JP4613448B2

JP4613448B2 - Vertical casting method and apparatus

Info

Publication number: JP4613448B2
Application number: JP2001167345A
Authority: JP
Inventors: 高橋　　元; 肇天野; 総一郎久村
Original assignee: Daido Steel Co Ltd
Current assignee: Daido Steel Co Ltd
Priority date: 2001-06-01
Filing date: 2001-06-01
Publication date: 2011-01-19
Anticipated expiration: 2021-06-01
Also published as: JP2002361376A

Description

【０００１】
【発明の属する技術分野】
この発明は、鋳型内で冷却されて表面部のみが凝固した状態(シェルが形成された状態)の鋳片を垂直に引抜くことで、所定長さの鋳片を鋳造する垂直型鋳造方法および装置に関するものである。
【０００２】
【従来の技術】
アルミ等の非鉄の分野においては、上下に開口する鋳型(モールド)に溶鋼を鋳込み、該鋳型の下方に昇降可能に配設した昇降台のダミーヘッドに、鋳型内で冷却されて表面にシェルが形成された鋳片の下端を支持した状態で、該昇降台を所定速度で垂直に下降することで鋳型下部から鋳片を垂直に引抜いて、所定長さ寸法の鋳片を鋳造する垂直型鋳造方法が知られている。
【０００３】
【発明が解決しようとする課題】
前記垂直型鋳造方法は、造塊方法と比較して省エネルギーおよび省力化等の面で有利であるため、高合金鋼および工具鋼を含む特殊鋼全般の鋼種で、殊に断面の大きな鋳片を鋳造するのに採用する試みがなされている。しかるに、前記の鋼種を垂直型鋳造方法で鋳造すると、センターポロシティ、鋳片頭部キャビティ、中心偏析あるいはＶ状偏析等の内部欠陥が多く発生し、製品品質が低下すると共に歩留りも低下する問題があった。すなわち、製品品質の厳格化が要求される状況下においては、従来の垂直型鋳造方法では充分に対応し得るものではなかった。
【０００４】
【発明の目的】
この発明は、前述した従来の技術に内在している前記課題に鑑み、これを好適に解決するべく提案されたものであって、高合金鋼および工具鋼を含む特殊鋼等の鋳片を鋳造し、静置凝固させるに際して、センターポロシティ、鋳片頭部キャビティ、中心偏析あるいはＶ状偏析等の内部欠陥が発生するのを抑制し、製品品質および歩留りを向上し得る垂直型鋳造方法および装置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】
前述した課題を解決し、所期の目的を好適に達成するため、本発明に係る垂直型鋳造方法は、上下に開口する鋳型に高合金鋼および工具鋼を含む特殊鋼の溶鋼を鋳込むと共に、表面にシェルが形成された所要断面形状の鋳片を鋳型の下部から垂直に引抜いて所定長さ寸法の鋳片を鋳造するに際し、その鋳込み完了後において、昇降台が上昇し、表面に外殻が形成された鋳片の上端部を、鋳型の上端から所定長さだけ押し上げた後、所定温度に予熱しておいた蓋部材が下降して前記鋳型の上部を覆うと共に内部画成された加熱室を不活性ガスの雰囲気とした状態で、鋳型内の溶鋼を、湯面の温度を固相線温度以上に保持し得る加熱条件でプラズマまたはアークにより加熱することで、鋳造される鋳片に内部欠陥が発生するのを抑制することを特徴とする。
【０００６】
また前述した課題を解決し、所期の目的を好適に達成するため、本願の垂直型鋳造装置は、上下に開口する鋳型に高合金鋼および工具鋼を含む特殊鋼の溶鋼を鋳込み、表面にシェルが形成された鋳片の下端を、前記鋳型の下方に配設されて、昇降手段により垂直に昇降される昇降台で支持して鋳型の下部から引抜くことで所定長さ寸法の鋳片を鋳造する垂直型鋳造装置であって、前記鋳型の上部を覆い得ると共に内部画成された加熱室を不活性ガス雰囲気とし得る蓋部材と、前記蓋部材を予熱する予熱手段と、前記蓋部材で覆われた鋳型内の溶鋼を、鋳込み完了後に昇降台を上昇させて、プラズマまたはアークにより加熱する加熱手段とから構成したことを特徴とする。
【０００７】
【発明の実施の形態】
次に、本発明に係る垂直型鋳造方法および装置につき、好適な実施例を挙げて、添付図面を参照しながら以下説明する。
【０００８】
図１は、実施例に係る垂直型鋳造方法が実施される垂直型鋳造装置を概略的に示すものであって、該鋳造装置１０は、上下に開口する鋳型１２が鋳床１４に配設されており、該鋳型１２には、その上方に設けられた取鍋１６およびタンディッシュ１８を介して高合金鋼および工具鋼を含む特殊鋼等の溶鋼が鋳込まれるよう構成される。このタンディッシュ１８は、鋳床１４に設けられたレール(図示せず)に沿って移動可能に構成された台車２０に配設され、前記鋳型１２の上方に臨む鋳造位置と、鋳型１２から離間する退避位置との間を移動するよう構成されている。また、タンディッシュ１８は台車２０に対して適宜の昇降機構を介して昇降可能に配設され、鋳造位置と退避位置との間を移動する際には、タンディッシュ１８に設けられた浸漬ノズル１８ａが鋳型１２と干渉しない位置まで上昇されるようになっている。なお、前記鋳型１２には、図示しないオシレーション装置によって上下動が付与され、鋳型１２の下部から引抜かれる鋳片２２と該鋳型１２との間の摩擦を軽減し、焼付きを防止するよう構成される。
