CN115026250A - Control method for continuous casting large round billet tail end near liquidus electromagnetic stirring process - Google Patents
Control method for continuous casting large round billet tail end near liquidus electromagnetic stirring process Download PDFInfo
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- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/114—Treating the molten metal by using agitating or vibrating means
- B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22D11/18—Controlling or regulating processes or operations for pouring
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Abstract
The invention belongs to the technical field of continuous casting production, and particularly relates to a control method of a near-liquidus electromagnetic stirring process at the tail end of a continuous casting round billet. Aiming at the technical problems that the position of a solidification tail end is difficult to predict in the large round billet continuous casting process, stirring parameters are difficult to determine and the like, the invention provides a predictable and adjustable continuous casting large round billet tail end near liquidus electromagnetic stirring process control method, which predicts the distribution of columnar crystals and equiaxial crystals in the continuous casting billet solidification process by using a volume average method, determines the position of the solidification tail end (near liquidus), performs electromagnetic stirring adjustment according to the position of the solidification tail end, and applies electromagnetic stirring to the predicted position of the solidification tail end (near liquidus). The invention can accurately predict the position of the solidification tail end of the continuous casting round billet in the solidification process, thereby accurately controlling the position of the stirrer according to the process requirement of electromagnetic stirring of the solidification tail end, further effectively improving the flowing state of the molten steel of the solidification tail end and improving the core part quality of the round billet.
Description
Technical Field
The invention belongs to the technical field of continuous casting production, and particularly relates to a control method of a near-liquidus electromagnetic stirring process at the tail end of a continuous casting round billet.
Background
The large round billet is an important casting product, is mainly used for producing high-value-added rings such as large-specification and super-large-specification high-pressure boiler pipes, oil well pipes, bearing sleeves, gears, high-speed train wheels and the like, and has wide application prospect. At present, the die casting method is mainly adopted for preparation, but the die casting efficiency is low, and the yield is low. The continuous casting is used for replacing die casting, so that high efficiency and high yield of the die steel preparation can be realized. However, as the cross section of the continuous casting billet is enlarged, the heat capacity of the casting billet per unit length is increased, the heat dissipation area is reduced, the solidification mode is changed from rapid solidification to slow solidification, and the heat convection of the molten steel in the core part and the redistribution process of solute elements are aggravated. The problems of macrosegregation of some solute elements and loose shrinkage cavity caused by slow solidification are more prominent.
For different continuous casting billet varieties and specifications, at present, metallurgical workers at home and abroad adopt the technologies of improving the quality of molten steel, pouring at low superheat degree, lightly pressing the tail end and the like to improve the internal quality of the continuous casting billet. However, the improvement degree of the molten steel quality is limited, and the requirement is too high, so that the smelting difficulty is increased, and the smelting cost is increased; in actual production, when the superheat degree is reduced to be near a liquidus line, pouring can cause nozzle blockage, and floating of inclusions in steel is influenced; the difficulty in determining the technological parameters under the soft reduction of the tail end is high, and the requirements on equipment and control technology are high.
The electromagnetic stirring is the most effective technical means for improving the quality of the continuous casting large round billet and inhibiting the segregation of element components and the loosening and shrinkage of the hole. The solidification end electromagnetic stirring technology can generate electromagnetic force through a rotating magnetic field applied by an electromagnetic stirrer to form forced convection of molten steel so as to break or fuse columnar crystals to form equiaxed crystal nuclei; and has the functions of improving the uniformity of the thickness of the solidified shell and promoting the floating of the inclusion, thereby controlling the development of center segregation in a certain range.
The solidification process of the continuous casting large round billet can be optimized by the solidification tail end electromagnetic stirring process, but the solidification mode of the continuous casting large round billet is changed from quick solidification to slow solidification, so that the position of the solidification tail end is difficult to predict, the stirring parameters are also determined according to different sections and different steel types, and the method for trial and error of the experiment has high cost and long period.
