JP3362703B2 - Continuous casting method - Google Patents

Continuous casting method

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Publication number
JP3362703B2
JP3362703B2 JP19103399A JP19103399A JP3362703B2 JP 3362703 B2 JP3362703 B2 JP 3362703B2 JP 19103399 A JP19103399 A JP 19103399A JP 19103399 A JP19103399 A JP 19103399A JP 3362703 B2 JP3362703 B2 JP 3362703B2
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Japan
Prior art keywords
casting
slab
unsteady
amount
reduction
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JP2001018042A (en
Inventor
好徳 谷澤
晃三 太田
勇雄 野崎
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住友金属工業株式会社
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Description

【発明の詳細な説明】 【0001】 【発明の属する技術分野】本発明は、中心偏析やV偏析
の少ない鋳片を得ることができる鋼の連続鋳造方法に関
し、さらに詳しくは、鋳造末期の非定常鋳造時に鋳造さ
れる鋳片においても、中心偏析やV偏析が軽微な鋳片の
連続鋳造方法に関する。 【0002】 【従来の技術】連続鋳造法によって得られる鋼の鋳片の
厚み中心部近傍には、中心偏析やV偏析と呼ばれる内部
欠陥が発生する場合がある。中心偏析は鋳片の最終凝固
部にC、S、P、Mnなどの偏析成分が濃化して現れる
もので、V偏析は鋳片の最終凝固部近傍に、これらの偏
析成分がV字状に濃化するものである。鋳片のこれら偏
析は、製品である厚板の靱性の低下や、厚板から曲げ加
工後溶接して製造される大径鋼管の水素誘起割れの原因
となることが知られている。 【0003】これらの偏析の生成機構は、次のように考
えられている。凝固が進むにつれて、凝固組織であるデ
ンドライト樹間に偏析成分が濃化する。この偏析成分の
濃化した溶鋼が、凝固時の鋳片の収縮またはバルジング
と呼ばれる鋳片のふくれなどにより、デンドライト樹間
より流出する。流出した偏析成分の濃化した溶鋼は、最
終凝固部の凝固完了点に向かって流動し、そのまま凝固
して偏析成分の濃化帯が形成される。これらの濃化帯が
中心偏析やV偏析である。 【0004】これらの偏析の防止対策として、デンドラ
イト樹間に残った偏析成分の濃化した溶鋼の移動を防止
することと、偏析成分の濃化した溶鋼の局所的な集積を
防ぐことが効果的であり、次のような方法が提案されて
いる。その1つに、圧下ロール群による鋳片の軽圧下法
があるが、凝固収縮量を若干上回る程度の軽圧下では、
これら偏析の改善効果には限界がある。 【0005】効果的に鋳片のこれら偏析を改善するため
に、圧下ロール対で大きな圧下を鋳片に加える方法があ
るが、凝固が完了した鋳片の幅方向両端の短辺部も圧下
することになるので、大きな圧下力が必要である。大き
な圧下力をかけるため、圧下ロール対を支える支持枠に
撓みが発生し、充分な圧下効果が得られない場合があ
る。また、圧下ロール対が曲がったり、折損したり等の
設備上の事故により、操業が困難になる場合がある。 【0006】特開平7−210382号公報では、鋳片
の厚み中心部の固相率が0.1以下の位置で鋳片をバル
ジングさせ、幅方向中央部の鋳片の厚みを鋳型で生じる
短辺部の鋳片の厚みより20〜100mm厚くした後、
凝固完了点直前に少なくとも1つの圧下ロール対によ
り、1つの圧下ロール対当たりの圧下量を20mm以上
とする条件で、バルジング量相当分の厚みを圧下する方
法が提案されている。 【0007】しかし、この方法では、鋳造末期、すなわ
ち、鋳型への給湯を停止し、鋳片の最終鋳造端部を鋳型
から引き抜いた状態で、定常状態の鋳造速度を維持した
まま鋳片の圧下を続けると、鋳造方向の上流側に絞り出
された溶鋼が、鋳片の最終鋳造端部からあふれ出る、い
わゆる漏鋼が起きる場合がある。このような漏鋼は、作
業者にとって危険なばかりか、ガイドロールをはじめと
する鋳造設備を損傷する原因となる。そこで、漏鋼を避
けるために、鋳造末期に鋳片の圧下を行わない場合に
は、中心偏析が著しく発生しやすくなるので、これら鋳
造末期の鋳片を素材とする製品の用途を低級品に変更し
たり、極端な場合には、これらの鋳片が使用できなくな
るなどの問題がある。 【0008】 【発明が解決しようとする課題】本発明は、厚板や大径
鋼管製造用の素材を鋳造する連続鋳造に関し、鋳造末期
において漏鋼を起こすことなく、鋳片の末端部までも、
厚み中心部に中心偏析やV偏析の少ない内部品質の良好
な鋳片を得ることができる鋼の連続鋳造方法を提供する
ことを目的とする。 【0009】 【課題を解決するための手段】本発明の要旨は、未凝固
部を含む鋳片をバルジングさせた後、凝固完了までの間
でバルジングした鋳片を圧下する連続鋳造方法であっ