【０００９】
前記台車２０には、前記鋳型１２の上部を覆い得る蓋部材２４が配設され、この蓋部材２４は、前記タンディッシュ１８が鋳造位置に臨むときには鋳型１２から離間する待機位置(図１)に臨み、タンディッシュ１８が退避位置に臨むときには鋳型１２の上部を覆う加熱位置(図４)に臨むよう構成される。また、蓋部材２４は台車２０に対して適宜の昇降機構を介して昇降可能に配設され、待機位置と加熱位置との間を移動する際に、鋳型１２または鋳型１２の上端から突出する鋳片２２の上端部(後述)と干渉しない位置まで上昇されるようになっている。
【００１０】
前記蓋部材２４は、図２に示す如く、下方に開放する箱型に形成されると共に、耐火物からなる内張り部材２６と、該内張り部材２６の外側を被覆する断熱材からなる外張り部材２８および該外張り部材２８の外側を被覆する鉄皮３０からなる三層構造となっており、内張り部材２６の内側に加熱室２４ａを画成するよう構成される。また蓋部材２４の天井部には複数(実施例では２つ)の通孔２４ｂが形成され、前記台車２０に配設されて鋳型１２内の溶鋼を加熱するための加熱装置(加熱手段)３２を構成する電極３４が、各通孔２４ｂを介して加熱室２４ａ内に進退可能に挿入されるようになっている。そして、後述する鋳込み完了後、静置凝固させる際の溶鋼加熱に際して蓋部材２４が加熱位置において鋳型１２の上部を覆った状態で、鋳型１２内の鋳片２２と電極３４との間に所定電圧を印加することで、電極３４から放電するプラズマまたはアークにより鋳型１２内の溶鋼を加熱するよう構成される。なお、溶鋼加熱等に際して該加熱室２４ａ内には、前記通孔２４ｂを介してＡｒやＮ₂等の不活性ガスが供給され、室内を不活性ガス雰囲気とし得るようになっている。
【００１１】
前記内張り部材２６は、Ａｌ₂Ｏ₃を主成分とする耐火物が好適に使用され、また前記外張り部材２８は、Ａｌ₂Ｏ₃にＳｉＯ₂を添加することで断熱性を高めた断熱材が好適に使用されるが、その他の材質であってもよい。なお、外張り部材２８として熱伝導率の低い断熱材を用いることで、溶鋼加熱時および後述する予熱時における蓋部材２４の抜熱を低減することができ、投入電力を少なく抑えることができる。
【００１２】
前記加熱装置３２の各電極３４は、電気モータやパルスジェネレータ等を備える昇降装置３６により夫々昇降可能に支持されている。また前記蓋部材２４には、図３に示す如く、前記加熱室２４ａの温度を検出する温度センサ３８が配設され、該センサ３８の検出温度は、温度制御装置４０に入力される。この温度制御装置４０は、加熱室２４ａの温度を予め設定された目標温度に保持するベく、検出温度に基づいて加熱装置３２への投入電力量を設定すると共に、該電力量に基づいて投入電圧および投入電流を設定するよう構成される。そして、投入電圧に基づいて前記昇降装置３６を作動制御し、電極３４と溶鋼の湯面(メニスカス)との距離(ギャップ)を調整して加熱力を可変することで、加熱室２４ａの温度を目標温度に保持するようになっている。なお、加熱室２４ａの目標温度は、蓋部材２４で覆われている鋳型１２内の溶鋼における湯面の温度を固相線温度以上に保持し得る温度に設定され、これによって湯面が凝固するのを防止するよう構成される。すなわち、湯面からの抜熱と同じ熱量を供給することで、湯面温度を固相線温度以上の一定に保持するものである。
【００１３】
前記加熱装置３２による溶鋼の加熱は、鋳込み完了後、静置凝固させる際に行なわれるもので、そのときには表面に外殻(シェル)が形成された鋳片２２の上端部を、後述する昇降台５０の上昇により鋳型１２の上端から所定長さだけ押し上げ(図４(ａ)参照)、前記電極３４から放電されるプラズマやアークにより鋳型１２への電蝕や迷走電流発生を防止するよう構成してある。なお、前記電極３４の材質は、例えば炭素、タングステンまたはカッパー等が挙げられるが、その他の材質であってもよい。
【００１４】
図１に示す如く、前記待機位置に臨む蓋部材２４の下方の鋳床１４に、例えばカーボンを材質とする受電板４２が配置され、この受電板４２に蓋部材２４を載置すると共に加熱室２４ａに不活性ガスを供給した状態で、受電板４２と電極３４との間に所定電圧を印加することで、電極３４から放電するプラズマまたはアークにより加熱室２４ａ、すなわち蓋部材２４を所定温度まで予熱し得るよう構成される。実施例では、蓋部材２４を予熱する予熱手段は、溶鋼加熱に用いられる加熱装置３２が兼用しているが、独立した別の手段を用いてもよく、またその加熱方式もプラズマまたはアークによる加熱に限らず、バーナ等を用いることができる。なお、蓋部材２４の予熱温度は、前記加熱室２４ａの目標温度以上であることが最も好適であるが、それより低い温度であってもよい。
