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Standard AA5083 (ZSE000), AA5083 modified with 0.3 wt.% Zr and 0.3wt.% Sc (ZSE330) and AA5083 modified with 0.3 wt.% Zr, 0.2wt.% Sc and 0.1wt.%Er(ZSE321) sheets were fabricated through a short process (including a simulated twin-belt continuous casting, subsequent direct rolling, intermediate annealing, cold rolling and stress-relief annealing) to systematically investigate the influence of partially substituting Er for Sc on the microstructure, mechanical properties and corrosion resistance of short-processed Al-4.7Mg-0.6Mn-0.3Zr-0.3Sc sheets. The results show that ZSE321 presents the optimal tensile properties (UTS: 541 MPa; 0.2%PS: 469 MPa and EF:7.7%) among the three experimental sheets. This is attributed to significant grain refinement, the inhibition of the recrystallization and promotion on the precipitation of Al3(Sc, Zr, Er) nanoparticles. Furthermore, the corrosion properties of the experimental sheets were also explored in this study, and the short-processed ZSE321 sheet presents the optimum corrosion resistance. [ABSTRACT FROM AUTHOR]

The solidification structure characteristics are decisive for the production of extra-thick slabs. This study developed a solidification heat transfer model and a cellular automaton–finite element coupled model to investigate the solidification behavior and structure characteristics of a 475 mm extra-thick slab. The models were applied under various continuous casting process parameters and different alloy element content. The simulation results reveal that casting speed has the most significant effect on the solidification behavior of extra-thick slabs, surpassing the impact of specific water flow and superheat. The solidification structure characteristics of the 475 mm extra-thick slabs were investigated under various conditions. The findings indicate that at higher casting speeds and superheats, the average grain size increases and the grain number decreases. The average grain size initially decreases and then increases with the rise in specific water flow, reaching its minimum at approximately 0.17 L·kg−1. Additionally, the average grain radius first decreases and then slightly increases with an increase in carbon content, achieving the minimum value of about 0.17% carbon. Compared with carbon and manganese, silicon has a greater impact on the solidification structure of ultra-thick slabs, and a moderate increase in silicon content can effectively refine the grain size. This study provides a theoretical foundation for understanding the changes in solidification structure characteristics and optimizing continuous casting process parameters for 475 mm extra-thick slabs. [ABSTRACT FROM AUTHOR]

Longitudinal crack defects are a frequent occurrence on the surface of thin slabs during the high-speed continuous casting process. Therefore, this study undertakes a detailed analysis of the solidification characteristics of hyper-peritectic steel thin slabs. By establishing a three-dimensional heat transfer numerical model of the thin slab, the formation mechanism of longitudinal cracks caused by uneven growth of the initial shell is determined. Based on the mechanism of longitudinal crack formation, by adjusting the performance parameters of the mold flux, the contradiction between the heat transfer control and lubrication improvement of the mold flux is fully coordinated, further reducing the incidence of longitudinal cracks on the surface of the casting thin slab. The results show that, using the optimized mold flux, the basicity increases from 1.60 to 1.68, the F- mass fraction increases from 10.67% to 11.22%, the Na2O mass fraction increases from 4.35% to 5.28%, the Li2O mass fraction increases from 0.68% to 0.75%, and the carbon mass fraction reduces from 10.86% to 10.47%. The crystallization performance and rheological properties of the mold flux significantly improve, reducing the heat transfer performance while ensuring the lubrication ability of the molten slag. After optimizing the mold flux, a surface detection system was used to statistically analyze the longitudinal cracks on the surface of the casting thin slab. The proportion of longitudinal cracks (crack length/steel coil length, where each coil produced is about 32 m long) on the surface of the thin slab decreases from 0.056% to 0.031%, and the surface quality of the thin slab significantly improves. [ABSTRACT FROM AUTHOR]

The effect of Al or Cu content on the microstructure and mechanical properties of continuous casting and extrusion Zn alloys has been studied by a room temperature tensile test, X-ray diffraction, and scanning electron microscope. With the increase in Al content, the microstructure of continuous casting and extrusion Zn alloys slightly coarsens, and the lamellar eutectic structure increases. The changes in the above structural factors result in a slight decrease in strength and a significant increase in the elongation of Zn-Al alloys. The strength of Zn alloys increases as the Cu content increases due to the increased content and size of the second phase in the Zn alloys. This means that the mechanical properties of Zn alloys can be adjusted by a continuous casting and extrusion process, and the improvement of equipment capacity can improve the structure and morphology of the alloys. [ABSTRACT FROM AUTHOR]

To improve the strength of the metal while maintaining good plasticity, helical fibers are added to the metal matrix. How to form helical fiber and control its parameters in the preparation process are urgent problems to be solved in the study of helical fiber-reinforced metal matrix composites. In this paper, the continuous casting process of helical fiber-reinforced metal matrix composites was proposed. To reduce the difficulty of the experiment, the formation process of helical fiber on metal matrix and the relationship between the continuous casting process parameters and helical shape fiber parameters were studied by preparing helical carbon fiber-reinforced lead matrix composites with a low-melting-point metal matrix. The results show that this process can produce helical fiber-reinforced metal matrix composite stably and continuously, and the helical shape parameters of the composite can be controlled by changing the process parameters of continuous casting. To further improve the practical application of this process, helical carbon fiber-reinforced aluminum matrix composites were prepared. The test result in terms of mechanical property shows that the tensile strength and elongation of the composite were improved. This indicates that the reinforced phase of the helical structure of the metal matrix composite has higher strength and toughness compared with the matrix metal. [ABSTRACT FROM AUTHOR]

ŠTORE STEEL Ltd. is one of the three steel plants in Slovenia. Continuous cast 180 mm × 180 mm billets can undergo cooling to room temperature using a turnover cooling bed. They can also be cooled down under hoods or heat treated to reduce residual stresses. Additional operations of heat treatment from 36 h up to 72 h and cooling of the billets for 24 h, with limited capacities (with only two heat treatment furnaces and only six hoods), drastically influence productivity. Accordingly, the casting must be carefully planned (i.e., the main thing is casting in sequences), while the internal quality of the billets (i.e., the occurrence of inner defects) may be compromised. Also, the stock of billets can increase dramatically. As a result, it was necessary to consider the abandoning of cooling under hoods and heat treatment of billets. Based on the collected scrap data after ultrasonic examination of rolled bars, linear regression and genetic programming were used for prediction of the occurrence of inner defects. Based on modeling results, cooling under hoods and heat treatment of billets were abandoned at the casting of several steel grades. Accordingly, the casting sequences increased, and the stock of billets decreased drastically while the internal quality of the rolled bars remained the same. [ABSTRACT FROM AUTHOR]

