JP6451380B2 - Steel continuous casting method - Google Patents

Steel continuous casting method Download PDF

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JP6451380B2
JP6451380B2 JP2015027102A JP2015027102A JP6451380B2 JP 6451380 B2 JP6451380 B2 JP 6451380B2 JP 2015027102 A JP2015027102 A JP 2015027102A JP 2015027102 A JP2015027102 A JP 2015027102A JP 6451380 B2 JP6451380 B2 JP 6451380B2
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mold
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immersion nozzle
molten steel
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雅俊 川端
雅俊 川端
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Nippon Steel Corp
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本発明は、鋳型内に溶鋼を供給して鋳片を製造する鋼の連続鋳造方法に関するものである。   The present invention relates to a continuous casting method of steel in which molten steel is supplied into a mold to produce a slab.

鋼の連続鋳造時、鋳型内の溶鋼湯面(以下、メニスカスという)付近には溶鋼中の気泡が浮上してくるので、特にメニスカス位置の凝固シェルに前記浮上してきた気泡が捕捉されやすい。   During continuous casting of steel, bubbles in the molten steel rise near the molten steel surface (hereinafter referred to as meniscus) in the mold, so that the raised bubbles are particularly easily captured by the solidified shell at the meniscus position.

捕捉された気泡は、圧延時に表面疵となる場合があることから、鋼の連続鋳造においては、鋳片の表面性状を改善するため、鋳型のメニスカス位置近傍の外周部に設置した電磁攪拌装置を用いて鋳型内の溶鋼を攪拌して流動させることが一般的に行われている。   Since the trapped air bubbles may become surface defects during rolling, in order to improve the surface properties of the slab in continuous casting of steel, an electromagnetic stirrer installed on the outer periphery near the meniscus position of the mold is used. In general, the molten steel in the mold is stirred and fluidized.

鋳型内溶鋼の前記電磁攪拌によって発生する凝固シェルの前面の溶鋼流れにより、溶鋼中の気泡が凝固シェルに捕捉されることを抑制することができる。   It is possible to suppress trapping of bubbles in the molten steel by the solidified shell due to the molten steel flow in front of the solidified shell generated by the electromagnetic stirring of the molten steel in the mold.

しかしながら、鋳型の長辺中央部では浸漬ノズルと長辺壁面との距離が狭くなるので、電磁攪拌によって発生する鋳型内溶鋼のメニスカス位置における水平面の溶鋼流れが停滞する。   However, since the distance between the immersion nozzle and the long side wall surface becomes narrow at the central part of the long side of the mold, the molten steel flow in the horizontal plane at the meniscus position of the molten steel in the mold generated by electromagnetic stirring stagnates.

また、メニスカス位置における鋳型の短辺部分では短辺に向かう吐出流が短辺壁面と衝突して短辺壁面に沿って上昇し、メニスカス位置において鋳型の長辺中央部に向かう流れとなるので、前記電磁攪拌によって発生する溶鋼流れと干渉して溶鋼流れが停滞する。この溶鋼流れの停滞部分では気泡が凝固シェルに捕捉されやすくなる。   Also, in the short side portion of the mold at the meniscus position, the discharge flow toward the short side collides with the short side wall surface and rises along the short side wall surface, and at the meniscus position, it becomes a flow toward the long side center of the mold. The molten steel flow stagnates due to interference with the molten steel flow generated by the electromagnetic stirring. In the stagnation portion of the molten steel flow, bubbles are easily trapped by the solidified shell.

そのため、メニスカス位置における鋳型の長辺中央部の凝固シェル前面に一様な流速を持つ攪拌流が求められてきた。   Therefore, a stirring flow having a uniform flow velocity has been demanded on the front surface of the solidified shell at the center of the long side of the mold at the meniscus position.

例えば特許文献1には、鋳型の短辺壁面と相対する左右の吐出孔を側壁に対称となるように配置し、底壁には一端が右吐出孔に、他端が左吐出孔に達する一本のスリットを配した浸漬ノズルを用いた鋼の連続鋳造法が開示されている。   For example, in Patent Document 1, left and right discharge holes facing the short side wall of the mold are arranged symmetrically with respect to the side wall, and one end of the bottom wall reaches the right discharge hole and the other end reaches the left discharge hole. A continuous casting method of steel using an immersion nozzle provided with a slit is disclosed.

しかしながら、発明者が特許文献1で開示された連続鋳造方法について調査したところ、スリットの幅が大きくなると鋳型の長辺壁面に衝突した吐出流が鋳型の長辺壁面に沿って形成された凝固シェルを溶解させ、再溶解に伴う鋳片表面疵や最悪の場合ブレイクアウトなどにより操業に悪影響を及ぼすことが判明した。また、溶鋼流れが停滞する鋳型の長辺中央部に気泡等の浮上量が増加し、鋳型の長辺中央部で欠陥が増加することも判明した。   However, when the inventor investigated the continuous casting method disclosed in Patent Document 1, the solidified shell in which the discharge flow that collided with the long side wall surface of the mold was formed along the long side wall surface of the mold when the slit width was increased. It has been found that slab surface defects accompanying remelting and the worst case breakout have an adverse effect on operations. It was also found that the floating amount of bubbles and the like increased at the center of the long side of the mold where the molten steel flow stagnated, and defects increased at the center of the long side of the mold.

