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To clarify the mechanism of inclusion capture by solidified hook of low carbon steel, different types of solidification structure regions on the surface of slab were categorized into hook-typed oscillation mark zones, depression-typed oscillation mark zones and initial shell zones between oscillation marks. The Aspex was utilized to statistically analyze the distribution characteristics of inclusions in different zones. Moreover, the force model of inclusions at the solidification front of hook and shell was established, and the influence of hook characteristics and process parameters on the capture of inclusions at the solidification front of hook was revealed. The results show that the grain orientation will be affected by the formation of oscillation marks. A large number of small inclusions present in the hook-typed oscillation marks will hinder the growth of grains and form smaller grains. In hook-typed oscillation mark zone, the proportion of inclusions larger than 10 μm can reach over 15 pct, whereas in initial shell and depression-typed oscillation mark zones, the proportion of inclusions larger than 10 μm is below 10 pct. Therefore, the solidification front of hook-typed oscillation mark demonstrates a stronger capability to capture inclusions larger than 10 μm. Regarding hook characteristics, the number density of captured inclusions is positively correlated with the deflection angle of hook, while it shows no significant correlation with hook depth and length. At the shell solidification front, the critical size for inclusion escape is 170 μm, while at the hook solidification front, the critical size required for inclusion escape is 374 μm. Factors such as the sulfur content in the molten steel, the hook deflection angle, the solidification velocity, and the flow velocity can influence the critical size of inclusions captured by the hook. [ABSTRACT FROM AUTHOR] more...

The stable control of mold level is a key link in the production of high-quality continuous casting slabs. Periodic mold level fluctuation (PMLF) is common during the continuous casting process, and the abnormal PMLF has significant harmful effects on surface quality of slab. This article proposed an analysis and control method for abnormal PMLF. First, the finite impulse response (FIR) filter and fast Fourier transform (FFT) were used to remove noise interference in PMLF data and highlight the fluctuation characteristics of PMLM. Then, considering that uneven solidification has a significant impact on abnormal PMLF, the influence of chemical composition on the equilibrium Fe-C pseudo-binary diagram was calculated by Thermo-Calc software. Furthermore, roller diameter, roller spacing, casting speed, and chemical composition were chosen as the prediction indicator to predict the quality of PMLF. Random forest (RF) model shows good performance in predicting PMLF; the prediction accuracy of RF model is 92.76 pct, which is 21.39 pct higher than that of GA-BP model. Finally, the Feedforward fuzzy PID (F2FPID) controller designed in this article was used to eliminate abnormal PMLF. The average range of mold level fluctuation under the PID controller is ± 6.8 mm, while under the F2FPID controller, the average range of mold level fluctuation is ± 1.1 mm. And the F2FPID controller owns a lower overshoot of 0.48 pct and an adjusting time of 1.52 seconds, which are 94.8 pct and 59.5 pct, respectively, lower than those of the PID controller. [ABSTRACT FROM AUTHOR] more...

Thermodynamic data is of great significance to investigate the formation and control mechanisms of solidification defects during the casting process of H13 steel which is high in Si, Cr, Mo, and V elements. It has been proven that the conventional Ueshima model based on the equilibrium phase diagrams of Fe-X (X = C, Si, Mn, P, S, Cr, Mo, and V) binary alloys cannot accurately predict the phase transition in the solidification of H13 steel with multi components. So, the pseudo-binary phase diagrams of Fe-X alloys at different initial concentrations were calculated via Thermo-Calc software. And, the datasets of liquidus and δ/γ phase transition temperatures were obtained. Then, a backpropagation (BP) neural network model was developed to predict the δ/γ phase transition temperature. While, the slopes of liquidus lines were fitted. These updates were implanted into the Ueshima model. And, the BP-Ueshima model was validated with the phase transition temperatures measured via the differential scanning calorimetry (DSC) test. Subsequently, the phase transition and solute micro-segregation behaviors in the solidification of H13 steel were analyzed as well as the influences of solute elements. The results show that the predicted liquidus temperature (TL) and solidus temperature (TS) of H13 steel via BP-Ueshima model agree with the experimental results. As the cooling rate increases from 10 to 20 °C/min, the phase transition temperatures change slightly. Both the solidus and liquidus temperatures decrease with increase of the initial contents of solute elements. Increasing the initial contents of C and Mn can enhance TP and Tδ (the vanishing temperature of δ phase), whereas the trend is reversed for the other solute elements. Changes of the phase transition temperatures depends on the segregation behaviors of solute elements. The micro-segregation ratios of solute elements in the liquid phase at the end of solidification decreases in the order of S, P, Si, Mo, C, V, Mn, and Cr, respectively. It is determined by the redistributive capacity at the solid/liquid interface and the back diffusion in the solid phase of solute elements. [ABSTRACT FROM AUTHOR] more...

