Numerical analysis of the comprehensive effect of continuous casting process parameters on the continuous casting billet remelting

Different parameters can be used together in the continuous casting process known as an important steel production stage in the world. It is important to use metallurgical appropriate parameters to meet the product properties. Many innovations have been made in the continuous casting process from past to present. It is known that studies are carried out on many effective topics such as steel analysis, refractory materials, continuous casting parameters, in order to make the proper solidification that will meet the needs with its continuous casting capabilities. When continuous casting parameters are examined; the casting speed parameter was found to be effective in terms of quality needs in macro samples. Therefore, in this study, the effect of the increase of casting speed parameters on the quality of macro samples was investigated. As a method; in high carbon, micro-alloyed DIN EN ISO 16120-2: 2011-C66D quality steels, in different castings, this parameter was changed and macro samples were taken and evaluated in terms of quality needs. When macro sample quality results are compared; the effect of casting speed was observed. In this study; the effect of the increase in casting speed in continuous billet casting facility on optimum metallographic and physical quality has been investigated and the results have been interpreted.

Shrinkage porosity is a typical internal defect in the continuous casting billet, which occurs frequently and is difficult to solve. To explore the influence factors of central shrinkage porosity, a novel unsteady thermomechanical coupling analysis algorithm is developed based on the billet solidification characteristics, and the central shrinkage behavior during the ending solidification process is simulated. Results show that when the casting speed increases from 1.6 to 2.8 m·min−1 and the center outward displacement is reduced from 9.20 × 10−2 mm to 5.8 × 10−2 mm, it means casting speed has a significant effect on the formation of shrinkage porosity, and for this caster, the higher casting speed is more suitable for the secondary cooling zone. Without the changes in the solidification structure, when the superheat degree of molten steel increases from 10 to 40°C, the center outward displacement value decreases from 7.12 × 10−2 mm to 6.91 × 10−2 mm. In that case, the superheat degree has no obvious effect on the center displacement value.

Numerical Simulation of Influence of Casting Speed Variation on Surface Fluctuation of Molten Steel in Mold

The influence of casting speed variation on non-metallic inclusions in surface layers of IF steel slabs during continuous casting were investigated with OPA (Original Position Statistic Distribution Analysis) method. It was found that, when the casting speed was evenly decreased from 1.4 to 0.6 m/min, increases of the nonmetallic inclusions owing to the increase of the mold powder entrapment were observed only on those slabs which were cast at the start of casting speed change. While, in experiment of increasing casting speed evenly from 0.6 to 1.4 m/min, increases of nonmetallic inclusions were observed only on slabs which are cast at the time when the casting speed was stopped to increase after it had been increased to 1.4 m/min. For slabs which were cast during the casting speed evenly increasing or decreasing period and at the time when increasing or decreasing the casting speed at low casting speed level (0.6 m/min), the influence of casting speed change was very small. In addition, it was found that, at high casting speed level (1.4 m/min), even a little change of casting speed could result in remarkable increase of the non-metallic inclusions. Thus, at high casting speed, changing casting speed should be avoided or using much slower speed changing rate.

Effects of casting speed on microstructure and segregation of electro-magnetically stirred Aluminum alloy in continuous casting process

The solidification structure of a thin slab during the continuous casting process at high casting speed was simulated based on the cellular automaton-finite element (CAFE) model. The simulations were consistent with the solidification structures of actual steel samples, and the influence of the continuous casting process parameters and alloy elements were further studied in detail. The optimum process parameters obtained are as follows: the casting speed at 5.2–5.4 m min−1, the superheat at 20–25 °C, and the specific water flow at 1.62–1.64 L kg−1. Meanwhile, the Si content in the thin slab was appropriately increased to refine the grains and improve the production efficiency. This study provides important theoretical data for practical thin slab production, improvement of the continuous casting efficiency, thereby reducing accidents.

