Continuous casting process occupies a “central” position and plays a connecting role in steel production process. The development of continuous casting technology has significantly promoted high quality, high efficiency and green production in steel industry. By reviewing the award-winning projects in the field of continuous casting in the “Metallurgical Science and Technology Award” from 2020 to 2024, The new progress made in continuous casting theory, production efficiency, billet homogenization, products development, key process equipment and intelligent control technology in China were summarized. Billet homogeneity, stable production, and high efficiency are the main indicators of high-quality continuous casting process. The collaborative optimization of mold metallurgical functions, secondary cooling control, electromagnetic stirring, and end pressing are the main technical measures to improve the quality of continuous casting billets. From the award-winning projects in recent years, it can be seen that the intelligent control technologies, such as digital twin factory, mold liquid level fluctuation control, billet defect detection and prediction, automatic steel casting, etc. have made remarkable progress. Continuous casting equipment is developing towards the direction of high efficiency, stabilization, flexibility, long service life, and more intelligence, and at the same time meeting the production requirements of stable, high quality and energy saving. Reference for readers to understand the whole development of continuous casting technology in China will be provided.

With the increasing improvement of the performance requirements for steel in high-end equipment, high titanium steel has drawn wide attention due to its high strength, toughness, wear resistance and corrosion resistance. However, new challenge has encountered in smelting and casting of high Ti steel, due to the fact that Ti shows high activity and strong affinity to react with oxygen and nitrogen to form high melting point inclusions. The general characteristic of the submerged nozzle clogging in continuous casting of high Ti steel was reviewed, and the multilayer structure and chemical composition of the clog were revealed. The submerged nozzle clogging process and mechanism during continuous casting by Ti addition was summarized, and the chemical reaction type, sequence and clog component at the interface of the continuous casting nozzle were compared between Ti containing steel (w(Ti)≤0.01%) and high Ti steel (w(Ti)>0.1%). The inner wall erosion, temperature drop and physical adhesion were regarded as the key influencing mechanisms. Finally, the effective control strategy to solve the nozzle clogging problem in high Ti steel continuous casting has been proposed, and the new achievements on Ca treatment, nozzle material design and external field implementation has been outlined particularly.

A transient three-dimensional numerical model coupling multiple physical fields in the slab mold was developed to investigate the effects of electromagnetic stirring on molten steel flow, initial solidification, and the non-steady-state fluctuation behavior of the steel/slag interface in a 1 500 mm×230 mm slab mold. The accuracy of the electromagnetic stirring model was validated by measuring the magnetic field intensity and electromagnetic forces within the mold during actual production. The results show that, compared to conditions without electromagnetic stirring, the traveling wave magnetic field generated by increased stirring transforms the flow pattern in the mold from an upward circulating flow to a horizontal circulating flow. This enhances the horizontal flow of molten steel, reducing the velocity of the solidification front along the casting direction and thinning the solidified shell. For instance, when the current is 500 A, the solidified shell thickness at the mold outlet decreases by approximately 3 mm. Additionally, the weakening of the upward circulation leads to a more uniform velocity distribution at the steel/slag interface. With the increase in current intensity, the horizontal flow of molten steel is further promoted, reducing the downward circulation velocity and effectively decreasing the impact depth. To quantitatively characterize the overall level fluctuation and flow of the steel/slag interface in the mold, evaluation criteria for the average level fluctuation and velocity uniformity were proposed. The results indicate that the level fluctuation and molten steel flow at the steel/slag interface are optimal under the electromagnetic stirring parameters of 500 A and 3.2 Hz.

Inclusions in the steel have a significant impact on the performance. It is necessary to detect and analyze non-metallic inclusions to improve the quality and performance of steel products. A comprehensive introduction to the detection and characterization methods for inclusions in the steel was reviewed from three aspects: the characterization of inclusion features, the extraction of inclusions by dissolution, and non-destructive three-dimensional detection of inclusions. Different characterization methods were compared comprehensively from different aspects including size analysis range, advantages and disadvantages. Optical microscope and other methods can directly observe the morphology of inclusions with a wide analysis range, but their magnification is relatively low, making it difficult to distinguish the morphology characteristics of small inclusions. However, scanning electron microscopy and other methods can clearly observe the two-dimensional morphology and the composition of inclusions, but their analysis cost is relatively high. The erosion method can characterize the three-dimensional morphology of inclusions, but its operation is relatively complex and time-consuming. The application of non-destructive characterization methods such as ultrasonic testing can characterize inclusions without damaging the specimen, which is convenient and fast.

Carbon emissions from the iron and steel industry account for a large proportion of all industries in China, and how to realize carbon emission reduction and CO₂ resource utilization in the steelmaking process under the background of "double carbon" has attracted much attention. Taking the resource utilization of CO₂ in the iron and steel industry as an entry point, it introduces the current situation of CO₂ emission and resource utilization in the iron and steel industry, and focuses on the analysis of the technical status of applying CO₂ as reaction gas, stirring gas and protective gas in the steelmaking process. Through thermodynamic calculations, it is concluded that when CO₂ oxidizes 0.1 mass% of the metal elements in the iron liquid [M], the comprehensive exothermic heat release is reduced, and it plays a role of controlling the temperature. The analysis of CO₂ as a stirring gas shows that CO₂ is used in the steelmaking process to reduce carbon emission. As a stirring gas,CO₂withthe utilization rate of about 85% can provide twice as much stirring effect as Ar. CO₂ can be used as a kind of resource gas gradually applied in the steelmaking process, with energy saving and emission reduction and cost-effective effect, but needs to further clarify the reaction characteristics of CO₂ in the high-temperature melting pool and the role of the form, in order to accurately and efficiently realize the resourceful use of CO₂.

