Slab Continuous Casting Process Research Articles

Simulation and Experimental Study of Fluid Flow and Solidification Behavior in Thin Slabs Continuous Casting Process under Secondary Electromagnetic Stirring

During the thin slab continuous casting process of silicon steel, electromagnetic stirring (EMS) can control the flow, heat transfer, and solidification of molten steel through electromagnetic force. Herein, a 3D mathematical model coupling the fluid flow, heat transfer, solidification, and the electromagnetic field is built. The effects of varied current intensities on the flow, heat transfer, and solidification of molten steel in the thin slab under secondary EMS are explored based on applying the electromagnetic brake in the mold region. In the findings, it is demonstrated that increasing the current intensity increases the flow rate and vorticity of the molten steel in the second cooling zone, eliminating the superheating phenomenon and improving the uniformity of the molten steel's temperature distribution. Meanwhile, based on the nucleation and growth parameters determined from thermal simulation experiments, the cellular automation finite‐element model is used to simulate the microstructure evolution during the solidification of thin slab. In the results, it is shown that the stirring energy increases when the current intensity increases, potentially promoting equiaxed crystal growth and grain refinement. Compared to the production sample, a reasonable qualitative agreement is achieved for the grain morphology, equiaxed crystal ratio, and columnar to equiaxed transition.

Numerical simulation of macrosegregation in continuously cast slab with application of S-EMS and MR

A 3D numerical model was built to investigate the transport phenomena in slab continuous casting process to investigate the influence of strand electromagnetic stirring (S-EMS) combined with mechanical reduction (MR) on macrosegregation in continuously cast slab. The model was validated by measured strand surface temperature and magnetic induction intensity. The results show that the S-EMS with two pairs of electromagnetic stirring rollers in the opposite direction significantly affects the crater end profile and centerline carbon segregation in slab. The maximum solidification end position difference along the crater end profile of slab ΔL reduced from 0.82 m to 0.52 m, and the centerline carbon segregation is improved by the weak S-EMS, when the current intensity increases from 0 to 250 A. But, the maximum solidification end position difference along the crater end profile of slab ΔL increases from 0.52 m to 1.05 m, the carbon segregation at the 1/4 centerline length position near the right narrow side of slab deteriorates when the current intensity increases from 250 to 350 A. With the combined application of MR near the crater end of continuously cast slab, the solidification delay phenomenon caused by the S-EMS can be significantly improved. But, the solidification delayed cannot be suppressed with current intensity higher than 250A. Therefore, the harmonious application of weak stirring of S-EMS with current intensity of 250A and MR with reduction amount of 4 mm just before the crater end of slab is most benefit for the centerline carbon segregation improvement in continuously cast slab.

Computational investigation of the transient cyclic thermal distortion of funnel shaped mould in thin slab continuous casting process

The response of the thin slab continuous casting mould subjected to thermal and mechanical interactions needs to be studied, since they alter the shape of the mould. A 3D thermomechanical model is developed using non-linear kinematic and isotropic plasticity models along with the creep model to calculate the transient cyclic distortion, residual stress, and elastic–plastic-creep strains in an assembly of funnel-shaped copper mould and waterbox, as the mould undergoes multiple heating cycles in its lifetime. Most of the funnel transition region of the wide face is accumulated with higher temperatures and hence, displacements and strain distributions are maximum in that region. Distortion of the narrow face is majorly affected by the mechanical boundary condition. It is observed that excluding the time dependent creep model highly overestimated the mechanical behaviour of the mould. It is also observed that there is a cyclic variation of distortion of the mould towards the liquid metal side during the casting process and away from the liquid metal side during the cooling process which causes the development of residual stresses inside the mould. This phenomenon further leads to reduction in the magnitude of distortion during subsequent heating cycles of casting operation.

