Electromagnetic stirring(EMS) technology plays an important role in the cooling solidification process of molten steel for high efficiency continuous casting process, which can effectively improve the internal and external defects of continuous casting billets. Specifically, the EMS technology takes the benefit of the generation of Lorentz force to optimize the molten steel flow, so as to decrease flow instability, mold powder entrapment, and surface defects and the bloom quality is improved obviously. For this purpose, to gain a clear understanding of the effect of EMS technology on the continuous casting process, the principle of electromagnetic stirring is briefly expounded. Also, the latest research progress of mold electromagnetic stirring(M-EMS), secondary cooling zone electromagnetic stirring(S-EMS), final electromagnetic stirring(F-EMS) and electromagnetic stirring combination technology in continuous casting is analyzed in detail. The problems encountered in the application of electromagnetic stirring in continuous casting and the improvement ideas are pointed out. Finally, the future development trends of electromagnetic stirring are prospected.

The tundish plays the role of connecting the upper and lower levels in the continuous casting process of molten steel, and undertakes the role of diversion, pressure stabilization, component adjustment and temperature control. As the last refractory container in contact with molten steel, the tundish is regarded as an ideal place for the floating removal of non-metallic inclusions due to its large volume and stable flow conditions. With the increasing requirements of the quality of continuous casting billet and the cleanliness of molten steel, the function of tundish metallurgy has attracted more attention from researchers. Many advanced tundish metallurgical technologies have been developed. Researchers have investigated the multi-phase transport phenomena in the tundish with novel approaches, through water modeling, numerical simulation, on-line measurement, and so on. Based on the research status of tundish metallurgy in recent years, the new technologies of tundish metallurgy, including induction heating of tundish, micro-bubble metallurgy and porous ceramic filtration of inclusions are reviewed. The further progress of tundish metallurgy is also discussed.

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.

With the development direction of ultra-wide and ultra-thick design of caster, it is necessary to re-evaluate the flow field characteristics of casters under extreme conditions. Based on the probable future designs of ultra-wide slab caster in China, the numerical simulation is established for the flow of molds with large cross-section of 3 300 mm×180 mm, and the flow characteristics of molds with three typical slab continuous casting nozzles were studied. The results show that the flow field of the two-orifice nozzle mold is a classical double-circulation flow pattern, while the five-orifice nozzle mold increases the disturbance of the molten steel at the nozzle and the central axis. The flow field of the CSP-type water port casting mold is a large bottom-up circulation. The fluctuation of the liquid level of the five-orifice water orifice not only ensures the fluctuation of the liquid level within the safe value range, but also increases the disturbance of the flow dead zone of the meniscus, whose optimization effect of the flow field is remarkable. The typical structural parameters of the five-hole water outlet are as follows: the angle of the main side hole is 10°-20°, the insertion depth is 150-160 mm, and the distance between the main and secondary holes is 10-20 mm.

Mold fluxes play important role in ensuring the smooth casting and slab quality, which is closely related to the properties of mold fluxes. The viscosity and melting temperature of mold fluxes are key parameters in the design and production of mold fluxes; however, the determination of property is time-consuming and labor-intensive. In view of the development of machine learning technology, three machine learning algorithms including KNN, KRR and RF were employed to establish the prediction model to accurately predicting viscosity and melting temperature of mold fluxes, providing a guide to the fast and convenient design of mold fluxes. The experimental results show that compared to other two models, KRR-based model has the best performance in the viscosity prediction, in which the coefficient of determination (R²) is 0.983, the root mean squared error (RMSE) is 0.023, and the mean absolute error (MAE) is 0.014. The RF-based model is more reliable in predicting the melting temperature with R² of 0.823, RMSE of 14.004, and MAE of 8.974. The ranked importance analysis of the input features shows that the order of influence of viscosity is SiO₂, F, and Al₂O₃ and Na₂O has the greatest influence on melting temperature. Compared with the widely used viscosity and melting temperature prediction models, the mean relative errors (MRE) of the KRR-based viscosity prediction model and the RF-based melting temperature prediction model are 6.26% and 0.83%, respectively, which are much lower than MRE of the widely used prediction models, indicating that the machine learning-based models have a high reliability. Moreover, the viscosity and melting temperature distribution maps established based on the models could provide intuitive reference for the design of mold fluxes.

