JP7307339B2 - Rolling method for rectangular cross-section billet, continuous casting and rolling equipment, and rolling equipment - Google Patents

Rolling method for rectangular cross-section billet, continuous casting and rolling equipment, and rolling equipment Download PDF

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JP7307339B2
JP7307339B2 JP2019193462A JP2019193462A JP7307339B2 JP 7307339 B2 JP7307339 B2 JP 7307339B2 JP 2019193462 A JP2019193462 A JP 2019193462A JP 2019193462 A JP2019193462 A JP 2019193462A JP 7307339 B2 JP7307339 B2 JP 7307339B2
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billet
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JP2020075291A (en
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健二 山田
英夫 水上
寛 原田
悠衣 山下
透 明石
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Nippon Steel Corp
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本発明は、板製品の素材となる横断面形状が略矩形である鋼片を圧延する矩形断面鋼片の圧延方法、連続鋳造圧延設備及び圧延設備に関する。 TECHNICAL FIELD The present invention relates to a method for rolling rectangular cross-sectional steel billets, continuous casting and rolling equipment, and rolling equipment for rolling steel billets having a substantially rectangular cross-sectional shape, which are used as materials for plate products.

連続的に溶鋼を矩形断面の鋼片に凝固させる連続鋳造機において、従来から、鋼片の厚さ中央部分のポロシティーや偏析、柱状晶形成による内部欠陥や不均質な組織に起因する後続工程での鋼片割れや圧延中の板破断等、製品欠陥（表面欠陥や機械特性不良）の発生が課題となっている。 In a continuous casting machine that continuously solidifies molten steel into billets with a rectangular cross section, there have been problems with porosity and segregation in the central part of the thickness of the billet, internal defects due to the formation of columnar crystals, and subsequent processes caused by inhomogeneous structures. The problem is the occurrence of product defects (surface defects and mechanical property defects) such as billet cracking in rolling and plate breakage during rolling.

例えば、特許文献１には、鋼片中心が完全凝固後に、表層部と中心部との温度差に応じて圧下率（量）を規定して圧延することで、中心部組織を改善する方法が開示されている。この技術によれば、表層部と中心部との温度差が小さい場合に比べれば、鋼片中心部の静水圧応力が増大し、かつ塑性ひずみ量も増え、ポロシティー欠陥や中心偏析の改善が得られる。 For example, Patent Literature 1 discloses a method of improving the structure of the central part by rolling after the center of the billet is completely solidified, by specifying the reduction ratio (amount) according to the temperature difference between the surface layer and the central part. disclosed. Compared to when the temperature difference between the surface layer and the center is small, this technology increases the hydrostatic stress in the center of the billet, increases the amount of plastic strain, and improves porosity defects and center segregation. can get.

また、特許文献２には、幅中央部に厚肉部を有する異形断面鋼片を、鋼片中心部が完全凝固した後に圧下することで中心偏析を低減する技術が開示されている。当該技術では、鋼片の異形断面化によって、上述の特許文献１に開示された技術と比較して、鋼片中心部では圧延による塑性ひずみが増大し、かつ、静水圧応力も増大するため、中心部の組織が改善する。 Further, Patent Literature 2 discloses a technique for reducing center segregation by reducing a deformed section steel billet having a thick portion at the center of the width thereof after the center of the billet has completely solidified. In this technique, the deformed cross section of the steel slab increases the plastic strain due to rolling at the center of the steel slab and also increases the hydrostatic stress, compared to the technology disclosed in the above-mentioned Patent Document 1. The organization of the core is improved.

さらに、特許文献３には、金属板の平坦度制御に関する技術として、熱間圧延の仕上圧延機内または出側において、金属板の板幅方向に不均一な表面温度分布を生じさせることにより、見かけ上の波形状発生限界の臨界座屈応力を向上させ、金属板の冷却後の平坦度を改善する技術が開示されている。 Furthermore, in Patent Document 3, as a technique for controlling the flatness of a metal plate, an apparent Techniques have been disclosed for improving the critical buckling stress of the upper corrugation generation limit and improving the flatness of the metal plate after cooling.

また、特許文献４には、複数台のミルスタンド間に設けられ、特定のまたは各リバース圧延中に鋼板長手方向及び幅方向の加熱昇温を実施する誘導加熱装置を備えた圧延設備が開示されている。 In addition, Patent Document 4 discloses a rolling facility equipped with an induction heating device that is provided between a plurality of mill stands and performs heating in the longitudinal direction and the width direction of the steel plate during specific or each reverse rolling. ing.

特開２００４－２３７２９１号公報Japanese Patent Application Laid-Open No. 2004-237291 特開２０１６－０１６４５０号公報JP 2016-016450 A 特許第４３９２１１５号公報Japanese Patent No. 4392115 特許第６３６２１５１号公報Japanese Patent No. 6362151

しかし、上記特許文献１に関しては、通常、表層部と中心部との温度差は表面の熱伝達係数及び鋼片厚でほぼ決まり、また、圧下量は鋼片厚と、製品厚からほぼ設定される中間製品（通常、粗バーと呼ばれる）の厚さとの差で圧下量の上限が制約される。このため、十分な圧下量が実現できない場合も多く、圧下量の不足に起因して、特に厚さが大きい製品を製造する際には、十分な組織や品質の改善効果が得られないことが多い。 However, with respect to Patent Document 1, the temperature difference between the surface layer and the central portion is generally determined by the heat transfer coefficient of the surface and the billet thickness, and the reduction amount is generally set by the billet thickness and the product thickness. The difference in thickness of the intermediate product (usually called a rough bar) limits the upper limit of the reduction. For this reason, there are many cases where a sufficient amount of reduction cannot be achieved, and due to the lack of amount of reduction, when manufacturing a product with a particularly large thickness, a sufficient effect of improving the structure and quality may not be obtained. many.

また、上記特許文献２では、表層から鋼片厚の１／４の位置から表層近傍で生じる塑性ひずみが激減し、柱状晶組織が残留する。このため、当該部分での偏析は極めて悪化する。また、異形断面鋼片を連続鋳造すること自体が難しく、設備コストも膨大になる。 In addition, in Patent Document 2, the plastic strain generated in the vicinity of the surface layer from the position of 1/4 of the thickness of the billet from the surface layer is drastically reduced, and the columnar crystal structure remains. For this reason, segregation in this portion is extremely aggravated. Moreover, continuous casting of deformed cross-section steel billets itself is difficult, and the equipment cost is enormous.

さらに、上記特許文献３に記載の技術では、金属板の冷却後の平坦度を改善することは可能であるが、ポロシティー低減あるいは細粒化等の内部品質の改善については考慮されておらず、かかる技術による内部品質の改善は見込めない。 Furthermore, in the technique described in Patent Document 3, although it is possible to improve the flatness of the metal plate after cooling, it does not consider the improvement of internal quality such as porosity reduction or grain refinement. , improvement of internal quality by such technology is not expected.

また、上記特許文献４によれば、圧延前の幅方向および長手方向の温度分布を意図的に調整することは可能である。かかる誘導加熱装置による調整は、圧延中に生じる温度低下を補償するためのものであることから、目標とする温度分布は基本的に均一である。つまり、特許文献４においてもまた、圧延によってポロシティー低減あるいは細粒化等の内部品質を改善することは期待しがたい。 Further, according to Patent Document 4, it is possible to intentionally adjust the temperature distribution in the width direction and the longitudinal direction before rolling. Since the adjustment by the induction heating device is for compensating for the temperature drop that occurs during rolling, the target temperature distribution is basically uniform. In other words, in Patent Document 4 as well, it is difficult to expect that internal quality such as porosity reduction or grain refinement will be improved by rolling.

そこで、本発明は、上記問題に鑑みてなされたものであり、本発明の目的とするところは、鋼片の厚さ中央部分のポロシティーや偏析、及び柱状晶形成による内部欠陥や不均質な組織に起因する後続工程での鋼片割れや圧延中の板破断の発生を抑制し、表面欠陥や機械特性不良といった製品欠陥の発生を抑制することの可能な矩形断面鋼片の圧延方法、連続鋳造圧延設備及び圧延設備を提供することにある。 Therefore, the present invention has been made in view of the above-mentioned problems, and the purpose of the present invention is to solve the problem of internal defects and heterogeneity due to porosity and segregation in the central part of the thickness of a steel slab, and the formation of columnar crystals. Rolling method and continuous casting of rectangular cross-section billet that can suppress the occurrence of billet cracking in subsequent processes due to the structure and plate breakage during rolling, and suppress the occurrence of product defects such as surface defects and mechanical property defects. It is to provide rolling equipment and rolling equipment.

上記課題を解決するために、本発明のある観点によれば、横断面形状が略矩形の鋼片を圧延する矩形断面鋼片の圧延方法であって、圧延に先立ち、圧延ロールと接する鋼片の上下表面のうち少なくともいずれか一方を鋼片長手方向に間欠的に加熱または保熱して、鋼片長手方向に散在する局所加熱部を鋼片に形成し、局所加熱部が形成された鋼片を圧延する、矩形断面鋼片の圧延方法が提供される。 In order to solve the above problems, according to one aspect of the present invention, there is provided a method for rolling a rectangular cross-section steel billet for rolling a steel billet having a substantially rectangular cross-sectional shape, the steel billet being in contact with a rolling roll prior to rolling. At least one of the upper and lower surfaces of the billet is intermittently heated or retained in the longitudinal direction of the billet to form localized heated portions scattered in the longitudinal direction of the billet, and the billet with the locally heated portions formed A method for rolling a rectangular section billet is provided.

かかる圧延方法では、局所加熱部を、鋼片長手方向に周期的に形成してもよい。 In such a rolling method, the local heating portions may be formed periodically in the longitudinal direction of the billet.

また、かかる圧延方法では、局所加熱部は、鋼片厚さ方向における鋼片の表面からの局所加熱深さが、鋼片の厚さの０．０１倍以上０．４０倍以下の範囲内であり、圧延方向における局所加熱長さが、鋼片の厚さの０．０１倍以上１．５倍以下の範囲内にあるように形成してもよい。 Further, in this rolling method, the local heating part has a local heating depth from the surface of the billet in the billet thickness direction within the range of 0.01 times or more and 0.40 times or less of the thickness of the billet. Yes, the local heating length in the rolling direction may be in the range of 0.01 to 1.5 times the thickness of the billet.

さらに、かかる圧延方法では、局所加熱部は、当該局所加熱部の表面積が、圧延ロールと接する鋼片の上下表面の全表面積の０．０１倍以上０．５０倍以下の範囲内となるように形成してもよい。 Furthermore, in this rolling method, the surface area of the local heating part is in the range of 0.01 to 0.50 times the total surface area of the upper and lower surfaces of the billet in contact with the rolling rolls. may be formed.

また、かかる圧延方法では、局所加熱部は、鋼片が圧延される際の圧延ロールとの接触弧長の１／６０倍以上２倍以下の間隔を鋼片長手方向に有するように形成してもよい。 Further, in this rolling method, the local heating part is formed so as to have an interval in the longitudinal direction of the billet that is 1/60 to 2 times the arc length of contact with the rolling rolls when the billet is rolled. good too.

さらに、かかる圧延方法では、局所加熱部は、当該局所加熱部の温度が、圧延ロールに接する鋼片の表面の局所加熱部以外の部分の平均温度に対して＋１０℃以上であり、かつ、鋼片の融点温度未満となるように形成してもよい。 Furthermore, in this rolling method, the local heating part has a temperature of +10 ° C. or more with respect to the average temperature of the portion other than the local heating part on the surface of the steel slab in contact with the rolling roll, and the steel It may be formed to be below the melting point temperature of the piece.

局所加熱部は、鋼片幅方向に分散して形成されてもよい。 The local heating portions may be formed dispersedly in the width direction of the billet.

局所加熱部の幅は、鋼片の厚さの０．１倍以上であってもよい。 The width of the local heating portion may be 0.1 times or more the thickness of the billet.

鋼片を平面視したときの局所加熱部の形状は、鋼片幅方向に沿って延びる直線に対して交差する、斜線状、折れ線状、曲線状、周期関数状、または、千鳥状であってもよい。 When the billet is viewed from above, the shape of the local heating portion is oblique, polygonal, curved, periodic function, or zigzag that intersects a straight line extending along the width direction of the billet. good too.

局所加熱部は、鋼片のコーナー過冷部を含むように形成されてもよい。 Localized heating may be formed to include corner supercooling of the billet.

また、本発明の他の観点によれば、鋼片を鋳造する連続鋳造機と、連続鋳造機の下流側に配置され、連続鋳造機により鋳造された鋼片の上下表面のうち少なくともいずれか一方を鋼片長手方向に間欠的に加熱または保熱して、鋼片長手方向に散在する局所加熱部を鋼片に形成する加熱装置と、加熱装置の下流側に配置され、局所加熱部が形成された鋼片を圧延する圧延機と、を備える、連続鋳造圧延設備が提供される。 According to another aspect of the present invention, a continuous casting machine that casts a steel slab, and at least one of the upper and lower surfaces of the steel slab cast by the continuous casting machine and disposed downstream of the continuous casting machine. a heating device that intermittently heats or retains the heat in the longitudinal direction of the billet to form localized heated portions scattered in the longitudinal direction of the billet; and a rolling mill for rolling billets.

さらに、本発明の他の観点によれば、加熱炉にて加熱された鋼片の上下表面のうち少なくともいずれか一方を鋼片長手方向に間欠的に加熱または保熱して、鋼片長手方向に散在する局所加熱部を鋼片に形成する加熱装置と、加熱装置の下流側に配置され、局所加熱部が形成された鋼片を圧延する圧延機と、を備える、圧延設備が提供される。 Furthermore, according to another aspect of the present invention, at least one of the upper and lower surfaces of the billet heated in the heating furnace is intermittently heated or maintained in the longitudinal direction of the billet to A rolling facility is provided that includes a heating device for forming scattered localized hot spots in a billet, and a rolling mill located downstream of the heating device for rolling the billet with the localized hot spots.

以上説明したように本発明によれば、鋼片の厚さ中央部分のポロシティーや偏析、および柱状晶形成による内部欠陥や不均質な組織に起因する後続工程での鋼片割れや圧延中の板破断の発生を抑制し、表面欠陥や機械特性不良といった製品欠陥の発生を抑制することが可能となる。 As described above, according to the present invention, billet cracking in subsequent processes and strips during rolling due to internal defects and heterogeneous structures due to porosity and segregation in the central part of the thickness of the billet and columnar crystal formation It is possible to suppress the occurrence of breakage and suppress the occurrence of product defects such as surface defects and poor mechanical properties.

