JP3702807B2 - Continuous casting method - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、二次冷却の条件に特徴のある連続鋳造方法に関する。
【０００２】
【従来の技術】
厚鋼板には、その機械的特性の向上を目的として、Ｎｂ、Ｖ、Ｎｉ、Ｃｕなどの合金元素を含有させた低合金鋼が多く用いられている。しかし、これら低合金鋼を湾曲型または垂直曲げ型の連続鋳造機を用いて鋳造する際に、鋳片表面に横割れまたは横ひび割れ（以下、単に割れと記す場合がある）が発生しやすい。鋳片の矯正時に鋳片表面に働く応力が低合金鋼に固有の限界応力を超えて、割れが発生するのである。これら鋳片表面の割れは、その鋳片を素材として熱間圧延した厚鋼板の表面疵の原因となる。
【０００３】
低合金鋼の鋳片の熱間延性は、鋳片の凝固組織がオーステナイト（以下、γと記す場合がある）相からフェライト（以下、αと記す場合がある）相に変態するＡｒ３ 変態点の温度近傍、すなわち６００〜８５０℃の温度領域で著しく低下する。また、低合金鋼の鋳片では、二次冷却される過程において、ＡｌＮやＮｂＣなどがγ粒界に析出するので、γ粒界が脆化しやすい。したがって、６００〜８５０℃の温度領域でこれら低合金鋼の鋳片を矯正すると、熱間延性の低下およびγ粒界の脆化のために、鋳片表面に割れが発生しやすい。
【０００４】
そこで、矯正時の鋳片の表面温度を６００〜８５０℃の熱間延性の低下する温度領域（以下、脆化温度域と記す）の低温側または高温側に回避して、鋳片表面の割れの発生を防止する方法が一般的に採られている。しかし、鋳片の二次冷却、鋳造速度などの条件が鋳造中に変化するので、鋳片の表面温度は鋳造中に変化する。そのため、脆化温度域で鋳片が矯正される場合があり、その場合には、鋳片表面に割れが発生する。
【０００５】
特開平９−２５３８１４号公報には、鋳型出口の下方で鋳片を強冷却し、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度にした後、脆化温度域よりも高温側のＡｒ３ 変態点を超える温度に復熱させ、その後に鋳片を矯正することにより、鋳片表面の割れの発生を防止する方法が提案されている。
【０００６】
この方法は、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度にした後、Ａｒ３ 変態点を超える温度に復熱させて、鋳片の凝固組織を、γ粒界が不明瞭であるフェライトとパーライトの混合組織とすることにより、鋳片の割れ感受性を低下させて、矯正時の鋳片表面を割れの発生を防止する方法である。しかし、この方法では、鋳片の二次冷却条件によっては、鋳片表面に割れが発生する場合があり、さらなる改善が望まれている。
【０００７】
【発明が解決しようとする課題】
本発明は、横割れまたは横ひび割れのない良好な表面品質を有する鋳片を、安定して得ることができる連続鋳造方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明の要旨は、横断面形状が矩形の鋳片を湾曲型または垂直曲げ型の連続鋳造機を用いて鋳造する際に、鋳片を鋳型から引き抜いた直後から鋳片の二次冷却を行い、鋳片の表面温度をいったんＡｒ3変態点より低い温度に冷却した後に、Ａｒ3変態点を超える温度に復熱させ、その後に鋳片を矯正する連続鋳造方法であって、鋳片の表面温度をＡｒ3変態点より低い温度に保持する時間ｔ（ｓ）と、いったんＡｒ3変態点より低い温度に冷却した後にＡｒ3変態点を超える温度に復熱させるまでの間で、鋳片の表面温度が到達する最低の表面温度Ｔmin（℃）とが、下記の（イ）式および（ロ）式を満足するように鋳片の二次冷却を行うことにより、鋳片表面から少なくとも深さ２ｍｍまでの凝固組織を、オーステナイト粒界が不明瞭なフェライトおよびパーライトの混合組織とする連続鋳造方法にある。
５０≦ｔ（ｓ）≦５００ ・・・（イ）
０．１３×ｔ＋４９３≦Ｔmin（℃）≦０．０４５×ｔ＋７９８ ・・・（ロ）
本発明で規定する「横断面形状が矩形の鋳片」とは、横断面形状が長方形または正方形のスラブまたはブルームを意味する。
【０００９】
また、本発明で規定する「鋳片の表面温度」とは、たとえば、放射温度計により測定することができる表面温度であり、また、凝固伝熱解析による計算によっても求めることができる表面温度である。計算で求める際、鋼の化学組成、鋳片のサイズ、鋳造速度、鋳片の二次冷却条件などの条件が決まれば、鋳型内のメニスカスからの距離に応じた鋳片の表面温度を求めることができる。表面熱伝達係数を適切に選択することにより、この計算で求めた鋳片の表面温度を、実測した表面温度とよく一致させることができる。
【００１０】
低合金鋼の脆化温度域である６００〜８５０℃の温度領域を回避できずに鋳片を矯正しても、鋳片表面から少なくとも深さ２ｍｍまでの鋳片の凝固組織を、γ粒界が不明瞭なフェライトおよびパーライトの混合組織とすることにより、鋳片表面の横割れまたは横ひび割れの発生を安定して防止できる。その理由は、凝固組織が、γ粒界が不明瞭なフェライトおよびパーライトの混合組織となった鋳片表面では、割れに対する鋼に固有の限界応力が大きくなるためである。
【００１１】
このようなγ粒界が不明瞭なフェライトおよびパーライトの混合組織とは、高温側からＡｒ３ 変態点よりも低温側に鋳片が冷却される際に、フェライトがγ粒界に粒状に生成した状態の凝固組織のことを意味する。γ粒界に粒状にフェライトが生成するために、γ粒界が不明瞭になる。これらの凝固組織は、鋳片の横断面サンプルから、鋳片表面を含むように光学顕微鏡観察用サンプルを切り出して研磨し、たとえば、５％ナイタール腐食を行った後に１０〜５０倍程度の倍率で光学顕微鏡観察することにより確認できる。
【００１２】
鋳片表面からの深さが２ｍｍを超える鋳片内部の凝固組織がγ粒界の明瞭な組織であって、鋳片の矯正時に、たとえ、その深いγ粒界の明瞭な領域で割れが発生しても、その鋳片を素材として熱間圧延した厚鋼板の表面には、表面疵は発生しない。鋳片の割れが存在する領域が鋳片内部の深い位置であるので、圧延中にこれらの割れが圧着するからである。
【００１３】
前述の特開平９−２５３８１４号公報で提案された、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度にした後、Ａｒ３ 変態点を超える温度に復熱させることにより、鋳片の凝固組織を、γ粒界が不明瞭なフェライトとパーライトの混合組織とする方法を採っても、鋳片表面に割れが発生する場合がある。その理由は、鋳片の表面温度がＡｒ３ 変態点より低い温度で保持される時間およびＡｒ３ 変態点より低い温度である鋳片の表面温度が到達する最低の表面温度の条件によっては、鋳片表面の凝固組織を目的のγ粒界が不明瞭な凝固組織とすることが困難な場合があるからである。
【００１４】
図１は、γ粒界が不明瞭なフェライトおよびパーライトの混合組織の生成に及ぼす、鋳片の表面温度がＡｒ３ 変態点より低い温度で保持される時間ｔ（ｓ）およびＡｒ３ 変態点より低い温度である鋳片の表面温度が到達する最低の表面温度Ｔｍｉｎ （℃）の影響を示す図である。
【００１５】
垂直曲げ型連続鋳造機を用い、Ｃ：０．０５〜０．０７質量％、Ｎｉ：０．６〜０．７質量％などを含有する低合金鋼を、鋳造速度０．７５〜１．２ｍ／分で厚さ２３０ｍｍ、幅２３００ｍｍのスラブに、または鋳造速度０．５ｍ／分で厚さ３００ｍｍ、幅６５０ｍｍのブルームに、それぞれ鋳片の二次冷却条件を変更して鋳造した際の鋳片表面の割れの発生有無の試験結果を示す図である。
【００１６】
図１中に示す○印は、γ粒界の不明瞭なフェライトとパーライトの混合組織となっている領域が、鋳片表面から深さ２ｍｍ以上であり、鋳片表面には、横割れまたは横ひび割れが発生していないことを意味する。△印は、γ粒界の不明瞭なフェライトとパーライトの混合組織となっている領域が、鋳片表面から深さ２ｍｍ未満に存在することを意味する。また、×印は、少なくとも鋳片表面から深さ２ｍｍまでの領域が、γ粒界が明瞭なフェライトとパーライトの混合組織となっていることを意味する。△印および×印で示した鋳片表面には、横割れまたは横ひび割れが発生しているのが確認できた。
【００１７】
図１から、鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔ（ｓ）と、前述の鋳片の表面温度が到達する最低の表面温度Ｔｍｉｎ （℃）とが、前述の（イ）式および（ロ）式を満足するように鋳片の二次冷却を行うことにより、鋳片表面から少なくとも深さ２ｍｍまでの鋳片の凝固組織を、安定してγ粒界が不明瞭なフェライトおよびパーライトの混合組織とすることができることがわかった。さらに、このような凝固組織とすることにより、鋳片表面の横割れまたは横ひび割れの発生を安定して防止できることがわかった。
【００１８】
【発明の実施の形態】
本発明の方法では、横断面形状が長方形または正方形であるスラブまたはブルームを、湾曲型または垂直曲げ型の連続鋳造機を用いて鋳造する。また、本発明の方法は、Ｎｂ、Ｖ、Ｎｉ、Ｃｕなどの合金元素を含有した低合金鋼を、厚さ１５０〜４００ｍｍのスラブまたはブルームを鋳造することを対象とするのに好適である。このような低合金鋼を上記厚さのスラブまたはブルームに湾曲型または垂直曲げ型の連続鋳造機を用いて鋳造する際、鋳片の矯正時に、鋳片表面に横割れまたは横ひび割れが発生しやすいからである。
【００１９】
