Patent Grant
10987730
The present invention relates to a continuous casting apparatus and a continuous casting method for a multilayered slab.
Priority is claimed on the basis of Japanese Patent Application No. 2015-213678 filed in Japan on Oct. 30, 2015, the content of which is incorporated herein by reference.
Hitherto, attempts have been made in order to manufacture multilayer-shaped slabs having mutually different compositions in the surface layer and the inner layer. For example, Patent Document 1 discloses a method in which two immersion nozzles having different lengths are inserted into a pool of molten metal in a casting mold so that the depth locations of discharge holes of the immersion nozzles differ from each other, a direct-current magnetic field is applied between different kinds of molten metals so as to prevent the mixing of the molten metals, and a multilayered slab is manufactured.
However, in the method disclosed by Patent Document 1, two kinds of molten steels having different compositions are used, and thus it is necessary to separately produce these two kinds of molten steels at the same time by melting and convey the molten steels to a continuous casting process. In addition, as intermediate retention containers for the respective molten steels, it is necessary to prepare tundishes (that is, two tundishes become necessary in order to separately retain two kinds of molten steels). Furthermore, pouring flow rates significantly differ between molten steel for a surface layer and molten steel for an inner layer, and thus amounts of molten steels necessary every heating significantly differ. For these reasons, it has been difficult to realize the method disclosed by Patent Document 1 in ordinary steel mills.
Therefore, as methods for more conveniently casting slabs having mutually different compositions in the surface layer and the inner layer, mainly, two methods are being studied. As the first method, studies are underway regarding a method of reforming a slab surface layer by continuously supplying a wire or powder for continuous casting to which a predetermined element is added to the upper side of a direct-current magnetic field band using electromagnetic braking that can be obtained by applying a direct-current magnetic field having a uniform magnetic flux density distribution along the thickness direction of a casting mold in the thickness direction of the casting mold.
Examples of documents disclosing a method of adding an element to molten steel in a casting mold using a wire or the like include Patent Document 2. In the method disclosed by Patent Document 2, a direct-current magnetic field that blocks molten steel in a casting mold is formed at a location at least 200 mm below the meniscus of molten steel formed in the casting mold, a predetermined element is added to the molten steel in the upper portion or the molten steel in the lower portion, and the molten steel in the casting mold is stirred.
Examples of a method of continuously supplying powder for continuous casting to which a predetermined element is added or a method of adding an element to molten steel by continuously supplying metal powder or metal grains that do not easily react with powder from the upper side of a powder layer include the method disclosed by Patent Document 3. In the method disclosed by Patent Document 3, powder for continuous casting to which alloying elements are added is continuously supplied, and a stirring flow that dissolves and mixes the alloying elements in a horizontal cross section of upper portion molten steel in a continuous casting mold is formed using an electromagnetic stirring device installed in the upper portion in the casting mold. In addition, in the above-described method, a direct-current magnetic field band is formed on the lower side of the electromagnetic stirring device by applying a direct-current magnetic field in the thickness direction of a slab, and molten steel is supplied from an immersion nozzle to a location below the direct-current magnetic field band and cast. In Patent Document 3, a multilayer-shaped slab in which the concentration of the alloying elements in the slab surface layer area is higher than in the inner layer is manufactured using a method as described above.
However, in the casting mold, a powder layer is present in the upper portion, and the casting mold has a rectangular cross section and is cooled from the periphery. Therefore, it is not possible to sufficiently stir the molten steel in the casting mold, and it is difficult to make the concentration uniform. In addition, the amounts of molten steel supplied to the upper portion and the lower portion of a strand are not controlled independently, and thus there has been a problem in that the mixing of molten steels between the upper and lower pools cannot be avoided, and it is difficult to manufacture slabs having a high degree of separation.
As a method for reforming a slab surface after casting, for example, Patent Document 4 discloses a surface layer-reforming method of a slab in which the surface layer of a slab is melted by at least one of induction heating or plasma heating and an additive element or an alloy thereof is added to the surface layer area of the melted slab. However, in this method, the addition of the alloying element is possible, but the volume of a melting pool is small, and thus it is difficult to make the concentration uniform. Furthermore, in this method, there has been a problem in that it is difficult to melt the entire slab at once, and a plurality of times of melting and reforming are required to reform the entire circumference of the slab surface layer.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. S63-108947
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. H3-243245
[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. H8-290236
[Patent Document 4] Japanese Unexamined Patent Application, First Publication No. 2004-195512
The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a continuous casting apparatus and a continuous casting method for a multilayered slab capable of suppressing the quality degradation of a multilayered slab during the manufacture of the multilayered slab using one ladle and one tundish.
In order to achieve the above-described object, the present invention employs the followings.
(1) A continuous casting apparatus for a multilayered slab according to an aspect of the present invention includes a ladle having a molten steel supply nozzle; a tundish having a first retention portion that receives supply of the molten steel from the ladle through the molten steel supply nozzle and has a first immersion nozzle, and a second retention portion that is adjacent to the first retention portion with a flow path interposed therebetween and has a second immersion nozzle; an addition mechanism that adds a predetermined element to the molten steel in the second retention portion; and a casting mold that receives supply of the molten steel from an inside of the first retention portion through the first immersion nozzle and receives supply of the molten steel from an inside of the second retention portion through the second immersion nozzle, and, in the case of being seen in a planar view, in a path from the molten steel supply nozzle to the second immersion nozzle, the molten steel supply nozzle, the first immersion nozzle, the flow path, and the second immersion nozzle are disposed in this order.
(2) In the aspect according to (1), in the case of being seen in a cross section perpendicular to a communication direction of the flow path, a cross-sectional area of the flow path may be 10% or more and 70% or less of a cross-sectional area of the molten steel present in the first retention portion.
(3) In the aspect according to (1) or (2), the flow path may be formed of a communication pipe that communicates the first and second retention portions, and a pair of solenoid coils facing each other may be disposed so as to surround the communication pipe.
(4) In the aspect according to any one of (1) to (3), a direct-current magnetic field generator that generates a direct-current magnetic field in the casting mold along a thickness direction of the casting mold may be further provided.