本発明の一実施形態に係る矩形断面鋼片の圧延方法を実施する連続鋳造圧延設備の一構成例を示す概略構成図である。BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram showing one configuration example of a continuous casting and rolling facility that implements a method for rolling a rectangular cross-section steel billet according to one embodiment of the present invention; 図１の連続鋳造圧延設備の一変形例を示す概略構成図である。It is a schematic block diagram which shows the example of a changed completely type of the continuous casting-rolling equipment of FIG. 同実施形態に係る矩形断面鋼片の圧延方法を実施する圧延設備の一構成例を示す概略構成図である。FIG. 2 is a schematic configuration diagram showing one configuration example of a rolling facility that implements the method for rolling a rectangular cross-section steel billet according to the same embodiment. 局所加熱部が形成された鋼片を圧延したときの圧延ロールとの接触領域下とその近傍における鋼片内部の塑性変形の状態を示す概念図である。FIG. 4 is a conceptual diagram showing the state of plastic deformation inside the steel slab under and near the contact region with the rolling rolls when the steel slab in which the localized heating portion is formed is rolled. 局所加熱部の有無による、ロールバイト及びその近傍での鋼片の厚さ中央に生じる静水圧応力の分布を示す説明図である。FIG. 4 is an explanatory diagram showing the distribution of hydrostatic pressure stress generated at the center of the thickness of the billet at the roll bite and its vicinity, depending on the presence or absence of the local heating portion. 局所加熱部の有無による、圧延後の鋼片の厚さ中央位置及び表層から１／４厚さ位置における塑性ひずみの鋼片長手方向分布を示す説明図である。FIG. 4 is an explanatory diagram showing the distribution of plastic strain in the billet longitudinal direction at the thickness center position and the 1/4 thickness position from the surface layer of the billet after rolling, depending on the presence or absence of the local heating portion. 局所加熱深さを鋼片の厚さで除した値と塑性ひずみ増分との一関係例を示すグラフである。4 is a graph showing an example of the relationship between the value obtained by dividing the local heating depth by the thickness of the billet and the plastic strain increment. 局所加熱深さを鋼片の厚さで除した値と静水圧増分との一関係例を示すグラフである。5 is a graph showing an example of the relationship between the value obtained by dividing the local heating depth by the thickness of the billet and the hydrostatic pressure increment. 局所加熱長さを鋼片の厚さで除した値と塑性ひずみ増分との一関係例を示すグラフである。4 is a graph showing an example of the relationship between the value obtained by dividing the local heating length by the thickness of the billet and the plastic strain increment. 局所加熱長さを鋼片の厚さで除した値と静水圧増分との一関係例を示すグラフである。5 is a graph showing an example of the relationship between the value obtained by dividing the local heating length by the thickness of the billet and the hydrostatic pressure increment. 加熱面積率と塑性ひずみ増分との一関係例を示すグラフである。It is a graph which shows the relationship example of a heating area ratio and a plastic strain increment. 加熱面積率と静水圧増分との一関係例を示すグラフである。It is a graph which shows the relationship example of a heating area ratio and a hydrostatic pressure increment. 接触弧長を局所加熱部の間隔で除した値と塑性ひずみ増分との一関係例を示すグラフである。5 is a graph showing an example of the relationship between the value obtained by dividing the contact arc length by the spacing of the local heating portions and the plastic strain increment. 接触弧長を局所加熱部の間隔で除した値と静水圧増分との一関係例を示すグラフである。5 is a graph showing an example of the relationship between the value obtained by dividing the contact arc length by the spacing of the local heating portions and the hydrostatic pressure increment. 局所加熱部の温度上昇量と塑性ひずみ増分との一関係例を示すグラフである。It is a graph which shows the relationship example of the temperature rise amount of a local heating part, and a plastic strain increment. 局所加熱部の温度上昇量と静水圧増分との一関係例を示すグラフである。7 is a graph showing an example of the relationship between the temperature rise amount of the localized heating portion and the hydrostatic pressure increment. 鋼片幅方向に分散して形成された鋼片の局所加熱部の一例を示す説明図である。FIG. 5 is an explanatory view showing an example of locally heated portions of a steel billet formed dispersedly in the width direction of the billet; 鋼片幅方向に分散して形成された鋼片の局所加熱部の他の一例を示す説明図である。FIG. 10 is an explanatory view showing another example of locally heated portions of the billet formed dispersedly in the width direction of the billet; 局所加熱部の幅と塑性ひずみ増分との一関係を示すグラフである。4 is a graph showing the relationship between the width of a locally heated portion and the plastic strain increment. 局所加熱部の幅と静水圧増分との一関係例を示すグラフである。4 is a graph showing an example of the relationship between the width of the localized heating portion and the hydrostatic pressure increment; 鋼片幅方向に分散して形成された鋼片の局所加熱部の他の一例を示す説明図である。FIG. 10 is an explanatory view showing another example of locally heated portions of the billet formed dispersedly in the width direction of the billet; 鋼片幅方向に分散して形成された鋼片の局所加熱部の他の一例を示す説明図である。FIG. 10 is an explanatory view showing another example of locally heated portions of the billet formed dispersedly in the width direction of the billet; 鋼片幅方向に分散して形成された鋼片の局所加熱部の他の一例を示す説明図である。FIG. 10 is an explanatory view showing another example of locally heated portions of the billet formed dispersedly in the width direction of the billet; 鋼片幅方向に分散して形成された鋼片の局所加熱部の他の一例を示す説明図である。FIG. 10 is an explanatory view showing another example of locally heated portions of the billet formed dispersedly in the width direction of the billet; 鋼片幅方向に分散して形成された鋼片の局所加熱部の他の一例を示す説明図である。FIG. 10 is an explanatory view showing another example of locally heated portions of the billet formed dispersedly in the width direction of the billet; 鋼片幅方向に分散して形成された鋼片の局所加熱部の他の一例を示す説明図である。FIG. 10 is an explanatory view showing another example of locally heated portions of the billet formed dispersedly in the width direction of the billet; 鋼片幅方向に分散して形成された鋼片の局所加熱部の他の一例を示す説明図である。FIG. 10 is an explanatory view showing another example of locally heated portions of the billet formed dispersedly in the width direction of the billet; 鋼片幅方向に分散して形成された鋼片の局所加熱部の他の一例を示す説明図である。FIG. 10 is an explanatory view showing another example of locally heated portions of the billet formed dispersedly in the width direction of the billet; 鋼片のコーナー過冷部と局所加熱部との関係を示す説明図である。FIG. 4 is an explanatory diagram showing the relationship between a corner supercooled portion and a locally heated portion of a billet; 実施例２にて形成される局所加熱部を示す説明図である。FIG. 11 is an explanatory diagram showing a local heating portion formed in Example 2;

以下に添付図面を参照しながら、本発明の好適な実施の形態について詳細に説明する。なお、本明細書及び図面において、実質的に同一の機能構成を有する構成要素については、同一の符号を付することにより重複説明を省略する。 Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

＜１．設備構成＞
まず、図１及び図２に基づいて、本発明の一実施形態に係る矩形断面鋼片の圧延方法を実施する設備構成例を説明する。図１は、本実施形態に係る矩形断面鋼片の圧延方法を実施する連続鋳造圧延設備の一構成例を示す概略構成図である。図２は、本実施形態に係る矩形断面鋼片の圧延方法を実施する圧延設備の一構成例を示す概略構成図である。 <1. Equipment configuration>
First, based on FIGS. 1 and 2, an example of equipment configuration for carrying out a method for rolling a rectangular cross-section steel billet according to an embodiment of the present invention will be described. FIG. 1 is a schematic configuration diagram showing one configuration example of a continuous casting and rolling facility for carrying out a method for rolling a rectangular cross-section steel billet according to the present embodiment. FIG. 2 is a schematic configuration diagram showing one configuration example of a rolling facility for carrying out the method for rolling a rectangular cross-section steel billet according to the present embodiment.

［１－１．連続鋳造機により製造された鋼片の圧延］
本実施形態に係る矩形断面鋼片の圧延方法は、例えば図１に示すような連続鋳造圧延設備１により実施可能である。かかる連続鋳造圧延設備１は、例えば図１に示すように、鋼片５を鋳造する連続鋳造機１０と、加熱装置２０と、圧延機３０とを備える。なお、連続鋳造機１０によって製造される鋼片５の種類及びサイズは、特に限定されない。鋼片５は、例えばスラブ、ビレット及びブルームのいずれであってもよい。以下では、鋼片５の一例として、スラブを想定して説明する。 [1-1. Rolling of steel slabs produced by a continuous casting machine]
The method for rolling a rectangular cross-section steel billet according to the present embodiment can be carried out, for example, by a continuous casting and rolling facility 1 as shown in FIG. Such a continuous casting and rolling facility 1 includes, for example, a continuous casting machine 10 for casting billets 5, a heating device 20, and a rolling mill 30, as shown in FIG. The type and size of the billet 5 manufactured by the continuous casting machine 10 are not particularly limited. The billet 5 may be, for example, any of slabs, billets and blooms. In the following description, a slab is assumed as an example of the steel piece 5 .

（連続鋳造機）
連続鋳造機１０は、図１に示すように、連続鋳造用の鋳型１３を用いて溶融金属を連続鋳造し、スラブ等の鋼片５を製造するための装置である。連続鋳造機１０は、タンディッシュ１１と、浸漬ノズル１２と、鋳型１３と、二次冷却装置１４とを含む。 (continuous casting machine)
The continuous casting machine 10, as shown in FIG. 1, is an apparatus for continuously casting molten metal using a mold 13 for continuous casting to produce a billet 5 such as a slab. A continuous casting machine 10 includes a tundish 11 , a submerged nozzle 12 , a mold 13 and a secondary cooling device 14 .

タンディッシュ１１は、鋳型１３の上方に配置されており、取鍋（図示せず。）により搬送された溶融金属を貯蔵する。タンディッシュ１１では溶融金属を貯蔵している間に、溶融金属中の介在物を除去する。タンディッシュ１１の底部には、鋳型１３に溶融金属を供給する浸漬ノズル１２が設けられている。浸漬ノズル１２は、タンディッシュ１１にて介在物が除去された溶融金属を鋳型１３に連続供給する。 A tundish 11 is positioned above the mold 13 and stores molten metal conveyed by a ladle (not shown). While the molten metal is stored in the tundish 11, inclusions in the molten metal are removed. The bottom of the tundish 11 is provided with an immersion nozzle 12 for supplying molten metal to a mold 13 . The immersion nozzle 12 continuously supplies the molten metal from which inclusions have been removed in the tundish 11 to the mold 13 .

鋳型１３は、製造する鋼片５の幅及び厚さに応じて形成された略矩形状の中空を有する型枠である。鋳型１３は、例えば、４枚の水冷銅板からなる鋳型板を組み合わせて構成されている。浸漬ノズル１２を介して鋳型１３内に供給された溶融金属は、鋳型板と接触することで冷却され、外殻に溶融金属が凝固した凝固シェル５ａが形成される。外殻が凝固した状態で、鋼片５は鋳型１３から引き抜かれる。 The casting mold 13 is a mold having a substantially rectangular hollow formed according to the width and thickness of the steel billet 5 to be manufactured. The mold 13 is configured by, for example, combining mold plates made of four water-cooled copper plates. The molten metal supplied into the mold 13 through the immersion nozzle 12 is cooled by being brought into contact with the mold plate to form a solidified shell 5a in which the molten metal is solidified. With the outer shell solidified, the billet 5 is withdrawn from the mold 13 .

二次冷却装置１４は、鋳型１３に対して鋳造方向下流側に設けられ、鋳型１３の下端から引き抜かれた鋼片５を支持し、搬送しながら冷却する。二次冷却装置１４は、鋼片５の厚さ方向両側に配置される複数対の支持ロール１４ａと、鋼片５に対して冷却水を噴射する複数のスプレーノズル（図示せず。）とを有する。鋳型１３から引き抜かれた直後の鋼片５の凝固シェル５ａの内部には未凝固部５ｂが存在するが、二次冷却装置１４を移動する間に内部の未凝固部５ｂの凝固が進行し、外殻の凝固シェル５ａの厚さは、徐々に厚くなる。そして、鋼片５はほぼ完全凝固すると、連続鋳造機１０から加熱装置２０へ連続して搬送される。 The secondary cooling device 14 is provided on the downstream side of the mold 13 in the casting direction, supports the steel slab 5 pulled out from the lower end of the mold 13, and cools it while transporting it. The secondary cooling device 14 includes a plurality of pairs of support rolls 14a arranged on both sides in the thickness direction of the steel slab 5 and a plurality of spray nozzles (not shown) for injecting cooling water to the steel slab 5. have. An unsolidified portion 5b exists inside the solidified shell 5a of the billet 5 immediately after being pulled out of the mold 13, but solidification of the internal unsolidified portion 5b progresses while the billet 5 moves through the secondary cooling device 14, The thickness of the solidified shell 5a of the outer shell gradually increases. When the steel slab 5 is almost completely solidified, it is continuously transported from the continuous casting machine 10 to the heating device 20 .

なお、本発明に係る連続鋳造機１０は、図１に示すような垂直曲げ型の連続鋳造機１０に限定されず、湾曲型又は垂直型など他の各種の連続鋳造機であってもよい。 The continuous casting machine 10 according to the present invention is not limited to the vertical bending type continuous casting machine 10 shown in FIG.

（加熱装置）
加熱装置２０は、連続鋳造機１０の下流側に配置され、連続鋳造機１０により鋳造された鋼片５の上下表面のうち少なくともいずれか一方を鋼片長手方向に間欠的に加熱する。これにより、鋼片長手方向に散在する局所加熱部５ｃが鋼片５に形成される。図１に示す加熱装置２０は、鋼片５の上面及び下面の各表面を加熱可能なように、鋼片５の上面の上方及び鋼片５の下面の下方に、それぞれ加熱ユニットが配置されている。 (heating device)
The heating device 20 is arranged downstream of the continuous casting machine 10 and intermittently heats at least one of the upper and lower surfaces of the steel slab 5 cast by the continuous casting machine 10 in the longitudinal direction of the steel slab. As a result, local heating portions 5c scattered in the longitudinal direction of the billet 5 are formed. The heating device 20 shown in FIG. 1 has heating units arranged above the upper surface of the steel slab 5 and below the lower surface of the steel slab 5 so that the upper and lower surfaces of the steel slab 5 can be heated. there is

図１に示す加熱装置２０は、誘導加熱式の加熱装置である。加熱ユニットは、例えば交流電源２１に接続され、鋼片長手方向に所定の間隔を有して配置された複数の誘導加熱コイル部２３を備える。誘導加熱コイル部の間隔は、均一であってもよく、不均一であってもよい。誘導加熱コイル部２３は、例えば図１に示すように、交流電源２１に接続されたコイルを鉄等の磁性体に巻回して構成されている。 The heating device 20 shown in FIG. 1 is an induction heating type heating device. The heating unit is connected to, for example, an AC power source 21 and includes a plurality of induction heating coil portions 23 arranged at predetermined intervals in the longitudinal direction of the billet. The intervals between the induction heating coil portions may be uniform or non-uniform. For example, as shown in FIG. 1, the induction heating coil unit 23 is configured by winding a coil connected to the AC power supply 21 around a magnetic material such as iron.

