JP4263396B2 - Steel continuous casting method and equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the manufacture of a high-quality metal product by casting a piece of a cast having very few surface defects or inside inclusions caused by air bubbles caught, non-metal inclusions, surface segregation and mold flux. <P>SOLUTION: A vibration electromagnetic field whose phase is virtually inverted is made to act on a molten steel by placing electromagnets of not less than 3 pieces in the direction of the long side of a cast 10 and by virtually inverting a magnetic field which is generated by AC coils placed next to each other, and a local flow is excited by placing on the upper step an electromagnetic coil which piles up static magnetic fields in the direction of the thickness of the cast through DC coils and by placing DC coils on the lower step. <P>COPYRIGHT: (C)2003,JPO

Description

【００７３】
なお、スラブの幅は１５００〜１７００ｍｍ、厚みは２２０ｍｍ、溶鋼のスループット量は４〜５トン／分の範囲とした。
【００７４】
又、コイル構造として、図１に示した如く、幅方向に１２等分した櫛歯状の鉄芯を用い、幅方向に交互に位相が反転する磁場を発生するように配置した。交流磁界による磁束は最大１０００ガウスとした。又、静磁界による磁束は最大３０００ガウスとした。
【００７５】
又、コイル設置位置は、上段コイルはメニスカスから浸漬ノズルの吐出孔の間に鉄芯が存在するよう、下段コイルは浸漬ノズル吐出孔より下方位置に鉄芯が存在するように配置した。
【００７６】
鋳型長辺に対向する上下２段のコイルは、実施例１〜５について、図１０〜図１４にそれぞれ模式図を示したように、
実施例１；上段：交流振動磁界＋直流磁界、下段：直流磁界
実施例２；上段：直流磁界、下段：交流振動磁界＋直流磁界
実施例３；上段：交流振動磁界＋直流磁界、下段：交流移動磁界
実施例４；上段：交流移動磁界、下段：交流振動磁界＋直流磁界
実施例５；上段：交流振動磁界＋直流磁界、下段：交流振動磁界＋直流磁界
とした。なお、図１０に示す１２Ａは浸漬ノズル１２の吐出口である。
【００７７】
又、比較例として、
比較例１；上下段とも電磁石コイル無し
比較例２；上段：コイル無し、下段：直流磁界
比較例３；上段：交流移動磁界、下段：コイル無し
の条件で鋳造を実施した。
【００７８】
表２に、実験条件及び実験結果をまとめて示す。
【００７９】
【表２】

【００８０】
鋳片の表面偏析は、スラブ研削後、エッチングを行い、目視観察によって１ｍ²当たりの偏析個数を調査した。又、冷間圧延後のコイルの表面欠陥を目視検査し、欠陥サンプルを採取後、欠陥部を分析することによって、モールドフラックスによる欠陥個数を調査した。介在物量は、鋳片の１／４厚みの位置からスライム抽出法によって介在物を抽出後、重量を測定した。表面偏析、モールドフラックス欠陥及び介在物量とも、指数化に際しては、全条件のうち、もっとも悪かったものを１０とし、それに対する線形な比で表示した。
【００８１】
表２からわかるように、比較例に示した従来法の場合、表面品質あるいは内部品質のいずれかが非常に優れた結果となっている場合もあるが、表面品質と内部品質の両立については達成できていない。
【００８２】
これに対して本発明の実施例によれば、表面欠陥並びに内部欠陥の両方が安定して優れた結果を達成できている。
【００８３】
製品品質の要求や製造コストに応じて、上下段のコイルの組合せを本発明の実施例に示した組合せの中から選択することで、より厳格な仕様に対しても問題の無い製品を製造可能となる。
【００８４】
なお、前記説明においては、極数が１２極の櫛歯状の鉄芯が用いられていたが、磁極数や鉄芯の形状はこれに限定されず、例えば鉄芯が分割されていてもかまわない。
【００８５】
又、具体例としては電磁石コイルが２段の設備を示したいが、３段以上であってもよい。
【００８６】
【発明の効果】
本発明によれば、捕捉される気泡、非金属介在物及び鋳片表面偏析、モールドフラックス起因の表面欠陥や内部介在物の少ない鋳片を鋳造でき、高品質の金属製品の製造が可能になる。
【図面の簡単な説明】
【図１】本発明で用いられる電磁石と鋳型を模式的に示す水平断面図
【図２】本発明の原理を説明するための、磁場で誘起される、ある時点の溶湯流動の速度ベクトルの電磁場解析と流動解析による計算結果を模式的に示す正面図
【図３】図２のIII−III線に沿う水平断面図
【図４】図２のIV−IV線に沿う垂直断面図
【図５】本発明の原理を説明するための、磁場で誘起される、磁極が反転した次の時点の溶湯流動の速度ベクトルの電磁場解析と流動解析による計算結果を模式的に示す正面図
【図６】図５のVI−VI線に沿う水平断面図
【図７】図５のVII−VII線に沿う垂直断面図
【図８】本発明における印加電流と溶鋼流速の時間的な変化状態の例を示す線図
【図９】交流振動磁界に直流磁界を重畳して印加する連続鋳造設備の実施形態を模式的に示す水平断面図
【図１０】上段が交流振動磁界＋直流磁界、下段が直流磁界のコイル配置の模式図
【図１１】上段が直流磁界、下段が交流振動磁界＋直流磁界のコイル配置の模式図
【図１２】上段が交流振動磁界＋直流磁界、下段が交流移動磁界のコイル配置の模式図
【図１３】上段が交流移動磁界、下段が交流振動磁界＋直流磁界のコイル配置の模式図
【図１４】上下段とも交流振動磁界＋直流磁界のコイル配置の模式図
【符号の説明】
１０…鋳型
１２…浸漬ノズル
２０…振動磁界発生装置
２２…櫛歯状鉄芯
２４…交流コイル
２６ａ、２６ｂ…交流電源
２８…磁極
３０…静磁界発生装置
３２…直流電流
３４…直流コイル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel continuous casting method and equipment, and more particularly to improvement of molten steel flow in a mold by applying a magnetic field.