【００１５】
前記鋳型１２の直下には、図１に示す如く、該鋳型１２内で１次冷却されて表面にシェルが形成された鋳片２２を幅方向の両側から挟持する複数のガイドロール４４,４４が自由回転可能に配設され、鋳型１２の下部から引抜かれた直後の鋳片２２を該ロール４４,４４により両側から挟持することで、バルジングを防止するよう構成される。またガイドロール４４,４４の配設位置より下方には、上下方向に離間する複数のノズル４６が、鋳片２２を挟む幅方向の両側に対向的に配設されており、各ノズル４６から鋳片２２に向けて冷却水(水)を直接スプレーすることで、該鋳片２２の凝固を促進させる２次冷却を行なうよう構成される。なお、ガイドロール４４およびノズル４６は、後述する昇降台５０と干渉しない位置まで退避可能に構成され、幅方向に対向するガイドロール４４,４４およびノズル４６,４６間を昇降台５０が昇降するのを許容するようにしてある。
【００１６】
前記鋳型１２の下方には、鋳片２２の下端を支持するダミーヘッド４８を備えた昇降台５０が垂直昇降可能に配設されている。また、鋳片２２を挟む両側に滑車５２,５２が回動可能に配設され、一端が適宜の固定部位に接続されたワイヤ５４が両滑車５２,５２に巻掛けられると共に、その他端が可変速可能なウインチ５６に接続されている。そして、前記昇降台５０は、両滑車５２,５２の間に臨むワイヤ５４によって吊下げ支持され、該ワイヤ５４およびウインチ５６からなる昇降手段５８によって昇降台５０が昇降移動されるようになっている。すなわち、ワイヤ５４を巻上げる方向にウインチ５６を回転駆動することで、該ワイヤ５４を介して昇降台５０が上昇し、逆にワイヤ５４を繰出す方向にウインチ５６を回転駆動することで、ワイヤ５４を介して昇降台５０が下降するよう構成される。
【００１７】
【実施例の作用】
次に、前述した実施例に係る垂直型鋳造装置により実施される垂直型鋳造方法の作用につき説明する。前記ウインチ５６を所定方向に回転駆動して昇降台５０を上昇し、前記ダミーヘッド４８で鋳型１２の下部を閉塞した状態で、前記取鍋１６およびタンディッシュ１８を介して高合金鋼および工具鋼を含む特殊鋼等の溶鋼を鋳型１２に鋳込む。この鋳型１２に鋳込まれた溶鋼は、該鋳型１２による１次冷却により、その表面にシェルが形成される。またウインチ５６を逆転駆動して昇降台５０を所定の鋳造速度で垂直に下降することで、ダミーヘッド４８により下端が支持された鋳片２２は、鋳型１２の下部から引抜かれる。
【００１８】
前記鋳型１２から引抜かれた直後の鋳片２２は、図１に示す如く、前記ガイドロール４４,４４で幅方向から挟持されることで、バルジングが発生するのは防止される。また、前記複数のノズル４６,４６から鋳片２２に冷却水がスプレーされ、該鋳片２２は２次冷却される。
【００１９】
前記鋳型１２への鋳込み中に、図１に示す如く、前記待機位置において受電板４２に載置されている蓋部材２４では、前記加熱室２４ａに不活性ガスを供給した状態で前記加熱装置３２により加熱され、該蓋部材２４は前記目標温度近傍の温度まで予熱される。そして、鋳型１２への鋳込みが完了した後、前記取鍋１６が退避した状態で前記タンディッシュ１８が上昇すると共に、台車２０が移動し、該タンディッシュ１８が鋳造位置から退避位置に移動するのに伴って待機位置で上昇した蓋部材２４が加熱位置に移動する(図４(ａ)参照)。また鋳込み完了後には、前記昇降台５０が上昇し、表面に外殻が形成された鋳片２２の上端部を、鋳型１２の上端から所定長さだけ押し上げる。
【００２０】
次に、図４(ｂ)に示す如く、前記蓋部材２４が下降して鋳型１２の上部を覆うと共に、加熱室２４ａに不活性ガスを供給した状態で、鋳型１２内の溶鋼を、その湯面からの抜熱を補償するように加熱装置３２で加熱し、これによって鋳型１２内の溶鋼における湯面が凝固するのを防止し、鋳片２２内部の収縮孔や鋳片頭部キャビティが発生するのは抑制される。また、溶鋼湯面から加熱して、未凝固部の上下方向に大きな温度勾配を生じさせることによって、後述する凝固前面の角度θを大きくし、これによってセンターポロシティ、鋳片頭部キャビティ、中心偏析およびＶ状偏析等の内部欠陥の発生を好適に抑制することができる。この場合において、鋳型１２の上部を蓋部材２４で略密閉状態で覆っているから、加熱装置３２による溶鋼の効率的な加熱が達成される。しかも、蓋部材２４は予熱されているから、該蓋部材２４で鋳型１２を覆ってから加熱を開始するまでの間での湯面の温度降下を小さく抑えることができる。また実施例では、タンディッシュ１８と蓋部材２４および加熱装置３２を共通の台車２０に配設したから、鋳込み完了後に蓋部材２４で鋳型上部を覆うのに要する時間を短かくすることができ、その間での湯面の温度降下も小さくし得る。
【００２１】