図２は、本発明の連続鋳造方法を実施する場合の連続鋳造装置の例を示す模式図である。垂直曲げ型の連続鋳造機を用いる例を示す。鋳型１内に浸漬ノズル（図示していない）などを介して、溶鋼８が供給され、その溶鋼は鋳型で冷却されて凝固殻２となる。鋳型から引き抜かれた直後の凝固殻の厚さは薄いが、スプレーノズル４により水などを噴霧されて冷却され、その厚さが増す。未凝固の溶鋼を含む鋳片５および完全に凝固した鋳片９は、ガイドロール対３により支持されてピンチロール６により引き抜かれ、矯正位置にあるピンチロール７で矯正される。
【００２０】
本発明の方法では、鋳片を鋳型から引き抜いた直後から鋳片の二次冷却を行い、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却した後に、Ａｒ３ 変態点を超える温度に復熱させ、その後に鋳片を矯正する。その際、鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔ（ｓ）と、いったんＡｒ３ 変態点より低い温度に冷却した後にＡｒ３ 変態点を超える温度に復熱させるまでの間で、鋳片の表面温度が到達する最低の表面温度Ｔｍｉｎ （℃）とが、前述の（イ）式および（ロ）式を満足するように鋳片の二次冷却を行う。
【００２１】
鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却した後に、Ａｒ３ 変態点を超える温度に復熱させるのは、鋳片の凝固組織を、γ粒界が不明瞭なフェライトおよびパーライトの混合組織とするためである。
【００２２】
鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却した後に、Ａｒ３ 変態点を超える温度に復熱させ、その後に鋳片を矯正する際の鋳片の表面温度は、低合金鋼に固有の脆化温度域よりも高温であることが望ましいが、脆化温度域で矯正しても構わない。本発明の方法では、脆化温度域で矯正しても、鋳片表面の割れの発生を防止できる。
【００２３】
鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔが５０ｓ未満では、保持時間が短く、フェライトがγ粒界に粒状に十分生成できない。その後、鋳片の表面温度をＡｒ３ 変態点を超える温度に復熱させた際に、γ粒界に粒状に析出したフェライトの痕跡が残らないので、その後に鋳片の表面温度をＡｒ３ 変態点より低い温度にした場合に、鋳片の凝固組織は、γ粒界にフェライトがフィルム状に生成したフェライトおよびパーライトの混合組織となり、γ粒界が明瞭になる。この状態で鋳片を矯正すると、鋳片表面に割れが発生する。
【００２４】
また、Ａｒ３ 変態点より低い温度に保持する時間ｔが５００ｓを超えると、保持時間が長いので、γ粒界へのフェライトの生成が促進され、フェライトがγ粒界にフィルム状に発達する。その後、鋳片の表面温度をＡｒ３ 変態点を超える温度に復熱させた際に、γ粒界にフィルム状のフェライトの痕跡が残存する。その後に鋳片の表面温度をＡｒ３ 変態点より低い温度にした場合、γ粒界のフィルム状のフェライトの痕跡上に、フェライトがフィルム状に生成するので、鋳片の凝固組織は、γ粒界にフェライトがフィルム状に生成したフェライトおよびパーライトの混合組織となり、γ粒界が明瞭になる。この状態で鋳片を矯正すると、鋳片表面に割れが発生する。
【００２５】
Ａｒ３ 変態点より低い温度に保持する時間ｔが前述の（イ）式を満足する条件において、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却する際の鋳片の表面温度が到達する最低の表面温度Ｔｍｉｎ が、前述の（ロ）式の左辺の値未満であると、鋳片表面が過冷却されることを意味しており、鋳片表面の復熱時に鋳片の表面温度がＡｒ３ 変態点を超える温度に復熱しにくくなる。この状態から鋳片表面がさらに冷却されると、鋳片の凝固組織は、γ粒界にフェライトがフィルム状に生成したフェライトおよびパーライトの混合組織となり、γ粒界が明瞭になる。この状態で鋳片を矯正すると、鋳片表面に割れが発生する。
【００２６】
また、Ａｒ３ 変態点より低い温度に保持する時間ｔが前述の（イ）式を満足する条件において、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却する際の鋳片の表面温度が到達する最低の表面温度Ｔｍｉｎ が、前述の（ロ）式の右辺の値を超える場合で、Ａｒ３ 変態点より低い温度に保持する時間ｔが（イ）式を満足するなかで短い場合には、鋳片の凝固組織は、γ粒界にフェライトが粒状に生成したフェライトおよびパーライトの混合組織となり、γ粒界が不明瞭になる。ただし、その不明瞭な領域の鋳片表面からの厚さ方向の深さは２ｍｍ未満となる。この状態で鋳片を矯正すると、鋳片表面に割れが発生する。
【００２７】
一方、最低の表面温度Ｔｍｉｎ が、前述の（ロ）式の右辺の値を超える場合で、Ａｒ３ 変態点より低い温度に保持する時間ｔが（イ）式を満足するなかで長い場合には、鋳片の凝固組織は、γ粒界にフェライトがフィルム状に生成したフェライトおよびパーライトの混合組織となり、γ粒界が明瞭になる。この状態で鋳片を矯正すると、鋳片表面に割れが発生する。
【００２８】
厚さが１５０〜３００ｍｍのスラブの場合に、鋳型出口から１ｍまでの間において、鋳片の二次冷却の比水量を０．３〜０．６５リットル／ｋｇ−鋼とし、かつ、鋳型出口からの距離が、１ｍを超えて５ｍまでの任意の範囲において、鋳片の二次冷却の比水量を０．２５〜０．５５リットル／ｋｇ−鋼として鋳片を二次冷却するのが望ましく、また、厚さが１５０〜３００ｍｍのブルームの場合に、鋳型出口から１ｍまでの間において、鋳片の二次冷却の比水量を１．０５〜１．６リットル／ｋｇ−鋼とし、かつ、鋳型出口からの距離が、１ｍを超えて５ｍまでの任意の範囲において、鋳片の二次冷却の比水量を０．６５〜０．９５リットル／ｋｇ−鋼として鋳片を二次冷却するのが望ましい。
【００２９】
さらに、厚さが３００ｍｍ超〜４００ｍｍのスラブの場合に、鋳型出口から１ｍまでの間において、鋳片の二次冷却の比水量を０．６５〜１．０リットル／ｋｇ−鋼とし、かつ、鋳型出口からの距離が、１ｍを超えて５ｍまでの任意の範囲において、鋳片の二次冷却の比水量を０．５５〜０．７５リットル／ｋｇ−鋼として鋳片を二次冷却するのが望ましく、また、厚さが３００ｍｍ超〜４００ｍｍのブルームの場合に、鋳型出口から１ｍまでの間において、鋳片の二次冷却の比水量を１．６〜１．９５リットル／ｋｇ−鋼とし、かつ、鋳型出口からの距離が、１ｍを超えて５ｍまでの任意の範囲において、鋳片の二次冷却の比水量を０．９５〜１．１５リットル／ｋｇ−鋼として鋳片を二次冷却するのが望ましい。
【００３０】
上記のスラブまたはブルームの場合に、上記二次冷却の比水量とすることにより、表面から厚さ方向に少なくとも深さ２ｍｍまでの鋳片の凝固組織を、γ粒界が不明瞭なフェライトおよびパーライトの混合組織とすることができ、鋳片表面の割れの発生を安定して防止できる。
【００３１】
鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却した後に、Ａｒ３ 変態点を超える温度に復熱させる際に、鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔと、いったんＡｒ３ 変態点より低い温度に冷却した後にＡｒ３ 変態点を超える温度に復熱させるまでの間で、鋳片の表面温度が到達する最低の表面温度Ｔｍｉｎ とが、前述の（イ）式および（ロ）式を満足するように鋳片の二次冷却を行うことを、鋳片を矯正する前までに、さらに１回以上繰り返してもよい。γ粒界が不明瞭な凝固組織の存在する鋳片表面からの深さが、より効果的に深くなる。
【００３２】
【実施例】
図２に示す装置構成で、垂直部の長さが３ｍである垂直曲げ型連続鋳造機を用いて、鋳片の形状、鋳造速度および鋳片の二次冷却の比水量の条件を変化させて、表１に示す化学組成のＮｂ、ＣｕおよびＮｉを含む低合金鋼を鋳造した。この鋼のＡｒ３ 変態点は８９２℃で、脆化温度域は７２０〜８５０℃である。
【００３３】
【表１】
【００３４】
スラブおよびブルームの二次冷却の条件は、後述する表２に詳細を示すが、概略つぎのとおりとした。すなわち、鋳型出口から１．０ｍまでの間では、スラブおよびブルームともに、鋳片の二次冷却を行い、鋳片の表面温度をＡｒ３ 変態点より低い温度に低下させ、また、鋳片の表面温度が到達する最低の表面温度Ｔｍｉｎ （℃）を変化させた。また、鋳型出口からの距離が、１．０ｍを超えて５ｍまでの間では、１．０ｍから任意のＸｍまでの間で鋳片の二次冷却を行い、鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔ（ｓ）を変化させ、また、鋳片の表面温度が到達する最低の表面温度Ｔｍｉｎ （℃）を変化させた。上記二次冷却の条件は、鋳型出口から最長Ｘｍまで鋳片の二次冷却を行ったことを意味する。
【００３５】
ただし、一部のスラブを鋳造する試験では、鋳型出口からの距離が、１．０ｍを超えて５ｍまでの間で、鋳片の二次冷却を行わなかった。また、後述する試験Ｎｏ．２では、上記の二次冷却の領域の下流側で、さらに追加で鋳片の二次冷却を行い、矯正位置における鋳片の表面温度を調整した。
【００３６】
