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.

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.

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.

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.

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.

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 development of the modern industrial level puts more demanding on the comprehensive performance of special covering powder for plasma heating tundish. The design of the base composition of the covering powder directly determines its metallurgical properties. The covering powder should have a good adsorption and removal effect of inclusions in the liquid steel while taking into account the thermal physical properties, refractory erosion resistance and have a good foaming and submerged-arc effect. Based on the ion-molecule coexistence theory (IMCT), and the corresponding phase diagram and thermodynamic data, the mass action concentration calculation model of structural units and ion pairs in the CaO-Al₂O₃-SiO₂-MgO-Fe₂O₃ plasma heating special capping agent, and the desulfurization thermodynamic model of the slag system at 1 800 K were established. By writing a MATLAB program to call the function to solve the mass action concentration of structural units or ion pairs, we obtained the trends of N_SiO2,N_CaO,N_MgO and N_Al2O3 with the increase of MgO content in the slag system, and carried out industrial tests to verify the actual desulfurization effect of the slag. Industrial tests show that the matching use of the covering powder and plasma enables the further removal of sulfide inclusions in the steel and improves the level of steel cleanliness. The theoretical model and industrial test results corroborate each other well, and the results show that in the range of 0-12 mass%, with the increase of MgO mass fraction, the kinetic and thermodynamic conditions of the desulfurization reaction can be improved; the desulfurization capacity of the slag system has been greatly improved, which provides the necessary theoretical basis for the use and optimization of the covering agent in the future.

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.

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.

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.

The influence of immersion depth of the submerged entry nozzle on the mold flow field was studied by combination of numerical simulation, water simulation and high-temperature measurement. The results show that the results of the numerical simulation, water simulation and high temperature measurement of the surface velocity are in good agreement. When the immersion depth is increased from 140 to 155 and 170 mm, the molten steel surface velocity at 1/4 width of mold increases first and then decreases. Under the conditions of three immersion depths, the flow field in the mold presents a double circulation flow. The molten steel near the narrow wall and 1/4 width of mold flows from the narrow wall to the nozzle, while the molten steel near the nozzle flows from the nozzle to narrow wall. As the immersion depth of SEN is increased, the liquid level fluctuations near the narrow surface and 1/4 width gradually decrease, and the results of water simulation and numerical simulation are in good agreement.

The slag entrainment during the continuous casting (CC) process is one of the primary sources of large inclusions in CC slabs, and it is also a significant factor causing surface quality defects. In the current study, a three-dimensional numerical model based on an actual 1 300 mm × 230 mm slab CC mold was established. The molten steel-slag phase-air phase-argon gas transient multiphase flow inside the mold was investigated by coupling the large eddy simulation turbulent model, VOF multiphase flow model, and discrete phase model. Moreover, the occurrence of the slag entrainment on the meniscus and the variation of the size, number, and spatial distribution of slag droplets were quantitatively predicted using a user defined function. The results indicate that the flow pattern in the mold was a typically double roll flow with the current 1.4 m/min casting speed, 160 mm immersion depth of the submerged entry nozzle, and 6 L/min argon flow rate (stopper rod and upper nozzle) condition. The interaction between the jet flow and argon bubbles resulted in a fan-shaped distribution of argon bubbles inside the mold. The net slag entrainment rate on the meniscus was 0.005 24 kg/s. The slag entrainment occurred primarily near the 1/4 width of the mold and 130 mm away from the nozzle center in width direction of the mold, which was induced by the shear effect of the upper circulation flow and the vortex generated by the complex flow, respectively. The number of entrained slag droplets inside the mold exhibited transient variations, with most droplets having diameters between 2-5 mm. Density differences resulted in most entrained droplets ultimately refloating to the slag layer.

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.

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.