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The solidification structure and segregation behavior in 20Mn2 alloyed steel from continuously cast billet with different casting speed (2.0, 2.4, 2.7 m/min) has been investigated, and the dendrite evolution and solute enrichment characteristics in the billet at high speed casting has been revealed. It is found that the deflection angle in the columnar dendrite induced by M-EMS decreases as withdraw speed increases, mainly due to the decrease in the average stay time in the stirring zone instead of the increase of steel flow rate, indicating the effect of M-EMS on the homogeneity of temperature and promotion of free nucleus formation reduces. The equiaxed ratio in the billet increases as casting speed increases from 2.4 to 2.7 m/min, attributed to the F-EMS acting as S-EMS to stimulate the formation of nucleus. The alignment of equiaxed zone in the case of 2.4 and 2.7 m/min is much better than that in 2.0 m/min, due to the weakening effect of M-EMS and strengthening effect of early F-EMS, together with the increase of superheat. The center segregation in the billet shows no obvious change as casting speed increases from 2.0 to 2.4 and 2.7 m/min, and low superheat, appropriate F-EMS and F-EMS working as S-EMS is the explanation for different trials respectively. The spot segregation in the billet deteriorates as casting speed increases, involving the increase in the size, number and solute content. The most severe solute enrichment is in the vicinity zone where fine dendrite and coarse dendrite contact. The countermeasures to improve the center quality of continuously cast billet at high speed is proposed. Medium superheat, strengthened M-EMS, intense secondary cooling, appropriate S-EMS and F-EMS are beneficial for most steels. [ABSTRACT FROM AUTHOR]

In the process of continuous casting, the slab temperature is a particularly crucial production parameter. However, it is still being monitored on the surface of the slab. At present, the prediction of slab temperature using machine learning models is not feasible due to the lack of internal temperature data from actual production. In this paper, a prediction method based on DNNs algorithm integrating numerical simulation and SHAP analysis is proposed to monitor the temperature field of continuous casting slab in real-time. The dataset comprises 6 input features and 5 output features. Following data preprocessing, four distinct machine learning models were developed employing DNNs, SVM, XGBoost, RF algorithms to individually predict the temperature of the slab. The DNNs model is selected as the optimal model according to the performance comparison using performance parameters such as MAE, MSE, and R2. SHAP value is calculated for the sensitivity analysis of the influence of the characteristic parameters of DNNs prediction model on the prediction results. The experimental results indicate that the prediction model has an average success rate of 96.48 pct within a temperature accuracy of ± 20 °C. Moreover, the resident time, the amount of internal side water within the slab, and the internal side heat transfer coefficient of the slab have the most significant impact on the model. This study introduces a novel method for establishing machine learning models with machine learning techniques. [ABSTRACT FROM AUTHOR]

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]

To avoid coarse crystallization of CaO–SiO2–Al2O3 inclusions during the solidification stage of continuous casting process, the effect of MgO on crystallization behavior of these inclusions is investigated. The single hot thermocouple technology experiment results show that the low melting point CaO–SiO2–Al2O3 inclusions do not easily crystallize during the solidification stage. However, with increasing the MgO content from 4.5 to 15.7 wt pct, the initial crystallization temperature of inclusions increases from 1376 K to 1431 K (1103 °C to 1158 °C) and the crystallization ratio increases from 35.45 to 100 pct. The crystallization ability of the inclusions can be predicted by the initial crystallization potential and the viscosity at the melting point. With increasing the MgO content from 0 to 15.7 wt pct, the initial crystallization potential of the inclusions increases from 0.28 to 0.87 and the viscosity of the inclusions at the melting point decreases from 4.47 to 0.56 Pa s. The higher the initial crystallization potential and the lower the viscosity near the melting point, the easier the crystallization of the inclusions occurs. Al2O3 mainly acts as the network former and participates in the construction of the network structure. With the increase of MgO content, the crystallization ability of inclusions increases gradually, which is mainly related to the increase of melt structure depolymerization. [ABSTRACT FROM AUTHOR]

Solidification end reduction is an effective approach to control the central porosity during continuous casting of round bloom, although it is not widely reported. In the present work, a three-dimensional finite element model has been developed with coupling heat transfer and mechanical deformation for a φ690 mm continuously cast round bloom, and verified by the surface temperature, shrinkage zone width, reduction crack location, and deformed contour shape. It is found that the contact width between roller and the bloom increases with the increase of reduction amount and approximately in a parabolic relationship. To cover the whole range of the shrinkage zone, the total reduction amount should not be smaller than 25 mm as the width of the shrinkage zone is about 120 mm. The bulge width along the horizontal direction during reduction increases as the total reduction amount increases, and the relationship can be fitted by a parabolic equation. The reduction thickness in the shrinkage zone is larger when the reduction amount is higher, and it also follows parabolic relationship. The deformation in the shrinkage zone is more obvious when the reduction is conducted before crater end. The reduction efficiency for φ690 mm round bloom before solidification is between 20 and 30 pct, while after solidification is roughly between 12 and 20 pct. It increases with the increase of apparent reduction amount, mainly related to the increase of the strain rate. The deformation of the shrinkage zone in φ690 mm round bloom with 30 mm apparent reduction in continuous casting and hot rolling has been compared. The equivalent strain in the shrinkage zone of the round bloom in continuous casting is about 0.047 to 0.052, while that in hot rolling is about 0.031 to 0.036, indicating the reduction efficiency of the former is about 1.5 times higher than the latter. [ABSTRACT FROM AUTHOR]

During steel solidification, solute element segregation at dendrite boundaries intensifies the precipitation of MnS inclusions. The morphology, dimensions, and spatial distribution of these precipitates influence the high-temperature thermoplasticity of continuously cast slabs. Variations in the equilibrium partition coefficients (ki) of different cooling phases in Q355 microalloyed steel were investigated using thermodynamic calculations. To obtain accurate parameters, the thermodynamic behavior of the continuous casting process was simulated using Marc finite element software for thermal history data at each node of the cooling process. A real-time constant cooling rate model was established, and four different rates were selected to verify the model. Model predictions and observations demonstrated strong agreement, with an error range of 2.2 to 5.2 pct. A method for calculating variable cooling rates was proposed. Based on the heat transfer model, a real-time variable cooling rate model was established and high-temperature confocal laser scanning microscopy (HT-CLSM) was used for observation of the solidification process. This prediction model can effectively characterize MnS precipitation and growth and the effects of casting speed and superheating on the particle size distribution of MnS inclusions. This study provides a rapid and accurate method for predicting MnS precipitation, helpful for optimizing the process of continuous casting. [ABSTRACT FROM AUTHOR]

The excellent water-cooling structure contributes to achieve efficient and reasonable heat transfer in the mold, which is essential for achieving the ultra-large beam blank continuous casting (ULBBCC). Therefore, this work designed different ultra-large beam blank mold (ULBBM) which were composed of three wide face copper plates with different water-cooling structures and two narrow face copper plates with different water-cooling structures, on the basis of which a three-dimensional heat transfer model of the copper plate coupling with the cooling water flow in the water-cooling structure was developed with the consideration of fluid-solid coupling interaction. Then, the accuracy of the model was verified by comparing the model-predicted and measured water temperatures. Finally, the focus is comparing the heat transfer behavior of the mold under different water-cooling structures, as well as the temperature and flow evolution of the cooling water, and the most optimal water-cooling structure was proposed. The results show that the water-cooling structure of water slots with semicircular roots (Mold II) contributes the narrow face copper plate of ULBBM to obtain excellent temperature uniformity and achieve homogenization of heat transfer. The water-cooling structure of small hole water channel with a diameter of 10 mm (Mold III) decreases the maximum temperature at the fillet of wide face copper plate of ULBBM to 582.9 K and the maximum circumferential temperature difference near the meniscus to 103.3 K, and which contributes the wide face copper plate to obtain higher temperature uniformity and lower fillet temperature, and achieve homogenization of heat transfer. [ABSTRACT FROM AUTHOR]