The study investigates the effect of pulsed magnetic fields on undissolved carbides in high-carbon chromium bearing steel GCr15 billets. The billets were subjected to heat treatment at 950 °C, with a pulsed magnetic field of varying durations applied during the process. The influence of the pulsed magnetic field on the distribution of undissolved carbides within the billets was investigated, and the thermodynamic and kinetic mechanisms of undissolved carbides dissolution were explored. The results indicate that the area percentage of undissolved carbides in the microstructure decreases from 1.68% to 0.06% after applying a pulsed magnetic field for 10 min, and the size of undissolved carbides decreases from 17.5 μm to 4.9 μm. When a pulsed magnetic field is applied for 30 min, all undissolved carbides dissolve. The statistics demonstrate that the average size of undissolved carbides is reduced from 14.19 μm to 0.63 μm, with a reduction percentage reaching 96%. Over the same duration, the number density of the undissolved carbides decreases from (0.19~0.55)/mm2 to (0.03~0.1)/mm2, and the percentage area of the undissolved carbides decreases from (1.26~1.68)% to (0~0.02)%. Thermodynamically, applying a pulsed magnetic field lowers the dissolution energy barrier of undissolved carbides and modifies their transformation temperature. Kinetically, the rate of alloy element diffusion is enhanced by increasing the frequency of atomic jumps. This research aims to provide new insights into enhancing the contact fatigue life of bearing steel, increasing the proportion of special steel, and optimizing the steel deep-processing process. [ABSTRACT FROM AUTHOR]

Submerged entry nozzle (SEN) clogging will affect the production efficiency and product quality in the continuous casting process. In this work, the transient SEN clogging model is developed by coupling the porous media model defined by the user-defined function (UDF) and the discrete phase model (DPM). The effects of the transient SEN clogging process on the flow field, the distribution of argon gas bubbles and the fluctuation of the interface between steel and slag in the concave bottom SEN in the continuous casting slab mold with a cross-section of 1500 mm × 230 mm are studied by coupling transient SEN clogging model, DPM and volume of fluid (VOF) model. The results show that the actual morphology and thicknesses of SEN clogging are in good agreement with the numerical simulation results. The measurement result of the surface velocity is consistent with the numerical simulation result. With increasing the simulation time, the degree of SEN clogging increases. The flow velocities of molten steel flowing from the outlet of the side hole increase, because the flow space is occupied with the clogging inclusions, which leads to the increased number of argon gas bubbles near the narrow wall. The steel–slag interface fluctuation near the narrow walls also increases, resulting in the increased risk of slag entrapment. [ABSTRACT FROM AUTHOR]

During continuous slab casting, strand electromagnetic stirring (S-EMS) has a significant effect on improving the slab quality. In the current work, a numerical model based on the practical slab continuous casting machine and coupled electromagnetic field, flow field, solidification, and solute transport was established to investigate and evaluate the effect of the S-EMS installation position with various current intensities on metallurgical behavior. The model was verified by magnetic field measurement, infrared camera, and nail shooting experiments. The results show that moving the S-EMS installation position to the solidification end reduces the stirring effect due to the skin effect and the increasing thickness of the slab shell. A higher installation position is beneficial for improving the equiaxed grain rate, while a lower one is beneficial for reducing carbon segregation. The maximum segregation index and range decrease from 1.26 to 1.2 and from 0.42 to 0.36 with the installation position being decreased from −3 m to −12.8 m, respectively. The industrial trials show that S-EMS installed at 3 m has a significant effect on expanding the equiaxed grain zone and a deteriorating effect on reducing carbon segregation. [ABSTRACT FROM AUTHOR]

This study proposed a new method for homogenizing continuous casting blooms based on solidification simulation calculations and industrial tests. The text describes a theoretical analysis of the solidification route of a cast billet of high-carbon alloy steel (B300A) under different process conditions. It summarizes the changing law of different under-pressure process parameters and under-pressure efficiency. The text also presents a solution to the seriousness of center shrinkage defects in the continuous casting of a large square billet of high-carbon alloy steel with the synergistic control technology of mixed light and heavy mixing under pressure. The study indicates that the center carbon segregation index of a high carbon steel continuous casting billet is 1.05, with a carbon extreme difference of not more than 0.08% and a proportion of 98.4%. Additionally, the center shrinkage is not more than a 0.5 level with a proportion of 99.5%. Meanwhile, the internal quality of cast billets has been improved, allowing for the rolling of large-size bars with a low consolidation ratio. The pass rate for internal ultrasonic flaw detection using the GB/T4162A grade is now higher than 99.95%, significantly reducing process costs and improving production efficiency for continuous casting and rolling. [ABSTRACT FROM AUTHOR]

Electromagnetic continuous casting technology serves as a significant means for enhancing the casting performance of 2219 aluminum alloy. Investigating the influence of electromagnetic field variations on the solidification process is crucial for studying the microstructure and mechanical properties of electromagnetic cast billets. Through experimental research, variations in the microstructure and mechanical properties were examined for ordinary direct chill casting, as well as three different electromagnetic power casting ingots. The COMSOL software (COMSOL Multiphysics 6.0) was utilized to simulate the temperature and flow field, enabling an explanation of the resulting performance changes. The results showed the effect on electromagnetic continuous casting technology by the electromagnetic field generated by the Lorentz force and melt stirring, improving the melt flow and temperature distribution so that the melt center and the edge of the melt forcible convection were enhanced, thus realizing the tissue refinement, mechanical properties, and Cu element segregation of the improvement. With an increase in electromagnetic power, the distribution of the temperature field was more homogeneous, the segregation phenomenon was more alleviated, and the improvement in mechanical properties was more significant. The optimal microstructure and mechanical properties were achieved at a power of 20.0 kW, with a 74.7% improvement in grain refinement in the center and a tensile strength increase of 30.8%. Additionally, significant improvements were observed in segregation phenomena. [ABSTRACT FROM AUTHOR]

In this paper, the fluid flow, slag entrainment and solidification process in a slab mold were studied using physical modeling and numerical simulation. The effect of two types of submerged entry nozzles (SENs) was also studied. The results showed that the surface velocity for type A SEN was larger than that using type B SEN. For type A SEN, the maximum surface velocity was 0.63 m/s and 0.56 m/s, and it was 0.20 m/s and 0.18 m/s for type B SEN. The larger shear effect on the top surface made the slag at narrow face impacted to the vicinity of 1/4 wide face, while the slag layer at the top surface was relatively stable for type B SEN. Increasing the immersion depth of SEN decreased the surface velocity and slag entrainment. For type A SEN, the thickness of the solidified shell at the narrow face of the mold outlet was thin (12.3 mm) and there was a risk of breakout. For type B SEN, the liquid steel with high temperature would flow to the meniscus and it was beneficial to the melting of the mold flux. The thickness of the solidified shell at the narrow face of the mold outlet was increased. Furthermore, the surface velocity was also increased and it was not recommended for high casting speed. [ABSTRACT FROM AUTHOR]

