Continuous Casting Tundish Research Articles

Continuous Casting Tundish Dead Volume Study by Physical Modeling and Computational Investigation

Flow efficiency in a two‐strand continuous casting tundish is studied by analyzing the residential time distribution (RTD) curves in a small‐scale tundish water model using a conductive NaCl solution tracer. The velocity fields in the tundish water model are measured by particle image velocimetry, which is used to validate the results of the mathematical model in the article. It is found that the tracer concentration has a significant impact on the predicted dead volume fraction in the RTD analysis. Validated mathematical modeling of the computational fluid dynamics (CFD) technology is performed to explore the root cause of the defective results in the RTD analysis. It is found that the flow inside the tundish is sensitive to density variations caused by the injected tracer. A denser tracer will stay lower in the tundish by gravity and flow out of the tundish more quickly. A proper tracer concentration in the water model experiments is discussed to visualize the dead volume and improve tundish furniture design efficiently for future work, a new method using CFD modeling is proposed in this article, which can directly demonstrate the dead volume's location.

Continuous casting tundish quality study by mathematical & physical simulations, economics with plant result justifications

A combination of physical modeling, computational fluid dynamics modeling, and economics with plant trial studies was performed for quality improvement of Special Bar Quality (SBQ) and Oil Country Tubular Goods (OCTG) grade tundish steels. The present study consists of operating parameters like inert gas shrouding, non-isothermal conditions, and flow control devices (FCD) used on the billet product and slab quality. This work uses mathematical modeling using the fluid volume and discrete phase method (DPM) and the standard k-ε turbulence model validated with one-third scale physical water model experiments. A strong correlation between the physical model and computational simulation was found with rejection ratio and inclusion counts. Data about customer demands correlated with operating parameters for proper plant insights with an economic study to predict the cost-related issue. With the incorporation of FCD, the weight of the tundish skull was reduced by 6–10 M USD/year with a simulation studies expenditure of around 200 K. FCD also reduced the customer complaint index (CCI).

Structural optimisation of three-strand asymmetric tundish for super large round bloom continuous casting

Structural optimisation of three-strand asymmetric tundish for super large round bloom continuous casting

Analysis model of internal residence time distribution for fluid flow in a multi-strand continuous casting tundish

Analysis model of internal residence time distribution for fluid flow in a multi-strand continuous casting tundish

Hydraulic and numerical simulation of flow field characteristics in induction heating continuous casting tundish

The flow state of the melt inside the continuous casting tundish plays a decisive role in the realisation of metallurgical function. With the application of tundish induction heating, much attention has been paid to the influence of the internal non-isothermal state caused by supplementary heating on the flow field. In this study, hydraulic and numerical simulations combined with particle image velocimetry are used to quantitatively study the internal flow field under channel-type tundish with induction heating. Simultaneously, the effect of induction heating on the flow state of the flow field is investigated. The results show that the internal heating of the tundish channel not only enhances the range and intensity of turbulence distribution, but also significantly improves the flow state of the flow field. By comparing the velocity distribution of the tundish liquid surface measured by hydraulic simulation, it is found that the average velocity under non-isothermal conditions is 0.066 m/s, which is 47% higher than that under isothermal conditions. Finally, the standard deviation of peak time and actual residence time for the residence time distribution curve of tundish changes from 278 and 217 s to 202 and 148 s, respectively, before and after supplementing channel heating, which shows that it can indeed improve the consistency of each flow.