(5) In the aspect according to any one of (1) to (4), an electromagnetic stirring device that stirs an upper portion of the molten steel present in the casting mold may be further provided.
(6) A continuous casting method for a multilayered slab according to another aspect of the present invention is a method for manufacturing a multilayered slab using the continuous casting apparatus for a multilayered slab according to any one of (1) to (5), and the method has a first step of supplying the molten steel present in the ladle to the tundish; a second step of adding a predetermined element to the molten steel present in the second retention portion of the tundish; and a third step of supplying the molten steel present in the first retention portion of the tundish and the molten steel present in the second retention portion of the tundish to an inside of the casting mold.
(7) In the aspect according to (6), in the third step, in a case in which the tundish is seen in a planar view, when an area of the molten steel present in the first retention portion is represented by ST1 (m2), an area of the molten steel present in the second retention portion is represented by ST2 (m2), an amount of molten steel supplied from the first retention portion to the casting mold is represented by Q1 (kg/s), and an amount of molten steel supplied from the second retention portion to the casting mold is represented by Q2 (kg/s), the molten steel may be supplied to the casting mold so as to satisfy Expression (a) below,
(Q1/ST1)<(Q2/ST2) Expression (a)
According to the respective aspects of the present invention described above, it is possible to provide a continuous casting apparatus and a continuous casting method for a multilayered slab capable of suppressing the quality degradation of a multilayered slab during the manufacture of the multilayered slab using one ladle and one tundish.
Hereinafter, individual embodiments of the present invention will be described in detail with reference to drawings. Meanwhile, in the present specification and the drawings, constituent elements having substantially the same functional constitution will be give the same reference symbol and will not be duplicately described.
As shown in
The ladle 1 has a long nozzle 1a (molten steel supply nozzle) provided on the bottom surface thereof, retains molten steel that is component-adjusted in a secondary refining step, and supplies the molten steel to the tundish 2. Specifically, the long nozzle 1a of the ladle 1 is inserted into the tundish 2, and the molten steel in the ladle 1 is supplied to the tundish 2 through the long nozzle 1a. Meanwhile, in
The tundish 2 in the continuous casting apparatus 100 has a substantially rectangular shape in a planar view and has a bottom portion 2a, a pair of short-side wall portions 2b and a pair of long-side wall portions 2c provided in the outer circumference of the bottom portion 2a, and a plate-shaped weir 4 provided between inner surfaces of the pair of long-side wall portions 2c. In addition, in the tundish 2, the molten steel supplied from the ladle 1 is retained in a space formed by the bottom portion 2a, the pair of short-side wall portions 2b, and the pair of long-side wall portions 2c. Meanwhile, the tundish 2 is constituted of, for example, a refractory or the like. In addition, in the bottom portion 2a of the tundish 2, a first immersion nozzle 5 (first immersion nozzle) and a second immersion nozzle 6 (second immersion nozzle) which eject the molten steel retained in the inside of the tundish 2 into the inside of the casting mold 7 are provided.
The weir 4 in the tundish 2 has a height that is lower than those of the short-side wall portion 2b and the long-side wall portion 2c and is provided in the upper portion of the pair of long-side wall portions 2c so that a gap is formed between the bottom portion 2a and the weir. That is, the tundish 2 is partitioned into two sections by the weir 4, and a first retention chamber 11 (first retention portion) and a second retention chamber 12 (second retention portion) are formed. In addition, an opening portion 10 (flow path) that communicates the first retention chamber 11 and the second retention chamber 12 is formed between both retention chambers.
The first immersion nozzle 5 is provided in a portion that forms the first retention chamber 11 in the bottom portion 2a of the tundish 2. In addition, the first immersion nozzle 5 ejects molten steel 21 in the inside of the first retention chamber 11 to the inside of the casting mold 7. On the other hand, the second immersion nozzle 6 is provided in a portion that forms the second retention chamber 12 in the bottom portion 2a of the tundish 2. In addition, the second immersion nozzle 6 ejects molten steel 22 in the inside of the second retention chamber 12 to the inside of the casting mold 7.
The first immersion nozzle 5 and the second immersion nozzle 6 have mutually different lengths and are inserted into the inside of the casting mold 7. Specifically, the first immersion nozzle 5 is longer than the second immersion nozzle 6, and an ejection hole of the first immersion nozzle 5 is located below an ejection hole of the second immersion nozzle 6 in the vertical direction.
In addition, the long nozzle 1a of the ladle 1 is inserted into the inside of the first retention chamber 11 of the tundish 2. In addition, in a case in which the tundish 2 is seen in a planar view as shown in
The addition device 50 continuously injects a wire or the like into the molten steel 22 in the inside of the second retention chamber 12 of the tundish 2. Therefore, the molten steel 22 in the inside of the second retention chamber 12 of the tundish 2 becomes the molten steel 21 in the first retention chamber 11 to which a predetermined element is added and becomes molten steel having different components from the molten steel 21 in the inside of the first retention chamber 11. Meanwhile, the addition device 50 is, for example, a wire feeder or the like.
The element that is added to the molten steel is not particularly limited, and examples thereof include Ni, C, Si, Mn, P, S, B, Nb, Ti, Al, Cu, Mo, and the like. In addition, it is also possible to add an element that is contained in steel such as Ca, Mg, or REM which is a strong deoxidation and strong desulfurization element.
The electromagnetic stirring device 9 has an electromagnetic coil and is disposed along the outside surfaces of a pair of long-side walls of the casting mold 7. In addition, the electromagnetic stirring device 9 has a role of stirring the molten steel in the upper portion in the inside of the casting mold 7. In addition, the direct-current magnetic field generator 8 is disposed below the electromagnetic stirring device 9, and the direct-current magnetic field generator 8 applies a direct-current magnetic field in the thickness direction of the casting mold 7.
The control device 32 is connected to a sliding nozzle 33b provided in the first immersion nozzle 5, a sliding nozzle 33c provided in the second immersion nozzle 6, a sliding nozzle 33a provided in the long nozzle 1a of the ladle 1, a molten steel surface level meter 31, and a weighing device 35 provided in the ladle 1. A control method using this control device 32 will be described below.