Defects such as slab shape, surface cracks, center segregation, and center porosity are key issues limiting the production and development of ultra-thick slab continuous casting. A domestic steel plant has newly built a 460 mm thick slab casting machine. By studying the characteristics of the continuous casting production process for thick slabs and addressing the main defects of thick slabs, a 460 mm thick slab continuous casting production process technology has been developed, including high casting speed, secondary cooling dynamic amplitude cutting control process, high alkalinity and viscosity process of protective slag, low superheat control, and large pressing process at the solidification end of the slab. This has solved the problem of bulging of thick slabs, reduced the occurrence rate of surface cracks on thick slabs, and improved the center looseness and center segregation of thick slabs.

With the advancements in thin slab direct rolling and efficient continuous casting, the issue of funnel-shaped cracks in copper molds resulting from high-speed casting has become increasingly severe. Researchers had explored the formation mechanism and control of these cracks in thin slab casting by means of theoretical analysis, industrial experiments and numerical simulation methods, aiming to prolong the lifespan of copper molds and reduce production costs. The macroscopic morphology and hazards of funnel-shaped copper mold cracks were elucidated, and the mechanisms of crack formation, including thermal fatigue, creep fatigue, and elemental erosion, were summarized. A comprehensive review of the development of thermal/mechanical analysis models for copper molds was provided, along with an overview of measures for controlling copper mold cracks, new research directions were proposed for the mechanism of copper mold crack formation, thermal/mechanical analysis models, and control strategies.

The flow of liquid steel in continuous casting mold is a complex three-dimensional turbulent flow, which includes many complex phenomena, such as turbulence in the SEN and mold, the movement of bubbles and inclusions, and the influence of multiphase flow and electromagnetic force on liquid steel flow.The fluctuation of the liquid level of the mold is an important reason for the surface quality of the casting slab.In the actual production process, the fluctuation of liquid level generally only detects a single point or a single area, which cannot reflect the overall fluctuation state of the liquid level. However, there is no direct detection method for the flow field, which is generally analyzed and evaluated by a certain proportion of water model. The characteristic parameters (liquid level difference, liquid steel flow rate) at the mold meniscus are evaluated by numerical simulation andnail board test. The results of numerical simulation and nail board test are basically consistent. Numerical simulation results show that the EMBR current changes by 50A, the maximum surface flow rate changes by 0.01-0.02 m/s,while the maximum liquid level difference changes little. When the SEN insertion depth increases by 50 mm, the maximum surface flow rate decreases by 0.03-0.06 m/s, and the maximum liquid level difference decreases by 2 mm. The pulling speed increases by 0.3 m/min, the maximum surface flow rate increases by 0.04 m/s, and the maximum liquid level difference increases by 2 mm.SEN insertion depth and casting speed have great influence on liquid steel flow rate and liquid level difference, while EMBR current has little influence. Under the condition of casting speed 5.2 m/min, EMBR current 175A, SEN insertion depth 170 mm, the slab quality is better.

To address the issue of poor temperature compliance in IF steel production at a domestic steel factory, a statistical study was performed to examine the temperature evolution trend throughout the smelting process. The results show that the converter tapping and continuous casting temperature compliance rates were only 55.56% and 44.57%, respectively, with the converter continually producing excessive tapping temperatures. The RH arrival temperatures for both initial casting and continuous casting exceeded goal values by 15 ℃ and 10 ℃, respectively, necessitating scrap additions during secondary refining for temperature correction. Controlling the RH arrival temperature between 1 600 and 1 625 ℃ helps minimize scrap consumption during refining, limiting the influence on nitrogen pickup during RH treatment. Process optimization should focus on rational adjustment of converter tapping temperature, improvement of ladle heating systems and thermal management, and implementation of precise narrow-window temperature control throughout the entire production route to achieve more stable thermal conditions.

In the continuous casting process, tundish plays an important role in controlling the number of inclusions and improving the quality of the casting billet. A three-dimensional mathematical model was established by using the open-source computational fluid dynamics software OpenFOAM by numerical simulation, and the effects of particle size, molten steel flow rate and shape of non-metallic inclusions on the removal rate of non-metallic inclusions in tundish were analyzed. The results show that with the decrease of the particle size of the inclusions, the removal rate of non-metallic inclusions gradually decreases. When the flow rate of molten steel is 0.47 m³/min, the removal rate of non-metallic inclusions with a particle size of 200 μm reaches 97.64% and the removal rate of non-metallic inclusions with a particle size of 10 μm is only 1.298%. When the particle size of the inclusions is less than 100 μm, the removal rate increases significantly with the increase of particle size; and when the particle size of inclusions exceeds 100 μm, the increase of particle size has no obvious effect on the removal rate. With the increase of molten steel flow, the removal rate of non-metallic inclusions showed a decreasing trend, and the molten steel flow rate had a greater effect on the removal rate of non-metallic inclusions with particle sizes of 50 μm, 75 μm and 100 μm, but had little effect on the removal rate of non-metallic inclusions at 200 μm, 10 μm and 25 μm. With the decrease of the shape factor, the removal rate of non-metallic inclusions showed a decreasing trend, and the removal effect of spherical non-metallic inclusions (shape factor 1) was the best. And when the equivalent diameter of non-metallic inclusions was less than 100 μm, the influence of shape factor on the removal rate of inclusions gradually decreased with the decrease of the equivalent diameter of non-metallic inclusions.

At present, ingot casting has obvious advantages in producing special steel, manufacturing large-weight ingots and making small-lot castings. However, steel ingots generally have many internal defects, low yield, and high mold loss. How to optimize the ingot structure has become the fundamental method to improve the internal quality of steel ingots. Based on the multiphase solidification model, it took a 5 t cubic ingot as the research object and focuses on the effects of different feeding efficiency ratios, slow cooling process and strong cooling process on the macro segregation behavior of steel ingots. The results showed that increasing the rising capacity ratio or using the strong cooling process has a significant effect on improving the macroscopic segregation, while the slow cooling process has little effect. For this ingot, increasing the rising capacity ratio to more than 11.5% can restrain the positive segregation of the head above the riser line. It can save the design time of the ingot pattern for the designer and at the same time provide a data reference for the actual production on site.

