JP4203167B2 - Continuous casting method for molten steel - Google Patents

Continuous casting method for molten steel Download PDF

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Publication number
JP4203167B2
JP4203167B2 JP00375399A JP375399A JP4203167B2 JP 4203167 B2 JP4203167 B2 JP 4203167B2 JP 00375399 A JP00375399 A JP 00375399A JP 375399 A JP375399 A JP 375399A JP 4203167 B2 JP4203167 B2 JP 4203167B2
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molten steel
mold
immersion nozzle
bubbles
electromagnetic coil
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JP2000202603A (en
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孝幸 兼安
祐二 平本
逸朗 北川
龍介 三浦
尚久 本田
伸博 吉川
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Nippon Steel Corp
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Nippon Steel Corp
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Description

【0001】
【発明の属する技術分野】
本発明は、鋳型内の溶鋼を電磁攪拌してスラブ等を鋳造する際に、鋳片の表層に捕捉される気泡や介在物に起因するヘゲ疵やフクレ疵等の欠陥を防止する溶鋼の連続鋳造方法に関する。
【0002】
【従来の技術】
従来、溶鋼を連続鋳造する際には、ノズルや浸漬ノズルの詰まりを防止するために、アルゴンガスの供給を行って、アルミナ系の酸化物の付着とその成長を抑制している。
このノズルや浸漬ノズルに供給されたアルゴンガスは、溶鋼が凝固する際に、気泡として凝固シェル界面に捕捉され易く、その鋳片に圧延等の加工を行なうとフクレ疵等が発生し、手入れの増加や歩留り等の低下を招く。
また、溶鋼中には、脱酸剤を添加した際に生成した酸化物や耐火物の溶損等による極微量の酸化物が存在する。この酸化物は、鋳造中に凝集する場合があり、凝固した鋳片の表層部となる凝固シェル界面に捕捉され、前記と同様に圧延等の加工を行う過程において、ヘゲ疵や割れ等の表面欠陥が発生して手入れの増加や製品歩留り等の低下となる。
従って、鋳片の表層部に発生する気泡や介在物に起因する欠陥を防止するために、特開昭58−100955号公報には、鋳型の外壁に取り付けた複数の電磁コイルを用いて、加速と減速を組合せた電磁攪拌を行い、溶鋼に鋳型の周壁に沿った水平方向の旋回流を付与することにより、表層部(凝固シェル)の界面を洗浄して気泡や介在物等の少ない表層部を形成する連続鋳造が開示されている。
また、特開平8−174164号公報には、電磁攪拌装置を用いて溶鋼の水平旋回流の流速V(cm/sec)と鋳型の幅W(cm)の積V・Wが、103 〜104 (cm2 /sec)となるように、電磁コイルに印加する電流を調整して水平旋回流を制御することにより、凝固シェルの界面に捕捉される気泡や介在物を洗浄して除去する連続鋳造方法が提案されている。
【0003】
【発明が解決しようとする課題】
しかしながら、特開昭58−100955号公報では、鋳型の周壁に沿った溶鋼の流れを最初に加速し、鋳型の短片の近傍で前記の加速された流れを減速させるので、加速流と減速流の境界部に相当する鋳片の凝固シェルの界面に気泡や介在物の集積が発生し、圧延等の加工の際にヘゲ疵やフクレ疵等の欠陥となる。
更に、鋳型に設けた電磁コイルにより付与される溶鋼の旋回流の作用しない下方の凝固シェルの界面に気泡や介在物が捕捉される。この気泡や介在物は、鋳片の表面疵になったり、圧延等の加工の際にヘゲ疵やフクレ疵の欠陥となる等の問題がある。
また、特開平8−174164号公報では、浸漬ノズルからの溶鋼の吐出流に混入したアルゴンガスの気泡や酸化物からなる介在物が、電磁コイルにより付与される溶鋼の旋回流の作用しない下方の凝固シェルの界面に、浮上しながら捕捉される。鋳片の表層部となる凝固シェルの界面に気泡や介在物が存在する鋳片に圧延等の加工を行うと、ヘゲ疵やフクレ疵等の欠陥が発生し、前記の特開昭58−100955号公報の連続鋳造と同様の問題がある。
【0004】
本発明はかかる事情に鑑みてなされたもので、鋳型内の溶鋼を電磁攪拌してスラブ等を鋳造する際に、鋳片の表層部に捕捉される気泡や介在物に起因するヘゲ疵やフクレ疵等の欠陥を防止し、良製品の歩留り等に優れた溶鋼の連続鋳造方法を提供することを目的とする。