て、鋳造末期の非定常鋳造時の圧下量を、下記(A)式
で求まる非定常圧下量Dxa以下とする鋼の連続鋳造方
法。 【0010】 Dxa=D−(2Bav−Bxav) ・・・(A) ここで、D :定常鋳造時の圧下量(mm) Bav :定常鋳造時の平均バルジング量(mm) Bxav:鋳造末期の非定常鋳造時の平均バルジング量
(mm) 本発明の方法でいう鋳造末期の非定常鋳造時とは、タン
ディッシュから鋳型への溶鋼の注入の終了以降の時期を
いう。 【0011】定常鋳造時の鋳片の圧下量を変更して、上
記(A)式を満足する鋳造末期の非定常鋳造時の非定常
圧下量Dxa以下を開始する時期は、タンディッシュか
ら鋳型への溶鋼の注入が終了してから、鋳片の末端部が
鋳型の出口を抜けるまでの任意の時期とし、鋳片の末端
部の圧下が完了する時期まで、この非定常圧下量Dxa
以下で圧下する。 【0012】また、平均バルジング量(BavまたはB
xav)とは、後述する図2および図3に示すように、
鋳片のバルジングゾーンの長さに、鋳片をバルジングさ
せるために広げるガイドロール対のロール間隔の拡大量
の平均値をかけた値を、メニスカスからバルジングさせ
る最終のガイドロール対までの距離で除した値を意味す
る。 【0013】本発明の方法では、鋳造末期の非定常鋳造
時の圧下量を、前述する(A)式で求まる非定常圧下量
Dxa以下とする。以下に、その内容を説明する。 【0014】Bav=Bxavのときは、(A)式は、
Dxa=D−Bavとなる。このとき、鋳造末期の非定
常鋳造時に圧下量のみを変更することを意味する。すな
わち、定常鋳造時の圧下量Dより、定常鋳造時の平均バ
ルジング量Bavだけ少なくした圧下量Dxa以下で圧
下し、圧下後の鋳片の厚みを定常鋳造時の圧下後の厚み
より厚くすることを意味する。定常鋳造時の平均バルジ
ング量Bavに、鋳片の幅、バルジングゾーンの長さを
掛けたものは、漏鋼すると予想される溶鋼量に相当す
る。鋳片の幅、バルジングゾーンは一定であるので、変
更できる圧下量を、定常鋳造時の圧下量Dから非定常鋳
造時の圧下量Dxa以下に減少させることにより、漏鋼
の発生を防止することができる。 【0015】Bav<Bxavのときは、ガイドロール
対のロール間隔をさらに広げたり、バルジングゾーンの
長さを長くすることにより、鋳造末期の非定常鋳造時の
平均バルジング量Bxavを、定常鋳造時の平均バルジ
ング量Bavよりもさらに大きくすることを意味する。
鋳造末期の非定常鋳造時の平均バルジング量Bxav
を、定常鋳造時の平均バルジング量Bavよりも大きく
することによって、漏鋼を発生させることなく、Bxa
v=Bavのときよりも、大きな圧下量で圧下すること
ができる。 【0016】Bav>Bxavのときは、鋳造末期の非
定常鋳造時の平均バルジング量Bxavを、定常鋳造時
の平均バルジング量Bavよりも小さくすることを意味
する。このとき、Bxav=Bavのときよりも、小さ
な圧下量で圧下する。 【0017】上述するように上記(A)式を満足する非
定常圧下量Dxa以下で圧下することにより、漏鋼の発
生を防止できるとともに、定常鋳造時の圧下量Dの確保
はできないが、定常鋳造時の圧下量Dに近い非定常圧下
量Dxa以下で鋳片を圧下できるので、鋳片の中心偏析
やV偏析の発生を防止できる。 【0018】 【発明の実施の形態】図1は、本発明の方法を実施する
ための連続鋳造機の装置構成の例を示す図である。浸漬
ノズル7を経て鋳型1に注入された溶鋼6は、鋳型内で
凝固して凝固殻2aとなる。鋳型から引き抜かれ、その
下方のスプレーノズル群(図示していない)から噴射さ
れる水により冷却された凝固殻の厚みは、次第に増して
いく。厚みの増した凝固殻、すなわち、鋳片2は、ガイ
ドロール対3および圧下ロール対4を経てピンチロール
5により引き抜かれる。バルジングゾーン内で、ガイド
ロール対の鋳片の厚みに相当するロール間隔を段階的に
増加させることにより、鋳片にバルジングを起こさせ
る。その後、圧下ゾーン内で圧下ロール対により、鋳片
の未凝固部2bを含む位置を圧下する。定常鋳造時の鋳
片の圧下量を変更して、鋳造末期の非定常鋳造時の非定
常圧下量Dxa以下での圧下を開始する時期は、タンデ
ィッシュから鋳型への溶鋼の注入が終了してから、鋳片
の末端部が鋳型の出口を抜けるまでの任意の時期とす
る。それ以降、鋳片の末端部の圧下が完了する時期ま
で、この非定常圧下量Dxa以下で圧下する。 【0019】本発明の方法の具体的な実施方法につい
て、以下に説明する。 (イ)鋳造末期の非定常鋳造時に、圧下量のみを変更す
る方法 図2は、鋳造末期の非定常鋳造時に圧下量のみを変更す
る場合の本発明の方法の概念を説明するための図であ
る。図2(a)は、定常鋳造時の鋳片のバルジングと圧
下の状況を示す図で、鋳片の縦断面を示す。図2(b)
は、鋳造末期の非定常鋳造時に圧下量のみを変更した場
合の鋳片の縦断面を示す。図2(b)中の破線は、図2
(a)に示す定常鋳造時の鋳片の状況を表している。 【0020】鋳造末期の非定常鋳造時で、タンディッシ
ュから鋳型への溶鋼の注入が終了した状態で、定常鋳造
時の圧下量Dのままで圧下を続けるとき、漏鋼すると予
想される溶鋼量は、バルジングゾーンの長さL1の範囲
で、ガイドロール対の鋳片厚み相当のロール間隔の拡大
量(バルジングさせるガイドロール対のロール間隔と圧
下ロール対のロール間隔との差)を積分し、鋳片の幅を
掛けることによって求めることができる。近似的には、
複数のガイドロール対のロール間隔の拡大量の平均値を
T1として、T1とL1と鋳片の幅との積により、漏鋼
