CN108526421B - Thin slab narrow surface Gaussian concave curved surface crystallizer and design method thereof - Google Patents

Thin slab narrow surface Gaussian concave curved surface crystallizer and design method thereof Download PDF

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CN108526421B
CN108526421B CN201810329645.8A CN201810329645A CN108526421B CN 108526421 B CN108526421 B CN 108526421B CN 201810329645 A CN201810329645 A CN 201810329645A CN 108526421 B CN108526421 B CN 108526421B
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copper plate
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CN108526421A (en
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蔡兆镇
朱苗勇
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Northeastern University China
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    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
    • B22D11/043—Curved moulds
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Abstract

The invention provides a thin slab narrow surface Gaussian concave curved surface crystallizer and a design method thereof, and relates to the technical field of continuous casting and rolling of steel thin slabs. The working surface of the inner surface of the narrow-face copper plate of the crystallizer is of a concave structure which is symmetrically distributed in a Gaussian curve form by taking a transverse width central line as a center line from top to bottom and is of a continuously-changing curve structure which meets the solidification shrinkage characteristic of the narrow face of a blank shell along the height direction, and the central connecting line of the cross section of each water tank is of a Gaussian or circular arc structure. In the design method of the crystallizer, the solidification shrinkage of the narrow surface of a casting blank towards the center direction of the wide surface of the crystallizer is set as a distribution curve of the working surface of a narrow-surface copper plate along the height direction of the crystallizer, and a Gaussian function curve with the minimum corner stress in the casting blank liquid core reduction process is determined as a concave structure curve of the working surface of the narrow-surface crystallizer. The method can solve the problem that the edge part generates a brittle structure in the traditional production process, effectively promotes the metal at the corner part of the casting blank to flow to the narrow side of the casting blank in the liquid core reduction process, and obviously reduces the reduction stress of the edge part of the casting blank.

Description

Thin slab narrow surface Gaussian concave curved surface crystallizer and design method thereof
Technical Field
The invention relates to the technical field of continuous casting and rolling of thin steel slabs, in particular to a thin slab narrow-surface Gaussian concave curved surface crystallizer and a design method thereof.
Background
The thin slab continuous casting and rolling process is developed at the end of the last 80 th and early 90 th century, is a brand-new short-flow strip steel production new process, is remarkably different from the traditional strip steel production process, has the advantages of remarkable energy conservation, high product qualification rate, simplified production process, short production line, short product production period and the like, and is developed rapidly in recent years.
The continuous casting liquid core large deformation reduction is the core technology of the continuous casting and rolling process of thin slab such as CSP and the like, and is also called soft reduction, so that the method can effectively reduce the number of rolling mills, improve the center segregation of casting blanks, improve the productivity and the like. The core process is as follows: and (3) applying large deformation reduction within the range of 10-20 mm to the sheet billet which still has a large amount of non-solidified liquid cores in the crystallizer in the fan-shaped section 1 of the continuous casting machine, thereby achieving the purpose of obviously thinning the continuous casting billet. In the process, because the continuous casting speed of the sheet billet is high, the cooling strength of a crystallizer, secondary cooling and the like is high, the corner of the casting blank is extremely easy to generate supercooling, and the edge corner of the casting blank is extremely easy to crack due to stress concentration under the action of large deformation reduction of a liquid core.
Particularly, in the process of continuously casting and producing microalloy steel containing Nb, B, Al and the like by thin slabs such as CSP and the like, the heat transfer speed of the casting slab corner in a crystallizer is greatly reduced under the influence of concentrated distribution of air gaps and thick protective slag films in the corner area in the solidification process of the crystallizer, so that microalloy carbonitride is separated out from the corner structure of the casting slab along the crystal in a large scale, and the crystal boundary is embrittled. In the process of liquid core large deformation reduction, supercooled and embrittled corner tissues are severely cracked under the action of large stress, so that severe quality defects such as ' broken edges ', edge chipping ' and the like are caused in subsequent continuous rolling of coiled plates.
The crystallizer is a core component of a thin slab continuous casting production line, and the shape and the structure curve of an inner cavity of the crystallizer directly determine the blank structure of a casting blank and the solidification heat transfer behavior of the casting blank in the crystallizer, so that the solidification quality of a surface layer structure of the casting blank and the stress behavior of the surface layer structure of the casting blank under the subsequent solidification and deformation conditions are influenced. At present, narrow surfaces of traditional CSP, FTSR and other thin slab crystallizers at home and abroad are flat plate crystallizers. In order to effectively eliminate the corner crack defect in the continuous casting process of the microalloy steel sheet billet, the utility model patent with the application number of 201020149011.3 discloses a narrow-face copper plate structure of a crystallizer of a sheet billet continuous casting machine, wherein the working face of the narrow-face copper plate structure is in an inwards concave cambered surface structure and is arranged in a collineation mode by the axes of a cooling water tank. The casting blank corner cooling method has the advantages that the cooling speed of the corner is too high in the solidification process of the casting blank corner in the crystallizer, the heat transfer of the casting blank corner is slowed down by obtuse-angled casting blank corner and enabling the casting blank corner to be far away from a cooling water tank, the thickness of the casting blank corner of the crystallizer is guaranteed to be minimized, the center difference of a wide surface and a narrow surface is guaranteed, and the casting blank in the crystallizer is uniformly solidified and grows. The utility model discloses an application number 201120089500.9 discloses a chamfer crystallizer leptoprosopy copper for sheet bar continuous casting, and its working surface comprises plane area and 2 parts in bight curved surface region, and wherein the curved surface region is arc isotructure in horizontal structure, and with its width central line symmetric distribution. The narrow face working face is one of single taper, double taper or multi taper in the height direction. The method aims to mainly remove the right-angle structure of the casting blank through the structural design of the arc shape of the copper plate in the corner area of the crystallizer so as to improve the temperature of the corner of the casting blank in the processes of bending, straightening and the like and control the generation of cracks at the corner of a thin slab. The utility model patent of application number 200720089029.7 discloses a similar, the regional leptoprosopy crystallizer that passes through to the convex curved surface of broad face in leptoprosopy cross section bight with 201120089500.9 utility model patent equally, ensures that the cooling of molten steel solidification process casting blank bight is even relatively in the crystallizer, avoids slab bight cooling not to be and produces the surface quality defect.
It can be seen that the corners of the narrow-face copper plates of the disclosed thin slab continuous casting mold are optimized in passivation structure, and the purpose of the disclosed thin slab continuous casting mold is to reduce the cooling of the casting blank at the inner corners of the mold, promote the uniform growth of the casting blank in the mold, increase the corner temperature of the casting blank in the subsequent straightening process and the like, and reduce the generation of corner cracks of the casting blank. However, the root cause of the corner cracks of the microalloy steel continuous casting billet is that the casting billet is subjected to high-temperature links such as a crystallizer due to insufficient cooling speed of the corner parts, so that microalloy carbonitride is precipitated in a chain shape on the structure grain boundary of the microalloy carbonitride in a large scale, and the grain boundary is embrittled. The brittle structure of the corner part of the casting blank generates crystal-following cracking due to the concentration of compressive stress in the processes of liquid core large deformation, pressing and the like. Therefore, the published patent structure of the thin slab narrow-face crystallizer does not start from the root cause of the corner crack generation of the micro-alloy steel thin slab, theoretically, the corner crack generation of the micro-alloy steel continuous casting billet cannot be effectively solved, and the structure is not popularized and applied in the current domestic thin slab continuous casting production lines such as CSP, FTSR and the like.