In the critical process of metallurgical production, the continuous casting is closely linked to the quality of the cast slab products. Among various parameters, the liquid level fluctuation in the mold is one of the most crucial during the continuous casting process. Therefore, accurate monitoring of the liquid level fluctuation inside the mold is particularly critical. An artificial intelligence model aimed at real-time accurate prediction of the mold liquid level fluctuations was introduced. The model employs a genetic algorithm (GA) optimized random forest (RF) technique, referred to as the GA-RF model. The model optimizes the parameters of random forest network through genetic algorithm, aiming at finding the optimal parameters of the model and obtaining the model with the best prediction performance. Experimental results demonstrate that the GA-RF predictive model achieves a mean absolute error (MAE) of 0.534 and a mean squared error (MSE) of 0.73, with a high prediction success rate of 96%. Compared with CNN model, BP model and SVM model, it is found that GA-RF model MAE and MSE are superior to other models, confirming the model’s high precision and its ability to meet the stringent requirements of practical production applications. Furthermore, through sensitivity analysis, the influence of different production parameters on the model is also discussed.

In order to evaluate the influence of baffle wall structure on the flow field, improve the flow behaviour of liquid steel in the middle tundish of a steel plant, select the optimal solution in line with the current production conditions and improve the quality of special steel grades, the guide holes on the basis of the original baffle wall structure were designed and optimized.Orthogonal experiments are designed considering the number of guide holes, mounting height, and inclination angle factors.The flow field of the tundish under the prototype retaining wall structure is evaluated by the water simulation experiment method for conducting range analysis. Thus, considering the influence of various factors under the indexes of dead zone ratio and standard deviation of peak time, the optimal diversion hole structure can be found.Numerical simulation is carried out using Ansys Fluent to simulate the flow and temperature fields of the tundish before and after optimization. The experimental results show that the flow field of the prototype tundish has problems such as poor consistency at the mouth and poor flow characteristics of the internal liquid steel, with a dead zone ratio of 29.26% and a peak time standard deviation of 61.52 s.Under the water model experiment, the optimized tundish dead zone ratio is 27.92%, which is 1.34% higher than that of the prototype tundish.The standard deviation of peak time is 87.27% higher, and the water inlet temperature difference is reduced to 0.2 K.The flow field is very uniform as a whole, and the consistency of the two streams is significantly improved.

The inhomogeneous heat transfer, solidification, thickness of primary shell, temperature and stress of secondary cooling zone directly affect the surface and internal quality of slab. The temperature field and stress field of the whole process of Q235B slab in a steel plant were simulated by ANSYS Finite Element Software, the surface temperature, equivalent stress, shell inhomogeneity, heredity and crack sensitivity were analyzed. The results show that the non-uniformity of slab solidification thickness in mold is inherited to secondary cooling zone, and the non-uniformity of equivalent stress on slab surface is less inherited, the non-uniformity of surface equivalent stress wasgreatly improved. In the case study, the temperature at the left corner of the inner arc was the lowest (892 ℃), the equivalent stress was the highest (12.2 MPa), and the temperature at the deflection corner was the highest (1 263 ℃), the equivalent stress was the lowest (2.54 MPa). The sensitivity of slab surface crack is 1/4 center > 1/8 center > 1/2 center.The sensitivity index of slab surface crack reaches the maximum value of 0.52 in mold. In the early stage of secondary cooling, the crack sensitivity is increased.And in the late stage of solidification, the shell is thicker, the crack sensitivity is lower and the change range is small.

The clogging behaviors of sub-merged nozzle (SEN) in three types of Ti-baring Al-killed steels including ultra-pure ferritic stainless steel, austenitic stainless steel and interstitial-free steel were studied by cross section observation and acid dissolution method. The results show that Al₂O₃ inclusion is the main inclusion comprising the transition layer, and MgO·Al₂O₃ caused by poor calcium treatment is the main factor for the growth of nozzle clogs. TiO₂ formed by the reaction between liquid steel with refractory material is the main inclusion in the transition layer, and subsequently the TiN precipitation caused by poor control of titanium-nitrogen product and steel cleanliness combined with rapid heat transfer of transition layer deteriorates castability. Metallic iron comprises a major amount of the transient layer of interstitial-free steel and Al₂O₃inclusion plays a dominant role in the clogging layer. TiN inclusions have less influence on clogging behaviors during continuous of ultra-pure ferrite and interstitial-free steels. The good wettability of titanium-containing liquid steel and titanium oxide will accelerate the clogging process in interstitial-free steels. The personalized strategy should be adopted for the mitigation of SEN clogging according to the steel characteristics and refining equipment.

A full-structure physical model was established based on a 30-ton six-strand rectangular billet continuous casting tundish in a domestic steel plant, and the fluid-solid-thermal coupling numerical simulation was carried out. The flow field, temperature field and stress distribution behavior in the tundish were studied. Based on the von Mises stress considering the thermal effect, the damage of the refractory was evaluated. A damage model of the turbulence inhibitor-porous baffle integrated flow control element was established, and the flow and heat transfer behaviors in the tundish before and after the damage of the flow control element were compared and analyzed. The results show that the average volume temperature of each fluid domain and solid domain in the six-strand tundish is quite different. The maximum temperature difference between the working layer and the slag layer and the air layer can reach 312 and 578 K, respectively. The stress of the wall surface reaches 40-52 and 52-73 MPa, respectively, which is higher than that of the wall surface in contact with the molten steel(32-40 MPa).In the integrated flow control element, the easily damaged area is mainly three parts: a turbulence suppressor, a retaining wall diversion hole, and the connection between the corner of the porous retaining wall and the side wall as well as the bottom. The stress in these parts reaches 35-52 MPa. After the failure of the integrated flow control element, the response time of No.1 and No.2 outlets decreased by 26 and 17 s respectively, the volume fraction of the piston zone decreased by 25.5%, the volume fraction of the dead zone increased by 9.4%, and the consistency of each flow was obviously weakened. The minimum temperature of molten steel at the outer corner of No.3 outlet decreased by 14 K. The field industrial test shows that the failure morphology of the integrated flow control element obtained by numerical simulation in this paper is in good agreement with the actual failure situation.

