A method for compatible operation of electromagnetic stirring and argon blowing in a slab continuous casting mold

Abstract

The application relates to a compatible operation method of slab continuous casting crystallizer electromagnetic stirring and argon blowing, which comprises the following steps: step 1: according to a continuous casting production site, process parameters such as a casting blank section, a blank drawing speed, a nozzle immersion depth, an electromagnetic stirring frequency, an electromagnetic stirring current and an argon blowing flow are obtained through networking; step 2: the process parameters obtained in step 1 are substituted into a built mathematical model, and flow field and temperature field data in the crystallizer are calculated; step 3: the flow velocity of molten steel at a steel slag free interface is extracted from the flow field data obtained in step 2, the area occupied by a region with a molten steel flow velocity greater than 0.35 m / s at the steel slag interface is counted, and a slag entrapment index S high is calculated; the area occupied by a region with a molten steel flow velocity less than 0.15 m / s at the steel slag interface is counted, a meniscus freezing index S low is calculated; and the combination relationship between the slab continuous casting crystallizer electromagnetic stirring current and the argon blowing amount is adjusted, so that the casting blank quality is improved, and the use requirements of users are met.

Description

Technical Field

[0001] This invention relates to a method, specifically a compatible operation method for electromagnetic stirring and argon blowing in a slab continuous casting crystallizer, belonging to the field of steelmaking continuous casting technology. Background Technology

[0002] When a magnetic field moves relative to molten steel at a certain speed, an induced current is generated in the steel. The interaction between the molten steel and the magnetic field produces an electromagnetic force, which drives the steel to move. Electromagnetic stirring (EMS), which controls the flow of molten steel through electromagnetic force, helps to purify the molten steel, improve the solidification structure of the billet, enhance the surface and internal quality of the billet, and expand the variety of products. In slab continuous casting production, the use of crystallizer electromagnetic stirring (M-EMS) can uniformly heat the molten steel, reduce the temperature gradient within the crystallizer, promote the flotation of gases and inclusions, increase the number of equiaxed crystal nuclei, and remove subcutaneous bubbles and inclusions from the surface of the billet.

[0003] In slab continuous casting production, argon blowing through the submerged nozzle is also used to prevent nozzle blockage. Both electromagnetic stirring in the crystallizer and argon blowing through the nozzle provide kinetic energy to the flow of molten steel within the crystallizer. When these two processes are not properly coordinated, two adverse effects will occur: firstly, excessive kinetic energy leads to violent flow of molten steel within the crystallizer, causing slag entrapment and uneven billet shell thickness; secondly, insufficient kinetic energy fails to remove air bubbles and inclusions. Therefore, a proper coordination between the two is necessary to achieve mutual compatibility and promotion.

[0004] Currently, there is no publicly available method for compatible operation of electromagnetic stirring and argon blowing in a crystallizer. The purpose of this invention is to disclose a method for optimizing the selection of electromagnetic stirring parameters in a crystallizer. Summary of the Invention

[0005] This invention addresses the problems existing in the prior art by providing a compatible operation method for electromagnetic stirring and argon blowing in a slab continuous casting crystallizer. The purpose of this technical solution is to provide a control method that is compatible with electromagnetic stirring (M-EMS) in the crystallizer and argon blowing at the nozzle, so that the two can work together appropriately to effectively remove subcutaneous bubbles and inclusions on the surface of the slab, thereby improving the quality of the slab and meeting the user's requirements.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a compatible operation method for electromagnetic stirring and argon blowing in a slab continuous casting crystallizer, characterized in that the method includes the following steps:

[0007] Step 1: Based on the continuous casting production site, obtain process parameters such as billet cross-section S, billet pulling speed V, sprue immersion depth D, electromagnetic stirring frequency f, electromagnetic stirring current I, and argon blowing flow rate Q through the network;

[0008] Step 2: Substitute the process parameters obtained in Step 1 into the established mathematical model to calculate the flow field and temperature field data inside the crystallizer. This mathematical model is based on the fluid dynamics control equations and uses a turbulence model to obtain the flow conditions of molten steel inside the crystallizer according to the geometric and boundary conditions of the continuous casting process. This mathematical model is based on the heat transfer control equations with flow and uses the geometric and boundary conditions of the continuous casting process to obtain the solidification of molten steel inside the crystallizer and obtain the solidified billet shell growth thickness.