各試験では、連続して３ヒートの鋳造を行った。その際、鋳造中に放射温度計により、鋳型出口から矯正位置までの領域において鋳片の表面温度を測定した。これらの測定結果から、鋳片の表面温度がＡｒ３ 変態点より低い温度になったかどうかを確認するとともに、鋳片の表面温度がＡｒ３ 変態点より低い温度に保持された時間ｔ（ｓ）、いったんＡｒ３ 変態点より低い温度に冷却した後にＡｒ３ 変態点を超える温度に復熱させるまでの間で、鋳片の表面温度が到達する最低の表面温度Ｔｍｉｎ （℃）、および矯正位置における鋳片の表面温度を求めた。
【００３７】
また、一部の試験では、二次冷却直後の鋳片表面に熱電対を噛み込ませる方法で鋳片の表面温度を測定し、さらに、鋳片のサイズ、鋳造速度、鋳片の二次冷却条件などに対応した鋳片の表面温度を凝固伝熱解析による計算で求めた。これら放射温度計、熱電対および凝固伝熱解析による計算でそれぞれ求めた鋳片の表面温度が精度良く一致しているのが確認できた。
【００３８】
各試験では、鋳造方向の長さ１ｍの鋳片サンプルを採取し、鋳片表面の割れの観察を容易にするため、その表面をスカーフィングして鋳片表面の酸化物を取り除いた。その後にダイチェック（染色浸透探傷試験）を行って鋳片表面の横割れまたは横ひび割れの発生の状況を目視で観察し、割れの状況を評価した。評価Ａは、これら割れが発生していない状態、評価Ｂは、その鋳片を熱間で圧延する前に、鋳片表面の手入れが必要な程度に割れが発生している状態、評価Ｃは、手入れによっても除去が困難な程度に、著しい割れが発生している状態をそれぞれ意味する。
【００３９】
また、鋳片サンプルをスカーフィングする前に、切断面端部で幅中央部から、鋳片表面（鋳造中に上側の面に相当）の鋳造方向に１０ｍｍ、幅方向に２０ｍｍ、鋳片表面を含めて厚さ方向に２０ｍｍの光学顕微鏡観察用サンプルを切り出した。鋳片サンプルの横断面に相当する面を研磨した後、５％ナイタール腐食を行い、倍率３０倍で光学顕微鏡観察を行って、凝固組織、γ粒界におけるフィルム状のフェライトの生成の有無、不明瞭なγ粒界の鋳片表面からの深さなどを確認した。表２に試験条件と試験結果を示す。
【００４０】
【表２】
【００４１】
この試験Ｎｏ．１で得られた鋳片表面の凝固組織は、γ粒界に粒状のフェライトが生成したフェライトおよびパーライトの混合組織であり、γ粒界の不明瞭な凝固組織であった。また、それらγ粒界が不明瞭な深さは、鋳片表面から深さ３．７ｍｍまでの領域であった。鋳片表面の割れ発生の評価は評価Ａで、横割れなどの割れは発生しなかった。
【００４２】
本発明例の試験Ｎｏ．２では、鋳型出口から最長４．５ｍまでの間で鋳片を二次冷却しつつ、速度１．０ｍ／分でスラブを鋳造した。二次冷却の比水量は、鋳型出口から１ｍまでの間では０．４リットル／ｋｇ−鋼、鋳型出口からの距離が、１ｍを超えて４．５ｍまでの間では０．５リットル／ｋｇ−鋼とした。上記条件で鋳片を二次冷却することにより、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却した後に、Ａｒ３ 変態点を超える温度に復熱させることができた。その際、鋳片の表面温度が到達した最低の表面温度Ｔｍｉｎ は７７０℃であった。また、鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔは２１０ｓであった。上記鋳片の表面温度が到達した最低の表面温度Ｔｍｉｎ 、Ａｒ３ 変態点より低い温度に保持する時間ｔの条件は、本発明の方法で規定する条件の範囲内である。また、鋳片の表面温度をＡｒ３ 変態点を超える温度に復熱させた後、さらに鋳片の二次冷却を行ない、矯正位置での鋳片の表面温度を、この鋼の脆化温度域である８２１℃とした。
【００４３】
この試験Ｎｏ．２で得られた鋳片表面の凝固組織は、γ粒界に粒状のフェライトが生成したフェライトおよびパーライトの混合組織であり、γ粒界の不明瞭な凝固組織であった。また、それらγ粒界が不明瞭な深さは、鋳片表面から深さ２．３ｍｍまでの領域であった。矯正時の鋳片の表面温度を脆化温度域としたにもかかわらず、鋳片表面の割れ発生の評価は評価Ａで、横割れなどの割れは発生しなかった。
【００４４】
本発明例の試験Ｎｏ．３では、鋳型出口から最長２．０ｍまでの間で鋳片を二次冷却しつつ、速度０．５ｍ／分でブルームを鋳造した。二次冷却の比水量は、鋳型出口から１ｍまでの間では１．３リットル／ｋｇ−鋼、鋳型出口からの距離が、１ｍを超えて２．０ｍまでの間では０．７リットル／ｋｇ−鋼とした。上記条件で鋳片を二次冷却することにより、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却した後に、Ａｒ３ 変態点を超える温度に復熱させることができた。その際、鋳片の表面温度が到達した最低の表面温度Ｔｍｉｎ は６１０℃であった。また、鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔは１９０ｓであった。上記鋳片の表面温度が到達した最低の表面温度Ｔｍｉｎ 、Ａｒ３ 変態点より低い温度に保持する時間ｔの条件は、本発明の方法で規定する条件の範囲内である。また、矯正位置での鋳片の表面温度は、この鋼の脆化温度域よりも高い８７０℃であった。
【００４５】
この試験Ｎｏ．３で得られた鋳片表面の凝固組織は、γ粒界に粒状のフェライトが生成したフェライトおよびパーライトの混合組織であり、γ粒界の不明瞭な凝固組織であった。また、それらγ粒界が不明瞭な深さは、鋳片表面から深さ５．１ｍｍまでの領域であった。鋳片表面の割れ発生の評価は評価Ａで、横割れなどの割れは発生しなかった。
【００４６】
比較例の試験Ｎｏ．４では、鋳型出口から最長１．０ｍまでの間でのみ、鋳片を二次冷却しつつ、速度１．２ｍ／分でスラブを鋳造した。その間の二次冷却の比水量は０．４リットル／ｋｇ−鋼とした。上記条件で鋳片を二次冷却することにより、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却した後に、Ａｒ３ 変態点を超える温度に復熱させることができた。その際、鋳片の表面温度が到達した最低の表面温度Ｔｍｉｎ は７９０℃であった。この最低の表面温度Ｔｍｉｎ の条件は、本発明の方法で規定する条件の範囲内である。しかし、二次冷却を行う領域およびそのときの比水量が少ないため、鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔは４０ｓと短かった。このＡｒ３変態点より低い温度に保持する時間ｔの条件は、本発明の方法で規定する条件を外れて短い時間である。矯正位置での鋳片の表面温度は、この鋼の脆化温度域よりも高い９３５℃であった。
【００４７】
この試験Ｎｏ．４で得られた鋳片表面の凝固組織は、フェライトおよびパーライトの混合組織であったが、γ粒界にフェライトがフィルム状に生成して、明瞭なγ粒界が認められた。鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間が短かいので、フェライトをγ粒界に粒状に十分生成させることができず、鋳片の表面温度をＡｒ３ 変態点を超える温度に復熱させた際に、γ粒界に粒状に析出したフェライトの痕跡が残らなかった。そのため、その後に鋳片の表面温度がＡｒ３ 変態点より低い温度になる過程で、γ粒界にフェライトがフィルム状に生成したため、γ粒界が明瞭になった。したがって、脆化温度域より高温の９３５℃で矯正したにもかかわらず、鋳片表面の割れ発生の評価は評価Ｃで、γ粒界に沿って著しい横割れが発生した。
【００４８】
比較例の試験Ｎｏ．５では、鋳型出口から最長１．０ｍまでの間でのみ、鋳片を二次冷却しつつ、速度０．７５ｍ／分でスラブを鋳造した。その間の二次冷却の比水量は０．２リットル／ｋｇ−鋼とした。上記条件で鋳片を二次冷却することにより、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却した後に、Ａｒ３ 変態点を超える温度に復熱させることができた。その際、鋳片の表面温度が到達した最低の表面温度Ｔｍｉｎ は８１５℃であった。しかし、この最低の表面温度Ｔｍｉｎ の条件は、本発明の方法で規定する条件を外れて高い温度である。二次冷却を行う領域が短く、かつ、そのときの比水量が少ないためである。鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔは２００ｓであり、この保持する時間ｔの条件は、本発明の方法で規定する条件の範囲内の時間である。矯正位置での鋳片の表面温度は、この鋼の脆化温度域よりも高い８８０℃であった。
【００４９】
この試験Ｎｏ．５で得られた鋳片表面の凝固組織は、γ粒界に粒状のフェライトが生成したフェライトおよびパーライトの混合組織であり、γ粒界の不明瞭な凝固組織であった。しかし、それらγ粒界が不明瞭な厚さは、鋳片表面から深さ１．１ｍｍまでの浅い領域であった。鋳片の到達する最低の表面温度Ｔｍｉｎ が高く、Ａｒ３ 変態点より低い温度に保持する時間ｔが前述の（イ）式を満足するなかで短いので、不明瞭なγ粒界の存在する鋳片表面からの厚さ方向の深さが浅くなった。そのため、矯正位置での鋳片の表面温度は脆化温度域より高温であるものの、鋳片表面の割れ発生の評価は評価Ｂで、横割れなどの割れが発生した。γ粒界が不明瞭な鋳片表面からの厚さが薄いために、γ粒界が不明瞭な凝固組織よりも深い領域の鋳片の内部に発生した横割れなどの割れが、鋳片を矯正する際に鋳片表面に露出した。
【００５０】
