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.

Taking 42CrMo4 round billet with a section size of ϕ800 mm as the research object, a large round billet model was established with ProCAST finite element method and CAFE method. The effects of superheat, drawing speed and specific water volume in secondary cooling zone on solidification behavior and grain structure were compared. The results show that the influence of the drawing speed on the solidification temperature, solidification end point and the thickness of the solidified billet is greater, while the influence of superheat on the grain growth is greater. When the drawing speed is increased by 0.02 m/min, the solidification end point moves back about 3 m, and the change of superheat and specific water volume in the secondary cooling zone has no obvious effect on the temperature and central solid fraction. When the superheat is increased from 10 ℃ to 55 ℃, the equiaxial crystal rate decreases from 43.2% to 9.2%, while the influence of pulling speed and secondary cooling zone specific water volume on the equiaxial crystal rate is not obvious, and the change is less than 8%. Based on the electromagnetic stirring position of the end, an optimization scheme was proposed for the existing process. The superheat was reduced to 10 ℃, the specific water volume was reduced to 0.16 L/kg, which could effectively improve the equiaxed crystal rate and refine the grains.

Continuous casting is one of the most important processes in steelmaking. There are many factors affecting the breakout accidents in continuous casting process, among which the sticker breakout is the most common, accounting for about 70% of the total breakout. In order to better solve the sticker breakout accident, clarify the cause and provide a theoretical basis for establishing a more comprehensive and accurate prediction model, the occurrence mechanism, influencing factors and prediction model of sticker breakout in continuous casting were summarized and analyzed. The influence of mold power performance, molten steel conditions, crystallizer parameters, personnel operation and other factors on the sticker breakout accident law was mainly discussed. For the current commonly used logical judgment breakout prediction model and machine learning-based breakout prediction model, the current research status was analyzed, and the current shortcomings were put forward. It is predicted that the breakout prediction system will continue to develop in the direction of intelligence and high-end in the future, which provides a reference for the research of sticker breakout and how to effectively prevent it.

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.

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.

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.

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.

During the continuous casting process of steel, the microsegregation and macrosegregation will caused by the uneven distribution of solute elements. It should be noted that the macrosegregation in the billet cannot be removed by the subsequent heat treatment or rolling process, and it affects the product properties. Therefore, it is of great significance to simulate the macrosegregation by considering the microsegregation behavior, which aims at enchancing the simulation accuracy of macrosegregation, and improving the quality of billet and the performance of products. In this work, a macrosegregation model that couples microsegregation behavior in order to compare macrosegregation behavior with different microsegregation models was established. The best solute microsegregation will be chosen, and accurate prediction of solute macrosegregation behavior in continuous casting billet will be realized. Besides, the Won-Thomas microsegregation model was used to investigate the effects of secondary dendrite arm spacing on the solidification end point and macrosegregation defects for 82B cord steel billets, when the spacing of the secondary dendrite arms is reduced from 200 mm to 40 mm, the solidification end point is shifted forward by 1.4 m, and the carbon mass fraction in the center of the continuous casting billet decreases from 0.154% to 0.138%, indicating that the larger the spacing of the secondary dendrite arms, the slower the cooling and the more serious the segregation, and the rationality and reliability of the model were verified through a carbon sulfur analyzer.

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.

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.

Based on the full process control of steelmaking-hot rolling-cold rolling (heat treatment) process, a digital platform for full process quality control was built using modern data communication and database (data cloud), and an online quality rating system for continuous casting slab was developed based on this platform. This digital platform for quality control throughout the entire process monitors and tracks the parameters of raw materials, production, processes, equipment, and other aspects in the steelmaking process in real time. The tracking results are fed back to each furnace and slab in the form of process events. By formulating corresponding rules, continuous casting slabs are graded and evaluated to achieve online real-time prediction and evaluation of continuous casting slab quality, in order to determine the grading and repair treatment method of continuous casting slabs. The quality inspection and judgment results of the subsequent rolling process show that the quality rating system can classify and screen continuous casting slabs with different quality risk levels more intuitively and accurately, reducing the proportion of slab defects and improving the quality of continuous casting slabs.

