Liquid Steel Flow Research Articles

Influence of Multihole Ladle Shroud Construction on the Liquid Steel Flow in the One-strand Tundish during CSC Process

Influence of Multihole Ladle Shroud Construction on the Liquid Steel Flow in the One-strand Tundish during CSC Process

Numerical Analysis of the Influence of the Modification of the Ladle Shroud on Fluid Flow Behavior in a One-strand Tundish during Continuous Steel Casting

A tundish is a device from which liquid steel is pour into a mold. Therefore tundish hydrodynamic conditions have a significant impact on solidification during continuous steel casting (CSC) process. Modification of ladle shroud workspace, allows for the modification of liquid steel movement in the tundish. In the following work, numerical simulations were performed which allowed the impact of the modification of the ladle shroud workspace on the liquid steel flow structure in a one-strand tundish to be determined. In order to assess the impact of the modification of the ladle shroud on the behavior of the liquid steel in the tundish, simulations were performed, on the basis of which the percentage share of stagnant, ideal mixing and plug flow zones were determined. In addition, the mixing parameters were determined, allowing the estimation of casting duration during sequential casting. The flow fields of liquid steel for each modification of the ladle shroud were performed. The average velocity of liquid steel flowing through the tundish, the Reynolds number and turbulent intensity were also described. The obtained results showed, among others, that the application of three cylinders with a diameter of 0.041 m into the ladle shroud with a diameter of 0.11 m increases the share of active flow in the tundish in relation to the tundish with Conventional Ladle Shroud. At the same time, applying a ladle shroud with a diameter of 0.11 m during casting is the most favorable in relation to the hydrodynamics of the tundish.

Evolution of the Numerical Model Describing the Distribution of Non-Metallic Inclusions in the Tundish

Continuous casting is one of the steel production stages, during which the improvement in the metallurgical purity of steel can be additionally affected by removing nonmetallic inclusions (NMIs). This can be achieved by means of various types of flow controllers, installed in the working space of the tundish. The change in the steel flow structure, caused by those flow controllers, should lead to an intensification of NMIs removal from the liquid metal to the slag. Therefore, it is crucial to understand the behavior of nonmetallic inclusions during the flow of liquid steel through the tundish, and particularly during their distribution. The presented paper reports the results of the modeling studies of NMI distribution in liquid steel, flowing through the tundish. CFD modeling methods—using different models and computation variants—were employed in the study. The obtained CFD results were compared with the results of laboratory tests (using a tundish water model). The results of the performed investigations allow us to compare both methods of modeling; the investigated phenomena were microparticle distribution and mass microparticle concentration in the model fluid. The validation of the CFD results verified the analyzed computation variants. The aim of the research was to determine which numerical model is the best for describing the studied phenomenon. This will be used as the first phase of a larger research program which will provide for a comprehensive study of the distribution of NMIs flowing through tundish steel.

New Insight on Liquid Steel Microalloying by Pulse-Step Method in Two-Strand Slab Tundish by Numerical Simulations

Developing a technology for introducing alloy addition to liquid steel during the course of continuous casting process seems to be an interesting approach to enhancing the steelmaking process, especially as the effective introduction of micro-additives or non-metallic inclusion modifiers to the liquid steel is the key to the production of the highest-quality steel. This paper presents the results of investigation describing the process of liquid steel chemical homogenisation in the two-strand slab tundish. The alloy was fed to liquid steel by pulse-step method. Five tundish equipment variants with different flow control devices and alloy addition feeding positions were considered. The paper includes fields of liquid steel flow, alloy concentration vs. time curves, dimensionless mixing time, minimum time values and alloy concentration deviations at tundish outlets. The results pointed much more effectively with liquid steel mixing nickel than aluminium. For aluminium obtaining a 95% chemical homogenisation level requires three-fold more time. Moreover, it is definitely beneficial for chemical homogenisation to initiate the alloying process simultaneously in two sites. This procedure generates, among others, the least alloy deviation of concentration at tundish outlets.

