JP2010274299A

JP2010274299A - Continuous casting method for steel

Info

Publication number: JP2010274299A
Application number: JP2009128396A
Authority: JP
Inventors: Tetsuo Mochida; 哲男持田; Takeshi Murai; 剛村井; Yuji Miki; 祐司三木
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2009-05-28
Filing date: 2009-05-28
Publication date: 2010-12-09
Anticipated expiration: 2029-05-28
Also published as: JP5348406B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting method for steel where, utilizing a static magnetic field more excellent in flowing control than the conventional static magnetic field, the flowing of molten steel in a mold is braked, thus the distribution in the width direction of a slab at a solidification completion position is controlled so as to be more precisely compared with the conventional one, in this way, the effect of light rolling reduction is sufficiently made to appear, and a slab in which central segregation is slight is cast. <P>SOLUTION: First electromagnets 19, 20 applying static magnetic fields are split into two in the width direction of a mold with the installing position of an immersion nozzle 4 or the vicinity thereof as a boundary, and are arranged so as to be confronted with the back face of the mold, further, between the mold and the respective first electromagnets, second electromagnets 21 to 26 applying static magnetic fields are arranged in parallel to the width direction of the mold by two or more per first electromagnet, static magnetic fields are applied to the molten steel in the mold in such a manner that, regarding the respective first electromagnets and the second electromagnets, magnetic field intensities and polarities are independently controlled, and further, the slab is subjected to rolling reduction at a rolling reduction speed within the range of 0.6 to 1.5 mm/min from the point of time at which the solid phase ratio in the central part of the thickness in the slab is ≤0.4 at least to the point of time at which the solid phase ratio in the central part of the thickness in the slab reaches ≥0.7. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

本発明は、鋼の連続鋳造方法に関し、詳しくは、鋳型内溶鋼に静磁場を印加することにより凝固完了位置の鋳片幅方向分布を制御しながら凝固末期の鋳片を凝固収縮量に相当する程度の圧下量で圧下し、中心偏析の軽微な鋼の連続鋳造鋳片を製造する連続鋳造方法に関するものである。 The present invention relates to a steel continuous casting method, and more specifically, the slab at the end of solidification corresponds to the amount of solidification shrinkage while controlling the distribution in the slab width direction at the solidification completion position by applying a static magnetic field to the molten steel in the mold. The present invention relates to a continuous casting method for producing a continuous cast slab of light steel with a central segregation by reducing the amount by a reduction amount of a certain degree.

鋼の凝固過程では体積収縮（凝固収縮ともいう）が起こり、この収縮に伴って、連続鋳造鋳片の場合には、鋳片の引き抜き方向へ未凝固溶鋼が吸引されて流動する。凝固末期の未凝固相には十分な量の溶鋼が存在しないので、凝固収縮による、この吸引・流動に伴い、炭素、燐、硫黄などの溶質元素が濃縮されたデンドライト樹間の溶鋼（「濃化溶鋼」という）が流動を起こし、それが鋳片の厚み中心部に集積して凝固し、所謂、中心偏析が形成される。凝固末期の溶鋼が流動する要因としては、上記の凝固収縮の他に、溶鋼静圧によるロール間での鋳片バルジング（膨らみ）や、鋳片支持ロールのロールアライメントの不整合なども挙げられる。 In the solidification process of steel, volume shrinkage (also called solidification shrinkage) occurs. In the case of a continuous cast slab, unsolidified molten steel is sucked and flows in the drawing direction of the slab. Since there is not a sufficient amount of molten steel in the unsolidified phase at the end of solidification, the molten steel between dendritic trees (“concentrated”) is enriched with solute elements such as carbon, phosphorus and sulfur due to solidification shrinkage. ) Is caused to flow and accumulate at the thickness center of the slab and solidify to form so-called center segregation. Factors that cause the molten steel at the end of solidification to flow include, in addition to the above-described solidification shrinkage, slab bulging (swelling) between rolls due to the molten steel static pressure, and inconsistency in roll alignment of the slab support roll.

この中心偏析は、鋼製品、特に厚鋼板の品質を劣化させる。例えば、石油輸送用や天然ガス輸送用のラインパイプ材においては、サワーガスの作用により中心偏析を起点として水素誘起割れが発生し、また、海洋構造物、貯槽、石油タンクなどにおいても、同様の問題が発生する。しかも近年、鋼材の使用環境は、より低温下或いはより腐食環境下といった厳しい環境での使用を求められることが多く、鋳片の中心偏析を低減することの重要性は益々大きくなっている。 This central segregation deteriorates the quality of steel products, particularly thick steel plates. For example, in line pipe materials for oil transportation and natural gas transportation, hydrogen-induced cracking occurs from the center segregation due to the action of sour gas, and the same problem occurs in offshore structures, storage tanks, oil tanks, etc. Will occur. Moreover, in recent years, the use environment of steel materials is often required to be used in a severe environment such as a lower temperature or a more corrosive environment, and the importance of reducing the center segregation of the slab is increasing.

そこで、この中心偏析を防止する手段として、連続鋳造機の相対するロールとの間隔を鋳片引き抜き方向の下流側ほど狭くし、鋳片の引き抜き方向に沿って鋳片の厚み方向に圧下力を作用させて鋳片を凝固収縮量に相当する程度の圧下量で徐々に圧下し、鋳片中心部の体積を減少させ、鋳片の凝固収縮に起因して生じる濃化溶鋼の鋳片中心部への移動を防止する、所謂「軽圧下」が行われている（例えば特許文献１を参照）。 Therefore, as a means for preventing this center segregation, the distance from the opposing roll of the continuous casting machine is narrowed toward the downstream side in the slab drawing direction, and a reduction force is applied in the thickness direction of the slab along the drawing direction of the slab. The concentrated slab center part of the concentrated molten steel caused by the solidification shrinkage of the slab, reducing the volume of the slab center part by gradually reducing the volume of the slab center by reducing the volume of the slab. A so-called “light pressure reduction” is performed to prevent the movement to (see, for example, Patent Document 1).

鋳片に軽圧下を施す場合には、鋳片の凝固完了位置（「クレータエンド位置」ともいう）を、圧下ロールが配置された所謂「軽圧下帯」の範囲内またはその近傍に制御する必要があるとともに、スラブ鋳片（以下、単に「鋳片」とも記す）の場合には、鋳片幅方向の凝固完了位置を平坦状に制御することが重要となる。凝固完了位置が鋳片幅方向で異なると、軽圧下帯における圧下量が鋳片幅方向の各位置で異なってしまい、軽圧下量の少ない位置つまり凝固完了位置が鋳造方向に伸張した部位では、十分な圧下量が得られず、中心偏析を抑制できない場合が発生する。これは、軽圧下帯の圧下ロールは、設置スペースや設備コストの制限から、完全凝固した鋳片を圧延するほどの耐荷重を有しておらず、鋳片短辺以外の幅方向の一部分が完全凝固すると、この部分の変形抵抗が大きくなり、その他の部位にはそれ以降ほとんど圧下力が付与されなくなるからである。 When light reduction is applied to the slab, the solidification completion position of the slab (also referred to as “crater end position”) must be controlled within or near the so-called “light reduction zone” where the reduction roll is disposed. In the case of a slab slab (hereinafter also simply referred to as “slab”), it is important to control the solidification completion position in the slab width direction to be flat. If the solidification completion position is different in the slab width direction, the reduction amount in the light reduction zone will be different in each position in the slab width direction, and in the part where the light reduction amount is small, that is, the solidification completion position is extended in the casting direction, A sufficient amount of rolling reduction cannot be obtained and the center segregation cannot be suppressed. This is because the rolling roll of the light rolling belt does not have a load resistance enough to roll a completely solidified slab due to limitations on installation space and equipment cost, and a part in the width direction other than the short side of the slab is not. This is because, when completely solidified, the deformation resistance of this portion increases and almost no rolling force is applied to other portions thereafter.

そこで、鋳片幅方向における凝固完了位置を平坦化し、軽圧下の効果を鋳片幅方向全体に亘って発現させるべく、特許文献２には、凝固状態判定装置を用いて鋳片の凝固完了位置の鋳片幅方向形状を求め、当該形状に基づき、鋳型背面に設置した、鋳片の短辺側から浸漬ノズル側へ向かって水平方向に移動する移動磁界により発生する、浸漬ノズルからの溶鋼吐出流に対する制動力を調整して、凝固完了位置の鋳片幅方向形状を所定の形状に制御しながら、軽圧下帯にて鋳片を軽圧下する連続鋳造方法が提案されている。この技術は、スラブ鋳片における凝固完了位置の鋳片幅方向形状は、主に鋳型内の溶鋼流動に起因しており、この鋳型内溶鋼流動を移動磁場により制御することで、凝固完了位置の鋳片幅方向形状を所定の形状に調整するという技術である。 Therefore, in order to flatten the solidification completion position in the slab width direction and to express the effect of light reduction over the entire slab width direction, Patent Document 2 discloses a solidification completion position of the slab using a solidification state determination device. The slab width direction shape of the molten steel is discharged from the immersion nozzle, which is generated by a moving magnetic field that moves in the horizontal direction from the short side of the slab toward the immersion nozzle side, based on the shape. There has been proposed a continuous casting method in which the slab is lightly squeezed with a lightly squeezed belt while adjusting the braking force against the flow to control the slab width direction shape at the solidification completion position to a predetermined shape. In this technology, the shape in the slab width direction at the solidification completion position in the slab slab is mainly due to the flow of molten steel in the mold. This is a technique of adjusting the slab width direction shape to a predetermined shape.

特許文献２によって、スラブ鋳片における凝固完了位置の鋳片幅方向形状が比較的容易に制御可能となり、凝固完了位置の鋳片幅方向形状は従来に比べて大幅に改善された。しかしながら、特許文献２では、浸漬ノズルからの溶鋼吐出流の吐出方向とは逆向きに移動する移動磁場による制動力を利用して鋳型内の溶鋼流動を制御しており、移動磁場は静磁場に比較して制動力が弱く、鋳型内の溶鋼流動が十分に抑制されない恐れがあった。また、所望する制動力を得ようとすると、静磁場に比較して多大のエネルギーを費やす必要があった。 According to Patent Document 2, the slab width direction shape at the solidification completion position in the slab slab can be controlled relatively easily, and the slab width direction shape at the solidification completion position has been greatly improved as compared with the prior art. However, in Patent Document 2, the flow of molten steel in the mold is controlled by using a braking force generated by a moving magnetic field that moves in the direction opposite to the discharge direction of the molten steel discharge flow from the immersion nozzle. In comparison, the braking force was weak, and there was a fear that the molten steel flow in the mold was not sufficiently suppressed. In addition, in order to obtain a desired braking force, it is necessary to spend much energy compared to a static magnetic field.