[0009] Step 3: From the flow field data obtained in Step 2, extract the flow velocity of molten steel at the steel-slag free interface, count the area occupied by the region where the molten steel flow velocity at the steel-slag interface is greater than 0.35 m / s, and calculate the meniscus slag entrainment index S. high The area occupied by the region where the molten steel flow velocity at the steel-slag interface is less than 0.15 m / s was statistically analyzed, and the meniscus freezing index S was calculated. low ,

[0010] Step 4: Define S high The normal range for the value is [0, 0.65], S low The normal range for the value is [0, 0.05]. Based on S calculated in step 3... high and S low The system performs a judgment. If both parameters are within the normal range, proceed to step 5. If the condition that both parameters are within the normal range is not met, adjust the values ​​of the electromagnetic stirring current and the argon blowing rate, and return to steps 1 to 3 until S is satisfied. high and S low Both parameters are within the normal range, proceed to step 5.

[0011] Step 5: From the temperature field data obtained in Step 2, extract the solidified shell data at different heights from the meniscus of the crystallizer, and calculate the solidified shell uniformity index. When the solidified shell uniformity index is less than 0.9, change the values ​​of the electromagnetic stirring current and the argon blowing rate, and return to Steps 1 to 4 until the solidified shell uniformity index is greater than 0.9, then proceed to Step 6.

[0012] Step 6: Determine the matching range of stirring current and argon blowing rate under the continuous casting process parameters obtained in Step 1. When other continuous casting process parameters change, repeat steps 1-6 to obtain the optimal matching range of stirring current and argon blowing rate.

[0013] The dimensions of the cast billet cross-section range are: thickness 200-250mm, width 800-1600mm, and casting speed range:

[0014] 1.0-1.5 m / min, sprue immersion depth range: 120-170 mm.

[0015] The electromagnetic stirring device for the crystallizer has 24 coils (four pole pairs) and 25 turns; the distance from the upper edge of the iron core to the meniscus of the molten steel in the crystallizer is 0 mm; the frequency of the stirring magnetic field is 3.0-3.5 Hz; and the current of the stirring magnetic field is 0 A, 300 A, 400 A, 500 A, or 600 A. A typical arrangement of the stirring coils is shown in the attached figure. Figure 1 As shown. A certain stirring current in a stirrer generates a corresponding electromagnetic force. The larger the stirring current, the stronger the electromagnetic force. A typical correspondence between stirring current and electromagnetic force is shown in the attached figure. Figure 2 As shown.

[0016] Optionally, the argon blowing flow rate of the immersion nozzle is 0, 2, 4, or 6 L / min.

[0017] In step 3, the following definition is made:

[0018] The area at the steel-slag interface where the molten steel velocity is greater than 0.35 m / s, divided by the cross-sectional area of ​​the crystallizer, is defined as S. high ;

[0019] The area occupied by the region at the steel-slag interface where the molten steel flow velocity is less than 0.15 m / s, divided by the cross-sectional area of ​​the crystallizer, is defined as S. low .

[0020] S high A large value indicates vigorous flow at the steel-slag interface within the crystallizer, and a higher probability of slag entrapment; S low An increase in the value indicates insufficient flow at the steel-slag interface, poor slag formation in the protective slag leading to poor lubrication, an increased likelihood of meniscus hook-shaped structure formation, and an increased probability of subcutaneous bubble formation.

[0021] Typically, when the billet cross-section is 1120mm × 230mm, the billet pulling speed is 1.2m / min, the argon blowing rate is 4L / min, and the nozzle immersion depth is 150mm, the calculated effect of M-EMS current intensity on the interfacial flow velocity is shown in the attached figure. Figure 3 As shown. Based on this, S under these process parameters can be calculated. high and S low .

[0022] In step 5, the uniformity index of the billet shell at each height position (i.e., distance from the meniscus) in the crystallizer is defined as:

[0023]

[0024] In the formula: D avg The average thickness of the billet shell at this height is calculated as follows: The billet shell shape is cut out from the cross-section at this height, and the thickness values ​​are taken at N points at different locations on the billet shell (as shown in the attached figure). Figure 6 As shown), its average value is D.avg σ represents the standard deviation of the shell thickness at these N points. Generally, in a continuous casting mold, the shell uniformity index is required to be greater than or equal to 0.85.