Improvement of texture and magnetic properties of strip-cast grain-oriented electrical steel by trace Bi addition

The improvement of recrystallization texture and magnetic properties in grain-oriented electrical steel with trace Bi addition processed by strip casting process was studied in this study. Low casting temperature and sufficient liquid steel flow during strip casting process enabled relatively homogeneous distribution of Bi in the as-cast strip, which accelerated the precipitation during solidification and cooling process. As a result, relatively high density of duplex MnS + AlN, MnS and AlN was formed at grain boundaries and inside grain. Due to the synergistic effect of continuous precipitation and fragmentation of coarse precipitates during cold rolling, the number density of precipitates was increased and mean size was decreased along the processing route. High density of precipitates is attributed to severe inhomogeneous plastic deformation, which promoted the formation of high density in-grain shear bands during cold rolling and recrystallization Goss texture during annealing. Homogeneous microstructure with average grain size of ~ 11.6 μm, strong Goss texture with intensity of 2.5 multiples of random distribution, fine precipitates with number density of ~ 1.9 × 109 /cm2 and mean size of ~ 49 nm were formed after primary recrystallization annealing. Furthermore, grain-oriented electrical steel with Bi addition experienced complete secondary recrystallization of exact Goss grains during high-temperature annealing, which is attributed to beneficial optimization of Goss texture and strong inhibition effect, and superior magnetic induction B8 of 1.91 T was obtained. It is expected that this study paves a new way for fabrication of high-performance grain-oriented electrical steel.

Application of Tanks-in-Series Model to Characterize Non-Ideal Flow Regimes in Continuous Casting Tundish

This study describes a new tanks-in-series model for analyzing non-ideal flow regimes in a single-strand tundish. The tundish was divided into two interconnected tanks, namely an inlet tank and an outlet tank. A water model experiment was carried out to separately measure the residence-time distribution (RTD) of the two tanks. Drift beads were adopted in the water model experiment to simulate the non-metallic inclusions in molten steel. Dead volume fraction was evaluated by analyzing measured RTD curves. The ratio between mixed flow volume and plug flow volume was proposed as a new criterion to evaluate the inclusion removal. In the inlet tank, a higher mixed flow fraction was preferred to effectively release turbulent kinetic energy and enhance inclusion collision growth. In the outlet tank, a higher plug flow fraction was preferred to facilitate inclusion removal by flotation. The optimal positions of the weir were recommended based on the RTD analysis and the inclusion removal from the results of water model experiments. A theoretical equation was derived based on the tanks-in-series model, providing a good fitting function to analyze the experimental data. The confirmation test was performed by applying computational fluid dynamics simulations of liquid steel flow in the real tundish.

Mathematical Modelling and Simulation of liquid steel flow phenomena and temperature distribution in an optimized tundish design of a continuous caster

The objective of this study was to analyze the fluid flow of molten steel in a continuous casting tundish using numerical simulations for better inclusion floatation and its separation. The tundish geometry was designed using Autodesk FUSION 360 and the analysis were performed on ANSYS FLUENT. The investigations were done on steady-state as well as transient conditions. To scale back vortexing and turbulence within the tundish, turbo stoppers and flow modulators, e.g. dam and weirs were placed for an optimized and efficient flow inside the tundish and its behavior on the spacious flow structure was explored. The strategic placements of the flow modifiers produced higher turbulence in the recess region of the tundish resulting in better turbulent flow withinside the inlet region of the tundish. Thereby a more homogeneous fluid flow is formed with better conditions for particle separation. Analysing the flow behavior we have determined the inclusion floatation using particle tracking method form dense discrete phase modelling along with multiphase eulerian-lagragian model. Reduction in dead volumes was achieved in the spatial flow due to better intermixing which further reduced the metal loss and increased the yield of the tundish using the fluid flow analysis. Analyzing eddy formations in the spatial geometry of the tundish structure made it easy to evenly distributes the flow-induced shear. This determined the lesser turbulence on the free surface of the steel flow resulting in less reduction of the liquid steel surface.