すると予想される溶鋼量は求まる。バルジングゾーンの
長さL1と鋳片の幅を一定とすれば、漏鋼すると予想さ
れる溶鋼量は、T1に比例する。この漏鋼すると予想さ
れる溶鋼量に相当する量を、圧下量を減少し、圧下後の
鋳片厚みを厚くすることによって相殺すれば、漏鋼を防
止できる。すなわち、近似的に求まる定常鋳造時の平均
バルジング量Bavだけ圧下量を減少し、前述する
(A)式においてBxav=Bavとしたときの、下記
(B)式を満足する鋳造末期の非定常鋳造時の非定常圧
下量Dxa以下で圧下すれば、漏鋼を防止できる。 【0021】Dxa=D−Bav ・・・(B) ここで、D:定常鋳造時の圧下量(mm) Bav=(T1×L1)/L T1:定常鋳造時のカ゛イト゛ロール対のロール間隔の拡大量の
平均値(mm) L1:定常鋳造時のバルジングゾーンの長さ(mm) L :メニスカスから最終のハ゛ルシ゛ンク゛させるカ゛イト゛ロール対まで
の距離(mm) T1 =Tα + Tβ D =Dα + Dβ Dxa=Dxα+ Dxβ Tα、Tβ:定常鋳造時の片側のガイドロール間隔の拡
大量の平均値 Dα、Dβ:定常鋳造時の片側の圧下量 Dxα、Dxβ:鋳造末期の片側の圧下量 (ロ)鋳造末期の非定常鋳造時に、圧下量、バルジング
ゾーンの長さ、平均バルジング量を変更する方法 Bav<Bxavとするとき、すなわち、鋳造末期の非
定常鋳造時の平均バルジング量Bxavを、定常鋳造時
の平均バルジング量Bavよりもさらに大きくするとき
について、以下に具体的に説明する。 【0022】図3は、鋳造末期の非定常鋳造時に圧下
量、バルジングゾーンの長さおよび平均バルジング量を
変更する場合の概念を説明するための図である。図3
(a)は、定常鋳造時の鋳片のバルジングと圧下の状況
を示す図で、鋳片の縦断面を示す。図3(b)は、鋳造
末期の非定常鋳造時に圧下量、バルジングゾーンの長さ
および平均バルジング量を変更した場合の鋳片の縦断面
を示す。図3(b)中の破線は、図3(a)に示す定常
鋳造時の鋳片の状況を表している。 【0023】鋳造末期の非定常鋳造時にバルジングゾー
ンの長さを長くしたり、ガイドロール対のロール間隔の
拡大量をさらに広げることにより、鋳造末期の非定常鋳
造時の平均バルジング量Bxavを、定常鋳造時の平均
バルジング量Bavより大きくするとき、漏鋼すると予
想される溶鋼量に相当する量を相殺できる鋳造末期の非
定常鋳造時の非定常圧下量Dxaは、前述する(B)式
で表される圧下量だけを変更する場合の鋳造末期の非定
常鋳造時の非定常圧下量Dxaよりも、下記(C)式に
示すようにBxavとBavの差の分だけ大きくでき
る。 【0024】すなわち、Dxa=(D−Bav)+(B
xav−Bav)となり、したがって、下記式となる。 【0025】 Dxa=D−(2Bav−Bxav) ・・・(C) ここで、D:定常鋳造時の圧下量(mm) 定常鋳造時の平均バルジング量Bav=(T1×L1)
/L 鋳造末期の非定常鋳造時の平均ハ゛ルシ゛ンク゛量Bxav=
(T2×L2)/L T1:定常鋳造時のカ゛イト゛ロール対のロール間隔の拡大量の
平均値(mm) T2:鋳造末期の非定常鋳造時のカ゛イト゛ロール対のロール間隔
の拡大量の平均値(mm) L1:定常鋳造時のバルジングゾーンの長さ(mm) L2:鋳造末期のバルジングゾーンの長さ(mm) L:メニスカスから最終のハ゛ルシ゛ンク゛させるカ゛イト゛ロール対までの
距離(mm) T1 =Tα+Tβ T2 =Txα+Txβ D =Dα+Dβ Dxa=Dxα+Dxβ Tα、Tβ:定常鋳造時の片側のガイドロール間隔の拡
大量の平均値 Txα、Txβ:鋳造末期の非定常鋳造時の片側のガイ
ドロール間隔の拡大量の平均値 Dα、Dβ:定常鋳造時の片側の圧下量 Dxα、Dxβ:鋳造末期の片側の圧下量 本発明の方法では、鋳造末期の非定常鋳造時の非定常圧
下量を、前述する(A)式で表される非定常圧下量Dx
a以下とする。鋳片の末端部のように、溶鋼静鉄圧が小
さいところでは、設定通りのバルジング量、すなわち、
設定した鋳片厚みにならなかったり、凝固殻の倒れ込み
などで漏鋼量が多くなったりすることが予想されること
から、非定常圧下量はDxa以下とする。圧下量が零で
は、中心偏析低減効果が得られない。 【0026】定常鋳造時の鋳片の圧下量を変更して、前
述する(A)式を満足する鋳造末期の非定常鋳造時の非
定常圧下量Dxa以下での圧下を開始する時期は、タン
ディッシュから鋳型への溶鋼の注入が終了してから、鋳
片の末端部が鋳型の出口を抜けるまでの任意の時期とす
る。鋳型への溶鋼の注入終了前とすると、鋳片内の湯面
位置はいったんは下がるが、その後もしばらく給湯があ
るので漏鋼防止の効果が得られない。一方、鋳片の末端
部が鋳型の出口を抜けた後では、鋳片内の湯面位置が十
分に低下していないので、漏鋼が発生する。 【0027】鋳造末期の非定常鋳造時の鋳造速度は、定
常鋳造時の時の速度と同じでもよいが、圧下量を減少さ
せ、鋳片の厚みが厚くなる分だけ凝固完了位置が鋳造方
向の下流側になるため、圧下による中心偏析改善効果が
効果的に発揮できるように、鋳造速度を低下させ、凝固
完了位置を圧下位置に近づけるのがよい。 【0028】 【実施例】図1に示す装置構成のスラブ連続鋳造装置を
用いて、鋳片をバルジングさせた後に圧下する試験を実
施し、とくに、鋳造末期の非定常鋳造時の漏鋼の発生状
況と鋳片の中心偏析の発生状況を調査した。鋳片の幅は
2000mmとし、厚みは、バルジング開始時の厚みを
235mmとした。C含有率が0.15〜0.20重量
%の厚板用鋼を鋳造した。定常鋳造時の鋳造速度は1.
