Continuous Casting Process Research Articles

Defects of the steel billet in continuous casting

In continuous casting process, defects of the steel billet (e.g. crack, pinhole, blowhole, central shrinkage, slag entrapment and appearance deviation, etc.) negatively affect the quality and the yield of rolled products. This research has been carried out to investigate some defects which often occurred in Vietnamese steel plants. The experimental work was conducted in an industrial 4-strands continuous casting machine with the billet’s cross-section of 130×130 mm2. The position, generating cause identification of these defects and proper measures have been discussed. A change in the steel compositions and the water distribution during secondary cooling was applied to improve the steel billet quality It has shown that the billet defects have greatly decreased and the quality of billet has obviously increased.

Effects of Homogenization Conditions on the Microstructure Evolution of Aluminium Alloy EN AW 8006

The industrial production of products, such as foil and aluminium alloy strips, begins with the production of semi-finished products in the form of slabs. These are produced by the continuous casting process, which is quick and does not allow the equilibrium conditions of solidification. Non-homogeneity—such as micro and macro segregation, non-equilibrium phases and microstructural constituents, as well as stresses arising during non-equilibrium solidification—are eliminated by means of homogenization annealing. In this way, a number of technological difficulties in the further processing of semi-finished products can be avoided. The aim of this research was the optimization of the homogenization annealing of the EN AW 8006 alloy. With the Thermo-Calc software, a thermodynamic simulation of equilibrium and non-equilibrium solidification was performed. Differential scanning calorimetry (DSC) was performed on selected samples in as-cast state and after various regimes of homogenization annealing and was used for the simulation of homogenization annealing. Using an optical microscope (OM), a scanning electron microscope (SEM) and an energy dispersion spectrometer (EDS), the microstructure of the samples was examined. Based on the results, it was concluded that homogenization annealing has already taken place after 8 h at 580 °C to the extent, that the material is then suitable for further processing.

Development, physical‐chemical properties, and photodegradation of pectin film reinforced with malt bagasse fibers by continuous casting

AbstractThis work aims to develop composite films from renewable sources and to use a residue from the brewing industry, malt bagasse, as a reinforcing agent. The composites were prepared with 0–15 wt%/wt% of malt bagasse, using the continuous casting process. All films were characterized in terms of their microstructure, physicochemical, mechanical, and photodegradation properties. The properties of the films were influenced by the concentration variation of the malt bagasse fiber, allowing the deformation of the films to increase by approximately 57%. The incorporation of 15 wt%/wt% of malt bagasse provided a reduction in the water vapor transmission rate and in the hygroscopicity of the pectin films. However, the fibers acted as UV light blockers, making it difficult to photodegradate the films. Therefore, the composite films based on pectin and malt bagasse presented adequate properties to be used in the packaging industry.

Scaled-up production of gelatin-cellulose nanocrystal bionanocomposite films by continuous casting

In this study, continuous casting is proposed as a suitable approach to scale up the production of gelatin-cellulose nanocrystals (CNCs) bionanocomposites. The processing conditions and bionanocomposite properties were established based on the ζ-potential and gelatin content, and CNCs concentration, respectively. Gelatin film-forming solution at 20 wt% was required for proper continuous casting processing, leading to a productivity of 0.20 m2 film/min, which was at least 1000-fold higher than that of the classical bench casting. The gelatin-CNCs bionanocomposites displayed transparency, flexibility, and improved UV-barrier and thermal properties. Adding only 0.5 wt% of CNCs resulted in an increase of 77 % and 48 % in the tensile strength and Young’s modulus of gelatin, respectively. Comparison with previous nanocellulose-based nanocomposites pointed out the relatively superior performance of the gelatin-CNCs bionanocomposites obtained by continuous casting for various applications, including flexible food packaging.

Utilization of Experimental Data as Boundary Conditions for the Solidification Model Tempsimu-3D

Solidification models are an important tool for the prediction of temperatures and shell growth during the process of continuous casting of steel. To gain reliable simulation results, it is crucial to use highly sophisticated material data and boundary conditions depending on different process parameters. The focus of this work lies on the utilization of experimental data to describe the secondary cooling zone (SCZ) of a slab caster in the solidification model Tempsimu-3D. In this part of the caster, water and air-mist sprays are used to cool down the strand. To calculate the heat transfer coefficient caused by spray cooling (HTCspray), the model uses a correlation between the water impact density (WID) and the surface temperature of the slab. Together with the heat removal due to roll contact and radiation, this HTCspray is applied as a boundary condition for the SCZ. To adjust the parameters of the correlation formula, results from WID and HTC measurements are used. For validation, the simulation results are compared with a measurement of the slab surface temperature.

