JP4279947B2 - Mg treatment method for molten steel - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、金属ＭｇやＭｇ合金のＭｇ歩留りを高くし、鋳造した鋳片の凝固組織や鋼材の組織を微細にする溶鋼のＭｇ処理方法に関する。
【０００２】
【従来の技術】
従来、鋳片は、溶鋼を造塊法や連続鋳造法等により、スラブやブルーム、ビレット、薄肉鋳片等に鋳造し、これを所定のサイズに切断することにより製造している。また、鋳片を均熱炉等を用いて加熱し、圧延や鍛造等の加工を施すことにより、鋼板や形鋼等の鋼材が製造される。
しかし、鋳片の凝固組織（以下組織という）や鋼材の組織が粗大な場合、組織の粗大化に起因した表面割れ等の表面欠陥や内部割れ、中心偏析、センターポロシティ等の内部欠陥が発生し、鋳片や鋼材の手入れや屑化等による歩留りの低下を招く等の問題がある。
この対策として、特開平７−４８６１６号公報には、溶鋼を覆ったスラグのＭｇＯの含有量を３〜１５質量％、ＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯの総量を５質量％以下に調整したＣａＯ−ＳｉＯ2−Ａｌ2Ｏ3系である溶鋼に、金属ＭｇやＭｇ合金を添加する方法が記載されている。そして、溶鋼に添加したＭｇ歩留りの向上を図り、粗大化し易いＡｌ2Ｏ3を微細な酸化物にして、鋳片や鋼材の欠陥を防止している。
また、特開平９−１９４９８６号公報には、溶鋼にＮｂ、Ｖ、Ｍｏ等を微量添加し、Ｍｇを添加して、さらに加速冷却圧延することにより、微細ベイナイト組織を備えた高強度で靱性に優れた鋼材を製造する方法が開示されている。
【０００３】
【発明が解決しようとする課題】
しかしながら、特開平７−４８６１６号公報では、溶鋼を覆ったスラグのＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯの総量を５質量％以下に調整しているため、スラグ中のＳｉＯ2の含有量が多い場合は、金属ＭｇやＭｇ合金を添加した際に、含まれるＳｉＯ2と反応してＭｇ歩留りが低下する。しかも、Ｍｇ歩留りの低下は、溶鋼中のＡｌ2Ｏ3等をＭｇＯを含む酸化物に改質することができず、Ａｌ2Ｏ3系の粗大な酸化物が形成されて鋳片や鋼材の品質欠陥が生じる。
更に、スラグのＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ（以下スラグ酸化物という）の総量が低下し過ぎると、溶鋼中に添加されたＭｇと反応するスラグ酸化物が不足してＭｇＯを十分に生成できず、凝固核として作用するＭｇＯやＭｇＯを含んだ酸化物を形成することができない。
その結果、鋳片や鋼材等の組織が粗大化して、表面あるいは内部に、割れや中心偏析、センターポロシティ等の欠陥が生じる。
また、特開平９−１９４９８６号公報では、Ｎｂ、Ｖ、Ｍｏ等の微量元素とＭｇを併用添加するため、この微量元素によって鋼材の機械強度が変化し、加工性や絞り性等が要求される鋼材への適用が難しいと言う難点がある。
更に、鋳片を圧延する際に、加速冷却（圧延のパス間で水冷却を行う圧延方法）を行うことによって、鋼材を微細組織にするため、水冷却時間が増加し、圧延等の生産性が低下する。
このように、いずれの方法においても溶鋼に金属ＭｇやＭｇ合金を添加した際に、操業に支障を生じることなく、Ｍｇが酸化してＭｇＯになる歩留りを高め、鋳片の組織や鋼材の組織を微細にして、鋳片及び鋼材の表面や内部の欠陥を抑制し、鋳片及び鋼材の手入れや屑化等を防止して品質の向上を図る方法について具体的に示されていない等の問題がある。
【０００４】
本発明はかかる事情に鑑みてなされたもので、操業に支障を生じることなく、溶鋼中におけるＭｇＯの生成を高めて、鋳片や鋼材の組織を微細にすることができる溶鋼のＭｇ処理方法を提供することを目的とする。
【０００５】
【課題を解決するための手段】
前記目的に沿う本発明の溶鋼のＭｇ処理方法は、溶鋼にＭｇを添加して、凝固組織を微細化する処理方法において、前記溶鋼を覆うスラグ中に、ＦｅＯ、Ｆｅ 2 Ｏ 3 、ＭｎＯ、ＳｉＯ 2 の総重量を１〜１１．３質量％の濃度で含有させ、前記溶鋼を覆う前記スラグの厚みを５０〜２００ｍｍに調整している。
この方法により、スラグに含まれる酸化物の総重量を所定値にしているので、溶鋼に添加したＭｇをＭｇＯやＭｇＯを含む酸化物に生成する歩留りを高くでき、微細なＭｇＯあるいはＭｇＯを含む酸化物（以下ＭｇＯ酸化物という）にして溶鋼中に分散させることができる。
