JP4311097B2

JP4311097B2 - Method for preventing slag flow in converter

Info

Publication number: JP4311097B2
Application number: JP2003185294A
Authority: JP
Inventors: 純一椎野; 由枝中井; 郁宏鷲見; 良輝菊地; 宏清水; 幸代森田
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2003-06-27
Filing date: 2003-06-27
Publication date: 2009-08-12
Anticipated expiration: 2023-06-27
Also published as: JP2005015889A

Description

【０００１】
【発明の属する技術分野】
本発明は、転炉から取鍋への出鋼時における転炉内スラグの取鍋への流出防止方法に関し、詳しくは、転炉内スラグの固相率を高めることによってスラグの流出を防止する方法に関するものである。
【０００２】
【従来の技術】
溶銑を転炉内で脱炭精錬する場合には、溶銑の脱燐反応促進のために、或いは転炉での脱燐が不要な、予備脱燐処理が施された溶銑の脱炭精錬でも、転炉内に添加されるＭｎ鉱石や鉄鉱石の脈石として持ち来されるＳｉＯ₂ 分に応じて、ＣａＯ系の造滓剤が添加され、塩基度（ＣａＯ／ＳｉＯ₂ ）が２〜６程度のスラグが形成されている。スラグは、溶銑表面を覆うことにより、供給される酸素ジェットによる溶湯の飛散を低減する効果も有している。このスラグは、転炉から取鍋への出鋼時、転炉からの溶鋼流に混入して取鍋内に流出する。
【０００３】
通常、溶鋼は、転炉での脱炭精錬終了後に取鍋内で金属Ａｌやフェロシリコン等の強脱酸剤によって脱酸処理され、酸素吹錬によって増加した溶鋼中溶存酸素が低減される。特に、高い清浄性を要求される鋼種では、金属Ａｌによる脱酸処理が行われており、溶鋼中溶存酸素は実質的にゼロまで低減される。このように、溶鋼は脱酸処理され、溶鋼中の溶存酸素量は減少するが、この溶鋼と接触している溶鋼上のスラグ中にはＦｅＯやＭｎＯ等の低級酸化物が含まれており、ＦｅやＭｎはＡｌやＳｉ等の強脱酸元素よりも酸素との親和力が小さいため、脱酸処理後にスラグ中のＦｅＯやＭｎＯが溶鋼中のＡｌやＳｉによって還元される反応が継続して発生し、溶鋼中には反応生成物であるＡｌ₂ Ｏ₃ やＳｉＯ₂ が生成し、ＡｌやＳｉの歩留まりが低下するのみならず、清浄性の高い溶鋼を得ることができない。又、取鍋内スラグそれ自体が、溶鋼中に巻き込まれて非金属介在物となる場合もある。
【０００４】
この問題を解決すべく、従来から、転炉からのスラグの流出を防止する方法が多数提案されている。例えば、特許文献１には、酸素吹錬末期に転炉内にＣａＯ分を添加して、炉内スラグの塩基度を高めると同時にスラグ中のT.Fe濃度を希釈し、スラグの融点を上昇せしめてスラグを固化し、出鋼時のスラグ流出を防止する方法が提案されており、又、特許文献２には、酸素吹錬末期又は酸素吹錬終了後に、転炉内スラグの固相率が３０％以上となる量のＭｇＯを転炉内に添加し、スラグを固化して出鋼時のスラグ流出を防止する方法が提案されている。尚、スラグ中のT.Feとは、スラグ中の全ての鉄酸化物の鉄分の合計値のことである。
【０００５】
【特許文献１】
特開昭６４−３６７１７号公報
【０００６】
【特許文献２】
特開平２−１１１８１０号公報
【０００７】
【発明が解決しようとする課題】
ところで近年、溶銑予備処理技術の発展に伴い、転炉の脱炭精錬で必要とする造滓剤が減少し、転炉精錬における生成スラグ量が大幅に低減した結果、従来のフェロマンガン等の合金鉄を添加して溶鋼のＭｎ濃度を調整する方法に代わって、転炉内にＭｎ鉱石を添加して溶融還元する方法が一般的になってきた。炉内のスラグ量が少なくなった上に、Ｍｎ鉱石を添加しているので、スラグのＭｎＯ濃度は従来のスラグと比較すると格段に高くなる。スラグ中のＭｎＯ濃度が増加すると、スラグの融点が低下すると同時に、溶鋼温度範囲におけるスラグの粘性が低下するため、出鋼時、溶鋼流に混入するスラグ量が増大し、スラグの転炉からの流出量は従来に比べて大幅に増加する。
【０００８】
前述した特許文献１では、スラグの固化率を、スラグの塩基度とスラグ中T.Fe濃度の２つの因子の関数として捉えており、スラグの固化率に及ぼすＭｎＯ濃度の影響を全く考慮していない。又、同様に、特許文献２では、スラグの固化率を、スラグの塩基度とスラグ中T.Fe濃度とスラグ中ＭｇＯ濃度の３つの因子の関数として捉えており、スラグの固化率に及ぼすＭｎＯ濃度の影響を全く考慮していない。従って、特許文献１及び特許文献２の方法では、スラグ量が少なく且つＭｎ鉱石が添加されことによってスラグ中のＭｎＯ濃度が高くなる転炉精錬においては、スラグの転炉からの流出を十分に防止することができない。
【０００９】
本発明は上記事情に鑑みてなされたもので、その目的とするところは、スラグ量が少なく、スラグ中のＭｎＯ濃度が高い転炉精錬の場合でも、出鋼時の転炉からのスラグの流出を十分に防止することが可能であるスラグ流出防止方法を提供することである。
【００１０】
【課題を解決するための手段】
本発明者等は、上記課題を解決すべく鋭意検討・研究を行った。以下に、検討・研究結果を説明する。
【００１１】
出鋼時のスラグの流出を防止するため、先ず、スラグ中の成分がスラグの固相率に及ぼす影響について調査した。その結果、スラグ中のT.Fe濃度の上昇によってスラグの固相率は大幅に低下し、又、T.Feと同様に、転炉内でＭｎ鉱石を溶融還元した場合に増加するＭｎＯもスラグの固相率を大幅に低下させることが明らかとなった。スラグ中のＭｎＯ濃度は、スラグ量を抑え且つＭｎ鉱石を添加した転炉精錬では２０〜３０mass％に達することもあり、スラグを固化するための精錬剤を添加し、添加した精錬剤の冷却効果でスラグを固化させてスラグの流出を防止する上で、スラグ中のＭｎＯ濃度を考慮することが極めて重要であるとの知見が得られた。
【００１２】
そこで、転炉脱炭精錬におけるスラグ組成の範囲において、T.Fe濃度及びＭｎＯ濃度を変化させ、T.Fe濃度及びＭｎＯ濃度とスラグ固相率との関係を、汎用の熱力学計算ソフトを使用して算出・検討した。計算に当たっては、スラグの温度を１６５０〜１７００℃、スラグの塩基度（ＣａＯ／ＳｉＯ₂ ）を２〜４、スラグ中のＭｇＯ濃度を５〜１５mass％とした。計算結果を図１に示す。
【００１３】
固相率に及ぼすT.Fe及びＭｎＯの影響はほぼ同等であったため、図１に示すように、指標としてT.Fe＋ＭｎＯを用いた。又、固相率にはインデックスを用い、スラグ流出の抑制効果が現れる固相率インデックスを１００とした。即ち、T.Fe＋ＭｎＯが１０mass％以下の組成のスラグではスラグ流出は抑制されており、従って、この範囲は固相率インデックスを１００とした。スラグの固相率インデックスは、T.Fe＋ＭｎＯの上昇に伴って減少し即ちスラグは流出し易くなり、T.Fe＋ＭｎＯが約２０mass％の位置を境界として、固相率インデックスの傾斜が変化することが分かった。
【００１４】
図１に示す結果に基づき、実炉試験を実施した。酸素吹錬終了後、ＣａＯを主成分とする生石灰をスラグ固化用の精錬剤として転炉内に添加し、固化用精錬剤の添加量を変更して出鋼時のスラグの流出量を測定した。スラグ流出量の測定方法は、取鍋内に流出したスラグの厚みを測定し、スラグ厚みの測定値に基づいて流出量を換算する方法、又は、転炉内スラグに所定量のトレーサー元素を添加し、取鍋内スラグのトレーサー元素の濃度に基づいて流出量を換算する方法を用いた。
【００１５】
精錬剤の添加量が同一であっても炉内のスラグ量によって固相率に及ぼす精錬剤の影響が異なるため、炉内スラグ量に対する精錬剤添加量の比（精錬剤添加量／炉内スラグ量）を操作因子として、図１に示す固相率の近似直線にのっとり近似させた結果、図２に示すように、スラグ流出抑制効果の有無の境界線が求められた。即ち、スラグ中のT.Fe濃度とＭｎＯ濃度との合計値が２０mass％以下の場合には、下記の（１）式を満たす範囲内でスラグを固化するためのＣａＯを主成分とする精錬剤を転炉内に添加し、一方、スラグ中のT.Fe濃度とＭｎＯ濃度との合計値が２０mass％を越える場合には、下記の（２）式を満たす範囲内で前記精錬剤を転炉内に添加することで、添加した精錬剤によって転炉内のスラグを固化させ、スラグの流出量を低減可能であることが分かった。但し、（１）式及び（２）式において、Ｗｃはスラグを固化するための精錬剤の添加量（ｋｇ）、Ｗｓは転炉内の推定スラグ量（ｋｇ）であり、図２に示す境界線が（１）式及び（２）式によって表される。
【００１６】
【数１】