0m/分、鋳片の二次冷却比水量は1〜2リットル/k
g−鋼とし、タンディッシュ内の溶鋼過熱度は20℃と
した。メニスカスからバルジングさせる最終のガイドロ
ール対までの距離Lは19500mmで一定である。 【0029】各鋳造試験の鋳片の末端部の位置の鋳片サ
ンプルを採取し、最終鋳造端部から鋳造方向に5mの位
置で、鋳造方向に長さ200mmの横断面サンプルを採
取した。横断面サンプルの厚みおよび幅方向の中心部か
ら縦50mm、横300mmの断面形状の試験片を採取
し、この試験片の表面を200μmメッシュの粗さに分
け、それぞれのメッシュの中でのPの平均含有率をマッ
ピングアナライザ(MA)法で調査した。平均のP含有
率の中で、最大のP含有率を求め、レードル分析値のP
含有率P0 との比P/P0 で、中心偏析を評価した。な
お、定常鋳造時のPの最大偏析度は、3.0〜4.0で
あった。各試験条件と試験結果を表1および表2に示
す。 【0030】 【表1】【0031】 【表2】【0032】本発明例の試験No.1、No.2および
比較例の試験No.3、No.4では、定常鋳造時と鋳
造末期の非定常鋳造時のそれぞれのバルジングゾーンの
長さを3000mm一定とし、変更せずに試験した。ま
た、試験No.1と試験No.3では、定常鋳造時と鋳
造末期の非定常鋳造時でのそれぞれの平均バルジング量
も3.1mmで一定とした。 【0033】本発明の方法で規定する鋳造末期の非定常
鋳造時の圧下量16.9mm以下の16mmの厚みを圧
下した試験No.1では、漏鋼は発生しなかったが、2
0mmの厚みを圧下した試験No.3では漏鋼が発生し
た。いずれも、Pの最大偏析P/P0 は定常鋳造時の値
程度であった。 【0034】鋳造末期の非定常鋳造時の平均バルジング
量を6.2mmと大きくし、本発明の方法で規定する鋳
造末期の非定常鋳造時の圧下量の範囲内の20mmの厚
みを圧下した試験No.2では、漏鋼は発生せず、Pの
最大偏析P/P0 は定常鋳造時の値程度であった。鋳造
末期の非定常鋳造時の平均バルジング量を5.4mmと
大きくしたが、本発明の方法で規定する鋳造末期の非定
常鋳造時の圧下量の上限外の20mmの厚みを圧下した
試験No.4では、漏鋼が発生した。 【0035】本発明例の試験No.5、No.6および
比較例の試験No.7、No.8では、鋳造末期の非定
常鋳造時のバルジングゾーンの長さを6000mmとし
て、定常鋳造時の5000mmより長くした。また、鋳
造末期の非定常鋳造時の平均バルジング量を定常鋳造時
の平均バルジング量より大きくした。さらに、鋳造末期
の非定常鋳造時の鋳造速度を0.9m/分として、定常
鋳造速度よりも遅くして鋳造した。 【0036】本発明の方法で規定する鋳造末期の非定常
鋳造時の圧下量17.9mm以下の17mmの厚みを圧
下した試験No.5では、漏鋼は発生せず、また、Pの
最大偏析P/P0 は、試験No.1より良好な結果であ
った。鋳造末期の非定常鋳造時に鋳造速度を遅くした効
果である。本発明の方法で規定する鋳造末期の非定常鋳
造時の圧下量の上限外の20mmの厚みを圧下した試験
No.7では、漏鋼が発生した。 【0037】鋳造末期の非定常鋳造時の平均バルジング
量を6.2mmと大きくし、本発明の方法で規定する鋳
造末期の非定常鋳造時の圧下量の範囲内の20mmの厚
みを圧下した試験No.6では、漏鋼は発生せず、Pの
最大偏析P/P0 は、試験No.2よりも良好な結果で
あった。鋳造速度低下の効果である。鋳造末期の非定常
鋳造時の平均バルジング量を4.6mmと大きくした
が、本発明の方法で規定する鋳造末期の非定常鋳造時の
圧下量の上限外の20mmの厚みを圧下した試験No.