For decades, the fixed-grid method (FGM) has undergone extensive development and widespread application in addressing phase change problems. Nonetheless, comparative studies on various FGMs in convective regime are considerably scarce. Moreover, it has been proven that two-dimensional (2D) numerical simulations can cause large deviations from experimental observations. Therefore, this study, based on a reference experiment involving gallium melting, seeks to comprehensively and quantitatively compare three prevalent FGMs: enthalpy method (EM), total enthalpy method (TEM), and heat source method (HSM). The TEM validates overestimation of temperature at low Péclet numbers, as the heat dissipation induced by non-uniform thermal properties in solid and liquid phases is not accounted for. To address this issue, a revised TEM has been introduced. The three FGMs were implemented within the OpenFOAM software, with over 150 simulations conducted on 3D meshes. The comparison focused on evaluating the numerical robustness, accuracy and stability of these FGMs, along with exploring their similarities and differences in flow patterns and velocities. Results obtained reveal that EM offers accuracy but lacks robustness, TEM manifests relatively large errors and instability due to oscillation with variations in grid size and time step, while HSM excels in robustness, accuracy, and stability. Under an identical discretization scheme, all FGMs predict similar melt front shapes, vortex structures, and velocity magnitudes. However, with the upwind scheme, the velocity magnitude of the secondary flow is approximately 50 pct of that with high-order schemes, yet it tends to overestimate the melting rate. The reason lies in the limited capacity of the slow secondary flow to effectively disrupt the stable and persistent vortex in the primary flow direction, consequently enhancing heat transfer efficiency in this direction. [ABSTRACT FROM AUTHOR] more...

The behavior of the meniscus region is crucial to the surface quality of continuous cast steel. A two-dimensional model was developed to study the evolution of the meniscus region during the initial casting stage of continuous casting process. The flow of multiphase fluids, transient heat transfer, melting and re-solidification of slag, and the solidification process of the steel shell were also considered in the model. The calculated results show a good agreement with experimental data of previous literature, which demonstrates the reliability of the model in predicting the behavior of the meniscus region. After the start of withdrawal, liquid slag infiltrates into the gaps, forming a slag layer structure composed of liquid slag films and solid slag films between the shell and the mold. As the distribution of each phase approaches stability, the initial shape of the meniscus was established. During the initial casting stage, as the casting speed increases, the curvature of the meniscus increases, accompanied by an elevated level of heat transfer within the meniscus region. Furthermore, from the perspective of the associated heat transfer and fluid flow variations during the increase in casting speed, the reasons for the decrease of the depth of the oscillation mark and the slag consumption are explained. This study provides new insights into the continuous and complex flow and heat transfer behavior within the meniscus region during the initial casting stage of continuous casting process. [ABSTRACT FROM AUTHOR] more...

During an oscillation cycle of the mold, the fluid flow, heat transfer, and solidification behavior within the meniscus region control the slag infiltration, lubrication, and formation of oscillation marks, which are of great significance to the smooth running of continuous casting and the surface quality of slab. A comprehensive two-dimensional (2D) transient thermal-fluid model has been developed to study the fluid flow, heat transfer, dynamic shape of steel/slag interface, as well as the growth of shell in the meniscus region during an oscillation cycle. In addition, calculations of slag consumption were performed, and the results were consistent with previous research, thereby the reliability of the model is validated. During an oscillation cycle, the upstroke and downstroke cause the meniscus profile to bulge and collapse, which dominates the increase and decrease of heat flux in the Eulerian reference frame reference frame. However, the variation of heat flux in the Lagrangian reference frame is determined by the instantaneous position. The freezing and overflow behaviors of the meniscus are the primary factors contributing to the formation of oscillation marks, and the final profile of oscillation marks is determined by the two freezing events of the meniscus within an oscillation cycle. The positive slag consumption primarily occurs during the negative strip time (NST), while there is also positive slag consumption during certain periods of positive strip time (PST), which is closer to the motion state of the mold. This research contributes to explaining and understanding the formation mechanism of surface defects and issues of continuous casting strands, aiming to facilitate the improvement of related problems. [ABSTRACT FROM AUTHOR] more...