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.

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.

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 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.

In order to improve the internal quality of 42CrMoA steel in a factory and reduce the casting of billet center segregation, the ProCAST software was used to simulate the casting of billet solidification structure, and the effect of continuous casting parameters on the distribution of solidification organization, the rate of equiaxial crystal and equiaxial crystalline area density was studied. When the casting speed was increased from 0.8 to 1.1 m/min, the proportion of equiaxial crystal zone has increased by 5.26%; When the cooling water flows increases from 0.144 to 0.192 L/kg, the proportion of equiaxial crystal zone has decreases by 3.34%; The superheat increases from 5 to 35 ℃, and the proportion of isometric crystal zone decreases by 7.98%. It is concluded that it is possible to reduce the macroscopic segregation of 42CrMoA steel by appropriately increasing the casting speed, decreasing the amount of water in the second cooling ratio and reducing the superheat of the steel.

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.

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.

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 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 order to solve the problem of internal cracking of vanadium-containing steel in the continuous casting process, the solidification process analysis, organization prediction and surface temperature control of HRB500E rebar steel were carried out by using thermodynamic calculations, solidification organization simulation and the method of second-cooling water distribution control. It was found that the thermodynamic precipitation temperature of V(C,N) in the rebar steel was 1118 ℃ and the maximum precipitation amount was 0.06 wt%, which indicated that vanadium had the dual raction of precipitation strengthening and solid solution strengthening; the organization analysis of the as-cast billet showed that when vanadium was increased from 0 wt% to 0.089 wt%, the grain radius was reduced by 2 times, the number of grains was increased by 2.8 times, and the central equiaxial crystal was increased by 2.2%. It shows that the addition of vanadium can refine the grain, improve the organizational properties and gain metallurgical properties; at the same time, it is found that the reason for cracks and other defects is mainly due to the unreasonable water distribution of the second cold, resulting in the surface of the billet return temperature is too large. Based on this, a corresponding optimization of secondary cooling water distribution process has been proposed, along with the introduction of a three-section program for 2.9 m length of secondary cooling process, and ultimately designed a 1.4-2.7 m/min pulling rate of the water table, the surface of the billet return temperature was below 100 ℃ and the return temperature met the metallurgical guidelines. Industrial production has proved that the internal quality of billet has been greatly improved by the optimization of water distribution in the secondary cooling.

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.

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.

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.

The technology of feeding steel strip to mold in continuous casting process is an effective method to control the temperature field distribution of molten steel and restrain or reduce the internal defects such as central segregation and central porosity. However, the continuous casting process is invisible at high temperature, so it is impossible to observe and measure the evolution of solidification structure in the mold online. A visual solidification experiment system was set up to investigate the effects of no cold strip, fixed cold strip and vibrational strip feeding on the microstructure evolution of NH₄Cl-70% H₂O solution during solidification. The results show that: firstly, feeding cold strip can significantly reduce the superheat in the center of mold, fuse dendrites, effectively increase the number of free grains, and then increase the volume ratio of equiaxed grains in solidification structure. Secondly, the superheat in the mold center decreases more rapidly after the cold strip is vibrated, and the nuclei formed by fusing are more and finer, and the proportion of equiaxed crystal volume increases further. The proportion of equiaxed crystal volume under three conditions of no cold strip, fixed cold strip and vibrational feeding strip is 26%, 31% and 36%, respectively.