【００１７】
【数２】

【００１８】
本発明は上記検討・研究結果に基づいてなされたものであり、第１の発明に係る転炉内スラグの流出防止方法は、溶銑予備処理にて脱燐処理した溶銑を転炉に装入し、転炉内で酸素吹錬して溶銑を脱炭精錬する際に、当該酸素吹錬中に転炉内にＭｎ鉱石を添加してＭｎ鉱石を転炉内で還元すると共に、酸素吹錬の末期又は酸素吹錬終了後に、転炉内スラグのＴ．Ｆｅ濃度及びＭｎＯ濃度に応じ、スラグ中のＴ．Ｆｅ濃度とＭｎＯ濃度との合計値が２０ｍａｓｓ％以下の場合には、上記の（１）式を満たす範囲内で、石灰石、生石灰、ドロマイト、焼成ドロマイトのうちの１種以上からなる精錬剤を転炉内に添加し、一方、スラグ中のＴ．Ｆｅ濃度とＭｎＯ濃度との合計値が２０ｍａｓｓ％を越える場合には、上記の（２）式を満たす範囲内で、石灰石、生石灰、ドロマイト、焼成ドロマイトのうちの１種以上からなる精錬剤を転炉内に添加し、添加した精錬剤によって転炉内のスラグを固化させ、出鋼時のスラグの転炉からの流出を抑制することを特徴とするものである。
【００２０】
第２の発明に係る転炉内スラグの流出防止方法は、第１の発明において、前記転炉内スラグの量を溶鋼トン当たり２０ｋｇ以下とするか、又は、造滓剤として転炉内に装入する生石灰を溶鋼トン当たり１０ｋｇ以下とすることを特徴とするものである。
【００２１】
第３の発明に係る転炉内スラグの流出防止方法は、第１または第２の発明において、前記転炉内スラグの塩基度（ＣａＯ／ＳｉＯ₂ ）を４．０以下とすることを特徴とするものである。
【００２２】
【発明の実施の形態】
以下、本発明の実施の形態を説明する。
【００２３】
高炉から出銑された溶銑を溶銑鍋やトーピードカー等の溶銑保持・搬送用容器で受銑し、次工程の脱炭精錬を行う転炉に搬送する。本発明では、フェロマンガン等の合金鉄の使用量を削減する目的から、転炉における溶銑の脱炭精錬時に、転炉内にＭｎ鉱石を添加してＭｎ鉱石を溶融還元するので、Ｍｎ鉱石の歩留まりを向上させるために、転炉におけるスラグ量を極力減少させる必要があり、そのため、この搬送途中で、溶銑に対して脱硫処理や脱燐処理等の溶銑予備処理を施す。近年、溶銑の予備処理を転炉で行う場合もあるので、搬送途中に限らず転炉で予備処理を行ってもよい。
【００２４】
この場合、転炉内のスラグ量を極力少なくさせるために、溶銑の燐濃度を製品の燐濃度レベル以下、具体的には０．０１５mass％程度以下まで予備処理で脱燐することが好ましい。製品の燐濃度レベルまで溶銑の燐濃度を低減した場合には、転炉精錬で必要とする生石灰等の造滓剤は溶鋼トン当たり１０ｋｇ（以下、「ｋｇ／ｔ」と記す）以下となり、生成スラグ量はおよそ２０ｋｇ／ｔ以下まで低減させることができる。
【００２５】
このように、転炉精錬は、生成スラグ量が少ないほど好ましく、従って、炉内のスラグ量を５０ｋｇ／ｔ以下、即ち、生石灰等の造滓剤の転炉内添加量を２０ｋｇ／ｔ以下とする、望ましくは、炉内のスラグ量を２０ｋｇ／ｔ以下、即ち、生石灰等の造滓剤の転炉内添加量を１０ｋｇ／ｔ以下とし、酸素を上吹き又は底吹きして溶銑の脱炭酸素吹錬を行う。この場合に、炉内のスラグ量を少なくする観点から、スラグの塩基度（ＣａＯ／ＳｉＯ₂ ）は４．０以下とすることが好ましい。但し、スラグの塩基度が低すぎると、転炉炉体の塩基性耐火物を損傷するので、スラグの塩基度の下限は１．５程度とすることが好ましい。そして、この転炉精錬では、溶鋼のＭｎ成分源としてＭｎ鉱石を転炉内に添加する。Ｍｎ鉱石の添加量は、目的とする溶鋼のＭｎ成分に応じて適宜の量を添加し、Ｍｎ鉱石の添加時期は酸素吹錬の初期から中期の範囲とする。Ｍｎ鉱石を酸素吹錬の中期以降に添加することは、還元時間が確保できなくなるので、好ましくない。
【００２６】
このような酸素吹錬の末期、又は酸素吹錬終了後から出鋼までの期間に、スラグを固化させるための冷却用精錬剤を転炉内に添加する。取鍋へのスラグ流出量を極力少なくするために、転炉を傾動させた出鋼中に、出鋼口の鉛直上方位置に存在するスラグに向かって局所的に精錬剤を添加する、或いは吹き付けてもよい。このような局所的な添加は、スラグ量が２０ｋｇ／ｔ以下、即ち造滓剤の添加量を１０ｋｇ／ｔ以下にした操業で顕著なスラグ流出の抑制効果を発揮する。
【００２７】