Exploring the mechanism of the α-ferrite precipitation process on high-temperature properties plays an important guiding role in avoiding slab cracks and effectively regulating quality. In this work, in situ observation of the α-ferrite sustained precipitation behavior for peritectic steel during the austenitic phase transition process has been investigated using high-temperature confocal scanning laser microscopy. Meanwhile, the high-temperature evolution of the phase fractions during the phase transition process was quantitatively analyzed based on the high-temperature expansion experiment using the peak separation method. Furthermore, the high-temperature properties variations of the casting slab during the α-ferrite sustained precipitation process were investigated with the Gleeble thermomechanical simulator. The results show that the film-like ferrite precipitated along the austenite grain boundaries at the initial stage of phase transition, then needle-like ferrite initiates rapid precipitation on film-like ferrite when the average thickness reaches 15~20 μm. Hot ductility reached a minimum at the ferrite phase fraction fα = 10~15%, while high-temperature properties returned to a higher level after fα > 40~45%. The appearance of a considerable amount of needle-like ferrite and grain refinement effectively improves the high-temperature properties with the α-ferrite precipitation process advances. [ABSTRACT FROM AUTHOR]

The bearing steel's high-temperature brittle zone (1250 °C–1100 °C), second brittle zone (1100 °C–950 °C), and low-temperature brittle zone (800 °C–600 °C) were determined by the reduction in area and true fracture toughness. The crack sensitivity was strongest at temperatures of 1200 °C, 1000 °C, and 600 °C, respectively. Various experimental and computational methods were used to establish the phase type, microstructure, size, and mechanical properties of carbides in bearing steel. The critical conditions for crack initiation in the matrix (FCC-Fe, FCC-Fe, and BCC-Fe)/carbides (striped Fe0.875Cr0.125C, netted Fe2.36Cr0.64C, and spherical Fe5.25Cr1.75C3) were also investigated. The values for the high-temperature brittle zone, the second brittle zone, and the low-temperature brittle zone were 13.85 MPa and 8.21 × 10−3, 4.64 MPa and 6.52 × 10−3, and 17.86 MPa and 1.86 × 10−2, respectively. These were calculated using Eshelby's theory and ABAQUS 2021 version software. The ability of the three carbides to cause crack propagation was measured quantitatively by energy diffusion: M3C > MC > M7C3. This study analyzed the mechanism of carbide precipitation on the formation of high-temperature cracks in bearing steel casting. It also provided the critical conditions for carbide/matrix interface cracks in bearing steel continuous casting, thus providing effective support for improving the quality of bearing steel casting. [ABSTRACT FROM AUTHOR]

The intermediate-temperature embrittlement range was examined for Fe, Al, Cu, and Ni alloys. It was found that this embrittlement occurs in many alloys, although the causes are very diverse. Embrittlement can be due to fine matrix precipitation, precipitate free zones, melting of compounds at the grain boundaries, segregation of elements to the boundaries, and, additionally for steel, the presence of the soft ferrite film surrounding the harder austenite matrix. Grain boundary sliding and segregation to the boundaries seem to dominate the failure mode at the base of the trough when intergranular failure takes place. When cracking is due to the presence of hydrogen or liquid films at the boundary, then the dissociation along the boundaries is so easy, it is often independent of the strain rate and is always intergranular. In the other cases when failure occurs, if the deformation is carried out at a high strain rate, it is normally transgranular (e.g., hot rolling giving rise to edge cracking). However, when the strain rate is reduced to that of creep (e.g., bending during continuous casting of steel), failure can also take place by grain boundary sliding, and intergranular failure then becomes the favoured mode. [ABSTRACT FROM AUTHOR]

The influence of centerline segregation on the low-temperature impact toughness of the heat-affected zone (HAZ) of welded joints was studied by welding experiments on X70 steel plates rolled from continuous casting slabs with segregation grades of class 2 and class 3. The experimental results show that the impact toughness at HAZ from class 2 slab steel plate is more stable and has excellent low-temperature toughness than that of class 3 slab steel plate. The impact toughness of the HAZ of the class 3 slab steel plate is low to 100 J at −40 °C and has a severe fluctuation range (~150 J), and the delamination phenomenon is also observed in the fracture cross-section. The reason for this phenomenon is due to the enrichment of C and Mn elements in the centerline segregation zone. The formation of abnormal microstructure (martensite/bainite) in the segregation zone leads to stress concentration, which easily weakens the low-temperature toughness of the joint. [ABSTRACT FROM AUTHOR]

A mathematical model of the macrosegregation of continuous cast high carbon steel billet was developed based upon a representative volume element, considering the flow of enriched liquid, solidification rate, and solidification shrinkage as well. It was found that a lower casting velocity, higher cooling intensity, and shorter solidification interval positively contributed to the inhibition of macrosegregation in a continuously cast billet when a mechanical reduction process was not applied. A numerical expression for the relative flow velocity of liquid was further proposed incorporating such aspects as casting velocity, densities of different phases, and the variation of cross section areas as well. The analysis based on this numerical expression indicated that the overall effect of the reduction process on the macrosegregation of billets depended not only on the reduction zone but also on the reduction amount and its distribution for the active reduction rolls. The test results of further practical plant trials demonstrated a reasonable agreement with the predictions obtained from the proposed numerical model, indicating the reliability of this analysis model to be employed for the continuous casting of high carbon steel billet with strand reduction process. [ABSTRACT FROM AUTHOR]

Variations in the corrosion behavior of biomedical NiTi alloys in Cl− containing and acidic environments present a problem with their biological implantation. The objective of this research was to evaluate the synergy of the microstructure, the corrosion behavior, and the biocompatibility of novel continuous-cast NiTi alloys and to compare them with commercial NiTi alloys. The two alloys have a practically identical nominal chemical composition, but they differ in production technology. The continuous casting technology involved vacuum induction melting of the basic components and vertical continuous casting, while the commercial NiTi alloy was produced through a process of casting, hot rolling, and forming into square shapes. The microstructure was revealed to determine the surface area and size of grains. The corrosion of a commercial nickel–titanium alloy and one prepared by a novel continuous casting method in acidic and chloride-containing solutions was studied via analytical and electrochemical tests. Localized corrosion characteristics related to oxide properties, when exposed to 9 g L−1 NaCl solution, were examined with focused ion beam analysis and subsequent microchemical analysis of the formed corrosive products. Corrosion potential over time and the oxide film resistance were analyzed using linear polarization measurements. To obtain a preliminary estimate of biocompatibility, human fibroblast cells were used in indirect contact, i.e., alloy conditioning medium. The continuous casting method resulted in a reduction in the average grain size in comparison to the commercial sample and better corrosion stability of the sample in an acidic environment. Also, in a solution of 9 g L−1 NaCl the commercial sample showed high values for the corrosion current density (jcorr = 6 μA cm−2), which indicated low corrosion resistance, while the continuous casting sample possessed much better corrosion stability and lower values for the corrosion current density (jcorr = 0.2 μA cm−2). In line with that, elemental analysis of the corroded surfaces showed higher Cl− ion deposition over the surface layer of the commercial sample, suggesting local oxide breakdown. Moreover, NiTicc reached a value three times higher for polarization resistance (Rp = 270 kΩ cm2) over time in comparison to the commercial sample (Rp~100 kΩ cm2). Biocompatibility evaluation showed that human fibroblast cells exhibited altered metabolic activity. An MTT assay showed that cells' mitochondrial activity dropped below that of control cells in the presence of both materials' supernatants. [ABSTRACT FROM AUTHOR]