8では、漏鋼が発生した。 【0038】 【発明の効果】本発明の方法の適用により、厚板や大径
鋼管製造用の素材を鋳造する連続鋳造において、鋳造末
期において漏鋼を起こすことなく、鋳片の末端部まで
も、厚み中心部に中心偏析やV偏析の少ない内部品質の
良好な鋳片を得ることができる。
Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method of steel capable of obtaining a slab with less center segregation and V segregation. The present invention also relates to a continuous casting method for a cast piece in which center segregation and V segregation are slight even in a cast piece cast during steady casting. [0002] Internal defects called center segregation and V segregation may occur near the center of the thickness of a steel slab obtained by a continuous casting method. Central segregation is a phenomenon in which segregated components such as C, S, P, and Mn appear in the final solidified portion of the slab, and V segregation appears in the vicinity of the final solidified portion of the slab. It thickens. It is known that such segregation of cast slabs causes a decrease in toughness of a thick plate as a product and hydrogen-induced cracking of a large-diameter steel pipe manufactured by bending and welding a thick plate. [0003] The mechanism of generation of these segregations is considered as follows. As the solidification progresses, segregated components are concentrated between dendrite trees, which are solidified structures. The molten steel in which the segregated components are concentrated flows out from between the dendrite trees due to shrinkage of the slab during solidification or swelling of the slab called bulging. The flowed-out molten steel in which the segregation component is concentrated flows toward the solidification completion point of the final solidification part, and solidifies as it is to form a concentrated zone of the segregation component. These concentrated zones are center segregation and V segregation. [0004] As countermeasures to prevent these segregations, it is effective to prevent the movement of the molten steel in which the segregated components remain between the dendrite trees and to prevent the local accumulation of the molten steel in which the segregated components are concentrated. The following method has been proposed. As one of them, there is a light reduction method of a slab by a reduction roll group, but under a light reduction slightly exceeding the solidification shrinkage amount,
The effect of improving these segregations is limited. In order to effectively improve the segregation of the slab, there is a method in which a large reduction is applied to the slab using a pair of reduction rolls. However, the short sides at both ends in the width direction of the solidified slab are also reduced. Therefore, a large rolling force is required. Since a large rolling force is applied, the supporting frame supporting the rolling roll pair may be bent, and a sufficient rolling effect may not be obtained. In addition, the operation may be difficult due to equipment accidents such as bending or breakage of the reduction roll pair. In Japanese Patent Application Laid-Open No. 7-210382, the slab is bulged at a position where the solid phase ratio at the center of the slab thickness is 0.1 or less, and the thickness of the slab at the center in the width direction is reduced by a mold. After making the thickness of the side slab 20 ~ 100mm thick,
A method has been proposed in which, just before the solidification completion point, the thickness corresponding to the bulging amount is reduced by using at least one reduction roll pair and reducing the reduction amount per one reduction roll pair to 20 mm or more. However, in this method, at the end of casting, that is, when the supply of hot water to the mold is stopped and the final casting end of the slab is pulled out of the mold, the reduction of the slab is maintained while maintaining the casting speed in a steady state. If so, the molten steel squeezed out to the upstream side in the casting direction overflows from the final casting end of the slab, so-called so-called steel leakage may occur. Such steel leakage is not only dangerous for workers, but also causes damage to casting equipment including guide rolls. Therefore, if the slab is not rolled down at the end of casting to avoid steel leakage, center segregation is likely to occur significantly. There are problems such as the change or extreme use of these slabs. [0008] The present invention relates to continuous casting for casting a material for manufacturing a thick plate or a large diameter steel pipe, and does not cause steel leakage at the final stage of casting, even to the end of the slab. ,
It is an object of the present invention to provide a continuous casting method of steel capable of obtaining a cast slab having a good internal quality with little center segregation or V segregation at the center of the thickness. The gist of the present invention is to provide a continuous casting method in which a slab including an unsolidified portion is bulged, and the bulged slab is rolled down until solidification is completed. A continuous casting method for steel in which the rolling reduction during unsteady casting at the end of casting is not more than the unsteady rolling reduction Dxa determined by the following equation (A). Dxa = D− (2Bav−Bxav) (A) where D: rolling reduction during steady casting (mm) Bav: average bulging amount during steady casting (mm) Bxav: non-finished casting volume Average bulging amount during steady casting (mm) The term “unsteady casting at the end of casting” referred to in the method of the present invention refers to a time after the end of pouring molten steel from a tundish into a mold. The time when the rolling reduction of the slab at the time of steady casting is changed and the unsteady rolling reduction Dxa at the time of unsteady casting at the end of casting that satisfies the above equation (A) is started is from the tundish to the mold. This unsteady rolling amount Dxa is set at any time from the end of the injection of molten steel until the end of the slab passes through the exit of the mold until the end of the slab is completely reduced.
Reduce below. Further, the average bulging amount (Bav or B
xav) is, as shown in FIGS. 2 and 3 described below,
The value obtained by multiplying the length of the slab bulging zone by the average value of the amount of expansion of the roll interval between the guide roll pairs to be bulged to the slab is divided by the distance from the meniscus to the final guide roll pair to be bulged. Means the value of In the method of the present invention, the rolling reduction at the time of unsteady casting at the end of casting is set to be not more than the unsteady rolling reduction Dxa obtained by the above-mentioned equation (A). The contents will be described below. When Bav = Bxav, the equation (A) becomes:
Dxa = D-Bav. At this time, it means that only the reduction amount is changed at the time of unsteady casting at the end of casting. That is, the reduction is performed at a reduction amount Dxa or less which is smaller than the reduction amount D at the time of steady casting by the average bulging amount Bav at the time of steady casting, and the thickness of the slab after the reduction is made larger than the thickness after reduction at the time of the steady casting. Means The product of the average bulging amount Bav at the time of steady casting multiplied by the width of the slab and the length of the bulging zone corresponds to the amount of molten steel expected to leak steel. Since the width of the slab and the bulging zone are constant, the reduction amount that can be changed is reduced from the reduction amount D at the time of steady casting to the reduction amount Dxa at the time of unsteady casting to prevent occurrence of steel leakage. Can be. When Bav <Bxav, the average bulging amount Bxav during unsteady casting at the end of casting can be reduced by further increasing the roll spacing of the guide roll pair or increasing the length of the bulging zone. This means that the average bulging amount Bav is further increased.