Endless rolling urgently requires an increase in the casting speed of continuous casting. For the continuous casting process of a high-casting-speed billet, the heat flux of the mold would be much higher, requiring a stronger cooling performance and longer mold life to match the high-speed casting. Mold material, thickness, and slot structure have a great influence on the casting speed. To design a more efficient billet casting mold, a three-dimensional thermal-stress-coupled analysis model of a 150 mm × 150 mm mold was established in this research to analyze the thermal state of a mold with high casting speed; in addition, the material, thickness, and water slot structure, which pertain to the mold cooling performance, were also studied. The results show that the billet mold of Cu-Ag with a thinner thickness and right-corner water slot is better in terms of casting speed. Regarding the material, the Cu-Ag mold has a higher thermal conductivity efficiency; its hot surface temperature is 4.89 °C lower, its equivalent stress is 7 MPa lower, and its longitudinal deformation is 0.0023% lower compared with the deoxidized phosphorus copper mold. Regarding the thickness, the thinner mold has a 60.76 °C lower hot surface temperature, its equivalent stress is 340 MPa lower, and its longitudinal deformation is 0.0443% lower compared with the thicker mold. For the water slot structure, the mold with the right-angled water slot has a 2.895 °C lower hot surface temperature, its equivalent stress is 37 MPa lower, and its longitudinal deformation is 0.0039% lower compared with the mold with a rounded-corner water slot.

In the current paper, a kinetic model was developed to study the entrapment of inclusions in the molten steel flowing through a Submerged Entry Nozzle (SEN) during billet continuous casting process. The trajectory of inclusions was calculated by considering the drag force, lift force and gravitational force. The entrapment locations of inclusions on SEN wall were predicted. The effects of nozzle diameter, casting speed, billet dimension, and inclusion diameter on SEN clogging were quantitatively discussed. The results indicate the inclusions with diameter larger than 100 μm are not able to be entrapped by the nozzle wall; and the entrapment probability will increase quickly with decreasing size of inclusions. The distribution of the entrapped inclusions along the nozzle length is non-uniform and the volume fraction of inclusions in the clogging materials should be considered in order to more precisely predict the accumulated weight of molten steel that can be poured before the nozzle is fully blocked by clogging. Under the conditions assumed: 150 mm×150 mm billet, 2.0 m/min casting speed, approximately 25°C superheat, 1 m length of the SEN (Al2O3–C materials), 20 μm inclusions diameter in a single size, 30 ppm T.O and 40 mm nozzle diameters, the prediction shows that ~351 ton steel can be poured for the current billet continuous caster.

A three-dimensional finite-element heat-transfer model was established to predict temperature of hot copper plates in a slab continuous casting mold with high casting speed and the temperature distribution and effect of casting speed on thermal behavior were simulated in detail. The results show that the calculated temperature agree well with the measured ones and the temperature of hot copper surface is influenced by the flash welded chrome (Cr) layer to a certain extent. The temperature profile of hot copper surface is determined by heat flux, material properties, solidifying shell shrinkage and mold taper and presents a certain shape. Temperature distributions in different transverse sections along effective casting height of mold are all similar and depend on mold structure and contact state between mold wall and slab. The centre temperature of hot copper surface at casting speed 1.8 m·min−1 and 2.0 m·min−1 are higher than that of 1.6 m·min−1 casting speed 4.7–5.2°C and 11.2–12.2°C respectively and temperature is not increased linearly with casting speed. Temperature difference adjacent to meniscus between mold wall and shell surface is influenced obviously by casting speed and increased 4.0–6.0°C with increment of casting speed 0.2 m·min−1. Fluctuation of temperature difference in meniscus should be a main reason to deteriorate casting effectiveness as increasing casting speed.

