JP2004314096A - Continuous casting method for steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the production of a metallic product of high quality by casting a slab reduced in surface defects and internal inclusions when performing continuous casting without blowing an inert gas from a nozzle feeding molten steel into a mold. <P>SOLUTION: In the continuous casting method for steel, three or more electromagnets (28) are arranged in the long side direction of a mold 10 fed with molten steel in which the melting point of inclusions is made low, and magnetic fields generated on adjoining coils 24 are substantially inverted, so that vibration electromagnetic fields in which phases are substantially inverted are acted on the molten steel to induce local fluidity by electromagnetic force. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１１７】
表１から分かるように、振動磁界を印加することによって、表面偏析、モールドフラックス巻込による欠陥、ブローホール、非金属介在物低減が可能となる。
【０１１８】
同様に、振動磁界の強度が強すぎると、溶湯表面のフラックスの巻き込みが大きくなって、表面品質を悪化させ、周波数が高すぎると、磁界に溶湯が追随できなくなって、凝固界面の洗浄効果が低下し、気泡、介在物欠陥が増加している。
【０１１９】
【発明の効果】
本発明によれば、捕捉される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の組合せの一例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６】本発明で用いられる電磁石と鋳型の組合せの他の一例を模式的に示す水平断面図
【図７】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８】図７のＩＩＩ−ＩＩＩ線に沿う水平断面図
【図９】図７のＩＶ−ＩＶ線に沿う垂直断面図
【図１０】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１１】図１０のＶＩ−ＶＩ線に沿う水平断面図
【図１２】図１０のＶＩＩ−ＶＩＩ線に沿う垂直断面図
【図１３】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を示す線図
【図１４】本発明によるコイルと鋳型の関係を示した平面模式図
【図１５】移動磁界の場合のコイルの位相を示した模式図
【図１６】振動磁界の場合のコイルの位相を示した模式図
【図１７】振動磁界のピーク位置を局所的に移動させる場合のコイルの位相を示した模式図
【図１８】振動磁界のピーク位置を局所的に移動させる場合のコイルの位相を示した他の模式図
【図１９】第１実施形態の連続鋳造設備を模式的に示す水平断面図
【図２０】第２実施形態の連続鋳造設備を模式的に示す水平断面図
【図２１】本発明による効果を示す線図
【図２２】本発明による静磁界を重畳した場合の効果を示す線図
【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…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]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a continuous casting method for steel, and more particularly to a continuous casting method for steel which is suitable for continuous casting without blowing an inert gas from a nozzle for supplying molten steel to a mold.
[0002]
[Prior art]
In recent years, the demands for improving the quality of steel products centering on steel plates for automobiles have become strict, and the demand for high-quality slabs having excellent cleanliness from the slab stage has been increasing. As a method of manufacturing such a high-quality slab, the inclusion of the molten steel in the molten steel is reduced to prevent the immersion nozzle for supplying the molten steel to the mold from being clogged. A gasless casting technique for continuously casting the molten steel without blowing an inert gas such as Ar) is known (for example, see Patent Document 1).
[0003]
As described above, when continuous casting is performed without blowing the inert gas, blow holes are not captured on the surface of the obtained slab, so that the surface properties can be improved as compared with the case where gas is blown. However, as the temperature of the molten steel in the mold decreases, the solidification of the mold flux occurs locally, which gets caught in the molten steel and causes internal defects. Improvement was also required.
[0004]
By the way, some defects in slabs are caused by inclusions and bubbles, and some are caused by segregation of components in molten steel.Molten steel flow in the mold has a deeper relationship with these, Research and inventions have been made. As one of them, a flow control method in a mold using a magnetic field has been considered.
[0005]
For example, (A) assuming that a DC magnetic field is superimposed on a moving magnetic field, two upper and lower magnetic poles opposed to each other across the long side of the mold are arranged on the back of the long side of the mold, and (1) a DC static magnetic field Or (2) a magnetic field in which a DC static magnetic field and an AC moving magnetic field are superimposed on a magnetic pole arranged on the upper side, and a DC static magnetic field is applied on a magnetic pole arranged in a lower side. A method of controlling the flow of molten steel in a mold to be applied is disclosed (for example, see Patent Document 2).
[0006]
Further, there is disclosed an apparatus for controlling the flow of molten steel in a mold by supplying an appropriate linear drive AC current and braking DC current to a plurality of installed electric coils (for example, see Patent Document 3).
[0007]
Further, a flow control method in a mold is disclosed in which an AC moving magnetic field and a DC static magnetic field whose phases are shifted by 120 degrees are superimposed (for example, see Patent Document 4).
[0008]
Also, a method of casting steel in which a static magnetic field and a high-frequency magnetic field are superimposed and act on the entire width direction by a magnet placed above the discharge hole of the immersion nozzle, and a static magnetic field is actuated by a magnet placed below the discharge hole. Is disclosed (for example, see Patent Document 5).
[0009]
(B) As a combination of an upper DC magnetic field and a lower moving magnetic field, a static magnetic field is applied to a position surrounding the molten steel flow discharged from the immersion nozzle to reduce the flow velocity, and an electromagnetic stirrer is provided downstream of the static magnetic field. There is disclosed an electromagnetic stirring method in which a stirrer is installed and stirring is performed in the horizontal direction (for example, see Patent Document 6).
[0010]
(C) Assuming a combination of an upper moving magnetic field and a lower DC magnetic field, a moving magnetic field is acted on by a magnet having a pole center located between the molten metal surface and a discharge hole (downward of 50 degrees or more), and the pole center is moved. There is disclosed a casting method in which a static magnetic field is applied by a magnet provided below an immersion nozzle (for example, see Patent Document 7).
