Electromagnetic stirring parameter determination method for continuous casting bloom

Abstract

The invention discloses a method for determining electromagnetic stirring parameters of a continuous casting bloom, which comprises the following steps of: collecting field technical parameters and steel type parameters, and establishing a continuous casting bloom solidification heat transfer model to obtain a continuous casting bloom solidification end point position, a center solid fraction and a surface temperature; for the tail end electromagnetic stirring process, reasonable condition assumption is carried out on a general physical model, and the influence of displacement current and molten steel movement on an electromagnetic field is neglected in calculation as analog; calculating an electromagnetic stirrer of the bloom continuous casting machine, and modeling and simplifying; calculating electromagnetic field distribution characteristics in the casting blank of the bloom crystallizer by utilizing the established model; and comparing calculation based on the model with material object sampling analysis, and performing corresponding electromagnetic force adjustment according to a comparison result so as to finish final determination of electromagnetic stirring parameters. By adopting the parameter determination method, proper electromagnetic stirring current and other parameters can be optimized and determined so as to improve bloom segregation and internal quality.

Description

Technical Field

[0001] The invention relates to electromagnetic stirring control technology, and in particular to a method for determining electromagnetic stirring parameters of continuous casting large square billets. Background Art

[0002] During the solidification process of steel, segregation will occur due to selective crystallization, solidification shrinkage, etc. The central shrinkage cavity and looseness will seriously affect the internal quality of the ingot and subsequent rolled products. Macro segregation will cause faults, unqualified materials, and a large number of carbides to gather and form cracks. Micro segregation will cause banded structure in the subsequent rolling process, making the material's mechanical properties different in all directions, reducing the plasticity, toughness, and cross-sectional shrinkage rate of the steel. Central shrinkage cavity and looseness will form cracks in the subsequent rolling process, seriously endangering product quality. Therefore, it is of great significance to improve the internal quality of the ingot.

[0003] There have been many studies on methods to improve the internal quality of ingots. Among them, the use of electromagnetic stirring technology in the continuous casting process is an effective method to improve the internal quality of ingots. As early as the beginning of the last century, relevant scholars proposed that during the solidification of metals, an electromagnetic field should be applied to control the solidification structure and improve the internal quality. In the middle of the last century, Germans Junghans and Schaber first applied electromagnetic stirring technology to the continuous casting process, installed it in the secondary cooling zone, and achieved good experimental results. Domestic electromagnetic stirring technology started in the 1970s. In the early stage, relevant electromagnetic stirring technology was mainly introduced from Europe and Japan, and then studied and improved on this basis. However, due to insufficient theoretical knowledge, the performance has been unstable. After the unremitting efforts of a large number of researchers and scholars, my country has made great breakthroughs in the field of continuous casting electromagnetic stirring technology. In 1997, the large slab continuous casting S-EMS was successfully developed. The successful independent research and development of the crystallizer electromagnetic stirring technology marked the ability to develop high-performance electromagnetic stirring technology. At present, electromagnetic stirring technology has been widely used in the industry.

[0004] Patents such as CN201910370772, entitled "Electromagnetic Stirrer Control Method and System for Measuring and Controlling Stirring Strength", CN201510161833, entitled "An Electromagnetic Stirrer for Continuous Casting Solidification End and Dynamic Control Method thereof", and CN201510527998, entitled "Electromagnetic Stirring Device and Method with Adjustable Stirring Area", are all for slabs. However, for billets, the difference in steel type and shape leads to differences in technology, and the difficulty of implementation is greater than the above-mentioned public technologies. In addition, the above-mentioned public technologies mostly involve theoretical model deduction or ignore the treatment of the influence of displacement current magnetic quasi-static field and molten steel movement on the electromagnetic field. Literatures such as "Calculation of Electromagnetic Force in Electromagnetic Stirring Process of Steel Continuous Casting" and "Influence of Electromagnetic Stirring Parameters of Billet Crystallizer on Magnetic Field Distribution" also focus on calculation and simulation, and have not formed a closed-loop verification effect for field application. Summary of the invention

[0005] In order to solve the above problems in the prior art, the present invention provides a method for determining electromagnetic stirring parameters of continuous casting large square billets, which can optimize and determine appropriate electromagnetic stirring current and other parameters to improve the segregation and internal quality of the large square billets.