In the current study, a three-dimensional mathematical model that integrated the large eddy simulation (LES) turbulent model, volume of fluid (VOF) multiphase model, and the dynamic mesh model, was developed to investigate the influence of the mold oscillation on the steel, slag, and air multiphase flow and the slag entrainment in a slab continuous casting mold. The results indicated that the mold oscillation led to an increase of about 0.35 m/s in the speed of molten steel at the impact point of the upper and lower circulation on the narrow surface. However, it reduced about 0.047 m/s in the maximum speed of the meniscus at 1/4 width of the mold. The Fast Fourier Transform (FFT) analysis revealed that the characteristic frequency of the speed fluctuation in the gravity direction of the meniscus near the narrow surface was 1.27 Hz without the consideration of the mold oscillation. Upon the application of the mold oscillation, a new characteristic frequency of 3 Hz, matching the mold oscillation frequency, emerged with twice the intensity of the original 1.27 Hz frequency. Moreover, the mold oscillation had little effect on the characteristic frequency of the speed fluctuation on the meniscus far away from the narrow surface. A user-defined function (UDF) was employed to quantify the number, size, and spatial distribution of entrained slag droplets. The net slag entrainment rate was reduced from 0.0152 to 0.0113 kg/s after the consideration of the mold oscillation, and the number of entrained slag droplets was also decreased. The effect of mold oscillation on the size distribution of entrained slag droplets and the occurrence location of the slag entrainment on the meniscus were not significant. [ABSTRACT FROM AUTHOR]

As a typical metallurgical defect, macrosegregation seriously affects the internal quality of the continuous casting billet, and it cannot be solved by processes such as high-temperature diffusion and rolling. For continuous casting billet, the solidification shrinkage and thermal shrinkage of the microstructure directly affect the macrosegregation defect. In order to reveal the effects of solidification shrinkage and thermal shrinkage on the melt flow, microstructure distribution, and solute segregation, a multiphase solidification model based on the Eulerian–Eulerian approach was established in this work. The growth behaviors of the columnar dendrite trunk and the columnar dendrite tip were fully considered, as well as the nucleation, growth, free migration of equiaxed grains, and the columnar-to-equiaxed transition (CET). Besides, the corresponding relationship between the secondary dendrite arm spacing (SDAS) and the cooling rate has also been taken into account in the model, which makes the net mass transport source term of the mass conservation equations more accurate. The calculation results show that when no any shrinkage behavior is considered in the model, the melt flow velocity in front of the solidification end will gradually decrease until it is the same as the casting speed, and the segregation index at the billet center will gradually increase until it reaches the maximum value at the solidification end. Both thermal shrinkage and solidification shrinkage can generate a negative pressure zone in the billet center, sucking the poor-solute melt located the upstream of continuous casting strand flows towards the solidification end, and mixing with the enriched-solute melt before the solidification end, thereby inhibiting macrosegregation. However, compared with the solidification shrinkage, the effect of thermal shrinkage on reducing the positive segregation index in the billet center is limited. [ABSTRACT FROM AUTHOR]

Understanding the formation of a slag rim on the mold meniscus is crucial for controlling surface defects in the initial shell. However, there is a scarcity of quantitative studies on this matter. This study has developed a comprehensive three-dimensional (3D) numerical model for analyzing the meniscus multi-phase flow, heat transfer, and solidification, considering mold oscillation. The 3D morphology of the solidifying shell and the slag rim in the meniscus region were accurately reproduced. The solidification depth (DIS), solidification length (LIS) and oscillation mark depth (DOM) of the initial shell were used to quantify the morphological characteristics of the initial shell. The results confirmed that the formation position difference of the slag rim along the circumferential direction of the mold significantly affects the initial solidification and uniform growth of the shell. In the corner of the mold, the deeper overflow makes the oscillation mark extend 2.8 to 3.2 mm in the direction of casting. In addition, in order to quantitatively investigate the influence of the slag rim, a two-dimensional (2D) model is established with phenomena and parameters considered the same as those of the 3D model. According to the slag rim morphology obtained by the 3D model, in the 2D model, it is proposed to construct three slag rims with the same maximum thickness of 6 mm at 10, 20 and 35 mm above the meniscus (HRim). The simulation of initial shell morphology revealed that a lower formation position of the slag rim led to more severe overflow of molten steel from the meniscus, resulting in non-uniform continuous growth of the initial shell. This increases the likelihood of potential blockage in the liquid slag flow towards the slag channel between solidified shell and mold. [ABSTRACT FROM AUTHOR]

Direct measurement of the wetting angles of the mold fluxes is a strenuous work and time-consuming, and a mathematical model relating the wetting angle of mold flux to its chemical composition is rarely found up to now. In this work, multiple linear regression (MLR), backpropagation neural network (BPNN), and GA-BP neural network (GA-BPNN) are used to model and predict the wetting angle of mold flux. Results show that the accuracy of MLR, BPNN, and GA-BPNN model is 76, 62, and 83 pct; the GA-BPNN model has the highest prediction accuracy. In addition, according to the standardized coefficients in the MLR model, the influence degree of different chemical components on the wetting angle of mold fluxes is analyzed. The importance of the influence of various components on the wetting angle is Fe2O3, F−, Li2O, Na2O, R, MnO, Al2O3, B2O3, and MgO from high to low. Among them, Fe2O3, Li2O, Na2O, R, and MnO have a negative effect on the wetting angle of mold flux, while F−, Al2O3, B2O3, and MgO have a positive effect. The established GA-BPNN model could facilitate the design and optimization of mold slag in the steel continuous casting process. [ABSTRACT FROM AUTHOR]

Feeding strip significantly enhances continuous cast slab quality. To clarify its impact on inclusion distribution, a mathematical model coupling flow, solidification and inclusion motion have been developed. The upper recirculation, lower recirculation, and unformed recirculation flow occur during continuous casting. Under the resultant forces of drag, virtual mass, pressure gradient, Saffman, gravity, buoyancy, etc., the inclusion motion can be divided into two stages: Injection and Split flow. Feeding strip mainly affects inclusion motion by altering the drag, virtual mass, pressure gradient, and Saffman forces, which are closely related to the molten steel flow. After feeding strip, the lower recirculation on the strip feeding side is compressed, while it on the no-feeding side is expanded. The unformed recirculation flow on strip feeding side squeezes the flow below lower recirculation on no-feeding side. A higher strip feeding speed promotes downward inclusion motion, increasing the chance of being captured between the slab edge and strip. Unformed recirculation flow guides inclusions on the no-feeding side toward the slab edge, while expanded flow directs them toward the center. Consequently, inclusions on strip feeding side gradually gather between slab edge and quarter, while inclusions on no-feeding side first gather toward center and then toward edge of slab with increased strip feeding speed. [ABSTRACT FROM AUTHOR]