In order to improve the metallurgical effect of “T” shaped billet tundish, we researched the flow field and temperature field in tundish by numerically and physically simulated methods. Through analyzing the influence of the size of impact zone, opening angle of stabilizer, opening elevation angle of stabilizer and the type of vertical wall of stabilizer on the flow field, we had obtained the optimum tundish size and the tundish structure for the profiled billet. The industrial test shows that the metallurgical effect of the improved tundish is obviously better than that of the original tundish. The results of temperature measurement and sampling before and after tundish optimization show that the average temperature difference between the first and the third flow and the second flow decreases from 11.8 ℃ to 3.95 ℃, and the reduction is more than 66.5%. After optimization, the mass fraction of oxygen and nitrogen in 1 and 2 streams are the same, and the average mass fraction of oxygen decreases by 17.17%.The flow field of the optimized tundish is obviously better than that of the original tundish. The improved tundish is beneficial to the uniformity of molten steel temperature, composition and the improvement of billet cleanliness and surface quality. After optimization, the slag line erosion of face tundish is also improved, which is reduced from 55 mm in 32 h to 45 mm in 48 h, and the tundish life is increased remarkably.

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.

In order to solve the problems of low metal yield rate and insufficient modification of inclusions in high Al steel with traditional feeding calcium wire technology, feeding composite calcium aluminate cored wire was fed into molten steel. The melting behavior of composite cored wires with different diameters in molten steel as well as the effect of feeding cored wire on the flow field of molten steel and the removal ratio of inclusions were studied by the numerical simulation and water model test methods. The numerical simulation results of the cored wire melting showed that the composite cored wire with a core powder diameter of 11 mm and a skin thickness of 1.07 mm satisfied the ideal condition for feeding speed of 2-4 m/s. The water model experiment results of feeding composite cored wire showed that when the feeding depth was 100-300 mm, the removal ratio of inclusions ≤ 50 μm, 50-100 μm and 100-150 μm increased by 3.29%, 2.71% and 2.56%, respectively. When the feeding depth was 100 mm from the bottom of the ladle, with the composite core powder size increasing per 50 μm, the removal rate of inclusions ≤50 μm, 50-100 μm and 100-150 μm increased by 4.58%, 3.01% and 2.42%.

To further reduce the mixing length of grades transition in the slab casting process, research on accurate prediction of mixing process and transition slab division had been carried out in view of the time-varying control and its influence on the composition mixing in the continuous casting process. Through the industrial test, the influence of the amount of remaining steel in the tundish and the casting speed on the composition mixing during the transition casting process had been investigated. It has been found that with the same casting speed and section size the smaller the amount of remaining steel in the tundish is, the closer the mixed composition is to the composition of the subsequent heat in the position of 5 m after new heat opened, which is the main influencing factor, and with the same residual tundish weight and section size the smaller the casting speed is, the closer the mixed composition is to the composition of the subsequent heat in the position of 5 m after new heat opened, which is the secondary influencing factor. By collecting the production data of continuous casting process and combining the numerical simulation results, a time series model based on LSTM neuron network has been established. Through the offline calculation of the model, it is found that the lower residual steel in the tundish in the early stage can accelerate the mixing process in the case of equal average tundish weight during mixing process. Deployed model online results show that the average prediction deviation is 3.69%, and the accuracy meets the actual production needs.

IF steel is produced by the LF-RH-CSP process in a domestic steel mill, the process has high requirements for the C and N content and the cleanliness of the molten steel. Samples were taken and analyzed at different process nodes to investigate the main source of increasing C and N and the variation of composition, size, and quantity of inclusions in the LF-RH refining process. The results show that the heating slag-making and the slag modification are accompanied by bottom argon blowing and strong stirring phenomenon, which exposes the molten steel and thus lead to a severe C and N increase. The inclusions are mainly irregular Al₂O₃ after Al deoxidization in the LF station, and the inclusions are transformed into MgO·Al₂O₃ spinel during LF slagging and leaving the LF station. The inclusions are MgO·Al₂O₃ and a few single Al₂O₃ after secondary Al deoxidization at the RH station, and all of the inclusions are modified into spherical CaS-12CaO·7Al₂O₃-MgO·Al₂O₃ composite inclusions when leaving the RH station. The inclusion number density shows an overall downward trend, the average diameter gradually decreases from 6.0 μm to 2.3 μm, and the cleanliness of molten steel is significantly improved. Thermodynamic calculations show a strong tendency for the generation of MgO·Al₂O₃ inclusions, which are the nucleation core of CaS-12CaO·7Al₂O₃-MgO·Al₂O₃ composite inclusions. A kinetic model of inclusion evolution was established. The research results provide theoretical support for optimizing the IF steel production process and improving the castability of the steel.