Prediction on the three-dimensional spatial distribution of the number density of inclusions on the entire cross section of a steel continuous casting slab

In the current study, the LES turbulent model, heat transfer, solidification, species transport model, and discrete phase model (DPM) were coupled to investigate the three-dimensional transient flow, temperature, solidification, segregation, and inclusion transport during the slab continuous casting (CC) process. The number, size, and spatial distribution of inclusions on the entire cross section of the CC slab were successfully predicted using the coupled full solidification model, DPM, and capture criteria at the solidification front. The improved capture criteria that considering the primary dendrite arm spacing (PDAS), different forces acting on inclusions, and the critical capture speed, successfully eliminated the banded distribution characteristics of inclusions under the simple capture criterion. The prediction results were in good agreement with the detection results. Four accumulation zones of inclusions along the thickness of the CC slab were predicted, including the 1/4 thickness and 3/4 thickness from the loose side, and the layer beneath the surface of the CC slab. Two accumulation zones near the layer beneath the surface of the CC slab were issued from the double roll flow pattern in the CC strand. The probability of inclusions contacting the solidification front in the upper recirculation zone increased, increasing the entrapment rate. The accumulation zones near the 1/4 thickness and 3/4 thickness from the loose side were corresponded to the peak value of the Marangoni force on inclusions at the 1/4 thickness and 3/4 thickness from the loose side. The Marangoni force increased the probability of inclusions being pushed to the solidification front. In addition, the accumulation near the 1/4 thickness from the loose side became more severe as the diameter of the inclusions increased due to the buoyancy.

Modelling of thermofluidic behaviour and mechanical deformation in thin slab continuous casting of steel: an overview

ABSTRACT The thin slab continuous casting (TSCC) process has emerged as one of the most potential technologies, growingly used in several developed nations, since last two decades. Although a good number of works have been published in the field of continuous casting by pioneering research groups headed by Samarasekera, Brimacombe, Thomas, etc. there is a huge scope of improvement in the physical understanding and modelling aspects of the TSCC process. The higher velocities, higher aspect ratio and funnel shape of the mould in this process have been found to pose major challenges. This work is aimed at compiling the essential summary from literature and providing a comprehensive overview for carrying forward this technology to the next level. The thermal, fluid flow and mechanical aspects of this process have been investigated in detail from the available literature and presented in a lucid form for gaining an in-depth understanding of its state-of-the-art technology.

Influence of Austenitizing Parameters on the Microstructures and Mechanical Properties of 22MnB5 Hot Stamping Steel Produced by TSCR Process

Thin gauge hot strip steel can be produced by thin slab continuous casting and rolling (TSCR) process without the aid of cold rolling. However, few attempts have been made to produce hot stamping steel by using TSCR technology. As given steel, the hot stamping steel produced by the TSCR process was used to study the influence of austenitizing parameters on the final microstructures and mechanical properties. A Gleeble3500 thermal simulator was employed to heat the samples to obtain different austenite microstructures. After quenching, the Vickers hardness examination along the thickness of the sample and tensile testing were conducted. The microstructure was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that on the condition of relatively lower temperature and shorter holding time, the sample exhibited better mechanical properties at the cost of microstructure uniformity along the thickness, although higher austenitizing temperature enhanced the carbide dissolution which would increase the effective carbon content in the martensite matrix. Lower heating temperature led to small prior austenite grain size and small blocks which contributed greatly to the mechanical properties.

Numerical Simulation of Heat Transfer between Roll and Slab under Dry Secondary Cooling in Ultrathick Slab Continuous Casting

A 3D model of heat transfer between the circular‐distributed water channel roll (CDWCR) and slab during ultrathick slab continuous casting process is established, considering the structure of water channels inside CDWCR and rotating contact between the roll and slab. The results show that the contribution of conduction heat transfer in the heating process of the roll is greater than that of radiation heat transfer, and maximum surface temperature of the roll is 460 K, located at the place where it is right out of contact with the slab, and the change of internal temperature of the roll lags behind the change of surface temperature. The temperature decreases gradually from the outside to the inside in the radial direction. The temperature of the CDWCR inside the circle of cooling water channels is no more than 325 K. The yield strength of CDWCR is analyzed, showing that the strength of the roll meets the requirements of using it in the process. In addition, the orthogonal method is used to analyze the influence factors on CDWCR temperature. The results indicate that the orders of factors affecting more are the contact angle, the slab temperature, the casting speed, and the inlet speed of cooling water.