Therefore, by combining the actual high-temperature solidification characteristics of microalloyed steel and continuous casting production processes such as stepless width adjustment of thin slabs, if a narrow-face copper plate structure of the crystallizer capable of improving the solidification shape and the structure of a casting blank in the crystallizer can be developed, on one hand, the plasticity of the corner structure of the casting blank is obviously improved, on the other hand, the narrow-face metal of the casting blank in the liquid core reduction process flows towards the lateral arc direction, and the stress of the corner part of the casting blank is obviously reduced, so that the corner crack generation in the continuous casting process of the microalloyed steel thin slabs.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a thin slab narrow surface Gaussian concave curved surface crystallizer and a design method thereof, which aim to realize the full-process efficient bonding heat transfer of the actual narrow surface and the corner of a microalloy steel thin slab in the crystallizer in the solidification process, quickly cool the edge corner of the thin slab, refine the primary solidification structure grains and disperse the microalloy carbonitride precipitation, obviously improve the structure plasticity of the structure corner, simultaneously ensure that narrow surface metal efficiently flows towards the center direction of the narrow side in the casting blank thinning process such as liquid core pressing after the casting blank exits the crystallizer, obviously reduce the stress of the edge corner of the casting blank, and fundamentally solve the problem of frequent edge corner grain generation in the production of the microalloy steel thin slab.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
on one hand, the invention provides a thin slab narrow surface Gaussian concave curved surface crystallizer, wherein the narrow surface copper plate of the crystallizer is characterized in that the working surface of the inner surface of the narrow surface copper plate is symmetrical by taking the transverse width central line as a Gaussian concave curve structure from top to bottom, and the vertical distance value from the curve peak point of the Gaussian concave curve structure to the connecting line of two corner parts on the working surface side at the corresponding height of the narrow surface copper plate of the crystallizer is 4.5-10.0 mm according to different thin slab thicknesses;
the inner surface working surface of the narrow-surface copper plate is a continuously-changed curve-shaped structure meeting the solidification shrinkage characteristic of the narrow surface of the casting blank along the height direction; the back side and the two side surfaces of the narrow-surface copper plate are both in a linear structure;
the cooling water tanks of the narrow-face copper plate are of a circular structure and are vertically distributed along the height direction of the crystallizer, the number of the water tanks is determined by the width of the narrow-face copper plate and the size of the cross section of each water tank, and the size of the cross section of each water tank close to the corner area of the crystallizer is 1.0-1.2 times that of the cross section of each water tank in the middle area of the narrow-face copper plate in the width direction; the connecting line of the centers of the cross sections of the water tanks is integrally in a Gaussian curve or arc-shaped structure concave to the working surface of the narrow-surface copper plate, and the water tanks are symmetrically distributed by the transverse width center line of the narrow-surface copper plate; wherein, the distance from the water tank center at the center line of the narrow-face copper plate width or the center connecting line of 2 water tanks which are distributed most close to the narrow-face copper plate width center line to the narrow-face copper plate working face is 20.0 mm-30.0 mm; the distance change range between the connecting line of the centers of the water tanks at the center line of the width of the narrow-face copper plate or the connecting line of the centers of the 2 water tanks which are symmetrically distributed closest to the center line of the width of the narrow-face copper plate and the connecting line of the centers of the 2 water tanks which are closest to the side face of the copper plate is 2.0 mm-15.0 mm; the water tank closest to the side surface of the narrow-surface copper plate is 5.0 mm-10.0 mm away from the corresponding side surface of the narrow-surface copper plate, and the distribution positions of other water tanks are distributed at equal intervals along the width direction of the copper plate from the central connecting line of the cross section of the water tanks;
the narrow-face copper plate is of a structure with a wide upper opening and a narrow lower opening, the width difference between the upper opening and the lower opening of the narrow-face copper plate is 0.2-1.0 mm according to the thickness of a casting blank produced by continuous casting, and the width difference is linearly reduced from the upper opening to the lower opening along the height direction; the larger the thickness of the narrow-face copper plate is, the larger the width difference between the upper opening and the lower opening is; the thickness of the upper opening and the lower opening of the narrow-face copper plate is the same, and the thickness of the middle area in the height direction of the narrow-face copper plate is the thickness of the upper opening or the lower opening plus the value of a continuous change curve of the corresponding working surface in the height direction; the height range of the narrow-face copper plate is 900 mm-1300 mm;
the narrow-face copper plate is suitable for all thin slabs with the thickness of a continuous casting section of 50-135 mm, and the installation positions of the meniscus and the lower opening of the crystallizer are the same as those of the meniscus and the lower opening of the flat-plate narrow-face crystallizer copper plate in the using process.
On the other hand, the invention also provides a design method for realizing the thin slab narrow surface Gaussian concave curved surface crystallizer, which comprises the following steps:
step 1, selecting proper finite element commercial software, and establishing 1/4 thin slab and a three-dimensional solid model of a crystallizer system thereof according to the actual section size of the microalloyed steel right-angle thin slab on site and the traditional narrow-surface flat plate and wide-surface funnel crystallizer copper plate structure under the corresponding section, wherein the height of the three-dimensional solid model of the thin slab is 1.2-1.5 times of the length of a liquid core reduction segment, and the lower end of a casting blank is positioned at the meniscus of the crystallizer;
step 2, carrying out grid division on the established 1/4 thin slab and the three-dimensional solid model of the crystallizer system thereof, and setting simulated steel grades and heat transfer and mechanical properties of the crystallizer for corresponding units, wherein the method specifically comprises the following steps:
step 2-1, adopting a non-uniform grid division method to encrypt the surface grid of the casting blank within a range of 0-20 mm close to the surface, and processing the surface grid in a mode of gradually encrypting the casting blank from the center of the wide surface and the narrow surface to the corner part, wherein the grid of the inner layer of the casting blank can be divided loosely;
step 2-2, freely dividing the wide-surface copper plate and the narrow-surface copper plate of the thin slab crystallizer by adopting a free division grid method in a mode of setting the grid unit length of each boundary structure line of the crystallizer copper plate;
step 2-3, according to the components of the steel grade and the composition of the copper plate and the copper alloy, determining the heat conductivity coefficient, the density, the enthalpy, the elastic modulus and the Poisson ratio parameters of the corresponding steel grade in a consulting mode, and respectively correspondingly endowing the casting blank and the crystallizer copper plate with unit attributes;
step 3, setting three-dimensional heat transfer and mechanical boundary conditions of a crystallizer copper plate and a casting blank in a crystallizer, establishing an unsteady three-dimensional heat/force coupling analysis model of a sheet billet and a crystallizer system thereof by adopting a heat transfer and stress real-time coupling method, and simulating the dynamic solidification heat transfer and shrinkage deformation behaviors of the casting blank in the crystallizer in the continuous casting process of the microalloy steel sheet billet; the method comprises the following specific steps:
3-1, respectively selecting three-dimensional heat transfer control equations of a crystallizer copper plate and a continuous casting billet unit based on the selected finite element commercial software;
3-2, selecting a copper plate mechanical control equation as a three-dimensional elastic-plastic constitutive equation and a casting blank mechanical control equation as an Anand rate related constitutive equation based on the selected finite element commercial software;
step 3-3, assuming that the thickness of the covering slag in the meniscus area of the crystallizer is the same, calculating the thickness of the covering slag flowing into the casting blank/crystallizer interface according to the actual steel slag consumption, the perimeter of the meniscus of the crystallizer, the pulling speed and the density of the covering slag, and setting the thickness as the initial thickness;
step 3-4, assuming that the temperature distribution of the casting blank surface of the meniscus of the crystallizer and the corresponding copper plate of the crystallizer is uniform, the initial temperature of the casting blank unit at the meniscus is the molten steel pouring temperature, the temperature of the copper plate is set to be 200-290 ℃ according to the actual casting speed, and the casting blank/crystallizer interface gaps are set to be the initial thickness of the casting powder;