The production of high-speed continuous casting is the achievement and realization ways of the high efficiency, green and intelligent development of continuous casting. Aiming at realizing high-speed continuous casting, the mold is studied on the process control and equipment design, and the mold model is established. Based on the heat transfer analysis of mold, it is proposed that the key to optimize high-speed mold is to improve the homogeneity of Cu plate with the premise of increasing the cooling efficiency. By the multi-objective optimization, a new method to optimize the water seam of mold is proposed. After optimization, the hot surface temperature and the temperature difference of Cu plate of the mold are reduced significantly, which can obviously reduce the risk of breakout caused by the uneven cooling of the slab at high speed casting. This is of great significance for the promotion and application of high speed production technology of caster.

In order to solve the problem of poor steel flow consistency inside the four-stream tundish of a steel plant, the guide hole structure of the tundish baffle is designed, and turbulence suppressors are added to form a combined structure of the flow control device to optimize the flow field of the tundish. Orthogonal tests are designed for the structure of baffle deflector holes, and the residence time distribution (RTD) curves of each scheme are obtained through water modeling to determine the optimal structural parameters of the baffle deflector holes as well as the degree of influence of factors by combining with the polar analysis method and the actual situation. On this basis, turbulence suppressors of different structures were designed and combined with the baffle for water modeling, and the optimal production scheme was finally obtained. The results show that the scheme U2 is the optimal structure of the baffle. The parameters of the guide hole are 25° of vertical inclination, 140 mm in diameter, 400 mm in height, and 10° of horizontal inclination for the optimal structure. The dead zone ratio of this scheme is 17.83%, which is 2.12% less than that of the original scheme, and the flow consistency is improved by 84.61% compared with that of the original scheme. The flow behavior of the steel is optimal after the polygonal turbulence suppressors are applied in combination with U2. The dead zone ratio of this scheme is 16.1%, which is 3.85% less than the prototype tundish, and the flow consistency is improved by 71.54%. Compared with a single baffle structure, the combined structure of U-type baffle and polygonal turbulence suppressors can effectively reduce the dead zone ratio and the standard deviation of the stagnation time, significantly reduce the peak concentration of the water outlet, extend the peak time, enhance the consistency of the water outlet, and achieve the optimization of the flow field inside the tundish, which provides the theoretical basis for the subsequent development of the optimization of the flow field of the combination of flow control devices.

Aiming at the problem of the slag entrapment in the thin slab mold of a steel mill, the funnel mold was used as the research object, and the VOF method was established to model and calculate the steel-slag interface, and the 1:2 physical model and 1:1 numerical model were constructed to analyze the effects of casting speed, viscosity of mold flux and immersion depth on the flow field of the mold and the fluctuation behavior of the steel-slag interface. The surface velocity, the phase distribution at the steel slag interface, and the height of the liquid level fluctuation of the mold were chosen as the evaluation standard. The results show that the liquid level is relatively stable when the flow rate of steel-slag interface is 0.12-0.26 m/s and the viscosity of the slag is greater than 0.253 Pa·s. With the increase in immersion depth, the impact depth of the molten steel decreases, the range of the upper turning zone becomes larger, and the fluctuation height of the slag interface decreases to 5.4 mm. When the immersion depth is greater than 190 mm, the viscosity of the mold flux is 0.324 Pa·s, and the surface flow rate of the steel slag is less than 0.26 m/s, the appearance of slag rolling can be effectively inhibited, which provides a reference for improving the quality of the casting billet and the safety and stability of industrial production.

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 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.

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.

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.

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.