Process Diagnosis of Liquid Steel Flow in a Slab Mold Operated with a Slide Valve

Slab molds receive liquid steel from the tundish through bifurcated submerged entry nozzles (SEN) using a slide valve as throughput control. Due to the off-centering position of the three plates’ orifices that conform to the valve to control the steel passage, the flow inside the nozzle and mold is inherently biased toward the valve opening side. In the practical casting, a biased flow induces inhomogeneous heat fluxes through the mold copper plates. The nozzle design itself is also a challenge, and has direct consequences on the quality of the product. A diagnosis of the casting process regarding the internal and external flows, performed through experimental and mathematical simulation tools, made it possible to reach concrete results. The mathematical simulations predicted the flow dynamics, and the topography and levels variations of the meniscus characterized through a full-scale water model. The flows are biased, and the meniscus level fluctuations indicated that the current nozzle is not reliable to cast at the two extremes of the casting speeds of 0.9 m/min and 1.65 m/min, due to the danger of mold flux entrainment. A redesign of the nozzle is recommended, based on the experimental and mathematical results presented here.

Hydrodynamic Analysis of the Flow inside the Submerged Entry Nozzle

The quality of steel produced by continuous casting depends mainly on the characteristics of the liquid steel flow pattern within the mold. This pattern depends on the flow dynamics of the nozzle that is immersed in liquid steel. This work characterizes the fluid dynamics within two separate submerged entry nozzle models with a square cross section bore. The Froude similarity criterion and water as working fluid have been used. The models consist of a square-shaped tube with one inlet and two lateral squared exits at the bottom. To enhance the flow visualization, the models do not have exit ports. Moreover, one of the models has a “pool,” a volume at the bottom, and the other prescinds of it. The geometrical parameters and operational conditions of physical experiments were reproduced in the numerical simulations. The turbulence model used in this work is large eddy simulation (LES) with dynamic k-equation filtering. It was found that transient numerical simulations reproduce the dynamic nature of the internal flow pattern seen in physical experiments. The results show that the flow pattern within the pool nozzle is defined by only one large vortex; on the other hand, in the nozzle, without the pool, the flow pattern achieves a complex behavior characterized by two small vortexes. This study will allow to build nozzles that produce a symmetric, regular fluid flow pattern inside the mold, which leads to improvements on the process such as low energy consumption and finally in cost reductions.

Numeric Simulation of the Steel Flow in a Slab Caster with a Box‐Type Electromagnetic Stirrer

The usage of electromagnetic actuators in the continuous steel‐casting process is on a steady rise, due to its possibilities for a sophisticated, contactless flow control. The complexity of the casting process and the ever‐increasing quality demands require a well‐founded knowledge of the interaction between the electromagnetic actuators and the liquid steel flow. Numeric modeling provides a detailed view and is therefore crucial for understanding the interaction between the electromagnetic fields and the liquid steel flow. Only a deep insight into the coupling between the liquid steel flow and the electromagnetic forces makes it possible to improve/optimize the continuous casting process. The work presented here is part of an ongoing research to bridge the gap between the liquid steel flow and the grain structure of the end product. The article's focus lies on the liquid steel flow modified by a traveling magnetic field—relying mainly on numerical simulations. Different modeling approaches are used to simulate linear electromagnetic stirring in the secondary cooling zone of a slab caster. An appropriate model is chosen to investigate the influence of various stirring parameters, stirring modes, and stirring positions. From the results, conclusions for the real casting process can be drawn.