比較例の試験Ｎｏ．６では、鋳型出口から最長５．０ｍまでの間で鋳片を二次冷却しつつ、速度０．７５ｍ／分でスラブを鋳造した。二次冷却の比水量は、鋳型出口から１ｍまでの間では０．１リットル／ｋｇ−鋼、鋳型出口からの距離が、１ｍを超えて５．０ｍまでの間では０．４リットル／ｋｇ−鋼とした。上記条件で鋳片を二次冷却することにより、鋳片の表面温度をいったんＡｒ３ 変態点より低い温度に冷却した後に、Ａｒ３ 変態点を超える温度に復熱させ、その後に鋳片を矯正することができた。いったんＡｒ３ 変態点より低い温度に冷却した後にＡｒ３ 変態点を超える温度に復熱させるまでの間で、鋳片の表面温度が到達した最低の表面温度Ｔｍｉｎ は８３０℃であった。しかし、この最低の表面温度の条件は、本発明の方法で規定する条件を外れて高い温度である。二次冷却の比水量が少ないためである。鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔは４００ｓであり、この保持する時間ｔは、本発明の方法で規定する条件の範囲内の時間である。矯正位置での鋳片の表面温度は、この鋼の脆化温度域よりも高い８６１℃であった。
【００５１】
この試験Ｎｏ．６で得られた鋳片表面の凝固組織は、フェライトおよびパーライトの混合組織であったが、γ粒界にフェライトがフィルム状に生成して、明瞭なγ粒界が認められた。鋳片の到達する最低の表面温度Ｔｍｉｎ が高く、Ａｒ３ 変態点より低い温度に保持する時間ｔが前述の（イ）式を満足するなかで長目であったので、γ粒界にフェライトがフィルム状に生成した。したがって、脆化温度域より高温の８６１℃で矯正したにもかかわらず、鋳片表面の割れ発生の評価は評価Ｃで、γ粒界に沿って著しい横割れが発生した。
【００５２】
比較例の試験Ｎｏ．７では、鋳型出口から最長５．０ｍまでの間で鋳片を二次冷却しつつ、速度０．５ｍ／分でブルームを鋳造した。二次冷却の比水量は、鋳型出口から１ｍまでの間では１．３リットル／ｋｇ−鋼、鋳型出口からの距離が、１ｍを超えて５．０ｍまでの間では２．０リットル／ｋｇ−鋼とした。鋳片の表面温度が到達した最低の表面温度Ｔｍｉｎ は６０５℃と低く、しかも、鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔは５２０ｓと長くなった。上記最低の表面温度の条件は、本発明の方法で規定する条件の範囲内であるが、上記Ａｒ３ 変態点より低い温度に保持する時間ｔの条件は、本発明の方法で規定する条件を外れて、時間が長い。その後、鋳片の表面温度は復熱したが、Ａｒ３ 変態点を超えなかった。このＡｒ３ 変態点を超える温度に復熱しなかったことは、本発明の方法で規定する条件を外れている。また、矯正位置での鋳片の表面温度は、この鋼の脆化温度域よりも高い８６０℃であった。
【００５３】
この試験Ｎｏ．７では、得られた鋳片表面の凝固組織はフェライトおよびパーライトの混合組織であり、γ粒界にはフェライトがフィルム状に生成していた。Ａｒ３ 変態点より低い温度に保持する時間ｔが長いため、γ粒界へのフェライトの生成が促進され、フェライトがγ粒界にフィルム状に発達し、さらに、Ａｒ３ 変態点を超える温度に復熱しなかったため、さらにフェライトがγ粒界にフィルム状に発達した。そのため、脆化温度域より高温の８６０℃で矯正したにもかかわらず、鋳片表面の割れ発生の評価は評価Ｃで、γ粒界に沿って著しい横割れが発生した。
【００５４】
比較例の試験Ｎｏ．８では、鋳型出口から最長２．０ｍまでの間を二次冷却しつつ、速度０．５ｍ／分でブルームを鋳造した。二次冷却の比水量は、鋳型出口から１ｍまでの間では２．０リットル／ｋｇ−鋼、鋳型出口からの距離が、１ｍを超えて５．０ｍまでの間では０．７リットル／ｋｇ−鋼とした。鋳片の表面温度が到達した最低の表面温度Ｔｍｉｎ は４８０℃と低く、鋳片の表面温度をＡｒ３ 変態点より低い温度に保持する時間ｔは１９０ｓであった。上記最低の表面温度の条件は、本発明の方法で規定する条件を外れて低い温度である。とくに、鋳型出口からの距離が、１ｍを超えて５．０ｍまでの間における二次冷却の比水量が多いためである。また、上記Ａｒ３ 変態点より低い温度に保持する時間ｔの条件は、本発明の方法で規定する条件の範囲内である。その後、鋳片の表面温度は復熱したが、Ａｒ３ 変態点を超えなかった。このＡｒ３ 変態点を超える温度に復熱しなかったことは、本発明の方法で規定する条件を外れている。また、矯正位置での鋳片の表面温度は、この鋼の脆化温度域よりも高い８５２℃であった。
【００５５】
この試験Ｎｏ．８では、得られた鋳片表面の凝固組織はフェライトおよびパーライトの混合組織であり、γ粒界にはフェライトがフィルム状に生成していた。鋳片表面が過冷却され、復熱時に鋳片の表面温度がＡｒ３ 変態点を超える温度に復熱しなかったため、鋳片の冷却過程で、γ粒界にフェライトがフィルム状に生成し、明瞭なγ粒界が認められた。そのため、脆化温度域より高温の８５２℃で矯正したにもかかわらず、鋳片表面の割れ発生の評価は評価Ｃで、γ粒界に沿って著しい横割れが発生した。
【００５６】
【発明の効果】
本発明の連続鋳造方法の適用により、横割れ、横ひび割れなどの割れのない良好な表面品質を有する鋳片を安定して得ることができる。
【図面の簡単な説明】
【図１】γ粒界が不明瞭なフェライトおよびパーライトの混合組織の生成に及ぼす、鋳片の表面温度がＡｒ３ 変態点より低い温度で保持される時間およびＡｒ３ 変態点より低い温度である鋳片の表面温度が到達する最低の表面温度の影響を示す図である。
【図２】本発明の連続鋳造方法を実施する場合の連続鋳造装置の例を示す模式図である。
【符号の説明】
１：鋳型 ２：凝固殻
３：ガイドロール対 ４：スプレーノズル
５：未凝固の溶鋼を含む鋳片 ６：ピンチロール
７：矯正位置のピンチロール ８：溶鋼
９：完全に凝固した鋳片[0001]
BACKGROUND OF THE INVENTION
The present invention is a continuous casting method characterized by secondary cooling conditions.To the lawRelated.
[0002]
[Prior art]
For the purpose of improving the mechanical properties of the thick steel plate, a low alloy steel containing an alloy element such as Nb, V, Ni, or Cu is often used. However, when these low alloy steels are cast using a curved or vertical bending type continuous casting machine, lateral cracks or lateral cracks (hereinafter sometimes simply referred to as cracks) are likely to occur on the surface of the slab. The stress acting on the slab surface during straightening of the slab exceeds the limit stress inherent in the low alloy steel, and cracks occur. These cracks on the slab surface cause surface flaws on a thick steel plate that is hot-rolled using the slab as a raw material.
[0003]
The hot ductility of a slab of low alloy steel is such that the solidification structure of the slab is transformed from an austenite (hereinafter sometimes referred to as γ) phase to a ferrite (hereinafter sometimes referred to as α) phase.3 In the vicinity of the temperature of the transformation point, that is, in the temperature range of 600 to 850 ° C., the temperature drops significantly. Further, in a slab of low alloy steel, AlN, NbC, and the like are precipitated at the γ grain boundary during the secondary cooling, so that the γ grain boundary is easily embrittled. Therefore, when these low alloy steel slabs are straightened in the temperature range of 600 to 850 ° C., cracks are likely to occur on the slab surface due to a decrease in hot ductility and embrittlement of γ grain boundaries.
