Driven by the global energy transformation and the "double carbon" goal, green low-carbon continuous casting technology has become the core path of emission reduction in the iron and steel industry. This paper systematically reviews the key technologies of electromagnetic metallurgy, near net shape continuous casting and rolling (ESP, MCCR), waste heat recovery, high casting speed and so on, and reveals the potential of energy saving and carbon reduction through solidification control, short process integration, intelligent scheduling and hydrogen energy substitution. The results show that the integrated application of these technologies can significantly reduce the energy consumption and carbon emissions of the continuous casting process, and promote the development of the steel industry in the direction of high-efficiency, intelligence, and greenness. In the future, it is necessary to deeply integrate digital technologies, hydrogen energy substitution technologies, and circular technologies, break through the bottlenecks in large-scale applications, and provide theoretical support and technical solutions for the low-carbon transformation of the steel industry.
Continuous casting is the key link of iron and steel production, and the cooling effect of its secondary cooling zone(secondary cooling zone)directly affects the quality of slab. The cooling heat flux density in the secondary cooling zone is an important basic data for the rational design of secondary cooling water distribution. Aiming at the high temperature and high heat flux conditions involved in continuous casting secondary cooling, a set of heat transfer experimental device for continuous casting secondary cooling jet cooling slab was developed based on the steady-state heat flux measurement method, which can be used to measure the heat flux density of high temperature surface jet cooling at 900-1 200 ℃. During the experiment, the surface of the local area of the high temperature steel material was cooled by the mist jet. The cooling object was a specimen with a diameter of 10 mm and a thickness of 2.5 mm, and the induction heating was used as the internal heat source to keep it in a high temperature state. The PID controller adjusts the output power of the high-frequency generator to balance the heat taken away by the induction heating and jet cooling of the cooling object, so that the specimen is maintained at the set temperature. The electrical parameters of the output power of the induction heater are measured when the temperature of the cooling object is maintained, and the heat flux density of the surface heat dissipation of the jet cooling specimen is calculated by the induction heating mathematical model. The experimental results show that the equipment can realize the measurement of the cooling heat flux density of the high temperature surface by the typical continuous casting secondary cooling air mist jet on the surface of the high temperature slab,and the distribution of cooling heat flux density in the jet area shows the trend of high center and low edge.When the nozzle is used to cool the specimen with a surface temperature of 1 200 ℃ under the conditions of air pressure of 0.3 MPa and water pressure of 0.8 MPa, the heat flux density can reach 4.78 MW/m2 The heat flux of jet cooling does not increase significantly with the increase of cooling surface temperature.
Accurate and rapid prediction of meniscus flow velocity under different process conditions is crucial for preventing slag entrapment in continuous casting. Due to the complexity of high-temperature, multi-physics coupling, real-time measurement of the mold flow field in mold is challenging. The paper develops a numerical model coupling mold melt flow and SEN argon blowing. Based on precise simulations, a fitting formula is proposed to predict the maximum meniscus velocity using liquid level differences. To achieve real-time meniscus velocity prediction, a GA-SVM model is developed, which integrates genetic algorithms, support vector machines, and numerical simulations using 24 sets of simulation data. The GA-SVM model achieves an R2 of 0.93, providing high accuracy while avoiding complex numerical calculations. It enables rapid velocity prediction while avoiding complex simulations and serves as a surrogate model for digital twin applications in continuous casting.
This study takes the soft reduction process during continuous casting of large square blooms (325 mm × 280 mm) at a steel plant as the research object. Reduction models were established for different combination modes of flat rolls, convex rolls, right-angle blooms, and chamfered blooms. The distribution of equivalent strain on the bloom surface and the strain transfer efficiency in the thickness direction were investigated through numerical simulation, with the effectiveness verified by industrial trials. The results show that: convex rolls optimize the surface strain distribution of the bloom, reduce corner strain magnitude, improve stress conditions at the corners, and decrease crack occurrence. Chamfered blooms exhibit superior strain transfer efficiency in the thickness direction compared to right-angle blooms, with efficiency increasing from 13.3%～14.7% to 43.2%～50%. Convex rolls outperform flat rolls in strain transfer efficiency, efficiency increases from 13.3% to 14.7% for right-angle blooms and from 43.2% to 50% for chamfered blooms. Industrial trials demonstrate that applying flat rolls to chamfered blooms significantly improves core quality. Furthermore, the chamfering method of the cast billet has a more significant effect on improving the macrosegregation of the billet compared to the convex roller pressing method.