During the continuous casting process, the instantaneous abnormal mold level fluctuation has great detrimental effects on slab quality, thus the mold level fluctuation is a key parameter for continuous casting process of high-quality steel. In the present study, the slab continuous casting process data for low carbon steel, medium carbon steel, hypo-peritectic steel and peritectic steel are collected to investigate the effect of process parameter on the instantaneous abnormal mold level fluctuation. The frequency domain coherence results illustrate that the stopper-rod position is the key influence factor on the instantaneous abnormal mold level fluctuation during the continuous casting process of different steel grades. The time–frequency characteristics of instantaneous abnormal mold level fluctuation and stopper-rod position were analyzed by continuous wavelet transform (CWT), and the results show that before the instantaneous abnormal mold level fluctuation occurrence, the high-frequency region amplitude of stopper-rod position shows a linear increase trend. For the continuous casting process with constant casting speed, the increase rate is within the range of 0.1/s to 0.2/s. For the instantaneous abnormal mold level fluctuation induced by steep casting speed change, the increase rate can reach 0.67/s. For the instantaneous abnormal mold level fluctuation induced by ladle change, the increase rate can reach 0.85/s. Therefore, the instantaneous abnormal mold level fluctuation can be predicted by CWT analysis for the high-frequency region amplitude of stopper-rod position. [ABSTRACT FROM AUTHOR] more...

For improving the quality and performance of bearings, it is necessary to investigate the precipitation mechanism of carbides in the solidification of GCr15 steel under conditions of continuous casting. Thus, the present work took the continuously cast GCr15 steel with the transverse section of 240 mm × 240 mm in a domestic steel plant as the research object. First, a two-dimensional solidification heat transfer model was developed and verified with the temperature measured via the infrared thermal imager. So, the average cooling rate in the mushy zone at 20, 40, 60, 80, 100, and 120 mm below the inner surface of the billet were determined. Second, the solidification of GCr15 steel at these locations under the corresponding continuous casting condition was simulated via a high-temperature confocal scanning laser microscope (HT-CSLM). Third, the effects of cooling rates on the characteristics of the solidification microstructure and carbides were analyzed. The results show that at 20, 40, 60, 80, 100, and 120 mm below the inner surface, the average cooling rates in the mushy zone are 57.28, 24.70, 18.44, 17.02, 17.54, and 18.95 K/min, the average equivalent diameters of the carbides are 7.93, 8.64, 10.50, 11.40, 11.21, and 9.99 μm, respectively. The carbides usually precipitate together with phosphides and grow in the inter-dendritic region which is the last area to solidify. Besides the homogeneous nucleation, carbides sometimes nucleate on Al2O3-MnS or MnS inclusions. Carbides are irregular polygons usually with sharp corners and arc edges. The atom ratio between metal and non-metallic elements is within 3.33 to 4.89. Dot-like segregation and uniform segregation of P are observed in the carbides at the cooling rate of 57.28 and 17.02 K/min. However, the segregation characteristics of C and Cr change little with the cooling rate. The geometric mean of primary and secondary dendrite arm spacings ( λ ¯ , μm) decreases with the increase of the cooling rate (Rc, K/min), and their functional relationship is λ ¯ = 823. 56 · R c - 0. 51 . Because of the decrease of the size of the solidification structure, the carbides become overall smaller with the increase in the cooling rate. According to the micro-segregation calculation, solutes of C, Cr, and P elements gradually enrich in the liquid phase, especially P at the end of solidification. The cooling rate influences not only the time for the back diffusion, but also the size of the local solidification region. Under the premise of the present work, the segregation ratio of the interstitial element C increases slightly with the decrease of the cooling rate. However, for Cr and P with the limited diffusivity, the segregation ratio first decreases as the cooling rate declines from 57.28 to 24.70 K/min, and then increases closely to that at 57.28 K/min as the cooling rate decreases to 17.02 K/min. Compared with C and Cr, P is influenced more by the cooling rate. So, the segregation characteristics of C, Cr, and P in the carbide are qualitatively interpreted. [ABSTRACT FROM AUTHOR] more...