Next, a method for manufacturing a multilayered slab using the continuous casting apparatus 100 will be described using
In the manufacture of a multilayered slab, molten steel is supplied to the inside of the casting mold 7 from the first immersion nozzle 5 and the second immersion nozzle 6 of the tundish 2. At this time, as described above, the ejection hole of the second immersion nozzle 6 is disposed above the direct-current magnetic field generator 8, and, on the other hand, the ejection hole of the first immersion nozzle 5 is disposed below the direct-current magnetic field generator 8. Therefore, the molten steel 22 in the inside of the second retention chamber 12 of the tundish 2 is ejected from a location higher than the molten steel 21 in the inside of the first retention chamber 11 of the tundish 2.
The casting mold 7 is cooled using a cooling device (not illustrated), and thus the molten steel 22 supplied to the inside of the casting mold 7 from the second immersion nozzle 6 is solidified in the casting mold 7, and a solidified shell is formed. In addition, the formed solidified shell is pulled downwards at a predetermined casting speed. The solidified shell formed by the solidification of the molten steel 22 becomes a surface layer 24 of the multilayered slab which has a thickness D. Meanwhile, the first immersion nozzle 5 supplies the molten steel 21 from below the molten steel 22 that is supplied from the second immersion nozzle 6 and the direct-current magnetic field generator 8, and thus the molten steel 21 is supplied to the inside of a space surrounded by the surface layer 24. As a result, the molten steel 21 is supplied so as to be buried in the space surrounded by the surface layer 24, and an inner layer 25 of the multilayered slab is formed. Therefore, a multilayered slab having mutually different compositions in the surface layer and the inner layer can be manufactured.
In the above-described manufacturing method, the flow rate (the amount of the molten steel supplied per unit time) of the molten steel 21 that is supplied to the inside of the casting mold 7 from the first immersion nozzle 5 and the flow rate of the molten steel 22 that is supplied to the inside of the casting mold 7 from the second immersion nozzle 6 are adjusted so that a meniscus 17 (molten steel surface) in the inside of the casting mold 7 becomes constant. Specifically, the flow rates of the molten steels 21 and 22 are respectively adjusted so that the flow rate per unit time of the molten steel that is solidified as the surface layer 24 and consumed by being pulled downwards and the flow rate of the molten steel 22 that is supplied to the inside of the casting mold 7 from the second immersion nozzle 6 becomes identical to each other and the flow rate per unit time of the molten steel that is solidified as the inner layer 25 and consumed by being pulled downwards and the flow rate of the molten steel 21 that is supplied to the inside of the casting mold 7 from the first immersion nozzle 5 becomes identical to each other. That is, the molten steel 21 and the molten steel 22 are supplied from the first immersion nozzle 5 and the second immersion nozzle 6 respectively as much as an amount that is consumed as the solidified shell. Therefore, in the casting mold 7, an interface 27 is formed between the molten steel 21 and the molten steel 22, and a strand is divided into an upper side molten steel pool 15 and a lower side molten steel pool 16.
Here, the ratio between the flow rate of the molten steel 21 and the flow rate of the molten steel 22 changes depending on the thickness of the surface layer and the casting width; however, under the conditions of slab casting, the flow rate in the inner layer (that is, the flow rate of the molten steel 21) is four to ten times the flow rate in the surface layer (that is, the flow rate of the molten steel 22), and the flow rate in the inner layer becomes overwhelmingly great. Therefore, a molten steel flux phenomenon is caused in the inside of the casting mold 7 due to the flow of the molten steel flowing out from the ejection hole of the first immersion nozzle 5 that supplies the molten steel 21 to the lower side molten steel pool 16. Specifically, the ejection flow of the molten steel 21 collides with a solidified shell 24 that forms the surface layer and forms a lower side reverse flow and an upper side reverse flow. Between these reverse flows, when the upper side reverse flow is formed, the molten steel 21 in the lower side molten steel pool 16 moves to the upper side molten steel pool 15, and thus the molten steels in the lower side molten steel pool 16 and the upper side molten steel pool 15 are exchanged with each other. When the above-described exchange of the molten steels occurs, the molten steel 21 and the molten steel 22 are mixed together, and thus the qualities of a multilayered slab degrade.
In order to avoid the above-described quality degradation, a direct-current magnetic field having a uniform magnetic flux density is applied using the direct-current magnetic field generator 8 in the thickness direction of the casting mold 7 so as to pass through the interface 27 throughout the casting mold 7 in the width direction (a direction orthogonal to the short-side wall 7a of the casting mold 7), thereby forming a direct-current magnetic field band 14. Here, the direct-current magnetic field band 14 is formed in the same range as the core height of the direct-current magnetic field generator 8. This is because, when the direct-current magnetic field band is formed in the above-described range, a direct-current magnetic field having a uniform magnetic flux density is applied.
A principle that the mixing of the upper side molten steel pool 15 and the lower side molten steel pool 16 can be avoided by forming the direct-current magnetic field band 14 using the direct-current magnetic field generator 8 will be described.
Meanwhile, the magnetic flux density necessary to suppress the mixing can be regulated using the following Stewart number St which is expressed as Expression (1) below and refers to the ratio between the inertia force and the braking force.
St=(σB2L)/(ρVc) Expression (1)
Here, when St is 100 or more, it is possible to suppress the mixing of the molten steels, and, when calculated with a molten steel electric conductivity (σ) of 650,000 (S/m), a molten steel density (ρ) of 7,200 (kg/m3), a casting speed (Vc) of 0.0167 (m/s), a representative length (L) of (2W×T)/(W+T), a casting width (W) of 0.8 (m), and a casting thickness (T) of 0.17 (m), a magnetic flux density B for suppressing the mixing reaches approximately 0.3 (T). Meanwhile, the upper limit of the magnetic flux density is not particularly limited, but is preferably great; however, in a case in which the direct-current magnetic field is formed without using a superconducting magnet, the upper limit reaches approximately 1.0 (T).
