JP3634046B2

JP3634046B2 - Reduction and recovery method for valuable metals in slag with improved accuracy of molten steel components

Info

Publication number: JP3634046B2
Application number: JP03434996A
Authority: JP
Inventors: 昭人小松; 淳一香月; 幸雄八島; 隆山内
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 1995-03-28
Filing date: 1996-01-29
Publication date: 2005-03-30
Anticipated expiration: 2016-01-29
Also published as: JPH08325626A

Description

【０００１】
【産業上の利用分野】
本発明は、製錬後の溶鋼表面を覆うスラグ層に懸濁している易還元性酸化物中の有価金属を溶鋼に還元回収する際、溶鋼の成分適中精度を高めたスラグ中有価金属の還元回収方法に関する。
【０００２】
【従来の技術】
転炉，真空脱ガス装置等でステンレス鋼等の合金鋼を脱炭精錬するとき、溶鋼中の炭素が吹錬酸素と反応しＣＯガスとなって溶鋼から除去されると同時に、有用成分であるＣｒ，Ｆｅ，Ｍｎ等も一部が次の反応に従って酸化される。
４［Ｃｒ］＋３Ｏ_２ →２（Ｃｒ_２Ｏ_３）
２［Ｆｅ］＋Ｏ_２ →２（ＦｅＯ）
２［Ｍｎ］＋Ｏ_２ →２（ＭｎＯ）
酸化物となったＣｒ，Ｆｅ，Ｍｎ等の金属元素は、溶鋼表面に浮遊しているスラグに移行する。スラグ中の金属元素は、製鋼の最終段階で酸化物から金属状態に還元され、メタルとして溶鋼に回収される。回収は、Ｃｒ，Ｆｅ，Ｍｎ等の金属元素がＳｉによって容易に金属状態に還元されることを利用し、たとえば真空精錬時に所定量のＳｉを取鍋内溶鋼に添加することにより行われている。Ｓｉによる還元反応は、次の通りである。
２（Ｃｒ_２Ｏ_３）＋３Ｓｉ→４［Ｃｒ］＋３（ＳｉＯ_２）
２（ＦｅＯ）＋Ｓｉ→２［Ｆｅ］＋（ＳｉＯ_２）
２（ＭｎＯ）＋Ｓｉ→２［Ｍｎ］＋（ＳｉＯ_２）
【０００３】
金属状態になったＣｒ，Ｆｅ，Ｍｎ等は溶鋼に移行し、その結果、溶鋼成分濃度が変化する。成分調整を高精度で行うためには、最終段階でスラグから溶鋼に移行する金属元素を定量的に把握しておく必要がある。また、最近では、Ｓｉ含有量に関する規格が極めて厳しい鋼種が使用され始めている。このような高精度の成分調整やＳｉ含有量が厳格に管理された鋼種に対応するためには、Ｓｉによって還元される易還元性酸化物がスラグ中に含まれている量を正確に把握することが必要である。
スラグに含まれている易還元性酸化物の酸素量は、Ｓｉで還元されるＣｒ_２Ｏ_３，ＦｅＯ，ＭｎＯ等の金属酸化物中の酸素濃度及びスラグ量に対する割合で示される。算出された酸素量は、還元剤として必要なＳｉの添加量を定めるときの基準になる。
【０００４】
【発明が解決しようとする課題】
金属酸化物中の酸素濃度を定量する方法として、スラグ試料を蛍光Ｘ線分析する方法が知られている。蛍光Ｘ線分析は、ガラスビード法又はプレス成形法の何れにおいても試料の秤量から分析値の算出までに２０〜２５分を必要とする。しかも、試料に含まれている金属酸化物が化学量論的な形態を採っているものと仮定し、金属と酸化物との化学量論的な関係から定まる係数を金属元素の定量値に乗じることによって酸素分析値を算出している。そのため、金属状態のＣｒ，Ｆｅ，Ｍｎ等が含まれている試料や、酸素価が異なる金属酸化物等が含まれている試料では、必然的に測定誤差が生じる。
本発明者等は、このような測定誤差を解消し、分析時間の短縮を図るため、製鋼スラグから採取された試料と炭素源との反応により系外に排出される酸素濃度に基づき、製鋼スラグに含まれている易還元性酸化物の酸素濃度を定量する方法を開発し、特願平４−３１９３６４号として出願した。この方法によると、分析誤差を最小限に抑え、約１０分間でスラグを酸素定量することが可能になる。
【０００５】
ところで、ステンレス鋼の需要が増加してきている近年、既存設備で需要量に応答するためには単位時間当りの生産量を増やす必要があり、タップ時間の短縮が課題とされる。そのため、スラグ中の易還元性酸素量を更に短時間で把握するための技術開発が急務とされる。
本発明は、このような要望に応えるべく案出されたものであり、溶鋼酸素濃度又は脱炭精錬前後における溶鋼中のＣｒ濃度及びＳｉ濃度の減少量からスラグ中で有価金属と結合している酸素の濃度を容易且つ迅速に把握し、この値と別途求めたスラグ量に基づき最適添加量を決定して還元剤を投入することにより、有価金属を効率よく溶鋼に回収すると共に、高い適中精度で成分調整された溶鋼を得ることを目的とする。
【０００６】
【課題を解決するための手段】
本発明の有価金属還元回収方法は、その目的を達成するため、溶鋼の表面に浮遊するスラグから易還元性酸化物中の有価金属を前記溶鋼に還元回収する際、酸素濃淡電池を用いて溶鋼酸素値を測定し、予め求めている検量線に前記溶鋼酸素値を挿入してスラグ中易還元性酸化物の酸素濃度を推定すると共に、前記スラグ及び前記溶鋼の表面位置を検出し、検出された表面位置の差からスラグの厚みを算出し、該スラグの厚みに基づいて前記スラグの重量を求め、前記スラグ中易還元酸化物の酸素濃度及び前記スラグ重量から還元剤の必要添加量を演算し、演算結果の添加量で前記還元剤を前記スラグに投入することを特徴とする。
