Continuous Casting Research Articles

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.

The temperature field characteristics and amorphous formation ability during the continuous casting process of Zr-based bulk metallic glass

This study utilized FLUENT dynamic mesh simulation technology to simulate the temperature field distribution characteristics during the continuous casting (CC) process of 5 mm thick Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 (Vit1) bulk metallic glass (BMG), analyzed and discussed the amorphous forming ability of the Vit1 BMG plate prepared through CC. The results indicate that during the CC process, the temperature gradient and cooling rate of Vit1 BMG plate decrease with increasing distance from the cooling copper block surface and prolonged solidification time. Even at the lowest cooling rate, it still remains significantly higher than the critical cooling rate (Rc) of Vit1 bulk amorphous alloy. The temperature variations recorded by the thermocouple during the alloy melt solidification process are in basic agreement with the simulation data. The experimental test and simulation results show that 5 mm thick Vit1 BMG slab can be prepared theoretically by continuous casting technology. Finally, XRD, DSC and TEM were used to analyze the amorphous formation ability and microstructure of the Vit1 BMG slab.

Stress state of billet – mandrel system during production of hollow steel billet in a unit of continuous casting and deformation. Part 2

The paper presents the results of theoretical research of stress-strain state of a billet – mandrel system when producing steel hollow billets in a unit of combined continuous casting and deformation, in which the working surface of the calibrated anvils are made with a variable radius. The necessity of making the working surface of the calibrated anvils with a variable radius is substantiated and initial data for the calculations is given. The calculation results are considered along the lines of the volumetric model passing through the characteristic points of deformation centers. The authors determined the forces when the anvils compress the wall of a hollow billet and the force of pulling the hollow billet from the mold. The laws of metal axial displacements and stresses in the deformation centers during compressing the wall of a hollow billet was established at the combined process of continuous casting and deformation in the unit. Nature of the stressed state of the metal wall of a hollow billet is considered from the perspective of improving its quality. The technique studied allows to determine the stress-strain state of a mandrel when producing a hollow steel billet using such a unit. The authors provided the recommendations for reliable gripping and compression with calibrated anvils of a hollow steel billet coming from a water-cooled copper mold of the unit of combined continuous casting and deformation.

Multi-grooved channel design in continuous casting mold for enhancing heat transfer efficiency considering pressure drop and flow rate loss

An efficient, speedy, multi-grooved (ESMG) mold was designed and manufactured for optimization to address issues such as low heat transfer rate, slow casting speed, and quality defects in traditional continuous casting molds. The flow resistance mechanism of multi-grooved channels with varying parameters was investigated by considering the ESMG geometric model, the convective heat transfer characteristic variation trends were revealed with different channel designs. Considering constraints of the dimensional chain and supply pressure, variation trends and mechanisms of the pressure drop, flow rate loss, and convective heat transfer coefficient of the ESMG mold were explored using multiple channel variables. Based on the numerical model of the ESMG channel, temperature variation trends in the copper mold were verified by comparison with relevant literature data, supporting the convective-heat-transfer model and variation trends of the ESMG mold. A high-efficiency heat-transfer ESMG assembly that casts U71Mn high-carbon large rectangular billets was fabricated, achieving a closed-loop dimensional chain and replacing traditional molds. Experimental validation on the continuous casting machine (CCM) proved directly that redesigning the ESMG mold cooling channel improved heat transfer efficiency and reduced CO2 emissions. After 504 h on the CCM, the ESMG mold casting speed increased from 1.1 to 1.6 m/min, the heat transfer efficiency was 17.6% higher than that of traditional molds and CO2 emissions were estimated to decrease by 31.2%. The billets produced by the ESMG mold had no quality defects in shape or surface with the original casting conditions, which provided enhanced support for accelerating continuous casting lines.

Photopolymerization of Stainless Steel 420 Metal Suspension: Printing System and Process Development of Additive Manufacturing Technology toward High-Volume Production

As the metal additive manufacturing (AM) field evolves with an increasing demand for highly complex and customizable products, there is a critical need to close the gap in productivity between metal AM and traditional manufacturing (TM) processes such as continuous casting, machining, etc., designed for mass production. This paper presents the development of the scalable and expeditious additive manufacturing (SEAM) process, which hybridizes binder jet printing and stereolithography principles, and capitalizes on their advantages to improve productivity. The proposed SEAM process was applied to stainless steel 420 (SS420) and the processing conditions (green part printing, debinding, and sintering) were optimized. Finally, an SS420 turbine fabricated using these conditions successfully reached a relative density of 99.7%. The SEAM process is not only suitable for a high-volume production environment but is also capable of fabricating components with excellent accuracy and resolution. Once fully developed, the process is well-suited to bridge the productivity gap between metal AM and TM processes, making it an attractive candidate for further development and future commercialization as a feasible solution to high-volume production AM.