In the steel production process, continuous casting billets are cut according to length; rolled steel is rolled by weight; and the inconsistency of steel rolling implementation standards directly causes fluctuations in the total length of rolled products. These all resulted in the generation of a large number of short length materials and waste materials, which has become an industry pain point that needs to be solved urgently. The basic principles of fixed-weight cutting technology, influencing factors of fixed-weight cutting and related models of continuous casting billet are expounded. The intelligent fixed-weight system is developed to make continuous casting billets cut by weight to realize steel-rolling coupling, which has been successfully applied to Hebei Tangyin Iron and Steel Co., Ltd. The results of the model show that the difference between the theoretical weight and the actual weight is ±0.2%, the fixed weight pass rate reaches more than 90%, the actual weight yield reaches more than 97.5%, and the fixed size rate is stable at more than 99.5%. This greatly improves the negative difference stability and yield level of small bar size products while maintaining high yield, and provides a reference for the development of fixed weight cutting technology for related enterprises.

In the steel continuous casting process, center porosity and shrinkage cavity are two common quality defects that can significantly affect product performance. Accurately predicting these defects is essential, as it not only avoids destructive testing but also supports technicians in adjusting process parameters, thereby ensuring the smooth progression of subsequent rolling operations. However, due to the nonlinear dynamics, strong coupling characteristics, and multiple external disturbances inherent in the continuous casting process, predicting center porosity and shrinkage cavity levels remains highly challenging. Existing approaches typically rely on single-task learning, which limits their ability to predict multiple defects simultaneously. This constraint not only reduces prediction efficiency but also often results in suboptimal accuracy that fails to meet production requirements. To overcome these limitations, this study proposes a novel defect prediction method based on a multi-task learning framework, which integrates multi-task learning with the TabNet deep learning model designed for tabular data. This approach enables simultaneous prediction of both center porosity and shrinkage cavity levels by leveraging the intrinsic relationship between the two defects, thereby improving both efficiency and predictive accuracy. Extensive experiments using real-world production data from a steel plant demonstrate that the proposed method achieves outstanding performance in industrial defect prediction, with prediction accuracies of 100% for center porosity and 99.9% for shrinkage cavity, and a 53.47% reduction in inference time, fully validating the effectiveness and practical value of the proposed multi-task learning strategy.

Center porosity is one of the main defects of continuous casting round billet. In order to reduce the center defect of the continuous casting round billet, the mechanical reduction is performed at the solidification end of the continuous casting round billet. According to the actual production situation of a factory, a three-dimensional finite heat transfer model of the continuous casting round billet was first established to simulate solidification, and according to the results of the heat transfer model, different reduction positions were determined. Then, the mechanical reduction processes of the continuous casting round billet with a diameter of 350 mm were simulated using a thermodynamic coupling model. At the same time, the relative change of the shrinkage cavity volume was used as the standard to evaluate the influence of the reduction position on the shrinkage cavity healing. Finally, the experiment of continuous casting round billet pressing was carried out. The results show that during the reduction process of continuous casting of round billet, the central shrinkage cavity became closed under the combined effects of metal filling and compression deformation. The reduction position corresponds to the solid fraction in the center of the continuous casting billet, and the metal flow condition is different at various reduction positions. Under the same reduction amount, when the central solid fraction of the continuous casting round billet increases, the flow range of the central metal of the continuous casting round billet will gradually decrease, and the relative flow distance of the metal will first increase, then remain unchanged, and finally decrease, and the central shrinkage cavity of the casting round billet will gradually decrease and finally become close. When the reduction is 15 mm, the optimal reduction interval of the continuous casting round billet is f_s=0.6-1.0. The experimental results show that the inner porosity of continuous casting round billet decreases after reduction.

To investigate the synergistic effects of electromagnetic stirring in the secondary cooling zone and at the solidification end during the slab continuous casting process, a slab arc continuous casting machine from a specific plant was used as a prototype. A three-dimensional transient electromagnetic field model was developed using the finite element method to analyze the electromagnetic stirring characteristics of the traveling wave magnetic field. Additionally, a three-dimensional transient model for flow, heat transfer, and solidification was created using the finite volume method, incorporating the time-averaged Lorentz force into the momentum equation through one-way coupling. Numerical simulations reveal the influence of different electromagnetic stirring configurations on the solidified shell growth behavior during continuous casting. In the reverse mode of electromagnetic stirring of the secondary cooling zone, the magnetic induction generated by the two stirring rollers is in opposite directions, with a maximum intensity of 0.15 T. Correspondingly, the Lorentz force acting on the molten steel also has opposite directions, reaching a peak value of 15 324 N/m³. The molten steel exhibits a flow pattern resembling the shape of an “8” with a maximum flow speed of 0.42 m/s, and the temperature distribution is symmetric. The solidified shells formed on the left narrow face at point A and the right narrow face at point B are thinner. In the co-directional mode of electromagnetic stirring, the magnetic induction generated by the two stirring rollers is aligned in the same direction, with a maximum intensity of 0.22 T. The Lorentz force on the molten steel also aligns in the same direction, with a peak value of 42 000 N/m³. The molten steel flow forms a double circulation pattern with a maximum speed of 0.78 m/s. At the mold exit, the temperature is higher on the left side, resulting in thinner solidified shells at points A and B on the left narrow faces. The metallurgical length is approximately 33.04 m, which is about 12% longer than in the reverse mode.