誘導加熱コイル部２３は、板幅方向に少なくとも鋼片５の板幅と略同一の範囲をカバーするように配置されている。誘導加熱コイル部２３には、交流電源２１からの電流の供給の有無を切り替えるためのスイッチ２５が接続されている。スイッチ２５をオンにすると誘導加熱コイル部２３に電流が流れ、高周波磁場により直下及びその近傍の鋼片５の表面が加熱される。スイッチ２５がオフのときには誘導加熱コイル部２３には電流は流れず、鋼片５の表面は加熱されなくなる。誘導加熱コイル部２３のスイッチ２５を適宜オンオフすることにより、鋼片長手方向の任意の位置を局所的に加熱することができる。 The induction heating coil portion 23 is arranged so as to cover at least a range substantially equal to the plate width of the billet 5 in the plate width direction. A switch 25 is connected to the induction heating coil section 23 for switching whether or not the current is supplied from the AC power supply 21 . When the switch 25 is turned on, current flows through the induction heating coil portion 23, and the high-frequency magnetic field heats the surface of the steel piece 5 immediately below and in the vicinity thereof. When the switch 25 is off, no current flows through the induction heating coil portion 23 and the surface of the steel piece 5 is no longer heated. By appropriately turning on and off the switch 25 of the induction heating coil portion 23, any position in the longitudinal direction of the billet can be locally heated.

加熱装置２０は、鋼片５が加熱装置２０を通過する間、鋼片５の同位置が加熱されるように、鋼片５の移動速度に基づき誘導加熱コイル部２３のスイッチ２５をオンオフする。これにより、鋼片５の表面には、局所的に加熱された局所加熱部５ｃが、鋼片長手方向に所定の間隔で形成される。 The heating device 20 turns on and off the switch 25 of the induction heating coil portion 23 based on the moving speed of the billet 5 so that the same position of the billet 5 is heated while the billet 5 passes through the heating device 20 . As a result, locally heated portions 5c are formed on the surface of the billet 5 at predetermined intervals in the longitudinal direction of the billet.

（圧延機）
圧延機３０は、加熱装置２０の下流側に配置され、加熱装置２０により局所加熱部５ｃが形成された鋼片５を圧延する。圧延機３０は、一対の圧延ロール３１ａ、３１ｂからなり、所定の圧下率で鋼片５を圧延する。圧延ロール３１ａ、３１ｂはフラットロールである。なお、圧延機３０は、図１に示すような２段圧延機であってもよく、４段圧延機もしくはその他の形式の板圧延機であってもよい。圧延ロール３１ａ、３１ｂは、フラットロール以外のロールであってもよく、任意の断面形状を有することができる。 (rolling mill)
The rolling mill 30 is arranged on the downstream side of the heating device 20 and rolls the billet 5 on which the locally heated portions 5 c are formed by the heating device 20 . The rolling mill 30 comprises a pair of rolling rolls 31a and 31b, and rolls the steel billet 5 at a predetermined rolling reduction. The rolling rolls 31a and 31b are flat rolls. The rolling mill 30 may be a two-high rolling mill as shown in FIG. 1, a four-high rolling mill, or any other type of plate rolling mill. The rolling rolls 31a and 31b may be rolls other than flat rolls and may have any cross-sectional shape.

図１に示す連続鋳造圧延設備１では、加熱装置２０により鋼片５の表面に局所加熱部５ｃを形成したが、鋼片５の表面を加熱する代わりに保熱しても同様に局所加熱部５ｃを形成可能である。例えば、本実施形態に係る連続鋳造圧延設備は、図２に示すように、図１に示した加熱装置２０の代わりに保熱装置４０を設置した連続鋳造圧延設備２であってもよい。 In the continuous casting and rolling facility 1 shown in FIG. 1, the heating device 20 forms the locally heated portion 5c on the surface of the billet 5. However, even if the surface of the billet 5 is heated instead of being heated, the locally heated portion 5c can be similarly heated. can be formed. For example, as shown in FIG. 2, the continuous casting and rolling facility according to this embodiment may be a continuous casting and rolling facility 2 in which a heat retaining device 40 is installed instead of the heating device 20 shown in FIG.

（保熱装置）
保熱装置４０は、図２に示すように、連続鋳造機１０の下流側に配置され、連続鋳造機１０により鋳造された鋼片５の上下表面のうち少なくともいずれか一方を鋼片長手方向に間欠的に保熱する。これにより、鋼片長手方向に散在する局所加熱部５ｃが鋼片５に形成される。図２に示す保熱装置４０は、鋼片５の上面及び下面の各表面を鋼片長手方向に間欠的に保熱するように、鋼片５の上面の上方及び鋼片５の下面の下方に、それぞれ保熱ユニットが配置されている。 (Heat retaining device)
As shown in FIG. 2, the heat retaining device 40 is arranged downstream of the continuous casting machine 10, and extends at least one of the upper and lower surfaces of the billet 5 cast by the continuous casting machine 10 in the longitudinal direction of the billet. Keep warm intermittently. As a result, local heating portions 5c scattered in the longitudinal direction of the billet 5 are formed. The heat retaining device 40 shown in FIG. 2 is provided above the upper surface of the steel slab 5 and below the lower surface of the steel slab 5 so as to intermittently retain heat on the upper and lower surfaces of the steel slab 5 in the longitudinal direction of the steel slab. A heat retention unit is arranged in each.

保熱ユニットは、例えば保熱部材４５を鋼片長手方向に所定の間隔で複数配置させることにより、鋼片５の表面が局所的に空冷されないようにする。保熱部材４５は、断熱性及び耐熱性を有する材料から形成される板状の部材である。保熱部材４５は、板幅方向に少なくとも鋼片５の板幅と略同一の長さを有する。図２に示す保熱装置４０では、保熱ユニットは、一対のローラ４１ａ、４１ｂにより支持された無端ベルト４３の外周面に保熱部材４５が複数配置された構成となっている。無端ベルト４３は、鋼片長手方向（すなわち、鋳造方向）に沿って、鋼片５の移動速度と同一速度で回転している。なお、無端ベルト４３に設けられている保熱部材４５の間隔は等間隔であってもよく、不均一であってもよい。 The heat retaining unit prevents the surface of the billet 5 from being locally air-cooled by, for example, arranging a plurality of heat retaining members 45 in the longitudinal direction of the billet at predetermined intervals. The heat-retaining member 45 is a plate-like member made of a heat-insulating and heat-resistant material. The heat-retaining member 45 has at least a length substantially equal to the width of the billet 5 in the width direction. In the heat retaining device 40 shown in FIG. 2, the heat retaining unit has a configuration in which a plurality of heat retaining members 45 are arranged on the outer peripheral surface of an endless belt 43 supported by a pair of rollers 41a and 41b. The endless belt 43 rotates at the same speed as the moving speed of the billet 5 along the longitudinal direction of the billet (that is, the casting direction). The intervals between the heat retaining members 45 provided on the endless belt 43 may be equal or may be uneven.

保熱ユニットの保熱部材４５により表面が覆われた鋼片５の表面部位は空冷され難い。無端ベルト４３が鋼片５と同一速度で回転しているため、鋼片５が保熱装置４０を通過する間、鋼片５の同部位が保熱され続ける。これにより、鋼片５の表面には、局所的に保熱されることで周囲より相対的に高温となった局所加熱部５ｃが、鋼片長手方向に保熱部材４５の設置間隔で形成される。 The surface portion of the steel piece 5 covered with the heat-insulating member 45 of the heat-insulating unit is difficult to be air-cooled. Since the endless belt 43 rotates at the same speed as the steel billet 5 , the same portion of the steel billet 5 continues to be heat-retained while the steel billet 5 passes through the heat retaining device 40 . As a result, on the surface of the billet 5, a locally heated portion 5c having a relatively higher temperature than the surrounding area due to local heat retention is formed in the longitudinal direction of the billet at intervals at which the heat retaining members 45 are installed. .

［１－２．加熱炉により加熱された鋼片の圧延］
本実施形態に係る矩形断面鋼片の圧延方法は、例えば図３に示すような圧延設備３によっても実施可能である。かかる圧延設備３は、例えば図３に示すように、加熱炉５０により加熱された鋼片５をさらに加熱する加熱装置７０と、圧延機８０とを備える。 [1-2. Rolling of billet heated by heating furnace]
The method for rolling a rectangular cross-section steel billet according to this embodiment can also be carried out by a rolling facility 3 as shown in FIG. 3, for example. The rolling facility 3 includes, for example, a heating device 70 for further heating the steel slab 5 heated by the heating furnace 50, and a rolling mill 80, as shown in FIG.

例えば、連続鋳造機等によって製造された鋼片５が一旦冷却された後に圧延する場合には、図３に示すように、加熱炉５０により再加熱された鋼片５は、加熱炉５０から抽出された後ロール１８により搬送され、加熱によって生じた鋼片５の表面のスケールがスケール除去装置６０により除去された後、加熱装置７０へ搬送される。なお、スケール除去が不要な鋼片については、スケール除去装置６０は稼働させなくともよく、設置自体も不要である。 For example, when the steel slab 5 produced by a continuous casting machine or the like is cooled once and then rolled, as shown in FIG. After being heated, the steel slab 5 is transported by the rolls 18 , scales on the surface of the steel slab 5 caused by heating are removed by the scale removing device 60 , and then transported to the heating device 70 . For steel billets that do not require descaling, the descaling device 60 does not need to be operated, and installation itself is unnecessary.

（加熱装置）
加熱装置７０は、加熱炉５０にて加熱された鋼片５の上下表面のうち少なくともいずれか一方を鋼片長手方向に間欠的に加熱する。これにより、鋼片長手方向に散在する局所加熱部が鋼片５に形成される。図３に加熱装置７０は、鋼片５の上面の上方に配置されており、鋼片５の上面のみを局所加熱する構成となっている。 (heating device)
The heating device 70 intermittently heats at least one of the upper and lower surfaces of the billet 5 heated in the heating furnace 50 in the longitudinal direction of the billet. As a result, local heating portions scattered in the longitudinal direction of the billet are formed in the billet 5 . The heating device 70 shown in FIG. 3 is arranged above the upper surface of the steel piece 5 and is configured to locally heat only the upper surface of the steel piece 5 .

加熱装置７０は、例えば図１の加熱装置２０と同様に誘導加熱式の加熱装置であってもよい。加熱装置７０は、例えば交流電源７１に接続され、鋼片長手方向に所定の間隔を有して配置された複数の誘導加熱コイル部７３を備える。誘導加熱コイル部７３の間隔は、均一であってもよく、不均一であってもよい。誘導加熱コイル部７３は、交流電源７１に接続されたコイルを鉄等の磁性体に巻回して構成されている。誘導加熱コイル部７３は、板幅方向に少なくとも鋼片５の板幅と略同一の範囲をカバーするように配置されている。誘導加熱コイル部７３に電流が流れると、誘導加熱コイル部７３の直下及びその近傍の鋼片５の表面が加熱され、鋼片５の表面を局所的に加熱することができる。 The heating device 70 may be, for example, an induction heating type heating device similar to the heating device 20 in FIG. The heating device 70 is connected to, for example, an AC power source 71 and includes a plurality of induction heating coil portions 73 arranged at predetermined intervals in the longitudinal direction of the billet. The intervals between the induction heating coil portions 73 may be uniform or non-uniform. The induction heating coil portion 73 is configured by winding a coil connected to the AC power supply 71 around a magnetic material such as iron. The induction heating coil part 73 is arranged so as to cover at least a range substantially equal to the plate width of the billet 5 in the plate width direction. When an electric current flows through the induction heating coil portion 73, the surface of the steel piece 5 immediately below and in the vicinity of the induction heating coil portion 73 is heated, and the surface of the steel piece 5 can be locally heated.

図３に示す加熱装置７０は、鋼片５の搬送方向（すなわち、圧延方向）及びその逆方向に往復移動可能に構成されている。加熱装置７０の搬送方向への移動は始点位置（図３の破線位置）に始まり、鋼片５の移動速度と同一の速度で終点位置（図３の実線位置）まで移動する。終点位置に到達した加熱装置７０は移動方向を反転し、搬送方向への移動速度よりも高速で始点位置まで逆方向に移動する。加熱装置７０は、この搬送方向への移動と逆方向への移動を鋼片５の長さに応じた回数分繰り返す。加熱装置７０が搬送方向へ移動する間、鋼片５の同位置が加熱され続ける。加熱装置７０が往復移動を繰り返すことで、鋼片５の表面には、局所的に加熱された局所加熱部５ｃが、鋼片長手方向に稼働する誘導加熱コイル部７３の間隔で形成される。 The heating device 70 shown in FIG. 3 is configured to be able to reciprocate in the conveying direction (ie, rolling direction) of the steel billet 5 and in the reverse direction. The movement of the heating device 70 in the conveying direction starts at the starting point position (broken line position in FIG. 3) and moves to the end point position (solid line position in FIG. 3) at the same speed as the billet 5 moving speed. When the heating device 70 reaches the end position, it reverses its movement direction and moves in the opposite direction to the start position at a higher speed than the movement speed in the conveying direction. The heating device 70 repeats the movement in the conveying direction and the movement in the opposite direction a number of times corresponding to the length of the steel piece 5 . The same position of the billet 5 continues to be heated while the heating device 70 moves in the conveying direction. By repeating the reciprocating movement of the heating device 70, locally heated local heating portions 5c are formed on the surface of the billet 5 at intervals of the induction heating coil portions 73 operating in the longitudinal direction of the billet.

なお、加熱装置７０において、搬送方向への移動中に必ずしもすべての誘導加熱コイル部７３を常時稼働させなくともよく、鋼片５に形成する局所加熱部５ｃの間隔に応じて適宜稼働させればよい。加熱装置７０の逆方向への移動速度は、例えば、鋼片５の移動速度に｛（始点位置と終点位置との間の搬送方向距離）÷（局所加熱部５ｃの間隔）｝を乗じた値より高速であれば十分である。 In the heating device 70, it is not always necessary to operate all the induction heating coils 73 during movement in the conveying direction. good. The moving speed of the heating device 70 in the opposite direction is, for example, a value obtained by multiplying the moving speed of the billet 5 by {(conveyance direction distance between the start point position and the end point position)/(interval between the local heating portions 5c)}. Higher speed is sufficient.

