JP2004307952A - METHOD FOR ADDING Cr IN CONVERTER - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for adding Cr, which can adjust a Cr content with a high Cr yield even when manufacturing a high-Cr steel through refining it under a condition of a small amount of slag in a converter, without causing any trouble in a refining operation. <P>SOLUTION: The method for adding Cr in the converter comprises, in the refinement step in the converter, adding Cr oxides after starting oxygen blowing, and charging a Cr-containing ferroalloy after having added the Cr oxides. The method preferably comprises charging the Cr oxides, then supplying particularly a specified amount of oxygen in the following expression 1: (0.28×S-3)≤V≤(0.28×S+10) (1), wherein V is a supplied amount of oxygen (Nm<SP>3</SP>/t) after charging of the Cr oxides and before charging of the Cr-containing ferroalloy; and S is S(%)=[(mass of Cr<SB>2</SB>O<SB>3</SB>forming FeO-Cr<SB>2</SB>O<SB>3</SB>out of charged Cr oxides)/(mass of Cr<SB>2</SB>O<SB>3</SB>on the assumption that all charged oxides are Cr<SB>2</SB>O<SB>3</SB>)] ×100, subsequently charging the Cr-containing ferroalloy, and afterwards supplying oxygen of 2 to 10 Nm<SP>3</SP>/t to finish the blowing. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

図５から次の様なことがわかる。
【００２２】
（ａ）Ｓ＝０の場合（Ｃｒ酸化物は、Ｃｒ_２Ｏ_３からなりＦｅＯ・Ｃｒ_２Ｏ_３を含まないものである場合）
Ｃｒ酸化物を投入した直後にＣｒ含有合金鉄を投入すると、高いＣｒ歩留りを達成できることがわかる。
【００２３】
Ｃｒ酸化物がこの様にＣｒ_２Ｏ_３からなる場合、該Ｃｒ酸化物は投入してすぐに（若干のスラグ中に懸濁するための時間：１分間程度は必要であるが）スラグ中のＣｒ_２Ｏ_３濃度を高めることができるので、該Ｃｒ酸化物投入直後にＣｒ含有合金鉄を添加しても、Ｃｒ含有合金鉄の酸化ロスはほとんどなく高いＣｒ歩留りを達成できる。
【００２４】
一方、過度に酸素を供給した後にＣｒ含有合金鉄を投入すると、図１に示す通りスラグ中のＣｒ_２Ｏ_３濃度増加に伴いスラグ中のＴ．Ｆｅ濃度（スラグ中のＦｅ酸化物であるＦｅＯとＦｅ_２Ｏ_３の合計中の鉄純分濃度）も増大して滓化が促進され、スラグ酸化度の上昇を招き、図５に示す通りＣｒ歩留りが低下するので好ましくない。
【００２５】
Ｓ＝０のＣｒ酸化物の具体例として、例えば高Ｃｒ鋼を溶製した後に残るスラグ等が挙げられる。
【００２６】
（ｂ）Ｓ＝１００の場合（Ｃｒ酸化物は、ＦｅＯ・Ｃｒ_２Ｏ_３からなりＣｒ_２Ｏ_３を含まないものである場合）
Ｃｒ酸化物を投入し、上記化学式（３）の反応に要する時間を十分確保した後にＣｒ含有合金鉄を投入すると、高Ｃｒ歩留りを達成できることがわかる。上記Ｓ＝０の場合の様に、Ｃｒ酸化物投入直後にＣｒ含有合金鉄を投入すると、上記化学式（３）の反応が十分に進んでおらずスラグのＣｒ_２Ｏ_３量が確保されていないので、投入したＣｒ含有合金鉄が酸化され易く、Ｃｒ歩留りが低下するおそれがある。
【００２７】
一方、過度に酸素を供給してからＣｒ含有合金鉄を投入すると、上記Ｓ＝０の場合と同様にスラグの滓化が促進されてＣｒ歩留りが低下するので好ましくない。
【００２８】
Ｃｒ酸化物（Ｓ＝１００）の具体例として、例えば予備還元処理を施していないＣｒ鉱石や同組成の耐火物廃材等が挙げられる。
【００２９】
（ｃ）Ｓ＝５０の場合（Ｃｒ酸化物は、Ｃｒ_２Ｏ_３とＦｅＯ・Ｃｒ_２Ｏ_３が１：１で混合したものである場合）
この場合には上記Ｓ＝０の場合とＳ＝１００の場合の中間挙動を示す。Ｃｒ酸化物（Ｓ＝５０）の具体例として、例えば予備還元処理が完全に施されていない半還元Ｃｒ鉱石や、上記Ｓ値が０％のＣｒ鉱石とＳ値が１００％のＣｒ鉱石をＳ値が５０％となるように配合したもの等が挙げられる。
【００３０】
前記図５の結果をもとに、上記Ｓ値とＣｒ酸化物投入後からＣｒ含有合金鉄投入までの酸素供給量との関係を求めた。その結果を図２に示す。
【００３１】
図２から、スラグ中のＣｒ_２Ｏ_３濃度を高めて高いＣｒ歩留りを達成するには、Ｃｒ酸化物投入後からＣｒ含有合金鉄投入までの酸素供給量をＳ値に応じて決定すればよいことがわかる。本発明者らは、図２の結果から、Ｃｒ酸化物投入後からＣｒ含有合金鉄投入までの酸素供給量（Ｖ）を、上記式（１）の範囲内とした。
【００３２】
即ち、Ｃｒ酸化物投入後からＣｒ含有合金鉄投入までの酸素供給量（Ｖ）が（０．２８×Ｓ−３）Ｎｍ^３／ｔに満たない場合には、スラグ中のＣｒ_２Ｏ_３量が十分確保されておらず、この状態でＣｒ含有合金鉄を投入しても該Ｃｒ含有合金鉄の酸化ロスが生じ易く高いＣｒ歩留りを達成することができない。より好ましくは、上記式（１）において、前記図５でＣｒ歩留りが最高値となるよう、Ｃｒ酸化物投入後の酸素供給量が（０．２８×Ｓ＋２）Ｎｍ^３／ｔの時点でＣｒ含有合金鉄を投入するのがよい。
【００３３】
一方、過剰に酸素を供給しても、上述した通り滓化促進によりＣｒ歩留りが徐々に低下するため、酸素供給量は（０．２８×Ｓ＋１０）Ｎｍ^３／ｔ以下とするのが好ましい。
【００３４】
Ｃｒ酸化物として微粉末状（粒径約５ｍｍ以下）のものを使用する場合には、上記式（１）を満たす範囲内で酸素供給量を比較的少なくすることができる。該微粉末状のＣｒ酸化物であれば、すぐに溶解してスラグ中のＣｒ_２Ｏ_３濃度を高めたり、上記化学式（３）の反応が促進されるからである。しかし粒径約１０ｍｍ以上のＣｒ酸化物を投入する場合には、上記式（１）を満たす範囲内で酸素供給量を比較的多くして、該Ｃｒ酸化物を十分に溶融させるのがよい。
【００３５】
（Ｂ）またＣｒ含有合金鉄を投入した後の酸素供給量は２〜１０Ｎｍ^３／ｔの範囲とするのがよい。
【００３６】
転炉精錬では、酸素を吹き込むことで脱炭処理が行われるが、Ｃｒ含有合金鉄を投入した後に、多量の酸素を供給すると、添加したＣｒ含有合金鉄中のＣｒが酸化されてＣｒ_２Ｏ_３となりＣｒ歩留りが低下するので好ましくない。
【００３７】