ところで、連続鋳造機の鋳型内の溶鋼流動を制動（減速）する手段として、一般的に、静磁場が利用されている。例えば、特許文献３には、鋳型の幅方向全域において静磁場を印加し、浸漬ノズルから鋳型内に供給される溶鋼の吐出流を制動する技術が開示され、特許文献４には、鋳型の幅方向全域に亘って静磁場を印加して溶鋼流動を制御する際に、浸漬ノズルの吐出孔近傍の磁場強度を相対的に小さくする技術が開示され、特許文献５には、鋳型の幅方向全域に亘って静磁場を印加して溶鋼流動を制御する際に、浸漬ノズルの吐出孔近傍の磁場強度を相対的に大きくする技術が開示されている。 Incidentally, a static magnetic field is generally used as means for braking (decelerating) the flow of molten steel in the mold of a continuous casting machine. For example, Patent Document 3 discloses a technique in which a static magnetic field is applied in the entire width direction of the mold to brake the discharge flow of molten steel supplied from the immersion nozzle into the mold, and Patent Document 4 discloses the width of the mold. When a static magnetic field is applied over the entire direction to control the flow of molten steel, a technique for relatively reducing the magnetic field strength in the vicinity of the discharge hole of the immersion nozzle is disclosed, and Patent Document 5 discloses the entire region in the width direction of the mold. A technique for relatively increasing the magnetic field strength in the vicinity of the discharge hole of the immersion nozzle when applying a static magnetic field to control the flow of molten steel is disclosed.

また、特許文献６には、複数の鉄心とそれらを取り巻く１個のコイルとからなる、静磁場を発生するための電磁石を鋳型長辺背面に相対させて配置し、分割した各鉄心を、鋳型長辺との間隔がそれぞれ異なるように移動させることにより、鋳型内溶鋼に印加される磁場強度を変化させる技術が開示されている。 In Patent Document 6, an electromagnet for generating a static magnetic field, which is composed of a plurality of iron cores and a single coil surrounding them, is disposed relative to the back side of the long side of the mold, and the divided iron cores are molded. A technique is disclosed in which the magnetic field strength applied to the molten steel in the mold is changed by moving the gaps with the long sides so as to be different from each other.

特開昭５４−１０７８３１号公報JP 54-107831 A 特開２００４−３５１４８１号公報JP 2004-351482 A 特開平２−２８４７５０号公報JP-A-2-284750 特開２００３−１１７６３６号公報JP 2003-117636 A 特開平１０−２６３７６３号公報JP-A-10-263766 特開平８−７１７１７号公報JP-A-8-71717

鋳型内の溶鋼流動を制動する手段として、静磁場は移動磁場に比較して効果的であり、移動磁場に替えて静磁場を利用することで、凝固完了位置の鋳片幅方向分布はより均一に制御され、軽圧下による中心偏析低減効果がより一層発現される。しかしながら、従来の静磁場印加技術である特許文献３〜６には以下の問題点がある。 The static magnetic field is more effective than the moving magnetic field as a means to brake the molten steel flow in the mold. By using the static magnetic field instead of the moving magnetic field, the slab width direction distribution at the solidification completion position is more uniform. Therefore, the center segregation reducing effect by light pressure is further exhibited. However, Patent Documents 3 to 6 which are conventional static magnetic field application techniques have the following problems.

即ち、特許文献３の方法は、鋳型長辺幅方向で均一に静磁場を印加しており、浸漬ノズル吐出流による上昇反転流（吐出流が短辺側に衝突した後、短辺面に沿って鋳型上方に向かう溶鋼流）を制動すべくそれ相応の静磁場を印加すると、吐出流の影響の小さい鋳型長辺中央部では溶鋼流速が極端に遅くなってしまい、凝固シェルへの非金属介在物及び気泡の捕捉が増加する恐れがある。逆に、鋳型長辺中央部の溶鋼流速を所定速度にするために磁場強度を弱くすると、上昇反転流の制動が不可能となる。 That is, in the method of Patent Document 3, a static magnetic field is uniformly applied in the long side width direction of the mold, and the upward reversal flow due to the submerged nozzle discharge flow (after the discharge flow collides with the short side, along the short side surface). If a corresponding static magnetic field is applied to brake the molten steel flow toward the upper part of the mold, the flow velocity of the molten steel becomes extremely slow at the center of the long side of the mold where the influence of the discharge flow is small, and non-metallic inclusions in the solidified shell There is a risk of increased trapping of objects and bubbles. On the contrary, if the magnetic field strength is weakened in order to make the molten steel flow velocity at the center of the mold long side a predetermined speed, it becomes impossible to brake the upward reversal flow.

特許文献４及び特許文献５の方法は、鋳型幅方向で磁場強度を変化させることはできるが、磁場強度の鋳型幅方向分布は固定であり、鋳造条件の変化などに応じて鋳型幅方向で磁場強度を任意に変更することはできない。特に、浸漬ノズルの左右の吐出孔からの吐出流に偏流（アルミナの付着やアルミナによる閉塞などに起因して一方の吐出孔からの溶鋼流が強くなる現象）が発生しても、鋳型幅方向左右で不均一な磁場強度を印加することができず、偏流に対応した流動制御が実施できない。 The methods of Patent Literature 4 and Patent Literature 5 can change the magnetic field strength in the mold width direction, but the distribution of the magnetic field strength in the mold width direction is fixed, and the magnetic field strength in the mold width direction according to changes in casting conditions and the like. The intensity cannot be changed arbitrarily. In particular, even if there is a drift in the discharge flow from the left and right discharge holes of the immersion nozzle (a phenomenon in which the molten steel flow from one discharge hole becomes stronger due to alumina adhesion or clogging with alumina), the mold width direction It is impossible to apply a non-uniform magnetic field strength on the left and right, and flow control corresponding to drift cannot be performed.

また、特許文献６の方法は、鋳片幅方向の磁場強度が変更可能であるが、鉄心の数を増やせば増やすほど各鉄心から発生可能な磁力が小さくなり、鉄心を分割しない場合と比較して溶鋼に付与される磁場強度が小さくなる。また、磁場分布を変更するためには、各鉄心を前後に移動させるアクチュエーターなどが必要であり、設備構造が煩雑であり設備費が高くなる。また、移動する部位を有することから、故障発生の可能性が高い。 The method of Patent Document 6 can change the magnetic field strength in the slab width direction. However, as the number of iron cores is increased, the magnetic force that can be generated from each iron core becomes smaller, compared with the case where the iron core is not divided. Thus, the magnetic field strength applied to the molten steel is reduced. Further, in order to change the magnetic field distribution, an actuator or the like that moves each iron core back and forth is necessary, and the equipment structure is complicated and the equipment cost is increased. Moreover, since it has the site | part to move, possibility of a failure generation is high.

本発明は上記事情に鑑みてなされたもので、その目的とするところは、凝固完了位置の鋳片幅方向分布を鋳型内溶鋼の流動制御によって制御しながら、凝固末期の鋳片を凝固収縮量に相当する程度の圧下量で圧下する連続鋳造方法において、従来の移動磁場に替えて、しかも従来の静磁場よりも流動制御に優れた静磁場を利用して鋳型内の溶鋼流動を制動することで、凝固完了位置の鋳片幅方向形状を従来に比較して精度良く制御し、これにより軽圧下の効果を十分に発現させ、中心偏析の軽微な鋳片を鋳造することの可能な、鋼の連続鋳造方法を提供することである。 The present invention has been made in view of the above circumstances, and the object of the present invention is to control the slab width at the end of solidification while controlling the slab width direction distribution at the solidification completion position by flow control of the molten steel in the mold. In the continuous casting method that reduces the amount of reduction equivalent to the above, the molten steel flow in the mold is braked by using a static magnetic field that is superior to the conventional moving magnetic field and has better flow control than the conventional moving magnetic field. Therefore, it is possible to control the shape in the width direction of the slab at the solidification completion position with higher accuracy than before, and to fully exhibit the effect of light reduction, and to cast a small slab with central segregation. It is to provide a continuous casting method.

上記課題を解決するための第１の発明に係る鋼の連続鋳造方法は、鋳片全幅に亘って鋳片を貫通する静磁場を印加するための第１の電磁石を、鋳型内に溶鋼を注入する浸漬ノズルの設置位置またはその近傍を境として鋳型長辺幅方向に２つに分割して、鋳型長辺背面に鋳型長辺を挟んで相対させて配置するとともに、鋳型長辺とそれぞれの第１の電磁石との間に、鋳片を貫通する静磁場を印加するための第２の電磁石を、それぞれの第１の電磁石あたり２基以上、鋳型長辺幅方向に並べて配置し、それぞれの第１の電磁石及び第２の電磁石で独立して磁場強度及び極性を制御して鋳型内の溶鋼に静磁場を印加し、鋳型内の溶鋼流動を制御するとともに、鋳片の厚み中心部の固相率が０．４以下の時点から、少なくとも鋳片の厚み中心部の固相率が０．７以上になる時点まで、０．６〜１．５ｍｍ／分の範囲内の圧下速度で鋳片を圧下することを特徴とするものである。 The continuous casting method of steel according to the first invention for solving the above-mentioned problem is the injection of molten steel into the mold with the first electromagnet for applying a static magnetic field penetrating the slab over the entire width of the slab. The mold is divided into two in the mold long side width direction with the installation position of the immersion nozzle or the vicinity thereof as a boundary, and the mold long side is placed opposite to the mold long side on the back side of the mold long side. Two or more second electromagnets for applying a static magnetic field penetrating the slab between the two electromagnets are arranged in the mold long side width direction for each first electromagnet. The magnetic field strength and polarity are independently controlled by the electromagnet 1 and the second electromagnet to apply a static magnetic field to the molten steel in the mold to control the flow of the molten steel in the mold, and the solid phase at the center of the thickness of the slab From the time when the rate is 0.4 or less, at least the solid phase at the thickness center of the slab There to the point to be 0.7 or more, characterized in that reduction of the slab at a reduction rate in the range of 0.6 to 1.5 mm / min.