また前記加熱装置３２では、前記加熱室２４ａの温度を検出する温度センサ３８からの検出温度に基づいて前記温度制御装置４０により電極３４と湯面とのギャップ調整が行なわれ、加熱室２４ａの温度を目標温度に保持するようフィードバック制御される。これにより、鋳型１２内の溶鋼は、鋳片２２の凝固完了近くまでその湯面の温度降下が固相線温度以上に保たれ、湯面の凝固は好適に防止される。そして、予め設定された時間の経過後、加熱装置３２による加熱力を徐々に下げて加熱を終了する。
【００２２】
ここで、前記センターポロシティ、中心偏析およびＶ状偏析等の内部欠陥の発生は、鋳片内部における凝固前面の角度が影響していると考えられる。すなわち、従来は図５(ａ)に示すように、鋳片２２の内部における凝固前面の角度(凝固界面の中心線に対する角度)θが小さくなり、Ｃ,Ｓ,Ｐ等が濃化した溶鋼のサクションが助長され、前記の内部欠陥が多く発生していた。これに対し、実施例の場合は、図５(ｂ)に示す如く、その凝固界面付近では上方の幅が広がって前記角度θは大きくなり、Ｃ,Ｓ,Ｐ等が濃化した溶鋼のサクションが低減され、前記の内部欠陥の発生を好適に抑制することができるものである。なお、凝固前面の角度θは、鋳片２２のマクロ組織の観察で判断される。
【００２３】
すなわち、高合金鋼および工具鋼を含む特殊鋼等のように製品品質の厳格化が要求される鋼種においても、発明例の垂直型鋳造方法によれば、内部にセンターポロシティ、鋳片頭部キャビティ、中心偏析およびＶ状偏析等の内部欠陥が少ない良質の製品が得られる。なお、上端部における断面寸法が、厚み５００ｍｍ以上、幅５００ｍｍ以上の鋳片２２を鋳造する場合に、発明例の垂直型鋳造方法および装置は特に有効である。
【００２４】
前述した実施例では、タンディッシュの台車に蓋部材および加熱装置を配設した場合で説明したが、蓋部材や加熱装置を別の台車や移動手段等に配設し、タンディッシュが鋳造位置から退避位置に移動したときに、蓋部材を加熱位置に速やかに移動させるよう構成してもよい。
【００２５】
【実験例】
工具鋼を材質として、鋳片厚み６５０ｍｍ，幅８５０ｍｍの鋳片を鋳造する場合に、鋳込み完了後、静置凝固時に溶鋼を加熱しない場合(従来例)と、加熱する場合(発明例)とについて、鋳造された鋳片上端部切捨長さについて測定した結果を図６に示し、Ｃ(炭素)の偏析を測定した結果を図７に示す。また、凝固前面角度θを図８に示す。
【００２６】
図６から判明する如く、加熱を実施しない従来例では、鋳片頭部キャビティ、中心偏析およびＶ状偏析等の内部欠陥が多く発生し、多くの鋳片を切捨てなければならず、歩留りが低下する。これに対し、加熱を実施した発明例では、鋳片上端部における前記の内部欠陥の発生は抑制され、これによって鋳片上端部切捨長さが著しく低下することが確認された。
【００２７】
図７から判明する如く、従来例に比べ、加熱を実施することで、Ｃの偏析を抑制することが確認された。また図８から判明する如く、加熱を実施することで、凝固前面角度θは大きくなることが確認された。すなわち、凝固前面角度θの広角化によってセンターポロシティ、鋳片頭部キャビティ、中心偏析およびＶ状偏析等の内部欠陥の発生を好適に抑制し得ることが判った。
【００２８】
【発明の効果】
以上説明した如く、本発明に係る垂直型鋳造方法および装置によれば、製品品質の厳格化が要求される高合金鋼および工具鋼を含む特殊鋼等の鋼種においても、鋳込み完了後の静置凝固時に蓋部材で鋳型上部を覆ったもとで鋳型内の溶鋼を加熱することで、センターポロシティ、鋳片頭部キャビティ、中心偏析またはＶ状偏析等の内部欠陥の少ない高品質の鋳片を鋳造することができ、歩留りを向上することができる。また蓋部材を予熱しておくことで、加熱を開始するまでの湯面の温度降下を少なく抑えることができる。
【図面の簡単な説明】
【図１】本発明の好適な実施例に係る垂直型鋳造装置を示す概略構成図である。
【図２】実施例に係る垂直型鋳造装置の蓋部材を示す概略断面図である。
【図３】実施例に係る垂直型鋳造装置の加熱手段を示す概略説明図である。
【図４】実施例に係る垂直型鋳造装置の加熱工程を示す概略説明図である。
【図５】従来例および発明例に係る鋳片における凝固前面角度を示す説明図である。
【図６】鋳片上端部切捨長さの測定結果を示すグラフ図である。
【図７】Ｃの偏析を測定した結果を示すグラフ図である。
【図８】凝固前面角度の測定結果を示すグラフ図である。
【符号の説明】
１２鋳型
２２鋳片
２４蓋部材
２４ａ加熱室
２６内張り部材
２８外張り部材
３２加熱装置(加熱手段)
５０昇降台
５８昇降手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vertical casting method for casting a slab of a predetermined length by vertically pulling out a slab that is cooled in a mold and solidified only on a surface portion (a state in which a shell is formed) and It relates to the device.