As described above, when the amounts of the molten steels supplied to the inside of the casting mold 7 are controlled, and electromagnetic braking is carried out using the direct-current magnetic field generator 8, it is possible to suppress the mixing of the molten steel 21 and the molten steel 22 in the inside of the casting mold 7.
Meanwhile, in order to suppress the quality degradation of a multilayered slab in the manufacture of the multilayered slab by supplying the molten steel 21 and the molten steel 22 having different compositions to the inside of the casting mold 7 using one tundish, it is necessary to suppress the mixing of the molten steel 21 and the molten steel 22 in the inside of the tundish 2.
In a tundish 80 of the related art (that is, a tundish not provided with the weir 4) as shown in
Therefore, in the continuous casting apparatus 100 according to the first embodiment of the present invention, the immersion nozzles are disposed so that the first immersion nozzle 5 of the tundish 2 is located between the long nozzle 1a of the ladle 1 and the second immersion nozzle 6 of the tundish 2 as shown in
Furthermore, in order to prevent the molten steel 22 in the second retention chamber 12 from flowing back to the first retention chamber 11, when the area of a molten steel surface level 18 in the first retention chamber 11 is represented by ST1 (m2) (the area of the molten steel 21 in the first retention chamber 11 in a case in which the tundish 2 is seen in a planar view), the area of the molten steel surface level 18 in the second retention chamber 12 is represented by ST2 (m2) (the area of the molten steel 22 in the second retention chamber 12 in a case in which the tundish 2 is seen in a planar view), the amount of molten steel supplied to the inside of the casting mold 7 from the first retention chamber 11 is represented by Q1 (kg/s), and the amount of molten steel supplied to the inside of the casting mold 7 from the second retention chamber 12 is represented by Q2 (kg/s), the amounts Q1 and Q2 of molten steel supplied are controlled so as to satisfy Expression (2) below.
(Q1/ST1)≤(Q2/ST2) Expression (2)
In a case in which the amounts Q1 and Q2 of molten steel supplied satisfy Expression (2), the molten steel surface level 18 in the inside of the second retention chamber 12 descends faster than the molten steel surface level 18 in the inside of the first retention chamber 11, and thus the molten steel is supplied from the first retention chamber 11 to the second retention chamber 12 so as to remove the head difference. Therefore, it is possible to further suppress the molten steel 22 in the second retention chamber 12 moving to the first retention chamber 11.
In addition, in the continuous casting apparatus 100, the addition device 50 injects a wire or the like into the second retention chamber 12 of the tundish 2 as described above, thereby adding a predetermined element or alloy to the molten steel 22 in the inside of the second retention chamber 12 (refer to
Therefore, in the tundish 2, it is possible to suppress the flow of the molten steel from the second immersion nozzle 6 toward the first immersion nozzle 5, and thus the movement of the molten steel 21 to the first retention chamber 11 can be suppressed. That is, the mixing between the molten steel 21 and the molten steel 22 is suppressed, and it is possible to stably retain the molten steel 21 and the molten steel 22 in the inside of one tundish.
Meanwhile, to the second retention chamber 12, the predetermined element or alloy is added using the wire or the like, and thus it is preferable to impart a stirring force from, for example, the bottom portion 2a of the tundish 2 by Ar bubbling or the like and make the concentration of the molten steel 22 in the inside of the second retention chamber 12 uniform.
Here, as shown in
In addition, the area ratio of opening of the weir 4 is preferably 10% or more and 70% or less. Meanwhile, the “area ratio of opening” of the weir 4 refers to a value (%) obtained by dividing the area of the opening portion 10 (the area of a region surrounded by a bottom surface 4a of the weir 4, inner surfaces of the pair of long-side wall portions 2c, and an inner surface of the bottom portion 2a) by the area of the molten steel 21 in the inside of the first retention chamber 11 of the tundish 2 (that is, the area of a region surrounded by the molten steel surface level 18, the inner surfaces of the pair of long-side wall portions 2c, and the inner surface of the bottom portion 2a) in the case of being seen in a direction perpendicular to the surface of the weir 4 (in the case of being seen in a direction in which the opening portion 10 communicates the first retention chamber 11 and the second retention chamber 12). In other words, the “area ratio of opening” of the weir 4 refers to the proportion (%) of the cross-sectional area of the opening portion 10 in the cross-sectional area of the molten steel 21 in the inside of the first retention chamber 11 in the case of being seen in a cross section perpendicular to the communication direction of the opening portion 10 (a direction perpendicular to the surface of the weir 4).
When the area ratio of opening of the weir 4 is set to 70% or less, it is possible to further suppress the mixing of the molten steels in the first retention chamber 11 and the second retention chamber 12. Therefore, the area ratio of opening of the weir 4 is preferably 70% or less. On the other hand, in a case in which the area ratio of opening of the weir 4 is less than 10%, the pressure loss becomes great when the molten steel flows from the first retention chamber 11 to the second retention chamber 12, and there is a concern that component unevenness may be caused. Therefore, the area ratio of opening of the weir 4 is preferably 10% or more.
In addition, regarding the shape of the weir 4, a round through hole is provided in the weir 4 as shown in
As described above, in the manufacture of a multilayered slab, the strand is split into two segments by the direct-current magnetic field band 14 formed in the casting mold 7, and the molten steels are respectively supplied from the first retention chamber 11 and the second retention chamber 12 of the tundish 2 as much as the amounts Q1 and Q2 of molten steels that are consumed by solidification in the respective regions (refer to
Q=Q1+Q2 Expression (3)
Q1=ρ1S1Vc Expression (4)
Q2=ρ2S2Vc Expression (5)
In addition, in a continuous casting method for a multilayered slab according to the present invention, the amounts Q, Q1, and Q2 of molten steel are controlled so that the interface 27 between the molten steel 21 and the molten steel 22 in the casting mold 7 is located in the direct-current magnetic field band 14. A specific control method will be described using
First, the area ratio of opening of the sliding nozzle 33a provided in the long nozzle 1a of the ladle 1 is controlled so that the amount Q of molten steel that is supplied to the inside of the tundish 2 from the ladle 1 becomes constant. At this time, it is possible to measure the weight of the ladle 1 using the weighing device 35a and compute the amount Q of molten steel on the basis of the amount of the weight changed per unit time. Meanwhile, the amount Q of molten steel may be computed by disposing the weighing device 35a immediately below the tundish 2 and measuring the amount of the weight of the tundish 2 changed.