そして、この溶鋼を鋳造した鋳片の組織を微細にすることができ、鋳片の表面に発生する割れやへこみ疵、内部に生じる割れや中心偏析、センターポロシティ等を抑制し、鋳片の手入れや屑化等を防止して良鋳片の歩留りを向上でき、この鋳片に圧延等の加工を施した鋼材の品質も向上できる。
【０００６】
ここで、前記スラグ中の酸化物をＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2とする。
これにより、スラグ中の酸化物によるＭｇの消費を抑制して溶鋼温度の低下やスラグ性状の変化等の操業への支障をなくして、Ｍｇの歩留りを高くして溶鋼に効率良く添加することができる。しかも、溶鋼内にＭｇＯ酸化物を生成し、溶鋼が凝固する際に凝固核として作用させることができる。
【０００７】
更に、前記溶鋼中に含まれるＡｌ2Ｏ3を０．００５〜０．１０質量％にすることが好ましい。
これにより、Ａｌ2Ｏ3系の酸化物の粗大化を抑制し、融点の高いＡｌ2Ｏ3をＭｇＯ・Ａｌ2Ｏ3等の複合酸化物にでき、しかも、ＭｇＯの分散性を利用して微細にして、凝固核として作用するＭｇＯ酸化物の比率を高めることができる。
【０００８】
【発明の実施の形態】
続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態につき説明し、本発明の理解に供する。
図１は本発明の一実施の形態に係る溶鋼のＭｇ処理方法に適用されるＭｇの添加装置の説明図、図２はＭｇ添加前のスラグ中のＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2の総質量％とＭｇ処理後の溶鋼中のＭｇ歩留りの関係を表すグラフである。
図１に示すように、本発明の一実施の形態に係る溶鋼のＭｇ処理方法に適用されるＭｇの添加装置１０は、金属ＭｇあるいはＭｇ合金からなり、外周を鉄板でくるんだ棒状のワイヤー１１と、ワイヤー１１を案内するガイドパイプ１２と、ワイヤー１１を送り出す供給装置１３とを有しており、図示しない転炉、真空二次精錬炉等を用いて溶製され、取鍋１４に受湯された溶鋼１６にＭｇを供給する。
【０００９】
以下、Ｍｇの添加装置１０を用いた溶鋼のＭｇ処理方法について説明する。
転炉を用いて脱炭精錬した後、真空二次精錬（二次精錬）を行って溶製した溶鋼１６を取鍋１４に受湯する。
溶鋼１６中には、Ａｌ2Ｏ3をアルミニウムやアルミ合金の脱酸剤で調整等を行うことにより、０．００５〜０．１０質量％含ませておく。
これは、ＭｇＯ・Ａｌ2Ｏ3等の複合酸化物の生成を促進して高融点のＭｇＯ酸化物を形成するためであり、更に、分散性が悪く凝集し易いＡｌ2Ｏ3をＭｇＯと結合させることにより、微細化と分散性を良くし、凝固核としての働きを高め、鋳片や鋼材の組織を微細にするためである。
なお、溶鋼中に含まれるＡｌ2Ｏ3が０．００５質量％より少ないと、生成したＭｇＯがＦｅ2Ｏ3、ＳｉＯ2等と結合して低融点の酸化物を形成し、凝固核としての働きが低下する。一方、溶鋼中に含まれるＡｌ2Ｏ3が０．１０質量％より多くなると、凝集し易いＡｌ2Ｏ3が多くなり過ぎて、鋳片や鋼材に酸化物に起因した欠陥が生じる場合がある。
溶鋼１６を受湯する際に、転炉から混入したり、二次精錬で添加したフラックス等により生成したスラグ１５も流入して取鍋１４内の溶鋼１６の表面を覆うことになる。このスラグ１５は、スラグストッパー等を操作して５０〜２００ｍｍの厚みに調整する。
次に、供給装置１３を作動してガイドパイプ１２により金属ＭｇやＭｇ合金のワイヤー１１を案内しながら２〜５０ｍ／分の速度で、スラグ１５を貫通して溶鋼１６に侵入させ、溶鋼１６の熱により溶解させ溶鋼１６中にＭｇを添加する。
【００１０】
従来、溶鋼の表面を覆うスラグは、ＣａＯ、ＳｉＯ2、Ａｌ2Ｏ3、ＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ等を主成分としているので、このスラグに覆われた溶鋼にＭｇを添加すると、溶鋼とスラグの界面で、スラグ中の酸化物と金属ＭｇやＭｇ合金が反応して生じたＭｇＯがスラグ中に取り込まれる。その結果、溶鋼中のＭｇの濃度を高めることができず、溶鋼中でＭｇＯ酸化物を生成するためのＭｇ歩留りが低下していた。
この現象について、研究を積み重ねた結果、酸化物の生成自由エネルギーがＭｇＯより大きい、言い換えると、熱力学的に不安定である酸化物の総重量と溶鋼中でのＭｇＯ酸化物を生成するためのＭｇ歩留りに重要な関係があることを知見し得た。
【００１１】