【0005】
【課題を解決するための手段】
前記目的に沿う本発明の溶鋼の連続鋳造方法は、鋳型の長片の外側に電磁コイルを設け、前記鋳型の内壁に沿った旋回流を付与する溶鋼の連続鋳造方法であって、
前記電磁コイルは前記鋳型内の溶鋼を電磁攪拌することのみを行い、しかも、該電磁コイルの上端を該鋳型内の溶鋼の湯面の20〜60mm下方に位置させ、浸漬ノズルの吐出角度を水平線に対して1〜30°下向きにし、前記溶鋼を電磁攪拌する最大推力を5〜35mm鉄柱とし、前記浸漬ノズルにはアルゴンガスを供給して、前記電磁コイルの中心から下方450mmの範囲に相当する凝固シェルに、前記溶鋼を注湯する浸漬ノズルの吐出流が当たるようにする。この方法により、電磁コイルにより付与される溶鋼の旋回流の作用しない下方の鋳片の表層部である凝固シェルの界面に捕捉される気泡や介在物を界面の洗浄により除去することができ、鋳片の表面疵や圧延等の加工を行った際のヘゲ疵やフクレ疵等の欠陥を防止できる。
浸漬ノズルの吐出流が凝固シェルに当たる範囲が電磁コイルの中心よりも上方になると、鋳型内の湯面が吐出流の影響を受けて変動してパウダーの潤滑の不均一やパウダー巻き込み等が発生する。一方、浸漬ノズルの吐出流が凝固シェルに当たる範囲が電磁コイルの中心から下方500mmを超えると、吐出流が当たる部位が深くなり過ぎて電磁攪拌による旋回流の下方の界面に捕捉される気泡や介在物を洗浄、除去することができない。
【0006】
ここで、前記溶鋼を電磁攪拌する推力を5〜35mm鉄柱にしている
これにより、気泡や介在物の浮上を促進しながら、細かな気泡や介在物を溶鋼の旋回流により洗浄して、鋳片の凝固シェルの界面を清浄化することができる。
なお、溶鋼を攪拌する推力が5mm鉄柱より小さいと、溶鋼の旋回流が弱くなり、凝固シェルの界面に捕捉される気泡や介在物を洗浄して除去できない。
また、溶鋼を攪拌する推力が35mm鉄柱を超えると、溶鋼の旋回流が強くなり過ぎて、溶鋼中に混入した気泡や介在物が浮上するのを阻害する。
【0007】
更に、前記浸漬ノズルの吐出角度を1〜30°下向きにする。
これにより、鋳型内の湯面の変動やパウダー巻き込み及び気泡や介在物の侵入量や侵入深さ等を抑制しながら、浸漬ノズルからの吐出流により凝固シェルの界面に捕捉される気泡や介在物の洗浄をより適正に行うことができる。
ここで、ノズルの吐出角度は、鋳型内に形成される湯面と平行をなす線に対して下向きの角度であり、この浸漬ノズルの吐出角度が1°より小さいと、鋳型内の湯面の変動やパウダー巻き込み、ノロカミ等を招き、鋳片の表面欠陥の原因となる。
また、浸漬ノズルの吐出角度が30°より大きいと、溶鋼の吐出流に随伴する気泡や介在物の侵入量が増加すると共に侵入が深くなり、溶鋼の吐出流によって除去できなくなる。
【0008】
【発明の実施の形態】
続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態につき説明し、本発明の理解に供する。
図1は本発明の一実施の形態に係る溶鋼の連続鋳造方法に適用される連続鋳造装置の側断面図、図2は同連続鋳造装置の鋳型部の平断面図、図3は図1の矢視A−A断面図である。
図1、図2に示すように、本発明の一実施の形態に係る溶鋼の連続鋳造方法に用いられる連続鋳造装置10は、溶鋼11を貯湯する耐火物を内張りしたタンディッシュ13と、タンディッシュ13から溶鋼11を吐出口15を介して鋳型12に注湯する浸漬ノズル14と、鋳型12内の溶鋼11を攪拌するために、鋳型12の長片12aの外側に電磁コイル16a、16bと、長片12bの外側に電磁コイル17a、17bを備えている。
この鋳型12の長片12aの電磁コイル16aを強い推力にし、電磁コイル16bに弱い推力を付与し、長片12bの電磁コイル17aに弱い推力、電磁コイル17bに強い推力が出るようにして強弱の組合せによる攪拌を行う。
更に、鋳型12の冷却により凝固シェル18を形成した鋳片19は、図示しない鋳片支持装置及びピンチロールにより、引き続き冷却されながら所定の速度で引き抜きが行われる。
また、図3に示すように、鋳型12の長片12bの外側に設けた電磁コイル17a、17bのコイル高さLの範囲に浸漬ノズル14の下端が位置するようにしており、この浸漬ノズル14の吐出口15は、鋳型12内の溶鋼11の湯面20と平行な水平線に対して、1〜30゜の下向きの吐出角度θを有している。
なお、長片12aの外側の電磁コイル16a、16bについても電磁コイル17a、17bと同じ条件にしている。
更に、電磁コイル17a、電磁コイル17bは、その水平方向長さを前記鋳型12の長片12bの横幅よりも長くし、その上端が鋳型12内の溶鋼12の湯面20よりも20〜60mm下方にくるように配置している。
【0009】
次に、本発明の一実施の形態に係る連続鋳造装置10を用いた溶鋼の連続鋳造方法について説明する。
転炉等の精錬炉を用いて脱炭精錬と減圧二次精錬を行ってから、300トンの溶鋼11を溶製し、タンディッシュ13に注湯を行った。そして、タンディッシュ13内に設けた図示しないストッパーにより、浸漬ノズル14に供給する溶鋼11の量を調整しながら、鋳型12に注湯を行った。