従って、Ｃｒ歩留りの向上という観点からは、Ｃｒ含有合金鉄投入後の酸素供給時間を短くするのがよく、吹錬末期に投入するのがよい。また、スラグ中のＣｒ_２Ｏ_３からＣｒへの還元反応は吸熱反応であるため、溶鋼温度が高温となる吹錬末期に該還元反応は優位となる。従って、この吹錬末期にＣｒ含有合金鉄を投入すれば、Ｃｒの酸化ロスも抑えられるので、この様な観点からも、Ｃｒ含有合金鉄を吹錬末期に投入するのが好ましい。いずれにしても本発明では、Ｃｒ含有合金鉄を溶鋼に投入後、吹錬終了までの酸素供給量を１０Ｎｍ^３／ｔ以下とするのがよい。Ｃｒ含有合金鉄の酸化を抑制して更にＣｒ歩留りを高めるには、Ｃｒ含有合金鉄投入後、吹錬終了までの酸素供給量を８Ｎｍ^３／ｔ以下とするのがより好ましい。
【００３８】
しかし、Ｃｒ含有合金鉄投入後の吹錬時間が極端に短い（即ち、吹錬終了までの酸素供給量が少ない）と、次の様な問題が生じる。
【００３９】
（ｉ）吹錬終了間際には、転炉ダイナミックコントロール、即ち、吹錬中にサブランスでＣ濃度と溶鋼温度（Ｔ）を直接測定し、数秒毎にＣ濃度と溶鋼温度（Ｔ）を逐次計算表示して吹錬終了の判断が行われるが、この際、吹錬終了直前にＣｒ含有合金鉄を添加すると、吹錬終了の判断基準であるＣ濃度と溶鋼温度（Ｔ）が目標設定値から外れ易くなる。
【００４０】
（ｉｉ）Ｃｒ含有合金鉄を投入した後に吹錬を十分行うことによって、不純物であるＣが脱炭処理され、水分が蒸発し、またＴｉ等の不純物がスラグに捕捉されて除去される。
【００４１】
しかし、吹錬終了直前にＣｒ含有合金鉄を添加すると、Ｃｒ含有合金鉄中に含まれるこれらの不純物（Ｃ、Ｈ_２Ｏ、Ｔｉ等）が十分除去されず、溶鋼中に残存したままとなり、上述した様に吹錬終了時のＣ濃度が目標値から外れるといった不具合が生じる他、該不純物の除去処理を別途行う必要が生じてくる。例えば吹錬終了後に脱ガス工程等を設ける等の必要が生じ、連々鋳を実施する場合等に効率よく作業を進めることができない。
【００４２】
（ｉｉｉ）Ｃｒ含有合金鉄が十分に攪拌・混合されない状態で吹錬を終了すると、添加したＣｒ含有合金鉄の分散が不均一となって、成分バラツキ等が生じるおそれがある。
【００４３】
従って、Ｃｒ含有合金鉄を投入した後は、少なくとも２Ｎｍ^３／ｔの酸素を供給して吹錬を行い、Ｃｒ含有合金鉄中の不純物の除去や攪拌等を行うのがよい。該不純物の除去等や攪拌を十分に行うには、Ｃｒ含有合金鉄を投入したのち３Ｎｍ^３／ｔ以上の酸素を供給して吹錬を行うことがより好ましい。
【００４４】
本発明では、この様な適正時期にＣｒ酸化物およびＣｒ含有合金鉄を投入することで、脱燐や脱炭等といった精錬操業に支障をきたすことなく高Ｃｒ歩留りで溶鋼中のＣｒ量を確保することができる。
【００４５】
図３は、Ｃｒ酸化物およびＣｒ含有合金鉄のどちらも本発明で規定する時期に投入した場合（Ｃｒ酸化物の投入時期：精錬開始後，Ｃｒ含有合金鉄の投入時期：精錬中期以降）と、Ｃｒ含有合金鉄のみを規定の時期に投入し、Ｃｒ酸化物は精錬開始前に投入した場合（Ｃｒ酸化物の投入時期：精錬開始前，Ｃｒ含有合金鉄の投入時期：精錬中期以降）について、スラグ中のＣｒ_２Ｏ_３濃度とＣｒ歩留りとの関係を示している。この図３から、本発明で規定する時期にＣｒ酸化物およびＣｒ含有合金鉄を投入することで、高いＣｒ歩留りを達成できることがわかる。
【００４６】
Ｃｒ酸化物は、上記適正時期に投入することに加えて、Ｃｒ純分換算で下記式（２）を満たす量を投入するのがよい。
Ｃｒ酸化物の投入量（ｋｇ／ｔ）＝炉内スラグ量（ｋｇ／ｔ）×１．４６×Ｂ_{Ｃｒ２Ｏ３} …（２）
（但し、Ｂ_{Ｃｒ２Ｏ３}はスラグ中のＣｒ_２Ｏ_３濃度の最適必要増加分を示し、２〜１５質量％の範囲内とする）
上記Ｃｒ酸化物の投入量は、例えば次の様にして求めることができる。通常行う操業下での溶鋼中のＣｒ濃度［Ｃｒ］が０．５質量％、溶鋼中のＦｅ濃度（Ｔ．Ｆｅ）が８質量％、スラグ中のＣｒ_２Ｏ_３濃度（Ｃｒ_２Ｏ_３）が４質量％であり、目標値として溶鋼中のＣｒ目標濃度［Ｃｒ］’を１．０質量％、溶鋼中のＦｅ目標濃度（Ｔ．Ｆｅ）’を１０質量％にしようとするとき、スラグ中のＣｒ_２Ｏ_３目標濃度（Ｃｒ_２Ｏ_３）’は、平衡状態の関係から求まる下記式（５）より１０質量％となる。
【００４７】
（Ｃｒ_２Ｏ_３） ’＝［（Ｔ．Ｆｅ）’／（Ｔ．Ｆｅ）｝×｛［Ｃｒ］’／ ［Ｃｒ］｝×（Ｃｒ_２Ｏ_３） …（５）
従ってＢ_{Ｃｒ２Ｏ３}（スラグ中のＣｒ_２Ｏ_３濃度の最適必要増加分）は、
Ｂ_{Ｃｒ２Ｏ３}＝（Ｃｒ_２Ｏ_３）’−（Ｃｒ_２Ｏ_３）＝６（質量％）となる。
【００４８】
よって、この場合のＣｒ酸化物の投入量は、［炉内スラグ量（ｋｇ／ｔ）×１．４６×６］ （ｋｇ／ｔ）とするのが最適であることがわかる。尚、スラグ中のＣｒ_２Ｏ_３濃度の最適必要増加分（質量％）は、この様に操業条件に応じて適宜設定することができるが、Ｃｒ酸化物を過剰に添加するとスラグが酸化性になりやすいので、Ｃｒ歩留りの低下の抑制を考慮すると２〜１５質量％の範囲内とするのがよい。
【００４９】
この様にＣｒ酸化物を適正量投入して、スラグ中のＣｒ_２Ｏ_３濃度を最適濃度にした状態でＣｒ含有合金鉄を投入することによって、より高いＣｒ歩留りを達成することができる。
【００５０】
尚、Ｃｒ酸化物の投入量が上記式（５）で規定した量を下回る場合には、スラグ中のＣｒ_２Ｏ_３濃度を、平衡時のＣｒ_２Ｏ_３濃度まで十分に高めることができず、Ｃｒ含有合金鉄を投入したときに、該Ｃｒ含有合金鉄中のＣｒの酸化反応が進行し易くＣｒ歩留りを高めることが難しい。好ましくは前記Ｃｒ酸化物を少なくとも２ｋｇ／ｔ以上投入するのがよい。
【００５１】
一方、Ｃｒ酸化物の投入量が上記式（５）で規定した量を上回る場合には、スラグ中のＣｒ_２Ｏ_３量が過度に増加し、該Ｃｒ_２Ｏ_３濃度の増加に伴い前記図１に示すようにスラグ中のＴ．Ｆｅ濃度（スラグ中のＦｅ酸化物であるＦｅＯとＦｅ_２Ｏ_３の合計中の鉄純分濃度）も増大しスラグが高酸化性となる。一旦、高酸化性のスラグが形成されると、該スラグを低酸化性に迅速に戻すのは、酸素を供給しつつ精錬する酸化精錬では非常に困難である。従ってこの様な状態になると、Ｃｒ歩留りが低下するばかりか溶鋼中のＣｒ濃度を十分に高めることもできないので好ましくない。前記Ｃｒ酸化物の投入量は多くとも１５ｋｇ／ｔ以下とするのが好ましい。
【００５２】
本発明ではこの様に、スラグ中のＣｒ_２Ｏ_３量確保にＦｅＯ・Ｃｒ_２Ｏ_３を用いる場合も考慮しているので、前記Ｃｒ酸化物としては、該ＦｅＯ・Ｃｒ_２Ｏ_３を比較的多く含むＣｒ鉱石を用いることができる他、Ｃｒ濃度の高い鋼種を溶製したときに生じるＣｒ_２Ｏ_３濃度やＦｅＯ・Ｃｒ_２Ｏ_３濃度の高いスラグをリサイクルして使用することができる。
【００５３】
尚、Ｃｒ酸化物としてＣｒ鉱石を用いる場合には、粉砕された粉末状のＣｒ鉱石（粒径約１〜５ｍｍ）が安価であり、かつ、効率的にスラグ中のＣｒ_２Ｏ_３濃度を高めて、投入するＣｒ含有合金鉄の酸化を確実に抑制できるので好ましい。また、この様な粉末状のＣｒ鉱石を転炉上部から添加すると、溶鋼まで到達せずスラグ中に留まって該スラグと混合するので、塊鉱石の場合より効率的にスラグ中のＣｒ_２Ｏ_３濃度を高めることができる。
【００５４】
Ｃｒ含有合金鉄については、特にその投入量を限定するものでなく、目標Ｃｒ値に併せて適量添加することができる。投入するＣｒ含有合金鉄中の不純物も精錬時に十分除去できるので、該Ｃｒ含有合金鉄として、Ｆｅ−Ｃｒ系合金を用いる場合に、不純物をあまり含まない高級品の他、不純物を比較的多く含むＦｅ−Ｃｒ系合金の中級品や低級品を使用することもできる。
【００５５】
【実施例】
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも可能であり、それらはいずれも本発明の技術的範囲に含まれる。