すなわち図２に示すように、Ｍｇ添加前のスラグ中における熱力学的に不安定な酸化物であるＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2（スラグ酸化物）の総質量％を１〜３０質量％の範囲にして、金属ＭｇやＭｇ合金のワイヤーをスラグを貫通して溶鋼に供給することにより、１０質量％以上のＭｇ歩留りを達成することが判った。
なお、このＭｇ歩留りは、溶鋼中に含まれるＭｇやＭｇＯ酸化物の全てをＭｇ量に換算した際の歩留りである。実際に溶鋼中でのＭｇの存在の形態は、その殆どがＭｇＯの単体か、あるいはＭｇＯ・Ａｌ2Ｏ3等の複合酸化物の状態で存在する。
溶鋼にＭｇを添加すると前記スラグ酸化物は、下記の（１）〜（４）式で示す化学反応によってＭｇにより還元されるものと考えられる。
ＦｅＯ＋Ｍｇ→ＭｇＯ＋Ｆｅ ・・・（１）
Ｆｅ2Ｏ3＋３Ｍｇ→３ＭｇＯ＋２Ｆｅ ・・・（２）
ＭｎＯ＋Ｍｇ→ＭｇＯ＋Ｍｎ ・・・（３）
ＳｉＯ2＋２Ｍｇ→２ＭｇＯ＋Ｓｉ ・・・（４）
つまり、溶鋼に添加されたＭｇは、前記（１）〜（４）式で示す化学反応で消費され、生成したＭｇＯがスラグ中に移行する。
この場合、スラグ中のＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2（スラグ酸化物）の総質量％が１質量％より少ないと、添加した金属ＭｇやＭｇ合金中のＭｇとスラグとの反応を抑制できるが、スラグと溶鋼の熱力学的平衡によって決定される溶鋼中の溶解酸素の量も少なくなる。
その結果、一旦溶鋼中に添加されたＭｇそのものがＭｇＯあるいはＭｇＯ・Ａｌ2Ｏ3等の複合酸化物を形成せずに、時間が経過するにつれて蒸発してＭｇ歩留りが低下する。
【００１２】
また、前記スラグ酸化物の総質量％が３０質量％を超えると、溶鋼に添加した金属ＭｇやＭｇ合金中のＭｇとスラグの反応が激しくなって、添加したＭｇの多くが前記（１）〜（４）式の化学反応でＭｇＯを生成してスラグ中に移行するので、溶鋼中で凝固核として機能する微細なＭｇＯ酸化物を形成する量が減少し、添加したＭｇの歩留りが低下し、鋳片の組織の微細化が図れない。
しかも、微細化に必要なＭｇ濃度にするには、添加量を増加する必要があり、製造コストの上昇や金属ＭｇやＭｇ合金の添加による温度の低下、スラグ性状の変化等により操業に支障が生じる。
【００１３】
このように、溶鋼１６に添加したＭｇの歩留りを高め、ＭｇＯ、ＭｇＯ・Ａｌ2Ｏ3等の高融点の複合酸化物を形成して、より安定して微細な凝固核を生成するには、スラグ１５中のスラグ酸化物を（５）式で示される範囲にすると良く、さらに２〜２０質量％の範囲にするとより好ましい結果が得られる。
１質量％≦ＦｅＯ＋Ｆｅ2Ｏ3＋ＭｎＯ＋ＳｉＯ2≦３０質量％・・・（５）
溶鋼１６を覆うスラグ１５中のスラグ酸化物の濃度を（５）で示す範囲に調整するには、Ｍｇを添加する前のスラグ１５を掻き出してスラグ１５の量を減少して、溶鋼１６中の還元成分による還元を容易にするか、あるいはスラグ１５に還元剤を添加して処理する等の一般に用いる方法を適用することができる。
なお、溶鋼１６に添加するＭｇ合金としては、Ｓｉ−Ｍｇ、Ｆｅ−Ｓｉ−Ｍｇ、Ａｌ−Ｍｇ、Ｆｅ−Ｓｉ−Ｍｎ−Ｍｇ等の合金を用いることができる。
【００１４】
【実施例】
次に、溶鋼のＭｇ処理方法の実施例について説明する。
取鍋に１５０トンの溶鋼を受湯し、この溶鋼を覆うスラグの厚みを１００ｍｍにし、ＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2の総重量を所定の範囲に調整し、このスラグを貫通して溶鋼にＭｇ純分で５０ｋｇ（０．０３３３質量％）となるようにＭｇ合金ワイヤーを供給した。
更に、この溶鋼を鋳型内寸法が厚み２５０ｍｍ、幅１２００ｍｍである連続鋳造装置を用いて０．６ｍ／分の鋳造速度で鋳造した。
そして、Ｍｇ処理後の溶鋼中のＭｇ質量％、鋳片中のＭｇ質量％、鋳片の組織の微細化状態を調査した。その結果を表１に示す。
実施例１は、Ｍｇ添加前のスラグ中のＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2の総重量を２．５質量％にした場合であり、溶鋼中のＭｇを０．００４１質量％、鋳片中のＭｇを０．００１５質量％にでき、鋳片組織も微細であり、良好な結果が得られた。
実施例２、参考例３、４は、Ｍｇ添加前のスラグ中のＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2の総重量をそれぞれ１１．３、１６．１、２２．４質量％にした場合であり、溶鋼中のＭｇがそれぞれ０．００６１、０．００６５、０．００６３質量％、鋳片中のＭｇが０．００２０、０．００３５、０．００３１質量％と歩留りが安定して高くでき、鋳片組織も微細であり、優れた結果が得られた。