Formation mechanism of edge crack during hot rolling process of high-grade non-oriented electrical steel

Edge crack formed during the hot rolling process significantly affected the quality of high-grade non-oriented electrical steel (NOES), posing substantial challenges to production. This study investigated the formation mechanism of serrated edge cracks in hot rolled strip, characterized by unusually coarse strip-like grains with typical thicknesses ranging from 0.5 to 0.8 mm and lengths ranging from 10 to 15 mm. These coarse strip-like grains evolved from abnormal columnar grains at the edges of reheating slab. During the continuous casting process, the bulge phenomenon occurred easily in high-grade NOES slabs, due to its lower yield strength at high temperatures. This bulge induced high internal stress at the slab edge, leading to abnormal growth of the columnar grains during the slab reheating process at high temperature. The orientation of coarse grains gradually changed to a rotated cube texture ({100}<011>) throughout the hot rolling process. These grains with rotated cube texture exhibited fewer slip systems and lower deformation storage energy, which is not conducive to the plastic deformation in thickness direction. Consequently, coarse grains at the slab edge deformed along TD direction and overflowed towards the lower surface of hot rolled strip, resulting in the original edge boundary enveloped by the overflowed metal to generate crack source. Finally, the serrated edge crack was formed from crack source under tensile stress during finish hot rolling.

Deformation strengthening mechanism of laser remelted high manganese steel

In order to further improve the deformation hardening ability of high manganese steel (HMnS) under low stress or small deformation, a low speed laser remelting technology was proposed to process the HMnS surface. Through parameters optimization, microstructure characterization, wear testing, and deformation strengthening analysis, the deformation strengthening mechanism of laser remelted HMnS (LR-HMnS) was systematically studied, and excellent wear resistance properties was also achieved. Firstly, by optimizing the parameters of laser remelting, high-quality microstructures with large remelting depth and fewer porosities were obtained. Then, the sliding wear tests showed that although the surface hardness of LR-HMnS (252.83HV0.3) was only 2.56 % higher than that of continuous casting HMnS (CC-HMnS) (246.53HV0.3), its volume wear rate (1.87×10−5 mm3/N·m) was only 10 % of CC-HMnS (18.71×10−5 mm3/N·m), which exhibited excellent wear resistance properties. Finally, for quantitative evaluating its work hardening at high strain rates, Hopkinson compression test of LR-HMnS was conduced according to the operating conditions of HMnS parts. The microstructure after small compression deformation was analyzed using EBSD and TEM. It was found that the larger grain size of LR-HMnS was helpful of reducing the nucleation stress of twins, forming high-density nano-twins, high-density stacking faults, and high-density dislocations. The synergistic effect of stacking faults, dislocations, and twins which segmented the matrix and refined the grains, and achieved the dynamic Hall-Petch effect. The superior deformation strengthening and wear resistance exhibited by larger grain HMnS were called the inverse grain size effect. Additionally, the large number of C-Mn strong bond networks formed by element segregation could enhance the pinning effect of dislocations, promote deformation hardening rate and wear resistance properties under low stress or small deformation. The research results provided a new method for pre-hardening of HMnS, and will also expand the application potential of HMnS in combined conditions of high, medium, and low impact.

Study on the control of transverse cracks at the corners of large square billets for continuous casting of marine 945 hypo-peritectic micro-alloyed steel

Hypo-peritectic micro-alloyed steel has strong crack sensitivity, and marine 945 steel, as a kind of sub-encapsulated crystalline micro-alloyed steel, has frequent corner cracks during production, which seriously affects the production rhythm and reduces the product quality. Through the study of the morphology and composition of the matrix near the crack, the study and analysis of the high-temperature mechanical properties of the steel itself, and combined with the actual production situation, the causes of the corner cracks were clarified and the process optimisation was carried out accordingly. The results of the study show that the generation of corner cracks is due to the improper deoxidation process, uneven heat transfer inside the crystallizer and inappropriate cooling water parameters in the steelmaking process. By changing the deoxygenation method, crystallizer protective slag performance, crystallizer cooling water volume, water volume in the second cooling zone and other measures, the occurrence of billet corner cracks was effectively reduced, and the frequency of billet corner cracks was reduced from 6.3 to 2/m.

