-sectional change was made, and the macrosegregation in different parts of the as-solidified sample was investigated (Ghods et al. in J Cryst Growth 441:107–116, 2016; J Cryst Growth 449:134–147, 2016). The current study is to use a two-phase columnar solidification model to analyze the segregation mechanisms as used in this experiment. Following flow phenomena and their contributions to the formation of macrosegregation are simulated and compared: (1) solidification shrinkage-induced feeding flow; (2) thermo-solutal convection; and (3) combined thermo-solutal convection and shrinkage-induced feeding flow. The shrinkage-induced feeding flow leads to an inverse (positive) segregation in the bottom part, and a severe negative segregation in the part below cross-sectional change. Thermo-solutal buoyancy leads to a so-called steepling convection in the main part of the sample (away from the bottom and cross-sectional change), and this kind of flow leads to a positive macrosegregation near the sample surface. The calculations have successfully explained the experimental result of macrosegregation.

During twin-roll casting, an alloy melt is passing the gap between two counter-rotating rolls, where cooling and solidification leads to the continuous formation of a solid strand. In order to describe this process, a two-phase Eulerian–Eulerian volume-averaging model is presented that accounts for (1) transport and growth of spherical grains within a flowing melt, (2) the formation of a coherent solid network above a specific solid fraction and (3) the viscoplastic flow of the solid network with the interstitial melt during casting and compression. For the considered case of an inoculated Al–4wt%Cu alloy, the process conditions are chosen such that two relatively thick viscoplastic semi-solid shells meet between the rolls, and thus, the material is pressed together and squeezed against the casting direction. The squeezed out material consists of segregated melt and some solid that quickly disappears after melting. It is observed during this study that macrosegregation distributions are inherently connected to the mush deformation that is enforced during the hot rolling process.

Ammonium chloride is commonly used as a buffer solution to control pH levels in a wide variety of chemical and medical applications and is also used as a fertilizer because it acts as a sufficient source of nitrogen for the soil. More recently it is used to create an experimental benchmark, useful to model/simulate metal solidification. In electronics and metallurgy it is also used for cleaning, to prevent the formation of oxides during welding or smelting of metals. In the literature different values are available for the thermo-physical parameters and in the current paper an overview of measured or calculated values of the most important properties is presented. For an ammonium chloride–water solution different phase diagrams are accessible, and the calculation of the liquidus and solidus line is completed. A comparison of calculated heat capacity values for ammonium chloride is made with the literature values. Measured data for the ammonium chloride density are available in the literature, and the values for different temperatures and concentrations are presented here. Thermal conductivity values are gathered in the present work. The viscosity can be estimated in between 283 and 333 K and for mass fraction up to 0.324 kg·kg–1, with a model for the calculation of the aqueous solutions viscosity, based on the viscosity of solute and water. The variation curve of diffusivity values with the concentration, exists only for 293 and 298 K. For this reason an approximation with NH3diffusivity values, which are measured for different temperatures and concentrations, can be recommended. Additional analysis of two experimental measurements, performed in order to estimate the ammonium chloride diffusivity in water and further extract the Gibbs–Thomson coefficient, is done.

Macrosegregation originates from the solute partitioning at the liquid-solid interface and the relative motion between liquid and solid phases during solidification of metal alloys. A suitable macrosegregation model should incorporate solidification thermodynamics, crystal growth kinetics, multiphase computational fluid dynamics, and even thermal-structural mechanics. No current model includes all those phenomena, hence leading to assumptions having to be made. This paper discusses some modeling assumptions regarding the treatment of (1) diffusion kinetics of crystal growth, (2) crystal dendritic morphology and (3) solidification shrinkage. Theoretical analyses based on test calculations were made. We find that some previous models, which over-simplified some of the aspects mentioned above for the purpose of computational efficiency, can only be applied to study macrosegregation qualitatively. They lead to significant error estimations of macrosegregation. When the quantitative accuracy for macrosegregation is of primary importance, the multiphase-based models with an appropriate treatment of these aspects, despite the sophisticated computational requirements, are recommended.

