JP2023089832A - Casting condition setter, continuous caster, casting condition setting method, continuous casting method and high-tensile steel slab producing method - Google Patents

Abstract

To provide a casting condition setter, continuous caster, casting condition setting method, continuous casting method and high-tensile steel slab producing method allowing for inhibiting a steel slab from cracking by preventing a segregation of constituent elements of molten steel occurring at a portion nearby a corner in a longer-sided wall at an inside of a mold.SOLUTION: A casting condition setter according to one embodiment of the present invention comprises a mold, an immersion nozzle, an electromagnetic stirring device and an electromagnetic brake device, so as to set up a casting condition of a continuous caster to continuously cast a steel slab, and further comprises a casting condition calculating section that, in the case of producing a high-tensile steel slab, calculates a casting condition for a hit velocity, at which an ejection flow hits against the longer-sided wall of the mold, to become smaller than a predetermined reference value, and a setting section that sets, for the continuous caster, a setting value allowing for casting under the casting condition calculated by the casting condition calculating section.SELECTED DRAWING: Figure 7

Description

TECHNICAL FIELD The present invention relates to a casting condition setting apparatus, a continuous casting apparatus, a casting condition setting method, a continuous casting method, and a method for producing a high-strength steel slab.

Steel billets are sometimes cast continuously by continuous casting equipment. In continuous casting equipment, electromagnetic stirrers and electromagnetic brakes are widely used in molds to improve the surface quality of steel slabs.

For example, Patent Document 1 discloses that the magnetic flux density at the discharge port of an immersion nozzle is controlled by an electromagnetic stirrer to ensure a stable state with respect to fluctuations in the molten metal surface during casting and to easily obtain a slab with excellent surface and internal quality. Disclosed is a continuous casting method in which a discharge port of an immersion nozzle is set at a position where the maximum magnetic flux density is 50% or less, a discharge flow is discharged from the immersion nozzle, and this discharge flow is introduced into a static magnetic field formed by an electromagnetic brake. It is

Further, in Patent Document 2, in order to reduce Ar gas bubbles and inclusions contained in continuously cast slabs and improve the quality of the slabs, an electromagnetic stirrer is disclosed while blowing Ar gas into an immersion nozzle. stirs the molten steel in the upper part of the mold to form a swirling flow of the molten steel in the horizontal cross section of the mold, and the electromagnetic brake device applies a DC magnetic field to the molten steel discharged from the discharge hole of the immersion nozzle. In the continuous casting method of steel in which the molten steel is cast by acting, a continuous casting method of steel is disclosed in which the molten steel discharged from the submerged nozzle is controlled.

Japanese Patent Application Laid-Open No. 2001-47195 JP 2009-66618 A

Tadayoshi Takahashi, Hiroshi Ichikawa, Masayuki Kudo, Koichi Shimahara, "Effect of molten metal flow on solidification segregation of steel ingot", Tetsu to Hagane, 61 (1975), No. 9, pp. 2198-2213. Shuji Nagata, Toru Matsumiya, Kosaku Ozawa, Tetsuro Ohashi, "Estimation of Internal Cracking Critical Strain of Continuously Cast Slab", Tetsu to Hagane, 76 (1990), No. 2, pp. 214-221. A. Jablonka, K. Harste and K. Schwerdtfeger, “Thermomechanical properties of iron and iron-carbon alloys: density and thermal contraction, Steel Research, 62 (1991), 24-33. J. Ni and C. Beckermann, “A Volume-Averaged Two-Phase model for Transport Phenomena during Solidification”, Metallurgical Transactions B, 22B, June, 1991, 349-361

In recent years, with the increasing need for high-value-added products, high-alloying of steel slabs is progressing, and in the continuous casting of high-alloy steel, segregation of constituents due to electromagnetic stirring can become a problem. For example, in high-strength steel containing a large amount of Si and Mn, local segregation occurs near the corners inside the mold due to flow due to electromagnetic stirring and discharge flow. As a result, the structure of the high-alloy steel slab becomes non-uniform, and cracks are likely to occur in the steel slab.

The present invention has been made in view of the above situation, and prevents the segregation of the constituent elements of the molten steel that occurs near the corners of the long side walls inside the mold, thereby suppressing the cracking of the steel slab. It is an object of the present invention to provide a casting condition setting device, a continuous casting device, a casting condition setting method, a continuous casting method, and a method for producing a high-strength steel slab.

In order to solve the above problems, the inventors of the present invention conducted intensive studies and found that, in the solidification of an alloy, alloy components such as C, Si, and Mn are discharged from the solid phase to the molten steel side during solidification, but the molten steel does not flow. In this case, the above-mentioned alloy components discharged into the molten steel are washed away, so it was found that the density of the components on a scale of several millimeters after solidification, so-called macro-segregation, is likely to occur. The inventors have found that the macro segregation tends to occur near the corners of the long side walls inside the mold when a continuous casting facility equipped with an electromagnetic stirrer is used to produce steel slabs. As a result of further studies, the present inventors found that peritectic solidification can be achieved by braking the discharge flow with an electromagnetic brake device and suppressing macrosegregation near the corners of the long side walls inside the mold. It has been found that the occurrence of spatial non-uniformity can be suppressed, thereby preventing cracking of the steel slab. Then, the inventors have arrived at the present invention.

The gist of the present invention is as follows.
[1] According to one aspect of the present invention, a mold having a rectangular cross section formed by a pair of long side walls and a pair of short side walls, and 2 arranged opposite to each of the pair of short side walls of the mold an immersion nozzle having four discharge holes for supplying molten steel to the inside of the mold from each of the discharge holes; an electromagnetic stirring device; an electromagnetic braking device that generates a magnetic field and applies an electromagnetic force to the molten steel that constitutes the discharge flow, which is the main flow of the molten steel discharged from the discharge hole, to brake the discharge flow; a casting condition setting device for setting casting conditions for a continuous casting device for continuously casting steel slabs, wherein the discharge flow is subjected to the action of electromagnetic force from the electromagnetic stirring device and the electromagnetic braking device a casting condition calculation unit for calculating the casting conditions for making the speed of collision with the long side wall of the mold less than a predetermined reference value; and the casting conditions calculated by the casting condition calculation unit. and a setting unit for setting a set value for casting in the continuous casting apparatus.
[2] In the casting condition setting device described in [1] above, in the case of producing a high-strength steel slab, the predetermined reference value is the concentration of Si and Mn contained in the molten steel due to the discharge flow. It may be a value determined based on the degree of influence of the change on peritectic solidification.
[3] In the casting condition setting device described in [1] or [2], the casting conditions may include at least the intensity of the magnetic field generated by the electromagnetic stirring device.
[4] In the casting condition setting device according to any one of [1] to [3], the casting conditions may include the strength of the magnetic field generated by the electromagnetic brake device.
[5] In the casting condition setting device according to any one of [1] to [4] above, even if the setting unit sets the setting value so that the collision speed satisfies the following formula (1): good.
U2<0.015×7500×V/{(|0.1×(1−k_Si)×%Si|+|0.02×(1−k_Mn)×%Mn|)−0.015} . (1) where
V=6.45×10 ⁻⁵ ×K×(Vc/Hb) ^0.5
however,
% X: mass concentration of component X (% by mass)
k_X: Equilibrium partition coefficient of component X (-)
U2: Collision speed (m/s)
Vc: Casting speed (m/s)
Hb: Distance from surface of molten steel to upper end of core of electromagnetic brake (m)
K: coagulation coefficient (mm/min ^0.5 )
[6] In the casting condition setting device according to any one of the above [1] to [5], the setting unit sets the ΔCE represented by the following formula (2) to be less than 0.015. You can set the value.
ΔCE=(|0.1×(1−k_Si)×%Si|+|0.02×(1−k_Mn)×%Mn|)/(7500×V/U2+1) Expression (2) where ,
V=6.45×10 ⁻⁵ ×K×(Vc/Hb) ^0.5
U2=U0-(σ×Lb×Bb ² ) (if U0>σ×Lb×Bb ² )
U2=0 (however, when U0≦σ×Lb×Bb ² )
U0=( ^Vp2 +4*Cs*Ls) ^0.5
Ls=(Hb−D)/sin θ
Lb=0.5×(W−D1)/cos θ−Ls
Cs=0.5×σ×f×Δx×Bs ²
Vp = Vc x (Ss/Sp)
however,
% X: mass concentration of component X (% by mass)
k_X: Equilibrium partition coefficient of component X (-)
σ: Conductivity per unit mass of molten steel (Sm ² /kg)
U2: Collision speed (m/s)
Bb: Average magnetic flux density (T) of the magnetic field generated by the electromagnetic brake device
Bs: average magnetic flux density (T) of the magnetic field generated by the electromagnetic stirrer
Hb: Distance from surface of molten steel to upper end of core of electromagnetic brake (m)
Vc: Casting speed (m/s)
Vp: flow velocity (m/s) of the discharge flow at the discharge hole of the submerged nozzle
Sp: Cross-sectional area of the discharge hole (m ² )
Ss: cross-sectional area of the internal space of the mold in the horizontal cross section (m ² )
W: Distance between the long side walls in the internal space of the mold (m)
Δx: Interpolar distance (m) of alternating current applied to the electromagnetic stirrer
f: frequency of alternating current applied to the electromagnetic stirrer (1/s)
D: Depth position (m) of the discharge hole
D1: outer diameter of the submerged nozzle (m)
θ: downward angle (rad) of the discharge hole
K: coagulation coefficient (mm/min ^0.5 )
[7] In the casting condition setting device described in [6], casting may be performed such that U0, Bb, and Lb satisfy U0≦σ×Lb× ^Bb2 .
[8] In the casting condition setting device according to any one of [1] to [7] above, the molten steel contains 0.1 to 0.5% by mass of C and 0.8% by mass or more of Si. Alternatively, at least one of Mn: 4.0% by mass or more may be contained.

[9] According to another aspect of the present invention, there is provided a continuous casting apparatus for casting steel slabs under the above casting conditions set by the casting condition setting device according to any one of [1] to [8] above. is provided.