第２の発明に係る鋼の連続鋳造方法は、第１の発明において、前記鋳型長辺には、鋳型長辺温度を測定するための測温素子が鋳型長辺の幅方向に設置されており、この測温素子により測定される鋳型長辺温度の浸漬ノズル左右の平均値に基づいて前記第１の電磁石の磁場強度を制御し、測温素子により測定される鋳型長辺温度の温度分布に基づいて前記第２の電磁石の磁場強度及び極性を制御することを特徴とするものである。 In the continuous casting method for steel according to the second invention, in the first invention, a temperature measuring element for measuring the mold long side temperature is installed in the mold long side in the width direction of the mold long side. The magnetic field intensity of the first electromagnet is controlled based on the average value of the left and right of the immersion nozzle of the mold long side temperature measured by the temperature measuring element, and the temperature distribution of the mold long side temperature measured by the temperature measuring element is obtained. Based on this, the magnetic field intensity and polarity of the second electromagnet are controlled.

本発明によれば、連続鋳造機の鋳型内の溶鋼流動が適正に制御されて鋳型内の凝固シェル厚みが均一化し、これにより、凝固完了位置の鋳片幅方向の形状が平坦化し、軽圧下による中心偏析改善効果が鋳片幅方向全体で発現し、中心偏析の軽微な、内部品質に優れた鋳片を鋳造することが実現される。 According to the present invention, the flow of molten steel in the mold of a continuous casting machine is appropriately controlled, and the thickness of the solidified shell in the mold is made uniform, thereby flattening the shape in the slab width direction at the solidification completion position. The effect of improving the center segregation due to is manifested in the entire width direction of the slab, and it is possible to cast a slab having a small center segregation and excellent internal quality.

本発明を適用した垂直曲げ型のスラブ連続鋳造機の概略図である。It is the schematic of the vertical bending type slab continuous casting machine to which this invention is applied. 図１に示すスラブ連続鋳造機の鋳型部の概略側断面図である。It is a schematic sectional side view of the casting_mold | template part of the slab continuous casting machine shown in FIG. 図１に示すスラブ連続鋳造機の鋳型部の概略平面図である。It is a schematic plan view of the casting_mold | template part of the slab continuous casting machine shown in FIG. 鋳型長辺幅方向における鋳型銅板温度の分布をパターン別に示す図である。It is a figure which shows distribution of the mold copper plate temperature in a mold long side width direction according to a pattern. 鋳片幅方向における凝固完了位置の分布をパターン別に示す図である。It is a figure which shows distribution of the solidification completion position in a slab width direction according to a pattern. 本発明例における炭素の偏析度（Ｃi／Ｃo）の鋳片幅方向の分布を示す図である。It is a figure which shows distribution of the slab width direction of the segregation degree of carbon (Ci / Co) in the example of this invention. 比較例における炭素の偏析度（Ｃi／Ｃo）の鋳片幅方向の分布を示す図である。It is a figure which shows distribution of the slab width direction of the segregation degree of carbon (Ci / Co) in a comparative example.

以下、本発明を具体的に説明する。先ず、本発明に至った経緯について説明する。 The present invention will be specifically described below. First, the background to the present invention will be described.

本発明者らは、軽圧下の効果を鋳片幅方向全体に亘って発現させることを最終的な目的とし、凝固完了位置の鋳片幅方向分布を平坦化するためには、二次冷却帯における鋳片幅方向の冷却強度の制御のみでは十分ではなく、鋳型内における凝固シェル厚みを鋳片幅方向で均一にすることが極めて重要であるとの知見から、凝固完了位置の鋳片幅方向分布を平坦化するための最適な鋳型内溶鋼流動制御方法を検討した。 In order to flatten the slab width direction distribution at the solidification completion position, the present inventors have finally aimed to develop the effect of light pressure over the entire slab width direction. Control of the cooling strength in the slab width direction at the slab width is not sufficient, and it is extremely important to make the solidified shell thickness in the mold uniform in the slab width direction. The optimum molten steel flow control method in the mold for flattening the distribution was studied.

その結果、溶鋼流動の制動作用に優れた静磁場を利用することを必須条件とし、仮に、この静磁場の磁場強度を鋳型幅方向で任意に変更することが可能であれば、溶鋼流速の速い位置では、静磁場の強度を上げて溶鋼流動を制動して、凝固シェルへの溶鋼流動による入熱を抑制し、逆に、溶鋼流速が遅い位置では、静磁場の強度を下げて溶鋼流速を確保して、凝固シェルへの溶鋼流動による入熱を確保することで、凝固シェル厚みを鋳片幅方向で均一化でき、また、浸漬ノズルからの吐出流に偏流が発生した場合には、溶鋼吐出量の多い側の磁場強度を相対的に大きくするとともに、溶鋼吐出量の少ない側の磁場強度を相対的に小さくすることで、偏流の影響が抑えられ、凝固シェル厚みを鋳片幅方向で均一化できると考えた。即ち、鋳片幅方向で磁場強度の異なる静磁場を溶鋼流速に応じて印加することで、鋳片幅方向で均一な厚みの凝固シェルが形成されると考えた。 As a result, it is essential to use a static magnetic field that is excellent in the braking action of molten steel flow, and if the magnetic field strength of this static magnetic field can be arbitrarily changed in the mold width direction, the molten steel flow rate is fast. At the position, the strength of the static magnetic field is increased to brake the molten steel flow and the heat input due to the molten steel flow to the solidified shell is suppressed. Conversely, at the position where the molten steel flow velocity is slow, the strength of the static magnetic field is decreased to reduce the molten steel flow velocity. By securing the heat input by the molten steel flow to the solidified shell, the thickness of the solidified shell can be made uniform in the slab width direction, and if there is a drift in the discharge flow from the immersion nozzle, the molten steel By relatively increasing the magnetic field strength on the side with a large discharge amount and relatively decreasing the magnetic field strength on the side with a small discharge amount of molten steel, the influence of drift is suppressed, and the thickness of the solidified shell is reduced in the slab width direction. We thought that it could be made uniform. That is, it was considered that a solidified shell having a uniform thickness in the slab width direction was formed by applying a static magnetic field having a different magnetic field strength in the slab width direction according to the molten steel flow velocity.

このような磁場分布の静磁場を鋳型内の溶鋼に印加するために、先ず、鋳型内での幅方向の溶鋼流動が不均一化される主たる原因である偏流の抑制を目的に、鋳型幅の中央部、つまり浸漬ノズルが設置される位置またはその近傍を境として鋳型幅方向の左右に、それぞれ、鋳片の幅方向約半分に静磁場を印加することのできる電磁石（「第１の電磁石」と定義する）を１基づつ鋳型長辺背面に鋳型長辺を挟んで相対させて配置することとした。左右の第１の電磁石から印加する磁場強度を相対的に変えることで、左右非対称の偏流を抑制することが可能となる。 In order to apply a static magnetic field with such a magnetic field distribution to the molten steel in the mold, first of all, for the purpose of suppressing the drift that is the main cause of non-uniformity of the molten steel flow in the width direction in the mold, An electromagnet ("first electromagnet") that can apply a static magnetic field to the left and right in the mold width direction at the center, that is, at or near the position where the immersion nozzle is installed, about half the width direction of the slab. Are defined one by one on the back side of the long side of the mold, with the long side of the mold facing each other. By relatively changing the intensity of the magnetic field applied from the left and right first electromagnets, it is possible to suppress left-right asymmetric drift.

更に、第１の電磁石を用いて左右のマクロ的な偏流を抑止した上で、鋳型長辺とそれぞれの第１の電磁石との間に、鋳型長辺幅方向に２基以上の電磁石（「第２の電磁石」と定義する）を配置することとした。鋳型内溶鋼に印加される磁場を強くする場合には、第１の電磁石と第２の電磁石との極性を同一として静磁場を印加し、溶鋼に印加される磁場を弱くする場合には、第１の電磁石と第２の電磁石との極性を逆として静磁場を印加し、また、第１の電磁石で印加される磁場強度を維持する場合には、第２の電磁石からの印加を止めることで、鋳型長辺幅方向における磁場強度分布を変えることが可能となる。つまり、鋳片幅方向各位置の溶鋼流速に応じて磁場強度を調整可能となる。電磁石をこのようにして配置することで、効果的な流動制御が可能になると考えた。 Further, the first electromagnet is used to suppress left and right macroscopic drift, and two or more electromagnets (“first” are arranged between the mold long side and each of the first electromagnets in the mold long side width direction. 2 ”), which is defined as“ 2 electromagnets ”. When the magnetic field applied to the molten steel in the mold is strengthened, the first and second electromagnets have the same polarity, the static magnetic field is applied, and when the magnetic field applied to the molten steel is weakened, When applying a static magnetic field with the polarity of the first electromagnet and the second electromagnet reversed, and when maintaining the magnetic field strength applied by the first electromagnet, stop the application from the second electromagnet. The magnetic field strength distribution in the mold long side width direction can be changed. That is, the magnetic field strength can be adjusted according to the molten steel flow velocity at each position in the slab width direction. We thought that effective flow control would be possible by arranging the electromagnet in this way.

その効果を検証するために、実機スラブ連続鋳造機の１／４のサイズの低融点合金（Ｂｉ−Ｐｄ−Ｓｎ−Ｃｄ合金：融点７０℃）の連続鋳造実験装置を用い、鋳型内溶湯湯面（以下、「メニスカス」と記す）における溶融合金の流速を測定した。第１の電磁石は、浸漬ノズルの吐出孔の直下に電磁石の上端位置が位置するように配置し、また、メニスカスでの流速の測定は、耐火物の小片ブロックを溶融合金中に浸漬させ、これに働くトルクを測定し、測定されるトルクから流速を換算した。 In order to verify the effect, the molten metal surface in the mold was used using a continuous casting experimental device of a low melting point alloy (Bi-Pd-Sn-Cd alloy: melting point 70 ° C) of 1/4 size of an actual slab continuous casting machine. The flow rate of the molten alloy was measured (hereinafter referred to as “meniscus”). The first electromagnet is arranged so that the upper end position of the electromagnet is located directly under the discharge hole of the immersion nozzle, and the flow velocity at the meniscus is measured by immersing a small block of refractory in the molten alloy. Torque acting on was measured, and the flow velocity was converted from the measured torque.

先ず、磁場を印加しない場合と、鋳型幅方向左右の第１の電磁石に同じ電流を流して鋳型幅方向に均一な静磁場を印加した場合とでメニスカスの流速を測定し、両者を比較した。その結果、メニスカスの流速は、静磁場を印加することで低減することが確認され、鋳型幅方向では、鋳型短辺近傍よりも浸漬ノズル近傍での流速の低減割合の方が大きいことが確認された。 First, the flow velocity of the meniscus was measured and compared between the case where no magnetic field was applied and the case where a uniform static magnetic field was applied in the mold width direction by applying the same current to the first electromagnets on the left and right of the mold width direction. As a result, it was confirmed that the meniscus flow rate was reduced by applying a static magnetic field, and in the mold width direction, it was confirmed that the rate of reduction of the flow rate near the immersion nozzle was larger than that near the mold short side. It was.