Abnormal mold level fluctuation during slab casting of peritectic steels

Abnormal mold level fluctuation is frequently observed in high-speed casting, especially for peritectic steels, which has been shown to severely deteriorate product quality. Both an online electromagnetic sensor and an ibaAnalyzer are used to analyze the frequency and amplitude of massive mold level fluctuation data from the slab casting process of different steel grades using different casting speeds, slab widths and physical parameters of mold flux. The results show that in the slab continuous casting process of peritectic steels, the main frequency and equivalent amplitude of abnormal mold level fluctuations first increase and then decrease with increasing the carbon content. In the production of various grades of steel, the main frequency of abnormal mold level fluctuation and the equivalent amplitude increase with increasing the casting speed, while the main frequency of abnormal mold level fluctuation changes little with increasing the casting width. The main frequency of abnormal mold level fluctuation is positively related to the surface tension of the mold flux. Based on these results, a new mechanism has been presented. It is shown that the abnormal mold level fluctuation is mainly induced by shell bulging while moving through the rollers, and resonance occurs when the frequency approaches the natural frequency of the molten steel in mold, which results in a large amplitude of the abnormal mold level fluctuation. Based on this mechanism, a new equation for the resonance frequency of molten steel is proposed. The improved method based on this mechanism has proved to be effective in controlling abnormal mold fluctuations.

Numerical Simulation of Solidification Behavior and Solute Transport in Slab Continuous Casting with S-EMS

A 3D numerical model was built to investigate the transport phenomena in slab continuous casting process with secondary electromagnetic stirring (S-EMS). In the model, the columnar grain grew from strand surface and it should be treated as a porous media. While for the equiaxed zone, the nucleated grain moves with fluid flow in the earlier stage and it was regarded as a slurry. The model was validated by measured strand surface temperature and magnetic induction intensity. The results show that the solidification end near the 1/4 width of slab was postponed, due to the liquid flow from a submerged entry nozzle injected to the strand’s narrow face. As the linear stirring in the same direction is applied, liquid moves from side B to side A and then penetrates deep downward with higher temperature. In the later stage, the solidification end near the side A is postponed and the solute element is concentrated. When linear stirring in the opposite direction is used, the solidification end near the side A moves backward, while that near the side B moves forward. Moreover, it is found that the solute segregation in the side B is deteriorated, but that in the side A is reduced. As rotational stirring mode is applied, the evenness of solidification end profile is improved and the centerline segregation is reduced, especially with higher current intensity. Therefore, it is concluded that the linear stirring mode is not appropriated for slab casting, while the rotational stirring mode is more suitable.

Effect of cooling process on mechanical properties of thin-gauge hot-rolled dual-phase steel

The high strength hot-rolled dual-phase steel suitable for a thin slab continuous casting and rolling (TSCR) process was developed by a low C and Nb micro-alloyed design with the controlled rolling and cooling technology. The effect of the isothermal temperature and holding time on the microstructure and mechanical properties of the dual-phase steel was studied using a uniaxial tensile test and optical microscope (OM). The results showed that with the decrease of the isothermal temperature in the ferrite phase transformation region, the thermodynamic conditions of the ferrite transformation were enhanced. The proportion of the ferrite increased while that of martensite decreased, resulting in the reduction of the yield strength and tensile strength and the increase of elongation. With the rise in the isothermal time, the kinetic conditions of the ferrite transformation were enhanced and the proportion of the ferrite increased. The ferrite transformation has completed after 8 seconds of the isothermal holding time, and it was not apparent for increased amount of the transformed ferrite to increase the isothermal time.

Structural Optimization of Electromagnetic Swirling Flow in Nozzle of Slab Continuous Casting

During the slab continuous casting process, the flow field of molten steel in the mold plays a decisive role in the quality of the slab. In this paper, electromagnetic swirling flow in nozzle technology is proposed to control the flow field in mold. This technology can drive molten steel to rotate inside the submerged entry nozzle by electromagnetic force, thereby controlling the flow field. This research shows that it can reduce the impact of molten steel on the bottom of nozzle and partly reduce the negative pressure at the upper part of nozzle outlet which is even eliminated by optimizing the structure and angle of nozzle. The area of heat flux of the mold wall becomes larger, and the crest value of heat flux gets lower than that without swirling in nozzle and any nozzle optimization. The meniscus fluctuates smoothly, and the flow velocity at the top surface is within a reasonable range. The temperature field distribution in the mold is uniform which was beneficial to the growth of equiaxed crystal and decreased element segregation.