[0002]
[Prior art]
In the field of non-ferrous metals such as aluminum, molten steel is cast into a mold (mold) that opens up and down, and a dummy head of a lifting platform that is arranged to be movable up and down below the mold is cooled in the mold and has a shell on the surface. Vertical casting that casts a slab of a predetermined length by pulling the slab vertically from the bottom of the mold by vertically lowering the lifting platform at a predetermined speed while supporting the lower end of the formed slab. The method is known.
[0003]
[Problems to be solved by the invention]
The vertical casting method is advantageous in terms of energy saving and labor saving as compared with the ingot forming method. Therefore, it is a general steel grade including high alloy steels and tool steels. Attempts have been made to employ casting. However, when the above steel types are cast by the vertical casting method, there are many internal defects such as center porosity, slab head cavity, center segregation or V-shaped segregation, and there is a problem that the product quality is lowered and the yield is also lowered. It was. That is, in the situation where stricter product quality is required, the conventional vertical casting method cannot sufficiently cope.
[0004]
OBJECT OF THE INVENTION
In view of the above-mentioned problems inherent in the prior art, the present invention has been proposed to suitably solve this problem, and casts slabs such as high alloy steel and special steel including tool steel. Provided is a vertical casting method and apparatus that can suppress the occurrence of internal defects such as center porosity, slab head cavity, center segregation or V-shaped segregation during stationary solidification, and improve product quality and yield. The purpose is to do.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problems and to achieve the intended purpose suitably, a vertical casting method according to the present invention casts molten steel of special steel including high alloy steel and tool steel into a mold opening up and down. When casting a slab having a required cross-sectional shape with a shell formed on the surface vertically from the lower part of the mold to cast a slab of a predetermined length, after the casting is completed, the lifting platform rises to the outside of the surface. the upper end portion of the slab which shell is formed, after pushing up the upper end of the mold by a predetermined length, the lid member that has been preheated to a predetermined temperature is made Utotomoni internal image covering an upper portion of the mold is lowered In a state where the heated chamber is in an inert gas atmosphere, the molten steel in the mold is heated by plasma or arc under heating conditions that can maintain the surface temperature of the molten metal at or above the solidus temperature. It is characterized by suppressing the occurrence of internal defects in the piece. To.
[0006]
Further to solve the problems described above, in order to suitably achieve the expected object, vertical-type casting apparatus of the present application, casting the molten steel of a special steel including a high-alloy steel and tool steel in a mold which opens vertically, the surface The lower end of the slab formed with a shell is supported by a lifting platform disposed below the mold and vertically lifted by a lifting means, and is pulled out from the lower portion of the mold to cast a casting having a predetermined length. A vertical casting apparatus for casting a piece, a cover member capable of covering an upper part of the mold and an internally defined heating chamber as an inert gas atmosphere, preheating means for preheating the cover member, and the cover The molten steel in the mold covered with the member is characterized by comprising heating means for raising the elevator after completion of casting and heating it by plasma or arc.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Next, the vertical casting method and apparatus according to the present invention will be described below with reference to the accompanying drawings by way of preferred embodiments.
[0008]
FIG. 1 schematically shows a vertical casting apparatus in which a vertical casting method according to an embodiment is carried out. The casting apparatus 10 includes a mold 12 that is opened up and down and disposed on a casting floor 14. The mold 12 is configured such that molten steel such as high alloy steel and special steel including tool steel is cast through a ladle 16 and a tundish 18 provided above the mold 12. The tundish 18 is disposed on a carriage 20 configured to be movable along a rail (not shown) provided on the casting floor 14, and is separated from the casting position where the casting position faces the mold 12. It is comprised so that it may move between the retracted positions. Further, the tundish 18 is disposed so as to be movable up and down with respect to the carriage 20 via an appropriate lifting mechanism. When the tundish 18 moves between the casting position and the retracted position, the immersion nozzle 18a provided in the tundish 18 is disposed. Is raised to a position where it does not interfere with the mold 12. The mold 12 is moved up and down by an oscillation device (not shown) to reduce friction between the cast piece 22 pulled out from the lower part of the mold 12 and the mold 12 and prevent seizure. Is done.
[0009]
The carriage 20 is provided with a lid member 24 that can cover the upper part of the mold 12, and the lid member 24 is in a standby position (FIG. 1) that is separated from the mold 12 when the tundish 18 faces the casting position. When the tundish 18 faces the retracted position, it faces the heating position (FIG. 4) that covers the upper part of the mold 12. The lid member 24 is disposed so as to be movable up and down with respect to the carriage 20 via an appropriate lifting mechanism, and is cast from the mold 12 or the upper end of the mold 12 when moving between the standby position and the heating position. It is raised to a position where it does not interfere with the upper end (described later) of the piece 22.