参考例５は、Ｍｇ添加前のスラグ中のＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2の総重量を２８．５質量％にした場合であり、溶鋼中のＭｇを０．００３６質量％、鋳片中のＭｇを０．００１９質量％にでき、鋳片組織も微細であり、良好な結果が得られた。
【００１５】
【表１】
これに対して、比較例１は、Ｍｇ添加前のスラグ中のＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2の総重量を０．５質量％にした場合であり、溶鋼中のＭｇが０．００２５質量％、鋳片中のＭｇが０．０００９質量％となり、Ｍｇの歩留りが悪く、鋳片組織の一部が粗大になり悪い結果となった。
比較例２は、Ｍｇ添加前のスラグ中のＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2の総重量を３６．３質量％にした場合であり、溶鋼中のＭｇが０．００２８質量％、鋳片中のＭｇが０．０００８質量％になり、Ｍｇの歩留りが悪く、鋳片組織の一部が粗大になり悪い結果であった。
【００１７】
以上、本発明の実施の形態を説明したが、本発明は、上記した形態に限定されるものでなく、要旨を逸脱しない条件の変更等は全て本発明の適用範囲である。
例えば、金属ＭｇあるいはＭｇ合金のワイヤーによってＭｇを添加する際に、取鍋１６の他に、タンディッシュや鋳型内の溶鋼に添加することができる。
更に、金属ＭｇやＭｇ合金を粒状にしたものを窒素ガスやアルゴンガス等の気体で搬送し、ランスから溶鋼中に吹き込んで添加することもできる。
また、金属ＭｇやＭｇ合金の添加位置を溶鋼面から１ｍ以上の深さにすることにより、Ｍｇの蒸発を抑制し、歩留りを高めることができる。
【００１８】
【発明の効果】
請求項１、２記載の溶鋼のＭｇ処理方法は、溶鋼にＭｇを添加して、凝固組織を微細化する処理方法において、溶鋼を覆うスラグ中に、Ｍｇによって還元されるＦｅＯ、Ｆｅ 2 Ｏ 3 、ＭｎＯ、ＳｉＯ 2 を１〜１１．３質量％の濃度で含有させているので、溶鋼に添加したＭｇ歩留りを高くでき、高価なＭｇの使用量を節減して製造コストを低減し、しかも、安定した操業を可能にできる。
更に、溶鋼中に微細なＭｇＯあるいはＭｇＯ酸化物を効率良く生成し、鋳造した鋳片及び鋼材の組織を微細にして表面及び内部欠陥を抑制し、手入れや屑化等を防止して良製品歩留りや品質特性等を向上することができる。
【００１９】
特に、請求項１記載の溶鋼のＭｇ処理方法は、スラグ中にＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2 を含有させるので、スラグによるＭｇのロスを最小限にし、溶鋼へのＭｇ歩留りをより安定して高くできる。
しかも、Ｍｇの添加に伴う溶鋼の温度低下やスラグの性状の変化を確実に抑制して、より安定した操業を行うことができる。
【００２０】
請求項２記載の溶鋼のＭｇ処理方法は、溶鋼中に含まれるＡｌ2Ｏ3を０．００５〜０．１０質量％にするので、有害なＡｌ2Ｏ3をＭｇＯ・Ａｌ2Ｏ3の複合酸化物にし、ＭｇＯの分散性を利用して微細化の効果を高め、鋳片及び鋼材の組織を安定して微細にし、手入れや屑化等のない良製品の歩留りを向上することができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る溶鋼のＭｇ処理方法に適用されるＭｇの添加装置の説明図である。
【図２】Ｍｇ添加前のスラグ中のＦｅＯ、Ｆｅ2Ｏ3、ＭｎＯ、ＳｉＯ2の総質量％とＭｇ処理後の溶鋼中のＭｇ歩留りの関係を表すグラフである。
【符号の説明】
１０：Ｍｇの添加装置、１１：ワイヤー、１２：ガイドパイプ、１３：供給装置、１４：取鍋、１５：スラグ、１６：溶鋼[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Mg treatment method for molten steel in which the Mg yield of metal Mg or Mg alloy is increased and the solidification structure of a cast slab or the structure of a steel material is made fine.
