WO2013069121A1

WO2013069121A1 - Continuous casting device for steel

Info

Publication number: WO2013069121A1
Application number: PCT/JP2011/075868
Authority: WO
Inventors: 藤　健彦; 中島　潤二; 保雄丸木; 伯公山崎; 敬二恒成; 健司梅津
Original assignee: 新日鐵住金株式会社
Priority date: 2011-11-09
Filing date: 2011-11-09
Publication date: 2013-05-16
Also published as: EP2754513A4; CA2844450C; EP2754513B1; CN103781572B; CN103781572A; EP2754513A1; CA2844450A1; BR112014005417B1; PL2754513T3; BR112014005417A2; ES2695045T3; US20140190655A1; KR20140053279A

Abstract

This continuous casting device for steel is provided with: a mold for molten steel casting, which is provided with a pair of long side walls and a pair of short side walls; a submerged nozzle that discharges molten steel within this mold; and electromagnetic stirring devices, which are disposed along the outside surfaces of each of the long side walls and which stir the upper part of the molten steel that is within the mold. In a plane view of the long side walls, curved parts that are curved convexly toward the electromagnetic stirring devices are formed at least in positions facing the nozzle, and the long side walls have a uniform thickness, inclusive of the curved parts. When the inside surface of a curved part is viewed in a plane view, the shortest horizontal distance between the apex, which is the deepest recessed position, and the outer peripheral surface of the submerged nozzle is 30 - 80 mm in a range from the lower end part of the electromagnetic stirring devices up to a position 50 mm higher than the upper end part of the electromagnetic stirring devices when viewed along the perpendicular direction.

Description

Steel continuous casting equipment

The present invention relates to a steel continuous casting apparatus that supplies molten steel into a mold to produce a slab.

In continuous casting of steel, in order to improve the surface properties of the slab, conventionally, the molten steel in this mold is electromagnetically stirred using an electromagnetic stirring device having an electromagnetic coil installed near the upper part of the mold. Has been done.

In this electromagnetic stirring, for example, an electromagnetic stirring device is arranged along a pair of long side walls forming a mold. And when molten steel is discharged in a casting_mold | template from an immersion nozzle, an electric current is supplied to an electromagnetic stirring apparatus and a thrust is provided with respect to the upper part of the molten steel in a casting_mold | template. With this thrust, the molten steel is stirred in a horizontal plane, and a swirling flow of the molten steel is formed. This swirling flow prevents inclusions, bubbles, etc. near the meniscus in the upper part of the mold from being trapped by the solidified shell formed on the side surface in the mold.

However, since the immersion nozzle is immersed in the mold, the region between the long side wall and the immersion nozzle is narrower than the other regions. For this reason, in the area | region between a long side wall and an immersion nozzle, compared with the area | region other than that, molten steel becomes difficult to flow.
In addition, inclusions and the like are easily deposited around the immersion nozzle in the mold. The deposits thus deposited may reach a thickness of several tens of millimeters. For this reason, the area | region between a long side wall and an immersion nozzle becomes narrower than another site | part. If it does so, the above-mentioned flow path of a swirl flow will become partially narrow, and it will become difficult to flow molten steel in the field between a long side wall and an immersion nozzle.

Accordingly, the above-described electromagnetic stirring device is used, and instead of the parallel mold having a flat furnace inner surface,

surfaces

104 and 105 facing the immersion nozzle 103 in the

long side walls

101 and 102 as shown in FIG. However, it has been proposed to use so-called deformed molds that are convexly curved toward the

electromagnetic stirrers

106 and 107, respectively (Patent Document 1). In FIG. 7, the cooling water flow path (not shown) for cooling the

long side walls

101 and 102 is disposed between the

long side walls

101 and 102 and the

electromagnetic stirrers

106 and 107. The stainless

steel back plates

108 and 109 are provided.

According to the deformed mold, the

surfaces

104 and 105 facing the immersion nozzle 103 in the

long side walls

101 and 102 are curved to protrude toward the

electromagnetic stirrers

106 and 107, respectively. The shortest horizontal distance between the

side walls

101 and 102 is longer than that of the conventional parallel mold, and accordingly, the flow paths of the swirl flows 110 and 111 can be secured widely, so that the molten steel flows easily.

Japanese Laid-Open Patent Publication No. 2008-183597

However, in the above-described prior art, the central portions of the

long side walls

101 and 102 made of copper are shaved so that the

surfaces

104 and 105 facing the immersion nozzle 103 in the

long side walls

101 and 102 are curved in a concave shape. Therefore, the thickness of the

long side walls

101 and 102 is extremely thin at the

curved surfaces

104 and 105. Generally, since the electromagnetic field generated by the electromagnetic

stirring devices

106 and 107 is an alternating magnetic field, the magnetic field attenuates in the conductor. Therefore, in these

curved surfaces

104 and 105, the attenuation of the magnetic field is smaller than in the other linear portions, so that the electromagnetic force is increased, and the region between the

curved surfaces

104 and 105 and the immersion nozzle 103 is increased. The flow rate of the stirring flow is faster than other areas. As a result, the flow rates of the

stirring flows

110 and 111 are partially non-uniform, and flow turbulence and stagnation occur in the regions 112 and 113 downstream of the

stirring flows

110 and 111 in the

long side walls

101 and 102. There is a problem that objects, bubbles, and the like are easily captured by the solidified shell. Therefore, the improvement of the quality of steel as expected was not obtained.