Due to the high carbon and manganese content in high manganese steel Mn13, as-cast high manganese steel usually suffers from coarse solidification structure and carbide, which have a great detrimental effect on the high temperature mechanical properties of high manganese steel Mn13, and thus it is difficult to be produced by continuous casting process. In order to elucidate the solidification structure formation and carbide precipitation in the continuously cast slab of high manganese steel Mn13, several experiment methods, such as optical microscope (OM), electron backscatter diffraction (EBSD), field emission electron probe microanalyzer (EPMA), scanning electron microscope (SEM) and infrared C/S analyzer, and thermodynamic software Thermo-Calc were used to investigate the as-cast solidification structure, macro/micro solute segregation, and 2D/3D carbide morphology in the continuously cast slab of high manganese steel Mn13. The results show that the solidification structure of the Mn13 slab is mainly composed of coarse columnar crystals and the proportion of coarse columnar crystals is as high as 65.22 pct. The proportion of high angle grain boundaries (HAGB) in the equiaxed zone is 46.12 pct, but the proportion of HAGB in the columnar zone is only 11.98 pct. Both the C solute and Mn solute are rejected from the solid and enriched at the grain boundary, especially at the HAGB, where the growth direction of adjacent grains is quite different. The significant solute segregation and high grain boundary energy are both beneficial for the eutectic carbide formation and growth at the HAGB. Thus, the eutectic carbide is prone to form at the HAGB than the low angle grain boundaries (LAGB), and the thickness of the eutectic carbide at the HAGB is significantly thicker than that at the LAGB. The morphology of carbide from the slab subsurface to the center changes as follows: slender strip and small block → long strip and needle → long strip and lamellar. The secondary dendrite arm spacing (λII, μm) and the average carbide thickness (λc,μm), in the continuously cast slab of Mn13 steel, are formulated as functions of local cooling rate, (ν, °C s−1), and determined by λ II = 54.98 × ν - 0.34 , R 2 = 0.9802 λ c = 31.10 × e - 10.59 × v + 2.26 × e - 4.17 × 10 - 2 × v , R 2 = 0.9327 . [ABSTRACT FROM AUTHOR] more...

Based on the gauge-gravity duality, we study the three-dimensional QCD (QCD3) and Chern-Simons theory by constructing the anisotropic black D3-brane solution in IIB supergravity. The deformed bulk geometry is obtained by performing a double Wick rotation and dimension reduction which becomes an anisotropic bubble configuration exhibiting confinement in the dual theory. And its anisotropy also reduces to a Chern-Simons term due to the presence of the dissolved D7-branes or the axion field in bulk. Using the bubble geometry, we investigate the ground-state energy density, quark potential, entanglement entropy and the baryon vertex according to the standard methods in the AdS/CFT dictionary. Our calculation shows that the ground-state energy illustrates degenerate to the Chern-Simons coupling coefficient which is in agreement with the properties of the gauge Chern-Simons theory. The behavior of the quark tension, entanglement entropy and the embedding of the baryon vertex further implies strong anisotropy may destroy the confinement. Afterwards, we additionally introduce various D7-branes as flavor and Chern-Simons branes to include the fundamental matter and effective Chern-Simons level in the dual theory. By counting their orientation, we finally obtain the associated topological phase in the dual theory and the critical mass for the phase transition. Interestingly the formula of the critical mass reveals the flavor symmetry, which may relate to the chiral symmetry, would be restored if the anisotropy increases greatly. As all of the analysis is consistent with characteristics of quark-gluon plasma, we therefore believe our framework provides a remarkable way to understand the features of Chern-Simons theory, the strong coupled nuclear matter and its deconfinement condition with anisotropy. [ABSTRACT FROM AUTHOR] more...

In the present study, an improved multiphase field model with taking into consideration the S/L interface anisotropy is proposed to simulate the dendritic growth with peritectic transition of low-carbon steel, and a new random heterogeneous nucleation method is proposed to treat the γ phase nucleation during the peritectic solidification process. The γ phase growth around the dendrite (the single dendrite and polycrystalline ferrite) and the subsequent peritectic transformation during the peritectic solidification are simulated. The results show that when the temperature reaches the γ phase nucleation temperature, γ nuclei suddenly nucleate at the δ/L interface, and laterally grow with the movement of L/γ/δ triple point around the δ/L interface of δ dendrite. After the δ dendrite is fully wrapped by the continuous intervening γ phase, the γ phase continues to grow with direct phase transformation from both δ phase and liquid phase. With the increase of melt undercooling, more δ phase and liquid phase are consumed to form γ phase, and the intervening γ phase between the δ dendrite and liquid phase becomes more and more thick, but the δ dendrite arm becomes more and more thin. During the dendritic solidification process, the solute would be rejected from dendrite trunk with the dendritic growth and enriched at the dendrite boundary, especially at the dendrite root. The solute enrichment at the dendrite root would inhibit the γ phase growth at the dendrite root and thus the thickness of intervening γ phase at the dendrite root is thinnest around the dendrite. Moreover, the solute concentration in γ phase is among the δ phase and liquid phase, because the carbon solubility in γ phase is higher than that in δ phase, but lower than that in liquid phase. [ABSTRACT FROM AUTHOR] more...