Average bulging amount Bxav during unsteady casting at the end of casting
Is larger than the average bulging amount Bav at the time of steady casting, so that Bxa
The rolling can be reduced with a larger rolling reduction than when v = Bav. When Bav> Bxav, it means that the average bulging amount Bxav during unsteady casting at the end of casting is smaller than the average bulging amount Bav during steady casting. At this time, the pressure is reduced by a smaller reduction amount than when Bxav = Bav. As described above, when the rolling is reduced with the unsteady rolling amount Dxa or less satisfying the above equation (A), it is possible to prevent the occurrence of steel leakage and to secure the rolling amount D at the time of steady casting. Since the slab can be rolled down with the unsteady rolling reduction Dxa which is close to the rolling reduction D at the time of casting, the center segregation and V segregation of the slab can be prevented. FIG. 1 is a diagram showing an example of an apparatus configuration of a continuous casting machine for carrying out the method of the present invention. The molten steel 6 injected into the mold 1 through the immersion nozzle 7 is solidified in the mold to form a solidified shell 2a. The thickness of the solidified shell that is pulled out of the mold and cooled by water sprayed from a group of spray nozzles (not shown) below the mold gradually increases. The thickened solidified shell, that is, the slab 2, is pulled out by the pinch roll 5 via the guide roll pair 3 and the pressing roll pair 4. In the bulging zone, the slab is caused to bulge by gradually increasing the roll interval corresponding to the thickness of the slab of the guide roll pair. Thereafter, the position including the unsolidified portion 2b of the slab is reduced by the pair of reduction rolls in the reduction zone. At the time of changing the rolling reduction of the slab at the time of steady casting and starting rolling at the unsteady rolling reduction Dxa or less at the time of unsteady casting at the end of casting, the injection of molten steel from the tundish into the mold is completed. From when the end of the slab passes through the exit of the mold. Thereafter, the rolling is reduced with the unsteady rolling reduction Dxa or less until the rolling of the end portion of the slab is completed. A specific method of carrying out the method of the present invention will be described below. (A) Method of changing only the rolling reduction during unsteady casting at the end of casting FIG. 2 is a diagram for explaining the concept of the method of the present invention in the case of changing only the rolling reduction during unsteady casting at the end of casting. is there. FIG. 2A is a diagram showing a state of slab bulging and reduction during steady casting, and shows a longitudinal section of the slab. FIG. 2 (b)
Shows a longitudinal section of the slab when only the rolling reduction is changed during the unsteady casting at the end of casting. The dashed line in FIG.
The situation of the slab at the time of steady casting shown in FIG. In the unsteady casting at the end of casting, when the molten steel is poured from the tundish into the mold and the reduction is continued with the reduction D during the steady casting, the amount of molten steel expected to leak Integrates the expansion amount of the roll interval (the difference between the roll interval of the guide roll pair to be bulged and the roll interval of the roll-down roll pair) within the range of the length L1 of the bulging zone, It can be determined by multiplying the width of the slab. Approximately,
Assuming that the average value of the expansion amount of the roll interval between the plurality of guide roll pairs is T1, the amount of molten steel expected to leak steel is obtained from the product of T1, L1, and the width of the slab. Assuming that the length L1 of the bulging zone and the width of the slab are constant, the amount of molten steel expected to leak steel is proportional to T1. If the amount corresponding to the amount of molten steel expected to leak steel is offset by reducing the rolling reduction and increasing the thickness of the slab after rolling, steel leakage can be prevented. That is, the reduction amount is reduced by the average bulging amount Bav at the time of steady casting, which is approximately determined, and the unsteady casting at the end of casting that satisfies the following formula (B) when Bxav = Bav in the above formula (A). If the rolling is performed with the unsteady rolling reduction Dxa at the time or less, steel leakage can be prevented. Dxa = D−Bav (B) where D: reduction amount (mm) during steady casting Bav = (T1 × L1) / L T1: roll interval of the pair of rolls during steady casting Average value of expansion amount (mm) L1: Length of bulging zone in steady casting (mm) L: Distance from meniscus to final pair of rolls to be welded (mm) T1 = Tα + Tβ D = Dα + Dβ Dxa = Dxα + Dxβ Tα, Tβ: Average value Dα, Dβ: One-side rolling reduction during steady casting Dxα, Dxβ: One-side rolling reduction at the end of casting (B) End of casting Method of changing rolling reduction, length of bulging zone, and average bulging amount at the time of unsteady casting when Bav <Bxav, that is, average bulge during unsteady casting at the end of casting The grayed amount Bxav, for when more larger than the average bulging amount Bav of steady state casting, specifically described below. FIG. 3 is a diagram for explaining the concept of changing the rolling reduction, the length of the bulging zone, and the average bulging during the unsteady casting at the end of casting. FIG.
(A) is a figure which shows the state of the bulging and rolling of the slab at the time of steady casting, and shows the longitudinal section of a slab. FIG. 3B shows a longitudinal section of a slab when the rolling reduction, the length of the bulging zone, and the average bulging amount are changed during unsteady casting at the end of casting. The dashed line in FIG. 3B indicates the condition of the slab at the time of steady casting shown in FIG. By increasing the length of the bulging zone during unsteady casting at the end of casting, or by further increasing the amount of roll spacing between the guide roll pairs, the average bulging amount Bxav during unsteady casting at the end of casting can be reduced to a steady state. When the average bulging amount Bav at casting is larger than the average bulging amount Bav, the unsteady rolling reduction Dxa at the time of unsteady casting at the end of casting, which can offset the amount corresponding to the molten steel amount expected to leak steel, is expressed by the above-mentioned equation (B). As shown in the following equation (C), the difference between Bxav and Bav can be made larger than the unsteady reduction amount Dxa in the unsteady casting at the end of casting when only the reduction amount to be changed is changed. That is, Dxa = (D-Bav) + (B
xav-Bav), and therefore: Dxa = D− (2Bav−Bxav) (C) where D: reduction amount during steady casting (mm) Average bulging amount Bav during steady casting Bav = (T1 × L1)
/ L Average bulk amount Bxav at the time of unsteady casting at the end of casting
(T2 × L2) / L T1: Average value of expansion of roll interval between pair of rolls during steady casting (mm) T2: Average value of expansion of roll interval between pair of rolls during unsteady casting at the end of casting (Mm) L1: Length of bulging zone at the time of steady casting (mm) L2: Length of bulging zone at the end of casting (mm) L: Distance (men) from meniscus to final pair of rolls to be welded (mm) T1 = Tα + Tβ T2 = Txα + Txβ D = Dα + Dβ Dxa = Dxα + Dxβ Tα, Tβ: Average value of expansion of one-side guide roll interval during steady casting Txα, Txβ: Average of expansion of one-side guide roll interval during unsteady casting at the end of casting Values Dα, Dβ: One-sided reduction amount during steady casting Dxα, Dxβ: One-sided reduction amount at end of casting Unsteady reduction ratio Dx of the unsteady rolling reduction at the time of casting is represented by the above for formula (A)