To improve the solidification microstructure of CuNiCoSi rectangular continuous casting billets, a CuNiCoSi rectangular billet cross-section solidification microstructure model was established using the CA-FE method. The effects of different superheats and pulling speeds on the solidification microstructure were investigated using this model. The results indicate that reducing superheat can increase the proportion of equiaxed crystal zone in the solidification microstructure and improve the uniformity of the equiaxed crystal zone. Keeping other conditions constant, decreasing superheat from 30 ℃ to 15 ℃ resulted in an increase in the equiaxed crystal zone area from 42.90% to 47.32%, while the maximum equiaxed grain area decreased from 42.06 mm² to 33.94 mm². Increasing the pulling speed can increase the proportion of equiaxed grains in the solidification structure and obtain finer equiaxed grains. Increasing the pulling speed from 100 mm/min to 400 mm/min resulted in an increase in the equiaxed crystal zone area from 42.48% to 50.14%, while the average equiaxed crystal area decreased from 10.59 mm² to 9.38 mm². After optimizing the superheat and pulling speed, the quality of the billet solidification microstructure has significantly improved.

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.

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.

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.

Mold flux is an important functional material in continuous casting. In order to accurately, quickly, and low-costly obtain the physical and chemical properties of mold flux, a model was established for predicting the physical and chemical properties of the mold flux (composition, melting point, melting rate, and viscosity data) using BP neural network combined with particle swarm optimization (PSO) algorithm based on the testing data from laboratory. Thirteen untrained test samples were selected to test the prediction accuracy of the PSO-BP model. The results showed that compared with the BP neural network prediction model, the average absolute errors of melting point, melting rate, and viscosity were reduced from 8.9 ℃, 4.7 s, and 0.012 Pa·s to 8.1 ℃, 2.8 s, and 0.010 Pa·s, respectively. Moreover, the error fluctuations of individual samples were reduced, and the overall prediction accuracy was improved. Based on this model, the influence of single or multiple changes in the composition of mold flux on the physical and chemical properties was studied. By controlling other components to remain unchanged, when the basicity increased from 0.8 to 1.2, the viscosity value decreased from 0.23 Pa·s to 0.18 Pa·s. In addition, the effects of single variable adjustment and simultaneous variation of Al₂O₃ and MgO on the viscosity performance of mold flux were demonstrated. The model calculation results were consistent with actual theoretical laws, indicating that the predictive model of mold flux based on PSO-BP neural network can be applied to the development and research of mold flux, shorten the research cycle, and reduce costs.

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.

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.

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.

Slag entrapment in the continuous casting bloom has a significant effect on the sub-skin temperature, shell thickness, first principal stress and equivalent stress. Based on the temperature inheritance algorithm, a two-dimensional transient thermal conductivity model of steel solidification was established by using ANSYS finite element software to analyze the behavior of slag entrapment on bloom heat transfer and stress. In common 1/4 position from the center of the continuous casting bloom, the 10 mm wide and 4 mm deep protective slag is usually found. The study shows that with the slag entrapment, the sub-skin temperature rises by 60 ℃ in average, the shell thickness becomes 3.3 mm, the first principal stress distribution is uneven and locally smaller, and the equivalent stress becomes smaller.

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.

Aiming at the problem of whether there are certain key characteristic shape subsequences in high-frequency time series in industrial control processes and the specific location of this subsequence in the time series, identification and positioning algorithm for key shape characteristic subsequences in industrial time series is proposed based on shapelet. Shapelet are the most discriminative continuous subsequences in time series. The shapelet set can be applied to the similarity calculation of subsequences of different lengths, and the sequence identification results are interpretable. In order to improve the speed and accuracy of identifying and positioning key shape characteristic subsequences in time series, shapelet sets with specific shape are first extracted and screened from the time series data set based on genetic algorithms. Secondly, the method of data standardization and sliding Euclidean distance is used to calculate the similarity measurement value between the shapelet and the subsequence in the time series, which is used to evaluate the similarity of shape characteristic. Then, the concepts of adaptive similarity threshold and lag time are defined to achieve accurate identification and positioning of characteristic shape subsequences existing in time series and improve the recognition accuracy of key shape subsequences. Finally, the feasibility and accuracy of the method were verified using public standard data sets and time series data of casting speed during continuous casting process.

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.