Accurate heat flux estimation in continuous casting Molds via MH-MCMC Bayesian Inverse Method

The present work focuses on accurately estimating heat flux variations on the hot faces of the billet and slab molds during continuous casting using the Metropolis Hastings–Markov Chain Monte Carlo (MH-MCMC) Bayesian inverse method and experimental data. Accurate estimation of heat flux variation is crucial for operational efficiency and ensuring high-quality steel products. The variation in the hot face heat flux (qn(y)) of the billet mold is estimated using the proposed MH-MCMC Bayesian inverse method and experimental data for various casting speeds. The study extends this methodology to the slab mold for estimating the variations in the heat fluxes (qnr(y), qw(x,y)) on the hot narrow and wide faces of the slab mold. The estimated heat fluxes for both molds are used in respective forward models to obtain temperatures. The temperatures obtained excellently match experimental temperatures and show superior accuracy in estimating the heat fluxes. From the present methodology, the errors between these simulated and experimental temperatures are much less compared with the literature. The predicted heat flux variations on the hot faces of the billet and slab molds are also compared with the heat flux obtained from the literature.This study provides valuable insights into accurately estimating heat fluxes in continuous casting molds (billet and slab) using the MH-MCMC Bayesian inverse method. The accurately estimated heat fluxes of the molds are essential for ensuring the quality, efficiency, and innovation of continuous casting processes.

GPU-accelerated estimation of heat transfer coefficients in continuous casting under large interference by a novel multiagent-based dimensional learning Jaya algorithm

This paper addresses the challenge of estimating heat transfer coefficients (HTCs) through the measured surface temperatures under large interference in the secondary cooling zone (SCZ) of continuous casting processes. Conventional methods for calculating HTCs, typically reliant on surface temperature data, face significant challenges in achieving accuracy. These challenges primarily stem from the limitations inherent in traditional methodologies and the distortions caused by temperature outliers, which are a consequence of large interference. To address these issues more effectively, we introduced a novel algorithm–multi-agent and dimensional learning based Jaya algorithm (MADL-Jaya)–specifically designed to estimate HTCs. Furthermore, a hybrid method that integrates weighted least squares (WLS) with the MADL-Jaya was proposed to mitigate the impact of outliers. Additionally, estimating HTCs entails substantial computational demands. Consequently, a double-deck parallel algorithm employing graphics processing unit (GPU) acceleration was presented. This architecture facilitates both parallel heat transfer models and parallel MADL-Jaya calculations, thus significantly reducing the computational time required for HTC estimation. The experimental results unequivocally affirm the efficacy of the proposed algorithm in the accurate estimation of HTCs within the SCZ of continuous casting, effectively neutralizing the detrimental influence of outlier values while markedly improving computational speed.

Improvement of carbon segregation in billet by final-EMS, based on segmented continuous casting model

Improvement of carbon segregation in billet by final-EMS, based on segmented continuous casting model

Formation mechanism of cracks formed during drilling of a cold drawn prestressing 1215 free-cutting steel

1215 steel is a low-carbon free-cutting steel with the largest production, and its quality issues are complex and diverse. The formation mechanism of cracks formed during drilling of a cold drawn prestressing 1215 free-cutting steel was investigated by means of optical microscopy, scanning electron microscopy, high-temperature laser scanning confocal microscopy, and Thermo-Calc software. The failure was caused by abnormally wide pearlite with large amounts of sulfide nearby. We speculate the abnormal microstructure was related to C and S segregation in columnar-to-equiaxed transition zone during continuous casting process. However, element segregation was an inherent property in the continuous casting process. Reheating was an important process for homogenization to eliminate segregation, but the reheating temperature was lowered to reduce production costs. The lower reheating temperature resulted in incomplete elimination of columnar-to-equiaxed transition zone segregation, ultimately leading to the formation of abnormal microstructure. This batch of 1215 steel wire was not suitable for producing component required transverse plasticity during machining, but could be used to produce circular shaft components. In the future, it is suggested to increase the reheating and hot-rolling temperature, or take effective measures to reduce segregation during continuous casting.