[0010]
As shown in FIG. 2, the lid member 24 is formed in a box shape that opens downward, and has a lining member 26 made of a refractory material, and an outer lining member 28 made of a heat insulating material covering the outside of the lining member 26. And a three-layer structure comprising an iron skin 30 that covers the outer side of the lining member 28, and is configured to define a heating chamber 24 a inside the lining member 26. In addition, a plurality of (two in the embodiment) through holes 24b are formed in the ceiling portion of the lid member 24. The heating device (heating means) 32 is provided in the carriage 20 to heat the molten steel in the mold 12. Are inserted into the heating chamber 24a through the respective through holes 24b so as to be able to advance and retract. Then, after completion of casting described later, a predetermined voltage is applied between the slab 22 and the electrode 34 in the mold 12 in a state where the lid member 24 covers the upper part of the mold 12 at the heating position when the molten steel is heated for stationary solidification. Is applied to heat the molten steel in the mold 12 by plasma or arc discharged from the electrode 34. It should be noted that an inert gas such as Ar or N ₂ is supplied into the heating chamber 24a through the through hole 24b when the molten steel is heated, so that the interior of the chamber can be made an inert gas atmosphere.
[0011]
The lining member 26 is preferably made of a refractory material mainly composed of Al ₂ O ₃ , and the outer lining member 28 is a heat insulating material having improved heat insulating properties by adding SiO ₂ to Al ₂ O _3. Is preferably used, but other materials may be used. In addition, by using a heat insulating material having a low thermal conductivity as the outer member 28, it is possible to reduce the heat removal of the lid member 24 when the molten steel is heated and during preheating described later, and the input power can be reduced.
[0012]
Each electrode 34 of the heating device 32 is supported by an elevating device 36 having an electric motor, a pulse generator and the like so as to be able to be raised and lowered. Further, as shown in FIG. 3, a temperature sensor 38 for detecting the temperature of the heating chamber 24 a is disposed on the lid member 24, and the detected temperature of the sensor 38 is input to the temperature control device 40. This temperature control device 40 should keep the temperature of the heating chamber 24a at a preset target temperature, set the input power amount to the heating device 32 based on the detected temperature, and input based on the power amount Configured to set voltage and input current. Then, the operation of the lifting device 36 is controlled based on the input voltage, the distance (gap) between the electrode 34 and the molten steel surface (meniscus) is adjusted, and the heating power is varied, whereby the temperature of the heating chamber 24a is changed. It is designed to maintain the target temperature. Note that the target temperature of the heating chamber 24a is set to a temperature at which the temperature of the molten metal in the molten steel in the mold 12 covered with the lid member 24 can be maintained at or above the solidus temperature, thereby solidifying the molten metal surface. Configured to prevent That is, by supplying the same amount of heat as the heat removal from the molten metal surface, the molten metal surface temperature is kept constant above the solidus temperature.
[0013]
The molten steel is heated by the heating device 32 when it is allowed to stand and solidify after the completion of casting. At that time, the upper end of the slab 22 having an outer shell (shell) formed on the surface thereof is used as a lifting platform described later. 50 is pushed up by a predetermined length from the upper end of the mold 12 (see FIG. 4A), and the plasma and arc discharged from the electrode 34 are configured to prevent electric corrosion and stray current generation on the mold 12. It is. The material of the electrode 34 is, for example, carbon, tungsten or copper, but other materials may be used.
[0014]
As shown in FIG. 1, a power receiving plate 42 made of, for example, carbon is disposed on the casting floor 14 below the lid member 24 facing the standby position, and the lid member 24 is placed on the power receiving plate 42 and a heating chamber. In a state where an inert gas is supplied to 24a, a predetermined voltage is applied between the power receiving plate 42 and the electrode 34, whereby the heating chamber 24a, that is, the lid member 24 is brought to a predetermined temperature by plasma or arc discharged from the electrode 34. Configured for preheating. In the embodiment, the heating device 32 used for heating the molten steel is also used as the preheating means for preheating the lid member 24. However, another independent means may be used, and the heating system is also heated by plasma or arc. Not limited to this, a burner or the like can be used. The preheating temperature of the lid member 24 is most preferably equal to or higher than the target temperature of the heating chamber 24a, but may be a lower temperature.
[0015]
Immediately below the mold 12, as shown in FIG. 1, a plurality of guide rolls 44, 44 are sandwiched from both sides in the width direction of the slab 22 which is primarily cooled in the mold 12 and has a shell formed on the surface. The slab 22 is disposed so as to be freely rotatable, and is configured to prevent bulging by sandwiching the slab 22 immediately after being pulled out from the lower portion of the mold 12 from both sides by the rolls 44 and 44. Below the position where the guide rolls 44 are disposed, a plurality of nozzles 46 spaced in the vertical direction are disposed oppositely on both sides in the width direction across the cast piece 22. By directly spraying cooling water (water) toward the piece 22, secondary cooling that promotes solidification of the cast piece 22 is performed. Note that the guide roll 44 and the nozzle 46 are configured to be retractable to a position that does not interfere with an elevator 50 described later, and the elevator 50 moves up and down between the guide rolls 44 and 44 and the nozzles 46 and 46 facing in the width direction. Is allowed.