[0002]
[Prior art]
In recent years, mainly for steel sheets for automobiles, the demand for quality improvement of steel products has become strict, and the demand for high-quality slabs with excellent cleanliness has increased from the slab stage. Slab defects include those caused by inclusions and bubbles, and those caused by segregation of components in the molten steel, and the flow in the mold is closely related to these, so many studies and inventions have been made. I came. As one of them, a flow control method in a mold using a magnetic field is considered.
[0003]
For example, assuming that a direct current magnetic field is superimposed on a moving magnetic field (A), Japanese Patent Laid-Open No. 10-305353 discloses two upper and lower magnetic poles facing each other with the long side of the mold interposed therebetween, and (1) A magnetic field in which a DC static magnetic field and an AC moving magnetic field are superimposed on the magnetic pole arranged on the lower side, or (2) a magnetic field in which a DC static magnetic field and an AC moving magnetic field are superimposed on the magnetic pole arranged on the upper side, A method of controlling molten steel flow in a mold by applying a DC static magnetic field to a magnetic pole arranged on the side is disclosed.
[0004]
Japanese Patent No. 3067916 discloses an apparatus for controlling the flow of molten steel in a mold by flowing appropriate linear driving AC current and braking DC current through a plurality of installed electric coils.
[0005]
Japanese Patent Application Laid-Open No. 5-154623 discloses a flow control method in a mold in which an AC moving magnetic field whose phase is shifted by 120 degrees and a DC static magnetic field are superimposed.
[0006]
Japanese Patent Laid-Open No. 6-190520 discloses that a magnet placed above the submerged nozzle discharge hole causes a static magnetic field and a high-frequency magnetic field to overlap each other in the entire width direction, and a magnet placed below the discharge hole A method for casting steel in which a magnetic field is applied is disclosed.
[0007]
In addition, as a combination of (B) the upper DC magnetic field and the lower moving magnetic field, Japanese Patent Application Laid-Open No. 61-193755 discloses that a static magnetic field is applied to a position surrounding the molten steel flow discharged from the immersion nozzle to reduce the flow velocity. In addition, an electromagnetic stirring method is disclosed in which an electromagnetic stirring device is installed at a position downstream of the static magnetic field and stirring is performed in the horizontal direction.
[0008]
In addition, as a combination of (C) an upper moving magnetic field and a lower DC magnetic field, Japanese Patent Application Laid-Open No. 6-226409 discloses a magnet in which a center of a pole is installed between a molten metal surface and a discharge hole (downward 50 degrees or more). A casting method is disclosed in which a moving magnetic field is applied and a static magnetic field is applied by a magnet having the center of the core located below the immersion nozzle.
[0009]
In JP-A-9-262651, an electromagnetic stirring magnet is installed above the lower end of the immersion nozzle, and a magnet that can apply a moving magnetic field and a static magnetic field is installed below the lower end of the immersion nozzle. Accordingly, a casting method for selectively using a static magnetic field and a moving magnetic field is disclosed.
[0010]
In JP 2000-271710 A, when casting steel while blowing Ar gas into an immersion nozzle, a magnetic field with a magnetic flux density of 0.1 Tesla or more is applied to the molten steel flow immediately after coming out of the immersion nozzle, A method of continuously stirring by an electromagnetic stirrer in the upper part or a method of periodically changing the stirring direction is disclosed.
[0011]
Japanese Patent Application Laid-Open No. 61-140355 has a static magnetic field arranged to control the molten steel current supplied into the mold on the long side of the mold, and a moving magnetic field generator is arranged on the upper side. A mold that causes the upper surface to flow from the center of the horizontal section to the short side and a structure above the mold are disclosed.