The systematic traceability analysis was conducted on the issue of linear defects (“sliver”) affecting the product qualification rate during the production of IF steel automotive panels using BOF-RH rimming steelmaking/vacuum decarburization/aluminum deoxidation process on a domestic production line. Through sampling, testing, and process data analysis of the entire smelting casting rolling process, the influencing factors and laws of the upstream process conditions of steelmaking and continuous casting on the “sliver” defects on the surface of the strip steel were systematically evaluated, and the process parameters were further improved. The research has shown that the “sliver” defects on the surface of IF cold-rolled strip steel are mainly caused by large-sized Al and O deoxidation products in the molten steel, and slag containing elements such as Si, Ca, Na, Mg, which are captured by the solidification of the casting slab and extended and exposed on the surface during the rolling process of the strip steel. The tapping temperature of the IF steel converter was controlled between 1 600 ℃ and 1 630 ℃, which was shown to reduce the necessity of oxygen blowing and aluminum heating operations due to low RH arrival temperatures, thereby effectively decreasing both total aluminum consumption and the quantity of Al-O inclusions in the steel liquid. The tapping temperature of the IF steel converter was controlled between 1 600 ℃ and 1 630 ℃, which was shown to reduce the necessity of oxygen blowing and aluminum heating operations due to low RH arrival temperatures, thereby effectively decreasing both total aluminum consumption and the quantity of Al-O inclusions in the steel liquid. Measures such as controlling the superheat of the ladle in the continuous casting process to 20-30 ℃ were implemented to alleviate the pressure on the heating value requirements of the upstream process. Additionally, the protection of the casting process was further strengthened, and the water nozzle insertion depth was optimized, which effectively promoted the upward floating of oxides in the steel to the powder slag. “sliver” defect coils are mostly located in the later stage of casting, mainly distributed from the inner arc to the center of the billet. Immersion nozzles are used to ensure active steel tapping, with a frequency of nozzle replacement less than 6 ladles and small steps adjustments to the cast speed. These measures can achieve stable control of the crystallizer flow field and slag/steel interface, effectively reducing the probability of slag rolling in the crystallizer.

Abnormal large austenite grains are considered a significant cause of transverse cracks in continuous cast billets. Thermal simulation methods combined with in-situ liquid quenching experiments are employed to investigate the growth process of surface austenite grains in nine types of microalloyed steel during the bending-type continuous casting process. Results show that at the straightening starting point, where corner transverse crack defects are likely to occur, the size of abnormally coarse austenite grains increases with rising austenite start growth temperature T_γ, exhibiting an extremum near the peritectic point. As the absolute difference |ΔT| between T_γ and the precipitation temperature of TiN increases monotonically, it indicates that the austenite start growth temperature and the TiN precipitation temperature are key factors influencing abnormal austenite growth. High-temperature tensile tests demonstrate that steels with higher austenite start growth temperatures and larger |ΔT| show greater crack sensitivity, which is consistent with the pattern of abnormal austenite growth.

During the continuous casting process of producing high aluminum steel, at the liquid level of the crystallizer, there is a strong interface reaction between the Al element in the molten steel and the mold slag, which leads to serious denaturation of the mold slag and directly endangers the quality of the billet and the smooth operation of continuous casting production. The mold slag layer was dynamically sampled during the continuous casting process of high aluminum steel, and analyzed the changes in the composition and physicochemical properties of the slag layer during the continuous casting process. The reaction behavior between steel slag was studied through thermodynamics and kinetics. The results showed that during the pouring process, the Al₂O₃ content in the slag increased from 1.40% to 24.75%, and the SiO₂ content decreased from 32.26% to 17.69%. The average viscosity of the liquid slag increased from 0.38 Pa·s of the original slag to 0.58 Pa·s, and the average melting temperature increased from 1 112 ℃ of the original slag to 1 189 ℃. The trend of changes in the composition of mold slag conforms to the thermodynamic law of steel slag reaction, and the mass transfer behavior of Al₂O₃ in the liquid slag layer is a limiting link in the interface reaction of steel slag and the degree of liquid slag denaturation.

Focusing on slab defects such as longitudinal cracks and depressions in 2Cr13 martensitic stainless steel produced at a steel plant, the high-temperature characteristics of the steel and the physicochemical properties of the used mold fluxes were systematically investigated. Results indicate that 2Cr13 martensitic stainless steel undergoes a peritectic reaction during solidification, with the initial solid fraction reaching 88.77% at the onset of this reaction. The DSC curves exhibit significant fluctuations at high-temperature stage, indicating a poor thermal stability of the steel. Additionally, the steel has also the characteristics of high tensile strength but low thermal plasticity. These characteristics will easy to cause the non-uniform growth of the initial solidification shell, leading to the formation of the slab defects. Comparative analysis of two commercial mold fluxes (S1 and S2) reveals similar effective chemical compositions, viscosity, and melting temperature. However, S2 flux contains a significant lower proportion of pre-melted material compared to S1 flux. During actual application, low-melting-point Na₂CO₃ in the S2 flux tends to melt preferentially, inducing segregation phenomena. Consequently, the Na₂CO₃ content in the liquid slag exceeds designed values, reducing both the viscosity and break temperature of the slag. This results in an uneven distribution of flux films and weakens the heat transfer regulation capacity, thereby increasing the propensity for longitudinal cracks and depressions in the cast slab. These findings provide crucial insights for optimizing mold flux design and casting parameters in the continuous casting of martensitic stainless steels.