[10] According to still another aspect of the present invention, a mold having a rectangular cross section formed by a pair of long side walls and a pair of short side walls, and an immersion nozzle for supplying molten steel to the inside of the mold from each of the injection holes; An electromagnetic stirrer for agitation, and an electromagnetic brake device for braking the discharge flow by generating a magnetic field and applying an electromagnetic force to the molten steel constituting the discharge flow, which is the main flow of the molten steel discharged from the discharge hole. and a casting condition setting method for setting casting conditions for a continuous casting apparatus for continuously casting steel slabs, wherein the discharge flow is caused by the electromagnetic stirring a casting condition calculation step of calculating the casting conditions so that the collision speed of the mold when it collides with the long side walls under the action of the electromagnetic force by the device and the electromagnetic brake device is less than a predetermined reference value; and a setting step of setting, in the continuous casting apparatus, setting values that enable casting under the casting conditions calculated in the casting condition calculating step.

[11] According to still another aspect of the present invention, there is provided a continuous casting method for casting a steel slab under the casting conditions set by the method for setting casting conditions described in [10] above.

[12] According to still another aspect of the present invention, a mold having a rectangular cross section formed by a pair of long side walls and a pair of short side walls, and an immersion nozzle for supplying molten steel to the inside of the mold from each of the injection holes; An electromagnetic stirrer for agitation, and an electromagnetic brake device for braking the discharge flow by generating a magnetic field and applying an electromagnetic force to the molten steel constituting the discharge flow, which is the main flow of the molten steel discharged from the discharge hole. and a continuous casting apparatus comprising: A force is applied to cause the molten steel to swirl in a horizontal direction, and the magnetic field generated by the electromagnetic brake device acts on the molten steel forming the discharge flow, and the electromagnetic force acting on the discharge flow brakes the discharge flow. A method for producing a high-strength steel cast slab is provided, characterized in that a collision speed of the discharged flow curved by the swirling flow and colliding with the long side wall of the mold is set to be less than a predetermined reference value.
[13] In the method for producing a high-strength steel slab described in [12] above, the collision speed may satisfy the following formula (1).
U2<0.015×7500×V/{(|0.1×(1−k_Si)×%Si|+|0.02×(1−k_Mn)×%Mn|)−0.015} . (1) where
V=6.45×10 ⁻⁵ ×K×(Vc/Hb) ^0.5
however,
% X: mass concentration of component X (% by mass)
k_X: Equilibrium partition coefficient of component X (-)
U2: Collision speed (m/s)
Vc: Casting speed (m/s)
Hb: Distance from surface of molten steel to upper end of core of electromagnetic brake (m)
K: coagulation coefficient (mm/min ^0.5 )
[14] In the method for producing a high-strength steel slab described in [12] or [13] above, the reference value is ΔCE represented by the following formula (2), and the ΔCE is less than 0.015. The setting value of the continuous casting apparatus may be determined as follows.
ΔCE=(|0.1×(1−k_Si)×%Si|+|0.02×(1−k_Mn)×%Mn|)/(7500×V/U2+1) Expression (2) where ,
V=6.45×10 ⁻⁵ ×K×(Vc/Hb) ^0.5
U2=U0-(σ×Lb×Bb ² ) (if U0>σ×Lb×Bb ² )
U2=0 (however, when U0≦σ×Lb×Bb ² )
U0=( ^Vp2 +4*Cs*Ls) ^0.5
Ls=(Hb−D)/sin θ
Lb=0.5×(W−D1)/cos θ−Ls
Cs=0.5×σ×f×Δx×Bs ²
Vp = Vc x (Ss/Sp)
however,
% X: mass concentration of component X (% by mass)
k_X: Equilibrium partition coefficient of component X (-)
σ: Conductivity per unit mass of molten steel (Sm ² /kg)
U2: Collision speed (m/s)
Bb: Average magnetic flux density (T) of the magnetic field generated by the electromagnetic brake device
Bs: average magnetic flux density (T) of the magnetic field generated by the electromagnetic stirrer
Hb: Distance from surface of molten steel to upper end of core of electromagnetic brake (m)
Vc: Casting speed (m/s)
Vp: flow velocity (m/s) of the discharge flow at the discharge hole of the submerged nozzle
Sp: Cross-sectional area of the discharge hole (m ² )
Ss: cross-sectional area of the internal space of the mold in the horizontal cross section (m ² )
W: Distance between the long side walls in the internal space of the mold (m)
Δx: Interpolar distance (m) of alternating current applied to the electromagnetic stirrer
f: frequency of alternating current applied to the electromagnetic stirrer (1/s)
D: Depth position (m) of the discharge hole
D1: outer diameter of the submerged nozzle (m)
θ: downward angle (rad) of the discharge hole
K: coagulation coefficient (mm/min ^0.5 )
[15] In the method for producing a high-strength steel slab described in [14] above, the above U0, the above Bb and the above Lb may satisfy U0≦σ×Lb× ^Bb2 .
[16] In the method for producing a high-strength steel slab according to any one of [12] to [15] above, the molten steel contains C: 0.1 to 0.5 mass% and Si: 0.8 At least one of Mn: 4.0 mass % or more may be contained.

According to the present invention, the collision speed when the discharge flow collides with the long side walls of the mold is less than the reference value, so the segregation of the constituent elements of the molten steel occurring near the corners of the long side walls inside the mold is suppressed. Therefore, it is possible to suppress the cracking of the steel slab.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic explanatory drawing which shows an example of a continuous casting manufacturing apparatus. FIG. 2 is a partial cross-sectional view along the YZ plane showing the positional relationship between the mold, the electromagnetic stirrer, and the electromagnetic brake, and the configuration of the electromagnetic stirrer and the electromagnetic brake. FIG. 3 is a cross-sectional view along the line AA shown in FIG. 2; 4 is a cross-sectional view along the line BB shown in FIG. 3; FIG. 4 is a cross-sectional view along the CC cross section shown in FIG. 3; FIG. FIG. 4 is a diagram for explaining the direction of electromagnetic force acting on molten steel by an electromagnetic brake device; 1 is a block diagram showing the configuration of a casting condition setting device according to an embodiment of the present invention; FIG. FIG. 5 is a conceptual diagram for explaining the flow of the discharge flow when an electromagnetic brake does not act and when it acts sufficiently; It is a conceptual diagram for demonstrating the flow of a discharge flow. 4 is a graph showing the relationship between the EMBr intensity and the segregation ratio Δ%Si/%Si when the EMS intensity is changed. 4 is a graph showing the relationship between the EMBr strength and the segregation ratio Δ%Si/%Si when the casting speed Vc is changed. 4 is a graph of the relationship between EMBr intensity and ΔCE′ when EMS intensity is changed. 4 is a graph showing the relationship between EMBr strength and ΔCE′ when casting speed Vc is changed. 4 is a graph showing the relationship between EMS strength and EMBr electromagnetic brake strength at ΔCE=0.015 when the steel type is 0.13% C-0.1% Si-0.1% Mn steel. 4 is a graph showing the relationship between EMS strength and EMBr electromagnetic brake strength at ΔCE=0.015 when the steel type is 0.13%C-1.0%Si-0.1%Mn steel. 4 is a graph showing the relationship between EMS strength and EMBr electromagnetic brake strength at ΔCE=0.015 when the steel type is 0.13%C-0.1%Si-6.0%Mn steel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A steel cast slab manufacturing facility according to an embodiment of the present invention will be described below with reference to the attached drawings. In addition, this invention is not limited to the following embodiment. Also, in each drawing shown in this specification, the size of some of the constituent members may be exaggerated for the sake of explanation. The relative size of each member illustrated in each drawing does not necessarily represent the actual size relationship between the members accurately.

<<Configuration of Continuous Casting Equipment>>
First, with reference to FIG. 1, the overall configuration of a continuous casting apparatus to which a casting condition setting apparatus according to an embodiment of the present invention can be applied will be described. FIG. 1 is a schematic explanatory diagram showing an example of a continuous casting apparatus.

As shown in FIG. 1, a continuous casting apparatus 1 according to the present embodiment is an apparatus for continuously casting molten steel 2 using a continuous casting mold 110 to produce a slab 3 such as a slab. The continuous casting apparatus 1 includes a mold 110 , a ladle 4 , a tundish 5 , a submerged nozzle 6 , a secondary cooling device 7 and a cast strip cutter 8 .

The ladle 4 is a movable container for conveying the molten steel 2 to the tundish 5 from the outside. A ladle 4 is arranged above a tundish 5 and molten steel 2 in the ladle 4 is supplied to the tundish 5 . The tundish 5 is arranged above the mold 110 to store the molten steel 2 and remove inclusions in the molten steel 2 . The immersion nozzle 6 extends downward from the lower end of the tundish 5 toward the mold 110 and its tip is immersed in the molten steel 2 inside the mold 110 . The immersion nozzle 6 continuously supplies the molten steel 2 from which inclusions have been removed in the tundish 5 into the mold 110 .

The mold 110 has a rectangular cylindrical shape corresponding to the width and thickness of the slab 3. For example, a pair of long-side mold plates (corresponding to the long-side mold plates 111 shown in FIG. It is assembled so as to sandwich the side mold plate (corresponding to the short side mold plate 112 shown in FIG. 4 etc., which will be described later) from both sides. The long-side mold plate and the short-side mold plate (hereinafter sometimes collectively referred to as mold plate) are, for example, water-cooled copper plates provided with channels through which cooling water flows. The mold 110 cools the molten steel 2 in contact with the mold plate to produce the slab 3 . As the slab 3 moves downward from the mold 110, solidification of the unsolidified portion 3b inside progresses, and the thickness of the solidified shell 3a of the outer shell gradually increases. The slab 3 including the solidified shell 3a and the unsolidified portion 3b is pulled out from the lower end of the mold 110. As shown in FIG.

In the following description, the vertical direction (that is, the direction in which the slab 3 is pulled out from the mold 110) is also referred to as the Z-axis direction. The Z-axis direction is also called the vertical direction. In addition, two mutually orthogonal directions in a plane (horizontal plane) perpendicular to the Z-axis direction are also referred to as an X-axis direction and a Y-axis direction, respectively. In addition, the X-axis direction is defined as a direction parallel to the long side of the mold 110 in the horizontal plane (i.e., the mold width direction), and the Y-axis direction is defined as the direction parallel to the short side of the mold 110 in the horizontal plane (i.e., mold thickness direction). A direction parallel to the XY plane is also called a horizontal direction. In addition, in the following description, when expressing the size of each member, the length of the member in the Z-axis direction is also referred to as the height, and the length of the member in the X-axis direction or the Y-axis direction. is sometimes called width.