Deeper Flow Behavior Explanation of Temperature Effects on the Fluid Dynamic inside a Tundish

The continuous casting tundish is non-isothermal due to heat losses and temperature variation from the inlet stream, which generate relevant convection forces. This condition is commonly avoided through qualitative fluid dynamic analysis only. This work searches to establish the conditions for which non-isothermal simulations are mandatory or for which isothermal simulations are enough to accurately describe the fluid dynamics inside the tundish by quantifying the buoyant and inertial forces. The mathematical model, simulated by CFD software, considers the Navier-Stokes equations, the realizable k-ε model for solving the turbulence, and the Lagrangian discrete phase to track the inclusion trajectories. The results show that temperature does not significantly impact the volume fraction percentages or the mean residence time results; nevertheless, bigger velocity magnitudes under non-isothermal conditions than in isothermal conditions and noticeable changes in the fluid dynamics between isothermal and non-isothermal cases in all the zones where buoyancy forces dominate over inertial forces were observed. Because of the results, it is concluded that isothermal simulations can accurately describe the flow behavior in tundishes when the flow control devices control the fluid dynamics, but simulations without control devices or with a weak fluid dynamic dependence on the control devices require non-isothermal simulations.

Simulation of the effect of continuous casting tundish filter on removing inclusions in steel

The control of inclusions in clean steel production is one of the key processes and a key factor determining the quality of high-end steel materials. The inhomogeneous hydrodynamic equations have been numerically solved to obtain a transient and multiphase field inside the caster tundish with filter to predict the inclusion movement track and percentage of inclusion removal during continuous casting process. The simulation result is validated with the samples taken during casting continuous process in X steelworks. The method of bulk-sample-electrolysis is taken to analyze the percentage of inclusion removal of the samples. The results imply: the inclusions through the filter are influenced on velocity and separated from liquid steel with high turbulence. Thus the inclusions’ residence time in tundish is prolonged, which causes the probability of inclusion removal increasing. The fluctuations on percentage of inclusion removal are found when the diameter of inclusions is less than 80μm. However, the fluctuation is not so severely for the inclusions of more than 100μm. The percentage of inclusion in tundish as 100 tones remaining in ladle is larger than that as 200 tones remaining in ladle. The percentage of inclusion removal is proportional to time. The filter can reduce the irregular inclusions to improve the quality of product.

A hybrid approach using multiple linear regression and random forest regression to predict molten steel temperature in a continuous casting tundish

ABSTRACT The temperature control of molten steel is essential to ensure operational stability in a steelmaking plant. The calculation of thermal losses in the steelmaking plant’s operations depends on highly dynamic variables, which motivates the construction of predictive models for the steel temperature. This paper proposed a hybrid ensemble method using multiple linear and random forest regression to predict the end molten steel temperature at the secondary refining required to achieve a target tundish temperature. Combining these two methods makes it possible to account for the linear and non-linear relationships in the data. The implemented models were trained on industrial data, and their performance was assessed using root mean squared error (RMSE) and a custom accuracy metric. The results showed that the proposed hybrid method achieves up to 5% better accuracy compared to linear regression or random forest regression methods alone, thus can enhance molten steel prediction in steelmaking plants.

Multiphase flow inside a four-strand continuous casting tundish using three types of ladle shrouds

Multiphase flow inside a four-strand continuous casting tundish using three types of ladle shrouds

Design Improvement of Four-Strand Continuous-Casting Tundish Using Physical and Numerical Simulation.

The flow pattern is vital for the metallurgical performance of continuous casting tundishes. The purpose of this study was to design and optimize the flow characteristics inside a four-strand tundish. Numerical simulations and water model experiments were validated and utilized to investigate the flow behavior. The effect of different flow rates in the original tundish was evaluated; two modified retaining walls and a new ladle shroud were designed for optimization. The molten steel inside the original tundish tends to be more active as the flow rate increases from 3.8 L/min to 6.2 L/min, which results in a reduction in dead volume from 36.47% to 17.59% and better consistency between different outlets. The dead volume and outlet consistency inside the tundish are improved significantly when the modified walls are applied. The proper design of the diversion hole further enhances the plug volume from 6.39% to 13.44% of the tundish by forming an upstream circular flow in the casting zone. In addition, the new trumpet ladle shroud demonstrates an advantage in increasing the response time from 152.5 s to 167.5 s and alleviating the turbulence in the pouring zone, which is beneficial for clean steel production.

Channel-Type Induction Heating Tundish Technology for Continuous Casting: A Review.