[0011]
In addition, a magnet for electromagnetic stirring is installed above the lower end of the immersion nozzle, a magnet that can apply a moving magnetic field and a static magnetic field is installed below the lower end of the immersion nozzle, and the static magnetic field and the moving magnetic field are set according to the steel type and casting speed. A casting method to be properly used is disclosed (for example, see Patent Document 8).
[0012]
Also, when casting steel while blowing Ar gas into the immersion nozzle, a static magnetic field with a magnetic flux density of 0.1 Tesla or more is applied to the molten steel flow immediately after exiting from the immersion nozzle, and a continuous magnetic stirrer is used above the molten steel flow. A method of mechanically stirring or periodically changing the stirring direction is disclosed (for example, see Patent Document 9).
[0013]
In addition, the long side of the mold has a static magnetic field arranged to control the current of the molten steel supplied into the mold, and a moving magnetic field generator is arranged above, so that the upper surface of the molten steel is short-sided from the center of the horizontal cross section. A mold flowing to the side and a structure above the mold are disclosed (for example, see Patent Document 10).
[0014]
In addition, there is a technology to control the discharge flow from the immersion nozzle by installing an electromagnetic stirring device at the top of the mold to generate a horizontal flow in the molten steel and installing an electromagnetic brake at the bottom of the mold to reduce the discharge flow from the immersion nozzle. It is disclosed (for example, see Patent Document 11).
[0015]
Also disclosed is a flow control technology of molten steel in a mold that uses a static magnetic field on the surface of molten steel in a continuous mold, uses a straight nozzle as a nozzle for continuous casting, uses a traveling magnetic field in the discharge port, and uses a static magnetic field in the lower part. (For example, see Patent Document 12).
[0016]
(D) An electromagnetic brake that applies a DC magnetic field independently and that applies a static magnetic field by an electromagnet that is installed to face the long side of the mold and that is approximately the same length as the long side is disclosed (for example, Patent Reference 13).
[0017]
Also, a magnetic pole bent or inclined upward from the center of the mold or from the predetermined position inside the mold short side to the vicinity of both ends is installed below the immersion nozzle discharge hole at the center of the mold, and a DC magnetic field or low magnetic field is applied. A method of controlling the flow of molten steel in a mold by applying a high-frequency alternating magnetic field has been disclosed (for example, see Patent Document 14).
[0018]
Further, by applying a DC magnetic field having a substantially uniform magnetic flux density distribution over the entire width of the mold in the thickness direction of the mold and controlling the discharge flow from the immersion nozzle, the meniscus flow rate is reduced to 0.20 to 0.40 m / s. A control technique is disclosed (for example, see Patent Document 15).
[0019]
Also disclosed is a technique in which a uniform static magnetic field in the thickness direction of the mold is applied to the upper and lower portions of the immersion nozzle discharge hole over the entire slab width to give an effective braking force to the molten steel discharge flow and to make the flow uniform. (For example, see Patent Document 16).
[0020]
(E) As a means for applying a DC magnetic field or a moving magnetic field, a static magnetic field is applied by flowing a DC current to a plurality of coils provided below a discharge port of an immersion nozzle, or a moving magnetic field is applied by flowing an AC current. For example, a casting method for controlling the flow of molten steel is disclosed (see, for example, Patent Document 17).
[0021]
Further, there is disclosed a technique of braking (EMLS) or accelerating (EMLA) a discharge molten steel flow by applying an AC moving magnetic field to a discharge flow from an immersion nozzle (for example, see Non-Patent Document 1). ).
[0022]
(F) A technique of applying a static alternating 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, assuming that only a moving magnetic field is applied. 18).
[0023]
Further, in a continuous slab caster, a technique (M-EMS) for obtaining a swirling flow of molten steel in a horizontal direction along a mold wall by electromagnetic stirring is disclosed (for example, see Non-Patent Document 2).
[0024]
However, the techniques described in the above-mentioned patent documents and non-patent documents involve the problem that the mold powder is not involved, or the inclusion of inclusions at the solidification interface cannot be prevented, and the surface quality of the slab does not sufficiently improve. there were.
[0025]
(G) Assuming that only an oscillating magnetic field is applied, a low-frequency alternating static magnetic field that does not move over time is applied to excite the low-frequency electromagnetic vibration immediately before solidification, thereby breaking columnar dendrites on the front of solidification and melting molten metal. A method is disclosed in which the solidified structure is suspended to reduce the size of the solidified structure and the center segregation, but the effect of reducing the surface defects of the slab is small (for example, see Patent Document 19).
[0026]
[Patent Document 1]
JP-A-11-100611
[Patent Document 2]
JP-A-10-305353
[Patent Document 3]
Japanese Patent No. 3067916
[Patent Document 4]
JP-A-5-154623
[Patent Document 5]
JP-A-6-190520
[Patent Document 6]
JP-A-61-193755
[Patent Document 7]
JP-A-6-226409
[Patent Document 8]
JP-A-9-262652
[Patent Document 9]
JP 2000-271710 A
[Patent Document 10]
JP-A-61-140355
[Patent Document 11]
JP-A-63-119959
[Patent Document 12]
Patent No. 2856960
[Patent Document 13]
JP-A-3-258442
[Patent Document 14]
JP-A-8-19841
[Patent Document 15]
International Publication WO95 / 26243
[Patent Document 16]
JP-A-2-284750
[Patent Document 17]
JP-A-9-262650
[Patent Document 18]
JP-A-8-19840
[Patent Document 19]
Patent No. 2917223
[Non-patent document 1]
"Materials and Processes" vol. 3 (1990) p. 256
[Non-patent document 2]
"Iron and Steel," 66 (1980) p. 797
[0027]
[Problems to be solved by the invention]
In recent years, the need for surface quality has increased and the demand for cost reduction has been increasing, so that further techniques for improving the quality of the slab surface and inside have been desired, and more effective control of the flow in the mold has been required.