[0012]
In Japanese Patent Laid-Open No. 63-119959, an electromagnetic stirring device for causing horizontal flow in molten steel is provided at the upper part of the mold, and an electromagnetic brake for reducing the discharge flow from the immersion nozzle is provided at the lower part of the mold. A technique for controlling the discharge flow exiting from the vehicle is disclosed.
[0013]
In Japanese Patent No. 2856960, a static magnetic field is used for the molten steel surface in a continuous mold, a straight nozzle is used as a continuous casting nozzle, a traveling magnetic field is used for the discharge port, and a static magnetic field is used for the lower part. Molten steel flow control technology is disclosed.
[0014]
Further, (D) as a method of applying a direct magnetic field alone, Japanese Patent Laid-Open No. 3-258442 discloses that a static magnetic field is generated by an electromagnet having a length substantially the same as the long side, which is disposed opposite to the long side of the mold. An electromagnetic brake is disclosed.
[0015]
Japanese Patent Laid-Open No. 8-19841 discloses that a magnetic pole bent or inclined toward the upper side of the mold from the predetermined position inside the mold width center or the short side of the mold to the vicinity of both ends is below the submerged nozzle discharge hole at the center of the width. And a method of controlling the flow of molten steel in a mold by applying a DC magnetic field or a low-frequency AC magnetic field.
[0016]
In International Publication No. WO95 / 26243, a meniscus flow velocity is set to 0 by controlling a discharge flow from an immersion nozzle by applying a DC magnetic field having a substantially uniform magnetic flux density distribution in the mold thickness direction over the entire width of the mold. A technique for controlling to 20 to 0.40 m / s is disclosed.
[0017]
In Japanese Patent Laid-Open No. 2-284750, a uniform static magnetic field in the mold thickness direction is applied to the entire slab width on the upper and lower portions of the submerged nozzle discharge hole to give an effective braking force to the molten steel discharge flow. A technique for making the above uniform is disclosed.
[0018]
In addition, (E) as a method for applying a DC magnetic field or a moving magnetic field, Japanese Patent Application Laid-Open No. 9-262650 applies a static magnetic field by applying a direct current to a plurality of coils provided below the immersion nozzle discharge hole. A casting method is disclosed in which the flow of molten steel is controlled by applying a moving magnetic field by passing an alternating current.
[0019]
“Materials and Processes” vol3 (1990), page 256, includes techniques for braking (EMLS) or accelerating (EMLA) the discharge molten steel flow by applying an AC moving magnetic field to the discharge flow from the immersion nozzle. Is disclosed.
[0020]
Further, (F) As a method for applying only a moving magnetic field, Japanese Patent Application Laid-Open No. Hei 8-19840 applies a static AC magnetic field having a frequency of 1 to 15 Hz to molten steel when controlling the flow of molten steel in a mold by electromagnetic induction. Techniques to do this are disclosed.
[0021]
“Iron and Steel” 66 (1980), page 797 discloses a technique (M-EMS) for obtaining a horizontal molten steel swirl flow along a mold wall by electromagnetic stirring in a slab continuous casting machine.
[0022]
However, the techniques described in each of the above publications have a problem in that mold powder cannot be wound, inclusions in the solidification interface and trapping of bubbles cannot be prevented, and the surface quality of the slab is not sufficiently improved. .
[0023]
In addition, (G) Japanese Patent No. 2917223, which applies only an oscillating magnetic field, is applied with a low-frequency AC static magnetic field that does not move with time, and the low-frequency electromagnetic vibration is excited immediately before solidification, thereby solidifying the coagulation. Although a method has been disclosed in which the columnar dendrite on the front surface is broken and suspended in the molten metal in order to refine the solidified structure and reduce center segregation, the effect of reducing the surface defects of the slab is small.
[0024]
[Problems to be solved by the invention]
Due to increasing surface quality needs in recent years and demands for cost reduction, further slab surface quality improvement technology and internal quality improvement technology are desired, and more effective control of mold flow is required.
[0025]
The present invention has been made to solve the above-mentioned conventional problems, and can suppress the entrainment of mold flux and suppress the inclusion and inclusion trapped in the solidification nucleus, thereby improving the surface quality of the slab. When Both aims to provide a continuous casting method and equipment for steel that can improve the internal quality of the slab.
[0026]
[Means for Solving the Invention]
The present invention relates to a continuous casting method of steel, in which a plurality of electromagnet coils are arranged on the upper and lower sides facing and sandwiching the long mold side of a continuous casting mold, and at least one stage includes three or more electromagnets in the mold long side direction. The magnetic field generated by the adjacent coils To each other By reversing the phase in the molten steel Is against Roll Dynamic magnetism The problem is solved by inducing local flow by applying a field and superimposing a static magnetic field in the thickness direction of the mold.