Furthermore, as a result of investigations by the present inventors, it was found that the inclusions were solidified shells of the

long side walls

101 and 102 simply by forming the

curved surfaces

104 and 105 to facilitate the flow of the

stirring flows

110 and 111 as described above. It was found that it was not possible to suppress the trapping. That is, if the horizontal distance between the

curved surfaces

104 and 105 and the immersion nozzle 103 is increased, the trapping of bubbles can be suppressed. However, the

curved surfaces

104 and 105 also have a strong electromagnetic force and are curved. Since the flow rate of the stirring flow that flows through the region between the

surfaces

104 and 105 and the immersion nozzle 103 is faster than the flow rate of the stirring flow that flows through the other regions, the region 112 and 113 downstream of the

stirring flow

110 and 111 It has been found that the problem of turbulence and stagnation in the flow and the inclusion being easily trapped by the solidified shell cannot be solved.

The present invention has been made in view of the above points, and in a continuous casting apparatus for steel having an electromagnetic stirring device, the flow rate of the molten steel at the upper part in the mold is made uniform even in a deformed mold. It aims at improving the quality of the cast slab cast by making the horizontal distance between the concave curved surface inside and the immersion nozzle appropriate.

In order to achieve the above object, the present invention employs the following means.
(1) That is, a continuous casting apparatus for steel according to an aspect of the present invention includes a mold for casting molten steel having a pair of long side walls and a pair of short side walls; and an immersion nozzle for discharging the molten steel into the mold And an electromagnetic stirrer disposed along each outer side surface of each long side wall and stirring the upper part of the molten steel in the mold, and facing at least the immersion nozzle of each long side wall Curved portions that are convexly curved toward the electromagnetic stirrer when viewed in a plan view are formed, and the long side walls have a uniform thickness including the curved portions; The bottom end of the electromagnetic stirrer when the shortest horizontal distance between the apex that is the deepest depression when viewed in plan and the outer peripheral surface of the immersion nozzle is viewed along the vertical direction To a position 50 mm higher than the upper end of the electromagnetic stirrer Oite is 30mm or more and 80mm or less.

(2) In the above aspect (1), the electromagnetic brake device further includes an electromagnetic brake device disposed below each of the electromagnetic stirring devices; when the electromagnetic brake device is viewed in a plan view, a mold along each of the long side walls A DC magnetic field having a uniform magnetic flux density distribution in the width direction is applied in the mold thickness direction along each short side wall;
Moreover, in the aspect of said (1), when the said shortest horizontal distance is seen along a perpendicular direction, in the range from the lower end part of the said electromagnetic stirring apparatus to a position 50 mm higher than the upper end part of the said electromagnetic stirring apparatus More preferably, it is 50 mm or more and 75 mm or less.

According to the aspect as described in said (1), each long side wall has a curved part which curved at the position which opposes the said immersion nozzle at least toward the said electromagnetic stirring apparatus side, and each long side Since the wall is configured to have a uniform thickness including the curved portion, the electromagnetic force generated by the electromagnetic stirring device is uniform in both the curved portion and the other portions. The flow rate of the stirring flow can be made uniform. That is, when the long side walls are viewed in plan, the intensity distribution of the electromagnetic force is the same in the curved portion and the portions other than the curved portion. To prevent the electromagnetic force from increasing.
Therefore, it is possible to suppress the occurrence of the turbulent flow and the stagnation region as in the conventional case, and it is possible to suppress the bubbles and the like from being easily trapped by the solidified shell.

Further, the shortest horizontal distance between the top of the curved portion and the immersion nozzle is the upper end of the electromagnetic stirring device from the position of the lower end of the electromagnetic stirring device when viewed in the height direction of the continuous casting device. Since it was set to 30 mm or more and 80 mm or less in a range up to a position 50 mm higher than that, a smooth and uniform flow of molten steel can be ensured even in the region between the top of the curved portion and the immersion nozzle.

That is, according to the knowledge newly obtained by the present inventors, when the shortest horizontal distance between the top of the curved portion and the immersion nozzle is less than 30 mm, it becomes difficult for molten steel to flow in the curved region, and bubbles or the like in the molten steel become solidified shells. It becomes easy to be captured. On the other hand, when the shortest horizontal distance is more than 80 mm, it is difficult to ensure a uniform flow of the molten steel in the curved region, and in the region where the molten steel has a low flow rate, inclusions in the molten steel are easily captured by the solidified shell.

In the present invention, since the shortest horizontal distance between the top of the curved portion and the immersion nozzle is set to 30 mm or more and 80 mm or less based on such knowledge, the curved region between the top of the curved portion and the immersion nozzle is set. Therefore, it is possible to secure a smooth and uniform flow of the stirring flow of the molten steel, and to prevent the bubbles in the molten steel from being trapped by the solidified shell.