また、特許文献2には、電磁攪拌装置側に向かって凸に湾曲した鋳型を使用して鋼を連続鋳造することが開示されている。   Patent Document 2 discloses continuous casting of steel using a mold that is convexly curved toward the electromagnetic stirrer side.

しかしながら、電磁攪拌装置側に向かって凸に湾曲した鋳型を使用した連続鋳造の場合、鋳型の長辺端部で溶鋼と電磁攪拌装置との距離が大きくなって溶鋼流れが小さくなる。加えて、発明者が調査したところ、前記小さくなった鋳型の長辺端部での溶鋼流れと鋳型の短辺壁面からの吐出反転流が干渉して溶鋼流れが停滞、または電磁攪拌による流動と逆方向の流れとなることが判明した。そのため、鋳型と浸漬ノズルとの距離または鋳型の凸部の大きさに制約が発生する。   However, in the case of continuous casting using a mold that is convexly convex toward the electromagnetic stirrer side, the distance between the molten steel and the electromagnetic stirrer increases at the long side end of the mold, and the molten steel flow decreases. In addition, as a result of investigation by the inventors, the molten steel flow at the end of the long side of the reduced mold and the reverse flow of the discharge from the short side wall surface of the mold interfere with each other, and the molten steel flow stagnates or flows due to electromagnetic stirring. It was found that the flow was in the opposite direction. Therefore, there is a restriction on the distance between the mold and the immersion nozzle or the size of the convex portion of the mold.

特開2000−343188号公報JP 2000-343188 A 特開2011−224635号公報JP2011-224635A

本発明が解決しようとする問題点は、従来技術では、メニスカス位置における鋳型の長辺中央部の凝固シェル前面に一様な流速を持つ攪拌流を得ることが難しいという点である。   The problem to be solved by the present invention is that in the prior art, it is difficult to obtain a stirring flow having a uniform flow velocity in front of the solidified shell at the center of the long side of the mold at the meniscus position.

本発明は、
メニスカス位置における鋳型の長辺中央部の凝固シェル前面に一様な流速を持つ攪拌流を得るようにするために、
鋳型内のメニスカス近傍の溶鋼を電磁攪拌しつつ鋼を連続鋳造する方法であって、
連続鋳造時、鋳型内のメニスカス下方の鋳型の短辺壁面と相対する側壁部に設けた2つの吐出孔とつながったスリット状の吐出孔を底壁に形成した浸漬ノズルを用いて、
鋳型上部の各長辺の中央部分は鋳型の外側に凸に湾曲した湾曲部を有し、鋳型下部に向かうにつれて前記湾曲部の湾曲が小さくなって鋳型下部では前記湾曲部がない鋳型に給湯する際、
前記浸漬ノズルの底壁に形成したスリット状の吐出孔の厚み方向の幅aと、鋳型の前記湾曲部と前記浸漬ノズルの下端との最短水平距離bとの関係が、前記最短水平距離bが50mm以上で、a/b≦0.5となるようにして連続鋳造することを最も主要な特徴としている。
The present invention
In order to obtain a stirring flow having a uniform flow velocity in front of the solidified shell at the center of the long side of the mold at the meniscus position,
A method of continuously casting steel while electromagnetically stirring molten steel near a meniscus in a mold,
At the time of continuous casting, using a submerged nozzle formed with slit-like discharge holes connected to two discharge holes provided on the side wall portion facing the short side wall surface of the mold below the meniscus in the mold,
The central part of each long side of the upper part of the mold has a curved part that is convexly curved toward the outside of the mold, and the curvature of the curved part becomes smaller toward the lower part of the mold, and hot water is supplied to the mold without the curved part at the lower part of the mold. When
The relationship between the width a in the thickness direction of the slit-shaped discharge hole formed in the bottom wall of the immersion nozzle and the shortest horizontal distance b between the curved portion of the mold and the lower end of the immersion nozzle is the shortest horizontal distance b. The main feature is continuous casting so that a / b ≦ 0.5 at 50 mm or more .

本発明では、浸漬ノズルの底壁に形成したスリット状の吐出孔の厚み方向の幅aと、鋳型の各長辺の中央部分に形成した湾曲部と浸漬ノズルの下端との最短水平距離bの関係を最適範囲に規定することで、メニスカス位置における鋳型の長辺中央部の凝固シェル前面に一様な流速を持つ溶鋼流れを得ることができる。   In the present invention, the width a in the thickness direction of the slit-like discharge hole formed on the bottom wall of the immersion nozzle, and the shortest horizontal distance b between the curved portion formed at the center of each long side of the mold and the lower end of the immersion nozzle By defining the relationship within the optimum range, it is possible to obtain a molten steel flow having a uniform flow velocity on the front surface of the solidified shell at the center of the long side of the mold at the meniscus position.