Here, although illustration is omitted in FIG. 1 to avoid complication of the drawing, in this embodiment, an electromagnetic force generator 170 is installed on the outer surface of the long-side mold plate of the mold 110 . Then, continuous casting is performed while the electromagnetic force generator 170 is driven. The electromagnetic force generator 170 includes an electromagnetic stirrer 150 and an electromagnetic brake device 160 . In the present embodiment, by performing continuous casting while driving the electromagnetic force generator 170, it is possible to cast at a higher speed while ensuring the quality of the slab. The configuration of the electromagnetic force generator 170 and the installation position with respect to the mold 110 will be described later with reference to FIGS. 2 to 5. FIG.

The secondary cooling device 7 is provided in the secondary cooling zone 9 below the mold 110 and cools the cast slab 3 pulled out from the lower end of the mold 110 while supporting and transporting it. The secondary cooling device 7 includes a plurality of pairs of support rolls (for example, support rolls 11, pinch rolls 12 and segment rolls 13) arranged on both sides of the slab 3 in the thickness direction, and cooling water for the slab 3. and a plurality of spray nozzles (not shown) that spray the

The support rolls provided in the secondary cooling device 7 are arranged in pairs on both sides of the slab 3 in the thickness direction, and function as supporting and conveying means for supporting and conveying the slab 3 . By supporting the slab 3 from both sides in the thickness direction with the support rolls, it is possible to prevent breakout and bulging of the slab 3 during solidification in the secondary cooling zone 9 .

Support rolls 11 , pinch rolls 12 , and segment rolls 13 that are support rolls form a conveying path (pass line) for the slab 3 in the secondary cooling zone 9 . This pass line is vertical immediately below the mold 110, then curves into a curve, and finally becomes horizontal, as shown in FIG. In the secondary cooling zone 9, a portion where the pass line is vertical is called a vertical portion 9A, a curved portion is called a curved portion 9B, and a horizontal portion is called a horizontal portion 9C. A continuous casting apparatus 1 having such a pass line is called a vertical bending type continuous casting apparatus 1 . The present invention is not limited to the vertical bending type continuous casting apparatus 1 shown in FIG. 1, but can also be applied to other various types of continuous casting apparatus such as curved type or vertical type.

The support roll 11 is a non-driven roll provided in the vertical portion 9A directly below the mold 110, and supports the cast slab 3 immediately after being pulled out from the mold 110. As shown in FIG. Since the slab 3 immediately after being pulled out from the mold 110 has a thin solidified shell 3a, it needs to be supported at relatively short intervals (roll pitch) in order to prevent breakout and bulging. Therefore, as the support roll 11, it is desirable to use a small-diameter roll capable of shortening the roll pitch. In the example shown in FIG. 1, three pairs of support rolls 11 made of small-diameter rolls are provided at a relatively narrow roll pitch on both sides of the cast slab 3 in the vertical portion 9A.

The pinch rolls 12 are drive rolls that are rotated by drive means such as a motor, and have a function of pulling out the cast slab 3 from the mold 110 . The pinch rolls 12 are arranged at appropriate positions in the vertical section 9A, the curved section 9B and the horizontal section 9C. The cast slab 3 is pulled out from the mold 110 by the force transmitted from the pinch rolls 12 and conveyed along the pass line. The arrangement of the pinch rolls 12 is not limited to the example shown in FIG. 1, and the arrangement position may be set arbitrarily.

The segment rolls 13 (also referred to as guide rolls) are non-driven rolls provided on the curved portion 9B and the horizontal portion 9C, and support and guide the slab 3 along the pass line. The segment roll 13 is positioned on the pass line and on either the F surface (fixed surface, lower left surface in FIG. 1) or the L surface (loose surface, upper right surface in FIG. 1) of the slab 3. Depending on whether they are provided, they may be arranged with different roll diameters and roll pitches.

The slab cutting machine 8 is arranged at the terminal end of the horizontal portion 9C of the pass line, and cuts the slab 3 transported along the pass line into a predetermined length. The cut slab 14 in the form of a thick plate is transported to equipment for the next process by a table roll 15 .

The overall configuration of the continuous casting apparatus 1 according to the present embodiment has been described above with reference to FIG. Note that, in the present embodiment, an electromagnetic force generator 170 having a configuration described later may be installed in the mold 110, and continuous casting may be performed using the electromagnetic force generator 170. The configuration other than the force generator 170 may be the same as that of a general conventional continuous casting apparatus. Therefore, the configuration of the continuous casting apparatus 1 is not limited to the illustrated one, and any configuration may be used as the continuous casting apparatus 1 .

<<Electromagnetic force generator 170>>
<Configuration of electromagnetic force generator 170>
The configuration of the electromagnetic force generator 170 installed with respect to the mold 110 described above will be described in detail with reference to FIGS. 2 to 5. FIG.

FIG. 2 is a cross-sectional view along the YZ plane of the mold facility 10 according to this embodiment. FIG. 3 is a cross-sectional view of the mold facility 10 taken along line AA shown in FIG. FIG. 4 is a cross-sectional view of the mold facility 10 taken along the line BB shown in FIG. FIG. 5 is a cross-sectional view of the mold facility 10 taken along line CC shown in FIG. Since the mold facility 10 has a symmetrical configuration with respect to the center of the mold 110 in the Y-axis direction, FIGS. showing. 2, 4 and 5 also show the molten steel 2 in the mold 110 for easy understanding.

Referring to FIGS. 2 to 5, the mold facility 10 according to the present embodiment includes two water boxes 130 and 140 and an electromagnetic force generating A device 170 is installed and configured.

As described above, the mold 110 is assembled such that the pair of long-side mold plates 111 sandwiches the pair of short-side mold plates 112 from both sides. The mold plates 111 and 112 are made of copper plates. However, the present embodiment is not limited to such an example, and the mold plates 111 and 112 may be made of various materials generally used as molds for continuous casting apparatuses.

Here, in this embodiment, continuous casting of steel slabs is targeted, and the slab size is about 800 to 2300 mm in width (that is, length in the X-axis direction) and about 800 mm to 2300 mm in thickness (that is, length in the Y-axis direction). ) is about 200 to 300 mm. That is, the mold plates 111 and 112 also have sizes corresponding to the size of the slab. That is, the long side mold plate 111 has a width in the X-axis direction that is at least longer than the width of the slab 3 of 800 to 2300 mm, and the short side mold plate 112 has a Y It has an axial width.

In general, when the molten steel 2 solidifies in the mold 110, the slab 3 separates from the inner wall of the mold 110 due to solidification shrinkage, which may result in insufficient cooling of the slab 3. Are known. Therefore, the length of the mold 110 in the Z-axis direction is limited to about 1000 mm at most from the surface of the molten steel.

The backup plates 121 and 122 are made of stainless steel, for example, and are provided so as to cover the outer surfaces of the mold plates 111 and 112 of the mold 110 in order to reinforce the mold plates 111 and 112 . Hereinafter, for distinction, the backup plate 121 provided on the outer surface of the long-side mold plate 111 is also referred to as the long-side backup plate 121, and the backup plate 122 provided on the outer surface of the short-side mold plate 112 is referred to as the short side plate. It is also called side backup plate 122 .

Since the electromagnetic force generator 170 applies an electromagnetic force to the molten steel 2 in the mold 110 via the long side backup plate 121, at least the long side backup plate 121 is made of a non-magnetic material (for example, non-magnetic stainless steel). etc.).

The long-side backup plate 121 is further provided with a pair of backup plates 123 extending in a direction perpendicular to the long-side backup plate 121 (that is, the Y-axis direction). As shown in FIGS. 3 to 5, an electromagnetic force generator 170 is installed between the pair of backup plates 123. FIG. In this way, the backup plate 123 can define the width (that is, the length in the X-axis direction) of the electromagnetic force generator 170 and the installation position in the X-axis direction. In other words, the mounting position of the backup plate 123 is determined so that the electromagnetic force generator 170 can apply electromagnetic force to a desired range of the molten steel 2 in the mold 110 . Hereinafter, the backup plate 123 is also referred to as a width direction backup plate 123 for distinction. The width direction backup plate 123 is also made of stainless steel, for example, like the backup plates 121 and 122 .

Water boxes 130 and 140 store cooling water for cooling mold 110 . In this embodiment, as shown in the figure, one water box 130 is installed in a region at a predetermined distance from the upper end of the long side mold plate 111, and the other water box 140 is installed in a region at a predetermined distance from the lower end of the long side mold plate 111. to be installed. By providing the water boxes 130 and 140 above and below the mold 110 in this manner, it is possible to secure a space between the water boxes 130 and 140 for installing the electromagnetic force generator 170 . Hereinafter, for distinction, the water box 130 provided above the long side mold plate 111 is also referred to as the upper water box 130, and the water box 140 provided below the long side mold plate 111 is also referred to as the lower water box 140.

Inside the long-side mold plate 111 or between the long-side mold plate 111 and the long-side backup plate 121, water channels (not shown) through which cooling water passes are formed. The waterway extends to water boxes 130 and 140 . A pump (not shown) causes cooling water to flow through the channel from one water box 130, 140 to the other water box 130, 140 (for example, from the lower water box 140 to the upper water box 130). Thereby, the long-side mold plate 111 is cooled, and the molten steel 2 inside the mold 110 is cooled through the long-side mold plate 111 . Although not shown, the short side mold plate 112 is similarly provided with a water box and a water channel, and the short side mold plate 112 is cooled by flowing cooling water.

The electromagnetic force generator 170 includes an electromagnetic stirrer 150 and an electromagnetic brake device 160 . As shown, the electromagnetic stirring device 150 and the electromagnetic braking device 160 are installed in the space between the water boxes 130,140. In the space, the electromagnetic stirring device 150 is installed above and the electromagnetic braking device 160 is installed below.