a. As in the end of the slab, where the molten steel static iron pressure is small, the bulging amount as set, that is,
The unsteady rolling reduction is set to Dxa or less because it is expected that the set slab thickness will not be attained or the amount of steel leakage will increase due to falling of the solidified shell. If the rolling reduction is zero, the effect of reducing center segregation cannot be obtained. The time when the rolling reduction of the slab at the time of steady casting is changed and the rolling reduction at or below the unsteady rolling reduction Dxa at the time of the unsteady casting at the end of casting, which satisfies the above-mentioned equation (A), is started by the tank. It is an arbitrary time from the end of the injection of the molten steel from the dish to the mold to the end of the slab passing through the exit of the mold. Before the completion of the injection of molten steel into the mold, the level of the molten metal in the slab temporarily drops, but there is no hot water supply for a while thereafter, so that the effect of preventing steel leakage cannot be obtained. On the other hand, after the end of the slab has passed through the exit of the mold, the molten steel surface position in the slab has not been sufficiently reduced, so that steel leakage occurs. The casting speed at the time of unsteady casting at the end of casting may be the same as that at the time of steady casting, but the reduction amount is reduced, and the solidification completion position in the casting direction is reduced by the thickness of the slab. Since it is on the downstream side, it is preferable to lower the casting speed and bring the solidification completion position closer to the reduction position so that the center segregation improvement effect by the reduction can be effectively exerted. EXAMPLE A slab continuous casting apparatus having the apparatus configuration shown in FIG. 1 was used to perform a test in which slabs were bulged and then reduced in pressure. Particularly, the occurrence of steel leakage during unsteady casting at the end of casting was performed. The situation and the occurrence of center segregation in the slab were investigated. The width of the slab was 2000 mm, and the thickness at the start of bulging was 235 mm. Steel for thick plates having a C content of 0.15 to 0.20% by weight was cast. The casting speed during steady casting is 1.
0 m / min, secondary cooling specific water volume of slab is 1-2 liter / k
g-steel, and the degree of superheat of molten steel in the tundish was 20 ° C. The distance L from the meniscus to the final pair of guide rolls to be bulged is constant at 19500 mm. A slab sample was taken at the end of the slab in each casting test, and a 200 mm long cross section sample was taken in the casting direction at a position 5 m from the final casting end in the casting direction. A test piece having a cross-sectional shape of 50 mm in length and 300 mm in width was collected from the center of the cross-sectional sample in the thickness and width directions, and the surface of the test piece was divided into a roughness of 200 μm mesh. The average content was investigated by the mapping analyzer (MA) method. Among the average P contents, the maximum P content is determined, and the P value of the ladle analysis value is obtained.
The ratio P / P 0 of the content P 0, were evaluated center segregation. In addition, the maximum segregation degree of P at the time of steady casting was 3.0 to 4.0. Tables 1 and 2 show the test conditions and test results. [Table 1] [Table 2] Test No. of the present invention example 1, No. Test No. 2 and Comparative Example No. 3, No. In No. 4, the length of each of the bulging zones at the time of steady casting and at the time of unsteady casting at the end of casting was fixed at 3000 mm, and the test was performed without change. Test No. 1 and test no. In No. 3, the average bulging amount at the time of steady casting and at the time of unsteady casting at the end of casting was also constant at 3.1 mm. In the test No. 1 in which a thickness of 16 mm was reduced to a rolling reduction of 16.9 mm or less during unsteady casting at the end of casting specified by the method of the present invention. In the case of 1, no steel leakage occurred, but in the case of 2
Test No. 0 was reduced to a thickness of 0 mm. In No. 3, steel leakage occurred. In each case, the maximum segregation P / P 0 of P was about the value at the time of steady casting. A test in which the average bulging amount at the time of unsteady casting at the end of casting was increased to 6.2 mm, and the thickness was reduced by 20 mm within the range of the amount of reduction at the time of unsteady casting at the end of casting specified by the method of the present invention. No. In No. 2, no steel leakage occurred, and the maximum segregation P / P 0 of P was about the value at the time of steady casting. Although the average bulging amount at the time of the unsteady casting at the end of casting was increased to 5.4 mm, the test No. 2 in which the thickness was reduced by 20 mm outside the upper limit of the amount of reduction at the time of the unsteady casting at the end of casting specified by the method of the present invention. In No. 4, steel leakage occurred. Test No. of the present invention example 5, no. Test No. 6 and Comparative Example No. 7, no. In No. 8, the length of the bulging zone during unsteady casting at the end of casting was 6000 mm, which was longer than 5000 mm during steady casting. Further, the average bulging amount at the time of unsteady casting at the end of casting was made larger than the average bulging amount at the time of steady casting. Further, the casting speed at the time of unsteady casting at the end of casting was set to 0.9 m / min, and the casting was performed at a speed lower than the steady casting speed. In the test No. 1 in which a 17 mm-thickness reduction of 17.9 mm or less at the time of unsteady casting at the end of casting specified by the method of the present invention was reduced. In Test No. 5, no steel leakage occurred, and the maximum segregation of P, P / P 0, was determined in Test No. 5. The result was better than 1. This is the effect of reducing the casting speed during the unsteady casting at the end of casting. Test No. 2 in which the thickness was reduced by 20 mm outside the upper limit of the reduction amount during the unsteady casting at the end of casting specified by the method of the present invention. In No. 7, steel leakage occurred. A test in which the average bulging amount at the time of unsteady casting at the end of casting was increased to 6.2 mm and the thickness was reduced by 20 mm within the range of the amount of reduction at the time of unsteady casting at the end of casting specified by the method of the present invention. No. In No. 6, no steel leakage occurred, and the maximum segregation P / P 0 of P was determined in Test No. The result was better than 2. This is the effect of lowering the casting speed. Although the average bulging amount at the time of unsteady casting at the end of casting was increased to 4.6 mm, the test No. 2 in which the thickness was reduced by 20 mm outside the upper limit of the amount of reduction at the time of unsteady casting at the end of casting specified by the method of the present invention.