この時の浸漬ノズル14は、浸漬深さを溶鋼11の湯面20から下方240mmにし、吐出口15の吐出角度θを1〜30゜にした。
更に、鋳型12内の溶鋼11の湯面20から下方50mmの位置に上端がくるように、長片12aの外側に電磁コイル16a、16b、長片12bの外側に電磁コイル17a、17bをそれぞれ配置し、各電磁コイル16a、16b、17a、17bに300〜800アンペアの電流を流し、周波数を1.0〜10.0Hzになるように通電し、鋳型12の長片12a、12bの内壁に沿った溶鋼11の旋回流(図2の矢印)を付与した。
この鋳型12の長片12a及び長片12bの外側に設ける電磁コイル16a、16b、及び電磁コイル17a、17bのコイル高さLの中心から下方に500mmの範囲に相当する凝固シェル18に、浸漬ノズル14の吐出口15からの溶鋼11の吐出流が当たるようにしている。
この溶鋼11の吐出流が凝固シェル18に当たる位置が電磁コイル16a、16b、17a、17bのコイル高さLの中心より高くなると、鋳型12内の湯面20が吐出流の影響を受けて波動的に変動し、パウダーの潤滑の不均一やパウダー巻き込み等が生じる。一方、吐出流の当たる凝固シェル18の部位が電磁コイル16a、16b、17a、17bの中心から下方に500mmを超えた位置になると、吐出流の当たる部位が深くなり過ぎて、電磁攪拌による旋回流の下方に位置する凝固シェル18の界面に捕捉される気泡や介在物を洗浄、除去することができない。
上記の条件を満足するには、浸漬ノズル14の吐出口15の吐出角度θを1〜30゜にすることが必要である。
この吐出角度θが1゜より小さくなると、溶鋼11の吐出流の影響を受けて、鋳型12内の湯面20が変動し、浮遊するパウダーを巻き込んだり、ノロカミ等を生じて鋳片19の表面欠陥の要因となる。
また、浸漬ノズル14の吐出角度θが30°より大きいと、溶鋼11の吐出流に随伴する気泡や介在物の浸入量が増加し、浸入する深さも深くなるので、溶鋼11の浸漬ノズル14からの吐出流等の流れにより容易に浮上させて除去することができない。
この理由から、浸漬ノズル14の吐出口15の吐出角度θは、5〜20゜にすると、気泡や介在物を洗浄して効率よく除去できるのでより好ましい結果が得られる。
【0010】
また、電磁コイル16a、16b、17a、17bに通電する電流値を変化させることにより、旋回流を付与する推力を調整することができ、その推力が5〜70mm鉄柱になるように、前記の電流値を設定する。
この攪拌する推力が5mm鉄柱より小さくなると、電磁攪拌による旋回流が弱くなり、凝固シェル18の界面に捕捉される気泡や介在物を洗浄、除去できない。一方、推力が70mm鉄柱を超えると、旋回流が強くなり過ぎて、浮上途中にある気泡や介在物を旋回流に巻き込んで、その浮上を阻害し、溶鋼11中に残存する気泡等が凝固シェル18の界面に捕捉される。更に、鋳型12の短片12c、12d側に衝突した旋回流による淀みや偏流等が発生し、この部分の凝固シェル18の界面にも気泡や介在物が捕捉され、ヘゲ疵やフクレ疵等の欠陥を招く。
【0011】
そして、電磁コイル16a、16b、17a、17bに電流を流すことにより、溶鋼11の上層及び湯面20に5〜70mm鉄柱の推力を与えて、鋳型12の内壁に沿った例えば右回りの旋回流(図2中の矢印)によって攪拌が行われる。
この旋回流は、鋳型12の冷却により最初に凝固した凝固シェル18の界面に捕捉されようとしている気泡や介在物を洗浄して除去する。
その結果、旋回流の影響を受ける凝固シェル18の部分は、気泡や介在物の無い良好な状態となり、気泡や介在物に起因する欠陥を防止できる。
また、電磁コイル16a、16b、17a、17bの旋回流の影響を受けないところに位置する凝固シェル18においては、図3に示すように、吐出口15から鋳型12内に供給される溶鋼11の吐出流Aが、電磁コイル16a、16b、17a、17bの中心から下方向に500mmの範囲に相当する凝固シェル18部位に当たることにより、吐出流Aに随伴して侵入する気泡や介在物の侵入深さを浅くし、しかも、凝固が進行している凝固シェル18の界面を吐出流Aと分岐した下向きの吐出流Bにより洗浄することができ、侵入した気泡や介在物の凝固シェル18の界面への捕捉が防止される。
その結果、溶鋼11が鋳型12によって冷却されて形成される凝固シェル18(鋳片19表層部)は、気泡や介在物の無い健全な層となり、この健全な層を形成した鋳片19が連続して鋳造できる。
【0012】
【実施例】
次に、溶鋼の連続鋳造方法の実施例について説明する。
転炉を用いて脱炭精錬し、減圧二次精錬を行って炭素濃度が0.01重量%の薄板用の溶鋼を300トン溶製し、タンディッシュに注湯しながら、浸漬ノズルに供給するアルゴンガス量を4L/分にして、幅が1300mm、高さ900mm、の鋳型12に注湯を行った。
この時の浸漬ノズルの浸漬深さは、溶鋼の湯面から下方240mmにし、鋳型の対向する長片の外側に、それぞれコイル高さが300mmの電磁コイルを二個ずつ溶鋼の湯面から下方50mmの位置に上端がくるように配置した。
そして、鋳型の各長片の外側の二個の推力が交互に強弱となるようにして、攪拌を行い、1.3m/分の鋳造速度で鋳片の引き抜きを行い、鋳片を圧延加工した際のフクレ疵やヘゲ疵の発生、良製品の歩留り等を調査した。