[0016]
Below the mold 12, a lifting platform 50 having a dummy head 48 that supports the lower end of the slab 22 is disposed so as to be vertically movable. Further, pulleys 52, 52 are rotatably disposed on both sides of the slab 22, and a wire 54 having one end connected to an appropriate fixing portion is wound around the pulleys 52, 52, and the other end is allowed. It is connected to a winch 56 capable of shifting. The elevator 50 is suspended and supported by a wire 54 facing between the pulleys 52, 52, and the elevator 50 is moved up and down by an elevator 58 comprising the wire 54 and a winch 56. . That is, when the winch 56 is rotationally driven in the direction in which the wire 54 is wound up, the lifting platform 50 is raised via the wire 54, and conversely, the winch 56 is rotationally driven in the direction in which the wire 54 is fed out. The lifting platform 50 is configured to be lowered via 54.
[0017]
[Effect of the embodiment]
Next, the operation of the vertical casting method performed by the vertical casting apparatus according to the above-described embodiment will be described. The winch 56 is rotationally driven in a predetermined direction to raise the elevator 50, and in the state where the lower part of the mold 12 is closed by the dummy head 48, high alloy steel and tool steel are passed through the ladle 16 and tundish 18. Molten steel such as special steel is cast into the mold 12. The molten steel cast into the mold 12 forms a shell on the surface by primary cooling by the mold 12. Further, the winch 56 is reversely driven to vertically move the lifting platform 50 at a predetermined casting speed, whereby the slab 22 supported at the lower end by the dummy head 48 is pulled out from the lower portion of the mold 12.
[0018]
As shown in FIG. 1, the slab 22 immediately after being drawn from the mold 12 is sandwiched from the width direction by the guide rolls 44 and 44, thereby preventing bulging. Further, cooling water is sprayed onto the slab 22 from the plurality of nozzles 46, 46, and the slab 22 is secondarily cooled.
[0019]
As shown in FIG. 1, during the casting into the mold 12, the lid member 24 placed on the power receiving plate 42 in the standby position has the inert gas supplied to the heating chamber 24 a and the heating device 32. The lid member 24 is preheated to a temperature near the target temperature. Then, after the casting into the mold 12 is completed, the tundish 18 rises with the ladle 16 retracted, the carriage 20 moves, and the tundish 18 moves from the casting position to the retracted position. Accordingly, the lid member 24 raised at the standby position moves to the heating position (see FIG. 4A). Further, after the casting is completed, the lifting platform 50 is raised, and the upper end portion of the cast piece 22 having the outer shell formed on the surface is pushed up from the upper end of the mold 12 by a predetermined length.
[0020]
Next, as shown in FIG. 4 (b), the lid member 24 is lowered to cover the upper part of the mold 12, and the inert steel is supplied to the heating chamber 24a. Heating is performed by the heating device 32 so as to compensate for heat removal from the surface, thereby preventing the molten metal surface in the molten steel in the mold 12 from solidifying, and shrinkage holes and slab head cavities inside the slab 22 are generated. Is suppressed. In addition, by heating from the molten steel surface and generating a large temperature gradient in the vertical direction of the unsolidified part, the angle θ of the solidified front surface, which will be described later, is increased, whereby center porosity, slab head cavity, center segregation and Generation of internal defects such as V-shaped segregation can be suitably suppressed. In this case, since the upper part of the mold 12 is covered with the lid member 24 in a substantially sealed state, efficient heating of the molten steel by the heating device 32 is achieved. Moreover, since the lid member 24 is preheated, the temperature drop of the molten metal surface from when the mold member 12 is covered with the lid member 24 until the heating is started can be suppressed small. In the embodiment, since the tundish 18, the lid member 24, and the heating device 32 are disposed on the common carriage 20, the time required to cover the upper part of the mold with the lid member 24 after completion of casting can be shortened. During this time, the temperature drop of the hot water surface can be reduced.
[0021]
In the heating device 32, the temperature control device 40 adjusts the gap between the electrode 34 and the molten metal surface based on the detected temperature from the temperature sensor 38 that detects the temperature of the heating chamber 24a, and the temperature of the heating chamber 24a is adjusted. Is controlled to be kept at the target temperature. As a result, the molten steel in the mold 12 is kept at a temperature drop above the solidus temperature near the completion of the solidification of the slab 22, and solidification of the molten metal surface is preferably prevented. Then, after the elapse of a preset time, the heating power by the heating device 32 is gradually lowered to finish the heating.
[0022]
Here, it is considered that the occurrence of internal defects such as center porosity, center segregation, and V-shaped segregation is influenced by the angle of the solidification front surface inside the slab. That is, conventionally, as shown in FIG. 5 (a), the angle of the solidification front surface (angle with respect to the center line of the solidification interface) θ inside the slab 22 is reduced, and C, S, P, etc. are concentrated in the molten steel. Suction was promoted, and many internal defects were generated. On the other hand, in the case of the example, as shown in FIG. 5 (b), in the vicinity of the solidification interface, the upper width is widened and the angle θ is increased, and the suction of the molten steel in which C, S, P, etc. are concentrated. And the occurrence of the internal defects can be suitably suppressed. Note that the angle θ of the solidification front surface is determined by observing the macrostructure of the slab 22.