【００５６】
＜実施例１＞
まず、本発明で定める如くＣｒ酸化物とＣｒ含有合金鉄を併用し、Ｃｒ酸化物を予め投入してスラグ中のＣｒ_２Ｏ_３量を確保した上でＣｒ含有合金鉄を投入する方法として、Ｃｒ酸化物としてＣｒ鉱石を酸素供給積算量が２６．３Ｎｍ^３／ｔの時期に投入後、７．４Ｎｍ^３／ｔの酸素を供給してから、Ｃｒ含有合金鉄としてＦｅ−Ｃｒ系合金を投入し、該Ｆｅ−Ｃｒ系合金の投入後に５．６Ｎｍ^３／ｔの酸素を供給して吹錬を終了した。
【００５７】
またＣｒ酸化物としてＣｒ鉱石のみ用いて溶鋼中のＣｒ量を調整する従来法として、Ｃｒ鉱石を酸素供給積算量が５．３Ｎｍ^３／ｔの時期に投入後、３４．０Ｎｍ^３／ｔの酸素を供給して吹錬を終了した。それぞれの方法について、投入するＣｒ鉱石またはＦｅ−Ｃｒ系合金量を変化させて、溶鋼中のＣｒ濃度を調整したときのＣｒ歩留りを求めた。いずれの方法もその他の操業条件は下記の通りとした。
【００５８】

この様に夫々の方法でＣｒ量を調整したときの、Ｃｒ投入量（投入したＣｒ鉱石またはＦｅ−Ｃｒ系合金量のＣｒ純分換算量）とＣｒ歩留りとの関係を図４に示す。
【００５９】
この図４から、Ｃｒ酸化物のみ用いて溶鋼中Ｃｒ量を調整する場合には、Ｃｒ投入量を増加させるにつれてＣｒ歩留りが低下するのに対し、本発明の方法によれば、Ｃｒ投入量に関係なく高いＣｒ歩留りを達成できることがわかる。
【００６０】
＜実施例２＞
Ｃｒ酸化物とＣｒ含有合金鉄の投入時期の関係がＣｒ歩留りに及ぼす影響について調べた。
【００６１】
操業は次の様にして行った。即ち、前記Ｓ値が０％のＣｒ酸化物として、Ｃｒ_２Ｏ_３含有リサイクルスラグを、Ｓ値が５０％のＣｒ酸化物として、前記Ｃｒ_２Ｏ_３含有リサイクルスラグと生クロム鉱石を半々の割合で配合したものを、またＳ値が１０％のＣｒ酸化物として生クロム鉱石を使用し、Ｃｒ酸化物投入後Ｃｒ含有合金鉄投入までの酸素供給量を変化させた。それ以外は上記実施例１と同様にした。その結果を、Ｃｒ酸化物の投入時からＣｒ含有合金鉄の投入までの酸素供給量とＣｒ歩留りとの関係として図５に示す。
【００６２】
図５から、Ｃｒ酸化物の投入時からＣｒ含有合金鉄の投入までの酸素供給量が本発明で好ましいとする範囲を外れると、Ｃｒ歩留りが低下しており、Ｃｒ含有合金鉄の投入は、Ｃｒ酸化物の投入後、規定量の酸素を供給してから行うのがよいことがわかる。
【００６３】
＜実施例３＞
Ｃｒ含有合金鉄投入後の酸素供給量を変化させて、Ｃｒ歩留りおよび残存不純物量に与える影響を調べた。
【００６４】
操業条件は、Ｃｒ含有合金鉄投入後吹錬終了までの酸素供給量を０〜１８Ｎｍ^３／ｔの範囲で変化させ、Ｃｒ酸化物の投入した後Ｃｒ含有合金鉄を投入するまでの酸素供給量を２〜６Ｎｍ^３／ｔとする以外は、上記実施例１と同様の条件で操業した。この様にして操業したときの、Ｃｒ含有合金鉄投入後吹錬終了までの酸素供給量とＣｒ歩留りとの関係を図６に示す。
【００６５】
また、Ｃｒ含有合金鉄投入後吹錬終了までの酸素供給量と吹錬終了時の溶鋼中の残存不純物量との関係として、図７にＣｒ含有合金鉄投入後吹錬終了までの酸素供給量と吹錬終了時の溶鋼中Ｔｉ濃度の関係を示し、図８にＣｒ含有合金鉄投入後吹錬終了までの酸素供給量と吹錬終了時の溶鋼中Ｈ（水素）濃度の関係を示し、図９にＣｒ含有合金鉄投入後吹錬終了までの酸素供給量と吹錬終了時の溶鋼中Ｃ（炭素）濃度の関係を示す。
【００６６】
図６から、Ｃｒ含有合金鉄を投入後に多量の酸素を供給すると、Ｃｒ歩留りが低下することが分かる。Ｃｒ歩留りを９０％以上とするには、Ｃｒ含有合金鉄を投入後の酸素供給量を１０Ｎｍ^３／ｔ以下に抑える、換言すれば、酸素供給量が１０Ｎｍ^３／ｔを超えないうちに吹錬操業を終了するのがよいことがわかる。また、図７および図８から、特に安価なＣｒ含有合金鉄に多く含まれている水分やＴｉ等の不純物を十分除去して溶鋼中の残存不純物量を低減するには、Ｃｒ含有合金鉄を投入後、吹錬終了までに少なくとも２Ｎｍ^３／ｔ以上の酸素を供給して吹錬処理を行うのがよいことがわかる。
【００６７】
また低Ｃ濃度の鋼種を製造する場合には、投入するＣｒ含有合金鉄に含まれるＣ量が多いと、吹錬終了時のＣ濃度が目標値より高くなるといった不具合が生じる。従って、図９に示す様に溶鋼中のＣ量を低減すべく、酸素を供給して吹錬処理を行うのがよいことがわかる。
【００６８】
【発明の効果】
本発明は上記のように構成されており、本発明の方法で転炉にＣｒを添加すれば、高Ｃｒ鋼を製造する場合であっても脱炭や脱燐等といった精錬操業に支障をきたすことなく高Ｃｒ歩留りで溶鋼中のＣｒ量を調整することができる。
【００６９】
この様な方法を実施することで、更に、Ｃｒ酸化物として安価なＣｒ鉱石等をＦｅＯ・Ｃｒ_２Ｏ_３の割合に関係なく使用した場合にも、高いＣｒ歩留りを達成することができる。また、Ｃｒ酸化物を予め投入するため、Ｆｅ−Ｃｒ系合金等の高価なＣｒ含有合金鉄を使用する場合であっても高いＣｒ歩留りを達成することができ、該Ｃｒ含有合金鉄として、Ｃ、Ｈ_２Ｏ、Ｔｉ等の不純物量の多いＦｅ−Ｃｒ系合金等の低級品を使用した場合でも、脱ガス等の工程をあらためて設ける必要なく効率良くＣｒ量を調整することができる。
【図面の簡単な説明】
【図１】スラグ中のＣｒ_２Ｏ_３濃度とスラグ中のＴ．Ｆｅ濃度の関係を示したグラフである。
【図２】Ｃｒ酸化物投入後からＣｒ含有合金鉄投入までの酸素供給量（Ｖ）とＳ値との関係を示したグラフ（スラグ量が４０ｋｇ／ｔ以下の場合）である。
【図３】Ｃｒ含有合金鉄投入時のスラグ中のＣｒ_２Ｏ_３濃度とＣｒ歩留りとの関係を、Ｃｒ酸化物の投入時期別に示したグラフである。
【図４】本発明法または従来法で溶鋼中Ｃｒ量を調整した場合の、Ｃｒ投入量とＣｒ歩留りの関係を示したグラフである。
【図５】Ｃｒ酸化物の投入時からＣｒ含有合金鉄の投入までの酸素供給量とＣｒ歩留りとの関係を示すグラフである。
【図６】Ｃｒ含有合金鉄（Ｆｅ−Ｃｒ系合金）投入後吹錬終了までの酸素供給量とＣｒ歩留りとの関係を示したグラフである。
【図７】Ｃｒ含有合金鉄（Ｆｅ−Ｃｒ系合金）投入後吹錬終了までの酸素供給量と吹錬終了時の溶鋼中のＴｉ濃度との関係を示したグラフである。
【図８】Ｃｒ含有合金鉄（Ｆｅ−Ｃｒ系合金）投入後吹錬終了までの酸素供給量と吹錬終了時の溶鋼中のＨ（水素）濃度との関係を示したグラフである。
【図９】Ｃｒ含有合金鉄（Ｆｅ−Ｃｒ系合金）投入後吹錬終了までの酸素供給量と吹錬終了時の溶鋼中のＣ（炭素）濃度との関係を示したグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for adding Cr in a converter, and secures the amount of Cr in molten steel at a high Cr yield without hindering the refining operation performed under a small amount of slag even when producing high Cr steel. And a useful method for adding Cr.
[0002]
[Prior art]
As a method of adding Cr to molten steel in a converter operation process, a method of adding an Fe—Cr alloy after refining is used. However, the Fe-Cr-based alloy is expensive, and part of the Fe-Cr-based alloy is oxidized at the time of blowing to form slag (Cr ₂ O ₃ ), The Cr yield is poor and not economical.