Further, the range in the height direction in which the shortest horizontal distance between the top of the curved portion and the immersion nozzle is set to 30 mm to 80 mm is 50 mm from the lower end portion of the electromagnetic stirring device to the upper end portion of the electromagnetic stirring device. The range is up to a high position. This is because the portion where the molten steel is directly stirred by the electromagnetic force generated by the electromagnetic stirring device corresponds to the upper end portion from the lower end portion of the electromagnetic stirring device, but in the actual operation, the upper end of the electromagnetic stirring device. This is because the meniscus surface may be positioned higher than the portion. In general, when the meniscus surface is located at a position higher than the upper end portion of the electromagnetic stirring device, the height is approximately 50 mm higher than the upper end portion of the electromagnetic stirring device. Therefore, the range in the height direction in which the shortest horizontal distance between the top of the curved portion and the immersion nozzle is set to 30 mm or more and 80 mm or less is 50 mm from the lower end portion of the electromagnetic stirring device to the upper end portion of the electromagnetic stirring device. It is going to the high position.

Note that the uniform thickness of the long side wall means that the change in the degree of penetration of the electromagnetic field into the molten steel due to the variation in thickness, excluding the parts where bolt holes and cooling water grooves are formed, is an allowable error. The thickness is less than 10%. To explain this, when a magnetic field having a predetermined magnetic flux density is applied from the outside of the long side wall toward the inside of the mold, the magnetic field strength induced inside the mold is lost depending on the thickness of the long side wall. Produce. That is, when the thickness of the long side wall changes, the penetration depth of the magnetic field into the mold changes. When the long side wall is thick, the magnetic field is less likely to penetrate. Therefore, the magnetic field strength in the mold fluctuates with the magnitude of the loss, but the fluctuation of the long side wall is such that this fluctuation is less than 10% when viewed in the horizontal direction along the wall surface of the long side wall. The thickness is uniform.
Moreover, the range of the height direction of the uniform thickness which a long side wall has is from the lower end part of an electromagnetic stirring apparatus to the position 50 mm higher than the upper end part of an electromagnetic stirring apparatus from the effect of an electromagnetic stirring apparatus. Any range is acceptable.
In addition, a supplementary explanation will be given for the “uniform thickness of the long side wall”. When the long side wall arranged along the vertical direction is viewed in plan, the relative relationship between the thickness of the curved portion and the thickness of the adjacent portion other than the curved portion is particularly important. That is, in the above (1), it means “each long side wall has a uniform thickness including each curved portion”, but the thickness of the curved portion is t1, and the portion other than the curved portion. T1 is within ± 10% of t2 (0.9 × t2 ≦ t1 ≦ 1.1 × t2). It is most preferable that t1 = t2.

Further, as described in (2) above, in this steel continuous casting apparatus, a so-called electromagnetic brake device may be used in combination with an electromagnetic stirring device. That is, a DC magnetic field that is disposed below the electromagnetic stirrer and has a uniform magnetic flux density distribution in the mold width direction along the long side wall of the mold is applied in the mold thickness direction along the short side wall of the mold. You may further provide the electromagnetic brake device to provide.
In this case, the bubbles and inclusions in the molten steel discharged from the immersion nozzle are promoted to float, and the bubbles and inclusions float in the molten steel, which remains in the cast slab and causes quality deterioration. You can suppress things. Therefore, the quality of the slab can be further improved.
In addition, to explain the “uniform magnetic flux density” in (2) above, when the magnetic flux density distribution in the mold width direction along the long side wall is viewed in plan view, the electromagnetic brake device It means that the variation in magnetic flux density within the length dimension of the coil portion is within ± 30% of the average.

As described above, according to the present invention, bubbles and the like contained in a cast slab can be reduced, and the quality can be improved.

It is a plane schematic diagram which shows schematic structure of the casting_mold | template vicinity part of the continuous casting apparatus concerning one embodiment of this invention. FIG. 2 is a longitudinal sectional view when the continuous casting apparatus is viewed in the AA section of FIG. 1. FIG. 2 is a longitudinal sectional view of the continuous casting apparatus when viewed in the section BB of FIG. It is a perspective view of the long side wall of the continuous casting apparatus. FIG. 4 is a view corresponding to FIG. 3, which is a longitudinal sectional view for showing a size around a mold of the continuous casting apparatus. It is a figure which shows the modification of the same continuous casting apparatus, Comprising: It is a longitudinal cross-sectional view corresponded in FIG. 2 in the case of having a curved part of another shape. It is a plane schematic diagram for showing the schematic structure of the mold vicinity part of the conventional continuous casting apparatus.

Hereinafter, embodiments of the present invention will be described. FIG. 1 is an explanatory view schematically showing a configuration in the vicinity of a mold of a continuous casting apparatus 1 for steel according to the present embodiment, and FIG. 2 schematically shows a front cross section. It is explanatory drawing and FIG. 3 is explanatory drawing which showed the cross section of the side surface similarly.

As shown in FIG. 1, the continuous casting apparatus 1 has a substantially rectangular mold 2 in a plan view, for example. The mold 2 has a pair of

long side walls

3a and 3b and a pair of

short side walls

4a and 4b. The

long side walls

3a and 3b and the

short side walls

4a and 4b are all made of a copper plate, and on the outside thereof, a non-magnetic austenitic stainless steel that reinforces the

long side walls

3a and 3b and the short side walls 4a and 4b. Made back

plates

5a, 5b, 6a, 6b are arranged. That is, the back plate 5a is arranged outside the long side wall 3a, the back plate 5b is arranged outside the long side wall 3b, the back plate 6a is arranged outside the short side wall 4a, and the short side wall A back plate 6b is disposed outside 4b.