In situ steel solidification imaging in continuous casting using magnetic induction tomography

The solidification process in continuous casting is a critical part of steel production. The speed and quality of the solidification process determines the quality of the final product. Computational fluid dynamics (CFD) simulations are often used to describe the process and to design its control system but, so far, there has been no tool that provides an online measurement of the solidification front of hot steel during the continuous casting process. This paper presents a novel magnetic induction tomography (MIT) solution, developed in the EU-funded SHELL-THICK project, to work in a real casting setting and to provide a real-time and reliable measurement of the shell thickness in a cross section of the strand. The new MIT system was installed at the end of the secondary cooling chamber of a casting unit and tested over several days in a real production process. MIT is able to create an internal map of the electrical conductivity of hot steel deep inside the billet. The image of electrical conductivity is then converted to a temperature profile that allows the measurement of the solid, mushy and liquid layers. In this study, such a conversion is done by synchronizing in one time step the MIT measurement and the thermal map generated with the actual process parameters available at that time. The MIT results were then compared with the results obtained with the CFD and thermal modelling of the industrial process. This is the first time in situ monitoring of the interior structure has been carried out during a real continuous casting.

Uncertainty analysis of the influence of delivery system nozzle structure on fluid-thermal coupling in casting molten Pool

The quality of thin strip products is determined by the flow and heat transfer in a molten pool of twin-roll casting, thus it is of great significance to study the structure parameters of the delivery system, including the angle and height of end face nozzle, the angle and height of side nozzle as well as the taper angle of side nozzle. A methodology for simulation of twin-roll thin strips continuous casting process under uncertainty is presented by a three-dimensional numerical model of the flow field and solidification of liquid steel in the molten pool. A sampling-based stochastic model is developed to elucidate the effects of uncertainty in several nozzle structure parameters on the variability of maximum outlet temperature difference and maximum liquid surface turbulence kinetic energy. The results show that taper angle of side nozzle significantly affects the variability in maximum outlet temperature difference, and the uncertainty in angle and height of end face nozzle as well as the height of the side nozzle affects the variability in maximum liquid surface turbulence difference evidently.

Development of prediction method for mold sticking breakout based on density-based spatial clustering of applications with noise and dynamic time warping

As the core component of continuous casting machines, complex behaviors of fluid flow, heat transfer, mass transfer, and solidification occurring inside the mold are the key factors affecting the slabs quality. Breakout is one of the most catastrophic accidents in continuous casting process, which brings severe impacts on personal security, smooth producing, slab quality, and caster equipment. In particular, with the development of the high-speed casting technology, quality defects and sticking breakouts caused by high-load emerge frequently and missing or false alarms for online prediction of breakout occasionally occur. Thus, accurate identification and prediction for the mold breakout is a top priority for online processing control. Considering the typical temperature characteristics of “time lag” and “space inversion” during a breakout, this paper introduced the concepts of dynamic time warping (DTW) and density-based spatial clustering of applications with noise (DBSCAN) in machine learning. On the basis of collecting and distinguishing the typical change modes of mold temperature, an integrated novel method for predicting breakout was developed. The proposed method applied DTW to measure the similarity of mold thermocouple temperature under different casting speeds, steel grades, and other operating conditions, while DBSCAN was used to cluster and separate the temperature samples between normal casting status and sticking breakout. On the basis of the above mentioned method, the results show that the mold sticking breakout can be effectively detected and predicted. Compared with the traditional method based on logical judgment and artificial neural network, the clustering-based breakout prediction method does not require manual setting of thresholds or parameters. According to the common rule of temperature variation in historical samples of breakout, the typical characteristics of temperature in time and space can be extracted and fused, and the breakout can be accurately distinguished and predicted, which shows good self-adaptability and robustness.