When the amount Q of molten steel is set to be constant, the molten steel head (the molten steel surface level 18 of the molten steel in the inside of the tundish 2) in the inside of the tundish 2 is retained at a constant height location. In this state, the flow rate Q1 of the molten steel 21 that is consumed in the lower portion of the strand (the lower side molten steel pool 16) is controlled to be constant. Specifically, the molten steel head in the inside of the tundish 2 is retained at a constant height location, and the area ratio of opening of the sliding nozzle 33b is retained at a constant level using a pre-specified table of the area ratio of opening of the sliding nozzle 33b and the flow rate, thereby controlling the amount Q1 of molten steel to be constant. However, the control of the amount Q1 of molten steel alone to be constant is not enough for the amount Q of molten steel that is supplied to the inside of the casting mold 7, and thus the amount Q2 of molten steel of the component-adjusted molten steel 22 is controlled by controlling the area ratio of opening of the sliding nozzle 33c so that the molten steel surface level (the location of the meniscus 17 of the molten steel in the inside of the casting mold 7) in the inside of the casting mold 7 becomes constant. As a result, the amount Q of molten steel and the amounts Q1 and Q2 of molten steels that are consumed in the upper and lower portions of the strand can be controlled, and it is possible to stably maintain the interface 27 between the molten steel 21 and the molten steel 22 shown in
Meanwhile, in the above-described control, a problem of the relationship between the area ratio of opening of the sliding nozzle 33b and the flow rate being not constant every time of the control can be considered. Therefore, it is necessary to understand the relationship between the area ratio of opening of the sliding nozzle 33b and the flow rate characteristic using the casting start time and correct the characteristic. At the casting start time, the components of the molten steel 22 in the inside of the second retention chamber 12 are not adjusted, and thus only the molten steel 21 ejected from the first immersion nozzle 5 is cast. At this time as well, the molten steel head in the inside of the tundish 2 is set to be constant, the molten steel surface level in the inside of the casting mold 7 is controlled to be constant, and the relationship between the area ratio of opening of the sliding nozzle 33b and the flow rate is adjusted, whereby it becomes possible to adjust the flow rate.
Hitherto, a case in which the molten steel is continuously supplied to the tundish 2 from the ladle 1 has been described; however, the molten steel is not supplied from the ladle to the tundish, for example, at the time of exchanging ladles or in the final phase of casting, and thus it is not possible to control the molten steel head in the inside of the tundish 2 to be constant (the molten steel head in the inside of the tundish 2 descends as the molten steel is supplied to the inside of the casting mold 7 from the tundish 2). However, even under conditions in which the molten steel head in the inside of the tundish 2 changes, it is possible to deal with the above-described case by previously obtaining the relationship between the area ratio of opening of the sliding nozzle and the flow rate. That is, the flow rate of molten steel supplied to the casting mold is regulated on the basis of the size of the slab and the casting speed, and thus, even when the head in the inside of the tundish 2 has changed, it is necessary to control the flow rate of the molten steel 21 to be retained constant and furthermore control the flow rate of the molten steel 22 so that the molten steel surface level in the inside of the casting mold 7 becomes constant.
Even under conditions in which the molten steel head in the inside of the tundish 2 is not retained constant as described above (for example, conditions in which the supply of the molten steel from the ladle ends), when the area of the molten steel surface level 18 in the first retention chamber 11 is represented by ST1 (m2), the area of the molten steel surface level 18 in the second retention chamber 12 is represented by ST2 (m2), the amount of molten steel supplied to the inside of the casting mold 7 from the first retention chamber 11 is represented by Q1 (kg/s), and the amount of molten steel supplied to the inside of the casting mold 7 from the second retention chamber 12 is represented by Q2 (kg/s) as described above, the area ST1 of the molten steel surface level 18 in the first retention chamber 11 and the area ST2 of the molten steel surface level 18 in the second retention chamber 12 are adjusted depending on the amounts Q1 and Q2 of molten steel supplied so as to satisfy Expression (2).
In a case in which the amounts Q1 and Q2 of molten steel supplied satisfy Expression (2), the molten steel surface level 18 in the inside of the second retention chamber 12 descends faster than the molten steel surface level 18 in the inside of the first retention chamber 11, and thus the molten steel is supplied from the first retention chamber 11 to the second retention chamber 12 so as to remove the head difference. Therefore, it is possible to suppress the molten steel 22 in the second retention chamber 12 moving to the first retention chamber 11, and consequently, even in a state in which molten steel is not supplied from the ladle, it is possible to suppress the mixing of the molten steel 21 in the inside of the first retention chamber 11 and the molten steel 22 in the inside of the second retention chamber 12.
Meanwhile, the strand is split into the upper and lower portions using the direct-current magnetic field as described above, but the amount of the molten steel that is supplied to the upper portion pool above the direct-current magnetic field band becomes smaller than the amount of the molten steel that is supplied to the lower portion pool. Therefore, as means for making the solidification of the molten steel in the inside of the casting mold 7 uniform, it is preferable to dispose the electromagnetic stirring device 9 near the molten steel surface in the inside of the casting mold 7. In such a case, it is possible to impart a swirl flow in the inside of a horizontal cross section and make the molten steel flux and the solidification uniform in the circumferential direction.