Fe-Mn-C-Al high manganese steel has a large tendency to hot tearing, making it difficult to continuously cast and even leading to steel leakage accidents. In this paper, the effects of cooling rate and strain rate on the hot tearing behavior of Fe-18Mn-0.6C-2.6Al (18Mn) steel are investigated. The results show that 18Mn steel is prone to forming multiple cracks. When cracks propagate at higher temperatures, the stress rapidly decreases and exhibits brittle fracture characteristics. However, when the crack propagation temperature is lower, the rate of stress reduction significantly decreases, exhibiting ductile fracture characteristics. The temperature range of hot tearing of 18Mn steel is 1364 °C to 1344 °C, corresponding to the solid fraction of 0.88 to 0.99, and the initial crack propagation stress was 10.73 to 20.03 MPa. It indicates that, with the increase of the strain rate or the decrease of the cooling rate, the cracking temperature increases, and the peak stress decreases. In addition, when the propagation temperature is lower than the solidus, the cracks are no longer called hot tearing, but it will still cause damage in production. This study is valuable for the prediction of hot tearing and process design of continuous casting of Fe-Mn-C-Al high manganese steel. [ABSTRACT FROM AUTHOR]

Thin slab casting and rolling (TSCR) is a near-net-shape manufacturing process and a key development technology in China's iron and steel industry. This study uses cross-scale calculations to analyze the complete process of thin slab casting. The focus is on simulating and predicting the final solidification structure by adjusting process parameters. The aim is to enable further investigation into material performance and establish a foundation for researching deformation and phase transformation. To achieve this, a coupled model has been developed to simulate the entire thin slab casting process, using hot stamping steel as the research subject. The model encompasses fluid flow, heat transfer, and solidification. The study identifies the optimal combination for flow field, temperature distribution, and equiaxed grain ratio within the specified parameter range at a casting speed of 4.0 m/min and a superheat of 40 °C. The aim of the study is to establish an integrated computational materials engineering (ICME) research system for near-net-shape automotive steel casting processes. [ABSTRACT FROM AUTHOR]

In the current study, the quantity, size, and spatial distribution of non-metallic inclusions along the thickness direction of an ultralow carbon IF steel were detected employing an automatic SEM-EDS scanning system. And the distribution of the slab subsurface inclusions was mainly analyzed. In addition, the total oxygen content in the steel and the solidification structure of the slab were analyzed. Upon the application of M-EMS, the solidification front was flushed due to the stirring effect generated by the electromagnetic force, promoting the floating removal of inclusions, thereby improving the overall cleanliness of the slab. However, the probability of the collision and agglomeration of inclusions was increased by applying M-EMS, resulting in an increase in the size of inclusions. The influence of M-EMS on inclusions was primarily on the slab subsurface. Following the application of M-EMS, the inclusions in the slab subsurface were experienced a reduction in number density from 9.99 to 6.11 #/mm2, and the area fraction was decreased from 69.51 × 10−6 to 57.31 × 10−6. However, the average size of inclusions was increased from 2.45 to 2.87 μm. With the application of M-EMS, the total oxygen content in the subsurface of the slab was reduced by 1–3 ppm, and the total oxygen content in the center of the slab was reduced by 0–1 ppm. These results indicated that the adoption of M-EMS contributed positively to the reduction of inclusions from the slab subsurface, thereby enhancing the surface quality of the slabs. Furthermore, the analysis revealed that the equiaxed crystal area comprised 12.06 pct of the total area without the consideration of M-EMS, while with the application of M-EMS, this proportion increased to 20.99 pct. [ABSTRACT FROM AUTHOR]

Non-uniform solidification of shell in continuous casting mold is the main cause of the high incidence of surface cracks of ultra-large beam blank (ULBB). To investigate the behaviors of the shell non-uniform heat transfer and its micro-structure growth, a thermomechanical model (TMM) of shell solidification in mold with the consideration of the mold flux and air gap dynamically filling in the shell-mold interface and a cellular automata-finite element (CAFE) model to describe the micro-structure growth of the shell were developed. In the models, the interfacial heat flux between the ULBB surface and mold calculated from the TMM was loaded on the CAFE model, and therefore, the cross-scale simulation of the shell solidification and the micro-structure growth were coupled. The results show that the air gap would not form at the positions of the web, fillet, and the center area of narrow face of the ULBB during the whole solidification in the mold. The thick air gap forms and concentrates in the flange tip, inner and outer corners of the flange as well as theirs surrounding areas. The thick mold flux mainly distributes in the areas of the flange outer corner, and the flange tip and the narrow face that are 0 to 45 mm and 0 to 31 mm away from the two edges of the flange outer corner. The maximum thicknesses of the air gap and mold flux appear at the positions of the inner and outer corners of the flange to the joints of the flange tip at the mold exit, which are about 0.75 mm and 0.99 mm, respectively. The maximum differences of the thickness of air gap and mold flux along the circumference of the mold are about 0.75 mm and 0.67 mm at the mold exit. The highest and lowest temperatures of the shell with a difference of 215 K appear at the flange tip and the flange inner corner. The maximum and minimum thickness of the shell appear at the center of the flange inner corner and the fillet of 617 mm from the center of the web, which are about 27.0 mm and 16.3 mm, with a difference of 10.7 mm. The maximum and minimum average grain sizes of the shell appear at the fillet and the flange inner corner, which are about 507.1 μm and 474.5 μm, with a difference of 32.6 μm. [ABSTRACT FROM AUTHOR]

In the continuous casting process, clogging of the submerged entry nozzle (SEN) significantly increases the risk of slag entrainment and the incidence of defects in the slab. A water model at 0.6 scale was created for this study. Acrylic glass particles of different sizes were pasted on the inner walls of the SEN to simulate different clogging rates. Wavelet transform combined with energy was used to analyze the mold level fluctuation. The mold flow field and the distribution of the mold slag were observed. According to the findings, it is necessary to monitor fluctuations on both sides of the narrow face of the mold (NF). An accurate assessment of the bias flow may be made by the wavelet transform combined with energy to analyze the mold level fluctuation at the NF on both sides of the mold. This is a promotion and innovation in traditional fluctuations analysis methods. The frequency at NF is higher on the side with a larger clogging rate when asymmetric clogging occurs in SEN. The upper circulating flow (UCF) velocity on the side with lower clogging is more significant. The mold slag cannot completely cover the molten steel because of the velocity difference. The UCF vortex center on the severe side of the clogging shifts toward the NF as the asymmetric clogging increases, and the velocity of the molten steel there gradually rises. This increases the frequency of slag entrainment and the range of molten steel exposure. [ABSTRACT FROM AUTHOR]

In the current study, a three-dimensional mathematical model was established, integrating with the large eddy simulation (LES) turbulent model, the volume of fluid (VOF) multiphase model, and the magnetohydrodynamics (MHD) model to investigate the influence of the mold electromagnetic stirring (M-EMS) on the multiphase flow field in a slab continuous casting mold. The results indicated that the application of M-EMS altered the flow pattern of molten steel in the mold, thereby intensifying the meniscus fluctuation. Moreover, it increased the probability of the slag entrainment, elevating the net slag entrainment rate by nearly ten times. With the increase in current intensity, the stirring effect of M-EMS not only intensified the meniscus fluctuation but also increased the net slag entrainment rate. A user-defined function (UDF) was employed to quantify the number, size, and spatial distribution of entrained slag droplets. The increase in current intensity led to an increase in the number of large-size entrained slag droplets. The greater stirring intensity at a current intensity of 600 A led to the fragmentation of the larger entrained slag droplets into several smaller droplets, thus the proportion of large-size entrained slag droplets was reduced. The stirring effect of the electromagnetic force led to the formation of numerous vortices along the centerline of the mold thickness. Consequently, this phenomenon led to an increase in the occurrence and probability of slag entrainment along the centerline of the mold thickness. Under the influence of M-EMS, the effect of slag viscosity on the multiphase flow field appeared to be less significant, while an increase in viscosity reduced the slag entrainment rate. The submerged entry nozzle angle directly influenced the flow field in the upper circulation, consequently affecting the slag entrainment rate. The size distribution of entrained slag droplets remained unaffected by the slag viscosity and the nozzle angle. [ABSTRACT FROM AUTHOR]