Influence of Submerged Entry Nozzle Port Blockage on the Meniscus Fluctuation Considering Various Operational Parameters

The continuous casting process (CCP) is the most vital part of steelmaking. The flow pattern near the submerged entry nozzle (SEN) and mould greatly influence the quality of the slab produced. The present investigation was carried out to gain knowledge regarding the meniscus fluctuation under different nozzle port blockage conditions by water model experiments. The experiments were carried out to study the effect of no blockage, 25% blockage, 50% blockage, and 75% blockage of the nozzle port on mould-level fluctuations. The result shows that when the liquid flow rate increases, the wave amplitude increases. In these experiments, the average and maximum meniscus fluctuations were measured while changing different variables such as the water flow rate, gas flow rate, and one-side percentage blockage of the SEN port while the other side was fully open. The observation shows that when the port size decreases, the fluid steel mixed from the obstructing side to the open side results in asymmetry. The average and maximum wave amplitude increases with decreasing submergence depth. It was observed that the maximum height of the standing waves in the mould continued rising on the non-blocked side of the SEN. Blockage increases from 25% to 75%, and with 75% blockage of the right side of the SEN port, the mould-level fluctuation at the left side of the mould was extreme, while that of the right side was relatively quiet.

Fluid flow and heat transfer with nail dipping method in mould during continuous casting process

ABSTRACTThe character and cause of sliver defect on IF steel sheet surface are studied by means of SEM, unstable flow in mould could induce surface velocity and level fluctuations, leading to surface defects during continuous casting of steel. The nozzle clogging is a serious problem during the continuous casting of steel, due to its influence on the casting operations and products quality. In this study, the nail dipping method for measuring surface velocity and flow direction in molten steel were employed. The fluid flow in mould of whole casting sequence was investigated, especially during the nozzle clogging conditions. The results showed that when nozzle clogging occurred in the 7th heat, the flow velocities on R and L side of nozzle were 0.280 and 0.402 m/s, respectively. The surface defect ratio of hot-rolled and cold-rolled plates increases with the increase of heat flux deviation on both sides of the mould copper. The different clogging per cent on both sides of the nozzle will lead to asymmetry flow, the surface velocity is higher with the small clogging per cent side compared to that of relatively large per cent clogging side.

Effect of strip feeding into mold on fluid flow and heat transfer in continuous casting process

Steel strip feeding into the mold during continuous casting is known as an innovative technology. The newly applied technology is designed to further improve the slab quality. To analyze the complex phase change processes, molten sodium thiosulphate (Na2S2O3·5H2O) was used in the experimental investigation as a transparent analog for metallic alloys. Then, a numerical model incorporating fluid flow, heat transfer and phase change during strip feeding into the mold process was developed. The generalized enthalpy-based method was applied to describe the phase change behavior, and the porous media theory was used to model the blockage of fluid flow by the dendrites in the mushy zone between the strip and melt as well as the solidified shell and melt. The validated model was then used for the simulation of the real strip feeding into the mold process in an industrial scale. The whole shape of the strip under the effect of jet flow from the submerged entry nozzle (SEN) was presented. Results show that the strip will reach a pseudo-steady state after experiencing steel sheath formation, steel sheath melting and strip melting processes. When using the feeding method that is the strip narrow side toward the SEN in the present condition, the strip immersion length can reach 4.5 m below the meniscus and the slab centerline temperature can be decreased by 21 K to a maximum. When the strip feeding speed increased from 0.3 to 0.5 m/s, the minimum temperature of the centerline could be lowered by 4 K or so.

Determination of thermal resistance at mould-strand interface due to shrinkage in billet continuous casting – Development and application of a novel integrated numerical model

An industrial continuous casting process of steel billet is analysed using a novel, integrated numerical model for the heat transfer and solidification of the molten metal as it passes through the mould. One of the major difficulties related to determination of thermal resistance at the mould-strand interface is addressed in the present study. Contrary to empirical or semi-empirical methods commonly used in the industry for determination of the heat transfer at the interface, the present work deals with the determination of the interfacial thermal resistance by adopting a novel mathematical approach. A two-dimensional, transient, finite difference method based code is developed for a plane slice of molten steel moving with a given casting speed down the mould. The resultant solidification and thermal shrinkage are calculated from the temperature distribution and knowledge of the temperature dependent density of steel. The heat transfer from the cast strand to the cooling water is modelled by a network of thermal resistance. The model is validated against experimental data obtained from literature. The numerical results reveal a dominant role of advection of the gaseous mixture of air and other components from pyrolysis of casting oil, in the interfacial gap formed due to the shrinkage of steel, which has not been considered previously in the formulation of thermal resistance. The numerical model is also used to analyse the heat transfer in the mould and the growth of the solidified shell as the strand moves down the mould. In particular, the corner regions of the strand are found to be hotter than the off-corner regions, due to non-uniform heat transfer across the periphery. Also, the effect of casting speed in the mould is found to be dominant in comparison to other casting parameters, such as mould thickness and cooling water velocity.

