JP3679475B2

JP3679475B2 - Method for refining stainless steel

Info

Publication number: JP3679475B2
Application number: JP27345395A
Authority: JP
Inventors: 勝彦加藤; 敏隆湯木; 健一郎宮本
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1995-09-26
Filing date: 1995-09-26
Publication date: 2005-08-03
Anticipated expiration: 2015-09-26
Also published as: JPH0987722A

Description

【０００１】
【発明の属する技術分野】
本発明は、ステンレス粗溶鋼の精錬方法に係り、更に詳しくは、前チャージで生成された脱炭スラグを精錬炉内に残滓したまま次チャージの脱炭精錬を開始し、脱炭スラグ中のクロム分を次チャージの溶銑中に還元するとともに、クロム分を還元して生成されたクロム回収済スラグを脱炭精錬中に排滓した後、引き続き同一精錬炉内で溶銑の脱炭精錬を継続するステンレス粗溶鋼の精錬方法に関する。
【０００２】
【従来の技術】
従来、ステンレス粗溶鋼の精錬方法では、ＬＤ転炉等の精錬炉内に溶銑（又は溶鉄という）を投入するとともに、精錬炉内にランス等を介して酸素（以下Ｏ₂という）を吹き込んで、溶銑中に含有される炭素（以下［Ｃ］_Mという）に下記（１）式に示す酸化反応を生じせしめ、脱炭している。
２［Ｃ］_M＋Ｏ₂→２ＣＯ・・・・・・・・・・・（１）
【０００３】
また、精錬時には、精錬炉内に投入された造滓剤等によってクロム分（通常クロム酸化物（以下（Ｃｒ₂Ｏ₃）_Sという））を含有する脱炭スラグが生成されている。そして、この脱炭スラグ中のクロム分と溶銑中の炭素に下記（２）式に示す還元反応を生じせしめ、溶銑中に還元させている。
（Ｃｒ₂Ｏ₃）_S＋３［Ｃ］_M→２［Ｃｒ］_M＋３ＣＯ・・（２）
なお、前記（２）式中［Ｃｒ］_Mは、溶銑中に還元されたクロムをいう。
【０００４】
しかしながら、前記（２）式の還元反応によって脱炭スラグ中のクロム分を溶銑中に還元しているが、精錬終了時に溶銑中のＣｒ濃度を１１〜１９ｗｔ％と高くするために、脱炭スラグ中のＣｒ含有率もやはり１１〜１９ｗｔ％と高くなってしまい、溶銑中の炭素のみによる還元反応だけでは脱炭スラグ中のクロム分を全て還元することができず、この結果、高Ｃｒ含有率の脱炭スラグをそのまま廃棄するしかなかった。
【０００５】
一方、精錬操業中、前記（１）式の脱炭反応や前記（２）式の還元反応等の炭素の燃焼反応等によって一酸化炭素ガス（以下ＣＯガスという）が生じることで、通常、脱炭スラグが発泡（又はフォーミング或いはスロッピングという）している。
【０００６】
しかしながら、精錬操業中に脱炭スラグがフォーミングし過ぎると、この脱炭スラグが精錬炉外に溢れて精錬炉の周辺設備を溶損させる等、極めて作業性や生産性を阻害する一方、脱炭スラグの排滓（又は出滓という）時である精錬操業終了時に脱炭スラグがフォーミングしないと排滓作業が困難となる等、やはり極めて作業性や生産性を阻害するという問題点を有していた。
【０００７】
このため、ステンレス粗溶鋼の精錬操業では、脱炭スラグ中のクロム分を回収したり、脱炭スラグのフォーミングを制御する何等かの方法が希求されていた。
【０００８】
そこで、これらの問題点を解決するために、▲１▼特開昭６３−１９５２０６号公報には、上方から酸化性ガスを吹込みつつ、炉底羽口を介して酸素あるいは不活性ガスを供給して溶鉄にクロム鉱石と炭材を添加して溶融還元する上底吹転炉精錬において、５〜５０mmの直径を有する塊状炭材を上吹酸素ジェットの火点部以外の場所に添加すると共に、該塊状炭材を全酸素供給速度Ｆ（Ｎｍ³／（Ｔ・Ｈｒ））に対して０．１Ｆ〜０．５Ｆ（ｋｇ／（Ｔ・Ｈｒ））の速度で添加するクロム酸化物の溶解還元方法が提案されている。
【０００９】
また、▲２▼特開昭５３−１１９２１０号公報には、製鋼炉にて溶製された１３％以上のクロム含有量を有する含クロム鋼の残滓を冷却固化せしめ、転炉における他の含クロム鋼用チャージの吹錬時に前記の固体残滓を添加せしめる含クロム鋼滓よりのクロム回収利用方法や、▲３▼脱炭スラグの排滓前に珪素（以下Ｓｉという）を添加し、下記（３）式に示す還元反応を生じせしめる方法が提案されている。
２（Ｃｒ₂Ｏ₃）_S＋３Ｓｉ→４［Ｃｒ］_M＋３（ＳｉＯ₂）_S・・（３）
【００１０】
【発明が解決しようとする課題】
しかしながら、▲１▼の特開昭６３−１９５２０６号公報に示されたクロム酸化物の溶解還元方法では、塊状炭材の添加速度を規定することによりクロム酸化物を高速で還元することはできるが、クロム分を還元した（又は回収した）スラグを排滓する際に、このスラグの厚みが薄いことに起因してスラグの排滓率にバラツキが生じ易く、この結果、スラグと共に溶銑が出銑される所謂メタルロスが発生し、歩留りが低下するという問題点を有していた。また、脱炭スラグのフォーミングを制御することができないという問題点を有していた。
【００１１】
また、▲２▼の特開昭５３−１１９２１０号公報に示された含クロム鋼滓よりのクロム回収利用方法では、製鋼炉にて溶製された１３％以上のクロム含有鋼の残滓を冷却固化し、他の含クロム鋼用チャージの吹錬時に固体残滓を添加しているため、吹錬時に冷却固化された残滓を昇温する必要が生じるとともに、冷却固化された残滓上に高温の溶銑を投入しても溶銑温度が低下しやはり昇温作業が必要となり、このため、昇温還元時間を大幅に延長させ、精錬操業を迅速に行うことができず、極めて生産性を阻害するという問題点を有していた。また、脱炭スラグのフォーミングを制御することができないという問題点を有していた。
【００１２】
さらに、▲３▼のＳｉを添加する方法では、このＳｉがＣに比べ高価であることから製造原価が高騰するとともに、前記（３）式により生じた二酸化硅素（（ＳｉＯ₂）_S）による耐火物の溶損等を防止するために、生石灰等を投入してスラグの塩基度を高めること（又は高塩基度化という）が必要であるため、生石灰等の投入により生成されたスラグの量が増大するという問題点を有していた。
【００１３】
本発明はこのような事情に鑑みてなされたもので、前チャージの仕上げ精錬期終了時の高Ｃｒ含有率の脱炭スラグを精錬炉内に残滓させたまま次チャージの溶銑を投入し、前記溶銑と前記脱炭スラグのＣｒ濃度差を利用して脱炭スラグ中のクロム分を高還元速度で回収するとともに、吹酸昇温還元期終了時の低Ｃｒ含有率のクロム回収済スラグを排滓させることで、従来廃棄等していた脱炭スラグ中のクロム分をステンレス鋼中に回収させることができ、さらに、吹酸昇温還元期に投入される炭材の脱炭スラグ又はクロム回収済スラグに対する重量比率を適宜選択することで、吹酸昇温還元期の脱炭スラグ又はクロム回収済スラグのフォーミングを制御して異常フォーミング等を防止するとともに、効率的且つ安定的なクロム回収済スラグの排滓を行うことができるステンレス粗溶鋼の精錬方法を提供することを目的とする。
【００１４】
【課題を解決するための手段】
前記目的に沿う請求項１記載のステンレス粗溶鋼の精錬方法は、精錬炉内に前チャージの仕上げ精錬期で生成されクロム酸化物を含有する脱炭スラグを残留させたまま次チャージの溶銑を投入するとともに、前記精錬炉内に炭材を添加し且つ酸化性ガスを吹き込んで前記脱炭スラグ中のクロム酸化物を前記溶銑中に還元する吹酸昇温還元期と、前記吹酸昇温還元期でクロム酸化物を前記溶銑中に還元して得たクロム回収済スラグを排滓する中間排滓期と、前記中間排滓期で前記精錬炉内に残留された溶銑にフェロクロム合金を溶解しながら脱炭精錬する前記仕上げ精錬期とを備え、しかも、前記吹酸昇温還元期の前記炭材の含有率（Ｖ _C ）を前記脱炭スラグに対し重量比率で３ｗｔ％≦Ｖ _C ≦６ｗｔ％とし、前記吹酸昇温還元期終了時の前記炭材の含有率（Ｖ _C ）を前記クロム回収済スラグに対し重量比率で０．５ｗｔ％≦Ｖ _C ≦３ｗｔ％とする。
【００１６】
さらに、請求項２記載のステンレス粗溶鋼の精錬方法は、請求項１記載のステンレス粗溶鋼の精錬方法において、前記脱炭スラグ又は前記クロム回収済スラグの塩基度（（ＣａＯ／ＳｉＯ₂ ）_S ）を重量比率で１．２≦（ＣａＯ／ＳｉＯ₂ ）_S ≦４．５とし、及び／又は、前記脱炭スラグのＡｌ₂ Ｏ₃ の含有率（（Ａｌ₂ Ｏ₃ ）_S ）を３ｗｔ％≦（Ａｌ₂ Ｏ₃ ）_S ≦２３ｗｔ％とする。
【００１７】
なお、ステンレス粗溶鋼の精錬方法を適用する精錬炉としては、上底吹転炉、底吹転炉、上吹転炉等のＬＤ（ＬｉｎｚＤｏｎａｗｉｔｚ）転炉、ＡＯＤ（ＡｒｇｏｎＯｘｉｇｅｎＤｅｃａｒｂｕｒｉｚａｔｉｏｎ）転炉、電気炉等が適用可能である。
【００１８】
吹酸昇温還元期とは、前チャージで生成されクロム酸化物を含有する脱炭スラグを残留させた精錬炉内に次チャージの溶銑を投入した後、酸化性ガスを吹き込むとともに炭材を投入して、少なくとも前記（２）式に示した還元反応を生じせしめ、脱炭スラグ中のクロム酸化物を溶銑中に還元して、クロムを除去したクロム回収済スラグを生成する期間をいう。
【００１９】
また、中間排滓期（又はクロム回収済スラグ排滓期という）とは、吹酸昇温還元期でクロム酸化物を溶銑中に還元して得たクロム回収済スラグを排滓する期間をいう。さらに、仕上げ精錬期（又は脱炭期という）とは、中間排滓期で精錬炉内に残留され脱炭スラグ中のクロム分を回収した溶銑にフェロクロム合金等を添加し、必要に応じて酸化性ガスの吹き込みによる脱炭を行い、その他、温度の調整を行う期間をいう。