[0002]
[Prior art]
Conventionally, slabs are manufactured by casting molten steel into slabs, blooms, billets, thin-walled slabs, etc. by an ingot-making method or a continuous casting method, and cutting them into a predetermined size. Moreover, steel materials, such as a steel plate and a shaped steel, are manufactured by heating slab using a soaking furnace etc. and performing processes, such as rolling and forging.
However, if the solidification structure of the slab (hereinafter referred to as the structure) or the structure of the steel material is coarse, surface defects such as surface cracks, internal cracks, center segregation, center porosity, and other internal defects are caused by the coarsening of the structure. However, there is a problem in that the yield decreases due to the care and scraping of slabs and steel materials.
As a countermeasure, Japanese Patent Laid-Open No. 7-48616 discloses CaO in which the content of MgO in the slag covering the molten steel is adjusted to 3 to 15 % by mass , and the total amount of FeO, Fe 2 O 3 and MnO is adjusted to 5 % by mass or less. A method of adding metal Mg or Mg alloy to molten steel that is —SiO 2 —Al 2 O 3 type is described. And the improvement of the Mg yield added to molten steel is aimed at, Al 2 O 3 which is easy to coarsen is made into a fine oxide, and the defect of a slab and steel materials is prevented.
Further, in JP-A-9-194986, a small amount of Nb, V, Mo or the like is added to molten steel, Mg is added, and accelerated cooling and rolling are performed, thereby achieving high strength and toughness with a fine bainite structure. A method for producing an excellent steel material is disclosed.
[0003]
[Problems to be solved by the invention]
However, in JP-A-7-48616, since the total amount of FeO, Fe 2 O 3 and MnO in the slag covering the molten steel is adjusted to 5 % by mass or less, the content of SiO 2 in the slag is large. When Mg or Mg alloy is added, it reacts with SiO 2 contained to lower the Mg yield. In addition, the decrease in Mg yield cannot be achieved by modifying Al 2 O 3 or the like in molten steel into an oxide containing MgO, and an Al 2 O 3 based coarse oxide is formed, resulting in slabs and steel materials. Quality defects occur.
Furthermore, if the total amount of FeO, Fe 2 O 3 and MnO (hereinafter referred to as slag oxide) in the slag is too low, the slag oxide that reacts with Mg added to the molten steel will be insufficient and sufficient MgO can be generated. Therefore, an oxide containing MgO or MgO that acts as a solidification nucleus cannot be formed.
As a result, the structure of the slab or steel material becomes coarse, and defects such as cracks, center segregation, and center porosity occur on the surface or inside.
Further, in Japanese Patent Laid-Open No. 9-194986, since trace elements such as Nb, V, and Mo are added together with Mg, the mechanical strength of the steel material is changed by the trace elements, and workability, squeezability, and the like are required. There is a difficulty that it is difficult to apply to steel.
Furthermore, when the slab is rolled, accelerated cooling (rolling method in which water cooling is performed between rolling passes) is performed to make the steel material a fine structure, so that the water cooling time is increased and productivity such as rolling is increased. Decreases.
As described above, in any method, when metal Mg or Mg alloy is added to molten steel, the yield of Mg is oxidized to MgO without causing any trouble in operation, and the structure of slab or steel material Is not specifically shown on how to improve the quality by minimizing the surface of the slab and steel, suppressing defects on the surface and inside of the slab and preventing the slab and steel from being cared for and scrapped. There is.
[0004]
The present invention has been made in view of such circumstances, and provides a Mg treatment method for molten steel that can increase the production of MgO in molten steel and make the structure of a slab or steel material finer without causing trouble in operation. The purpose is to provide.
[0005]
[Means for Solving the Problems]
The Mg treatment method of the molten steel of the present invention that meets the above-mentioned object is a treatment method in which Mg is added to the molten steel to refine the solidification structure. In the slag covering the molten steel, FeO, Fe 2 O 3 , MnO, SiO The total weight of 2 is contained at a concentration of 1 to 11.3 mass%, and the thickness of the slag covering the molten steel is adjusted to 50 to 200 mm .
By this method, since the total weight of oxides contained in the slag is set to a predetermined value, the yield of producing Mg added to molten steel into oxides containing MgO and MgO can be increased, and oxidation containing fine MgO or MgO is possible. Can be dispersed in the molten steel (hereinafter referred to as MgO oxide).