With the increasing demand for high-efficient continuous casting, parameter optimization during high-speed continuous casting is critical. To clarify the changes in flow characteristics in a multistrand tundish and the optimization principles for the diversion wall, a numerical investigation of an eight-strand tundish during continuous casting of billet was carried out in this paper. The simulation results were validated with the physical results of a 1:3 water model experiment. The results show that, for a tundish with the same flow control device, the average residence time and the maximum residence time difference of liquid steel in different strands are significantly reduced with higher casting speed. At different casting speeds, the effect of the hole diameter and deflection angle of diversion wall on the average residence time and the dead region proportion is very minor, while that on the maximum residence time difference of liquid steel in different strands is significant. For a given tundish, to improve the flow uniformity among multiple strands, parameter optimization of diversion wall should be optimized when the casting speed increases. When the casting speed is 4.4 m/min, the hole diameter of the diversion wall is 80 mm, and the deflection angle of the diversion wall is 74°, the flow field parameters of liquid steel in the eight-strand tundish are good, especially flow uniformity among multiple strands.

The particle image velocimetry (PIV) technique was used to study the fluid flow phenomena that occurred during continuous casting, using a water model with dimensions of 1 840 mm × 280 mm. Two types of solidified shells, i. e., the smooth type and the coarse type, were used to characterize the dendrite in order to simulate different liquid-solid interfacial conditions. The influence of the nozzle angle and the immersion depth of nozzle, as well as the casting speed on the flow behavior was investigated quantitatively. The results were as follows: (1) There are two large recirculations above and below the fluid jet in the mold, respectively, under the smooth interface condition. However, in the case of the dendrite solidified shell, it was found that the flow velocity of the fluid decreased and more smaller vortices appeared in the upper region of the mold. (2) The angle and the immersion depth of nozzle are two important factors affecting the flow pattern, and they are also capable of bringing about the change in the flow direction. (3) The higher the casting speed, the higher are the jet stream and the impacting point on the narrow face. However, the high casting speed causes serious fluctuation of the meniscus, and correspondingly leads to various defects.

The complex cross-sectional shape of oversized beam blanks and the size effect of ultra-large-section beam blanks create severe issues related to the surface and internal quality of the castings. To ensure quality and control in the production of ultra-large-section beam blanks, a numerical and physical model of molten steel flow in the three-port submerged entrance nozzle (SEN) mould, with section dimensions of 1300 × 510 × 140 mm, was established. This model was created using numerical simulations and NSGA-II genetic algorithm optimisation, and the impact of the casting speed and SEN immersion depth on the mould’s flow behaviour was investigated. The results showed that a deeper SEN immersion depth resulted in, a greater impact depth of the molten steel, and the surface flow velocity decreased. Both the impact depth and the surface flow velocity of the molten steel increased with increasing casting speed. The physical simulation and numerical simulation of the molten steel flow form and flow velocity distribution in the mould were in good agreement with each other, thus verifying the accuracy of the numerical simulation. The process parameters derived from this study were all within an appropriate range, which can help to improve the quality of continuously cast beam blanks. This also provides guidance for selecting optimal parameters for actual continuous casting production processes.

The research of carbon content along the casting direction of 82B cord steel billets is of great significance for improving the quality of cord products from subsequent processing. However, the traditional segregation and billets quality evaluation methods have certain limitations, such as sampling length and analysis area, which affect the accuracy of quality judgment. Thus, the statistics of extreme values (SEV) was introduced to predict the maximum value of carbon element content along the casting direction, which can quantitatively characterize the segregation degree. The size of the selected billet is 150 mm × 150 mm, and the sampling location is the centerline of the billet. The experiment was conducted by considering the effect of cooling intensity and casting speed on the maximum value of carbon element content. Firstly, the calculation results show that the SEV method can predict the maximum value of carbon element content along the casting direction of 82B cord steel, and the SEV method is proved to be effective by analyzing the carbon distribution and fluctuation in billets. To some extent, the SEV method can break the limitations of the sampling length and analysis area by predicting the maximum value of carbon element on a larger range of continuous casting billets with few samples. During the continuous casting process, the increase in cooling intensity makes the surface shrinking rate increase, which can slow down the flow of solute-enriched liquid to the center, and the center segregation can be reduced. On the other hand, the function area of the final electromagnetic stirring can be expanded with the increase in the casting speed, which can reduce the concentration of carbon element in the center of the billets and reduce the maximum value of carbon element content. It can provide a new theoretical reference for the quantitative calculation of carbon content in continuous casting billets and the quality evaluation of continuous casting billets.