【００２０】
なお、吹酸昇温還元期及び仕上げ精錬期では、効率良く脱炭反応させるために、各種方法で溶銑を攪拌するのが好ましい。例えば、底吹転炉や上底吹転炉では、これら精錬炉の底部から各種ガスを装入することで溶銑を攪拌することができる。また、フェロクロム合金は溶銑のＣｒ含有率を調整するために使用されるものであり、このフェロクロム合金としては、Ｃｒ含有率が１０ｗｔ％〜５０ｗｔ％の一般クロム鉱石は勿論、高炭素フェロクロム、中炭素フェロクロム、低炭素フェロクロム等の貧鉱を富化処理したもの、或いは還元処理されたペレット等のクロム鉱石類等が使用されている。また、この他ステンレス鋼屑等を使用してもよい。
【００２１】
また、脱炭スラグを残存した精錬炉内に溶銑を装入する際の溶銑温度（Ｔ_P）としては、１２００℃≦Ｔ_P≦１５００℃の範囲とされるのが好ましい。溶銑温度が１２００℃未満では溶銑温度が低過ぎて酸化還元反応を促進させるべく溶銑温度を上昇させねばならず、このため精錬時間が長くなる等精錬効率が低下する傾向が現れ、また、溶銑温度が１５００℃を越えると高炉の出銑温度を高めねばならず、このため高炉を構成する耐火物が溶損し易くなる傾向が現れるので、いずれも好ましくない。
【００２２】
また、酸化性ガスとしては、上底吹転炉又は上吹転炉で、受銑口からランスを介して吹き込まれる酸素等や、上底吹転炉でガス送入口から吹き込まれる酸素、アルゴンガスや窒素ガス等の不活性ガス、炭酸ガス、燃料ガス等の混合ガス等が挙げられる。また、吹酸昇温還元期にランスから吹き込まれる酸素の送酸速度（Ｖ_P：（単位：Ｎｍ³／ｍｉｎ／Ｔ））としては、１．５≦Ｖ_P≦６の範囲とされるのが好ましい。吹酸昇温還元期の送酸速度が１．５Ｎｍ³／ｍｉｎ／Ｔ未満では酸素供給量が減少することに起因して溶銑中の炭素によるクロム酸化物の還元速度（以下クロム還元速度という）が小さくなり、このため精錬時間が長くなる等精錬効率が低下する傾向が現れ、また、吹酸昇温還元期の送酸速度が６Ｎｍ³／ｍｉｎ／Ｔを越えると溶銑や溶滓の温度が高くなり過ぎて耐火物が溶損する傾向が現れるので、いずれも好ましくない。
【００２３】
また、炭材としては，粉状コークスや、この粉状コークスを各種バインダーで塊状に固結した塊状コークス、更に、前記粉状コークスと粒状鉄とを前記バインダーで塊状にした成形コークス、或いは粉状無煙炭を前記バインダーで塊状にした無煙炭ブリケット等が挙げられる。その他、脱炭スラグ中のクロム分を還元するために、アルミドロス等の還元材等を用いてもよい。また、特に、アルミドロスは昇温材の役目も兼ねており、極めて有用である。その他、脱炭スラグの組成の制御や、これによる脱炭スラグ中のクロム分の還元速度の向上に寄与することができる。
【００２４】
また、吹酸昇温還元期の炭材の含有率（Ｖ_C）としては、脱炭スラグに対し重量比率で３ｗｔ％≦Ｖ_C≦６ｗｔ％、好適には４ｗｔ％≦Ｖ_C≦５ｗｔ％の範囲とされるのが好ましい。吹酸昇温還元期の炭材の含有率が脱炭スラグに対し重量比率で４ｗｔ％未満では前記（１）及び（２）式に示した炭素の燃焼反応等で生成されたＣＯガスによって形成された気泡によって脱炭スラグの異常フォーミングが発生する傾向が現れ、特に３ｗｔ％未満ではその傾向が著しくなり、また、吹酸昇温還元期の炭材の含有率が脱炭スラグに対し重量比率で５ｗｔ％を越えると前記（１）及び（２）式に示した炭素の燃焼反応等で生成されたＣＯガス量が増加することで気泡が破壊される等して脱炭スラグ（又はクロム回収済スラグ）のフォーミング不足を招き、地金が飛散する所謂地金飛散ロス等により歩留りが低下する傾向が現れ、特に６ｗｔ％を越えるとその傾向が著しくなるので、いずれも好ましくない。また、吹酸昇温還元期の炭材の含有率を前記範囲とするために、精錬操業にあたって炭材は精錬炉内に予め投入されたり精錬炉内に連続的に投入等される。
【００２５】
特に、吹酸昇温還元期終了時の炭材の含有率（Ｖ_C）としては、クロム回収済スラグに対し重量比率で０．５ｗｔ％≦Ｖ_C≦３ｗｔ％、好適には１ｗｔ％≦Ｖ_C≦１．５ｗｔ％の範囲とされるのが好ましい。吹酸昇温還元期終了時の炭材の含有率がクロム回収済スラグに対し重量比率で１ｗｔ％未満では前記（１）及び（２）式に示した炭素の燃焼反応等で生成されたＣＯガスの合体集積不足のために、脱炭スラグの異常フォーミングが急速に発生し排滓前に脱炭スラグが精錬炉外に溢れて作業生や生産生を阻害する傾向が現れ、特に０．５ｗｔ％未満ではその傾向が著しくなり、また、吹酸昇温還元期終了時の炭材の含有率がクロム回収済スラグに対し重量比率で１．５ｗｔ％を越えるとクロム回収済スラグ（又は脱炭スラグ）の粘度が低下して、クロム回収済スラグ（又は脱炭スラグ）のスラグフォーミング不足によりスラグ厚みが不十分となってクロム回収済スラグと共に溶銑を排出する所謂地金ロスを招き、排滓率が低下する傾向が現れ、特に３ｗｔ％を越えるとその傾向が著しくなるので、いずれも好ましくない。
【００２６】
また、吹酸昇温還元期や仕上げ精錬期の脱炭スラグ又は中間排滓期のクロム回収済スラグの、ＣａＯとＳｉＯ₂の比で示される塩基度（（ＣａＯ／ＳｉＯ₂）_S）としては、重量比率で１．２≦（ＣａＯ／ＳｉＯ₂）_S≦４．５、好適には１．８≦（ＣａＯ／ＳｉＯ₂）_S≦３．５の範囲とされるのが好ましい。吹酸昇温還元期等の脱炭スラグ等の塩基度が１．８未満では脱炭スラグの塩基度が低過ぎて精錬炉を構成する耐火物の溶損が進行する傾向が現れ、特に１．２未満ではその傾向が著しくなり、また、吹酸昇温還元期等の脱炭スラグ等の塩基度が３．５を越えると脱炭スラグの量（以下スラグ量という）が増大し、この結果、脱炭スラグからのクロム回収率が低下したり、中間排滓期のクロム回収済スラグの排滓率が低下したり、或いは地金ロスの増加を招く傾向が現れ、特に４．５を越えるとその傾向が著しくなるので、いずれも好ましくない。
【００２７】
また、吹酸昇温還元期の脱炭スラグのＡｌ₂Ｏ₃の含有率（（Ａｌ₂Ｏ₃）_S）としては、３ｗｔ％≦（Ａｌ₂Ｏ₃）_S≦２３ｗｔ％、好適には８ｗｔ％≦（Ａｌ₂Ｏ₃）_S≦２０ｗｔ％の範囲とされるのが好ましい。吹酸昇温還元期の脱炭スラグのＡｌ₂Ｏ₃の含有率が８ｗｔ％未満ではダイカルシウムシリケートの析出による脱炭スラグの液相率の低下に伴って、クロム還元速度が低下する傾向が現れ、特に３ｗｔ％未満ではその傾向が著しくなり、また、吹酸昇温還元期の脱炭スラグのＡｌ₂Ｏ₃の含有率が２０ｗｔ％を越えると脱炭スラグの粘度が上昇することで脱炭スラグの異常フォーミングが発生し易くなるとともに、精錬炉を構成する耐火物の溶損も進行する傾向が現れ、特に２３ｗｔ％を越えるとその傾向が著しくなるので、いずれも好ましくない。
【００２８】
また、吹酸昇温還元期の脱炭スラグのＭｇＯの含有率（（ＭｇＯ）_S）としては、５ｗｔ％≦（ＭｇＯ）_S≦１５ｗｔ％の範囲とされるのが好ましい。吹酸昇温還元期の脱炭スラグのＭｇＯの含有率が５ｗｔ％未満では精錬炉を構成する耐火物からＭｇＯが溶出し易くなるために、耐火物の溶損が進行する傾向が現れ、また、吹酸昇温還元期の脱炭スラグのＭｇＯの含有率が１５ｗｔ％を越えると脱炭スラグ中のクロム酸化物とＭｇＯが結合してスピネルを形成し易くなるために、クロム還元速度が低下するとともに、スラグ量の増大化によるクロム回収率の低下や中間排滓期のクロム回収済スラグの排滓率低下、更に地金ロスを招く傾向が現れるので、いずれも好ましくない。
【００２９】
また、仕上げ精錬期のフェロクロム合金等の添加前の溶銑中の炭素含有率（［Ｃ］_M）としては、１．５ｗｔ％≦［Ｃ］_M≦４ｗｔ％の範囲とされるのが好ましい。仕上げ精錬期のフェロクロム合金等の添加前の溶銑中の炭素含有率が１．５ｗｔ％未満では吹酸昇温還元期でのクロム還元速度が低下する傾向が現れ、また、仕上げ精錬期のフェロクロム合金等の添加前の溶銑中の炭素含有率が４ｗｔ％を越えると仕上げ精錬期、特に仕上げ精錬末期での溶銑温度の上昇によって精錬炉を構成する耐火物の溶損が進行したり精錬制御性が悪化する傾向が現れるので、いずれも好ましくない。
【００３０】
また、仕上げ精錬期の溶銑温度（Ｔ_R）としては、１４５０℃≦Ｔ_R≦１６００℃とされるのが好ましい。仕上げ精錬期の溶銑温度が１４５０℃未満では溶銑中の炭素の酸化ロスが増大する傾向が現れ、また、仕上げ精錬期の溶銑温度が１６００℃を越えると精錬炉を構成する耐火物の溶損が著しくなる傾向が現れるので、いずれも好ましくない。
【００３１】
【作用】
本発明者等は鋭意研究を進めた結果、通常、精錬操業中では脱炭スラグや溶銑中の種々含有成分の含有率（又は濃度）が変動し、特に吹酸昇温還元期終了時の脱炭スラグのＣｒ含有率が３ｗｔ％と低い一方、仕上げ精錬期終了時の脱炭スラグＣｒ含有率が１１〜１９ｗｔ％と高いことに注目することで、仕上げ精錬期終了時の高Ｃｒ含有率の脱炭スラグを精錬炉内に残滓させたまま精錬を開始すると溶銑と脱炭スラグのＣｒ濃度差と炭材による還元を利用して容易に溶銑中にＣｒを還元させることができるとともに、吹酸昇温還元期と仕上げ精錬期との間に中間排滓期を設けて極めて低Ｃｒ含有率のクロム回収済スラグを排滓することで、Ｃｒを高効率で溶銑中に回収することができることを知見し得た。
【００３２】