また、メニスカスの流速測定後に鋳型内部に冷却水を通水して鋳型を水冷し、鋳型内壁面に凝固シェルを生成させ、凝固シェル厚みを測定した。その結果、浸漬ノズルと鋳型長辺との間隙が最も小さくなる部位での凝固シェル厚みが、静磁場を印加しない場合に比較して厚くなっていたことから、静磁場を印加することによりこの部位の流速が極端に小さくなり、溶湯が滞留したと推定された。溶湯が滞留すると、その部位への新たな熱の供給が行われず、その部位での凝固シェル厚みが周囲に比べて増加する。また更に、静磁場の強度を低下させて実験したところ、鋳型短辺近傍の流速は静磁場を印加しない場合と比較して余り低下せず、鋳型短辺近傍の凝固シェル厚みは薄くなっていた。 Further, after measuring the meniscus flow rate, cooling water was passed through the mold to cool the mold, and a solidified shell was formed on the inner wall surface of the mold, and the thickness of the solidified shell was measured. As a result, the solidified shell thickness at the part where the gap between the immersion nozzle and the mold long side is the smallest was thicker than when no static magnetic field was applied. It was estimated that the melt flow rate became extremely small and the molten metal stayed. When the molten metal stays, new heat is not supplied to the site, and the thickness of the solidified shell at the site increases compared to the surrounding area. Furthermore, when the experiment was performed with the strength of the static magnetic field decreased, the flow velocity near the short side of the mold did not decrease much compared to the case where no static magnetic field was applied, and the thickness of the solidified shell near the short side of the mold was thin. .

即ち、これらの結果から、静磁場の強度調整により、凝固シェル厚みの制御が可能であることが示された。 That is, from these results, it was shown that the thickness of the solidified shell can be controlled by adjusting the strength of the static magnetic field.

そこで、鋳型長辺と第１の電磁石との間に、鋳型幅の１／６の幅を有する第２の電磁石を鋳型幅方向に３基（全体では６基）配置し、各第２の電磁石で極性及び磁場強度を独立して制御可能として実験した。メニスカスの流速を測定しながら第１及び第２の各電磁石の極性及び磁場強度をそれぞれ調整した結果、メニスカスの流速は鋳型幅方向のどの位置においてもほぼ一定の流速に制御できることが分かった。また、その条件下での凝固シェル厚みは、静磁場を印加しない場合及び鋳型幅方向に均一の静磁場を印加した場合に比較して、鋳型幅方向で均一化することが分かった。 Therefore, three second electromagnets having a width of 1/6 of the mold width are arranged between the long side of the mold and the first electromagnet in the mold width direction (6 in total), and each second electromagnet is arranged. In this experiment, the polarity and the magnetic field strength were controlled independently. As a result of adjusting the polarities and magnetic field strengths of the first and second electromagnets while measuring the meniscus flow rate, it was found that the meniscus flow rate can be controlled to be substantially constant at any position in the mold width direction. Further, it was found that the thickness of the solidified shell under the conditions was made uniform in the mold width direction as compared with the case where no static magnetic field was applied and the case where a uniform static magnetic field was applied in the mold width direction.

また、例えば浸漬ノズルの吐出孔の一方が付着物などにより流路が狭くなることで偏流が発生する場合を想定し、意図的に吐出孔の左右の吐出孔断面積を変更した試験も実施した。メニスカスの流速を測定しながら、メニスカスの流速が速い方の側（＝吐出孔断面積の大きい側）の磁場強度が大きくなるように、左右の第１の電磁石の磁場強度を調整することで、浸漬ノズル左右のメニスカスの流速をほぼ対称にすることができ、更には、第２の電磁石の極性及び磁場強度をそれぞれ調整することで、メニスカスの流速を鋳型幅方向のどの位置においてもほぼ一定の流速に制御できることが確認された。つまり、偏流が発生した場合であっても、鋳片幅方向で均一な流速に制御できることが分かった。 In addition, for example, assuming that one of the discharge holes of the immersion nozzle narrows the flow path due to deposits or the like, a flow is generated, and a test was performed by intentionally changing the left and right discharge hole cross-sectional areas of the discharge holes. . While measuring the meniscus flow rate, by adjusting the magnetic field strength of the left and right first electromagnets so that the magnetic field strength on the side where the meniscus flow rate is faster (= the side with the larger discharge hole cross-sectional area) becomes larger, The flow velocity of the meniscus on the left and right of the immersion nozzle can be made almost symmetrical, and furthermore, by adjusting the polarity and magnetic field strength of the second electromagnet, the meniscus flow velocity is almost constant at any position in the mold width direction. It was confirmed that the flow rate could be controlled. That is, it was found that even when a drift occurs, the flow rate can be controlled to be uniform in the slab width direction.

本発明は、上記検討結果に基づきなされたものであり、鋳片全幅に亘って鋳片を貫通する静磁場を印加するための第１の電磁石を、鋳型内に溶鋼を注入する浸漬ノズルの設置位置またはその近傍を境として鋳型長辺幅方向に２つに分割して、鋳型長辺背面に鋳型長辺を挟んで相対させて配置するとともに、鋳型長辺とそれぞれの第１の電磁石との間に、鋳片を貫通する静磁場を印加するための第２の電磁石を、それぞれの第１の電磁石あたり２基以上、鋳型長辺幅方向に並べて配置し、それぞれの第１の電磁石及び第２の電磁石で独立して磁場強度及び極性を制御して鋳型内の溶鋼に静磁場を印加し、鋳型内の溶鋼流動を制御するとともに、鋳片の厚み中心部の固相率が０．４以下の時点から、少なくとも鋳片の厚み中心部の固相率が０．７以上になる時点まで、０．６〜１．５ｍｍ／分の範囲内の圧下速度で鋳片を圧下することを特徴とする。 The present invention has been made based on the above examination results, and is provided with a submerged nozzle for injecting molten steel into a mold with a first electromagnet for applying a static magnetic field penetrating the slab over the entire width of the slab. It is divided into two in the mold long side width direction with the position or its vicinity as a boundary, and the mold long side is arranged opposite to the mold long side on the back side of the mold long side, and the mold long side and each of the first electromagnets In between, two or more second electromagnets for applying a static magnetic field penetrating the slab are arranged in the mold long side width direction for each first electromagnet, and each of the first electromagnet and the second electromagnet The magnetic field strength and polarity are independently controlled by the electromagnet 2 to apply a static magnetic field to the molten steel in the mold to control the flow of the molten steel in the mold, and the solid phase ratio at the thickness center of the slab is 0.4. From the following time point, the solid phase ratio of at least the thickness center of the slab is 0.7. To the point made above, characterized by rolling the slab at a reduction rate in the range of 0.6 to 1.5 mm / min.

鋳片の軽圧下は、鋳片厚み中心部の固相率が０．４以下の時点から開始し、少なくとも鋳片厚み中心部の固相率が０．７以上となる時点まで行う。これは、鋳片厚み中心部の固相率が０．４を越えてから軽圧下を開始しても、それ以前に濃化溶鋼の流動が発生する可能性があり、これにより中心偏析が発生し、軽圧下の効果を十分に発揮することができず、また、溶鋼の流動は、固相率が０．７未満では発生する可能性があり、それよりも早期に軽圧下を停止してしまうと、濃化溶鋼の流動が発生し、これにより中心偏析が発生して、軽圧下の効果を十分に発揮することができないからである。鋳片厚み中心部の固相率は、二次元伝熱凝固計算によって求めることができる。鋳片厚み中心部の固相率が１．０となる位置が凝固完了位置である。 The slab is lightly pressed at a time when the solid phase ratio at the center of the slab thickness is 0.4 or less and at least until the solid phase ratio at the center of the slab thickness is 0.7 or more. This is because, even if light reduction starts after the solid phase ratio at the center of the slab thickness exceeds 0.4, the flow of concentrated molten steel may occur before that, which causes center segregation. However, the effect of light pressure cannot be fully exhibited, and the flow of molten steel may occur when the solid phase ratio is less than 0.7, and the light pressure is stopped earlier than that. This is because the flow of the concentrated molten steel occurs, which causes central segregation, and the effect of light pressure cannot be fully exhibited. The solid phase ratio at the center of the slab thickness can be obtained by two-dimensional heat transfer solidification calculation. The position where the solid phase ratio at the center of the slab thickness is 1.0 is the solidification completion position.

また、軽圧下の圧下速度は０．６〜１．５ｍｍ／分の範囲内とすることが必要である。圧下速度が０．６ｍｍ／分未満の場合は圧下速度が凝固収縮量に対して小さ過ぎて、濃化溶鋼の流動を抑えることができない恐れがある。一方、圧下速度が１．５ｍｍ／分を超える場合は、圧下速度が凝固収縮量よりも大きくなり、濃化溶鋼を絞り出すことによって、鋳片中心部に負偏析を形成する恐れがあるからである。更に、軽圧下セグメントのベアリングへの荷重が高くなり、ベアリング寿命の観点からも望ましくない。また、中心偏析の改善のための軽圧下帯における総圧下量は２〜６ｍｍ程度とすれば十分である。 In addition, the reduction speed under light pressure needs to be in the range of 0.6 to 1.5 mm / min. When the rolling speed is less than 0.6 mm / min, the rolling speed is too small with respect to the solidification shrinkage, and there is a possibility that the flow of the concentrated molten steel cannot be suppressed. On the other hand, when the rolling speed exceeds 1.5 mm / min, the rolling speed becomes larger than the amount of solidification shrinkage, and squeezing the concentrated molten steel may cause negative segregation at the center of the slab. . Further, the load on the bearing of the lightly compressed segment is increased, which is not desirable from the viewpoint of bearing life. Moreover, it is sufficient that the total reduction amount in the light reduction zone for improving the center segregation is about 2 to 6 mm.

次いで、本発明の具体的な実施方法を、図面を参照して説明する。図１は、本発明を適用した垂直曲げ型のスラブ連続鋳造機の概略図、図２は、図１に示すスラブ連続鋳造機の鋳型部の概略側断面図、図３は、図１に示すスラブ連続鋳造機の鋳型部の概略平面図である。 Next, a specific implementation method of the present invention will be described with reference to the drawings. 1 is a schematic view of a vertical bending type slab continuous casting machine to which the present invention is applied, FIG. 2 is a schematic side sectional view of a mold part of the slab continuous casting machine shown in FIG. 1, and FIG. 3 is shown in FIG. It is a schematic plan view of the casting_mold | template part of a slab continuous casting machine.