Through hot acid washing inspection of 55SiCr spring steel billets, it was found that there were longitudinal crack patterns on the inner arc surface of the 8th batch of billets in the 8th batch of casting. Energy spectrum analysis was conducted on the inclusions inside the crack, and it was found that the content of elements such as Na and F was relatively high, indicating that the inclusion of crystallizer protective slag was involved. To understand the causes of cracks, scanning electron microscopy was used to inspect the attached samples on the inner wall of the nozzle, and combined with the control of the steelmaking production process, research and analysis were conducted. The results indicate that the high content of Al_s in molten steel is the fundamental reason for the occurrence of longitudinal cracks on the surface of castings. Due to the tight production rhythm, the steel ladle used in this pouring is an aluminum containing steel turnover ladle. Before production, no aluminum free steel is used for ladle cleaning, resulting in a high content of molten steel with an Al_s content of ≤0.005 0%. The actual control is between 0.005 5% and 0.008 0%. During the casting process, Al₂O₃ inclusions formed by secondary oxidation accumulate on the inner wall of the nozzle, gradually forming large adherents. Due to the continuous erosion of high-temperature molten steel, the adherents on the inner wall of the nozzle suddenly fall off, causing a sharp change in the liquid level of each flow crystallizer. The liquid level of the 8th stream crystallizer is required to be controlled within the range of (70±5) mm, but at the end of casting, the liquid level of the crystallizer is controlled between 34-85 mm, and the casting speed of the billet changes from a constant drawing speed of 1.80 m/min to 1.4-2.0 m/min, with excessive fluctuations. The liquid level of the crystallizer loses control for a long time, lasting for about 30 minutes, causing slag inclusion on the surface of the casting billet. When the surface of the casting billet is subjected to tensile stress, stress concentration occurs at the slag inclusion position, resulting in longitudinal cracks. By implementing strict low aluminum control measures for alloy materials, refractory materials, and strengthening continuous casting protection pouring, there has been no problem of longitudinal cracks caused by slag inclusion on the surface of the billet, and the improvement effect is significant.

The star cracks are hidden in the subsurface of continuous casting slab, which are difficult to be detected in manual on-line inspection, and it is easy to cause a large number of peeling defects when the burning loss of heating furnace is insufficient. Through metallographic analysis of rolled piece and slab, it is clear that the cause of defects comes from star cracks of the slab. In view of the star crack of the slab using the full-arc continuous casting machine, the influences of typical elements (C, Al, N, V), cooling intensity of mold, slag in the continuous casting, secondary cooling strength and others on the crack defects of casting slab were analyzed. The causes of the cracks in casting slab were clarified that deep vibration marks and a large amount of precipitates form the crack initiation, and the slab is located in the brittle zone in the caster and suffers excessive stress. The effective measures to control the cracks are put forward, including reducing the contents of typical elements, increasing and stabilizing the casting speed, employing improved continuous casting slag, weakening the mold strength and secondary cooling strength, improving the quality of caster, etc. After a large number of actual applications, the crack defects of low alloy steel slab are reduced, and the peeling defect rate of hot-rolled plate is reduced from 21.84% to 0.47%.

The effect of electromagnetic stirring, degree of superheat and secondary cooling intensity on the homogeneity of 200 mm×200 mm continuous casting SWRH82B billet was studied and the influence of the homogeneity of casting billet on the rating of the central grain boundary cementite of wire rod was investigated through central and semi-macro segregation tests and macrostructure tests on the continuous casting billet. The key continuous casting process of 200 mm×200 mm SWRH82B steel was developed. The low segregation control of the continuous casting billet was achieved, and an important homogeneous foundation for the control of microstructure and performance was laid. The test results showed that the homogeneity of continuous casting billet can be optimized by using the technologic parameters of M-EMS current intensity of 300 A, F-EMS current intensity of 200 A, superheat degree of (25±2) ℃ and weak secondary cooling process. With these process technologic parameters, the central carbon segregation degree of the billet can be decreased to 1.08 in average, the proportion of grain boundary cementite of as-rolled wire rod rating not higher than 2.0 reached 96%, and the average wire breaking rate was decreased to 2.3 times per 100 tons in average.

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.

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.

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.

Oriented silicon steel is known as “art” in iron and steel materials for the reason of complex production process and strict manufacturing technology. In order to improve the casting speed of conventional slab of oriented silicon steel and improve the profit level of enterprises, the solidification end test and the bulging behavior of casting slab under different casting speeds were carried out, and the following results could be drawn. At the casting speeds of 0.9 and 1.0 m/min, the solidification end of oriented silicon steel slab is located in first 7 sections, while at high casting speed of, the solidification end is in the 8th section. When the casting speed is increased from 0.9 to 1.1 m/min, the thickness of the billet shell decreases. Under the same static pressure, the bulge volume and bulge deformation rate increase, with the maximum bulge deformation rate of 0.107%. When the casting speed increases by 0.1 m/min, the bulge volume of the billet at the same position increases by about 3.7%-16.6%. Combining the experimental study of liquid level fluctuation of mold, bulging behavior of billet and solidification end position, the casting speed of conventional slab of oriented silicon steel can be increased from 0.9 to 1.1 m/min.