なお、図３に示す圧延設備３においては、加熱装置７０の代わりに保熱装置を設けてもよい。この場合、保熱装置は、図２に示したような保熱装置であってもよい。 In addition, in the rolling facility 3 shown in FIG. 3, a heat retaining device may be provided instead of the heating device 70 . In this case, the heat retaining device may be the heat retaining device as shown in FIG.

（圧延機）
圧延機８０は、加熱装置７０の下流側に配置され、加熱装置７０により局所加熱部５ｃが形成された鋼片５を圧延する。圧延機８０は、一対の圧延ロール８１ａ、８１ｂからなり、所定の圧下率で鋼片５を圧延する。圧延ロール８１ａ、８１ｂはフラットロールである。なお、圧延機８０は、図３に示すような２段圧延機であってもよく、４段圧延機もしくはその他の形式の板圧延機であってもよい。圧延ロール８１ａ、８１ｂは、フラットロール以外のロールであってもよく、任意の断面形状を有することができる。 (rolling mill)
The rolling mill 80 is arranged on the downstream side of the heating device 70 and rolls the billet 5 on which the locally heated portions 5 c are formed by the heating device 70 . The rolling mill 80 comprises a pair of rolling rolls 81a and 81b, and rolls the steel billet 5 at a predetermined rolling reduction. The pressure rolls 81a and 81b are flat rolls. Note that the rolling mill 80 may be a two-high rolling mill as shown in FIG. 3, a four-high rolling mill, or any other type of plate rolling mill. The rolling rolls 81a and 81b may be rolls other than flat rolls and may have any cross-sectional shape.

以上、本実施形態に係る矩形断面鋼片の圧延方法を実施するための設備例を説明した。なお、図１の連続鋳造圧延設備１において、加熱装置２０の代わりに図３の加熱装置７０を用いてもよい。同様に、図３の圧延設備３において、加熱装置７０の代わりに図１の加熱装置２０を用いてもよい。また、本実施形態に係る矩形断面鋼片の圧延方法を実施するための設備は図１～図３の例に限定されるものではなく、鋼片５の圧延に先立ち、鋼片５の表面に鋼片長手方向に局所加熱部５ｃを散在させる加熱装置または保熱装置を備える設備であれば、本実施形態に係る矩形断面鋼片の圧延方法を実施し得る。 An example of equipment for carrying out the method for rolling a rectangular cross-section steel billet according to the present embodiment has been described above. 3 may be used instead of the heating device 20 in the continuous casting and rolling equipment 1 of FIG. Similarly, the heating device 20 of FIG. 1 may be used instead of the heating device 70 in the rolling mill 3 of FIG. Further, the equipment for carrying out the rolling method for the rectangular cross-section steel billet according to the present embodiment is not limited to the examples shown in FIGS. The rolling method of the rectangular cross-section steel bill according to the present embodiment can be carried out in any facility equipped with a heating device or a heat retaining device that disperses the local heating portions 5c in the longitudinal direction of the billet.

＜２．圧延前局所加熱によるひずみの付与＞
本実施形態に係る矩形断面鋼片の圧延方法では、図１～図３に示したような設備を用いて、圧延機による圧延前の鋼片５に対して、圧延ロールと接する鋼片５の上下表面のうち少なくともいずれか一方を鋼片長手方向に間欠的に加熱または保熱して、鋼片長手方向に散在する局所加熱部５ｃを鋼片５に形成する。このような局所加熱部５ｃが形成された鋼片５を圧延機により圧延することで、同一の鋼片圧下量条件で、圧延中の材料内部の応力やひずみ等の変形状態を有意かつ意図的に変化させることができ、鋼片厚を変更することなく鋼片品質を向上させることを可能とする。すなわち、厚さ中央での静水圧応力の増大はポロシティー圧着に有効であり、塑性ひずみの増大は偏析の改善や結晶粒の微細化に繋がる。 <2. Application of strain by local heating before rolling>
In the method for rolling a rectangular cross-section steel billet according to the present embodiment, equipment such as that shown in FIGS. At least one of the upper and lower surfaces is intermittently heated or retained in the longitudinal direction of the billet to form locally heated portions 5c scattered in the longitudinal direction of the billet 5 . By rolling the billet 5 in which such a locally heated portion 5c is formed by a rolling mill, the deformation state such as stress and strain inside the material during rolling can be significantly and intentionally controlled under the same billet reduction amount condition. can be changed to improve the billet quality without changing the billet thickness. That is, an increase in hydrostatic stress at the center of the thickness is effective for porosity crimping, and an increase in plastic strain leads to improvement in segregation and grain refinement.

[２－１．圧延前局所加熱による作用]
まず、図４～図６に基づいて、本実施形態に係る矩形断面鋼片の圧延方法において、圧延に先立って鋼片５に局所加熱部５ｃを形成する理由を説明する。図４は、局所加熱部５ｃが形成された鋼片５を圧延したときの圧延ロール３１ａとの接触領域下（以下、「ロールバイト」と称する。）とその近傍における鋼片内部の塑性変形の状態（応力、塑性ひずみ及びメタルフロー）を示す概念図である。図５は、局所加熱部５ｃの有無による、ロールバイト及びその近傍での鋼片５の厚さ中央に生じる静水圧応力の分布を示す説明図である。なお、図５では、静水圧応力の圧縮側を正として示している。図６は、局所加熱部５ｃの有無による、圧延後の鋼片の厚さ中央位置及び表層から１／４厚さ位置における塑性ひずみの鋼片長手方向分布を示す説明図である。 [2-1. Action by local heating before rolling]
First, with reference to FIGS. 4 to 6, the reason why the locally heated portion 5c is formed in the steel billet 5 prior to rolling in the method for rolling a rectangular cross-section steel billet according to the present embodiment will be described. FIG. 4 shows the plastic deformation inside the billet under and near the contact area with the rolling rolls 31a (hereinafter referred to as "roll bite") when the billet 5 in which the localized heating portion 5c is formed is rolled. It is a conceptual diagram showing states (stress, plastic strain and metal flow). FIG. 5 is an explanatory diagram showing the distribution of hydrostatic pressure stress generated at the center of the thickness of the billet 5 at the roll bite and its vicinity, depending on the presence or absence of the local heating portion 5c. In addition, in FIG. 5, the compressive side of the hydrostatic pressure stress is shown as positive. FIG. 6 is an explanatory diagram showing the distribution of plastic strain in the billet longitudinal direction at the thickness center position and the 1/4 thickness position from the surface layer of the billet after rolling, depending on the presence or absence of the local heating portion 5c.

鋼片５に鋼片長手方向に散在する局所加熱部５ｃを形成してから圧延すると、鋼片５の表面近傍の変形状態が鋼片長さ方向に顕著に変動し、当該変動が鋼片の厚さ中央まで伝播する。すなわち、図４に示すように、鋼片５が圧延ロール３１ａにて圧延される際、局所加熱部５ｃにおいて、相対的に硬く変形し難い局所加熱部５ｃの前後領域による拘束の影響で局所加熱部５ｃに塑性変形が集中し、鋼片５の塑性ひずみが大きくなる。すなわち、局所加熱部５ｃが変形の起点となって、鋼片５の内部に大きな塑性ひずみを生じさせる。図４では、局所加熱部５ｃから大きな塑性ひずみが生じた部分を変形増大部分５ｅとして示している。図４示すように、１つの局所加熱部５ｃから１つの変形増大部分５ｅが生じる。 When the locally heated portions 5c scattered in the longitudinal direction of the billet 5 are formed in the billet 5 and then rolled, the deformation state near the surface of the billet 5 remarkably fluctuates in the longitudinal direction of the billet. propagate to the center. That is, as shown in FIG. 4, when the steel slab 5 is rolled by the rolling rolls 31a, the local heating is effected by the restraint by the front and rear regions of the local heating portion 5c, which is relatively hard and difficult to deform, in the local heating portion 5c. Plastic deformation concentrates on the portion 5c, and the plastic strain of the billet 5 increases. That is, the locally heated portion 5c becomes a starting point of deformation, causing a large plastic strain inside the billet 5. As shown in FIG. In FIG. 4, a portion where a large plastic strain is generated from the locally heated portion 5c is shown as an increased deformation portion 5e. As shown in FIG. 4, one deformation increase portion 5e is generated from one local heating portion 5c.

変形増大部分５ｅは、静水圧応力が増大する部分と概ね相似する。図５の実線は、局所加熱部５ｃが形成されていない鋼片５を圧延ロールにより押圧したときの鋼片の厚さ中央における静水圧応力の圧延方向分布を示している。また、図５の破線は、局所加熱部５ｃが形成されている鋼片５を圧延ロールによる押圧したときの静水圧応力の圧延方向分布を示している。図５では、図４における変形増大部分５ｅが、静水圧応力が最大となる圧延方向位置を通過する際の分布を表示している。 The increased deformation portion 5e is generally similar to the portion where the hydrostatic pressure stress increases. The solid line in FIG. 5 shows the rolling direction distribution of the hydrostatic pressure stress at the center of the thickness of the billet when the billet 5 without the locally heated portion 5c is pressed by the rolling rolls. The dashed line in FIG. 5 indicates the rolling direction distribution of the hydrostatic pressure stress when the steel slab 5 having the locally heated portion 5c is pressed by the rolling rolls. FIG. 5 shows the distribution when the increased deformation portion 5e in FIG. 4 passes through the rolling direction position where the hydrostatic pressure stress is maximum.

このとき、塑性ひずみは、局所加熱部５ｃを起点とした変形増大部分５ｅの領域を伝播し、厚さ中央に到達する。この変形増大部分５ｅの領域内の塑性変形の主体は圧延方向の延び変形であり、当該領域の周囲に在る相対的に小さい延び変形しか生じない部分に拘束されて、変形増大部分５ｅの静水圧応力が圧縮側に変化する。したがって、圧延ロールと鋼片５との接触領域の略中央部から出口近傍において最大となる圧縮応力値（すなわち、静水圧応力のピーク値）σpeak １／２は、局所加熱部５ｃが形成されていない場合と比較して、静水圧増分値ｄσpeak １／２だけ大きくなる。これより、鋼片５に局所加熱部５ｃを形成することで、局所加熱部５ｃが形成されていない場合よりも静水圧応力を増加できることがわかる。 At this time, the plastic strain propagates through the area of the deformation increase portion 5e starting from the local heating portion 5c and reaches the center of the thickness. The main plastic deformation in the region of the increased deformation portion 5e is extensional deformation in the rolling direction. Hydraulic stress changes to compression side. Therefore, the maximum compressive stress value (that is, peak value of hydrostatic pressure stress) σ peak 1/2 in the vicinity of the exit from the approximate center of the contact area between the rolling rolls and the billet 5 is The hydrostatic pressure increment value dσ peak 1/2 is increased compared to the case without. From this, it can be seen that by forming the locally heated portion 5c in the billet 5, the hydrostatic pressure stress can be increased more than when the locally heated portion 5c is not formed.

変形増大部分５ｅは、鋼片長手方向に略周期的に生じる。同じロールバイト内に変形増大部分５ｅとそれ以外の部分が共存すると、静水圧応力の勾配が生じ、変形増大部分５ｅから他の部分に向かう副次的なメタルフローが発生する。接触長に略等しい長さのロールバイト内に塑性変形が大きい部分と小さい部分とが繰り返し現れることで、副次的なメタルフローがより顕著になり、塑性ひずみが有意に増大する。したがって、鋼片５に局所加熱部５ｃを形成することで、より効果的に塑性ひずみを増大させることができる。 The increased deformation portion 5e is generated substantially periodically in the longitudinal direction of the billet. If the deformation-increased portion 5e and other portions coexist in the same roll bite, a hydrostatic stress gradient occurs, and secondary metal flow from the deformation-increased portion 5e to other portions occurs. The recurrence of large and small plastic deformation portions within the roll bite with a length approximately equal to the contact length makes the secondary metal flow more pronounced, resulting in a significant increase in plastic strain. Therefore, by forming the local heating portion 5c in the steel piece 5, the plastic strain can be increased more effectively.

図６に、局所加熱部５ｃが形成された鋼片５を圧延したときの、圧延後の鋼片長手方向における塑性ひずみの分布を示す。図６に示すように、局所加熱部５ｃが形成された鋼片５を圧延することにより、鋼片厚さ方向の１／４厚さ位置及び鋼片厚さ方向の中央位置において、塑性ひずみは非対称な波形で略周期的に変化する。 FIG. 6 shows the distribution of plastic strain in the longitudinal direction of the billet after rolling when the billet 5 in which the locally heated portions 5c are formed is rolled. As shown in FIG. 6, by rolling the billet 5 in which the localized heating portion 5c is formed, the plastic strain is It has an asymmetrical waveform and changes almost periodically.

厚さ方向中央位置の塑性ひずみの変動幅は、鋼片５の表面の局所加熱部５ｃの寸法や周囲との温度差（降伏応力差）に対応すると考えられる。このとき、厚さ中央よりも鋼片表面寄り、例えば厚さ中央から鋼片厚さの１／４だけ鋼片表面に向かった位置（以下、「１／４厚さ位置」ともいう。）の方が中央位置よりも振幅が大きくなっている。また、１／４厚さ位置の位相よりも中央位置の位相は遅れたものとなる。この位相の遅れは、図４に示したように、変形増大部分５ｅの表面近傍部分が厚さ中央部分よりも圧延方向上流側に位置し、変形増大部分５ｅが厚さ方向に対して傾斜していることに符合する。 It is considered that the variation width of the plastic strain at the central position in the thickness direction corresponds to the size of the locally heated portion 5c on the surface of the billet 5 and the temperature difference (yield stress difference) with the surroundings. At this time, the position closer to the surface of the billet than the center of the thickness, for example, the position toward the surface of the billet by 1/4 of the thickness of the billet from the center of the thickness (hereinafter also referred to as "1/4 thickness position"). The amplitude is larger at the central position. Also, the phase at the center position is delayed from the phase at the quarter thickness position. As shown in FIG. 4, this phase delay is such that the surface vicinity portion of the increased deformation portion 5e is positioned upstream in the rolling direction from the thickness center portion, and the increased deformation portion 5e is inclined with respect to the thickness direction. corresponds to

なお、図６には、比較として、局所加熱部５ｃが形成されていない鋼片５を圧延した場合の鋼片５の塑性ひずみを示している。局所加熱部５ｃが形成されていない鋼片５を圧延したときの圧下量は、局所加熱部５ｃが形成された鋼片５を圧延した場合と同一とした。このとき、鋼片５の厚さ方向の中央位置及び１／４厚さ位置のいずれについても、鋼片に局所加熱部５ｃを形成することで塑性ひずみが長さ方向の大半の部分で増大し、かつ平均的なひずみ値も増大していることがわかる。図６では、鋼片５の厚さ方向の中央位置及び１／４厚さ位置における、局所加熱部５ｃが形成されていない鋼片５を圧延したときの塑性ひずみからの局所加熱部５ｃが形成された鋼片５を圧延したときの塑性ひずみの増分量（以下、「塑性ひずみ増分量」ともいう。）のピーク値を、それぞれピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４と表している。 For comparison, FIG. 6 shows the plastic strain of the steel slab 5 in the case where the steel slab 5 in which the local heating portion 5c is not formed is rolled. The amount of reduction when rolling the billet 5 without the locally heated portions 5c was the same as when rolling the billet 5 with the locally heated portions 5c. At this time, by forming the local heating portion 5c in the steel piece 5 both at the center position in the thickness direction of the steel piece 5 and at the quarter thickness position, the plastic strain increases in most of the length direction. , and the average strain value also increases. In FIG. 6, localized heated portions 5c are formed due to plastic strain when rolling the billet 5 in which the localized heated portions 5c are not formed at the central position and the quarter thickness position of the steel bill 5 in the thickness direction. The peak values of the plastic strain increment (hereinafter also referred to as “plastic strain increment”) when rolling the steel slab 5 are peak strain increments dε peak 1/2 and dε peak 1/4 , respectively. represent.