スラグを固化させるための精錬剤の添加量は、炉内スラグのT.Fe濃度及びＭｎＯ濃度に応じて決定する。即ち、スラグ中のT.Fe濃度とＭｎＯ濃度との合計値が２０mass％以下の場合には、上記の（１）式を満たす範囲内で精錬剤を転炉内に添加し、一方、スラグ中のT.Fe濃度とＭｎＯ濃度との合計値が２０mass％を越える場合には、上記の（２）式を満たす範囲内で精錬剤を転炉内に添加する。
【００２８】
（１）式及び（２）式を算出する際に、スラグ中のT.Fe濃度及びＭｎＯ濃度は、転炉内からスラグを採取し、採取したスラグを分析することで求めることができる。又、多数のスラグの分析値データと、送酸量、酸素吹錬終点の溶鋼中炭素濃度、終点温度、Ｍｎ鉱石添加量等の転炉操業条件とを照らし合わせ、両者の相関を解析することで、転炉操業条件からもスラグ中のT.Fe濃度及びＭｎＯ濃度を推定することができる。推定スラグ量Ｗｓは、スラグのＣａＯ分析値と造滓剤として添加した生石灰中のＣａＯ純分量とのマスバランスから求めることができる。又、造滓剤として添加した生石灰中のＣａＯ純分量と、送酸量、酸素吹錬終点の溶鋼中炭素濃度、終点温度、Ｍｎ鉱石添加量等の転炉操業条件とを照らし合わせ、両者の相関を解析することで、転炉操業条件からも推定スラグ量Ｗｓを推定することができる。
【００２９】
スラグを固化するための精錬剤としては、安価であり、又、転炉炉体耐火物を損傷させないことから、ＣａＯ又はＣａＣＯ₃ を主成分とする精錬剤を用いることが好ましい。特に、ＣａＣＯ₃ を主成分とする精錬剤は炉内で加熱されると熱分解し、この熱分解の際に多量の熱を奪うので、スラグの固化に一層効果を発揮する。ＣａＯ又はＣａＣＯ₃ を主成分とする安価な精錬剤としては、石灰石、生石灰、ドロマイト、焼成ドロマイトがあり、これらのうちの１種又は２種以上を用いることができる。
【００３０】
このようにして溶銑を転炉で精錬することによって、転炉内スラグの出鋼時の取鍋への流出が抑制される。その結果、スラグと溶鋼中の脱酸元素との反応が抑制され、清浄性の高い溶鋼を溶製することができる。又、取鍋内のスラグ量が少ないので、スラグを無害化するためのスラグ改質に使用する金属ＡｌやＡｌドロス等の使用量を削減することも可能となる。
【００３１】
【実施例】
以下、本発明の実施例（実施例１〜１５）を比較例（比較例１〜１０）と共に説明する。容量が２５０トンで、酸素を上吹きし、撹拌用ガスを底吹きする、上底吹き複合吹錬用転炉内に、約２５０トンの溶銑を装入して脱炭吹錬を行った。用いた溶銑は、溶銑予備処理設備にて脱硫処理及び脱燐処理が施された溶銑であり、溶銑の成分は、Ｓｉ濃度が０．０７mass％以下、Ｓ濃度が０．０１mass％以下、Ｐ濃度が０．０１０〜０．０１５mass％に統一した。
【００３２】
転炉での酸素吹錬の初期には、転炉内にＭｎ鉱石を添加した。又、造滓剤として生石灰を添加してスラグを生成させた。スラグ分析値から求められた、冷却剤としての精錬剤を添加する前のスラグの塩基度（ＣａＯ／ＳｉＯ₂ ）は１．９〜４．０であり、おおむね２．５〜３．５であった。精錬剤を添加する前のスラグ中のT.Fe濃度及びＭｎＯ濃度は採取したスラグの分析値から求め、転炉内のスラグ量はＣａＯバランスによって求めた。
【００３３】
転炉炉底に設置した羽口から、溶銑の攪拌を目的として攪拌用Ａｒガス又は窒素ガスを毎分１０〜２０Ｎｍ³ 程度吹き込んだ。酸素供給は上吹きランスで行い、酸素吹錬の初期から脱炭最盛期にかけての送酸速度を６００００Ｎｍ³ ／ｈｒ、脱炭速度の遅くなる酸素吹錬末期では３００００Ｎｍ³ ／ｈｒとした。そして、酸素吹錬の末期或いは酸素吹錬終了後に、転炉内に生石灰、石灰石、未焼成ドロマイトの内の一種を添加した。取鍋へのスラグの流出量は、出鋼後に取鍋内のスラグ厚みを測定し、スラグ厚みに基づいてスラグ流出量を求めた。
【００３４】
表１に、実施例１〜１５及び比較例１〜１０の操業条件及び操業結果を示す。尚、表１の「添加量／最低必要量」の欄の「最低必要量」とは、スラグ中のT.Fe濃度とＭｎＯ濃度との合計濃度に応じて、前述した（１）式及び（２）式によって算出される添加量の下限値であり、添加量／最低必要量の比が１．０以上となる条件が本発明の範囲内となる。
【００３５】
【表１】