溶鋼酸素値としては、酸素濃淡電池を用いた測定値に代えて発光分光分析法で測定した溶鋼酸素値を使用してもよい。Ｓｉ及びＣｒを含む合金鋼を転炉又は真空脱ガス装置で脱炭精錬する際には、脱炭精錬前後の溶鋼中のＣｒ濃度及びＳｉ濃度の減少量を測定し、予め求めている検量線に前記Ｃｒ濃度及びＳｉ濃度の減少量を挿入して脱炭精錬後の溶鋼の表面に浮遊するスラグ中易還元酸化物の酸素濃度を推定することもできる。
【０００７】
【作用】
製鋼スラグに含まれている易還元性酸化物は、脱炭精錬時の吹錬酸素によって生成したものであり、その酸素値は溶鋼中の酸素濃度と高い相関関係をもっている。また、本発明者等の調査・研究によるとき、脱炭精錬前後の溶鋼中のＣｒ濃度及びＳｉ濃度の減少量から算出した易還元酸化物の酸素値とも高い相関関係にあることが判明した。
以上のことは、溶鋼中の酸素濃度又は脱炭精錬前後における溶鋼中のＣｒ濃度及びＳｉ濃度の減少量を測定することにより、製鋼スラグに含まれている易還元性酸化物の酸素濃度が求められることを示唆する。溶鋼の酸素濃度は、酸素濃淡電池又は発光分光分析装置によってわずか２分程度で容易に測定できる。また、脱炭精錬前後の溶鋼中のＣｒ濃度及びＳｉ濃度の減少量は、それぞれ脱炭精錬前後の溶鋼中のＳｉ濃度及びＣｒ濃度の差である。これらの濃度差は、発光分光分析装置によってわずか２分程度で容易に測定できる。したがって、溶鋼中の酸素濃度又はＳｉ濃度及びＣｒ濃度から製鋼スラグの酸素濃度を推定するとき、スラグの採取作業時間，粉砕から分析値を得るための一連の作業時間が省略され、結果としてタップ時間の大幅な短縮が図られる。
【０００８】
他方、スラグ重量を計量する方法としては、基準点からのスラグ面の位置Ｘ_１と溶鋼面の位置Ｘ_２を検出し、その位置の差からスラグの厚み（Ｘ_１ −Ｘ_２）を求めると共に、真空脱ガス容器，取鍋等の容器内径Ｒからスラグ体積Ｖ_Ｓを求め、前記スラグの比重ρを乗じることによってスラグ重量Ｗ_Ｓを演算する方法が採用される。
スラグの表面位置は、渦電流，レーザ，マイクロ波，放射線等を用いた距離計や、スラグ表面に直接接触させるタッチ式センサー，スラグの輝度を測定する方法等によって検出される。渦電流センサーとしては、周波数が５００ｋＨｚ以上で１ＭＨｚ以下の高周波交流電流が供給される渦電流式センサーを使用することが好ましい。周波数が５００ｋＨｚ以上で１ＭＨｚ以下の高周波交流電流は、スラグの表面にのみ渦電流を発生させるため、スラグの表面位置を検出できる。
【０００９】
スラグ下にある湯面の位置は、渦電流式センサーを使用して検出する方法，一対の電極をスラグからメタルにわたって浸漬させ、スラグ，メタルそれぞれの導電性の差を電気的にとらえる方法，常に一定量のガスが流れているガスプローブをスラグからメタルにわたって浸漬させ、スラグとメタルの比重差から生じるガスプローブ中の背圧変化を用いる方法等で検出される。たとえば、渦電流センサーを使用するとき、周波数０．５〜５００ｋＨｚの高周波交流電流を供給して溶鋼の表面位置を検出する。周波数０．５〜５００ｋＨｚの高周波交流電流を供給することにより、スラグ層に懸濁している金属液滴に起因する渦電流による誤差要因が渦電流センサーの受信コイルに取り込まれることなく、スラグ下にある溶鋼の表面位置が高精度で検出される。
【００１０】
以上のようにして測定された溶鋼の酸素濃度又は脱炭精錬前後の溶鋼中のＣｒ濃度及びＳｉ濃度の減少量とスラグの重量から、図１に示すフローに従って還元剤の必要添加量が演算される。この添加量で還元剤を投入するとき、スラグ中の易還元性酸化物が還元され、金属状態で溶鋼に回収される。この方法によるとき、過剰の還元剤を添加することがないので、溶鋼に持ち込まれる余分な還元剤を少なくすることができる。すなわち、スラグの組成及び重量を基準にして定められた量の還元剤を添加することにより、還元剤Ｓｉが溶鋼に規格成分以上に余分に持ち込まれることなく、しかもＭｎ，Ｃｒ等の合金成分の含有量適中精度を向上させた溶鋼が得られる。
溶鋼に還元回収される有価金属は、使用する還元剤の還元能に応じて選択できる。たとえば、Ｓｉ又はフェロシリコンを還元剤として使用すると、Ｆｅ，Ｍｎ及びＣｒが溶鋼に還元回収される。Ａｌ，Ｔｉ，Ｃａ，Ｍｇ又はそれらの合金を還元剤として使用すると、Ｆｅ，Ｍｎ，Ｃｒ及びＳｉが還元回収される。Ａｌ，Ｃａ，Ｍｇ又はそれらの合金を還元剤として添加すると、Ｆｅ，Ｍｎ，Ｃｒ，Ｓｉ及びＴｉが溶鋼に還元回収される。何れの場合にも、スラグ中の易還元性酸化物の酸素量及びスラグ重量から還元剤の必要添加量が定まっているので、規格成分以上に余分な還元剤を添加することなく、目標組成に高精度で一致した溶鋼が得られる。
【００１１】
−スラグ重量の計測−
スラグ及び溶鋼の表面位置が基準点からの距離Ｘ_１，Ｘ_２として検出される。溶鋼の表面位置はスラグ層との界面にあるので、スラグ層の厚みは（Ｘ_１ −Ｘ_２）と算出される。他方、真空脱ガス容器，取鍋等の容器の内側半径Ｒは予め判っているので、スラグの体積Ｖ_ＳはＶ_Ｓ＝πＲ^２ ×（Ｘ_１ −Ｘ_２）となる。スラグの重量Ｗ_Ｓは、体積Ｖ_Ｓにスラグの比重ρを乗じることにより、Ｗ_Ｓ＝ρ×Ｖ_Ｓ＝ρ×πＲ^２ ×（Ｘ_１ −Ｘ_２）として算出される。得られたスラグ重量Ｗ_Ｓは、溶鋼重量Ｗ_Ｍを介在させることなく、スラグ層の厚みから直接的に算出された値である。図１は、この間のフローを示す。このようにして、誤差要因が取り込まれることが少なく、スラグ重量Ｗ_Ｓが高精度で求められる。