［２－２．局所加熱部の形成］
上述のように鋼片５の塑性ひずみの増大を実現するためには、鋼片５に局所加熱部５ｃを適切に設ける必要がある。本願発明者はこの条件を検討した結果、局所加熱部５ｃの局所加熱深さ、局所加熱長さ、局所加熱表面積、局所加熱部間隔、局所加熱部温度を以下のようにすることで、同一の鋼片圧下量条件下で鋼片内部の塑性ひずみを厚さ方向全域にわたって有意に大きくし、かつ厚さ中央近傍の静水圧応力を圧縮側に高めることができ、鋼片の厚さ方向中央近傍のポロシティーの圧着効果や中心偏析の改善のみならず、鋼片の表層近傍での柱状晶の形成によるミクロ偏析も改善されるとの知見を得た。なお、局所加熱深さは、局所加熱部５ｃの厚さ方向深さをいい、局所加熱長さは、局所加熱部５ｃの圧延方向長さをいい、局所加熱部間隔は、鋼片長手方向に隣接する局所加熱部５ｃの間隔であり、局所加熱部５ｃの鋼片長手方向中心間の距離をいう。 [2-2. Formation of Local Heated Part]
In order to increase the plastic strain of the billet 5 as described above, the billet 5 needs to be appropriately provided with the local heating portion 5c. As a result of examining this condition, the inventors of the present application have found that the same The plastic strain inside the billet can be significantly increased over the entire thickness direction under the conditions of the billet reduction amount, and the hydrostatic stress near the center of the thickness can be increased toward the compression side. It was found that not only the crimping effect of porosity and the improvement of center segregation, but also the micro-segregation due to the formation of columnar crystals near the surface layer of the billet was improved. The local heating depth refers to the thickness direction depth of the local heating part 5c, the local heating length refers to the rolling direction length of the local heating part 5c, and the local heating part interval refers to the longitudinal direction of the billet. It is the interval between adjacent local heating portions 5c, and refers to the distance between the centers of the billets in the longitudinal direction of the local heating portions 5c.

（１）局所加熱深さ、局所加熱長さ
局所加熱部５ｃは、鋼片厚さ方向における鋼片５の表面からの局所加熱深さが、鋼片５の厚さの０．０１倍以上０．４０倍以下の範囲内に形成され、かつ、圧延方向における局所加熱長さが、鋼片５の厚さの０．０１倍以上１．５倍以下の範囲内にあるのが望ましい。局所加熱深さとは、圧延ロールに圧下される直前における局所加熱部５ｃの鋼片厚さ方向における深さをいう。局所加熱長さとは、圧延ロールに圧下される直前における局所加熱部５ｃの圧延方向における長さをいう。局所加熱深さ及び局所加熱長さは、例えば圧延機入側での表面温度の測定値から熱伝導計算等を用いて推定し得る。なお、後述の局所加熱部寸法因子も、局所加熱深さと同様に推定し得る。 (1) Local Heating Depth, Local Heating Length The local heating portion 5c has a local heating depth from the surface of the billet 5 in the billet thickness direction of 0.01 times the thickness of the billet 5 or more. 40 times or less, and the local heating length in the rolling direction is preferably in the range of 0.01 to 1.5 times the thickness of the billet 5 . The local heating depth is the depth of the locally heated portion 5c in the thickness direction of the billet immediately before being rolled down by the rolling rolls. The locally heated length refers to the length in the rolling direction of the locally heated portion 5c just before being rolled down by the rolling rolls. The local heating depth and the local heating length can be estimated, for example, from the measured surface temperature at the entry side of the rolling mill using heat conduction calculation or the like. Note that the local heating portion size factor, which will be described later, can also be estimated in the same manner as the local heating depth.

図７に、局所加熱深さを鋼片５の厚さで除した値（すなわち、「局所加熱深さ／鋼片厚さ」）と塑性ひずみ増分との関係を示す。なお、図７において、局所加熱深さを鋼片５の厚さで除した値の座標を示す横軸は対数目盛で表している。後述する図８の横軸も同様である。図７に示すように、図６に示した鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４について、いずれも凸形状の曲線を有する。ここで、通常の圧延における圧下ひずみが０．１のオーダーであることを考慮すると、局所加熱部５ｃが形成されていない鋼片５を圧延したときの塑性ひずみからのひずみ増分量が０．０１（すなわち１％）以上であればその効果は実質的に有意であると考えられる。図７より、鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４が０．０１を超える範囲は、局所加熱深さを鋼片５の厚さで除した値が０．０１以上０．４以下の範囲である。すなわち、局所加熱部５ｃの局所加熱深さを鋼片厚さの０．０１倍以上０．４０倍の範囲に設定すればよい。 FIG. 7 shows the relationship between the value obtained by dividing the local heating depth by the thickness of the billet 5 (that is, "local heating depth/slab thickness") and the plastic strain increment. In FIG. 7, the horizontal axis indicating the coordinates of the value obtained by dividing the local heating depth by the thickness of the steel billet 5 is represented on a logarithmic scale. The same applies to the horizontal axis of FIG. 8, which will be described later. As shown in FIG. 7, for the peak strain increments dε peak 1/2 and dε peak 1/4 at the center position and 1/4 thickness position in the thickness direction of the billet 5 shown in FIG. It has a convex curve. Here, considering that the rolling strain in normal rolling is on the order of 0.1, the strain increment from the plastic strain when rolling the billet 5 in which the local heating portion 5c is not formed is 0.01 (ie, 1%) or more, the effect is considered substantially significant. From FIG. 7, the range where the peak strain increments dε peak 1/2 and dε peak 1/4 for the central position and quarter thickness position in the thickness direction of the billet 5 exceeds 0.01 is the local heating depth The value obtained by dividing the thickness by the thickness of the billet 5 is in the range of 0.01 or more and 0.4 or less. That is, the local heating depth of the local heating portion 5c may be set in the range of 0.01 to 0.40 times the thickness of the billet.

局所加熱部５ｃの局所加熱深さが鋼片厚さの０．０１倍以上であれば、ひずみの増大効果を有意に得ることができる。また、局所加熱部５ｃの局所加熱深さを鋼片厚さの０．４０倍以下とすることで、局所加熱部５ｃを形成することによる温度上昇に起因する材質影響が製品全体の品質評価に及ぶことがなく、好適である。 If the local heating depth of the local heating portion 5c is 0.01 times or more the thickness of the steel slab, a significant strain increasing effect can be obtained. In addition, by setting the local heating depth of the local heating part 5c to 0.40 times or less of the thickness of the billet, the effect of the material due to the temperature rise due to the formation of the local heating part 5c can be used to evaluate the quality of the entire product. It does not reach, and is suitable.

したがって、塑性ひずみを有意に増大させるには、局所加熱部５ｃの局所加熱深さを、鋼片厚さの０．０１倍以上０．４０倍の範囲に設定するのがよい。なお、図５に示したように、ロールバイト内の静水圧応力は１００ＭＰａのオーダーであり、１０ＭＰａ以上の静水圧応力の増加は実質的にも有意な効果をもたらすと考えられる。このため、図８に示すように、局所加熱深さを鋼片５の厚さで除した値（すなわち、「局所加熱深さ／鋼片厚さ」）が０．０１以上０．４以下の範囲、すなわち、局所加熱部５ｃの局所加熱深さを鋼片厚さの０．０１倍以上０．４０倍の範囲に設定すれば、常に１０ＭＰａを大きく超える静水圧応力増分量が得られており、鋼片の厚さ方向中央近傍のポロシティー圧着に関して実用上十分な効果を享受することができる。 Therefore, in order to significantly increase the plastic strain, it is preferable to set the local heating depth of the local heating portion 5c in the range of 0.01 to 0.40 times the thickness of the steel slab. As shown in FIG. 5, the hydrostatic stress in the roll bite is on the order of 100 MPa, and an increase in the hydrostatic stress of 10 MPa or more is considered to have a substantially significant effect. Therefore, as shown in FIG. 8, the value obtained by dividing the local heating depth by the thickness of the billet 5 (i.e., “local heating depth/slab thickness”) is 0.01 or more and 0.4 or less. If the range, that is, the local heating depth of the local heating portion 5c is set in the range of 0.01 to 0.40 times the thickness of the billet, a hydrostatic pressure stress increment that greatly exceeds 10 MPa is always obtained. , Practically sufficient effects can be obtained with respect to porosity crimping in the vicinity of the center in the thickness direction of the billet.

また、図９に、局所加熱長さを鋼片５の厚さで除した値（すなわち、「局所加熱長さ／鋼片厚さ」）と塑性ひずみ増分との関係を示す。なお、図９において、局所加熱長さを鋼片５の厚さで除した値の座標を示す横軸は対数目盛で表している。後述する図１０の横軸も同様である。局所加熱深さの場合と同様、局所加熱長さについても、図９に示すように、図６に示した鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４について、いずれも凸形状の曲線を有する。ここで、通常の圧延における圧下ひずみが０．１のオーダーであることを考慮すると、局所加熱部５ｃが形成されていない鋼片５を圧延したときの塑性ひずみからのひずみ増分量が０．０１（すなわち１％）以上であればその効果は実質的に有意であると考えられる。図９より、鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４が０．０１を超える範囲は、局所加熱長さを鋼片５の厚さで除した値が０．０１以上１．５以下の範囲である。すなわち、局所加熱部５ｃの局所加熱長さを、鋼片厚さの０．０１倍以上１．５倍以下の範囲に設定すればよい。 Further, FIG. 9 shows the relationship between the value obtained by dividing the locally heated length by the thickness of the billet 5 (that is, “locally heated length/slab thickness”) and the plastic strain increment. In FIG. 9, the horizontal axis indicating the coordinates of the value obtained by dividing the local heating length by the thickness of the steel billet 5 is expressed in a logarithmic scale. The same applies to the horizontal axis of FIG. 10, which will be described later. As in the case of the local heating depth, as shown in FIG. 9, for the local heating length, the peak strain increase at the center position and quarter thickness position in the thickness direction of the billet 5 shown in FIG. Both of the quantities dε peak 1/2 and dε peak 1/4 have convex curves. Here, considering that the rolling strain in normal rolling is on the order of 0.1, the strain increment from the plastic strain when rolling the billet 5 in which the local heating portion 5c is not formed is 0.01 (ie, 1%) or more, the effect is considered substantially significant. From FIG. 9, the range where the peak strain increments dε peak 1/2 and dε peak 1/4 for the center position and 1/4 thickness position in the thickness direction of the billet 5 exceeds 0.01 is the local heating length The value obtained by dividing the thickness by the thickness of the billet 5 is in the range of 0.01 or more and 1.5 or less. That is, the local heating length of the local heating portion 5c may be set in the range of 0.01 to 1.5 times the thickness of the billet.

局所加熱部５ｃの局所加熱長さが鋼片厚さの０．０１倍以上であれば、ひずみの増大効果を有意に得ることができる。また、局所加熱部５ｃの局所加熱長さを鋼片厚さの１．５倍以下とすることで、局所加熱部５ｃを形成することによる温度上昇に起因する材質影響が製品全体の品質評価に及ぶことがなく、好適である。 If the local heating length of the local heating portion 5c is 0.01 times or more the thickness of the steel slab, a significant strain increasing effect can be obtained. In addition, by setting the local heating length of the local heating part 5c to 1.5 times or less than the thickness of the billet, the effect of the material due to the temperature rise due to the formation of the local heating part 5c is reflected in the quality evaluation of the entire product. It does not reach, and is suitable.

したがって、塑性ひずみを有意に増大させるには、局所加熱部５ｃの局所加熱長さを、鋼片５の表面から鋼片厚さの０．０１倍以上１．５倍の範囲に設定するのがよい。なお、図５に示したように、ロールバイト内の静水圧応力は１００ＭＰａのオーダーであり、１０ＭＰａ以上の静水圧応力の増加は実質的にも有意な効果をもたらすと考えられる。このため、図１０に示すように、局所加熱長さを鋼片５の厚さで除した値（すなわち、「局所加熱長さ／鋼片厚さ」）が０．０１以上１．５以下の範囲、すなわち、局所加熱部５ｃの局所加熱長さを鋼片厚さの０．０１倍以上１．５倍の範囲に設定すれば、常に１０ＭＰａを大きく超える静水圧応力増分量が得られており、鋼片の厚さ方向中央近傍のポロシティー圧着に関して実用上十分な効果を享受することができる。 Therefore, in order to significantly increase the plastic strain, it is preferable to set the local heating length of the local heating portion 5c from the surface of the billet 5 to a range of 0.01 to 1.5 times the thickness of the billet. good. As shown in FIG. 5, the hydrostatic stress in the roll bite is on the order of 100 MPa, and an increase in the hydrostatic stress of 10 MPa or more is considered to have a substantially significant effect. Therefore, as shown in FIG. 10, the value obtained by dividing the locally heated length by the thickness of the billet 5 (that is, “locally heated length/slab thickness”) is 0.01 or more and 1.5 or less. If the range, that is, the local heating length of the local heating portion 5c is set in the range of 0.01 to 1.5 times the thickness of the billet, a hydrostatic pressure stress increment that greatly exceeds 10 MPa is always obtained. , Practically sufficient effects can be obtained with respect to porosity crimping in the vicinity of the center in the thickness direction of the billet.