[0004]
Therefore, the surface temperature of the slab at the time of straightening is avoided on the low temperature side or the high temperature side of the temperature range (hereinafter referred to as the embrittlement temperature range) where the hot ductility is reduced to 600 to 850 ° C. Generally, a method for preventing the occurrence of the above is taken. However, since conditions such as secondary cooling of the slab and casting speed change during casting, the surface temperature of the slab changes during casting. Therefore, the slab may be corrected in the embrittlement temperature range, and in that case, a crack occurs on the surface of the slab.
[0005]
In JP-A-9-253814, the slab is strongly cooled below the mold outlet, and the surface temperature of the slab is once set to Ar.3 After the temperature lower than the transformation point, Ar on the higher temperature side than the embrittlement temperature range3 There has been proposed a method for preventing the occurrence of cracks on the surface of the slab by reheating to a temperature exceeding the transformation point and then correcting the slab.
[0006]
In this method, the surface temperature of the slab is once set to Ar.3 After making the temperature lower than the transformation point, Ar3 By reheating to a temperature exceeding the transformation point, and making the solidified structure of the slab a mixed structure of ferrite and pearlite in which the γ grain boundary is unclear, the cracking susceptibility of the slab is reduced, and at the time of correction This is a method for preventing the occurrence of cracks on the slab surface. However, in this method, cracks may occur on the surface of the slab depending on the secondary cooling conditions of the slab, and further improvement is desired.
[0007]
[Problems to be solved by the invention]
The present invention provides a continuous casting method capable of stably obtaining a slab having a good surface quality free from transverse cracks or lateral cracks.The lawThe purpose is to provide.
[0008]
[Means for Solving the Problems]
The gist of the present invention is,sideWhen casting a slab with a rectangular cross-section using a curved or vertical bending type continuous casting machine, secondary chilling of the slab is performed immediately after the slab is pulled out of the mold, and the surface temperature of the slab is adjusted. Once ArThreeAfter cooling to a temperature below the transformation point, ArThreeA continuous casting method for reheating to a temperature exceeding the transformation point and then correcting the slab, wherein the surface temperature of the slab is ArThreeHolding time t (s) at a temperature lower than the transformation point, and once ArThreeAfter cooling to a temperature below the transformation point, ArThreeThe minimum surface temperature T at which the surface temperature of the slab reaches the temperature until reheating to a temperature exceeding the transformation pointmin(° C.) is subjected to secondary cooling of the slab so that the following formulas (a) and (b) are satisfied, whereby the solidified structure from the slab surface to a depth of at least 2 mm is changed to an austenite grain boundary. Casting method with mixed structure of ferrite and pearlite with unclearIt is in.
50 ≦ t (s) ≦ 500 (A)
0.13 × t + 493 ≦ Tmin(° C.) ≦ 0.045 × t + 798 (B)
BookThe “slab having a rectangular cross-sectional shape” as defined in the invention means a slab or bloom having a rectangular or square cross-sectional shape.
[0009]
The “slab surface temperature” defined in the present invention is, for example, a surface temperature that can be measured by a radiation thermometer, and a surface temperature that can also be obtained by calculation by solidification heat transfer analysis. is there. When determining the chemical composition of the steel, the size of the slab, the casting speed, the secondary cooling conditions of the slab, etc., the surface temperature of the slab according to the distance from the meniscus in the mold should be obtained. Can do. By appropriately selecting the surface heat transfer coefficient, the surface temperature of the slab obtained by this calculation can be made to agree well with the actually measured surface temperature.
[0010]
Even if the slab is corrected without avoiding the temperature range of 600 to 850 ° C., which is the embrittlement temperature range of the low alloy steel, the solidification structure of the slab from the slab surface to a depth of at least 2 mm becomes a γ grain boundary. However, it is possible to stably prevent the occurrence of lateral cracks or lateral cracks on the surface of the slab by using a mixed structure of ferrite and pearlite that is unclear. The reason is that, on the slab surface in which the solidified structure is a mixed structure of ferrite and pearlite in which the γ grain boundary is unclear, the limit stress inherent to the steel against cracking increases.
[0011]
Such a mixed structure of ferrite and pearlite in which the γ grain boundary is unclear is from the high temperature side to the Ar3 When the slab is cooled to a lower temperature side than the transformation point, it means a solidified structure in which ferrite is produced in a granular form at the γ grain boundary. Since the ferrite is formed granularly at the γ grain boundary, the γ grain boundary becomes unclear. These solidified structures are obtained by cutting and polishing an optical microscope observation sample so as to include the slab surface from the slab cross-sectional sample, and, for example, at a magnification of about 10 to 50 times after performing 5% nital corrosion. This can be confirmed by observing with an optical microscope.
[0012]
The solidified structure inside the slab whose depth from the slab surface exceeds 2 mm is a clear structure of the γ grain boundary, and cracks occur in the clear region of the deep γ grain boundary when the slab is straightened. Even so, surface flaws do not occur on the surface of the thick steel plate hot-rolled using the slab as a raw material. This is because the area where the cracks of the slab are present is a deep position inside the slab, and these cracks are pressure-bonded during rolling.
[0013]
The surface temperature of the slab proposed in the aforementioned Japanese Patent Application Laid-Open No. 9-253814 is once determined as Ar.3 After making the temperature lower than the transformation point, Ar3 By reheating to a temperature exceeding the transformation point, cracks may occur on the surface of the slab even if the solidified structure of the slab is made a mixed structure of ferrite and pearlite whose γ grain boundary is unclear. is there. The reason is that the surface temperature of the slab is Ar3 Time held at a temperature lower than the transformation point and Ar3 Depending on the condition of the minimum surface temperature at which the surface temperature of the slab that is lower than the transformation point reaches, it may be difficult to make the solidified structure of the surface of the slab into a solidified structure with an unclear target γ grain boundary. Because there is.
[0014]
FIG. 1 shows that the surface temperature of the slab affected by the formation of a mixed structure of ferrite and pearlite with an unclear γ grain boundary is Ar3 Time t (s) held at a temperature lower than the transformation point and Ar3 The lowest surface temperature T reached by the surface temperature of the slab, which is lower than the transformation pointmin It is a figure which shows the influence of (degreeC).
[0015]
Using a vertical bending type continuous casting machine, a low alloy steel containing C: 0.05 to 0.07 mass%, Ni: 0.6 to 0.7 mass%, etc. is cast at a casting speed of 0.75 to 1.2 m. Slabs when cast by changing the secondary cooling conditions of slabs to slabs with a thickness of 230 mm and width of 2300 mm per minute, or to blooms with a thickness of 300 mm and width of 650 mm at a casting speed of 0.5 m / min. It is a figure which shows the test result of the presence or absence of generation | occurrence | production of the crack of the surface.
[0016]
The circles in FIG. 1 indicate that the region where the mixed structure of ferrite and pearlite in which the γ grain boundary is unclear is a depth of 2 mm or more from the slab surface. It means that there are no cracks. The symbol “Δ” means that a region having a mixed structure of ferrite and pearlite in which the γ grain boundary is unclear exists at a depth of less than 2 mm from the slab surface. Further, the x mark means that at least a region from the slab surface to a depth of 2 mm has a mixed structure of ferrite and pearlite with a clear γ grain boundary. It was confirmed that lateral cracks or lateral cracks were generated on the surface of the slab indicated by Δ and X.
[0017]
From FIG. 1, the surface temperature of the slab is expressed as Ar.3 The time t (s) for holding at a temperature lower than the transformation point, and the lowest surface temperature T at which the surface temperature of the slab reachesmin By performing secondary cooling of the slab so that (° C.) satisfies the above-mentioned formulas (a) and (b), the solidified structure of the slab from the slab surface to a depth of at least 2 mm, It was found that a mixed structure of ferrite and pearlite having a stable γ grain boundary could be obtained. Furthermore, it was found that such a solidified structure can stably prevent occurrence of lateral cracks or lateral cracks on the surface of the slab.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In the method of the present invention, a slab or bloom having a rectangular or square cross-sectional shape is cast using a curved or vertical bending type continuous casting machine. The method of the present invention is suitable for casting a slab or bloom having a thickness of 150 to 400 mm from a low alloy steel containing an alloy element such as Nb, V, Ni, or Cu. When casting such a low alloy steel to a slab or bloom of the above thickness using a curved or vertical bending type continuous casting machine, lateral cracks or lateral cracks occur on the slab surface during straightening of the slab. It is easy.
[0019]
FIG. 2 is a schematic view showing an example of a continuous casting apparatus when the continuous casting method of the present invention is carried out. An example using a vertical bending type continuous casting machine will be described.
[0020]
In the method of the present invention, secondary cooling of the slab is performed immediately after the slab is pulled out of the mold, and the surface temperature of the slab is once set to Ar.3 After cooling to a temperature below the transformation point, Ar3 Reheat to a temperature above the transformation point, and then correct the slab. At that time, the surface temperature of the slab is set to Ar.3 Holding time t (s) at a temperature lower than the transformation point, and once Ar3 After cooling to a temperature below the transformation point, Ar3 The minimum surface temperature T at which the surface temperature of the slab reaches the temperature until reheating to a temperature exceeding the transformation pointmin The slab is subjected to secondary cooling so that (° C.) satisfies the above-mentioned formulas (a) and (b).