Hot delivery and hot charging technology can significantly reduce energy consumption of heating furnaces, improve production efficiency, and reduce carbon emissions during steelmaking and rolling process. However, hot delivery cracks are easily existed on the plate surface after high temperature hot delivery of microalloyed steel slabs, which limits the application of this technology. In this work, the high temperature tensile test experiment was carried out to investigate the reasonable cooling rate during the hot charging pretreatment process of 300 mm slab. The variation process of surface temperature and microstructure of slab during the hot charging pretreatment process was studied through industrial experiments. The surface quality and mechanical properties of steel plates with hot charging pretreatment process were studied using statistical methods. The results indicate that the surface temperature of 300 mm thick slab is deceased from 920 ℃ to 387 ℃, and the cooling rate is about 4.2 ℃/s during the segment hot charging pretreatment process. The surface temperature is return to 742 ℃, and the heating rate is about 1.2 ℃/s. Fine bainite structures are formed through rapid cooling and reheating on the surface of the slab. After the implementation of the hot charging pre-treatment process, the hot charging temperature of the slab is increased from 500-550 ℃ to 600-650 ℃, and the hot delivery cracks are eliminated, and the mechanical properties of the steel plate are stable.

To study the heat transfer during solidification of large round billets, the continuous casting process of large round billets was taken in a certain steel plant as the research object. Based on the differential equation of heat transfer, the implicit difference method in finite difference methods was adopted to solve the problem and a two-dimensional solidification heat transfer model of large round billets was established in polar coordinates. The computer language C++ for program compilation was used and the model was verified through on-site temperature measurement. Through the application of the model, it is found that the change of casting speed has a great influence on the mold outlet temperature, solidification end point and other data. For every 0.02 m/min increase in casting speed, the solidification end point moves backward by 1.8 m. The change of superheat has a small influence on the surface temperature of the billet and the length of the liquid phase. For every 10 ℃ increase in superheat, the length of the liquid phase only increases by 0.6 m. Judging from the rate of temperature drop on the surface of the billet, the temperature drop in the mold stage is the fastest, during which the billet is in the rapid growth stage of the primary shell, and there is a temperature recovery phenomenon in the secondary cooling zone II. The quality of slab can be improved by adjusting the process according to the simulation.

The construction of high-quality clean steel platform is an important means to achieve high efficiency and low cost production of clean steel. The production of clean steel is a systematic project involving the quality evaluation and control of raw and auxiliary materials, the automation and precise control of refining process, strict protection and stable casting. At present, the research on the construction of clean steel platform is mainly about production process and technology integration, and a large amount of data and information in clean production have not been effectively used. Therefore, based on the real-time database, an integrated platform of the whole process and information is built to realize the integration, feedback, sharing, access and problem traceability of information among various processes of clean steel production. At the same time, relying on big data analysis and other means, a process knowledge base is established to achieve the unity of clean steel production operation control, process technology, data resources, and monitoring management, so as to achieve the whole process quality control of steelmaking.

Reasonable secondary cooling process system of continuous casting is one of the keys to improve the quality of spring steel billets. This paper takes 150 mm×150 mm billet of 55SiCr spring steel as the research object, adopting the method of in-situ temperature measurement and Procast numerical simulation calculation,the influence of secondary cooling water amount on the longitudinal-transverse cooling non-uniformity of the continuous casting billet was analyzed by the heat transfer and solidification model considering the water flux distribution along transverse direction, and optimization scheme for secondary cooling water amount was proposed to control the longitudinal-transverse cooling non-uniformity.The research results show that the longitudinal temperature distribution is unreasonable under the current secondary cooling water configuration scheme, and the corner temperature at the straightening point of casting billet is 922 ℃, which is in the third brittle temperature region of 55SiCr steel. Moreover, the maximum difference of transverse temperature on casting billet surface in the secondary cooling zone is large, and its value is 360 ℃, which is tend to cause corner and surface cracks. Based on the above research results, this paper proposed a new configuration strategy and scheme of secondary cooling water amount for this steel grade,keeping the water amount in foot roll section unchanged,reducing the specific water ratio in the secondary cooling zone from 0.80 to 0.58 L/kg,and regulating the water amount of in the first and second sections of the secondary cooling zone to 3∶2. After the optimization of water amount in secondary cooling zone,the spray water proportion at the center of billet surface in the first and second sections of the second cooling zone are increased from 7.47% and 5.57% to 14.48% and 13.02%,the spray water proportion at the corner of billet are reduced from 3.46% and 5.45% to 0 and 2.13%.The corner temperature of billet at the straightening point is increased to 997 ℃, where avoiding the third brittle temperature region,the maximum transverse temperature difference on the surface of billet is reduced to 209 ℃, which is beneficial to reduce the incidence of crack defects on the surface and corners of the continuous casting billet.