本発明では、メニスカス位置における水平面の凝固シェル前面に幅方向に一様な流速を持つ溶鋼流れを得ることができるので、鋳型の長辺中央部と長辺端部での溶鋼流れの停滞がおこらず、鋳型の長辺中央部の凝固シェルが再溶解することがない。従って、メニスカス位置における鋳型の長辺中央部及び長辺端部で凝固シェルへの気泡の捕捉を防止でき、良好な表面品質を有する鋳片をトラブルなく鋳造することができる。   In the present invention, a molten steel flow having a uniform flow velocity in the width direction can be obtained in front of the solidified shell in the horizontal plane at the meniscus position, so that the molten steel flow stagnates at the long side center and long side end of the mold. Therefore, the solidified shell at the center of the long side of the mold does not redissolve. Accordingly, it is possible to prevent trapping of bubbles in the solidified shell at the long side center portion and the long side end portion of the mold at the meniscus position, and it is possible to cast a slab having good surface quality without any trouble.

本発明の鋼の連続鋳造方法に使用する鋳型形状と浸漬ノズルの形状及び両者の相対位置関係を説明する図で、(a)は平面方向から見た図、(b)は(a)のA−A方向から見た図である。It is a figure explaining the mold shape used for the continuous casting method of steel of this invention, the shape of an immersion nozzle, and both relative position relationship, (a) is the figure seen from the plane direction, (b) is A of (a). It is the figure seen from -A direction. 鋳片の長辺中央部における気泡捕捉密度を算出した際の長辺中央部のサンプル位置を説明する図である。It is a figure explaining the sample position of the long side center part at the time of calculating the bubble capture density in the long side center part of slab. 鋳片の長辺端部における気泡捕捉密度を算出した際の長辺端部のサンプル位置を説明する図である。It is a figure explaining the sample position of the long side edge part at the time of calculating the bubble capture density in the long side edge part of a slab. 表1,2を基に作成した、電磁ブレーキを併用しない場合と併用した場合における、浸漬ノズルの底壁に形成したスリット状の吐出孔の厚み方向の幅aと、鋳型の長辺中央部に形成した湾曲部と浸漬ノズルの下端との最短水平距離bとの比a/bと、鋳造状況の関係を示した図である。The width a in the thickness direction of the slit-shaped discharge hole formed in the bottom wall of the immersion nozzle and the central part of the long side of the mold when the electromagnetic brake is not used together with the case created based on Tables 1 and 2 It is the figure which showed ratio a / b of the shortest horizontal distance b of the formed curved part and the lower end of an immersion nozzle, and the relationship of a casting condition. 表1,2を基に作成した、電磁ブレーキを併用しない場合と併用した場合における、浸漬ノズルの底壁に形成したスリット状の吐出孔の厚み方向の幅aと、鋳型の長辺端部の気泡捕捉指数の関係を示した図である。The width a in the thickness direction of the slit-shaped discharge hole formed in the bottom wall of the immersion nozzle and the case where the electromagnetic brake is not used together with the case where the electromagnetic brake is used together based on Tables 1 and 2, and the long side end of the mold It is the figure which showed the relationship of the bubble trap index. 表1,2を基に作成した、電磁ブレーキを併用しない場合と併用した場合における、鋳型の長辺中央部と浸漬ノズルの下端との最短水平距離b´又はbと、鋳型の長辺中央部の気泡捕捉指数の関係を示した図である。The shortest horizontal distance b ′ or b between the long side center part of the mold and the lower end of the submerged nozzle and the long side center part of the mold when the electromagnetic brake is not used together and when it is used based on Tables 1 and 2 It is the figure which showed the relationship of the bubble trapping index. 表1を基に作成した、電磁ブレーキを併用しない場合における、a/b´又はa/bと鋳型の長辺端部の気泡捕捉指数の関係を示した図である。It is the figure which created based on Table 1 and showed the relationship between a / b 'or a / b and the bubble capture index | exponent of the long side edge part of a casting_mold | template when not using an electromagnetic brake together.

本発明では、メニスカス位置における鋳型の長辺中央部の凝固シェル前面に一様な流速を持つ攪拌流を得るという目的を、浸漬ノズルの底壁に形成したスリット状の吐出孔の厚み方向の幅aと、鋳型の各長辺の中央部分に形成した湾曲部と浸漬ノズルの下端との最短水平距離bの関係を最適範囲に規定することで実現した。   The purpose of the present invention is to obtain a stirring flow having a uniform flow velocity on the front surface of the solidified shell at the center of the long side of the mold at the meniscus position. This is realized by defining the relationship between a and the shortest horizontal distance b between the curved portion formed at the center of each long side of the mold and the lower end of the immersion nozzle within the optimum range.

先ず、本発明の鋼の連続鋳造方法についての新しい着想について説明する。
電磁攪拌装置により鋳型の長辺方向に移動磁場を印加した際、鋳型の長辺壁面の凝固シェル前面における鋳型の長辺方向の溶鋼流れは、鋳型の長辺中央部及び長辺端部において停滞しやすい。
First, the new idea about the continuous casting method of steel of the present invention will be described.
When a moving magnetic field is applied in the long side direction of the mold by an electromagnetic stirrer, the molten steel flow in the long side direction of the mold on the front surface of the solidified shell on the long side wall surface of the mold is stagnated at the central part of the long side and at the end of the long side. It's easy to do.