As an important refractory material in the continuous casting process, the clogging of submerged entry nozzle (SEN) can negatively affect the quality of the slab. In this paper, the effect of electric current pulse (ECP) on the interfacial reaction between molten steel and SEN during continuous casting of ultra-low carbon steel was studied. The results show that the application of ECP can effectively inhibit the adhesion and growth of clogging. After employing ECP, the structure of clogging at the interface changes and its density increases. The newly formed clogging is more stable and can effectively resist the impact of high-speed molten steel. In particular, applying ECP improves the qualification rate of liquid level fluctuation on the mold. The number of large-size inclusions and defects in the slab are significantly reduced, which has a positive effect on improving the quality of the slab and prolonging the service life of the SEN. [ABSTRACT FROM AUTHOR]

Breakout is the most destructive accident that interrupts the smooth production process of continuous casting, which needs to take effective and accurate measures to predict. In light of the "Y" form tear trace left at slab surface when sticking breakout happens, computer vision techniques are used in this paper to convert the one-dimensional temperature signal measured in time sequence by thermocouples into two-dimensional temperature rate thermography of mold copper plate, forecasting breakout by capturing the "Y" shape sticking region characteristic in thermography. In an effort to process big quantity of thermography data in a precise and stable way and differentiate between sticking breakout sample and normal condition sample, deep convolutional neural network model is constructed for recognizing between these two, and we develop a mold breakout prediction model based on identifying abnormal visual sticking region through CNN (convolutional neural network). The test result indicates that model is able to detect sticking breakout samples out of different temperature patterns and exclude normal condition samples at the same time. With achieving a 100 pct prediction accuracy for true sticking breakout, fine-grained classification model obtains a lower false positive rate compared to transfer learning model and a better generalization performance, offering a new train of thought into establishing data-driven abnormality detection methods during continuous casting process. [ABSTRACT FROM AUTHOR]

Three-dimensional mathematical model was established to investigate the solidification behavior during the continuous casting of a round bloom with the diameter of 0.7 m, where a novel swirling flow submerged entry nozzle (SEN) combined with mold electromagnetic stirring (M-EMS) method was used. The results show that an impinging flow phenomenon, which was normally formed in conventional single-port SEN casting, was effectively eliminated by adopting the new method. Molten steel from the swirling flow SEN port uniformly moved to the solidification front, which improved the dissipation rate of molten steel super-heat. When the rotational direction of the swirling flow in SEN was in the same direction as M-EMS, the super-heat of molten steel in mold can be decreased by 5 K, compared to the use of a conventional SEN with M-EMS. As the current intensity decreased from 310 to 100 A, the super-heat of molten steel in the mold center region was reduced by 3 K. This is due to that the shielding effect of M-EMS on rotational flow momentum from the swirling flow SEN became weak as the stirring intensity decreased. In addition, molten steel temperature near the meniscus under the current intensity of 310 and 100 A was 1787 K and 1790 K, respectively. The solidified shell thickness obtained by using 100 A current intensity was about 1 × 10−3 m larger than that of 310 A current intensity. [ABSTRACT FROM AUTHOR]

Strand electromagnetic stirring (SEMS) is widely applied in thin-slab continuous casting to promote the equiaxed crystal ratio (ECR). However, the effects of alternate electromagnetic stirring on the evolution of solidification macrostructure and ECR remain poorly understood. And the formation of the equiaxed crystal region beneath the stand and equiaxed-to-columnar transition (ECT) have been overlooked in most previous models. This study first introduces a novel equiaxed-columnar solidification model to comprehensively analyze the effects of alternate electromagnetic stirring in thin-slab continuous casting. A complete macrostructure feature of the slab, including the equiaxed crystal region beneath the strand, ECT, well-developed columnar dendrites, columnar-to-equiaxed transition, and center equiaxed crystal zone, could be simulated accurately. The multiphase model was validated by the measured ECR and columnar growing direction from a pickling corrosion experiment. Results showed that alternate stirring could improve the ECR effectively. The ECR was increased by 26 pct compared to the one-way stirring when the switching period of alternate stirring was 8–12 seconds. A multi-vortex flow structure was observed in the secondary cooling zone, which could increase the residence time of the molten steel and the nucleation rate. Furthermore, the vortex-shedding behavior of the upper recirculation alleviated the remelting of equiaxed crystals during the sedimentation. The behavior of multiphase flow under alternate SEMS is a novel finding. These preliminary results are encouraging and should be validated in other continuous casting processes. [ABSTRACT FROM AUTHOR]

Hollow granular mold flux is an essential functional material in the continuous casting process, and its melting behavior significantly influences continuous casting. The existing research mainly focuses on the influence of the characteristics of mold flux on the melting behavior and does not involve the operation of mold flux. This study explored the effect of flux layer thickness on the melting behavior of mold fluxes using a melting rate test method based on a copper bath and numerical simulation. The results show that with the increase in the flux layer thickness, the melting rate of mold fluxes shows the trend of the 'M curve,' including two upward and two downward stages. The 'M curve' is related to the temperature and combustion behavior of carbonaceous materials in the flux layer. In the first stage, as the thickness increases, the thermal insulation of the flux layer is significantly improved, which promotes the melting of the mold flux. In the second stage, the increase in flux layer thickness hinders the diffusion of O2 from the air to the flux layer, and the carbon–oxygen reaction rate decreases, which is not conducive to the combustion of carbonaceous materials and the flux melting. In the third stage, the increase in the flux layer thickness hinders the diffusion of CO2 to the outside, increases the CO2 concentration in the flux layer, promotes the Boudouard reaction, and increases the melting rate. In the fourth stage, with the increase in the flux layer thickness, O2 can only diffuse to the low-temperature zone (< 400 °C) of the flux layer and cannot participate in the carbon–oxygen reaction and form CO2, which decreases the rate of Boudouard reaction and the melting rate of mold flux. [ABSTRACT FROM AUTHOR]

The mold electromagnetic stirring technology and mold feeding steel strip technology are both effective method of reducing center segregation and shrinkage cavities in continuous casting bloom. In this work, a bidirectional flow-solid coupling model was established to investigate the swing and depth of steel strip feeding with the influence of both molten steel and electromagnetic forces. The results indicate that increasing the strip's feeding speed from 0.2 to 0.4 m/s without electromagnetic stirring results in an increase in the swinging amplitude from 6.26 to 11.89 mm. With the implementation of mold electromagnetic stirring, the bottom of the steel strip moves on the "Z" shape periodically, and the swing amplitude increasing with the current strength rising. When the feeding speeds are 0.2, 0.3, and 0.4 m/s, and the current is increased from 200 to 300 A, the maximum swing amplitude of the steel strip increases from 7.30, 12.18, and 21.09 to 10.34, 19.47, and 41.14 mm, respectively. [ABSTRACT FROM AUTHOR]

A new two-way coupled magnetohydrodynamic (MHD) model considering the dynamics change of electromagnetic force at steel–slag interface was established to investigate the multiphase flow and slag entrapment in slab continuous casting under mold electromagnetic stirring (EMS). The transient turbulent flow and the steel–slag interface behavior were described by solving the large eddy simulation (LES) model and volume of fluid (VOF) model. The level fluctuation, the location, and net mass of slag entrapment were quantitatively evaluated. By comparing the predicted level height within the in-situ measurement, the results show that the two-way coupled MHD model can better reveal the multiphase flow under EMS. The type of slag entrapment is closely related to the flow pattern, the vortex formation is predominant under the lower EMS current, while it changes to the shear-layer instability under the relatively high EMS current, the proportion of vortex formation slag entrapment decreases to 30.7 pct under the EMS current is 600 A. The tendency of net slag entrapment rate is the same as that of level fluctuation, with the increase of EMS current and casting speed, both the level height and net slag entrapment rate decrease firstly and then increase. Therefore, it is necessary to match the casting speed and EMS current to avoid the slag entrapment in actual production. The net slag entrapment rate is 0.034 kg/s, under the condition of 1.2 m/min casting speed and 600 A EMS current. [ABSTRACT FROM AUTHOR]