【００１２】
−還元剤の必要添加量の算出−
還元剤の必要添加量は、スラグ中に含まれている易還元酸化物濃度を求めて、スラグ重量を掛け合せることにより定まる。スラグ中に含まれている易還元性酸化物濃度は、酸素濃淡電池又は発光分光分析法を用いて求めた溶鋼の酸素濃度又は脱炭精錬前後の溶鋼中のＣｒ濃度及びＳｉ濃度の減少量から定まる。本発明者等が種々実験を重ねた結果、スラグ中易還元酸化物の酸素濃度（Ｏ）は、それぞれ次式で精度良く推定できることが判明した。
（Ｏ）＝ａ・［Ｏ］＋ｂ
（Ｏ）＝ｃ・ΔＣｒ＋ｄ・ΔＳｉ＋ｅ
式中、ａ，ｂ，ｃ，ｄ，ｅは、係数又は定数を示す。また、［Ｏ］は酸素濃淡電池又は発光分光分析法で求めた溶鋼の酸素濃度を示し、ΔＣｒ，ΔＳｉはそれぞれ脱炭精錬前後の溶鋼中のＣｒ濃度及びＳｉ濃度の減少量を示す。得られたスラグ中易還元酸化物の酸素濃度（Ｏ）にスラグ重量Ｗ_Ｓを乗じることによって、取鍋内にあるスラグの易還元酸化物の酸素量が求められる。算出された酸素量に応じて、還元に必要は還元剤の投入量が定められる。
このようにして調整された量の還元剤を投入するとき、スラグから溶鋼に所定の量で易還元性酸化物中のＣｒ，Ｆｅ，Ｍｎ等が回収され、また投入された還元剤が過剰に持ち込まれることがなくなる。その結果、還元剤を効率よく消費できることは勿論、溶製後の溶鋼成分適中度が向上する。特に還元剤に由来するＳｉの含有量に関して厳格な管理が要求される鋼種を精度良く溶製することが可能になる。
【００１３】
【実施例】
実施例１：
転炉吹錬が終了したＣｒ含有量が１１〜２０重量％の範囲にあるフェライト系ステンレス鋼及びオーステナイト系ステンレス鋼の合計１００チャージ（７７〜８１トン／チャージ）について、酸素濃淡電池を浸漬して酸素濃度を測定した。このとき、全チャージとも酸素濃度が得られるまでの時間は、僅か１０秒であった。
溶鋼を取鍋に出鋼した後、直ちにセンサーを用いてスラグ面及び湯面位置を検出した。このときの測定時間は、約１分であった。なお、スラグ面の位置は直接接触させるタッチ式センサーを用いて測定し、湯面の位置は渦電流式センサーで測定した。スラグ厚みを計測した後、スラグ体積を算出し、一定値のスラグ比重を乗じてスラグ重量を求めた。得られた酸素濃度とスラグ重量からスラグ中の易還元性酸化物の全重量を算出し、還元に必要な還元剤の投入量を求めた。
【００１４】
１００チャージ中の一例を具体的に説明する。転炉脱炭精錬後の酸素濃淡電池で求めた溶鋼酸素濃度は、０．１１重量％であった。この溶鋼酸素濃度に対応するスラグ中の易還元性酸化物の酸素濃度は、図２の相関線図から１２．４重量％であることが判る。なお、図２は、Ｃｒ含有量が１１〜２０重量％の範囲にあるフェライト系ステンレス鋼及びオーステナイト系ステンレス鋼の合計１００チャージ（７７〜８１トン／チャージ）の溶鋼について、スラグ中易還元性酸化物の酸素濃度を炭素還元法で求め、酸素濃淡電池で測定した溶鋼中の酸素濃度との関係から予め求めた検量線である。
【００１５】
一方、スラグ重量は、測定したスラグ厚み２２．３ｃｍに予め求められているスラグの比重３．５を乗じて４．１トンと算出された。したがって、スラグ中の易還元性酸化物の酸素濃度は、１２．４重量％×４．４トン＝５０８ｋｇとなり、Ｃｒ，Ｆｅ，Ｍｎを溶鋼に回収するために必要なＳｉ量は４４５ｋｇと算出された。
このＳｉ純分４４５ｋｇに相当するフェロシリコンを投入した後、真空脱ガス，脱酸処理を施し、スラグを再度サンプリングし、スラグに含まれている易還元性酸化物の酸素濃度を測定した。その結果、易還元性酸化物の酸素濃度は、０．０３重量％であった。このことから、Ｃｒ，Ｆｅ及びＭｎは、十分に溶鋼に回収されていることが確認された。
【００１６】
実施例２：
転炉脱炭精錬が終了したＣｒ含有量が１１〜２０重量％の範囲にあるフェライト系ステンレス鋼及びオーステナイト系ステンレス鋼の計１００チャージ（７７〜８１トン／チャージ）の溶鋼について、発光分光分析法で酸素濃度を測定した。このとき、全チャージとも酸素濃度の測定値が得られるまでの時間はわずか２分程度であった。
溶鋼を取鍋に出鋼した後、直ちにタッチ式センサーでスラグ面位置を測定し、渦電流式センサーで湯面位置を測定した。スラグ厚みを計測した後、スラグ体積を算出し、一定値のスラグ比重を乗じてスラグ重量を求めた。得られたスラグ中の易還元酸化物の酸素濃度とスラグ重量からスラグ中の易還元酸化物の全酸素量を算出し、還元に必要な還元剤の投入量を求めた。
【００１７】
１００チャージ中の一例を具体的に説明する。転炉脱炭精錬後に発光分光分析法で測定した溶鋼酸素濃度は、０．０９重量％であった。分光法で求めたこの溶鋼酸素濃度に対応するスラグ中の易還元性酸化物の酸素濃度は、図２に示した酸素濃淡電池を用いて求めた溶鋼酸素濃度とスラグ中の易還元酸化物の酸素濃度との関係に一致したことから、図２の相関線図において溶鋼酸素濃度０．０９重量％に対応する１１．１重量％がスラグ中易還元性酸化物の酸素濃度であることが判る。
一方、スラグ重量は、測定したスラグ厚み２９．３ｃｍに予め求められているスラグの比重３．５を乗じて５．４トンと算出された。したがって、スラグ中の易還元性酸化物の酸素濃度は、１１．１重量％×５．４トン＝６００ｋｇとなり、Ｃｒ，Ｆｅ，Ｍｎを溶鋼に回収するために必要なＳｉ量は５２５ｋｇと算出された。
このＳｉ純分５２５ｋｇに相当するフェロシリコンを投入した後、真空脱ガス，脱酸処理を施し、スラグを再度サンプリングし、スラグに含まれている易還元性酸化物の酸素濃度を測定した。その結果、易還元性酸化物の酸素濃度は、０．０２重量％であった。このことから、Ｃｒ，Ｆｅ及びＭｎは、十分に溶鋼に回収されていることが確認された。