[0028]
The present invention has been made in order to solve the above conventional problems, when continuous casting without blowing inert gas from the immersion nozzle, while suppressing the entrainment of mold flux, while improving the internal quality of the slab It is another object of the present invention to provide a continuous casting method for steel capable of improving the surface quality of a slab by suppressing inclusions from solidifying nuclei.
[0029]
[Means for Solving the Invention]
The present invention provides a continuous casting method for steel, in which molten steel supplied to a continuous casting mold is continuously cast, by reducing inclusions of the molten steel to prevent a nozzle for supplying the molten steel to the mold from being blocked. Then, when performing continuous casting without blowing an inert gas from the nozzle, the above problem is solved by reducing the surface defects of the cast slab by electromagnetically stirring the molten steel in the mold.
[0030]
Further, in electromagnetically stirring the molten steel in the mold, three or more electromagnets are arranged in the direction of the long side of the mold of the continuous casting mold, and the magnetic field generated by the adjacent coils is substantially inverted, thereby forming the molten steel. In this method, an oscillating electromagnetic field whose phase is substantially reversed is applied to induce local flow without causing the dendrite in front of the solidification nucleus to break by electromagnetic force.
[0031]
Further, the magnetic field generated by the adjacent coils is supplied with an AC current having substantially the opposite phase to the adjacent coils, or an AC current having the same phase is supplied by reversing the winding direction of the coils. By doing so, the structure is substantially reversed.
[0032]
Further, the magnetic flux density of the maximum AC magnetic field is less than 1000 gauss and / or the frequency of the oscillating magnetic field is 1 Hz to 8 Hz.
[0033]
Further, in electromagnetically stirring the molten steel in the mold, three or more electromagnets are arranged in the long side direction of the continuous casting mold, and while generating an oscillating magnetic field by these electromagnets, a peak position of the oscillating magnetic field is generated. Is locally moved along the long side of the mold.
[0034]
At this time, the phase of three or more adjacent coils is n, 2n, n or the array portion of n, 3n, 2n (however, n = 60 ° or 120 ° in three-phase AC, n in two-phase AC). = 90 °).
[0035]
Also, a static magnetic field is superimposed on the oscillating magnetic field in the thickness direction of the mold.
[0036]
Further, the molten steel obtained by lowering the melting point of the inclusion contains C ≦ 0.020 wt%, Si ≦ 0.2 wt%, Mn ≦ 1.0 wt%, S ≦ 0.050 wt%, Ti ≧ 0.010 wt%, This is an ultra-low carbon Ti deoxidized steel having a composition satisfying the condition of Al ≦ (wt% Ti) / 5. Further, in producing the molten steel, the molten steel is first decarburized by a vacuum degassing device, then deoxidized by a Ti-containing alloy, and then, in the deoxidized molten steel, Ca ≧ 10 wt% and REM ≧ 5 wt% are added. By adding an alloy for adjusting the composition of inclusions containing one or more kinds selected from Fe or Al and one or more kinds selected from Fe, Al, Si and Ti, the oxide composition in the molten steel is changed to Ti oxide. 90 wt% or less, the content of at least one of CaO and REM oxide is 10 wt% or more and 50 wt% or less, and Al ₂ O ₃ Is 70% by weight or less.
[0037]
Further, prior to the deoxidizing treatment with the Ti-containing alloy, the molten steel after the decarburizing treatment is preliminarily deoxidized with any of Al, Si, and Mn to reduce the dissolved oxygen concentration in the molten steel to 200 ppm or less in advance. It is like that.
[0038]
In the present invention, when casting without blowing inert gas from the immersion nozzle that supplies molten steel to the mold, electromagnetic stirring is applied to make the molten steel temperature in the mold uniform. For that purpose, the flow velocity distribution in the thickness direction of the mold is defined. In other words, while reducing the flow velocity near the center of the thickness to suppress entrainment of the mold flux, local flow is given to the molten steel at the solidification interface near the mold wall surface to prevent air bubbles and inclusions from being trapped, and to reduce the surface of the slab. Reduce defects.
[0039]
As a method for this, it is necessary to devise a method of applying an AC magnetic field, and as a result of performing model experiments and simulation calculations, the following conclusions have been reached.
[0040]
1. In the magnetic field in the thickness direction as shown in Patent Document 5, the Lorentz force was concentrated on the solidification interface or the molten steel surface by using the skin effect of the alternating current. In order to concentrate the Lorentz force on the solidification interface because the Lorentz force cannot be concentrated, it is necessary to control the magnetic field line distribution.
[0041]
2. As a method for this, it is effective to arrange electromagnets whose phases are alternately inverted in the width direction and to alternate them. When the magnetic field is vibrated in the thickness direction, the electromagnetic force cannot be concentrated on the mold wall surface, that is, on the solidification interface. Therefore, it is necessary to vibrate the magnetic field in the width direction. Here, the phases of the currents flowing through the alternate electromagnets need to be substantially inverted, and for that purpose, the phases need to differ by 130 ° or more.
[0042]
3. As a coil structure for this purpose, as illustrated in FIG. 1, a coil is wound around a comb-shaped iron core 22 having three or more magnetic poles in the width direction, and the phases of currents adjacent to each other are substantially inverted. , The magnetic field in the width direction can be vibrated. In the figure, reference numeral 10 denotes a mold, 12 denotes a submerged nozzle, and 14 denotes molten steel (shaded portions are in a low speed region).
[0043]
4. 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 the range of 1 Hz to 8 Hz is appropriate.