and 3-5, setting heat transfer boundary conditions of the casting blank and the crystallizer, wherein the specific conditions are as follows:
setting the heat transfer of the crystallizer copper plate water tank as convection heat transfer, wherein the heat transfer boundary is exerted by a convection heat transfer coefficient;
the heat flows of the wide-surface central symmetry plane and the narrow-surface central symmetry plane of the crystallizer copper plate and the casting blank, the contact area of the copper plate back plate and the stainless steel back plate, the upper opening of the crystallizer and the lower opening of the crystallizer are all set to be 0;
applying heat transfer boundary conditions of the surface of the casting blank and the hot surface of the crystallizer in a heat flow mode, which comprises the following specific steps:
3-5-1, extracting the temperature of each unit node on the surface of the casting blank and the copper plate at the corresponding position of the casting blank and the corresponding width of the casting blank/crystallizer interface gap;
3-5-2, judging the relation between the casting blank surface node temperature and the casting powder solidification temperature, if the current casting blank surface node temperature is higher than the casting powder solidification temperature, taking liquid casting powder and solid casting powder as heat transfer media in a casting blank/crystallizer interface, and turning to the step 3-5-3; otherwise, the heat transfer medium in the casting blank/crystallizer interface is air gap and solid protection slag, and the step 3-5-4 is carried out;
3-5-3, extracting the temperature of each unit node on the surface of the casting blank and the hot surface of the copper plate at the position corresponding to the unit, calculating and obtaining the heat flow of the surface of the casting blank and the corresponding hot surface unit of the copper plate by utilizing the heat flow phase principle of flowing through the liquid slag layer and the solid slag layer based on the heat conduction and radiation heat transfer parallel connection characteristics in the liquid slag layer and the solid slag layer, and respectively applying corresponding heat flow values to each solid surface unit one by one;
3-5-4, extracting the temperature of each unit node on the surface of the casting blank and the hot surface temperature of the copper plate at the position corresponding to the unit, calculating and obtaining the heat flow of the surface of the casting blank and the corresponding hot surface unit of the copper plate by utilizing the heat flow phase principle of flowing through the air gap layer and the solid slag layer based on the heat conduction and radiation heat transfer parallel connection characteristics of the heat in the solid slag layer and the air gap layer, and respectively applying corresponding heat flow values to each solid surface unit one by one;
3-6, setting mechanical boundary conditions of the casting blank and the crystallizer, which are as follows:
setting the displacement of the wide-surface symmetrical surface of the casting blank along the direction of the narrow surface of the casting blank to be 0, setting the displacement of the narrow-surface symmetrical surface of the casting blank along the direction of the wide surface of the casting blank to be 0, and vertically moving the casting blank towards the outlet direction of the crystallizer under the boundary condition of taking the pulling speed as the speed;
the ferrostatic pressure is vertically applied to the grid unit at the solidification front of the casting blank;
the contact behavior of the casting blank and the copper plate is set by adopting a rigid-flexible contact analysis algorithm;
the wide face and the narrow face copper plate of the crystallizer are fixed;
3-7, according to the steps 3-1 to 3-6, a casting blank adopts a dead unit control method, namely when the casting blank is in a crystallizer, a unit corresponding to the casting blank is in an activated state, if the casting blank is above a meniscus or is discharged out of the crystallizer, the unit corresponding to the casting blank is frozen, and an unsteady state heat/force real-time coupling analysis model of a thin slab and a crystallizer system thereof is established;
3-8, inputting actual continuous casting production process parameters of the microalloyed steel sheet billet into an analysis model, and simulating and analyzing dynamic solidification heat transfer and shrinkage deformation behaviors of a casting blank in a crystallizer in the continuous casting process of the microalloyed steel sheet billet, wherein the process parameters comprise: the casting method comprises the following steps of (1) drawing speed, molten steel casting temperature, cooling water flow rate of a wide surface and a narrow surface of a crystallizer, cooling water temperature of the wide surface and the narrow surface of the crystallizer, temperature difference between a cooling water inlet and a cooling water outlet of the wide surface and the narrow surface of the crystallizer, consumption of casting powder and solidification temperature of the casting powder;
3-9, judging whether the tail end of the casting blank entity enters a meniscus of the crystallizer, if so, executing a step 4, otherwise, executing a step 3-5;
step 4, determining the solidification shrinkage of the narrow surface of the casting blank towards the center direction of the wide surface of the crystallizer according to the simulation result of the dynamic solidification heat transfer and shrinkage deformation behaviors of the casting blank, and setting the solidification shrinkage as a distribution curve of the working surface of the narrow-surface copper plate along the height direction of the crystallizer;
step 5, setting the cross section size of the water tank in the middle area of the narrow-face copper plate as the cross section size of the water tank in the middle area of the original narrow-face copper plate, and designing the cross section size of the cooling water tank in the corner area to be 1.0-1.2 times of the cross section size of the water tank in the middle area;
step 6, comprehensively selecting a transverse proper Gaussian curve distribution function of the narrow-face working surface of the crystallizer according to the width of the thin slab, the position of the lower section of the liquid core pressure, the continuous casting drawing speed of the main flow of the microalloyed steel and the reduction amount information of the liquid core;
step 7, designing a Gaussian concave curved surface structure of the narrow-side copper plate working surface of the crystallizer by combining the distribution curve of the narrow-side copper plate working surface of the crystallizer obtained by calculation in the step 4 along the height direction and the transverse Gaussian curve distribution function of the working surface selected in the step 6;
step 8, setting the central distribution of the cross sections of the water tanks based on the size of the cross sections of the set water tanks;
step 9, calculating and inspecting the uniformity of the temperature distribution of the Gaussian concave curved surface crystallizer copper plate and the temperature field distribution of the corner part of the casting blank by adopting the methods in the steps 1 to 3, and selecting a water tank distribution structure with the most uniform cross section temperature field distribution and the casting blank corner part cooling speed exceeding the diffusion precipitation cooling speed of the microalloy carbonitride as a narrow-surface copper plate water tank distribution structure of the crystallizer;
step 10, based on the unsteady three-dimensional heat/force coupling analysis model of the thin slab established in the steps 1 to 3 and the whole casting blank temperature field obtained by calculation in the step 9, establishing a three-dimensional finite element calculation model of heat transfer and stress of a thin slab secondary cold grid area and a liquid core reduction process by adopting the following boundary conditions and analysis methods:
step 10-1, assuming that the heat transfer of the casting blank in the grid area is uniform, applying a heat transfer boundary condition to the heat transfer of the casting blank in the grid area and the liquid core reduction process by adopting an equivalent heat exchange method;
step 10-2, setting a rigid-flexible contact analysis method between the casting blank and the liquid core lower-section casting roll;
step 10-3, establishing a calculation analysis model by adopting a real-time coupling method;
step 11, calculating the reduction of each pressing roller according to the total reduction of the liquid core pressing lower section, and simulating and calculating three-dimensional heat transfer and stress behaviors in the casting blank pressing process;
and step 12, determining a Gaussian function curve with the minimum corner stress in the casting blank liquid core reduction process as a narrow-face crystallizer working surface concave structure curve according to the calculation result in the step 11, and designing a crystallizer copper plate working surface by combining the curve in the height direction to complete the design of a thin slab narrow-face Gaussian concave curved surface crystallizer.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: the thin slab narrow surface Gaussian concave curved surface crystallizer and the design method thereof can fully compensate the shrinkage of a casting blank in the crystallizer, greatly increase the cooling speed of the corner part of the cast narrow surface slab, refine the initial solidification structure crystal grains of the corner part of the casting blank and disperse the precipitation of carbonitride in the crystal and the crystal boundary, and solve the problem that the corner part generates brittle tissue in the traditional micro-alloy steel thin slab continuous casting production process; the narrow-face structure of the thin slab crystallizer designed by the invention can effectively promote the metal at the corner of the casting blank to flow to the narrow side of the casting blank in the liquid core reduction process, and obviously reduce the reduction stress at the corner of the casting blank.