【００３６】
表１に示すように、生石灰を添加した実施例１〜６では、スラグ流出量は安定して２．０ｋｇ／ｔ程度になった。特に、スラグを固化させるための精錬剤を最低必要量の１．５倍以上添加すると、スラグ流出量を１．５ｋｇ／ｔ程度まで抑制することができた。
【００３７】
石灰石又は未焼成ドロマイトを添加した実施例７〜１５では、生石灰を使用した実施例に較べ、更にスラグ流出量を抑制することができ、安定してスラグ流出量を１．５ｋｇ／ｔ以下にすることができた。特に、スラグを固化させるための精錬剤を最低必要量の１．５倍以上添加すると、スラグ流出量を１．０ｋｇ／ｔ程度まで抑制することができ、更に、スラグを固化させるための精錬剤を最低必要量の２．０倍以上添加すると、スラグ流出量を安定して１．０ｋｇ／ｔ以下に抑制することができた。
【００３８】
これに対して、スラグを固化させるための精錬剤を添加しない比較例、並びに、スラグを固化させるための精錬剤の添加量が少なく、本発明の範囲を満足しない比較例では、スラグ流出量は多く、２．０ｋｇ／ｔ以下にはならなかった。
【００３９】
又、スラグを固化させるための精錬剤を、炉内スラグ量に対して４．９％の同一量添加した比較例８、実施例３及び実施例７を比較すると、スラグ中のT.Fe濃度とＭｎＯ濃度とに応じて添加した実施例３及び実施例７ではスラグ流出量は２．０ｋｇ／ｔであったが、比較例８ではスラグ流出量は３．０ｋｇ／ｔであり、スラグを固化させるための精錬剤を単に同一量添加しても、スラグ流出を抑制できないことが分かった。即ち、スラグのT.Fe濃度及びＭｎＯ濃度に応じて添加量を決める必要があることが分かった。又、何れの精錬剤を用いても、溶鋼の温度低下は５℃程度で、わずかであった。
【００４０】
【発明の効果】
以上説明したように、本発明によれば、スラグを固化させるための精錬剤を、スラグ中のT.Fe濃度及びＭｎＯ濃度に応じて添加するので、スラグ中のＭｎＯ濃度が高い転炉精錬の場合でも、安定して出鋼時のスラグ流出を抑制することが可能となり、その結果、溶鋼清浄性の向上、合金鉄歩留まりの向上等の工業上有益な効果がもたらされる。
【図面の簡単な説明】
【図１】スラグの固相率に及ぼすスラグ中のT.Fe濃度及びＭｎＯ濃度の影響を示す図である。
【図２】スラグ中のT.Fe濃度及びＭｎＯ濃度と精錬剤の添加量とを因子として、スラグ流出抑制効果の有無の境界線を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for preventing outflow of slag in a converter to a ladle at the time of steel output from a converter to a ladle. Specifically, the slag outflow is prevented by increasing the solid phase ratio of the slag in the converter. It is about the method.
[0002]
[Prior art]
When hot metal is decarburized and refined in the converter, it is necessary to promote dephosphorization reaction of the hot metal, or to decarburize and refine the hot metal that has been subjected to preliminary dephosphorization treatment that does not require dephosphorization in the converter. A CaO-based fossilizer is added according to the SiO ₂ content brought into the converter as Mn ore or iron ore gangue, and the basicity (CaO / SiO ₂ ) is about 2-6. The slag is formed. By covering the hot metal surface, the slag also has an effect of reducing the scattering of the molten metal due to the supplied oxygen jet. This slag is mixed into the molten steel flow from the converter when flowing out from the converter to the ladle and flows out into the ladle.
[0003]
Usually, molten steel is deoxidized by a strong deoxidizer such as metal Al or ferrosilicon in the ladle after decarburization refining in the converter, and dissolved oxygen in the molten steel increased by oxygen blowing is reduced. In particular, in a steel type that requires high cleanliness, deoxidation treatment with metal Al is performed, and dissolved oxygen in the molten steel is reduced to substantially zero. Thus, although the molten steel is deoxidized and the amount of dissolved oxygen in the molten steel is reduced, the slag on the molten steel in contact with the molten steel contains lower oxides such as FeO and MnO, Since Fe and Mn have a lower affinity for oxygen than strong deoxidation elements such as Al and Si, the reaction in which FeO or MnO in the slag is reduced by Al or Si in the molten steel continues after deoxidation. However, reaction products such as Al ₂ O ₃ and SiO ₂ are generated in the molten steel, and not only the yield of Al or Si is lowered, but also a highly clean molten steel cannot be obtained. In addition, the ladle slag itself may be rolled into the molten steel to become non-metallic inclusions.
[0004]
In order to solve this problem, many methods for preventing the outflow of slag from the converter have been proposed. For example, in Patent Document 1, CaO content is added to the converter at the end of oxygen blowing to increase the basicity of the slag in the furnace and simultaneously dilute the T.Fe concentration in the slag to increase the melting point of the slag. A method for solidifying slag and preventing slag outflow at the time of steel output has been proposed. Patent Document 2 discloses a solid phase ratio of slag in a converter at the end of oxygen blowing or after completion of oxygen blowing. A method has been proposed in which MgO in an amount of 30% or more is added to the converter and the slag is solidified to prevent slag outflow during steel output. In addition, T.Fe in slag is a total value of the iron content of all the iron oxides in slag.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 64-36717
[Patent Document 2]
Japanese Laid-Open Patent Publication No. 2-111810
[Problems to be solved by the invention]
By the way, with the development of hot metal pretreatment technology in recent years, the amount of slagging agent required for decarburization and refining of converters has decreased, and the amount of slag generated in converter refining has been greatly reduced. Instead of a method of adjusting the Mn concentration of molten steel by adding iron, a method of adding a Mn ore to a converter and performing smelting reduction has become common. Since the amount of slag in the furnace is reduced and Mn ore is added, the MnO concentration in the slag is significantly higher than that of conventional slag. As the MnO concentration in the slag increases, the melting point of the slag decreases and at the same time the viscosity of the slag decreases in the molten steel temperature range. The amount of spillage is greatly increased compared to the conventional method.
[0008]