さらに、本発明者等は鋭意研究を進め、吹酸昇温還元期における脱炭スラグ中の炭材の重量比率と脱炭スラグのフォーミング高さの関係を調べた結果、図２に示すように、吹酸昇温還元期に精錬炉内に投入される炭材を脱炭スラグに対し適量存在させると前記（１）及び（２）式等の炭素の燃焼反応により発生したＣＯガスを合体集積することで、脱炭スラグの異常フォーミングを抑制しつつクロム酸化物の還元速度を高位に維持することができるとともに、吹酸昇温還元期終了時のクロム回収済スラグ中の炭材をクロム回収済スラグに対し適量存在させると中間排滓期に地金の流出を抑制しつつクロム回収済スラグの排滓を高位に安定化することができることを知見しえた。
【００３３】
なお、図２中横軸は脱炭スラグ中の炭材の重量比率、図２中縦軸は脱炭スラグのフォーミング高さ（すなわちフォーミング時の脱炭スラグの高さ）、図２中破線ａは精錬炉の容積から得られた脱炭スラグの高さ上限を示し、図２中破線ｂは中間排滓性から得られた脱炭スラグの高さ下限を示している。なお、脱炭スラグのフォーミング高さは、下記（４）式で求められる。すなわち、
Ｌ＝ｈ₁／（ｈ₂−ｈ₃）・・・・・・・・・・・（４）
但し、Ｌ：脱炭スラグのフォーミング高さ
ｈ₁：精錬炉中の脱炭スラグの高さ（ｍ）
ｈ₂：精錬炉中の内底面から受銑口までの高さ（ｍ）
ｈ₃：精錬炉中の溶銑又は溶鋼の高さ（ｍ）
また、前記（４）式で得られた脱炭スラグの高さ下限は０．１５、脱炭スラグの高さ上限は０．８５とした。脱炭スラグの高さ下限が０．１５未満では、脱炭スラグの排滓時に排滓作業が困難となる傾向が現れ、また、脱炭スラグの高さ上限が０．８５を越えると脱炭スラグが精錬炉外に溢れて精錬炉の周辺設備を溶損させる傾向が現れるからである。
【００３４】
以上のことから、請求項１、２記載のステンレス粗溶鋼の精錬方法においては、前チャージで生成されクロム酸化物を含有する脱炭スラグを精錬炉内に残留させたまま次チャージの溶銑を投入し、次いで、酸化性ガスを吹き込むとともに炭材を投入して脱炭スラグ中のクロム酸化物を還元した後、脱炭スラグ中のクロム酸化物を溶銑中に還元して得たクロム回収済スラグを排滓し、次いで、フェロクロム合金を溶解する等して溶銑の成分調整等を行った後、溶鋼を出鋼する。
このように溶銑を脱炭精錬することにより、吹酸昇温還元期では、精錬炉内に仕上げ精錬期の高Ｃｒ含有率の脱炭スラグを残滓させたまま溶銑を投入等して精錬操業を開始することで、溶銑と脱炭スラグのＣｒ濃度差と炭材による還元を利用して脱炭スラグ中のクロム分を容易にかつ効率よく溶銑中に回収することができる。また、精錬炉内に残留された脱炭スラグが冷却固化等しないので、従来の如く残滓を一旦冷却固化した後、昇温する作業等を必要とせず、極めて迅速な精錬作業を行うことができる。
【００３５】
特に、吹酸昇温還元期の炭材の含有率（Ｖ_C ）を脱炭スラグに対し重量比率で３ｗｔ％≦Ｖ_C ≦６ｗｔ％としたことにより、精錬操業中前記（１）及び（２）式等の炭素の燃焼反応が主に脱炭スラグ中の炭材表面で発生することからＣＯガスの脱炭スラグから容易に離脱することができ、この結果、吹酸昇温還元期における脱炭スラグの異常フォーミングを抑制できる等、脱炭スラグ（又はクロム回収済スラグ）のフォーミングを制御することができる。さらに、脱炭スラグの異常フォーミングを抑制できるので、この異常フォーミングで脱炭スラグが精錬炉外に流出して脱炭スラグ中の未回収クロムのロスを防止することができる。
【００３６】
また、吹酸昇温還元期の溶銑装入時、この溶銑中の炭素と精錬炉内に残滓された前チャージの脱炭スラグ中の酸素（以下［Ｏ］_Sという）とで下記（５）式に示す還元反応を生じるが、溶銑中の炭素含有率が３〜４ｗｔ％と高いこと、さらに脱炭スラグ中の酸素含有率が高いことに起因して、過剰な還元反応を起こす虞れがあるが、溶銑装入時又は溶銑装入前に炭材を前記範囲内で投入することや、脱炭スラグ中の（Ａｌ₂Ｏ₃）_S濃度調整用に例えば金属Ａｌ分を３０ｗｔ％含むアルミドロス等のアルミナ源を投入することで、この過剰な還元反応を抑制することができるので、溶銑や脱炭スラグが急激に溢れ出す所謂突沸を防止することができる。
［Ｃ］_M＋［Ｏ］_S→ＣＯ・・・・・・・・・・・（５）
【００３７】
また、吹酸昇温還元期終了時の炭材の含有率（Ｖ_C）を脱炭スラグに対し重量比率で０．５ｗｔ％≦Ｖ_C≦３ｗｔ％としたことにより、中間排滓期において、クロム回収済スラグに適度なフォーミングを付与することができるので、この結果、クロム回収済スラグのスラグ厚さが薄いこと等に起因する地金の流出を抑制しつつ、クロム回収済スラグの排滓を高位に安定化することができる。
【００３８】
特に、請求項２記載のステンレス粗溶鋼の精錬方法においては、脱炭スラグ又はクロム回収済スラグの塩基度（（ＣａＯ／ＳｉＯ₂ ）_S ）を重量比率で１．２≦（ＣａＯ／ＳｉＯ₂ ）_S ≦４．５としたことにより、適度の塩基度を有することで精錬炉を構成する耐火物の溶損を防止できるとともに、スラグ量の増大化を抑制し、脱炭スラグからのクロム回収率の低下やクロム回収済スラグの排滓率の低下、更に地金ロスの増加を防止することができる。また、脱炭スラグのＡｌ₂ Ｏ₃ の含有率（（Ａｌ₂ Ｏ₃ ）_S ）を３ｗｔ％≦（Ａｌ₂ Ｏ₃ ）_S ≦２３ｗｔ％としたことにより、適度の塩基度を有することで精錬炉を構成する耐火物の溶損を防止できるとともに、適度な液相率とクロム酸化物活量を付与することで、この脱炭スラグからのクロム還元速度を高位に安定化させることができる。さらに、脱炭スラグ又はクロム回収済スラグの塩基度を前記範囲内とし且つＡｌ₂ Ｏ₃ の含有率を前記範囲としたことにより、精錬炉を構成する耐火物の溶損を防止しつつ、クロム還元速度とクロム回収済スラグの排滓率を高位に安定化させることができる。
【００３９】
【発明の効果】
請求項１、２記載のステンレス粗溶鋼の精錬方法においては、仕上げ精錬期終了時の高Ｃｒ含有率の脱炭スラグを精錬炉内に残滓させたまま溶銑を投入することで、溶銑と脱炭スラグ中のクロム分を高い還元速度で回収できるとともに、吹酸昇温還元期終了時の低Ｃｒ含有率のクロム回収済スラグを排滓させることで、脱炭スラグ中のクロム分を廃棄等することなくステンレス鋼中に回収させることができる。さらに、吹酸昇温還元期に投入される炭材の脱炭スラグ又はクロム回収済スラグに対する重量比率を適宜選択することで、吹酸昇温還元期の脱炭スラグ又はクロム回収済スラグのフォーミングを制御して異常フォーミング等を防止することができるとともに、中間排滓期において地金の流出等なく高い排滓率でクロム回収済スラグを排滓することができる。従って、高価な還元材等を必要とせず、低コストで効率的且つ安定的な精錬操業を行うことができる。
【００４０】
特に、吹酸昇温還元期の炭材の含有率（Ｖ_C ）を脱炭スラグに対し重量比率で３ｗｔ％≦Ｖ_C ≦６ｗｔ％としたので、吹酸昇温還元期で発生したＣＯガスが容易に脱炭スラグから離脱することができ、脱炭スラグの異常フォーミング等を抑制する等、脱炭スラグ又はクロム回収済スラグのフォーミングを制御することができ、さらに、クロム酸化物の還元速度を高位に維持することができる。また、吹酸昇温還元期終了時の炭材の含有率（Ｖ_C ）を脱炭スラグに対し重量比率で０．５ｗｔ％≦Ｖ_C ≦３ｗｔ％としたので、中間排滓期において、地金の流出を抑制しつつ効率的かつ安定的にクロム回収済スラグを排滓することができる。
【００４１】
特に、請求項２記載のステンレス粗溶鋼の精錬方法においては、脱炭スラグ又はクロム回収済スラグの塩基度（（ＣａＯ／ＳｉＯ₂ ）_S ）を重量比率で１．２≦（ＣａＯ／ＳｉＯ₂ ）_S ≦４．５とし、及び／又は、脱炭スラグのＡｌ₂ Ｏ₃ の含有率（（Ａｌ₂ Ｏ₃ ）_S ）を３ｗｔ％≦（Ａｌ₂ Ｏ₃ ）_S ≦２３ｗｔ％としたので、脱炭スラグやクロム回収済スラグに適度の塩基度を有することで精錬炉を構成する耐火物の溶損するのを防止できるとともに、脱炭スラグ中のクロム酸化物の還元速度を高位に保つことができ、適度な粘度を付与してクロム回収済スラグの排滓率の低下や地金ロスの増加、さらに脱炭スラグの異常フォーミング等を防止することができる。
【００４２】
【発明の実施の形態】
続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態につき説明し、本発明の理解に供する。
ここに、図１（Ａ）〜（Ｅ）はそれぞれ本発明の一実施の形態に係るステンレス粗溶鋼の精錬方法を適用した上底吹転炉の操業状態を示す説明図、図２は吹酸昇温還元期における脱炭スラグ中の炭材の含有率と脱炭スラグのフォーミング高さの関係を示す特性図である。詳述すると、図１（Ａ）は本発明の一実施の形態に係るステンレス粗溶鋼の精錬方法を適用した上底吹転炉内に溶銑を投入する状態を示す説明図、図１（Ｂ）は同上底吹転炉の吹酸昇温還元期を示す説明図、図１（Ｃ）は同上底吹転炉の中間排滓期を示す説明図、図１（Ｄ）は同上底吹転炉の仕上げ精錬期を示す説明図、図１（Ｅ）は同上底吹転炉の出鋼期を示す説明図である。
【００４３】