そこで、発明者は、鋳型の長辺中央部を、電磁攪拌装置を設けた鋳型の外側に凸に湾曲させることにより、鋳型の長辺中央部での溶鋼流れの停滞を防止するのと共に、通常の浸漬ノズルの底壁にスリット状の吐出孔(以下、スリットという)を設けて鋳型の短辺に向かう吐出流を弱めることにより、鋳型の長辺端部での溶鋼流れの停滞を防止できると考えた。   Therefore, the inventor prevents the stagnation of the molten steel flow at the central part of the long side of the mold by curving the central part of the long side of the mold so as to protrude outward from the mold provided with the electromagnetic stirring device. By providing a slit-like discharge hole (hereinafter referred to as a slit) in the bottom wall of the immersion nozzle to weaken the discharge flow toward the short side of the mold, the stagnation of the molten steel flow at the long side end of the mold can be prevented. Thought.

しかしながら、発明者が調査したところ、底壁にスリットを設けた浸漬ノズルの場合、特に高スループット鋳造で下方向の吐出流が鋳型の長辺壁面に沿って形成された凝固シェルに衝突して当該凝固シェルが再溶解し、溶鋼が漏れ出すトラブルが発生する場合があることが分かった。   However, as a result of investigation by the inventor, in the case of an immersion nozzle provided with a slit in the bottom wall, the downward discharge flow collides with a solidified shell formed along the long side wall surface of the mold, particularly in high-throughput casting. It has been found that there is a case where the solidified shell is remelted and the molten steel leaks.

また、単純に鋳型の長辺中央部を鋳型の外側に凸に湾曲させた鋳型と、浸漬ノズルの底壁にスリットを設けた浸漬ノズルを組み合わせるだけで、鋳型の長辺中央部に形成した湾曲部と浸漬ノズル下端との最短水平距離と、浸漬ノズルの底壁のスリットの幅を調節しない場合、前記の流動停滞や鋳型の長辺中央部の凝固シェルの再溶解が防止できないことが分かった。   In addition, a curve formed at the center of the long side of the mold simply by combining a mold with the center of the long side convexly protruding outward from the mold and an immersion nozzle provided with a slit in the bottom wall of the immersion nozzle. It was found that the flow stagnation and remelting of the solidified shell at the center of the long side of the mold could not be prevented without adjusting the shortest horizontal distance between the bottom part and the lower end of the immersion nozzle and the width of the slit of the bottom wall of the immersion nozzle. .

本発明は上記新しい着想に基づき、次に説明する実験を経てなされたものである。   The present invention has been made through experiments described below based on the above-described new idea.

〔実験A〕
両長辺壁面が直線の横断面矩形状の鋳型内に、底壁にスリットを設けた浸漬ノズルを、当該浸漬ノズルの下端と鋳型の各長辺壁面との最短水平距離b´を37.5mmとして鋳型の両短辺方向に向けて設置し、1分当たり4.0トンの溶鋼を注入しながら、鋳型内の溶鋼に電磁攪拌装置により移動磁場を印加しつつ鋼を連続鋳造した。
[Experiment A]
In the mold having a rectangular cross section with both long side walls straight, an immersion nozzle provided with a slit in the bottom wall, and the shortest horizontal distance b ′ between the lower end of the immersion nozzle and each long side wall surface of the mold is 37.5 mm. The steel was continuously cast while applying a moving magnetic field to the molten steel in the mold by an electromagnetic stirrer while injecting 4.0 tons of molten steel per minute.

次に、鋳型上部の各長辺の中央部分は電磁攪拌装置側に凸に湾曲した湾曲部を有し、鋳型下部に向かうにつれて前記湾曲部の湾曲が小さくなって鋳型下部では前記湾曲部がない鋳型を使用し、前記湾曲部の凸湾曲量を変化させることで、鋳型の前記湾曲部と浸漬ノズルの下端との最短水平距離bを変化させて上記と同様の条件で鋳造を行った。   Next, the central part of each long side of the upper part of the mold has a curved part that is convexly curved toward the electromagnetic stirrer, and the curvature of the curved part becomes smaller toward the lower part of the mold, and there is no curved part at the lower part of the mold. Casting was performed under the same conditions as described above by changing the shortest horizontal distance b between the curved portion of the mold and the lower end of the immersion nozzle by changing the convex curve amount of the curved portion using a mold.

鋳造結果を下記表1に示す。
下記表1には、連続鋳造に使用した浸漬ノズルの底壁に設けたスリットの幅aと、前記最短水平距離b´又はbと、これらの関係a/b´又はa/bと、ブレイクアウトの発生の有無と、鋳型の長辺中央部と長辺端部での気泡の捕捉密度指数、および請求項1を満たすか否かを示す。
The casting results are shown in Table 1 below.
Table 1 below shows the width a of the slit provided on the bottom wall of the immersion nozzle used for continuous casting, the shortest horizontal distance b ′ or b, the relationship a / b ′ or a / b, and the breakout. And the occurrence density of bubbles, the trap density index of bubbles at the center and the end of the long side of the mold, and whether or not claim 1 is satisfied.