During solidification of castings, equiaxed crystals that is formed sink downwards, sediment and form a packed bed. The behavior of separated moving crystals can be described by a submerged object approach, whereas the viscoplastic behavior of a semi-solid slurry follows a volume-averaged viscoplastic constitutive equation. In this work, a two-phase Eulerian–Eulerian volume-averaging approach is used to combine both flow regimes. The transition happens at a certain solid volume fraction, the so-called coherency limit. Starting with a uniform distribution of crystals at rest, sedimentation and packing of crystals are described. In addition, the material density of the crystal is assumed to increase on cooling and thus the domain shrinks which is also accounted for in this report. It is demonstrated how sensitive the model is, on the considered crystal diameters and on the assumed value for the coherency limits.

Electroslag remelting (ESR) is an advanced process to produce high quality steel. During the ESR process, the steel electrode is melted and then solidified directionally in a water-cooled mold. The quality of the ingot is strongly dependent on the shape of melt pool, i.e. the depth and thickness of mushy zone, which is in turn influenced by the bulk and interdendritic flow. Here, we perform a numerical study to investigate the effect of crystal morphological parameter such as primary dendrite arm spacing on the solidification of the ESR ingot ( 750 mm). The crystal morphology is dominantly columnar and dendritic, thus a mixture enthalpy-based solidification model is used. Accordingly the mushy zone is considered as a porous media where the interdendritic flow is calculated based on the permeability. The permeability is determined as function of the liquid fraction and primary dendrite arm spacing according to Heinrich and Poirier [Comptes Rendus Mecanique, 2004, pp. 429-44]. The modeling results were verified against experimental results.

The simulation of macrosegregation in a 2.45-ton steel ingot with the three-phase mixed columnar-equiaxed model was presented previously. The results showed an overestimation of the intensity of bottom negative segregation. The reason is due to the assumed globular morphology for the equiaxed crystal. Therefore, in this paper a simple approach is suggested to treat the dendritic morphology of equiaxed crystals. Three aspects are improved: the drag force between the moving equiaxed crystals and the surrounding melt, the mechanism of the columnar-to-equiaxed transition, the packing limit of the equiaxed crystals. The modified model is used to calculate the macrosegregation of the same ingot. It is found that the modified model predicts less severe negative segregation in the bottom equiaxed zone than the previous globular equiaxed model does, i.e. it agrees better to the experiment. The model considering simplified-dendritic morphology improves the calculation accuracy.

This article is to assess the modeling treatment of the growth kinetics (finite or infinite diffusion in liquid and solid phases) during solidification and its influence on the calculation of macrosegregation. A model of diffusion-governed growth kinetic for ternary alloy is developed and used for this assessment. Solidification of a 2D casting (50 x 50 mm2) of a ternary alloy (Fe-0.45 wt.% C-1.06 wt.%Mn) is considered. The result shows that finite diffusion in liquid, important for the initial stage of solidification, plays very important role in the formation of macrosegregation. Moreover, the role of the finite diffusion kinetics in the formation of macrosegregation shows differently in the two extreme cases of solidification structures (columnar or equiaxed).

The Electro-Slag-Remelting (ESR) is an advanced technology for the production of components of e.g. high quality steels. In the present study a comprehensive computational model using the VOF technique for the prediction of the slag/pool interface is presented for axisymmetric and steady state conditions. In this model the distribution of the electric current is not constant in time, but is dynamically computed according to the evolution of the slag and steel phase distribution. The turbulent flow, created by the Lorentz and buoyancy forces, is computed by solving the time-averaged mass and momentum conservation equations. The turbulence effect is modelled by using a k-model. Two numerical simulations were performed, one assuming a flat interface, and a second leaving the interface free to find an equilibrium shape. The results are then analysed and compared for both cases.