[0044]
5. By using such an electromagnet, it is possible to induce a flow in a direction in which the molten metal (molten steel) is separated from the solidification front surface, and since the excited flow velocity is small, the effect of cleaning the solidification interface without breaking the dendrite. was gotten. 2 (front view), FIG. 3 (horizontal sectional view along the line III-III in FIG. 2), and FIG. 4 (vertical sectional view along the line IV-IV in FIG. 2) show that the number of magnetic poles 28 is four. In the case, the flow of the molten metal induced by the oscillating magnetic field of the present invention is schematically shown based on an example calculated by electromagnetic field analysis and flow analysis.
[0045]
In the present invention, as shown in FIG. 5, the direction of the flow generated according to the Lorentz force F shown in the following equation is the same, and only the flow velocity v fluctuates in a half cycle of the applied current I.
[0046]
F∝J × B (1)
Here, J is an induced current, and B is a magnetic field.
[0047]
6. By reversing the winding direction of the coil, the phase of the magnetic field can be reversed even if the phase of the current is the same.
[0048]
7. In Patent Document 19, by applying a low-frequency AC static magnetic field that does not move with time, and exciting low-frequency electromagnetic vibrations on the solidification front, the columnar dendrites on the solidification front are broken and suspended in the molten metal, Although a method aiming at miniaturization of the solidified structure and reduction of center segregation is disclosed, if a large electromagnetic force is applied to break the dendrite, the mold flux on the upper surface of the molten metal is involved, thereby deteriorating the surface quality. Therefore, the magnetic flux density of the AC oscillating magnetic field is desirably less than 1000 Gauss. Note that depending on the coil arrangement, there is a case where the dendrite can be prevented from breaking even at 1000 gauss or more.
[0049]
8. Further, in the method of Patent Document 19, the dendrite is broken, and the structure changes from a columnar crystal structure to an equiaxed crystal structure. In ultra-low carbon steel and the like, since only the columnar crystal structure is easier to control as a texture during rolling, there is a problem that it is difficult to make the crystal orientation uniform by performing equiaxed crystallization. For this reason, it is important that the dendrite on the solidification front surface is not broken by the electromagnetic force.
[0050]
From the above findings, by vibrating the magnetic field in the direction of the long side of the mold, the thickness of the slab, the flow in the casting direction is induced, and the flow that separates the bubbles and inclusions from the solidification interface is given. It was concluded that preventing trapping was effective.
[0051]
According to the present invention, only the solidification interface can be efficiently vibrated to suppress the capture of bubbles and inclusions, so that the surface quality of the slab can be significantly improved.
[0052]
Furthermore, as a result of performing model experiments and simulation calculations to improve the quality of the slab, it was found that it is also effective to apply the oscillating magnetic field to the molten steel in the mold and to superimpose a static magnetic field in the thickness direction of the mold. was gotten.
[0053]
9. As a coil structure for this purpose, as shown in FIG. 6, a coil structure in which a DC coil 34 is further added to the structure shown in FIG.
[0054]
10. Thus, by providing the DC coil 34 and superimposing the static magnetic field, the magnetic field B term of F = J × B (where F: Lorentz force, J: induced current, B: magnetic field) increases. The Lorentz force F can be increased, but the direction of the Lorentz force is significantly different from the case where the Lorentz force is not superimposed, the flow also changes, and the flow in the width direction and the casting direction increases. The effect of cleaning air bubbles and inclusions can be expected.
[0055]
11. In addition, by overlapping, the flow velocity at the center of the thickness can be reduced, and entrainment of the mold flux can be more effectively prevented.
[0056]
FIGS. 7 (front view), FIG. 8 (horizontal sectional view along line III-III in FIG. 7), and FIG. 9 (vertical sectional view along line IV-IV in FIG. 7) show that 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. FIG. 10 (front view), FIG. 11 (horizontal sectional view along line VI-VI in FIG. 10), and FIG. 12 (vertical sectional view along line VII-VII in FIG. 10) show the flow of molten metal at the next time point. Is schematically shown.
[0057]
In the present invention, as shown in FIG. 13, 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.
[0058]
F∝J × Bt (2)
Bt = Bdc + Bac> 0 (3)
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.
[0059]
Also in this case, the frequency of the alternating current for oscillating the magnetic field is the same as that of 4. The range of 1 Hz to 8 Hz is appropriate as described in the section. In addition, 6. Items to 8. Items described in the section also apply.
[0060]
From the above findings, applying a DC magnetic field in the thickness direction while oscillating the magnetic field in the mold long side direction, induces a flow that is significantly different from the conventional in the mold long side direction and casting direction, and efficiently only the solidification interface By vibrating the slab, the trapping of bubbles and inclusions can be suppressed, and the surface quality of the slab can be greatly improved.
[0061]
Furthermore, as a result of performing a model experiment and a simulation calculation in order to devise an application mode of the AC magnetic field, the following conclusions were obtained.
[0062]
12. The macro flow caused by the moving magnetic field suppresses the trapping of bubbles and inclusions at the solidification interface, but sometimes increases the entrainment of the mold flux, which may degrade the quality.
[0063]
13. When the position where the oscillating magnetic field is strongly applied when the oscillating magnetic field is applied is fixed, a portion where the inclusion of the inclusion cannot be sufficiently suppressed may occur at a position where the electromagnetic force is weak.
[0064]
14． Therefore, it is effective to move the peak position of the Lorentz force due to the oscillating magnetic field.
[0065]
15. In order to move the peak position of the Lorentz force, the phases of three adjacent coils or a group of coils may be set so that the phase of the middle coil is the last. Here, the oscillating magnetic field refers to a magnetic field in which the direction of the Lorentz force reverses with time.