Numerical study on the characteristics of solute distribution and the formation of centerline segregation in continuous casting (CC) slab

To reveal the characteristics of solute distribution and the formation of centerline segregation in continuous casting (CC) slab, a 3D simulation model for the prediction of centerline segregation during a slab CC process was developed. Experiments including the morphology of strand transverse section obtained by acid etch and the segregation degree of C tested by chemical analyzer were carried out to verify the accuracy of the numerical model. The maximum deviation between the calculated and experimented results reaches as low as 3.22%. In the turbulent flow region, the solute distribution in the liquid pool is relatively uniform and its distribution pattern is similar to that of flow pattern. In the final stage of solidification during a slab CC process, the solidification of molten steel in the centerline region is not simultaneous and the pattern of solute distribution is highly depended on the shape of liquid pool. The final solidification and serious segregation occur at a position roughly 595 mm from the slab center. Moreover, the quantitative relations between the position of solidification front and the solute concentration on the centerline were studied. The results show that solute redistribution and the solidification front moving continuously toward centerline lead to the formation of centerline segregation in CC slab. The central segregation degree of solutes in steel Q345 arranged in weakening order is S, C, P, Si, and Mn.

Numerical modeling of centerline segregation by a combined 3-D and 2-D hybrid model during slab continuous casting

Abstract

State of the Art Technology in Slab Continuous Casting:

Over the last 50 years, numerous slab continuous casters have been widely installed all over the world to take advantage of the enhanced productivity, yield, energy efficiency, and cost efficiency. To meet a variety of product quality demands from the steel market, the slab continuous casting process has been diversified into several types. In the 1960s, 200–300 mm thickness slab casters opened the continuous casting era by substituting the ingot process widely applied at that time, and now the major part of slab production is for the hot strip rolling. The thick slab of 400–600 mm thickness casting process with a casting speed range of 0.2–0.6 m/min was introduced to guarantee the internal quality of heavy gauge plates for the energy industry and shipbuilding applications. For the ultra-thick, over 600 mm, the semi-continuous casting technology with a casting speed of 0.05–0.2 m/min has been developed as an alternative way to replace the ingot process, with higher yield and productivity compared to the case of the ingot process.

超低碳钢连铸板坯近表面非金属夹杂物分布

本文针对1350 mm × 230 mm断面超低碳钢板坯连铸过程，通过连铸坯取样与定量金相分析，考察了恒拉速和变拉速条件下板坯近表面非金属夹杂物的分布情况。结果表明，小于10 μm夹杂物在各厚度层分布较为均匀，大于10 μm夹杂物主要分布在铸坯距表面0~5 mm厚度范围内。当拉速约为1.2 m∙min−1时，有利于控制卷渣和夹杂物聚集的发生，近表面夹杂物密度较低；拉速过低(0.8 m∙min−1)或过高(1.4 m∙min−1)以及拉速变化过程均可导致铸坯近表面夹杂物数密度显著升高，需采取技术措施以控制结晶器钢液流场稳定。 In this paper, focusing on the slab continuous casting process of ultra-low-carbon steel with 1350 mm × 230 mm cross section, via sampling and quantitative metallography analysis, the effect of continuous casting speed and its variation during operation on the distribution of no-metallic in-clusion near the slab surface were verified. Results show that, the inclusions with particle size less than 10 μm distribute in the slab sub-surface uniformly from 0 mm to 9 mm, but those with particle size larger than 10 μm mainly distribute within 5 mm. When the continuous casting speed is 1.2 m•min−1, the inclusion number density in the slab sub-surface is low for the reason of inhibiting mold flux entrapment and inclusion aggregation. Under the condition of lower continuous casting speed e.g. 0.8 m•min−1, higher continuous casting speed e.g. 1.4 m•min−1, and decreasing of continuous casting speed, the inclusion number density increases significantly, so suitable tech-nologies should be applied to control the stabilization of fluid flow in the mold.