その結果、表1に示すように、実施例1では、電磁コイルの最大推力を5mm鉄柱とし、電磁コイルの中心から下方10mmの位置の凝固シェルに溶鋼の吐出流が当たるように、浸漬ノズルの吐出口の吐出角度θを1゜にした場合であり、表面疵の発生を指数は、比較例の1に対して0.8と大幅に低減でき、良製品の歩留り指数についても比較例の0.8に対して1.0と良好であった。
また、実施例2では、電磁コイルの最大推力を35mm鉄柱とし、電磁コイルの中心から下方450mmの位置の凝固シェルに溶鋼の吐出流が当たるように、浸漬ノズルの吐出口の吐出角度θを30゜にした場合であり、表面疵の発生指数を比較例の1に対して0.7と大幅に低減でき、良製品の歩留り指数も1.0と良好であった。
【0013】
【表1】
【0014】
これに対し、電磁コイルの最大推力を5mm鉄柱とし、電磁コイルの中心から下方600mmの位置の凝固シェルに溶鋼の吐出流が当たるように、浸漬ノズルの吐出口の吐出角度θを40゜にした比較例では、表面疵の発生が多くなり、良製品の歩留り指数も0.8に低下した悪い結果となった。
【0015】
以上、本発明の実施の形態を説明したが、本発明は、上記した形態に限定されるものでなく、要旨を逸脱しない条件の変更等は全て本発明の適用範囲である。
例えば、鋳型の上部の溶鋼に内壁に沿った旋回流を付与できるものであれば鋳型の各長片に、溶鋼を攪拌する電磁コイルを一個、あるいは三個以上設けても良い。
また、浸漬ノズルに供給するアルゴンガスについては、浸漬ノズルの外側に導通したスリットを介して内側の多孔体から浸漬ノズルの溶鋼内に全量供給しても良く、浸漬ノズルとその上方のタンディッシュのノズル等から溶鋼へ供給しても良い。
【0016】
【発明の効果】
請求項1記載の溶鋼の連続鋳造方法は、鋳型内の溶鋼を電磁攪拌して、鋳型の内壁に沿った旋回流を付与し、鋳型に設けた電磁コイルの中心から下方450mmの範囲に相当する凝固シェルに、溶鋼を注湯する浸漬ノズルの吐出流が当たるようにするので、鋳片の表層に気泡や介在物が捕捉されるのを抑制し、圧延等の加工を行った際に発生するヘゲ疵やフクレ疵等を防止して良製品の歩留りを向上できる。
【0017】
特に、溶鋼を電磁攪拌する推力を5〜35mm鉄柱にするので、鋳片の表層部となる凝固シェルの界面に捕捉される気泡や介在物をさらに効率良く洗浄して除去することができる。
【0018】
また、浸漬ノズルの吐出角度を1〜30°下向きにするので、鋳型内の湯面の変動やパウダー巻き込み及び気泡や介在物の浸入量や深さ等を抑制し、浸漬ノズルからの吐出流により凝固シェルの界面に捕捉される気泡や介在物の洗浄をより適正に行うことができ、鋳片の表面疵の生成を抑制して、鋳片の手入れの減少や圧延等の加工の際に発生するヘゲ疵やフクレ疵等を防止できる。
【図面の簡単な説明】
【図1】本発明の一実施の形態に係る溶鋼の連続鋳造方法に適用される連続鋳造装置の側断面図である。
【図2】同連続鋳造装置の鋳型部の平断面図である。
【図3】図1の矢視A−A断面図である。
【符号の説明】
10 連続鋳造装置 11 溶鋼
12 鋳型 12a 長片
12b 長片 12c 短片
12d 短片 13 タンディッシュ
14 浸漬ノズル 15 吐出口
16a 電磁コイル 16b 電磁コイル
17a 電磁コイル 17b 電磁コイル
18 凝固シェル 19 鋳片
20 湯面 θ 吐出角度
[0001]
BACKGROUND OF THE INVENTION
In the present invention, when casting molten steel in a mold by electromagnetically stirring a slab or the like, the molten steel prevents defects such as baldness and swelling caused by bubbles and inclusions trapped in the surface layer of the slab. The present invention relates to a continuous casting method.
[0002]
[Prior art]
Conventionally, when continuously casting molten steel, in order to prevent clogging of nozzles and immersion nozzles, argon gas is supplied to suppress adhesion and growth of alumina-based oxides.
The argon gas supplied to this nozzle or immersion nozzle is easily trapped at the interface of the solidified shell as bubbles when the molten steel solidifies. Increases and decreases yield.