[0021]
Once the surface temperature of the slab is Ar3 After cooling to a temperature below the transformation point, Ar3 The reason for reheating to a temperature exceeding the transformation point is to make the solidified structure of the slab a mixed structure of ferrite and pearlite in which the γ grain boundary is unclear.
[0022]
Once the surface temperature of the slab is Ar3 After cooling to a temperature below the transformation point, Ar3 The surface temperature of the slab when reheating to a temperature exceeding the transformation point and then straightening the slab is preferably higher than the embrittlement temperature range inherent to low alloy steel, but the embrittlement temperature range You can correct it with In the method of the present invention, even if correction is performed in the embrittlement temperature range, the occurrence of cracks on the surface of the slab can be prevented.
[0023]
The surface temperature of the slab is Ar3 If the time t kept at a temperature lower than the transformation point is less than 50 s, the holding time is short, and ferrite cannot be sufficiently formed in the γ grain boundary. Then, the surface temperature of the slab is changed to Ar3 When reheated to a temperature exceeding the transformation point, no trace of ferrite precipitated in the gamma grain boundary remains, so the surface temperature of the slab is set to Ar after that.3 When the temperature is lower than the transformation point, the solidified structure of the slab becomes a mixed structure of ferrite and pearlite in which ferrite is formed in a film shape at the γ grain boundary, and the γ grain boundary becomes clear. If the slab is corrected in this state, cracks occur on the surface of the slab.
[0024]
Ar3 When the time t kept at a temperature lower than the transformation point exceeds 500 s, since the holding time is long, the generation of ferrite at the γ grain boundary is promoted, and the ferrite develops in a film form at the γ grain boundary. Then, the surface temperature of the slab is changed to Ar3 When reheated to a temperature exceeding the transformation point, traces of film-like ferrite remain at the γ grain boundaries. After that, the surface temperature of the slab is changed to Ar3 When the temperature is lower than the transformation point, ferrite is formed in a film form on the film-like ferrite traces at the γ grain boundary, so the solidified structure of the slab is a ferrite in which ferrite is formed in a film form at the γ grain boundary. And a pearlite mixed structure, and the γ grain boundary becomes clear. If the slab is corrected in this state, cracks occur on the surface of the slab.
[0025]
Ar3 Under the condition that the time t for maintaining the temperature lower than the transformation point satisfies the above-mentioned formula (a), the surface temperature of the slab is once set to Ar.3 The lowest surface temperature T that the slab surface temperature reaches when cooling to a temperature lower than the transformation pointmin However, if the value is less than the value on the left side of the above-mentioned formula (b), it means that the slab surface is supercooled, and the surface temperature of the slab is Ar when the slab surface is reheated.3 It becomes difficult to reheat to a temperature exceeding the transformation point. When the slab surface is further cooled from this state, the solidified structure of the slab becomes a mixed structure of ferrite and pearlite in which ferrite is formed in a film shape at the γ grain boundary, and the γ grain boundary becomes clear. If the slab is corrected in this state, cracks occur on the surface of the slab.
[0026]
Ar3 Under the condition that the time t for maintaining the temperature lower than the transformation point satisfies the above-mentioned formula (a), the surface temperature of the slab is once set to Ar.3 The lowest surface temperature T that the slab surface temperature reaches when cooling to a temperature lower than the transformation pointmin Is greater than the value on the right side of the aforementioned equation (b), Ar3 When the time t maintained at a temperature lower than the transformation point is short while satisfying the formula (a), the solidified structure of the slab becomes a mixed structure of ferrite and pearlite in which ferrite is produced in a granular form at the γ grain boundary, The γ grain boundary becomes unclear. However, the depth in the thickness direction from the slab surface of the unclear region is less than 2 mm. If the slab is corrected in this state, cracks occur on the surface of the slab.
[0027]
On the other hand, the lowest surface temperature Tmin Is greater than the value on the right side of the aforementioned equation (b), Ar3 When the time t kept at a temperature lower than the transformation point is long while satisfying the formula (a), the solidified structure of the slab becomes a mixed structure of ferrite and pearlite in which ferrite is formed in a film shape at the γ grain boundary. Γ grain boundary becomes clear. If the slab is corrected in this state, cracks occur on the surface of the slab.
[0028]
In the case of a slab having a thickness of 150 to 300 mm, the specific water amount for secondary cooling of the slab is 0.3 to 0.65 liter / kg-steel between 1 m from the mold outlet and from the mold outlet. It is desirable that the slab is secondary cooled with a specific water amount of secondary cooling of the slab of 0.25 to 0.55 liter / kg-steel in an arbitrary range from 1 m to 5 m. In the case of a bloom having a thickness of 150 to 300 mm, the specific water amount for secondary cooling of the slab is 1.05 to 1.6 liter / kg-steel between the mold outlet and 1 m, and the mold The secondary cooling of the slab is performed by setting the specific water amount of secondary cooling of the slab to 0.65 to 0.95 liter / kg-steel in an arbitrary range from 1 m to 5 m from the outlet. desirable.
[0029]
Furthermore, in the case of a slab having a thickness of more than 300 mm to 400 mm, the specific water amount for secondary cooling of the slab is 0.65 to 1.0 liter / kg-steel between the mold outlet and 1 m, and When the distance from the mold outlet exceeds 1 m to 5 m, secondary cooling of the slab is performed by setting the specific water amount of secondary cooling of the slab to 0.55 to 0.75 liter / kg-steel. In addition, in the case of a bloom having a thickness of more than 300 mm to 400 mm, the specific water amount for secondary cooling of the slab is 1.6 to 1.95 liters / kg-steel between the mold outlet and 1 m. And in the arbitrary range where the distance from the mold outlet exceeds 1 m to 5 m, the secondary water of the secondary cooling of the slab is 0.95 to 1.15 liter / kg-steel, and the slab is secondary It is desirable to cool.
[0030]
In the case of the slab or bloom described above, by setting the specific water amount for the secondary cooling, the solidified structure of the slab from the surface to a depth of at least 2 mm in the thickness direction, ferrite and pearlite with unclear γ grain boundaries. Therefore, the occurrence of cracks on the surface of the slab can be stably prevented.
[0031]
Once the surface temperature of the slab is Ar3 After cooling to a temperature below the transformation point, Ar3 When reheating to a temperature exceeding the transformation point, the surface temperature of the slab is changed to Ar3 Holding time t below the transformation point, and once Ar3 After cooling to a temperature below the transformation point, Ar3 The minimum surface temperature T at which the surface temperature of the slab reaches the temperature until reheating to a temperature exceeding the transformation pointmin However, the secondary cooling of the slab so as to satisfy the above-mentioned formulas (a) and (b) may be repeated one or more times before the slab is corrected. The depth from the surface of the slab where a solidified structure in which the γ grain boundary is unclear exists more effectively.
[0032]
【Example】
In the apparatus configuration shown in FIG. 2, a vertical bending type continuous casting machine having a vertical portion length of 3 m is used to change the conditions of the shape of the slab, the casting speed, and the specific water amount of the secondary cooling of the slab. A low alloy steel containing Nb, Cu and Ni having chemical compositions shown in Table 1 was cast. Ar of this steel3 The transformation point is 892 ° C and the embrittlement temperature range is 720-850 ° C.
[0033]
[Table 1]
[0034]
The conditions for secondary cooling of the slab and bloom are shown in detail in Table 2 to be described later. That is, between the mold outlet and 1.0 m, both the slab and the bloom are subjected to secondary cooling of the slab and the surface temperature of the slab is set to Ar.3 The temperature is lowered to a temperature lower than the transformation point, and the minimum surface temperature T reached by the surface temperature of the slabmin (° C) was changed. In addition, when the distance from the mold outlet exceeds 1.0 m to 5 m, secondary cooling of the slab is performed between 1.0 m and an arbitrary Xm, and the surface temperature of the slab is set to Ar.3 The time t (s) for holding at a temperature lower than the transformation point is changed, and the minimum surface temperature T at which the surface temperature of the slab reaches is reached.min (° C) was changed. The condition of the secondary cooling means that the secondary cooling of the slab was performed from the mold outlet to the longest Xm.
[0035]
However, in the test for casting a part of the slab, secondary cooling of the slab was not performed when the distance from the mold outlet exceeded 1.0 m to 5 m. Further, test No. described later. In No. 2, the secondary cooling of the slab was additionally performed on the downstream side of the secondary cooling region, and the surface temperature of the slab at the correction position was adjusted.
[0036]
In each test, casting was continuously performed for 3 heats. At that time, the surface temperature of the slab was measured in a region from the mold exit to the correction position by a radiation thermometer during casting. From these measurement results, the surface temperature of the slab is Ar3 Check whether the temperature is lower than the transformation point, and the surface temperature of the slab is Ar3 Time t (s) held at a temperature lower than the transformation point, once Ar3 After cooling to a temperature below the transformation point, Ar3 The minimum surface temperature T at which the surface temperature of the slab reaches the temperature until reheating to a temperature exceeding the transformation pointmin (° C.) and the surface temperature of the slab at the correction position.
[0037]
In some tests, the surface temperature of the slab is measured by inserting a thermocouple into the slab surface immediately after secondary cooling, and the slab size, casting speed, and secondary cooling of the slab are measured. The surface temperature of the slab corresponding to the conditions was calculated by calculation by solidification heat transfer analysis. It was confirmed that the surface temperatures of the slabs obtained by calculation using these radiation thermometers, thermocouples and solidification heat transfer analysis were in good agreement.