Machine learning (ML) algorithms have been proven to be effective methods in steel design and production processes. In this study, the feature analysis and prediction of slag entrapment in continuous casting process were carried out based on XGBoost model. Results show that the area under the curve (AUC) and accuracy of BO-XGBoost are 0.811 and 0.756, respectively, which are higher than PSO-XGBoost and GA-XGBoost. Feature analysis shows that mold flux, oscillation frequency, serial number, inner arc, casting speed (CS) and slab width are the key features which affect the entrapped slag defect, based on Gini coefficient and SHAP values. In addition, partial dependence plots of SHAP value suggest that it is conducive to product the qualified slabs with less entrapped slag defect, when the oscillation frequency is 60–140 cpm, inner arc is 7.5–9.5 m, CS is 0.35–1.2 m/min, serial number is less than 5, slab width is less than 1300 mm and 2# mold flux. [ABSTRACT FROM AUTHOR]

In this study, we developed a numerical model of a slab continuous casting mold coupled with multi-phase and multi-physical fields, known as MPF-Mold, and explored the effect of Fc-Mold on fluid flow, heat transfer, and solidification in the mold. Firstly, the simulation results were carefully verified from five perspectives. Next, the fast Fourier transform (FFT) is introduced to discuss the difference between MPF-Mold and the model considering only the fluid flow in the simulation results of level fluctuation. Typically, mold oscillation can be disregarded when analyzing the degree of level fluctuation through numerical simulation. However, neglecting multi-phase heat transfer and solidification may lead to overestimations of the severity of level fluctuation, especially in the region near the narrow meniscus. When coupling MPF-Mold with Fc-Mold, the upper backflow in the mold becomes stable, increasing symmetry and reducing level fluctuation severity and abnormalities. The shell uniformity index on the wide face meniscus and the lower part of the narrow face in the mold is significantly improved. This suggests that the upper and lower magnetic poles of Fc-Mold are beneficial to the shell uniform growth of the wide face meniscus and lower part of the narrow face, respectively. However, a new 'concave' appears in the shell near the corner of the mold, as a result of the horizontal vortex caused by deviations in the jet flow. Therefore, the magnetic field needs to be optimized to stabilize the flow field. MPF-Mold demonstrates advantages in achieving a reasonable match of steel grade, equipment, and process, and contributing to the digital transformation of continuous casting. [ABSTRACT FROM AUTHOR]

Longitudinal surface cracks are prevalent in the continuous casting of hypo-peritectic beam blanks, primarily related to multiphysics non-uniformity (multi-phase field, flow field, temperature field) within the mold. Therefore, multi-phase and coupled flow-thermal models were constructed to investigate the non-uniform multiphysics characteristics in the beam blank mold with a single nozzle and its effect on the formation of longitudinal cracks. First, the three-phase flow model reveals significant unevenness slag distribution along the web width, positively correlated to surface velocity of the molten steel. Subsequently, considering the impact of the solidification shell, surface velocity decreases nonlinearly with increasing immersion depth, influenced by web vortex position in the X-direction, which is also influenced by mold curvature, and interaction between web and side vortexes. Furthermore, the temperature field distribution inside the mold is non-uniform. Under the effect of the single-web recirculation flow, the temperature near the meniscus at the NN (position near the nozzle) side of the web is lower than that at the FN (position far away from the nozzle) side, resulting in more intensive initial cooling at this position. Meanwhile, a reheating zone exists at the mold exit of the NN side. Statistical analysis revealed that the absolute values of Spearman coefficient between the non-uniformity of shell thickness and the temperature and flow velocity of the molten steel exceed 0.6, which is related to the depth of the web vortex. Finally, from the perspective of the influence of SEN's immersion depth on multiphysics, the high surface velocity of the steel, strong cooling near the meniscus, and non-uniform shell thickness at the mold exit can be relieved with an immersion depth of 75 mm. The plant experiment confirmed that increasing the immersion depth from 65 to 75 mm leads to a relative reduction of 39 and 43 pct in the longitudinal cracks ratio for strands and rolled products, respectively. [ABSTRACT FROM AUTHOR]

The deleterious effects of brittle and rigid oxides on the quality of high-speed railway wheel steel can be mitigated by wrapping the oxides with sulfides. The investigation reveals the presence of three types of oxide–sulfide complex inclusions in the continuous casting billet. Type 1 possesses a core oxide with high CaO content, and its shell sulfide predominantly comprises CaS. Type 2 presents a core oxide with low CaO content, accompanied by a (Mn,Ca)S shell. The core oxide in Type 3 contains almost no CaO, and the shell sulfide is primarily MnS. The area ratio, defined as the ratio of sulfide area to oxide area, increases successively among the three types of complex inclusions. The formation mechanisms of the three types of complex inclusions vary. In Type 1, the core oxide originates from the refining process. The CaS in the shell sulfide is a product of the reaction between Al and S in the liquid steel and CaO in the oxide. In Type 2, the core oxide is formed during the cooling and solidification process. As the liquid steel solidifies, the segregation of Ca, Mn, and S leads to the formation of (Mn,Ca)S shell around the oxide. The formation temperature of the core oxide in Type 3 is lower than that of Type 1 and Type 2, occurring in the late stages of solidification. A substantial amount of MnS is formed around the oxide near the end of solidification. In the finished wheel, Type 2, characterized by its (Mn,Ca)S shell, exhibits appropriate hardness and resistance to deformation, rendering it the most optimal among three types of complex inclusions. [ABSTRACT FROM AUTHOR]

In the current study, the influence of Li2O and Na2O on the viscosity, crystallization, and structure of the high TiO2-containing mold slag for the continuous casting of high-Ti steel was investigated to improve the property of the CaO–SiO2–TiO2-based slag under the steel-slag reaction through the measurement of the viscosity-temperature relationship, crystallization temperature and phases, and the Raman spectrum. With the increase of Li2O content from 0 to 8 pct, the viscosity at 1300 °C and melting temperature decreased from 0.54 to 0.01 Pa s, and 1151 to 884 °C, respectively. While the viscosity of the slag at 1300 °C increased from 0.20 to 0.62 Pa s, the viscosity of the slag at 1400 °C decreased from 0.16 to 0.09 Pa s, and the melting temperature decreased from 1195 to 1077 °C with the Na2O content from 2 to 10 pct. According to the thermodynamic calculation and XRD measurement, the main crystallization phase of high TiO2 slags was CaTiO3 with the content of Li2O below 4 pct and Na2O of 2 to 10 pct, the crystallization phase gradually changed from CaTiO3 to LiTiO2 with Li2O from 4 to 8 pct, and the morphology of the crystalline nucleus changed from the type of spiky star to barbed sphere. Similarly, with the Li2O content from 2 to 6 pct the initial and complete crystallization temperature decreased and increased, respectively, while those increased with the increase of Na2O content, indicating that the increase of the Li2O below 4 pct and the decrease of the Na2O in the current slag resulted in the weak crystallization ability. With the addition of Li2O content, the complex structural units of Q1, Q2 and Q3 were depolymerized, and the slag viscosity decreased. With the increase of Na2O content, structural units of Q0, Q1 and Q2 structure units had the tendency to increase, and the viscosity of slag at 1400 °C decreased. These results could be used for the selection of typical components of mold slags for continuous casting of high-Ti steel. [ABSTRACT FROM AUTHOR]