【００１８】
実施例３：
転炉脱炭精錬が終了したＣｒ含有量が１１〜２０重量％の範囲にあるフェライト系ステンレス鋼及びオーステナイト系ステンレス鋼の計１００チャージ（７７〜８１トン／チャージ）の溶鋼について、転炉脱炭精錬前後の溶鋼中のＣｒ濃度及びＳｉ濃度の減少量、すなわち転炉脱炭精錬前後の溶鋼中のＣｒ及びＳｉの濃度差を発光分光分析法で測定した。このとき、全チャージとも転炉脱炭精錬前後の溶鋼中のＣｒ濃度及びＳｉ濃度の減少量を表した測定値が得られるまでの時間はわずか２分程度であった。
溶鋼を取鍋に出鋼した後、直ちにタッチ式センサーでスラグ面位置を測定し、渦電流式センサーで湯面位置を測定した。スラグ厚みを計測した後、スラグ体積を算出し、一定値のスラグ比重を乗じてスラグ重量を求めた。得られたスラグ中の易還元酸化物の酸素濃度とスラグ重量からスラグ中の易還元酸化物の全酸素量を算出し、還元に必要な還元剤の投入量を求めた。
【００１９】
１００チャージ中の一例を具体的に説明する。転炉で脱炭精錬し、脱炭精錬前後のＣｒ濃度及びＳｉ濃度を発光分光分析法で測定した。Ｃｒ濃度及びＳｉ濃度の減少量から推定したスラグ中の易還元酸化物の酸素濃度は１０．７重量％であり、この推定値から図３の相関線図に基づいて求めたスラグ中の易還元酸化物の酸素濃度は１０．８重量％であった。なお、図３は、Ｃｒ含有量が１１〜２０重量％の範囲にあるフェライト系ステンレス鋼及びオーステナイト系ステンレス鋼の合計１００チャージ（７７〜８１トン／チャージ）の溶鋼について、脱炭精錬前後の溶鋼中にＣｒ濃度及びＳｉ濃度の減少量を用いて推定したスラグ中易還元酸化物の酸素濃度と炭素還元法で求めたスラグ中易還元性酸化物の酸素濃度との関係から求めた検量線である。
【００２０】
一方、スラグ重量は、測定したスラグ厚み３１．２ｃｍに予め求められているスラグの比重３．５を乗じて５．８トンと算出された。したがって、スラグ中の易還元性酸化物の酸素濃度は、１０．８重量％×５．８トン＝６２６ｋｇとなり、Ｃｒ，Ｆｅ，Ｍｎを溶鋼に回収するために必要なＳｉ量は５４８ｋｇと算出された。
このＳｉ純分５４８ｋｇに相当するフェロシリコンを投入した後、真空脱ガス，脱酸処理を施し、スラグを再度サンプリングし、スラグに含まれている易還元性酸化物の酸素濃度を測定した。その結果、易還元性酸化物の酸素濃度は、０．０３重量％であった。このことから、Ｃｒ，Ｆｅ及びＭｎは、十分に溶鋼に回収されていることが確認された。
【００２１】
表１に１００チャージの溶鋼酸素濃度又は転炉脱炭精錬前後の溶鋼中のＣｒ濃度及びＳｉ濃度の減少量からスラグ中易還元性酸化物の酸素濃度を求め、投入フェロシリコン量を決定した場合と、直接スラグを分析して易還元性酸化物の酸素濃度を求めて投入フェロシリコン量を決定した場合、それぞれの溶鋼中のＳｉ含有量の適中率の平均値と作業時間の平均値とを比較して示す。
表１の結果に示されているように、溶鋼の酸素濃度からスラグ中易還元性酸化物の酸素濃度を算出し、投入フェロシリコン量を決定した場合における溶鋼中のＳｉ含有量の適中率の平均値は、直接スラグを分析して易還元性酸化物の酸素濃度を求めて投入フェロシリコン量を決定した場合に比較して作業所要時間が約１０分間短縮された。この短縮時間は、１時間当り８０トンの粗鋼を生産するラインを想定すると、月産９，６００トンの増産に相当する値であり、大幅な生産量のアップにつながることが判る。また、作業時間も、変動が±１分以内に収まることが判った。
【００２２】

【００２３】
【発明の効果】
以上に説明したように、本発明においては、最短時間で還元剤の最適添加量を知ることができ、最適添加量で還元剤を添加することによりスラグに含まれているＦｅ，Ｍｎ，Ｃｒ等の易還元性酸化物を金属状態に還元して溶鋼に回収すると共に、還元剤の過剰添加に起因して処理後の溶鋼におけるＳｉ含有量，Ａｌ含有量等が上昇することを抑制している。その結果、作業時間が大幅に短縮され、目標組成に対する適中率が高い溶鋼が溶製される。また、還元剤の消費量を必要最小限とすることができるので、製造コストも低減される。
【図面の簡単な説明】
【図１】本発明に従って脱酸剤の必要投入量を決定するまでのフロー
【図２】酸素濃淡電池により測定した溶鋼の酸素濃度と炭素還元法で求めたスラグ中易還元性酸化物の酸素濃度との間に密接な関係があることを示したグラフ
【図３】脱炭精錬前後で酸化した溶鋼中のＳｉ濃度及びＣｒ濃度の減少量から推定したスラグ中易還元酸化物の酸素濃度と炭素還元法で求めたスラグ中易還元酸化物の酸素濃度分析値との間に密接な関係があることを示したグラフ[0001]
[Industrial application fields]
The present invention reduces the valuable metal in the slag with high accuracy in the composition of the molten steel when recovering the valuable metal in the easily reducible oxide suspended in the slag layer covering the molten steel surface after smelting to the molten steel. It relates to a collection method.