The Muzhailing extra-long highway tunnel and corresponding inclined shafts in Lanzhou, Gansu Province, China passes through structurally complex carbonaceous slate that is under high ground stress. Rationally-designed and effective support is of high importance for achieving safe and efficient tunnel construction. The No. 2 inclined shaft of Muzhailing Tunnel was taken as the engineering background prototype, for which, a similar model test was conducted to evaluate the effect of highly pre-tightened constant resistance (NPR, Negative Poisson's Ratio) anchor cable support provision to the geologically complex carbonaceous slate at different depths. Two schemes were proposed during testing: one scheme was without support and the second was with asymmetric support from highly pre-tightened constant resistance anchor cable. Digital speckle displacement analysis system and micro-ground-stress sensors were employed to measure the deformation and shear stress distribution of the tunnel. The results demonstrated that through the second support scheme, the deformation of the surrounding rock could be effectively ameliorated, while this support scheme was applied on the project site of the No.2 inclined shaft, to explore the rationality of the scheme through field engineering tests. On-site monitoring indicated that the deformation of the surrounding rock was within the reasonable design range and the problem of severe tunnel deformation was effectively controlled. The research methods and related conclusions can be used as a reference for the treatment of large deformation problems in deep-buried soft rock tunnels. [ABSTRACT FROM AUTHOR] more...

The motion of free grains has a significant influence on the solidification structure, solute distribution, and defects of large casts. However, few studies have modeled the solidification structure of large casts considering grain motion. In this paper, taking into account the motion of free grains, a multiscale cellular automaton model is proposed to predict the solidification structure of continuously cast billets. The model is validated with experimental measurements. Then, the proposed model is adopted to investigate the solidification structure evolution of a wire steel 82b cast by a bow-type continuous caster with a billet section size of 160 mm × 160 mm. The results show that the growth of columnar grains in inner arc of billet strand is promoted by the sedimentation of free equiaxed grains. But the columnar grains in outer arc of strand are blocked once free grains nucleate before them. Thus, asymmetric morphology of solidification structure in the 82b billet with casting speed of 1.8 m/min is quantitatively determined and the length of the columnar grains in the inner arc and the outer arc of strand is 57.0 mm and 31.0 mm, respectively. Moreover, compared with the difference of cooling intensity between inner arc and outer arc in secondary cooling zone, the motion of free grains dominates the asymmetric morphology in the 82b billet. [ABSTRACT FROM AUTHOR] more...

In the present study, a two-dimensional phase field model coupled with Lattice Boltzmann method (PF-LBM) is proposed to predict the dendritic growth and motion in the melt of Fe-C binary alloy, where the phase field method (PF) is used to calculate the dendritic growth, including the phase field and the concentration field, and the lattice Boltzmann method (LBM) is used to calculate the flow field. The dendrite motion is determined by Newton's Second Law and tracked by Lagrangian point in a Cartesian coordinate system. Later, the model validations were performed with the benchmark of a solid particle settlement in a stagnant fluid and particle motion in a shear flow, and the results show that the present model is capable of predicting the solid particle motion in the fluid flow. Finally, the model is adopted to investigate the dendritic growth and motion in a forced fluid flow (laminar flow or rotational flow), and the dendrite settlement in a terrestrial environment. The results show that when the forced fluid flow is a laminar flow, the free dendrite would be driven to translate, and the relative velocity between the dendrite and flow fluid decreases, resulting in weak influence of fluid flow on the dendritic growth. When the forced fluid flow is a rotational fluid flow, the dendrite would centrifugally rotate on the domain center with a counterclockwise self-spinning, and the rotation radius becomes larger and larger. For the case of dendrite settlement in a terrestrial environment, the relative movement between the dendrite and melt promotes the downward branch growth, but inhibits the upward branch growth, and two vortices form at the wake region of dendrite. Therefore, the settling dendrite shows a significant asymmetrical morphology. [ABSTRACT FROM AUTHOR] more...

In the present study, both in situ experiment and multiphase field modeling are adopted to investigate the peritectic solidification of a low-carbon steel. The results show that the peritectic reaction occurs at the temperature of 3.4 K lower than the equilibrium peritectic temperature, the γ-austenite first nucleates at the δ/L boundary, and then rapidly propagates along the δ/L boundary by the advance of the L/γ/δ triple point till the δ-ferrite is encircled by the γ austenite. The whole peritectic reaction process is very fast, and the measured and predicted average propagation velocity of L/γ/δ triple point along the δ/L boundary are, respectively, 1.36 and 1.09 mm/s. This small difference between the measurement and prediction means that the developed multiphase field model is capable of predicting the peritectic reaction and peritectic transformation during the peritectic solidification process of Fe-C alloy, and the peritectic reaction can be regarded as a solute diffusion-controlled process. With the increase of cooling rate and undercooling, the advancing velocities of L/γ/δ triple point, L/γ interface and γ/δ interface increase, and thus the γ-austenite between the liquid phase and δ phase becomes longer and thicker for the same elapsed time. [ABSTRACT FROM AUTHOR] more...