During continuous casting, accurate real-time prediction of strand solidification ensures the effective implementation of reduction. Due to the influences of the continuous casting production environment, equipment, and other factors, the calculations from a thermal tracking model deviate; these deviations are difficult to find and correct in real time, affecting the effective implementation of the casting process. In this paper, the online calculation processes are explored for the stress–strain and force–reduction relationships during reduction. Based on the calculation results of the finite element model for the cross-sectional strain distribution during reduction, the influences of certain parameters, such as reduction, dimension, steel, and reduction position, on the strain distribution of the bloom cross section during reduction are analyzed. Reduction amount is the main factor affecting the strain distribution; within a certain range, the element strain is linear with the reduction. Based on this finding, a real-time bloom force prediction model is proposed in this paper. The model combines the strain distribution trend of the finite element model of thermal–mechanical coupling and calculates the strain and strain rate of each element of the cross section according to the actual reduction process. By combining the real-time temperature results of the thermal tracking model with the constitutive characteristics of the steel determined in the experiment, the stress–strain and force–reduction relationships during continuous casting are accurately predicted. According to a comparison with the actual force of the on-site reduction process, the error is generally less than 5 pct; however, the error differs for equipment problems. The calculation results show that the ambient temperature (5 °C and 10 °C) also affects the actual compaction force during the reduction process. The force deviation at different ambient temperatures is about 5 to 10 pct. Through a comparison of bloom temperature and force data, the on-site thermal tracking model can be verified in real time, and the conditions of the reduction equipment can be preliminarily diagnosed. [ABSTRACT FROM AUTHOR]

In this study, a novel technique of Vertical Linear Electromagnetic Stirring (V-LEMS) was proposed and applied in the final solidification zone of the 260 mm × 300 mm GCr15 bearing steel continuous casting (CC) bloom. The effects of V-LEMS on melt flow, heat transfer, and solidification have been investigated by establishing a three-dimensional numerical simulation model. The results demonstrate that an effective longitudinal magnetic field is formed in the inner arc of the bloom by applying V-LEMS, which is 1.9 times the height of the V-LEMS device, and the electromagnetic force within this effective longitudinal magnetic field is greater than 1.0 × 10 3 N · m - 3 . The V-LEMS induces longitudinal circulation flow in the liquid core of the bloom, whose height reaches 1.8 times of the V-LEMS device, so as to promote longitudinal mixing of the melt. The longitudinal circulation flow transports the high-temperature melt in the upper region of the liquid core to the lower region of the bloom, which improves the temperature uniformity of the liquid core, and it is beneficial to increase the proportion of equiaxed grains in the center of the bloom. By applying V-LEMS in the final solidification zone of the bloom, the melt temperature near the solidification front in the liquid core is 6.5 K higher than that without V-LEMS, and the width of the liquid core is 4.3 mm wider than that without V-LEMS. These effects are beneficial to improve the fluidity and feeding ability of the melt in the liquid core and reduce defects such as porosity, shrinkage cavity, and cracks in the center of the bloom. [ABSTRACT FROM AUTHOR]

In this paper, a neural network model is introduced, which uses Convolutional Neural Network model optimized by Genetic Algorithm (GA-CNN) to predict the liquid level fluctuation of continuous casting mold in real time. The experimental data were obtained from the practical production process of an iron and steel plant in China. For the two-stream continuous caster in this factory, two sets of mold liquid level fluctuation value data sets were established. These data sets are categorized into the first- and the second-stream mold liquid surface fluctuation data set. Both data sets comprise 138 production parameters along with the mold liquid level fluctuation values. Random Forest feature screening and data preprocessing are carried out on the data set, so that the processed data can be learned and trained by the model, thus obtaining the mold liquid level fluctuation prediction model. To facilitate the analysis, the sensitivity analysis of related continuous casting production parameters and mold level fluctuation data was carried out. Subsequently, the influence of production parameters on the fluctuation value of mold liquid level was investigated by characteristic thermal diagram and Shapley additional explanations diagram, and the influence degree of each parameter on the model performance was determined. The results indicate that the GA-CNN model demonstrates strong predictive capability, with a high correlation coefficient (R2) of 0.98, a low mean absolute error (MAE) of 0.1093, and a mean square error (MSE) of 0.0225. Notably, the position of the stopper was identified as a critical factor significantly affecting mold level fluctuations. The model has high prediction accuracy and can meet the needs of practical application in steel plants. [ABSTRACT FROM AUTHOR]

A decision support system was developed using supervised machine learning (ML) approach for optimization of calcium (Ca) additions by continuously monitoring the physical state of non-metallic inclusions (NMIs) inside low-alloyed liquid steels. In this work, two instances were considered to design the base algorithm for the proposed supervisory system: (1) Clogging of submerged entry nozzle (SEN) during continuous casting of steels due to accumulation of solid oxide non-metallic inclusions (NMIs) and (2) Ca treatment during secondary steelmaking for modification of oxide NMIs from solid to liquid state to avoid SEN clogging. At first, experimental investigations were carried out on liquid steel samples from three low-alloyed Ca-treated steel grades from the same steel family to evaluate the characteristics of solid oxide NMIs that cause SEN clogging. In the next step, data-driven models were developed using an in-house ML algorithm trained primarily with process data for calculating the value of the newly proposed dummy parameter 'Clog.' These models, after testing, were architected to develop a supervisory system based on experimental investigations and data-driven models. The objective of this proposed supervisory system was to predict the optimum quantity of Ca needed for successful modification of NMIs from solid to liquid state to avoid SEN clogging based on the forecasted 'Clog' value. Finally, industrial data from ~ 3000 heats were tested to verify the results obtained from the developed supervisory system. The results confirmed that this novel supervisory system could predict the optimum class of Ca for all studied steel grades with 95 to 98 pct accuracy. The integration of this online supervisory system in steel production is expected to minimize operators' corrective actions in achieving realistic control of Ca additions. [ABSTRACT FROM AUTHOR]

Multiscale titanium carbides are one of the main causes of corner crack defects of 0.37 pct Ti–Mo steel slab. In this work, the evolution of titanium carbides precipitation under different cooling rates were investigated by high-temperature laser scanning confocal microscopy, transmission electron microscope, and thermal simulation. The research revealed that micron TiC particles are derived from eutectic reactions at the end of solidification which are divided into dendritic TiC and lamellar TiC according to the precipitation order. According to Thermo-Calc simulation, the titanium elements play a leading role on the titanium-carbide/γ interface movement. Nano-(Ti,Mo)C are mainly precipitated from the high-temperature austenite after solidification. The micrometer TiC is gradually broken and refined, and the distribution is transferred from grain boundary to grain interior with the increase of cooling rate. High cooling rate can reduce the production of micron TiC but promote the formation of ferrite film and destroy the hot ductility. [ABSTRACT FROM AUTHOR]

An integrated model was proposed in the current study to predict the composition distribution of inclusions along the thickness of a tire cord steel continuous casting billet. The thermodynamics, kinetics, fluid flow, heat transfer, solidification, and element segregation were combined in the integrated model. More accurate results were obtained using the current model compared with the published work, indicating the great importance of the kinetics and element segregation in the inclusion predication. Thermodynamic calculation showed the equilibrium composition of inclusions at 1073 K was approximately 92 wt pct SiO2–3 wt pct MnO–4 wt pct Al2O3–1 wt pct CaO, which was obviously different from measured results, even though the element segregation was premeditated, indicating the insufficiency of the thermodynamics in predicting the inclusions composition in the billet. A large positive segregation of C, Si, Mn, and S at the center of the billet was revealed, and the average segregation index was simulated to be 1.89, 1.05, 1.08, and 1.26, respectively. The strong element segregation of the steel induced a fluctuation in the composition of inclusions along billet thickness, which was more accurate compared with the model ignoring the element segregation. [ABSTRACT FROM AUTHOR]