[0025] Compared to existing technologies, this invention has the following advantages: the control method of using electromagnetic stirring in the crystallizer (M-EMS) and argon blowing at the sprue allows for proper coordination between the two, effectively removing subcutaneous bubbles and inclusions on the surface of the cast slab, thereby improving product quality and meeting user requirements. In the experimental stage, after adopting the above-mentioned optimization method, production practice showed that the incidence of longitudinal cracks on the surface of all steel grades decreased from 3.13% to 1.44%, the slag inclusion sealing rate decreased from 6.50% to 5.39%, and the steel defect rate decreased from 8.19% to 6.74%. The overall effect is that subcutaneous bubbles and inclusion defects on the surface of continuously cast slabs are effectively controlled. Attached Figure Description

[0026] Figure 1 M-EMS stirrer coil arrangement;

[0027] Figure 2 The relationship between M-EMS electromagnetic force distribution and current;

[0028] Figure 3 The effect of M-EMS current intensity on interfacial flow velocity;

[0029] Figure 4 The effect of M-EMS current intensity on the thickness distribution of billet shell;

[0030] Figure 5 The effect of argon blowing flow rate on the thickness distribution of the billet shell;

[0031] Figure 6 Method for calculating the uniformity index of solidified shell;

[0032] Figure 7 Flowchart of compatible operation method for electromagnetic stirring and argon blowing in slab continuous casting crystallizer. Detailed Implementation

[0033] To enhance understanding of the present invention, the embodiments will be described in detail below with reference to the accompanying drawings.

[0034] Example 1: See Figures 1-7 A compatible operation method for electromagnetic stirring and argon blowing in a slab continuous casting crystallizer, the method comprising the following steps:

[0035] Step 1: Based on the continuous casting production site, obtain process parameters such as billet cross-section S, billet pulling speed V, sprue immersion depth D, electromagnetic stirring frequency f, electromagnetic stirring current I, and argon blowing flow rate Q through the network;

[0036] Step 2: Substitute the process parameters obtained in Step 1 into the established mathematical model to calculate the flow field and temperature field data inside the crystallizer. This mathematical model is based on the fluid dynamics control equations and uses a turbulence model to obtain the flow conditions of molten steel inside the crystallizer according to the geometric and boundary conditions of the continuous casting process. This mathematical model is based on the heat transfer control equations with flow and uses the geometric and boundary conditions of the continuous casting process to obtain the solidification of molten steel inside the crystallizer and obtain the solidified billet shell growth thickness.

[0037] Step 3: From the flow field data obtained in Step 2, extract the flow velocity of molten steel at the steel-slag free interface, count the area occupied by the region where the molten steel flow velocity at the steel-slag interface is greater than 0.35 m / s, and calculate the meniscus slag entrainment index S. high The area occupied by the region where the molten steel flow velocity at the steel-slag interface is less than 0.15 m / s was statistically analyzed, and the meniscus freezing index S was calculated. low ,

[0038] Step 4: Define S high The normal range for the value is [0, 0.65], S low The normal range for the value is [0, 0.05]. Based on S calculated in step 3... high and S low The system performs a judgment. If both parameters are within the normal range, proceed to step 5. If the condition that both parameters are within the normal range is not met, adjust the values ​​of the electromagnetic stirring current and the argon blowing rate, and return to steps 1 to 3 until S is satisfied. high and S low Both parameters are within the normal range, proceed to step 5.

[0039] Step 5: From the temperature field data obtained in Step 2, extract the solidified shell data at different heights from the meniscus of the crystallizer, and calculate the solidified shell uniformity index. When the solidified shell uniformity index is less than 0.9, change the values ​​of the electromagnetic stirring current and the argon blowing rate, and return to Steps 1 to 4 until the solidified shell uniformity index is greater than 0.9, then proceed to Step 6.

[0040] Step 6: Determine the matching range of stirring current and argon blowing rate under the continuous casting process parameters obtained in Step 1. When other continuous casting process parameters change, repeat steps 1-6 to obtain the optimal matching range of stirring current and argon blowing rate.

[0041] The dimensions of the cast billet cross-section range are: thickness 200-250mm, width 800-1600mm, and casting speed range:

[0042] 1.0-1.5 m / min, sprue immersion depth range: 120-170 mm.