Disclosure of Invention
Aiming at the technical problems that the position of a solidification tail end is difficult to predict in the large round billet continuous casting process, stirring parameters are difficult to determine and the like, the invention provides a predictable and adjustable continuous casting large round billet tail end near liquidus electromagnetic stirring process control method, which predicts the distribution of columnar crystals and equiaxial crystals in the continuous casting billet solidification process by using a volume average method, determines the position of the solidification tail end (near liquidus), performs electromagnetic stirring adjustment according to the position of the solidification tail end, and applies electromagnetic stirring to the predicted position of the solidification tail end (near liquidus).
Specifically, the method of the present invention comprises the steps of:
s1, creating a geometric model: and creating a model of the large round billet according to the size of the continuous casting large round billet in the actual production process.
S2, grid division: and adopting finite element simulation software to perform structured grid division on the model and encrypt the edge grids.
S3, formulating boundary conditions and physical property parameters: and determining each calculation boundary condition according to the operation parameters of the actual production working condition, and determining the physical property parameters of the cast alloy according to the steel grade.
The physical parameters of the casting alloy comprise density, specific heat capacity, heat conductivity coefficient, liquid dynamic viscosity, liquid solute diffusion coefficient, solid solute diffusion coefficient, phase change latent heat, thermal expansion coefficient, liquidus slope and the like.
The boundary conditions may be set according to actual production conditions and operating parameters. For example, the boundary condition can adopt convection heat transfer, and the boundary of the large round billet can adopt the condition of sectional cooling.
S4, performing simulation calculation: and (3) performing simulation calculation on the temperature inside the large round billet and the distribution of each phase in the continuous casting process by using a three-phase volume average method. And (3) dividing the interior of the large round billet into three continuous phases of a liquid phase l, an isometric crystal phase e and a columnar crystal phase c, and modeling to determine mass, momentum and component transmission source items among the phases.
Corresponding phase volume fractions of f l 、f e And f c . Wherein the liquid phase and the isometric phase are movable phases, and the solution of the movement can adopt a corresponding N-S equation; the columnar crystal phase is an immobile phase that grows toward the liquid phase direction adhering to the cooling wall surface. For each local node of the large round billet and the whole large round billet, the sum of the volume fractions of three phases is 1, namely f l +f e +f c ＝1。
And predicting the distribution of liquid phase, columnar crystal phase and equiaxed crystal phase in the solidification process of the continuous casting billet by determining the mass, momentum and component transmission source items among all phases and solving a control equation. The control equations comprise continuity equations, momentum equations, species transport equations, energy equations, and other self-defined scalar equations for simulating transmission or diffusion according to actual conditions. The control equation can be solved by the control volume based on the finite difference method, more than 60 iterations are adopted in each time step, and the convergence criterion of the normalized residual errors of the continuity equation, the momentum equation, the species transport equation and the user-defined scalar equation is 10 -4 The convergence criterion for the normalized residual of the energy equation is 10 below -7 The following.
S5, determining the position of a solidification tail end: from f l 1 region boundary contour to f l The region between the region boundary contours of 0 is the solidification end of the round billet.
Wherein f is l The zone boundary contour line of 1 is also the liquidus temperature end point (T) of the large round billet alloy l ) Isotherm of (f) l The zone boundary contour line of 0 is also the solidus temperature end point (T) of the large round billet alloy s ) The isotherm of (a).
S6, adjusting electromagnetic stirring according to the position of the solidification tail end, and applying a required magnetic field at the solidification tail end. Preferably, the position of the electromagnetic stirrer for applying the magnetic field is f l The region boundary contour is 1 in a section 3 meters above the end point of the contour and can be adjusted up and down within the section.