During the casting process of the tundish, the removal rate of inclusions is a key index used to measure the optimization effect of the flow field of the tundish. Water model and numerical simulation methods respectively have significant operational errors, complex particle flow models and high computing power costs when simulating the migration and removal of inclusions, which are the bottlenecks restricting the determination of the optimized structure of the tundish flow field. To predict the flow field optimization effect of different structures of tundishes quickly and accurately, this paper proposes a prediction model for the removal rate of inclusions in tundishes based on BP neural network. By learning the characteristic rules among the flow characteristic parameters of different tundishes, the removal rate of inclusions of different particle sizes can be predicted. Through the grid search algorithm optimization, it is found that when the number of hidden layer nodes n=13 and the learning rate η=0.08, the root mean square loss function value of the model test set reaches the minimum. Three algorithms, genetic algorithm, particle swarm optimization, and simulated annealing, are used to optimize the weights and biases, and it is found that the PSO-BP model has the best optimization effect, with an average hit rate of 92.29%. To further verify the production practicability of the model, it is combined with the water model and mathematical model, and the prediction results of the model are in good agreement with the experimental results with 5% Gaussian noise.
Optical microscopy, scanning electron microscopy and electron probe were used to study the ingots and wire rods of the same batch of SWRH82B, in order to reveal the influence of the as-cast microstructure of the continuous casting billet on the microstructure of the hot-rolled wire rods in the subsequent process. Within 4 mm from the surface of the continuous casting billet, there is a fine-grained surface layer, from 4 mm to 57 mm is the columnar crystal zone, and the rest is the central equiaxed crystal zone, with an area ratio of about 9%. The porosity is located in the central equiaxed crystal zone and the junction zone between the columnar crystal and the equiaxed crystal, with an area ratio of 15% and a grade of 1. Through electron probe, it was found that there were different degrees of positive segregation of C, P, S, Cr and Mn in both the central equiaxed crystal zone and the columnar crystal zone. Band-like structures can be observed in the longitudinal section of the wire rod, mainly concentrated in the center, and the width and quantity gradually decrease from the center to the surface, and disappear at positions 3.5 mm and 4 mm from both sides respectively. The band-like structure is still spheroidite, but the lamellar spacing is finer than that of the matrix. The range where the band-like structure appears on the wire rod corresponds to the entire equiaxed crystal zone of the continuous casting billet and part of the adjacent columnar crystal zone. It was found that there was C negative segregation and different degrees of positive segregation of P, S, Cr and Mn in the band-like structure area. Except for C, the segregation pattern of the elements in the band-like structure is similar to that at the corresponding position in the continuous casting billet. The degree of segregation of each element in the wire rod is reduced to varying degrees compared with that in the continuous casting billet.
The wear-resistant steel is characterized by its high hardness, toughness, and wear-resistance. It is primarily used in construction and agricultural machinery. The wear and brittle fracture failures observed in wear-resistant steel during service are closely related to solute segregation within the steel. To elucidate the solute microsegregation behavior during the solidification process of wear-resistant steel, a microsegregation model, which takes the eutectoid transformation, inclusion precipitation, and dendrite coarsening during the solidification into consideration, was established. The model's accuracy was verified, and then the effects of C, Mn and S content, precipitation of MnS inclusions and cooling rate on the solute microsegregation behavior, zero ductility temperature (ZDT), and zero strength temperature (ZST) were analyzed. The results indicate that S and P exhibit significant microsegregation during the solidification process of wear-resistant steel, and MnS precipitation reduces the segregation degree of Mn and S. The C content has a pronounced impact on the microsegregation of solute elements, while Mn and S contents exert minimal influence on the microsegregation of solute elements. Additionally, it is observed that the effect of cooling rate on solute microsegregation varies with different solid phase fraction. The content of C, Mn and S, as well as the cooling rate, all influence the precipitation amount of MnS inclusion. Increasing C content and Mn content result in a decrease in both ZDT and ZST. With the increase of S content and cooling rate, ZDT decreases, while the variation of ZST remains minimal. The findings have important implications for the continuous casting production of wear-resistant steel.