（２）局所加熱表面積
局所加熱部５ｃは、当該局所加熱部５ｃの表面積である局所加熱表面積が、圧延ロールと接する鋼片５の上下表面の全表面積の０．０１倍以上０．５倍以下の範囲内となるように形成されるのがよい。ここで、局所加熱表面積を全表面積で除した値（すなわち、「局所加熱表面積／全表面積」）を加熱面積率と称する。 (2) Local heating surface area The local heating surface area, which is the surface area of the local heating part 5c, is 0.01 to 0.5 times the total surface area of the upper and lower surfaces of the billet 5 in contact with the rolling rolls. is preferably formed so as to be within the range of Here, the value obtained by dividing the locally heated surface area by the total surface area (that is, "locally heated surface area/total surface area") is referred to as the heated area ratio.

図１１に、加熱面積率と塑性ひずみ増分との関係を示す。なお、図１１において、加熱面積率の座標を示す横軸は対数目盛で表している。後述する図１２の横軸も同様である。図１１に示すように、図５に示した鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４について、いずれも加熱面積率が大きくなるほど塑性ひずみ増分は大きくなっている。ここで、通常の圧延における圧下ひずみが０．１のオーダーであることを考慮すると、局所加熱部５ｃが形成されていない鋼片５を圧延したときの塑性ひずみからのひずみ増分量が０．０１（すなわち１％）以上であればその効果は実質的に有意であると考えられる。図１１より、鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４が０．０１を超える範囲は、加熱面積率が０．０１以上０．５以下の範囲である。すなわち、局所加熱表面積が圧延ロールと接する鋼片５の上下表面の全表面積の０．０１倍以上０．５倍以下の範囲内となるように、局所加熱部５ｃを形成すればよい。 FIG. 11 shows the relationship between the heating area ratio and the plastic strain increment. In FIG. 11, the horizontal axis indicating the coordinates of the heating area ratio is expressed in a logarithmic scale. The same applies to the horizontal axis of FIG. 12, which will be described later. As shown in FIG. 11, for the peak strain increments dε peak 1/2 and dε peak 1/4 at the center position and 1/4 thickness position in the thickness direction of the billet 5 shown in FIG. The larger the heating area ratio, the larger the plastic strain increment. Here, considering that the rolling strain in normal rolling is on the order of 0.1, the strain increment from the plastic strain when rolling the billet 5 in which the local heating portion 5c is not formed is 0.01 (ie, 1%) or more, the effect is considered substantially significant. From FIG. 11, the range where the peak strain increment dε peak 1/2 and dε peak 1/4 for the central position and 1/4 thickness position in the thickness direction of the billet 5 exceeds 0.01 is the heating area ratio is in the range of 0.01 to 0.5. That is, the locally heated portion 5c may be formed so that the locally heated surface area is in the range of 0.01 to 0.5 times the total surface area of the upper and lower surfaces of the billet 5 in contact with the rolling rolls.

加熱面積率が０．０１以上であれば、ひずみの増大効果を有意に得ることができる。また、加熱面積率を０．５以下とすることで、局所加熱部５ｃを形成することによる温度上昇に起因する材質影響が製品全体の品質評価に及ぶことがなく、好適である。なお、静水圧応力の増大効果については、図１２に示すように、加熱面積率が０．０１以上０．５以下の範囲であれば静水圧応力増分量は常に１０ＭＰａ以上あるため、ポロシティー圧着に関して実用十分な効果を享受することができる。 If the heating area ratio is 0.01 or more, the strain increasing effect can be significantly obtained. Further, by setting the heating area ratio to 0.5 or less, the quality evaluation of the entire product is not affected by the material quality caused by the temperature rise due to the formation of the local heating portion 5c, which is preferable. Regarding the effect of increasing the hydrostatic pressure stress, as shown in FIG. It is possible to enjoy practically sufficient effects with respect to.

（３）局所加熱部間隔
局所加熱部５ｃは、鋼片５が圧延される際の圧延ロールとの接触弧長の１／６０倍以上２倍以下の間隔を局所加熱部間隔として鋼片長手方向に有するように形成されるのがよい。局所加熱部間隔は、圧延直前の鋼片５において、鋼片５と圧延ロールとの接触弧長に対応する長さで表される。 (3) Spacing between Local Heating Parts The local heating parts 5c are arranged in the longitudinal direction of the billet with a gap of 1/60 to 2 times the arc length of contact with the rolling rolls when the billet 5 is rolled. It is preferably formed so as to have The local heating interval is represented by the length corresponding to the contact arc length between the billet 5 and the rolling rolls in the billet 5 immediately before rolling.

図１３に、接触弧長を局所加熱部間隔で除した値（すなわち、「接触弧長／局所加熱部間隔」）と塑性ひずみ増分との関係を示す。図１３に示すように、図５に示した鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４について、いずれも凸形状の曲線を有する。ここで、通常の圧延における圧下ひずみが０．１のオーダーであることを考慮すると、局所加熱部５ｃが形成されていない鋼片５を圧延したときの塑性ひずみからのひずみ増分量が０．０１（すなわち１％）以上であればその効果は実質的に有意であると考えられる。図１３より、鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４が０．０１を超える範囲は、接触弧長を局所加熱部間隔で除した値が０．５以上６０以下の範囲である。すなわち、局所加熱部間隔を、鋼片５が圧延される際の圧延ロールとの接触弧長の１／６０倍以上２倍以下の範囲に設定すればよい。局所加熱部間隔が、鋼片５が圧延される際の圧延ロールとの接触弧長の１／６０倍以上２倍以下であれば、ひずみの増大効果を有意に得ることができる。 FIG. 13 shows the relationship between the value obtained by dividing the contact arc length by the local heating portion interval (that is, “contact arc length/local heating portion interval”) and the plastic strain increment. As shown in FIG. 13, for the peak strain increments dε peak 1/2 and dε peak 1/4 at the center position and 1/4 thickness position in the thickness direction of the billet 5 shown in FIG. It has a convex curve. Here, considering that the rolling strain in normal rolling is on the order of 0.1, the strain increment from the plastic strain when rolling the billet 5 in which the local heating portion 5c is not formed is 0.01 (ie, 1%) or more, the effect is considered substantially significant. From FIG. 13, the peak strain increments dε peak 1/2 and dε peak 1/4 at the center position and quarter thickness position of the billet 5 in the thickness direction exceed 0.01, the contact arc length is in the range of 0.5 or more and 60 or less. That is, the interval between the local heating portions may be set in the range of 1/60 to 2 times the arc length of contact with the rolling rolls when the billet 5 is rolled. If the interval between the local heating portions is 1/60 to 2 times the arc length of contact with the rolling rolls when the billet 5 is rolled, a significant strain increasing effect can be obtained.

なお、図５に示したように、ロールバイト内の静水圧応力は１００ＭＰａのオーダーであり、１０ＭＰａ以上の静水圧応力の増加は実質的にも有意な効果をもたらすと考えられる。このため、図１４に示すように、局所加熱部間隔を、鋼片５が圧延される際の圧延ロールとの接触弧長の１／６０倍以上２倍以下の範囲に設定すれば、常に１０ＭＰａを大きく超える静水圧応力増分量が得られており、鋼片の厚さ方向中央近傍のポロシティー圧着に関して実用上十分な効果を享受することができる。 As shown in FIG. 5, the hydrostatic stress in the roll bite is on the order of 100 MPa, and an increase in the hydrostatic stress of 10 MPa or more is considered to have a substantially significant effect. Therefore, as shown in FIG. 14, if the interval between the local heating portions is set in the range of 1/60 times or more and 2 times or less of the contact arc length with the rolling rolls when the billet 5 is rolled, the pressure is always 10 MPa. is obtained, and a practically sufficient effect can be obtained with respect to porosity crimping near the center in the thickness direction of the billet.

（４）局所加熱部温度
局所加熱部５ｃは、当該局所加熱部５ｃの平均温度（すなわち、局所加熱部温度）が、圧延ロールに接する鋼片５の表面の局所加熱部５ｃ以外の部分の平均温度に対して＋１０℃以上の範囲内であり、かつ、融点温度未満となるように形成されるのがよい。 (4) Temperature of Local Heating Part The average temperature of the local heating part 5c (that is, the temperature of the local heating part) is the average of the parts other than the local heating part 5c on the surface of the billet 5 in contact with the rolling rolls. It is preferably formed so as to be within the range of +10° C. or more with respect to the temperature and below the melting point temperature.

図１５に、局所加熱部５ｃの温度上昇量と塑性ひずみ増分との関係を示す。ここで、局所加熱部５ｃの温度上昇量とは、局所加熱部５ｃ以外の部分の平均温度に対する局所加熱部温度の上昇量である。なお、図１５において、局所加熱部５ｃの温度上昇量の座標を示す横軸は対数目盛で表している。後述する図１６の横軸も同様である。 FIG. 15 shows the relationship between the temperature rise amount of the local heating portion 5c and the plastic strain increment. Here, the amount of temperature rise of the local heating portion 5c is the amount of increase of the temperature of the local heating portion with respect to the average temperature of the portions other than the local heating portion 5c. In FIG. 15, the horizontal axis indicating the coordinates of the temperature rise amount of the local heating portion 5c is expressed in a logarithmic scale. The same applies to the horizontal axis of FIG. 16, which will be described later.

図１５に示すように、図５に示した鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４について、いずれも局所加熱部５ｃの温度上昇量が大きくなるほど塑性ひずみ増分は大きくなっている。ここで、通常の圧延における圧下ひずみが０．１のオーダーであることを考慮すると、局所加熱部５ｃが形成されていない鋼片５を圧延したときの塑性ひずみからのひずみ増分量が０．０１（すなわち１％）以上であればその効果は実質的に有意であると考えられる。図１５より、鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４が０．０１を超える範囲は、局所加熱部５ｃの温度上昇量が１０℃以上、かつ、局所加熱部温度が融点温度未満の範囲である。すなわち、局所加熱部５ｃの温度上昇量が＋１０℃以下の範囲内であり、かつ、局所加熱部温度が融点温度未満となるように、局所加熱部５ｃを形成すればよい。 As shown in FIG. 15, for the peak strain increments dε peak 1/2 and dε peak 1/4 at the center position and 1/4 thickness position in the thickness direction of the billet 5 shown in FIG. The plastic strain increment increases as the temperature rise amount of the local heating portion 5c increases. Here, considering that the rolling strain in normal rolling is on the order of 0.1, the strain increment from the plastic strain when rolling the billet 5 in which the local heating portion 5c is not formed is 0.01 (ie, 1%) or more, the effect is considered substantially significant. From FIG. 15, the range where the peak strain increment dε peak 1/2 and dε peak 1/4 for the center position and 1/4 thickness position in the thickness direction of the billet 5 exceeds 0.01 is the local heating part The amount of temperature rise in 5c is 10° C. or more, and the temperature of the local heating part is in the range of less than the melting point temperature. That is, the local heating portion 5c may be formed so that the amount of temperature rise of the local heating portion 5c is within the range of +10° C. or less and the temperature of the local heating portion is lower than the melting point temperature.

局所加熱による鋼片５の温度変化が＋１０℃以上であれば、ひずみの増大効果を有意に得ることができる。また、局所加熱部温度を融点温度未満とすることで、局所加熱部５ｃの溶融後、再凝固による表面欠陥の発生や材質不合などの問題を回避することができる。 If the temperature change of the steel slab 5 due to local heating is +10° C. or more, a significant strain increasing effect can be obtained. Further, by setting the temperature of the locally heated portion to be lower than the melting point temperature, it is possible to avoid problems such as occurrence of surface defects and material incompatibility due to re-solidification after melting of the locally heated portion 5c.

なお、静水圧応力の増大効果については、図１６に示すように、局所加熱部５ｃの温度上昇量が＋１０℃以上、かつ、局所加熱部温度が融点温度未満の範囲であれば静水圧応力増分量は常に１０ＭＰａ以上あるため、ポロシティー圧着に関して実用十分な効果を享受することができる。 As for the effect of increasing the hydrostatic pressure stress, as shown in FIG. 16, if the temperature rise amount of the local heating portion 5c is +10° C. or more and the temperature of the local heating portion is in the range of less than the melting point temperature, the hydrostatic pressure stress increases. Since the amount is always 10 MPa or more, a practically sufficient effect can be obtained for porosity crimping.

（５）鋼片幅方向における配置
局所加熱部５ｃは、鋼片５の幅方向において必ずしも全幅に亘って連続的に形成される必要はなく、分散して形成されてもよい。 (5) Arrangement in Billet Width Direction The local heating portions 5c do not necessarily need to be formed continuously over the entire width of the billet 5 in the width direction, and may be formed dispersedly.

例えば、当該局所加熱部５ｃを鋼片５の全幅に亘って形成したときに、当該局所加熱部５ｃの形成時に不均一な鋼片表面スケールの生成や剥離が生じ、製品の表面品質の低下を来す場合もある。このような場合には、例えば図１７Ａに示すように、局所加熱部５ｃを幅方向に分散させ、表面性状の均一化を図ればよい。 For example, when the localized heating portion 5c is formed over the entire width of the billet 5, non-uniform surface scale of the billet may be generated or peeled off during the formation of the localized heating portion 5c, resulting in deterioration of the surface quality of the product. They may come. In such a case, for example, as shown in FIG. 17A, the local heating portions 5c may be dispersed in the width direction to make the surface properties uniform.

また、例えば、鋼片５の幅方向端部付近（例えば鋼片５の幅方向端部から鋼片さの０．５倍程度の距離だけ幅中央側へ入った位置Ｌａ）より幅中央側の位置において、鋼片厚さ中心近傍にポロシティーや中心偏析が集中して生じる場合もある。このような場合には、例えば図１７Ｂに示すように、鋼片５の幅方向端部付近（例えば位置Ｌａ）からポロシティーや中心偏析が生じる幅中央寄りの境界Ｌｂ近傍までの間に、局所加熱部５ｃを形成すればよい。なお、局所加熱部５ｃの幅Ｗは、鋼片５の厚さの０．１倍以上であるのがよい。局所加熱部５ｃの幅Ｗは、連続する局所加熱部５ｃを鋼片幅方向に投影したときの局所加熱部５ｃの長さをいう。 Further, for example, near the width direction end of the billet 5 (for example, a position La that enters the width center side from the width direction end of the billet 5 by a distance of about 0.5 times the billet height) Porosity and center segregation may occur intensively near the center of the billet thickness. In such a case, for example, as shown in FIG. 17B, a local A heating portion 5c may be formed. The width W of the locally heated portion 5c is preferably 0.1 times or more the thickness of the billet 5. The width W of the local heating portion 5c is the length of the local heating portion 5c when the continuous local heating portions 5c are projected in the billet width direction.