図１に示すように、スラブ連続鋳造機１には、溶鋼９を注入して凝固させ、鋳片１０の外殻形状を形成するための鋳型５が設置され、この鋳型５の上方所定位置には、取鍋（図示せず）から供給される溶鋼９を鋳型５に中継供給するためのタンディッシュ２が設置されている。一方、鋳型５の下方には、サポートロール、ガイドロール及びピンチロールからなる複数対の鋳片支持ロール６が配置されている。鋳造方向に隣り合う鋳片支持ロール６の間隙には、水スプレーノズル或いはエアーミストスプレーノズルなどのスプレーノズル（図示せず）が配置された二次冷却帯が構成され、二次冷却帯のスプレーノズルから噴霧される冷却水（「二次冷却水」ともいう）によって鋳片１０は引き抜かれながら冷却されるようになっている。 As shown in FIG. 1, a slab continuous casting machine 1 is provided with a mold 5 for injecting and solidifying molten steel 9 to form an outer shell shape of a slab 10, and a predetermined position above the mold 5. Is provided with a tundish 2 for relaying and supplying molten steel 9 supplied from a ladle (not shown) to the mold 5. On the other hand, a plurality of pairs of slab support rolls 6 including a support roll, a guide roll, and a pinch roll are arranged below the mold 5. A secondary cooling zone in which a spray nozzle (not shown) such as a water spray nozzle or an air mist spray nozzle is arranged is formed in the gap between the slab support rolls 6 adjacent in the casting direction. The slab 10 is cooled while being drawn out by cooling water sprayed from the nozzle (also referred to as “secondary cooling water”).

タンディッシュ２の底部には、溶鋼９の流量を調整するためのスライディングノズル３が設置され、このスライディングノズル３の下面には、浸漬ノズル４が設置されている。また、鋳片支持ロール６の下流側には、鋳造された鋳片１０を搬送するための複数の搬送ロール７が設置されており、この搬送ロール７の上方には、鋳造される鋳片１０から所定の長さの鋳片１０ａを切断するための鋳片切断機８が配置されている。 A sliding nozzle 3 for adjusting the flow rate of the molten steel 9 is installed at the bottom of the tundish 2, and an immersion nozzle 4 is installed on the lower surface of the sliding nozzle 3. A plurality of transport rolls 7 for transporting the cast slab 10 are installed on the downstream side of the slab support roll 6. Above the transport roll 7, the cast slab 10 to be cast is provided. A slab cutting machine 8 for cutting a slab 10a having a predetermined length is disposed.

鋳片１０の凝固完了位置１３を挟んで鋳造方向の前後には、相対する鋳片支持ロール６とのロール間隔を鋳造方向下流に向かって順次狭くなるように設定された、複数対の鋳片支持ロール群から構成される軽圧下帯１４が設置されている。ここでは、その全域または一部選択した領域で、鋳片１０に軽圧下を行うことが可能である。軽圧下帯１４の各鋳片支持ロール間にも鋳片１０を冷却するためのスプレーノズルが配置されている。 A plurality of pairs of slabs that are set so that the roll interval between the slab support rolls 6 and the opposing slab support rolls 6 becomes narrower sequentially downstream in the casting direction across the solidification completion position 13 of the slab 10. A light pressure lower belt 14 composed of a support roll group is provided. Here, it is possible to perform light reduction on the slab 10 in the entire region or a partially selected region. A spray nozzle for cooling the slab 10 is also disposed between the slab support rolls of the light pressure lower belt 14.

相対する鋳片支持ロール６とのロール間隔を鋳造方向下流に向かって順次狭くなるように設定することを、「ロール勾配」とも呼んでおり、ロール勾配（単位：ｍｍ／ｍ）に鋳造速度（ｍ／分）を乗算した数値が圧下速度（ｍｍ／分）となる。従って、所定の圧下速度となるように、鋳造速度に応じてロール勾配を設定する。尚、図１では、軽圧下帯１４の範囲内に凝固完了位置１３が位置しているが、凝固完了位置１３が軽圧下帯１４の範囲内に位置することは必須ではなく、鋳片厚み中心部の固相率が０．７となる位置が軽圧下帯１４の範囲内に存在すればよい。また、軽圧下帯１４に配置される鋳片支持ロール６は「圧下ロール」とも呼ばれている。 Setting the roll interval with the opposing slab support roll 6 so as to become narrower in the downstream direction in the casting direction is also called “roll gradient”, and the casting speed (unit: mm / m) is set to the casting speed (unit: mm / m). The value obtained by multiplying m / min) is the reduction speed (mm / min). Accordingly, the roll gradient is set according to the casting speed so as to obtain a predetermined reduction speed. In FIG. 1, the solidification completion position 13 is located within the range of the light pressure lower belt 14, but it is not essential that the solidification completion position 13 is located within the range of the light pressure lower belt 14. It suffices that the position where the solid phase ratio of the portion is 0.7 exists within the range of the light pressure lower belt 14. Further, the slab support roll 6 disposed in the light reduction belt 14 is also called “a reduction roll”.

図２及び図３に示すように、鋳型５は、相対する一対の鋳型長辺５ａと、この鋳型長辺５ａに挟持された鋳型短辺５ｂとで構成され、鋳型長辺５ａの背面には、鋳型長辺５ａの中心位置、つまり浸漬ノズル４の設置位置を境として鋳片幅方向の左右に、鋳型長辺５ａの幅方向のほぼ半分を覆うように、それぞれ第１の電磁石１９及び第１の電磁石２０が配置されている。鋳型長辺５ａを挟んでそれぞれ相対する電磁石１９−１９間及び電磁石２０−２０間で、鋳型長辺５ａを貫通する静磁場が発生し、鋳型内の未凝固相１２には鋳片全幅に亘る静磁場が印加される。第１の電磁石１９及び第１の電磁石２０は、それぞれ独立して、極性及び磁場強度が調整できるように構成されている。ここで、「極性の調整」とは、例えば図３における上側の電磁石１９をＮ極とするかまたはＳ極とするかという意味である。当然ながら相対する下側の電磁石１９はその逆の極となる。 2 and 3, the mold 5 is composed of a pair of opposed mold long sides 5a and a mold short side 5b sandwiched between the mold long sides 5a. The first electromagnet 19 and the first electromagnet 19 and the second electromagnet 19 so as to cover almost half of the mold long side 5a in the width direction on the left and right in the slab width direction with the center position of the mold long side 5a, that is, the installation position of the immersion nozzle 4 as a boundary One electromagnet 20 is arranged. A static magnetic field penetrating the mold long side 5a is generated between the electromagnets 19-19 and the electromagnets 20-20 facing each other across the mold long side 5a, and the unsolidified phase 12 in the mold covers the entire slab width. A static magnetic field is applied. The first electromagnet 19 and the first electromagnet 20 are configured such that the polarity and the magnetic field strength can be adjusted independently. Here, “polarity adjustment” means, for example, whether the upper electromagnet 19 in FIG. 3 is an N pole or an S pole. Of course, the opposite lower electromagnet 19 is the opposite pole.

第１の電磁石１９及び第１の電磁石２０の鋳造方向設置位置は、目的によって変更すればよく、例えば、浸漬ノズル４の吐出孔４ａから吐出される溶鋼９の吐出流１５を直接制動しようとする場合には、吐出孔４ａの位置に設置すればよく、メニスカス１６の溶鋼流速を直接制御しようとする場合には、メニスカス１６の位置にすればよい。また、第１の電磁石を鋳造方向に複数段設置することもできる。 The position where the first electromagnet 19 and the first electromagnet 20 are installed in the casting direction may be changed depending on the purpose. For example, the discharge flow 15 of the molten steel 9 discharged from the discharge hole 4a of the immersion nozzle 4 is directly braked. In this case, it may be installed at the position of the discharge hole 4a. When the molten steel flow velocity of the meniscus 16 is to be directly controlled, the position of the meniscus 16 may be used. Further, the first electromagnet can be installed in a plurality of stages in the casting direction.

また、第１の電磁石１９と鋳型長辺５ａとの間には、鋳型長辺５ａを挟んで相対する第２の電磁石２１、電磁石２２、電磁石２３が配置され、同様に、第１の電磁石２０と鋳型長辺５ａとの間には、鋳型長辺５ａを挟んで相対する第２の電磁石２４、電磁石２５、電磁石２６が配置されている。ここでは、第１の電磁石１９及び第１の電磁石２０に対してそれぞれ３基の第２の電磁石が配置されているが、２基以上であればその数に制限はない。但し、設置数が増加すると第２の電磁石の寸法が小さくなり、コイルの巻き数が少なくなり、必要な磁場強度を印加できなくなる場合もあるので、必要とする磁場強度に基づき、第２の電磁石の寸法を定め、それにより設置数を決めることが好ましい。 Further, a second electromagnet 21, an electromagnet 22, and an electromagnet 23 are arranged between the first electromagnet 19 and the mold long side 5a so as to sandwich the mold long side 5a, and similarly, the first electromagnet 20 is disposed. The second electromagnet 24, the electromagnet 25, and the electromagnet 26 that are opposed to each other with the mold long side 5a interposed therebetween are arranged between the mold long side 5a and the mold. Here, three second electromagnets are arranged for each of the first electromagnet 19 and the first electromagnet 20, but the number is not limited as long as it is two or more. However, as the number of installations increases, the size of the second electromagnet decreases, the number of turns of the coil decreases, and the necessary magnetic field strength may not be applied. Therefore, the second electromagnet is based on the required magnetic field strength. It is preferable to determine the size of and to determine the number of installation.

第２の電磁石２１〜２６も、第１の電磁石１９、２０と同様に、それぞれ独立して、極性及び磁場強度が調整できるように構成されている。第２の電磁石の極性を第１の電磁石の極性と同一にすれば、鋳型内の未凝固相１２に印加される静磁場の強度が増し、逆に、第２の電磁石の極性を第１の電磁石の極性と逆にすれば、鋳型内の未凝固相１２に印加される静磁場の強度が小さくなる。 Similarly to the first electromagnets 19 and 20, the second electromagnets 21 to 26 are configured such that the polarity and the magnetic field strength can be adjusted independently. If the polarity of the second electromagnet is the same as the polarity of the first electromagnet, the strength of the static magnetic field applied to the unsolidified phase 12 in the mold increases, and conversely, the polarity of the second electromagnet is changed to the first electromagnet. If the polarity of the electromagnet is reversed, the strength of the static magnetic field applied to the unsolidified phase 12 in the mold is reduced.

