High-speed Casting Research Articles

Corner structure optimisation design of billet mould tube for Q235 with high casting speed

Reasonable corner design of the mould is conducive to the uniform heat transfer of the billet, especially for the crack-sensitive steel such as Q235 under high casting speed. Based on the Ansys finite element analysis platform, three kinds of mould corner configurations were designed in this study, and the temperature and stress distribution of the billet and mould corresponding to different mould were compared and analysed. The results show that the cooling uniformity of the C-type mould (petal-type) was better than that of other corner configurations, the maximum temperature at the mould corner was reduced by 43.66 °C, the minimum temperature at the billet corner was increased by 109.73 °C, and the maximum Von-Mises equivalent stress at the corner of the billet was reduced by 28.09 MPa. Therefore, the C-type mould can further improve the quality of the billet and is conducive to the improvement of production efficiency.

Large eddy simulation of various EMBr effects on the fluid flow, heat transfer and solidification process in an ultra-high speed thin slab casting mould with multi-port SEN

Effective control of intense turbulence is a crucial challenge for achieving steady production with ultra-high casting speed in thin slab continuous casting. In thin slab casting process, specially designed multi-port submerged entry nozzle (SEN) with four outlets is utilised to ensure an ample supply of molten steel, necessitating the selection and optimisation of suitable Electromagnetic Braking (EMBr) equipment for steel jet control. This study established a comprehensive three-dimensional model of a funnel-type mould, employing a combined experimental-numerical approach to validate and investigate the flow, heat transfer, solidification and electromagnetic behaviour in the mould. The steel grade studied in the simulation is Q235B, and its physical properties were calculated based on its composition with a temperature range of 1450–1826 K. To analyse the influence of high casting speed on the flow and solidification behaviour in the mould, three casting speeds were selected for the study, which were 6, 7 and 8 m/min. The results indicate that the novel Bowl EMBr significantly suppressed the penetration of steel jet and thus enhanced the thickness and uniformity of the solidified shell. As the casting speed increases from 6 to 8 m/min, the solidified shell thickness at the mould exit decreases from 7.91 to 5.94 mm, with the stagnant growth region approaching the mould exit. This highlights the requirement to correspondingly increase EMBr strength under ultra-high casting speed condition to avoid remelting of the shell and the risk of molten steel leakage. The coupled mathematical model established in this study provides guidance for optimising EMBr structures and casting speed under special multi-port SEN conditions, offering recommendations for the rational control of flow, heat transfer and solidification process in the mould.

Analysis of carbon shell of billets with high casting speed

Abstract The increasing casting speed of billets is beneficial for improving single-machine production efficiency, reducing refractory material consumption, and achieving energy conservation and consumption reduction. However, as the casting speed increases, the probability of steel leakage also increases. An analysis of the thickness of the billet shell under high casting speed allows us to analyze the reasons for steel leakage and propose targeted solutions. This article analyzes the steel leakage billet shell of grade 40 steel and concludes that the thickness of the billet shell is between 8-20 mm at the upper of the mold, and only 5-10 mm at the lower of the mold. At the beginning of its formation, the shell of the cast billet is not uniform, with a maximum difference of up to 8 mm. As the casting progresses, the shell of the billet actually becomes thinner. At a distance of 100-200 mm from the mold, the maximum air gap between the billet shell and the copper tube reaches about 5.5 mm. The air gap reduces the uniformity of heat transfer, resulting in an uneven billet shell. After the liquid steel is injected into the shell, it will cause remelting of the solidification shell, resulting in thinning of the casting shell and causing steel leakage at the outlet of the mold.

Graphics‐Processing‐Unit‐Accelerated 3D Online Heat Transfer and Solidification Model for Continuously Cast Slab

A graphics‐processing‐unit (GPU)‐accelerated 3D heat‐transfer and solidification model is proposed to predict the temperature field and solidification field for continuously cast slab. The fully 3D model is developed based on the finite difference method and implemented on the compute unified device architecture (CUDA)/C++ platform. The model is verified by solving the 1D Stefan problem and validated by surface temperature measurements. The model is proven to be 18.91 times faster for the coarsest mesh of 35 million nodes and 22.92 times faster for the finest mesh of 50 million nodes than a central‐processing‐unit (CPU)‐based parallel version with 28 threads. The corresponding relative calculational times are 0.19 and 0.32, which indicate that the model has great computation efficiency. The model is proven to be robust enough for the dynamic continuous casting (CC) process via a test of dynamic casting speed. Further analysis of the nonuniform heat transfer and solidification shows that the model is able to predict the nonuniform heat transfer efficiently. In the studied cases, a higher casting speed will lead to a remarkable enhancement of the unevenness of heat transfer and solidification in general.