[0066]
Hereinafter, the above 15. Items will be described. As shown in FIG. 14 having substantially the same structure as that of FIG. 6, an oscillating magnetic field is applied to each coil (shown in FIG. 20 described later) of the comb-shaped coil 24 to change the phase for each coil. FIG. 15 to FIG. 18 are explanatory diagrams of the phase given to each of such coils. In the figure, the numbers attached beside the respective coils of the oscillating magnetic field generating coils 24a and 24b indicate the phase angle (degree) of the current of the coil at a certain time. 15 to 18 show the case of two-phase alternating current, FIG. 15 shows an example in which the moving magnetic field, FIG. 16 shows an example in which the oscillating magnetic field, and FIGS.
[0067]
As shown in FIGS. 17 and 18, three or more electromagnets are arranged in the width direction of the casting mold of the continuous casting mold, and the phase of the current supplied to adjacent electromagnets increases or decreases in one direction. Instead, by setting at least the middle phase to lag behind the phases on both sides, the magnetic field does not simply move in one direction, but moves locally while oscillating.
[0068]
As described above, the phases of three or more adjacent coils are n, 2n, n or n, 3n, 2n (where n is 90 ° for two-phase AC and 60 ° or 120 ° for three-phase AC). By providing the arrangement portion, the peak position of the oscillating magnetic field can be locally moved.
[0069]
Here, when the oscillating magnetic field is simply induced, there are places where the amplitude of the oscillating magnetic field is large and where the amplitude is small. By moving the peak position locally, the solidification interface can be cleaned at all positions.
[0070]
Although the example in which the number of comb teeth of the coil is 12 is shown here, the number of comb teeth can be selected from 4, 6, 8, 10, 12, 16 and the like. Any of three phases may be used.
[0071]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a first embodiment of the present invention in which only an oscillating magnetic field acts will be described in detail with reference to the drawings.
[0072]
In the first embodiment, by lowering the melting point of the inclusions of the molten steel, the nozzle for supplying the molten steel to the mold is prevented from being blocked, and the continuous casting is performed without blowing an inert gas such as Ar from the nozzle. I do.
[0073]
As a molten steel in which inclusions used in this gasless continuous casting have a low melting point, C ≦ 0.020 wt%, Si ≦ 0.2 wt%, Mn ≦ 1.0 wt%, S An ultra-low carbon Ti deoxidized steel having a composition that satisfies the condition of Al ≦ (wt% Ti) / 5, including ≦ 0.050 wt% and Ti ≧ 0.010 wt%. In the production of this molten steel, the molten steel is first decarburized by a vacuum degassing device, then deoxidized by a Ti-containing alloy, and then one of Ca ≧ 10 wt% and REM ≧ 5 wt% is contained in the deoxidized molten steel. Alternatively, by adding an alloy for adjusting the composition of inclusions containing two or more of one or more selected from Fe, Al, Si and Ti, the oxide composition in the molten steel can be reduced to 90 wt. % Or less, the content of at least one of CaO and REM (rare earth element) oxide is 10 wt% or more and 50 wt% or less, and Al ₂ O ₃ Is 70% by weight or less. At that time, prior to the deoxidizing treatment with the Ti-containing alloy, the molten steel of the decarburizing treatment is preliminarily deoxidized with any of Al, Si, and Mn to reduce the dissolved oxygen concentration in the molten steel to 200 ppm or less in advance. It is desirable.
[0074]
When the molten steel thus manufactured is subjected to gasless continuous casting, the molten steel in the mold is electromagnetically stirred as described below to reduce surface defects of the slab.
[0075]
An example of a continuous steel casting facility suitable for carrying out the present invention is shown in FIG. 19 in a schematic view of a horizontal section. In the figure, 10 is a mold, 12 is an immersion nozzle, 20 is an oscillating magnetic field generator, 22 is a comb-shaped iron core, 24 is a coil, 26a and 26b are AC power supplies, and 28 is a magnetic pole.
[0076]
In the present invention, continuous casting is performed while applying a magnetic field to molten steel in the mold 10 having the opposite long side and short side. The applied magnetic field is a magnetic field that vibrates in the long side direction of the mold (hereinafter, also referred to as an oscillating magnetic field). The applied oscillating magnetic field is an alternating magnetic field having the long side direction of the mold as an application direction, the direction of which is periodically inverted, and is a magnetic field that does not induce macro flow of molten steel.
[0077]
The oscillating magnetic field can be generated, for example, using an oscillating magnetic field generator 20 as shown in FIG. In an oscillating magnetic field generator 20 shown in FIG. 19, a coil 24 is disposed on each of the comb teeth using a comb-shaped iron core 22 having three or more (12 in the figure) comb teeth in the long side direction of the mold. The magnetic pole 28 is obtained. The magnetic pole 28 adjusts the winding 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 windings of the coils of the adjacent magnetic poles are set in opposite directions, and the currents flowing through the coils are alternating currents having the same phase and a predetermined frequency. Alternatively, it is preferable that the winding of the coils of the adjacent magnetic poles be in the same direction, and the current flowing through the coils be an alternating current having a predetermined frequency and a phase shifted between the adjacent magnetic poles. It is preferable that the phase shift of the alternating current flowing through the coil of the adjacent magnetic pole be 130 ° or more and 230 ° or less, where the phase is substantially inverted.
[0078]
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. 19 is a case where adjacent magnetic poles have different phases (substantially invert the phase) of an alternating current flowing through the coil with the winding direction of the coil being the same. However, the present invention is not limited to this.
[0079]
In the present invention, since the adjacent magnetic poles have different polarities, the directions of 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 substantially opposite, Macro flow of molten steel is not induced. Further, 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 cycle, and vibration can be induced in the molten steel near the solidification interface in the long side width direction of the mold. Thereby, trapping of inclusions and bubbles at the solidification interface can be suppressed, and the surface quality of the slab can be significantly improved.