The electromagnetic stirrer 150 applies a dynamic magnetic field to the molten steel 2 in the mold 110 to act an electromagnetic force on the molten steel 2 . The electromagnetic stirrer 150 is driven so that the electromagnetic force in the width direction (that is, the X-axis direction) of the long side mold plate 111 on which it is installed acts on the molten steel 2 . In FIG. 4, the direction of the electromagnetic force acting on the molten steel 2 by the electromagnetic stirrer 150 is schematically indicated by thick arrows. Here, the electromagnetic stirrer 150 provided on the long-side mold plate 111 not shown (that is, the long-side mold plate 111 facing the long-side mold plate 111 shown in the drawing) is installed on the long side Along the width direction of the mold plate 111, it is driven so that an electromagnetic force acts in a direction opposite to the illustrated direction. Thus, the pair of electromagnetic stirrers 150 are driven to generate a swirling flow in the horizontal plane. According to the electromagnetic stirrer 150, by generating such a swirling flow, the molten steel 2 at the interface of the solidified shell is made to flow, and a cleaning effect of suppressing the trapping of air bubbles and inclusions in the solidified shell 3a is obtained. The surface quality of the piece 3 can be improved.

A detailed configuration of the electromagnetic stirring device 150 will be described. The electromagnetic stirring device 150 includes a case 151, an iron core 152 (hereinafter also referred to as an electromagnetic stirring core 152) stored in the case 151, and a conductive wire wound around the electromagnetic stirring core 152. and a plurality of coils 153.

The case 151 is a hollow member having a substantially rectangular parallelepiped shape. The size of the case 151 is such that the electromagnetic stirrer 150 can apply an electromagnetic force to a desired range of the molten steel 2 , that is, the coil 153 provided inside is arranged at an appropriate position with respect to the molten steel 2 . can be determined as appropriate. In addition, in the electromagnetic stirring device 150, an electromagnetic force is applied to the molten steel 2 from the coil 153 through the side wall of the case 151. Therefore, the material of the case 151 is, for example, non-magnetic stainless steel or FRP (Fiber Reinforced Plastics). ), etc., which are non-magnetic and whose strength can be secured.

The electromagnetic stirring core 152 is a solid member having a substantially rectangular parallelepiped main body and a plurality of teeth 154 projecting from the main body. It is installed so as to be substantially parallel to the width direction of the plate 111 (that is, the X-axis direction). The electromagnetic stirring core 152 is formed by laminating electromagnetic steel sheets, for example.

A coil 153 is formed by winding a conductive wire around the electromagnetic stirring core 152 with the X-axis direction as the winding axis direction (that is, the coil 153 is formed so as to magnetize the electromagnetic stirring core 152 in the X-axis direction). is formed). As the conducting wire, for example, a copper wire having a cross section of 10 mm×10 mm and a cooling water channel with a diameter of about 5 mm inside is used. When current is applied, the conducting wire is cooled using the cooling water passage. The conducting wire has its surface layer insulated with insulating paper or the like, and can be wound in layers. For example, one coil 153 is formed by winding the conductive wire in two to four layers. Coils 153 having a similar configuration are arranged in parallel at predetermined intervals in the X-axis direction.

Specifically, a substantially rectangular parallelepiped main body of the electromagnetic stirring core 152 is installed so as to extend in the X-axis direction, and a plurality of teeth 154 are provided so as to horizontally protrude from the main body toward the mold 110. be provided. These teeth portions 154 are arranged side by side with a predetermined interval in the X-axis direction. Conductive wires are wound around the regions between the plurality of teeth 154 with the X-axis direction as the winding axis direction to form the plurality of coils 153 . The width of the tooth portion 154 (that is, the length in the X-axis direction) Wt and the width of the coil 153 (that is, the length of the coil 153 in the X-axis direction, which is the distance between adjacent teeth portions 154 in the X-axis direction) ) Wc is appropriately set in consideration of the size of the width W1 of the electromagnetic stirring core 152 and obtaining a desired stirring force capable of improving the quality of the slab 3 . For example, the width Wt of the tooth portion 154 is approximately 30 mm to 120 mm, and the width Wc of the coil 153 is approximately 20 mm to 120 mm.

A power supply device (not shown) is connected to each of the plurality of coils 153 . By the power supply device, an alternating current is applied to the plurality of coils 153 so that the phase of the current is appropriately shifted in the arrangement order of the plurality of coils 153, thereby generating a swirling flow in the molten steel 2. An electromagnetic force can be applied. The driving of the power supply device can be appropriately controlled by a control device (not shown) consisting of a processor or the like operating according to a predetermined program. The amount of current applied to each of the coils 153, the phase of the alternating current applied to each of the coils 153, and the like are appropriately controlled by the control device, and the strength of the electromagnetic force applied to the molten steel 2 is controlled. obtain.

The width W1 of the electromagnetic stirring core 152 in the X-axis direction is such that the electromagnetic stirring device 150 can apply an electromagnetic force to a desired range of the molten steel 2, that is, the coil 153 is positioned appropriately with respect to the molten steel 2. can be determined as appropriate. For example, W1 is about 1800 mm.

Although the electromagnetic stirring core 152 has teeth 154 in the illustrated configuration example, the first embodiment is not limited to this example. In the first embodiment, the teeth 154 may not be provided on the electromagnetic stirring core 152 . In this case, the electromagnetic stirring core 152 is configured in a substantially rectangular parallelepiped shape, and the conductive wires are wound around the electromagnetic stirring core 152 at predetermined intervals in the X-axis direction. A plurality of coils 153 are formed which are arranged axially at predetermined intervals.

The electromagnetic brake device 160 applies a static magnetic field to the molten steel 2 in the mold 110 so that an electromagnetic force acts on the molten steel 2 . Here, FIG. 6 is a diagram for explaining the direction of the electromagnetic force acting on the molten steel 2 by the electromagnetic brake device 160. As shown in FIG. FIG. 6 schematically shows a cross-section of the configuration near the mold 110 in the XZ plane. In FIG. 6, the positions of the electromagnetic stirring core 152 and the electromagnetic brake core 162, which will be described later, are schematically indicated by dashed lines.

As shown in FIG. 6 , the submerged nozzle 6 may be provided with a pair of discharge holes 61 at positions facing the short-side mold plate 112 . The electromagnetic brake device 160 is driven so that an electromagnetic force acts on the molten steel 2 in a direction to suppress the flow (discharge flow) of the molten steel 2 from the discharge hole 61 of the submerged nozzle 6 . In FIG. 6, the directions of the discharge flows discharged from the two discharge holes 61 are shown by thin arrows in a simulated manner, and the direction of the electromagnetic force acting on the molten steel 2 from the discharge holes 61 by the electromagnetic brake device 160. is simulatively indicated by thick arrows. According to the electromagnetic brake device 160, the flow in the area below the electromagnetic brake can be cleared by generating an electromagnetic force in the direction of suppressing the discharge flow. Note that the discharge flow refers to the main flow of the molten steel 2 discharged from the discharge hole 61, and the direction of the flow is, for example, generally downward when the discharge hole 61 is tilted downward by 30 degrees from the horizontal plane. Tilted 30 degrees. In addition, the discharge flow is not necessarily linear, and in the above example, if the flow tilted downward by 30 degrees hits the mold wall after that and changes its direction, for example, in the vertical direction, the flow after changing the direction In some cases, this is also called a discharge flow.

A detailed configuration of the electromagnetic brake device 160 will be described. As shown in FIG. 5, the electromagnetic brake device 160 includes a case 161, an electromagnetic brake core 162 stored in the case 161, a coil 163 formed by winding a conductive wire around the electromagnetic brake core 162, consists of

The case 161 is a hollow member having a substantially rectangular parallelepiped shape. The size of the case 161 is such that the electromagnetic force can act on a desired range of the molten steel 2 by the electromagnetic brake device 160, that is, the coil 163 provided inside is arranged at an appropriate position with respect to the molten steel 2. can be determined as appropriate. However, the width of the electromagnetic stirring device 150 and the width of the electromagnetic braking device 160 may be different.

In addition, in the electromagnetic brake device 160, since the electromagnetic force is applied to the molten steel 2 from the coil 163 through the side wall of the case 161, the case 161, like the case 151, is made of, for example, non-magnetic stainless steel or FRP. , which is non-magnetic and whose strength can be ensured.

A coil 163 is formed by winding a conductive wire around the end of the electromagnetic brake core 162 with the Y-axis direction as the winding axis direction (that is, magnetizing the electromagnetic brake core 162 in the Y-axis direction). (a coil 163 is formed in ). The structure of the coil 163 is the same as the coil 153 of the electromagnetic stirring device 150 described above.

A power supply (not shown) is connected to each of the coils 163 . By applying a direct current to each coil 163 by the power supply device, an electromagnetic force can be applied to the molten steel 2 to weaken the momentum of the discharge flow. The driving of the power supply device can be appropriately controlled by a control device (not shown) consisting of a processor or the like operating according to a predetermined program. The amount of current applied to each coil 163 can be appropriately controlled by the controller, and the strength of the electromagnetic force applied to the molten steel 2 can be controlled.

The width W0 of the electromagnetic brake core 162 in the X-axis direction is such that the electromagnetic stirrer 150 can apply an electromagnetic force to a desired range of the molten steel 2, that is, the coil 163 is positioned appropriately with respect to the molten steel 2. can be determined as appropriate. For example, W0 is about 1600 mm.
So far, the electromagnetic force generator 170 has been described.

(Molten steel 2)
Molten steel 2 is not particularly limited to the following as long as the steel slab to be cast is in the process of manufacturing a high-strength steel plate, but C: 0.1 to 0.5 mass% with peritectic solidification If the composition of molten steel contains relatively large amounts of Si and Mn, cracks are likely to occur during the production of steel slabs. Therefore, in the present invention, when the molten steel 2 contains C: 0.1 to 0.5% by mass and at least one of Si: 0.8% by mass or more or Mn: 4.0% by mass or more It is particularly preferred to apply

So far, the steel slab manufacturing apparatus (continuous casting apparatus 1) has been described. The continuous casting apparatus 1 can manufacture high-strength steel slabs under casting conditions set by a casting condition setting device, which will be described later.