Electromagnetic stirrers

7a and 7b each having an electromagnetic coil are disposed outside the

back plates

5a and 5b. And

electromagnetic brake device

8a, 8b is arrange | positioned directly under

electromagnetic stirring apparatus

7a, 7b. That is, the electromagnetic stirring device 7a and the electromagnetic brake device 8a are disposed outside the back plate 5a, and the electromagnetic brake device 8a is disposed directly below the electromagnetic stirring device 7a. Further, an electromagnetic stirring device 7b and an electromagnetic brake device 8b are disposed outside the back plate 5b, and the electromagnetic brake device 8b is disposed directly below the electromagnetic stirring device 7b.

In the present embodiment, the length (casting thickness) when the

short side walls

4a and 4b are viewed in plan is, for example, about 50 mm to 300 mm. This length is determined by the required slab width. For thin slabs, it is about 50 mm to 80 mm. For medium thickness slabs, it is about 80 mm to 150 mm. If there is, it is about 150 mm to 300 mm. The horizontal direction along the

long side walls

3a and 3b (X direction in FIGS. 1 to 3) is referred to as the mold width direction, and the horizontal direction along the

short side walls

4a and 4b (in FIGS. 1 and 3). (Y direction) is called mold thickness direction.

Curved portions

11a and 11b that are convexly curved toward the

electromagnetic stirrers

7a and 7b are formed at the center of each inner surface when the

long side walls

3a and 3b are viewed in plan. Each bending

part

11a, 11b is formed in the position which opposes the immersion nozzle 21 provided in the casting_mold | template 2 mentioned later. When the

long side walls

3a and 3b are viewed in plan, the thickness distribution along the extending direction of the

long side walls

3a and 3b does not change between the

curved portions

11a and 11b and the linear portions adjacent to both sides, and the thickness distribution along the horizontal direction. And has a uniform thickness. Specifically, the

curved portions

11a and 11b are formed on the

long side walls

3a and 3b, for example, by press molding or the like.
More specifically, the curved portion 11 a includes an inner side surface 11 a 1 that is curved so that an inner wall surface of the long side wall 3 a is separated from the immersion nozzle 21, and an outer wall surface of the long side wall 3 a is separated from the immersion nozzle 21. And an outer surface 11a2 that is curved. Similarly, the curved portion 11 b is curved so that the inner wall surface 11 b 1 curved so that the inner wall surface of the long side wall 3 b is separated from the immersion nozzle 21 and the outer wall surface of the long side wall 3 b are separated from the immersion nozzle 21. The outer surface 11b2 is formed.

Since the

long side walls

3a and 3b have a uniform thickness at all positions including the

curved portions

11a and 11b, the outer side surfaces of the

long side walls

3a and 3b have the above-mentioned outer sides forming the

curved portions

11a and 11b. The side surfaces 11a2 and 11b2 are convexly curved toward the

electromagnetic stirring devices

7a and 7b.
In addition, to further explain the uniform thickness of the

long side walls

3a, 3b, when the

long side walls

3a, 3b are viewed in plan, the thickness of the

curved portions

11a, 11b is t1, and the

curved portions

11a, 11b, This means that t1 is within ± 10% of t2 (0.9 × t2 ≦ t1 ≦ 1.1 × t2), where t2 is the thickness of both adjacent portions other than 11b. It is most preferable that t1 = t2.
The central inner side surfaces of the

back plates

5a and 5b have

electromagnetic stirring devices

7a and 7b so as to match the curved shapes formed by the outer side surfaces 11a2 and 11b2 of the

curved portions

11a and 11b of the

long side walls

3a and 3b. It has a portion that is curved convexly toward the side. However, the outer surfaces of the

back plates

5a and 5b, that is, the surfaces facing the

electromagnetic stirrers

7a and 7b are formed flat (planar).

Normally, this type of back plate has a cooling water channel for cooling the long side wall made of copper formed therein, but in order to form this channel in the

back plates

5a and 5b, for example, By forming a groove-like channel on the surface (inner side surface) of the

back plate

5a, 5b on the side in contact with the

long side walls

3a, 3b, it is possible to easily form the cooling water channel. That is, the

back plates

5a and 5b having the groove-shaped flow paths formed on the inner side surfaces are assembled so that the inner side surfaces are in close contact with the outer side surfaces of the

long side walls

3a and 3b. The flow path can be easily formed.

The

curved portions

11a and 11b are formed to face the immersion nozzle 21 downward from the upper end positions of the

long side walls

3a and 3b, for example, as shown in FIGS. The lower end positions of the

curved portions

11 a and 11 b may be the same height as the lower end position of the immersion nozzle 21, or may be formed below the lower end position of the immersion nozzle 21. As shown in FIG. 1,

curved regions

9a and 9b are formed in spaces (gap) between the

curved portions

11a and 11b and the immersion nozzle 21, respectively.