In the above-mentioned Patent Document 1, the solidification rate of slag is regarded as a function of two factors of slag basicity and T.Fe concentration in slag, and the influence of MnO concentration on the solidification rate of slag is completely taken into consideration. Absent. Similarly, in Patent Document 2, the solidification rate of slag is regarded as a function of three factors of slag basicity, T.Fe concentration in slag, and MgO concentration in slag, and the effect of MnO on the solidification rate of slag. The concentration effect is not taken into account at all. Therefore, in the methods of Patent Document 1 and Patent Document 2, in the refining of the converter in which the MnO concentration in the slag is increased by adding the Mn ore with a small amount of slag, the outflow of the slag from the converter is sufficiently prevented. Can not do it.
[0009]
The present invention has been made in view of the above circumstances, and the object of the present invention is to discharge slag from the converter at the time of steel output even in the case of converter refining with a small amount of slag and a high MnO concentration in the slag. It is an object of the present invention to provide a slag outflow prevention method capable of sufficiently preventing the slag.
[0010]
[Means for Solving the Problems]
The inventors of the present invention diligently studied and studied to solve the above problems. The results of the examination and research are explained below.
[0011]
In order to prevent the outflow of slag at the time of steel production, first, the effect of the components in the slag on the solid phase rate of the slag was investigated. As a result, as the T.Fe concentration in the slag increases, the solid phase ratio of the slag decreases significantly. Similarly to T.Fe, the MnO that increases when Mn ore is melted and reduced in the converter is also slag. It has been clarified that the solid-phase ratio of s. The MnO concentration in the slag may reach 20 to 30 mass% in the converter refining in which the amount of slag is suppressed and the Mn ore is added. In order to solidify the slag and prevent the slag from flowing out, it was found that it was extremely important to consider the MnO concentration in the slag.
[0012]
Therefore, in the range of slag composition in converter decarburization refining, the T.Fe concentration and MnO concentration are changed, and the relationship between the T.Fe concentration and MnO concentration and the slag solid phase ratio is used using general-purpose thermodynamic calculation software. It was calculated and examined. In the calculation, the slag temperature was set to 1650 to 1700 ° C., the slag basicity (CaO / SiO ₂ ) was set to ₂ to 4, and the MgO concentration in the slag was set to 5 to 15 mass%. The calculation results are shown in FIG.
[0013]
Since the effects of T.Fe and MnO on the solid phase ratio were almost equal, T.Fe + MnO was used as an index as shown in FIG. Further, an index was used as the solid phase ratio, and the solid phase ratio index at which the effect of suppressing the outflow of slag appeared was 100. That is, slag outflow was suppressed in the slag having a composition of T.Fe + MnO of 10 mass% or less. Therefore, the solid phase ratio index was set to 100 in this range. The solid phase index of slag decreases with increasing T.Fe + MnO, that is, the slag tends to flow out, and the slope of the solid phase index changes at the position where T.Fe + MnO is about 20 mass%. I understood.
[0014]
Based on the results shown in FIG. 1, an actual furnace test was conducted. After the oxygen blowing, quick lime mainly composed of CaO was added to the converter as a slag solidifying refining agent, and the amount of slag outflow was measured by changing the amount of solidifying refining agent added. . The slag outflow is measured by measuring the thickness of the slag that has flowed into the ladle and converting the outflow based on the measured slag thickness, or adding a predetermined amount of tracer element to the converter slag. And the method of converting the outflow amount based on the concentration of the tracer element of the slag in the ladle was used.
[0015]
Since the influence of the refining agent on the solid phase ratio varies depending on the amount of slag in the furnace even if the amount of refining agent is the same, the ratio of the amount of refining agent to the amount of slag in the furnace (refining agent addition amount / slag in the furnace) As a result of approximation using the approximate line of solid phase ratio shown in FIG. 1 as an operation factor, a boundary line indicating whether or not there is a slag outflow suppression effect was obtained as shown in FIG. That is, when the total value of T.Fe concentration and MnO concentration in the slag is 20 mass% or less, the refining agent mainly composed of CaO for solidifying the slag within the range satisfying the following formula (1). Is added to the converter. On the other hand, when the total value of T.Fe concentration and MnO concentration in the slag exceeds 20 mass%, the refining agent is converted into the converter within the range satisfying the following formula (2). It was found that by adding the slag, the slag in the converter was solidified by the added refining agent, and the outflow amount of the slag could be reduced. However, in the formulas (1) and (2), Wc is the addition amount (kg) of the refining agent for solidifying the slag, Ws is the estimated slag amount (kg) in the converter, and the boundary shown in FIG. A line is represented by the formulas (1) and (2).
[0016]
[Expression 1]