[0080]
If the frequency of the alternating current flowing through the coil is less than 1 Hz, the flow is too low to induce a sufficient flow. On the other hand, when the frequency exceeds 8 Hz, the molten steel does not follow the oscillating magnetic field, and the effect of applying the magnetic field is reduced. For this reason, it is preferable that the frequency of the alternating current flowing through the coil be 1 to 8 Hz and the oscillation period of the oscillating magnetic field be 1/8 to 1 s.
[0081]
In the present invention, the magnetic flux density of the applied oscillating magnetic field is preferably less than 1000 gauss. When the magnetic flux density becomes 1000 gauss or more, there is a problem that not only the dendrite is broken but also the fluctuation of the molten metal surface is increased, and the entrainment of the mold flux is promoted.
[0082]
(First embodiment)
Next, the present invention will be described in more detail based on examples.
[0083]
First, a typical example of molten steel will be described. After exiting the converter, 300 tons of molten steel was decarburized by an RH vacuum degasser, and the composition of the molten steel was changed to C = 0.0035 wt%, Si = 0.02 wt%, Mn = 0.20 wt%, P = 0.015 wt%, S = 0.010 wt%, and the temperature were adjusted to 1600 ° C. 0.5 kg / ton of Al was added to the molten steel to reduce the concentration of dissolved oxygen in the molten steel to 150 ppm. At this time, the Al concentration in the molten steel was 0.003 wt%. Then, 1.2 kg / ton of a 70 wt% Ti-Fe alloy was added to the molten steel and deoxidized. Thereafter, 0.5 kg / ton of 20 wt% Ca-10 wt% REM-50 wt% Ti-Fe alloy was added to the molten steel to adjust the composition. After this treatment, the Ti concentration was 0.050 wt% and the Al concentration was 0.003 wt%.
[0084]
Next, a casting experiment was performed with the continuous casting facility shown in FIG. As a result of examining the inclusions in the tundish at this time, 65 wt% Ti ₂ O ₃ -15wt% CaO-10wt% Ce ₂ O ₃ -10wt% Al ₂ O ₃ Of spherical inclusions. After casting, there was almost no deposit in the immersion nozzle.
[0085]
The width of the slab was 1500 to 1700 mm, the thickness was 220 mm, and the throughput of molten steel was in the range of 4 to 5 ton / min.
[0086]
As shown in FIG. 1, a comb-shaped iron core divided into 12 equal parts in the width direction was used as the coil structure, and the coil structure was arranged so as to generate a magnetic field whose phase was alternately inverted in the width direction.
[0087]
FIG. 21 collectively shows the experimental conditions and the experimental results (defect mixing ratio) for the ultra-low carbon steel. In this figure, the defect mixing ratio refers to defects caused by inclusions, mold flux entanglement, blow holes and surface defects.
[0088]
In addition, the surface segregation of the slab was performed by etching after slab grinding, and 1 m by visual observation. ² The number of segregation per unit was investigated. Further, the surface defect of the coil after the cold rolling was visually inspected, a defect sample was collected, and the defective portion was analyzed to investigate the number of defects due to the mold flux. The amount of inclusions was determined by extracting inclusions from the position of 1/4 thickness of the slab by the slime extraction method, and then measuring the weight. Regarding the surface segregation, the mold flux defect and the amount of inclusions, the worst of all the conditions was set to 10 in the indexing, and the ratio was expressed as a linear ratio.
[0089]
As can be seen from FIG. 21, the AC magnetic flux density enables reduction of surface segregation, defects due to mold flux entrainment, blowholes, and nonmetallic inclusions.
[0090]
Here, if the intensity of the oscillating magnetic field is too strong, the flux on the surface of the molten metal becomes large and the surface quality deteriorates.If the frequency is too high, the molten metal cannot follow the magnetic field, and the effect of cleaning the solidification interface is reduced. It is presumed that the number of blow holes and inclusion defects increased.
[0091]
In the above description, a comb-shaped iron core having 12 poles has been used, but the number of magnetic poles and the shape of the iron core are not limited thereto, and for example, the iron core may be divided.
[0092]
Next, a second embodiment of the present invention in which a static magnetic field is superimposed on an oscillating magnetic field will be described in detail with reference to the drawings.
[0093]
FIG. 20 is a schematic cross-sectional view of an example of a continuous steel casting facility suitable for carrying out the present invention. This figure corresponds to FIG. 19 provided with 30 static magnetic field generators.
[0094]
In the present invention, continuous casting is performed while applying a magnetic field to molten steel in the mold 10 having the opposite long side and short side. The applied magnetic field is a magnetic field oscillating 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 having the long side direction of the mold as an application direction, the direction of which is periodically inverted, and is a magnetic field that does not induce macro flow of molten steel.
[0095]
The oscillating magnetic field can be generated, for example, using an oscillating magnetic field generator 20 as shown in FIG. The oscillating magnetic field generator 20 shown in FIG. 20 is substantially the same as that shown in FIG. 19 of the first embodiment, and therefore, detailed description is omitted.
[0096]
Further, in the present invention, a static magnetic field is applied in addition to the application of the oscillating magnetic field as in the first embodiment. As shown in FIG. 20, the static magnetic field is applied in the direction of the short side of the mold (the thickness direction of the mold) by installing the static magnetic field generator 30 on the long side of the mold 10.
[0097]
By applying a static magnetic field in the thickness direction of the mold, the flow velocity of molten steel near the center of the mold can be reduced, and entrainment of mold flux can be prevented. In addition, by superimposing the application of the static magnetic field on the application of the oscillating magnetic field, the B term in F = J × B can be increased, so that the Lorentz force can be further increased.
[0098]
Further, in the present invention, it is preferable that the magnetic flux density of the applied static magnetic field be 200 gauss or more and 3000 gauss or less. If the magnetic flux density is less than 200 gauss, the effect of reducing the flow rate of the molten steel is small, and if it exceeds 3000 gauss, there is a problem that braking is too large to cause uneven solidification.