[0027]
Further, in the continuous casting method, the magnetic field generated in the adjacent coils is phase-shifted to the adjacent coils. Is the opposite Or by applying the same phase AC current with the coil winding direction reversed. , Anti It is intended to be turned.
[0028]
In addition, two upper and lower electromagnet coils facing each other with the long side of the mold interposed therebetween are arranged, the static magnetic field is superimposed on the oscillating magnetic field on the upper stage, and the static magnetic field is applied on the lower stage.
[0029]
Further, two upper and lower electromagnet coils facing each other with the long side of the mold interposed therebetween are arranged, a static magnetic field is applied to the upper stage, and a static magnetic field is superimposed and applied to the oscillating magnetic field in the lower stage.
[0030]
In addition, two upper and lower electromagnet coils facing each other with the long side of the mold interposed therebetween are arranged, a static magnetic field is superimposed on the oscillating magnetic field on the upper stage, and an AC moving magnetic field is applied on the lower stage.
[0031]
In addition, two upper and lower electromagnet coils facing each other with the long side of the mold interposed therebetween are arranged, an AC moving magnetic field is applied to the upper stage, and a static magnetic field is superimposed on the oscillating magnetic field and applied to the lower stage.
[0032]
In addition, two upper and lower electromagnet coils facing each other across the long side of the mold are disposed, and a static magnetic field is superimposed and applied to the oscillating magnetic field in both the upper and lower stages.
[0033]
Further, the magnetic flux density of the maximum AC magnetic field is 1000 gauss or less, the DC magnetic field is 3000 gauss or less, and / or the frequency of the oscillating magnetic field is 1 Hz to 8 Hz.
[0034]
The present invention also provides a continuous casting equipment for steel, a mold composed of opposed long sides and short sides for holding and solidifying molten steel, and a plurality of electromagnet coils arranged vertically on opposite sides of the mold long side. And at least one stage has three or more magnetic poles in the long side direction of the mold, and adjacent magnetic poles To each other Different polarity and the polarity The Invert at a predetermined cycle Let An oscillating magnetic field generator for generating an oscillating magnetic field without macroscopic molten steel flow in the molten steel in the mold, and a DC magnetic field generator for generating a DC magnetic field in the short side width direction of the mold, It solves the problem.
[0035]
In the continuous casting facility, the oscillating magnetic field generator includes a comb-like iron core having three or more comb teeth along the long side direction of the mold and a coil disposed on each comb tooth. It comprises an electromagnet and an AC power supply for supplying an AC current having a predetermined frequency and a predetermined phase to the coil.
[0036]
The present invention proposes a magnetic field technology that meets the requirements of product quality. That is, the requirements for steel materials can be broadly divided into surface defects and internal defects, but the present invention makes it possible to completely suppress the occurrence of both of these two defects. As a technique for this, in the present invention, two or more magnetic fields are used in the casting direction (vertical direction).
[0037]
By the way, many methods for applying a plurality of magnetic fields to the mold in the casting direction have been reported in the past. For example, in Japanese Patent Application Laid-Open Nos. 2-284750 and 3-142049, a two-stage static magnetic field is applied in the casting direction. Japanese Patent Application Laid-Open Nos. 5-177317 and 5-212511 propose a method in which a moving magnetic field is applied to the upper pole and a magnetic field different from the static magnetic field is applied to the lower pole in the casting direction.
[0038]
The present invention is characterized by not only using a plurality of magnetic fields in the casting direction but also having a coil that generates both an oscillating magnetic field and a static magnetic field in at least one of a plurality of stages of electromagnetic coils.
[0039]
The effectiveness of using a coil that generates both an oscillating magnetic field and a static magnetic field will be described below.
[0040]
In the present invention, the flow velocity distribution in the thickness direction of the mold is defined. That is, the flow rate is reduced near the center of the thickness to suppress the entrainment of mold flux and inclusions and bubbles to the lower side, while giving a local flow to the solidification interface near the mold wall surface to solidify the bubbles and inclusions. Prevents the shell from being captured and reduces the surface defects of the slab.
[0041]
As a method for this purpose, it is necessary to devise an AC magnetic field application method, and as a result of conducting model experiments and simulation calculations, the following conclusions have been reached.
[0042]
1. In order to concentrate the Lorentz force on the solidification interface, it is necessary to control the distribution of magnetic lines of force.
[0043]
2. As a method for this, it is effective to arrange and alternate electromagnets whose phases are alternately reversed in the width direction. When the magnetic field is vibrated in the thickness direction, the electromagnetic force cannot be concentrated on the mold wall surface, that is, the solidification interface, and thus the magnetic field needs to be vibrated in the width direction. Here, the phase of the current applied to the alternating electromagnets needs to be substantially reversed, and for this purpose, the phase needs to be different by 130 ° or more.