[0038]
In each test, a slab sample having a length of 1 m in the casting direction was collected, and in order to facilitate observation of cracks on the slab surface, the surface was scarfed to remove oxide on the slab surface. Thereafter, a die check (dye penetration test) was performed to visually observe the occurrence of lateral cracks or lateral cracks on the slab surface, and the cracks were evaluated. Evaluation A is a state in which these cracks are not generated, Evaluation B is a state in which cracks are generated to the extent that the slab surface needs to be cleaned before rolling the slab hot, Evaluation C is Each means a state in which significant cracking has occurred to such an extent that it is difficult to remove even by maintenance.
[0039]
Moreover, before scarfing the slab sample, from the center of the width at the end of the cut surface, 10 mm in the casting direction of the slab surface (corresponding to the upper surface during casting), 20 mm in the width direction, and the slab surface A 20 mm sample for optical microscope observation was cut out in the thickness direction. After the surface corresponding to the cross section of the slab sample is polished, 5% nital corrosion is performed, and optical microscope observation is performed at a magnification of 30 times, whether or not film-like ferrite is formed at the solidified structure and γ grain boundary. The depth of the clear γ grain boundary from the slab surface was confirmed. Table 2 shows test conditions and test results.
[0040]
[Table 2]
[0041]
This test No. The solidified structure on the surface of the slab obtained in 1 was a mixed structure of ferrite and pearlite in which granular ferrite was formed at the γ grain boundary, and was an unclear solidified structure at the γ grain boundary. The depth at which the γ grain boundaries are unclear was a region from the slab surface to a depth of 3.7 mm. Evaluation of occurrence of cracks on the surface of the slab was evaluation A, and cracks such as transverse cracks did not occur.
[0042]
Test no. In No. 2, the slab was cast at a speed of 1.0 m / min while the slab was secondarily cooled from the mold outlet to a maximum length of 4.5 m. The specific water amount of the secondary cooling is 0.4 liter / kg − steel between 1 m from the mold outlet and 0.5 liter / kg − when the distance from the mold outlet exceeds 1 m to 4.5 m. Made of steel. By secondary cooling of the slab under the above conditions, the surface temperature of the slab is once set to Ar3 After cooling to a temperature below the transformation point, Ar3 It was possible to reheat to a temperature exceeding the transformation point. At that time, the lowest surface temperature T reached by the surface temperature of the slabmin Was 770 ° C. Also, the surface temperature of the slab is Ar3 The time t kept at a temperature lower than the transformation point was 210 s. Minimum surface temperature T reached by the surface temperature of the slabmin , Ar3 The condition for the time t to be held at a temperature lower than the transformation point is within the range of the conditions specified by the method of the present invention. Also, the surface temperature of the slab is Ar3 After reheating to a temperature exceeding the transformation point, secondary cooling of the slab was further performed, and the surface temperature of the slab at the correction position was set to 821 ° C., which is an embrittlement temperature range of this steel.
[0043]
This test No. The solidified structure on the surface of the slab obtained in 2 was a mixed structure of ferrite and pearlite in which granular ferrite was formed at the γ grain boundary, and was an unclear solidified structure at the γ grain boundary. The depth at which the γ grain boundaries are unclear was a region from the slab surface to a depth of 2.3 mm. Although the surface temperature of the slab at the time of straightening was set to the embrittlement temperature range, the evaluation of the crack generation on the surface of the slab was Evaluation A, and cracks such as transverse cracks did not occur.
[0044]
Test no. In No. 3, the bloom was cast at a speed of 0.5 m / min while the slab was secondarily cooled from the mold outlet to a maximum of 2.0 m. The specific water amount of the secondary cooling is 1.3 liter / kg for steel from the mold outlet to 1 m and 0.7 liter / kg for the distance from the mold outlet to more than 2.0 m to 2.0 m. Made of steel. By secondary cooling of the slab under the above conditions, the surface temperature of the slab is once set to Ar3 After cooling to a temperature below the transformation point, Ar3 It was possible to reheat to a temperature exceeding the transformation point. At that time, the lowest surface temperature T reached by the surface temperature of the slabmin Was 610 ° C. Also, the surface temperature of the slab is Ar3 The time t kept at a temperature lower than the transformation point was 190 s. Minimum surface temperature T reached by the surface temperature of the slabmin , Ar3 The condition for the time t to be held at a temperature lower than the transformation point is within the range of the conditions specified by the method of the present invention. Further, the surface temperature of the slab at the correction position was 870 ° C., which was higher than the embrittlement temperature range of this steel.
[0045]
This test No. The solidified structure on the surface of the slab obtained in No. 3 was a mixed structure of ferrite and pearlite in which granular ferrite was formed at the γ grain boundary, and was an unclear solidified structure at the γ grain boundary. The depth at which the γ grain boundaries are unclear was a region from the slab surface to a depth of 5.1 mm. Evaluation of occurrence of cracks on the surface of the slab was evaluation A, and cracks such as transverse cracks did not occur.
[0046]
Test No. of the comparative example. In No. 4, the slab was cast at a speed of 1.2 m / min while the slab was secondarily cooled only from the mold outlet to a maximum of 1.0 m. The specific water amount of the secondary cooling during that period was 0.4 liter / kg-steel. By secondary cooling of the slab under the above conditions, the surface temperature of the slab is once set to Ar3 After cooling to a temperature below the transformation point, Ar3 It was possible to reheat to a temperature exceeding the transformation point. At that time, the lowest surface temperature T reached by the surface temperature of the slabmin Was 790 ° C. This minimum surface temperature Tmin These conditions are within the range defined by the method of the present invention. However, since the secondary cooling area and the specific water amount at that time are small, the surface temperature of the slab is set to Ar.3 The time t kept at a temperature lower than the transformation point was as short as 40 s. This Ar3The condition of the time t that is maintained at a temperature lower than the transformation point is a short time that is outside the condition defined by the method of the present invention. The surface temperature of the slab at the straightening position was 935 ° C., which is higher than the embrittlement temperature range of this steel.
[0047]
This test No. The solidified structure on the surface of the slab obtained in No. 4 was a mixed structure of ferrite and pearlite, but ferrite was formed in a film shape at the γ grain boundary, and a clear γ grain boundary was observed. The surface temperature of the slab is Ar3 Since the time for keeping the temperature lower than the transformation point is short, ferrite cannot be sufficiently formed in the γ grain boundary and the surface temperature of the slab is set to Ar.3 When reheated to a temperature exceeding the transformation point, no trace of ferrite precipitated granularly at the γ grain boundary. Therefore, after that, the surface temperature of the slab is Ar3 In the process of lowering the temperature below the transformation point, ferrite was formed in a film shape at the γ grain boundary, so that the γ grain boundary became clear. Therefore, despite the correction at 935 ° C., which is higher than the embrittlement temperature range, the evaluation of crack generation on the slab surface was evaluation C, and significant lateral cracks occurred along the γ grain boundaries.
[0048]
Test No. of the comparative example. In No. 5, the slab was cast at a speed of 0.75 m / min while the slab was secondarily cooled only from the mold outlet to a maximum of 1.0 m. The specific water quantity of the secondary cooling during that period was 0.2 liter / kg-steel. By secondary cooling of the slab under the above conditions, the surface temperature of the slab is once set to Ar3 After cooling to a temperature below the transformation point, Ar3 It was possible to reheat to a temperature exceeding the transformation point. At that time, the lowest surface temperature T reached by the surface temperature of the slabmin Was 815 ° C. However, this minimum surface temperature Tmin These conditions are high temperatures outside the conditions specified in the method of the present invention. This is because the secondary cooling region is short and the specific water amount at that time is small. The surface temperature of the slab is Ar3 The time t kept at a temperature lower than the transformation point is 200 s, and the condition of the time t kept is a time within the range defined by the method of the present invention. The surface temperature of the slab at the straightening position was 880 ° C., which is higher than the embrittlement temperature range of this steel.
[0049]
This test No. The solidified structure on the surface of the slab obtained in No. 5 was a mixed structure of ferrite and pearlite in which granular ferrite was formed at the γ grain boundary, and was an unclear solidified structure at the γ grain boundary. However, the thickness in which the γ grain boundaries are unclear was a shallow region from the slab surface to a depth of 1.1 mm. Minimum surface temperature T reached by the slabmin Is high, Ar3 Since the time t for holding at a temperature lower than the transformation point is short while satisfying the above-mentioned formula (a), the depth in the thickness direction from the surface of the slab where an unclear γ grain boundary exists becomes shallow. Therefore, although the surface temperature of the slab at the correction position is higher than the embrittlement temperature region, the evaluation of the occurrence of cracks on the surface of the slab was Evaluation B, and cracks such as transverse cracks occurred. Since the thickness from the surface of the slab where the γ grain boundary is unclear is thin, cracks such as transverse cracks generated inside the slab deeper than the solidified structure where the γ grain boundary is unclear It was exposed on the slab surface during correction.