第１の電磁石１９、２０及び第２の電磁石２１〜２６は、鋳型内の溶鋼流動を制御して鋳片幅方向で均一な凝固シェル１１を形成させるための装置であり、従って、鋳型内の溶鋼流動状況をオンラインで把握し、把握した溶鋼流動状況に応じて、印加する静磁場の極性及び磁場強度を調整することが重要となる。本発明では、鋳型内の溶鋼流動を把握するにあたって、鋳型長辺５ａの幅方向に埋め込んだ測温素子による鋳型長辺５ａの銅板温度に基づいて、鋳型内の溶鋼流動状況を把握する。 The first electromagnets 19 and 20 and the second electromagnets 21 to 26 are devices for controlling the flow of molten steel in the mold to form a uniform solidified shell 11 in the slab width direction. It is important to grasp the molten steel flow status online and adjust the polarity of the applied static magnetic field and the magnetic field strength in accordance with the grasped molten steel flow status. In the present invention, when the molten steel flow in the mold is grasped, the molten steel flow state in the mold is grasped based on the copper plate temperature of the mold long side 5a by the temperature measuring element embedded in the width direction of the mold long side 5a.

従って、鋳型長辺５ａには、メニスカス１６から鋳造方向に１０〜１３５ｍｍ離れた位置に測温素子１８が埋め込まれている。測温素子１８の設置位置が、メニスカス１６から鋳造方向に１０ｍｍ未満では、メニスカス１６の鋳造中の上下変動の影響を受けて銅板温度が変動し、溶鋼の流動に起因する温度変化を正確に把握できなく、一方、メニスカス１６から鋳造方向に１３５ｍｍを超えると、溶鋼流速の減衰が大きく、溶鋼流速に起因する銅板温度変化が把握しにくくなる。また、銅板温度の変化を精度良く検出するために、鋳型長辺５ａの溶鋼側表面から測温素子１８の先端までの距離は１５ｍｍ程度以下とし、銅板温度の鋳片幅方向分布を精度良く検出するために、測温素子１８の鋳型幅方向の設置間隔は２００ｍｍ以下とすることが好ましい。図２では、測温素子１８を鋳型長辺５ａの背面側から埋め込んでいるが、鋳型長辺５ａの上面側から細孔を開け、その中に測温素子１８を配置するようにしてもよい。図３では、測温素子１８を省略している。 Therefore, the temperature measuring element 18 is embedded in the long mold side 5a at a position 10 to 135 mm away from the meniscus 16 in the casting direction. If the position of the temperature measuring element 18 is less than 10 mm in the casting direction from the meniscus 16, the copper plate temperature fluctuates due to the vertical fluctuation during the casting of the meniscus 16, and the temperature change caused by the flow of molten steel is accurately grasped. On the other hand, if it exceeds 135 mm from the meniscus 16 in the casting direction, the molten steel flow velocity is greatly attenuated, and it becomes difficult to grasp the change in the copper plate temperature caused by the molten steel flow velocity. In addition, in order to detect the change in the copper plate temperature with high accuracy, the distance from the molten steel side surface of the mold long side 5a to the tip of the temperature measuring element 18 should be about 15 mm or less, and the slab width direction distribution of the copper plate temperature can be detected with high accuracy. Therefore, the installation interval of the temperature measuring element 18 in the mold width direction is preferably 200 mm or less. In FIG. 2, the temperature measuring element 18 is embedded from the back side of the mold long side 5a. However, a pore may be opened from the upper surface side of the mold long side 5a, and the temperature measuring element 18 may be disposed therein. . In FIG. 3, the temperature measuring element 18 is omitted.

ここで、本発明者らが、実機連続鋳造機の鋳造において調査した、鋳型長辺５ａの銅板温度分布と凝固完了位置１３の鋳片幅方向分布との関係を説明する。尚、凝固完了位置１３の鋳片幅方向形状は、鋳片１０に横波超音波を透過させる方法（例えば、特開２００６−２０８３９３号公報を参照）を用いて測定した。 Here, the relationship between the copper plate temperature distribution of the mold long side 5a and the slab width direction distribution of the solidification completion position 13 investigated by the present inventors in the casting of the actual continuous casting machine will be described. The shape in the width direction of the slab at the solidification completion position 13 was measured by using a method in which a transverse wave ultrasonic wave is transmitted through the slab 10 (see, for example, JP-A-2006-208393).

図４−Ａに示すように、浸漬ノズル内壁へのアルミナ付着により偏流が発生した場合には、鋳型長辺５ａの銅板温度は、鋳型幅方向左右の銅板温度絶対値に明らかな差が見られた（左右の銅板温度絶対値に差がある場合を「パターンＡ」という）。図４−Ａの場合、左側の吐出孔４ａが閉塞気味であり、右側の吐出孔４ａからの吐出流１５が強く、右側では鋳片短辺へ衝突した後の上昇反転流が強く、右側のメニスカス１６の溶鋼流速が増大し、その結果、右側の銅板温度が左側に比べて高くなったものである。このように、左右の銅板温度を比較することで、偏流の発生を検知することができる。 As shown in FIG. 4-A, when drift occurs due to alumina adhering to the inner wall of the immersion nozzle, the copper plate temperature of the mold long side 5a shows a clear difference between the absolute values of the copper plate temperatures on the left and right sides of the mold width direction. (The case where there is a difference between the absolute values of the temperature of the left and right copper plates is referred to as “pattern A”). In the case of FIG. 4-A, the discharge hole 4a on the left side is almost closed, the discharge flow 15 from the discharge hole 4a on the right side is strong, and the upward reversal flow after colliding with the short side of the slab is strong on the right side. The molten steel flow velocity of the meniscus 16 is increased, and as a result, the copper plate temperature on the right side is higher than that on the left side. Thus, the occurrence of drift can be detected by comparing the left and right copper plate temperatures.

また、鋳型幅方向左右の銅板温度がほぼ対称である場合にも、その分布は、図４−Ｂ（パターンＢ）、Ｃ（パターンＣ）、Ｄ（パターンＤ）に示すように、概ね３つのパターンに分類された。パターンＢは、幅中央部に比べて短辺側の銅板温度が高い場合、パターンＣは、鋳型幅方向にほぼ均一な温度分布である場合、パターンＤは、幅中央部の銅板温度が短辺側に比べて高い場合である。このような温度パターンになる原因は必ずしも明らかではないが、以下のように考えられる。 Further, even when the copper plate temperatures on the left and right sides in the mold width direction are substantially symmetrical, the distribution is roughly three as shown in FIGS. 4-B (pattern B), C (pattern C), and D (pattern D). Classified into patterns. When the pattern B has a higher copper temperature on the short side than the width center portion, the pattern C has a substantially uniform temperature distribution in the mold width direction, and the pattern D has a shorter copper plate temperature at the width center portion. It is a case that is higher than the side. The cause of such a temperature pattern is not necessarily clear, but is considered as follows.

即ち、パターンＢは、吐出流１５の短辺衝突後の上昇反転流が強く、そのために、両短辺側の溶鋼表面流速が大きくなっている場合である。この場合には、両短辺近傍の凝固シェル厚が薄くなる。パターンＣは、溶鋼流速が鋳型幅方向でほぼ均一になっている場合である。この場合には、凝固シェル１１の厚みが幅方向で均一になる。パターンＤは、鋳型内の溶鋼流動が全体的に不足していることに加え、浸漬ノズル４に吹き込まれたＡrガスの気泡により上昇流が形成され、鋳型幅方向中央部の銅板温度が相対的に高くなったと考えられる。この場合には、鋳型幅方向中央部の凝固シェル厚が薄くなる。 That is, the pattern B is a case where the upward reversal flow after the short side collision of the discharge flow 15 is strong, and therefore the molten steel surface flow velocity on both short sides is large. In this case, the thickness of the solidified shell near both short sides is reduced. Pattern C is a case where the molten steel flow velocity is substantially uniform in the mold width direction. In this case, the thickness of the solidified shell 11 becomes uniform in the width direction. In the pattern D, in addition to the fact that the molten steel flow in the mold is generally insufficient, an upward flow is formed by bubbles of Ar gas blown into the immersion nozzle 4, and the copper plate temperature at the center in the mold width direction is relatively It is thought that it became high. In this case, the thickness of the solidified shell at the center in the mold width direction is reduced.

上記の図４−Ａ、Ｂ、Ｃ、Ｄに示す銅板温度パターンとなった条件下で測定した凝固完了位置１３の鋳片幅方向分布の測定結果を図５−Ａ、Ｂ、Ｃ、Ｄに示す。図４と図５とのパターン符合は一致しており、銅板温度分布が例えば図４のパターンＡのときの凝固完了位置１３の鋳片幅方向分布が図５のパターンＡである。 4-A, B, C, and D show the measurement results of the slab width direction distribution at the solidification completion position 13 measured under the conditions of the copper plate temperature patterns shown in FIGS. Show. The pattern signs in FIG. 4 and FIG. 5 match, and the slab width direction distribution at the solidification completion position 13 when the copper plate temperature distribution is, for example, the pattern A in FIG. 4 is the pattern A in FIG.

図４及び図５を対比すると、概ね相対的に銅板温度の高かった幅方向位置に相当する部位の凝固完了位置１３が下流側に伸びた分布を呈することが分かる。即ち、鋳型内での溶鋼流動に起因する鋳型長辺５ａの銅板温度分布から、鋳型内での初期凝固シェル１１の形成を通じて凝固完了位置１３の鋳片幅方向分布を把握できること、更に、鋳型内の溶鋼流動を制御することで凝固完了位置１３の鋳片幅方向分布を制御できることが示された。また更に、凝固完了位置１３の鋳片幅方向分布が平坦となるパターンＣとなるように鋳型内の溶鋼流動を制御することが重要であることも分かった。 Comparing FIG. 4 and FIG. 5, it can be seen that the solidification completion position 13 of the portion corresponding to the position in the width direction where the copper plate temperature is relatively high exhibits a distribution extending downstream. That is, it is possible to grasp the slab width direction distribution at the solidification completion position 13 through the formation of the initial solidification shell 11 in the mold from the copper plate temperature distribution of the mold long side 5a due to the molten steel flow in the mold, It was shown that the distribution in the slab width direction at the solidification completion position 13 can be controlled by controlling the molten steel flow. Furthermore, it has been found that it is important to control the flow of molten steel in the mold so that the slab width direction distribution at the solidification completion position 13 becomes a pattern C that becomes flat.