And the structure of the slab cast from this molten steel can be made finer, and cracks and dents generated on the surface of the slab, cracks and central segregation occurring inside, center porosity, etc. can be suppressed, and the slab can be maintained. The yield of good cast slabs can be improved by preventing scraps and the like, and the quality of steel materials obtained by subjecting the slabs to processing such as rolling can be improved.
[0006]
Here, FeO oxide in said slag, Fe 2 O 3, MnO, shall be the SiO 2.
As a result, the consumption of Mg by oxides in the slag is suppressed, there is no hindrance to operations such as a decrease in molten steel temperature and slag properties change, and the yield of Mg can be increased and efficiently added to the molten steel. it can. In addition, MgO oxide can be generated in the molten steel and can act as a solidification nucleus when the molten steel is solidified.
[0007]
Furthermore, it is preferable that the Al 2 O 3 contained in the molten steel to 0.005 to 0.10 mass%.
As a result, the coarsening of the Al 2 O 3 oxide can be suppressed, and Al 2 O 3 having a high melting point can be made into a composite oxide such as MgO · Al 2 O 3 , and the dispersibility of MgO can be utilized. The ratio of MgO oxide acting as solidification nuclei can be increased by making it fine.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
FIG. 1 is an explanatory diagram of an apparatus for adding Mg applied to an Mg treatment method for molten steel according to an embodiment of the present invention, and FIG. 2 is a diagram of FeO, Fe 2 O 3 , MnO, and SiO 2 in slag before Mg addition. It is a graph showing the relationship of the total mass% of Mg, and the Mg yield in the molten steel after Mg processing.
As shown in FIG. 1, a
[0009]
Hereinafter, the Mg processing method of the molten steel using the
After decarburizing and refining using a converter, the
The
This is to promote the formation of composite oxides such as MgO · Al 2 O 3 to form a high melting point MgO oxide. Furthermore, Al 2 O 3 which has poor dispersibility and easily aggregates is combined with MgO. This is to improve the miniaturization and dispersibility, enhance the function as solidification nuclei, and make the structure of the slab and steel material fine.
When the Al 2 O 3 content in the molten steel is less than 0.005 % by mass , the produced MgO combines with Fe 2 O 3 , SiO 2 and the like to form a low melting point oxide, Work decreases. On the other hand, if Al 2 O 3 contained in the molten steel is more than 0.10 % by mass, the amount of Al 2 O 3 that tends to agglomerate increases too much, and defects due to oxides may occur in the slab or steel material. .
When the
Next, the
[0010]
Conventionally, the slag covering the surface of the molten steel is mainly composed of CaO, SiO 2 , Al 2 O 3 , FeO, Fe 2 O 3 , MnO, etc. Therefore, when Mg is added to the molten steel covered with this slag, MgO produced by the reaction of the oxide in the slag with the metal Mg or Mg alloy is taken into the slag at the interface between the slag and the slag. As a result, the Mg concentration in the molten steel could not be increased, and the Mg yield for generating MgO oxide in the molten steel was reduced.
As a result of accumulated research on this phenomenon, the free energy of formation of oxide is larger than MgO, in other words, the total weight of oxide that is thermodynamically unstable and the formation of MgO oxide in molten steel. It was found that there was an important relationship with Mg yield.
[0011]
That is, as shown in FIG. 2, the total mass% of FeO, Fe 2 O 3 , MnO, and SiO 2 (slag oxide), which are thermodynamically unstable oxides in the slag before the addition of Mg, is 1-30. It has been found that Mg yield of 10 % by mass or more can be achieved by supplying a metal Mg or Mg alloy wire to the molten steel through the slag in the mass% range.
In addition, this Mg yield is a yield at the time of converting all the Mg and MgO oxide contained in molten steel into the amount of Mg. Actually, most of Mg exists in molten steel in the form of a simple substance of MgO or a complex oxide such as MgO.Al 2 O 3 .
When Mg is added to molten steel, the slag oxide is considered to be reduced by Mg by chemical reactions represented by the following formulas (1) to (4).
FeO + Mg → MgO + Fe (1)
Fe 2 O 3 + 3Mg → 3MgO + 2Fe (2)
MnO + Mg → MgO + Mn (3)
SiO 2 + 2Mg → 2MgO + Si (4)
That is, Mg added to the molten steel is consumed by the chemical reaction represented by the above formulas (1) to (4), and the generated MgO moves into the slag.
In this case, when the total mass% of FeO, Fe 2 O 3 , MnO, and SiO 2 (slag oxide) in the slag is less than 1 mass% , the reaction between Mg in the added metal Mg or Mg alloy and the slag occurs. Although it can be suppressed, the amount of dissolved oxygen in the molten steel determined by the thermodynamic equilibrium between the slag and molten steel is also reduced.
As a result, Mg itself once added to the molten steel does not form a composite oxide such as MgO or MgO.Al 2 O 3 , but evaporates over time and the Mg yield decreases.
[0012]
Moreover, when the total mass% of the slag oxide exceeds 30 mass% , the reaction between Mg in the molten steel and Mg in the Mg alloy and the slag becomes intense, and most of the added Mg is (1) to Since MgO is generated by the chemical reaction of formula (4) and moves into the slag, the amount of fine MgO oxide that functions as solidification nuclei in the molten steel decreases, and the yield of added Mg decreases, The structure of the slab cannot be refined.
In addition, in order to obtain the Mg concentration necessary for miniaturization, it is necessary to increase the amount of addition, which hinders operation due to an increase in manufacturing cost, a decrease in temperature due to the addition of metallic Mg or Mg alloy, a change in slag properties, etc. Arise.
[0013]
Thus, in order to increase the yield of Mg added to the
1 % by mass ≦ FeO + Fe 2 O 3 + MnO + SiO 2 ≦ 30 % by mass (5)
In order to adjust the concentration of the slag oxide in the
In addition, as Mg alloy added to the
[0014]
【Example】
Next, an example of the Mg treatment method for molten steel will be described.
The ladle receives 150 tons of molten steel, the thickness of the slag covering this molten steel is 100 mm, the total weight of FeO, Fe 2 O 3 , MnO, and SiO 2 is adjusted to a predetermined range, and this slag is penetrated. Then, the Mg alloy wire was supplied to the molten steel so that the pure Mg content was 50 kg (0.0333 mass% ).
Further, this molten steel was cast at a casting speed of 0.6 m / min using a continuous casting apparatus having a mold inner dimension of 250 mm thickness and a width of 1200 mm.
Then, the Mg mass% in the molten steel after Mg treatment, the Mg mass% in the slab, and the refined state of the slab structure were investigated. The results are shown in Table 1.
Example 1 is a case where the total weight of FeO, Fe 2 O 3 , MnO, and SiO 2 in the slag before the addition of Mg is 2.5 % by mass. Mg in the molten steel is 0.0041 % by mass , casting Mg in the piece could be 0.0015 % by mass , the slab structure was fine, and good results were obtained.
In Example 2 and Reference Examples 3 and 4, the total weight of FeO, Fe 2 O 3 , MnO, and SiO 2 in the slag before adding Mg was 11.3, 16.1, 22.4 % by mass , respectively. , and the 0.0061,0.0065,0.0063 mass% Mg in the molten steel, respectively, Mg in the cast slab is 0.0020,0.0035,0.0031 wt% and the yield can be increased stably The slab structure was also fine, and excellent results were obtained.
Reference Example 5 is a case where the total weight of FeO, Fe 2 O 3 , MnO, and SiO 2 in the slag before the addition of Mg was 28.5 % by mass , and the Mg in the molten steel was 0.0036 % by mass , Mg in the piece could be 0.0019 % by mass , the slab structure was fine, and good results were obtained.
[0015]
[Table 1]
On the other hand, Comparative Example 1 is a case where the total weight of FeO, Fe 2 O 3 , MnO, and SiO 2 in the slag before adding Mg is 0.5 mass% , and Mg in the molten steel is 0.00. 0025 mass% , Mg in the slab was 0.0009 mass% , the yield of Mg was poor, part of the slab structure became coarse, and the result was bad.
Comparative Example 2 is a case where the total weight of FeO, Fe 2 O 3 , MnO, and SiO 2 in the slag before the addition of Mg is 36.3 % by mass , and Mg in the molten steel is 0.0028 % by mass . Mg in the piece was 0.0008 % by mass , the yield of Mg was poor, and a part of the slab structure became coarse, which was a bad result.
[0017]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and all changes in conditions and the like that do not depart from the gist are within the scope of the present invention.
For example, when adding Mg by a metal Mg or Mg alloy wire, in addition to the
Further, the metal Mg or Mg alloy in a granular form can be conveyed by a gas such as nitrogen gas or argon gas, and blown into the molten steel from the lance and added.
Further, by making the addition position of metal Mg or Mg alloy at a depth of 1 m or more from the molten steel surface, it is possible to suppress the evaporation of Mg and increase the yield.
[0018]
【The invention's effect】
The Mg treatment method for molten steel according to claim 1 or 2 is a treatment method in which Mg is added to the molten steel to refine the solidification structure. FeO, Fe 2 O 3 reduced by Mg in the slag covering the molten steel. Since MnO and SiO 2 are contained at a concentration of 1 to 11.3 mass%, the Mg yield added to the molten steel can be increased, the amount of expensive Mg used is reduced, and the manufacturing cost is reduced. Enables stable operation.