Influence of Different Submerged Entry Nozzles for Continuous Casting of Ultrathick Slab

Controlling the flow activity at the meniscus in the mold during the continuous casting of ultrathick slab is challenging due to the complex flow behavior, which is not extensively documented. Herein, a multiphase transient model of the ultrathick slab mold has been developed to describe the flow of molten steel, velocity distribution, and stream pattern at different submerged entry nozzle (SEN) outlets. The position of impact points and the fluctuation of liquid level are discussed as well. After ejecting from the port, the stream of the S‐shaped SEN splits into upper and lower streams. The upper stream moves to the liquid level, which improves the liquid level activity near the SEN. However, the reduced mainstream momentum alleviates the occurrence of slag layer exposure. Industrial application of the S‐shaped SEN results in uniform slag distribution and smooth casting operations.

Analysis of Longitudinal Cracking and Mold Flux Optimization in High-Speed Continuous Casting of Hyper-Peritectic Steel Thin Slabs

Longitudinal crack defects are a frequent occurrence on the surface of thin slabs during the high-speed continuous casting process. Therefore, this study undertakes a detailed analysis of the solidification characteristics of hyper-peritectic steel thin slabs. By establishing a three-dimensional heat transfer numerical model of the thin slab, the formation mechanism of longitudinal cracks caused by uneven growth of the initial shell is determined. Based on the mechanism of longitudinal crack formation, by adjusting the performance parameters of the mold flux, the contradiction between the heat transfer control and lubrication improvement of the mold flux is fully coordinated, further reducing the incidence of longitudinal cracks on the surface of the casting thin slab. The results show that, using the optimized mold flux, the basicity increases from 1.60 to 1.68, the F- mass fraction increases from 10.67% to 11.22%, the Na2O mass fraction increases from 4.35% to 5.28%, the Li2O mass fraction increases from 0.68% to 0.75%, and the carbon mass fraction reduces from 10.86% to 10.47%. The crystallization performance and rheological properties of the mold flux significantly improve, reducing the heat transfer performance while ensuring the lubrication ability of the molten slag. After optimizing the mold flux, a surface detection system was used to statistically analyze the longitudinal cracks on the surface of the casting thin slab. The proportion of longitudinal cracks (crack length/steel coil length, where each coil produced is about 32 m long) on the surface of the thin slab decreases from 0.056% to 0.031%, and the surface quality of the thin slab significantly improves.

Experimental Study on the Characteristics and High‐Temperature Heat Transfer of Secondary Cooling Nozzle for High‐Efficiency Slab Continuous Casting Process

In the continuous casting process, the heat transfer effect of secondary cooling plays an important role in the quality of the slab. The cooling intensity and cooling uniformity of the secondary cooling nozzle need more efficient spray cooling to achieve. Herein, the cold characteristics of different types of nozzles were compared. It is found that the second type of air mist nozzles have more uniform water density and striking force. On this basis, high‐temperature heat transfer experiments for casting billets were carried out to study the heat transfer coefficients of different air mist nozzles in the secondary cooling zone of continuous casting. It is found that the heat transfer coefficient increases as the distance of the temperature measurement point from the nozzle directly below increases. The heat transfer coefficients of the casting billet in both the jet and non‐jet zones are decreasing to varying degrees. When the temperature drops to 600 °C, the second type of air mist nozzle shows a faster temperature drop at the point of measurement, a smaller difference in time taken for temperature drop between jet and non‐jet zones, and faster and more uniform spraying, leading to a more significant trend of increasing heat transfer coefficient.

Effect of Al or Cu Content on Microstructure and Mechanical Properties of Zn Alloys Fabricated Using Continuous Casting and Extrusion

The effect of Al or Cu content on the microstructure and mechanical properties of continuous casting and extrusion Zn alloys has been studied by a room temperature tensile test, X-ray diffraction, and scanning electron microscope. With the increase in Al content, the microstructure of continuous casting and extrusion Zn alloys slightly coarsens, and the lamellar eutectic structure increases. The changes in the above structural factors result in a slight decrease in strength and a significant increase in the elongation of Zn-Al alloys. The strength of Zn alloys increases as the Cu content increases due to the increased content and size of the second phase in the Zn alloys. This means that the mechanical properties of Zn alloys can be adjusted by a continuous casting and extrusion process, and the improvement of equipment capacity can improve the structure and morphology of the alloys.