[0099]
FIG. 20 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 disposed on the long side of the mold with the mold interposed therebetween, and allows a flowing current as a DC current to flow from the DC power supply 32 to the coil 34 to apply a static magnetic field in the thickness direction of the mold. . The installation positions of the static magnetic field generating device 30 and the oscillating magnetic field generating device 20 may be the same in the vertical direction or may be different.
[0100]
(Second embodiment)
Next, the present invention will be described in more detail based on examples.
[0101]
A slab was cast by the continuous caster shown in FIG. 20 using the same molten steel as in the first embodiment produced by the converter. At that time, similarly, the width of the slab was 1500 to 1700 mm, the thickness was 220 mm, and the throughput of molten steel was in the range of 4 to 5 ton / min.
[0102]
As shown in FIG. 6, a comb-shaped iron core divided into 12 equal parts in the width direction was used as the coil structure, and was arranged so as to generate a magnetic field whose phase was alternately inverted in the width direction.
[0103]
FIG. 22 collectively shows the experimental conditions and results when the ultralow carbon steel was performed under a constant DC magnetic field of 1200 Gauss. The method of analyzing the experimental results described in this table is the same as in the first embodiment.
[0104]
As can be seen from FIG. 22, the superposition of the oscillating magnetic field and the static magnetic field makes it possible to reduce surface segregation, defects due to the inclusion of mold flux, blowholes, and nonmetallic inclusions.
[0105]
In this case, too, if the intensity of the oscillating magnetic field is too strong, the flux on the surface of the molten metal becomes large, and the surface quality is deteriorated. Is estimated to have decreased, and blowholes and inclusion defects increased.
[0106]
Next, a third embodiment of the present invention in which the peak position of the oscillating magnetic field is locally moved along the long side of the mold will be described in detail with reference to the drawings.
[0107]
FIG. 14 shows a plan view of the steel continuous casting mold 10 and an arrangement example of the AC electromagnet (coil) 24 and the DC electromagnet (coil) 34.
[0108]
A continuous casting immersion nozzle 12 connected to the bottom of the upper tundish is immersed in the mold 10 to supply molten steel 14. As shown in FIG. 20, twelve comb-shaped AC electromagnets (coils) 24 are provided along the long side of the continuous casting mold 10, and a DC coil 34 is provided outside thereof. An oscillating current for generating an oscillating magnetic field is supplied to each of the twelve coils 24, and the peak value of the oscillating current is applied so as to move along the long side width direction of the mold. The movement of the peak value is realized by applying so that the phases of adjacent coils have an arrangement portion of n, 2n, n or n, 3n, 2n.
[0109]
FIGS. 15 to 18 show the distribution of the phase of the oscillating magnetic field in each of the twelve coils constituting the coils 24a and 24b at a certain moment by using numerical values (phase angle values). The peak position of the oscillating magnetic field sequentially moves in the direction along the long side of the mold 10.
[0110]
FIG. 15 shows a moving magnetic field of two-phase alternating current in which adjacent coils have a phase difference of 90 ° and opposing coils 24a and 24b have a difference of 180 °. In FIG. 16, the phase difference between the adjacent coils is 180 °, and the two-phase alternating oscillating magnetic field having the same phase is applied to the opposing coils 24a and 24b. In FIG. 17, a half-wave rectified two-phase alternating current having a phase difference of 90 ° between adjacent coils and a 180 ° difference between opposite coils 24a and 24b is applied. In FIG. 18, a half-wave rectified two-phase alternating current having a phase difference of 120 ° from an adjacent coil and a difference of 60 ° in an opposing coil is applied.
[0111]
According to the method of the present invention in which the peak position of the oscillating magnetic field is locally moved, the same molten steel as in the first embodiment is subjected to gasless continuous casting, so that only the solidification interface is efficiently vibrated to capture inclusions. Therefore, the surface quality of the slab can be significantly improved.
[0112]
(Third embodiment)
As a coil structure, a comb-shaped iron core divided into 12 equal parts in the width direction as shown in FIG. 14 was used, and was arranged so as to generate a magnetic field whose phase was alternately inverted in the width direction of the mold 21. The magnetic flux due to the alternating magnetic field was 1000 gauss at the maximum.
[0113]
Table 3 summarizes the experimental conditions and experimental results. The method of analyzing the experimental results is the same as in Table 1.
[0114]
The symbols of the coil patterns in Table 3 are as follows.
[0115]
A: n, 2n, n (Example)
B: n, 3n, 2n (Example)
C: 0, n, 2n, 3n (Comparative Example)
D: 0, 2n, 0, 2n (Comparative Example)
Here, n is a phase angle, n = 90 ° for two-phase AC, and n = 60 ° or 120 ° for three-phase AC.
[0116]
[Table 1]

[0117]
As can be seen from Table 1, by applying an oscillating magnetic field, it becomes possible to reduce surface segregation, defects due to the inclusion of mold flux, blowholes, and nonmetallic inclusions.
[0118]
Similarly, if the intensity of the oscillating magnetic field is too strong, the flux on the surface of the molten metal becomes large and the surface quality deteriorates.If the frequency is too high, the molten metal cannot follow the magnetic field, and the effect of cleaning the solidification interface is reduced. Decrease, bubbles and inclusion defects increase.
[0119]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the slab with few trapped nonmetallic inclusions and slab surface segregation, surface defects caused by mold flux, and internal inclusions can be cast, and high-quality metal products can be manufactured.
[Brief description of the drawings]
FIG. 1 is a horizontal sectional view schematically showing an example of a combination of 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 by a magnetic field, for explaining the principle of the present invention.
