Alert Billet Casting (February 2016)

Transcription

1 Alert Billet Casting (February 2016) 1. Effect of water vapor on evaporation and melt crystallization of mold fluxes. J. Baek, J. Cho, S. Kim. Read more 2. A review of mold flux development for the casting of high-al steels. W. Wang, B. Lu, D. Xiao. Read more 3. A comparative study of fluid flow and mass transfer in a trumpet-shaped ladle shroud using large eddy simulation. J. Zhang, J. Li, Y. Yan, Z. Chen, S. Yang, J. Zhao, Z. Jiang. Read more 4. Physical modeling of slag eye in an inert gas-shrouded tundish using dimensional analysis. S. Chatterjee, K. Chattopadhyay. Read more 5. Modeling and measurements of multiphase flow and bubble entrapment in steel continuous casting. K. Jin, B. Thomas, X. Ruan. Read more 6. Numerical simulation of solidification structure of 6.5 wt-%si steel ingot slab. W. Song, J. Zhang, Y. Liu, S. Wang, B. Wang. Read more 7. Optimisation of electromagnetic field and flow field in round billet continuous casting mould with electromagnetic stirring. X. Geng, X. Li, F. B. Liu, H. B. Li, Z. Jiang. Read more 8. Formation and control of macrosegregation for round bloom continuous casting. H. Sun, L. Li. Read more 9. Prediction model for steel/slag interfacial instability in continuous casting process. L. Zhang, Y. Li, Q. Wang, C. Yan. Read more 10. Enhanced diagnostic capabilities by integration of digital models into a condition monitoring system. A. Haschke, A. Müller. Read more 11. Solutions for efficient modernization of continuous casting machines for billets and blooms. H. Thöne, A. Pühringer. Read more 12. Next steps in high-speed billet casting at Ege Celik (Aliaga, Turkey). J. Morton, N. Kapaj, M. Sezar. Read more 13. From the caster to the rolling mill transport, inspection, conditioning, and treatment of cast products. P. Wieser, S. Hahn, F. Wimmer, B. Winkler-Ebner, D. Burzic. Read more 14. Latest bloom caster solutions for automotive steel grades. D. Burzic, R. Simon. Read more 15. Research of argon protection technology in ingot casting. Z. Tongjun. Read more Metallurgical and Materials Transactions B, February 2016 Effect of water vapor on evaporation and melt crystallization of mold fluxes. J. Baek, J. Cho, S. Kim Melt crystallization behavior of both the fluorine-containing and fluorine-free mold fluxes has been investigated using a single hot thermocouple technique (SHTT). By increasing the dew point of atmosphere from 223 K to K (-50 C and 12.5 C), the primary crystalline phase of fluorine-containing mold flux was changed from cuspidine (Ca4Si2O7F2) to Ca2SiO4 with accelerated nucleation rates. Enhancement of fluorine evaporation due to hydroxyl is attributed to the main reason for the abnormal crystallization behavior of the fluorine-containing mold flux under humid atmosphere, which may bring a sticking-type breakout during the commercial continuous casting process. In contrast, the effect of water vapor on crystallization of fluorine-free mold flux was negligible. This implies that the application of fluorine-free mold fluxes can become a countermeasure to prevent the hydrogen-induced breakout during the continuous casting process under wet atmosphere. A review of mold flux development for the casting of high-al steels. W. Wang, B. Lu, D. Xiao