A three-dimensional model is established to investigate the effect of argon injection mode, argon flow rate and casting speed on the gas–liquid two-phase flow behavior inside a slab continuous casting mold. The Eulerian–Eulerian model is employed to simulate the gas–liquid flow, and the population balance model is applied to describe the bubble breakage and coalescence process in the mold. The numerical simulation results of the bubble size distribution are verified using the water model experiment. The results show that the flow field and bubble distribution are similar between the argon injection at the upper submerged entry nozzle (SEN) and tundish upper nozzle (TUN), while the number density is larger for the argon injection of TUN. The coalescence rate of bubbles and the bubble size inside the mold increase with increasing argon flow rate. When the argon flow rate exceeds 4 L/min, the flow pattern of liquid steel changes from double-roll flow to complex flow, with aggravation of the level fluctuation of the top surface near the SEN. When the casting speed increases, the bubble breakup rate increases and results in a decrease in the size of bubbles inside the mold. At a high casting speed, the flow pattern tends to form double-roll flow, and the liquid level at the narrow face of the top surface increases. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the journal Metals titled "Advances in Molten Metal Refining Process." The issue includes ten articles that cover various aspects of molten metal refining processes, focusing on iron, steel, aluminum, magnesium, and titanium. The articles discuss topics such as the evolution of vortex structures in continuous casting molds, the excitation of micro-scale flow near the solid-liquid interface, the optimization of electrode insertion depths in magnesia furnaces, the behavior of hydraulic jumps during the continuous casting process, the bubble size distribution in single-snorkel furnaces, the refining process of slot-porous matched dual tuyeres, the desulfurization process in Kanbara reactors, the wear and efficiency of graphite rotors in aluminum refinement, and the prediction of bending forces in hot-rolled plates. The articles present mathematical models, numerical simulations, and experimental results to advance the understanding and optimization of molten metal refining processes. [Extracted from the article]

Argon injection is usually applied in the continuous casting mold to prevent submerged entry nozzle (SEN) clogging. However, the stability of the slag–steel interface is affected by the injected gas, even leading to the formation of the slag eye. A computational fluid dynamics–discrete bubble model–volume of fluid (CFD-DBM-VOF) model is established to predict the argon–slag–steel–air four-phase flow in the continuous casting mold. The bubble behavior is treated with the Lagrangian approach considering bubble coalescence and breakup. The movement behavior of the slag–steel interface is analyzed with and without argon blowing, validated with the water model. The results show that the large bubble tends to float up into the slag–steel interface near the SEN with argon injection, resulting in fluctuations in the slag–steel interface near the SEN. The bubble distribution, flow field, fluctuation height of the slag–steel interface and configuration of the slag eye in the mold are analyzed. Furthermore, the effect on the casting speed, gas flow rate and thickness of the slag layer is obtained based on the result. The mathematical prediction results showcase a combination of well-established phenomena and newly generated predictions. [ABSTRACT FROM AUTHOR]

A novel YOLOv5 network is presented in this paper to quantify the degree of defects in continuously cast billets. The proposed network addresses the challenges posed by noise or dirty spots and different defect sizes in the images of these billets. The CBAM-YOLOv5 network integrates the channel and spatial attention of the Convolutional Block Attention Module (CBAM) with the C3 layer of the YOLOv5 network structure to better fuse channel and spatial information, with focus on the defect target, and improve the network's detection capability, particularly for different levels of segregation. As a result, the feature pyramid is improved. The feature map obtained after the fourth down-sampling of the backbone network is fed into the feature pyramid through CBAM to improve the perceptual field of the target and reduce information loss during the fusion process. Finally, a self-built dataset of continuously cast billets collected from different sources is used, and several experiments are conducted using this database. The experimental results show that the average accuracy (mAP) of the network is 93.7%, which can achieve intelligent rating. [ABSTRACT FROM AUTHOR]

The purpose of this investigation is to improve the mechanical properties of AlMnFeMgSi wrought alloys by forming a high number density of nano-scaled strengthening dispersoids during homogenisation annealing. The process chain for AlMnFeMgSi wrought alloys includes homogenisation annealing after continuous casting. In this step, inhomogeneities and segregations are dissolved and dispersoids are precipitated. The formed dispersoids hinder grain growth, but usually cannot increase the strength due to their coarse size of some 100 nm. Lower homogenisation temperatures should result in the precipitation of smaller dispersoids during homogenisation. The addition of Zr was investigated to increase this effect. Zr should form further dispersoids from the Al3Zr phase. This requires a fundamental understanding of the temperature-dependent kinetics and the nature of precipitation formation during homogenisation. For this purpose, the as-cast state is first characterised via differential scanning calorimetry. Subsequently, a large number of homogenisation parameters are investigated and quantified via hardness testing. The micro- and nanostructure are investigated for promising parameters and a particle analysis is performed. In the present study, it was possible to precipitate fine dispersoids of few 10 nm by reducing the homogenisation temperature, which resulted in a significant increase in hardness. Alloying with Zr enabled the precipitation of further dispersoids with a size of a few nm in a high number density, which further increased the strength. [ABSTRACT FROM AUTHOR]

In the presented research, machine learning methods were applied to the prediction of longitudinal cracks in steel slabs during continuous casting. We employ a deep learning approach to process 68 thermocouple signals as a multivariate time series (MTS) along with 32 static features, which encompass both chemical composition and process information. Our deep learning approach integrates two distinct parallel modules, followed by an aggregation block; a Convolutional Neural Network (CNN) processes the thermocouple MTS, while in parallel, the static data undergo processing via a Fully Connected Network (FCN). To enhance the performance of the CNN, we incorporate two Squeeze and Excitation (SE) blocks, which act as an attention mechanism across different channels. By integrating chemical information with MTS in the detection system, we improve the performance of defect detection by 15% relatively. [ABSTRACT FROM AUTHOR]