Recalescence and segregation are two characteristic phenomena for the equiaxed dendritic solidification of alloys. The present work developed a two-dimensional dendritic model with cellular automaton (CA) method to investigate influence mechanisms of thermal conditions on recalescence and segregation behaviors of Fe-0.82wt pct C alloy. The released latent heat reduces the undercooling around the equiaxed dendrite, and thus eases its growth velocity. The predicted steady growth velocity agrees well with the analytical results as the melt undercooling is 9 K. Additionally, the present CA model can ensure the growth consistence of equiaxed dendrites in the undercooled melt. With improving the convective heat transfer coefficients applied around the domain boundaries, the temperature recalescence in the domain center becomes more significant, and the corresponding solid fractions enhance. It is because that the stronger cooling promotes the solidification, resulting in more latent heat released. Accordingly, the heat dissipation can be neutralized. Moreover, a deeper undercooling for the temperature recalescence is needed under a stronger cooling condition. With the increase of both the cooling rate and the convection coefficient, secondary arms of the equiaxed dendrite become more developed. At the lower cooling rate range, the segregation ratio in the domain enlarges with the improvement of the cooling rate. However, it gets weaker under the condition with super cooling intensity due to the expansion of the low concentration region. As the convection coefficient is enhanced, the solute segregation in the domain gets less pronounced. [ABSTRACT FROM AUTHOR] more...

In order to predict the dendritic evolution during the continuous steel casting process, a simple mechanism to connect the heat transfer at the macroscopic scale and the dendritic growth at the microscopic scale was proposed in the present work. As the core of the across-scale simulation, a two-dimensional cell automaton (CA) model with a decentered square algorithm was developed and parallelized. Apart from nucleation undercooling and probability, a temperature gradient was introduced to deal with the columnar-to-equiaxed transition (CET) by considering its variation during continuous casting. Based on the thermal history, the dendritic evolution in a 4 mm × 40 mm region near the centerline of a SWRH82B steel billet was predicted. The influences of the secondary cooling intensity, superheat, and casting speed on the dendritic structure of the billet were investigated in detail. The results show that the predicted equiaxed dendritic solidification of Fe-5.3Si alloy and columnar dendritic solidification of Fe-0.45C alloy are consistent with in situ experimental results [Yasuda et al. Int J Cast Metals Res 22:15-21 (2009); Yasuda et al. ISIJ Int 51:402-408 (2011)]. Moreover, the predicted dendritic arm spacing and CET location agree well with the actual results in the billet. The primary dendrite arm spacing of columnar dendrites decreases with increasing secondary cooling intensity, or decreasing superheat and casting speed. Meanwhile, the CET is promoted as the secondary cooling intensity and superheat decrease. However, the CET is not influenced by the casting speed, owing to the adjusting of the flow rate of secondary spray water. Compared with the superheat and casting speed, the secondary cooling intensity can influence the cooling rate and temperature gradient in deeper locations, and accordingly exerts a more significant influence on the equiaxed dendritic structure. [ABSTRACT FROM AUTHOR] more...

A 3D parallel cellular automaton-finite volume method (CA-FVM) model was used to simulate the equiaxed dendritic growth of an Fe-0.82 wt pct C alloy with xy- in- out and xyz- in- out type forced flows and the columnar dendritic growth with y- in- out type forced flow. In addition, the similarities and differences between the results of the 3D and 2D models are discussed and summarized in detail. The capabilities of the 3D and 2D CA-FVM models to predict the dendritic growth of the alloy with forced flow are validated through comparison with the boundary layer correction and Oseen-Ivanstov models, respectively. Because the forced flow can pass around perpendicular arms of the dendrites, the secondary arms at the sides upstream from the perpendicular arms are more developed than those on the upstream side of the upstream arms, especially at higher inlet velocities. In addition, compared to the xy- in- out case, the growth of the downstream arms is less inhibited and the secondary arms are more developed in the xyz- in- out case because of the greater lateral flow around their tips. Compared to the 3D case, the 2D equiaxed dendrites are more asymmetrical and lack secondary arms because of the thicker solute envelope. In the 3D case, the columnar dendrites on the upstream side (left one) are promoted, while the middle and downstream dendrites are inhibited in sequence. However, the sequential inhibition starts on the upstream side in the 2D case. This is mainly because the melt can pass around the upstream branch in 3D space. However, it can only climb over the upstream tip in 2D space. Additionally, the secondary arms show upstream development, which is more significant with increasing inlet velocity. The level of development of the secondary arms is also affected by the decay of the forced flow in the flow direction. [ABSTRACT FROM AUTHOR] more...