Further, in the molten steel, there are oxides generated when a deoxidizer is added, and trace amounts of oxides due to refractory erosion or the like. This oxide may agglomerate during casting, and is captured at the solidified shell interface that becomes the surface layer part of the solidified slab, and in the process of rolling or the like as described above, hege wrinkles, cracks, etc. Surface defects occur, resulting in an increase in care and a decrease in product yield.
Therefore, in order to prevent defects caused by bubbles and inclusions generated in the surface layer portion of the slab, Japanese Patent Application Laid-Open No. 58-100555 uses a plurality of electromagnetic coils attached to the outer wall of the mold to accelerate. The surface layer is free from bubbles and inclusions by washing the interface of the surface layer (solidified shell) by applying a horizontal swirl flow along the peripheral wall of the mold to the molten steel with electromagnetic stirring Continuous casting to form is disclosed.
JP-A-8-174164 discloses that a product V · W of a horizontal swirling flow velocity V (cm / sec) and a mold width W (cm) of a molten steel is 10 3 to 10 using an electromagnetic stirrer. Continuously cleans and removes bubbles and inclusions trapped at the interface of the solidified shell by controlling the horizontal swirling flow by adjusting the current applied to the electromagnetic coil so that it becomes 4 (cm 2 / sec) A casting method has been proposed.
[0003]
[Problems to be solved by the invention]
However, in Japanese Patent Laid-Open No. 58-100555, the flow of molten steel along the peripheral wall of the mold is first accelerated, and the accelerated flow is decelerated in the vicinity of the short piece of the mold. Bubbles and inclusions are accumulated at the interface of the solidified shell of the slab corresponding to the boundary portion, and defects such as baldness and blisters occur during processing such as rolling.
Furthermore, bubbles and inclusions are trapped at the interface of the lower solidified shell where the swirling flow of the molten steel provided by the electromagnetic coil provided in the mold does not act. These bubbles and inclusions have problems such as becoming a surface defect of the slab, and causing defects such as baldness and swelling at the time of processing such as rolling.
In JP-A-8-174164, inclusions made of bubbles and oxides of argon gas mixed in the discharge flow of molten steel from the immersion nozzle are not affected by the swirling flow of molten steel provided by the electromagnetic coil. Captured while rising to the interface of the solidified shell. When rolling or the like is performed on a slab in which bubbles or inclusions are present at the interface of the solidified shell, which is the surface layer portion of the slab, defects such as baldness and swelling occur, and the above-mentioned JP-A 58- There is a problem similar to the continuous casting disclosed in Japanese Patent No. 100555.
[0004]
The present invention has been made in view of such circumstances, and when casting molten steel in a mold by electromagnetic stirring to cast a slab or the like, hesitation marks caused by bubbles or inclusions trapped in the surface layer portion of the slab An object of the present invention is to provide a continuous casting method of molten steel that prevents defects such as bulge and the like, and is excellent in yield of good products.
[0005]
[Means for Solving the Problems]
The continuous casting method of the molten steel of the present invention that meets the object is a continuous casting method of molten steel in which an electromagnetic coil is provided outside the long piece of the mold, and a swirl flow is provided along the inner wall of the mold,
The electromagnetic coil only performs electromagnetic stirring of the molten steel in the mold, and the upper end of the electromagnetic coil is positioned 20 to 60 mm below the molten steel surface in the mold, and the discharge angle of the immersion nozzle is set to a horizontal line. 1 to 30 ° downward, the maximum thrust for electromagnetic stirring of the molten steel is 5 to 35 mm iron pillar, argon gas is supplied to the immersion nozzle, and corresponds to a range of 450 mm below the center of the electromagnetic coil The discharge flow of the immersion nozzle for pouring the molten steel is applied to the solidified shell. By this method, bubbles and inclusions trapped at the interface of the solidified shell, which is the surface layer portion of the lower slab where the swirl flow of the molten steel applied by the electromagnetic coil does not act, can be removed by washing the interface. It is possible to prevent defects such as baldness and blisters when processing such as surface flaws and rolling.
When the area where the discharge flow of the immersion nozzle hits the solidified shell is above the center of the electromagnetic coil, the molten metal surface in the mold fluctuates due to the influence of the discharge flow, resulting in uneven powder lubrication and powder entrainment. . On the other hand, when the range in which the discharge flow of the immersion nozzle hits the solidified shell exceeds 500 mm below the center of the electromagnetic coil, the portion where the discharge flow hits becomes too deep, and bubbles or intervening trapped at the lower interface of the swirling flow by electromagnetic stirring Things cannot be washed and removed.
[0006]
Here, it has a thrust electromagnetically stirring the molten steel. 5 to 35 mm steel pole.
Thereby, while facilitating the rise of bubbles and inclusions, fine bubbles and inclusions can be washed by the swirling flow of the molten steel, and the interface of the solidified shell of the slab can be cleaned.
If the thrust for stirring the molten steel is smaller than the 5 mm iron pillar, the swirling flow of the molten steel becomes weak, and bubbles and inclusions trapped at the interface of the solidified shell cannot be washed and removed.