To explore the causes of sliver defects on the surface of SPHC hot rolled plates produced by the third generation thin slab continuous casting and rolling technology in a factory, a comprehensive analysis was conducted. Samples of the SPHC hot rolled plates were collected, and both the morphology and composition of the defect surfaces and cross sections were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and large sample electrolysis. The study revealed that the primary components of the inclusions at the defect sites were CaO-SiO₂-Al₂O₃-MgO-Na₂O composite inclusions and Al₂O₃ particles. The presence of CaO-SiO₂-Al₂O₃-MgO-Na₂O composite inclusions is attributed to mold slag entrainment, while the Al₂O₃ particles are likely a result of secondary oxidation of molten steel and nozzle clogging. Additionally, an analysis of the slab quality produced under identical process conditions was performed. Following slime electrolysis of the slab, it was determined that the major composition of large inclusions in the slab was Ca-Al-O. Out of 131 large inclusions extracted, 13% were primarily composed of Ca, Al, Si, Mg, K, and Na, supporting the hypothesis that these inclusions also arise from mold slag entrainment. Furthermore, 31.8% of the large inclusions contained more than 10% of elements such as Nb, Mo, Ni, and W. These elements are believed to originate mainly from scrap or alloy additions during the steelmaking or refining process prior to continuous casting, with the high content potentially due to ladle slag involvement during pouring. In conclusion, the research identified mold slag entrainment and secondary oxidation as significant contributors to the sliver defects on SPHC hot rolled plates.

To address the significant erosion observed in the tundish dam with jet hole, a 65 t billet tundish from a domestic steel plant is researched. It employs numerical simulation to examine the distribution of impact stress on the upstream surface of the dam. The findings clarify the factors affecting the impact stress on tundish dam. Results indicate that the impact stress along the upper edge of the upstream surface is negative. Additionally, a specific impact stress exists at the lower section of the central axis, with peak stress recorded around the jet hole. The peak impact stress on the dam’s upstream surface exhibits a positive correlation with increasing casting speed. Variations in the distance between the weir and long nozzle show minimal effects on the peak impact stress, yet significantly alter the stress distribution around the jet hole. The impact stress distribution shows non-uniform characteristics at 1 400 mm, but demonstrates significantly improved uniformity at 1 800 mm.

Aiming at the bulging deformation and internal quality defects of 510 L slab of automobile beam steel, a slab solidification heat transfer model was established to study the effects of different casting speeds and specific water flow on the slab solidification process and shell thickness, and the effect of soft reduction process characteristic parameters on the quality defects of slab core before and after process optimization was analyzed. Based on the simulation analysis of solidification heat transfer and production conditions, the specific water flow of secondary cooling was increased from 1.01 L/kg to 1.41 L/kg; the soft reduction position was optimized from three segments to two segments and the reduction amount was adjusted. The results showed that the bulging deformation of the slab is the largest at the entrance of the first segment. After the process optimization, the shell thickness at the entrance of the first segment increases from 39.05 mm to 40.78 mm, and the bulging deformation decreases from 0.69 mm to 0.51 mm. The reduction rates of the 7th and 8th segment increase to 0.94 mm/m and 1.19 mm/m, and the overall internal quality of the slab is significantly improved. The center segregation rating is reduced to C 0.5, and the porosity is 0.5.

In order to optimize the metallurgical effect of four-strand tundish for extra-large round billet, the flow control devices were explored and optimized through physical simulation experiments firstly, and the influence of U-shaped baffles with different parameters, turbulence inhibitor and dam on flow field was analyzed. The optimal flow control device was selected. And then the flow field, temperature field and concentration field of tundish before and after optimization were simulated and verified by CFD/FLUENT software. Through the physical and numerical simulation, it is found that the flow field and temperature field of optimized tundish are greatly improved. The actual average residence time, stagnation time and peak time of each outlet are extended and the consistency is increased to more than 80%. The proportion of dead zone volume decreases from 32.18% of bare tundish to less than 10%, and the proportion of plug flow volume increases from 9.52% to more than 20%. The maximum temperature difference of tundish decreases from 39.01 K of bare tundish to 16.22 K, and the temperature difference of each outlet decrease from 3.15 K of bare tundish to 0.31 K.

As an important operation procedure in continuous casting process, tundish casting can be divided into two stages: steady casting and unsteady casting. Although the unsteady casting process is short, the pollution caused by the process is often the most serious. In order to reduce the pollution of molten steel during the unsteady and steady casting process and improve the quality of liquid steel, the parameters in tundish were optimized better, and a second-flow tundish water model with geometric similarity ratio of 1∶4 was established. The tracer experiment, residence time distribution (RTD) experiment and three-phase cold water model experiment were carried out respectively. The effects of insertion depth and filling flow rate on the flow pattern, mixing characteristics and the evolution of slag-steel interface were analyzed. Experimental results from steady casting tests demonstrate that both the average residence time and dead zone volume fraction decrease with increasing flow rate at the long nozzle. Additionally, increasing the insertion depth of the long nozzle extends the average residence time of liquid steel from 226 to 246 s. In the unsteady casting test, it is found that the slag layer will appear in the filling process, that is, the slag eye will appear around the long water outlet, and the slag eye will not disappear immediately after the filling of the stable stage. The increase of the filling flow rate and the insertion depth of the long water outlet will lead to the increase of the area of the slag eye and the increase of the appearance time of the slag eye in the re-stability stage. When the insertion depth of the long water outlet is 90 mm, the charging flow rate increased from 2.18 to 3.30 m³/h, the maximum slag hole area increased from 1 871 to 19 001 mm², and the existence time of the re-stable slag hole also increased from 41 to 232 s. Considering the overall performance during the pouring stage, a long nozzle insertion depth of 90 mm demonstrates optimal performance.