図１（Ａ）〜（Ｅ）に示すように、上底吹転炉１０は、耐火レンガ等を積み重ねて略対称形の略徳利状に形成されている。本発明の一実施の形態では、溶銑受鋼量１７５トンの上底吹転炉１０を用いた。また、図示しないが、上底吹転炉１０は、トラニオンリング方式又はトラニオンリングレス方式等を採用し、所定方向、すなわち図１（Ａ）〜（Ｅ）中時計回り方向及び反時計回り方向に傾動自在（又は回動自在）に保持されている。また、上底吹転炉１０には、後述する溶銑を投入するための受銑口１０ａが形成されている。また、上底吹転炉１０の受銑口１０ａより下方の側壁部、すなわち図１（Ａ）中上底吹転炉１０の右側壁部には、この上底吹転炉１０で脱炭精錬された溶鋼を出鋼するための出鋼口１０ｂが形成されている。また、上底吹転炉１０の底部には複数のガス送気口１０ｃが形成され、さらに、このガス送気口１０ｃには、ガス送気管１０ｄが取り付けられている。また、上底吹転炉１０の受銑口１０ａの近傍部には、取鍋１１がこの上底吹転炉１０に近接自在（又は横方向移動自在）に配置されている。また、上底吹転炉１０の受銑口１０ａの上部には、酸素等の酸化性ガスを供給するためのランス１２が昇降自在に配置されている。なお、図示しないが、ランス１２に近接して溶銑（又は溶鋼）やスラグの成分測定や温度測定等を行うためのサブランスも配置されている。
【００４４】
続いて、この上底吹転炉１０を用いた本発明の一実施の形態に係るステンレス粗溶鋼の精錬方法について説明する。
まず、上底吹転炉１０内に前チャージの仕上げ精錬期に生成された脱炭スラグ１３を残存させたまま、還元材として金属Ａｌ分を３０ｗｔ％含むアルミドロスを適量添加する。次いで、図１（Ａ）に示すように、上底吹転炉１０を取鍋１１の方へ反時計回りに傾動させ、受銑口１０ａを介して取鍋１１から上底吹転炉１０内に次チャージ用の溶銑１４を装入するとともに、石灰やホタル石等の造滓剤（又はフラックスという）を装入する。
【００４５】
次に、粉状コークス等の炭材の含有率（Ｖ_C）を脱炭スラグ１３に対し重量比率で３ｗｔ％≦Ｖ_C≦６ｗｔ％の範囲になるように連続的に投入しながら添加するとともに、図１（Ｂ）に示すように、ランス１２の先端部を受銑口１０ａを介して上底吹転炉１０内まで下降させ、このランス１２から酸素を供給する。このような上吹吹酸により、溶銑１４及び脱炭スラグ１３の昇温を行うとともに、前記（２）式に示した反応により脱炭スラグ１３中のクロム酸化物を溶銑１４中に還元し、溶銑１４中にクロムを回収させる。なお、炭材の含有率を前記範囲内としたことで、前記（１）及び（２）式等の炭素の燃焼反応で生じたＣＯガスが集積されて脱炭スラグ１３中に適度に気泡を生じることによって、脱炭スラグ１３の異常フォーミング等を抑制して適度にフォーミングさせることができた。
【００４６】
次に、脱炭スラグ１３中のクロム酸化物が還元されて、Ｃｒ含有率が３ｗｔ％以下となったクロム回収済スラグ１３ａが生成されると、図１（Ｃ）に示すように、上底吹転炉１０を、出鋼口１０ｂとは反対方向に反時計回りに傾動して、クロム回収済スラグ１３ａの一部もしくは大部分を排滓する。なお、吹酸昇温還元期終了時の炭材の含有率（Ｖ_C）をクロム回収済スラグ１３ａに対し重量比率で０．５ｗｔ％≦Ｖ_C≦３ｗｔ％以下とすることで、クロム回収済スラグ１３ａの粘度の低下等を防止して十分な厚さを持ってクロム回収済スラグ１３ａを形成できるので、クロム回収済スラグ１３ａが適度にフォーミングして地金の流出を抑制しつつクロム回収済スラグ１３ａを効率よく且つ安定的に排滓することができた。なお、溶銑１４は、脱炭スラグ１３中のクロムを回収したことで、Ｃｒ含有率が増加した溶鋼１４ａとなっている。
【００４７】
次に、図１（Ｄ）に示すように、上底吹転炉１０内に、受銑口１０ａを介してフェロクロム合金やフラックスを添加し、さらに前述したように、上吹吹酸を行い、脱炭精錬を行った。これにより、溶鋼１４ａ上には、新たにスラグ１３ｂが生成される。次に、所定組成で所定温度の溶鋼１４ｂが生成されると、図１（Ｅ）に示すように、上底吹転炉１０を、出鋼口１０ｂ側に時計回りに傾動して、この出鋼口１０ｂから溶鋼１４ｂを出鋼する。なお、脱炭スラグ１３のＣｒ含有率は１１ｗｔ％〜１９ｗｔ％とした。ここで、生成された脱炭スラグ１３はそのまま上底吹転炉１０内に残存させる。
【００４８】
以上の操業動作を繰り返して、複数チャージでステンレス鋼が精錬される。なお、精錬操業中、脱炭スラグ１３又はクロム回収済スラグ１３ａの塩基度（（ＣａＯ／ＳｉＯ₂）_S）を重量比率で１．２≦（ＣａＯ／ＳｉＯ₂）_S≦４．５の範囲内としたため、上底吹転炉１０を構成する耐火物の溶損等がなく、さらにクロム回収済スラグ１３ａの粘性低下による排滓率の低下等を防止できた。さらに、脱炭スラグ１３のＡｌ₂Ｏ₃の含有率（（Ａｌ₂Ｏ₃）_S）を３ｗｔ％≦（Ａｌ₂Ｏ₃）_S≦２３ｗｔ％の範囲内としたため、上底吹転炉１０を構成する耐火物の溶損等がなく、さらにクロム還元速度の促進と脱炭スラグ１３の異常フォーミング等を防止できた。
【００４９】
次に、本発明の一実施の形態に係るステンレス粗溶鋼の精錬方法の確認試験を行った。以下その結果について説明する。
（実験例１〜６）
まず、本発明の一実施の形態に係るステンレス粗溶鋼の精錬方法を用いてステンレス粗溶鋼の脱炭精錬を６チャージ行った（試験番号１〜６）。ここで、各チャージにおける吹酸昇温還元期の脱炭スラグ中の炭材の重量比率、塩基度（（ＣａＯ／ＳｉＯ₂）_S）及びＡｌ₂Ｏ₃含有率は表１に示す通りとした。
【００５０】
【表１】

【００５１】
また、各チャージにおける吹酸昇温還元期のＣｒ還元速度（ｋｇ／ｍｉｎ／Ｔ）及び脱炭スラグの異常フォーミングの有無、中間排滓期のクロム回収済スラグの排滓率（％) 及び地金ロス量（ｋｇ／Ｔ）、各チャージ毎の精錬終了後の耐火物溶損を調べた。その結果を表１に示した。なお、Ｃｒ還元速度とは吹酸昇温還元期における単位時間当りのＣｒ還元量をいう。また、地金ロス量とは中間排滓期にクロム回収済スラグと共に排滓された溶銑（又は溶鋼）の重量をいう。
【００５２】
また、排滓率は下記（６）式で求められる。すなわち、
排滓率（％) ＝Ｖ_sd／（Ｖ_sd＋Ｖ_sr）・・・・・（６）
但し、Ｖ_sd：上底吹転炉から排滓されたクロム回収済スラグの重量
Ｖ_sr：上底吹転炉内に残存したクロム回収済スラグの重量
である。
【００５３】
（実験例７〜１１）
次に、吹酸昇温還元期の脱炭スラグ中の炭材の含有率、吹酸昇温還元期終了時の脱炭スラグ中の炭材の含有率、吹酸昇温還元期の脱炭スラグの塩基度及びＡｌ₂Ｏ₃含有率をそれぞれ変更してステンレス粗溶鋼の脱炭精錬を５チャージ行った（試験番号７〜１１）。具体的には、吹酸昇温還元期の脱炭スラグ中の炭材を重量比率で３ｗｔ％未満とし（試験番号７）、吹酸昇温還元期の脱炭スラグ中の炭材を重量比率で３ｗｔ％未満とすると共に、吹酸昇温還元期終了時の脱炭スラグ中の炭材を重量比率で３ｗｔ％を越えさせ（試験番号８）、吹酸昇温還元期の脱炭スラグ中の炭材を重量比率で３ｗｔ％未満とすると共に、吹酸昇温還元期の脱炭スラグの塩基度を１．２未満とし（試験番号９）、吹酸昇温還元期の脱炭スラグ中の炭材を重量比率で３ｗｔ％未満とすると共に、吹酸昇温還元期の脱炭スラグの塩基度を４．５を越えさせ（試験番号１０）、吹酸昇温還元期の脱炭スラグ中の炭材を重量比率で３ｗｔ％未満とすると共に、吹酸昇温還元期終了時の炭材の重量比率を０．５％未満とし、更に吹酸昇温還元期の脱炭スラグ中のＡｌ₂Ｏ₃含有率を２３ｗｔ％を越えさせた（試験番号１１）以外は、実験例１〜６と同様にして、吹酸昇温還元期のＣｒ還元速度（ｋｇ／ｍｉｎ／Ｔ）及び脱炭スラグの異常フォーミングの有無、中間排滓期のクロム回収済スラグの排滓率（％) 及び地金ロス量（ｋｇ／Ｔ）、各チャージ毎の精錬終了後の耐火物溶損を調べた。その結果を表１に示した。
【００５４】
表１から明らかなように、吹酸昇温還元期の脱炭スラグ中の炭材を重量比率で３ｗｔ％未満とした場合（試験番号７）、炭素の燃焼反応により発生したＣＯガスの脱炭スラグからの離脱不足により、吹酸昇温還元期に脱炭スラグの異常フォーミングが発生していることがわかった。この結果、吹酸昇温還元期の脱炭スラグ中の炭材は重量比率で３ｗｔ％以上とするのが良好であることが確認された。
【００５５】
また、表１から明らかなように、吹酸昇温還元期の脱炭スラグ中の炭材が重量比率で３ｗｔ％未満で、かつ、吹酸昇温還元期終了時のクロム回収済スラグ中の炭材が重量比率で３ｗｔ％を越えた場合（試験番号８）、炭材によるフォーミング抑制でクロム回収済スラグの中間排滓期のスラグ厚みが不十分なため、排滓率の低下及び地金ロスを招いていることがわかった。この結果、吹酸昇温還元期の脱炭スラグ中の炭材は重量比率で３ｗｔ％以上で、かつ、吹酸昇温還元期終了時のクロム回収済スラグ中の炭材は重量比率で３ｗｔ％未満とするのが良好であることが確認された。
【００５６】
また、表１から明らかなように、吹酸昇温還元期の脱炭スラグ中の炭材が重量比率で３ｗｔ％未満で、かつ、吹酸昇温還元期の脱炭スラグの塩基度が１．２未満の場合（試験番号９）、低塩基度スラグによる耐火物溶損が進行していることがわかった。この結果、吹酸昇温還元期の脱炭スラグ中の炭材は重量比率で３ｗｔ％以上で、かつ、吹酸昇温還元期の脱炭スラグの塩基度は１．２以上とするのが良好であることが確認された。
【００５７】
また、表１から明らかなように、吹酸昇温還元期の脱炭スラグ中の炭材が重量比率で３ｗｔ％未満で、かつ、吹酸昇温還元期の脱炭スラグの塩基度が４．５を越えた場合（試験番号１０）、スラグ量の増大に起因して中間排滓期のクロム回収済スラグの排滓率の低下及び地金ロスの増加を招いていることがわかった。この結果、吹酸昇温還元期の脱炭スラグ中の炭材は重量比率で３ｗｔ％以上で、かつ、吹酸昇温還元期の脱炭スラグの塩基度は４．５以下とするのが良好であることが確認された。
【００５８】