[0003]
Therefore, it has been proposed to use inexpensive Cr ore instead of the Fe-Cr alloy. Patent Literature 1 discloses that in the reduction and recovery of Cr oxide in slag, the slag basicity during smelting reduction refining, It has been proposed to control the medium residual carbon, the carbon content in the molten iron and the temperature of the molten iron, and to recover the chromium oxide in the slag by keeping the amount of Si after refining within a certain range.
[0004]
Further, in producing stainless steel using chromium oxide raw materials such as recycled chromium oxide-containing slag and chromium ore, there has been proposed a method of efficiently recovering chromium from the slag and chromium ore (for example, Patent Documents) 2-9).
[0005]
Patent Literature 10 discloses a method capable of solving the problem of undissolved chromium only by carbon reduction without using two furnaces, a smelting reduction furnace and a decarburization furnace, and reducing the amount of slag-making agent used in the decarburization period. It is shown. Patent Literature 11 also discloses a method of suppressing chromium oxidation in converter blowing acid decarburization refining, which effectively suppresses the oxidation of added ferrochrome alloy iron during the initial to middle stages of decarburization, and reduces the chromium generated in the later stage of decarburization. A method for reducing and recovering oxides in molten steel has been proposed.
[0006]
Patent Literature 12 discloses a method of efficiently reducing chromium oxide contained in slag, reducing the cost of a chromium alloy, improving the quality of the slag, such as its expandability, and enabling resource recycling.
[0007]
In the above technology, in order to effectively use chromium oxide such as slag as a Cr source, a method for securing the amount of Cr in the hot metal by reducing the slag or the Cr ore is examined, or the method occurs during the reduction reaction of the Cr ore. Trying to solve the problem. However, when the amount of Cr in molten steel is adjusted using only slag or Cr ore as described above, if the amount of Cr ore added is increased to increase the amount of Cr, the amount of slag increases and the Cr yield decreases. In addition, the increase in the slag causes forming or the like, which hinders the refining operation. Therefore, further improvement is required to efficiently increase the Cr content in molten steel with a high Cr yield.
[0008]
[Patent Document 1]
Japanese Patent Publication No. 4-31015
[Patent Document 2]
Japanese Patent No. 2947063
[Patent Document 3]
JP-A-10-46225
[Patent Document 4]
JP-A-7-216429
[Patent Document 5]
JP-A-8-295914
[Patent Document 6]
JP-A-9-31514
[Patent Document 7]
JP-A-9-31515
[Patent Document 8]
JP-A-9-67608
[Patent Document 9]
JP-A-9-87722
[Patent Document 10]
JP-A-8-319508
[Patent Document 11]
JP-A-11-172317
[Patent Document 12]
JP 2001-294926 A
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and its purpose is to prevent the refining operation performed under a small amount of slag in a converter even when producing high Cr steel, An object of the present invention is to provide a useful Cr addition method capable of adjusting the amount of Cr in molten steel with a high Cr yield.