<<Casting condition setting device>>
Next, a casting condition setting device according to an embodiment of the present invention will be described with reference to FIG. FIG. 7 is a block diagram showing the configuration of a casting condition setting device according to an embodiment of the present invention. A casting condition setting device 50 shown in FIG. 7 is a casting condition setting device according to one embodiment of the present invention. A casting condition calculation unit 51 for calculating a casting condition for making the collision speed at a time less than a predetermined reference value; and a setting unit 52 for setting. The high-strength steel slab referred to here is a steel slab that contains relatively large amounts of Si and Mn and is cast in the manufacturing process of a high-strength steel plate having a tensile strength of, for example, about 780 MPa.

<Reference value of collision speed when the discharge flow collides with the long side wall of the mold 110>
Referring to FIG. 8, the reference value of the collision speed when the discharge flow collides with the long side walls of the mold 110 will be described. FIG. 8 is a conceptual diagram for explaining the flow of the discharge flow when the electromagnetic brake does not work and when it works sufficiently. FIG. 8 shows the flow of the molten steel 2 in the mold 110 in a cross section (XY plane) perpendicular to the Z axis.

The molten steel 2 discharged from the discharge hole 61 of the submerged nozzle 6 is accelerated by the electromagnetic force exerted by the magnetic field generated by the electromagnetic stirrer 150 , and is curved in the swirling direction of the molten steel 2 in the mold 110 . When the electromagnetic brake does not act on the discharge flow, as shown in the left diagram of FIG. It strongly collides with the long side wall of the corner located in the direction (hereinafter, it is considered that the velocity of the discharge flow when colliding with the short side wall is equal to the velocity of the discharge flow when colliding with the long side wall). The solidification of the molten steel 2 progresses even on the long side walls of the corners, but the solidification is affected by the strong flow of the molten steel 2 coupled with the collision of the discharge flow against the long side walls of the corners. Become. On the other hand, when the electromagnetic brake sufficiently acts on the discharge flow, the speed of the discharge flow decreases due to the electromagnetic force acting on the molten steel 2 that constitutes the discharge flow, and the discharge flow is generated in the vicinity of the corners of the long side walls. is not reached, or even if it is reached, the degree of collision is weak.

Normally, in the solidification of molten steel without strong flow, the concentration of components on the scale of several tens of micrometers, so-called micro-segregation, occurs. There are few cases where it has a negative impact.
On the other hand, when the molten steel flows strongly, macrosegregation tends to occur due to the flow of components such as C, Si, and Mn that are discharged into the molten steel during the solidification process. Si and Mn have a slower diffusion rate in the solid phase than C, and the segregation of Si and Mn tends to adversely affect the steel slab (the structure of the steel slab becomes uneven and cracks are likely to occur ). When casting a steel type with a low Si and Mn content such as ordinary steel, the content of Si and Mn, which diffuse slowly in the solid phase, is low, so macrosegregation occurring near the inner wall surface of the mold 110 has an adverse effect. difficult to influence. However, in steel grades with peritectic solidification containing a large amount of Si or Mn and containing about 0.1 to 0.5% by mass of C, such as high-strength steel, macrosegregation adversely affects the quality of steel slabs. may affect In the above steel types, if the concentration distribution of Si, which is a ferrite-stabilizing element, or Mn, which is an austenite-stabilizing element, varies locally during solidification, the generated peritectic structure is spatially unevenly distributed. For example, in portions where the concentration of Si is high, a large amount of δ-phase is locally generated, and the δ-phase is unevenly distributed. In the portion where the Si concentration is high, the volume contraction due to the δγ transformation, which transforms from the δ phase to the γ phase, becomes larger than that in the region where the δ phase is less generated, which causes strain in the solidified shell and cracks in the steel slab. may occur.
Therefore, by braking the discharge flow with the electromagnetic brake device 160 and suppressing the macro segregation near the corners where the flow strongly flows when the electromagnetic brake device 160 is not installed, the peritectic solidification is made spatially uniform. , can suppress cracking of steel slabs.

From the above, the reference value of the collision speed when the discharge flow collides with the part near the corner of the long side wall of the mold 110 is that the change in concentration of Si and Mn contained in the molten steel 2 due to the discharge flow causes peritectic solidification. It is preferably determined based on the degree of influence.

Next, with reference to FIG. 9, an example of the reference value of the collision speed when the discharge flow collides with the long side walls of the mold 110 will be described in detail. As an example of the reference value, there is a calculation formula for determining the degree of influence ΔCE that local Si concentration changes and Mn concentration changes due to segregation have on the peritectic structure. Explain why it can be used as a reference value.

(Flow velocity U0 of discharge flow when flowing into upper end of electromagnetic brake core 162)
The discharge flow velocity Vp of the molten steel 2 discharged from the discharge hole 61 is perpendicular to the flow direction of the discharge hole 61 and the cross-sectional area Sp of the cross section including the four sides of the discharge hole 61, along the XY plane of the internal space of the mold 110 It can be expressed by the following equation (1) using the cross-sectional area Ss in the horizontal cross section and the casting speed Vc.
Vp=Vc×(Ss/Sp) Expression (1)

The discharge flow is accelerated by the electromagnetic force F1 generated by the magnetic field generated by the electromagnetic stirrer 150 between the lower end of the discharge hole 61 and the upper end of the electromagnetic brake core 162 . D is the distance from the upper end of the electromagnetic stirring core 152 to the lower end of the discharge hole 61, Hb is the distance from the upper end of the electromagnetic stirring core 152 to the upper end of the electromagnetic brake core 162, and θ (rad. ), the distance Ls at which the discharge flow accelerates is expressed by the following equation (2). The angle between the horizontal plane and the discharge flow is the angle between the horizontal plane and the direction along the long side wall of the mold 110 at the lower end of the discharge hole 61 .
Ls=(Hb−D)/sin θ (2) formula

The above Ls is the distance in the region located above the electromagnetic brake core 162, and the region is the momentum of the molten steel 2 due to the magnetic field generated by the electromagnetic stirring device 150 and the turbulent flow caused by the magnetic field and the discharge flow. is the dominant region of forced convection, strongly affected by the diffusion of The electromagnetic force F1 acting on the discharge flow by the electromagnetic stirring device 150 within the range of Ls can be approximated by the following equation (3).
F1=σ×Es×Bs Equation (3) where σ is the electrical conductivity per unit mass of the molten steel 2 (discharge flow), and Es is generated by the time change of the magnetic field generated by the electromagnetic stirrer 150. Bs is the spatial average magnetic flux density of the magnetic field generated by the electromagnetic stirrer 150 .

The electric field Es can be approximated using the frequency f of the alternating current applied to the coil 153 of the electromagnetic stirrer 150 and the wavelength Δx of the phase of the alternating current, and is expressed by the following equation (4).
Es=f×Δx×Bs (4) formula

Therefore, the above equation (3) is expressed by the following equation (5) based on the above equation (4).
F1=σ×f×Δx×Bs ² (5) formula

Therefore, the equation of motion of the molten steel 2 on which the electromagnetic force F1 generated by the magnetic field generated by the electromagnetic stirrer 150 acts is represented by the following equation (6).
du/dt=σ×f×Δx×Bs ² (6) formula

When the above equation of motion (Equation (6)) is solved with the moment when the molten steel 2 is ejected from the ejection hole 61 is t=0, the velocity u1 of the molten steel 2 at time t is given by the following equation (7) is represented by
u1=Vp+2*Cs*t (7) where Cs=0.5*[sigma]*f*[Delta] ^x *Bs2.

The following equation (8) is obtained by integrating the above equation (7) from time t=0 to time t=T1 when the discharge flow reaches the upper end of the electromagnetic brake core 162. Solving for T1, the time T1 at which the discharge flow reaches the upper end of the electromagnetic brake core 162 is expressed by the following equation (9).
Vp×T1+Cs×T1 ² =Ls Equation (8) T1=0.5/Cs×(−Vp+(Vp ² +4×Cs×Ls) ^0.5 ) Equation (9)

Here, by substituting the above equation (9) into the equation (7), the flow velocity of the discharge flow at time t=T1, that is, the flow velocity U0 of the discharge flow when it flows into the upper end P of the electromagnetic brake core 162 is obtained as follows. (10) is represented by the formula.
U0=(Vp ² +4×Cs×Ls) ^0.5 Expression (10)

(Flow velocity U2 of the discharge flow when colliding with the inner surface of the mold 110 (collision velocity U2))
The discharge flow that has flowed into the height where the electromagnetic brake core 162 is arranged is decelerated by the magnetic field generated by the electromagnetic brake device 160 until it reaches the short side wall of the mold 110 . The distance Lb traveled while the discharge flow flowing into the height where the electromagnetic brake core 162 is arranged is decelerated by the electromagnetic brake device 160 is determined by the width of the mold 110 (the distance between the short side walls) W and the width of the immersion nozzle 6 Using the outer diameter D1, it is represented by the following equation (11).
Lb=0.5×(W−D1)/cos θ−Ls (11) formula

Here, unless the device configuration is such that Lb>0, the direct braking effect of the discharge flow by the electromagnetic brake device 160 cannot be expected.

An electromagnetic force F2 generated in the molten steel 2 by the magnetic field generated by the electromagnetic brake device 160 in the distance Lb that the discharge flow advances while being decelerated by the electromagnetic brake device 160 is represented by the following equation (12).
F2=σ×(u×Bb)×Bb (12) where u is the flow velocity of the discharge flow, and Bb is the spatial average magnetic flux density of the magnetic field generated by the electromagnetic brake device 160 .