The

curved portions

11a and 11b have shapes in which the curved portions gradually disappear as they go to the lower ends thereof (that is, shapes in which the recessed portions forming the

curved portions

11a and 11b gradually become shallower and disappear). There is no. In the present embodiment, as shown in FIG. 4, for example, on the inner surface of the long side wall 3a, the boundary line between the curved portion 11a and the other flat portion is the long side wall at the lower end portion of the curved portion 11a. 3a is a straight line parallel to the length direction of 3a (horizontal straight line SL along the X direction in FIG. 4), and is a straight line parallel to the height direction of the long side wall 3a at both side edges of the curved portion 11a. (A straight line VL in the extending direction along the Z direction in FIG. 4).

As shown in FIG. 5, when the

curved portions

11 a and 11 b are viewed in a cross section along the plate thickness direction, between the curved top portions (the deepest recessed portions) and the peripheral surface of the immersion nozzle 21. Since the shortest horizontal distance L has a tapered shape in which the depth of the concave portion gradually decreases toward the lower ends of the

curved portions

11a and 11b and disappears, the length varies depending on the height direction. In the present embodiment, the shortest horizontal distance L is 30 mm to 80 mm in the range from the position of each lower end of the

electromagnetic stirring devices

7a and 7b to a position 50 mm higher than the upper end of the

electromagnetic stirring devices

7a and 7b. It is set to be. The shortest horizontal distance L is preferably 30 mm to 80 mm as defined herein, but more preferably 50 mm or more and 75 mm or less.

That is, this will be described with reference to FIG. 5. The shortest horizontal distance L between the curved top portions of the

curved portions

11 a and 11 b and the peripheral surface of the immersion nozzle 21 is determined from the position of the lower end portions of the

electromagnetic stirring devices

7 a and 7 b. In the range H up to a position 50 mm higher than the upper end portions of the

electromagnetic stirring devices

7a and 7b, it is set to be 30 mm to 80 mm. The length of h in FIG. 5 is 50 mm.

The depth D of the depressions forming the

curved portions

11a and 11b in order to ensure 30 mm to 80 mm as the shortest horizontal distance L between the curved top portions of the

curved portions

11a and 11b and the peripheral surface of the immersion nozzle 21 is the long side Although depending on the thickness of the

walls

3a and 3b, the

electromagnetic stirrers

7a and 7b are considered to be weak when the

electromagnetic stirrers

7a and 7b are moved away from the molten steel in consideration of the strength of the

back plates

5a and 5b. The depth D of the dent can be appropriately set in consideration of the point of suppressing the thickness of the dent. As an upper limit of the depth D of a hollow, 50 mm or less, Preferably 40 mm or less can be illustrated. On the other hand, the lower limit of the depth D of the recess is 5 mm or more, preferably 10 mm or more. That is, the depth D is preferably 5 mm or more and 50 mm or less, and more preferably 10 mm or more and 40 mm or less.

As shown in FIG. 3, the lower part of the immersion nozzle 21 is immersed in the molten steel M in the mold 2 at the time of casting. In FIG. 3, hatching of the molten steel M is omitted in order to clearly show the structure in the continuous casting apparatus 1. Near the lower end of the side surface of the immersion nozzle 21, two discharge holes 22 for discharging molten steel into the mold 2 obliquely downward are formed. These discharge holes 22 are formed at positions facing the

short side walls

4 a and 4 b of the mold 2. The discharge flow 23 discharged from each discharge hole 22 includes bubbles of Ar gas blown for nozzle cleaning, and other inclusions such as alumina and slag. These bubbles and inclusions float up to the vicinity of the meniscus 24. On the meniscus 24, a molten powder 25 having a molten oxide is supplied by a supply mechanism (not shown).

As shown in FIG. 3, a solidified shell 26 is formed on the inner surface of the mold 2 by cooling and solidifying the molten steel M.

The

electromagnetic stirring devices

7a and 7b each have an electromagnetic coil, receive an AC power supplied from a power source (not shown), generate an electromagnetic force, and apply a thrust to the molten steel M in the upper part of the mold 2. . And the molten steel M which received this thrust generate | occur | produces the stirring flow which swirls around the immersion nozzle 21 horizontally in the casting_mold | template 2, and stirs the molten steel M. FIG. By this stirring flow, inclusions, bubbles, etc. near the meniscus 24 in the upper part of the mold 2 are suppressed from being trapped by the solidified shell 26 formed on the side surface in the mold 2.

The

electromagnetic brake devices

8a and 8b, which are arranged below the

electromagnetic stirring devices

7a and 7b and are constituted by electromagnets or the like, are used for the mold 2 with respect to the discharge flow 23 of the molten steel M immediately after being discharged from the discharge holes 22. A DC magnetic field having a substantially uniform magnetic flux density distribution in the mold width direction (X direction in FIGS. 1 and 2) along the

long side walls

3a and 3b is applied to the

short side walls

4a and 4b of the mold 2. It can be applied in the mold thickness direction (Y direction in FIGS. 1 and 2) along. The DC magnetic field and the discharge flow 23 of the molten steel M discharged from each discharge hole 22 generate an induced current in the mold width direction (X direction in FIGS. 1 and 2), and this induced current and the DC magnetic field As a result, an opposing flow directed in the opposite direction to the discharge flow 23 is formed in the vicinity of the discharge flow 23. By this counterflow, it is possible to prevent bubbles and intervening portions in the discharge flow 23 from entering deeply into the molten steel M, and to promote the rising of these bubbles and intervening portions and be captured by the solidified shell 26. Can be suppressed.
The “uniform magnetic flux density” will be supplementarily explained. When the magnetic flux density distribution in the mold width direction along the

long side walls

3a and 3b is seen after the mold 2 is viewed in plan, the electromagnetic brake device 8a. , 8b, the variation in magnetic flux density within the length of the coil portion is within ± 30% of the average.