The effects of annealing process on the microstructure and properties of 00Cr13Si2Cu2Al steel were studied by optical microscope, scanning electron microscope and REMAGRAPHC-500 soft magnetic DC measuring device. The results show that the microstructure of the air-cooled process and the furnace-cooled process shows obvious differences after different annealing processes. In the annealing temperature range of 700-800 ℃, two different annealing processes of No.3 test steel can obtain a good match of mechanical properties and magnetic properties. However, under the conditions of 800 ℃×3 h annealing temperature, the strength and magnetic flux density of the furnace cooling process are better than those of the air-cooled process, with a tensile strength of 559 MPa, a yield strength of 411 MPa, a B2 000 of 1.29 T, a B5 000 of 1.43 T, and a B10 000 of 1.54 T.
This study primarily investigates the impact of mold electromagnetic stirring on inclusions in interstitial-free steel slabs. The results indicate that mold electromagnetic stirring has no significant effect on the types of inclusions in IF steel slabs, with the primary inclusion types being irregular and clustered Al2O3-based, Al2O3-Ti2O3-based, Al2O3-TiN-based, polygonal Al2O3-Ti2O3-TiN-based, and pure TiN-based inclusions. In terms of inclusion size, the inclusions in IF steel slabs are primarily concentrated between 1-10 μm, and mold electromagnetic stirring contributes to the miniaturization of inclusions, with the proportion of microscopic inclusions with the size less than 2.5 μm increasing from 52.48% to 58.66%, while the proportion of inclusions between 5-10 μm decreases accordingly. Furthermore, mold electromagnetic stirring demonstrates a significant effect in reducing non-metallic inclusions on the slab surface and subsurface. Under mold electromagnetic stirring conditions, the inclusion number density is 1.5-9.3 mm-2, which is significantly lower compared to 4.4-15.6 mm-2 under non-stirring conditions. Regardless of whether mold electromagnetic stirring is applied, the distribution trend of slab inclusions in the thickness direction is consistent, with the number density of non-metallic inclusions increasing significantly as the distance from the slab surface increases. This study provides an important basis for understanding the production of high-grade automotive steel using mold electromagnetic stirring.
To address the segregation issue in the radial 1/4R~1/2R region of 42CrMoA alloy structural steel hot-rolled bars, this paper systematically elucidates its formation mechanism and proposes improvement measures. These measures were validated through industrial production, ultimately establishing a clear control method for segregation in rolled materials. The results indicate that segregation in rolled materials is inherited from the CET zone (Columnar to Equiaxed Transition) segregation in the casting billet, primarily caused by the disordered growth of the CET zone hindering solute diffusion, combined with the cavity suction effect induced by electromagnetic stirring and billet reheating. By reducing the Mold Electromagnetic Stirring (M-EMS) current from 400 A to 200 A and adopting low superheat, the standard deviation of carbon content on the cross-section of rolled materials decreased from 0.024 to 0.018, the carbon range decreased from 0.073 to 0.05, and the segregation index decreased from 1.090 to 1.057, significantly improving compositional uniformity. Adjusting M-EMS intensity demonstrated a more pronounced effect on mitigating segregation. Ultimately, the optimal segregation control method for 42CrMoA rolled bars was determined as follows: M-EMS current of approximately 200 A and superheat of around 30 ℃.
In order to identify the reasons for the low and unstable qualified rate of flaw detection of 800 MPa hydroelectric steel plates, in this study, samples were taken from the steel plates that did not meet the flaw detection requirements after rolling, and the samples were detected by optical microscope, scanning electron microscope and energy spectrometer. Research shows that internal cracks in steel plates are the direct cause of non-conformity in flaw detection. The length of the cracks increases with the increase of the grade of Class B inclusions in the steel plates. The length of the cracks in the steel plates rolled from the continuous casting billets of the first and last castings is twice that of the middle castings. Severe segregation and enrichment phenomena of P, S and microalloying elements occurred inside the steel plates that did not meet the flaw detection requirements. On this basis, the smelting process and steel grade composition of 800 MPa hydroelectric steel were optimized and controlled, increasing the qualified rate of steel plate flaw detection from 95.6% to 98.6%, and stabilizing the fluctuation range from 92.5%-98.8% to 96.8%-99.5%.
When producing peritectic steel slabs with an aspect ratio (width-thickness ratio) greater than 10 by continuous casting, the incidence of longitudinal surface cracks in continuous casting slabs is significantly higher than that of conventional slabs, which has become a core problem restricting product quality. Key process control points, including mold cooling water flow rate, mold cooling water temperature, mold taper, mold flux, and submerged entry nozzle (SEN) type, were emphatically analyzed and studied, and targeted process improvement measures were adopted. The practical results show that by controlling the inlet temperature of mold cooling water at 33-38 ℃, the water gap flow rate of the wide-side copper plate of the mold at 6.23 m/s, and the mold taper at 1.10%-1.15%, as well as adopting high-basicity mold flux and convex-bottom SEN, the incidence of longitudinal surface cracks in peritectic steel slabs with high aspect ratio is reduced from 13% to 0.38%, and the longitudinal surface cracks of the slabs are effectively controlled.