Crystallization Behavior of the CaO–SiO2–Al2O3–MgO System Inclusions

The crystallization process of low melting point CaO–SiO2–Al2O3–MgO system inclusions during the continuous casting and hot rolling process greatly affects the deformability of inclusions. The effect of Al2O3 and MgO contents on the crystallization characteristics of CaO–SiO2–Al2O3–MgO system melts representing the typical oxide inclusions in Si–Mn deoxidized steels is systematically investigated. The continuous cooling transformation and time–temperature transformation experiments are carried out. The results reveal that the increase of Al2O3 contents restrains the crystallization process of the melt, whereas the crystallization tendency of the melt is promoted with the increase of MgO contents. The precipitated phases are predominately 2CaO·MgO·2SiO2 and 3CaO·MgO·2SiO2, and the primary crystalline phase is unaffected by the changes of Al2O3 and MgO contents. To obtain low melting point plasticized inclusions with limited crystallization ability, it is recommended to control the Al2O3 and MgO contents greater than 15 wt% and below 5 wt%, respectively. The isothermal treatment is suggested to be controlled within a proper temperature range (1175–1250 °C) to decrease the crystallization kinetics. The oxide system's viscosity change is the limiting kinetic factor in the crystallization process, and it can be utilized to predict the system's crystallization tendency.

Effect of charging temperature of continuous casting slab on the surface cracks of HSLA steel thick plate

In order to investigate the formation mechanism of the surface cracks on high-strength low-alloy (HSLA) steel thick plates, this paper simulated the temperature history of different hot charging processes, and deduced the microstructural transformation behavior and recrystallization austenitization process under different charging temperatures. This paper proposed four hot charging modes and ultimately elucidated the effect of charging temperature on the surface cracks of HSLA steel thick plates. Experimental results showed significant differences in the microstructure and recrystallized austenite grains under different charging temperatures. Analysis revealed that the recrystallized austenite grains were determined by the microstructure. The presence of austenite in the microstructure significantly increased the size of recrystallized austenite grains, thereby disrupting the uniformity of grains. Based on the relationship between charging temperature, microstructure, and recrystallized austenite grain state, the hot charging process of HSLA steel was divided into four temperature zones: high-temperature single-phase zone, high-temperature two-phase zone, medium-temperature three-phase zone, and low-temperature two-phase stable zone. The occurrence of the surface cracks in HSLA steel was caused by the recrystallized austenite mixcrystal structure generated during charging in the medium-temperature three-phase zone. The uneven recrystallized austenite grains caused by undercooled austenite were the direct cause of the surface cracks, while high charging temperature was the root cause. When the charging temperature entered the medium-temperature three-phase temperature zone, recrystallized austenite grains would exhibit mixcrystal structure. These mixcrystal structure deteriorated the surface quality, promoting the formation, deformation, and propagation of surface cracks. To reduce the occurrence rate of surface cracks, for steel grades sensitive to surface quality, the charging temperature should be controlled in the low-temperature two-phase stable zone.

Fault diagnosis method for continuous casting machine’s sector segment based on SG-PCA-LSTM

Abstract To address challenges such as the high variability of variables and difficulties in feature extraction during the casting process of the continuous casting machine’s sector segment, a fault diagnosis method based on SG-PCA-LSTM is proposed. This method aims to overcome the issue of fault features obscured by noise in the total tension time series by employing the SG smoothing algorithm for filtering and denoising. By leveraging the inter-segment data correlation and the advantage of PCA in extracting fault feature information, combined with the powerful learning capability of LSTM in modeling, a Principal Component Analysis - Long Short-Term Memory (PCA-LSTM) fault diagnosis model is established. Through comparative analysis against different diagnostic methods in terms of recognition rate, false positive rate, etc., the results obtained by this method are compared against those obtained by using other algorithms. Experimental results demonstrate that the proposed method exhibits good overall performance in terms of accuracy and training time.

Flow and fluctuation of molten steel under permanent magnet flow control-mold in continuous casting process

Flow and fluctuation of molten steel under permanent magnet flow control-mold in continuous casting process