Low carbon containing Al2O3-C refractories with nanocarbon as the sole carbon source

The functional refractories used in the continuous casting process of steel are mostly made up of alumina (Al2O3) - carbon (C) system. Graphite is used as the main carbon source because of the properties it offered. Generally, these refractories contain about 30% residual carbon after coking. But the use of high carbon content leads to several disadvantages like carbon pickup by steel, high heat loss and generation of higher extent of COx gases, etc. Hence, the development of low carbon Al2O3-C refractories without conceding any beneficial properties is the challenge to the refractory technologists. Such a challenge is intended in current study with the use of nanocarbon as a complete alternative for graphite. The variation in physical, mechanical and thermo-mechanical properties with variation in amount of nanocarbon in the composition is studied. Phase analysis and microstructural developments are also evaluated along with the oxidation resistance at different temperatures. Because of its high reactivity, nanocarbon helps to form in-situ ceramic phases at much lower temperatures thereby enhances strength and other properties. But the increase in amount of nanocarbon above 2% found to deteriorate the properties.

Application of k-means clustering for temperature timing characteristics in breakout prediction during continuous casting

Breakout is the most serious incident in continuous casting. The missing and false alarms will seriously damage the caster and greatly affect the quality of slabs. In view of the defects of existing breakout prediction methods, k-means clustering and dynamic time warping (DTW) are combined to investigate and develop an effectual prediction method. Through extracting the typical temperature timing characteristics from the temporal and spatial perspectives, the method based on k-means clustering and DTW is proposed to distinguish and recognize the breakout. Compared with in-service breakout prediction system (BPS), the prediction results of the proposed method confirm that the number of false alarms can be reduced from 50 to 8 while ensuring a 100% correct alarm rate. The excellent prediction performance demonstrates that the clustering-based breakout prediction method exhibits good application potential, while it offers a novel approach to monitoring abnormalities in the continuous casting process.

Towards Efficient Robust Optimization using Data based Optimal Segmentation of Uncertain Space

Performing multi-objective optimization under uncertainty is a common requirement in industries and academia. Robust optimization (RO) is considered as an efficient and tractable approach provided one has access to behavioral data for the uncertain parameters. However, solutions of RO may be far from the real solution and less reliable due to inability to map the uncertain space accurately, especially when the data appears discontinuous and scattered in the uncertain domain. Amalgamating machine learning algorithms with RO, this paper proposes a data-driven methodology, where a novel fuzzy clustering mechanism is implemented along-with boundary construction, to transcript the uncertain space such that the specific regions of uncertainty are identified. Subsequently, using intelligent Sobol sampling, samples are generated in the mapped uncertain regions. Results of two test cases are presented along with a comprehensive comparison study. Considered case-studies include highly nonlinear model for continuous casting process from steelmaking industries, where a multi-objective optimization problem under uncertainty is solved to balance the conflict between productivity and energy consumption. The Pareto-optimal solutions of the resulting RO problem are obtained through Non-Dominated Sorting Genetic Algorithm – II, and ~23–29% improvement is observed in the uncertain objective function. Further, the spread and diversity metrics are enhanced by ~10–95% as compared to those obtained using other standard uncertainty sets.

Scheduling of steelmaking-continuous casting process using deflected surrogate Lagrangian relaxation approach and DC algorithm

This paper investigates a hybrid flowshop scheduling (HFS) problem in the steelmaking continuous casting (SCC) process. Firstly, a mathematical model is built for the SCC scheduling problem. By relaxing the machine capacity constraint, the SCC scheduling problem can be transformed into a DC (difference of convex functions) programming problem, which can solved by using DC algorithm. Under some reasonable assumptions, the convergence of the DC algorithm is analyzed. Secondly, we propose an effective and efficient deflected surrogate subgradient method with global convergence to solve the Lagrangian dual (LD) problem. Thirdly, a simple heuristic method is designed to obtain a feasible scheduling. Lastly, we report some computational experiments to demonstrate the effectiveness of the proposed surrogate subgradient method by comparing with other similar surrogate subgradient methods.