Drawings
FIG. 1 is a schematic perspective view of a narrow-face copper plate of a crystallizer provided in an embodiment of the present invention;
FIG. 2 is a schematic structural view of an upper opening or a lower opening of a narrow-face copper plate of a crystallizer provided by an embodiment of the invention;
fig. 3 is a flow chart of a design method of a thin slab narrow surface gaussian concave curved surface crystallizer provided by the embodiment of the invention.
In the figure: 1. a narrow surface Gaussian concave curved surface of the crystallizer; 2. a cooling water tank on the narrow surface of the crystallizer; 3. an upper opening of a narrow-face copper plate of the crystallizer; 4. a narrow-face copper plate lower opening of the crystallizer; 5. narrow-faced copper plate side faces.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
The embodiment of the narrow face of the CSP crystallizer, wherein the thickness of the cast blank of the crystallizer is 90mm, and the reduction of the lower section of the liquid core pressure is 17.5mm, is further explained with reference to the attached drawings.
In the present embodiment, the slab narrow surface gaussian concave curved surface crystallizer is shown in fig. 1 and fig. 2, wherein 1 represents a narrow surface gaussian concave curved surface of the crystallizer, i.e. an inner surface working surface, 2 represents a narrow surface cooling water tank of the crystallizer, 3 represents an upper opening of a narrow surface copper plate of the crystallizer, 4 represents a lower opening of the narrow surface copper plate of the crystallizer, 5 represents a side surface of the narrow surface copper plate, and l represents a side surface of the narrow surface copper plate1Indicates the height of the narrow-face copper plate of the crystallizer, l2The width of the upper opening of the narrow-side copper plate of the crystallizer is represented by l3Showing the width of the lower opening of the narrow-face copper plate of the crystallizer, C1The distribution curve of the working surface of the narrow face of the crystallizer along the height direction is shown, C2Transverse Gaussian curve representing narrow working direction of crystallizer42 water tank center connecting lines which are symmetrically distributed closest to the width center line of the narrow copper plate or the water tank center to the narrow copper plate work closest to the width center line of the narrow copper plateDistance of faces,/5The distance between the narrow copper plate of the crystallizer, which is closest to the side water tank, and the corresponding side is shown as l6The thickness of the upper opening or the lower opening of the narrow-face copper plate of the crystallizer is represented by l7And delta l represents the distance between the center of the water tank at the center line of the width of the narrow-face copper plate or the center lines of 2 water tanks which are symmetrically distributed closest to the center line of the width of the narrow-face copper plate and the center line of 2 water tanks which are closest to the side face of the narrow-face copper plate. The height l of the narrow copper plate of the crystallizer11100mm, a structure with a wide upper opening and a narrow lower opening, 90mm of the width of the lower opening of the crystallizer, and a width difference l between the upper opening 3 and the lower opening 42-l3Is 0.2mm and is linearly reduced from the upper opening 3 to the lower opening 4 along the height direction of the crystallizer; in the thickness direction of the narrow-face copper plate of the crystallizer, the thickness l of an upper opening 3 of the narrow-face copper plate is designed6The thickness of the lower opening 4 is the same as that of the lower opening, and the thickness of the lower opening is 60 mm. The thickness of the middle area of the narrow-face copper plate in the height direction is the thickness of an upper opening or a lower opening plus a distribution curve C of the corresponding working face in the height direction1Value, C1The values of the curves are shown in table 1.
TABLE 1 Curve value of narrow copper plate working surface of thin slab along height direction
In this embodiment, the transverse gaussian curve distribution function of the working surface of the narrow-side copper plate of the crystallizer is determined as
Figure GDA0002204305850000082
The coordinate system takes one corner point on the working surface side of the narrow-surface copper plate as an origin, X is along the width direction of the narrow-surface copper plate, and Y is along the thickness direction of the narrow-surface copper plate and points from the inner surface working surface to the back surface. The narrow-face copper plate working face is in a transverse concave structure by taking the Gaussian curve function from top to bottom, compensation is carried out along the C1 curve, a Gaussian concave curved surface structure is formed from top to bottom,the vertical distance value l between the peak point of the Gaussian curve of the concave curved surface and the connecting line of two corner parts on the working surface side at the corresponding height of the narrow-side copper plate of the crystallizer7Is 6.0 mm.
The back side and the two outer side surfaces 5 of the narrow-surface copper plate are both in a linear structure.
In the embodiment, the cooling water tanks 2 of the narrow-face copper plate of the crystallizer are of a circular structure, 4 water tanks are designed, and the cross section diameter of each water tank is 13mm and is vertically distributed in a through manner along the height direction of the crystallizer; the connecting line of the centers of the cross sections of the water tanks is of a Gaussian curve structure which is concave to the working surface and is symmetrically distributed by the transverse width center line of the narrow-surface copper plate, and the distribution function of the Gaussian curve is
Figure GDA0002204305850000083
Wherein, the distance l from the central connecting line of the cross sections of the middle 2 water tanks of the upper opening or the lower opening of the crystallizer to the working surface of the narrow-face copper plate423.69 mm. The distance l from 2 water tanks at the edge of the narrow-face copper plate to the corresponding side of the narrow-face copper plate5The distance delta l between the center connecting lines of the 2 water tanks which are symmetrically distributed closest to the width center line of the narrow-face copper plate and the center connecting lines of the 2 water tanks which are closest to the side face of the narrow-face copper plate is 4.1 mm; the 4 water tanks are distributed at equal intervals along the width direction of the narrow-face copper plate.
In this embodiment, in the use process of the crystallizer narrow-face copper plate, it is only necessary to ensure that the installation positions of the meniscus and the lower port 4 of the crystallizer are the same as those of the meniscus and the lower port of the conventional flat-plate narrow-face crystallizer copper plate.
In the embodiment, through the design of the curved surface structure with the Gaussian concave shape on the inner surface of the narrow-surface copper plate and the distribution of the Gaussian curve along the height direction and the design of the Gaussian curve distribution of the horizontal central connecting line of the water tank, the narrow-surface copper plate of the crystallizer effectively compensates the shrinkage of a thin slab in the solidification process to the central direction of a wide surface, and meanwhile, the water tank structure at the edge part is closer to the corner part of a casting blank, so that the heat transfer speed of the corner part area of the casting blank in the crystallizer is accelerated, the precipitation of microalloy carbonitride in the solidification process of the corner part tissue of the. Meanwhile, the narrow-surface Gaussian high-efficiency structural design can remarkably promote the metal of the casting blank to efficiently flow to the narrow side in the liquid core reduction process, and reduce the stress of the corner part of the casting blank, thereby fundamentally eliminating the generation of corner part cracks in the continuous casting process of the microalloy steel sheet blank.
The method for designing the thin slab narrow surface Gaussian concave curved surface crystallizer is shown in a flow chart of fig. 3, and specifically comprises the following steps:
step 1, selecting proper finite element commercial software, and establishing 1/4 thin slab and a three-dimensional solid model of a crystallizer system thereof according to the actual section size of the microalloyed steel right-angle thin slab on site and the traditional narrow-surface flat plate and wide-surface funnel crystallizer copper plate structure under the corresponding section, wherein the height of the three-dimensional solid model of the thin slab is 1.2-1.5 times of the length of the crystallizer, and the lower end of a casting blank is positioned at the meniscus of the crystallizer.
In the embodiment, the selected finite element commercial software is Ansys, and according to the 1230mm multiplied by 90mm section size produced by the actual mainstream microalloy steel continuous casting billet in a steel mill, three-dimensional solid models of a crystallizer and a casting billet 1/4 are respectively established, wherein the actual wide-surface and narrow-surface (flat plate) copper plate structure is selected as the crystallizer structure, and the casting billet length is determined to be 2.0 m; the lower end of the casting blank entity is positioned at the meniscus of the crystallizer.