Solidified shell bulging is supposed to be the main reason for slab center segregation, while the influence of thermal shrinkage rarely has been considered. In this article, a thermal shrinkage model coupled with the multiphase solidification model is developed to investigate the effect of the thermal shrinkage, solidification shrinkage, grain sedimentation, and thermal flow on solute transport in the continuous casting slab. In this model, the initial equiaxed grains contract freely with the temperature decrease, while the coherent equiaxed grains and columnar phase move directionally toward the slab surface. The results demonstrate that the center positive segregation accompanied by negative segregation in the periphery zone is mainly caused by thermal shrinkage. During the solidification process, liquid phase first transports toward the slab surface to compensate for thermal shrinkage, which is similar to the case considering solidification shrinkage, and then it moves opposite to the slab center near the solidification end. It is attributed to the sharp decrease of center temperature and the intensive contract of solid phase, which cause the enriched liquid to be squeezed out. With the effect of grain sedimentation and thermal flow, the negative segregation at the external arc side (zone A1) and the positive segregation near the columnar-to-equiaxed transition at the inner arc side (position B1) come into being. Besides, it is found that the grain sedimentation and thermal flow only influence solute transport before equiaxed grains impinge with each other, while the solidification and thermal shrinkage still affect solute redistribution in the later stage. [ABSTRACT FROM AUTHOR] more...

Objective: To investigate the effect of ginsenosides from stems and leaves of ginseng on ethanol-induced lipid deposition in human L02 hepatocytes. Methods: L02 cells were exposed to ethanol for 36 h and treated with or without ginsenosides. The viability of L02 cells was evaluated by methylthiazolyldiphenyl-tetrazolium bromide assay and the triglyceride (TG) content was detected. Lipid droplets were determined by oil red O staining. Intracellular reactive oxygen species (ROS) production and the mitochondrial membrane potential were tested by flow cytometry. The ATP level was measured by reverse phase high performance liquid chromatography. The expression of cytochrome p450 2E1 (CYP2E1) and peroxisome proliferator-activated receptor α (PPARα) was detected by reverse transcriptase-polymerase chain reaction and Western blotting, respectively. Results: Ethanol exposure resulted in the increase of TG level, lipid accumulation and ROS generation, and the decrease of mitochondrial membrane potential and ATP production in the cells. However, ginsenosides significantly reduced TG content (9.69±0.22 μg/mg protein vs. 4.93±0.49 μg/mg protein, P<0.01), and ROS formation (7254.8±385.7 vs. 5825.2±375.9, P<0.01). Meanwhile, improvements in mitochondrial membrane potential (10655.33±331.34 vs. 11129.52±262.35, P<0.05) and ATP level (1.20±0.18 nmol/mg protein vs. 2.53±0.25 nmol/mg protein, P<0.01) were observed by treatment with ginsenosides. Furthermore, ginsenosides could down-regulate CYP2E1 expression ( P<0.01) and upregulate PPARα expression ( P<0.01) in ethanol-treated cells. Conclusions: Ginsenosides could prevent ethanol-induced hepatocyte steatosis in vitro related to the inhibition of oxidative stress and the improvement of mitochondrial function. In addition, the modulation of CYP2E1 and PPARα expression may also play an important role in the protective effect of ginsenosides against lipid accumulation. [ABSTRACT FROM AUTHOR] more...

To improve the computational efficiency of the three-dimensional (3D) cellular-automaton-finite-volume-method (CA-FVM) model for describing the dendritic growth of alloy, the block-correction technique (BCT) and the parallel computation approach are introduced. Accordingly, a serial of investigations on the efficiency of the optimized codes in dealing with the designed cases for the melt flow and the heat transfer problems is carried out. Moreover, the accuracy of the present codes is evaluated by the comparisons between the solution to the melt flow and the heat transfer problems and the results from analytical equations and the commercial software. Additionally, the capability of the present CA model is evaluated by comparing the steady growth parameters of the equiaxed dendritic tip and the morphology and the secondary dendrite arm spacing (SDAS) of columnar dendrites with the LGK analytical model and the experimental results of the unidirectional solidification of high-carbon steels. The results show that with the introduction of the 3D BCT, the iteration process of the serial tri-diagonal matrix algorithm (TDMA) code changes from the fluctuation type to the smooth one, and thus, the computational cost is reduced significantly. Moreover, the parallel Jacobi code with one two-dimensional (2D) iteration in 3D BCT is proved to be the most efficient one among the codes compiled in the present work, and therefore, accordingly it is employed to simulate the 3D dendritic growth of alloys. The calculated velocity distribution and temperature variation agree well with the results from the analytical equations and the commercial software. The predicted steady tip velocities agree with the LGK analytical model as the undercooling is 6 K to 7 K. Moreover, the predicted columnar dendritic morphology and SDAS of high-carbon Fe-C alloys during the unidirectional solidification agree with the experimental results. [ABSTRACT FROM AUTHOR] more...