As described above, according to the continuous casting apparatus 100 according to the present embodiment, the immersion nozzles are disposed in an order of the long nozzle 1a of the ladle 1, the first immersion nozzle 5 of the tundish 2, and the second immersion nozzle 6 of the tundish 2 (that is, the long nozzle 1a of the ladle 1 is not disposed between the first immersion nozzle 5 and the second immersion nozzle 6), and thus it is possible to generate a molten steel flux in one direction from the long nozzle 1a of the ladle 1 toward the first immersion nozzle 5 and the second immersion nozzle 6 of the tundish 2 in the inside of the tundish 2. In addition, the tundish 2 is partitioned into the first retention chamber 11 and the second retention chamber 12 by providing the weir 4, and thus it is possible to prevent the molten steel in the inside of the second retention chamber 12 from moving to the inside of the first retention chamber 11. Furthermore, the predetermined element is added to the molten steel in the inside of the second retention chamber 12, and thus it is possible to manufacture molten steel having a different composition from the molten steel in the inside of the first retention chamber 11 in the second retention chamber 12. Therefore, it is possible to retain molten steels having different compositions in one tundish while suppressing the mixing thereof. As a result, it is possible to suppress the quality degradation during the manufacture of a multilayered slab using one ladle and one tundish.
Next, a continuous casting apparatus 200 according to a second embodiment of the present invention will be described.
The direct-current magnetic field generator 240 has a pair of solenoid coils 241 and 242 as shown in
In the tundish 202 of the continuous casting apparatus 200, the first retention chamber 211 and the second retention chamber 212 are communication with each other through the communication pipe 210 as described above, and thus, similar to the case of the first embodiment, it is possible to suppress the mixing of the molten steel 21 in the inside of the first retention chamber 211 and the molten steel 22 in the inside of the second retention chamber 212. Meanwhile, similar to the case of the first embodiment, the area ratio of opening of the communication pipe 210 is preferably 10% or more and 70% or less.
In addition, in the continuous casting apparatus 200, the solenoid coils 241 and 242 that generate magnetic fields in the inside of the communication pipe 210 are disposed in the periphery of the communication pipe 210 as described above. At this time, in the solenoid coils 241 and 242, as shown in
Here, the reason for disposing the two solenoid coils 241 and 242 in the communication pipe 210 will be described.
Meanwhile, a method for manufacturing a multilayered slab using the continuous casting apparatus 200 is the same as in the case of the first embodiment and thus will not be described.
Next, a continuous casting apparatus 300 according to a third embodiment of the present invention will be described.
That is, in the continuous casting apparatus 300 according to the present embodiment, the molten steel 21 in the inside of the first retention chamber 11 is ejected into the inside of the casting mold 7 through the second immersion nozzle 6 of the first retention chamber 11 of the tundish 2, and the molten steel 22 in the inside of the second retention chamber 12 is ejected into the inside of the casting mold 7 through the first immersion nozzle 5 of the second retention chamber 12 of the tundish 2. As a result, in a case in which a multilayered slab is manufactured using the continuous casting apparatus 300 according to the present embodiment, the surface layer area of the slab is formed using the molten steel 21 in the inside of the first retention chamber 11, and the inner layer portion of the slab is formed using the molten steel 22 in the inside of the second retention chamber 12. Meanwhile, a method for manufacturing a multilayered slab using the continuous casting apparatus 300 is the same as in the case of the first embodiment and thus will not be described.
Next, examples carried out to confirm the operation and effect of the present invention will be described.
A multilayered slab having a width of 800 (mm) and a thickness of 170 (mm) was manufactured using the continuous casting apparatus 100 according to the first embodiment. At this time, the electromagnetic stirring device 9 was disposed so that the core center of the electromagnetic stirring device 9 was located 75 (mm) below the molten steel surface level (the location of the meniscus 17) in the inside of the casting mold 7, and a swirl flow having a maximum speed of 0.6 (m/s) was imparted in a horizontal cross section near the molten steel surface (the meniscus 17) in the inside of the casting mold 7. Furthermore, the direct-current magnetic field generator 8 was disposed so that the core center of the direct-current magnetic field generator 8 was located 400 (mm) below the molten steel surface level. Meanwhile, the core thickness of the direct-current magnetic field generator 8 was 200 (mm), and a maximum of 0.5 (T) of a direct-current magnetic field having an almost uniform magnetic flux density was applied across a range of 300 to 500 (mm) from the molten steel surface level.
The specification of the tundish 2 was set as described below. The capacity of the tundish 2 was 20 (t), and the interval between the first immersion nozzle 5 and the second immersion nozzle 6 of the tundish 2 was set to 400 (mm). The weir 4 was installed at the middle location between the nozzles, and the depth of the weir 4 was changed depending on conditions. Furthermore, the area ST1 of the molten steel surface level in the first retention chamber 11 and the area ST2 of the molten steel surface level in the second retention chamber 12 were adjusted depending on the amounts Q1 and Q2 of molten steel supplied so as to satisfy Expression (2).
The locations of the ejection holes of the first immersion nozzle 5 and the second immersion nozzle 6 in the width direction of the casting mold 7 were set to ¼ width locations respectively with the width center interposed therebetween. In addition, the locations of the ejection holes of the first immersion nozzle 5 and the second immersion nozzle 6 in the depth direction of the casting mold 7 were set to be below and above the direct-current magnetic field band 14 that was formed using the direct-current magnetic field generator 8 respectively. Specifically, the height location of the ejection hole of the second immersion nozzle 6 that supplied the molten steel 22 that was to form a surface layer was set to 150 (mm) from the molten steel surface level, and the height location of the ejection hole of the first immersion nozzle 5 that supplied the molten steel 21 that was to form an inner layer was set to 550 (mm) from the molten steel surface level.
The solidification coefficient K (mm/min0.5) in the inside of the casting mold 7 was approximately 25, and the casting speed V, (m/min) was set to 1. The surface layer thickness D (mm) (refer to
D=K√(H/Vc) Expression (6)
Regarding the control of the flow rates of the molten steel 21 and the molten steel 22, at the time of initiating casting, only the molten steel 21 was used in the casting, and the area ratio of opening of the sliding nozzle for supplying a necessary molten steel flow rate was confirmed. After that, the pouring amount from the ladle 1 was controlled to be constant so that the molten steel head in the inside of the tundish 2 became constant, and then the area ratio of opening of the sliding nozzle was controlled to be constant. Furthermore, for the molten steel 22, the pouring amount was controlled so that the molten steel surface level became constant.