[0043] The electromagnetic stirring device for the crystallizer has 24 coils (four pole pairs) and 25 turns; the distance from the upper edge of the iron core to the meniscus of the molten steel in the crystallizer is 0 mm; the frequency of the stirring magnetic field is 3.0-3.5 Hz; and the current of the stirring magnetic field is 0 A, 300 A, 400 A, 500 A, or 600 A. A typical arrangement of the stirring coils is shown in the attached figure. Figure 1 As shown. A certain stirring current in a stirrer generates a corresponding electromagnetic force. The larger the stirring current, the stronger the electromagnetic force. A typical correspondence between stirring current and electromagnetic force is shown in the attached figure. Figure 2 As shown.

[0044] Optionally, the argon blowing flow rate of the immersion nozzle is 0, 2, 4, or 6 L / min.

[0045] In step 3, the following definition is made:

[0046] The area at the steel-slag interface where the molten steel velocity is greater than 0.35 m / s, divided by the cross-sectional area of ​​the crystallizer, is defined as S. high ;

[0047] The area occupied by the region at the steel-slag interface where the molten steel flow velocity is less than 0.15 m / s, divided by the cross-sectional area of ​​the crystallizer, is defined as S. low .

[0048] S high A large value indicates vigorous flow at the steel-slag interface within the crystallizer, and a higher probability of slag entrapment; S low An increase in the value indicates insufficient flow at the steel-slag interface, poor slag formation in the protective slag leading to poor lubrication, an increased likelihood of meniscus hook-shaped structure formation, and an increased probability of subcutaneous bubble formation.

[0049] Typically, when the billet cross-section is 1120mm × 230mm, the billet pulling speed is 1.2m / min, the argon blowing rate is 4L / min, and the nozzle immersion depth is 150mm, the calculated effect of M-EMS current intensity on the interfacial flow velocity is shown in the attached figure. Figure 3 As shown. Based on this, S under these process parameters can be calculated. high and S low .

[0050] In step 5, the uniformity index of the billet shell at each height position (i.e., distance from the meniscus) in the crystallizer is defined as:

[0051]

[0052] In the formula: D avg The average thickness of the billet shell at this height is calculated as follows: The billet shell shape is cut out from the cross-section at this height, and the thickness values ​​are taken at N points at different locations on the billet shell (as shown in the attached figure). Figure 6 As shown), its average value is D.avg σ represents the standard deviation of the shell thickness at these N points. Generally, in a continuous casting mold, the shell uniformity index is required to be greater than or equal to 0.85. Specific Implementation Example 1:

[0054] When the billet cross-section is 1120mm × 230mm and the sprue immersion depth is 150mm, and the casting speed is 1.0m / min, the optimal space for matching the down-blowing argon quantity and the electromagnetic stirring current is determined according to the method disclosed in this invention as follows:

[0055] 2 450～500A 4 420～550A Specific Implementation Example 2:

[0057] When the billet cross-section is 1120mm × 230mm and the sprue immersion depth is 150mm, and the casting speed is 1.1m / min, the optimal space for matching the downblown argon quantity and the electromagnetic stirring current is determined according to the method disclosed in this invention as follows:

[0058] 2 400～500A 4 500～550A Specific Implementation Example 3:

[0060] When the billet cross-section is 1120mm × 230mm and the sprue immersion depth is 150mm, and the casting speed is 1.2m / min, the optimal space for matching the down-blowing argon quantity and the electromagnetic stirring current is determined according to the method disclosed in this invention as follows:

[0061]

[0062] Specific Implementation Example 4:

[0064] When the billet cross-section is 1120mm × 230mm and the sprue immersion depth is 150mm, and the casting speed is 1.3m / min, the optimal space for matching the downblown argon quantity and the electromagnetic stirring current is determined according to the method disclosed in this invention as follows:

[0065] 0 300A 2 400～500A 4 450～550A Specific Implementation Example 5:

[0067] When the billet cross-section is 1120mm × 230mm and the sprue immersion depth is 150mm, and the casting speed is 1.4m / min, the optimal space for matching the down-blowing argon quantity and the electromagnetic stirring current is determined according to the method disclosed in this invention as follows:

[0068] 0 400A 2 400～450A 4 420～500A

[0069] According to the process combination described, within a suitable billet drawing speed range, the surface quality of the continuously cast slab obtained is good.