The numerical methods based on the unsteady Reynolds-averaged Navier–Stokes (URANS) equations are robust tools to model the turbulent flow for the industrial processes. They allow an acceptable grid resolution along with reasonable calculation time. Herein, the URANS approach is validated against a water model experiment for the special single port submerged entry nozzle (SEN) design used in the thin slab casting (TSC) process. A 1-to-2 under-scaled water model was constructed, including the SEN, mold, and strand Plexiglas segments. Paddle-type sensors were instrumented to measure the submeniscus velocity supported by videorecording of the dye injections to provide both qualitative and quantitative verification of the SEN flow simulations. Two advanced URANS-type models (realizable k–ε and shear stress transport k–ω) were applied to calculate velocity pattern on meshes with various resolutions. An oscillating single jet flow was detected in the experiment, which the URANS simulations initially struggled to reflect. The dimensionless analysis of the mesh properties and corresponding adjustment of the boundary layers inside the SEN allowed to resolve the flow pattern. The performed fast Fourier transform (FFT) verified a good numerical prediction of the flow frequency spectrum. The corresponding simulation strategy is proposed for the industrial CC process using the URANS approach. [ABSTRACT FROM AUTHOR]

Clogging in the submerged entry nozzle is a common concern during the continuous casting of Al-killed steels, deteriorating the steel quality and impeding the continuity of mold operations. Water experiments were carried out to investigate the multiphase flow in the mold under different nozzle clogging modes. Bubble measurement was achieved by projection methodology using a high-speed camera. The LES-VOF-DPM model was developed based on size distributions of bubbles obtained from water modeling, to evaluate the effects of nozzle clogging on bubble capture by solidifying shell and slag-metal interface behaviors. The results show that clogging at the nozzle groove inhibits the bubble break-up by turbulent flow. Bubbles remaining in large sizes float vertically, leading to concentrated impacts on the slag-metal interface. Clogging at two nozzle ports increases the entry velocity under a constant casting speed. Due to the broken effect of the strong turbulent flow, 9.23 pct of the bubbles are smaller than 0.5mm. Small bubbles tend to reach a narrow face following the entry flow and then are trapped by the solidifying shell. The present study provides a comprehensive approach to evaluating the life cycle of SEN. [ABSTRACT FROM AUTHOR]

The growth of columnar grains and the distribution of equiaxed grains in the continuous casting process of round blooms had a significant impact on the solute distribution properties of the product. External physical fields, including gravity, electromagnetic stirring (EMS), and temperature, directly affected the growth of the columnar grains and the nucleation, growth, and movement of the equiaxed grains, and thereby influenced the final distribution characteristics of the solidification structure and of the phase fractions. In this study, a model for the growth of the columnar grains, and the nucleation, growth, and movement of the equiaxed grains was developed. The control variable method was employed, and the effects of different mold electromagnetic stirring (M-EMS) parameters, casting temperatures, and casting speeds on the solidification structure were individually calculated and analyzed. The results indicated that under the influence of gravity, the equiaxed grains migrated from the inner arc side to the outer arc side, which resulted in asymmetry in the microstructure on both sides. By increasing the electromagnetic stirring current, reducing the casting temperature, and lowering the casting speed, the equiaxed grain ratio can be increased. The effect of reducing the casting temperature is most significant, with the equiaxed grain ratio raising from 51.2 to 65.5 pct when the casting temperature is reduced from 1519 °C to 1514 °C. Lowering the superheat, lowering the casting speed, and enhancing M-EMS all lower the overall temperature of the blooms, leading to more pronounced asymmetrical characteristics in the structure. This model can efficiently calculate the heat transfer behavior, evolution, and distribution characteristics of the solidification structure of continuous casting round blooms under different external field effects and casting process parameters, providing a theoretical basis for improving the internal quality of round blooms in production. [ABSTRACT FROM AUTHOR]

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]

Microsegregation of the steel in continuous casting is inevitable and results in the banded structure of the rolled steel, which reduces the anisotropy machinability and service life of the steel. Microsegregation can be categorized into dendrite segregation and porosity segregation, with the latter posing a more significant risk, which can only be improved by high-temperature diffusion of hot charging. To accurately characterize the degree of microsegregation, a new evaluation method based on clustering algorithm is developed in this work, which takes into account the influence of area distribution on the segregation ratio. On this basis, a three-dimensional carbon diffusion kinetic model is established, which could predict the circumferential carbon diffusion of dendrites segregation and porosity segregation together during heating process as well as determining the optimal heating process. Combining with orthogonal experiments, the effects of heating time and temperature on the improvement elimination of porosity segregation in gear steel continuous casting blooms were investigated, and the average prediction error of three-dimensional diffusion kinetic model was no less than 4.62 pct. The results indicate that the optimum conditions for diffusing porosity segregation are achieved by holding at 1250 °C for 1.5 hours. [ABSTRACT FROM AUTHOR]

During the continuous casting and isothermal soaking process, the steel casting blank undergoes complex temperature variation. Accurately predicting the continuous growth of austenite grains in this procedure is crucial for ensuring quality control in casting blanks and final products. Based on the classical isothermal austenite grain growth model and the driving force of grain boundary migration, the prediction model for continuous growth of austenite grains has been established. This model considered the complex temperature control process and the influence of temperature change rate. The results indicated a strong agreement between the model's predictions and experimental data, demonstrating the ability to accurately simulate complex temperature variation such as heating and soaking processes. Furthermore, this model could predict the evolution of the mean austenite grain size of steel casting blank. Both the exponent and activation energy of grain growth were observed to exhibit a negative correlation with temperature, displaying a linear relationship. The model was employed to investigate the behavior of austenite grain growth during heating and soaking processes, as well as to predict its response under complex temperature variable rates. These findings provide a basis for regulating austenite grain size and ensuring the quality of casting blank during various casting processes. [ABSTRACT FROM AUTHOR]

The prevention of nozzle clogging in the tundish upper nozzle through argon blowing has been commonly practiced. However, there is still a lack of understanding regarding the specific factors and mechanisms that influence the formation of the argon film. In this paper, the movement behavior of argon bubbles in upper nozzle of tundish during argon blowing process was studied. Results indicate that the movement behavior of argon bubbles is influenced by several factors, such as pore diameter, volume flow rate of the fluid, argon blowing rate, and number of effective pores. It was observed that the departure radius of the bubble increases with a lower pore position and a larger pore diameter in a given upper nozzle. Additionally, the departure time of the bubble increases with a lower pore position, a lower argon blowing rate, a larger pore diameter, and a larger number of effective pores. Moreover, the movement time of the bubble increases with a lower pore position, a smaller volume flow rate of the fluid, and a larger pore diameter. Under specific process parameters, the distribution of bubbles in the upper nozzle appears as bubble chains. For actual continuous casting production, it is recommended to consider using smaller pore diameters and layered permeable bricks, as this can serve as a theoretical and technological basis for optimizing argon blowing parameters and permeable brick design. [ABSTRACT FROM AUTHOR]