Influence of FC-Mold on the Full Solidification of Continuous Casting Slab

A three-dimensional model coupling fluid flow, heat transfer, solidification for slab continuous casting process with flow control mold (FC-Mold) was constructed. The full solidification process from the meniscus to the solidification end of slab was obtained for the first time. The calculation domain was designed according to the actual dimension of the continuous caster. The main results show that the calculated flow speed on the meniscus at different casting speeds and the calculated shell profile had a good agreement with the measured flow speed using nail board measurement and the shell with breakout. The application of FC-Mold could improve the symmetry of flow in width, and suppress the formation of vortices on the meniscus. The decrease of upper magnetic field intensity of FC-Mold reduced the washing effect on the solidifying front, and favored the shell growth in the mold region. In the secondary cooling zone, the shell thickness increased gradually, and the shell grew quickly at the final stage of solidification for the whole mushy form of steel. In addition, FC-Mold had an effect on the shape and position of the solidification end.

Modelling of Bubble Aggregation, Breakage and Transport in Slab Continuous Casting Mold

The bubble-liquid flow, especially the aggregation and breakage behavior, plays a significant role in the slab continuous casting process. A 1/4th water model was employed to investigate the two-phase flow characteristics and the bubble size distribution. A mathematical model based on the Euler-Euler approach was developed to analyze the bubble aggregation and breakage in the bubbly flow. The population balance model (PBM) was applied to calculate bubble size distribution, and the simulation was implemented through the MUSIG (multiple size group) model. The numerical predictions were verified by the water model experiment. The results show that the PBM is a useful approach for analyzing bubble size distribution and can be taken into industrial applications of gas-liquid two phase flow inside the continuous casting mold. The ratio of big bubbles and bubble mean diameter in the upper recirculation zone are found to decrease with the increment of water flow rate and increase with the increment of gas flow rate. The bubble aggregation and breakage behavior, bubble size distribution and the effect of gas bubbles on flow field in the continuous casting mold are revealed. The numerical results are compared with the experiment and they show good agreement.

Heat Transfer and Solidification Model of Slab Continuous Casting Based on Nail-Shooting Experiments

A heat transfer and solidification model of slab continuous casting process was developed, and the nail-shooting experiments were carried out to verify and improve the prediction accuracy. The comparison between the simulation and the measurements results showed that, there exists difference between the model predicted liquid core length and the calculated liquid core length according to the measurement results of the solidification shell thickness. In the present study, the value of constant a in the heat transfer coefficient calculation formula was corrected through back-calculation, results showed that, the suitable value of a is 31.650, 33.468 and 35.126 when the casting speed is 0.8m·min-1, 0.9m·min-1 and 1.0m·min-1 respectively, which can meet the liquid core length of the measurement results. The developed model built a foundation for the application of dynamic secondary cooling, and dynamic soft reduction.

Numerical Analysis of Fluctuation Behavior of Steel/Slag Interface in Continuous Casting Mold with Static Magnetic Field

Utilizing ANSYS CFX commercial software and volume fraction of fluid (VOF) model, fluctuation behavior of steel/slag interface was numerically simulated in continuous casting mold with static magnetic field, and the influence of metal jet characteristics on the behavior of steel/slag interface was investigated. The results indicated that the behavior of steel/slag interface is similar at different process parameters, which is closely related to the characteristic of the flow field. The steel/slag interface has an obvious trough characteristic, which can be divided into three zones: frontal valley zone, back valley zone and horizontal zone; as the magnetic flux density increases, the fluctuation of liquid level increases firstly and then decreases, and a reasonable magnetic flux density can make steel/slag interface obtain a relatively flat interface, which can prevent slag from being entrapped into liquid steel. For a thin slab continuous casting process, when the casting speed is 4 m/min, a reasonable magnetic flux density is about 0.5 T, and the interfacial fluctuation is weaker. No matter the position of magnetic field is horizontal or vertical, for different operating parameters, there is a corresponding reasonable magnetic field position where the steel/slag interface fluctuation can be properly controlled and slag entrapment can be prevented.

Metallurgical Secondary Cooling of Continuous Casting Based on Neural Network Adaptive System Design of Water Distribution

Efficient secondary cooling water control level slab continuous casting process and quality are closely related. Casting solidification heat transfer model is the basis of process control and optimization, heat transfer model based on determining the secondary cooling system is the most widely used method for casting production process can be simulated. However, when considering the many factors affecting the production and input conditions change significantly, real-time and strain of this method is not guaranteed. Therefore, the artificial intelligence optimization algorithms such as genetic algorithms, neural networks, fuzzy controllers, introducing continuous casting secondary cooling water distribution and dynamics of optimal control methods, the rational allocation of caster secondary cooling water and dynamic control is important.