In the second part (Part II) of the present simulation work, the three-dimensional (3D) dendritic growth of Fe-0.82wtpctC alloy is investigated with the 3D CA-FVM cellular automaton-finite volume method model developed in Part I. The influences of the melt undercooling, the interfacial anisotropy, and the forced flow on the equiaxed dendritic growth, especially the formation of secondary arms, are discussed. The comparisons of equiaxed dendritic growth in 3D and two-dimensional (2D) are also carried out. Finally, the columnar dendritic growth under different cooling conditions is investigated including the morphology and the secondary dendrite arm spacing (SDAS). The results show that the high undercooling can promote the formation of secondary arms as the anisotropy parameter is 0.04. With the increase of the anisotropy parameter, the secondary arms first reduce and then well develop again; meanwhile the tertiary arms are gradually developed. However, the secondary arms vanish at the undercooling of 5 K as the anisotropy parameter increases to 0.04. With the introduction of the forced flow with the inlet velocity of 0.001 m/s along the x axis, the secondary arms at the left (upstream) arm become more developed. However, they become slightly less developed with the forced flow intensifying. Secondary arms at the left side (upstream) of the perpendicular arms and in the y-z symmetrical plane become more and more developed as the inlet velocity increases. The competition of the secondary arms at the right side (downstream) of the perpendicular arms and at the right (downstream) arm becomes significant as the undercooling increases from 10 to 15 K. The solute-enriched envelope in 2D is much thicker than in the 3D case, so that the dendritic growth in 2D is influenced more by the melt flow and the undercooling; moreover, the secondary arms in 2D are hard to form even at the undercooling of 15 K and with the forced convection in the present article. Meanwhile, the variation tendency of the movement of columnar dendritic tip and the decrement of the average SDAS with every 0.025-MW/m increment of the heat flux are quite different. [ABSTRACT FROM AUTHOR] more...

Considering the influence of the latent heat released during the solidification of high carbon liquid steel, a cellular automaton (CA) model coupled with the heat transfer was developed to investigate the growth of equiaxed dendrites which is controlled by the solute diffusion during the continuous casting process. Additionally, the growth of columnar dendrites and primary dendrite arm spacings were predicted and measured. The results show that the CA model is able to describe the growth behavior of equiaxed dendrites, especially at 5 K to 7 K melt undercoolings, and the approach adjusting the cooling medium temperature is reliable to keep the undercooling condition stable for equiaxed dendrites although its hysteresis is reinforced as the pre-set undercooling increases. With the increase of the melt undercooling, the growth of equiaxed dendrites becomes faster, and the thickness of dendritic arms increases slightly, however, the thickness of the diffusion layer in front of dendritic tips keeps constant. The growth of thin and tiny columnar dendrites will be confined due to the competition and absorbed by neighboring strong columnar dendrites, giving rise to the coarsening of columnar dendrites, which is observed both from the experimental observation and the numerical simulation. With the decrease of the cooling intensity, columnar dendrites get sparser, primary dendrite arm spacings increase, and secondary dendritic arms become undeveloped. [ABSTRACT FROM AUTHOR] more...

Quality-of-Service (QoS) performance guarantee for service-oriented systems (SOS) has become a critical problem. With the increasing number of offered services comes the challenge of efficiently building large-scale SOS to meet the required QoS criteria. Optimization of QoS-driven semantic Web service composition is known to be NP-hard. We address the efficiency issue by developing a polynomial time algorithm (QDA) for shortest sequence composition. We use dynamic programming to find service candidates for each execution. When all the services are searched, we use a depth-first trace back to derive the execution plan. We have tested our approach under Web-scale demands 20,000 services and 150,000 semantic concepts. In comparison with existing approaches, our experimental results show that QDA can be used to solve large-scale service composition problem effectively and efficiently with QoS guarantee. [ABSTRACT FROM AUTHOR] more...