[0070] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention. Equivalent transformations or substitutions made based on the above technical solutions all fall within the scope of protection of the claims of the present invention.

Claims

1. A compatible operation method for electromagnetic stirring and argon blowing in a slab continuous casting crystallizer, characterized in that, The method includes the following steps: Step 1: Based on the continuous casting production site, obtain the following process parameters via network connection: billet cross-section S, billet pulling speed V, sprue immersion depth D, electromagnetic stirring frequency f, electromagnetic stirring current I, and argon blowing flow rate Q; Step 2: Substitute the process parameters obtained in Step 1 into the established mathematical model to calculate the flow field and temperature field data within the crystallizer. This mathematical model is based on the fluid dynamics control equations and uses a turbulence model to obtain the flow conditions of the molten steel within the crystallizer according to the geometric and boundary conditions of the continuous casting process. Based on the heat transfer control equations for flow, and according to the geometric and boundary conditions of the continuous casting process, this mathematical model obtains the solidification conditions of the molten steel within the crystallizer, and thus the thickness of the solidified billet shell. Step 3: From the flow field data obtained in Step 2, extract the flow velocity of molten steel at the steel-slag free interface, count the area occupied by the region where the molten steel flow velocity at the steel-slag interface is greater than 0.35 m / s, and calculate the meniscus slag entrainment index S. high The area occupied by the region where the molten steel flow velocity at the steel-slag interface is less than 0.15 m / s was statistically analyzed, and the meniscus freezing index S was calculated. low , Step 4: Define S high The normal range for S is [0, 0.65]. low The normal range for the value is [0, 0.05]. Based on S calculated in step 3... high and S low The system performs a judgment. If both parameters are within the normal range, proceed to step 5. If the condition that both parameters are within the normal range is not met, adjust the values ​​of the electromagnetic stirring current and the argon blowing rate, and return to steps 1 to 3 until S is satisfied. high and S low Both parameters are within the normal range, proceed to step 5. Step 5: From the temperature field data obtained in Step 2, extract the solidified shell data at different heights from the meniscus of the crystallizer, and calculate the solidified shell uniformity index. When the solidified shell uniformity index is less than 0.9, change the values ​​of the electromagnetic stirring current and the argon blowing rate, and return to Steps 1 to 4 until the solidified shell uniformity index is greater than 0.9, then proceed to Step 6. Step 6: Determine the matching range of stirring current and argon blowing amount under the continuous casting process parameters obtained in Step 1. When other continuous casting process parameters change, repeat Steps 1-6 to obtain the optimal matching range of stirring current and argon blowing amount.

2. The compatible operation method of electromagnetic stirring and argon blowing in a slab continuous casting crystallizer according to claim 1, characterized in that, The dimensions of the billet cross section are as follows: thickness 200-250mm, width 800-1600mm, billet pulling speed range: 1.0-1.5m / min, and sprue immersion depth range: 120-170mm.

3. The compatible operation method of electromagnetic stirring and argon blowing in a slab continuous casting crystallizer according to claim 2, characterized in that, The number of coils in a single electromagnetic stirring device for the crystallizer is 24; the number of turns is 25; the distance from the upper edge of the iron core to the meniscus of the molten steel in the crystallizer is 0mm; the frequency of the stirring magnetic field is 3.0-3.5Hz; and the current of the stirring magnetic field is 0A, 300A, 400A, 500A, or 600A.

4. The compatible operation method of electromagnetic stirring and argon blowing in a slab continuous casting crystallizer according to claim 3, characterized in that, In step 3, the following definition is made: The area at the steel-slag interface where the molten steel velocity is greater than 0.35 m / s, divided by the cross-sectional area of ​​the crystallizer, is defined as S. high ; The area occupied by the region at the steel-slag interface where the molten steel flow velocity is less than 0.15 m / s, divided by the cross-sectional area of ​​the crystallizer, is defined as S. low .

5. The compatible operation method of electromagnetic stirring and argon blowing in a slab continuous casting crystallizer according to claim 3 or 4, characterized in that, In step 5, the uniformity index of the billet shell at each height position in the crystallizer is defined as: (1) In the formula: D avg The average thickness of the billet shell at this height is calculated as follows: The billet shell shape is cut from a cross-section at this height, and the thickness values ​​are taken at N points at different locations on the billet shell. The average value is D. avg σ is the standard deviation of the shell thickness at these N points.

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