As the molten steel that was supplied from the ladle 1 to the tundish 2, low-carbon Al-killed steel was used. That is, the molten steel 21 was low-carbon Al-killed steel. Meanwhile, to the second retention chamber 12 of the tundish 2, an iron wire (containing Ni grains in the inside: (420 g/m)) swaged with a 0.3 mm-thick soft steel plate was added using a wire feeder at an addition speed of 3 (m/min). That is, the molten steel 22 was the molten steel 21 to which the above-described iron wire was added. Meanwhile, the above-described addition of the iron wire (the addition of the above-described iron wire at an addition speed of 3 (m/min)) corresponds to the addition of 0.5% of Ni to the molten steel 21.
In order to inspect the Ni concentration distribution in the multilayered slab, regarding the concentration distribution in the surface layer, analysis specimens were sampled at central locations of both short sides (two places), ¼ width locations (four places), and ½ width locations (two places) in a location 8 mm away from the surface (the center of the surface layer thickness), and the concentrations were inspected. In addition, regarding the concentration distribution in the inner layer, analysis specimens were sampled at central locations of both short sides (two places), ¼ width locations (four places), and ½ width locations (two places) in a location 40 mm away from the surface (slab ¼ thickness), and the concentrations were inspected. Meanwhile, regarding the thickness of the surface layer, in the portions from which the analysis specimens had been sampled, samples were cut out at almost the same locations as those from which the analysis specimens had been sampled from a region raging from the surface to a depth of 40 mm as a subject, the concentration distribution in the thickness direction was inspected by means of EPMA, and a thickness in which the concentration of the added element increased was obtained.
Regarding the obtained analysis results, the degrees of separation in the surface layer and the inner layer and the uniformity of the surface layer concentration were evaluated on the basis of the following indexes. The slab surface layer concentration CO (%), the slab inner surface concentration C1 (%), the in-ladle concentration CL (%), the degree of separation in the surface layer XO (%) that was obtained from the concentration CT (%) added to the inside of the tundish, the average value in the circumferential direction in the slab surface layer thickness CM (%), and the degree of concentration uniformity Y that was obtained from the standard deviation σ (%) were obtained using Expressions (7) and (8) below.
XO=(CO−C1)/(CT−CL) Expression (7)
Y=σ/CM Expression (8)
In Example 1, an experiment of changing the opening area (the area ratio of opening of the weir 4) in the tundish 2 by changing the depth of the weir 4 in the tundish 2 was carried out, and the degree of separation in the surface layer XO and the degree of concentration uniformity Y were inspected. Meanwhile, the magnetic flux density that was applied to the inside of the casting mold 7 was set to 0.4 (T), the location of the interface 27 was set to 450 (mm) in the braking region, and the stirring flow velocity by the electromagnetic stirring device 9 in the inside of the casting mold 7 was set to 0.4 (m/s). These results are shown in
It was confirmed that, as shown in
Next, as Example 2, the location of the interface 27 with respect to the direct-current magnetic field band 14 was changed by changing the flow rate balance between the molten steel 21 and the molten steel 22, and the influence of the location of the interface 27 with respect to the direct-current magnetic field band 14 on the degree of separation in the surface layer XO and the degree of concentration uniformity Y was inspected. Meanwhile, the area ratio of opening of the weir 4 in the tundish 2 was set to 40(%), and the other conditions were set in the same manner as in the case of Example 1. The results are shown in
In
Next, as Example 3, the thicknesses of the two short side portions of the surface layer and the thickness of the width center portion of the surface layer were inspected by changing the stirring flow velocity by the electromagnetic stirring device 9 in the inside of the casting mold 7, and the relationship with the stirring conditions was inspected. The area ratio of opening in the tundish 2 was set to, similar to Example 2, 40(%). The other conditions were the same manner as in Example 1. The results are shown in
As shown in
Next, as Example 4, a multilayered slab having a width of 800 (mm) and a thickness of 170 (mm) was manufactured using the continuous casting apparatus 200 according to the second embodiment. At this time, the inner diameter ϕ of the communication pipe 210 constituted of refractory was set to 100 (mm). The influence of changes in the magnetic flux density on the degree of separation in the surface layer XO and the degree of concentration uniformity Y was inspected by changing the magnetic flux density of a magnetic field that was generated by the two solenoid coils 241 and 242 disposed in the circumference of the communication pipe 210. The other conditions were the same manner as in Example 1. The results are shown in
As shown in
Next, as Example 5, the degree of separation in the surface layer XO and the degree of concentration uniformity Y in a case in which the molten steel head in the inside of the tundish 202 descended as time elapsed were inspected using the continuous casting apparatus 200 according to the second embodiment. That is, in Examples 1 to 4, cases in which the multilayered slabs were manufactured while the molten steel was continuously supplied to the tundish from the ladle have been described; however, in Example 5, in order to verify the effect of a case in which Expression (2) is satisfied, the degree of separation in the surface layer XO and the degree of concentration uniformity Y were inspected under conditions in which a multilayered slab was manufactured while continuously supplying the molten steel to the tundish from the ladle (that is, conditions in which the molten steel head in the tundish remained constant) and conditions in which the supply of molten steel from the ladle was stopped and a multilayered slab was manufactured (that is, conditions in which the molten steel head in the tundish descended as time elapsed).