Since this electromagnetic force F2 acts in the opposite direction to the flow velocity u of the molten steel 2, the equation of motion of the molten steel 2 acting on the electromagnetic force F2 generated by the magnetic field generated by the electromagnetic brake device 160 is expressed by the following equation (13). .
du/dt=−σ×u×Bb ² (13) formula

When the above equation of motion (equation (13)) is solved with the time at which the discharged flow flows into the upper end of the electromagnetic brake core 162 as t=0, the velocity u2 of the molten steel 2 at time t is given by the following (14) is represented by the formula
u2=U0×exp(−σ×Bb ² ×t) Expression (14)

Equation (14) is integrated in the range of time t=T when the discharge flow advances by distance L from time t=0 when the discharge flow enters the upper end of the electromagnetic brake core 162, and the following equation (15) is obtained. is obtained.
(U0/(σ×Bb ² ))×(1−exp(−σ×Bb ² ×T))=L Expression (15)

Therefore, from the above equation (15), when the maximum value Lmax of L (the distance that the discharge flow travels until the flow velocity becomes 0) satisfies the following equation (16), the discharge flow is generated by the electromagnetic brake device 160. Braking by the electromagnetic force acting by the magnetic field, in other words, by the electromagnetic braking by the electromagnetic braking device 160 sufficiently decelerates, so macro segregation does not occur. Therefore, preferably, by operating under conditions that satisfy U0 / (σ × Bb ² ) ≤ Lb, the flow of the molten steel 2 in the surface layer of the mold 110 is almost completely damped, further preventing macrosegregation. be able to.
Lmax=U0/(σ×Bb ² )≦Lb (16) formula

On the other hand, when the maximum value Lmax of L does not satisfy the above equation (16), in other words, when U0/(σ×Bb ² )>Lb, the flow velocity U2 of the discharge flow at time t=T2 when L=Lb is It can be approximated as the following equation (17).
U2=U0-σ×Lb×Bb ² (17) formula

(Influence of flow velocity of molten steel 2 when molten steel 2 solidifies on segregation of molten steel components)
Next, the effect of the flow velocity of the molten steel when it solidifies on the segregation of the components of the molten steel will be described. According to Non-Patent Document 1, the aforementioned macro segregation is affected by the flow velocity U of molten steel and the solidification velocity V of the molten steel, and the extent can be approximated by the following equation (19).
Cm/C0=1-(1-k)/((7500×V/U)+1) (19) where Cm is the alloy component concentration in the solid phase after solidification and Co is the molten steel before solidification and k is the equilibrium partition coefficient of the alloy components.

Here, regarding the solidification rate V, the following empirical formula (formula (20)) is often used with respect to the solidified shell thickness d (mm) in continuous casting. The solidification speed V of the molten steel 2 at the upper end position Hb of the brake core 162 can be approximated by the following equation (21).
d=K√t Formula (20) V=6.45×10 ⁻⁵ ×K×(Vc/Hb) ^0.5 Formula (21) In formula (20) above, K is 15 to It is a constant of about 30, and t is the time (min.). Also, in the above formula (21), Vc is the casting speed.

(Influence ΔCE of local Si concentration change and Mn concentration change due to segregation on peritectic structure)
Next, the effect of local Si concentration change and Mn concentration change due to segregation on the peritectic structure will be described. The Si concentration change ΔC_Si=C0_Si−Cm_Si, which is the difference between the Si concentration C0_Si in the molten steel before solidification and the Si concentration Cm_Si in the solid phase after solidification, is expressed by the following equation (22) from the above equation (19). .
ΔC_Si=(C0_Si)×(1−k_Si)/((7500×V/U)+1) Equation (22) In Equation (22) above, k_Si is the equilibrium partition coefficient of Si.

Similarly for Mn, the Mn concentration change ΔC_Mn=C0_Mn−Cm_Mn, which is the difference between the Mn concentration C0_Mn in the molten steel before solidification and the Mn concentration Cm_Mn in the solid phase after solidification, is expressed by the following equation (23). .
ΔC_Mn=(C0_Mn)×(1−k_Mn)/((7500×V/U)+1) Equation (23) In Equation (23) above, k_Mn is the equilibrium distribution coefficient of Mn.

The degree of influence of the Si concentration change ΔC_Si on peritectic solidification can be estimated as 0.1×ΔC_Si, where the degree of influence of the C (carbon) concentration change on peritectic solidification is 1.0. Also, Mn can be estimated as 0.02×ΔC_Mn. The degree of Si concentration and the degree of Mn concentration each affect the ease of formation of the δ phase and the γ phase, but their interaction is small. Therefore, the degree of influence ΔCE of the Si concentration change ΔC_Si and the Mn concentration change ΔC_Mn on peritectic solidification can be expressed by the following equation (24) from the above equations (22) and (23). In addition, hereinafter, the degree of influence ΔCE that the concentration change ΔC_Si of Si and the concentration change ΔC_Mn of Mn exert on peritectic solidification may be simply referred to as the degree of influence ΔCE. )
ΔCE = (|0.1×(1−k_Si)×C0_Si|+|0.02×(1−k_Mn)×C0_Mn|)/(7500×V/U+1) (24) Equation So far, influence The reason why the degree ΔCE can be used as the reference value has been explained.

(Influence ΔCE<0.015)
The inventors of the present invention have found that by casting such that the degree of influence ΔCE is less than 0.015, cracking of slabs can be suppressed even in continuous casting of high-strength steel. By optimizing the operating conditions according to the Si and Mn contents of the molten steel 2 and making the degree of influence ΔCE less than 0.015, slab defects can be reduced.

The grounds for setting the threshold value of the degree of influence ΔCE to 0.015 will be described.
There are various types of cracks in steel slabs in continuous casting. In particular, cracks occur in the high-temperature embrittlement region, where cracks occur under mild strain. Fractures often occur in the pieces. For example, according to Non-Patent Document 2, the critical strain εcr of the solidified shell when cracks occur in the steel slab is about 0.32×10 ⁻² to 3.8×10 ⁻² . Therefore, by setting the strain generated in the solidified shell during casting to less than 0.32×10 ⁻² , cracking of the steel slab can be reduced.

The strain ε caused by the δγ transformation of the hypoperitectic steel is expressed as ε=|1−(ργ/ρδ) ^1/3 | when the strain occurs isotropically, and ε when the strain occurs in one direction. =|1−(ργ/ρδ)|. where ργ is the density of the γ phase and ρδ is the density of the δ phase. The strain that occurs in the mold during solidification is not necessarily isotropic, and the strain is more concentrated in one direction than isotropically. Therefore, the conditions under which the cracking of steel slabs can be sufficiently reduced can be expressed by the following equation (25).
ε=|1−(ργ/ρδ)|<εcr Expression (25)

According to Non-Patent Document 3, the density ργ of the γ phase is expressed by the following equation (26), and the density ρδ of the δ phase is expressed by the following equation (27).
ργ=8099.8−0.5×T (26) ρδ=7876.0−0.3×T (27)

Assuming T = 1750 K as an approximate temperature during casting, the strain due to the δγ transformation is ε ≈ 0 from the above equation ε = |1-(ργ/ρδ)| and from the above equations (26) and (27). .017. Therefore, assuming that the volume fraction of the δ-ferrite phase generated in peritectic solidification is fδ and that the volume fraction of the δ-ferrite phase varies by |Δfδ| It can be estimated as ×|Δfδ|.

Here, when the volume fraction of the δ ferrite phase immediately after complete solidification was calculated using the thermodynamic calculation software Thermo-Calc, the results shown in Table 1 were obtained.

From this result, the change ΔfδC in the volume fraction of the δ ferrite phase due to the change _ΔC in the C concentration can be estimated by the following equation (28).
Δfδ _C =−12.7×ΔC (28) formula

Using the influence degree ΔCE obtained by converting the influence degree of the Si concentration change ΔC_Si and the Mn concentration change ΔC_Mn into the C concentration, the above equation (28) becomes the following equation (29).
|Δfδ|=−12.7×ΔCE (ΔC_Si, ΔC_Mn) Equation (29)

From the above, in order to reduce the cracking of steel slabs, the following equation (30) should be satisfied from the above equations (25), (29), and εcr = 0.32 × 10 ^-2 .
0.017×12.7×ΔCE (ΔC_Si, ΔC_Mn)<0.32×10 ⁻² (30) formula

The following equation (31) is obtained from the above equation (30).
ΔCE (ΔC_Si, ΔC_Mn) < 1.5 × 10 ^-2 (31) formula

Therefore, by setting the casting conditions so that ΔCE is less than 0.015 according to the above equation (31), cracks in the steel slab can be reduced.
So far, the grounds for setting the threshold value of the degree of influence ΔCE to 0.015 have been explained.

Using the threshold value of 0.015 for ΔCE, it is preferable that the flow velocity U2 of the discharge flow when colliding with the inner surface of the mold 110 is set so as to satisfy the following equation (32).
U2<0.015×7500×V/{(|0.1×(1-k_Si)×%Si|+|0.02×(1-k_Mn)×%Mn|)-0.015}... (32) formula

<Casting condition calculator 51>
As described above, the casting condition calculation unit 51 sets the collision speed when the discharge flow collides with the long side wall of the mold 110 in the case of manufacturing a high-strength steel slab, to be less than the predetermined reference value. Calculate the casting conditions. Then, as described above, the predetermined reference value is a value determined based on the degree of influence on peritectic solidification of the change in the concentration of the element having a low diffusion rate in the solid phase contained in the molten steel 2 due to the discharge flow. is preferable, and it is more preferable to set the degree of influence ΔCE=0.015 as the reference value. Conventionally, in the production of steel slabs, cracks often occur on the long sides of steel slabs. Therefore, the casting conditions calculated by the casting condition calculation unit 51 are set so that the collision speed when the discharge flow collides with the long side walls of the mold 110 is less than a predetermined reference value.

Further, as described above, when the maximum value Lmax of L satisfies the above equation (16), the electromagnetic braking by the electromagnetic braking device 160 sufficiently decelerates the motor, so macro segregation is less likely to occur. Therefore, it is preferable to operate under conditions that satisfy U0/(σ×Bb ² )≦Lb.

In addition, as described above, the strength of the magnetic field generated by the electromagnetic stirrer 150 changes the velocity of the discharge flow. Further, the speed of the swirl flow of the molten steel 2 also changes depending on the intensity of the magnetic field generated by the electromagnetic stirring device 150, and the behavior of the discharge flow also changes according to the speed of the swirl flow. Therefore, it is preferable that the casting conditions calculated by the casting condition calculator 51 include at least the strength of the magnetic field generated by the electromagnetic stirring device 150 .

Moreover, as described above, the velocity of the discharge flow changes depending on the strength of the magnetic field generated by the electromagnetic brake device 160 . Therefore, it is preferable that the casting conditions calculated by the casting condition calculator 51 include the strength of the magnetic field generated by the electromagnetic brake device.