Step 2, carrying out grid division on the established 1/4 thin slab and the three-dimensional solid model of the crystallizer system thereof, and setting simulated steel grades and heat transfer and mechanical properties of the crystallizer for corresponding units, wherein the method specifically comprises the following steps:
step 2-1, adopting a non-uniform grid division method to encrypt the surface grid of the casting blank within a range of 0-20 mm close to the surface, and processing the surface grid in a mode of gradually encrypting the casting blank from the center of the wide surface and the narrow surface to the corner part, wherein the grid of the inner layer of the casting blank can be divided loosely;
step 2-2, freely dividing the wide-surface copper plate and the narrow-surface copper plate of the thin slab crystallizer by adopting a free division grid method in a mode of setting the grid unit length of each boundary structure line of the crystallizer copper plate; in the embodiment, the length of the copper plate linear structure unit is selected to be 5mm, and the length of the non-linear structure unit is selected to be 2 mm;
and 2-3, calculating the components of the steel grade and the composition of the copper plate and the copper alloy according to the simulation, determining the heat conductivity coefficient, the density, the enthalpy, the elastic modulus and the Poisson ratio parameters of the corresponding steel grade by adopting a reference mode, and correspondingly endowing the casting blank and the crystallizer copper plate with unit attributes respectively.
In the present example, the selected microalloyed steel composition is shown in table 2.
TABLE 2 microalloyed steel composition Table
Element(s) C Mn Si P S AlS V Nb
Content (a) of 0.07 1.50 0.30 0.020 0.008 0.035 0.065 0.030
Step 3, setting three-dimensional heat transfer and mechanical boundary conditions of a crystallizer copper plate and a casting blank in a crystallizer, establishing an unsteady three-dimensional heat/force coupling analysis model of a sheet billet and a crystallizer system thereof by adopting a heat transfer and stress real-time coupling method, and simulating the dynamic solidification heat transfer and shrinkage deformation behaviors of the casting blank in the crystallizer in the continuous casting process of the microalloy steel sheet billet; the method comprises the following specific steps:
step 3-1, based on Ansys finite element commercial software, respectively selecting three-dimensional heat transfer control equations of a crystallizer copper plate and a continuous casting billet unit as follows:
wherein rho represents the density of steel or copper, c represents the specific heat of the steel or copper, lambda represents the thermal conductivity of the steel or copper, T represents time, T represents temperature, x represents the x coordinate of 1/4 three-dimensional solid model in the coordinate system, y represents the y coordinate of 1/4 three-dimensional solid model in the coordinate system, and z represents the z coordinate of 1/4 three-dimensional solid model in the coordinate system;
3-2, selecting a copper plate mechanical control equation as a three-dimensional elastic-plastic constitutive equation and a casting blank mechanical control equation as an Anand rate related constitutive equation based on Ansys finite element commercial software;
the Anand rate-related constitutive equation is as follows:
Figure GDA0002204305850000101
wherein the content of the first and second substances,representing equivalent inelastic strain rate, A is pre-exponential factor, l/s; qAThe ratio of the viscoplastic deformation activation energy to the gas constant, K; xi is a stress multiplier; m is a strain sensitivity index;
Figure GDA0002204305850000103
representing the equivalent stress;
s is deformation resistance, MPa; the evolution of s is:
in the formula (I), the compound is shown in the specification,
Figure GDA0002204305850000105
representing the time-dependent derivative of the deformation impedance, h0Hardening/softening constant, MPa;
Figure GDA0002204305850000106
the saturation value of S at a given temperature and strain rate, MPa; strain rate sensitivity of n strain impedance saturation values; α is the strain rate sensitivity index associated with hardening/softening;
in this example, s has an initial value of 43MPa, QA32514K, A1.0 × 1011l/s, ξ 1.15, m 0.147, h0Taking the pressure of 1329MPa,
Figure GDA0002204305850000107
taking 147.6MPa, n 0.06869 and alpha 1;
step 3-3, assuming that the thickness of the covering slag in the meniscus area of the crystallizer is the same, calculating the thickness of the covering slag flowing into the casting blank/crystallizer interface according to the actual steel slag consumption, the perimeter of the meniscus of the crystallizer, the pulling speed and the density of the covering slag, and setting the thickness as the initial thickness;
in the embodiment, the thickness of the protective slag film in the meniscus area of the crystallizer is calculated to be 0.23 mm;
step 3-4, assuming that the temperature distribution of the casting blank surface of the meniscus of the crystallizer and the corresponding copper plate of the crystallizer is uniform, the initial temperature of the casting blank unit at the meniscus is the molten steel pouring temperature, the temperature of the copper plate is set to be 270 ℃ according to the actual casting speed, and the gap between the casting blank and the crystallizer interface is set to be 0.23 mm;
and 3-5, setting heat transfer boundary conditions of the casting blank and the crystallizer, wherein the specific conditions are as follows:
setting the heat transfer of the crystallizer copper plate water tank as convection heat transfer, wherein the heat transfer boundary is exerted by a convection heat transfer coefficient;
the application formula is as follows:
Figure GDA0002204305850000111
wherein h iswIs the convective heat transfer coefficient of the water tank and the cooling water, W/(m)2·℃)；λwIs the heat conductivity coefficient of cooling water, W/(m.DEG C); dwIs the equivalent diameter of the water tank, m; rhowFor the density of cooling water, kg/m3；uwIs the flow rate of cooling water, m/s; mu.swIs the viscosity of cooling water, Pa.s; c. CwSpecific heat of cooling water, J/(kg. DEG C);
the wide-surface central symmetry plane and the narrow-surface central symmetry plane of the crystallizer copper plate and the casting blank, the contact area between the copper plate back plate and the stainless steel back plate, the heat flow of the upper opening of the crystallizer and the heat flow of the lower opening of the crystallizer are all set to be 0;
applying heat transfer boundary conditions of the surface of the casting blank and the hot surface of the crystallizer in a heat flow mode, which comprises the following specific steps:
3-5-1, extracting the node temperature of each unit on the surfaces of the casting blank and the copper plate thereof and the corresponding casting blank/crystallizer interface gap width;
in the embodiment, the initial gap width is 0.23mm, and then the vertical distance from the surface of the casting blank to the working surface of the corresponding copper plate is given by calculating the deformation behavior result of the casting blank in the previous step in the calculation process;
3-5-2, judging the relation between the casting blank surface node temperature and the casting powder solidification temperature, if the current casting blank surface node temperature is higher than the casting powder solidification temperature, taking liquid casting powder and solid casting powder as heat transfer media in a casting blank/crystallizer interface, and turning to the step 3-5-3; otherwise, the heat transfer medium in the casting blank/crystallizer interface is air gap and solid protection slag, and the step 3-5-4 is carried out;
in the embodiment, the solidification temperature of the crystallizer casting powder is 1080 ℃;
3-5-3, extracting the temperature of each unit node on the surface of the casting blank and the hot surface of the copper plate at the position corresponding to the unit, calculating and obtaining the heat flow of the surface of the casting blank and the corresponding hot surface unit of the copper plate by utilizing the heat flow phase principle of flowing through the liquid slag layer and the solid slag layer based on the heat conduction and radiation heat transfer parallel connection characteristics in the liquid slag layer and the solid slag layer, and respectively applying corresponding heat flow values to each solid surface unit one by one;
the specific heat flow calculation formula is as follows:
thermal resistance of liquid slag layer:
Figure GDA0002204305850000112
in the formula (I), the compound is shown in the specification,
Figure GDA0002204305850000113
is a heat conduction and resistance of the liquid slag layer,is the radiation thermal resistance of the liquid slag layer, RliquidIs the thermal resistance of the liquid slag layer, dliquidThickness of liquid slag layer, kliquidIs the thermal conductivity of the liquid slag, sigma is the Botzmann constant, EliquidIs the extinction coefficient of the liquid slag, nliquidIs the refractive index of the liquid slag,. epsilonshellIs the emissivity of the cast slab, epsilonfEmissivity of the mold flux, TshellThe surface temperature of the casting blank is measured in DEG C and TsolThe solidification temperature of the mold flux is DEG C;
thermal resistance of a solid slag layer:
Figure GDA0002204305850000121
in the formula (I), the compound is shown in the specification,
Figure GDA0002204305850000122
is a heat conduction and resistance of the solid slag layer,