[0044]
3. As a coil structure for this purpose, as illustrated in FIG. 1, an AC coil 24 is wound around a comb-shaped iron core having three or more magnetic poles in the width direction, and the phases of adjacent currents are substantially reversed. Thus, the magnetic field in the width direction can be vibrated. In the figure, 10 is a mold, 12 is an immersion nozzle, and 14 is molten steel (the shaded area is a low speed region).
[0045]
4). Further, by providing a direct current coil 34 and superposing a static magnetic field, the magnetic field B term of F = J × B (where F: Lorentz force, J: induced current, B: magnetic field) becomes large, so Lorentz Although the force F can be increased, the direction of the Lorentz force is greatly different from that in the case where the Lorentz force is not superimposed, and the flow is also changed, so that the flow in the width direction and the casting direction is increased. The cleaning effect of inclusions can be expected.
[0046]
5. Moreover, by superimposing, the flow velocity in the thickness center can be reduced, and the entrainment of mold flux can also be prevented.
[0047]
2 (front view), FIG. 3 (horizontal sectional view taken along line III-III in FIG. 2), and FIG. 4 (vertical sectional view taken along line IV-IV in FIG. 2), the number of magnetic poles 28 is four. The case is schematically shown based on an example in which the melt flow at a certain point induced by the oscillating magnetic field of the present invention is calculated by electromagnetic field analysis and flow analysis. In addition, FIG. 5 (front view), FIG. 6 (horizontal sectional view taken along line VI-VI in FIG. 5), and FIG. 7 (vertical sectional view taken along line VII-VII in FIG. 5) Is shown schematically.
[0048]
In the present invention, as shown in FIG. 8, the direction of the flow generated according to the Lorentz force F shown in the following equation is reversed at the same cycle as the applied current I.
[0049]
F∝J × Bt (1)
Bt = Bdc + Bac> 0 (2)
Here, J is an induced current, Bt is a total magnetic field, Bdc is a DC magnetic field, and Bac is an AC magnetic field.
[0050]
6). If the frequency of the alternating current at this time is too low, sufficient flow is not excited, and if it is too high, the molten steel does not follow the electromagnetic field, so a range of 1 Hz to 8 Hz is appropriate.
[0051]
7). If the winding direction of the coil is reversed, the phase of the magnetic field can be reversed even if the phase of the current is the same.
[0052]
8). In Japanese Patent No. 2917223, a low-frequency AC static magnetic field that does not move with time is applied, and low-frequency electromagnetic vibration is excited on the solidification front surface, thereby breaking the columnar dendrite on the solidification front surface and floating it in the molten metal. Although a method aiming to refine the solidification structure and reduce the center segregation is disclosed, if a large electromagnetic force is applied that causes the dendrite to break, the mold flux on the upper surface of the molten metal is involved and the surface quality is deteriorated. . Therefore, the magnetic flux density of the alternating oscillating magnetic field is desirably 1000 gauss or less. Depending on the coil arrangement, the dendrite may be prevented from breaking even at 1000 gauss or more.
[0053]
9. Furthermore, in the method of Japanese Patent No. 2917223, the dendrite breaks and changes from a columnar crystal structure to an equiaxed crystal structure. In ultra-low carbon steel and the like, the columnar crystal structure alone is easier to control as a texture during rolling, so that there is a problem that it is difficult to align the crystal orientation by equiaxed crystallization. For this reason, it is important that the dendrite on the solidified front surface is not broken by electromagnetic force.
[0054]
From the above knowledge, by applying a DC magnetic field in the thickness direction while oscillating the magnetic field in the mold long side direction, a flow greatly different from the conventional one is induced in the mold long side direction and casting direction, and only the solidification interface is efficiently It is possible to suppress the trapping of bubbles and inclusions and greatly improve the surface quality of the slab.
[0055]
In addition, when the electromagnet coils are arranged in two upper and lower stages, the position of the magnets facing the upper and lower stages is not limited because the optimum position changes depending on the casting conditions. The coil core is preferably present in the range up to the discharge hole, and the lower coil is preferably located below the immersion nozzle discharge hole.
[0056]
Further, it is desirable that the maximum AC magnetic flux density is 1000 Gauss or less, the DC magnetic field is 3000 Gauss or less, and the frequency of the oscillating magnetic field is 1 Hz to 8 Hz.
[0057]
By virtue of the present invention, it is possible to efficiently vibrate only the solidification interface and suppress the trapping of bubbles and inclusions into the solidification shell. In addition, the surface quality of the slab can be greatly improved since the intrusion of bubbles and bubbles into the lower part of the mold can be prevented.