Moreover, when the thrust which stirs molten steel exceeds a 35- mm iron pillar, the swirling flow of molten steel will become strong too much and will inhibit the bubble and inclusion which mixed in molten steel floating.
[0007]
Furthermore, the discharge angle of the immersion nozzle is set downward by 1 to 30 °.
As a result, bubbles and inclusions trapped at the interface of the solidified shell by the discharge flow from the immersion nozzle while suppressing fluctuations in the molten metal surface in the mold, powder entrainment, and the amount and depth of penetration of bubbles and inclusions Can be performed more appropriately.
Here, the discharge angle of the nozzle is an angle downward with respect to a line parallel to the molten metal surface formed in the mold, and if the discharge angle of this immersion nozzle is smaller than 1 °, the molten metal surface in the mold It causes fluctuations, powder entrainment, blade damage, etc., and causes surface defects on the slab.
Moreover, if the discharge angle of the immersion nozzle is larger than 30 °, the amount of bubbles and inclusions accompanying the discharge flow of the molten steel increases and the penetration becomes deep and cannot be removed by the discharge flow of the molten steel.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
FIG. 1 is a side sectional view of a continuous casting apparatus applied to a molten steel continuous casting method according to an embodiment of the present invention, FIG. 2 is a plan sectional view of a mold part of the continuous casting apparatus, and FIG. It is arrow AA sectional drawing.
As shown in FIGS. 1 and 2, a continuous casting apparatus 10 used for a molten steel continuous casting method according to an embodiment of the present invention includes a tundish 13 lined with a refractory for storing molten steel 11, and a tundish. 13, an immersion nozzle 14 for pouring the molten steel 11 into the mold 12 through the discharge port 15, and electromagnetic coils 16 a, 16 b on the outside of the long piece 12 a of the mold 12 for stirring the molten steel 11 in the mold 12, Electromagnetic coils 17a and 17b are provided outside the long piece 12b.
The electromagnetic coil 16a of the long piece 12a of the mold 12 is made to have a strong thrust, a weak thrust is applied to the electromagnetic coil 16b, a weak thrust is given to the electromagnetic coil 17a of the long piece 12b, and a strong thrust is given to the electromagnetic coil 17b. Stir in combination.
Further, the slab 19 in which the solidified shell 18 is formed by cooling the mold 12 is pulled out at a predetermined speed while being continuously cooled by a slab support device and a pinch roll (not shown).
Further, as shown in FIG. 3, the lower end of the immersion nozzle 14 is positioned in the range of the coil height L of the electromagnetic coils 17a and 17b provided outside the long piece 12b of the mold 12, and the immersion nozzle 14 The discharge port 15 has a downward discharge angle θ of 1 to 30 ° with respect to a horizontal line parallel to the molten metal surface 20 of the molten steel 11 in the mold 12.
Note that the electromagnetic coils 16a and 16b outside the long piece 12a have the same conditions as the electromagnetic coils 17a and 17b.
Furthermore, the electromagnetic coil 17a and the electromagnetic coil 17b have a horizontal length longer than the lateral width of the long piece 12b of the mold 12, and the upper end is 20 to 60 mm below the molten metal surface 20 of the molten steel 12 in the mold 12. It is arranged to come to.
[0009]
Next, the continuous casting method of the molten steel using the continuous casting apparatus 10 which concerns on one embodiment of this invention is demonstrated.
After performing decarburization refining and reduced pressure secondary refining using a refining furnace such as a converter, 300 tons of molten steel 11 was melted and poured into the tundish 13. The mold 12 was poured while adjusting the amount of the molten steel 11 supplied to the immersion nozzle 14 with a stopper (not shown) provided in the tundish 13.
At this time, the immersion nozzle 14 had an immersion depth of 240 mm below the molten metal surface 20 of the molten steel 11, and the discharge angle θ of the discharge port 15 was 1 to 30 °.
Furthermore, the electromagnetic coils 16a and 16b are arranged outside the long piece 12a and the electromagnetic coils 17a and 17b are arranged outside the long piece 12b so that the upper end comes to a position 50 mm below the molten metal surface 20 of the molten steel 11 in the mold 12. Then, a current of 300 to 800 amperes is passed through each of the electromagnetic coils 16a, 16b, 17a and 17b, and the frequency is set to 1.0 to 10.0 Hz, along the inner walls of the long pieces 12a and 12b of the mold 12. A swirling flow (arrow in FIG. 2) of the molten steel 11 was applied.
A submerged nozzle 18 is provided on the solidified shell 18 corresponding to a range of 500 mm downward from the center of the coil height L of the electromagnetic coils 16a and 16b and the electromagnetic coils 17a and 17b provided outside the long pieces 12a and 12b of the mold 12. The discharge flow of the molten steel 11 from the 14 discharge ports 15 is made to hit.
When the position where the discharge flow of the molten steel 11 hits the solidified shell 18 becomes higher than the center of the coil height L of the electromagnetic coils 16a, 16b, 17a, 17b, the molten metal surface 20 in the mold 12 is affected by the discharge flow and is waved. To cause uneven powder lubrication and powder entrainment. On the other hand, when the part of the solidified shell 18 on which the discharge flow hits is located at a position exceeding 500 mm downward from the center of the electromagnetic coils 16a, 16b, 17a, 17b, the part on which the discharge flow hits becomes too deep, and the swirl flow by electromagnetic stirring The bubbles and inclusions trapped at the interface of the solidified shell 18 located below the surface cannot be washed and removed.