Figure GDA0002204305850000123
is the radiation thermal resistance of the solid slag layer, RsolidThermal resistance of the slag-fixing layer, dsolidThickness of solid slag layer, ksolidThermal conductivity of the solid slag, EsolidExtinction coefficient, n, for solid slagsolidIs the refractive index of the solid slag, epsilonmoldEmissivity of the copper plate of the crystallizer, Tm/mThe temperature of the hot surface-solid slag interface of the crystallizer is measured at DEG C;
Figure GDA0002204305850000124
in the formula, TmThe temperature of the hot surface of the copper plate is DEG C; dfluxIs the thickness of the mold flux;
Figure GDA0002204305850000125
in the formula, q is the heat flow of a casting blank-crystallizer interface;
3-5-4, extracting the temperature of each unit node on the surface of the casting blank and the hot surface temperature of the copper plate at the position corresponding to the unit, calculating and obtaining the heat transfer coefficients of the surface of the casting blank and the corresponding hot surface units of the copper plate by utilizing the heat flow phase principle of flowing through the air gap layer and the solid slag layer based on the heat conduction and radiation heat transfer parallel characteristics in the solid slag layer and the air gap layer, and respectively applying the corresponding heat transfer coefficients to the surface units of each entity one by one;
the specific heat flow calculation formula is as follows:
Figure GDA0002204305850000126
in the formula (I), the compound is shown in the specification,
Figure GDA0002204305850000127
is the heat conduction resistance of the air gap layer,is air gap layer radiation thermal resistance, RairIs air gap layer thermal resistance, dairThickness of the air gap layer, kairIs the thermal conductivity of the air gap, Ta/mAir gap-solid slag interface temperature, deg.C;
Figure GDA0002204305850000131
Figure GDA0002204305850000132
in the formula (d)tThe width of the casting blank-crystallizer interface gap is defined;
Figure GDA0002204305850000133
3-6, setting mechanical boundary conditions of the casting blank and the crystallizer, which are as follows:
setting the displacement of the casting blank wide surface symmetry plane along the casting blank narrow surface direction to be 0 respectively, setting the displacement of the casting blank narrow surface symmetry plane and the displacement of the casting blank wide surface direction to be 0 respectively, and vertically moving the casting blank towards the outlet direction of the crystallizer under the boundary condition of the pulling speed of 4.0 m/min;
the ferrostatic pressure is vertically applied to the grid unit at the solidification front of the casting blank;
the contact behavior of the casting blank and the copper plate is set by adopting a rigid-flexible contact analysis algorithm;
the wide face and the narrow face copper plate of the crystallizer are fixed;
3-7, according to the steps 3-1 to 3-6, a casting blank adopts a dead unit control method, namely when the casting blank is in a crystallizer, a unit corresponding to the casting blank is in an activated state, if the casting blank is above a meniscus or is discharged out of the crystallizer, the unit corresponding to the casting blank is frozen, and an unsteady state heat/force real-time coupling analysis model of a thin slab and a crystallizer system thereof is established;
3-8, inputting actual continuous casting production process parameters of the microalloyed steel sheet billet into an analysis model, and simulating and analyzing dynamic solidification heat transfer and shrinkage deformation behaviors of a casting blank in a crystallizer in the continuous casting process of the microalloyed steel sheet billet, wherein the process parameters comprise: the casting method comprises the following steps of (1) drawing speed, molten steel casting temperature, cooling water flow rate of a wide surface and a narrow surface of a crystallizer, cooling water temperature of the wide surface and the narrow surface of the crystallizer, temperature difference between a cooling water inlet and a cooling water outlet of the wide surface and the narrow surface of the crystallizer, consumption of casting powder and solidification temperature of the casting powder;
in the embodiment, the continuous casting production process parameters are specifically as follows: the casting temperature of the molten steel is 1547 ℃, the flow rate of cooling water of the crystallizer is 14.0m/s, the temperature of the cooling water of the crystallizer is 35 ℃, the temperature difference between the wide surface water and the narrow surface water is 5.2 ℃, and other parameters are as above;
3-9, judging whether the tail end of the casting blank entity enters a meniscus of the crystallizer, if so, executing a step 4, otherwise, executing a step 3-5;
and 4, determining the solidification shrinkage of the narrow surface of the casting blank towards the center direction of the wide surface of the crystallizer according to the result of simulating the dynamic solidification heat transfer and shrinkage deformation behaviors of the casting blank, and setting the solidification shrinkage as a distribution curve of the working surface of the narrow-surface copper plate along the height direction of the crystallizer.
This example finally determined the distribution curve of the narrow-faced copper plate working face along the mold height direction as shown in table 1.
And 5, setting the cross section size of the water tank in the middle area of the narrow-face copper plate to be the cross section size of the water tank in the middle area of the original narrow-face copper plate, and designing the cross section size of the cooling water tank in the corner area to be 1.0-1.2 times of the cross section size of the water tank in the middle area.
In this embodiment, the cross-sectional diameters of 4 water tanks on the narrow-face copper plate of the crystallizer are all
Figure GDA0002204305850000141
Namely, the cross-sectional dimension of the cooling water tank in the corner area is designed to be 1.0 times that of the water tank in the middle area.
And 6, comprehensively selecting a transverse proper Gaussian curve distribution function of the narrow-face working surface of the crystallizer according to the width of the thin slab, the position of the liquid core lower pressure section, the continuous casting drawing speed of the main flow of the microalloyed steel and the liquid core reduction amount information.
In the embodiment, the transverse appropriate Gaussian curve distribution function of the working face of the narrow face of the crystallizer is selected as
Figure GDA0002204305850000142
The coordinate system takes one corner point of the narrow-face copper plate as an origin, X is along the width direction of the narrow-face copper plate, and Y is along the thickness direction of the narrow-face copper plate and points to the back from the working face of the copper plate.
And 7, designing a Gaussian concave curved surface structure of the narrow-face copper plate working face of the crystallizer by combining the distribution curve of the narrow-face copper plate working face of the crystallizer obtained by calculation in the step 4 along the height direction, which is detailed in Table 1, and the transverse Gaussian curve distribution function of the working face selected in the step 6.
Step 8, setting the water based on the cross section size of the water tankThe center of the cross section of the groove is distributed as
Figure GDA0002204305850000143
And 9, calculating and inspecting the uniformity of the temperature distribution of the Gaussian concave curved surface crystallizer copper plate and the temperature field distribution of the corner part of the casting blank by adopting the methods in the steps 1 to 3, and selecting a water tank distribution structure with the most uniform cross section temperature field distribution and the cooling speed of the corner part of the casting blank exceeding the dispersion precipitation cooling speed of the microalloy carbonitride as the water tank distribution structure of the narrow-face copper plate of the crystallizer.
The cooling rate of the edge portion of the cast slab in this embodiment is required to be 5 ℃/s or more.
Step 10, based on the unsteady three-dimensional heat/force coupling analysis model of the thin slab established in the steps 1 to 3 and the whole casting blank temperature field obtained by calculation in the step 9, establishing a three-dimensional finite element calculation model of heat transfer and stress of a thin slab secondary cold grid area and a liquid core reduction process by adopting the following boundary conditions and analysis methods:
step 10-1, assuming that the heat transfer of the casting blank in the grid area is uniform, applying a heat transfer boundary condition to the heat transfer of the casting blank in the grid area and the liquid core reduction process by adopting an equivalent heat exchange method;
the equivalent heat transfer coefficient calculation formula is as follows:
h＝0.61W0.597(3＜W＜10L/(m2·s)，ts＝800℃)
h＝0.59W0.385(3＜W＜20L/(m2·s)，ts＝900℃) (13)
h＝0.42W0.351(3＜W＜12L/(m2·s)，ts＝1000℃)
in the formula, h represents the comprehensive heat transfer coefficient kW/(m)2DEG C.); w represents the secondary water spray density, L/(m)2·s)；tsRepresents the surface temperature of the casting blank, DEG C;
step 10-2, setting a rigid-flexible contact analysis method between the casting blank and the liquid core lower-section casting roll;
and step 10-3, establishing a calculation analysis model by adopting a real-time coupling method.