Analysis of Fluid Flow of Liquid Steel through Clogged Nozzles: Thermodynamic Analysis and Flow Simulations

Selected raw materials, surface treatment, and control of the internal flow fundamentals are applied to manufacture an anticlogging nozzle. This nozzle is compared with another one manufactured with a conventional alumina–graphite (AG) composite in a plant trial. The two nozzles, with and without clogging, are replicated with plastic and rubber materials and the flows, under unclogged and clogged conditions, are characterized using water modelling and mathematical simulations. The new nozzle material yields considerably less clogging than the nozzle with the conventional AG after casting four heats, yet, there is still clogging. Flow patterns, because of clogging, change radically and represent serious conditions for slab integrity and the productivity of the caster.

Intensification of liquid steel active flow volume in one-strand tundish using a modified ladle shroud

This work presents the numerical and physical simulation results of the liquid steel flow in the one-strand tundish. The results obtained during the numerical simulations and the water modeling results were compared to each other. Six types of turbulence models were tested. Among tested turbulence models the BSL k-ω was turned out the best correlating with the results from the laboratory experiments. Besides, the ladle shroud modification was proposed by the authors and the influence of the modified ladle shroud immersion depth in the liquid steel on the hydrodynamic structure in the tundish was checked. The ladle shroud modification depended on the expansion, narrowing, and re-expansion of the liquid steel feed stream. The four tundish variants with the four different ladle shroud immersion depths (at 0.1, 0.2, 0.3 and 0.4 m) in the liquid steel were tested. The liquid steel flow volumes were calculated and according to the generated active flow volume, the most beneficial research case was indicated. The tundish variant with the ladle shroud immersion depth of 0.3 m in the liquid steel was characterized by the lowest stagnant flow volume. The numerical simulations were performed by using the Ansys-Fluent computer program.

Simulation of the flow-heat transfer process in billet mold and analysis of the billet rhomboidity phenomenon

To investigate the influence of inlet temperature and velocity of mold cooling water on the heat transfer effects in a continuous casting mold, a three-dimensional fluid flow and heat transfer coupled model was established, containing steel, copper tube and cooling water zone. Using Fluent, this model simulated the flow and heat transfer of liquid steel and cooling water, solidified shell growth, and heat transfer through air gap and mold fluxes. Furthermore, the accuracy of the model was verified by comparing the shell thickness and temperature fields in this study with those from other studies. The model results suggested that the inlet water temperature notably affects the temperatures of the mold cold surface. If the inlet water temperature exceeded 313 K, the highest temperature of the cold surface surpassed the boiling point of water, which could be a reason for billet rhomboidity. An increase of 0.49 m∙s−1 in water velocity diminished the adverse effects of an increase of 4 K in inlet water temperature. Off-squareness can be prevented in the actual production process by following this method.

Improvement in Castability of Al Killed Steel in Billet Casters by Process Optimisation

Sticking of alumina as well as spinel inclusions inside the sub entry nozzles (SEN) as well as tundish nozzle is perennial problem during continuous casting of aluminum killed steel through billet casters. This results in restriction or completely blockage of flow of liquid steel through the nozzles eventually leading to abortion of sequence in billet casters and stopping of continuous casting machine. Nozzle clogging not only restricts the productivity by restraining the casting sequence, intermittent extrication of clogged alumina particles or dislodged refractory materials are a significant source of non-metallic macro-inclusions in the cast sections of billet casters. If these inclusions are not removed completely during secondary refining of steel they causes excessive clogging mainly in low carbon Al killed steels. In other grades of Al killed steel cogging is also very prominent if the deoxidation and secondary refining is not carried out properly. IISCO Steel Plant (ISP), Burnpur a new, modernised unit of Steel Authority of India Limited (SAIL) was facing problems of nozzle clogging in low carbon, low Si, Al killed grade (EWNR –electrode quality grade) resulting in premature abortion of casting sequence leading to huge productivity loss. To solve the problem of nozzle clogging in low carbon Al killed grades and other grades at ISP, optimisation of various steelmaking parameters viz. amount of Al addition & its sequence, purging regime in ladle furnace, optimisation of Ca treatment process etc has been carried out which has resulted in improvement in castability of Al Killed Steel in billet caster of ISP.