[0006] A method for determining electromagnetic stirring parameters for continuous casting blooms comprises the following steps:

[0007] S1. Collect on-site technical parameters and steel grade parameters, establish a continuous casting billet solidification heat transfer model to obtain the solidification endpoint position, center solid phase ratio, and surface temperature of the continuous casting billet;

[0008] S2. For the end electromagnetic stirring process, reasonable assumptions are made for the general physical model, and the influence of displacement current and molten steel movement on the electromagnetic field is ignored in the calculation;

[0009] S3. The coil winding is symmetrically wound on the yoke of the stirrer, and three-phase alternating current is passed through the coil to simulate and calculate the electromagnetic stirrer of the large square billet continuous casting machine, and the model is modeled and simplified;

[0010] S4. Calculate the electromagnetic field distribution characteristics inside the billet crystallizer using the established model;

[0011] S5. Compare the calculation based on the model with the actual sampling analysis, and adjust the electromagnetic force accordingly according to the comparison result, so as to complete the determination of the final electromagnetic stirring parameters.

[0012] In step S1, the on-site technical parameters and steel grade parameters include the on-site commonly used pulling speed range, superheat range, continuous casting machine parameters, electromagnetic stirring parameters, equipment pressing capacity, crystallizer length, secondary cooling water volume, and steel grade composition.

[0013] In step S3, the simplification includes: modeling the ingot and air in the agitator part for the crystallizer and the electromagnetic agitator at the end of solidification; considering that the ingot is divided into a solid phase zone and a mushy zone, and the flow in the mushy zone is considered by increasing the viscosity; modeling the air equivalent to 3-5 times the volume of the magnet.

[0014] In step S3, the modeling is based on the coupling of electromagnetic field and flow field through electromagnetic fluid dynamics control equations based on Maxwell equations, constitutive equations and continuity equations.

[0015] The Maxwell equations are:

[0016]

[0017] Where: E is the electric field strength, unit is V / m; B is the magnetic induction strength, unit is T; H is the magnetic field strength, unit is A / m; J is the current density, unit is A / m 2 ; t is time, unit is s.

[0018] The constitutive equation is: D = ε 0 ε r E, B = μ 0 μ r H,j = σE;

[0019] Where: ε 0 =8.85×10 -12 F / m is the dielectric constant of vacuum; εr is the relative dielectric constant, dimensionless; μ 0 =4π×10 -7 H / m is the magnetic permeability of vacuum; μr is the relative magnetic permeability, dimensionless; σ is the electrical conductivity of the medium.

[0020] The electromagnetic fluid dynamics control equation is:

[0021]

[0022] Where: F is the electromagnetic force, unit is N / m 3 ; Re is the real part of the complex expression; B * is the conjugate complex number of B, with the unit of T.

[0023] The electromagnetic stirring parameter determination method for continuous casting large square billet of the present invention has the following advantages:

[0024] 1. Focus on practical verification and application, not just theoretical model deduction, or ignore the treatment of the influence of displacement current magnetic quasi-static field and molten steel movement on the electromagnetic field. It is formed after verifying the effectiveness through physical quality judgment based on practical application;

[0025] 2. Optimize and determine appropriate parameters such as electromagnetic stirring current to effectively improve the segregation and internal quality of large square billets.

[0026] 3. It is accurate, effective and low risk. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a distribution diagram of magnetic induction intensity on the central axis of the crystallizer casting billet of the present invention;

[0028] Figure 2 It is a distribution diagram of magnetic induction intensity on the central axis of the terminal casting billet of the present invention;

[0029] Figure 3a-3c They are respectively the magnetic induction intensity distribution diagrams at different positions of the crystallizer of the present invention. DETAILED DESCRIPTION

[0030] The following is a further description of a method for determining electromagnetic stirring parameters of a continuous casting bloom according to the present invention, which method comprises the following steps:

[0031] The first step is to collect on-site technical parameters and steel grade parameters, establish a continuous casting billet solidification heat transfer model, and obtain the continuous casting billet solidification end point position, central solid phase ratio, and surface temperature.