With the increasing demand for special steel, the quality of steel has become critical during the continuous casting tundish process. In recent years, tundish heating technology has played a key role in low superheat casting. Toward this, researchers have reported on the metallurgical effects of induction heating tundish (IHT). From 1984 to date, the channel-type IHT has been investigated in the production of continuous casting of special steel. In this article, the principle of this channel-type IHT technology and equipment composition were illustrated. A brief summary and comments were undertaken on the channel-type IHT, including physical modeling and numerical modeling. The application development trend of tundish induction heating equipment is summarized combined with industrial application data, which provide a reference for a better understanding of the induction heating process of tundish.

Laboratory Evaluation of Tundish Covering Powders and Rice Hull Ash on Cleanliness for a SAE 1055 Modified Steel

The continuous casting tundish is the last metallurgical reactor where molten metal flows before solidifying in the continuous casting mold. A tundish covering powder can be used for improving steel cleanliness; in this case it is named ‘active tundish slag’. The objective of this work is to evaluate, in laboratory, the effect of three kinds of tundish covering powders on cleanliness for a SAE 1055 modified steel - a Ca-aluminate, a Ca-Mg-aluminate, and an Al-silicate powder, analysing their interaction with rice hull ash. The forementioned materials were molten on liquid steel, representing different kinds of tundish covering powders which are used in the steel industry: a Ca-Mg-aluminate, an Al-silicate, and a Ca-aluminate. Experiments were performed with and without a top layer of rice hull ash, simulating industrial conditions. Distribution, density, and mean diameter of inclusions were measured through automated inclusion analyses. Through computational thermodynamics it was possible to evaluate deviation from saturation (considering Al2O3 and MgO from refractory) and slag viscosity. It can be stated that the Ca-aluminate tundish covering powder gives better results regarding cleanliness for the SAE 1055 modified steel under laboratory conditions.

Numerical investigation and physical modeling for optimisation hydrodynamic processes in continuous casting tundish

The article presents the results of comprehensive studies of hydrodynamic processes and features of single-strand tundish ladles, which can be used for continuous or semicontinuous casting of steel at small metallurgical plants. The results of physical and mathematical modelling of the movement of the melt flows in the tundish using various designs of metal receivers are shown in this article. In addition to this, the article shows how the presence of a stagnant zone between the metal receiver and the right narrow wall of the Tundish increases in time of metal flow into the dispenser zone by an average of 35–60%. It has been established that the position and height of the walls of the metal receiver relative to the axis of the incident jet are very significant for providing a rational picture of the movement of convective flows. When the height of the wall of the metal receiver (from the side of the dispenser) is reduced by 40–60 mm, the zones of increased turbulence may appear in the liquid bath of the tundish in the areas between the metal receiver and the dispenser. The results of evaluating the efficiency of floating non-metallic inclusions in the tundish volume and optimizing the hydrodynamic pattern flows in the central part of the tundish to increase the refining effect by installing a special recess.

Physical properties and corrosion resistance of magnesia-calcium hexaaluminate refractories to molten steel

The continuous casting tundish serves as the final vessel for molten steel in the smelting process. Resistance to steel corrosion and penetration is critical for clean steel smelting and the durability of working linings. In this study, calcium hexaaluminate (CA6) was selected to gradually replace the commonly used MgO refractory. We analyzed the phase composition, cold modulus of fracture, cold crushing strength, bulk density, porosity, and resistance to molten steel corrosion and penetration of MgO–CA6 refractories. It was observed that the mechanical properties of the material were reduced by the addition of CA6; however, a certain percentage of CA6 and MgO formed a small amount of MgO·Al2O3 at high temperatures to retain its high performance. The materials are less likely to react with [Mn], [Si] and other alloying elements in steel after the addition of CA6 and it exhibits excellent resistance to steel corrosion, which is important for clean steel production and the durability of working linings.