Further, step S6 may be implemented by the following scheme: according to different requirements of the large round billets with different section sizes on internal flow and heat transfer, by means of low-frequency electromagnetic field simulation software such as Maxwell and the like, the effect of the electromagnetic stirrer of the large round billets for continuous casting is calculated by a finite element method, electromagnetic stirring parameters (current and frequency) are determined, magnetic field distribution is predicted, and a proper region (such as a region with relatively large magnetic induction intensity) of a magnetic field is applied to the previously determined solidification end position. Specifically, this can be achieved by:
s6.1 creates a geometric model: and (3) creating a model according to the type and the size of the electromagnetic stirrer adopted at the solidification end of the continuous casting round billet in the actual production process, and defining a calculation domain.
S6.2, grid division: and dividing a calculation domain into unstructured grids based on Maxwell isoelectric electromagnetic field simulation software, and encrypting the geometric body edge position grids.
S6.3, setting solving type and excitation: setting to solve a transient magnetic field and activating eddy current analysis inside the casting blank; and generating the cross section of the winding coil, inputting the number of turns, and setting the current and the phase of each winding coil.
S6.4, distributing material attributes of each part in the calculation domain, and formulating boundary conditions; the material properties comprise a copper wire, a magnet yoke, a casting blank and an air domain, wherein the air domain is the outer edge of the calculation domain; due to the constraint of the magnetic yoke on the magnetic field, a Nieman boundary condition is adopted, namely no magnetic flux passes through.
S6.5, performing simulation calculation: according to different requirements of large round billets with different section sizes on internal flow and heat transfer, electromagnetic stirring parameters (mainly current and frequency) are determined, and magnetic induction intensity distribution, induced current and electromagnetic force distribution in the continuous casting billets are predicted according to the electromagnetic stirring parameters.
S6.6 adjusts the position of the electromagnetic stirrer so that an appropriate region of the magnetic field acts on the solidification end, based on the simulation results of the magnetic induction intensity distribution, the induced current, and the electromagnetic force distribution, and the solidification end position determined in step S5.
The method applies electromagnetic agitation at the solidification end (near liquidus) position. The electromagnetic stirrer can move up and down according to electromagnetic stirring parameters (current and frequency), electromagnetic stirring is applied to the solidification end by adjusting the position, the edge of the dendritic crystal is passivated to form a nearly spherical body, the stabilization of the spherical crystal and the transformation from the dendritic crystal to the spherical crystal are promoted, and the nucleation rate of the spherical crystal is improved.
Compared with the prior art, the invention has the following advantages:
1. the invention implements electromagnetic stirring at the near liquidus of the solidification tail end of the continuous casting large round billet, can realize the passivation of the dendritic crystal edge, enables the dendritic crystal edge to form a near sphere, promotes nucleation, and also has the functions of improving the uniformity of the casting blank and promoting inclusions to float upwards.
2. The invention adopts a numerical simulation method to determine the position of the solidification tail end and the electromagnetic stirring parameters (current and frequency), and compared with an experimental trial and error method, the invention can reduce the cost, shorten the period and improve the efficiency.
3. The method for predicting the solidification tail end of the continuous casting round billet can accurately predict the position of the solidification tail end of the continuous casting round billet in the solidification process, so that the position of a stirrer can be accurately controlled according to the process requirement of electromagnetic stirring of the solidification tail end, the flowing state of molten steel at the solidification tail end can be further effectively improved, and the core part quality of the round billet is improved.
4. The predictable and adjustable continuous casting round billet tail end near liquidus electromagnetic stirring process control method provided by the invention has wide applicability, is suitable for round billets of different sizes and materials in actual production, and provides guidance for field electromagnetic stirring setting.
In conclusion, the technical scheme of the invention can optimize the existing continuous casting round billet electromagnetic stirring process and can be widely popularized in the fields of steel and nonferrous metallurgy casting and the like.
Drawings
FIG. 1 is a schematic representation of a near liquidus solidification end electromagnetic stirring zone of the present invention; 1-f l 1-zone boundary contour, 2-f l 0 region boundary contour, 3-f l 1-zone boundary isopipe point, 4-f l Zone boundary isoline endpoint 0, 5-electromagnetic stirrer.