[0032] Among them, the on-site technical parameters and steel grade parameters include: the commonly used on-site casting speed range, superheat range, continuous casting machine parameters, electromagnetic stirring parameters, equipment pressing capacity, crystallizer length, secondary cooling water volume, steel grade composition, etc. In addition, the secondary cooling water volume can be combined with the on-site process to achieve accurate docking of the solidification endpoint and the stirring position.

[0033] The second step is to use mathematical formulas to describe the simulation, and first make reasonable assumptions about the general physical model. For the end electromagnetic stirring process, without affecting the authenticity and rationality of the model, in line with the principle of simplifying the calculation, the following assumptions are made:

[0034] (1) The current frequency used in electromagnetic stirring is generally 1.0 to 10.0 Hz. The magnetic field generated by the excitation belongs to a magnetic quasi-static field, and the displacement current generated has little effect, so the displacement current is ignored in the calculation.

[0035] (2) During electromagnetic stirring, the magnetic Reynolds number is very small, estimated to be about 0.01. Therefore, when calculating the electromagnetic field problem, the two-phase region is regarded as stationary and the influence of the movement of molten steel on the electromagnetic field is ignored.

[0036] In the third step, the simulated stirrer uses 6 coil windings symmetrically distributed and wound on the yoke of the stirrer. Three-phase alternating current is passed into the coil. By changing the magnitude and frequency of the current, the magnitude of the electromagnetic force can be changed to obtain a suitable stirring intensity. The present invention simulates and calculates the electromagnetic stirrer of the large square billet continuous casting machine, and the model parameters are obtained from the production site.

[0037] When modeling, the following simplifications are made as needed: (1) For the crystallizer and the electromagnetic stirrer at the end of solidification, the ingot and air in the stirrer part are modeled; (2) The ingot is considered to be divided into a solid phase area and a mushy phase area, and the flow in the mushy phase area is considered by increasing the viscosity; (3) In order to ensure the calculation accuracy, due to the effect of the yoke and the core, the magnetic field outside a certain range is almost zero, so a finite volume of air can be modeled. According to experience, air with a volume equivalent to 3 to 5 times that of the magnet is generally modeled.

[0038] The modeling is based on the coupling of electromagnetic field and flow field through electromagnetic fluid dynamics control equations based on Maxwell equations, constitutive equations and continuity equations.

[0039] The distribution of electromagnetic fields in space is described by Maxwell's equations. For the magnetic quasistatic field in this article, the differential form of Maxwell's equations is expressed as follows:

[0040]

[0041]

[0042]

[0043]

[0044] Where: E is the electric field intensity, V / m; B is the magnetic induction intensity, T; H is the magnetic field intensity, A / m; J is the current density, A / m 2 ; t is time, s; μ is magnetic permeability, H / m; σ is electrical conductivity, unit S / m.

[0045] Maxwell's equations reflect the relationship between the field vectors E, D, H, B and the field sources J and ρ at every point in space at any moment.

[0046] To solve the spatial distribution of electromagnetic fields and characterize the macroscopic properties of materials under the action of electromagnetic fields, it is not enough to have only the Maxwell equations. It is also necessary to supplement the constitutive equations that describe the electromagnetic properties of materials:

[0047] D=ε 0 ε r E (1.5)

[0048] B=μ 0 μ r H (1.6)

[0049] j=σE (1.7)

[0050] In the formula, ε 0 =8.85×10 -12 F / m is the dielectric constant of vacuum; εr is the relative dielectric constant, dimensionless; μ 0 =4π×10 -7 H / m is the magnetic permeability of vacuum; μr is the relative magnetic permeability, dimensionless; σ is the electrical conductivity of the medium.

[0051] In the solution calculation, the electromagnetic force obtained is expressed as the time average:

[0052]

[0053] Where F is the electromagnetic force, in N / m3; Re is the real part of the complex expression; B * is the conjugate complex number of B, with the unit of T.