Structure optimization of continuous casting tundish with channel-type induction heating using mathematical modeling

Abstract There are few studies on the shape and structure of the channel-type induction heating tundish on multi-physics field. Computational fluid dynamics has been used to study the influence of the structure of the tundish on the macroscopic transport behavior of the tundish with channel induction heating. The results show that increasing the depth of the molten pool is conducive to dynamic behavior of multiphase, the deeper the molten pool, the larger the active area, the longer residence time, the more inclusions removal and the higher ratio of plug to dead volume. Meanwhile, the larger the channel diameter, the more inclusions removal in the receiving chamber and channel. The channel induction heating has enough ability to increase the superheat and temperature compensate for the heat loss caused by the excessive residence time of the molten steel in the tundish. The change in the channel structure is crucial to the macroscopic transport behavior of the fluid. The change in channel diameter has the greatest effect on the multi-physics field in the molten pool.

Residence Time Distribution (RTD) Applications in Continuous Casting Tundish: A Review and New Perspectives

The continuous casting tundish is a very important metallurgical reactor in continuous casting production. The flow characteristics of tundishes are usually evaluated by residence time distribution (RTD) curves. At present, the analysis model of RTD curves still has limitations. In this study, we reviewed RTD curve analysis models of the single flow and multi-flow tundish. We compared the mixing model and modified combination model for RTD curves of single flow tundish. At the same time, multi-strand tundish flow characteristics analysis models for RTD curves were analyzed. Based on the RTD curves obtained from a tundish water experiment, the applicability of various models is discussed, providing a reference for the selection of RTD analysis models. Finally, we proposed a flow characteristics analysis of multi-strand tundish based on a cumulative time distribution curve (F-curve). The F-curve and intensity curve can be used to analyze and compare the flow characteristics of multi-strand tundishes. The modified dead zone calculation method is also more reasonable. This method provides a new perspective for the study of multi-strand tundishes or other reactor flow characteristics analysis models.

Effect of Flow Field Optimization of an Asymmetric Multi-Strand Tundish on the Quality Consistency of Cracking Con-Rod Steel.

Cracking con-rod is an advanced high-precision connecting structure based on brittle expansion, breaking and reconnection of steel, to solve the problem of assembly circle missing. High carbon micro-alloyed steel C70S6, as a dominant material for the production of cracking con-rod, has extremely strict requirements on non-metallic inclusions in steel and microstructure stability. Continuous casting tundish plays an important role in removing large-sized inclusions and stabilizing casting quality. Aiming at the inconsistent casting quality of C70S6 steel produced by a three-strand asymmetric tundish and the frequent occurrence of slag entrapment problems in Xining Special Steel, the tundish structure was optimized by means of physical modelling combined with numerical simulation, and the quality of the bloom castings and subsequent hot-rolled products before and after optimization were compared based on volume production. The results show that a new flow control design to the tundish can effectively improve the consistency of its metallurgical effect for each of the three strands and the following overall product quality, in which the flow field and temperature field in the tundish are more uniform. This is due to the adoption of a vortex inhibitor and an optimized wall structure according to the measured RTD curve, ink trajectory and numerical simulation on the 3-D streamline contours and temperature distribution in the tundish. The peak concentration of outlet 1 is decreased from 6.5 before optimization to less than 2.0 after optimization, which means the elimination or alleviation of the local short-circuit flow. The maximum temperature difference of C70S6 molten steel measured at the outlets of the tundish three strands is decreased from 2–5 °C to 1–3 °C, which is in good agreement with the numerical simulation results. The difference in columnar crystal ratio of the corresponding bloom castings is decreased from 2.27–3.17% to 1.26–1.85%, and the consistency of central carbon segregation index is also significantly improved. In addition, the difference in oxygen content among the three strand blooms is decreased from 1.7–3.5 ppm to 0.8–1.9 ppm. As a result, the overall mechanical properties and microstructure stability of the hot-rolled products are improved statistically, in which the hardness fluctuation is decreased from 84 HBW to 60 HBW, the inclusion grade of types B + C + D + Ds is reduced to 1.105, and the occurrence rate of Ds dropped to 0.118%. Accordingly, the failure rate of the cracking con-rod is controlled stably within 4‰, and the fracture is generally smoother than that before tundish optimization. In summary, the flow field optimization to a multi-strand asymmetric tundish has a clear effect on improving the overall quality of its bloom castings and rolled products, which should be paid more attention industrially. Meanwhile, the present study provides a reliable theoretical and experimental reference for the improvement of metallurgical effects of an asymmetric-typed tundish commonly used in special steel production.