また、表１から明らかなように、吹酸昇温還元期の脱炭スラグ中の炭材が重量比率で３ｗｔ％未満で、かつ、吹酸昇温還元期終了時の炭材の重量比率を０．５％未満とし、更に吹酸昇温還元期の脱炭スラグ中のＡｌ₂Ｏ₃の含有率が２３ｗｔ％を越えた場合（試験番号１１）、Ａｌ₂Ｏ₃含有率の増加に伴う脱炭スラグの粘性の増加に起因した異常フォーミングが発生し、さらに耐火物の溶損も助長されていることがわかった。この結果、吹酸昇温還元期の脱炭スラグ中の炭材は重量比率で３ｗｔ％以上で、かつ、吹酸昇温還元期の脱炭スラグ中のＡｌ₂Ｏ₃の含有率が２３ｗｔ％以下とするのが良好であることが確認された。
【００５９】
以上、本発明の実施の形態を説明したが、本発明はこれらの実施の形態に限定されるものではなく、要旨を逸脱しない条件の変更等は全て本発明の適用範囲である。
【図面の簡単な説明】
【図１】（Ａ）本発明の一実施の形態に係るステンレス粗溶鋼の精錬方法を適用した上底吹転炉内に溶銑を投入する状態を示す説明図である。
（Ｂ）同上底吹転炉の吹酸昇温還元期を示す説明図である。
（Ｃ）同上底吹転炉の中間排滓期を示す説明図である。
（Ｄ）同上底吹転炉の仕上げ精錬期を示す説明図である。
（Ｅ）同上底吹転炉の出鋼期を示す説明図である。
【図２】吹酸昇温還元期における脱炭スラグ中の炭材の重量比率と脱炭スラグのフォーミング高さの関係を示す特性図である。
【符号の説明】
１０上底吹転炉１０ａ受銑口
１０ｂ出鋼口１０ｃガス送気口
１０ｄガス送気管１１取鍋
１２ランス１３脱炭スラグ
１３ａクロム回収済スラグ１３ｂスラグ
１４溶銑１４ａ溶銑又は溶鋼
１４ｂ溶鋼[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for refining stainless coarse molten steel, and more specifically, decarburization and refining of the next charge is started while decarburization slag generated in the previous charge remains in the refining furnace, and chromium in the decarburized slag is In addition to reducing the amount of slag to the next charge hot metal, the chromium recovered slag produced by reducing the chromium content is discharged during decarburization and refining, and then the decarburization and refining of hot metal is continued in the same smelting furnace. The present invention relates to a method for refining stainless steel.
[0002]
[Prior art]
Conventionally, in a method for refining crude stainless steel, hot metal (or molten iron) is introduced into a refining furnace such as an LD converter, and oxygen (hereinafter referred to as O) is introduced into the refining furnace through a lance or the like.₂The carbon contained in the hot metal (hereinafter referred to as [C])_MThe oxidation reaction shown in the following formula (1) is caused to decarburize.
2 [C]_M+ O₂→ 2CO (1)
[0003]
During refining, chromium content (usually chromium oxide (hereinafter referred to as Cr₂O_Three)_SDecarburized slag containing)). And the reduction | restoration reaction shown to the following (2) formula is produced in the chromium content in this decarburization slag, and the carbon in hot metal, and it is made to reduce in hot metal.
(Cr₂O_Three)_S+3 [C]_M→ 2 [Cr]_M+ 3CO (2)
In the formula (2), [Cr]_MRefers to chromium reduced in the hot metal.
[0004]
However, although the chromium content in the decarburized slag is reduced into the hot metal by the reduction reaction of the formula (2), in order to increase the Cr concentration in the hot metal to 11 to 19 wt% at the end of refining, the decarburized slag is reduced. The Cr content in the steel is also as high as 11 to 19 wt%, and the chromium content in the decarburized slag cannot be reduced only by the reduction reaction with only the carbon in the hot metal. As a result, the high Cr content The only decarburization slag had to be discarded.
[0005]
On the other hand, during the refining operation, carbon monoxide gas (hereinafter referred to as CO gas) is usually generated due to carbon combustion reaction such as the decarburization reaction of the above formula (1) and the reduction reaction of the above formula (2). Charcoal slag is foaming (or forming or slopping).
[0006]
However, if the decarburization slag is excessively formed during the refining operation, this decarburization slag overflows outside the refining furnace and melts down the peripheral equipment of the refining furnace. There is still a problem that the workability and productivity are extremely hindered, for example, if the decarburization slag does not form at the end of the refining operation, which is the time of slag evacuation (or output), the evacuation work becomes difficult. It was.
[0007]
For this reason, in the refining operation of the stainless crude molten steel, there has been a demand for some method for recovering the chromium content in the decarburized slag and controlling the forming of the decarburized slag.
[0008]