また、図1に鋳型1の長辺中央部1a及び長辺端部1bの位置、および浸漬ノズル2の2つの吐出孔2aとつながって、浸漬ノズル2の底壁に設けたスリット2bの幅aと、鋳造時における鋳型1の長辺中央部1aに設けた湾曲部1cと浸漬ノズル2の下端との最短水平距離bを示す。   Further, the width a of the slit 2b provided in the bottom wall of the immersion nozzle 2 connected to the positions of the long side central portion 1a and the long side end portion 1b of the mold 1 and the two discharge holes 2a of the immersion nozzle 2 in FIG. And the shortest horizontal distance b of the curved part 1c provided in the long side center part 1a of the casting_mold | template 1 at the time of casting, and the lower end of the immersion nozzle 2 is shown.

下記表1におけるブレイクアウトの欄は、ブレイクアウトが発生しなかった場合を〇、ブレイクアウトが発生した場合を×とした。また、ブレイクアウトは発生しなかったが、鋳型の長辺中央部の浸漬ノズルの下端から鋳片引抜方向に100mm隔てた位置の鋳型内に設置した熱電対の温度が、同じ高さ位置の鋳型長辺の短辺寄りの位置に設置した他の熱電対の温度の平均値よりも1.2倍以上上昇した場合を△とした。   In the breakout column in Table 1 below, the case where breakout did not occur was marked as ◯, and the case where breakout occurred was marked as x. Moreover, although the breakout did not occur, the temperature of the thermocouple installed in the mold at a position 100 mm away from the lower end of the immersion nozzle at the center of the long side of the mold in the slab drawing direction was the same height position. A case where the temperature rises 1.2 times or more than the average value of the temperature of other thermocouples installed at positions near the short side of the long side is indicated by Δ.

また、気泡の捕捉密度指数は、鋳片中に捕捉された気泡捕捉密度を指数化したもので、底壁にスリットがなく、縦70mm、横55mmの2つの吐出孔を有する浸漬ノズルを、2つの吐出孔が鋳型の両短辺方向に向くように設置し、前記最短水平距離b´が37.5mmで、鋳型の両長辺壁面が直線の横断面矩形状の鋳型を使用した場合の気泡捕捉密度を1とした。   The bubble trapping density index is an index of the bubble trapping density trapped in the slab, and an immersion nozzle having two slits of 70 mm in length and 55 mm in width without slits on the bottom wall is 2 Bubbles in the case of using a mold having two discharge holes facing both short sides of the mold, the shortest horizontal distance b 'being 37.5 mm, and both long side walls of the mold having a straight transverse section The trap density was 1.

すなわち、気泡捕捉密度が1より大きい場合は、前記鋳造条件で鋳造した鋳片よりも気泡の捕捉量が増加し、気泡捕捉密度が1より小さい場合は、前記鋳造条件で鋳造した鋳片よりも気泡の捕捉量が減少したことを意味する。   That is, when the bubble trapping density is larger than 1, the trapped amount of bubbles is increased as compared with the slab cast under the casting condition, and when the bubble trapping density is smaller than 1, the slab cast under the casting condition. This means that the amount of trapped air bubbles has decreased.

鋳型の長辺中央部での気泡捕捉密度は、図2に示すように、鋳造した鋳片3の長辺の中央から長辺の両端方向に各100mm(合計200mm)、短辺の両端から短辺の中央方向に10mm、鋳造方向に10mmのサンプル4を作製した後、当該サンプル4にX線を透過させて気泡数を測定し、サンプル4の体積で測定した気泡数を除して算出した。   As shown in FIG. 2, the bubble trapping density at the center of the long side of the mold is 100 mm each from the center of the long side of the cast slab 3 to both ends of the long side (total 200 mm), and short from both ends of the short side. A sample 4 having 10 mm in the center direction of the side and 10 mm in the casting direction was prepared, and then the number of bubbles was measured by transmitting X-rays through the sample 4, and the number of bubbles measured by the volume of the sample 4 was divided and calculated. .

一方、鋳型の長辺端部での気泡捕捉密度は、図3に示すように、鋳造した鋳片3の長辺の両端から50mmの位置より長辺の中央方向に100mm、短辺の両端から短辺の中央方向に10mm、鋳造方向に10mmのサンプル4を作製した後、当該サンプルにX線を透過させて気泡数を測定し、サンプルの体積で測定した気泡数を除して算出した。   On the other hand, as shown in FIG. 3, the bubble trapping density at the long side end portion of the mold is 100 mm from the both ends of the long side of the cast slab 3 toward the center of the long side from the both ends of the long side, and from both ends of the short side. A sample 4 having a length of 10 mm in the central direction of the short side and 10 mm in the casting direction was prepared, and the number of bubbles was measured by transmitting X-rays through the sample, and the number of bubbles measured by the volume of the sample was divided.

なお、ブレイクアウトが発生したものについては、ブレイクアウトが発生する以前に鋳造した部分より気泡捕捉密度の調査を行った。   In addition, about what a breakout generate | occur | produced, the bubble capture density was investigated from the part cast before breakout generate | occur | produced.