A two-dimensional transient inverse heat-conduction problem (2DIHCP) was established to determine the mold heat flux using observed temperatures. The sequential regularization method (SRM) was used with zeroth-, first-, and second-order spatial regularization to solve the 2DIHCP. The accuracy of the 2DIHCP was investigated under two strict test conditions (Case 1: heat flux with time-spatial periodically varying, and Case 2: that with sharp variations). The effects of the number of future time steps, regularization parameters, order of regularization, discrete grids, and time step size on the accuracy of the 2DIHCP were analyzed. The results showed that the minimum relative error (epred) of the predicted Case 1 heat flux is 5.05%, 5.39%, and 5.88% for zeroth-, first-, and second-order spatial regularization, respectively. The corresponding values for the predicted Case 2 heat flux are 6.31%, 6.30%, and 6.36%. Notably, zeroth- and first-order spatial regularization had higher accuracy than second-order spatial regularization, while zeroth-order spatial regularization was comparable to first-order. Additionally, first-order spatial regularization was more accurate in reconstructing heat flux containing sharp spatial variations. The CPU time of the predicted Case 2 heat flux is 1.71, 1.71, and 1.70 s for zeroth-, first-, and second-order spatial regularization, respectively. The corresponding values for the predicted Case 1 heat flux are 6.18, 6.15, and 6.17 s. It is noteworthy that the choice of spatial regularization order does not significantly impact the required computing time. Lastly, the minimum epred of Case 2 heat flux with zeroth-order spatial regularization is 7.96%, 6.42%, and 7.87% for time step sizes of 1/fs, 1/2fs, and 1/5fs, respectively. The accuracy of the inverse analysis displays an initial improvement followed by degradation as the time step size decreases. A recommended time step size is 1/2fs, where fs denotes the temperature-sampling rate. [ABSTRACT FROM AUTHOR]

It is critical in the metal continuous casting process to estimate the temperature evolution of the casted section along the machine from the meniscus (the point where liquid metal is poured) to the cutting machine, where the product is cut to commercial length. A convenient approximated model to achieve this goal with a feasible computational effort, particularly in the case of large sections, is the so-called travelling slice: the transversal section of casted product is subjected to different thermal boundary conditions (e.g., thermal flux, radiation, convection) that are found during the movement at constant speed from meniscus to the end of machine. In this work, the results obtained with the approximated travelling slice model are analyzed in the favorable case of an axisymmetric section. In this case, the reference model is 2D, whereas the travelling slice model degenerates in a simple 1D model. Three different casted shapes were investigated, rounds with diameters of 200 mm, 850 mm, and 1200 mm, spanning from traditional to only recently adopted product diameter sizes. To properly test the validity of the travelling slice model, other casting speeds were considered, even outside the industrial range. Results demonstrate the advantage of using the travelling slice, particularly the much lower computational cost without sacrificing precision, even at low casting speed and large dimensions. [ABSTRACT FROM AUTHOR]

In this study, the relationship between macro segregation and the equiaxed zone in high-carbon grades with continuous casting parameters was investigated and optimized at the İsdemir iron and steel plant. The work was conducted for the 1080 quality of the SAE J403 standard. In this study, some parameters, such as casting speed, secondary cooling, EMS current value and EMS frequency value, were examined. When the results of the experiments are examined, it can be observed that the equiaxed zone in the macrostructure decreases significantly with the reduction of the EMS frequency value. The decrease in casting speed and increase in EMS current value caused an increase in the equiaxed zone. The increment in secondary cooling led to a decline in the equiaxed zone. Once the macro segregation results are examined, it can be seen that it is very important to optimize the continuous casting parameters in order to reduce the macro segregation results of—especially—carbon, sulfur and phosphorus elements. It has also been determined that the macro segregation values of carbon, sulfur and phosphorus elements are low in casting conditions where casting speed is low, and the EMS current value and EMS frequency value are high. In addition, macro segregation measurements of manganese, silicon, chromium and vanadium elements are found to be low under similar casting conditions. It is critical to optimize the continuous casting parameters before production, especially in high-carbon grades to be used for prestressed concrete wire and cord wire applications. As a result of the work conducted using the İsdemir billet continuous casting machine for the 1080-grade SAE J403 standard, aiming to optimize macro segregation and the equiaxed zone, the effective results have been achieved by using process parameters of 2.8 m/min casting speed, 360 A EMS current, 5 Hz EMS frequency and low secondary cooling intensity. [ABSTRACT FROM AUTHOR]

A laboratory study was carried out to better understand the factors that contribute to the formation of complex inclusions, as inclusions play an important role during steel production; if not properly managed, inclusions can cause nozzle clogging during continuous casting and also damage the steel's mechanical properties and machineability. To determine the chemical composition of inclusions that are less detrimental to the machineability of Al-deoxidized and Ca-treated gear steels, thermodynamic calculations and automated scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), as well as electron probe micro-X-ray analysis (EPMA) with the wavelength dispersive spectroscopy (WDS) technique, were utilized. The findings demonstrated that the morphology of inclusions changed from irregular to a more spherical type and the composition also changed to dual oxy-sulfides from pure oxides and sulfides as the Ca concentration in the steel was increased up to 36 ppm. The amount of Pure MnS sulfides also reduced significantly after Ca treatment. The ternary phase diagram and stability diagram for the inclusions revealed that 15–25 ppm Ca is the optimal range for the modification of both oxides and sulfides into the desired morphology and composition under the stipulation that the concentration of O in the steel is maintained at or below 50 ppm. [ABSTRACT FROM AUTHOR]

The present work is devoted to the study of the influence of the parameters of the structural anisotropy of rolled products on the low-temperature impact strength of alloyed steels. A quantitative metallographic analysis of the microstructure of rolled steel samples obtained after testing for low-temperature toughness was carried out. It was established that the main reason for the decrease in the low-temperature impact strength of rolled steel samples is a highly developed segregation band enriched with carbon films formed at the stage of steelmaking conversion in violation of the technology of continuous casting of steel. The microstructural analysis of rolled stock samples was used in the work, and studies of the fracture surface of rolled stock samples were carried out with a scanning electron microscope using X-ray microanalysis methods. The studies carried out showed that the metallurgical quality of sheets of one heat, as well as individual samples within one sheet, varied over a wide range, from satisfactory to unacceptably low. It was established that the main reason for the decreasing low-temperature impact strength of rolled products was a highly developed segregation band enriched with carbon films, formed at the stage of steelmaking in case of violation of the continuous casting of steel technology. The multivariate statistical analysis carried out showed that only the size of the segregation band has an effect on the low-temperature impact strength of 10 mm thick rolled coil samples. [ABSTRACT FROM AUTHOR]

This paper characterizes the surface crack morphology and elements of 09CrCuSb steel continuous casting slabs and studies the high-temperature thermo-plasticity of continuous casting slabs using a Gleeble 3500 thermal simulator. Combining the macro/micro fracture morphology and microstructure characteristics, the formation rules of slab cracks are discussed. The research results show that the increase in Ae3 temperature caused by changes in alloy elements results in the precipitation of a thin, film-like coexisting ferrite along the grain boundaries at a certain temperature, as well as the element segregation behavior of low-melting-point alloy elements at the original austenite grain boundaries, which are the main factors inducing cracks in 09CrCuSb steel continuous casting billets. The plasticity of 09CrCuSb steel at high temperatures is poor at 800~900 °C. In continuous casting process control, it is necessary to try to avoid long-term stay of the billet at this temperature range. [ABSTRACT FROM AUTHOR]