[0010]
[Means for Solving the Problems]
The method for adding Cr in the converter according to the present invention is characterized in that a Cr oxide is added after the start of blowing, and a Cr-containing ferromagnetic iron is charged after the addition of the Cr oxide. Ore, Cr ore or Cr-containing slag can be used. Also,
(A) After charging the Cr oxide, supplying an amount (V) of oxygen satisfying the following formula (1), then charging the Cr-containing ferromagnetic iron, and
(0.28 × S-3) ≦ V ≦ (0.28 × S + 10) (where V ≧ 0) (1)
中 In equation (1),
V: The amount of oxygen supply (Nm ³ / T)
S (%) = [(FeO.Cr in input Cr oxide) ₂ O ₃ Forming Cr ₂ O ₃ Mass) / (All input Cr oxides are Cr ₂ O ₃ Cr assuming that ₂ O ₃ Mass)] x 100 mm
(B) Oxygen of 2 to 10 Nm after introduction of Cr-containing ferromagnetic iron ³ / T (N means a standard state, t means per ton of molten steel, the same applies hereinafter) and the blowing should be terminated.
[0011]
Further, it is preferable that the input amount of the Cr oxide satisfy the following formula (2) in terms of pure Cr content.
Cr oxide input (kg / t) = furnace slag (kg / t) x 1.46 x B _Cr2O3 … (2)
(However, B _Cr2O3 Is Cr in slag ₂ O ₃ It indicates the optimum necessary increase in the concentration, and is within the range of 2 to 15% by mass.)
The “Cr yield” refers to the Cr content in the molten steel at the time of blowing off, of the Cr content charged into the converter during blowing, ie, [Cr in steel bath (kg / charge)]. ] / [(Added Cr alloy iron + added Cr-containing alloy iron + hot metal + scrap) contained Cr (kg / charge)] × 100 (%) (the same applies hereinafter).
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have found that in converter refining performed under a small amount of slag, when adjusting the amount of Cr in molten steel by adding a Cr-containing material, even when producing steel having a relatively high Cr concentration, the operation is hindered. The study was conducted from various angles to establish a method capable of adjusting the amount of Cr in molten steel at a high Cr yield without any problem.
[0013]
As a result, in particular,
{Circle around (1)} Instead of using only Cr oxide or Cr-containing ferrous iron as in the past, Cr oxide in the slag is added in advance after oxygen blowing is started. ₂ O ₃ It is important to supply Cr-containing ferroalloys after securing the amount,
{Circle around (2)} In order to dramatically increase the Cr yield, there are optimal timings for the introduction of these Cr oxides and the Cr-containing ferroalloys. Cr ₂ O ₃ When the concentration is raised to an appropriate range, it is good to introduce Cr-containing ferroalloys,
(3) It is better to add a predetermined amount of Cr oxide
The present invention has been made. Hereinafter, the reason for defining the above requirements in the present invention will be described in detail.
[0014]
As described above, the present inventors use a combination of a Cr oxide and a Cr-containing ferromagnetic alloy, and before the blowing (preferably after the middle of the blowing), introduce the Cr oxide in advance to obtain a target Cr amount of molten steel and Cr in slag in thermal equilibrium ₂ O ₃ It has been found that if Cr-containing ferromagnetic iron is added after securing the amount, high Cr steel can be produced at a high Cr yield without hindering the refining operation.
[0015]
In particular, in order to dramatically increase the Cr yield, there are optimal timings for the introduction of the Cr oxide and the Cr-containing ferroalloy, respectively, and the Cr oxide and the Cr-containing ferroalloy are introduced so as to satisfy the following conditions. Turned out to be good.
[0016]
(A) The Cr-containing ferromagnetic iron is preferably charged after supplying the Cr oxide and then supplying oxygen in an amount (V) satisfying the following formula (1).
[0017]
(0.28 × S-3) ≦ V ≦ (0.28 × S + 10) (where V ≧ 0) (1)
中 In equation (1),
V: The amount of oxygen supply (Nm ³ / T)
S (%) = [(FeO.Cr in input Cr oxide) ₂ O ₃ Forming Cr ₂ O ₃ Mass) / (All input Cr oxides are Cr ₂ O ₃ Cr assuming that ₂ O ₃ Mass)] x 100 mm
Cr oxide used in the present invention is Cr ₂ O ₃ In addition, FeO.Cr, which is chemically very stable and is also used as a refractory ₂ O ₃ And these Cr ₂ O ₃ And FeO / Cr ₂ O ₃ Mixtures are mentioned as the main ones. The FeO · Cr ₂ O ₃ And the Cr in the slag ₂ O ₃ To secure the amount, a separation reaction with FeO is necessary as shown in the following chemical formula (3), ₂ O ₃ Compared to the case of adding a simple substance, the amount of Cr in the slag is reduced by the reaction of the following chemical formula (3). ₂ O ₃ It takes time to increase the concentration.
[0018]
FeO ・ Cr ₂ O ₃ → FeO + Cr ₂ O ₃ … (3)
Therefore, the input Cr oxide is Cr ₂ O ₃ FeO ・ Cr ₂ O ₃ Is small, the Cr in the slag ₂ O ₃ Although the concentration can be increased to the optimum value at an early stage, the Cr oxide ₂ O ₃ FeO ・ Cr ₂ O ₃ Is large, the Cr in the slag ₂ O ₃ It takes time to secure the amount.
[0019]
Thus, FeO.Cr in the input Cr oxide ₂ O ₃ Of Cr in the slag ₂ O ₃ Since the time required to increase the concentration to a certain concentration is different, the Cr ₂ O ₃ When the concentration reaches the optimum value, the FeO.Cr contained in the input Cr oxide ₂ O ₃ It has been found that it is better to determine according to the ratio of.
[0020]
Therefore, the present inventors have developed FeO.Cr contained in the Cr oxide. ₂ O ₃ Is expressed as S (%) as shown in the following (4), and using Cr oxides (S = 0, 50, 100) having different S values, the Cr-containing ferrous alloy is charged after the Cr oxide is charged. The relationship between the oxygen supply up to and the Cr yield was examined. The result is shown in FIG. 5 described later.
[0021]

The following can be seen from FIG.
[0022]
(A) When S = 0 (Cr oxide is Cr ₂ O ₃ Consisting of FeO and Cr ₂ O ₃ Is not included)
It can be seen that a high Cr yield can be achieved by introducing the Cr-containing ferromagnetic iron immediately after the introduction of the Cr oxide.
[0023]
Cr oxide is thus Cr ₂ O ₃ , The Cr oxide is immediately charged (time for suspending in some slag: about 1 minute is necessary) ₂ O ₃ Since the concentration can be increased, even if the Cr-containing ferromagnetic iron is added immediately after the introduction of the Cr oxide, a high Cr yield can be achieved with almost no oxidation loss of the Cr-containing ferromagnetic iron.
[0024]
On the other hand, when the Cr-containing ferromagnetic iron is charged after excessively supplying oxygen, the Cr in the slag as shown in FIG. ₂ O ₃ T. in slag with increasing concentration Fe concentration (FeO, Fe oxide in slag and Fe ₂ O ₃ , The slag formation is promoted, the slag oxidation degree is increased, and the Cr yield is reduced as shown in FIG. 5, which is not preferable.
[0025]
As a specific example of the Cr oxide with S = 0, for example, slag or the like remaining after melting high Cr steel is given.