Mixed baroclinic convection in a cavity

We study the convective patterns that arise in a nearly semicylindrical cavity fed in with hot fluid at the upper boundary, bounded by a cold, porous semicircular boundary at the bottom, and infinitely extended in the third direction. While this configuration is relevant to continuous casting processes that are significantly more complex, we focus on the flow patterns associated with the particular form of mixed convection that arises in it. Linear stability analysis (LSA) and direct numerical simulations (DNS) are conducted, using the spectral-element method to identify observable states. The nature of the bifurcations is determined through Stuart–Landau analysis for completeness. The base flow consists of two counter-rotating rolls driven by the baroclinic imbalance due to the curved isothermal boundary. These are, however, suppressed by the through-flow, which is found to have a stabilising influence as soon as the Reynolds number based on the through-flow exceeds 25. For a sufficiently high Rayleigh number, this base flow is linearly unstable to three different modes, depending on . For , the rolls destabilise through a supercritical bifurcation into a travelling wave. For , a subcritical bifurcation leads to a standing oscillatory mode, whereas for , the unstable mode is non-oscillatory and grows out of a supercritical bifurcation. The DNS confirm that in all cases the dominant mode returned by the LSA precisely matches the topology and evolution of the flow patterns that arise out of the fully nonlinear dynamics.

Physical modelling of fluids’ interaction during liquid steel alloying by pulse-step method in the continuous casting slab tundish

ABSTRACT The continuous steel casting process is characterised by physico-chemical phenomena that are considered in the macro- and microscale. This paper attempts to assess the impact of local changes in the hydrodynamics of liquid steel flow in a one-strand slab tundish on the behaviour of the alloy addition, and consequently, the chemical homogenisation of the liquid steel entering the mould. Four variants of feeding the alloy addition to the liquid steel were considered. Water glass model was used for laboratory experiments. A tracer was fed into the water using the pulse-step method. Based on the mixing curves, the mixing time was calculated. Based on the laboratory experiments carried out, it has been found that, the alloy addition feeding site affects the mixing time, both for symmetric and asymmetric feeding relative to the longitudinal axis of the tundish.

The Significance of Central Segregation of Continuously Cast Billet on Banded Microstructure and Mechanical Properties of Section Steel

The solidification structure and segregation of continuously cast billets produced by different continuous casting processes are investigated to elucidate their effect on segregated bands in hot-rolled section steel. It suggested that segregated spots are mainly observed in the equiaxed crystal zone of a billet. The solidification structure is directly related to superheating and the intensities of secondary cooling. To a certain extent, the ratio of the columnar crystal increases with the increase of superheating and secondary cooling. Moreover, the number of spot segregations decreases with the decrease of the equiaxed crystal ratio. After hot rolling, the segregation spots are deformed to form segregated bands in steels. The severe segregation of Mn in segregated bands corresponds with that in the segregation spots. The elongation ratio and low temperature toughness deteriorate significantly by a high fraction of degenerate pearlite caused by central segregation. With a decrease of central segregation, the total elongation is increased by 10% and the ductile–brittle transition temperature (DBTT) is also reduced from −10 to −40 °C. According to the experimental results, columnar crystal in billets is preferred to effectively reduce the degree of central segregation and further improve low temperature toughness and the elongation ratio.

Experimental study on accelerometer-based ladle slag detection in continuous casting process

The share of continuous casting method is increased day by day among steel production methods. In continuous casting plants, steel production is carried out using BOF (basic oxygen furnace) or EAF (electric arc furnace). During the journey of the liquid steel through whole steelmaking stages, the carryover ladle slag can turn into one of the most detrimental element in casters. It is known that a carryover ladle slag consists of mainly oxides such as CaO, SiO2, Al2O3, and MgO. Carryover slag has to be kept under control otherwise one can end up with negative results. With the development of sensor technology, the detection of carryover ladle slag becomes possible at the end of heats. The main advantage of the sensor type is early detection over a human-controlled system. A few seconds can make a big difference on safety, quality, yield, castability, and cost when the casting sequence lengthens due to the amount of slag. Nowadays, steel production via BOF which is performed with very low profit margins makes it important to solve this problem. Especially steelmaking produced by BOF, the detection methods of carryover slag are human controlled, electromagnetic based, ultrasonic based, image processing based, acoustic based, and vibration based. In this study, it is seen that the vibration-based detection system has many advantages over others when considering investment cost, product quality, castability, and accuracy. The scope of the study aimed to design a vibration-based carryover slag detection system on BOF steel production line. The designed detection system has an accelerometer, data processor, and controller system. After the experimental study, the cost, the product quality, and the productivity analyses were performed for the condition of use and non-use of the vibration-based detection system. At the end of this study, it is seen that the vibration-based carryover slag detection system is affordable and feasible.