Cu-Al composites are widely applied materials exhibiting advanced properties of both matrix metals. Controlling the brittle interfacial phases is a key factor in improving the interfacial strength of Cu-Al composites. This paper studied the interfacial formation process of Cu-Al composites fabricated by continuous composite casting. The phase formation sequence, growth direction and formation mechanism were clarified via element marking and thermodynamic calculations. The spatial distribution of the interfacial phases from the aluminum side to the copper side is as follows: the α + θ layer (α-Al + CuAl2), the θ layer (CuAl2) and the γ layer (Cu9Al4). Moreover, insular η phases (CuAl) and δ phases (Cu3Al2) exist in the γ phase sublayer. The formation sequence of interfacial phases is as follows: the θ phase, the η phase, the δ phase and the γ phase. The θ layer and α + θ layer are transformed from a liquid diffusion layer formed by scouring the surface of copper with liquid aluminum, the η and δ phases grow towards the θ layer and the γ phase simultaneously grows towards both the copper matrix and the θ layer. [ABSTRACT FROM AUTHOR]

Ultrahigh-speed continuous casting is a critical element in achieving high-efficiency continuous casting. In the present work, a three-dimensional model of a 160 mm × 160 mm billet ultrahigh-speed continuous casting mold was developed for use in studying the influences of different casting parameters on molten steel flow. The results showed that the flow pattern in the mold was not associated with its casting speeds, submerged entry nozzle (SEN) immersion depths, or inner diameters. Variation in casting speeds significantly affected the liquid level of the steel–slag interface. Its liquid level fluctuation was reasonable at an SEN immersion depth of 80 mm. Its impact depth reached the shallowest point, which was conducive to upward movement within high-velocity and high-temperature regions, and accelerated the floating of non-metallic inclusions. Expanding the inner diameter of the SEN could effectively weaken the initial kinetic energy of the jet. However, it may cause a deeper impact depth and a degree of upward movement in the raceway, which exhibited the shallowest impact depth in the jet and the most reasonable behavior of molten steel at a liquid level for which the inner diameter of the SEN was 40 mm. [ABSTRACT FROM AUTHOR]

Continuous casting production is an important stage in smelting high-quality steel, and automatic casting control based on artificial intelligence is a key technology to improve the continuous casting process and the product quality. By controlling the opening degree of the stopper rod reasonably, the mold can be filled with liquid steel stably in the specified time window, and automatic casting can be realized. In this paper, an automatic casting control method of continuous casting based on an improved Soft Actor–Critic (SAC) algorithm is proposed. Firstly, a relational model of the stopper rod opening degree and the liquid steel outflow velocity is established according to historical casting data. Then the Markov Decision Process (MDP) model of the automatic casting problem and the reinforcement learning framework based on the SAC algorithm are established. Finally, a Heterogeneous Experience Pool (HEP) is introduced to improve the SAC algorithm. According to the simulation results, the proposed algorithm can predict the stopper rod opening degree sequence under the constraint of the target liquid level curve. Under different billet specifications and interference conditions, an accuracy of 80% of liquid level in the mold and a stopper rod opening degree stability rate of 75% can be achieved, which is 4.29% and 3.17% higher than those for the baseline algorithms, respectively. [ABSTRACT FROM AUTHOR]

A digital-twin-model-based optimal control system is presented for the steel continuous casting process. The system is designed for the coordinated optimization and dynamic control of secondary cooling and final electromagnetic stirring (FEMS), and involves three related parts. Firstly, a three dimensional real-time heat transfer model is established as the digital twin of the heat transfer process of continuous casting; for high accuracy, it is calibrated offline and calibrated online using measurements of the surface temperatures and shell thicknesses (only offline). Secondly, according to metallurgical rules, cooling and stirring are optimized coordinatively, based on the established digital-twin model and chaos particle swarm optimization algorithm. Thirdly, cooling and stirring are further dynamically controlled for quality stability. Finally, the system is applied in a bloom caster with model errors ≤ ±10 °C and control errors ≤ ±4 °C, which reduces the macro-segregation over grade 1.5 from 11% to 3.3%. [ABSTRACT FROM AUTHOR]

The initial solidification of the shell and the effect of the negative strip on oscillation marks were studied during the oscillation of the mold. A two-dimensional model was established concerning mold oscillation, which was coupled with fluid flow, heat transfer, and solidification, and the validity of the model was verified. The results show that oscillation marks were formed at the negative strip stage and that the quality of the slabs can be improved by reducing the duration of the negative strip stage. During the negative strip stage, the shell was affected by the strong backflow of liquid slag and the pressure on the surface sharply increased, resulting in the formation of a depression oscillation mark on the shell. The effects of the negative strip stage on the initial solidified shell during each cycle were compared. As the depth of the oscillation mark decreased, the upward shear stress on the shell's surface increased, without the occurrence of a negative strip stage during one cycle. The results provided a new method for reducing oscillation marks and are of great significance for improving casting slabs' quality. [ABSTRACT FROM AUTHOR]

High-aluminium steels contain a significant amount of aluminium. The reaction between Al in the liquid steel and SiO2 in lime-silica-based mould powders during the continuous casting process of high Al steel causes chemical compositional changes in the mould powders, subsequently affecting the surface quality of slabs. In order to solve the aforementioned problem, lime-alumina-based mould powders have been developed, which can lead to an increase in the surface quality of cast slabs by inhibiting steel/slag interaction. However, the mould slag tends to crystallise easily, which leads to a deterioration of the mould lubrication. In view of this aspect, it is important to develop and optimize lime-alumina-based mould powders to meet the requirements of continuous casting of high-aluminium steels. In this study, the changes in crystallinity, viscosity and melting temperature of lime-alumina-based mould powders with the effects of increasing the CaO/Al2O3 ratio have been observed through STA (Simultaneous Thermal Analysis), HSM (Hot Stage Microscopy), XRD (X-ray Diffraction), IPT (Inclined Plate Test) and rotational viscometer. The crystallisation behaviour of these mould powders was evaluated by generating CCT (continuous cooling transformation) diagrams. Additionally, the changes in steel chemistry have also been analysed using XRF (X-ray fluorescence) and ICP (Inductively Coupled Plasma Mass Spectrometer). The results of these analyses demonstrated that crystallinity of lime-alumina-based mould powder is increased while the initial crystallisation temperature and viscosity are decreased by CaO/Al2O3 additions. However, the degree of steel/slag interaction decreases with an increase in Al2O3 content. [ABSTRACT FROM AUTHOR]

In continuous casting, it is common to close single or multiple submerged nozzles of multi-strands tundish to adapt to production rhythm due to insufficient liquid steel or equipment failure. However, the closure of the nozzle will change the flow field in the tundish and further affect the removal efficiency of inclusions in the tundish. For this reason, based on numerical simulation, the flow behavior of liquid steel and the removal of inclusion in tundish with different nozzle closed were studied, and the optimal nozzle closing scheme was obtained, which provided a basis for the selection of nozzle closing in tundish. At the same time, the gas curtain is set in the tundish to alleviate the negative effects such as the increase of dead zone caused by closing nozzle. The results show that the removal rate of inclusions with sizes 10, 30, 50, 70, and 90 μm change from 12.4%, 39.1%, 74.2%, 93.3%, and 95.6% to 14.7%, 36.4%, 76.4%, 85.3%, and 93.8%, respectively. The volume of the tundish dead zone is increased after closure of nozzle, the dead zone of the tundish is improved when the gas is installed, and the dead zone volume was reduced from 14.8% and 16.4% to 13.9 and 14.1%. [ABSTRACT FROM AUTHOR]