The distribution law of heat flow inside the mold is crucial for calculating the temperature field of the casting billet, which will affect the process design of high casting speed. The average heat flux empirical formula, the maximum heat flux and the heat flux distribution formula related to the high drawing speed range in the literature were studied and analyzed. Based on the measured data of high speed for billet, the average heat flux formula was proposed. In response to the problems in the heat transfer distribution law of mold in the calculation and simulation of high speed temperature fields, the method for determining heat flux distribution was improved. The results show that the average heat flux fitting formula suitable for high pulling speed is 1.34·v_c^0.502 (v_c unit: m/min), and the simulated average heat flux is consistent with the measured value. According to this method, the average heat flux obtained by simulating the heat flux distribution of the mold is strictly equal to the given (according to regression or on-site measurement) average heat flux, ensuring that the calculated heat flux of the model is the same as the measured one. Combining with the actual example of high speed of billet, the decisive influence of heat flow distribution in the mold on the calculation results is demonstrated, and the selection of model coefficients is discussed. The most important thing is that the distribution index n is around -0.5, which is related to the variation of shell thickness in mechanism analysis.

Linear slag defects, classified into parallel double-line, strip-type, and blister-type morphologies based on their characteristic features, have been identified as the predominant quality issue in cold-rolled automotive sheet production. Through systematic analysis, the formation mechanisms of these defect morphologies were determined to be correlated with the entrapment depth of liquid slag in the slab and its subsequent exposure characteristics during rolling. The defect distribution characteristics were quantitatively established, with parallel double-line and strip-type defects being predominantly observed at an average depth of 5 mm beneath the slab surface, with 95% of occurrences confined within an 8 mm subsurface layer. A proprietary defect tracing system was employed, revealing that 80% of cold-rolled slag defects were inherited from hot-rolled products, with slag entrapment primarily occurring within 200 mm of the mold meniscus. The mold flow field dynamics were investigated through combined thin steel plate and deflection rod measurement techniques, enabling both qualitative and quantitative characterization. Based on these findings, an optimized argon injection strategy was developed, incorporating low flow rates, increased nozzle immersion depth, and enhanced downward angle. This technological innovation resulted in the proportion of meniscus fluctuations within ±3 mm being elevated from 55% to over 90%, leading to a significant reduction in linear slag defect occurrence rates.

Tundish plasma heating technology could reduce the tapping temperature and superheat fluctuation range, as well as improve the quality of casting billets, whose equipment has the advantages of easy installation, high heating efficiency, and low energy consumption. Focusing on the hot issues related to tundish plasma heating technology, the equipment characteristics were systematically described, the application progress of plasma heating technology in slab production was introduced, and the metallurgical effects of plasma heating technology in practical applications were analyzed. The effect of the device on the temperature, chemical composition, and inclusion removal in molten steel was revealed. It is demonstrated that the first domestically developed new hollow graphite electrode heating device has achieved a breakthrough in tundish heating technology. It effectively meets the production requirements of low-, medium-, and high-carbon steels, offering an effective solution to the problem of temperature heat loss in the tundish, and achieving the goal of energy-saving and consumption reduction.

Ti-bearing steel in continuous casting process exists serious problems such as nozzle clogging and steel slag reaction. The interface behavior of mold flux with different basicity on TiC substrates were investigated by the sessile drop method, which can provide a theoretical basis for optimizing the composition of the mold flux for Ti-bearing steel. Firstly, the evolution law of wetting behavior with temperature in the contact process between mold flux and TiC was analyzed. As the increase of the basicity of mold flux, the wettability between mold flux and TiC substrate gradually decreased, and the contact angle was CS slag(CaO-SiO₂, 19.8°)>CSA slag(CaO-SiO₂-Al₂O₃, 20.9°)>CA slag(CaO-Al₂O₃, 31.5°). The results show that there is no interfacial reaction behavior between the mold flux and the TiC, but there is a mass transfer process between the two interfacial phases. The basicity of mold flux is an important factor affecting the mass transfer process between mold flux and TiC interface, and the increase of basicity can inhibit the mass transfer process. The SEM-EDS analysis results show that the interaction layer between CS slag and TiC inclusion is the thickest, about 30-80 μm, and the absorption capacity of CS slag to TiC inclusion is the strongest. On the contrary, the interaction layer between CA slag and TiC inclusion is the thinnest, about 30-50 μm, and the absorption capacity of CA slag to TiC inclusion is the worst.

Continuous casting is one of the most critical processes in steelmaking. The occurrence of breakouts during continuous casting is influenced by multiple factors, with sticker-type breakouts being the most prevalent, accounting for approximately 70% of all breakout incidents. Breakout accidents in continuous casting can lead to molten steel leakage, posing severe safety hazards such as scalding, fires, and even explosions. These incidents may result in casualties and significant property damage. In view of the above difficulties, the factors influencing the bonded steel leakage of continuous casting from the process parameters of continuous casting production are systematically sorted out and the influence of slab size, casting speed, cooling water and heat flow on the bonded steel leakage of slabs are analyzed. The analysis of bonding in slabs with different widths (1 350, 1 500 and 1 550 mm) shows that the average heat flow fluctuates most significantly in the 1 550 mm thickness slab, and as the slab width increases, the fluctuation in average heat flow becomes more pronounced, leading to a higher likelihood of slab bonding. And for slabs with large wide surface sizes, a reasonable drawing speed should be selected during production to avoid the occurrence of bonding accidents. Finally, preventive measures are proposed to avoid bonded steel leakage, addressing process parameters, personnel operations, and management systems. These recommendations provide theoretical and technical support for the safe production of continuous casting.