The continuous casting apparatus 1 according to the present embodiment is configured as described above. Next, the continuous casting method of the molten steel M using this continuous casting apparatus 1 is demonstrated.

First, molten steel M is discharged from the discharge holes 22 of the immersion nozzle 21 into the mold 2 while Ar gas is blown into the immersion nozzle 21. Molten steel M is discharged obliquely downward, and a discharge flow 23 is formed from each discharge hole 22 toward the

short side walls

4 a and 4 b of the mold 2. These discharge flows 23 contain Ar gas bubbles and other inclusions, which float in the molten steel M in the mold 2 and eventually rise by buoyancy due to the specific gravity difference between them and the molten steel M.

And at the same time as the molten steel M is discharged from the immersion nozzle 21, the

electromagnetic brake devices

8a and 8b may be operated. When these

electromagnetic brake devices

8a and 8b are used, a counter flow opposite to the flow of the discharge flow 23 is formed in the molten steel M. As a result, as described above, bubbles and other inclusions in the discharge flow 23 can be prevented from penetrating deeply into the molten steel M, and diffusion to the periphery of the immersion nozzle 21 can be suppressed. And then rises to the vicinity of the meniscus 24 in the counterflow.

Then, the

electromagnetic stirrers

7a and 7b are also operated simultaneously with the operation of the

electromagnetic brake devices

8a and 8b, so that the stir flow is generated in the molten steel M near the meniscus 24 in the mold 2 by the electromagnetic agitation as described above. Is formed. Then, the Ar gas bubbles, etc., which have risen up to the vicinity of the meniscus 24 in the above-described countercurrent flow, are swirled by this stirring flow, and are not trapped by the solidified shell 26 of the mold 2, for example, melted with molten oxide. It is taken in and removed by the powder 25.

Since the

curved portions

11a and 11b are formed at the upper center positions of the

long side walls

3a and 3b of the mold 2,

curved regions

9a and 9b are formed between the

curved portions

11a and 11b and the immersion nozzle 21, respectively. The At this time, since the

long side walls

3a and 3b have a uniform thickness including the

curved portions

11a and 11b, the electromagnetic force applied to the molten steel M by the

electromagnetic stirring devices

7a and 7b described above. The magnetic flux density is about the same in both (1) molten steel M flowing in the

curved regions

9a and 9b and (2) molten steel M flowing linearly at positions other than the

curved regions

9a and 9b. Accordingly, since a stirring flow having a uniform flow rate can be formed along the flow direction of the molten steel M, the region on the downstream side of the stirring flow in the

long side walls

3a and 3b (the above-described conventional technology described with reference to FIG. 7). It is possible to suppress the occurrence of turbulence and stagnation in the regions 112 and 113). Therefore, it is possible to suppress trapping of bubbles and the like in the solidified shell due to the occurrence of these stagnant areas.

Although the

long side walls

3a and 3b have a uniform thickness at each position including the

curved portions

11a and 11b, the

back plates

5a and 5b are portions corresponding to the

curved portions

11a and 11b. As a result, the magnetic flux density is uneven. However, since the electromagnetic field of electromagnetic stirring is generally an alternating magnetic field, it is attenuated in the conductor, and the attenuation is more severe as the electrical conductivity is higher. Since this type of

back plate

5a, 5b is made of nonmagnetic austenitic stainless steel, its electrical conductivity is much smaller than that of copper

long side walls

3a, 3b. Therefore, even if the thickness of the

back plates

5a and 5b is partially reduced, there is almost no influence, and a uniform magnetic flux density can be obtained even in the molten steel M flowing in the

curved regions

9a and 9b.

When the inventors actually measured the magnetic flux density with a gauss meter and found it, the following was found. That is, when viewed along the height direction of the continuous casting apparatus 1, from the curved top portion of the curved portion 11a having the central position of the electromagnetic stirrer 7a and the recess depth D of 30 mm to the immersion nozzle 21 side. When the magnetic flux density was measured using a gauss meter at a point 10 mm away, the fluctuation was only 10% or less compared to the magnetic flux density of the linear portion other than the curved portion 11a of the long side wall 3a. Was confirmed. That is, when the magnetic flux density at the same height of the continuous casting apparatus 1 is measured at a plurality of locations and compared, the measured value at the point corresponding to the curved portion 11a and the flat portions on both sides of the curved portion 11a. It was confirmed that there was no difference of about 10% with the measured value at.
For reference, when a curved part having a dent depth D of 30 mm is formed by cutting the long side wall by a curved concave surface as in the prior art, and the thickness of the curved part is reduced, It was also confirmed that the magnetic flux density was about 40% higher than the magnetic flux density of the linear portion of the long side wall. That is, like the structure of the prior art shown in FIG. 7, the outer side surface of the long side wall is kept flat, only the inner side surface is formed with a curved concave surface similar to the above embodiment, and the magnetic flux density is measured. Similar evaluations were made. As a result, it was confirmed that the measured value at the point corresponding to the curved portion was about 40% higher than the measured value at the flat portions on both sides of the curved portion. Therefore, it can confirm also from the point which the effect of this embodiment takes.