第１の電磁石１９、２０及び第２の電磁石２１〜２６の具体的な運転方法は、例えば以下のようにして実施することができる。 The specific operation method of the first electromagnets 19 and 20 and the second electromagnets 21 to 26 can be implemented as follows, for example.

第１の電磁石１９及び第１の電磁石２０で偏流を制御する場合には、図４−Ａに示すように、鋳型長辺５ａの幅方向左右の平均値（Ｔr及びＴl）を求め、両者の差の絶対値（｜Ｔr−Ｔl｜）に基づき左右の第１の電磁石１９及び第１の電磁石２０の印加強度を制御する。つまり、平均温度の高い側の方を磁場強度を強くし、左右の磁場強度の差は両者の平均温度の差に基づく。また、第１の電磁石１９、２０は、鋳型内の全体の溶鋼流動を制御しており、偏流がない場合には、メニスカス１６における溶鋼流速が所定の値になるように、即ち、銅板温度の平均温度が鋳造速度で決まる所定の値になるように、第１の電磁石１９及び第１の電磁石２０から同一の磁場強度の静磁場を印加する。 When the drift is controlled by the first electromagnet 19 and the first electromagnet 20, as shown in FIG. 4-A, average values (Tr and Tl) in the width direction of the mold long side 5a are obtained. The applied intensity of the left and right first electromagnets 19 and the first electromagnet 20 is controlled based on the absolute value of the difference (| Tr−Tl |). That is, the magnetic field strength is increased on the higher average temperature side, and the difference between the left and right magnetic field strengths is based on the difference between the average temperatures of the two. The first electromagnets 19 and 20 control the flow of the entire molten steel in the mold. When there is no drift, the molten steel flow velocity in the meniscus 16 becomes a predetermined value, that is, the copper plate temperature is increased. A static magnetic field having the same magnetic field strength is applied from the first electromagnet 19 and the first electromagnet 20 so that the average temperature becomes a predetermined value determined by the casting speed.

第２の電磁石２１〜２６は、パターンＣに示すように、鋳型長辺５ａの銅板温度を鋳型幅方向で均一にする役割を担っており、溶鋼流速が速いつまり銅板温度が高い部位では、第１の電磁石１９または第１の電磁石２０と極性を同一として静磁場を印加し、磁場強度を増加させて溶鋼への制動力を高め、逆に、溶鋼流速が遅いつまり銅板温度が低い部位では、第１の電磁石１９または第１の電磁石２０と極性を逆として静磁場を印加し、磁場強度を減少させて溶鋼への制動力を弱める。このようにすることで、メニスカス１６の溶鋼流速が均一化され、凝固完了位置１３の鋳片幅方向分布が平坦化される。このように、第２の電磁石２１〜２６から印加する静磁場の磁場強度は鋳型銅板温度分布に基づくものとする。尚、溶鋼流動の制御を容易とするために、鋳型長辺５ａの幅方向左右の第２の電磁石毎に磁場強度を調整すればよい。つまり、例えば鋳型長辺右側の温度分布において、温度が相対的に高い位置では磁場強度を強くし、温度が相対的に低い位置では磁場強度を弱くし、これらの磁場強度の差は銅板温度の差に基づくものとする。 As shown in the pattern C, the second electromagnets 21 to 26 play a role of making the copper plate temperature of the mold long side 5a uniform in the mold width direction, and at a portion where the molten steel flow rate is high, that is, the copper plate temperature is high, Applying a static magnetic field with the same polarity as the first electromagnet 19 or the first electromagnet 20, increasing the magnetic field strength and increasing the braking force on the molten steel, conversely, at the site where the molten steel flow rate is slow, that is, the copper plate temperature is low, A static magnetic field is applied with the polarity opposite to that of the first electromagnet 19 or the first electromagnet 20 to decrease the magnetic field strength and weaken the braking force on the molten steel. By doing in this way, the molten steel flow velocity of the meniscus 16 is made uniform, and the slab width direction distribution at the solidification completion position 13 is flattened. Thus, the magnetic field strength of the static magnetic field applied from the second electromagnets 21 to 26 is based on the temperature distribution of the mold copper plate. In order to facilitate the control of the molten steel flow, the magnetic field strength may be adjusted for each second electromagnet on the left and right sides of the mold long side 5a in the width direction. That is, for example, in the temperature distribution on the right side of the mold long side, the magnetic field strength is increased at a position where the temperature is relatively high, and the magnetic field strength is decreased at a position where the temperature is relatively low. Based on the difference.

第１の電磁石１９、２０及び第２の電磁石２１〜２６は、制御装置（図示せず）により、自動的に上記のように運転するように構成されている。 The first electromagnets 19 and 20 and the second electromagnets 21 to 26 are configured to automatically operate as described above by a control device (not shown).

このように構成されるスラブ連続鋳造機１を用い、以下のようにして溶鋼９を連続鋳造する。 Using the slab continuous casting machine 1 configured as described above, the molten steel 9 is continuously cast as follows.

溶鋼９を取鍋（図示せず）からタンディッシュ２に注入し、タンディッシュ内の溶鋼量が所定量になったなら、スライディングノズル３を開き、浸漬ノズル４を介して溶鋼９を鋳型５に注入する。溶鋼９は、吐出孔４ａから鋳型短辺５ｂに向かう吐出流１５となって鋳型内に注入される。鋳型内に注入された溶鋼９は鋳型５で冷却され、凝固シェル１１を形成する。そして、鋳型内に所定量の溶鋼９が注入されたなら鋳片支持ロール６の内のピンチロールを駆動して、外殻を凝固シェル１１とし、内部に溶鋼９の未凝固相１２を有する鋳片１０の引き抜きを開始する。鋳片１０は、鋳片支持ロール６に支持されつつ下方に連続的に引き抜かれる。引き抜き開始後は、メニスカス１６の位置を鋳型内のほぼ一定位置に制御しながら、鋳造速度を増速して所定の鋳造速度とする。メニスカス１６の上にはモールドパウダー１７を添加する。モールドパウダー１７は溶融して、溶鋼９の酸化防止や、凝固シェル１１と鋳型５との間に流れ込んで潤滑剤としての効果を発揮する。 When the molten steel 9 is poured from a ladle (not shown) into the tundish 2 and the amount of molten steel in the tundish reaches a predetermined amount, the sliding nozzle 3 is opened and the molten steel 9 is put into the mold 5 via the immersion nozzle 4. inject. The molten steel 9 is injected into the mold as a discharge flow 15 from the discharge hole 4a toward the mold short side 5b. The molten steel 9 injected into the mold is cooled by the mold 5 to form a solidified shell 11. Then, when a predetermined amount of molten steel 9 is injected into the mold, the pinch roll in the slab support roll 6 is driven to make the outer shell a solidified shell 11 and the casting having an unsolidified phase 12 of the molten steel 9 inside. The drawing of the piece 10 is started. The slab 10 is continuously drawn downward while being supported by the slab support roll 6. After the start of drawing, the casting speed is increased to a predetermined casting speed while controlling the position of the meniscus 16 to a substantially constant position in the mold. Mold powder 17 is added on the meniscus 16. The mold powder 17 melts to prevent oxidation of the molten steel 9 and flows between the solidified shell 11 and the mold 5 to exert an effect as a lubricant.

鋳造速度が所定値になった以降、第１の電磁石１９、２０及び第２の電磁石２１〜２６は、測温素子１８によって測定される銅板温度に基づき、鋳型内の溶鋼９に静磁場を印加する。静磁場の強度及び極性は、測温素子１８によって測定される銅板温度が変化すれば、それに応じて変化する。そして、鋳片１０は、二次冷却帯で冷却され、凝固シェル１１の厚みを増大して、軽圧下帯１４にて適宜な量の軽圧下量が付加され、凝固完了位置１３で中心部までの凝固を完了する。中心部まで凝固完了した鋳片１０を鋳片切断機８により切断して鋳片１０ａを得る。 After the casting speed reaches a predetermined value, the first electromagnets 19 and 20 and the second electromagnets 21 to 26 apply a static magnetic field to the molten steel 9 in the mold based on the copper plate temperature measured by the temperature measuring element 18. To do. If the copper plate temperature measured by the temperature measuring element 18 changes, the strength and polarity of the static magnetic field change accordingly. Then, the slab 10 is cooled in the secondary cooling zone, the thickness of the solidified shell 11 is increased, and an appropriate amount of light reduction is added in the light pressure lower zone 14, until the solidification completion position 13 reaches the center. Complete the coagulation. The slab 10 that has been solidified to the center is cut by a slab cutting machine 8 to obtain a slab 10a.

この場合、予め伝熱凝固計算などを用いて、種々の鋳造条件下における凝固シェル１１の厚み並びに鋳片厚み中心部の固相率を求めておき、軽圧下帯１４に入る時点での鋳片厚み中心部の固相率が０．４以下になるように、鋳造速度及び二次冷却水量などの鋳造条件を調整する。軽圧下を開始する時点の鋳片厚み中心部の固相率は０．４以下であればいくらであっても構わない。また、少なくとも鋳片１０の厚み中心部の固相率が０．７以上になる時点までは、鋳片１０の圧下を継続する。圧下速度が０．６〜１．５ｍｍ／分の範囲内になるように、予定する鋳造速度に応じてロール勾配を予め調整しておく。 In this case, the thickness of the solidified shell 11 under various casting conditions and the solid phase ratio at the center of the slab thickness are obtained in advance by using heat transfer solidification calculation and the slab at the time of entering the light pressure lower zone 14. The casting conditions such as the casting speed and the amount of secondary cooling water are adjusted so that the solid phase ratio at the thickness center portion is 0.4 or less. The solid phase ratio at the center of the slab thickness at the start of light reduction may be any amount as long as it is 0.4 or less. Further, the reduction of the slab 10 is continued at least until the solid phase ratio at the thickness center portion of the slab 10 becomes 0.7 or more. The roll gradient is adjusted in advance according to the expected casting speed so that the rolling speed falls within the range of 0.6 to 1.5 mm / min.

以上説明したように、本発明によれば、鋳型内の溶鋼流動が適正に制御されて鋳型内の凝固シェル厚みが均一化し、これにより、鋳片幅方向の凝固完了位置１３の形状が平坦化し、軽圧下による中心偏析改善効果が鋳片幅方向全体で発現し、中心偏析の軽微な、内部品質に優れた鋳片１０ａを鋳造することが実現される。 As described above, according to the present invention, the molten steel flow in the mold is properly controlled, and the thickness of the solidified shell in the mold is made uniform, thereby flattening the shape of the solidification completion position 13 in the slab width direction. The effect of improving the center segregation due to light reduction is manifested in the entire width direction of the slab, and it is possible to cast the slab 10a having a small center segregation and excellent internal quality.