[0058]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0059]
FIG. 9 is a schematic diagram of a horizontal cross section of the facility, showing an example of an electromagnetic coil that is applied to the oscillating magnetic field, which is a feature of the continuous casting facility of steel, suitable for implementing the present invention. In the figure, 10 is a mold, 12 is an immersion nozzle, 20 is an oscillating magnetic field generator, 22 is a comb-like iron core, 24 is a coil, 26a and 26b are AC power supplies, 28 is a magnetic pole, and 30 is a static magnetic field generator. .
[0060]
In the present invention, continuous casting is performed while applying a magnetic field to the molten steel in the mold 10 having long sides and short sides facing each other by electromagnetic coils arranged in a plurality of stages in the vertical direction (casting direction). The magnetic field applied at least in one stage is a magnetic field that vibrates in the long side direction of the mold (hereinafter also referred to as an oscillating magnetic field) and a static magnetic field in the thickness direction. The applied oscillating magnetic field is an alternating magnetic field whose application direction is the long side direction of the mold, and is a magnetic field that does not induce macroscopic flow of molten steel by periodically reversing its direction.
[0061]
The oscillating magnetic field can be generated using, for example, an oscillating magnetic field generator 20 as shown in FIG. In the oscillating magnetic field generator 20 shown in FIG. 9, a comb-like iron core 22 having three or more (12 in the figure) comb teeth in the long side direction of the mold is used, and a coil 24 is arranged on these comb teeth. Thus, the magnetic pole 28 is obtained. The magnetic pole 28 adjusts the winding method of the coil and the alternating current flowing through the coil so that adjacent magnetic poles have different polarities (N and S poles). In order to make the adjacent magnetic poles have different polarities (N and S poles), the winding direction of the coils of the adjacent magnetic poles is set in the opposite direction, and the current flowing through the coil is changed to an alternating current having the same phase and a predetermined frequency. Alternatively, it is preferable that the winding direction of the coils of the adjacent magnetic poles is the same direction, and the current flowing through the coil is an alternating current having a predetermined frequency with a phase shift between the adjacent magnetic poles. The phase shift of the alternating current flowing in the adjacent magnetic pole is preferably 130 ° or more and 230 ° or less so that the phase is substantially reversed.
[0062]
The predetermined frequency of the alternating current is preferably 1 to 8 Hz, and more preferably 3 to 6 Hz. The example shown in FIG. 9 is a case where adjacent magnetic poles have different directions (substantially inversion of the phase) of alternating currents flowing through the coil with the coil winding direction being the same direction. It is not limited to.
[0063]
In the present invention, since the adjacent magnetic poles have different polarities, the electromagnetic force acting on the molten steel between the adjacent magnetic poles and the electromagnetic force acting on the molten steel between the adjacent magnetic poles are almost opposite in direction, Macro flow of molten steel is not induced. In the present invention, since the current flowing through the coil is an alternating current, the polarity of each magnetic pole is reversed at a predetermined period, and vibration can be induced in the molten steel near the solidification interface in the long side width direction of the mold. Thereby, inclusions and bubbles in the solidification interface can be suppressed, and the surface quality of the slab can be remarkably improved.
[0064]
If the frequency of the alternating current flowing through the coil is less than 1 Hz, it is too low to induce sufficient flow. On the other hand, if it exceeds 8 Hz, the molten steel will not follow the oscillating magnetic field, and the effect of applying the magnetic field will be reduced. For this reason, it is preferable that the frequency of the alternating current flowing through the coil is 1 to 8 Hz and the vibration period of the oscillating magnetic field is 1/8 to 1 s.
[0065]
In the present invention, the magnetic flux density of the oscillating magnetic field to be applied is preferably 1000 gauss or less. When the magnetic flux density exceeds 1000 gauss, there is a problem that not only the dendrite is broken, but also the molten metal surface fluctuation becomes large and the entrainment of mold flux is promoted.
[0066]
In the present invention, a static magnetic field is applied in addition to the application of the oscillating magnetic field. As shown in FIG. 9, the static magnetic field is applied in the direction of the short side of the mold (the thickness direction of the mold) by installing a static magnetic field generator 30 on the long side of the mold 10.
[0067]
By applying a static magnetic field in the thickness direction of the mold, it is possible to reduce the molten steel flow velocity in the vicinity of the center of the mold indicated by the broken line area in FIG. 9, and to prevent entrainment of mold flux. By superimposing the application of the static magnetic field on the application of the oscillating magnetic field, the B term at F = J × B can be increased, and the Lorentz force can be further increased.
[0068]
In the present invention, the magnetic flux density of the applied static magnetic field is preferably 200 gauss or more and 3000 gauss or less. When the magnetic flux density is less than 200 gauss, the effect of reducing the molten steel flow rate is small, and when it exceeds 3000 gauss, there is a problem that braking is too large and non-uniform solidification occurs.