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.

Flow monitoring for continuous steel casting using Contactless Inductive Flow Tomography (CIFT)

The control of the liquid steel flow in the mould of a continuous caster based on real time flow measurements is a challenging task due to the lack of appropriate measurement techniques. The opaqueness, the high temperature of 1500°C and the chemical aggressiveness of the melt require non-optical contactless methods. In order to reconstruct the complex flow structure in the mould, the Contactless Inductive Flow Tomography (CIFT) is a promising candidate, since it allows the visualization of the flow structure in the melt by applying a magnetic field to the melt, measuring the flow induced perturbation of that field and solving subsequently a linear inverse problem. The combination of this new measurement technique with typical electromagnetic actuators like electromagnetic brakes used in continuous casting pose a challenge to the CIFT measurement system, because the flow induced magnetic field is in the range of 100 nT and has to be measured robustly on the background of the static magnetic field with the amplitude of 300 mT generated by the brake. In this work we will show recent developments regarding this topic for a small model of a continuous caster in the lab. Furthermore, we will present a new method on how the complex linear inverse problem can be solved in real time providing a time resolution of about 1 Hz.

Improvement in Castability of Al-Killed Steel in Billet Casters by Process Optimization

Sticking of alumina as well as spinel inclusions inside the sub-entry nozzles as well as tundish nozzle is a perennial problem during continuous casting of aluminum-killed steel through billet casters. This results in restriction or complete blockage of flow of liquid steel through the nozzles eventually leading to abortion of sequence in billet casters and stopping of continuous casting machine. Nozzle clogging not only restricts the productivity by restraining the casting sequence, intermittent extrication of clogged alumina particles or dislodged refractory materials which are a significant source of non-metallic macro-inclusions in the cast sections of billet casters. If these inclusions are not removed completely during secondary refining of steel, they cause excessive clogging mainly in low-carbon Al-killed steels. In other grades of Al-killed steel, clogging is also very prominent if the deoxidation and secondary refining is not carried out properly. IISCO Steel Plant (ISP), Burnpur, a new, modernized unit of Steel Authority of India Limited, was facing problems of nozzle clogging in low-carbon, low-Si, Al-killed grade (EWNR—electrode quality grade) resulting in premature abortion of casting sequence leading to huge productivity loss. To solve the problem of nozzle clogging in low-carbon Al-killed grades and other grades at ISP, optimization of various steelmaking parameters, viz., amount of Al addition and its sequence, purging regime in ladle furnace, optimization of Ca treatment process, etc. has been carried out which has resulted in improvement in castability of Al-killed steel in billet caster of ISP.

CURRENT PROBLEMS AND PERSPECTIVES OF COMPUTER SIMULATION OF CONTINUOUS STEEL CASTING

Nowadays we can see increase in using of engineering analysis systems in the field of continuous steel casting simulation due to their high accuracy and convergence with industrial experiments results. Such powerful systems as «ANSYS» and «ProCast» allows solving gas-, hydrodynamic and thermal problems, the parallel interaction of which constitutes the essence of most metallurgical processes. Group of authors from the LSTU Chair “Metallurgical technology” have successfully carried out computer experiments in tundish and continuous casting mold processes simulation. The experiments were aimed at first, on studying of further improving in liquid steel flow modifiers (partitions, turbo-stops, thresholds) design, at second, on influence of argon blowing regime on liquid steel flow parameters in the 50-ton tundish workspace, and, at third, on influence of submerged nozzles design on the liquid steel flow in crystallizer, assuming deterministic-dynamic operation mode. The results of calculations are velocity fields of liquid steel flow and flow temperatures fields in tundish and crystallizer, as well as temperature fields in the tundish refractory lining. An equation of primary flow average velocity change on exit from submerged nozzle was also formulated. These preliminary results allow us to assess the velocity changes and direction of the melt flow and formation of volumes with different melt temperatures when using flow modifiers in the ladle, including using of “argon curtain” in the casting chamber. Obtained data on melt flow motion and on location of erosion spots in crystallizing «crust», also on the presence of temperature gradient zones in various regions of crystallizer workspace may be useful to practice engineers engaged in choice of crystallizer submerged nozzle design. Effective control of melt flow in tundish and in crystallizer allows significant improvements in continuous cast slabs and rolled products quality in context of reducing metal products rejection due to defects associated with slag or nonmetallic inclusions presence and due to cracks formed as the result of insufficient thickness of crystallized «crust».