FIG. 2 shows the results of three-phase distribution (a) liquid phase (b) equiaxial crystal (c) columnar crystal predicted by the volume averaging method in the present invention.
FIG. 3 shows a model schematic diagram and a calculation result of the embodiment of the invention, which are used for calculating the effect of the electromagnetic stirrer for the continuous casting large round billet by using a finite element method by means of low-frequency electromagnetic field simulation software Maxwell: (a) the geometric model (b) magnetic induction intensity distribution (c) electromagnetic force vector distribution. The steel plate comprises 6-casting blank, 7-iron core, 8-coil W1, 9-coil W2 and 10-coil W3.
Detailed Description
The method of the present invention will be described in detail with reference to specific examples.
Firstly, simulating the distribution of liquid phase, columnar crystal phase and equiaxed crystal phase in the casting process of a continuous casting round billet with the diameter of 600mm by a volume average method, and determining the position of a solidification end (near liquidus), wherein the method comprises the following specific steps:
s1, creating a geometric model: and creating a model according to the size of the continuous casting large round billet in the actual production process.
S2, grid division: and carrying out structured grid division and encrypting the edge grid.
S3, establishing boundary conditions and physical parameters: according to the operation parameters of the actual production working condition, determining each calculation boundary condition, wherein in the embodiment, the boundary condition adopts convection heat transfer, the boundary of the large round billet adopts a segmented cooling condition, the vibration of the crystallizer is ignored, and the heat transfer, inclusion and reaction between the crystallizer mold flux and the molten steel are ignored.
And simultaneously determining physical parameters of the cast alloy according to the steel grade, wherein the physical parameters comprise density, specific heat capacity, heat conductivity coefficient, liquid dynamic viscosity, liquid solute diffusion coefficient, solid solute diffusion coefficient, phase change latent heat, thermal expansion coefficient, liquidus slope and the like.
S4, simulation calculation is carried out: carrying out analog calculation on the temperature and the phase distribution in the large round billet by using a three-phase volume average method, dividing the interior of the large round billet into three continuous phases of a liquid phase l, an isometric crystal phase e and a columnar crystal phase c, modeling, determining mass, momentum and component transmission source terms among the phases, wherein the corresponding phase volume fractions are f l 、f e And f c . Wherein the liquid phase and the isometric phase are movable phases, and the solution of the movement can adopt a corresponding N-S equation; the columnar crystal phase is an immobile phase which is adhered to the cooling wall surface and grows towards the liquid phase direction。
For each local node of the large round billet and the whole large round billet, the sum of the volume fractions of three phases is 1, namely f l +f e +f c ＝1。
Predicting the distribution of liquid phase, columnar crystal phase and equiaxed crystal phase in the solidification process of the continuous casting billet by determining the mass, momentum and component transmission source items among all phases and solving a control equation; the control equations comprise continuity equations, momentum equations, species transport equations, energy equations, and other self-defined scalar equations for simulating transmission or diffusion according to actual conditions. Solving a control equation by using a control volume based on a finite difference method, wherein each time step adopts more than 60 iterations, and the convergence criterion of the normalized residual errors of a continuity equation, a momentum equation, a species transport equation and a self-defined scalar equation is 10 -4 The convergence criterion for the normalized residual of the energy equation is 10 below -7 The following.
The three-phase distribution simulated in this example is shown in fig. 2.
S5, determining the position of the solidification tail end: as shown in FIG. 1, 1 is f l The 1 region boundary contour line, namely the boundary line of a pure liquid phase region in the large round billet, can also be regarded as the liquidus temperature end point (T) of the large round billet alloy l ) Isotherm of (f) l The region above 1 which is the region boundary contour is f l A complete liquid phase region of 1; 2 is f l The boundary isoline of 0 region, namely the boundary line of pure solid phase region in the large round billet, can also be regarded as the solidus temperature end point (T) of the large round billet alloy s ) Isotherm of (f) l The region below the 0 region boundary contour line 2 is f l A completely solid phase region of 0; the region between 1 and 2 is the location of the coagulation tip.