The flow behavior of molten steel in the mold of the thin slab continuous casting is complicated and the level fluctuates violently, which has a great influence on the quality of the slab. A multiphase transient model of thin slab mold has been developed to describe the asymmetric flow behavior of molten steel. The difference of flow field between three-dimensional and two-dimensional models was compared, and the influence of heat transfer and solidification behavior on the steel flow was discussed. The cause of the asymmetric flow of molten steel in the thin slab mold and its influence on the steel/slag interface were investigated. The effect of the SEN parameters on the deviation flow was analyzed by statistics the maximum deviation ratio and the deviation frequency. The results show that the uneven flow rate on both sides of the nozzle is considered to be a congenital factor of the deviation phenomenon in the mold, and the cavity structure of the mold is an inevitable condition for the asymmetric flow of molten steel. The deviation flow on both sides alternates aperiodically, and the interface fluctuation is the most severe in the transition stage. Optimizing the SEN parameters will reduce the amplitude and prolong the conversion period of the deviation flow, thus improving the stability of the flow field and the interface. [ABSTRACT FROM AUTHOR]

Hollow granular mold flux is an essential functional material in the continuous casting process, and its melting behavior significantly influences continuous casting. Existing researches mainly focus on the influence of carbonaceous materials and carbonates on the melting behavior of mold flux. This study investigates the influence of granule shape parameters on the melting behavior of mold flux using a melting rate tester based on a copper bath. The results show that the gas diffusivity in the powder layer decreases with the decrease in the granule size, which improves the thermal insulation of the powder layer, and promotes the melting of the mold flux. In the mold flux with composite granule size, fine granules will fill in the pores formed by the accumulation of coarse granules, reduce the gas diffusivity, and promote the melting of the mold flux. When the granules have poor sphericity and large porosity, uneven sintering is prone to occur during the heating process, resulting in uneven pores in the sintered layer and affecting the melting uniformity of the mold flux. [ABSTRACT FROM AUTHOR]

To ensure accurate estimation of mold heat flux, this study investigated the impacts of the thermocouples placement inserted in the mold wall, the temperature sampling rate (fs), and the noise level of temperature data on the precision of two-dimensional Inverse Heat Conduction Problem (2DIHCP). The results showed the accuracy of heat flux estimations decreases as the distance between the thermocouple and the mold surface increases, and it is recommended that the distance should not exceed 3 mm. The accuracy of the heat flux initially increases as fs increases from 5 to 10 Hz, reaches a relatively stable state as fs increases from 10 to 60 Hz, and eventually decreases as fs increases from 60 to 100 Hz. Additionally, higher temperature measurement errors typically lead to decreased accuracy in inverse analysis. 2DIHCP was employed to compute the heat flux for a mold simulator experiment, and the results demonstrated its effectiveness in reconstructing the mold heat flux at the meniscus level during the time lapse of a mold oscillation cycle. [ABSTRACT FROM AUTHOR]

Electromagnetic braking (EMBr) is critical for suppressing the turbulence in the mold and developing a high-speed thin-slab continuous casting technology. The main problem is that the relationship between EMBr strength and flow patterns in a funnel mold is still inconclusive. Effects of magnetic induction intensity on the flow pattern and slag-metal behavior were numerically analyzed using the potential method. The variation of the electrical conductivity during solidification was considered to predict a physical-justified distribution of induced current. Results show that the induced current is mainly distributed in nozzle jets and solidified shells. Two induced e-current loops in opposite-rotated directions can be observed between the nozzle jet and solid shell, indicating that the shear stress caused by the induced e-current loops is a potential disadvantage for the thermal-mechanical behavior of the solidified shell. The flow pattern changes from classic double-roll flow to three-roll flow and then to single-roll flow with the increase of magnetic induction intensity. Backflows form near nozzle outlets at 0.17 T and occupy the entire slag-metal interface at 0.215 T. The core of the upward reverse flow from nozzle jets moves down, and the downward reverse flow gradually converges inward with EMBr intensity. Particular attention should be paid to the three-roll flow pattern. The flow field on the slag-metal interface will become unstable and asymmetrical, especially at 0.193 T. The plug-like flow is formed only when the magnetic induction is strong enough. [ABSTRACT FROM AUTHOR]

As one of the most serious defects in the products of continuous casting steel, the surface depressions with longitudinal cracks originated from the mold were clearly characterized. A mold simulator technique was developed to investigate the effects of different mold cooling flow rates (3.5, 6.0, 7.5 L/min) on the evolution of depression-type cracks and mold flux infiltration for the steel continuous casting in this study. The mold simulator results indicated that the depression and longitudinal crack become more serious with the increasing of mold cooling intensities. Furthermore, when the cooling intensity enhanced from 3.5 to 7.5 L/min, the average solidification factor of shell increased rapidly from 2.37 to 2.91 (mm/s)1/2, and the mean heat flux in the initial solidified shells with depressions reduced by 0.723 MW/m2 during the initial 0 to 1.5 seconds solidification stage. In addition, the higher mold cooling intensities of 6.0 to 7.5 L/min could result in an increasing of slag film thickness and the formation of amorphous slag, which contributed to the uneven infiltration of mold flux. [ABSTRACT FROM AUTHOR]

Strand electromagnetic stirring (SEMS) is widely applied in thin slab continuous casting to improve the equiaxed crystal ratio (ECR) of steel. To provide a deeper insight into the role of SEMS in controlling the flow pattern, superheat transportation, macrosegregation, and as-cast structure in the whole strand. A three-phase equiaxed-columnar solidification model was developed to predict the solidification process. The anisotropic permeability of directional columnar structures was integrated into the model by tracking the columnar growing direction. Numerical results showed that two recirculating flow regions came into being under the one-way moving magnetic field induced by the SEMS. The upward recirculating flow deflected the nozzle jet and assembled a superheat melt impinging towards the narrow face under the electromagnetic stirring. Level velocity and level height in the stirring direction were disturbed by the upward flow. Equiaxed grains formed in the stirring direction were less than the volume fraction on the other side. The one-way magnetic field also caused an asymmetric distribution of equiaxed grains in the thickness direction. Applying SEMS was beneficial to the improvement of ECR. The ECR in the strand was 4 pct in the absence of electromagnetic stirring, and it increased to 17.4 pct after applying the SEMS. [ABSTRACT FROM AUTHOR]

Properly coordinating the initial solidification and heat transfer behavior of the meniscus of the mold is crucial for stabilizing and improving the surface quality of continuous casting slabs. The study comprehensively considers the geometric, contact, and motion characteristics of the meniscus under mold periodic oscillation, and develops a three-dimensional numerical model that couples the heat transfer of molten steel, shell solidification, and multiphase flow. The transient periodic heat transfer behavior of the meniscus in the mold is simulated and analyzed. The investigation begins with analyzing the distribution and variation of heat flux, and then focuses on analyzing the effects of steel level height, upper backflow, and thickness of mold flux on the formation of local high heat flux regions, periodic severe fluctuations, and sharp changes in corner heat flux. The transient variation and signal characteristics of heat flux near the meniscus are analyzed through Fast Fourier Transform (FFT) and Power Spectral Density (PSD). The analysis reveals that the high steel level with circulation is the main factor contributing to the formation of a local high heat flux zone. The flow patterns of molten steel and the uneven distribution of solid slag film can result in discontinuities in the region of sharp fluctuations. The variation of transient heat flux is affected by the relative motion between the initial solidified shell and the copper plate in the meniscus. The low-frequency heat flux is closely related to the melt flow fluctuations and the shell solidification, while the high-frequency heat flux is introduced by the mold oscillation. The signal difference of the heat flux near the meniscus is determined by its solidification rate and height. The results are beneficial for monitor the formation of initial solidification shell defects of the meniscus. [ABSTRACT FROM AUTHOR]