[0069]
FIG. 9 shows an example in which an oscillating magnetic field generator 20 and a static magnetic field generator 30 are arranged on the long side of the mold 10. The static magnetic field generator 30 has a pair of magnetic poles arranged on the long side of the mold with the mold sandwiched between them. . The installation positions of the static magnetic field generator 30 and the oscillating magnetic field generator 20 may be the same position in the vertical (up and down) direction, or may be slightly shifted.
[0070]
【Example】
Next, based on an Example, this invention is demonstrated still in detail.
[0071]
About 300 tons of molten steel was melted in a converter and made into ultra-low carbon steel Al killed steel by RH treatment, and a slab was cast by a continuous casting machine. Table 1 shows typical molten steel components.
[0072]
[Table 1]

[0073]
The width of the slab was 1500-1700 mm, the thickness was 220 mm, and the throughput of the molten steel was in the range of 4-5 tons / min.
[0074]
Further, as shown in FIG. 1, a comb-shaped iron core divided into 12 parts in the width direction is used as the coil structure, and the coil structure is arranged so as to generate a magnetic field whose phase is alternately reversed in the width direction. The maximum magnetic flux by the AC magnetic field was 1000 gauss. The maximum magnetic flux by the static magnetic field was 3000 gauss.
[0075]
In addition, the coil installation positions were such that the upper coil had an iron core between the meniscus and the discharge hole of the immersion nozzle, and the lower coil had the iron core at a position below the immersion nozzle discharge hole.
[0076]
The upper and lower two-stage coils facing the long side of the mold, for Examples 1 to 5, as schematically shown in FIGS.
Example 1; upper stage: AC oscillating magnetic field + DC magnetic field, lower stage: DC magnetic field
Example 2: Upper: DC magnetic field, Lower: AC oscillating magnetic field + DC magnetic field
Example 3; upper stage: AC oscillating magnetic field + DC magnetic field, lower stage: AC moving magnetic field
Example 4; upper stage: AC moving magnetic field, lower stage: AC oscillating magnetic field + DC magnetic field
Example 5: Upper part: AC oscillating magnetic field + DC magnetic field, lower part: AC oscillating magnetic field + DC magnetic field
It was. In addition, 12A shown in FIG. 10 is a discharge port of the immersion nozzle 12.
[0077]
As a comparative example,
Comparative Example 1: No electromagnetic coil on the upper and lower stages
Comparative example 2; upper stage: no coil, lower stage: DC magnetic field
Comparative example 3; upper row: AC moving magnetic field, lower row: no coil
Casting was carried out under the following conditions.
[0078]
Table 2 summarizes the experimental conditions and the experimental results.
[0079]
[Table 2]

[0080]
The surface segregation of the slab is 1 m by visual observation after etching after slab grinding. ² The number of segregation per hit was investigated. Moreover, the surface defect of the coil after cold rolling was visually inspected, and after collecting a defect sample, the number of defects due to mold flux was investigated by analyzing the defect portion. The amount of inclusions was measured by extracting the inclusions by a slime extraction method from a 1/4 thickness position of the slab. The surface segregation, mold flux defects, and amount of inclusions were indexed with 10 being the worst of all conditions, and displayed as a linear ratio.
[0081]
As can be seen from Table 2, in the case of the conventional method shown in the comparative example, either the surface quality or the internal quality may be very excellent, but both the surface quality and the internal quality are achieved. Not done.
[0082]
On the other hand, according to the embodiment of the present invention, both surface defects and internal defects can be stably achieved with excellent results.
[0083]
By selecting the upper and lower coil combinations from the combinations shown in the embodiments of the present invention according to product quality requirements and manufacturing costs, it is possible to manufacture products with no problems even for stricter specifications. It becomes.
[0084]
In the above description, a comb-like iron core having 12 poles is used. However, the number of magnetic poles and the shape of the iron core are not limited to this, and the iron core may be divided, for example. Absent.
[0085]
In addition, as a specific example, an electromagnetic coil is desired to be installed in two stages, but may be three or more stages.
[0086]
【The invention's effect】
According to the present invention, it is possible to cast a slab having less trapped bubbles, non-metallic inclusions and slab surface segregation, surface defects caused by mold flux and internal inclusions, and high-quality metal products can be manufactured. .
[Brief description of the drawings]
FIG. 1 is a horizontal sectional view schematically showing an electromagnet and a mold used in the present invention.
FIG. 2 is a front view schematically showing a calculation result by electromagnetic field analysis and flow analysis of a velocity vector of a molten metal flow induced at a certain time point induced by a magnetic field, for explaining the principle of the present invention.
3 is a horizontal sectional view taken along line III-III in FIG.
4 is a vertical sectional view taken along line IV-IV in FIG.
FIG. 5 is a front view schematically showing the calculation result by the electromagnetic field analysis and flow analysis of the velocity vector of the molten metal flow at the next time point when the magnetic pole is reversed, induced by the magnetic field, for explaining the principle of the present invention.