2 Mold flux plays key roles during the continuous casting process of molten steel, which accounts for the quality of final slabs. With the development of advanced high strength steels (AHSS), certain amounts of Al have been added into steels that would introduce severe slag/metal interaction problems during process of continuous casting. The reaction is between Al and SiO2 that is the major component in the mold flux system. Intensive efforts have been conducted to optimize the mold flux and a CaO-Al2O3- based mold flux system has been proposed, which shows the potential to be applied for the casting process of AHSS. The latest developments for this new mold flux system were summarized with the aim to offer technical guidance for the design of new generation mold flux system for the casting of AHSS. A comparative study of fluid flow and mass transfer in a trumpet-shaped ladle shroud using large eddy simulation. J. Zhang, J. Li, Y. Yan, Z. Chen, S. Yang, J. Zhao, Z. Jiang The advantages of trumpet-shaped ladle shrouds (TLS) have been frequently demonstrated over conventional straight-bore ladle shrouds (CLS) with respect to production efficiency and molten steel quality in continuous casting practices. The present study is to shed some lights on why the TLS are better than the CLS design by examining the fluid dynamics and mass transfer using large eddy simulation. The obtained numerical results were validated with particle imaging velocimetry experiments. Flow velocity, deformation, turbulent energy dissipation, and mixing kinetics of tracer were discussed. The results showed that the entering jet of the CLS flowed straight down into the tundish with a relatively high speed (average at to m/s) and turbulent kinetic energy. However, the trumpet section of a TLS intensified velocity differences, strain rates, and vortices, and promoted an increase on turbulence dissipation rate in the interior of the ladle shroud. The average speed of the entering jet to the tundish was decreased to to m/s from the m/s of the inlet speed. The entering jet from the TLS swung, twisted and well mixed with surrounding fluid in the tundish, and dissipated its kinetic energy. Consequently, the turbulence of the whole flow field as well as the mean skin friction coefficient of tundish wall and the velocity of free liquid surface were reduced. A tracer experiment was carried out to study mass transfer and flow mixing behavior, and the results demonstrated that the use of the TLS increased the plug volume and decreased the dead zone, thereby enhancing inclusion flotation. Physical modeling of slag eye in an inert gas-shrouded tundish using dimensional analysis. S. Chatterjee, K. Chattopadhyay The formation of an exposed eye in the gas-stirred metallurgical vessels such as ladle or tundish is a common observation. Although gas stirring results in proper homogenization of melt composition and temperature, the resulting exposed eye leads to higher heat losses, re-oxidation of liquid steel, and formation of inclusions. Most of the previous research related to slag eye were carried out explicitly for ladles. In the present work, a large number of experiments were performed to measure the slag eye area in full scale and one-third scale water models of an inert gas-shrouded tundish under various operating conditions. Based on the polynomial regression of experimental data, and the method of dimensional analysis, correlations for diameter of gas bubbles and plume velocity were developed. Subsequently, these results were used to obtain correlations for the slag eye area, and critical gas flow rate in an inert gas-shrouded tundish in terms of the operational parameters viz., gas flow rate, thickness of the slag and melt baths, along with the physical properties of the liquids viz., kinematic viscosity and density. It was observed that the dimensionless slag eye area can be expressed in terms of dimensionless numbers such as the density ratio, Froude number, and Reynolds number. Modeling and measurements of multiphase flow and bubble entrapment in steel continuous casting. K. Jin, B. Thomas, X. Ruan

3 In steel continuous casting, argon gas is usually injected to prevent clogging, but the bubbles also affect the flow pattern, and may become entrapped to form defects in the final product. To investigate this behavior, plant measurements were conducted, and a computational model was applied to simulate turbulent flow of the molten steel and the transport and capture of argon gas bubbles into the solidifying shell in a continuous slab caster. First, the flow field was solved with an Eulerian k e model of the steel, which was two-way coupled with a Lagrangian model of the large bubbles using a discrete random walk method to simulate their turbulent dispersion. The flow predicted on the top surface agreed well with nailboard measurements and indicated strong cross flow caused by biased flow of Ar gas due to the slide-gate orientation. Then, the trajectories and capture of over two million bubbles (25 lm to 5 mm diameter range) were simulated using two different capture criteria (simple and advanced). Results with the advanced capture criterion agreed well with measurements of the number, locations, and sizes of captured bubbles, especially for larger bubbles. The relative capture fraction of 0.3 pct was close to the measured 0.4 pct for 1 mm bubbles and occurred mainly near the top surface. About 85 pct of smaller bubbles were captured, mostly deeper down in the caster. Due to the biased flow, more bubbles were captured on the inner radius, especially near the nozzle. On the outer radius, more bubbles were captured near to narrow face. The model presented here is an efficient tool to study the capture of bubbles and inclusion particles in solidification processes. Ironmaking & Steelmaking, October 2015 Numerical simulation of solidification structure of 6.5 wt-%si steel ingot slab. W. Song, J. Zhang, Y. Liu, S. Wang, B. Wang The solidification structure of 6.5%Si steel ingot was simulated based on the cellular automaton finite element (CAFE) method and compared with an actual casting. The results showed that both the average grain size and proportion of columnar crystals agreed well with the experimental ones. The parameters suitable for simulating the microstructure of 6.5%Si steel ingot were determined. The influence of superheat and cooling conditions on the solidification structure was also studied in detail. The results show that the proportion of columnar crystals decreases with decreasing superheat, and the average grain size becomes smaller. The microstructure under the condition of slow cooling is finer than of air cooling. Optimisation of electromagnetic field and flow field in round billet continuous casting mould with electromagnetic stirring. X. Geng, X. Li, F. B. Liu, H. B. Li, Z. Jiang A three-dimensional mathematical model of mould electromagnetic stirring (M-EMS) was established. Based on Maxwell s equations, the continuity equation and the momentum equation, the distribution characteristics of electromagnetic and flow fields with M-EMS were numerically simulated by the finite element software ANSYS and the finite volume software CFX. The influence of M-EMS on electromagnetic and flow fields was examined, and the process parameters of M-EMS were optimised by industrial plant trials. By the model verification, there was a good agreement between the calculated results and the measured data. The results indicate that the tangential electromagnetic force increases with the increasing current intensity, and increases at first and then decreases with the increasing current frequency. The tangential velocity increases with the increasing current intensity and current frequency (2 6 Hz). According to statistical results of the centre equiaxial crystal proportion and the macroscopic defects of round billet for different process parameters in industrial plant trials, the optimal process parameters of the M-EMS are as follows: the current intensity is 400 A, and the current frequency is 2 Hz. Formation and control of macrosegregation for round bloom continuous casting. H. Sun, L. Li