Study on electromagnetic stirring–braking structure layout design and its synergistic mechanism in electromagnetic metallurgy

During the continuous casting process, electromagnetic stirring (EMS) can control the flow pattern of the molten steel on the meniscus in the slab mould, while it is difficult to effectively control the entire molten steel. To this end, a novel composite magnetic field structure of EMS and electromagnetic braking (EMBr) is proposed, and the EMS–EMBr synergistic mechanism is analysed. The flow field of molten steel without a magnetic field is analysed. The magnetic field regulation strategy required to control the molten steel is clarified. The coil core structure layout of existing EMS is analysed. The action mechanism of EMS is studied through simulation, revealing the poor control effect of EMS on the molten steel under high casting speeds. Thus, a novel EMS–EMBr structure layout is proposed to enable the braking magnetic field to cover the key areas within the slab mould, ensuring that the main flow is effectively suppressed. On this basis, the effects of EMS–EMBr synergy and different process parameters on the flow pattern of molten steel are studied. The results indicate that the EMS–EMBr composite magnetic field structure proposed can more effectively control the molten steel, providing technical support for the development of electromagnetic metallurgical equipment.

Investigation of segregation behaviour in 2060 aluminium-lithium alloy during twin-roll casting

The utilization of the twin-roll casting process to fabricate aluminium (Al) - lithium (Li) alloys is regarded as an efficient and energy-saving strategy to meet the aerospace industry’s demands for reducing processing steps, cost-effectiveness, and corrosion resistance. This study successfully achieved the preparation of Al-Li alloy twin-roll cast slabs across various processing ranges to investigate the corrosion resistance differences in different processing conditions. Remarkable macro segregation phenomena were observed in the fabrication under high twin-roll casting speeds for TRC-3. By combining temperature and flow rate calculations, we comprehensively analysed the results of this segregation mechanism. The segregation is inherited into the final T6 state microstructure, exacerbating the precipitation of the T1 phases and deteriorating the ultimate corrosion resistance performance. We delved into a profound discussion regarding the mechanistic impact of segregation on corrosion behaviour. Ultimately, this study postulates a process parameter range for twin-roll casting of Al-Li alloys, aimed at attaining minimal segregation and maximal corrosion resistance.

Influence of Submerged Entry Nozzles on Fluid Flow, Slag Entrainment, and Solidification in Slab Continuous Casting

In this paper, the fluid flow, slag entrainment and solidification process in a slab mold were studied using physical modeling and numerical simulation. The effect of two types of submerged entry nozzles (SENs) was also studied. The results showed that the surface velocity for type A SEN was larger than that using type B SEN. For type A SEN, the maximum surface velocity was 0.63 m/s and 0.56 m/s, and it was 0.20 m/s and 0.18 m/s for type B SEN. The larger shear effect on the top surface made the slag at narrow face impacted to the vicinity of 1/4 wide face, while the slag layer at the top surface was relatively stable for type B SEN. Increasing the immersion depth of SEN decreased the surface velocity and slag entrainment. For type A SEN, the thickness of the solidified shell at the narrow face of the mold outlet was thin (12.3 mm) and there was a risk of breakout. For type B SEN, the liquid steel with high temperature would flow to the meniscus and it was beneficial to the melting of the mold flux. The thickness of the solidified shell at the narrow face of the mold outlet was increased. Furthermore, the surface velocity was also increased and it was not recommended for high casting speed.

Reduction of Surface Cracking for Al-4.6%Mg Strips Cast Surface Using an Unequal-Diameter Twin-Roll Caster by Back-Dam Plate with Lip

Cracks occur on the surface of Al-Mg strips cast using a high-speed twin-roll caster. Surface cracking of the as-cast strip decreases with decreasing roll load. However, the difficulty of roll casting increases as the roll load is decreased because the strip becomes brittle and is easily broken because the strip is not completely solidified. In the present study, an unequal-diameter twin-roll caster, which is capable of high-speed casting, was used with a lip attached to a back-dam plate in an attempt to decrease surface cracking without deceasing the roll load. The thickness of the solidified layer was found to decrease as the length of the solidified region decreased. The thickness of the solidified layer at the center of the width direction of a strip on the lower roll decreased by shortening the solidification length by a lip attached to a back dam-plate. The solidified layer at the edges was thicker than that inside the cast strip. The thickness of semisolid metal inside the cast strip increased more than that at the edges of the roll bite. The roll load at the width of the lip decreased. The effect of the lip length on surface cracks was investigated.