In No. 8, steel leakage occurred. According to the method of the present invention, in the continuous casting for casting a material for producing a thick plate or a large diameter steel pipe, even in the final stage of the casting, there is no leakage of the steel and even the end of the slab. In addition, it is possible to obtain a slab of good internal quality with little center segregation or V segregation at the center of the thickness.
【図面の簡単な説明】 【図1】本発明の方法を実施するための連続鋳造機の装
置構成の例を示す図である。 【図2】鋳造末期の非定常鋳造時に圧下量のみを変更す
る場合の概念を説明するための図である。 【図3】鋳造末期にの非定常鋳造時に圧下量、バルジン
グゾーンの長さおよびバルジング量を変更する場合の概
念を説明するための図である。 【符号の説明】 1:鋳型 2:鋳片 2a:凝固殻 2b:未凝固部 3:ガイドロール対 4:圧下ロール対 5:ピンチロール 6:溶鋼 7:浸漬ノズル L:メニスカスから最終のバルジングさせるガイドロー
ル対までの距離 L1:定常鋳造時のバルジングゾーンの長さ L2:鋳造末期の非定常鋳造時のバルジングゾーンの長
さ Tα、Tβ:定常鋳造時の片側のガイドロール間隔の拡
大量の平均値 Dα、Dβ:定常鋳造時の片側の圧下量 Txα、Txβ:鋳造末期の非定常鋳造時の片側のガイ
ドロール間隔の拡大量の平均値 Dxα、Dxβ:鋳造末期の片側の圧下量
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of an apparatus configuration of a continuous casting machine for performing a method of the present invention. FIG. 2 is a diagram for explaining a concept in a case where only a reduction amount is changed during unsteady casting at the end of casting. FIG. 3 is a diagram for explaining a concept of changing a rolling reduction, a length of a bulging zone, and a bulging amount during unsteady casting at the end of casting. [Description of Signs] 1: Mold 2: Cast slab 2a: Solidified shell 2b: Unsolidified portion 3: Guide roll pair 4: Rolling roll pair 5: Pinch roll 6: Molten steel 7: Immersion nozzle L: Final bulging from meniscus Distance to guide roll pair L1: Length of bulging zone during steady casting L2: Length of bulging zone Tα, Tβ during unsteady casting at the end of casting: Average of expansion amount of guide roll interval on one side during steady casting Values Dα, Dβ: One-side reduction amount Txα during steady casting, Txβ: Average value of expansion amount of one-side guide roll interval during unsteady casting at the end of casting Dxα, Dxβ: One-side reduction amount at end of casting
フロントページの続き (56)参考文献 特開 平11−156508(JP,A) 特開 平11−156509(JP,A) 特開 平10−244347(JP,A) 特開 平9−314289(JP,A) 特開 平9−122845(JP,A) 特開2000−288686(JP,A) 特開2000−5853(JP,A) (58)調査した分野(Int.Cl.7,DB名) B22D 11/128 350 B22D 11/10 B22D 11/20 Continuation of the front page (56) References JP-A-11-156508 (JP, A) JP-A-11-156509 (JP, A) JP-A-10-244347 (JP, A) JP-A-9-314289 (JP, A) , A) JP-A-9-122845 (JP, A) JP-A-2000-288686 (JP, A) JP-A-2000-5585 (JP, A) (58) Fields investigated (Int. Cl. 7 , DB name) B22D 11/128 350 B22D 11/10 B22D 11/20

Claims (1)

  1. (57)【特許請求の範囲】 【請求項1】未凝固部を含む鋳片をバルジングさせた
    後、凝固完了までの間でバルジングした鋳片を圧下する
    連続鋳造方法であって、鋳造末期の非定常鋳造時の圧下
    量を、下記(A)式で求まる非定常圧下量Dxa以下と
    することを特徴とする鋼の連続鋳造方法。 Dxa=D−(2Bav−Bxav) ・・・(A) ここで、D :定常鋳造時の圧下量(mm) Bav :定常鋳造時の平均バルジング量(mm) Bxav:鋳造末期の非定常鋳造時の平均バルジング量
    (mm)
    (1) Claims 1. A continuous casting method in which a slab including an unsolidified portion is bulged, and the bulged slab is rolled down until solidification is completed. A continuous casting method for steel, characterized in that the rolling reduction during unsteady casting is not more than the unsteady rolling reduction Dxa determined by the following equation (A). Dxa = D− (2Bav−Bxav) (A) where D: reduction amount during steady casting (mm) Bav: average bulging amount during steady casting (mm) Bxav: unsteady casting at the end of casting Average bulging amount (mm)
JP19103399A 1999-07-05 1999-07-05 Continuous casting method Expired - Fee Related JP3362703B2 (en)

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JP4218383B2 (en) * 2002-04-08 2009-02-04 住友金属工業株式会社 Continuous casting method, continuous casting apparatus and continuous cast slab
JP5018441B2 (en) * 2007-12-07 2012-09-05 住友金属工業株式会社 Method of drawing slab after completion of casting in continuous casting
JP5477269B2 (en) * 2010-12-03 2014-04-23 新日鐵住金株式会社 Continuous casting method for slabs
CN107008874B (en) * 2017-03-29 2018-11-27 东北大学 A kind of continuous casting billet solidifying end pressing control method during unsteady statecalculation

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