[0026]
(B) When S = 100 (Cr oxide is FeO.Cr ₂ O ₃ Consisting of Cr ₂ O ₃ Is not included)
It can be seen that a high Cr yield can be achieved by introducing a Cr oxide and then introducing a Cr-containing ferromagnetic alloy after sufficiently securing the time required for the reaction of the above chemical formula (3). As in the case of S = 0, when the Cr-containing ferromagnetic iron is introduced immediately after the introduction of the Cr oxide, the reaction of the chemical formula (3) has not sufficiently proceeded and the slag Cr ₂ O ₃ Since the amount is not ensured, the charged Cr-containing ferromagnetic iron is easily oxidized, and the Cr yield may be reduced.
[0027]
On the other hand, if the Cr-containing ferromagnetic iron is supplied after excessively supplying oxygen, slag formation is promoted as in the case of S = 0, and the Cr yield is undesirably reduced.
[0028]
Specific examples of the Cr oxide (S = 100) include, for example, Cr ore that has not been subjected to a preliminary reduction treatment, refractory waste materials having the same composition, and the like.
[0029]
(C) When S = 50 (Cr oxide is Cr ₂ O ₃ And FeO / Cr ₂ O ₃ Is a 1: 1 mixture)
In this case, an intermediate behavior between the case of S = 0 and the case of S = 100 is shown. Specific examples of the Cr oxide (S = 50) include, for example, a semi-reduced Cr ore that has not been completely subjected to a pre-reduction treatment, a Cr ore having an S value of 0%, and a Cr ore having an S value of 100%. And the like blended so that the value becomes 50%.
[0030]
Based on the results of FIG. 5, the relationship between the S value and the oxygen supply amount from the input of the Cr oxide to the input of the Cr-containing ferromagnetic iron was determined. The result is shown in FIG.
[0031]
From FIG. 2, it can be seen that Cr in slag ₂ O ₃ It can be seen that in order to achieve a high Cr yield by increasing the concentration, the oxygen supply amount from the input of the Cr oxide to the input of the Cr-containing ferromagnetic alloy should be determined according to the S value. From the results of FIG. 2, the present inventors set the oxygen supply amount (V) from the input of the Cr oxide to the input of the Cr-containing ferromagnetic iron within the range of the above formula (1).
[0032]
That is, the oxygen supply amount (V) from the input of the Cr oxide to the input of the Cr-containing ferromagnetic iron is (0.28 × S−3) Nm ³ / T, the Cr in the slag ₂ O ₃ The amount is not sufficiently secured, and even if the Cr-containing ferromagnetic iron is charged in this state, oxidation loss of the Cr-containing ferromagnetic iron easily occurs, and a high Cr yield cannot be achieved. More preferably, in the above formula (1), the oxygen supply amount after the introduction of the Cr oxide is (0.28 × S + 2) Nm so that the Cr yield in FIG. ³ It is preferable to introduce a Cr-containing ferromagnetic alloy at the time point of / t.
[0033]
On the other hand, even if oxygen is excessively supplied, the Cr yield is gradually reduced due to the promotion of slagging as described above, so the oxygen supply amount is (0.28 × S + 10) Nm ³ / T or less.
[0034]
When a fine powder (particle diameter of about 5 mm or less) is used as the Cr oxide, the oxygen supply amount can be relatively reduced as long as the above formula (1) is satisfied. If the fine powdery Cr oxide is used, it is immediately dissolved to remove the Cr in the slag. ₂ O ₃ This is because the concentration is increased or the reaction of the above chemical formula (3) is promoted. However, when introducing a Cr oxide having a particle size of about 10 mm or more, it is preferable to sufficiently increase the oxygen supply amount within a range satisfying the above formula (1) to sufficiently melt the Cr oxide.
[0035]
(B) In addition, the oxygen supply amount after charging the Cr-containing ferromagnetic iron is 2 to 10 Nm. ³ / T range.
[0036]
In converter refining, decarburization treatment is performed by blowing oxygen. However, if a large amount of oxygen is supplied after charging the Cr-containing ferromagnetic iron, Cr in the added Cr-containing ferromagnetic iron is oxidized and Cr is added. ₂ O ₃ And the Cr yield is undesirably reduced.
[0037]
Therefore, from the viewpoint of improving the Cr yield, it is preferable to shorten the oxygen supply time after the introduction of the Cr-containing ferromagnetic iron, and it is better to introduce the oxygen at the end of blowing. In addition, Cr in slag ₂ O ₃ Since the reduction reaction from iron to Cr is an endothermic reaction, the reduction reaction becomes dominant at the end of blowing, when the temperature of the molten steel becomes high. Therefore, if the Cr-containing ferromagnetic iron is charged at the end of the blowing, the oxidation loss of Cr can be suppressed, and from such a viewpoint, it is preferable to feed the Cr-containing ferroalloy at the end of the blowing. In any case, according to the present invention, the oxygen supply amount from the introduction of the Cr-containing ferromagnetic iron into the molten steel until the end of the blowing is 10 Nm. ³ / T or less. In order to further suppress the oxidation of the Cr-containing ferroalloys and further increase the Cr yield, the oxygen supply amount after the introduction of the Cr-containing ferroalloys until the end of blowing is 8 Nm ³ / T or less is more preferable.
[0038]
However, if the blowing time after the introduction of the Cr-containing ferroalloys is extremely short (that is, the amount of oxygen supplied until the end of the blowing is small), the following problem occurs.
[0039]
(I) Immediately before the end of blowing, converter dynamic control, that is, the C concentration and the molten steel temperature (T) are directly measured by a sublance during the blowing, and the C concentration and the molten steel temperature (T) are sequentially calculated every few seconds. In this case, if the Cr-containing ferromagnetic iron is added immediately before the end of the blowing, the C concentration and the molten steel temperature (T) which are the criteria for the end of the blowing are determined from the target set values. It is easy to come off.
[0040]
(Ii) By performing blowing sufficiently after charging the Cr-containing ferromagnetic iron, C, which is an impurity, is decarburized, moisture is evaporated, and impurities such as Ti are captured and removed by the slag.
[0041]
However, when Cr-containing ferromagnetic iron is added immediately before the end of blowing, these impurities (C, H) contained in the Cr-containing ferromagnetic iron are added. ₂ O, Ti, etc.) are not sufficiently removed and remain in the molten steel, causing the problem that the C concentration at the end of the blowing deviates from the target value as described above. In addition, the impurity must be removed separately. Will occur. For example, there is a need to provide a degassing step or the like after the end of blowing, so that it is not possible to efficiently perform the work when performing continuous casting.
[0042]
(Iii) If the blowing is terminated in a state where the Cr-containing ferromagnetic iron is not sufficiently stirred and mixed, the dispersion of the added Cr-containing ferroalloy becomes non-uniform, and there is a possibility that component dispersion or the like may occur.
[0043]
Therefore, after charging the Cr-containing ferromagnetic iron, at least 2 Nm ³ It is preferable to perform blowing by supplying oxygen at / t to remove impurities in the Cr-containing ferromagnetic alloy, stir, and the like. In order to sufficiently remove the impurities and perform stirring, 3 Nm ³ It is more preferable to perform blowing by supplying oxygen of / t or more.
[0044]
In the present invention, by introducing Cr oxide and Cr-containing ferromagnetic iron at such an appropriate time, the Cr content in the molten steel can be secured at a high Cr yield without hindering the refining operations such as dephosphorization and decarburization. can do.