In addition to the above, the casting conditions calculated by the casting condition calculation unit 51 may include the casting speed, the shape of the submerged nozzle 6, the mold size, and the like. For example, the casting condition calculation unit 51 inputs a casting condition other than the desired casting condition (adjustment condition) to adjust the adjustment condition such that ΔCE calculated by the equation (24) satisfies the equation (31). A mechanism for outputting a range may be used. For example, when the casting speed is the adjustment condition, other casting conditions such as the mold width, the position of the electromagnetic stirring device 150, the position of the electromagnetic braking device 160, and the immersion depth are input, and the casting that ΔCE is less than 0.015 It is sufficient to calculate the speed range and output it. When there are a plurality of adjustment conditions, the casting condition calculation unit 51 graphs the relationship between the adjustment conditions when ΔCE becomes a threshold value that satisfies the expression (31), that is, when ΔCE=0.015. An output mechanism may be used, and in that case, an adjustment condition that satisfies the condition of ΔCE may be determined by visually observing the graph. For example, when the three conditions of the casting speed, the magnetic flux density of the electromagnetic stirrer 150, and the magnetic flux density of the electromagnetic brake device 160 are set as adjustment conditions, other casting conditions are input, and the three adjustment conditions are set on the x, y, and z axes, respectively. , a graph is created and output when ΔCE is 0.015. If there are two adjustment conditions, the graph is two-dimensional. If there are four or more, for example, the process of creating a graph by fixing the fourth and subsequent adjustment conditions to temporary values is performed using multiple temporary values. to create multiple graphs.

<Setting unit 52>
As described above, the setting unit 52 sets, to the continuous casting apparatus 1, setting values that enable casting under the casting conditions calculated by the casting condition calculation unit 51. FIG. The setting unit 52 receives information on casting conditions from the casting condition calculation unit 51 and outputs the information to the continuous casting apparatus 1 . The continuous casting apparatus 1 casts steel slabs based on the received information.

Although one embodiment of the present invention has been described above, the present invention is not limited to such an example. It is obvious that a person skilled in the art can conceive of various modifications or modifications within the scope of the technical idea described in the claims, and these are also within the technical scope of the present invention. be understood to belong to

For example, Patent Literature 2 describes a method for suppressing bubble defects on the surface and inside of a cast slab when an electromagnetic stirrer and an electromagnetic brake are used together. According to this, it is stated that if the electromagnetic brake is too strong, the flow due to the electromagnetic stirring is obstructed, so that surface bubble defects are likely to occur. Therefore, if it is desired to suppress cracking of steel slabs and further suppress cellular defects, the method described above is used to suppress macrosegregation and slab cracking using an electromagnetic brake, and then an upper limit is set for the electromagnetic brake strength. All you have to do is

<<How to set casting conditions>>
In order to set the casting conditions, as described above, the casting condition calculation unit 51 calculates the casting conditions, and the setting unit 52 sets the set values that enable casting under the casting conditions calculated by the casting condition calculation unit 51 to the continuous casting apparatus 1. set for Therefore, the method of setting the casting conditions is as follows. an immersion nozzle for supplying molten steel to the inside of the mold from each of the discharge holes; an electromagnetic stirring device for generating a magnetic field and applying an electromagnetic force to the molten steel inside the mold to stir the molten steel; and an electromagnetic brake device for braking the discharge flow by applying an electromagnetic force to the molten steel constituting the discharge flow, which is the flow of the molten steel discharged from the discharge hole, and continuously casting steel slabs. A method for setting casting conditions for setting casting conditions for an apparatus, wherein, in the case of manufacturing high-strength steel slabs, the collision speed of the discharge flow when it collides with the long side walls of the mold is less than a predetermined reference value. and a setting step of setting a setting value that allows casting under the casting conditions calculated in the casting condition calculating step to the continuous casting apparatus.

<<Method for producing high-strength steel slab>>
Using the continuous casting apparatus 1 and the casting condition setting apparatus 50, high-strength steel slabs can be produced. Specifically, the method for producing a high-strength steel cast slab comprises: a mold having a rectangular cross section formed by a pair of long side walls and a pair of short side walls; and an immersion nozzle that supplies molten steel into the mold from each of the injection holes, and an electromagnetic stirring that generates a magnetic field and applies electromagnetic force to the molten steel inside the mold to stir the molten steel. and an electromagnetic brake device that generates a magnetic field and applies an electromagnetic force to molten steel forming a discharge flow, which is the flow of molten steel discharged from a discharge hole, to brake the discharge flow. A method for producing high-strength steel slabs by continuously casting high-strength steel slabs using a The electromagnetic force acting on the molten steel forming the discharge flow by the magnetic field generated by the electromagnetic brake device brakes the discharge flow, and the discharge flow bends due to the swirl flow and collides with the long side wall of the mold. collision speed below a predetermined reference value. Needless to say, the configuration of each device used in the method for producing a high-strength steel cast slab is not limited to the configuration provided in the continuous casting apparatus 1 .

(Example 1)
For a steel grade represented by 0.13% C-1.0% Si-0.1% Mn, a thermal fluid simulation was performed in the mold considering solidification and component segregation, and the concentration segregation of Si and Mn was calculated. . The in-mold thermal fluid simulation was performed using the numerical simulation model described in Non-Patent Document 4. Furthermore, from the maximum value of the concentration segregation values of Si and Mn obtained by the in-mold thermal fluid simulation, the degree of influence ΔCE′ of the concentration change of Si and Mn on peritectic solidification was calculated by the following formula.
ΔCE′=|0.1×Δ%Si|+|0.02×Δ%Mn|

Table 2 shows the values of ΔCE' obtained from the results of the numerical simulation of the in-mold thermal fluid for the steel grades with a composition of 0.13%C-1.0%Si-0.1%Mn. Table 2 shows the degree of influence ΔCE of the Si concentration change and the Mn concentration change on peritectic solidification calculated based on the above equation (24). Further, FIG. 10 shows a graph of the relationship between the EMBr intensity and the segregation ratio Δ%Si/%Si when the EMS intensity is changed. FIG. 11 shows a graph of the relationship between the EMBr strength and the segregation ratio Δ%Si/%Si when the casting speed Vc is changed. The segregation ratio Δ%Si/%Si is calculated by the following formula.
Δ%Si/%Si=(C0_Si−Cm_Si)/Cm_Si=ΔC_Si/Cm_Si
FIG. 12 shows a graph of the relationship between the EMBr intensity and ΔCE′ when the EMS intensity is changed. FIG. 13 shows a graph of the relationship between EMBr strength and ΔCE′ when casting speed Vc is changed. 10 and 12, the width w of the mold is 1.6 m and the casting speed is 1.6 m/min. is obtained from the results of in-mold thermal fluid simulation. 11 and 13 are obtained from the results of thermal fluid simulation in the mold, where the width w of the mold is 1.6 m and the magnitude of the alternating current applied to the electromagnetic stirrer is 300A.

As shown in FIGS. 10 and 11, when the electromagnetic brake is not applied, the value of the segregation ratio Δ%Si/%Si is large. It was found that the value of the ratio Δ%Si/%Si becomes smaller. Moreover, as shown in FIGS. 12 and 13, when the electromagnetic brake is not applied, the segregation of Si is large, and the Si content is 1.0% by mass, which is large compared to ordinary steel, so the value of ΔCE' is large. became. In order to suppress ΔCE', it is effective to apply an electromagnetic brake. It was found that ΔCE' can be reduced to less than 0.015 even when . It was found that when the alternating current applied to the electromagnetic stirrer is 400 A and the average magnetic flux density of the magnetic field generated by the electromagnetic braking device is 0.2 T or more, ΔCE' can be reduced to less than 0.015. ΔCE has a high correlation with ΔCE′, and by setting the set value using ΔCE as an index, segregation of the constituent elements of the molten steel that occurs near the corners of the long side walls inside the mold is prevented, and the steel casting It was found that cracking of the pieces can be suppressed.
In the numerical calculation by the in-mold thermo-fluid numerical simulation, even if the average magnetic flux density of the magnetic field generated by the electromagnetic brake device is set to 0.2 T or more, a slight unsteady It was found that the segregation ratio is sufficiently small and converges to a substantially constant value, although the segregation ratio does not become 0 in a strict sense because of the strong flow.

(Example 2)
Table 3 shows the composition 0.13% C-0.1% Si-0.1% Mn (A in Table 3), 0.13% C-1.0% Si-0.1% Mn (Table 3 In the middle, B), and the steel represented by 0.13% C-0.1% Si-6.0% Mn (C in Table 3), Si and Mn calculated based on the above formula (24) shows the degree of influence ΔCE on peritectic solidification caused by changes in the concentration of . Fig. 14 shows the EMS intensity (the intensity of the magnetic field generated by the electromagnetic stirrer) and the EMBr electromagnetic when ΔCE = 0.015 when the steel type is 0.13% C-0.1% Si-0.1% Mn steel. Fig. 15 shows the relationship between the brake strength (the strength of the magnetic field generated by the electromagnetic brake device) and ΔCE = 0.1% when the steel type is 0.13%C-1.0%Si-0.1%Mn steel. The relationship between the EMS strength of 015 and the EMBr electromagnetic brake strength is shown, and FIG. and EMBr electromagnetic braking strength. However, when the width w of the mold is 1.6 m and the casting speed is 1.6 m/min. and

As shown in FIG. 14, in the case of 0.13% C-0.1% Si-0.1% Mn steel, which does not contain large amounts of Si and Mn like ordinary steel, the electromagnetic brake was not applied. Also, ΔCE was less than 0.015 because the absolute change in component concentration due to segregation was small. However, regarding 0.13% C-1.0% Si-0.1% Mn steel and 0.13% C-0.1% Si-6.0% Mn steel containing a large amount of Si and Mn, If the electromagnetic brake is not applied, ΔCE becomes large, which may cause quality problems. The curves shown in FIGS. 15 and 16 and the range where the EMBr intensity is greater than the curves are the ranges where ΔCE is 0.015 or more. It was found that ΔCE can be controlled by adjusting the EMS strength and the EMBr strength, and cracking of the steel slab can be suppressed.