Optimization of Process Parameters for 40Cr Steel Continuous Casting Round Bloom with Pulsed Magneto‐Oscillation Treatment

To reduce the solidification structure defects and the macrosegregation of the Φ300 mm continuous casting round bloom, the pulsed magneto‐oscillation (PMO) treatment is added at the secondary cooling zone. A numerical model for calculating the pulsed electromagnetic field, flow field, and temperature field in continuous casting is established, and the coupling simulations of multiphysical fields under different casting parameters and PMO parameters are performed. Their influence on solidification process and the appropriate parameters are discussed. The industrial experiments conducted under the recommended parameters yield good results. Industrial experiments show that when the peak current is increased from 1350 to 1550 KIA and the casting speed is increased from 0.75 to 0.90 m min−1, PMO can increase the equiaxed grain zone and reduce the carbon macrosegregation of the bloom. Moreover, at high casting speed, PMO treatment can significantly promote columnar‐to‐equiaxed transition and increase the width of mixed grain zone.

Numerical Simulation of Flow and Argon Bubble Distribution in a Continuous Casting Slab Mold under Different Argon Injection Modes

A three-dimensional model is established to investigate the effect of argon injection mode, argon flow rate and casting speed on the gas–liquid two-phase flow behavior inside a slab continuous casting mold. The Eulerian–Eulerian model is employed to simulate the gas–liquid flow, and the population balance model is applied to describe the bubble breakage and coalescence process in the mold. The numerical simulation results of the bubble size distribution are verified using the water model experiment. The results show that the flow field and bubble distribution are similar between the argon injection at the upper submerged entry nozzle (SEN) and tundish upper nozzle (TUN), while the number density is larger for the argon injection of TUN. The coalescence rate of bubbles and the bubble size inside the mold increase with increasing argon flow rate. When the argon flow rate exceeds 4 L/min, the flow pattern of liquid steel changes from double-roll flow to complex flow, with aggravation of the level fluctuation of the top surface near the SEN. When the casting speed increases, the bubble breakup rate increases and results in a decrease in the size of bubbles inside the mold. At a high casting speed, the flow pattern tends to form double-roll flow, and the liquid level at the narrow face of the top surface increases.

Physical modeling and numerical investigation of fluid flow and solidification behavior in a slab caster mold using hexa‐furcated nozzle

AbstractSlag entrapment from metal–slag interface during continuous casting operations has been a major area of concern for steelmakers globally. The presence of inactive regions in the upper region of the mold poses another challenge. Proper flow behavior of the molten metal coming out of the nozzle in the mold is required to overcome these challenges. Nozzle design greatly affects the flow pattern of the molten steel inside the mold. The present investigation is an attempt to study the flow and solidification behavior in a slab caster mold with the use of a novel‐designed hexa‐furcated nozzle using numerical investigation results. The casting speed and submerged entry nozzle (SEN) depth are varied to study the effect of these parameters on minimizing the inactive zones in the mold and the steel/slag interface fluctuations. The results show that the interface fluctuation increases at higher casting speed and lower SEN depth. The residence time distribution (RTD) analysis was also performed for different cases to investigate the flow behavior. The validation of the fluid flow and RTD curve inside the computational domain is carried out with the use of physical modeling.

Optimization of Billet Tube Mold Designs for High-Speed Continuous Casting

Endless rolling urgently requires an increase in the casting speed of continuous casting. For the continuous casting process of a high-casting-speed billet, the heat flux of the mold would be much higher, requiring a stronger cooling performance and longer mold life to match the high-speed casting. Mold material, thickness, and slot structure have a great influence on the casting speed. To design a more efficient billet casting mold, a three-dimensional thermal-stress-coupled analysis model of a 150 mm × 150 mm mold was established in this research to analyze the thermal state of a mold with high casting speed; in addition, the material, thickness, and water slot structure, which pertain to the mold cooling performance, were also studied. The results show that the billet mold of Cu-Ag with a thinner thickness and right-corner water slot is better in terms of casting speed. Regarding the material, the Cu-Ag mold has a higher thermal conductivity efficiency; its hot surface temperature is 4.89 °C lower, its equivalent stress is 7 MPa lower, and its longitudinal deformation is 0.0023% lower compared with the deoxidized phosphorus copper mold. Regarding the thickness, the thinner mold has a 60.76 °C lower hot surface temperature, its equivalent stress is 340 MPa lower, and its longitudinal deformation is 0.0443% lower compared with the thicker mold. For the water slot structure, the mold with the right-angled water slot has a 2.895 °C lower hot surface temperature, its equivalent stress is 37 MPa lower, and its longitudinal deformation is 0.0039% lower compared with the mold with a rounded-corner water slot.