[0002]
[Prior art]
When decarburizing and refining alloy steel such as stainless steel with a converter, vacuum degassing equipment, etc., carbon in the molten steel reacts with blown oxygen and becomes CO gas, which is removed from the molten steel and is a useful component. Some of Cr, Fe, Mn and the like are also oxidized according to the following reaction.
4 [Cr] + 3O ₂ → 2 (Cr ₂ O ₃ )
2 [Fe] + O ₂ → 2 (FeO)
2 [Mn] + O ₂ → 2 (MnO)
Metal elements such as Cr, Fe, and Mn that have become oxides migrate to the slag floating on the surface of the molten steel. The metal element in the slag is reduced from an oxide to a metal state at the final stage of steelmaking, and is recovered as molten metal in the molten steel. The recovery is performed by using a metal element such as Cr, Fe, Mn and the like that is easily reduced to a metal state by Si, for example, by adding a predetermined amount of Si to the molten steel in the ladle during vacuum refining. . The reduction reaction with Si is as follows.
2 (Cr ₂ O ₃ ) + 3Si → 4 [Cr] +3 (SiO ₂ )
2 (FeO) + Si → 2 [Fe] + (SiO ₂ )
2 (MnO) + Si → 2 [Mn] + (SiO ₂ )
[0003]
Cr, Fe, Mn, and the like that are in the metal state move to molten steel, and as a result, the molten steel component concentration changes. In order to perform component adjustment with high accuracy, it is necessary to quantitatively grasp the metal elements that migrate from slag to molten steel in the final stage. Recently, steel types with extremely strict standards regarding Si content have begun to be used. In order to cope with such high-precision component adjustment and steel types in which the Si content is strictly controlled, the amount of easily reduced oxides reduced by Si is accurately grasped. It is necessary.
The oxygen amount of the easily-reducible oxide contained in the slag is indicated by the oxygen concentration in the metal oxide such as Cr ₂ O ₃ , FeO, and MnO reduced by Si and the ratio to the slag amount. The calculated amount of oxygen becomes a reference when determining the amount of Si necessary as a reducing agent.
[0004]
[Problems to be solved by the invention]
As a method for quantifying the oxygen concentration in a metal oxide, a method for X-ray fluorescence analysis of a slag sample is known. X-ray fluorescence analysis requires 20 to 25 minutes from the weighing of the sample to the calculation of the analytical value in either the glass bead method or the press molding method. Moreover, assuming that the metal oxide contained in the sample has a stoichiometric form, the quantitative value of the metal element is multiplied by a coefficient determined from the stoichiometric relationship between the metal and the oxide. Thus, the oxygen analysis value is calculated. Therefore, a measurement error is inevitably caused in a sample containing Cr, Fe, Mn, or the like in a metal state or a sample containing a metal oxide having a different oxygen value.
In order to eliminate such measurement errors and shorten the analysis time, the present inventors have made steelmaking slag based on the oxygen concentration discharged out of the system due to the reaction between the sample collected from the steelmaking slag and the carbon source. Was developed as a method for quantifying the oxygen concentration of the easily-reducible oxide contained in Japanese Patent Application No. 4-319364. According to this method, it is possible to quantitate oxygen in slag in about 10 minutes while minimizing analysis errors.
[0005]
By the way, in recent years when the demand for stainless steel is increasing, it is necessary to increase the production amount per unit time in order to respond to the demand amount with the existing equipment, and shortening of the tap time is an issue. For this reason, there is an urgent need for technical development for grasping the amount of easily reducible oxygen in the slag in a shorter time.
The present invention has been devised to meet such a demand, and is combined with valuable metals in the slag from the amount of decrease in the molten steel oxygen concentration or Cr concentration and Si concentration in the molten steel before and after decarburization refining. By grasping the oxygen concentration easily and quickly, and determining the optimum addition amount based on this value and the separately obtained slag amount, and introducing a reducing agent, valuable metals are efficiently recovered in the molten steel, and high appropriate accuracy It aims at obtaining the molten steel by which component adjustment was carried out.
[0006]
[Means for Solving the Problems]
In order to achieve the purpose of the valuable metal reduction and recovery method of the present invention, when reducing and recovering valuable metal in the easily reducible oxide from the slag floating on the surface of the molten steel to the molten steel, the molten steel is used with an oxygen concentration cell. Measure the oxygen value, insert the molten steel oxygen value into the calibration curve determined in advance to estimate the oxygen concentration of the easily reducible oxide in the slag, and detect the surface position of the slag and the molten steel. The thickness of the slag is calculated from the difference in the surface position, the weight of the slag is obtained based on the thickness of the slag, and the required amount of reducing agent is calculated from the oxygen concentration of the easily reduced oxide in the slag and the slag weight. Then, the reducing agent is added to the slag with the addition amount of the calculation result.
As the molten steel oxygen value, a molten steel oxygen value measured by an emission spectroscopic analysis method may be used instead of a measured value using an oxygen concentration cell. When decarburizing and refining alloy steel containing Si and Cr with a converter or a vacuum degassing apparatus, the amount of decrease in Cr concentration and Si concentration in the molten steel before and after decarburization refining is measured, and a calibration curve obtained in advance. It is also possible to estimate the oxygen concentration of the easily reduced oxide in the slag floating on the surface of the molten steel after decarburization refining by inserting the decrease amount of the Cr concentration and the Si concentration.
[0007]
[Action]
The easily reducible oxide contained in steelmaking slag is produced by blown oxygen during decarburization refining, and the oxygen value has a high correlation with the oxygen concentration in molten steel. Further, according to the investigations and studies by the present inventors, it has been found that there is a high correlation with the oxygen value of the easily reduced oxide calculated from the decrease in Cr concentration and Si concentration in the molten steel before and after decarburization refining.