図１８に、局所加熱部５ｃの幅Ｗと塑性ひずみ増分との関係を示す。図１８の横軸は、局所加熱部５ｃの幅Ｗを鋼片厚さで除した値（すなわち、局所加熱部５ｃの幅Ｗ／鋼片厚さ）を示している。後述する図１９の横軸も同様である。図１８に示すように、図５に示した鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４について、いずれも局所加熱部５ｃの幅Ｗが大きくなるほど塑性ひずみ増分は大きくなっている。ここで、通常の圧延における圧下ひずみが０．１のオーダーであることを考慮すると、局所加熱部５ｃが形成されていない鋼片５を圧延したときの塑性ひずみからのひずみ増分量が０．０１（すなわち１％）以上であればその効果は実質的に有意であると考えられる。図１８より、鋼片５の厚さ方向の中央位置及び１／４厚さ位置についてのピークひずみ増分量ｄεpeak １／２、ｄεpeak １／４が０．０１を超える範囲は、局所加熱部５ｃの幅Ｗが鋼片５の厚さの０．１倍以上の範囲である。局所加熱により形成された鋼片５の局所加熱部５ｃの幅Ｗが鋼片５の厚さの０．１倍以上であれば、ひずみの増大効果を有意に得ることができる。 FIG. 18 shows the relationship between the width W of the local heating portion 5c and the plastic strain increment. The horizontal axis of FIG. 18 indicates the value obtained by dividing the width W of the locally heated portion 5c by the thickness of the billet (that is, the width W of the locally heated portion 5c/the thickness of the billet). The same applies to the horizontal axis of FIG. 19, which will be described later. As shown in FIG. 18, for the peak strain increments dε peak 1/2 and dε peak 1/4 at the center position and 1/4 thickness position in the thickness direction of the billet 5 shown in FIG. The larger the width W of the local heating portion 5c, the larger the plastic strain increment. Here, considering that the rolling strain in normal rolling is on the order of 0.1, the strain increment from the plastic strain when rolling the billet 5 in which the local heating portion 5c is not formed is 0.01 (ie, 1%) or more, the effect is considered substantially significant. From FIG. 18, the range where the peak strain increment dε peak 1/2 and dε peak 1/4 for the central position and 1/4 thickness position in the thickness direction of the billet 5 exceeds 0.01 is the local heating part The width W of 5c is in the range of 0.1 times or more the thickness of the billet 5. If the width W of the locally heated portion 5c of the steel billet 5 formed by local heating is 0.1 times or more the thickness of the steel billet 5, a significant effect of increasing strain can be obtained.

なお、静水圧応力の増大効果については、図１９に示すように、局所加熱部５ｃの幅Ｗが鋼片５の厚さの０．１倍以上の範囲であれば静水圧応力増分量は常に１０ＭＰａ以上あるため、ポロシティー圧着に関して実用十分な効果を享受することができる。 As for the effect of increasing the hydrostatic stress, as shown in FIG. Since it is 10 MPa or more, it is possible to enjoy a practically sufficient effect regarding porosity crimping.

鋼片幅方向に分散して形成される局所加熱部５ｃの例を図２０Ａ～図２０Ｈに示す。局所加熱部５ｃは、図２０Ａ及び図２０Ｂに示したように、必ずしも鋼片幅方向（Ｘ方向）に平行に形成される必要はなく、鋼片５を平面視したときの局所加熱部５ｃの形状は、鋼片幅方向に沿って延びる直線Ｌｘに対して交差する、斜線状、折れ線状、曲線状、周期関数状、または、千鳥状であってもよい。 20A to 20H show examples of the local heating portions 5c dispersedly formed in the width direction of the billet. As shown in FIGS. 20A and 20B, the local heating portion 5c does not necessarily need to be formed parallel to the billet width direction (X direction). The shape may be oblique, polygonal, curvilinear, periodic function, or zigzag that intersects the straight line Lx extending along the width direction of the billet.

局所加熱部５ｃが鋼片幅方向に略平行に形成される場合、当該局所加熱部５ｃによって生じる鋼片内部の変形状態の脈動は鋼片幅方向に略同時に起こる。このため、圧延条件や圧延機の状態（いわゆるガタの程度）によっては圧延中に顕著な振動が発生し、圧延操業の安定性や圧延機寿命の低下を来すことがある。このような場合には、当該局所加熱部５ｃを鋼片幅方向に対して有意に傾斜させ、斜線状（例えば図２０Ａ及び図２０Ｂ）、折れ線状（例えば図２０Ｃ）、曲線状（例えば図２０Ｄ及び図２０Ｅ）、千鳥状（例えば図２０Ｆ～図２０Ｈ）、またはこれらの組合せとする。このように局所加熱部５ｃを鋼片幅方向に分散させることで、上記変形状態の脈動が鋼片幅方向に略同時に生じることを抑制する。この結果、圧延中に顕著な振動は生じず、圧延操業の安定性や圧延機寿命の低下を回避できる。 When the local heating portions 5c are formed substantially parallel to the width direction of the billet, the pulsation of the deformed state inside the billet caused by the local heating portions 5c occurs substantially simultaneously in the width direction of the billet. Therefore, depending on the rolling conditions and the state of the rolling mill (the degree of so-called backlash), significant vibration may occur during rolling, which may lead to a decrease in the stability of the rolling operation and the life of the rolling mill. In such a case, the local heating portion 5c is significantly inclined with respect to the width direction of the billet, and is oblique (for example, FIGS. 20A and 20B), polygonal (for example, FIG. 20C), or curved (for example, FIG. 20D). and FIG. 20E), staggered (eg, FIGS. 20F-20H), or a combination thereof. By dispersing the local heating portions 5c in the width direction of the billet in this way, the pulsations in the deformed state described above are suppressed from occurring substantially simultaneously in the width direction of the billet. As a result, significant vibration does not occur during rolling, and reduction in the stability of the rolling operation and the life of the rolling mill can be avoided.

また、局所加熱部５ｃが鋼片幅方向に対して傾斜するように配置された場合、上述した局所加熱深さ及び局所加熱部間隔の要件は、鋼片厚さ方向と鋼片長さ方向（圧延方向と略同一）とがなす平面上で評価される寸法要件として定義される。なお、当該局所加熱深さ及び局所加熱部間隔の要件を満たすためには、当該局所加熱部５ｃの鋼片幅方向に対する傾斜角は４５°以下であることが望ましい。 In addition, when the local heating portion 5c is arranged so as to be inclined with respect to the billet width direction, the requirements for the above-mentioned local heating depth and local heating portion interval are the billet thickness direction and the billet length direction (rolling (substantially the same as the direction) is defined as a dimensional requirement evaluated on a plane. In addition, in order to satisfy the requirements for the local heating depth and the interval between the local heating portions, the inclination angle of the local heating portion 5c with respect to the billet width direction is preferably 45° or less.

さらに、連続鋳造機による連続鋳造工程の下流側のように、鋼片５の側面及び表裏面の双方からの冷却によって、図２１に示すように、コーナー部に顕著な温度低下部（以下、「コーナー過冷部５ｆ」ともいう。）が生じることがある。このとき、鋼片５の材質及びその温度依存性によってはコーナー過冷部５ｆの靭性低下が有意に生じる場合がある。このような場合にコーナー過冷部５ｆを含むように局所加熱部５ｃを形成すると、当該コーナー過冷部５ｆの平均温度が上昇し、製品品質の向上や鋼片破断による操業トラブルを防止することができる。なお、鋼片幅方向におけるコーナー過冷部５ｆの幅Ｗｅは、鋼片幅方向の端部から鋼片厚さの１．０倍程度中央側へ入った位置までの範囲に含まれる。 Furthermore, as in the downstream side of the continuous casting process by a continuous casting machine, by cooling from both the side surface and the front and back surfaces of the billet 5, as shown in FIG. Also referred to as "corner supercooled portion 5f") may occur. At this time, depending on the material of the steel piece 5 and its temperature dependence, the toughness of the corner supercooled portion 5f may significantly decrease. In such a case, if the local heating portion 5c is formed so as to include the corner supercooled portion 5f, the average temperature of the corner supercooled portion 5f increases, improving product quality and preventing operational troubles due to billet breakage. can be done. In addition, the width We of the corner supercooled portion 5f in the billet width direction is included in the range from the end portion in the billet width direction to the central position about 1.0 times the billet thickness.

［実施例１］
実施例１では、厚さ１００ｍｍ、幅６００ｍｍのスラブの鋳造が可能な連続鋳造機の機端に圧延機を設置し、連続鋳造圧延試験を行った。溶鋼の成分は、Ｃ：０．０９％、Ｓｉ：０．３１％、Ｍｎ：１．６８％、Ｐ：０．０１６％、Ｓ：０．０００８％、Ａｌ：０．００７％であった。溶鋼温度は１５７０℃であり、１．２ｍ／ｍｉｎの速度で鋳造した。圧延機入側におけるスラブ表面温度は１１００℃であった。 [Example 1]
In Example 1, a rolling mill was installed at the end of a continuous casting machine capable of casting a slab having a thickness of 100 mm and a width of 600 mm, and a continuous casting rolling test was conducted. The components of the molten steel were C: 0.09%, Si: 0.31%, Mn: 1.68%, P: 0.016%, S: 0.0008%, and Al: 0.007%. The molten steel temperature was 1570° C. and casting was performed at a speed of 1.2 m/min. The slab surface temperature at the entry side of the rolling mill was 1100°C.

設置した圧延機は２段圧延機であり、作業ロールの直径は６００ｍｍであった。圧延機での圧下量は３０ｍｍとした。本発明技術の適用例においては、図１に示した連続鋳造圧延設備のように、連続鋳造機と圧延機との間に加熱装置を設置し、鋼片表面を局所的に加熱することで鋼片長手方向に散在する局所加熱部を形成した。 The installed rolling mill was a two-high rolling mill, and the diameter of the work rolls was 600 mm. The reduction amount in the rolling mill was set to 30 mm. In an application example of the technology of the present invention, as in the continuous casting and rolling facility shown in FIG. Localized heating zones scattered along one longitudinal direction were formed.

本発明を適用した実施例Ａにおいては、鋼片の上面側にのみ局所加熱部を形成し、下面側は空冷ままとした。また、本発明を適用した実施例Ｂにおいては、鋼片の上面及び下面の双方に局所加熱部を形成した。いずれの場合も、局所加熱部はスラブの全幅に亘り、局所加熱深さが１０ｍｍ程度で鋼片厚さの約０．１倍、局所加熱長さが１５ｍｍ程度で鋼片厚さの約０．１５倍となるように形成した。また、局所加熱部間隔は約６０ｍｍ（接触弧長の約０．７倍）であった。加熱面積率は、実施例Ａでは約０．１倍、実施例Ｂでは約０．２倍であった。局所加熱部の温度は１１５０～１２００℃の範囲内であった。 In Example A to which the present invention was applied, the local heating portion was formed only on the upper surface side of the steel piece, and the lower surface side was air-cooled. Further, in Example B to which the present invention is applied, local heating portions are formed on both the upper surface and the lower surface of the steel slab. In either case, the local heating area extends over the entire width of the slab, the local heating depth is about 10 mm and the thickness is about 0.1 times the thickness of the billet, and the local heating length is about 15 mm and the thickness is about 0.1 times the thickness of the billet. It was formed so as to be 15 times larger. The interval between the local heating portions was approximately 60 mm (approximately 0.7 times the contact arc length). The heating area ratio was about 0.1 times in Example A and about 0.2 times in Example B. The temperature of the local heating portion was within the range of 1150-1200°C.

一方、従来技術を適用した比較例ａでは、局所加熱を行わず鋼片を圧延した。このとき、鋼片の表面温度はほぼ均一で約１１００℃であった。また、比較例ｂとして、鋼片を圧延機により全く圧下しなかった場合を示す。 On the other hand, in Comparative Example a to which the prior art was applied, the steel slab was rolled without local heating. At this time, the surface temperature of the steel slab was approximately uniform and about 1100°C. Moreover, as a comparative example b, the case where the steel slab was not reduced at all by the rolling mill is shown.

表１に、本実施例の圧延結果を示す。表１のλ０、ｄ０およびＡ０は、比較例ｂにおけるデンドライト組織の二次アーム間隔、平均結晶粒径（いずれも圧延後の鋼片幅中央の幅１００ｍｍ×長さ１００ｍｍ長さ×全厚の平均値）及び厚さ中央に残存したポロシティーの占積率（長さ１ｍ×幅６００ｍｍ内）である。すなわち、λ／λ０、ｄ／ｄ０、Ａ／Ａ０は、二次アーム間隔、結晶粒径、ポロシティー占積率それぞれの減少率を表しており、値が小さいほど鋼片の内部品質の改善度が高いことを表している。また備考欄には、圧延後の被圧延材形状もしくは圧延中から冷却後における表面性状を記載した。 Table 1 shows the rolling results of this example. λ0, d0, and A0 in Table 1 are the secondary arm spacing of the dendrite structure in Comparative Example b, and the average grain size (both are the average width of 100 mm in the center of the width of the billet after rolling × length 100 mm length × total thickness value) and the space factor of the porosity remaining in the center of the thickness (within a length of 1 m and a width of 600 mm). That is, λ/λ0, d/d0, and A/A0 represent the reduction rates of the secondary arm spacing, grain size, and porosity space factor. is high. In the remarks column, the shape of the material to be rolled after rolling or the surface properties during rolling and after cooling are described.

Figure 0007307339000001
Figure 0007307339000001

表１に示すように、実施例Ａ、Ｂでは、比較例ａと比較して、デンドライト組織の一次アーム間隔、平均結晶粒径およびポロシティーの占積率のいずれもが有意に減少した。実施例Ａでは圧延後に僅かな下反りが発生したが、その後の通板には問題ない程度に軽微であった。これより、本発明の適用により、表面欠陥の問題を生じることなく、後続工程に受け渡される鋼片の偏析や結晶組織、内部欠陥が顕著に改善されることは明らかである。 As shown in Table 1, in Examples A and B, compared with Comparative Example a, the primary arm spacing of the dendrite structure, the average crystal grain size, and the porosity space factor all decreased significantly. In Example A, a slight downward warp occurred after rolling, but it was so slight that there was no problem in subsequent sheet threading. From this, it is clear that the application of the present invention significantly improves the segregation, crystal structure, and internal defects of the slab delivered to subsequent processes without causing the problem of surface defects.

