Effect of Mold Electromagnetic Stirring and Final Electromagnetic Stirring on the Solidification Structure and Macrosegregation in Bloom Continuous Casting

Electromagnetic fields have emerged as powerful tools for addressing current problems in thin slab continuous casting processes in the iron and steel industry. Substantial studies have been undertaken on the fundamental effects of electromagnetic brakes (EMBr) and strand electromagnetic stirring (SEMS). However, little attention has been focused on melt flow and solidification in a thin slab continuous caster with the simultaneous application of an EMBr and SEMS. The present study aimed to predict transient fields in the caster using a large eddy simulation and an enthalpy-porosity method. The electric potential method was applied in the braking process, and the conductivity change with solidification was considered. The suppressive effect on the intensity of the nozzle jet, the balance effect on the mold flow, and a dispersion effect could be observed. The dispersion effect was a novel finding and was beneficial to a flatter nozzle jet. In contrast, SEMS caused a highly turbulent flow in the strand. A large vortex could be observed in the casting direction. The solidified shell became more uniform, and the solidification rate became obviously slower. These findings supported the view that a high-quality thin slab can be produced by the application of an EMBr and SEMS.

Combined Effects of EMBr and SEMS on Melt Flow and Solidification in a Thin Slab Continuous Caster

In the current study, a three-dimensional semi-coupling macrosegregation model was established for a curved bloom continuous casting strand. The fluid flow, heat transfer, and solidification were calculated firstly with the effect of the mold electromagnetic stirring (M-EMS) and final electromagnetic stirring (F-EMS). Then, the transport of the solute was solved after the fluid flow reached a steady state. Predicted values of the magnetic induction intensity, temperature, and content of carbon agreed well with the measured ones, respectively. The negative segregation in the subsurface of the bloom was generated due to the rotational flow induced by M-EMS. The rotational flow pattern was formed along the cross section of the F-EMS zone. The maximum tangential velocity 0.012 m/s was located near the solidification front. The distribution of the carbon was uniform and the concentration of the carbon was about 0.205 pct in the molten steel. From the position 11.1 to 20.1 m beneath the meniscus, the liquid fraction at the centerline of the bloom decreased gradually to 50 pct and the concentration of carbon increased from 0.2 to 0.24 pct. The concentration of the carbon at the centerline of bloom increased sharply to 0.29 pct at the solidification end.

Three-Dimensional Macrosegregation Model of Bloom in Curved Continuous Casting Process

The mathematical model of coupling fluid flow, heat transfer, solidification, solute transport, and the electromagnetic field of the bloom in the upper part of the strand was established with three nozzle types. Then, the flow field, distribution of the temperature, solidification, and macrosegregation of carbon were investigated and compared by numerical modeling. In the case of the straight submerged entry nozzle (SEN), the molten steel flows down deep into the liquid pool, and the depth of the jet flow reaches about 1.0 m beneath the meniscus. The jetting zone is the high-temperature zone. In the case of two-port SEN and four-port SEN, the flow patterns and distribution of temperature in the central longitudinal section are similar. The jet flow impinges directly on the initially solidified shell and then it is divided into two longitudinal circulations. The heat of molten steel is dissipated along with the longitudinal circulations. The negative segregation band was generated near the bloom surface due to the washing effect by the rotating flow at the solidification front with three nozzle types. The negative segregation deteriorates gradually with the number of ports decreasing.

Effect of nozzle type on fluid flow, solidification, and solute transport in mold with mold electromagnetic stirring

Modeling of the as-cast structure and macrosegregation in the continuous casting of a steel billet: Effect of M-EMS

Effect of the Gap Between Copper Mold and Solidified Shell on the Fluid Flow in the Continuous Casting Strand with Mold Electromagnetic Stirring

Simulation of Solidification Structure During Vacuum Arc Remelting Using Cellular Automaton−Finite Element Method

With the high temperature confocal laser scanning microscope applied, the effect of cooling rate, temperature interval, and cooling mechanism on the solidification microstructure and primary carbide participation in GCr15 steel are investigated. The solute distribution in interdendritic segregation and participation carbide are analyzed by EPMA. The results show that solute concentrate is low in the dendrite zone but it increases clearly in the segregation zone. The carbon concentration in the precipitation can reach 6.49%, which means the primary carbide is M3C. In the heating process, the solute segregation zone and carbide participation melt firstly before it reaches the solidus temperature. During the solidification stage, the microstructure is refined and the size of primary carbide is reduced with a higher cooling rate, but the number density of primary carbide is increased. Moreover, it is found that the solidification microstructure has formed in the earlier solidification process, before the temperature declines to 1673 K. While the primary carbide participates in the later cooling stage and the transition temperature for the primary carbide is 1503 K. Besides, it is obtained that the primary carbide size can be reduced with the cooling rate larger than 300 K/min in the subsequent cooling stage.

Influence of Cooling Parameters on the Microstructure and Primary Carbide Precipitation in GCr15 Steel

Center Segregation Evolution in Slab Continuous Casting with Mechanical Reduction: A 3D Simulation

The invention provides a device for heating molten steel in a submersed nozzle and a dynamic control method of the device, and relates to the technical field of steel continuous casting production. Submersed nozzle nodulation and congealed steel stacking can be effectively reduced, the service life of the submersed nozzle is prolonged, and the quality of a casting blank is improved. The device comprises a shell, an induction coil and a control unit. The shell comprises an inner shell and an outer shell, and the induction coil is wound between the inner shell and the outer shell and connected with the control unit. The shell sleeves the periphery of the submersed nozzle. A cooling unit is further arranged between the inner shell and the outer shell. According to the method, the real-time temperature of the molten steel is compared with the needed casting temperature, and when the real-time temperature is lower than the casting temperature, the heating degree is adjusted by calculating and adjusting the input current of the induction coil. The cooling degree is controlled by calculating and adjusting the flow of cooling media. The provided technical scheme is suitable for the steel continuous casting production process.

Dongbin Jiang

Papers

Effect of the Gap Between Copper Mold and Solidified Shell on the Fluid Flow in the Continuous Casting Strand with Mold Electromagnetic Stirring

Simulation of Solidification Structure During Vacuum Arc Remelting Using Cellular Automaton−Finite Element Method

Influence of Cooling Parameters on the Microstructure and Primary Carbide Precipitation in GCr15 Steel

Center Segregation Evolution in Slab Continuous Casting with Mechanical Reduction: A 3D Simulation

Device for heating molten steel in submersed nozzle and dynamic control method of device