FIG. 3 is a horizontal sectional view taken along line III-III in FIG. 2;
FIG. 4 is a vertical sectional view taken along the line IV-IV in FIG. 2;
FIG. 5 is a diagram showing an example of a temporal change state of an applied current and a flow rate of molten steel in the present invention.
FIG. 6 is a horizontal sectional view schematically showing another example of the combination of the electromagnet and the mold used in the present invention.
FIG. 7 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 at a certain point induced by a magnetic field, for explaining the principle of the present invention.
8 is a horizontal sectional view taken along the line III-III in FIG. 7;
9 is a vertical sectional view taken along the line IV-IV in FIG. 7;
FIG. 10 is a front view schematically illustrating a calculation result by electromagnetic field analysis and flow analysis of a velocity vector of a molten metal flow at the next time point when a magnetic pole is reversed, induced by a magnetic field, for explaining the principle of the present invention.
11 is a horizontal sectional view taken along the line VI-VI in FIG.
12 is a vertical sectional view taken along the line VII-VII in FIG.
FIG. 13 is a diagram showing a temporal change state of an applied current and molten steel flow velocity in the present invention.
FIG. 14 is a schematic plan view showing the relationship between a coil and a mold according to the present invention.
FIG. 15 is a schematic diagram showing a phase of a coil in the case of a moving magnetic field.
FIG. 16 is a schematic diagram showing the phase of a coil in the case of an oscillating magnetic field.
FIG. 17 is a schematic diagram showing a phase of a coil when a peak position of an oscillating magnetic field is locally moved.
FIG. 18 is another schematic diagram showing the phase of the coil when the peak position of the oscillating magnetic field is locally moved.
FIG. 19 is a horizontal sectional view schematically showing the continuous casting facility of the first embodiment.
FIG. 20 is a horizontal sectional view schematically showing a continuous casting facility according to a second embodiment.
FIG. 21 is a diagram showing the effect of the present invention.
FIG. 22 is a diagram showing an effect when a static magnetic field is superimposed according to the present invention.
[Explanation of symbols]
10 ... Mold
12 ... Immersion nozzle
20: Oscillating magnetic field generator
22 ... Comb-shaped iron core
24 ... Coil
26a, 26b ... AC power supply
28 ... magnetic pole
30 ... Static magnetic field generator
32 DC current
34… DC coil

Claims (11)

In a continuous casting method of steel to continuously cast molten steel supplied to a continuous casting mold,
By lowering the melting point of the inclusions in the molten steel, it is possible to prevent clogging of the nozzle that supplies the molten steel to the mold, and electromagnetically stir the molten steel in the mold during continuous casting without blowing inert gas from the nozzle. A continuous casting method for steel, characterized in that by reducing the surface defects of the slab. Upon electromagnetically stirring the molten steel in the mold,
Place three or more electromagnets in the mold long side direction of the continuous casting mold,
By substantially reversing the magnetic field generated by the adjacent coils, the oscillating electromagnetic field whose phase is substantially reversed acts on the molten steel,
The continuous casting method for steel according to claim 1, wherein a local flow is induced without causing the dendrite on the front surface of the solidification nucleus to break by an electromagnetic force. The magnetic field generated by the adjacent coils may be supplied with an alternating current having a substantially opposite phase to the adjacent coils, or an in-phase alternating current may be supplied by reversing the winding direction of the coils. 3. The method for continuously casting steel according to claim 2, wherein the steel is substantially reversed. 4. The method according to claim 2, wherein the magnetic flux density of the maximum alternating magnetic field is less than 1000 gauss. The method for continuously casting steel according to claim 2 or 3, wherein the frequency of the oscillating magnetic field is 1 Hz to 8 Hz. Upon electromagnetically stirring the molten steel in the mold,
Place three or more electromagnets in the mold long side direction of the continuous casting mold,
The continuous casting method for steel according to claim 1, wherein a peak position of the oscillating magnetic field is locally moved along a long side of the mold while generating an oscillating magnetic field by the electromagnets. The phase of three or more adjacent coils is n, 2n, n or n, 3n, 2n array portion (however, n = 60 ° or 120 ° for three-phase AC, n = 90 ° for two-phase AC) The continuous casting equipment for steel according to claim 6, wherein the steel has a continuous casting. The method according to claim 2, wherein a static magnetic field is superimposed on the oscillating magnetic field in a thickness direction of the mold. The molten steel in which the inclusions have a low melting point contains C ≦ 0.020 wt%, Si ≦ 0.2 wt%, Mn ≦ 1.0 wt%, S ≦ 0.050 wt%, Ti ≧ 0.010 wt%, and Al ≦ 2. The continuous casting method for steel according to claim 1, wherein the steel is an ultra low carbon Ti deoxidized steel having a composition satisfying a condition of (wt% Ti) / 5. In producing the molten steel, the molten steel is first decarburized by a vacuum degassing device, then deoxidized by a Ti-containing alloy, and then one or more of Ca ≧ 10 wt% and REM ≧ 5 wt% in the deoxidized molten steel. By adding an alloy for adjusting the composition of inclusions containing two or more of one or more selected from Fe, Al, Si and Ti, the oxide composition in the molten steel is reduced to 90 wt% of Ti oxide. hereinafter, CaO, at 50wt% or less at least any one of content than 10 wt% of REM oxides, the continuous casting of steel according to claim _{9, Al} 2 _{O 3} is characterized by the following 70 wt% Method. Prior to the deoxidizing treatment with the Ti-containing alloy, the molten steel after the decarburizing treatment is preliminarily deoxidized with any of Al, Si, and Mn to reduce the dissolved oxygen concentration in the molten steel to 200 ppm or less in advance. The method for continuously casting steel according to claim 10, wherein:

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