1 Continuous Caster 2 Molten Steel 3, 14 Slab 4 Ladle 5 Tundish 6 Immersion Nozzle 7 Secondary Cooling Device 8 Slab Cutting Machine 11 Support Roll 12 Pinch Roll 13 Segment Roll 15 Table Roll 16 Secondary Cooling Zone 50 Casting Conditions Setting device 51 Casting condition calculation unit 52 Setting unit 61 Discharge hole 110 Mold 111 Long-side mold plate 112 Short-side mold plates 121, 122 Backup plate 123 Backup plate (width direction backup plate)
130, 140 Water box 150 Electromagnetic stirring device 151 Case 152 Electromagnetic stirring core 153 Coil 154 Teeth part 160 Electromagnetic brake device 161 Case 162 Electromagnetic brake core 163 Coil 170 Electromagnetic force generator

Claims (16)

a mold having a rectangular cross section formed by a pair of long side walls and a pair of short side walls; an immersion nozzle for supplying molten steel to the inside of the mold from the an electromagnetic brake device for braking the discharge flow by applying an electromagnetic force to the molten steel constituting the discharge flow, which is the main flow of the molten steel discharged from the discharge hole, to continuously cast steel slabs. A casting condition setting device for setting casting conditions for a continuous casting apparatus,
The casting conditions for making the collision speed when the discharge flow collides with the long side wall of the mold under the action of the electromagnetic force by the electromagnetic stirrer and the electromagnetic brake device less than a predetermined reference value. A casting condition calculation unit that calculates
A setting device for setting casting conditions, comprising: a setting unit for setting a setting value that allows casting under the casting conditions calculated by the casting condition calculation unit to the continuous casting apparatus. In the case of manufacturing a high-strength steel cast slab, the predetermined reference value is a value determined based on the degree of influence of changes in the concentrations of Si and Mn contained in the molten steel due to the discharge flow on peritectic solidification. The apparatus for setting casting conditions according to claim 1. 3. The apparatus for setting casting conditions according to claim 1, wherein the casting conditions include at least the strength of the magnetic field generated by the electromagnetic stirrer. The casting condition setting device according to any one of claims 1 to 3, wherein the casting conditions include the strength of the magnetic field generated by the electromagnetic brake device. The casting condition setting device according to any one of claims 1 to 4, wherein the setting unit sets the set value so that the collision speed satisfies the following formula (1).
U2<0.015×7500×V/{(|0.1×(1−k_Si)×%Si|+|0.02×(1−k_Mn)×%Mn|)−0.015} . (1) where
V=6.45×10 ⁻⁵ ×K×(Vc/Hb) ^0.5
however,
% X: mass concentration of component X (% by mass)
k_X: Equilibrium partition coefficient of component X (-)
U2: Collision speed (m/s)
Vc: Casting speed (m/s)
Hb: Distance from surface of molten steel to upper end of core of electromagnetic brake (m)
K: coagulation coefficient (mm/min ^0.5 ) The casting condition setting device according to any one of claims 1 to 5, wherein the setting unit sets the setting value so that ΔCE represented by the following equation (2) is less than 0.015.
ΔCE=(|0.1×(1−k_Si)×%Si|+|0.02×(1−k_Mn)×%Mn|)/(7500×V/U2+1) Expression (2) where ,
V=6.45×10 ⁻⁵ ×K×(Vc/Hb) ^0.5
U2=U0-(σ×Lb×Bb ² ) (if U0>σ×Lb×Bb ² )
U2=0 (however, when U0≦σ×Lb×Bb ² )
U0=( ^Vp2 +4*Cs*Ls) ^0.5
Ls=(Hb−D)/sin θ
Lb=0.5×(W−D1)/cos θ−Ls
Cs=0.5×σ×f×Δx×Bs ²
Vp = Vc x (Ss/Sp)
however,
% X: mass concentration of component X (% by mass)
k_X: Equilibrium partition coefficient of component X (-)
σ: electrical conductivity per unit mass of the molten steel (Sm ² /kg)
U2: Collision speed (m/s)
Bb: Average magnetic flux density (T) of the magnetic field generated by the electromagnetic brake device
Bs: average magnetic flux density (T) of the magnetic field generated by the electromagnetic stirrer
Hb: Distance from surface of molten steel to upper end of core of electromagnetic brake (m)
Vc: Casting speed (m/s)
Vp: Flow velocity (m/s) of the discharge flow at the discharge hole of the submerged nozzle
Sp: Cross-sectional area of the discharge hole (m ² )
Ss: cross-sectional area of the internal space of the mold in the horizontal cross section (m ² )
W: Distance between the long side walls in the interior space of the mold (m)
Δx: Interpolar distance (m) of alternating current applied to the electromagnetic stirrer
f: frequency of alternating current applied to the electromagnetic stirrer (1/s)
D: Depth position (m) of the discharge hole
D1: outer diameter of the submerged nozzle (m)
θ: downward angle (rad) of the discharge hole
K: coagulation coefficient (mm/min ^0.5 ) 7. The apparatus for setting casting conditions according to claim 6, wherein said U0, said Bb and said Lb satisfy U0≦σ×Lb× ^Bb2 . Any one of claims 1 to 7, wherein the molten steel contains C: 0.1 to 0.5% by mass and at least one of Si: 0.8% by mass or more or Mn: 4.0% by mass or more. 1. A device for setting casting conditions according to claim 1. A continuous casting apparatus for casting steel slabs under the casting conditions set by the casting condition setting device according to any one of claims 1 to 8. a mold having a rectangular cross section formed by a pair of long side walls and a pair of short side walls; an immersion nozzle for supplying molten steel to the inside of the mold from the an electromagnetic brake device for braking the discharge flow by applying an electromagnetic force to the molten steel constituting the discharge flow, which is the main flow of the molten steel discharged from the discharge hole, to continuously cast steel slabs. A casting condition setting method for setting casting conditions for a continuous casting apparatus, comprising:
In the case of manufacturing high-strength steel slabs, the impact speed when the discharge flow collides with the long side walls of the mold under the action of electromagnetic force from the electromagnetic stirrer and the electromagnetic brake device is set to a predetermined speed. a casting condition calculation step of calculating the casting conditions for becoming less than the reference value;
and setting a setting value for the continuous casting apparatus that allows casting under the casting condition calculated in the casting condition calculating step. A continuous casting method for casting a steel slab under the casting conditions set by the method for setting casting conditions according to claim 10. a mold having a rectangular cross section formed by a pair of long side walls and a pair of short side walls; an immersion nozzle for supplying molten steel to the inside of the mold from the and an electromagnetic brake device that brakes the discharge flow by applying an electromagnetic force to the molten steel that constitutes the discharge flow that is the main flow of the molten steel discharged from the discharge hole. A method for producing a high-strength steel slab for casting a strength steel slab, comprising:
Electromagnetic force is applied to the molten steel in the mold by the magnetic field generated by the electromagnetic stirrer to generate a swirl flow in which the molten steel swirls in a horizontal direction,
electromagnetic force acting on the molten steel forming the discharge flow by the magnetic field generated by the electromagnetic braking device brakes the discharge flow;
A method for producing a high-strength steel cast slab, characterized in that a collision speed of the discharge flow curved by the swirl flow and colliding with the long side walls of the mold is set to less than a predetermined reference value. 13. The method for producing a high-strength steel cast slab according to claim 12, wherein the collision speed satisfies the following formula (1).
U2<0.015×7500×V/{(|0.1×(1−k_Si)×%Si|+|0.02×(1−k_Mn)×%Mn|)−0.015} . (1) where
V=6.45×10 ⁻⁵ ×K×(Vc/Hb) ^0.5
however,
% X: mass concentration of component X (% by mass)
k_X: Equilibrium partition coefficient of component X (-)
U2: Collision speed (m/s)
Vc: Casting speed (m/s)
Hb: Distance from surface of molten steel to upper end of core of electromagnetic brake (m)
K: coagulation coefficient (mm/min ^0.5 ) 14. The high-strength steel casting according to claim 12 or 13, wherein the reference value is ΔCE represented by the following formula (2), and the setting value of the continuous casting apparatus is determined so that the ΔCE is less than 0.015. How to make pieces.
ΔCE=(|0.1×(1−k_Si)×%Si|+|0.02×(1−k_Mn)×%Mn|)/(7500×V/U2+1) Expression (2) where ,
V=6.45×10 ⁻⁵ ×K×(Vc/Hb) ^0.5
U2=U0-(σ×Lb×Bb ² ) (if U0>σ×Lb×Bb ² )
U2=0 (however, when U0≦σ×Lb×Bb ² )
U0=( ^Vp2 +4*Cs*Ls) ^0.5
Ls=(Hb−D)/sin θ
Lb=0.5×(W−D1)/cos θ−Ls
Cs=0.5×σ×f×Δx×Bs ²
Vp = Vc x (Ss/Sp)
however,
% X: mass concentration of component X (% by mass)
k_X: Equilibrium partition coefficient of component X (-)
σ: electrical conductivity per unit mass of the molten steel (Sm ² /kg)
U2: Collision speed (m/s)
Bb: Average magnetic flux density (T) of the magnetic field generated by the electromagnetic brake device
Bs: average magnetic flux density (T) of the magnetic field generated by the electromagnetic stirrer
Hb: Distance from surface of molten steel to upper end of core of electromagnetic brake (m)
Vc: Casting speed (m/s)
Vp: Flow velocity (m/s) of the discharge flow at the discharge hole of the submerged nozzle
Sp: Cross-sectional area of the discharge hole (m ² )
Ss: cross-sectional area of the internal space of the mold in the horizontal cross section (m ² )
W: Distance between the long side walls in the interior space of the mold (m)
Δx: Interpolar distance (m) of alternating current applied to the electromagnetic stirrer
f: frequency of alternating current applied to the electromagnetic stirrer (1/s)
D: Depth position (m) of the discharge hole
D1: outer diameter of the submerged nozzle (m)
θ: downward angle (rad) of the discharge hole
K: coagulation coefficient (mm/min ^0.5 ) 15. The method for producing a high-strength steel slab according to claim 14, wherein said U0, said Bb and said Lb satisfy U0≦σ×Lb× ^Bb2 . Any one of claims 12 to 15, wherein the molten steel contains C: 0.1 to 0.5% by mass and at least one of Si: 0.8% by mass or more or Mn: 4.0% by mass or more. The method for producing a high-strength steel slab according to any one of items.

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