Numerical Investigation on Motion and Removal of Inclusions in Continuous Casting Tundish with Multiorifice Filter

A fluid–solid‐coupled numerical model is established on the motion and removal of inclusions in the continuous casting tundish with a multichannel filter. The flow field, heat transfer, and motion of inclusions in continuous casting tundish are simulated. The erosion of the lower part of the weir and filter is the most serious; at the casting speed of 2.2 m min−1, the maximum displacements in the upstream and downstream directions are 4.25 and −3.81 mm, respectively. The casting speed effect on the flow pattern and removal of inclusions is investigated. The weir and filter erosion increases with increased casting speed, the total removal efficiency is raised, and the dead zone fraction is reduced. After the casting speed exceeds 2.2 m min−1, the total removal efficiency of inclusions starts to decline. When the casting speed is raised from 1.4 to 3.0 m min−1, the share of inclusions removed by the filter drops from 8.2 to 2.5%, which is nearly 70%.

Evolution of Nonmetallic Inclusion during Steelmaking Process of Cold Heading Steel SWRCH35K

In order to analyze the evolution of the inclusions in the cold heading steel SWRCH35K during the steelmaking process, a systematic sampling of the steelmaking processes in a steel plant was carried out. Both SEM-EDS and the image processing software Image-Pro-Plus6.0 were employed to analyze the chemical composition, morphology, quantity and size of non-metal inclusions in the steel samples. The results show that from BOF tapping to continuous casting tundish, the composition of inclusions in SWRCH35K steel changes from Al2O3 → MgO·Al2O3 → CaO-MgO-Al2O3-CaS, and the typical morphology of the inclusions in the steel gradually changes from irregular blocks and clusters to spherical. The number of inclusions in the BOF argon blowing station is the largest, 213#/mm2, while the number of inclusions at the end of LF refining is the least, about 12#/mm2, and there are basically no inclusions above 5 μm. In addition, LF calcium treatment will adversely affect the size and quantity control of inclusions in steel. In order to effectively reduce the large-size calcium-containing spherical oxide inclusions in cold heading steel, it is necessary to find a technical method that can replace LF calcium treatment to solve the problem of molten steel continuous casting.

Effect of Tundish Flux on Compositional Changes in Non-metallic Inclusions in Stainless Steel Melts

The effect of the tundish flux on the evolution of non-metallic inclusions in Si-killed 304 (18%Cr-8%Ni) stainless steel has been investigated at 1773 K. The interfacial reaction between molten steel and the CaO–Al2O3–MgO flux causes the aluminum pick-up from the liquid slag into the steel melt, resulting in a decrease in the oxygen content in the steel. The aluminum originating from the slag modifies the pre-existing Mn-silicate inclusions into alumina-rich inclusions in the steel. Because the oxygen content in the steel decreases as it reacts with the CaO–Al2O3–MgO flux, the degree of supersaturation for alumina formation is too low to precipitate new-born alumina particles in the steel. By analyzing the population density function (PDF) results for inclusions, it can be observed that the growth of spinel-type inclusions occurs by the diffusion of aluminum and magnesium in the steel. On the other hand, the composition of the steel, as well as the evolution of inclusions, is negligibly changed when the CaO–SiO2–MgO flux is added to the molten steel. Furthermore, the computational simulation for predicting the evolution of inclusions in molten steel during a continuous casting tundish process was carried out based on a refractory-slag-metal-inclusion (ReSMI) multiphase reaction model.