Study on Mushy Zone Coefficient in Solidification Heat Transfer Mathematical Model of Thin Slab with High Casting Speed

When the casting speed of the thin slab continuous caster is increased, the ratios of the solid and liquid phases in the solidification front of the molten steel in the mold change, which affects the thickness of the solidified shell. In order to accurately calculate the thickness of the solidified shell and determine the value range of the mushy zone coefficient suitable for the mathematical model of solidification heat transfer at high casting speed, this paper established the solidification heat transfer mathematical model in thin slab funnel mold, and the influence of different mushy zone coefficients on the accuracy of solidification heat transfer mathematical model was analyzed and compared with the actual solidified shell thickness. The results showed that, when the casting speed was increased to 4~6 m/min and the coefficient of the mush zone coefficient was 3 × 108~9 × 108 kg/(m3⋅s), the thickness of solidified shell calculated by the solidification heat transfer model was in good agreement with that measured in practice. The research in this paper provides an important reference for the establishment of the solidification heat transfer mathematical model at high casting speed in the future.

The Influence of Formation Speed in Centrifugal Slip-Casting Method on the Microstructure of Al2O3-Cu-Cr Gradient Composites.

This work focuses on the production of gradient composite materials with an alumina matrix containing copper and chromium and examines the effect of the reinforcement and casting speed on the obtained microstructure. Al2O3-Cu-Cr composites with a microstructure gradient were produced via centrifugal slip casting. The research reveals that adding chromium to the Al2O3-Cu system improves the connection between the ceramic and metal particles, probably by reducing the contact angle at the interface between the ceramic and metallic phases during sintering. Additionally, it was found that higher casting speed was conducive to obtaining a better connection at the interface of ceramics and metal.

Numerical analysis of the comprehensive effect of continuous casting process parameters on the continuous casting billet remelting

In the present study, a coupled 3-D model of flow, solidification, and heat transfer was established to apply to gain new insights into the effects of casting speed and nozzle diameter on the remelting of continuous casting billets. The effects of nozzle diameters and casting speeds on the remelting of continuous casting billet were analyzed separately. Nozzle diameters vary from 20 mm to 50 mm, and casting speed varies from 1 m/min to 4 m/min. The flow behavior and velocity distribution, which are at different casting speeds, were calculated, and the reasons for shell remelting at high casting speeds were analyzed. The remelting of the billet shell, which is at different combinations of different nozzle diameters and casting speeds, was calculated. Then, the comprehensive effects of nozzle diameters and casting speeds on the remelting of the billet shell are analyzed. Finally, the remelting degree maps of different continuous casting process parameters were presented. By the simulation, it is found that the casting speed has more obvious effects on whether the remelting phenomenon occurs, while the diameter of the nozzle has more obvious effects on the degree of remelting. When the casting speed is lower than 2 m/min, remelting does not appear. When the casting speed is higher than 3 m/min, remelting will occur. When the casting speed is 3 m/min, as the nozzle diameter increases, the remelting degree continues to decrease, and the range of remelting first remains stable, then gradually decreases. It can be observed that when the casting speed is increased to 3–4 m/min, the nozzle diameter should be in the range of 30–40 mm.

Influence of submerged entry nozzle on funnel mold surface velocity

Abstract In this article, physical and numerical simulation of the flow field in flexible thin slab caster funnel mold at high casting speed is carried out with a five-hole submerged entry nozzle (FHSEN), and characteristics of the flow field on funnel mold liquid level under different casting speeds (4, 5, and 6 m·min−1) and different submerged depths (130, 160, and 190 mm) are studied by comparing with the new submerged entry nozzle (NSEN) designed. Physical simulation is based on the funnel mold prototype. Numerical simulation is carried out based on FLUENT software, and industrial experiments of two kinds of submerged entry nozzle are also carried out. The results show that in the case of both physical and numerical simulation, the maximum surface velocity of the FHSEN funnel mold is 0.58 m·s−1, and the funnel mold liquid level is prone to slag entrapment. The NSEN funnel mold’ maximum surface velocity is 0.37 m·s−1. Compared with the FHSEN, the NSEN funnel mold’ maximum surface velocity decreases by 0.21 m·s−1, and funnel mold surface velocity decreases significantly. Finally, the accuracy of simulation results is verified by industrial tests, and it is also show that NSEN can greatly reduce funnel mold surface velocity and probability of slag entrapment.