[0050]
Test No. of the comparative example. In No. 6, the slab was cast at a speed of 0.75 m / min while the slab was secondarily cooled from the mold outlet to a maximum of 5.0 m. The specific water amount of the secondary cooling is 0.1 liter / kg − steel between the mold outlet and 1 m, and 0.4 liter / kg − when the distance from the mold outlet exceeds 1 m and 5.0 m. Made of steel. By secondary cooling of the slab under the above conditions, the surface temperature of the slab is once set to Ar3 After cooling to a temperature below the transformation point, Ar3 It was possible to reheat to a temperature above the transformation point and then correct the slab. Once Ar3 After cooling to a temperature below the transformation point, Ar3 The minimum surface temperature T at which the surface temperature of the slab has reached before reheating to a temperature exceeding the transformation pointmin Was 830 ° C. However, this minimum surface temperature condition is a high temperature outside the conditions specified in the method of the present invention. This is because the amount of specific water for secondary cooling is small. The surface temperature of the slab is Ar3 The time t kept at a temperature lower than the transformation point is 400 s, and the time t kept is a time within the range defined by the method of the present invention. The surface temperature of the slab at the correction position was 861 ° C., which was higher than the embrittlement temperature range of this steel.
[0051]
This test No. The solidified structure on the surface of the slab obtained in No. 6 was a mixed structure of ferrite and pearlite, but ferrite formed in a film shape at the γ grain boundary, and a clear γ grain boundary was observed. Minimum surface temperature T reached by the slabmin Is high, Ar3 Since the time t kept at a temperature lower than the transformation point was long while satisfying the above-mentioned formula (a), ferrite was formed in a film shape at the γ grain boundary. Therefore, despite the correction at 861 ° C., which is higher than the embrittlement temperature range, the evaluation of crack generation on the surface of the slab was evaluation C, and significant lateral cracks occurred along the γ grain boundary.
[0052]
Test No. of the comparative example. In No. 7, bloom was cast at a speed of 0.5 m / min while the slab was secondarily cooled from the mold outlet to a maximum of 5.0 m. The specific water amount of the secondary cooling is 1.3 liters / kg for steel from the mold outlet to 1 m and 2.0 liters / kg for the distance from the mold outlet exceeding 1 m to 5.0 m. Made of steel. The lowest surface temperature T reached by the slab surface temperaturemin Is as low as 605 ° C, and the surface temperature of the slab is Ar3 The time t kept at a temperature lower than the transformation point was as long as 520 s. The minimum surface temperature condition is within the range defined by the method of the present invention.3 The condition of the time t that is held at a temperature lower than the transformation point is out of the condition defined by the method of the present invention, and the time is long. After that, the surface temperature of the slab was reheated, but Ar3 The transformation point was not exceeded. This Ar3 The fact that it did not reheat to a temperature exceeding the transformation point is outside the conditions specified by the method of the present invention. Moreover, the surface temperature of the slab in the correction position was 860 ° C., which is higher than the embrittlement temperature range of this steel.
[0053]
This test No. In No. 7, the solidified structure of the obtained slab surface was a mixed structure of ferrite and pearlite, and ferrite was formed in a film shape at the γ grain boundary. Ar3 Since the time t kept at a temperature lower than the transformation point is long, the formation of ferrite at the γ grain boundary is promoted, and the ferrite develops in the form of a film at the γ grain boundary.3 Since it did not reheat to a temperature exceeding the transformation point, ferrite further developed in the form of a film at the γ grain boundary. Therefore, despite the correction at 860 ° C., which is higher than the embrittlement temperature range, the evaluation of the occurrence of cracks on the slab surface was evaluation C, and significant lateral cracks occurred along the γ grain boundaries.
[0054]
Test No. of the comparative example. In No. 8, the bloom was cast at a speed of 0.5 m / min while performing secondary cooling from the mold outlet to a maximum of 2.0 m. The specific water amount of the secondary cooling is 2.0 liter / kg − steel between 1 m from the mold outlet and 0.7 liter / kg − when the distance from the mold outlet exceeds 1 m to 5.0 m. Made of steel. The lowest surface temperature T reached by the slab surface temperaturemin Is as low as 480 ° C, and the surface temperature of the slab is Ar3 The time t kept at a temperature lower than the transformation point was 190 s. The minimum surface temperature condition is a temperature lower than the condition defined by the method of the present invention. This is because the amount of specific water for secondary cooling is particularly large when the distance from the mold outlet exceeds 1 m and reaches 5.0 m. In addition, Ar3 The condition for the time t to be held at a temperature lower than the transformation point is within the range of the conditions specified by the method of the present invention. After that, the surface temperature of the slab was reheated, but Ar3 The transformation point was not exceeded. This Ar3 The fact that it did not reheat to a temperature exceeding the transformation point is outside the conditions specified by the method of the present invention. Moreover, the surface temperature of the slab in the correction position was 852 ° C., which is higher than the embrittlement temperature region of this steel.
[0055]
This test No. In No. 8, the solidified structure of the obtained slab surface was a mixed structure of ferrite and pearlite, and ferrite was formed in a film shape at the γ grain boundary. The surface of the slab is supercooled and the surface temperature of the slab is Ar3 Since it did not reheat to a temperature exceeding the transformation point, ferrite formed in a film shape at the γ grain boundary during the cooling of the slab, and a clear γ grain boundary was observed. Therefore, despite the correction at 852 ° C., which is higher than the embrittlement temperature range, the evaluation of the occurrence of cracks on the slab surface was evaluation C, and significant lateral cracks occurred along the γ grain boundaries.
[0056]
【The invention's effect】
By applying the continuous casting method of the present invention, it has good surface quality without cracks such as transverse cracks and lateral cracks.CastingA piece can be obtained stably.
[Brief description of the drawings]
FIG. 1 shows the effect of the surface temperature of a slab on the formation of a mixed structure of ferrite and pearlite in which the γ grain boundary is unclear.3 Time held at a temperature lower than the transformation point and Ar3 It is a figure which shows the influence of the minimum surface temperature which the surface temperature of the slab which is temperature lower than a transformation point reaches | attains.
FIG. 2 is a schematic view showing an example of a continuous casting apparatus when the continuous casting method of the present invention is carried out.
[Explanation of symbols]
1: Mold 2: Solidified shell
3: Guide roll pair 4: Spray nozzle
5: Cast slab containing unsolidified molten steel 6: Pinch roll
7: Pinch roll at straightening position 8: Molten steel
9: Completely solidified slab
Claims (1)
５０≦ｔ（ｓ）≦５００ ・・・（イ）
０．１３×ｔ＋４９３≦Ｔmin（℃）≦０．０４５×ｔ＋７９８ ・・・（ロ）When casting a slab with a rectangular cross-sectional shape using a continuous or vertical bending type continuous casting machine, the slab is cooled down immediately after it is pulled out of the mold, and the surface temperature of the slab is once after cooling to a temperature lower than the Ar 3 transformation point, is recuperation to a temperature above the Ar 3 transformation point, a continuous casting method then correcting cast slab, the surface temperature Ar 3 transformation point of the slab time t (s) for holding a lower temperature, once in until to recuperator to a temperature above the Ar 3 transformation point after cooling to a temperature lower than the Ar 3 transformation point, the lowest surface temperature of the slab is reached The secondary structure of the slab is cooled so that the surface temperature T min (° C.) satisfies the following formulas (A) and (B): A ferrite and parlor with an austenite grain boundary unclear Continuous casting method characterized by the bets mixed structure of.
50 ≦ t (s) ≦ 500 (A)
0.13 × t + 493 ≦ T min (° C.) ≦ 0.045 × t + 798 (B)
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| KR20170003669A (en) | 2014-07-24 | 2017-01-09 | 제이에프이 스틸 가부시키가이샤 | Method for continuous casting of steel |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| DE102006056683A1 (en) * | 2006-01-11 | 2007-07-12 | Sms Demag Ag | Continuous casting of metal profiles, first cools cast strip then permits thermal redistribution to re-heat surface before mechanical deformation |
| JP4932304B2 (en) * | 2006-03-30 | 2012-05-16 | 株式会社神戸製鋼所 | Steel manufacturing method |
| JP4600436B2 (en) * | 2007-06-20 | 2010-12-15 | 住友金属工業株式会社 | Continuous casting method for slabs |
| JP4445561B2 (en) | 2008-07-15 | 2010-04-07 | 新日本製鐵株式会社 | Continuous casting slab of steel and method for producing the same |
| JP5402790B2 (en) * | 2010-04-01 | 2014-01-29 | 新日鐵住金株式会社 | Method for cooling continuous cast bloom slab and method for manufacturing the slab |
| JP5854071B2 (en) * | 2013-03-29 | 2016-02-09 | Ｊｆｅスチール株式会社 | Steel continuous casting method |
| JP6131833B2 (en) * | 2013-11-08 | 2017-05-24 | 新日鐵住金株式会社 | Method for continuous casting of Ti deoxidized steel |
| JP6369571B2 (en) * | 2015-01-15 | 2018-08-08 | 新日鐵住金株式会社 | Continuous casting method for slabs |
| CN110756756B (en) * | 2019-10-10 | 2021-06-01 | 山东钢铁股份有限公司 | Method for reducing generation rate of cracks on surface of hot-delivery casting blank |
| WO2021256243A1 (en) | 2020-06-18 | 2021-12-23 | Ｊｆｅスチール株式会社 | Continuous casting method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| KR20170003669A (en) | 2014-07-24 | 2017-01-09 | 제이에프이 스틸 가부시키가이샤 | Method for continuous casting of steel |
| CN106536085A (en) * | 2014-07-24 | 2017-03-22 | 杰富意钢铁株式会社 | Method for continuous casting of steel |
| CN106536085B (en) * | 2014-07-24 | 2019-04-19 | 杰富意钢铁株式会社 | The continuous casing of steel |
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