In thin-slab continuous casting, due to the influence of the special shape of the funnel mold, cracks at the corner of the slab shell are more likely to occur than those in conventional slab shells, and a serious wear phenomenon also appears on the narrow face of the copper wall of the mold. Aimed at the corner cracks of thin slabs and the wear phenomenon of the copper wall, a new 3D stress analysis model in a funnel mold has been developed to simulate the stress-–train behavior of the slab shell under high-speed continuous casting. The results show that at the position 600 mm below the meniscus, the gap begins to appear at the corner of the slab; the maximum value of the first principal stress appears at the corner. The shell is squeezed by the copper wall during the downward movement in the funnel mold, and the slab shell in the funnel area moves towards the narrow face. The displacement causes the deformation of the slab shell to extend to the corners, the deformed shell is pressed against the corner of the copper wall. A new type of copper wall was designed for production, and it was found that the cracks at the corner of the slab shell were greatly reduced. [ABSTRACT FROM AUTHOR]

In this study, the two-phase flow coordination characteristics between α and β phases of H62 brass made by up-drawing continuous casting are investigated based on the upsetting process. An in situ and new research method for two-phase flow is put forward, and the two-phase flow and grain refinement characteristics are observed under different deformation conditions. The results show that α phase flows fast under 400 °C, β phase is pulled and overridden by α phase under this temperature. When the temperature increases to 500 °C, which is higher than β phase transition temperature, the flow velocity of β phase increases, and the deformation of β phase is found to bulge. The flow of β phase is more sensitive to low deformation rates than α phase. The deformation amount has a more significant impact on β phase than α phase, and the deformation of β phase promotes the grain fragmentation and refinement of α phase accompanied by huge β phase bulging obviously. Under the conditions of high temperature, low deformation rate, and large deformation amount, both phase α and β of up-drawing continuous casting brass alloy are broken and the grains are refined. Based on the two-phase flow characteristic, numerical simulation is used to obtain the optimal continuous extrusion parameters of the H-shaped wire of up-drawing continuous casting H62 brass. Then, the optimized complex cross-section wire is prepared by continuous extrusion experiment. This research aims to provide guidance for the complex processing of two-phase alloys. [ABSTRACT FROM AUTHOR]

A series of industrial trials of argon injection into ladle shroud (AIILS) with different argon-blowing rates were conducted in this study. Firstly, bubbles in actual liquid steel of the tundish were captured by the method of "cold steel plate dipping" and characterized by microscope examination. A detailed investigation on the three-dimension morphology of bubbles was carried out by using industrial computerized tomography (ICT). Then, the two-phase flow of liquid steel and argon gas in the tundish was numerically simulated to further investigate the motion behaviors of bubbles in liquid steel of the tundish. The simulated results showed that bubbles in the size range of this investigation had a large enough filtration rate to demonstrate a good performance on inclusion removal. Finally, the effect of AIILS on inclusion removal was analyzed by detecting the variations of inclusions as well as total oxygen content in steels taken from the ladle, tundish, and casting billet. The method of AIILS was more effective at improving the removal of inclusions in the range of 5 to 10 μm and obviously increased the removal rate of total oxygen content. [ABSTRACT FROM AUTHOR]

Complex multi-phase phenomena, including turbulent flow, solidification, and magnetohydrodynamics (MHD) forces, occur during the continuous casting (CC) under the applied electromagnetic brake (EMBr). The results of the small-scale experiment of the liquid metal model for continuous casting (mini-LIMMCAST) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), investigating MHD flow with a deep immersion depth of 100 mm, are supplemented by newly presented numerical studies with the shallow position of the submerged entry nozzle (SEN) at 50 mm below the meniscus. Herein, the focus is on the MHD effects at the meniscus level considering (i) a fully insulating domain boundary, (ii) a perfectly conductive mold, or (iii) the presence of the solid shell. The volume-of-fluid (VOF) approach is utilized to model a Galinstan flow, including free surface behavior. A multiphase solver is developed using conservative MHD formulations in the framework of the open-source computational fluid dynamics (CFD) package OpenFOAM®. The wall-adapting local eddy-viscosity (WALE) subgrid-scale (SGS) model is employed to model the turbulent effects on the free surface flow. We found that, for the deep immersion depth, the meniscus remains calm under the EMBr for the conductive and semi-conductive domain. For the insulated mold disregarding the SEN position, the self-inducing MHD vortices, aligned with the magnetic field, cause strong waving of the meniscus and air bubble entrapment for shallow immersion depth. Secondary MHD structures can form close to the meniscus under specific conditions. The influence of the EMBr and immersion depth on the flow energy characteristics is analyzed using power spectral density (PSD). [ABSTRACT FROM AUTHOR]

In this paper, the influence of small additions of Cr, Mo, Cu, Ni, B, Ca, Zr, and Ce on the hot ductility of advanced high-strength steels (AHSS) has been reviewed. Most of these small additions have a positive effect in improving hot ductility on straightening during continuous casting operations and should be considered when problems with cracking in continuous casting are encountered. In many of these cases, the reason for these generally small but important improvements in hot ductility is not known with certainty, but the segregation of these elements to the austenite grain boundaries, strengthening the bonding, is often suggested. [ABSTRACT FROM AUTHOR]

In the present work, inclusion analyses were carried out for inclusions in the tundish samples and in the 28 m transition slabs produced during the ladle exchange of heats A and B. At the beginning of heat B steel casting, the 12th meter of the casting slabs was in the position of the mold meniscus. The number of densities of the inclusions containing TiN and the inclusions containing Al2O3+TiN increased significantly from the 12th meter to the 22nd meter, while the number densities of the inclusions containing Al2O3 markedly increased from the 13th meter to the 20th meter. Therefore, the length of the transition slabs whose cleanliness was seriously reduced was about 10 m starting from the beginning of heat B steel casting. It was deduced that the contamination of the transition slabs could be caused by the liquid steel exposure in the tundish, the inflow of ladle filling sand of the next heat, or the entrainment of the tundish flux due to the fluctuation of the tundish liquid level at the beginning of heat B steel casting. [ABSTRACT FROM AUTHOR]