The above is the determination of the oxygen concentration of the easily reducible oxide contained in the steelmaking slag by measuring the oxygen concentration in the molten steel or the decrease in the Cr concentration and Si concentration in the molten steel before and after decarburization refining. It is suggested that The oxygen concentration of molten steel can be easily measured in only about 2 minutes using an oxygen concentration cell or an emission spectroscopic analyzer. Further, the decrease amounts of the Cr concentration and the Si concentration in the molten steel before and after decarburization refining are the differences in the Si concentration and the Cr concentration in the molten steel before and after decarburization refining, respectively. These concentration differences can be easily measured in about 2 minutes with an emission spectroscopic analyzer. Therefore, when estimating the oxygen concentration of the steelmaking slag from the oxygen concentration or Si concentration and Cr concentration in the molten steel, the slag sampling operation time and the series of operation time for obtaining the analytical value from the pulverization are omitted, resulting in the tap time. Is greatly shortened.
[0008]
On the other hand, along with a method for measuring the slag weight detects the position X ₂ of the position X ₁ and molten steel surface of the slag surface from a reference point to determine the thickness of the slag from the difference in the positions (X 1 _-X ₂₎ , the vacuum degassing vessel, determine the slag volume V _S from the container inner diameter R of the ladle or the like, a method of calculating the slag weight W _S by multiplying the specific gravity ρ of the slag is employed.
The surface position of the slag is detected by a distance meter using eddy current, laser, microwave, radiation or the like, a touch sensor that directly contacts the slag surface, a method of measuring the luminance of the slag, and the like. As the eddy current sensor, it is preferable to use an eddy current sensor to which a high-frequency alternating current having a frequency of 500 kHz or more and 1 MHz or less is supplied. Since the high-frequency alternating current having a frequency of 500 kHz or more and 1 MHz or less generates an eddy current only on the surface of the slag, the surface position of the slag can be detected.
[0009]
The method of detecting the position of the molten metal surface under the slag by using an eddy current sensor, the method of immersing a pair of electrodes from the slag to the metal, and electrically detecting the difference in conductivity between the slag and the metal. A gas probe in which a certain amount of gas is flowing is immersed from the slag to the metal, and is detected by a method using a back pressure change in the gas probe resulting from a difference in specific gravity between the slag and the metal. For example, when using an eddy current sensor, a high frequency alternating current with a frequency of 0.5 to 500 kHz is supplied to detect the surface position of the molten steel. By supplying a high-frequency alternating current with a frequency of 0.5 to 500 kHz, the error factor due to the eddy current caused by the metal droplet suspended in the slag layer is not taken into the receiving coil of the eddy current sensor, and under the slag. A surface position of a molten steel is detected with high accuracy.
[0010]
From the oxygen concentration of the molten steel measured as described above or the decrease in Cr concentration and Si concentration in the molten steel before and after decarburization refining and the weight of the slag, the required addition amount of the reducing agent is calculated according to the flow shown in FIG. The When the reducing agent is added in this addition amount, the easily reducible oxide in the slag is reduced and recovered in the molten steel in a metallic state. When this method is used, since an excessive reducing agent is not added, an extra reducing agent brought into the molten steel can be reduced. That is, by adding an amount of reducing agent determined based on the composition and weight of the slag, the reducing agent Si is not brought into the molten steel more than the standard component, and the alloy components such as Mn, Cr, etc. Molten steel with improved accuracy in content is obtained.
The valuable metal that is reduced and recovered in the molten steel can be selected according to the reducing ability of the reducing agent used. For example, when Si or ferrosilicon is used as a reducing agent, Fe, Mn and Cr are reduced and recovered in molten steel. When Al, Ti, Ca, Mg or an alloy thereof is used as a reducing agent, Fe, Mn, Cr and Si are reduced and recovered. When Al, Ca, Mg, or an alloy thereof is added as a reducing agent, Fe, Mn, Cr, Si, and Ti are reduced and recovered in the molten steel. In any case, the required addition amount of the reducing agent is determined from the oxygen amount of the easily reducible oxide in the slag and the slag weight, so the target composition can be achieved without adding extra reducing agent beyond the standard components. Highly accurate and consistent molten steel can be obtained.
[0011]
-Measurement of slag weight-
The surface positions of the slag and molten steel are detected as distances X ₁ and X ₂ from the reference point. Since the surface position of the molten steel is at the interface with the slag layer, the thickness of the slag layer is calculated as (X ₁ −X ₂ ). On the other hand, since the inner radius R of a container such as a vacuum degassing container or a ladle is known in advance, the volume V _S of the slag is V _S = πR ² × (X ₁ −X ₂ ). Weight _{W S} of the slag, by multiplying the specific gravity [rho slag volume _{V S,} is calculated as _{_{W S = ρ × V S =}} ρ × πR 2 × (X 1 -X 2). The resulting slag weight W _S, without an intervening molten steel weight W _M, which is directly calculated value from the thickness of the slag layer. FIG. 1 shows the flow during this time. In this way, less error factors are incorporated, slag weight W _S is determined with high precision.
[0012]
-Calculation of required amount of reducing agent-
The required addition amount of the reducing agent is determined by determining the concentration of easily reduced oxide contained in the slag and multiplying the slag weight. The concentration of easily reducible oxides contained in the slag is based on the oxygen concentration of the molten steel obtained using an oxygen concentration cell or emission spectroscopic analysis, or the decrease in the Cr concentration and Si concentration in the molten steel before and after decarburization refining. Determined. As a result of various experiments conducted by the present inventors, it has been found that the oxygen concentration (O) of the easily reduced oxide in the slag can be accurately estimated by the following equations.
(O) = a · [O] + b
(O) = c · ΔCr + d · ΔSi + e
In the formula, a, b, c, d, and e represent coefficients or constants. [O] represents the oxygen concentration of the molten steel obtained by an oxygen concentration cell or emission spectroscopic analysis, and ΔCr and ΔSi represent the reduction amounts of Cr concentration and Si concentration in the molten steel before and after decarburization refining, respectively. By multiplying the slag weight W _S of the oxygen concentration (O) of the resulting slag Nakayasu reducing oxides, the oxygen content of readily reducing oxides of the slag in the ladle is determined. Depending on the calculated amount of oxygen, the amount of reducing agent input is determined as necessary for the reduction.