4 Based on the developed coupled model of electromagnetism, heat and solute transportation, the macrosegregation formation and effect of secondary cooling water ratio on macrosegregation degree in strand during round bloom continuous casting process have been investigated. The solute segregation degree fluctuates from a positive to a negative value with distance from strand surface in the initial solidified shell region within thickness of 20 mm. A negative segregation region in concave shape and an irregular positive segregation zone are presented in the fixed and loosened side of strand respectively due to the gravity and thermosolutal convection. As the secondary cooling water ratio decreases from 0.25 to 0.15 L kg-1, the solidification ratio at final electromagnetic stirring (F-EMS) centre increases from to 77.83%. For the steel grade of 50Mn casted by round bloom casting within diameter of 0.35 m, the optimal solidification ratio at F-EMS centre is 75.05%, where the radial centre crack and shrinkage cavity at strand cross section are removed. Prediction model for steel/slag interfacial instability in continuous casting process. L. Zhang, Y. Li, Q. Wang, C. Yan In a continuous casting process, mould powder is typically adopted to cover molten steel, which prevents liquid steel from oxidation by air, preserves heat for the top layer of liquid steel, lubricates the initial shell and so on. However, mould powder may deteriorate the quality of the final product if the entrapment of mould powder forms, which is usually caused by the instability of the steel/slag interface. In the current work, a model to predict the critical point of interfacial instability for liquid liquid stratified flow was developed based on the Kelvin Helmholtz instability. To prove the validity of the prediction model, a water model experiment was carried out in a rectangular container. In this experiment, oil and water were used to simulate slag and molten steel respectively. The results of the water model prove that the prediction model is correct. Applying the prediction model to a steel slag system, the critical velocity of molten steel for mould powder entrapment is m s-1. When considering the most severe chemical reaction, the critical velocity decreases to 0.29 m s-1. The lowest critical velocity of molten steel is m s-1 when the viscosity of the slag and steel/slag interfacial tension is extremely low. METEC & 2 nd ESTAD, June 2015 Enhanced diagnostic capabilities by integration of digital models into a condition monitoring system. A. Haschke, A. Müller Offline simulation is often used by plant builders for the design of metallurgical plants and to ensure that performance expectations are met. Whereas some simulation models cover operations across the complete plant (e.g., throughput calculations), smaller simulation models focus on individual topics such as closed-loop control, vibration behavior and the functionality of single components. The concept of using offline simulation in an online mode for plant operation is not new. Nonetheless, the necessary steps for its application are complicated and timeintensive. These require extensive technological know-how, the buildup of digital models (using, for example, Matlab or Simulink) and the compilation of software that is ready to be used in the automation platform or in a condition monitoring system. As a plant builder with IT competency, Primetals Technologies has mastered this challenge and has defined a concept known as Control Builder. As described in this paper, it allows the reuse of offline digital models or simulations in the condition monitoring system (CMS). These digital models support condition-based maintenance activities by providing deep insight into parameters that cannot be measured directly (soft sensor methods), or by comparing complex operation states with design parameters. An example is the monitoring of hydraulic closed-loop control and the associated cylinder to determine the degenerative status of valves or if internal cylinder leaks are evident. Key performance indicators (KPIs) that are the output of such simulations can be further monitored with the CMS, and they also serve as an additional indicator for root causes.