And 11, calculating the reduction of each rolling roller according to the total reduction of the liquid core lower segment, and simulating and calculating three-dimensional heat transfer and stress behaviors in the casting blank reduction process.
In this example, the total amount of the press rolls was 17.5mm, and 9 press rolls were used in total.
And step 12, determining a Gaussian function curve with the minimum corner stress in the casting blank liquid core reduction process as a narrow-face crystallizer working surface concave structure curve according to the calculation result in the step 11, and designing a crystallizer copper plate working surface by combining the curve in the height direction to complete the design of a thin slab narrow-face Gaussian concave curved surface crystallizer.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions and scope of the present invention as defined in the appended claims.

Claims (5)

1. A thin slab narrow surface Gaussian concave curved surface crystallizer is characterized in that: the inner surface working surface (1) of the narrow-face copper plate of the crystallizer is of a Gaussian concave curve structure from top to bottom, the transverse width central line of the working surface is taken as symmetry, and according to different sheet billet thicknesses, the vertical distance value from a curve peak point of the Gaussian concave curve structure to a connecting line of two corner parts on the working surface side at the corresponding height of the narrow-face copper plate of the crystallizer is 4.5-10.0 mm;
the inner surface working surface (1) of the narrow-surface copper plate is a continuously-changed curve structure meeting the solidification shrinkage characteristic of the narrow surface of a casting blank along the height direction; the back side and the two side surfaces (5) of the narrow-surface copper plate are both linear structures;
the cooling water tanks (2) of the narrow-face copper plate are of a circular structure and are vertically distributed along the height direction of the crystallizer, the number of the water tanks is determined by the width of the narrow-face copper plate and the size of the cross section of each water tank, and the size of the cross section of each water tank close to the corner area of the crystallizer is 1.0-1.2 times that of the cross section of each water tank in the middle area of the narrow-face copper plate in the width direction; the connecting line of the centers of the cross sections of the water tanks is integrally in a Gaussian curve or arc-shaped structure concave to the working surface of the narrow-surface copper plate, and the water tanks are symmetrically distributed by the transverse width center line of the narrow-surface copper plate; wherein, the distance from the water tank center at the center line of the narrow-face copper plate width or the connecting line of the centers of 2 water tanks which are distributed most close to the narrow-face copper plate width center line to the narrow-face copper plate working face (1) is 20.0 mm-30.0 mm; the distance change range between the connecting line of the centers of the water tanks at the center line of the width of the narrow-face copper plate or the connecting line of the centers of the 2 water tanks which are symmetrically distributed closest to the center line of the width of the narrow-face copper plate and the connecting line of the centers of the 2 water tanks which are closest to the side face of the copper plate is 2.0 mm-10.0 mm; the distance between the water tanks closest to the side surface of the narrow-surface copper plate is 5.0 mm-10.0 mm corresponding to the side surface, and the distribution positions of other water tanks are distributed at equal intervals along the width direction of the copper plate from the central connecting line of the cross section of the water tanks;
the narrow-face copper plate is of a structure with a wide upper opening and a narrow lower opening, the width difference between the upper opening (3) and the lower opening (4) of the narrow-face copper plate is 0.2-1.0 mm according to the thickness of a casting blank produced by continuous casting, and the width difference is linearly reduced from the upper opening (3) to the lower opening (4) along the height direction; the larger the thickness of the narrow-face copper plate is, the larger the width difference between the upper opening (3) and the lower opening (4) is; the thickness of the upper opening (3) and the thickness of the lower opening (4) of the narrow-face copper plate are the same, and the thickness of the middle area in the height direction of the narrow-face copper plate is the thickness of the upper opening or the lower opening plus the value of a continuous change curve of the corresponding working surface in the height direction; the height range of the narrow-face copper plate is 900 mm-1300 mm;
the narrow-face copper plate is suitable for all thin slabs with the thickness of a continuous casting section of 50-135 mm, and the installation positions of the meniscus and the lower opening (4) of the crystallizer are the same as those of the meniscus and the lower opening of the traditional flat-plate narrow-face crystallizer copper plate in the using process.
2. A design method of a thin slab narrow surface gaussian concave curved surface crystallizer, which is used for realizing the design of the thin slab narrow surface gaussian concave curved surface crystallizer as claimed in claim 1, and is characterized in that: the method comprises the following steps:
step 1, selecting proper finite element commercial software, and establishing 1/4 thin slab and a three-dimensional solid model of a crystallizer system thereof according to the actual section size of the microalloyed steel right-angle thin slab on site and the traditional narrow-surface flat plate and wide-surface funnel crystallizer copper plate structure under the corresponding section, wherein the height of the three-dimensional solid model of the thin slab is 1.2-1.5 times of the length of a liquid core reduction segment, and the lower end of a casting blank is positioned at the meniscus of the crystallizer;
step 2, carrying out grid division on the established 1/4 thin slab and the three-dimensional solid model of the crystallizer system thereof, and setting simulated steel grades and heat transfer and mechanical properties of the crystallizer for corresponding units;
step 3, setting three-dimensional heat transfer and mechanical boundary conditions of a crystallizer copper plate and a casting blank in a crystallizer, establishing an unsteady three-dimensional heat/force coupling analysis model of a sheet billet and a crystallizer system thereof by adopting a heat transfer and stress real-time coupling method, and simulating the dynamic solidification heat transfer and shrinkage deformation behaviors of the casting blank in the crystallizer in the continuous casting process of the microalloy steel sheet billet;
step 4, determining the solidification shrinkage of the narrow surface of the casting blank towards the center direction of the wide surface of the crystallizer according to the result of simulating the dynamic solidification heat transfer and shrinkage deformation behaviors of the casting blank, and setting the solidification shrinkage as a distribution curve of the working surface of the narrow-surface copper plate along the height direction of the crystallizer;
step 5, setting the cross section size of the water tank in the middle area of the narrow-face copper plate as the cross section size of the water tank in the middle area of the original narrow-face copper plate, and designing the cross section size of the cooling water tank in the corner area to be 1.0-1.2 times of the cross section size of the water tank in the middle area;
step 6, comprehensively selecting a transverse proper Gaussian curve distribution function of the narrow-face working surface of the crystallizer according to the width of the thin slab, the position of the lower section of the liquid core pressure, the continuous casting drawing speed of the main flow of the microalloyed steel and the reduction amount information of the liquid core;
step 7, designing a Gaussian concave curved surface structure of the narrow-side copper plate working surface of the crystallizer by combining the distribution curve of the narrow-side copper plate working surface of the crystallizer obtained by calculation in the step 4 along the height direction and the transverse Gaussian curve distribution function of the working surface selected in the step 6;
step 8, setting the central distribution of the cross sections of the water tanks based on the size of the cross sections of the set water tanks;
step 9, calculating and inspecting the uniformity of the temperature distribution of the Gaussian concave curved surface crystallizer copper plate and the temperature field distribution of the corner part of the casting blank by adopting the methods in the steps 1 to 3, and selecting a water tank distribution structure with the most uniform cross section temperature field distribution and the casting blank corner part cooling speed exceeding the diffusion precipitation cooling speed of the microalloy carbonitride as a narrow-surface copper plate water tank distribution structure of the crystallizer;
step 10, based on the unsteady three-dimensional heat/force coupling analysis model of the thin slab established in the steps 1 to 3 and the whole casting blank temperature field obtained by calculation in the step 9, establishing a three-dimensional finite element calculation model of heat transfer and stress of a thin slab secondary cold grid area and a liquid core reduction process by adopting the following boundary conditions and analysis methods:
step 10-1, assuming that the heat transfer of the casting blank in the grid area is uniform, applying a heat transfer boundary condition to the heat transfer of the casting blank in the grid area and the liquid core reduction process by adopting an equivalent heat exchange method;
step 10-2, setting a rigid-flexible contact analysis method between the casting blank and the liquid core lower-section casting roll;
step 10-3, establishing a calculation analysis model by adopting a real-time coupling method;
step 11, calculating the reduction of each pressing roller according to the total reduction of the liquid core pressing lower section, and simulating and calculating three-dimensional heat transfer and stress behaviors in the casting blank pressing process;
and step 12, determining a Gaussian function curve with the minimum corner stress in the casting blank liquid core reduction process as a narrow-face crystallizer working surface concave structure curve according to the calculation result in the step 11, and designing a crystallizer copper plate working surface by combining the curve in the height direction to complete the design of a thin slab narrow-face Gaussian concave curved surface crystallizer.