When the amount of reducing agent adjusted in this way is charged, Cr, Fe, Mn, etc. in the easily-reducible oxide are recovered from the slag to the molten steel in a predetermined amount, and the amount of reducing agent charged is excessive. It will not be brought in. As a result, the reducing agent can be consumed efficiently, as well as the appropriate moderateness of the molten steel components after melting. In particular, it is possible to accurately produce a steel type that requires strict management with respect to the Si content derived from the reducing agent.
[0013]
【Example】
Example 1:
The oxygen concentration cell is immersed for a total of 100 charges (77 to 81 tons / charge) of ferritic stainless steel and austenitic stainless steel in which the Cr content after the converter blowing is in the range of 11 to 20% by weight. The oxygen concentration was measured. At this time, the time until the oxygen concentration was obtained for all charges was only 10 seconds.
After the molten steel was taken out into the ladle, the position of the slag surface and the molten metal surface was immediately detected using a sensor. The measurement time at this time was about 1 minute. In addition, the position of the slag surface was measured using a touch-type sensor that was in direct contact, and the position of the molten metal surface was measured using an eddy current sensor. After measuring the slag thickness, the slag volume was calculated, and the slag weight was determined by multiplying the slag specific gravity. The total weight of the easily reducible oxide in the slag was calculated from the obtained oxygen concentration and slag weight, and the amount of reducing agent required for the reduction was calculated.
[0014]
An example during 100 charges will be specifically described. The molten steel oxygen concentration determined by the oxygen concentration cell after converter decarburization refining was 0.11% by weight. It can be seen that the oxygen concentration of the easily reducible oxide in the slag corresponding to the molten steel oxygen concentration is 12.4% by weight from the correlation diagram of FIG. In addition, FIG. 2 shows easily reducible oxidation in slag for molten steel having a total of 100 charges (77 to 81 tons / charge) of ferritic stainless steel and austenitic stainless steel having a Cr content in the range of 11 to 20% by weight. It is a calibration curve obtained in advance from the relationship with the oxygen concentration in the molten steel obtained by the carbon reduction method to determine the oxygen concentration of the product and measured with an oxygen concentration cell.
[0015]
On the other hand, the slag weight was calculated to be 4.1 tons by multiplying the measured slag thickness of 22.3 cm by a specific slag specific gravity of 3.5. Therefore, the oxygen concentration of the easily-reducible oxide in the slag is 12.4 wt% × 4.4 tons = 508 kg, and the amount of Si necessary for recovering Cr, Fe, Mn into the molten steel is calculated as 445 kg. It was.
After introducing ferrosilicon corresponding to 445 kg of this pure Si, vacuum degassing and deoxidation treatment were performed, the slag was sampled again, and the oxygen concentration of the easily reducible oxide contained in the slag was measured. As a result, the oxygen concentration of the easily reducible oxide was 0.03% by weight. From this, it was confirmed that Cr, Fe and Mn were sufficiently recovered in the molten steel.
[0016]
Example 2:
Emission spectroscopic analysis of molten steel with a total of 100 charges (77 to 81 tons / charge) of ferritic stainless steel and austenitic stainless steel with Cr content in the range of 11 to 20 wt% after converter decarburization and refining The oxygen concentration was measured at At this time, the time until the measured value of the oxygen concentration was obtained for all charges was only about 2 minutes.
After the molten steel was taken out of the ladle, the slag surface position was immediately measured with a touch sensor, and the molten metal surface position was measured with an eddy current sensor. After measuring the slag thickness, the slag volume was calculated, and the slag weight was determined by multiplying the slag specific gravity. The total oxygen amount of the easily reduced oxide in the slag was calculated from the oxygen concentration of the easily reduced oxide in the obtained slag and the slag weight, and the input amount of the reducing agent necessary for the reduction was determined.
[0017]
An example during 100 charges will be specifically described. The molten steel oxygen concentration measured by emission spectroscopic analysis after converter decarburization refining was 0.09 wt%. The oxygen concentration of the easily reducible oxide in the slag corresponding to this molten steel oxygen concentration determined by the spectroscopic method is the molten steel oxygen concentration obtained using the oxygen concentration cell shown in FIG. 2 and the easily reduced oxide in the slag. Since it matched with the relationship with oxygen concentration, it turns out that 11.1 weight% corresponding to 0.09 weight% of molten steel oxygen concentration is an oxygen concentration of the easily reducible oxide in slag in the correlation diagram of FIG. .
On the other hand, the slag weight was calculated to be 5.4 tons by multiplying the measured slag thickness of 29.3 cm by a specific slag specific gravity of 3.5. Therefore, the oxygen concentration of the easily-reducible oxide in the slag is 11.1% by weight × 5.4 tons = 600 kg, and the amount of Si necessary for recovering Cr, Fe, Mn into the molten steel is calculated to be 525 kg. It was.
Ferrosilicon corresponding to 525 kg of pure Si was added, vacuum degassing and deoxidation were performed, slag was sampled again, and the oxygen concentration of the easily reducible oxide contained in the slag was measured. As a result, the oxygen concentration of the easily reducible oxide was 0.02% by weight. From this, it was confirmed that Cr, Fe and Mn were sufficiently recovered in the molten steel.
[0018]
Example 3:
Converter decarburization for molten steel with a total of 100 charges (77 to 81 tons / charge) of ferritic stainless steel and austenitic stainless steel with Cr content in the range of 11 to 20% by weight after converter decarburization refining The amount of decrease in Cr concentration and Si concentration in the molten steel before and after refining, that is, the difference in the concentration of Cr and Si in the molten steel before and after converter decarburization refining was measured by emission spectroscopy. At this time, it took only about 2 minutes until the measurement value showing the decrease amount of Cr concentration and Si concentration in the molten steel before and after converter decarburization refining was obtained for all charges.