To solve the instability of liquid steel in the continuous casting process and the inconsistent flaw detection of heavy rail steel, steel flow control was studied numerically in a tundish with a porous baffle wall by using the fluid dynamics software Fluent. The opening plan of the baffle wall was improved through orthogonal optimization of the design of the holes in the porous baffle wall. The test condition was set to a left inclination angle of α1 = 22°, a right inclination angle of α2 = 48°, an upward elevation angle of β = 30°, and an aperture of d = 70 mm. The simulation results of the optimization scheme showed that the uniformity of the flow and temperature fields had been significantly improved, and the flow in each strand became consistent. The maximum temperature difference was 21 K in the tundish, and the maximum temperature difference of three outlets was only 1.7 K. Dead zone volume was reduced by 10.0% compared to the original tundish, and plug flow volume was increased by 14.2%. Comparing the removal efficiency of Al2O3 inclusions of different size, the results showed that the removal efficiency of 10 μm and 30 μm smaller inclusions was above 87%. The removal rate of ≥50 μm larger inclusions also remained about 95%. [ABSTRACT FROM AUTHOR]

To optimize the submerged entry nozzle (SEN) for an ultra-thick slab mold, a mathematical model has been established. The molten steel flow and solidification, inclusion transports, and meniscus fluctuation have been investigated through the model. Compared with the concave-bottom SEN cases, the convex-bottom SEN decreases the imping depth of the jet flow and increases the horizontal velocity and temperature on the meniscus. However, the remelting of the solidified shell is dramatic for the convex-bottom case. The well depth of the concave-bottom SEN and the SEN's submerged depth have little influence on molten steel flow and solidification. The effects of SEN port shape and port angle on the molten steel flow are significant. As the port shape changes from rectangle to square or the port downward angle decreases, the imping depth of jet flow decreases, the horizontal velocity and the temperature on the mold free surface increase. For the ultra-thick mold, a square-shaped-port SEN with a −10° downward angle is more beneficial by comprehensive consideration of molten steel flow and solidification, inclusion removal, and mold powder melting. The optimized SEN has been applied to the actual caster and its performance has been assessed, indicating that the SEN optimization is efficient. [ABSTRACT FROM AUTHOR]

In this study, a funnel mold (FM) model of a multi-mode electromagnetic braking (EMBr) device was developed, and the magnetic flux density at different currents was obtained by MAXWELL software. By using the magnetohydrodynamics (MHD) module of FLUENT software, the volume of fluid binomial flow turbulence model and the EMBr mathematical model of the steel/slag flow field were coupled, and the characteristics of the molten steel flow and the liquid-level fluctuation in the 1520 mm × 90 mm FM with the casting speed of 6 m/min were calculated under the effect of the electromagnetic field. The FM liquid-level characteristic information under production conditions was obtained in a nail board industrial experiment and compared with the magnetic-fluid coupling model. The results show that the EMBr can significantly change the flow behavior of molten steel. When the magnetic pole current is not less than 800-600 A, the maximum liquid-level fluctuation height decreases from 18 mm without EMBr to less than 5 mm, and the liquid-level cannot easily entrap slag. Considering the EMBr effect and production cost, the reasonable magnetic pole current should be 800-600 A. The reliability of numerical simulation was also verified by the industrial test results of the nail board. [ABSTRACT FROM AUTHOR]

Based on the solidification heat transfer model and the CAFE model, the solidification behavior and structure of 2311 die steel, with a cross-section dimension of 415 × 2270 mm at different casting speeds, specific water flow and superheat, is numerically simulated. Nail-shooting and acid-etching experiments are carried out on the slab to verify the model's macroscopic size. With the increase in casting speed, the slab's central equiaxed grain ratio (ECR) decreases and the average grain size increases. The increase in superheat promotes the growth of columnar grains and inhibits the growth of central equiaxed grains. When the superheat increases from 23 to 38 K, the ECR decreases from 43.2 to 29.64%, and the average radius of grains increases from 0.89 to 1.01 mm. With the increase in specific water flow, the ECR decreases, and the average grain radius is the smallest when the specific water content is 0.32 L kg−1. Finally, the slab quality is improved by process optimization, and the central segregation index of carbon decreases from mean value of 1.15 to 1.05. [ABSTRACT FROM AUTHOR]

There is considerable interest in improving the resistance of fully austenitic TWIP steels to hydrogen embrittlement; one potential route is to use V additions to promote hydrogen trapping by V(C,N) precipitates. This has the dual benefit of increasing the yield strength through precipitation strengthening and grain refinement. However, the effect on slab quality during continuous casting has not been determined. In this study, the hot ductility of two twinning-induced plasticity (TWIP) steels, Fe-0.6C-22Mn and Fe-0.6C-22Mn-0.2V, was examined over the temperature range 650–1200 °C. Tensile samples were taken from continuous cast 225 mm slabs and from 36 mm transfer bars. The addition of V caused the ductility trough in the temperature range 650–900 °C to deepen and widen and the lowest reduction in area (RA) recorded in the as-cast condition was 30%. This deterioration of hot ductility was due to V(C,N) precipitation. Even though the minimum RA was below the value often accepted to avoid cracking, no transverse cracking was observed in industrial trials and the surface quality was acceptable. The RA values of Fe-0.6C-22Mn were found to be very sensitive to the P level. However, this sensitivity was less evident when V was added, possibly due to P trapping by VC at austenite boundaries. No transverse cracking was observed in industrially produced slabs with P in the range examined (0.02 to 0.04 wt.% P). [ABSTRACT FROM AUTHOR]

The influence of primary cooling and rebound temperature at C–Mn slab corner surfaces during continuous casting on ferrite film transformation and AlN precipitation was investigated. Laboratory simulations included primary cooling to minimum temperature, Tmin, rebounding to various maximum temperatures, Tmax, followed by secondary cooling. The negative effect of a low Tmin on hot ductility could not be readily reversed, even at relatively high temperatures. Quantitative metallography was employed to study the evolution of the microstructure during rebounding and secondary cooling. Following primary cooling to temperatures just above the Ar3, thin films of allotriomorphic ferrite formed on the austenite grain boundaries. These films did not completely transform to austenite during the rebound at 3 °C/s up to temperatures as high as 1130 °C and persisted during slow secondary cooling up to the simulated straightening operation. Whilst dilatometry did not indicate the presence of ferrite after high rebound temperatures, metallography provided clear evidence of its existence, albeit in very small quantities. Coincident with the ferrite at these high temperatures was the predicted (TC-PRISMA) grain boundary precipitation of AlN in bcc iron during the rebound from a Tmin of 730 °C. Importantly no thin ferrite films were observed, and AlN precipitation was not predicted to occur when Tmin was restricted to 830 °C. Cooling below this temperature promotes austenite grain boundary ferrite films and AlN precipitation, which both increase the risk of corner cracking in C–Mn steels. [ABSTRACT FROM AUTHOR]

There is significant evidence from light metals that turbulence in casting leads to bifilm defects; enfolded, doubled-over oxide films which act like cracks in the liquid, and are inherited as cracks by the solid. This population of introduced cracks is now known to significantly influence the tensile failure behaviour of light alloys. There is evidence that analogous defects exist in steels. This paper examines the possibility that bifilms may control the hot ductility of TWIP and TRIP steels, and therefore the problems of straightening during continuous casting. Techniques for overcoming these problems are indicated. [ABSTRACT FROM AUTHOR]