5 Solutions for efficient modernization of continuous casting machines for billets and blooms. H. Thöne, A. Pühringer For fast access to new or changing markets that cannot be served by a producer s installed continuous casting machine (CCM), modification of an existing caster is the most cost-efficient way to meet demands. During the past decades, Primetals Technologies has successfully executed numerous revamping projects for billet, bloom and beam-blank casters. Modernization can involve the installation of advanced technological packages such as the DynaFlex hydraulic oscillator, DiaMold mold tube, or LevCon mold-level control to increase casting speed and therefore throughput with simultaneous improvements in casting reliability and product quality. Modernization may also be a comprehensive caster transformation into a high-end bloom or beam-blank CCM within the footprint of the existing machine. Next steps in high-speed billet casting at Ege Celik (Aliaga, Turkey). J. Morton, N. Kapaj, M. Sezar After successful trials were executed at Ege Celik (Aliaga, Turkey) where a casting speed of 6.2 m/min on a 130x130 mm section was achieved on machine CCM4 more trials followed that stabilized the process in terms of steelmaking requirements and the casting machine set-up. Unique measurement instrumentation was utilized to collect a vast array of data, including temperatures in the mold, actual negative strip time measured below the mold, and laser measurement of the actual casting speed. An evaluation of the resulting data helped define the best machine characteristics for the high-speed casting of long products and led to the development of the latest Primetals Technologies high-speed billet mold. This paper describes the latest results obtained from the high-speed trials at Ege Celik and highlights some of the new features of the next generation of high-speed/high-quality molds. From the caster to the rolling mill transport, inspection, conditioning, and treatment of cast products. P. Wieser, S. Hahn, F. Wimmer, B. Winkler-Ebner, D. Burzic The handling, storage, and treatment of slabs, blooms, billets, and beam blanks after casting as well as their preparation for the rolling process is a challenging procedure in metallurgical plants. The hot strand leaving the casting machine typically with a surface temperatures ranging from 800 Celsius to 1,100 Celsius must be cut, marked, inspected, and if necessary conditioned. In the case of hot charging to the rolling mill, heat loss from the cast product must be minimized to reduce energy consumption in the reheating furnace. For several steel grades, special ambient conditions (for example, heat insulation) are required during the cooling process. In order to manage all of these requirements, this process must be thoroughly planned and controlled. The first step immediately after casting is product classification using a quality-prediction model based on the casting parameters and conditions (for example, Quality Expert). One benefit of this powerful system is that it provides assistance with the decision about whether conditioning (grinding, scarfing, or milling) is necessary or not, with the goal of optimizing yield. Automatic surface inspection of the hot products can further support conditioning decisions. The logistically complex process of handling and transporting cast products is ideally simulated using appropriate tools that help prevent collisions and enable the calculation of the cooling rate during the handling period. Multistrand casters in particular, even those with eight strands, require extensive discharge cycletime studies. Slab yards, cooling beds, quenching boxes, and slow-cooling boxes, all of which consume a lot of space in steel mills, must be designed using thermal calculations. When quenching or slow cooling are required, additional calculations regarding precipitation and continuous cooling transformations must be considered. These and other logistical, thermal, and quality-related aspects in the casting-rolling areas of steel mills are discussed in this paper.

6 Latest bloom caster solutions for automotive steel grades. D. Burzic, R. Simon As the economic environment for steelmakers gets more competitive, demands placed on quality, flexibility and more efficient casting operations are continually increasing. This calls for flexible and well-designed production plants with reduced maintenance and longer equipment lifetime. This paper provides an overview of the latest solutions for bloom continuous casters using the example of a heavysection bow-type caster equipped with latest technological packages. Bars and wires that are rolled out of the blooms serve as a crucial material for engine and gearbox parts. The caster is equipped with the latest mold-level control and an instrumented mold featuring breakout prediction. In combination with air-mist spray cooling and interior-cooled rollers in the strand guidance system, DynaGap Soft Reduction and other technology packages ensure uniformly high-quality blooms. Still hot, the blooms are then fed for direct use in the bar line. This saves energy during reheating and improves operating safety because there is no need to handle the blooms using cranes. For special grades, an inline bloom quenching facility is provided. Research of argon protection technology in ingot casting. Z. Tongjun With the continuous improvement of product quality and function, the mold steel quality control is becoming more and more strict, in which ingot casting is the key, and argon protection is the premise of ensuring casting quality. Only qualified argon protection can ensure casting process quality, and then improve product quality constantly. By the way of introducing the development of argon protection in ingot casting and the production process of enclosed argon protection in the 40-tons line, to discuss the related factors that are affecting oxygen flow in the argon protection cover. With the oxygen content detected by on-line oxygen monitor, ensure the optimized way and condition of improving the argon protection effects, in order to guide the operation, prevent the liquid steel from secondary oxidation, and improve the ingots quality.