6 is a horizontal sectional view taken along line VI-VI in FIG.
7 is a vertical sectional view taken along line VII-VII in FIG.
FIG. 8 is a diagram showing an example of a temporal change state of applied current and molten steel flow velocity in the present invention.
FIG. 9 is a horizontal sectional view schematically showing an embodiment of a continuous casting facility that applies a DC magnetic field superimposed on an AC oscillating magnetic field.
FIG. 10 is a schematic diagram of a coil arrangement in which the upper stage is an AC oscillating magnetic field + DC magnetic field, and the lower stage is a DC magnetic field.
FIG. 11 is a schematic diagram of a coil arrangement in which the upper stage is a DC magnetic field and the lower stage is an AC oscillating magnetic field + DC magnetic field.
FIG. 12 is a schematic diagram of a coil arrangement in which the upper row is an AC oscillating magnetic field + DC magnetic field and the lower row is an AC moving magnetic field.
FIG. 13 is a schematic diagram of a coil arrangement in which the upper stage is an AC moving magnetic field and the lower stage is an AC oscillating magnetic field + DC magnetic field.
FIG. 14 is a schematic diagram of a coil arrangement of AC oscillating magnetic field + DC magnetic field in both upper and lower stages.
[Explanation of symbols]
10 ... mold
12 ... Immersion nozzle
20 ... Oscillating magnetic field generator
22 ... Comb-shaped iron core
24 ... AC coil
26a, 26b ... AC power supply
28 ... Magnetic pole
30 ... Static magnetic field generator
32 ... DC current
34 ... DC coil

Claims (11)

While arranging a plurality of electromagnet coils on the upper and lower sides across the mold long side of the continuous casting mold,
At least one stage, to place three or more electromagnets to mold long side direction, next by reversing the magnetic field generated by the coil between each other, by the action of Do磁 field oscillation phase is inverted to the molten steel, and A continuous casting method for steel, wherein a local flow is induced by superimposing a static magnetic field in the thickness direction of the mold. The magnetic field generated by the coil between the adjacent or phase coils between neighboring passing a reverse alternating current, or by by the winding direction of the coil in the opposite energizing the alternating current of the same phase, anti The steel continuous casting method according to claim 1, wherein the steel is cast. The upper and lower two-stage electromagnet coils facing each other with the long side of the mold interposed therebetween are arranged, a static magnetic field is superimposed on an oscillating magnetic field on the upper stage, and a static magnetic field is applied on the lower stage. Steel continuous casting method. The upper and lower two-stage electromagnet coils facing each other with the long side of the mold interposed therebetween are disposed, a static magnetic field is applied to the upper stage, and a static magnetic field is superimposed on the oscillating magnetic field and applied to the lower stage. Steel continuous casting method. 3. The upper and lower two-stage electromagnet coils facing each other with the mold long side interposed therebetween are arranged, a static magnetic field is superimposed on an oscillating magnetic field in the upper stage, and an AC moving magnetic field is applied in the lower stage. The continuous casting method of the described steel. 3. The upper and lower two-stage electromagnet coils facing each other with the long side of the mold interposed therebetween are arranged, an AC moving magnetic field is applied to the upper stage, and a static magnetic field is superimposed on the oscillating magnetic field and applied to the lower stage. The continuous casting method of the described steel. 3. The steel continuous casting method according to claim 1, wherein two upper and lower electromagnet coils facing each other with the long side of the mold interposed therebetween are arranged, and a static magnetic field is superimposed and applied to the oscillating magnetic field in both the upper and lower stages. The continuous casting method for steel according to claim 1 or 2, wherein the magnetic flux density of the maximum AC magnetic field is 1000 gauss or less and the DC magnetic field is 3000 gauss or less. The continuous casting method for steel according to claim 1 or 2, wherein the frequency of the oscillating magnetic field is 1 Hz to 8 Hz. A mold composed of opposed long sides and short sides to hold and solidify molten steel;
A plurality of electromagnet coils arranged vertically on opposite sides of the mold long side;
At least one stage has three or more magnetic poles in the longitudinal direction of the mold, to reverse the and polar in different polarities adjacent magnetic poles to each other at a predetermined period, macroscopic molten steel in said mold An oscillating magnetic field generator for generating an oscillating magnetic field free from molten steel flow;
A DC magnetic field generator for generating a DC magnetic field in the short side width direction of the mold;
A continuous casting facility for steel, comprising: The oscillating magnetic field generator includes an electromagnet including a comb-like iron core having three or more comb teeth along a long side direction of the mold and a coil disposed on each comb tooth, The continuous casting equipment for steel according to claim 10, comprising an alternating current power source for supplying alternating current having a frequency and a predetermined phase.

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