[0054] The establishment of the electromagnetic field mathematical model and the solution of the equation group can be completed by the commercial finite element analysis software ANSYS 19.0.

[0055] The fourth step is to use the established model to calculate the electromagnetic field distribution characteristics in the billet crystallizer. The commonly used process parameters are 300A and 2.5Hz. Figure 1-Figure 2 ,in Figure 1 This is the distribution diagram of magnetic induction intensity in the mold casting under the current intensity of 300A. Figure 2 It is the distribution diagram of magnetic induction intensity on the central axis of the final casting billet.

[0056] Step 5: The electromagnetic stirring magnetic field distribution is determined.

[0057] Example 1

[0058] Taking a certain type of medium carbon steel bloom as an example, the content of each component of this steel is C: 0.18-0.22wt%, Si: 0.2-0.3wt%, Mn: 1.25-1.35wt%, P: 0-0.15wt%, S: 0.01-0.02wt%. The casting superheat is 30℃, the pulling speed is 0.65m / min-0.70m / min, the cross-sectional size is 320×425mm, the secondary cooling water volume adopts conventional water volume, and the solidification endpoint is fine-tuned according to the process characteristics when necessary to determine the reasonable electromagnetic stirring parameters that can improve the internal quality of this steel.

[0059] Step 1:

[0060] Collect on-site technical parameters and steel grade parameters, establish a continuous casting billet solidification heat transfer model, and obtain the solidification endpoint position, center solid phase ratio, and surface temperature of the continuous casting billet. In the step 1, the on-site technical parameters and steel grade parameters include: the commonly used on-site casting speed range, superheat range, continuous casting machine parameters, electromagnetic stirring parameters, equipment pressing capacity, crystallizer length, secondary cooling water volume, steel grade composition, etc.

[0061] Table 1 Dimensional parameters of electromagnetic stirrer model

[0062]

[0063] Step 2: Use mathematical formulas to describe the simulation, and first make reasonable assumptions about the physical model. For the end electromagnetic stirring process, make corresponding assumptions based on the principle of simplifying the calculation without affecting the authenticity and rationality of the model.

[0064] Table 2 Material properties used in the calculation

[0065]

[0066] Step 3:

[0067] The simulated stirrer has six coil windings symmetrically distributed and wound on the stirrer's yoke. Three-phase alternating current is passed through the coil. By changing the magnitude and frequency of the current, the magnitude of the electromagnetic force can be changed to obtain the appropriate stirring intensity. The electromagnetic stirrer of the large square billet continuous casting machine simulated in this paper uses model parameters from the production site.

[0068] Step 4:

[0069] The established model is used to calculate the electromagnetic field distribution characteristics in the billet crystallizer, with the commonly used process parameters being 300A and 2.5Hz. The magnetic induction intensity distribution in the crystallizer billet and the magnetic induction intensity distribution on the central axis of the terminal billet are obtained under a current intensity of 300A.

[0070] Step 5:

[0071] The electromagnetic stirring magnetic field distribution is determined.

[0072] An electromagnetic field calculation model was established based on the field data, and the distribution law of the electromagnetic field at the end of solidification was obtained. The main results are:

[0073] (1) For the six-pole electromagnetic stirrer, the distribution law of the electromagnetic stirring magnetic field in the crystallizer and at the end of solidification is roughly the same. The magnetic induction intensity of the electromagnetic stirring electromagnetic field is larger in the stirrer area and gradually decays toward the two ends.

[0074] (2) The magnetic induction intensity distribution on the central axis follows the rule of "large in the center and small at both ends". On the cross section, the magnetic induction intensity of the ingot gradually decreases from the edge to the center.

[0075] (3) On the cross section of the ingot, the electromagnetic force is distributed circumferentially, and the magnitude of the tangential electromagnetic force is proportional to the distance from the center. The electromagnetic force in the axial direction reaches its maximum value near the center of the stirrer.