尚、図１に示す連続鋳造機は垂直曲げ型連続鋳造機であるが、本発明は垂直曲げ型連続鋳造機に限定されるものではなく、湾曲型連続鋳造機であってもまた垂直型連続鋳造機であっても、上記と同様に本発明を適用することができる。 The continuous casting machine shown in FIG. 1 is a vertical bending type continuous casting machine. However, the present invention is not limited to the vertical bending type continuous casting machine. Even if it is a casting machine, this invention can be applied similarly to the above.

図１に示すスラブ連続鋳造機を用いて本発明を実施した本発明例を説明する。 An example of the present invention in which the present invention is implemented using the slab continuous casting machine shown in FIG. 1 will be described.

化学成分が、Ｃ：０．１５質量％、Ｓｉ：０．１５質量、Ｍｎ：１．０質量％、Ｐ：０．０１５質量％、Ｓ：０．００５質量％、Ｔｉ：０．０１質量％、sol.Ａｌ：０．０３質量％の中炭素鋼を、断面形状が、幅１９５０ｍｍ、厚み２５０ｍｍのスラブ鋳片に鋳造した。軽圧下帯におけるロール勾配を１ｍあたり０．５３ｍｍとし、鋳造速度は１．５ｍ／分とした。第１の電磁石からは最大０．１８テスラの静磁場が印加され、第２の電磁石からは、−０．０６（逆極性）〜＋０．０６（正極性）テスラの静磁場が印加される。測温素子としては熱電対を用い、メニスカスから５０ｍｍ下方の位置に５０ｍｍ間隔で設置した。 Chemical components are C: 0.15 mass%, Si: 0.15 mass, Mn: 1.0 mass%, P: 0.015 mass%, S: 0.005 mass%, Ti: 0.01 mass% , Sol.Al: 0.03% by mass of medium carbon steel was cast into a slab slab having a cross-sectional shape with a width of 1950 mm and a thickness of 250 mm. The roll gradient in the light pressure zone was 0.53 mm per meter, and the casting speed was 1.5 m / min. A maximum static magnetic field of 0.18 Tesla is applied from the first electromagnet, and a static magnetic field of -0.06 (reverse polarity) to +0.06 (positive polarity) Tesla is applied from the second electromagnet. A thermocouple was used as the temperature measuring element, and was installed at a 50 mm interval at a position 50 mm below the meniscus.

鋳型銅板温度が幅方向で均一になるように、つまりパターンＣとなるように、第１の電磁石及び第２の電磁石により鋳型内溶鋼に静磁場を印加するとともに、軽圧下帯で鋳片を圧下しながら軽圧下帯の範囲内で凝固させた。軽圧下帯入側での鋳片中心部の固相率は０．１であった。 A static magnetic field is applied to the molten steel in the mold by the first electromagnet and the second electromagnet so that the temperature of the mold copper plate becomes uniform in the width direction, that is, pattern C, and the slab is rolled down by a light rolling zone. The solution was solidified within the light pressure zone. The solid phase ratio at the center portion of the slab on the light pressure lower belt entrance side was 0.1.

また、比較のために、第１の電磁石及び第２の電磁石から鋳型内溶鋼に静磁場を印加せずに、その他の鋳造条件を同一とする鋳造（比較例）も実施した。 For comparison, casting (comparative example) was performed in which other casting conditions were the same without applying a static magnetic field from the first electromagnet and the second electromagnet to the molten steel in the mold.

鋳造後の鋳片から検査用の鋳片全幅試料を採取し、中心偏析を調査した。鋳片の厚み中心部から鋳片幅方向に１００ｍｍ間隔で５ｍｍ直径のドリルで切り粉を採取し、この切り粉を燃焼式炭素分析装置により定量分析して炭素濃度（Ｃi）を求め、炭素の偏析度（Ｃi／Ｃo）により中心偏析を評価した。ここで、Ｃoは、鋳片の厚み１／４位置から５ｍｍ直径のドリル採取した切り粉の炭素分析値であり、この値を代表値とした。 A slab full width sample for inspection was taken from the slab after casting, and center segregation was investigated. Chips are sampled with a 5 mm diameter drill at 100 mm intervals from the center of the slab thickness in the slab width direction, and the swarf is quantitatively analyzed by a combustion carbon analyzer to obtain a carbon concentration (Ci). Central segregation was evaluated by the degree of segregation (Ci / Co). Here, Co is a carbon analysis value of a cutting powder sampled by a 5 mm diameter drill from a ¼ thickness position of the slab, and this value was used as a representative value.

図６に、本発明例における炭素の偏析度（Ｃi／Ｃo）の鋳片幅方向の分布を示し、図７に、比較例における炭素の偏析度（Ｃi／Ｃo）の鋳片幅方向の分布を示す。 FIG. 6 shows the distribution of the carbon segregation degree (Ci / Co) in the slab width direction in the example of the present invention, and FIG. 7 shows the distribution of the carbon segregation degree (Ci / Co) in the slab width direction in the comparative example. Indicates.

図６及び図７を比較すると明らかなように、本発明例では偏析度（Ｃi／Ｃo）が鋳片幅方向で均一化され、しかも偏析度（Ｃi／Ｃo）が小さいことが分かる。これに対して、比較例では、鋳片短辺から２００〜３００ｍｍの領域において、偏析度（Ｃi／Ｃo）が高く、偏析が悪化していることが分かる。比較例の鋳型銅板温度分布は図４−Ｂに示すパターンＢであり、鋳型内溶鋼流動により短辺近傍の凝固シェル厚みが薄肉化し、短辺面から２００〜３００ｍｍの範囲の凝固完了位置が下流側に伸び、軽圧下の効果が得られなかったと考えられる。 6 and 7, it is clear that the segregation degree (Ci / Co) is uniform in the slab width direction and the segregation degree (Ci / Co) is small in the example of the present invention. In contrast, in the comparative example, the segregation degree (Ci / Co) is high in the region of 200 to 300 mm from the slab short side, and it can be seen that the segregation deteriorates. The mold copper plate temperature distribution of the comparative example is pattern B shown in FIG. 4-B. The solidified shell thickness near the short side is reduced by the molten steel flow in the mold, and the solidification completion position in the range of 200 to 300 mm from the short side surface is downstream. It is thought that the effect under light pressure was not obtained.

１スラブ連続鋳造機
２タンディッシュ
３スライディングノズル
４浸漬ノズル
４ａ吐出孔
５鋳型
５ａ鋳型長辺
５ｂ鋳型短辺
６鋳片支持ロール
７搬送ロール
８鋳片切断機
９溶鋼
１０鋳片
１１凝固シェル
１２未凝固相
１３凝固完了位置
１４軽圧下帯
１５吐出流
１６メニスカス
１７モールドパウダー
１８測温素子
１９、２０第１の電磁石
２１、２２、２３、２４、２５、２６第２の電磁石 DESCRIPTION OF SYMBOLS 1 Slab continuous casting machine 2 Tundish 3 Sliding nozzle 4 Immersion nozzle 4a Discharge hole 5 Mold 5a Mold long side 5b Mold short side 6 Cast piece support roll 7 Conveyance roll 8 Cast piece cutting machine 9 Molten steel 10 Cast piece 11 Solidified shell 12 Not yet Solidification phase 13 Solidification completion position 14 Light pressure lower zone 15 Discharge flow 16 Meniscus 17 Mold powder 18 Temperature measuring element 19, 20 First electromagnet 21, 22, 23, 24, 25, 26 Second electromagnet

Claims

鋳片全幅に亘って鋳片を貫通する静磁場を印加するための第１の電磁石を、鋳型内に溶鋼を注入する浸漬ノズルの設置位置またはその近傍を境として鋳型長辺幅方向に２つに分割して、鋳型長辺背面に鋳型長辺を挟んで相対させて配置するとともに、鋳型長辺とそれぞれの第１の電磁石との間に、鋳片を貫通する静磁場を印加するための第２の電磁石を、それぞれの第１の電磁石あたり２基以上、鋳型長辺幅方向に並べて配置し、それぞれの第１の電磁石及び第２の電磁石で独立して磁場強度及び極性を制御して鋳型内の溶鋼に静磁場を印加し、鋳型内の溶鋼流動を制御するとともに、鋳片の厚み中心部の固相率が０．４以下の時点から、少なくとも鋳片の厚み中心部の固相率が０．７以上になる時点まで、０．６〜１．５ｍｍ／分の範囲内の圧下速度で鋳片を圧下することを特徴とする、鋼の連続鋳造方法。 Two first electromagnets for applying a static magnetic field penetrating the slab over the entire width of the slab in the mold long side width direction at the position where the immersion nozzle for injecting molten steel is injected into the mold or in the vicinity thereof And is arranged so that the long side of the mold is opposed to the back of the long side of the mold, and a static magnetic field penetrating the slab is applied between the long side of the mold and each of the first electromagnets. Two or more second electromagnets are arranged side by side in the mold long side width direction for each first electromagnet, and the magnetic field strength and polarity are controlled independently by each first electromagnet and second electromagnet. A static magnetic field is applied to the molten steel in the mold to control the flow of molten steel in the mold, and at least the solid phase at the thickness center of the slab from the time when the solid phase ratio at the thickness center of the slab is 0.4 or less. Within the range of 0.6 to 1.5 mm / min until the rate reaches 0.7 or more Characterized by rolling the slab at a reduction rate, the continuous casting method of steel.

前記鋳型長辺には、鋳型長辺温度を測定するための測温素子が鋳型長辺の幅方向に設置されており、この測温素子により測定される鋳型長辺温度の浸漬ノズル左右の平均値に基づいて前記第１の電磁石の磁場強度を制御し、測温素子により測定される鋳型長辺温度の温度分布に基づいて前記第２の電磁石の磁場強度及び極性を制御することを特徴とする、請求項１に記載の鋼の連続鋳造方法。 In the mold long side, a temperature measuring element for measuring the mold long side temperature is installed in the width direction of the mold long side, and the average of the left and right of the immersion nozzle of the mold long side temperature measured by this temperature measuring element The magnetic field strength of the first electromagnet is controlled based on the value, and the magnetic field strength and polarity of the second electromagnet are controlled based on the temperature distribution of the mold long side temperature measured by the temperature measuring element. The steel continuous casting method according to claim 1.