If it demonstrates using FIG. 5, in this Embodiment, the shortest horizontal distance L between the curved top part of the

curved parts

11a and 11b and the immersion nozzle 21 will be from the lower end part of the

electromagnetic stirring apparatuses

7a and 7b. In a range H up to a position 50 mm higher than the upper end portions of 7 a and 7 b, it is set to be 30 mm to 80 mm. According to this configuration, the flow rate of the stirring flow that flows through the

curved regions

9a and 9b can be made uniform, and a smooth and uniform flow of the molten steel M can be ensured. Can be stirred. Therefore, it is possible to suppress trapping of bubbles and the like by the solidified shell 26 from this point.

Further, in the present embodiment, since the

electromagnetic brake devices

8a and 8b are also used, the floating of inclusions such as bubbles in the molten steel M is promoted, and the diffusion to the surroundings is further suppressed. It is possible to prevent bubbles and the like from being trapped by the solidified shell 26.

In the present embodiment, the shape of the bending

portions

11a and 11b is as shown in FIGS. 2 and 4, and the boundary of the flat portion between the bending portion 11a and the periphery thereof as it goes to the lower end is that of the bending portion 11a. The lower end portion is in a straight line shape (straight line SL along the X direction in 4 of FIGS. 2 and 4) parallel to the length direction of the long side wall 3a, and the long side wall 3a at both side portions of the curved portion 11a. The shape was a straight line parallel to the height direction (straight line VL along the Z direction in FIGS. 2 and 4). However, other shapes may be adopted as the shapes of the

curved portions

11a and 11b. For example, as shown in FIG. 6, the boundary line between the curved portion and the other flat portion becomes the lowermost end as it goes to the lower end. It may be a so-called inverted bell-shaped curved portion 11c that converges and disappears at one point. That is, as shown in FIG. 6, a curved portion 11c having a semi-elliptical boundary line that tapers downward when the long side wall 3a is viewed from the opposite side may be employed.

Hereinafter, the effect of removing Ar gas bubbles and inclusions contained in the molten steel when the continuous casting apparatus for steel according to the embodiment of the present invention is used will be described. In carrying out this example, the continuous casting apparatus 1 previously shown in FIGS. 1 to 3 was used as a continuous casting apparatus for steel.

At the formation position of the meniscus 24 in the mold 2 having a width of 1200 mm, a height of 900 mm, and a thickness of 250 mm, the upper end positions of the

electromagnetic stirring devices

7a and 7b having a height of 200 mm and a thrust of 100 mm Fe are the same height as the meniscus position. The

electromagnetic brake devices

8a and 8b arranged so as to exhibit the maximum magnetic flux density at a depth of 500 mm downward from the meniscus 24 were used. Further, casting was performed by inserting the immersion nozzle 21 having a maximum outer diameter of 190 mm and an inner diameter of 100 mm along the vertical direction from the meniscus 24 to the molten steel immersion portion which is located at a depth of 400 mm downward.

The continuous casting machine 1 of this example has a vertical portion with a bending radius of 7.5 m and 2.5 m. Using this continuous casting machine 1, low-carbon aluminum killed steel was cast at a casting speed of 2 m / min. The discharge holes 22 of the immersion nozzle 21 are two holes with a hole diameter of 70 mm, facing the inner surface of the

short side walls

4a and 4b of the space in the mold 2 and having a discharge angle θ (see FIG. 2) of 30 degrees downward. A nozzle was used as the immersion nozzle 21.

The

long side walls

3a and 3b have a constant thickness of 30 mm, and a mold in which a normal long side copper plate is parallel and a central portion of the long side copper plate are press-molded, and the depth D of the meniscus 24 is set to 0, 5, 10 , 20, 30, 40, 50, and 55 mm, and the

back plates

5a and 5b were cut. That is, when manufacturing the

long side walls

3a and 3b, a rectangular copper plate having a uniform thickness of 30 mm is prepared, and press molding is performed on the central portion of the upper side of the copper plate. Seven types of

long side walls

3a and 3b having a depth D of 0, 5, 10, 20, 30, 40, 50, and 55 mm at the vertical position were manufactured. In addition, the hollow depth D being 0 mm means a mold having a long side wall without a hollow.
On the other hand, seven types of

back plates

5a, 5b having different shapes (curved depths) of the curved concave portions so as to match the shapes (curved depth) of the

curved portions

11a, 11b of these seven types of

long side walls

3a, 3b. Was made. Although the thickness of each of the

back plates

5a and 5b is 80 mm, the portion where the curved concave portion is formed is thinner than this.
The

curved portions

11a and 11b in the

long side walls

3a and 3b are formed with lengths of 400 mm on both sides from the mold width center in the casting width direction, and as shown in FIG. 2, the curved portions 11a (11b ) And the other flat portion is a straight line parallel to the length direction of the long side wall 3a (X direction in FIG. 2) at the lower end portion of the curved portion 11a (11b), and both sides of the curved portion 11a. The portion has a rectangular shape that is a straight line parallel to the height direction of the long side wall 3a (the Z direction in FIG. 2). The

long side walls

3a and 3b having such

curved portions

11a and 11b were used as a part of the mold.