Based on the process parameters of 304 stainless steel production by ϕ350 mm billet mold, a three-dimensional electromagnetic stirring model of billet mold was established. The effects of M-EMS on the flow, temperature distribution and solidification behavior of molten steel in billet mold under different current intensities were studied, and the current intensity for optimal stirring was obtained. The results show that after the application of electromagnetic stirring intensity, the molten steel in the mold undergoes swirling motion, which produces periodic eccentricity with the stirring time. The tangential velocity of the molten steel at the solidification front increases with the increase in current intensity. The swirling molten steel promotes a more uniform temperature distribution of molten steel in the billet mold, the high-temperature area of molten steel expands, and the surface temperature of the billet with M-EMS increases. With appropriate current intensity, the increase in solidified billet shell caused by increasing the heat dissipation of molten steel is greater than the decrease of solidified billet shell caused by swirl scouring of molten steel, resulting in the increase in solidified billet shell thickness, and finally the optimal current intensity parameter of 295 A was selected.

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.

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 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.

The multi-roll solid-liquid cast-rolling bonding technology of metal cladding materials has the advantages of both multi-roll rolling technology and cast-rolling bonding technology, which is expected to realize the combination of continuous near-final forming and interfacial metallurgical bonding with high efficiency, short flow, and low energy consumption. The mold of the multi-roll solid-liquid casting-rolling bonding equipment has the dual functions of water cooling and rolling, which directly affects the solidification and deformation behaviors of the cladding metal. By designing the structure scheme of the grooved casting roll, the steady state temperature field analysis model of the grooved casting roll was established based on the FLUENT software, and the influence of the structural parameters and process parameters on the temperature distribution was revealed. The analysis results show that the width of the non-cooling area has little effect on the cooling capacity of the grooved casting roll, and the parameters are designed to meet the strength requirements of the casting roller. Besides, increasing the width of the cooling area and convective heat transfer coefficient, and reducing the cooling water temperature are conducive to improving the cooling capacity of the grooved casting roll. The optimized structural parameters were obtained based on the numerical simulation results, with a roller nominal radius of 250 mm, inner diameter of 180 mm, width of 50 mm, and groove diameter of 25 mm, and cooling zone width of 25 mm. Finally, the design and manufacture of the multi-roll solid-liquid cast-rolling bonding prototype for metal cladding materials were completed, which laid a platform for the subsequent experimental research.

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 improve the strength and toughness of steel base metal for large line energy welding, microalloying was applied to the development of ship plate steel DH36 based on oxide metallurgy technology, and the mechanism and process optimization measures of microalloying on the solidification structure of casting slab were investigated. The effect of microalloying elements and process parameters on solidification microstructure refinement was studied by establishing the mathematical model of solidification heat transfer and microstructure. The experimental steel was smelted by vacuum induction furnace and the simulation results were verified by metallographic microscope. The results show that the thinning effect is obvious when Mo content(mass fraction) is 0.040%-0.050%. When the content of Nb increases from 0.030% to 0.040%, the thinning effect of solidification structure is better. The thinning effect is obvious when the Mg content increases within 0.002%-0.003%. The increasing of V content has little effect on the solidification structure. Ti content in the range of 0.015%-0.016% is more conducive to grain refinement. The proper reduction of superheat is beneficial to microstructure refinement, and the low casting speed is more conducive to the improvement of casting quality. In the production of 2 400 mm×400 mm section ship plate steel DH36 casting slab, in order to obtain excellent liquid steel solidification structure and fine grain, the best process parameters should be adopted according to this study, casting speed 0.58 m/min-0.60 m/min, superheat of 25 ℃, Mo content 0.050%, Nb content 0.040%, Mg content 0.003%, V content 0.003 5%, Ti content 0.015%. The results show that the equiaxed crystal region of the solidification structure is 11 percent point higher than that of the conventional alloy content casting slab, and the optimization rate is 35%. On the basis of experiment and calculation analysis, the content range of microalloy and the optimization measures of process parameters for improving the properties of the base metal of the casting slab are proposed in this paper, which can provide reliable theoretical guidance for the optimization of the continuous casting process of the ship plate steel with large line energy welding.

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.

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.

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.