また、請求項1の欄は、それぞれの請求項を満たす場合は〇、満たさない場合は−とした。 Further, in the column of claim 1, “ Yes” is satisfied when each claim is satisfied, and “-” is not satisfied.

Figure 0006451380
Figure 0006451380

表1及び表1を基に作成した図4より、実験Aでブレイクアウトが発生した実施番号11,14,16,17はa/b´又はa/bが0.6を超えていた。また、a/b´又はa/bが0.5を超え、0.6以下の実施番号8,12では、ブレイクアウトは発生しなかったが、鋳型の長辺中央部における浸漬ノズルの下端から鋳片引抜方向に100mm隔てた位置の鋳型内に設置した熱電対の温度が、同じ高さ位置の鋳型長辺の短辺寄りの位置に設置した他の熱電対の温度の平均値よりも1.2倍以上上昇した。   According to Table 1 and FIG. 4 created based on Table 1, a / b ′ or a / b exceeded 0.6 in execution numbers 11, 14, 16, and 17 in which breakout occurred in Experiment A. Moreover, although breakout did not generate | occur | produce in the implementation numbers 8 and 12 with a / b 'or a / b exceeding 0.5 and 0.6 or less, from the lower end of the immersion nozzle in the long side center part of a casting_mold | template. The temperature of the thermocouple installed in the mold at a position 100 mm apart in the slab drawing direction is 1 than the average value of the temperatures of other thermocouples installed near the short side of the long side of the mold at the same height. Increased more than 2 times.

これは、実施番号8のa/b´(=0.53)を超える条件では、ブレイクアウトが発生する可能性があることを示唆している。実際に、例えば実施番号12ではブレイクアウトが発生せずに鋳型の長辺中央部における温度が上昇しただけであったが、実施番号12よりも前記スリットの幅a、すなわちa/bを大きくした実施番号17ではブレイクアウトが発生した。そのため、確実にブレイクアウトを防ぐためには、a/bを0.5より小さい値にすることが望ましいことが判明した。   This suggests that breakout may occur under conditions exceeding a / b ′ (= 0.53) of the execution number 8. Actually, for example, in No. 12, the breakout did not occur and the temperature at the central part of the long side of the mold only increased. However, the width a of the slit, that is, a / b, was made larger than that of No. 12. In run number 17, a breakout occurred. Therefore, it has been found that it is desirable to set a / b to a value smaller than 0.5 in order to surely prevent breakout.

また、表1及び表1を基に作成した図5より、浸漬ノズルの底壁に設けたスリットの幅aが10mmの実施番号5〜7では、鋳型の長辺端部の気泡捕捉指数が1.2又は0.8と十分に減少しなかったが、前記スリットの幅aが20mm以上の実施番号8〜18では、鋳型の長辺端部の気泡捕捉指数が0.2又は0.1となり、顕著に減少した。   Moreover, from FIG. 5 created based on Table 1 and Table 1, in the implementation numbers 5 to 7 where the width a of the slit provided on the bottom wall of the immersion nozzle is 10 mm, the bubble trapping index at the long side edge of the mold is 1 Although not sufficiently reduced to 2 or 0.8, in the case of run numbers 8 to 18 where the width a of the slit was 20 mm or more, the bubble trapping index at the long side edge of the mold was 0.2 or 0.1. , Markedly decreased.

また、表1及び表1を基に作成した図6より、鋳型上部の各長辺中央部分に湾曲部を設けた、前記最短水平距離bが50mm以上の実施番号2〜4,6,7,9,10,12〜15,17,18では、鋳型の長辺中央部の気泡捕捉指数は0.5以下となり、顕著に減少した。   Moreover, from FIG. 6 created based on Table 1 and Table 1, the shortest horizontal distance b provided the curved part in each long-side center part of a casting_mold | template upper part, and the implementation numbers 2-4, 6, 7, In 9, 10, 12 to 15, 17, and 18, the bubble trapping index at the center of the long side of the mold was 0.5 or less, which was significantly reduced.

上記実験Aでは、底壁にスリットがなく、両短辺方向に向けて設置する、縦70mm、横55mmの2つの吐出孔を有する浸漬ノズルを使用した場合を基準としたが(気泡捕捉密度が1)、前記吐出孔のサイズが変わった場合は、その変わったサイズでの気泡捕捉密度を1として、上記と同様な方法で好適なスリットの幅aを求めることができることは言うまでもない。   The above experiment A was based on the case of using an immersion nozzle having two outlet holes of 70 mm in length and 55 mm in width, which has no slit in the bottom wall and is installed in the direction of both short sides. 1) Needless to say, when the size of the ejection hole is changed, a suitable slit width a can be obtained by the same method as described above, assuming that the bubble trapping density at the changed size is 1.

上記実験Aにより、浸漬ノズルの底壁に形成した2つの吐出孔とつながったスリットからの吐出流が鋳型の長辺中央部の凝固シェルに衝突して発生する凝固シェルの再溶解を防止するためには、前記スリットの幅aと、前記最短水平距離bとの関係a/bを0.6以下とすればよいことが分かった。   In order to prevent remelting of the solidified shell caused by the discharge flow from the slit connected to the two discharge holes formed in the bottom wall of the submerged nozzle colliding with the solidified shell at the center of the long side of the mold by the above experiment A It was found that the relationship a / b between the slit width a and the shortest horizontal distance b should be 0.6 or less.

一方で、前記a/bを0.6以下とした場合であっても、鋳型の長辺中央部における浸漬ノズルの下端から鋳片引抜方向に100mm隔てた位置の鋳型内に設置した熱電対の温度が上昇しているので、鋳型の長辺中央部の凝固シェルの局所的な再溶解を避けてブレイクアウトの発生を完全に防止するためには、a/bを0.5以下とすることが望ましい。   On the other hand, even when the a / b is 0.6 or less, the thermocouple installed in the mold at a position 100 mm away from the lower end of the immersion nozzle at the center of the long side of the mold in the slab drawing direction. Since the temperature is rising, in order to prevent local remelting of the solidified shell at the center of the long side of the mold and completely prevent the occurrence of breakout, a / b should be 0.5 or less. Is desirable.

また、表1及び表1を基に作成した図7より、a/bが0.3より小さい場合、前記スリットの幅aが10mmでは、鋳型の長辺端部の気泡捕捉指数が増加している。従って、鋳型の長辺端部の気泡捕捉指数を効果的に減少するためには、a/bが0.3以上であることが望ましい。   Further, from FIG. 7 created based on Table 1 and Table 1, when a / b is smaller than 0.3, when the width a of the slit is 10 mm, the bubble trapping index at the end of the long side of the mold increases. Yes. Accordingly, in order to effectively reduce the bubble trapping index at the long side end of the mold, it is desirable that a / b is 0.3 or more.

〔実験B〕
実験Aと同じ条件で、両長辺壁面が直線の横断面矩形状の鋳型、及び、鋳型上部の各長辺の中央部分を鋳型の外側に凸に湾曲させた湾曲部を有し、鋳型下部に向かうにつれて前記湾曲部の湾曲が小さくなって鋳型下部では前記湾曲部がない鋳型を使用し、電磁攪拌装置と共に電磁ブレーキを作動させて浸漬ノズルの吐出孔部に鋳型の短辺方向に一様な0.3Tの磁束密度の直流磁場を印加した際の鋳造結果を下記表2に示す。下記表2における指標等は上記表1の場合と同様である。
[Experiment B]
Under the same conditions as in Experiment A, the mold has a rectangular shape with both long side walls straight, and a curved part in which the central part of each long side of the upper part of the mold is curved outwardly from the mold, The curve of the curved part becomes smaller as it goes to the bottom, and a mold without the curved part is used at the lower part of the mold, and the electromagnetic brake is operated together with the electromagnetic stirrer so that the discharge hole part of the immersion nozzle is uniform in the short side direction of the mold. Table 2 below shows the casting results when a DC magnetic field having a magnetic flux density of 0.3 T was applied. The indices in Table 2 below are the same as in Table 1 above.

Figure 0006451380
Figure 0006451380

表2及び表2を基に作成した図4〜6に示すように、電磁攪拌に電磁ブレーキを併用した場合は、電磁攪拌だけで電磁ブレーキを作動させない場合と比較して長辺中央部の凝固シェルの局所的な再溶解や鋳片への気泡の捕捉の防止について、同等或いは同等以上の効果が見られた。   As shown in FIGS. 4 to 6 created based on Table 2 and Table 2, when the electromagnetic brake is used in combination with the electromagnetic stirring, the solidification at the center of the long side is compared with the case where the electromagnetic brake is not operated only by the electromagnetic stirring. The same or equivalent effect was seen in the local remelting of the shell and the prevention of trapping of bubbles in the slab.

また、電磁攪拌に電磁ブレーキを併用した場合には、電磁攪拌だけで電磁ブレーキを作動させない場合と同じ条件で、かつ浸漬ノズルの底壁に形成したスリットの幅aを20mm以上とした場合には、鋳型の長辺端部の気泡捕捉を顕著に減少することができた。   In addition, when an electromagnetic brake is used in combination with electromagnetic stirring, when the width a of the slit formed on the bottom wall of the immersion nozzle is 20 mm or more under the same conditions as when the electromagnetic brake is not operated only by electromagnetic stirring. In addition, it was possible to remarkably reduce bubble trapping at the long side edge of the mold.

本発明は、発明者による上記実験A,Bの結果に基づいて成されたものである。
すなわち、本発明は、鋳型内のメニスカス近傍の溶鋼を電磁攪拌しつつ鋼を連続鋳造する方法であって、
連続鋳造時、鋳型内のメニスカス下方の鋳型の短辺壁面と相対する側壁部に設けた2つの吐出孔とつながったスリットを底壁に形成した浸漬ノズルを用いて、
鋳型上部の各長辺の中央部分は鋳型の外側に凸に湾曲した湾曲部を有し、鋳型下部に向かうにつれて前記湾曲部の湾曲が小さくなって鋳型下部では前記湾曲部がない鋳型に給湯する際、
前記浸漬ノズルの底壁に形成したスリットの厚み方向の幅aと、鋳型の前記湾曲部と前記浸漬ノズルの下端との最短水平距離bとの関係が、a/b≦0.となるようにして連続鋳造する鋼の連続鋳造方法である。
The present invention has been made based on the results of the experiments A and B by the inventors.
That is, the present invention is a method of continuously casting steel while electromagnetically stirring molten steel near the meniscus in a mold,
At the time of continuous casting, using a submerged nozzle formed on the bottom wall with a slit connected to two discharge holes provided in the side wall portion opposite to the short side wall surface of the mold below the meniscus in the mold,
The central part of each long side of the upper part of the mold has a curved part that is convexly curved toward the outside of the mold, and the curvature of the curved part becomes smaller toward the lower part of the mold, and hot water is supplied to the mold without the curved part at the lower part of the mold. When
The relationship between the width a in the thickness direction of the slit formed in the bottom wall of the immersion nozzle and the shortest horizontal distance b between the curved portion of the mold and the lower end of the immersion nozzle is a / b ≦ 0. This is a continuous casting method of steel that is continuously cast so as to be 5 .

上記本発明おいて、鋳型の湾曲部と浸漬ノズルの下端との最短水平距離bを50mm以上とした場合には、鋳型の長辺中央部と長辺端部の気泡捕捉をより効果的に行うことができる。 The Keep present invention, when the shortest horizontal distance b between the lower end of the cast type immersion nozzle and the curved portion of the above 50mm, the bubbles trapped in the long side central portion and the long side edge portion of the mold more effectively It can be carried out.

また、その際、電磁ブレーキを併用しても、鋳型長辺面の再溶解や鋳片への気泡の捕捉防止について同等、或いは同等以上の効果を得ることができる。   At that time, even if an electromagnetic brake is used in combination, the same or equivalent effect can be obtained with respect to remelting of the long side of the mold and prevention of trapping of bubbles in the slab.

本発明は上記の例に限らず、各請求項に記載された技術的思想の範疇であれば、適宜実施の形態を変更しても良いことは言うまでもない。   The present invention is not limited to the above example, and it goes without saying that the embodiments may be changed as appropriate within the scope of the technical idea described in each claim.

例えば上記説明では本発明で実施する電磁攪拌の条件について記載していないが、連続鋳造時に通常実施する範囲の条件であれば、本発明の効果を奏することができることを発明者は実験により確認している。   For example, the above description does not describe the conditions of electromagnetic stirring performed in the present invention, but the inventors have confirmed through experiments that the effects of the present invention can be achieved as long as the conditions are in a range that is normally performed during continuous casting. ing.

また、電磁ブレーキの条件も実験Bで実施した条件に限らず、連続鋳造時に通常実施する範囲の条件であれば、本発明の効果を奏することができることを発明者は実験により確認している。   In addition, the inventors have confirmed through experiments that the electromagnetic brake conditions are not limited to those performed in Experiment B, and that the effects of the present invention can be achieved as long as the conditions are in a range that is normally performed during continuous casting.

1 鋳型
1a 長辺中央部
1c 湾曲部
2 浸漬ノズル
2a 吐出孔
2b スリット
DESCRIPTION OF SYMBOLS 1 Mold 1a Long side center part 1c Curved part 2 Immersion nozzle 2a Discharge hole 2b Slit

Claims (1)

鋳型内の溶鋼湯面近傍の溶鋼を電磁攪拌しつつ鋼を連続鋳造する方法であって、
連続鋳造時、鋳型内の溶鋼湯面下方の鋳型の短辺壁面と相対する側壁部に設けた2つの吐出孔とつながったスリット状の吐出孔を底壁に形成した浸漬ノズルを用いて、
鋳型上部の各長辺の中央部分は鋳型の外側に凸に湾曲した湾曲部を有し、鋳型下部に向かうにつれて前記湾曲部の湾曲が小さくなって鋳型下部では前記湾曲部がない鋳型に給湯する際、
前記浸漬ノズルの底壁に形成したスリット状の吐出孔の厚み方向の幅aと、鋳型の前記湾曲部と前記浸漬ノズルの下端との最短水平距離bとの関係が、前記最短水平距離bが50mm以上で、a/b≦0.5となるようにして連続鋳造することを特徴とする鋼の連続鋳造方法。
A method of continuously casting steel while electromagnetically stirring the molten steel near the molten steel surface in the mold,
At the time of continuous casting, using a submerged nozzle in which slit-like discharge holes connected to two discharge holes provided on the side wall portion facing the short side wall surface of the mold below the molten steel surface in the mold are formed on the bottom wall,
The central part of each long side of the upper part of the mold has a curved part that is convexly curved toward the outside of the mold, and the curvature of the curved part becomes smaller toward the lower part of the mold, and hot water is supplied to the mold without the curved part at the lower part of the mold. When
The relationship between the width a in the thickness direction of the slit-shaped discharge hole formed in the bottom wall of the immersion nozzle and the shortest horizontal distance b between the curved portion of the mold and the lower end of the immersion nozzle is the shortest horizontal distance b. A continuous casting method of steel, wherein continuous casting is performed so that a / b ≦ 0.5 at 50 mm or more .
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