3. The design method of the thin slab narrow-face Gaussian concave curved surface crystallizer according to claim 2, characterized in that: the specific method of the step 2 is as follows:
step 2-1, adopting a non-uniform grid division method to encrypt the surface grid of the casting blank within a range of 0-20 mm close to the surface, and processing the surface grid in a mode of gradually encrypting the casting blank from the center of the wide surface and the narrow surface to the corner part, wherein the grid of the inner layer of the casting blank can be divided loosely;
step 2-2, freely dividing the wide-surface copper plate and the narrow-surface copper plate of the thin slab crystallizer by adopting a free division grid method in a mode of setting the grid unit length of each boundary structure line of the crystallizer copper plate;
and 2-3, calculating the components of the steel grade and the composition of the copper plate and the copper alloy according to the simulation, determining the heat conductivity coefficient, the density, the enthalpy, the elastic modulus and the Poisson ratio parameters of the corresponding steel grade by adopting a reference mode, and correspondingly endowing the casting blank and the crystallizer copper plate with unit attributes respectively.
4. The design method of the thin slab narrow-face Gaussian concave curved surface crystallizer according to claim 3, characterized in that: the specific method of the step 3 is as follows:
3-1, respectively selecting three-dimensional heat transfer control equations of a crystallizer copper plate and a continuous casting billet unit based on the selected finite element commercial software;
3-2, selecting a copper plate mechanical control equation as a three-dimensional elastic-plastic constitutive equation and a casting blank mechanical control equation as an Anand rate related constitutive equation based on the selected finite element commercial software;
step 3-3, assuming that the thickness of the covering slag in the meniscus area of the crystallizer is the same, calculating the thickness of the covering slag flowing into the casting blank/crystallizer interface according to the actual steel slag consumption, the perimeter of the meniscus of the crystallizer, the pulling speed and the density of the covering slag, and setting the thickness as the initial thickness;
step 3-4, assuming that the temperature distribution of the casting blank surface of the meniscus of the crystallizer and the corresponding copper plate of the crystallizer is uniform, the initial temperature of the casting blank unit at the meniscus is the molten steel pouring temperature, the temperature of the copper plate is set to be 200-290 ℃ according to the actual casting speed, and the casting blank/crystallizer interface gaps are set to be the initial thickness of the casting powder;
and 3-5, setting heat transfer boundary conditions of the casting blank and the crystallizer, wherein the specific conditions are as follows:
setting the heat transfer of the crystallizer copper plate water tank as convection heat transfer, wherein the heat transfer boundary is exerted by a convection heat transfer coefficient;
the heat flows of the wide-surface central symmetry plane and the narrow-surface central symmetry plane of the crystallizer copper plate and the casting blank, the contact area of the copper plate back plate and the stainless steel back plate, the upper opening of the crystallizer and the lower opening of the crystallizer are all set to be 0;
applying heat transfer boundary conditions of the surface of the casting blank and the hot surface of the crystallizer in a heat flow mode;
3-6, setting mechanical boundary conditions of the casting blank and the crystallizer, which are as follows:
setting the displacement of the wide-surface symmetrical surface of the casting blank along the direction of the narrow surface of the casting blank to be 0, setting the displacement of the narrow-surface symmetrical surface of the casting blank along the direction of the wide surface of the casting blank to be 0, and vertically moving the casting blank towards the outlet direction of the crystallizer under the boundary condition of taking the pulling speed as the speed;
the ferrostatic pressure is vertically applied to the grid unit at the solidification front of the casting blank;
the contact behavior of the casting blank and the copper plate is set by adopting a rigid-flexible contact analysis algorithm;
the wide face and the narrow face copper plate of the crystallizer are fixed;
3-7, according to the steps 3-1 to 3-6, a casting blank adopts a dead unit control method, namely when the casting blank is in a crystallizer, a unit corresponding to the casting blank is in an activated state, if the casting blank is above a meniscus or is discharged out of the crystallizer, the unit corresponding to the casting blank is frozen, and an unsteady state heat/force real-time coupling analysis model of a thin slab and a crystallizer system thereof is established;
3-8, inputting actual continuous casting production process parameters of the microalloyed steel sheet billet into an analysis model, and simulating and analyzing dynamic solidification heat transfer and shrinkage deformation behaviors of a casting blank in a crystallizer in the continuous casting process of the microalloyed steel sheet billet, wherein the process parameters comprise: the casting method comprises the following steps of (1) drawing speed, molten steel casting temperature, cooling water flow rate of a wide surface and a narrow surface of a crystallizer, cooling water temperature of the wide surface and the narrow surface of the crystallizer, temperature difference between a cooling water inlet and a cooling water outlet of the wide surface and the narrow surface of the crystallizer, consumption of casting powder and solidification temperature of the casting powder;
and 3-9, judging whether the tail end of the casting blank entity enters a meniscus of the crystallizer, if so, executing the step 4, otherwise, executing the steps 3-5.
5. The design method of the thin slab narrow surface Gaussian concave curved surface crystallizer according to claim 4, characterized in that: in the step 3-5, the heat transfer boundary condition between the surface of the casting blank and the hot surface of the crystallizer is applied in a heat flow mode, and the method specifically comprises the following steps:
3-5-1, extracting the temperature of each unit node on the surface of the casting blank and the copper plate at the corresponding position of the casting blank and the corresponding width of the casting blank/crystallizer interface gap;
3-5-2, judging the relation between the casting blank surface node temperature and the casting powder solidification temperature, if the current casting blank surface node temperature is higher than the casting powder solidification temperature, taking liquid casting powder and solid casting powder as heat transfer media in a casting blank/crystallizer interface, and turning to the step 3-5-3; otherwise, the heat transfer medium in the casting blank/crystallizer interface is air gap and solid protection slag, and the step 3-5-4 is carried out;
3-5-3, extracting the temperature of each unit node on the surface of the casting blank and the hot surface of the copper plate at the position corresponding to the unit, calculating and obtaining the heat flow of the surface of the casting blank and the corresponding hot surface unit of the copper plate by utilizing the heat flow phase principle of flowing through the liquid slag layer and the solid slag layer based on the heat conduction and radiation heat transfer parallel connection characteristics in the liquid slag layer and the solid slag layer, and respectively applying corresponding heat flow values to each solid surface unit one by one;
and 3-5-4, extracting the temperature of each unit node on the surface of the casting blank and the hot surface temperature of the copper plate at the position corresponding to the unit, calculating and obtaining the heat flow of the surface of the casting blank and the corresponding hot surface unit of the copper plate by utilizing the heat flow phase principle of flowing through the air gap layer and the solid slag layer on the basis of the heat conduction and radiation heat transfer parallel connection characteristics of heat in the solid slag layer and the air gap layer, and respectively applying corresponding heat flow values to each solid surface unit one by one.
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