[0017]
[Expression 2]

[0018]
The present invention has been made on the basis of the above examination and research results, and the method for preventing the outflow of slag in the converter according to the first invention includes charging the molten iron dephosphorized in the hot metal preliminary treatment into the converter. In addition, when decarburizing and refining the molten iron by oxygen blowing in the converter, Mn ore is added to the converter during the oxygen blowing and the Mn ore is reduced in the converter. At the end of the period or after the end of oxygen blowing, the T.O. Depending on the Fe concentration and MnO concentration, T.I. When the total value of Fe concentration and MnO concentration is 20 mass% or less, a refining agent composed of one or more of limestone, quicklime, dolomite, and calcined dolomite is converted within the range satisfying the above formula (1). Added to the furnace, while T. When the total value of Fe concentration and MnO concentration exceeds 20 mass%, a refining agent composed of one or more of limestone, quicklime, dolomite, and calcined dolomite is converted within the range satisfying the above formula (2). It is added to the furnace, and the slag in the converter is solidified by the added refining agent to suppress the outflow of the slag from the converter during steel output.
[0020]
According to a second aspect of the present invention, there is provided a method for preventing the outflow of slag in a converter according to the first aspect , wherein the amount of slag in the converter is 20 kg or less per ton of molten steel, or is installed in the converter as a fossilizer. The quick lime is 10 kg or less per ton of molten steel.
[0021]
The method for preventing the outflow of slag in the converter according to the third invention is characterized in that, in the first or second invention , the basicity (CaO / SiO ₂ ) of the slag in the converter is 4.0 or less. To do.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0023]
The hot metal discharged from the blast furnace is received in a hot metal holding / conveying vessel such as a hot metal ladle or torpedo car and transferred to a converter for decarburization and refining in the next step. In the present invention, for the purpose of reducing the amount of alloy iron such as ferromanganese, when decarburizing and refining the hot metal in the converter, Mn ore is added to the converter and the Mn ore is melt-reduced. In order to improve the yield, it is necessary to reduce the amount of slag in the converter as much as possible. For this reason, hot metal pretreatment such as desulfurization treatment or dephosphorization treatment is performed on the hot metal during the conveyance. In recent years, since the hot metal pretreatment may be performed in the converter, the pretreatment may be performed in the converter without being limited to the middle of conveyance.
[0024]
In this case, in order to reduce the amount of slag in the converter as much as possible, it is preferable to perform dephosphorization by preliminary treatment so that the phosphorus concentration of the hot metal is lower than the phosphorus concentration level of the product, specifically about 0.015 mass% or lower. When the phosphorus concentration of hot metal is reduced to the phosphorus concentration level of the product, the amount of ironmaking agent such as quick lime required for converter refining will be 10 kg or less per ton of molten steel (hereinafter referred to as “kg / t”). The amount of slag can be reduced to about 20 kg / t or less.
[0025]
Thus, converter refining is preferable as the amount of generated slag is smaller, and therefore, the amount of slag in the furnace is 50 kg / t or less, that is, the amount of addition of a fossilizing agent such as quick lime is 20 kg / t or less. Desirably, the amount of slag in the furnace is 20 kg / t or less, that is, the addition amount of a fossilizing agent such as quick lime is 10 kg / t or less, and oxygen is blown up or bottom to decarboxylate hot metal. Do blow blowing. In this case, from the viewpoint of reducing the amount of slag in the furnace, the slag basicity (CaO / SiO ₂ ) is preferably 4.0 or less. However, if the basicity of the slag is too low, the basic refractory of the converter furnace body is damaged. Therefore, the lower limit of the basicity of the slag is preferably about 1.5. And in this converter refining, Mn ore is added in a converter as a Mn component source of molten steel. The addition amount of Mn ore is added in an appropriate amount according to the Mn component of the target molten steel, and the addition time of Mn ore is in the range from the initial stage to the middle stage of oxygen blowing. It is not preferable to add Mn ore after the middle stage of oxygen blowing because reduction time cannot be secured.
[0026]
A refining agent for cooling for solidifying slag is added to the converter at the end of such oxygen blowing or the period from the end of oxygen blowing to the steel out. In order to minimize the outflow of slag to the ladle, a refining agent is locally added or sprayed toward the slag that exists vertically above the outlet in the steel output tilted to the converter. May be. Such local addition exerts a remarkable effect of suppressing slag outflow in an operation in which the amount of slag is 20 kg / t or less, that is, the amount of addition of the slagging agent is 10 kg / t or less.
[0027]
The addition amount of the refining agent for solidifying the slag is determined according to the T.Fe concentration and the MnO concentration of the slag in the furnace. That is, when the total value of T.Fe concentration and MnO concentration in the slag is 20 mass% or less, the refining agent is added to the converter within the range satisfying the above formula (1), while in the slag When the total value of the T.Fe concentration and the MnO concentration exceeds 20 mass%, the refining agent is added to the converter within the range satisfying the above-mentioned formula (2).
[0028]
When calculating the formulas (1) and (2), the T.Fe concentration and the MnO concentration in the slag can be obtained by collecting the slag from the converter and analyzing the collected slag. In addition, compare the analytical value data of many slags with the converter operating conditions such as the amount of acid sent, the carbon concentration in the molten steel at the end point of oxygen blowing, the end point temperature, the amount of Mn ore added, and analyze the correlation between them. Thus, the T.Fe concentration and the MnO concentration in the slag can also be estimated from the converter operating conditions. The estimated slag amount Ws can be determined from the mass balance between the CaO analysis value of slag and the pure CaO content in quicklime added as a koji making agent. In addition, by comparing the CaO pure content in quicklime added as a slagging agent, the amount of acid sent, the carbon concentration in the molten steel at the end point of oxygen blowing, the end point temperature, the Mn ore addition amount, etc. By analyzing the correlation, the estimated slag amount Ws can be estimated from the converter operating conditions.
[0029]
As the refining agent for solidifying the slag, it is preferable to use a refining agent mainly composed of CaO or CaCO ₃ because it is inexpensive and does not damage the converter refractory. Particularly, a refining agent mainly composed of CaCO ₃ is thermally decomposed when heated in a furnace, and a large amount of heat is taken away during the thermal decomposition, so that it is more effective in solidifying slag. Examples of inexpensive refining agents mainly composed of CaO or CaCO ₃ include limestone, quicklime, dolomite, and calcined dolomite, and one or more of these can be used.
[0030]
By refining the hot metal in the converter in this manner, the outflow of the slag in the converter to the ladle at the time of steelmaking is suppressed. As a result, the reaction between the slag and the deoxidizing element in the molten steel is suppressed, and molten steel with high cleanliness can be produced. In addition, since the amount of slag in the ladle is small, it is possible to reduce the amount of metal Al or Al dross used for slag reforming to make slag harmless.
[0031]
【Example】
Examples of the present invention (Examples 1 to 15) will be described below together with comparative examples (Comparative Examples 1 to 10). About 250 tons of hot metal was charged into a top-bottom-blown combined blowing converter having a capacity of 250 tons, oxygen was blown up, and stirring gas was blown at the bottom, and decarburization blowing was performed. The hot metal used is hot metal that has been subjected to desulfurization treatment and dephosphorization treatment in a hot metal pretreatment facility. The components of the hot metal have an Si concentration of 0.07 mass% or less, an S concentration of 0.01 mass% or less, and a P concentration. Was unified to 0.010 to 0.015 mass%.
[0032]
At the initial stage of oxygen blowing in the converter, Mn ore was added into the converter. Further, quick lime was added as a koji making agent to generate slag. The basicity (CaO / SiO ₂ ) of the slag before the addition of the refining agent as a coolant, obtained from the slag analysis value, is 1.9 to 4.0, and is generally 2.5 to 3.5. It was. The T.Fe concentration and MnO concentration in the slag before adding the refining agent were determined from the analytical values of the collected slag, and the amount of slag in the converter was determined from the CaO balance.
[0033]
From the tuyere installed at the bottom of the converter furnace, about 10 to 20 Nm ^{3 of} Ar gas for stirring or nitrogen gas was blown per minute for the purpose of stirring the molten iron. Oxygen supply is carried out in the top-blown lance, 60000Nm ³ / hr of oxygen-flow-rate from the initial oxygen blowing toward the peak decarburization, in a slower oxygen blowing the end of the decarburization rate was 30000Nm ³ / hr. Then, at the end of oxygen blowing or after completion of oxygen blowing, one of quick lime, limestone and unfired dolomite was added to the converter. The outflow amount of slag to the ladle was obtained by measuring the slag thickness in the ladle after steelmaking and obtaining the slag outflow amount based on the slag thickness.
[0034]
Table 1 shows the operation conditions and operation results of Examples 1 to 15 and Comparative Examples 1 to 10. The “minimum necessary amount” in the column of “addition amount / minimum necessary amount” in Table 1 is the above-described formula (1) and () according to the total concentration of the T.Fe concentration and the MnO concentration in the slag. 2) The lower limit value of the addition amount calculated by the formula, and the condition that the ratio of the addition amount / minimum required amount is 1.0 or more is within the scope of the present invention.
[0035]
[Table 1]