In order to solve these problems, (1) In Japanese Patent Laid-Open No. 63-195206, oxygen or inert gas is supplied through the furnace bottom tuyere while blowing oxidizing gas from above. In addition, in the refining of the top bottom furnace where chrome ore and carbonaceous material are added to the molten iron for melting reduction, a massive carbonaceous material having a diameter of 5 to 50 mm is added to a place other than the hot spot of the top blowing oxygen jet. , The bulk carbonaceous material is supplied with a total oxygen supply rate F (Nm^Three/ (T · Hr)), a chromium oxide dissolution and reduction method is proposed which is added at a rate of 0.1 F to 0.5 F (kg / (T · Hr)).
[0009]
In addition, (2) Japanese Patent Laid-Open No. 53-119210 discloses that a residue of chromium-containing steel having a chromium content of 13% or more melted in a steelmaking furnace is cooled and solidified, and other chromium-containing steel in a converter is obtained. A method for recovering and using chromium from a chromium-containing steel plate to which the above-mentioned solid residue is added at the time of blowing a charge for steel, or (3) silicon (hereinafter referred to as Si) is added before the decarburization slag is discharged, and the following (3 There has been proposed a method for causing the reduction reaction shown in the formula.
2 (Cr₂O_Three)_S+ 3Si → 4 [Cr]_M+3 (SiO₂)_S(3)
[0010]
[Problems to be solved by the invention]
However, in the chromium oxide dissolution and reduction method disclosed in JP-A-63-195206 of (1), the chromium oxide can be reduced at a high speed by defining the addition rate of the bulk carbonaceous material. When the slag with reduced chromium content (or recovered) is discharged, the slag discharge rate tends to vary due to the thin thickness of the slag. As a result, molten iron is produced together with the slag. The so-called metal loss occurs, and the yield is lowered. In addition, there is a problem that the forming of the decarburized slag cannot be controlled.
[0011]
Further, in the method of recovering and using chromium from the chromium-containing steel plate disclosed in Japanese Patent Laid-Open No. 53-119210 of (2), the residue of 13% or more chromium-containing steel melted in the steelmaking furnace is cooled and solidified. However, since the solid residue is added during the blowing of other chrome-containing steel charges, it is necessary to raise the temperature of the residue that has been cooled and solidified during blowing, and high-temperature hot metal is added to the cooled and solidified residue. Even if it is added, the hot metal temperature decreases, and it is still necessary to raise the temperature. Therefore, the temperature reduction time can be greatly extended, the refining operation cannot be performed quickly, and productivity is extremely hindered. Had. In addition, there is a problem that the forming of the decarburized slag cannot be controlled.
[0012]
Further, in the method of adding Si of (3), since this Si is more expensive than C, the manufacturing cost increases, and silicon dioxide ((SiO₂)_SIn order to prevent refractories from melting due to), it is necessary to increase the basicity of slag by adding quick lime, etc. (or to increase the basicity), so slag generated by adding quick lime, etc. There was a problem that the amount of the increased.
[0013]
The present invention was made in view of such circumstances, the molten iron of the next charge was charged while leaving the decarburized slag having a high Cr content at the end of the final refining period of the precharge in the refining furnace, Using the difference in Cr concentration between the hot metal and the decarburized slag, the chromium content in the decarburized slag is recovered at a high reduction rate, and the chromium-recovered slag having a low Cr content at the end of the blowing acid temperature reduction period is discharged. By dripping, the chromium content in the decarburized slag, which has been disposed of in the past, can be recovered in the stainless steel. By appropriately selecting the weight ratio with respect to the finished slag, the decarburization slag or the chrome recovered slag during the blown acid heating and reducing period is controlled to prevent abnormal forming, etc., and efficient and stable chrome recovered Slug And to provide a refining method for stainless crude molten steel can be performed slag.