Specifically, the tundish 202 in which capacities differed in the first retention chamber 211 and the second retention chamber 212 was prepared, and the area ST1 of the molten steel surface level in the first retention chamber 211 and the area ST2 of the molten steel surface level in the second retention chamber 212 were made to differ. In addition, the degree of separation and the uniformity were inspected by changing the relationship between a value (Q1/ST1) obtained by dividing the amount Q1 (kg/s) of molten steel supplied from the first retention chamber 211 by the area ST1 (m2) of the molten steel surface level in the first retention chamber 211 and a value (Q2/ST2) obtained by dividing the amount Q2 (kg/s) of molten steel supplied from the first retention chamber 211 by the area ST2 (m2) of the molten steel surface level in the second retention chamber 212. Meanwhile, the magnetic flux density that was applied to the communication pipe 210 in the tundish 202 was set to be constant at 0.1 (T), and the other conditions were set in the same manner as in the case of Example 4. The results are shown in
As shown in
As shown in
Next, as Example 6, the degree of separation in the surface layer XO and the degree of concentration uniformity Y in a case in which the magnetic flux density of the magnetic field by the solenoid coils 241 and 242 was changed, and the molten steel head in the tundish 202 descended as time elapsed were inspected using the continuous casting apparatus 200 according to the second embodiment. Specifically, the pouring from the ladle 1 was stopped, and the degree of separation in the surface layer XO and the degree of concentration uniformity Y were inspected by changing the magnetic flux density that was applied to the communication pipe 210 under conditions in which Expression (2) was not satisfied (conditions in which Q2/ST2−Q1/ST1=−1.2). Meanwhile, the other conditions were the same manner as in Example 5. The results are shown in
As shown in
Hitherto, the embodiments of the present invention have been described, but the above-described embodiments are proposed as examples, and the scope of the present invention is not limited only to the above-described embodiments. The above-described embodiments can be carried out in a variety of other forms, and a variety of omissions, substitutions, and modifications are allowed within the scope of the gist of the invention. The above-described embodiments or modifications thereof are also included in the scope of the invention described in the claims and equivalencies thereof in the same manner as being included in the scope or gist of the invention.
According to the present invention, it is possible to provide a continuous casting apparatus and a continuous casting method for a multilayered slab capable of suppressing the quality degradation of a multilayered slab during the manufacture of the multilayered slab using one ladle and one tundish.
1 LADLE
1
a LONG NOZZLE OF LADLE (MOLTEN STEEL SUPPLY NOZZLE)
2 TUNDISH
4 WEIR
5 FIRST IMMERSION NOZZLE
6 SECOND IMMERSION NOZZLE
7 CASTING MOLD
8 DIRECT-CURRENT MAGNETIC FIELD GENERATOR
9 ELECTROMAGNETIC STIRRING DEVICE
10 OPENING PORTION (FLOW PATH)
11 FIRST RETENTION CHAMBER (FIRST RETENTION PORTION)
12 SECOND RETENTION CHAMBER (SECOND RETENTION PORTION)
14 DIRECT-CURRENT MAGNETIC FIELD BAND
21 MOLTEN STEEL
22 MOLTEN STEEL
50 ADDITION DEVICE (ADDITION MECHANISM)
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2015-213678 | Oct 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/082286 | 10/31/2016 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2017/073784 | 5/4/2017 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3536122 | Fritz et al. | Oct 1970 | A |
| 4828015 | Takeuchi et al. | May 1989 | A |
| 6089309 | Ge | Jul 2000 | A |
| 20020157808 | Shibata et al. | Oct 2002 | A1 |
| 20090255642 | Kollberg | Oct 2009 | A1 |
| Number | Date | Country |
|---|---|---|
| 1174106 | Feb 1998 | CN |
| 101745627 | Jun 2010 | CN |
| 102688994 | Sep 2012 | CN |
| 0596134 | May 1994 | EP |
| 0 533 955 | Aug 1998 | EP |
| 51-71224 | Jun 1976 | JP |
| 50-145384 | Jul 1985 | JP |
| 60-152684 | Aug 1986 | JP |
| 62-16854 | Jan 1987 | JP |
| 63-108947 | May 1988 | JP |
| 1-271031 | Oct 1989 | JP |
| 1-271042 | Oct 1989 | JP |
| 2-138046 | Nov 1990 | JP |
| 3-243245 | Oct 1991 | JP |
| 03281043 | Dec 1991 | JP |
| 4-2309436 | Nov 1992 | JP |
| 5-185185 | Jul 1993 | JP |
| 5-208244 | Aug 1993 | JP |
| 6-262304 | Sep 1994 | JP |
| 6-320232 | Nov 1994 | JP |
| 7-80600 | Mar 1995 | JP |
| 7-256419 | Oct 1995 | JP |
| 8-290236 | Nov 1996 | JP |
| 2661797 | Oct 1997 | JP |
| 2001-232450 | Aug 2001 | JP |
| 2002-53932 | Feb 2002 | JP |
| 2002-346709 | Dec 2002 | JP |
| 2004-195512 | Jul 2004 | JP |
| 2007-105766 | Apr 2007 | JP |
| 10-2010-0127560 | Dec 2010 | KR |
| WO 0166282 | Sep 2001 | WO |
| Entry |
|---|
| English Machine Translation of JP 03281043 A (Year: 1991). |
| International Search Report for PCT/JP2016/082286 dated Dec. 27, 2016. Office Action for TW 105135276 dated Sep. 20, 2017. Written Opinion of the International Searching Authority for PCT/JP2016/082286 (PCT/ISA/237) dated Dec. 27, 2016. |
| Office Action for TW 105135276 dated Sep. 20, 2017. |
| Written Opinion of the International Searching Authority for PCT/JP2016/082286 (PCT/ISA/237) dated Dec. 27, 2016. |
| Chinese Office Action and Search Report, dated Jul. 3, 2019, for Chinese Application No. 201680063320.9, with an English translation. |
| Korean Office Action for Korean Application No. 10-2018-7013029, dated Jun. 12, 2019, with English translation. |
| Ba{hacek over (z)}an, “Steel Casting and Crystallization,” Technology of Production of Steel in Converters, Didactic Text, 2014, pp. 1-92. |
| Canadian Office Action and Search Report for Canadian Application No. 3,003,574, dated Oct. 17, 2019. |
| Office Action dated Dec. 18, 2018, in Japanese Patent Application No. 2015-151909, with English translation. |
| Office Action dated Dec. 18, 2018, in Japanese Patent Application No. 2015-151910, with English translation. |
| Chinese Office Action, dated Apr. 28, 2020, for Chinese Application No. 201688063320.9, with an English translation. |
| Shi et al., “Training Course for Continuous Casting Workers”. Metallurgical Industry Press, Jul. 2013, pp. 106 (3 pages). |
| Number | Date | Country | |
|---|---|---|---|
| 20180304349 A1 | Oct 2018 | US |