[0036]
As shown in Table 1, in Examples 1 to 6 to which quick lime was added, the slag outflow amount was stably about 2.0 kg / t. In particular, when a refining agent for solidifying slag was added at least 1.5 times the minimum required amount, the slag outflow amount could be suppressed to about 1.5 kg / t.
[0037]
In Examples 7 to 15 to which limestone or unbaked dolomite was added, the slag outflow amount can be further suppressed as compared with the examples using quick lime, and the slag outflow amount can be stably reduced to 1.5 kg / t or less. I was able to. In particular, when a refining agent for solidifying slag is added at least 1.5 times the minimum required amount, the outflow of slag can be suppressed to about 1.0 kg / t, and further, a refining agent for solidifying slag. Was added more than 2.0 times the minimum required amount, the slag outflow amount could be stably suppressed to 1.0 kg / t or less.
[0038]
On the other hand, in the comparative example in which the refining agent for solidifying the slag is not added, and in the comparative example in which the amount of the refining agent for solidifying the slag is small and does not satisfy the scope of the present invention, the slag outflow amount is In many cases, it was not less than 2.0 kg / t.
[0039]
Further, when Comparative Example 8, Example 3 and Example 7 in which the same amount of 4.9% of the refining agent for solidifying the slag was added to the amount of slag in the furnace were compared, the T.Fe concentration in the slag was compared. In Example 3 and Example 7 added according to the MnO concentration, the slag outflow amount was 2.0 kg / t. In Comparative Example 8, the slag outflow amount was 3.0 kg / t, and the slag was solidified. It was found that the slag outflow could not be suppressed by simply adding the same amount of the refining agent. That is, it was found that the addition amount must be determined according to the T.Fe concentration and MnO concentration of the slag. Moreover, even if any refining agent was used, the temperature drop of molten steel was about 5 degreeC and was slight.
[0040]
【The invention's effect】
As described above, according to the present invention, the refining agent for solidifying the slag is added according to the T.Fe concentration and the MnO concentration in the slag, so that the converter refining in which the MnO concentration in the slag is high. Even in this case, it is possible to stably suppress the outflow of slag at the time of steel output, and as a result, industrially beneficial effects such as improved molten steel cleanliness and improved alloy iron yield are brought about.
[Brief description of the drawings]
FIG. 1 is a graph showing the influence of T.Fe concentration and MnO concentration in slag on the solid phase rate of slag.
FIG. 2 is a diagram showing boundaries of whether or not there is an effect of suppressing slag outflow, with factors such as T.Fe concentration and MnO concentration in slag and the amount of refining agent added.