[0014]
[Means for Solving the Problems]
The method for refining coarsely molten stainless steel according to claim 1, which meets the above-mentioned object, throws molten iron of the next charge into the refining furnace while leaving decarburized slag generated in the final refining period of the precharge and containing chromium oxide. And a blowing acid temperature-reduction period in which a carbon material is added into the refining furnace and an oxidizing gas is blown to reduce chromium oxide in the decarburized slag into the hot metal, and the blowing acid temperature-reduction Ferrochromium alloy is dissolved in the hot metal remaining in the smelting furnace in the intermediate waste period in which the chromium recovered slag obtained by reducing chromium oxide into the hot metal in the stage is exhausted. With the finishing refining period to decarburize and refineIn addition, the content of the carbonaceous material (V _C ) 3 wt% ≦ V in weight ratio with respect to the decarburized slag _C ≦ 6 wt%, the carbon content at the end of the blown acid temperature reduction period (V _C ) 0.5 wt% ≦ V in weight ratio with respect to the chromium recovered slag _C ≦ 3wt%.
[0016]
And claims2The method for refining stainless steel as described above is claimed.1In the method for refining a crude stainless steel as described above, the basicity of the decarburized slag or the chromium recovered slag ((CaO / SiO₂ )_S ) By weight ratio 1.2 ≦ (CaO / SiO₂ )_S ≦ 4.5 and / or Al of the decarburized slag₂ O_Three Content of ((Al₂ O_Three )_S ) 3 wt% ≦ (Al₂ O_Three )_S ≦ 23 wt%.
[0017]
In addition, as a refining furnace to which a refining method of stainless coarse molten steel is applied, an LD (Linz Donawtz) converter such as an upper bottom blowing converter, a bottom blowing converter, an upper blowing converter, an AOD (Argon Oxigen Decarburization) converter, An electric furnace or the like is applicable.
[0018]
Blowing acid warming reduction period refers to the introduction of hot metal of the next charge into the refining furnace in which the decarburized slag generated in the previous charge and containing chromium oxide remains, and then the oxidizing gas and the carbon material are injected. Then, at least the reduction reaction shown in the formula (2) is caused to occur, and the chromium oxide in the decarburized slag is reduced into the molten iron to generate chromium-recovered slag from which chromium has been removed.
[0019]
Further, the intermediate waste period (or chrome recovered slag discharge period) refers to a period during which chromium recovered slag obtained by reducing chromium oxide into hot metal in the blowing acid temperature reduction period is discharged. . Furthermore, the finish refining period (or decarburization period) refers to the addition of ferrochromium alloy, etc., to the molten iron that remains in the refining furnace and recovers the chromium content in the decarburized slag during the intermediate depletion period, and oxidizes as necessary. This refers to the period of time during which decarburization is performed by blowing in nature gas and the temperature is adjusted.
[0020]
In addition, it is preferable to stir the hot metal by various methods in order to make the decarburization reaction efficiently in the blowing acid temperature reduction reduction period and the finish refining period. For example, in a bottom blowing converter and an upper bottom blowing converter, the hot metal can be stirred by charging various gases from the bottom of these refining furnaces. The ferrochrome alloy is used to adjust the Cr content of the hot metal. As the ferrochrome alloy, not only a general chromium ore having a Cr content of 10 wt% to 50 wt% but also high carbon ferrochrome, medium carbon A chrome ore such as a ferrochromium, a low-carbon ferrochromium-enriched ore or a reduced pellet is used. In addition, stainless steel scraps or the like may be used.
[0021]
Also, the hot metal temperature (T) when the hot metal is charged into the refining furnace where the decarburized slag remains._P) 1200 ° C ≦ T_P≦ 1500 ° C. is preferable. If the hot metal temperature is less than 1200 ° C, the hot metal temperature is too low and the hot metal temperature must be increased to promote the oxidation-reduction reaction. For this reason, the refining efficiency tends to decrease, for example, the refining time becomes longer. If the temperature exceeds 1500 ° C., the tapping temperature of the blast furnace must be increased, and the refractory constituting the blast furnace tends to be easily melted.
[0022]
In addition, as oxidizing gas, oxygen blown from the receiving port through the lance in the top bottom blowing converter or top blowing converter, oxygen and argon gas blown from the gas inlet in the top bottom blowing converter And an inert gas such as nitrogen gas, and a mixed gas such as carbon dioxide and fuel gas. Also, the oxygen feed rate (V_P: (Unit: Nm^Three/ Min / T)), 1.5 ≦ V_PA range of ≦ 6 is preferable. Acid delivery rate during blowing acid temperature increase and reduction period is 1.5 Nm^ThreeIf less than / min / T, the reduction rate of chromium oxide by the carbon in the hot metal (hereinafter referred to as the chromium reduction rate) is reduced due to a decrease in the oxygen supply rate, so that the refining efficiency is increased such that the refining time becomes longer. A tendency to decrease appears, and the acid feed rate during the temperature reduction / reduction period of the blowing acid is 6 Nm.^ThreeIf it exceeds / min / T, the temperature of the hot metal or hot metal becomes too high and the refractory tends to be melted.
[0023]
Carbonaceous materials include powdered coke, bulk coke obtained by consolidating the powdered coke with various binders, and further, molded coke obtained by forming the powdered coke and granular iron into blocks with the binder, or powder. Anthracite briquettes, etc. obtained by forming a solid anthracite with the binder. In addition, a reducing material such as aluminum dross may be used to reduce the chromium content in the decarburized slag. In particular, aluminum dross also serves as a temperature raising material and is extremely useful. In addition, it can contribute to the control of the composition of the decarburized slag and the improvement of the reduction rate of the chromium content in the decarburized slag.
[0024]
Also, the content of carbonaceous material (V_C) As a decarburization slag, the weight ratio is 3wt% ≦ V_C≤6wt%, preferably 4wt% ≤V_CThe range is preferably ≦ 5 wt%. When the content ratio of the carbonaceous material in the blowing acid heating and reducing period is less than 4 wt% with respect to the decarburized slag, it is formed by the CO gas generated by the carbon combustion reaction shown in the above formulas (1) and (2). Abnormal foaming of decarburized slag appears due to the generated bubbles, especially when the content is less than 3 wt%, and the carbon content in the blowing acid temperature reduction period is the weight ratio of decarburized slag. When the amount exceeds 5 wt%, decarburization slag (or chromium recovery) occurs due to the destruction of bubbles due to an increase in the amount of CO gas generated by the carbon combustion reaction shown in the above formulas (1) and (2). Inferior slag) is formed, and the yield tends to decrease due to the so-called bullion scattering loss in which the bullion scatters. Moreover, in order to make the content rate of the carbonaceous material in the blowing acid temperature rising reduction period into the above range, the carbonaceous material is charged in advance in the refining furnace or continuously charged in the refining furnace in the refining operation.
[0025]
In particular, the carbon content (V_C) As a weight ratio of 0.5 wt% ≤ V with respect to the chromium recovered slag_C≦ 3 wt%, preferably 1 wt% ≦ V_C≦ 1.5 wt% is preferable. If the content rate of the carbonaceous material at the end of the blowing acid temperature increase and reduction period is less than 1 wt% by weight with respect to the chromium-recovered slag, the CO generated by the carbon combustion reaction shown in the above formulas (1) and (2) Abnormal formation of decarburization slag occurs rapidly due to insufficient gas coalescence accumulation, and there is a tendency for decarburization slag to overflow outside the refining furnace before evacuation and inhibit work and production. If the content of the carbonaceous material at the end of the blowing acid heating and reducing period exceeds 1.5 wt% with respect to the chromium recovered slag, the recovered chromium slag (or decarburized) The viscosity of the slag is reduced, and the slag thickness is insufficient due to the lack of slag forming of the chrome recovered slag (or decarburized slag), leading to so-called metal loss that discharges hot metal together with the chrome recovered slag. There is a tendency for the rate to decline, Exceeds 3 wt% to the so its tendency becomes remarkable, both undesirable.
[0026]
Also, CaO and SiO of decarburized slag in the blowing acid temperature reduction reduction period and finish refining period, or chromium recovered slag in the intermediate elimination period₂The basicity ((CaO / SiO₂)_S) By weight ratio 1.2 ≦ (CaO / SiO₂)_S≦ 4.5, preferably 1.8 ≦ (CaO / SiO₂)_S≦ 3.5 is preferable. When the basicity of the decarburized slag or the like in the blowing acid temperature reduction reduction period is less than 1.8, the basicity of the decarburized slag is too low, and the refractory constituting the smelting furnace tends to be melted. If the basicity of decarburized slag, etc. during the blowing acid temperature reduction process, etc. exceeds 3.5, the amount of decarburized slag (hereinafter referred to as slag amount) increases. As a result, there is a tendency that the chromium recovery rate from decarburized slag is reduced, the waste rate of chromium recovered slag in the intermediate elimination period is reduced, or the loss of bullion is increased. Since the tendency will become remarkable when it exceeds, neither is preferable.