Numerical simulation of shrinkage porosity defect in billet continuous casting

Abstract Shrinkage porosity is a typical internal defect in the continuous casting billet, which occurs frequently and is difficult to solve. To explore the influence factors of central shrinkage porosity, a novel unsteady thermomechanical coupling analysis algorithm is developed based on the billet solidification characteristics, and the central shrinkage behavior during the ending solidification process is simulated. Results show that when the casting speed increases from 1.6 to 2.8 m·min−1 and the center outward displacement is reduced from 9.20 × 10−2 mm to 5.8 × 10−2 mm, it means casting speed has a significant effect on the formation of shrinkage porosity, and for this caster, the higher casting speed is more suitable for the secondary cooling zone. Without the changes in the solidification structure, when the superheat degree of molten steel increases from 10 to 40°C, the center outward displacement value decreases from 7.12 × 10−2 mm to 6.91 × 10−2 mm. In that case, the superheat degree has no obvious effect on the center displacement value.

Casting parameters and propagation behaviour of sticker breakout for the conventional slab

ABSTRACT The casting parameters and behaviour of 61 sticker breakouts were analysed during the continuous casting of the conventional slab. The difference of sticker breakouts between the conventional slabs and wide and heavy slabs was also studied. The results show that the high casting speed or change of casting speed is the main reason. The mould level of the conventional slab is small and not the reason for sticker breakouts, which is different from the causes of wide and heavy slab. In terms of propagation behaviour, there are 14 cases out of 61 sticker breakouts occurred only around one column of thermocouples. The vertical velocity is in the range of 0.3∼2.4 m·min−1, and the horizontal velocity is in the range of 1.0∼9.0 m·min−1. The vertical velocities of the three sticker breakouts are higher than their casting speeds, which is different from the wide and heavy slab.

Modeling Study on Melt Flow, Heat Transfer, and Inclusion Motion in the Funnel-shaped Molds for Two Thin-Slab Casters

For the purpose of studying compact strip production (CSP) funnel-shaped mold and flexible thin-slab rolling (FTSR) funnel-shaped mold, a three-dimensional (3D) multi-field coupling mathematical model was established to describe the electromagnetic braking (EMBr) continuous casting process. To investigate the metallurgical effect of EMBr in the CSP and FTSR funnel-shaped thin-slab molds, a Reynolds-averaged Navier–Stokes (RANS) turbulence model, together with an enthalpy–porosity approach, was established to numerically simulate the effect of ruler EMBr on the behaviors of melt flow, heat transfer, solidification, and inclusion movement in high-speed casting. The simulation results indicate that the application of ruler EMBr in the CSP and FTSR molds shows great potential to improve the surface temperature of molten steel and reduce the penetration depth of downward backflow. This contributes to the melting of the slag rim near the meniscus region and facilitates the floating removal of the inclusions in the molten pool. In addition, in comparison with the case of no EMBr, the parametric study shows that the braking effect of ruler EMBr with an electromagnetic parameter of 0.5 T can enhance the upward backflow in the two high-speed thin-slab molds. The enhanced upward backflow can successfully entrain the inclusions to the top of the mold and improve the activity of surface fluctuations to avoid the formation of the slag rim. For instance, for the ruler EMBr applied to the FTSR mold, the maximum amplitude of surface fluctuation and the floatation removal quantity of inclusions with a diameter of 100 μm are increased by 4.6 percent and 51 percent, respectively.

Controlling the Thermal and Rheological Properties of Silicate Glasses for Development of Advanced Mold Flux Systems

Development of the advanced mold flux is always mandatory to enhance both the quality and productivity of continuous casting of steels. Especially, the increasing demands for high alloy steels production and high speed casting reveals serious contradiction between two principal functions of mold flux: lubrication and controlling heat transfer. In order to overcome this problematic needs, some innovative research activities are being carried out. MAE (Mixed Alkali Effect) has been examined in alumino-borosilicate-based mold system to stabilize alkali cation and aluminum association, which enables chemically stable glassy mold flux film during casting of high alloy steels. Non-Newtonian mold fluxes could be developed by addition of Si3N4 or SiC due to the increase of stiffness of polymeric structure, which would be beneficial to satisfy the contradictory requirements of viscosity at mold top surface and mold wall. Some innovative ideas for controlling mold heat transfer without deteriorating the lubrication have been examined by dispersion of nano-size metallic particles and by modification of prenucleation motif. All these trials are closely related with glass science and engineering. Therefore, it should be highly beneficial to enhance the collaborative research activities between glass and metallurgy society for further development of advanced functional mold flux systems.