Claims

The molten iron dephosphorized in the hot metal pretreatment is charged into the converter, and when the hot metal is decarburized and refined by oxygen blowing in the converter, Mn ore is added to the converter during the oxygen blowing. Then, the Mn ore is reduced in the converter, and at the end of the oxygen blowing or after completion of the oxygen blowing, the T.O. Depending on the Fe concentration and MnO concentration, T.I. When the total value of Fe concentration and MnO concentration is 20 mass% or less, a refining agent comprising at least one of limestone, quicklime, dolomite, and calcined dolomite is converted within the range satisfying the following formula (1). Added to the furnace, while T. When the total value of Fe concentration and MnO concentration exceeds 20 mass%, a refining agent composed of one or more of limestone, quicklime, dolomite and calcined dolomite is converted within the range satisfying the following formula (2). A method for preventing the outflow of slag in a converter, comprising adding to the furnace and solidifying the slag in the converter with the added refining agent to suppress the outflow of the slag from the converter during steel output.
Wc × 100 ≧ 0.5 × Ws × [T.Fe (mass%) + MnO (mass%) − 10] (1)
Wc x 100 ≥ 0.2 x Ws x [T.Fe (mass%) + MnO (mass%) + 5] (2)
However, in the formulas (1) and (2), Wc is the addition amount (kg) of the refining agent for solidifying the slag, and Ws is the estimated slag amount (kg) in the converter.

The amount of the slag in the converter is set to 20 kg or less per ton of molten steel, or quick lime charged into the converter as a slagging agent is set to 10 kg or less per ton of molten steel. To prevent the outflow of slag in the converter.

The method for preventing the outflow of slag in the converter according to claim 1 or 2, wherein the basicity (CaO / SiO ₂ ) of the slag in the converter is 4.0 or less.