S6, adjusting electromagnetic stirring according to the position of the solidification tail end, and applying a required magnetic field at the solidification tail end. Specifically, the electromagnetic stirrer 5 may be provided at f l In the interval of more than 3 meters from the end point 3 (which is also the starting point of the complete liquid phase region in the center of the casting blank) of the 1-region boundary contour line 1, the adjustment is carried out up and down.
In the embodiment, according to the requirement of the large round billet with the size on internal flow and heat transfer, the low-frequency electromagnetic field simulation software Maxwell is used for calculating the effect of the electromagnetic stirrer of the continuous casting large round billet by adopting a finite element method, determining electromagnetic stirring parameters (current and frequency) and predicting magnetic field distribution, and applying a proper region (such as a region with relatively large magnetic induction intensity) of a magnetic field to the previously determined solidification end position. The method specifically comprises the following steps:
s6.1, creating a geometric model: and (3) creating a model according to the type and the size of the electromagnetic stirrer adopted at the solidification end of the continuous casting round billet in the actual production process, and defining a calculation domain. The model created is shown in fig. 3(a) and includes a cast slab 6 (round billet to be cast), an iron core 7 (serving as a yoke), three coils 8-10 wound with copper wire, and air regions around these components.
S6.2, grid division: and dividing a calculation domain into unstructured grids based on Maxwell isoelectric electromagnetic field simulation software, and encrypting the geometric body edge position grids.
S6.3, setting solving type and excitation: setting to solve a transient magnetic field and activating eddy current analysis inside the casting blank; and generating the cross section of the winding coil, inputting the number of turns, and setting the current and the phase of each winding coil.
S6.4, distributing material attributes of each part in the calculation domain, and formulating boundary conditions; the material properties comprise a copper wire, a magnet yoke, a casting blank and an air domain, wherein the air domain is the outer edge of the calculation domain; due to the constraint of the magnetic yoke on the magnetic field, a Nieman boundary condition is adopted, namely no magnetic flux passes through.
S6.5, performing simulation calculation: according to different requirements of large round billets with different section sizes on internal flow and heat transfer, electromagnetic stirring parameters (mainly current and frequency) are determined, and magnetic induction intensity distribution, induced current and electromagnetic force distribution in the continuous casting billets are predicted according to the electromagnetic stirring parameters, as shown in figures 3(b) and 3 (c).
S6.6 adjusts the position of the electromagnetic stirrer so that an appropriate region of the magnetic field acts on the solidification end, based on the simulation results of the magnetic induction intensity distribution, the induced current, and the electromagnetic force distribution, and the solidification end position determined in step S5, and applies a desired magnetic field to the solidification end.
Claims (8)
1. A near-liquidus electromagnetic stirring process control method for the tail end of a large continuous casting round billet is characterized in that a volume average method is used for predicting the distribution of columnar crystals and equiaxed crystals in the continuous casting billet solidification process, the solidification tail end position is determined, and electromagnetic stirring is adjusted according to the solidification tail end position.