[0076] The model was verified by measuring the regional distribution of the electromagnetic stirring field in the mold and at the end of solidification. The Tesla meter was used to (1) change the current frequency while keeping the current constant; (2) change the current magnitude while keeping the current frequency constant to confirm the accurate distribution law of the electromagnetic field. The on-site large square billet sampling and analysis method was combined to conduct low-power analysis and rating of the billet cross section, evaluate the improvement effect of the corresponding process on the structure and segregation, verify the rationality of the optimized electromagnetic stirring parameters, and finally solidify the relevant electromagnetic stirring parameters.

[0077] like Figure 3a-3c As shown in the figure, based on the measured results, the electromagnetic stirring model is modified. For this typical steel grade, the best electromagnetic stirring process parameters for the crystallizer are 400A, 2.5Hz, and the best electromagnetic stirring process parameters for the end of solidification are 350A, 8.0Hz.

[0078] However, those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for determining electromagnetic stirring parameters for continuous casting of large square billets. Features , including the following steps: S1. Collect on-site technical parameters and steel grade parameters, establish a continuous casting billet solidification heat transfer model to obtain the solidification endpoint position, center solid phase ratio, and surface temperature of the continuous casting billet; S2. For the end electromagnetic stirring process, reasonable condition assumptions are made for the general physical model, and the influence of displacement current and molten steel movement on the electromagnetic field is ignored in the calculation; S3. The coil winding is symmetrically wound on the yoke of the stirrer, and three-phase alternating current is passed through the coil to simulate and calculate the electromagnetic stirrer of the large square billet continuous casting machine, and the model is modeled and simplified; S4. Calculate the electromagnetic field distribution characteristics inside the billet crystallizer using the established model; S5. Compare the calculation based on the model with the actual sampling analysis, and adjust the electromagnetic force accordingly according to the comparison result, so as to complete the determination of the final electromagnetic stirring parameters.

2. A method for determining electromagnetic stirring parameters for continuous casting blooms according to claim 1, Features: In step S1, the on-site technical parameters and steel grade parameters include the on-site commonly used pulling speed range, superheat range, continuous casting machine parameters, electromagnetic stirring parameters, equipment pressing capacity, crystallizer length, secondary cooling water volume, and steel grade composition.

3. A method for determining electromagnetic stirring parameters for continuous casting blooms according to claim 1 or 2, Features: In step S3, the simplification includes: modeling the ingot and air in the agitator part for the crystallizer and the electromagnetic agitator at the end of solidification; considering that the ingot is divided into a solid phase zone and a mushy zone, and the flow in the mushy zone is considered by increasing the viscosity; modeling the air equivalent to 3-5 times the volume of the magnet.

4. A method for determining electromagnetic stirring parameters for continuous casting blooms as claimed in claim 1, Features: In step S3, the modeling is based on the coupling of electromagnetic field and flow field through electromagnetic fluid dynamics control equations based on Maxwell equations, constitutive equations and continuity equations.

5. A method for determining electromagnetic stirring parameters for continuous casting blooms as claimed in claim 4, Features: The Maxwell equations are: Where: E is the electric field strength, unit is V / m; B is the magnetic induction strength, unit is T; H is the magnetic field strength, unit is A / m; J is the current density, unit is A / m 2 ; t is time, unit is s.

6. A method for determining electromagnetic stirring parameters for continuous casting blooms as claimed in claim 4, Features: The constitutive equation is: D = ε 0 ε r E, B = μ 0 μ r H,j = σE; Where: ε 0 =8.85×10 -12 F / m is the dielectric constant of vacuum; εr is the relative dielectric constant, dimensionless; μ 0 =4π×10 - 7 H / m is the magnetic permeability of vacuum; μr is the relative magnetic permeability, dimensionless; σ is the electrical conductivity of the medium.

7. A method for determining electromagnetic stirring parameters for continuous casting blooms as claimed in claim 4, Features: The electromagnetic fluid dynamics control equation is: Where: F is the electromagnetic force, unit is N / m 3 ; Re is the real part of the complex expression; B * is the conjugate complex number of B, with the unit of T.

Images