In order to satisfy the above conditions, it is necessary to set the discharge angle θ of the discharge port 15 of the immersion nozzle 14 to 1 to 30 °.
When the discharge angle θ is smaller than 1 °, the surface of the slab 19 is affected by the influence of the discharge flow of the molten steel 11 and the molten metal surface 20 in the mold 12 fluctuates and entrains floating powder or generates swarf or the like. Causes defects.
In addition, if the discharge angle θ of the immersion nozzle 14 is larger than 30 °, the amount of bubbles and inclusions accompanying the discharge flow of the molten steel 11 increases, and the depth of penetration increases. It cannot be easily lifted and removed by a flow such as a discharge flow.
For this reason, when the discharge angle θ of the discharge port 15 of the immersion nozzle 14 is 5 to 20 °, more preferable results can be obtained because bubbles and inclusions can be efficiently removed by washing.
[0010]
In addition, by changing the current value to be applied to the electromagnetic coils 16a, 16b, 17a, 17b, the thrust that gives the swirling flow can be adjusted, and the current is adjusted so that the thrust becomes a 5-70 mm iron pillar. Set the value.
If the stirring thrust is smaller than that of the 5 mm iron pillar, the swirl flow due to electromagnetic stirring becomes weak, and bubbles and inclusions trapped at the interface of the solidified shell 18 cannot be washed and removed. On the other hand, if the thrust exceeds the 70 mm iron pillar, the swirling flow becomes too strong, and bubbles or inclusions in the middle of the levitation are entrained in the swirling flow and the levitation is inhibited, and the bubbles remaining in the molten steel 11 are solidified shell. Captured at 18 interfaces. Further, stagnation or drift due to the swirling flow that collides with the short pieces 12c and 12d of the mold 12 occurs, and bubbles and inclusions are trapped at the interface of the solidified shell 18 in this portion, and thus, such as baldness and bulges. Invite defects.
[0011]
Then, by passing an electric current through the electromagnetic coils 16a, 16b, 17a, 17b, a thrust of a 5-70 mm iron pillar is applied to the upper layer of the molten steel 11 and the molten metal surface 20, for example, a clockwise swirl flow along the inner wall of the mold 12 Stirring is performed according to (arrow in FIG. 2).
This swirling flow cleans and removes bubbles and inclusions that are about to be trapped at the interface of the solidified shell 18 that is first solidified by cooling the mold 12.
As a result, the portion of the solidified shell 18 that is affected by the swirling flow is in a good state free of bubbles and inclusions, and defects caused by the bubbles and inclusions can be prevented.
Further, in the solidified shell 18 located where the electromagnetic coils 16a, 16b, 17a, 17b are not affected by the swirling flow, as shown in FIG. 3, the molten steel 11 supplied into the mold 12 from the discharge port 15 is provided. When the discharge flow A hits the solidified shell 18 corresponding to a range of 500 mm downward from the center of the electromagnetic coils 16a, 16b, 17a, 17b, the intrusion depth of bubbles and inclusions that enter along with the discharge flow A In addition, the interface of the solidified shell 18 where the solidification is progressing can be cleaned by the downward discharge flow B branched off from the discharge flow A, and the invading bubbles and inclusions enter the interface of the solidification shell 18. Capture is prevented.
As a result, the solidified shell 18 (cast slab 19 surface layer portion) formed by cooling the molten steel 11 by the mold 12 becomes a healthy layer free of bubbles and inclusions, and the slab 19 forming this healthy layer is continuous. And can be cast.
[0012]
【Example】
Next, an example of a continuous casting method for molten steel will be described.
Decarburization refining using a converter, secondary refining under reduced pressure to melt 300 tons of molten steel for thin plates with a carbon concentration of 0.01% by weight, and supply to the immersion nozzle while pouring into a tundish The molten metal was poured into the mold 12 having a width of 1300 mm and a height of 900 mm at an argon gas amount of 4 L / min.
The immersion depth of the immersion nozzle at this time is 240 mm below the molten steel surface, and two electromagnetic coils each having a coil height of 300 mm are provided 50 mm below the molten steel surface on the outside of the opposing long pieces of the mold. It was arranged so that the upper end was at the position of.
Then, stirring was performed so that the two thrusts on the outside of each long piece of the mold alternately became strong, and the slab was drawn at a casting speed of 1.3 m / min, and the slab was rolled. The occurrence of bulges and lashes at the time, the yield of good products, etc. were investigated.
As a result, as shown in Table 1, in Example 1, the maximum thrust of the electromagnetic coil was a 5 mm iron pillar, and the submerged nozzle of the immersion nozzle was applied so that the discharge flow of the molten steel hit the solidified shell 10 mm below the center of the electromagnetic coil. This is the case where the discharge angle θ of the discharge port is 1 °, and the index of the occurrence of surface flaws can be greatly reduced to 0.8 compared to 1 of the comparative example, and the yield index of good products is also 0 of the comparative example .8 was 1.0 and good.