DEVELOPMENT AND INDUSTRIAL TESTING OF THE SYSTEM OF SLAG CUT-OFF AT STEEL CASTING PROCESS

The authors have analyzed the existing approaches to solve a problem of determining the moment of slag outcome beginning during steel casting from a ladle to a tundish. The solution of this problem is considered in two aspects: the first is the choice of best way to generate a diagnostic signal from the position of the price/quality ratio of its handling, and the second is the development of a method to process this signal in order to obtain useful information. A scheme is proposed to receive a signal of vibration acceleration from a sensor installed on a manipulator of the ladle protective tube. A product sample is developed to arrange that. It provides protection from the influence of industrial disturbances on the sensor. In order to analyze the vibration acceleration signal, the criteria to determine the moment of the slag outcome beginning were determined based on entropy energy calculation. This method and a system developed on its basis are tested under industrial conditions for a real object. The only condition for effective operation of the developed criteria is selection of the subsystem of steel level maintenance at final casting step to the manual mode to eliminate the disturbances from the movement of the slide shutter used to control the flow of liquid steel. According to the results of experiments under real conditions, it was found that the slide shutter control shutdown is to be performed if weight of the ladle content is from 18 to 19 tons approximately. In this mode of operation, the operator has always been able to found such a rate of steel discharge that the level of steel in the tundish is within the technological requirements. As a result, it is possible to ensure the proposed algorithm triggering for each casting earlier than the operator stops the process manually. At the same time, the amount of steel with slag left in ladle does not exceed 3.8 tons comparing to the moment of the slag cut-off made by the operator.

Physical simulation of liquid steel motion in a thin-slab continuous caster mold

Industrial experience of steel casting at the thin-slab continuous caster (CC) revealed processes, having negative effect on the quality of internal structure and surface of CC thin slab. The main problems are as follows: flat streams of liquid steel, flowing through submerged snorkel into restricted dead volume, form circulating flows of extremely high velocity in both liquid core and on the slab surface. This circumstance makes specific requirements to the design and parameters of the submerged snorkel to supply the metal into the thin-slab CC mold. Despite the more than 25 years’ experience of the snorkel form and geometric parameters development, there is no single opinion on its optimal design. Results of physical simulation of the liquid motion processes in a thinslab Caster mold presented (for slab maximum width 1800 mm, thickness – 90 mm) of JSC “Vyksa Steel-works” casting and rolling complex. Description of the physical model facility quoted, as well as description of the experiment methodology and its results. The speed was measured and structure of liquid steel flows revealed in depth and sub-surface layers, as well as in slag-forming mixture at the mold surface. The comparison of two principally different variants of liquid steel feeding into the mold made. The two variants were as follows: by a flat down-directed stream with a narrow central divider (direct-flow submerged snorkel) and by four streams , two of them directed down under an angle relating the vertical axe, and the other (about 20% of total liquid consumption) – directed upward to the bath mirror (the snorkel of “hammer” type). It was determined, that steel casting with technological speed through the direct-flow snorkel was most effective into the slab of 1400 mm width and less, since in this case the sub-surface flows speed did not resulted in the intensive waves formation, constant whirls formation and slag particles dragging into deep layers of the slab. For steel casting into slab of width more than 1400 mm, it is reasonable to use a snorkel of the “hammer” type, which enables to create a favorable stable structure of circulation and decrease the tendency of slag particles dragging in the deep layers of the slab.