[0045]
FIG. 3 shows the case where both the Cr oxide and the Cr-containing ferromagnetic iron are charged at the time specified in the present invention (Cr oxide input timing: after refining starts, and Cr-containing ferroalloy input timing: after refining middle stage). When only Cr-containing ferro-alloy is charged at the prescribed time and Cr oxide is charged before refining starts (Cr-oxide feeding time: before refining starts, Cr-containing ferro-alloy input timing: after middle refining) Cr in slag ₂ O ₃ The relationship between the concentration and the Cr yield is shown. From FIG. 3, it can be seen that a high Cr yield can be achieved by introducing the Cr oxide and the Cr-containing ferroalloy at the time specified in the present invention.
[0046]
It is preferable that the amount of the Cr oxide be such that it satisfies the following expression (2) in terms of pure Cr in addition to the above-mentioned time.
Cr oxide input (kg / t) = furnace slag (kg / t) x 1.46 x B _Cr2O3 … (2)
(However, B _Cr2O3 Is Cr in slag ₂ O ₃ It indicates the optimum necessary increase in the concentration, and is within the range of 2 to 15% by mass.)
The input amount of the Cr oxide can be determined, for example, as follows. Under normal operation, the Cr concentration in molten steel [Cr] is 0.5% by mass, the Fe concentration in molten steel (T.Fe) is 8% by mass, and Cr in slag is ₂ O ₃ Density (Cr ₂ O ₃ ) Is 4% by mass, and when the target Cr concentration in molten steel [Cr] ′ is 1.0% by mass and the target Fe concentration (T.Fe) ′ in molten steel is 10% by mass as target values, Cr in slag ₂ O ₃ Target density (Cr ₂ O ₃ ) ′ Is 10% by mass from the following equation (5) obtained from the relation of the equilibrium state.
[0047]
(Cr ₂ O ₃ ) '= [(T.Fe)' / (T.Fe)｝ × {[Cr] '/ [Cr]｝ × (Cr ₂ O ₃ …… (5)
Therefore B _Cr2O3 (Cr in slag ₂ O ₃ The optimal required increase in concentration)
B _Cr2O3 = (Cr ₂ O ₃ ) '-(Cr ₂ O ₃ ) = 6 (% by mass).
[0048]
Therefore, it is found that the optimal amount of the Cr oxide in this case is [the amount of slag in the furnace (kg / t) × 1.46 × 6] (kg / t). In addition, Cr in slag ₂ O ₃ The optimum necessary increase (mass%) of the concentration can be appropriately set according to the operating conditions as described above. However, if the Cr oxide is added excessively, the slag tends to become oxidizable, and thus the decrease in the Cr yield is reduced. In consideration of suppression, the content is preferably in the range of 2 to 15% by mass.
[0049]
In this way, an appropriate amount of Cr oxide is charged, and Cr in slag is added. ₂ O ₃ By introducing the Cr-containing ferromagnetic iron in a state where the concentration is set to the optimum concentration, a higher Cr yield can be achieved.
[0050]
If the input amount of the Cr oxide is less than the amount specified by the above formula (5), the Cr in the slag is ₂ O ₃ When the concentration is ₂ O ₃ The concentration cannot be sufficiently increased, and when the Cr-containing ferromagnetic iron is charged, the oxidation reaction of Cr in the Cr-containing ferromagnetic iron easily proceeds, and it is difficult to increase the Cr yield. Preferably, the Cr oxide is added at least 2 kg / t or more.
[0051]
On the other hand, when the input amount of the Cr oxide exceeds the amount specified by the above equation (5), ₂ O ₃ The amount increases excessively and the Cr ₂ O ₃ As shown in FIG. 1, the T.C. Fe concentration (FeO, Fe oxide in slag and Fe ₂ O ₃ And the slag becomes highly oxidizable. Once a highly oxidizing slag is formed, it is very difficult to quickly return the slag to a low oxidizing property by oxidizing refining in which refining is performed while supplying oxygen. Therefore, such a state is not preferable because not only the Cr yield decreases but also the Cr concentration in the molten steel cannot be sufficiently increased. It is preferable that the input amount of the Cr oxide be at most 15 kg / t or less.
[0052]
In the present invention, as described above, ₂ O ₃ FeO / Cr to secure quantity ₂ O ₃ Since the case where Cr is used is taken into consideration, the Cr oxide may be FeO · Cr. ₂ O ₃ Cr ore containing a relatively large amount of Cr can be used. ₂ O ₃ Concentration and FeO / Cr ₂ O ₃ Highly concentrated slag can be recycled and used.
[0053]
When Cr ore is used as the Cr oxide, pulverized powdery Cr ore (having a particle size of about 1 to 5 mm) is inexpensive, and efficiently removes Cr in slag. ₂ O ₃ It is preferable because the concentration can be increased to reliably suppress the oxidation of the Cr-containing ferroalloys to be charged. Also, when such powdered ore is added from the upper part of the converter, it does not reach the molten steel but stays in the slag and mixes with the slag. ₂ O ₃ The concentration can be increased.
[0054]
The amount of Cr-containing ferromagnetic iron is not particularly limited, and an appropriate amount can be added in accordance with the target Cr value. Since impurities in the added Cr-containing ferromagnetic iron can be sufficiently removed at the time of refining, when a Fe-Cr alloy is used as the Cr-containing ferroalloy, it contains a relatively large amount of impurities in addition to a high-grade product containing little impurities. Intermediate or low-grade Fe-Cr alloys can also be used.
[0055]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples. However, the present invention is not limited to the following Examples, and may be appropriately modified within a range that can be adapted to the purpose of the preceding and the following. The present invention can be implemented, and all of them are included in the technical scope of the present invention.
[0056]
<Example 1>
First, as specified in the present invention, a Cr oxide and a Cr-containing ferromagnetic iron are used in combination, and a Cr oxide is added in advance and the Cr ₂ O ₃ As a method of charging the Cr-containing ferromagnetic iron after securing the amount, Cr ore is used as a Cr oxide and the integrated oxygen supply amount is 26.3 Nm. ³ / N after loading at the time of / t ³ / T of oxygen is supplied, and then a Fe-Cr-based alloy is charged as Cr-containing ferromagnetic alloy, and 5.6 Nm is added after the Fe-Cr-based alloy is charged. ³ The blowing was terminated by supplying / t of oxygen.
[0057]
As a conventional method of adjusting the amount of Cr in molten steel using only Cr ore as a Cr oxide, a Cr ore having an integrated oxygen supply of 5.3 Nm is used. ³ /4.0t after injection at the time of / t ³ The blowing was terminated by supplying / t of oxygen. For each method, the Cr yield was determined when the amount of Cr ore or Fe—Cr alloy was changed to adjust the Cr concentration in the molten steel. Other operating conditions of each method were as follows.
[0058]

FIG. 4 shows the relationship between the amount of Cr input (the amount of the input Cr ore or the amount of the input Cr-Cr-based alloy in terms of pure Cr content) and the Cr yield when the amounts of Cr are adjusted by the respective methods.
[0059]
From FIG. 4, it can be seen that when the Cr content in molten steel is adjusted using only Cr oxide, the Cr yield decreases as the Cr input increases, whereas according to the method of the present invention, the Cr input is reduced. It can be seen that a high Cr yield can be achieved regardless of this.
[0060]
<Example 2>
The effect of the relationship between the charging time of the Cr oxide and the Cr-containing ferromagnetic iron on the Cr yield was investigated.