Continuous casting is the essential process converting liquid steel to solid in the form of slabs or billets/blooms in the steel plant. The economy and quality of the steel products are greatly dependent on how successfully the continuous casting is performed. New technologies have been actively developed in the process during the last decades in order to increase the productivity and, therefore, to decrease the operational cost. Since its first commissioning of a slab caster in 1976, POSCO has constructed a number of continuous slab, bloom and billet casters including a thin slab caster not only for plain carbon steels but for stainless steels. Through the operation of various types of continuous casters for more than 30 years so far, POSCO has steadily developed fundamental technologies and operational know-how and achieved the equipment innovations to improve the surface and internal qualities of cast products as well as to extend the productivity of continuous casters. Furthermore, POSCO has deepened the basic understanding on the solidification phenomena of liquid steel and also accumulated the engineering backgrounds to design the most optimal continuous casters. It has also devised the indispensable and auxiliary equipments and the key technologies to control the process precisely and efficiently in order to guarantee the quality and productivity. An innovative technology under development is the POCAST process, where controlled amount of the pre-molten mold flux instead of conventional powder mold flux is continuously fed into free surface of molten steel through the plunger-type feeding system from the flux melting furnace. In order to prevent the molten flux from freezing at the meniscus, a reflective insulation cover is installed, leading to the suppression of thermal radiation from the molten steel and flux. It is generally understood that, as casting speed increases, the occurrence of breakout increases since mold lubrication becomes insufficient due to the lack of mold flux flow from the meniscus into the solid shell/mold boundary. However, by utilizing the especially composition controlled pre-molten flux, it becomes possible to eliminate the formation of slag bear in the mold. Therefore, the mold flux consumption rate is increased even at the reduced oscillation rate & stroke and more importantly, the mold flux infiltration becomes more uniform throughout the boundary between the mold and the solidified shell. This consequently results in drastic reduction of the formation and depth of the oscillation mark and the occurrence of surface hooks without increasing the possibility of breakout, as has been proved in the casting trials carried out with the 10 ton pilot slab caster in Pohang. A key trend in the development of the continuous casting process is to reduce the thickness of cast products. Examples include thin slab casting and strip casting. In the thin slab casting process, a major drawback is the relatively low casting speed and, as a result, the inefficient equipment layout in the plant where two casters are connected to a hot rolling unit. The drawback could be resolved if the casting speed exceeds a certain limit. At the high casting speed, the productivity of casting becomes equivalent to that of hot rolling, and the thin slab casting plant is to be designed so that one strand

In this study, the relationship between macro segregation and the equiaxed zone in high-carbon grades with continuous casting parameters was investigated and optimized at the İsdemir iron and steel plant. The work was conducted for the 1080 quality of the SAE J403 standard. In this study, some parameters, such as casting speed, secondary cooling, EMS current value and EMS frequency value, were examined. When the results of the experiments are examined, it can be observed that the equiaxed zone in the macrostructure decreases significantly with the reduction of the EMS frequency value. The decrease in casting speed and increase in EMS current value caused an increase in the equiaxed zone. The increment in secondary cooling led to a decline in the equiaxed zone. Once the macro segregation results are examined, it can be seen that it is very important to optimize the continuous casting parameters in order to reduce the macro segregation results of—especially—carbon, sulfur and phosphorus elements. It has also been determined that the macro segregation values of carbon, sulfur and phosphorus elements are low in casting conditions where casting speed is low, and the EMS current value and EMS frequency value are high. In addition, macro segregation measurements of manganese, silicon, chromium and vanadium elements are found to be low under similar casting conditions. It is critical to optimize the continuous casting parameters before production, especially in high-carbon grades to be used for prestressed concrete wire and cord wire applications. As a result of the work conducted using the İsdemir billet continuous casting machine for the 1080-grade SAE J403 standard, aiming to optimize macro segregation and the equiaxed zone, the effective results have been achieved by using process parameters of 2.8 m/min casting speed, 360 A EMS current, 5 Hz EMS frequency and low secondary cooling intensity.