In Example 2, the maximum thrust of the electromagnetic coil is a 35 mm iron pillar, and the discharge angle θ of the discharge port of the immersion nozzle is set to 30 so that the discharge flow of the molten steel hits the solidified shell 450 mm below the center of the electromagnetic coil. The surface flaw generation index was significantly reduced to 0.7 compared to 1 in the comparative example, and the yield index of good products was as good as 1.0.
[0013]
[Table 1]
[0014]
On the other hand, the maximum thrust of the electromagnetic coil is a 5 mm iron pillar, and the discharge angle θ of the discharge port of the immersion nozzle is set to 40 ° so that the discharge flow of the molten steel hits the solidified shell 600 mm below the center of the electromagnetic coil. In the comparative example, the generation of surface flaws increased, and the yield index of good products decreased to 0.8.
[0015]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and all changes in conditions and the like that do not depart from the gist are within the scope of the present invention.
For example, as long as a swirl flow along the inner wall can be imparted to the molten steel at the top of the mold, one or three or more electromagnetic coils for stirring the molten steel may be provided on each long piece of the mold.
In addition, the argon gas supplied to the immersion nozzle may be supplied in its entirety from the inner porous body into the molten steel of the immersion nozzle through a slit connected to the outside of the immersion nozzle. You may supply to molten steel from a nozzle.
[0016]
【The invention's effect】
The continuous casting method for molten steel according to claim 1 corresponds to a range of 450 mm below the center of the electromagnetic coil provided in the mold by electromagnetically stirring the molten steel in the mold to give a swirl flow along the inner wall of the mold. Occurs when processing such as rolling is performed by suppressing the trapping of air bubbles and inclusions on the surface layer of the slab, so that the discharge flow of the immersion nozzle that pours molten steel hits the solidified shell The yield of good products can be improved by preventing scabs and swellings.
[0017]
In particular, since the thrust for electromagnetically stirring the molten steel is 5 to 35 mm iron pillar, bubbles and inclusions trapped at the interface of the solidified shell that becomes the surface layer portion of the slab can be more efficiently washed and removed.
[0018]
In addition, since the discharge angle of the immersion nozzle is 1-30 ° downward , the fluctuation of the molten metal surface in the mold, the entrainment of powder, the intrusion amount and depth of bubbles and inclusions, etc. are suppressed, and the discharge flow from the immersion nozzle Air bubbles and inclusions trapped at the interface of the solidified shell can be cleaned more appropriately, and the generation of surface flaws on the slab is suppressed, resulting in reduced slab care and rolling. Can prevent scabs and blisters.
[Brief description of the drawings]
FIG. 1 is a side sectional view of a continuous casting apparatus applied to a method for continuously casting molten steel according to an embodiment of the present invention.
FIG. 2 is a plan sectional view of a mold part of the continuous casting apparatus.
3 is a cross-sectional view taken along line AA in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Continuous casting apparatus 11 Molten steel 12 Mold 12a Long piece 12b Long piece 12c Short piece 12d Short piece 13 Tundish 14 Immersion nozzle 15 Discharge port 16a Electromagnetic coil 16b Electromagnetic coil 17a Electromagnetic coil 17b Electromagnetic coil 18 Solidified shell 19 Cast piece 20 Hot water surface θ discharge angle

Claims (1)

鋳型の長片の外側に電磁コイルを設け、前記鋳型の内壁に沿った旋回流を付与する溶鋼の連続鋳造方法であって、
前記電磁コイルは前記鋳型内の溶鋼を電磁攪拌することのみを行い、しかも、該電磁コイルの上端を該鋳型内の溶鋼の湯面の20〜60mm下方に位置させ、浸漬ノズルの吐出角度を水平線に対して1〜30°下向きにし、前記溶鋼を電磁攪拌する最大推力を5〜35mm鉄柱とし、前記浸漬ノズルにはアルゴンガスを供給して、前記電磁コイルの中心から下方450mmの範囲に相当する凝固シェルに、前記溶鋼を注湯する浸漬ノズルの吐出流が当たるようにすることを特徴とする溶鋼の連続鋳造方法。
A continuous casting method of molten steel in which an electromagnetic coil is provided outside a long piece of a mold, and a swirl flow is provided along the inner wall of the mold,
The electromagnetic coil only performs electromagnetic stirring of the molten steel in the mold, and the upper end of the electromagnetic coil is positioned 20 to 60 mm below the molten steel surface in the mold, and the discharge angle of the immersion nozzle is set to a horizontal line. 1 to 30 ° downward, the maximum thrust for electromagnetic stirring of the molten steel is 5 to 35 mm iron pillar, argon gas is supplied to the immersion nozzle, and corresponds to a range of 450 mm below the center of the electromagnetic coil A continuous casting method for molten steel, characterized in that a discharge flow of an immersion nozzle for pouring the molten steel is applied to the solidified shell.
JP00375399A 1999-01-11 1999-01-11 Continuous casting method for molten steel Expired - Lifetime JP4203167B2 (en)

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JP4714624B2 (en) * 2006-03-31 2011-06-29 新日本製鐵株式会社 Method of electromagnetic stirring of molten steel in mold
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