Continuous casting is a key process in steel production, serving as an intermediate step between steelmaking and rolling. In order to reduce the computational power requirements of the slab identification model in practical deployment, the research on lightweighting the slab identification model while ensuring its accuracy was conducted. Initially, a detection algorithm based on the AD-PAN feature fusion structure incorporates the lightweight MobileNetV3 backbone network to extract features of the slab numbers, with the goal of enhancing image classification performance while maintaining the model's lightweight characteristic. Subsequently, the model underwent Collaborative Mutual Learning (CML) distillation to ensure the precision of slab number detection. Ultimately, experimental comparisons were conducted to assess the performance of the lightweight model. The outcomes demonstrate that although there was a modest trade-off in model accuracy due to the lightweight research, there was a significant reduction in the model's parameter volume and a marked improvement in the model's detection speed.

To accurately calculate the transport behavior in the mold, considering the bending of the continuous casting bloom in the second half of the mold and in the secondary cooling zones, according to the bloom continuous casting using a curved continuous caster in a domestic special steel plant, a three-dimension curved model was established including mold zone, segment 1 and segment 2 of secondary cooling zones. The effect of casting speed, superheat, and inner diameter of submerged entry nozzle (SEN) on the fluid flow, heat transfer, solidification, and macrosegregation in the mold was investigated. With the casting speed increasing from 1.1 to 1.5 m/min, the speed of molten steel in the mold increased significantly, and the shell thickness near the outlet of the mold decreased from 15.0 to 11.0 mm. The minimum mass fraction of carbon in the negative segregation band of the subsurface of the bloom increased from 0.117% to 0.119%. When the superheat increased from 10 to 50 K, the speed of molten steel in the mold changed little, and the shell thickness near the outlet of the mold decreased from 13.1 to 10.0 mm. The minimum mass fraction of carbon in the negative segregation band of the subsurface of the bloom decreased from 0.120% to 0.117%. With the inner diameter of SEN increasing from 30 to 40 mm, the speed of molten steel in the mold decreased gradually, and the shell thickness near the outlet of the mold decreased from 10.9 to 10.2 mm. The minimum mass fraction of carbon in the negative segregation band of the subsurface of the bloom decreased from 0.119% to 0.118%. Appropriately increasing the casting speed, reducing the degree of superheat, and using a thinner nozzle can not only satisfy a certain solidification shell at the mold outlet, but also improve the negative segregation in the subsurface of the bloom.

Both the pre and prost processing modules for the calculation of heat transfer and solidification in continuous casting were compiled to integrate with ProCAST simulation software by the treatment of bow geometry of the caster machine and the non-uniform water spray flux in the secondary cooling zone. The temperature distribution and solid fraction in both the longitudinal and transverse sections of the extra-thick slab were obtained by the numerical simulation of the practical continuous casting process. The results show that the liquid pool in the shape of “W” would form in the central broad section of the slab with the less water flux in the edge compared to that in the central broad face. The solidification homogeneity in the slab cross section could be improved by adjusting the spray flux in the secondary cooling zone.

In the continuous casting process, numerous factors influence product quality, among which the temperature control of steel billets is particularly critical. Excessively high temperatures can cause surface oxidation of billets, leading to resource waste, while excessively low temperatures can reduce billet plasticity. The secondary cooling zone regulates strand temperature in continuous casting via water spray systems, with spray intensity being the dominant control parameter for surface temperature. Malfunctions in the cooling water system, improper operation by on-site personnel, or delayed maintenance can sometimes affect the spray volume of the secondary cooling nozzles, leading to water leakage. Such leakage leads to excessive water accumulation in localized regions of the strand, inducing severe localized cooling that generates thermal stresses sufficient to cause cracking defects. This paper employs infrared imaging, utilizing machine vision and a water leakage detection algorithm to separate foreground objects from the background in video streams, enabling precise identification of water leakage in spray equipment. Experimental results demonstrate that this method effectively detects leakage areas in secondary cooling nozzles, achieving a 100% alarm accuracy rate during testing, thereby providing technical support for subsequent maintenance.

For the continuous casting of high-speed small square billets, a solidification heat transfer model was constructed. A dual-mode water spray control algorithm based on the target surface temperature and effective casting speed was proposed, and front-end and back-end applications with a B/S architecture were developed using JAVA and VUE. This model was applied to the production of HRB400 steel grade on a 170 mm × 170 mm square billet continuous caster for practical verification. After application, the low magnification quality of the billets was significantly improved. The proportion of central segregation better than grade 1.5 increased by 3.5%, and the proportion of central porosity better than grade 1.0 increased by 1.2%.

In order to meet the automotive steel plate with very strict and high-grade surface quality requirements, inclusions with size larger than 5 μm in the internal arc within 0.5-5.0 mm of different types of slabs was studied by using ASPEX based on industrial test and sampling. The samples with machined to a depth of 3 mm and non-machining of hot rolled plates were quantitatively analyzed and evaluated. The results show that inclusions are concentrated within 0.5-3.0 mm from the top surface of the slab, and with the increase of the distance from the surface, the number density of inclusions gradually decreases, the number density of inclusions decreased from 2.25 to 1.32 per/mm² when the distance from the surface was 0.5 to 3.0 mm in the first slab. The number density of inclusions tended to be stable at 1.25 per/mm² within 3.5-5.0 mm from the surface. The number density of inclusions decreased from 0.89 to 0.71 per/mm² when the distance from the surface was 0.5 to 3.0 mm in the normal slab. The number density of inclusions tended to be stable 0.63/mm² within 3.5-5.0 mm from the surface. The inclusion type of non-scarfing plate is the same as that of scarfing plate. The inclusions in the plates are mainly Al₂O₃, TiN and Al₂O₃-TiN composite inclusions. The comparison of the number density of inclusions shows that the number density of inclusions is 0.64 and 0.88 per/mm² in the scarfing and non-scarfing plate, respectively.