Aiming at the edge peeling defects occurring in cold-rolled typical low-alloy steels P280VK and 590DP, the formation mechanism of such defects was systematically investigated by means of metallographic observation, electron microscopy detection, thermodynamic calculation of precipitates and temperature field simulation of continuous casting slabs. Metallographic analysis and SEM-EDS results show that the defects exhibit typical intergranular oxidation characteristics, which can be traced to the inheritance of corner microcracks in continuous casting slabs. Based on FactSage thermodynamic calculation and continuous casting temperature field simulation, the mechanism that LF desulfurization induced nitrogen increment promotes the preferential precipitation of AlN at slab corners is revealed: the corner temperature in the straightening zone falls into the temperature range of massive AlN precipitation, resulting in grain boundary embrittlement and further the initiation of microcracks. During hot rolling, the crack propagation is restrained when AlN precipitation is below 0.01%, while the complete precipitation of AlN during cold rolling promotes the unstable propagation of cracks and eventually leads to edge peeling. Accordingly, technical measures are proposed, including controlling the nitrogen content in finished products (mass fraction of N less than 34×10-6 for P280VK and less than 35×10-6 for 590DP) and offline chamfering of high-nitrogen casting slabs. After application, the edge peeling rate of cold-rolled low-alloy steel is reduced from above 1% to below 0.22%.
Addressing the issue of inclusion defects in automotive panels caused by slag entrainment in molten steel due to coriolis forces during the final stage of continuous casting ladle pouring, this paper systematically investigates the dynamic behavior and influencing factors of slag entrainment in the molten steel during the ladle pouring process by establishing a numerical simulation method based on the k-ε turbulence model coupled with the VOF multiphase flow model. The research reveals that the slag entrainment process can be divided into four stages: initial depression, formation of conical vortices, turbulence entrainment, and explosive slag entrainment. Among these, the steel throughput is the core factor affecting the critical slag entrainment level, showing a significant positive correlation with the critical level. Factors such as ladle age, slag layer thickness, and steel slag viscosity have negligible effects. Based on this, a prediction model for critical remaining steel in the ladle is constructed, incorporating multiple parameters such as steel throughput, casting speed, and ladle age. Additionally, a calculation equation for critical remaining steel is proposed, with a prediction error of less than 3%. Furthermore, an intelligent remaining steel control and early warning system is developed, enabling precise early warning before slag entrainment through real-time collection of process parameters. Industrial applications demonstrate that this system reduces the amount of remaining steel in the ladle by over 2 tons per ladle, lowers the slag entrainment rate to 0.5%, and decreases the incidence of inclusion defects by 0.1%. This significantly enhances the purity and surface quality of automotive panel steel, while reducing production costs and achieving significant economic benefits.
The used magnesia-based coating of the tundish was recycled and processed to make light-burned magnesia balls, and the recycling and utilization technology of the used magnesia-based coating of the tundish was studied. Through the performance testing and analysis of the prepared light-burned magnesia balls, as well as laboratory experiments and field tests, it was shown that the unsintered part of the used magnesia-based coating of the tundish, after being recycled and processed to make light-burned magnesia balls, had physical and chemical properties meet the requirements of the converter charge index. The MgO content in the formed slag is higher than that in the slag formed by using dolomite for magnesia burdening, and the basicity of the slag was also slightly higher. The prepared light-burned magnesia balls could provide more MgO to the slag, and the effect of mixing magnesia to make slag was better. It could completely replace caustic calcined dolomite, etc. as a converter final slag modification agent and be used in the converter magnesia burdening and slag making process and the slag splashing furnace protection process. It could fully inhibit the dissolution and diffusion of MgO in the furnace lining into the slag, playing a role in protecting the furnace lining. In addition, the light-burned magnesia balls made from the used magnesia-based coating of the tundish had a fast slag formation speed. Compared with the dolomite slag making process, the slag formation speed was about 1 to 2 minutes earlier. The used magnesia-based coating of the tundish had a high recycling and utilization value as a charge in converter steelmaking.
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