2. The near-liquidus electromagnetic stirring process control method for the tail end of the continuous casting round billet according to claim 1, characterized by comprising the following steps:
s1, creating a geometric model: establishing a model according to the size of a continuous casting large round billet in the actual production process;
s2, grid division: adopting finite element simulation software to perform structured grid division on the model and encrypt edge grids;
s3, formulating boundary conditions and physical property parameters: determining each calculation boundary condition according to the operation parameters of the actual production working condition, and determining the physical parameters of the cast alloy according to the steel grade;
s4, performing simulation calculation: utilizing a three-phase volume average method to carry out analog calculation on the temperature and phase distribution in the large round billet, dividing the interior of the large round billet into three continuous phases of a liquid phase l, an equiaxed crystal phase e and a columnar crystal phase c for modeling, wherein the corresponding phase volume fractions are respectively f l 、f e And f c Wherein the liquid phase and the equiaxed crystal phase are movable phases, and the columnar crystal phase is an immovable phase which is adhered on the cooling wall surface and grows towards the liquid phase direction;
predicting the distribution of liquid phase, columnar crystal phase and equiaxed crystal phase in the solidification process of the continuous casting billet by determining the mass, momentum and component transmission source items among all phases and solving a control equation;
s5, determining the position of a solidification tail end: from f l Region boundary contour to f of 1 l The region between the region boundary contour lines which are 0 is the solidification tail end of the round billet;
s6, adjusting electromagnetic stirring according to the position of the solidification tail end, and applying a required magnetic field at the solidification tail end.
3. The method for controlling the near-liquidus electromagnetic stirring process of the tail end of the continuous casting round billet according to claim 2, wherein in the step S3, the boundary conditions are as follows: convection heat transfer is adopted, and the boundary of the large round billet is cooled in a sectional manner.
4. The method for controlling a near-liquidus electromagnetic stirring process at the end of a continuous casting round billet according to claim 2, wherein in the step S4, the control equation is solved based on the control volume of the finite difference method, more than 60 iterations are adopted in each time step, and the convergence criterion of the normalized residuals of the continuity equation, the momentum equation, the species transport equation and the custom scalar equation is 10 -4 The convergence criterion for the normalized residual of the energy equation is 10 below -7 The following.
5. The method for controlling a near-liquidus electromagnetic stirring process of a terminal of a large round billet for continuous casting according to claim 2, wherein the position of the electromagnetic stirrer is f in step S6 l The region boundary contour is 1 in a section 3 meters above the end point of the contour and can be adjusted up and down within the section.
6. The method for controlling the near-liquidus electromagnetic stirring process of the tail end of the continuous casting round billet according to any one of claims 1 to 5, wherein the step S6 specifically comprises the following steps:
s6.1, creating a geometric model: according to the type and the size of an electromagnetic stirrer adopted at the solidification end of a continuous casting round billet in the actual production process, a model is created, and a calculation domain is defined;
s6.2, grid division: dividing a computational domain into unstructured grids based on electromagnetic field simulation software, and encrypting geometric body edge position grids;
s6.3, setting solving type and excitation: setting to solve a transient magnetic field and activating eddy current analysis inside the casting blank; generating the section of a winding coil, inputting the number of turns, and setting the current and the phase of each winding coil;
s6.4, distributing material attributes of each part in the calculation domain, and formulating boundary conditions;
s6.5, performing simulation calculation: determining electromagnetic stirring parameters according to different requirements of large round billets with different section sizes on internal flow and heat transfer, and predicting magnetic induction intensity distribution, induced current and electromagnetic force distribution in the continuous casting billets;
s6.6 adjusts the position of the electromagnetic stirrer so that an appropriate region of the magnetic field acts on the solidification end, based on the simulation results of the magnetic induction intensity distribution, the induced current, and the electromagnetic force distribution, and the solidification end position determined in step S5.
7. The method for controlling a near-liquidus electromagnetic stirring process of the tail end of a continuous casting round billet as claimed in claim 2, wherein the physical properties of the cast alloy in the step S3 include: density, specific heat capacity, thermal conductivity, liquid dynamic viscosity, liquid solute diffusion coefficient, solid solute diffusion coefficient, latent heat of phase change, coefficient of thermal expansion, and liquidus slope.
8. The method for controlling the near-liquidus electromagnetic stirring process of the tail end of the continuous casting round billet according to the claim 6, characterized in that in the step S6.4: the material properties comprise a copper wire, a magnet yoke, a casting blank and an air domain, wherein the air domain is the outer edge of the calculation domain; the niemann boundary condition without magnetic flux crossing is adopted.
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