Furthermore, fine MgO or MgO oxide is efficiently generated in molten steel, the structure of cast slabs and steel materials is refined to suppress surface and internal defects, and maintenance and scrapping are prevented, resulting in good product yield. And quality characteristics can be improved.
[0019]
In particular, Mg processing method of the molten steel according to claim 1 is, FeO in the slag, Fe 2 O 3, MnO, since the inclusion of SiO 2, to minimize the loss of Mg due to the slag, more the Mg yield in the molten steel Can be stable and high.
In addition, the temperature drop of the molten steel and the change in the properties of the slag accompanying the addition of Mg can be reliably suppressed, and more stable operation can be performed.
[0020]
Mg treatment method of the molten steel according to claim 2, since the Al 2 O 3 contained in molten steel 0.005 to 0.10 wt%, a harmful Al 2 O 3 of MgO · Al 2 O 3 composite It is possible to increase the effect of refinement by using oxides and dispersibility of MgO, to stably refine the structure of the slab and the steel material, and to improve the yield of good products without care or scrapping.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram of an Mg addition apparatus applied to a molten steel Mg treatment method according to an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the total mass% of FeO, Fe 2 O 3 , MnO, and SiO 2 in slag before Mg addition and the Mg yield in molten steel after Mg treatment.
[Explanation of symbols]
10: Mg addition device, 11: wire, 12: guide pipe, 13: feeding device, 14: ladle, 15: slag, 16: molten steel
Claims (2)
Priority Applications (15)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP18011299A JP4279947B2 (en) | 1999-06-25 | 1999-06-25 | Mg treatment method for molten steel |
| AU36746/00A AU753777B2 (en) | 1999-04-08 | 2000-04-07 | Cast steel piece and steel product excellent in forming characteristics and method for treatment of molted steel therefor and method for production thereof |
| KR1020057018257A KR100706973B1 (en) | 1999-04-08 | 2000-04-07 | Cast steel piece with fine solidification sturcture and excellent forming characteristics and steel product and seamless steel pipe produced by using the same |
| CNB2005100068043A CN1321766C (en) | 1999-04-08 | 2000-04-07 | Cast steel and steel material with excellent workability, method for processing molten steel therefor and method for manufacturing the cast steel and steel material |
| KR1020007013895A KR100550678B1 (en) | 1999-04-08 | 2000-04-07 | Treatment method of molten steel to refine solidification structure of cast steel |
| EP10186285.2A EP2308617B1 (en) | 1999-04-08 | 2000-04-07 | Method for processing molten steel |
| CN 00800836 CN1258413C (en) | 1999-04-08 | 2000-04-07 | Treatment method of molten steel |
| EP07005688.2A EP1803512B1 (en) | 1999-04-08 | 2000-04-07 | Cast steel with excellent workability and method for manufacturing the cast steel |
| EP10186292.8A EP2292352B1 (en) | 1999-04-08 | 2000-04-07 | Method for processing molten steel for cast steel and steel material with excellent workability |
| CA002334352A CA2334352C (en) | 1999-04-08 | 2000-04-07 | Cast steel piece and steel material with excellent workability, method for processing molten steel therefor and method for manufacutring the cast steel and steel material |
| EP00915437A EP1099498A4 (en) | 1999-04-08 | 2000-04-07 | STEEL CASTING PIECE AND STEEL PRODUCT WITH EXCELLENT FORMING PROPERTIES AND METHOD FOR TREATING IT FOR SUITABLE MOLTEN STEEL AND METHOD FOR THE PRODUCTION THEREOF |
| US09/719,206 US6585799B1 (en) | 1999-04-08 | 2000-04-07 | Cast steel piece and steel product excellent in forming characteristics and method for treatment of molted steel therefor and method for production thereof |
| EP10186277.9A EP2308616B1 (en) | 1999-04-08 | 2000-04-07 | Cast steel and steel material with excellent workability, method for processing molten steel therefor and method for manufacturing the cast steel and steel material |
| PCT/JP2000/002296 WO2000061322A1 (en) | 1999-04-08 | 2000-04-07 | Cast steel piece and steel product excellent in forming characteristics and method for treatment of molted steel therefor and method for production thereof |
| US10/222,362 US6918969B2 (en) | 1999-04-08 | 2002-08-16 | Cast steel and steel material with excellent workability, method for processing molten steel therefor and method for manufacturing the cast steel and steel material |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP18011299A JP4279947B2 (en) | 1999-06-25 | 1999-06-25 | Mg treatment method for molten steel |
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| JP2001011527A JP2001011527A (en) | 2001-01-16 |
| JP4279947B2 true JP4279947B2 (en) | 2009-06-17 |
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| JP18011299A Expired - Fee Related JP4279947B2 (en) | 1999-04-08 | 1999-06-25 | Mg treatment method for molten steel |
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