The bubbles and inclusion defects in the slab were evaluated by the index of the number of bubbles and inclusions having a diameter of 100 μm or more counted by observing the portion from the slab surface layer of the slab to a depth of 50 mm. The index of the number of Ar gas bubbles in Table 1 is that the distance L (see FIG. 5) between the

curved portions

11a and 11b and the immersion nozzle 21 is 25 mm, and the dent depth D is 0 mm, that is, the

curved portions

11a and 11b. The number of Ar gas bubbles in the case where the

long side walls

3a and 3b are not formed is set to 1, and the ratio of the number of Ar gas bubbles in each condition is shown.
Similarly, for the inclusion number index, the distance L between the

curved portions

11a and 11b and the immersion nozzle 21 is 25 mm and the depth D is 0 mm, that is, the

curved portions

11a and 11b are connected to the long side wall 3a. The number of inclusions when not forming in 3b is 1, and the ratio of the number of inclusions in each condition is shown. In addition, the distance L between the curved part and immersion nozzle in Table 1 has shown the dimension in the lower end position of the

electromagnetic stirring apparatuses

7a and 7b. Moreover, the hollow depth D has shown the dimension in the height position with the meniscus 24 as above-mentioned.

In addition, in order to confirm the effect of the example of the present invention, first, the

electromagnetic brake devices

8a and 8b are not operated, and only the

electromagnetic stirring devices

7a and 7b are operated.

According to the results shown in Table 1, when the distance L is 25 mm, even when the depression depth D is 5 mm and the

curved portions

11a and 11b are formed, the depression depth D is not different from the case of 0 mm. Both the Ar gas bubble number index and the inclusion number index remain 1, indicating that the number of Ar gas bubbles and inclusions cannot be reduced.
However, when the distance L is 30 mm, the Ar gas bubble number index is reduced to 0.6 even if the depth D is as shallow as 5 mm.
When the distance L is 80 mm, the Ar gas bubble number index is at a low level of 0.2, and the inclusion number index is also at a low level of 1.3, but when the distance L is 85 mm, the inclusion number index is Was found to increase dramatically to 2.0.

Next, Table 2 shows the results of operating the

electromagnetic brake devices

8a and 8b under the same conditions as in Example 1 and using them together with the

electromagnetic stirring devices

7a and 7b.

According to the results shown in Table 2, the same tendency as when the

electromagnetic brakes

8a and 8b were not operated was observed. That is, when the distance L is 25 mm, both the Ar gas bubble number index and the inclusion number index are 1, even if the

curved portions

11a and 11b are formed with the recess depth D being 5 mm, and the recess depth is 1. Since D is not different from 0 mm, the number of Ar gas bubbles and inclusions cannot be reduced.
On the other hand, when the distance L is 30 mm, the Ar gas bubble number index is halved to 0.5 even if the recess depth D is 5 mm.
When the distance L is 80 mm, the Ar gas bubble number index is 0.1, which is further reduced from 0.2 shown in Table 1. Therefore, when the

electromagnetic brake devices

8a and 8b were used in combination, it was confirmed that there was an effect in removing Ar gas bubbles. However, when the distance L was 85 mm, the effect of removing Ar gas bubbles was still high, but the inclusion number index increased dramatically to 1.8.

The present invention is useful when a molten steel is supplied into a mold to produce a slab.

DESCRIPTION OF SYMBOLS 1 Continuous casting apparatus 2

Mold

3a, 3b

Long side wall

4a, 4b

Short side wall

5a, 5b, 6a,

6b Back plate

7a, 7b

Electromagnetic stirrer

8a, 8b

Electromagnetic brake apparatus

9a, 9b

Curved area

11a, 11b, 11c Curve Part 21 Immersion nozzle 22 Discharge hole 23 Discharge flow 24 Meniscus 25 Molten powder 26 Solidified shell M Molten steel

Claims

A mold for casting molten steel having a pair of long side walls and a pair of short side walls;
An immersion nozzle for discharging molten steel into the mold;
An electromagnetic stirrer disposed along each outer side surface of each long side wall and stirring the upper part of the molten steel in the mold;
With
In each of the long side walls, at least a position facing the immersion nozzle, a curved portion that is convexly curved toward the electromagnetic stirring device when viewed in plan is formed, and each of the long side walls is each of the curved portions. Having a uniform thickness including
The electromagnetic stirrer when the shortest horizontal distance between the top portion which is the deepest recessed portion when viewed from the inside surface of the curved portion and the outer peripheral surface of the immersion nozzle is viewed along the vertical direction. In a range from the lower end of the upper end of the electromagnetic stirrer to a position 50 mm higher than the upper end of the electromagnetic stirrer;
A continuous casting apparatus for steel.
An electromagnetic brake device disposed below each of the electromagnetic stirring devices;
When viewed in plan, the electromagnetic brake device applies a DC magnetic field having a uniform magnetic flux density distribution in the mold width direction along the long side walls in the mold thickness direction along the short side walls. ;
The continuous casting apparatus for steel according to claim 1, wherein: