JP3747848B2 - Continuous casting method - Google Patents

Description

【０１０２】
垂直曲げ型連続鋳造機は、上ノズル、スライディングゲートおよび浸漬ノズルの１つ以上を電気伝導性を有する耐火物で構成し、電気伝導性を有する耐火物で構成した部材に他方の電極を埋設した溶鋼供給装置を備えたものを用いた。また、試験では、スライディングゲートの上プレートまたは上ノズル部分にガス吹き込み部を設置し、鋳込初期の開孔用に必要な２〜５Ｎｌ／ｍｉｎの少量のガスを吹き込んだ。この程度の吹き込みでは鋳片表面にピンホールは発生せず、鋳型内で湧出ガスも殆どないので、ほぼ全てのガスが鋳型内に持ち込まれることなくタンディッシュ側に浮き上がった。スライディングゲートの上プレートは、電極を備えない従来のものを使用したが、一部の試験では、電気伝導性を有する耐火物で構成し、他方の電極と接続したものを用いた。用いたタンデイッシュの形状は通常の箱形で、容量は約８５ｔであった。
【０１０３】
浸漬ノズルは、内径が９０ｍｍで、下向き３５°の２つの吐出孔を有するものを用いた。浸漬ノズルの材質は、質量％で、黒鉛３１％、ＳｉＯ₂１４％を含有し、残部がほぼＡｌ₂Ｏ₃からなる、溶鋼の温度で電気伝導性を有するアルミナグラファイト質とした。この浸漬ノズルの外周部に炭素鋼からなる他方の電極を取り付けた。また、アルミナグラファイトからなる一方の電極は、タンディッシュ内の溶鋼表面から溶鋼中に浸漬させた。
【０１０４】
浸漬ノズルとその浸漬ノズルと接するスライディングゲートとの間、および浸漬ノズルと浸漬ノズルをスライディングゲートに保持させるホルダーとの間を、Ａｌ₂Ｏ₃およびＳｉＯ₂を主成分とする耐火物製の繊維からなるシートおよび／またはＳｉＯ₂を主成分とする酸化防止剤を塗布して、それぞれ電気的な絶縁をおこなった。その際、シートおよび塗布材の厚さを変更して試験した。
【０１０５】
鋳造試験前には、タンディッシュ、上ノズル、スライディングゲート、浸漬ノズルなどを通常の燃焼ガスを用いて約３時間予熱し、タンディッシュの内張耐火物の表面温度を１０００〜１２００℃とした。予熱を終了する直前に、一方の電極と他方の電極との間の当初の電気抵抗を測定した。
【０１０６】
鋳造試験では、１ヒート約２７０ｔの溶鋼を連続して６ヒート鋳造した。このとき、タンディッシュ内の溶鋼の過熱度は２０〜３０℃とした。鋳造開始から終了までの間、一方の電極と他方の電極との間に電流一定または電圧一定で通電した。その際、電流は１０〜１００Ａ、電圧は３〜８０Ｖの値とした。これら電流と電圧から、一方の電極と他方の電極との間の鋳造中の電気抵抗を求めた。また、電流値ａおよび他方の電極と接合し溶鋼に面する耐火物内面のうち導電性を有する部分の表面積ｂを種々変化させて、下記（ｄ）式で規定される電流密度（Ａ／ｃｍ ² ）の変更試験を行った。
【０１０７】
電流密度（Ａ／ｃｍ ² ）＝ａ／ｂ ・・・（ｄ）
ここで、ａ：電流値（Ａ）
ｂ：他方の電極と接合し溶鋼に面する耐火物うち導電性を有する部分の内面の表面積（ｃｍ ² ）
直流を通電する際は、他方の電極側を正または負の電位とした。
【０１０８】
また、鋳造中にスライディングゲートに配置した多孔質耐火物から、その内部を通過する溶鋼中にＡｒガスを２〜５リットル（Ｎｌ）／分の流量で吹き込んだ。この吹き込み流量は、鋳片表面に気泡性欠陥を発生させる量ではないことを事前に確認した。
【０１０９】
鋳造終了後に浸漬ノズルを回収し、縦断した後、その内部の付着物の有無と、その付着物の厚さを調査した。内面の付着量の厚さは、上ノズル、スライディングゲートおよび浸漬ノズルのうち、他方の電極が設けられたものの長さ方向の３個所において、その内径を周方向２位置で測定し、その平均値を使用前の内径から減じた値の１／２で表す。
【０１１０】
また、２ヒート目と６ヒート目に得られた鋳片を４〜６ｍｍの厚さの鋼帯に熱間圧延し、次いで酸洗した後に冷間圧延し、厚さ１．６〜１．２ｍｍの鋼帯とした。製品表面疵の発生の有無とその発生状況を調査し、製品疵発生率を求めた。この製品疵発生率は、モールドパウダ、Ａｌの酸化物などの鋳片の欠陥に起因する製品表面疵が発生した部分の切り捨て長さの合計長さを鋼帯全長で除し、％表示することにより求めた。試験条件および試験結果を表２に示す。
【０１１１】
【表２】

【０１１２】
試験Ｎｏ．２８では、浸漬ノズルとスライディングゲートとの間に、耐火物製の繊維からなる厚さ２．５ｍｍのシートを挿入し、さらに、浸漬ノズルとそのホルダーとの間にＳｉＯ₂系の酸化防止剤を厚さ０．２ｍｍに塗布した。タンディッシュの予熱を終了する直前における、一方の電極と他方の電極との間の当初の電気抵抗は６００Ωであった。この値は、本発明で規定する条件の範囲内である。また、６ヒート目を鋳造終了直前の鋳造中の電気抵抗は７２Ωであった。この鋳造中の電気抵抗を当初の電気抵抗で除した値（以下、電気抵抗の比と記す）は１．２／１０であり、望ましい条件の範囲を僅かに外れた値であった。試験Ｎｏ．２８では、鋳造後の浸漬ノズルの付着物の厚さは５ｍｍと少なく良好な結果であった。また、２ヒート目および６ヒート目の鋳片を素材とした製品疵発生率は、それぞれ０．６％と０．９％とまずまず良好な結果であった。
【０１１３】
試験Ｎｏ．２９では、浸漬ノズルとスライディングゲートとの間に、耐火物製の繊維からなる厚さ２．５ｍｍのシートを挿入し、さらに、浸漬ノズルとそのホルダーとの間にＳｉＯ₂系の酸化防止剤を厚さ０．４ｍｍで塗布した。タンディッシュの予熱を終了する直前における、一方の電極と他方の電極との間の当初の電気抵抗は６００Ωであった。この値は、本発明で規定する条件の範囲内である。また、６ヒート目を鋳造終了直前の鋳造中の電気抵抗は５８Ωであった。この鋳造中の電気抵抗の比は０．９７／１０であり、望ましい条件の範囲内であった。試験Ｎｏ．２９では、鋳造後の浸漬ノズルの付着物の厚さは４ｍｍと少なく良好な結果であった。また、２ヒート目および６ヒート目の鋳片を素材とした製品疵発生率は、それぞれ０．３％と０．５％と少なく良好な結果であった。
【０１１４】
試験Ｎｏ．３０では、浸漬ノズルとスライディングゲートとの間に、厚さ４．０ｍｍのシートを挿入し、さらに、浸漬ノズルとそのホルダーとの間には、厚さ１．０ｍｍのシートを挿入するとともに、酸化防止剤を厚さ０．５ｍｍで塗布した。タンディッシュの予熱を終了する直前における、一方の電極と他方の電極との間の当初の電気抵抗は１２００Ωであった。この値は、本発明で規定する条件の範囲内の値である。試験Ｎｏ．２９に比べて、当初の電気抵抗が２倍の値となったのは、浸漬ノズルとスライディングゲートとの間のシートの厚さを厚くしたことと、浸漬ノズルとそのホルダーとの間に、シートに加えて、酸化防止剤を塗布したことによる。また、６ヒート目を鋳造終了直前の鋳造中の電気抵抗は８Ωであった。したがって、電気抵抗の比は０．０７／１０であり、望ましい条件の範囲内であった。試験Ｎｏ．３０では、鋳造後の浸漬ノズルの付着物の厚さは４ｍｍで少なく良好な結果であった。また、２ヒート目および６ヒート目の鋳片を用いた場合の製品疵発生率は、それぞれ０．３％と０．４％と少なく良好な結果であった。
【０１１５】
試験Ｎｏ．３１では、絶縁施工の方法は試験Ｎｏ．３０と同様とした。タンディッシュの予熱を終了する直前における、一方の電極と他方の電極との間の当初の電気抵抗は１０５０Ωであった。６ヒート目を鋳造終了直前の鋳造中の電気抵抗は０．５Ωであり、鋳造中の抵抗増加は少ない。したがって、電気抵抗の比は０．００５／１０であり、望ましい条件の範囲内であった。試験Ｎｏ．３１では、鋳造後の浸漬ノズルの付着物の厚さは２ｍｍで少なく良好な結果であった。また、２ヒート目および６ヒート目の鋳片を用いた場合の製品疵発生率は、それぞれ０．３％と少なく良好な結果であった。
【０１１６】
試験Ｎｏ．３２では、浸漬ノズルとスライディングゲートとの間のシートの厚さを２．０ｍｍとし、さらに３ｍｍ厚さのアルミナ板を挟んだ。また、浸漬ノズルとそのホルダーとの間のシートの厚さを１．８ｍｍとし、酸化防止剤の厚さを０．７ｍｍで塗布した。タンディッシュの予熱を終了する直前における、一方の電極と他方の電極との間の当初の電気抵抗は３８０×１０³Ωであった。この値は、本発明で規定する条件の範囲内である。シートおよび塗布材の厚さを厚くしたので、当初の電気抵抗は極めて大きな値となった。また、６ヒート目を鋳造終了直前の鋳造中の電気抵抗は１３Ωであった。したがって、電気抵抗の比は０．０００３／１０であり、望ましい条件の範囲内の値であった。試験Ｎｏ．３２では、鋳造後の浸漬ノズルの付着物の厚さは１ｍｍで著しく少なく最も良好な結果であった。また、２ヒート目および６ヒート目の鋳片を素材とした製品疵発生率は、それぞれ０．１％と０．２％で著しく少なく良好な結果であった。
【０１１７】
試験Ｎｏ．３３では、シートの厚さを２．０ｍｍとし、塗布材の厚さを０．６ｍｍとした。タンディッシュの予熱を終了する直前における、一方の電極と他方の電極との間の当初の電気抵抗は４２０Ωであった。この値は、本発明で規定する条件を外れて小さい値であった。また、６ヒート目を鋳造終了直前の鋳造中の電気抵抗は６４Ωであった。したがって、電気抵抗の比は１．５／１０に上昇し、望ましい条件を外れた。試験Ｎｏ．３３では、鋳造後の浸漬ノズルの付着物の厚さは７ｍｍでやや厚かった。また、２ヒート目および６ヒート目の鋳片を素材とした製品疵発生率は、それぞれ０．８％と７．９％であり、特に６ヒート目の結果が悪かった。
【０１１８】
試験Ｎｏ．３４では、耐火物製の繊維からなるシートを用いずに、浸漬ノズルとスライディングゲートとの間、および浸漬ノズルとそのホルダーとの間に、ともにＳｉＯ₂系の酸化防止剤を厚さ０．７ｍｍおよび０．５ｍｍで塗布した。タンディッシュの予熱を終了する直前における、一方の電極と他方の電極との間の当初の電気抵抗は３０Ωであった。 この値は、本発明で規定する条件を外れて著しく小さい値であった。また、６ヒート目を鋳造終了直前の電気抵抗は３２Ωであった。したがって、電気抵抗の比は１０．６／１０に上昇し、望ましい条件を外れて大きな値となった。試験Ｎｏ．３４では、鋳造後の浸漬ノズルの付着物の厚さは１１ｍｍでかなり厚かった。また、２ヒート目および６ヒート目の鋳片を素材とした製品疵発生率は、それぞれ８．４％と１２．３％で、ともに悪い結果であった。
【０１１９】
試験Ｎｏ．３５では、電気的な絶縁をおこなわず、通電も行わなかった。鋳造後の浸漬ノズルの付着物の厚さは１３ｍｍと最も厚く悪い結果であった。また、２ヒート目および６ヒート目の鋳片を素材とした製品疵発生率は、それぞれ９．８％と１１．８％であった。
【０１２０】
〔実施例３〕実施例１と同様の方法により、厚さ２７０ｍｍ、幅１０００ｍｍの鋳片を製造した。垂直曲げ型連続鋳造機は、図１に示す溶鋼供給装置であって、スライディングゲートの上プレートに、多孔質耐火物からなるガス吹き込み部を有する溶鋼供給装置を備えたものを用いた。
【０１２１】
連続鋳造の際は、一方の電極と浸漬ノズルとの間の電位差を１．５〜２５Ｖとし、それらの間に直流または交流を通電した。直流を通電する際には、浸漬ノズル側の電位を正または負とした。一部の試験では、一方の電極と浸漬ノズルとの間に通電しなかった。また、一部の試験では、スライディングゲートに設けたガス吹き込み部から、Ａｒガスを２０リットル（Ｎｌ）／分の流量で溶鋼中に吹き込んだ。
【０１２２】
鋳造後に浸漬ノズルを回収して縦断し、吐出孔近傍の付着物の発生の有無と、その付着厚さを調査した。また、得られた鋳片を実施例１と同様の方法により、厚さ０．８〜１．２ｍｍの鋼帯に冷間圧延し実施例１と同様の方法で表面疵発生率を調査した。試験条件および試験結果を表３に示す。
【０１２３】
【表３】

【０１２４】
試験Ｎｏ．３６では、浸漬ノズル側を正の電位、電流密度を０．１７Ａ／ｃｍ²として、直流を通電したので、浸漬ノズル内面の付着物厚さが３．０ｍｍ、表面疵発生率が１．８％であった。
【０１２５】
試験Ｎｏ．３７では、浸漬ノズル側を負の電位とし、その他の条件を試験Ｎｏ．３６と同じとした。その結果は、浸漬ノズルの内面の付着物厚さが１．３ｍｍ、表面疵発生率が０．２％であり、浸漬ノズル内面の付着物厚さおよび表面疵発生率ともに、試験Ｎｏ．３６に比べて優れている。
【０１２６】
試験Ｎｏ．３８では、浸漬ノズル側を正の電位、電流密度を０．０９２Ａ／ｃｍ²として、直流を通電したので、浸漬ノズル内面の付着物厚さが３．５ｍｍ、表面疵発生率が２．１％であった。
【０１２７】
試験Ｎｏ．３９は、浸漬ノズル側を負の電位とし、その他の条件を試験Ｎｏ．３８と同じとしたが、浸漬ノズル内面の付着物厚さが１．８ｍｍ、表面疵発生率が０．３％であり、浸漬ノズル内面の付着物厚さおよび表面疵発生率ともに、試験Ｎｏ．３８に比べて優れている。なお、試験Ｎｏ．３８および３９は、いずれも、電流密度が望ましい範囲内にあることから、消費電力が比較的低かった。
【０１２８】
試験Ｎｏ．４０では、電流密度を０．１７Ａ／ｃｍ²として、交流を通電し、その他の条件は試験Ｎｏ．３６と同じとしたが、浸漬ノズルの吐出孔近傍の付着物の付着厚さが３．０ｍｍ、表面疵発生率が１．８％であり、浸漬ノズル内面の付着物厚さおよび表面疵発生率ともに、試験Ｎｏ．３６と同程度であった。
【０１２９】
試験Ｎｏ．４１では、通電せずに、スライディングゲートから、Ａｒガスを２０リットル（Ｎｌ）／分の流量で溶鋼中に吹き込んだので、浸漬ノズルの吐出孔近傍の付着物の付着厚さが５．０ｍｍ、表面疵発生率は２．３％であり、浸漬ノズル内面の付着物厚さおよび表面疵発生率ともに、比較的悪い結果であった。
【０１３０】
試験Ｎｏ．４２では、通電せず、また、スライディングゲートからＡｒガスを溶鋼中に吹き込まなかったので、鋳造中に浸漬ノズルの詰まりが発生し、３ヒート目を鋳造中に、鋳造を中止せざるを得なかった。鋳造後の浸漬ノズルの吐出孔近傍には、厚さ１３ｍｍの付着物が付着し、また、表面疵発生率は５．１％であった。
【０１３１】
【発明の効果】
本発明の連続鋳造方法によれば、上ノズル、流量制御機構および浸漬ノズルの内面に溶鋼中のＡｌの酸化物などが付着するのを安定して防止することができる。さらに、得られた鋳片を素材とする製品に、モールドパウダ、Ａｌの酸化物、気泡などの鋳片の欠陥に起因する欠陥の発生を防止することができる。しかも、連続鋳造中に浸漬ノズルが閉塞することを有効に防止することができる。
【図面の簡単な説明】
【図１】本発明の方法で用いる溶鋼供給部の一例を模式的に示す縦断面図である。
【図２】他方の電極が浸漬ノズルに埋め込まれた他の例を示す縦断面図である。
【図３】他方の電極が浸漬ノズルの外面に取り付けられた一例を示す正面図である。
【図４】他方の電極が浸漬ノズルの外面に取り付けられた他の例を示す正面図である。
【図５】鋳造中の一方の電極と他方の電極との間の鋳造中の電気抵抗の変化を例示する図である。
【図６】冷間圧延製品の表面性状に及ぼす一方の電極と他方の電極との間の電気抵抗の影響を示す図である。
【図７】連続鋳造における浸漬ノズルの内面に付着するＡｌの酸化物などの付着物の厚さおよび他方の電極と一方の電極の間の印加電圧との関係を示す図である。
【符号の説明】
１：タンディッシュ、２：上ノズル、 ３：スライディングゲート（流量制御機構）、 ４：浸漬ノズル、 ５：一方の電極、 ６：他方の電極、 ７：電源部、 ８：溶鋼、 ９：鋳型、 １０：凝固殻、 １１：モールドパウダ。[0001]
BACKGROUND OF THE INVENTION
  The present invention is a continuous castingMeltingThe present invention relates to a continuous casting method that is effective for preventing clogging of an immersion nozzle or the like using a steel supply device and suppressing defects on the surface of a slab.
[0002]
[Prior art]
  Usually, as a method for continuously producing a slab, molten steel contained in a tundish is supplied from an immersion nozzle provided in the lower part of the mold to the upper part of the mold that is open at the top and bottom to solidify the shell in the mold. Is formed, and then the slab is continuously drawn by drawing from the lower part.
[0003]
  At this time, if the molten steel deoxidized by Al is continuously cast, the oxide of Al in the molten steel is likely to adhere to the inner surface of the immersion nozzle, and the flow of the molten steel in the immersion nozzle is hindered. Therefore, when casting using an immersion nozzle having a plurality of discharge holes, the flow of molten steel in the mold tends to become a single flow, for example, the discharge flow is not uniform and the specific discharge flow becomes strong. When a single flow occurs, mold powder added to the surface of the molten steel in the mold is engulfed in the molten steel, or Al oxide adhering to the inner surface of the immersion nozzle is peeled off and is easily entrapped in the molten steel.
[0004]
  Mold powder and Al oxides caught in molten steel in the mold are trapped by the solidified shell in the mold, which causes powder defects and slags on the slab surface. It becomes easy to do. These defects on the slab surface cause surface defects in products that are hot-rolled using the slab as a raw material.
[0005]
Further, when the amount of Al oxide deposited on the inner surface of the immersion nozzle becomes significant, so-called nozzle clogging occurs, and subsequent continuation of casting becomes difficult. At that time, although the nozzle clogging can be eliminated by cleaning the inner surface of the immersion nozzle with oxygen gas, the cleanliness of the slab is remarkably deteriorated.
[0006]
  In order to prevent Al oxide in the molten steel from adhering to the inner surface of the immersion nozzle, a method of blowing an inert gas into the molten steel passing through the immersion nozzle is known (iron and steel, vol. 66). , S868), and recently, various methods have been proposed as prevention methods applicable to operations. For example, Japanese Patent Application Laid-Open No. 4-319055 discloses a method in which an inert gas is blown into molten steel that passes through the immersion nozzle, and the molten steel flows into the molten steel according to the flow rate (t / min) of the molten steel that passes through the immersion nozzle. A method of adjusting the amount of inert gas to be blown (liter (Nl) / min) has been proposed.
[0007]
  JP-A-6-182513 discloses that an alternating current or a direct current is passed between a porous refractory for gas blowing provided on the inner wall of the immersion nozzle and the molten steel passing through the immersion nozzle. A method of blowing an inert gas has been proposed. In this method, an inert gas is blown into the molten steel to prevent Al oxides and the like from adhering to the inner surface of the immersion nozzle, and by passing an electric current between the inner wall of the immersion nozzle and the molten steel, The force acts to promote the release of the blown inert gas bubbles from the blown refractory, thereby reducing the generated bubbles. Therefore, the air bubbles trapped by the solidified shell in the mold are reduced, and defects caused by the air bubbles in the slab are less likely to occur on the surface of the product that is hot-rolled using the slab as a raw material.
[0008]
  However, in the methods proposed in these publications, since the inert gas bubbles are less likely to be trapped by the solidified shell in the mold, if the amount of inert gas blown is reduced, the Al content in the molten steel on the inner surface of the immersion nozzle On the other hand, if it is attempted to prevent the adhesion of oxides of Al in the molten steel to the inner surface of the immersion nozzle, the amount of inert gas blown in will increase. Many bubbles are trapped in the solidified shell in the mold, and surface defects may occur in a product made of the slab.
[0009]
  Thus, the conventional method cannot stably prevent the adhesion of Al oxide or the like in the molten steel to the inner surface of the immersion nozzle. In addition, even if it is possible to prevent the oxide of Al in the molten steel from adhering to the inner surface of the immersion nozzle, a bubble defect is generated in the surface portion of the slab, and the surface of the product using this slab as a raw material Defects may occur. Therefore, there is a demand for a method that can stably and effectively prevent the adhesion of Al oxides or the like in molten steel to the inner surface of the immersion nozzle without causing bubble defects on the surface of the slab.
[0010]
[Problems to be solved by the invention]
  The present invention prevents adhesion of Al oxide in molten steel to the inner surface of the immersion nozzle, generation of slab surface defects caused by mold powder, Al oxide, and the like, and the slab as a raw material. Steel supply equipment for continuous casting that can effectively prevent the occurrence of surface defects in productsPlaceIt aims at providing the used continuous casting method.
[0011]
[Means for Solving the Problems]
  In order to solve the above-mentioned problems, the present inventors have repeatedly studied focusing on the electrocapillary phenomenon as a method for preventing adhesion of Al oxide or the like in molten steel to the inner surface of the immersion nozzle. That is, the electrocapillary phenomenon is a phenomenon in which the interfacial tension between an electrode and a solution existing in an ionic solution changes depending on the potential of the electrode.(A)~(G)We were able to obtain the knowledge of.
[0012]
  (A)The upper nozzle, the flow rate control mechanism, and the immersion nozzle of the continuous casting apparatus are composed of refractories, and some of these refractories have electron conductivity and ion conductivity at high temperatures. Therefore, in continuous casting, if a potential difference is imparted between a refractory having electron conductivity or ionic conductivity at high temperatures and molten steel, an electrocapillary phenomenon occurs at the contact interface between them, and the tension at the interface decreases. The force with which the oxide of Al in molten steel adheres to the surface of the refractory is suppressed, making it difficult to adhere to the surface of the refractory.
[0013]
  (B)Based on the above estimation, using a crucible on an experimental scale, immerse a refractory rod and electrode having electrical conductivity in molten steel, and energize both to create a potential difference between the refractory rod and electrode. The experiment to give was performed. As a result, even if the potential difference is small, the amount of Al oxide in the molten steel that adheres to the surface of the refractory decreases, and the surface of the refractory increases as the absolute value of the potential difference increases regardless of the positive or negative potential. It was confirmed that the amount of adhesion of oxides of Al in the molten steel adhering to the iron was reduced.
[0014]
  (C)Based on the above test results, we are studying methods that can prevent the adhesion of oxides of Al in molten steel to the inner surface of the immersion nozzle, and are effective between electrically conductive refractories and molten steel passing through the immersion nozzle. As a method of energizing the electrodes, attention was paid to electrically insulating the pair of electrodes. Usually, the refractory used for insulation is 1 × 10 at room temperature.^FiveSufficient insulation can be secured if it has an electrical resistivity (specific resistance) of Ω · m or more, but ion conduction occurs at a high temperature such as the temperature of molten steel, and the electrical resistivity is significantly reduced, resulting in insulation. Performance decreases.
[0015]
  (D)the above(C)If the electrical insulation performance between the pair of electrodes deteriorates due to such a phenomenon, current does not sufficiently flow in the molten steel passing through the immersion nozzle, and current flows in a short circuit other than the molten steel. Therefore, sufficient adhesion preventing effects such as oxides of Al in the molten steel on the inner surface of the immersion nozzle cannot be obtained. Further, not only is the applied power wasted, but there is also a risk that a fine discharge will occur due to leakage to the outside, and an electric shock or malfunction of surrounding equipment may occur.
[0016]
  (E)When preheating a tundish, etc., or when reusing hot without preheating, the initial electrical resistance between one electrode and the other electrode immediately before starting to supply molten steel to the tundish is 500Ω. By setting it as the above, it can prevent that an electric current does not fully flow into the molten steel which passes the inside of an immersion nozzle between casting start and completion | finish of casting, and an electric current flows into short circuit circuits other than molten steel. The “between the start of casting and the end of casting” varies depending on the continuous casting machine, the slab size, the casting speed, the number of heats continuously cast, and the like, but is approximately 60 to 500 minutes.
[0017]
  (F)The electric resistance during casting calculated from the current and voltage between the pair of electrodes between the start and end of casting is at the end of preheating of the tundish before supplying molten steel into the tundish. Alternatively, when the tundish once used for casting is used again for casting without preheating, the initial tapping between the one electrode and the other electrode in the tundish before supplying molten steel into the tundish is performed. It is desirable that the electrical resistance be less than 1/10.
[0018]
  (G)the above(F)In other words, as the casting time elapses, the electrical resistance calculated from the current and voltage between the pair of electrodes having the molten steel passing through the immersion nozzle as an electrical circuit gradually increases. When the electrical resistance during casting increases after gradually increasing, current does not sufficiently flow in the molten steel passing through the immersion nozzle, and current starts to flow in a short circuit other than the molten steel. Therefore, by managing the electrical resistance during casting until the end of casting at less than 1/10 of the initial electrical resistance between one electrode and the other electrode immediately before supplying molten steel into the tundish, Effectively, the current can be sufficiently passed through the molten steel passing through the immersion nozzle, and the current can be prevented from flowing through a short circuit other than the molten steel.
[0019]
  The present invention has been completed based on the above findings,(1)~ (5) Is the gist of the continuous casting method.
[0020]
  (1) A tundish containing molten steel, an upper nozzle provided at the bottom of the tundish, a flow rate control mechanism for controlling the flow rate of supplying the molten steel to the mold, and an immersion nozzle for circulating the supplied molten steel A continuous casting method for supplying molten steel accommodated in a tundish to a mold using a molten steel supply device comprising a pair of electrodes and a power supply unit connected to these, the upper nozzle, the flow rate control mechanism, and the immersion The inner surface of the nozzle in contact with the molten steel is composed of a refractory having electrical conductivity at or above the melting point of the steel, and one electrode of the pair of electrodes includes the tundish, the upper nozzle, the flow control mechanism, and the immersion. The part which reached any internal space of the nozzle and contacted with the molten steel, and the other electrode was made of a refractory having the electrical conductivityWhere the one electrode is not installedIn addition, when the preheating of the tundish before supplying the molten steel into the tundish is completed, or when the tundish once used for casting is used for casting again without preheating, the molten steel is put into the tundish. Before supplying, a continuous casting method characterized in that an electric resistance between the one electrode and the other electrode is set to 500Ω or more, and a voltage is applied between the one electrode and the other electrode.
[0021]
  (2) Above (1)Used for continuous casting equipment described inIn the molten steel feeder, ElectricOf the upper nozzle, flow control mechanism and immersion nozzle that are not provided with polesOne or moreIt is desirable to provide a gas blowing part.
[0022]
  (3)the above(1)Or (2)In the continuous casting method described in 1), after starting the casting, the electric resistance obtained from the current and voltage applied to the one electrode and the other electrode until the end is obtained, and the molten steel is placed in the tundish. The one electrode at the end of preheating of the tundish before supply, or when the tundish once used for casting is used again for casting without being preheated, before supplying molten steel into the tundish It is desirable to make it less than 1/10 of the electrical resistance between the first electrode and the other electrode.
[0023]
  (4)the above(1) ~ (3), The applied current density is0.01A / cm²more than,0.1A / cm²It is desirable that the current is applied so as to be less than or less and / or the applied voltage is 0.5 V or more and 100 V or less.
[0024]
  (5) Above (1)In the continuous casting method according to any one of to (4)And at least the immersion nozzle is made of a refractory having electrical conductivity above the melting point of steel and othersDirectionThe continuous casting is characterized in that the immersion nozzle side is set to a negative potential and a direct current is passed between the immersion nozzle and the molten steel passing through the immersion nozzle to prevent the immersion nozzle from being blocked. Method.
[0025]
  In the present invention, the material constituting the immersion nozzle or the like is a refractory having electrical conductivity at a temperature equal to or higher than the melting point of steel in order to energize between the refractory and molten steel. In the following description, “a refractory having electrical conductivity above the melting point of steel” may be simply referred to as “a refractory having electrical conductivity”.
[0026]
  The above (1), (3“At the end of preheating of the tundish before supplying molten steel into the tundish” defined in the above) means the following.
[0027]
  That is, before supplying the molten steel into the tundish and starting continuous casting, the refractory provided inside the tundish, the upper nozzle, the gate for controlling the amount of molten steel supplied into the mold, the immersion nozzle, etc. Preheat refractory with combustion gas. This is to prevent breakage of the refractory due to thermal shock at the time of molten steel injection and prevent the molten steel supplied in the initial stage from becoming a bullion and adhering to these refractories. At that time, the surface temperature at the end of preheating of these refractories is usually 800 to 1300 ° C. However, the target surface temperature after preheating of these refractories, etc. depends on the casting work conditions such as the tundish capacity and the time from the start of supplying molten steel into the tundish until the start of supplying molten steel into the mold. Is different.
[0028]
  By the way, as an electric circuit between a pair of electrodes at the end of preheating in a state where molten steel is not supplied in the tundish, a refractory provided inside the tundish, a refractory such as an upper nozzle, a gate, and an immersion nozzle, and There are steel structures that support these refractories. The electrical resistance of these refractories and steel structures usually decreases with increasing temperature.
[0029]
  From these facts, “the electrical resistance between one electrode and the other electrode at the end of preheating” means the refractory, the upper nozzle, the gate, and the immersion nozzle provided inside the tundish preheated to the target surface temperature. It means the electrical resistance between one electrode and the other electrode in an electric circuit composed of refractories such as, and steel structures that support these refractories, and immediately before the supply of molten steel into the tundish This means the lowest electrical resistance at. In the following description, this electrical resistance may be referred to as “initial electrical resistance”.
[0030]
  Similarly, the above (1), (3"When the tundish once used for casting is used for casting again without preheating, the electrical resistance between one electrode and the other electrode before supplying molten steel into the tundish" Means the following:
[0031]
  That is, in recent years, from the viewpoint of reducing energy saving costs, so-called hot re-use of tundish has been carried out in order to reuse the tundish without cooling. Instead, new molten steel may be supplied into the tundish as it is. Even when it is not preheated, the surface temperature of the refractory provided inside the tundish is 1000 to 1400 ° C. It means the electrical resistance between one electrode and the other electrode in the electric circuit composed of the above-mentioned refractory and steel structure at the high temperature state, and the electricity just before the molten steel starts to be fed into the tundish. It means resistance, that is, the initial electrical resistance.
[0032]
  The above (3The electrical resistance obtained from the current and voltage between one electrode and the other electrode after the start of casting until the end is defined as the electrical resistance of the molten steel supplied in the tundish. It means the electrical resistance between one electrode and the other electrode of the circuit. The electric resistance using the molten steel as an electric circuit increases with the lapse of casting time. Hereinafter, this electric resistance may be referred to as “electric resistance during casting”.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
  Of the present inventionUsed for continuous casting methodThe contents of the molten steel supply device and the continuous casting method will be described by classifying the items into the structure of the device, the refractory having electrical conductivity, the insulation work, the gas blowing, the current, the voltage application, and the negative potential of the immersion nozzle.
1. Device configuration
  Of the present inventionUsed for continuous casting methodThe structure of a molten steel supply apparatus is demonstrated based on FIGS. FIG. 1 illustrates the present invention.Used for continuous casting methodIt is a longitudinal cross-sectional view which shows an example of a molten steel supply apparatus typically. In the figure, a three-layer sliding gate is shown as a flow control mechanism for molten steel.Steel supply equipment used for continuous casting methodIs2It may be a layered type or a type that is controlled using a stopper.
[0034]
  In FIG. 1, the molten steel supply apparatus includes a tundish 1 provided with an upper nozzle 2 at the bottom, a sliding gate 3 provided at a lower portion of the upper nozzle 2, and an immersion nozzle 4 provided following the sliding gate 3. And one electrode 5 provided on the side wall of the tundish 1, the other electrode 6 provided on the immersion nozzle 4, and a power supply unit 7 connected to the one electrode 5 and the other electrode 6. The shape of the tundish 1 that accommodates the molten steel 8 and the lining refractory may be those commonly used.
[0035]
  The upper nozzle 2 provided at the bottom of the tundish 1 has a supply hole 2a for supplying the molten steel 8 in the tundish 1 to the lower part, and is made of a refractory material. The sliding gate 3 has a three-layer structure including an upper plate 31, a lower plate 32, and a movable plate 33 provided therebetween. The upper plate 31, the lower plate 32, and the movable plate 33 are made of a refractory material provided with flow holes 31a, 32a, and 33a, respectively. And the supply amount of the molten steel 8 supplied to the lower part is controlled by moving the movable plate 33 horizontally by the drive mechanism which abbreviate | omitted illustration.
[0036]
  The immersion nozzle 4 has two discharge holes 4 a in the lower portion, and a portion including these discharge holes 4 a is inserted into the mold 9. The shape of the immersion nozzle 4 is not limited to that illustrated. For example, the number of the discharge holes 4a is more than 2, the inside has a step having a different diameter in the longitudinal direction, the inside has a longitudinal flow rectifying plate, the inside has a spiral projection, the top has an interior A double structure including a nozzle may be used.
[0037]
  One electrode 5 is provided so as to penetrate the side wall of the tundish 1, the tip reaches the internal space of the tundish 1, and when the molten steel 8 is supplied into the tundish 1, the tip is in the molten steel 8. Soaked. The surface area of one of the electrodes 5 that is immersed in the molten steel 8 and in contact with the molten steel 8 is 10 cm.²That is all you need.
[0038]
  The material constituting this one electrode 5 is required to endure for a long time in contact with the molten steel 8 in the tundish 1 and to have electrical conductivity, such as refractory, graphite, steel, molybdenum and tungsten A refractory metal or a composite material thereof can be used.
[0039]
  As shown in FIG. 1, the method of attaching one electrode 5 is a method in which holes for electrode attachment are provided in the iron skin and refractory on the tundish side wall, and the electrodes are arranged through the iron skin and refractory. Alternatively, a method of dipping in the molten steel from above the surface of the molten steel 8 in the tundish may be used. In addition, when a stopper is used as a mechanism for controlling the flow rate of molten steel into the mold, the stopper can be a refractory having electrical conductivity, and this stopper can be used as one electrode 5.
[0040]
  Further, the upper nozzle or the sliding gate may be a refractory having electrical conductivity, and they may be used as one electrode 5. In either case, the same effect can be obtained, so selection may be made based on cost, ease of construction, and the like. However, if one of the electrodes 5 is arranged in the mold, current easily flows through the outer surface of the immersion nozzle, and it is impossible to effectively prevent Al in the molten steel from adhering to the inner surface of the immersion nozzle. The method to arrange in cannot be adopted.
[0041]
  Since the other electrode 6 is not in direct contact with the molten steel, a metal electrode having heat resistance up to about 1200 ° C., or TiB₂, ZrB₂A refractory material such as SiC or graphite may be used. Metals such as carbon steel, stainless steel, and Ni have better electrical conductivity than these refractory materials, but have a problem that they react with the carbon contained in the immersion nozzle to lower the melting point and melt. Therefore, it is desirable to use an electrode of a refractory material when the heat load of the electrode is large.
[0042]
  The other electrode 6 is made of an electrically conductive refractory.Where the one electrode is not installedNeed to connect with. The other electrode 6 shown in FIG. 1 has a cylindrical shape that is arranged from the vicinity of the upper end of the immersion nozzle 4 to slightly above the molten steel surface in the mold 9 and is embedded in a refractory that constitutes the immersion nozzle 4. Yes. The other electrode 6 is desirably provided so as to face the entire inner surface of the immersion nozzle 4, but if it is provided in a portion immersed in the molten steel in the mold 9 of the immersion nozzle 4, it may be melted depending on the material. For this reason, an arrangement as shown in FIG. 1 is adopted.
[0043]
  If the other electrode 6 is cylindrical and arranged as described above, the other electrode 6 and the molten steel passing through the inner surface of the immersion nozzle 4 are close to each other in the majority of the immersion nozzle 4 during continuous casting. , The distance is also almost equal. Therefore, it is possible to prevent the voltage from partially dropping when the current passes through the refractory constituting the immersion nozzle 4.
[0044]
  The other electrode 6 is not limited to the arrangement and shape shown in FIG. 1, but may be those shown in FIGS. In addition, the material which comprises the other electrode 6 can use the same refractory material as the one electrode 5.
[0045]
  FIG. 2 is a longitudinal sectional view showing another example in which the other electrode 6 is embedded in the immersion nozzle 4. In the figure, the other electrode 6a is a rod-shaped body made of metal or conductive refractory, and is embedded in a part of the immersion nozzle 4 from the outer surface. This embedding may be performed when the immersion nozzle 4 is manufactured by press sintering or by providing a hole in the press-sintered immersion nozzle 4.
[0046]
  If a material with high electrical conductivity is used as the refractory that comes into contact with the molten steel, even if an electrode with such a simple structure is used, no local current is generated and the effect can be exerted in a wide range. it can. The electrode 6 a may be in the shape of being embedded in the immersion nozzle 4 and having a tip parallel to the axis of the immersion nozzle 4.
[0047]
  FIG. 3 is a front view showing an example in which the other electrode 6 is attached to the outer surface of the immersion nozzle. In the figure, the other electrode 6 b is a metal linear body or rod-like body and is wound around the outer surface of the immersion nozzle 4. The outer surface of the immersion nozzle 4 is usually coated with an antioxidant. Since this antioxidant has insulating properties, when the other electrode 6b is wound around the immersion nozzle 4, the coated antioxidant is removed.
[0048]
  FIG. 4 is a front view showing another example in which the other electrode 6 is attached to the outer surface of the immersion nozzle. In the figure, the other electrode 6c is provided with a tightening portion at a portion opened by a metal annular body that is partially opened, and after being fitted into the outer surface of the immersion nozzle 4, it is tightened with a bolt and a nut. Yes. Also in this case, the antioxidant coated on the outer surface of the immersion nozzle 4 is removed.
[0049]
  The power supply unit 7 is connected to one electrode 5 and the other electrode 6 which are a pair of electrodes by an electric wiring 7a, and energizes the electrodes 5 and 6 when necessary.
[0050]
  In the molten steel supply apparatus shown in FIG. 1, the immersion nozzle 4 is made of a refractory having electrical conductivity. However, even the upper nozzle 2 and the sliding gate 3 have an inner surface in contact with the molten steel that has electrical conductivity. What is necessary is just to comprise with a thing. However, in the member provided with the other electrode 6, that is, the immersion nozzle 4 in FIG. 1, the inner surface with which the molten steel comes into contact needs to be made of a refractory having electrical conductivity.
[0051]
  In the molten steel supply apparatus shown in FIG. 1, the other electrode 6 is provided in the immersion nozzle 4 because the oxide of Al is most easily attached to the inner surface of the immersion nozzle 4 during continuous casting. This is to energize the molten steel passing through the inner surface of the immersion nozzle 4.
[0052]
  When the immersion nozzle 4 is made of a refractory having electrical conductivity, the entire immersion nozzle 4 can be the refractory having the electrical conductivity. Further, the refractory of the immersion nozzle 4 may have a structure of two or more layers in the radial direction, the strength and the like may be secured in the outer layer portion, and the inner layer in contact with the molten steel may be a refractory having the above electrical conductivity. Furthermore, you may comprise a part of inner layer or an outer layer with materials with low electrical conductivity, such as high purity alumina.
[0053]
  On the other hand, when Al oxide or the like easily adheres to the sliding gate 3, the sliding gate 3 can be made of a refractory material having electrical conductivity, and the other electrode 6 can be provided on the sliding gate 3. Further, two or more of the upper nozzle 2, the sliding gate 3 and the immersion nozzle 4 may be made of a refractory material having electrical conductivity, and the other electrode 6 may be provided thereon.
[0054]
  When the sliding gate 3 is made of a refractory having electrical conductivity, the movable plate 33 having the narrowest flow path and easy to adhere such as Al oxide is made of the refractory having electrical conductivity. desirable. Also in this case, similarly to the upper nozzle 2, the structure has two or more layers in the radial direction, and the refractory on the inner surface in contact with the molten steel can be the refractory having the electrical conductivity.
[0055]
  When one of the upper nozzle 2, the sliding gate 3 and the immersion nozzle 4 is made of a refractory material having electrical conductivity and the other electrode 6 is provided, it is desirable that the other electrode 6 is provided on the immersion nozzle 4. . This is because, during continuous casting, oxides of Al adhering to the inner surface of the immersion nozzle 4 affect the stability of the continuous casting operation and the quality of the product. It is for energizing between molten steel.
[0056]
  Further, when the other electrode 6 is provided on a plurality of members, it is necessary to prevent a large difference in resistance values of the respective circuits. This is because if the difference in resistance value is large, current flows only in a specific path, hardly flows in other paths, and the adhesion preventing effect cannot be obtained in other paths.
2. Refractories with electrical conductivity
  As a refractory having electrical conductivity, the electrical conductivity is 1 × above the melting point of the molten steel 8 accommodated.10 ^Three S / m or more is desirable, 1 × 10^Four~ 1x10⁶S / m is more desirable. Generally, as a refractory having electrical conductivity, a refractory mainly composed of graphite such as alumina graphite, zirconia graphite and magnesia graphite, solid electrolyte, TiB₂And ZrB₂And boride-based materials such as The characteristics of each material will be described below.
[0057]
  Alumina-graphite refractories
An alumina graphite refractory material often used for an immersion nozzle or the like preferably contains 5 to 35 mass% of graphite. If the graphite content is 5% by mass or more, it can have electrical conductivity in the temperature range from room temperature to the molten state of steel. Furthermore, if it is about 12 mass% or more, electrical conductivity will be 1x10.^FourS / m or more is more preferable.
[0058]
  However, when the graphite content exceeds 35 mass%, the strength deteriorates. Moreover, corrosion resistance deteriorates with respect to molten steel, and a problem of melting damage occurs. This alumina graphite-like refractory is SiO 2₂Even if it is contained up to about 20% by mass, there is no problem in energization. SiO₂Is mainly effective in reducing the thermal expansion coefficient of alumina graphite refractories and preventing breakage due to thermal shock. In addition, SiO₂Instead of, SiC may be included.
[0059]
  Zirconia Graphite Refractory In the case of zirconia graphite refractory, it is desirable to contain 5 to 20% by mass of graphite. If the graphite content is 5% by mass or more, it has electrical conductivity in the temperature range from room temperature to the molten state of steel. Furthermore, if it is about 10 mass% or more, electrical conductivity will be 1x10.^FourSince it becomes more than S / m, it is more suitable. However, if the graphite content exceeds 20% by mass, there is a problem that the strength decreases. Here, the upper limit of the graphite content is less than that of alumina graphite refractories. The density change of the refractory itself when graphite containing zirconia is larger than alumina and smaller in density than graphite. This is because it becomes larger.
[0060]
  Solid electrolyte refractories are solid electrolyte refractories that do not contain graphite, such as zirconia solid electrolytes. This solid electrolyte refractory has electrical conductivity at the temperature of the molten state of steel. However, the electrical conductivity is about 1 × 10 at the melting temperature of the molten steel.²It is about S / m and cannot be said to be a sufficient value. When such a material is used, there arises a problem that the current flows in a short-circuited state and the current flows locally. For this reason, it becomes difficult to obtain an adhesion preventing effect such as alumina over a wide area.
[0061]
  In order to solve such a problem, it is necessary to provide an immersion nozzle 4 in which the other cylindrical electrode 6 as shown in FIG. 1 is provided so that the equal current flows in a wide range. Based on such knowledge, the present inventionUsed for continuous casting methodIn the molten steel feeder, the electrical conductivity is 1 × 10 at the melting point of the molten steel^ThreeUse refractories with S / m or moreIs desirabledid. In addition, since the solid electrolyte has poor thermal shock resistance, it is difficult to apply it to a process in which the molten steel is flowed after being preheated like continuous casting of molten steel. Moreover, when such a material is used, there also exists a problem that the manufacturing cost of a refractory material becomes high.
[0062]
  Boride refractories such as TiB₂And ZrB₂Then, the electrical conductivity is 1 × 10^FiveIt is S / m or more and can be used as a refractory for energizing steel.
[0063]
  As described above, a refractory based on graphite and a boride refractory can be used. However, boride-based refractories are expensive to manufacture and it is difficult to make large structures. For this reason, boride-based refractories can be used in a limited manner when a molten steel channel is used.
[0064]
  Therefore, the present inventionUsed in continuous casting methodThe refractory material is preferably a refractory material mainly composed of graphite. Considering the thermal shock resistance, strength, erosion resistance, and production cost, alumina graphite refractories are desirable.
3. Insulation construction
  Of the present inventionUsed in continuous casting methodIn the molten steel supply device, between the upper electrode 2, the sliding gate 3 and the immersion nozzle 4 made of a refractory having electrical conductivity, the member provided with the other electrode 6, and the one electrode 5, It is desirable to provide an insulator.
[0065]
  In the molten steel supply apparatus shown in FIG. 1, one electrode 5 is provided on the tundish 1 and the other electrode is provided on the immersion nozzle 4. In this case, the tundish 1 and the one electrode 5 It is desirable to provide an insulator between the tundish 1 and the upper nozzle 2, between the upper nozzle 2 and the sliding gate 3, and between the sliding gate 3 and the immersion nozzle 4.
[0066]
  Thereby, when it supplies with electricity, it can prevent that a short circuit is formed between the immersion nozzle 4 in which one electrode 5 and the other electrode 6 were provided. In this case, if an insulator is provided between the immersion nozzle 4 provided with the other electrode 6 and the sliding gate 3 adjacent thereto, current can be prevented from flowing through the sliding gate 3 when energized. It is possible to efficiently energize molten steel.
[0067]
  The level of insulation at this time is at the end of preheating of the tundish before supplying molten steel into the tundish, or when the tundish once used for casting is used again for casting without reheating, In the tundish before supplying molten steel into the tundish, the initial electrical resistance between one electrode 5 and the other electrode 6 is set to 500Ω or more. If the initial electrical resistance is less than 500Ω, current does not flow sufficiently in the molten steel passing through the immersion nozzle 4 during casting, current flows in a short circuit other than the molten steel, and oxidation of Al in the molten steel occurs on the inner surface of the immersion nozzle. It cannot effectively prevent the attachment of objects.
[0068]
  As forms of insulation construction, between the tundish 1 and one electrode 5, between the upper nozzle 2 and the refractory of the tundish 1 and the iron skin of the tundish, the sliding gate 3 and the iron skin of the tundish 1 A structure in which a refractory having low electrical conductivity is sandwiched may be provided between the two. Moreover, an insulating sheet made of glass fiber or the like can be inserted between them. An insulating sheet may be provided between the upper nozzle 2, the sliding gate 3, and the immersion nozzle 4, between these and the support member, or between the layers in the case of the two-layer structure.
[0069]
  More specifically, when the other electrode 6 is disposed as a refractory having electrical conductivity with the immersion nozzle 4 and energized between the immersion nozzle and the molten steel passing through the immersion nozzle,(A)Between tundish 1 and one electrode 5,(B)It is desirable to electrically insulate either or both of the immersion nozzle and the gate 3 in contact with the immersion nozzle and between the immersion nozzle and the holder that holds the immersion nozzle on the sliding gate. As a result, the dipping nozzle 4 and the tundish 1 main body composed of the tundish lining refractory and the iron skin are also electrically insulated.
[0070]
  Further, the immersion nozzle 4 and the gate 3 are refractories having electrical conductivity, and the other electrode is disposed on each of them, and electricity is passed between the immersion nozzle 4 and the upper nozzle 2 and the molten steel passing through the immersion nozzle. If you want to(A)Between tundish 1 and one electrode 5,(B)Electrically insulate one or both of the gate 3 and the tundish body, between the gate 3 and the upper nozzle, and between the gate 3 and the cassette holder that holds the gate on the tundish iron skin or the like. Is desirable.
[0071]
  Further, the immersion nozzle 4, the gate 3 and the upper nozzle 2 are refractories having electrical conductivity, and one electrode is disposed on each of them, and passes through the immersion nozzle 4, the gate 3 and the upper nozzle 2, and the inside of the immersion nozzle. When energizing between the molten steel(A)Between tundish 1 and one electrode 5,(B)It is desirable to electrically insulate either or both of the tundish main body and these immersion nozzle, gate and upper nozzle.
[0072]
  Mineral materials used for insulation are generally 1 × 10 at room temperature^FiveAlthough it has an electrical resistivity of Ω · m or more and exhibits sufficient insulation, ionic conduction occurs when exposed to high temperatures such as the temperature of molten steel with many materials, resulting in a decrease in electrical resistivity. Therefore, even at high temperatures such as the molten steel temperature, refractories with little decrease in electrical resistivity, such as Al₂O_Three, SiO₂Insulating sheets made of insulating refractory fiber, etc., these Al₂O_Three, SiO₂A coating material such as can be used.
[0073]
  As a specific construction method of these insulating sheets and coating materials, for example, the insulating sheet is applied to the part of the gate that is in contact with the immersion nozzle and the part of the holder that is in contact with the immersion nozzle and holds the immersion nozzle on the sliding gate. It is possible to adopt a structure of inserting and sandwiching. At that time, the thickness to be sandwiched is preferably 1 to 4 mm. Furthermore, it is more desirable to combine the method of applying the coating material to the portion to be insulated together with the adhesive. In that case, the thickness of the coating material is desirably 0.2 to 1.0 mm. Also, alumina or silica can be used as the adhesive.
[0074]
  The upper limit of the initial electric resistance is ideally infinite, but when considering an apparatus for supplying molten steel from the tundish of an actual continuous casting machine into the mold, it is practically 1 × 10.⁸Ω is the upper limit.
[0075]
  In the continuous casting method of the present invention, the electric resistance during casting calculated from the current and voltage between one electrode 5 and the other electrode 6 during the period from the start to the end of casting is reduced in the tundish. When the preheating of the tundish before supplying molten steel to the end or when the tundish once used for casting is used for casting again without preheating, the tundish before supplying molten steel into the tundish It is desirable that it is less than 1/10 of the initial electrical resistance between one electrode and the other electrode. The reason will be described below.
[0076]
  FIG. 5 is a diagram illustrating a change in electrical resistance during casting between one electrode during casting and the other electrode. In the figure, the initial electrical resistance is 0.7Ω. Although the resistance may hardly change even after the casting time, that is, the energization time has elapsed, the resistance of the electric circuit of the current flowing through the molten steel that normally passes through the immersion nozzle increases. This is presumably due to the fact that the surface of the refractory having electrical conductivity disposed on the immersion nozzle, which contacts the molten steel, has deteriorated over time, or a non-conductive substance such as alumina has adhered.
[0077]
  If the electrical resistance during casting becomes 1/10 or more of the initial electrical resistance, the current does not flow properly in the molten steel passing through the immersion nozzle, and a part of the current flows in the short circuit other than the molten steel. It becomes impossible to prevent the oxide of Al in the molten steel from adhering to the steel. In addition, if the electrical resistance during casting is significantly greater than 1/10 of the initial electrical resistance, not only is the applied power wasted, but a large amount of current flows through the short circuit other than molten steel, There is a danger that fine electric discharge occurs due to electric leakage. In that case, there is a case where an electric shock is caused or a malfunction of surrounding equipment is caused.
[0078]
  FIG. 6 is a diagram showing the influence of electrical resistance between one electrode and the other electrode on the surface properties of the cold rolled product. The horizontal axis is the value of the initial electrical resistance between one electrode and the other electrode at the time immediately before starting casting. The vertical axis is the value obtained by dividing the value of electrical resistance during casting calculated from the current and voltage between one electrode and the other electrode at the end of casting after the start of casting by the value of the initial electrical resistance. is there.
[0079]
  The slab was hot-rolled to a steel strip having a thickness of 5 mm, then pickled and cold-rolled to obtain a steel strip having a thickness of 0.8 mm. Investigate whether or not product surface flaws have occurred and their occurrence, and calculate the total length of the steel strip as the total cut-off length of the product surface flaws caused by defects in the castings such as mold powder and Al oxide The percentage of product defects was calculated by dividing the value by% and displaying the percentage. The circles in the figure mean that there is no defect on the surface of the product due to defects on the surface of the slab, such as mold powder on the surface of the slab and oxides of Al in the molten steel.
[0080]
  The Δ mark in FIG. 6 means that the product flaw occurrence rate is within 0.5% and a slight defect on the product surface has occurred. In addition, the ▲ mark in the figure means that a product surface defect occurred within the above product defect generation rate within 1%. However, if this product wrinkle generation rate is within 1%, it is not the state of occurrence of particularly problematic defects. In addition, the crosses in the figure mean that the product wrinkle generation rate exceeds 5% and the product surface has a lot of defects. The result of having tested the value of the initial electrical resistance by changing the construction method of the insulating part is shown.
[0081]
  From the results of FIG. 6, it can be seen that the occurrence of defects on the product surface can be prevented by setting the initial electrical resistance to 500Ω or more. In addition, castingEndIt can be seen that a better product surface can be obtained when the electrical resistance during casting calculated from the current and voltage between one electrode and the other electrode is less than 1/10 of the initial electrical resistance. . In addition, the lower limit of the ratio of the electrical resistance during casting to the initial electrical resistance is ideally zero, but when considering an apparatus that supplies molten steel from the tundish of an actual continuous casting machine into the mold, Specifically, 0.00001 / 10 is the lower limit.
4). Gas blowing
  You may provide the gas blowing part which consists of a porous refractory which abbreviate | omitted illustration in any of the upper nozzle 2, the sliding gate 3, and the immersion nozzle 4. FIG. This gas blowing part is used as follows.
[0082]
  In order to prevent Al oxide from adhering to the inner surface of the submerged nozzle 1 when processing this molten steel, the amount of Al oxide in the molten steel increases due to the operating conditions of the converter, RH, etc. Inject gas. Further, an inert gas is blown in order to prevent a defective opening of the immersion nozzle due to solidification of the molten steel at the start of casting and to improve the flow of the molten steel in the mold.
[0083]
  In this case, any one or two of the upper nozzle 2, the sliding gate 3 and the immersion nozzle 4, preferably the other electrode 6 is provided on the immersion nozzle 4 and the other electrode 6 is not provided. One or two gas blowing portions may be provided. In this way, since the other electrode 6 and the gas blowing portion do not exist in one member, it is possible to prevent the strength of the refractory from being lowered.
[0084]
  In the molten steel supply apparatus shown in FIG. 1, one electrode 5 is provided through the side wall of the tundish 1 so that the tip reaches the internal space of the tundish 1. You may provide so that it may reach internal space from the upper part of the tundish 1, without doing. Further, a part of the side wall of the tundish 1 may be made of a refractory having electrical conductivity, and this part may be used as one electrode 5.
[0085]
  Alternatively, the upper nozzle 2 or the sliding gate 3 may be made of a refractory having electrical conductivity, and one electrode 5 may be provided on the upper nozzle 2 or the sliding gate 3. When one electrode 5 is provided on the upper nozzle 2, either or both of the sliding gate 3 and the immersion nozzle 4 are made of a refractory material having electrical conductivity, and the other electrode 6 is provided on one or both of them. Is provided. When one electrode 5 is provided on the sliding gate 3, either one or both of the upper nozzle 2 and the immersion nozzle 4 are made of a refractory having electrical conductivity, and the other electrode 6 is provided on one or both of them. Provide. In either case, an insulator is provided between the member provided with one electrode 5 and the member provided with the other electrode 6. Further, an insulator may be provided between the upper nozzle 2 and the tundish 1 so that no current flows through the tundish 1.
5). Application of current and voltage
  In the continuous casting method using the molten steel supply device shown in FIG. 1, the molten steel supply device is disposed on the mold 9, and the molten steel 8 in the tundish 1 is cast by the upper nozzle 2, the sliding gate 3 and the immersion nozzle 4. 9 is supplied.
[0086]
  At this time, the power supply unit 7 is turned on. The power supply unit 7 is connected to one electrode 5 and the other electrode 6 by electric wiring 7a. One electrode 5 is immersed in molten steel in the tundish 1, and the other electrode 6 is provided in an immersion nozzle 4 made of a refractory having electrical conductivity. Therefore, electricity is supplied between the inner surface of the immersion nozzle 4 and the molten steel passing through the interior of the immersion nozzle 4.
[0087]
  The current to be energized may be either direct current or alternating current. In the case of direct current, the immersion nozzle side may have either positive or negative potential. Further, it may be a pulse wave or a rectangular wave. This energization may be intermittent rather than continuous.
[0088]
  As described above, when an electric current is applied between the inner surface of the immersion nozzle 4 and the molten steel passing through the immersion nozzle 4, the interfacial tension between the inner surface of the immersion nozzle 4 and the molten steel is reduced by the aforementioned electrocapillary phenomenon. Therefore, the force with which the oxide of Al in the molten steel adheres to the surface of the refractory is reduced, and the oxide of Al becomes difficult to adhere to the inner surface of the immersion nozzle 4.
[0089]
  When energized, the current density per surface area of the conductive part of the refractory having electrical conductivity is0.01~0.1Ampere / cm²(A / cm²) Is desirable.0.1A / cm²The effect is saturated when exceeding. TheIn addition, when a large current density is passed over a wide area, the power supply unit 7 and wiring devices are large, and a large amount of power is required. Also0.01A / cm²If it is less than 1, the effect of preventing adhesion cannot be obtained..
[0090]
  The applied voltage between the other electrode 6 and the one electrode 5 is a value determined by the current density, the electrical resistance of the refractory, and the electrical resistance due to deposits adhering to the inner surface of the refractory, but is 0.5 to 100 volts. (V) is desirable. When the applied voltage is less than 0.5 V, an effective current does not flow from the resistance of the energization path, and it becomes difficult to detect application of current and voltage. If the upper limit of the applied voltage is 100 V, a necessary current can be passed if the resistance of the energization path is appropriately set. However, when the voltage exceeds 100 V, the risk of electric shock increases suddenly. Therefore, a more desirable range of applied voltage is 1-60V.
[0091]
  FIG. 7 shows the immersion nozzle 4 when the immersion nozzle 4 is made of a refractory material having electrical conductivity and at the same time the other electrode 6 is embedded in the immersion nozzle 4 and continuously cast under the same conditions as in Example 1 described later. It is a figure which shows the relationship between the thickness of deposits, such as an oxide of Al adhering to the inner surface, and the applied voltage between the other electrode 6 and the one electrode 5. In FIG. 7, the current value and the current density are increased by a positive correlation with the voltage by making the energization path the same and making the contact area of the molten steel and the conductive refractory the same.
[0092]
  As is clear from the figure, when argon gas is not flowed (marked with ● in the figure), when the potential is 0 (zero), the thickness of the deposit is about 13 mm, but when the potential is + 1V or -1V, The thickness of the deposit is reduced to about 8 mm. When the potential is +5 V or −5 V, the thickness of the adhesion amount is reduced to about 4 mm. The thickness of this deposit is less than 5 mm when the potential is 0 and the flow rate of argon gas is 20 liters (Nl) / min (marked with a circle in the figure). Further, if the potential is + 20V or −20V, the thickness of the deposit is reduced to about 1 mm. In this figure, although there is no clear difference, the negative nozzle is attached to the inner surface of the immersion nozzle 4 in comparison with the positive (+) potential. The thickness of the deposits tends to decrease.
6). Make the immersion nozzle side negative potential
  If the immersion nozzle 4 is energized with molten steel as a negative potential rather than having a positive potential, the thickness of deposits attached to the inner surface of the immersion nozzle 4 tends to be reduced. This is due to the following reason.
[0093]
  When a current is passed, for example, in a refractory containing carbon such as alumina graphite, the electron conduction in carbon is the main component, but polarization occurs in the oxide. This polarization is the cause of the above-mentioned surface tension change, but the reactions shown by the following formulas (a) to (c) occur in the oxide constituting the refractory.
[0094]
Si⁴⁺+ 4e^-= Si (a)
Al³⁺+ 3e^-= Al (b)
O^2-= O + 2e^-     ... (c)
  At this time, if the refractory having electrical conductivity is set to a negative potential, the reactions (a) and (b) proceed to the right, but the reaction (c) does not proceed. For this reason, oxygen which is a generation source of alumina is not generated, and adhesion to the nozzle inner surface can be prevented.
[0095]
  When a refractory having electrical conductivity is set to a negative potential and a direct current is passed between the refractory and molten steel, in addition to a decrease in interfacial tension, as a result, the equation (c) Reaction is suppressed and it can prevent that the oxide of Al etc. in molten steel adheres to the surface of a refractory.
[0096]
  When direct current is applied with the refractory as a positive potential, the reaction of the above formula (c) is promoted even if the interfacial tension is lowered, so that an oxide of Al adheres to the surface of the refractory. The effect of preventing this is small. In addition, when an alternating current is passed between the electrically conductive refractory and the molten steel, acceleration and suppression of the reaction of the above formula (c) occur alternately, such as Al oxide in the molten steel, etc. Is less effective to prevent adhesion of refractory to the surface of the refractory. Therefore, it is desirable to apply a direct current with the immersion nozzle 4 having a negative (−) potential.
[0097]
  As described above, the molten steel 8 in the tundish 1 is supplied into the mold 9 while energizing between the inner surface of the immersion nozzle 2 and the molten steel 8 passing through the inside. A mold powder 11 is added to the upper surface of the molten steel in the mold 9 in order to keep the molten steel in the mold 9 warm and prevent oxidation and to lubricate the mold 9 and the solidified shell 10. The molten steel 8 supplied into the mold 9 is formed with a solidified shell 10 from the surface in contact with the mold 9 and then pulled out by a drawing device (not shown) to form a cast piece.
[0098]
  When the molten steel 8 passes through the immersion nozzle 4, it is energized between the inner surface of the immersion nozzle 4 and a potential difference is applied, so that an oxide of Al or the like does not adhere to the inner surface of the immersion nozzle 4. . In addition, since no inert gas such as argon gas is blown into the molten steel, there is no bubble defect in the slab.
[0099]
  In the continuous casting method of the present invention, in the molten steel that passes through the upper nozzle 2 to the extent that no bubble defects are generated from the upper nozzle to the slab surface layer portion using the molten steel supply portion provided with the gas blowing portion in the upper nozzle 2. It is desirable to blow in an inert gas. When inert gas bubbles rise in the molten steel in the mold, the oxide in the molten steel floats in the molten steel together with the bubbles and is captured outside by the molten mold powder on the molten steel surface. The Therefore, the cleanness of the slab is improved, and a product with a good cleanliness can be obtained. At that time, the flow rate of the inert gas is preferably 2 to 10 liters (Nl) / min, although it depends on the slab size.
[0100]
  As described above, the molten steel supply apparatus of the present invention is optimally employed in a continuous casting method of molten steel deoxidized with Al. However, the molten steel supply apparatus of the present invention is not limited to this, and further, in continuous casting of metals containing clogging elements such as immersion nozzles, such as zirconium, calcium, rare earth metals, It is possible to prevent the oxides of these elements from adhering to the inner surface of the immersion nozzle.
[0101]
【Example】
  [Example 2]From A and B molten steel deoxidized with Al using a vertical bending type continuous casting machine,A slab having a thickness of 270 mm and a width of 1200 to 1600 mm was cast at a speed of 1.4 to 1.7 m / min.Table 1 shows the chemical composition of the molten steel.
[Table 1]

[0102]
In the vertical bending type continuous casting machine, one or more of the upper nozzle, the sliding gate and the immersion nozzle are made of a refractory having electrical conductivity, and the other electrode is embedded in a member made of the refractory having electrical conductivity. What was equipped with the molten steel supply apparatus was used. In the test, a gas blowing portion was installed on the upper plate or upper nozzle portion of the sliding gate, and a small amount of gas of 2 to 5 Nl / min necessary for opening at the initial casting was blown. With this level of blowing, no pinholes were generated on the surface of the slab, and there was almost no outflow gas in the mold, so almost all of the gas floated to the tundish side without being brought into the mold. As the upper plate of the sliding gate, a conventional plate without an electrode was used, but in some tests, a refractory material having electrical conductivity and connected to the other electrode was used. The shape of the tundish used was a normal box shape, and the capacity was about 85 t.
[0103]
  The immersion nozzle used had an inner diameter of 90 mm and two discharge holes of 35 ° downward.The material of the immersion nozzle is mass%, graphite 31%, SiO₂Contains 14%, the balance is almost Al₂O_ThreeAlumina graphite having electrical conductivity at the temperature of molten steel. The outer periphery of this immersion nozzle is made of carbon steelThe otherThe electrode was attached. Also made of alumina graphiteon the other handThe electrode was immersed in the molten steel from the surface of the molten steel in the tundish.
[0104]
  Between the immersion nozzle and the sliding gate in contact with the immersion nozzle, and between the immersion nozzle and the holder that holds the immersion nozzle on the sliding gate, Al₂O_ThreeAnd SiO₂A sheet of refractory fibers and / or SiO₂An antioxidant containing as a main component was applied to electrically insulate each of them. At that time, the thickness of the sheet and the coating material was changed and tested.
[0105]
  Prior to the casting test, the tundish, upper nozzle, sliding gate, immersion nozzle and the like were preheated for about 3 hours using normal combustion gas, and the surface temperature of the tundish lining refractory was set to 1000 to 1200 ° C. Immediately before the end of preheating, the initial electrical resistance between one electrode and the other electrode was measured.
[0106]
  In the casting test, molten steel having a heat of about 270 t was continuously cast for 6 heats.At this time, the superheat degree of the molten steel in the tundish was 20-30 degreeC.During the period from the start to the end of casting, current was supplied at a constant current or voltage between one electrode and the other electrode. At that time, the current was 10 to 100 A, and the voltage was 3 to 80 V. From these currents and voltages, the electrical resistance during casting between one electrode and the other electrode was determined.Further, the current density a (A / cm) defined by the following formula (d) is varied by variously changing the surface area b of the electrically conductive portion of the refractory inner surface facing the molten steel that is joined to the other electrode. ² ) Change test.
[0107]
Current density (A / cm ² ) = A / b ... (d)
Where a: current value (A)
b: Surface area (cm) of the inner surface of the part having conductivity among the refractories that are bonded to the other electrode and face the molten steel ² )
When applying direct current, the other electrode side was set to a positive or negative potential.
[0108]
  In addition, Ar gas was blown into the molten steel passing through the porous refractory placed on the sliding gate during casting at a flow rate of 2 to 5 liters (Nl) / min. It was confirmed in advance that this blowing flow rate was not an amount that would cause bubble defects on the slab surface.
[0109]
  After the completion of casting, the immersion nozzle was collected and longitudinally cut, and then the presence or absence of the deposit and the thickness of the deposit were investigated.The thickness of the inner surface was measured by measuring the inner diameter at two positions in the length direction of the upper nozzle, sliding gate, and immersion nozzle provided with the other electrode, and averaging the values. Is represented by 1/2 of the value subtracted from the inner diameter before use.
[0110]
  Moreover, the slab obtained in the 2nd heat and 6th heat is hot-rolled to a steel strip having a thickness of 4 to 6 mm, then pickled and then cold-rolled to a thickness of 1.6 to 1.2 mm. Steel strip. The presence or absence and occurrence of product surface defects were investigated and the product defect rate was determined. The product flaw occurrence rate is expressed as a percentage by dividing the total length of the cut-off length of the product surface flaws caused by defects in the slab, such as mold powder and Al oxide, by the total length of the steel strip. Determined by Table of test conditions and test results2Shown in
[0111]
【table2]

[0112]
  Test No. 28, a 2.5 mm thick sheet made of refractory fiber is inserted between the immersion nozzle and the sliding gate, and SiO 2 is further interposed between the immersion nozzle and its holder.₂The system antioxidant was applied to a thickness of 0.2 mm. The initial electrical resistance between one electrode and the other electrode immediately before finishing the preheating of the tundish was 600Ω. This value is within the range defined by the present invention. Moreover, the electrical resistance during casting immediately before the end of casting for the sixth heat was 72Ω. The value obtained by dividing the electrical resistance during casting by the initial electrical resistance (hereinafter referred to as the ratio of electrical resistance) was 1.2 / 10, which was a value slightly outside the range of desirable conditions. Test No. In No. 28, the thickness of the deposit on the immersion nozzle after casting was as small as 5 mm, which was a good result. Moreover, the product flaw occurrence rates using the slabs of the second heat and the sixth heat as raw materials were 0.6% and 0.9%, respectively.
[0113]
  Test No. 29, a 2.5 mm thick sheet made of refractory fiber is inserted between the immersion nozzle and the sliding gate, and SiO 2 is further interposed between the immersion nozzle and its holder.₂The system antioxidant was applied at a thickness of 0.4 mm. The initial electrical resistance between one electrode and the other electrode immediately before finishing the preheating of the tundish was 600Ω. This value is within the range defined by the present invention. The electrical resistance during casting immediately before the end of casting for the sixth heat was 58Ω. The ratio of electrical resistance during casting was 0.97 / 10, which was within the desired range. Test No. In No. 29, the thickness of the deposit on the immersion nozzle after casting was as small as 4 mm, which was a good result. Moreover, the product flaw occurrence rates using the slabs of the second heat and the sixth heat as raw materials were as low as 0.3% and 0.5%, respectively.
[0114]
  Test No. 30, a sheet having a thickness of 4.0 mm is inserted between the immersion nozzle and the sliding gate, and a sheet having a thickness of 1.0 mm is inserted between the immersion nozzle and its holder. The inhibitor was applied with a thickness of 0.5 mm. The initial electrical resistance between one electrode and the other electrode immediately before finishing the preheating of the tundish was 1200Ω. This value is a value within the range defined by the present invention. Test No. Compared with 29, the initial electrical resistance was doubled because the sheet thickness between the immersion nozzle and the sliding gate was increased and the sheet was placed between the immersion nozzle and its holder. In addition to applying an antioxidant. Moreover, the electrical resistance during casting immediately before the end of casting for the sixth heat was 8Ω. Therefore, the electrical resistance ratio was 0.07 / 10, which was within the range of desirable conditions. Test No. In No. 30, the thickness of the deposit on the immersion nozzle after casting was 4 mm, which was a good result. In addition, when the second heat and sixth heat slabs were used, the product defect generation rates were as low as 0.3% and 0.4%, respectively.
[0115]
  Test No. In No. 31, the method of insulation construction is test no. 30. The initial electrical resistance between one electrode and the other electrode was 1050 Ω just before finishing the preheating of the tundish. The electrical resistance during casting immediately before the end of casting for the sixth heat is 0.5Ω, and the resistance increase during casting is small. Therefore, the electrical resistance ratio was 0.005 / 10, which was within the range of desirable conditions. Test No. In No. 31, the thickness of the deposit on the immersion nozzle after casting was 2 mm, which was a good result. Moreover, the product flaw occurrence rate in the case of using the second heat and sixth heat slabs was 0.3%, which was a good result.
[0116]
  Test No. In No. 32, the sheet thickness between the immersion nozzle and the sliding gate was 2.0 mm, and an alumina plate having a thickness of 3 mm was further sandwiched. Moreover, the thickness of the sheet | seat between an immersion nozzle and its holder was 1.8 mm, and the thickness of antioxidant was applied by 0.7 mm. The initial electrical resistance between one electrode and the other electrode immediately before finishing the preheating of the tundish is 380 × 10^ThreeΩ. This value is within the range defined by the present invention. Since the thickness of the sheet and the coating material was increased, the initial electric resistance was extremely large. The electrical resistance during casting immediately before the end of casting for the sixth heat was 13Ω. Therefore, the electrical resistance ratio was 0.0003 / 10, which was a value within the range of desirable conditions. Test No. In No. 32, the thickness of the deposit on the immersion nozzle after casting was 1 mm, which was remarkably small, which was the best result. Moreover, the product flaw occurrence rates using the slabs of the second heat and the sixth heat as raw materials were 0.1% and 0.2%, respectively.
[0117]
  Test No. In No. 33, the thickness of the sheet was 2.0 mm, and the thickness of the coating material was 0.6 mm. The initial electrical resistance between one electrode and the other electrode was 420Ω immediately before finishing the preheating of the tundish. This value was a small value outside the conditions defined in the present invention. The electrical resistance during casting immediately before the end of casting for the sixth heat was 64Ω. Therefore, the electrical resistance ratio rose to 1.5 / 10, which was not desirable. Test No. In No. 33, the thickness of the deposit on the immersion nozzle after casting was slightly thick at 7 mm. Moreover, the product flaw occurrence rates using the slabs of the second heat and the sixth heat were 0.8% and 7.9%, respectively, and the result of the sixth heat was particularly bad.
[0118]
  Test No. No. 34, without using a sheet made of refractory fiber, both between the immersion nozzle and the sliding gate and between the immersion nozzle and its holder are made of SiO.₂System antioxidants were applied at thicknesses of 0.7 mm and 0.5 mm. The initial electrical resistance between one electrode and the other electrode was 30Ω immediately before finishing the preheating of the tundish. This value was significantly smaller than the conditions specified in the present invention. Moreover, the electrical resistance immediately before the end of casting for the sixth heat was 32Ω. Therefore, the electrical resistance ratio rose to 10.6 / 10, which was a large value outside the desired conditions. Test No. In No. 34, the thickness of the deposit on the immersion nozzle after casting was 11 mm, which was considerably thick. Moreover, the product flaw occurrence rates using the slabs of the second heat and the sixth heat as raw materials were 8.4% and 12.3%, both of which were bad results.
[0119]
  Test No. In No. 35, no electrical insulation was performed and no current was supplied. The thickness of the deposit on the immersion nozzle after casting was 13 mm, which was the thickest and bad result. In addition, the occurrence rate of product defects using slabs of the second heat and the sixth heat was 9.8% and 11.8%, respectively.
[0120]
  [Example 3] A slab having a thickness of 270 mm and a width of 1000 mm was produced in the same manner as in Example 1. The vertical bending type continuous casting machine was a molten steel supply apparatus shown in FIG. 1, which was provided with a molten steel supply apparatus having a gas blowing portion made of a porous refractory on the upper plate of the sliding gate.
[0121]
  At the time of continuous casting, the potential difference between one electrode and the immersion nozzle was set to 1.5 to 25 V, and direct current or alternating current was passed between them. When direct current was applied, the potential on the immersion nozzle side was positive or negative. In some tests, no current was applied between one electrode and the immersion nozzle. In some tests, Ar gas was blown into the molten steel at a flow rate of 20 liters (Nl) / min from a gas blowing portion provided in the sliding gate.
[0122]
  After the casting, the immersion nozzle was collected and cut longitudinally, and the presence or absence of deposits near the discharge holes and the thickness of the deposits were investigated. Further, the obtained slab was cold-rolled into a steel strip having a thickness of 0.8 to 1.2 mm by the same method as in Example 1, and the surface flaw occurrence rate was investigated by the same method as in Example 1. Table of test conditions and test results3Shown in
[0123]
【table3]

[0124]
  Test No. 36, the immersion nozzle side has a positive potential and the current density is 0.17 A / cm.²As a direct current was applied, the deposit thickness on the inner surface of the immersion nozzle was 3.0 mm, and the surface flaw occurrence rate was 1.8%.
[0125]
  Test No. 37, the immersion nozzle side is set to a negative potential, and other conditions are set to test No. The same as 36. As a result, the deposit thickness on the inner surface of the immersion nozzle was 1.3 mm and the surface flaw occurrence rate was 0.2%. Compared to 36.
[0126]
  Test No. 38, the immersion nozzle side has a positive potential and the current density is 0.092 A / cm.²As a direct current was applied, the deposit thickness on the inner surface of the immersion nozzle was 3.5 mm, and the surface flaw occurrence rate was 2.1%.
[0127]
  Test No. No. 39 has a negative potential on the immersion nozzle side, and other conditions are set to test no. 38, but the deposit thickness on the inner surface of the immersion nozzle was 1.8 mm and the occurrence rate of surface flaws was 0.3%. It is superior to 38.In addition, Test No. Both 38 and 39 had relatively low power consumption because the current density was in the desired range.
[0128]
  Test No. 40, the current density is 0.17 A / cm.²As for the other conditions, test no. 36, but the deposit thickness near the discharge hole of the immersion nozzle is 3.0 mm and the surface flaw occurrence rate is 1.8%. The deposit thickness and surface flaw occurrence rate on the inner surface of the immersion nozzle In both cases, test no. It was about the same as 36.
[0129]
  Test No. In No. 41, Ar gas was blown into the molten steel from the sliding gate at a flow rate of 20 liters (Nl) / min without energizing, so that the deposit thickness near the discharge hole of the immersion nozzle was 5.0 mm, The surface flaw occurrence rate was 2.3%, and both the deposit thickness on the inner surface of the immersion nozzle and the surface flaw occurrence rate were relatively bad results.
[0130]
  Test No. In No. 42, current was not supplied, and Ar gas was not blown into the molten steel from the sliding gate. Therefore, the immersion nozzle was clogged during casting, and casting was forced to stop during the third heat casting. It was. A deposit with a thickness of 13 mm adhered to the vicinity of the discharge hole of the immersion nozzle after casting, and the surface flaw occurrence rate was 5.1%.
[0131]
【The invention's effect】
  Of the present inventionContinuous casting methodAccordingly, it is possible to stably prevent the oxide of Al in the molten steel from adhering to the inner surfaces of the upper nozzle, the flow rate control mechanism, and the immersion nozzle. furtherGetIt is possible to prevent the occurrence of defects due to defects in the slab, such as mold powder, Al oxide, and air bubbles, in the product made from the slab that has been made. Moreover, it is possible to effectively prevent the immersion nozzle from being blocked during continuous casting.
[Brief description of the drawings]
FIG. 1 of the present inventionUsed in the methodIt is a longitudinal cross-sectional view which shows an example of a molten steel supply part typically.
FIG. 2 is a longitudinal sectional view showing another example in which the other electrode is embedded in the immersion nozzle.
FIG. 3 is a front view showing an example in which the other electrode is attached to the outer surface of the immersion nozzle.
FIG. 4 is a front view showing another example in which the other electrode is attached to the outer surface of the immersion nozzle.
FIG. 5 is a diagram illustrating a change in electrical resistance during casting between one electrode and the other electrode during casting.
FIG. 6 is a diagram showing the influence of electrical resistance between one electrode and the other electrode on the surface properties of a cold-rolled product.
FIG. 7 is a diagram showing the relationship between the thickness of deposits such as Al oxide deposited on the inner surface of an immersion nozzle in continuous casting and the applied voltage between the other electrode and one electrode.
[Explanation of symbols]
  1: tundish, 2: upper nozzle, 3: sliding gate (flow rate control mechanism), 4: immersion nozzle, 5: one electrode, 6: the other electrode, 7: power supply, 8: molten steel, 9: mold, 10: Solidified shell, 11: Mold powder.

Claims (6)

A tundish for containing molten steel, an upper nozzle provided at the bottom of the tundish, a flow rate control mechanism for controlling the flow rate of supplying the contained molten steel to a mold, and an immersion nozzle for circulating the supplied molten steel A continuous casting method for supplying molten steel contained in a tundish to a mold using a molten steel supply device, comprising a pair of electrodes and a power supply unit connected thereto, and any of the upper nozzle, the flow control mechanism and the immersion nozzle The inner surface in contact with the molten steel is made of a refractory having an electrical conductivity at or above the melting point of the steel, and one of the pair of electrodes is any of the tundish, the upper nozzle, the flow control mechanism, and the immersion nozzle. was placed in contact with the molten steel reaches the Kano interior space, the other electrode is placed the one electrode is configured portion with refractory having the electrical conductivity There is provided at a position further to the preheating at the end of the previous tundish supplying molten steel into the tundish, or, once in the case of using a tundish used for casting again casting without preheating, the tundish A continuous casting method characterized in that, before supplying molten steel, an electric resistance between the one electrode and the other electrode is set to 500Ω or more, and a voltage is applied between the one electrode and the other electrode. . And Turkey to supply nozzle onto the electrode is not provided, the flow control mechanism and the molten steel contained in the tundish with molten steel supply device provided with one or two or more gas injection section of the immersion nozzle in the mold The continuous casting method according to claim 1 . The electric resistance obtained from the current and voltage applied to the one electrode and the other electrode from the start to the end of casting is preheated before the molten steel is supplied into the tundish. When the tundish once used for casting is used for casting again without being preheated, it is between the one electrode and the other electrode before supplying molten steel into the tundish. The continuous casting method according to claim 1 or 2 , wherein the electric resistance is less than 1/10. The continuous casting method according to any one of claims 1 to 3, wherein the current is applied so that an applied current density is 0.01 A / cm ² or more and less than 0.1 A / cm ² . The continuous casting method according to any one of claims 1 to 4 , wherein a voltage to be applied is 0.5 V or more and 100 V or less. Even without least provided with other side of the electrode as well as constituting a submerged nozzle in refractory material having an electrical conductivity at above the melting point of the steel, as the immersion nozzle side of the negative potential, and the molten steel passing through the immersion nozzle and the immersion nozzle The continuous casting method according to claim 1 , wherein blocking of the immersion nozzle is prevented by passing a direct current between the two.

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