[0023]
That is, even in steel types that require strict product quality, such as high alloy steel and special steel including tool steel, according to the vertical casting method of the invention example, the center porosity, the slab head cavity, Good quality products with few internal defects such as center segregation and V-shaped segregation can be obtained. Note that the vertical casting method and apparatus of the invention example are particularly effective when casting a slab 22 having a cross-sectional dimension of 500 mm or more in thickness and 500 mm or more in width at the upper end.
[0024]
In the above-described embodiment, the case where the lid member and the heating device are provided on the tundish cart has been described. However, the lid member and the heating device are provided on another cart, moving means, etc., and the tundish is moved from the casting position. You may comprise so that a cover member may be moved to a heating position rapidly, when it moves to a retracted position.
[0025]
[Experimental example]
When casting a slab of 650 mm in thickness and 850 mm in width using tool steel as a material, when the molten steel is not heated at the time of stationary solidification after casting (conventional example) and when heated (invention example) FIG. 6 shows the results of measuring the length of the cast slab upper end cut off, and FIG. 7 shows the results of measuring the segregation of C (carbon). Further, the solidification front surface angle θ is shown in FIG.
[0026]
As can be seen from FIG. 6, in the conventional example in which heating is not performed, many internal defects such as a slab head cavity, center segregation, and V-shaped segregation occur, and many slabs must be cut off, resulting in a decrease in yield. . On the other hand, in the invention example in which heating was performed, it was confirmed that the occurrence of the internal defects in the upper end portion of the slab was suppressed, and thereby the cut length of the upper end portion of the slab was significantly reduced.
[0027]
As can be seen from FIG. 7, it was confirmed that the segregation of C was suppressed by heating compared to the conventional example. Further, as can be seen from FIG. 8, it was confirmed that the solidification front surface angle θ is increased by performing the heating. That is, it has been found that the generation of internal defects such as center porosity, slab head cavity, center segregation, and V-shaped segregation can be suitably suppressed by widening the solidification front surface angle θ.
[0028]
【The invention's effect】
As described above, according to the vertical casting method and apparatus according to the present invention, even in steel types such as high alloy steel and special steel including tool steel that require stricter product quality, it is allowed to stand after completion of casting. Casting high quality slabs with few internal defects such as center porosity, slab head cavity, center segregation or V-shaped segregation by heating molten steel in the mold while covering the top of the mold with a lid member during solidification And the yield can be improved. In addition, by preheating the lid member, it is possible to suppress the temperature drop of the hot water surface until heating is started.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a vertical casting apparatus according to a preferred embodiment of the present invention.
FIG. 2 is a schematic sectional view showing a lid member of the vertical casting apparatus according to the embodiment.
FIG. 3 is a schematic explanatory view showing heating means of the vertical casting apparatus according to the embodiment.
FIG. 4 is a schematic explanatory view showing a heating process of the vertical casting apparatus according to the embodiment.
FIG. 5 is an explanatory view showing a solidification front surface angle in a slab according to a conventional example and an invention example.
FIG. 6 is a graph showing a measurement result of a cut length of a slab upper end portion.
FIG. 7 is a graph showing the results of measuring segregation of C.
FIG. 8 is a graph showing the measurement result of the solidification front surface angle.
[Explanation of symbols]
12 Mold 22 Casting piece 24 Lid member 24a Heating chamber 26 Inner member 28 Outer member 32 Heating device (heating means)
50 Lifting table 58 Lifting means

Claims

Cast the molten steel of special steel including high alloy steel and tool steel into the mold (12) opened up and down, and the slab (22) of the required cross-sectional shape with the shell formed on the surface from the bottom of the mold (12) When casting a slab (22) of a predetermined length by drawing vertically, the upper end of the slab (22) having an outer shell formed on the surface thereof after the casting is completed and, after pushing up the upper end of the mold (12) by a predetermined length, the lid member that has been preheated to a predetermined temperature (24) is made Utotomoni internal image covering an upper portion of the lowered mold (12) With the heating chamber (24a) in an inert gas atmosphere, the molten steel in the mold (12) is heated by plasma or arc under heating conditions that can maintain the temperature of the molten metal surface above the solidus temperature. A vertical casting method characterized by suppressing occurrence of internal defects in a cast slab (22).

Cast the molten steel of special steel including high alloy steel and tool steel into the mold (12) opening up and down, and the lower end of the slab (22) with a shell formed on the surface is placed below the mold (12) Vertical casting, in which a slab (22) having a predetermined length is cast by being pulled out from the lower part of the mold (12) supported by a lifting platform (50) that is vertically lifted by a lifting means (58) A device,
A lid member (24) capable of covering the upper part of the mold (12) and allowing the internally defined heating chamber (24a) to be an inert gas atmosphere;
Preheating means for preheating the lid member (24);
The molten steel in the mold (12) covered with the lid member (24) is composed of heating means (32) for raising the elevator (50) after completion of casting and heating it by plasma or arc. Vertical type casting equipment.

The vertical casting apparatus according to claim 2, wherein the lid member (24) is configured by covering the outer side of the lining member (26) made of a refractory material with an outer lining member (28) made of a heat insulating material.