［実施例２］
実施例２では、図２２に示すように、実施例１と同じ連続鋳造機とその機端の２段圧延機を用いて、実施例１と同様に、厚さ１００ｍｍ、幅６００ｍｍのスラブの連続鋳造圧延試験を行った。溶鋼の成分、溶鋼温度、鋳造速度、圧下量及び圧延機入側におけるスラブ表面温度も実施例１と略同一であった。 [Example 2]
In Example 2, as shown in FIG. 22, a slab having a thickness of 100 mm and a width of 600 mm was continuously cast in the same manner as in Example 1 using the same continuous casting machine as in Example 1 and a two-stage rolling mill at the end of the casting machine. A casting rolling test was performed. The components of the molten steel, the molten steel temperature, the casting speed, the amount of reduction, and the slab surface temperature at the entry side of the rolling mill were also substantially the same as in Example 1.

本発明を適用した実施例Ｃ～Ｅにおいては、図２２に示すように、連続鋳造機と圧延機との間に局所加熱装置を設置し、鋼片の上下双方の表面を局所的に加熱することで鋼片長手方向に散在する局所加熱部を形成した。またいずれの場合も、局所加熱部は、鋼片厚さ方向及び鋼片長さ方向で構成される断面において、局所加熱深さが１０ｍｍ程度（鋼片厚さの約０．１倍）、局所加熱部間隔が約６０ｍｍ（接触弧長の約０．７倍）、局所加熱部の鋼片長手方向の長さが１５ｍｍ程度であった。 In Examples C to E to which the present invention is applied, as shown in FIG. 22, a local heating device is installed between the continuous casting machine and the rolling mill to locally heat both the upper and lower surfaces of the billet. As a result, localized heating zones were formed in the longitudinal direction of the billet. In either case, the local heating part has a local heating depth of about 10 mm (about 0.1 times the thickness of the billet) in a cross section configured in the billet thickness direction and the billet length direction. The distance between the parts was about 60 mm (about 0.7 times the contact arc length), and the length of the billet longitudinal direction of the local heating part was about 15 mm.

本発明を適用した実施例Ｃにおいては、実施例１と同様に矩形鋼片の全幅に亘って局所加熱部を形成した。本発明を適用した実施例Ｄにおいては鋼片の左右の幅端面位置を基準に約３０ｍｍから約２３０ｍｍまでの区間に幅方向長さが約２００ｍｍの局所加熱部を左右それぞれに形成した。本発明を適用した実施例Ｅにおいては、実施例Ｄと同じ区間に鋼片幅方向に対して１５°だけ鋼片幅中央側が圧延方向に先行して傾斜する局所加熱部を形成した。加熱面積率は、実施例Ｃでは約０．２倍、実施例Ｄ及びＥでは約０．１５倍であった。局所加熱部の温度は１１５０～１２００℃の範囲内であった。 In Example C to which the present invention is applied, as in Example 1, a local heating portion is formed over the entire width of the rectangular steel piece. In Example D to which the present invention is applied, local heating portions having a width direction length of about 200 mm are formed on the left and right sides in a section from about 30 mm to about 230 mm based on the left and right width end face positions of the steel billet. In Example E to which the present invention is applied, a local heating portion is formed in the same section as in Example D so that the width center side of the billet is inclined 15° with respect to the width direction of the billet prior to the rolling direction. The heating area ratio was about 0.2 times for Example C and about 0.15 times for Examples D and E. The temperature of the local heating portion was within the range of 1150-1200°C.

一方、従来技術を適用した比較例ｃでは、実施例１と同様に、局所加熱を行わず鋼片を圧延した。このとき、鋼片の表面温度はほぼ均一で約１１００℃であった。 On the other hand, in Comparative Example c to which the prior art was applied, the steel slab was rolled without performing local heating as in Example 1. At this time, the surface temperature of the steel slab was approximately uniform and about 1100°C.

表２に、実施例２の圧延結果を示す。表２のＡ０は、比較例ｃにおいて圧延後の鋼片の厚さ中央に残存したポロシティーの占積率（長さ１ｍ×幅６００ｍｍ内）である。すなわち、Ａ／Ａ０は、ポロシティー占積率それぞれの減少率を表しており、値が小さいほど鋼片の内部品質の改善度が高いことを表している。また備考欄には、圧延中の圧延トルクの変動および圧延機の状態変化を記載した。 Table 2 shows the rolling results of Example 2. A0 in Table 2 is the space factor (within a length of 1 m and a width of 600 mm) remaining at the center of the thickness of the billet after rolling in Comparative Example c. That is, A/A0 represents the reduction rate of each porosity space factor, and the smaller the value, the higher the degree of improvement in the internal quality of the billet. Also, in the remarks column, fluctuations in rolling torque during rolling and changes in the state of the rolling mill are described.

Figure 0007307339000002
Figure 0007307339000002

表２に示すように、実施例Ｃ、Ｄ、Ｅのいずれも、比較例ｃと比較して、ポロシティーの占積率が有意に減少した。実施例Ｃでは圧延トルクの変動が顕著で若干の圧延機振動が検知されたが、実施例Ｄでは振動が治まり、実施例Ｅでは比較例ｃとほぼ同様の圧延状況となった。実施例Ｃを含めて、圧延中の負荷変動や振動が操業上及び設備保全上問題となる程度ではないことが確認された。これより、本発明の適用により、圧延操業上及び設備保全上の問題を生じることなく、後続工程に受け渡される鋼片の内部欠陥が顕著に改善されることは明らかである。 As shown in Table 2, in all of Examples C, D and E, the porosity space factor was significantly reduced compared to Comparative Example c. In Example C, rolling torque fluctuated significantly and some rolling mill vibration was detected. Including Example C, it was confirmed that the load fluctuations and vibrations during rolling did not pose a problem in terms of operation and facility maintenance. From this, it is clear that the application of the present invention can remarkably improve the internal defects of the billet delivered to the succeeding process without causing any problems in terms of rolling operation and facility maintenance.

以上、添付図面を参照しながら本発明の好適な実施形態について詳細に説明したが、本発明はかかる例に限定されない。本発明の属する技術の分野における通常の知識を有する者であれば、特許請求の範囲に記載された技術的思想の範疇内において、各種の変更例または修正例に想到し得ることは明らかであり、これらについても、当然に本発明の技術的範囲に属するものと了解される。 Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

１ 鋳型
５ 鋼片
５ａ 凝固シェル
５ｂ 未凝固部
５ｃ 局所加熱部
５ｅ 変形増大部分
５ｆ コーナー過冷部
１０ 連続鋳造機
１１ タンディッシュ
１２ 浸漬ノズル
１３ 鋳型
１４ 二次冷却装置
１４ａ 支持ロール
２０、７０ 加熱装置
２１、７１ 交流電源
２３、７３ 誘導加熱コイル部
２５ スイッチ
３０、８０ 圧延機
３１ａ、３１ｂ、８１ａ、８１ｂ 圧延ロール
４０ 保熱装置
４１ａ、４１ｂ ローラ
４３ 無端ベルト
４５ 保熱部材
５０ 加熱炉
６０ スケール除去装置 Reference Signs List 1 mold 5 billet 5a solidified shell 5b unsolidified portion 5c local heating portion 5e increased deformation portion 5f corner supercooling portion 10 continuous casting machine 11 tundish 12 immersion nozzle 13 mold 14 secondary cooling device 14a support rolls 20, 70 heating device 21, 71 AC power supply 23, 73 Induction heating coil section 25 Switch 30, 80 Rolling mill 31a, 31b, 81a, 81b Rolling roll 40 Heat retaining device 41a, 41b Roller 43 Endless belt 45 Heat retaining member 50 Heating furnace 60 Scale removing device

Claims (12)

横断面形状が略矩形の鋼片を圧延する矩形断面鋼片の圧延方法であって、
圧延に先立ち、圧延ロールと接する前記鋼片の上下表面のうち少なくともいずれか一方を鋼片長手方向に間欠的に加熱または保熱して、前記鋼片長手方向に散在する局所加熱部を前記鋼片に形成し、
前記局所加熱部が形成された前記鋼片を圧延する、矩形断面鋼片の圧延方法。 A method for rolling a rectangular cross-section steel billet for rolling a steel billet having a substantially rectangular cross-sectional shape, comprising:
Prior to rolling, at least one of the upper and lower surfaces of the billet in contact with the rolling rolls is intermittently heated or maintained in the longitudinal direction of the billet, so that the locally heated portions scattered in the longitudinal direction of the billet are heated. to form
A method for rolling a rectangular cross-section steel billet, wherein the steel billet on which the local heating portion is formed is rolled. 前記局所加熱部は、前記鋼片長手方向に周期的に形成される、請求項１に記載の矩形断面鋼片の圧延方法。 2. The method of rolling a rectangular cross-section billet according to claim 1, wherein the local heating portions are periodically formed in the longitudinal direction of the billet. 前記局所加熱部は、当該局所加熱部の温度が、前記圧延ロールに接する前記鋼片の表面の前記局所加熱部以外の部分の平均温度に対して＋１０℃以上であり、かつ、前記鋼片の融点温度未満となるように形成される、請求項１または２に記載の矩形断面鋼片の圧延方法。The temperature of the local heating part is +10°C or higher than the average temperature of the portion other than the local heating part of the surface of the steel billet in contact with the rolling roll, and the temperature of the steel billet is 3. The method of rolling a rectangular cross-section steel billet according to claim 1 or 2, wherein the rectangular cross-section steel billet is formed so as to be below the melting point temperature. 前記局所加熱部は、
鋼片厚さ方向における前記鋼片の表面からの局所加熱深さが、前記鋼片の厚さの０．０１倍以上０．４０倍以下の範囲内であり、
圧延方向における局所加熱長さが、前記鋼片の厚さの０．０１倍以上１．５倍以下の範囲内にある、請求項３に記載の矩形断面鋼片の圧延方法。 The local heating unit is
The local heating depth from the surface of the billet in the thickness direction of the billet is in the range of 0.01 times or more and 0.40 times or less as large as the thickness of the billet,
4. The method of rolling a rectangular cross-section billet according to claim 3 , wherein the local heating length in the rolling direction is in the range of 0.01 to 1.5 times the thickness of the billet. 前記局所加熱部は、当該局所加熱部の表面積が、前記圧延ロールと接する前記鋼片の上下表面の全表面積の０．０１倍以上０．５０倍以下の範囲内となるように形成される、請求項３または４に記載の矩形断面鋼片の圧延方法。 The local heating part is formed so that the surface area of the local heating part is in the range of 0.01 to 0.50 times the total surface area of the upper and lower surfaces of the billet in contact with the rolling rolls. The method for rolling a rectangular cross-section steel billet according to claim 3 or 4 . 前記局所加熱部は、前記鋼片が圧延される際の前記圧延ロールとの接触弧長の１／６０倍以上２倍以下の間隔を前記鋼片長手方向に有するように形成される、請求項３～５のいずれか１項に記載の矩形断面鋼片の圧延方法。 The said local heating part is formed so as to have an interval in the longitudinal direction of the billet that is 1/60 to 2 times the arc length of contact with the rolling rolls when the billet is rolled. 6. A method for rolling a rectangular cross-section billet according to any one of 3 to 5 . 前記局所加熱部は、鋼片幅方向に分散して形成される、請求項１～６のいずれか１項に記載の矩形断面鋼片の圧延方法。 The method for rolling a rectangular cross-section billet according to any one of claims 1 to 6, wherein the local heating portions are formed dispersedly in the width direction of the billet. 前記局所加熱部は、当該局所加熱部の温度が、前記圧延ロールに接する前記鋼片の表面の前記局所加熱部以外の部分の平均温度に対して＋１０℃以上であり、かつ、前記鋼片の融点温度未満となるように形成され、
前記局所加熱部の幅は、前記鋼片の厚さの０．１倍以上である、請求項７に記載の矩形断面鋼片の圧延方法。 The temperature of the local heating part is +10°C or higher than the average temperature of the portion other than the local heating part of the surface of the steel billet in contact with the rolling roll, and the temperature of the steel billet is Formed to be below the melting point temperature,
8. The method of rolling a rectangular cross-section billet according to claim 7, wherein the width of said locally heated portion is 0.1 times or more the thickness of said billet. 前記鋼片を平面視したときの前記局所加熱部の形状は、前記鋼片幅方向に沿って延びる直線に対して交差する、斜線状、折れ線状、曲線状、周期関数状、または、千鳥状である、請求項７または請求項８に記載の矩形断面鋼片の圧延方法。 When the billet is viewed in plan, the shape of the local heating portion is oblique, polygonal, curved, periodic function, or zigzag that intersects a straight line extending along the width direction of the billet. The method for rolling a rectangular cross-section steel billet according to claim 7 or 8, wherein: 前記局所加熱部は、前記鋼片のコーナー過冷部を含むように形成される、請求項７～９のいずれか１項に記載の矩形断面鋼片の圧延方法。 The method for rolling a rectangular cross-section billet according to any one of claims 7 to 9, wherein the local heating section is formed so as to include a corner supercooled section of the billet. 鋼片を鋳造する連続鋳造機と、
前記連続鋳造機の下流側に配置され、前記連続鋳造機により鋳造された前記鋼片の上下表面のうち少なくともいずれか一方を鋼片長手方向に間欠的に加熱または保熱して、前記鋼片長手方向に散在する局所加熱部を前記鋼片に形成する加熱装置と、
前記加熱装置の下流側に配置され、前記局所加熱部が形成された前記鋼片を圧延する圧延機と、
を備える、連続鋳造圧延設備。 a continuous casting machine for casting billets;
is disposed downstream of the continuous casting machine and intermittently heats or retains at least one of the upper and lower surfaces of the billet cast by the continuous casting machine in the longitudinal direction of the billet to a heating device for forming local heating portions scattered in the direction of the billet;
a rolling mill disposed on the downstream side of the heating device for rolling the billet on which the local heating portion is formed;
Continuous casting and rolling equipment. 加熱炉にて加熱された鋼片の上下表面のうち少なくともいずれか一方を鋼片長手方向に間欠的に加熱または保熱して、前記鋼片長手方向に散在する局所加熱部を前記鋼片に形成する加熱装置と、
前記加熱装置の下流側に配置され、前記局所加熱部が形成された前記鋼片を圧延する圧延機と、
を備える、圧延設備。 At least one of the upper and lower surfaces of a billet heated in a heating furnace is intermittently heated or maintained in the longitudinal direction of the billet to form locally heated portions scattered in the longitudinal direction of the billet. a heating device that
a rolling mill disposed on the downstream side of the heating device for rolling the billet on which the local heating portion is formed;
A rolling facility.
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