[0061]
The operation was performed as follows. That is, as the Cr oxide having the S value of 0%, ₂ O ₃ The recycled slag containing Cr is converted to a Cr oxide having an S value of 50%. ₂ O ₃ Using recycled slag containing raw chromium ore and raw chromium ore at a ratio of 50%, and using raw chromium ore as a Cr oxide with an S value of 10%, the amount of oxygen supplied from the input of the Cr oxide to the input of the Cr-containing ferroalloy Was changed. Otherwise, the procedure was the same as in Example 1 above. The results are shown in FIG. 5 as the relationship between the oxygen supply amount and the Cr yield from the introduction of the Cr oxide to the introduction of the Cr-containing ferromagnetic alloy.
[0062]
From FIG. 5, when the oxygen supply amount from the time of charging the Cr oxide to the time of charging the Cr-containing ferromagnetic iron is out of the preferable range in the present invention, the Cr yield decreases, and the charging of the Cr-containing ferromagnetic iron decreases. It can be seen that it is better to supply a specified amount of oxygen after charging the Cr oxide.
[0063]
<Example 3>
The effect on the Cr yield and the amount of residual impurities was examined by changing the amount of oxygen supply after the addition of the Cr-containing ferromagnetic iron.
[0064]
The operating conditions were such that the oxygen supply amount from 0 to 18 Nm after the addition of the Cr-containing ferroalloy until the end of blowing. ³ / T in the range of 2 to 6 Nm after the introduction of the Cr oxide until the introduction of the Cr-containing ferromagnetic iron. ³ The operation was carried out under the same conditions as in Example 1 except that / t was used. FIG. 6 shows the relationship between the oxygen supply amount and the Cr yield from the introduction of the Cr-containing ferrous alloy to the end of the blowing when the operation was performed in this manner.
[0065]
FIG. 7 shows the relationship between the oxygen supply amount from the input of the Cr-containing ferroalloy to the end of blowing and the amount of residual impurities in the molten steel at the end of the blowing. FIG. 8 shows the relationship between the oxygen supply amount and the H (hydrogen) concentration in the molten steel at the end of blowing, and FIG. FIG. 9 shows the relationship between the oxygen supply amount from the introduction of the Cr-containing ferroalloy to the end of blowing and the C (carbon) concentration in the molten steel at the end of blowing.
[0066]
FIG. 6 shows that when a large amount of oxygen is supplied after the addition of the Cr-containing ferromagnetic iron, the Cr yield decreases. In order to increase the Cr yield to 90% or more, the oxygen supply after adding the Cr-containing ferromagnetic alloy should be 10 Nm. ³ / T or less, in other words, the oxygen supply amount is 10 Nm ³ It can be seen that it is better to end the blowing operation within / t. From FIGS. 7 and 8, in order to sufficiently remove impurities such as moisture and Ti contained in particularly inexpensive Cr-containing ferroalloys to reduce the amount of residual impurities in the molten steel, it is necessary to use Cr-containing ferroalloys. After charging, at least 2 Nm by the end of blowing ³ It can be seen that it is preferable to perform the blowing process by supplying oxygen of / t or more.
[0067]
In the case of producing a steel type having a low C concentration, if the amount of C contained in the input Cr-containing ferromagnetic iron is large, there is a problem that the C concentration at the end of blowing is higher than a target value. Therefore, as shown in FIG. 9, it is found that it is better to supply oxygen to perform the blowing process in order to reduce the amount of C in the molten steel.
[0068]
【The invention's effect】
The present invention is configured as described above, and if Cr is added to a converter by the method of the present invention, even in the case of producing a high Cr steel, a smelting operation such as decarburization or dephosphorization is hindered. The Cr content in the molten steel can be adjusted at a high Cr yield without any increase.
[0069]
By carrying out such a method, it is possible to further reduce inexpensive Cr ore as Cr oxide by FeO.Cr ₂ O ₃ , A high Cr yield can be achieved. Further, since a Cr oxide is previously charged, a high Cr yield can be achieved even when an expensive Cr-containing ferromagnetic alloy such as an Fe-Cr alloy is used. , H ₂ Even when a low-grade product such as an Fe-Cr alloy having a large amount of impurities such as O and Ti is used, the Cr amount can be adjusted efficiently without the need to newly provide a step of degassing or the like.
[Brief description of the drawings]
Fig. 1 Cr in slag ₂ O ₃ Concentration and T. in slag 4 is a graph showing a relationship between Fe concentrations.
FIG. 2 is a graph showing the relationship between the oxygen supply amount (V) and the S value from the input of a Cr oxide to the input of a Cr-containing ferromagnetic alloy (when the slag amount is 40 kg / t or less).
FIG. 3 Cr in slag when Cr-containing ferroalloys are charged ₂ O ₃ 5 is a graph showing the relationship between the concentration and the Cr yield for each charging time of Cr oxide.
FIG. 4 is a graph showing the relationship between the amount of Cr input and the Cr yield when the amount of Cr in molten steel is adjusted by the method of the present invention or the conventional method.
FIG. 5 is a graph showing the relationship between the oxygen supply amount and the Cr yield from the time when a Cr oxide is charged to the time when a Cr-containing ferromagnetic iron is charged.
FIG. 6 is a graph showing the relationship between the oxygen supply amount and the Cr yield from the introduction of Cr-containing ferromagnetic alloy (Fe—Cr alloy) to the end of blowing.
FIG. 7 is a graph showing the relationship between the oxygen supply amount from the introduction of Cr-containing ferromagnetic alloy (Fe-Cr alloy) to the end of blowing and the concentration of Ti in molten steel at the end of blowing.
FIG. 8 is a graph showing the relationship between the oxygen supply amount from the introduction of a Cr-containing ferromagnetic alloy (Fe—Cr alloy) to the end of blowing and the H (hydrogen) concentration in molten steel at the end of blowing.
FIG. 9 is a graph showing the relationship between the oxygen supply amount from the introduction of Cr-containing ferromagnetic alloy (Fe—Cr alloy) to the end of blowing and the C (carbon) concentration in molten steel at the end of blowing.

Claims (4)

When refining in a converter, a Cr oxide is added to the converter after the start of blowing and a Cr-containing ferromagnetic iron is charged after the addition of the Cr oxide. The method for adding Cr in a converter according to claim 1, wherein Cr ore or Cr-containing slag is used as the Cr oxide. After supplying the Cr oxide, an amount of oxygen (V) satisfying the following formula (1) is supplied, and then the Cr-containing ferromagnetic iron is charged. After the Cr-containing ferromagnetic iron is charged, oxygen is supplied to ² to 10 Nm ^3. The method for adding Cr in a converter according to claim 1 or 2, wherein the blowing is completed by supplying / t (t means per ton of molten steel; the same applies hereinafter).
(0.28 × S-3) ≦ V ≦ (0.28 × S + 10) (where V ≧ 0) (1)
中 In equation (1),
V: oxygen supply amount (Nm ³ / t) from the input of Cr oxide to the input of Cr-containing ferromagnetic iron
_{S (%) = [(Cr} 2 O 3 by weight to form a FeO · _Cr 2 _{O 3} in the turned Cr oxide) / _(Cr 2 _{O 3} by weight in the case of a charged total Cr oxide was assumed _Cr 2 _{O 3} )] × 100｝ The method for adding Cr in a converter according to any one of claims 1 to 3, wherein the input amount of the Cr oxide satisfies the following expression (2) in terms of Cr pure content.
Input amount of Cr oxide (kg / t) = Slag amount in furnace (kg / t) × 1.46 × B _Cr2O3 (2)
_{(However, B Cr2 O3} show optimum required increase in _Cr 2 _{O 3} concentration in the slag, in the range of 2 to 15 wt%)

Images