After the molten steel was taken out of the ladle, the slag surface position was immediately measured with a touch sensor, and the molten metal surface position was measured with an eddy current sensor. After measuring the slag thickness, the slag volume was calculated, and the slag weight was determined by multiplying the slag specific gravity. The total oxygen amount of the easily reduced oxide in the slag was calculated from the oxygen concentration of the easily reduced oxide in the obtained slag and the slag weight, and the input amount of the reducing agent necessary for the reduction was determined.
[0019]
An example during 100 charges will be specifically described. Decarburization and refining were carried out in a converter, and Cr and Si concentrations before and after decarburization were measured by emission spectroscopic analysis. The oxygen concentration of the easily reduced oxide in the slag estimated from the decrease amount of the Cr concentration and the Si concentration is 10.7 wt%, and the easily reduced in the slag obtained from this estimated value based on the correlation diagram of FIG. The oxygen concentration of the oxide was 10.8% by weight. In addition, FIG. 3 shows the molten steel before and after decarburization refining for molten steel with a total of 100 charges (77 to 81 tons / charge) of ferritic stainless steel and austenitic stainless steel having a Cr content in the range of 11 to 20% by weight. In the calibration curve obtained from the relationship between the oxygen concentration of the easily reduced oxide in slag estimated using the reduction amount of Cr concentration and Si concentration in the slag and the oxygen concentration of the easily reduced oxide in slag obtained by the carbon reduction method is there.
[0020]
On the other hand, the slag weight was calculated to be 5.8 tons by multiplying the measured slag thickness of 31.2 cm by the specific gravity of slag determined in advance of 3.5. Therefore, the oxygen concentration of the easily-reducible oxide in the slag is 10.8 wt% × 5.8 tons = 626 kg, and the amount of Si necessary to recover Cr, Fe, Mn to the molten steel is calculated as 548 kg. It was.
After adding ferrosilicon corresponding to 548 kg of pure Si, vacuum degassing and deoxidation treatments were performed, the slag was sampled again, and the oxygen concentration of the easily-reducible oxide contained in the slag was measured. As a result, the oxygen concentration of the easily reducible oxide was 0.03% by weight. From this, it was confirmed that Cr, Fe and Mn were sufficiently recovered in the molten steel.
[0021]
When the oxygen concentration of the easily reduced oxide in the slag is determined from the amount of decrease in the molten steel oxygen concentration of 100 charges or the Cr concentration and Si concentration in the molten steel before and after converter decarburization refining, the amount of ferrosilicon input is determined When the amount of ferrosilicon input is determined by directly analyzing the slag and determining the oxygen concentration of the easily-reducible oxide, the average value of the moderate ratio of the Si content in each molten steel and the average value of the working time are obtained. Shown in comparison.
As shown in the results of Table 1, the oxygen concentration of the easily reducible oxide in the slag is calculated from the oxygen concentration of the molten steel, and when the amount of introduced ferrosilicon is determined, the moderate ratio of the Si content in the molten steel The average value was shortened by about 10 minutes compared to the case where the amount of ferrosilicon input was determined by directly analyzing the slag to determine the oxygen concentration of the easily reducible oxide. Assuming a line that produces 80 tons of crude steel per hour, this shortened time is equivalent to an increase of 9,600 tons per month, which can be seen to lead to a significant increase in production. The working time was also found to vary within ± 1 minute.
[0022]

[0023]
【The invention's effect】
As described above, in the present invention, the optimum addition amount of the reducing agent can be known in the shortest time, and Fe, Mn, Cr, etc. contained in the slag by adding the reducing agent at the optimum addition amount. In addition to reducing the easily reducible oxide to a metallic state and recovering it in molten steel, it suppresses an increase in Si content, Al content, etc. in the molten steel after treatment due to excessive addition of a reducing agent. . As a result, the working time is greatly shortened and molten steel having a high appropriateness ratio with respect to the target composition is produced. In addition, since the consumption of the reducing agent can be minimized, the manufacturing cost is also reduced.
[Brief description of the drawings]
FIG. 1 is a flow chart for determining the required amount of deoxidizer according to the present invention. FIG. 2 is an oxygen concentration of molten steel measured by an oxygen concentration cell and oxygen of an easily reducible oxide in slag obtained by a carbon reduction method. Graph showing that there is a close relationship between concentration and concentration. Fig. 3 Oxygen concentration of easily reduced oxide in slag estimated from the decrease of Si concentration and Cr concentration in molten steel oxidized before and after decarburization refining Graph showing that there is a close relationship with the oxygen concentration analysis value of easily reduced oxide in slag obtained by carbon reduction method

Claims

When recovering and recovering valuable metals in easily reducible oxides from the slag floating on the surface of the molten steel to the molten steel, the molten steel oxygen value is measured using an oxygen concentration cell, and the molten steel oxygen value is determined in advance on a calibration curve. To estimate the oxygen concentration of the easily reducible oxide in the slag, detect the surface position of the slag and the molten steel, calculate the thickness of the slag from the difference in the detected surface position, the thickness of the slag The amount of the slag is obtained based on the above, the required amount of the reducing agent is calculated from the oxygen concentration of the easily reduced oxide in the slag and the slag weight, and the reducing agent is added to the slag with the calculated addition amount. A method for reducing and recovering valuable metals in slag, which is improved in the accuracy of molten steel components.

As the molten steel oxygen value according to claim 1, reduction method of recovering valuable metals in the slag using a molten steel oxygen values measured by the measurement emission spectroscopy instead of using the oxygen concentration cell.

When reducing and recovering valuable metals in easily reducible oxides from the slag floating on the surface of the molten steel decarburized and refined with a converter or vacuum degassing equipment, alloy steel containing Si and Cr, before and after decarburization refining The amount of decrease in Cr concentration and Si concentration in molten steel is measured, and the amount of decrease in Cr concentration and Si concentration is inserted into the calibration curve obtained in advance, and the slag in the slag floats on the surface of the molten steel after decarburization refining. Estimating the oxygen concentration of the reduced oxide , detecting the surface position of the slag and the molten steel, calculating the thickness of the slag from the difference in the detected surface position, and calculating the weight of the slag based on the thickness of the slag Determining the required addition amount of the reducing agent from the oxygen concentration of the easily reduced oxide in the slag and the slag weight, and adding the reducing agent to the slag with the addition amount of the calculation result. with improved accuracy Reduction method of recovering valuable metals in the rug.