[0027]
Also, Al of decarburized slag in the blowing acid temperature reduction period₂O_ThreeContent of ((Al₂O_Three)_S) As 3 wt% ≦ (Al₂O_Three)_S≦ 23 wt%, preferably 8 wt% ≦ (Al₂O_Three)_S≦ 20 wt% is preferable. Al of decarburized slag during the temperature rise and reduction period of blowing acid₂O_ThreeWhen the content of the slag is less than 8 wt%, the reduction rate of the chromium reduction appears with a decrease in the liquid phase ratio of the decarburized slag due to the precipitation of dicalcium silicate, and particularly when the content is less than 3 wt%, the tendency becomes significant. Al of decarburized slag during the temperature rise and reduction period₂O_ThreeWhen the content of the slag exceeds 20 wt%, the viscosity of the decarburized slag increases, so that abnormal forming of the decarburized slag is likely to occur, and the refractory constituting the smelting furnace tends to progress in erosion. Since the tendency will become remarkable when it exceeds 23 wt%, neither is preferable.
[0028]
In addition, MgO content of decarburized slag during the blowing acid temperature reduction process ((MgO)_S) As 5 wt% ≦ (MgO)_SIt is preferable to be in the range of ≦ 15 wt%. If the content of MgO in the decarburized slag during the temperature reduction / reduction period of the blowing acid is less than 5 wt%, MgO tends to be eluted from the refractory constituting the smelting furnace, so that the refractory tends to progress in erosion, When the MgO content of the decarburized slag during the temperature rise and reduction period of the blowing acid exceeds 15 wt%, the chromium oxide in the decarburized slag and MgO are easily bonded to form spinel, so the chromium reduction rate decreases. At the same time, a decrease in the chromium recovery rate due to an increase in the amount of slag, a decrease in the rejection rate of the chromium-recovered slag during the intermediate rejection period, and a tendency to cause a loss of metal are not desirable.
[0029]
In addition, the carbon content ([C] in the hot metal before the addition of ferrochrome alloy, etc. in the final refining stage)_M) 1.5 wt% ≦ [C]_MIt is preferable to be in the range of ≦ 4 wt%. If the carbon content in the hot metal before the addition of ferrochrome alloy, etc. in the final refining stage is less than 1.5 wt%, the chromium reduction rate tends to decrease during the temperature increase / reduction period of the blowing acid, and the ferrochrome alloy in the final refining stage If the carbon content in the hot metal before the addition of etc. exceeds 4 wt%, the refractory constituting the smelting furnace will progress or the smelting controllability will increase due to the rise of the hot metal temperature in the final refining period, especially in the final refining stage. Since the tendency to worsen appears, neither is preferable.
[0030]
Also, the hot metal temperature (T_R) As 1450 ° C ≦ T_R≦ 1600 ° C. is preferable. If the hot metal temperature in the finishing smelting period is less than 1450 ° C, the oxidation loss of carbon in the hot metal tends to increase, and if the hot metal temperature in the finishing smelting period exceeds 1600 ° C, the refractory constituting the smelting furnace may be damaged. Since the tendency which becomes remarkable appears, neither is preferable.
[0031]
[Action]
As a result of diligent research, the inventors of the present invention usually changed the content (or concentration) of various components in the decarburized slag and hot metal during the refining operation. Noting that the Cr content of coal slag is as low as 3wt%, while decarburization slag Cr content at the end of finish refining period is high as 11 to 19wt%, high Cr content at the end of finish refining period When refining is started with decarburized slag remaining in the refining furnace, Cr can be easily reduced into hot metal using the difference in Cr concentration between hot metal and decarburized slag and reduction by carbonaceous material. It is possible to recover Cr in hot metal with high efficiency by providing an intermediate waste period between the temperature reduction and finishing refining periods and rejecting the chromium recovered slag with a very low Cr content. I was able to find out.
[0032]
Furthermore, the present inventors have conducted intensive research and investigated the relationship between the weight ratio of the carbonaceous material in the decarburized slag and the forming height of the decarburized slag in the blowing acid temperature-programmed reduction period, as shown in FIG. , CO gas generated by the carbon combustion reaction (1) and (2) is combined and accumulated when an appropriate amount of carbon material introduced into the smelting furnace in the blowing acid temperature reduction period is present in the decarburized slag. As a result, the reduction rate of chromium oxide can be maintained at a high level while suppressing abnormal forming of decarburized slag, and the carbon in the recovered slag at the end of the blowing acid temperature reduction period is recovered by chromium. It has been found that if an appropriate amount of slag is present in the slag, the slag slag removal can be stabilized at a high level while suppressing the outflow of bullion during the intermediate slag.
[0033]
2, the horizontal axis represents the weight ratio of the carbonaceous material in the decarburized slag, the vertical axis in FIG. 2 represents the forming height of the decarburized slag (that is, the height of the decarburized slag during forming), and the broken line a in FIG. Indicates the upper limit of the height of the decarburized slag obtained from the volume of the refining furnace, and the broken line b in FIG. 2 indicates the lower limit of the height of the decarburized slag obtained from the intermediate exhaustability. In addition, the forming height of the decarburized slag is obtained by the following equation (4). That is,
L = h₁/ (H₂-H_Three(4)
L: Forming height of decarburized slag
h₁: Decarburization slag height in the refining furnace (m)
h₂: Height from the inner bottom surface to the receiving port in the refining furnace (m)
h_Three: Height of hot metal or molten steel in smelting furnace (m)
Moreover, the height lower limit of the decarburization slag obtained by the above formula (4) was 0.15, and the height upper limit of the decarburization slag was 0.85. If the decarburization slag height lower limit is less than 0.15, the decarburization slag tends to be difficult to discharge, and if the decarburization slag height upper limit exceeds 0.85, the decarburization slag tends to be difficult. This is because the slag overflows outside the smelting furnace and tends to melt down the peripheral equipment of the smelting furnace.
[0034]
From the above, claims1, 2In the refining method for the coarsely molten stainless steel described, the decarburized slag produced in the previous charge and containing chromium oxide is left in the refining furnace, and then the hot metal of the next charge is introduced, and then the oxidizing gas is blown. After reducing the chromium oxide in the decarburized slag by introducing the carbon material, the chromium recovered slag obtained by reducing the chromium oxide in the decarburized slag into the hot metal is discharged, and then the ferrochrome alloy is removed. After melting and adjusting the hot metal composition, etc., the molten steel is removed.
By decarburizing and refining the hot metal in this way, in the blowing acid heating and reducing period, the refining operation is performed by introducing hot metal while leaving decarburized slag with a high Cr content in the finishing refining period in the refining furnace. By starting, the chromium content in the decarburized slag can be easily and efficiently recovered in the hot metal by utilizing the Cr concentration difference between the hot metal and the decarburized slag and the reduction by the carbonaceous material. Further, since the decarburized slag remaining in the refining furnace is not cooled and solidified, after the residue is once cooled and solidified as in the prior art, it is not necessary to perform a temperature raising operation or the like, and an extremely quick refining operation can be performed. .
[0035]
In particular,Carbonate content (V_C ) 3wt% ≦ V by weight with respect to decarburized slag_C ≦ 6wt% makes it easy from CO gas decarburization slag because carbon combustion reactions such as the above formulas (1) and (2) occur mainly on the surface of the carbonaceous material in the decarburization slag during refining operation As a result, it is possible to control the formation of the decarburized slag (or chromium recovered slag), such as suppressing the abnormal forming of the decarburized slag during the blowing acid temperature reduction reduction period. Furthermore, since abnormal forming of the decarburized slag can be suppressed, the decarburized slag flows out of the refining furnace by this abnormal forming, and loss of unrecovered chromium in the decarburized slag can be prevented.
[0036]
In addition, when the hot metal is charged in the hot acid heating and reducing period, the carbon in the hot metal and the oxygen in the precharged decarburized slag remaining in the smelting furnace (hereinafter referred to as [O])_SAnd the reduction reaction shown in the following formula (5) occurs, but the carbon content in the hot metal is as high as 3 to 4 wt%, and further, the oxygen content in the decarburized slag is high. Although there is a possibility of causing a reductive reduction reaction, it is possible to introduce a carbonaceous material within the above range at the time of hot metal charging or before hot metal charging, or (Al₂O_Three)_SFor example, by introducing an alumina source such as aluminum dross containing 30% by weight of metal Al for concentration adjustment, this excessive reduction reaction can be suppressed, so that so-called bumping in which hot metal or decarburized slag overflows rapidly is prevented. Can be prevented.
[C]_M+ [O]_S→ CO (5)
[0037]
Also, the carbon content at the end of the blown acid temperature reduction period (V_C) 0.5wt% ≦ V by weight ratio with respect to decarburized slag_CBy setting ≦ 3 wt%, it is possible to impart appropriate forming to the chrome recovered slag in the intermediate evacuation period. As a result, the bullion caused by the thin slag thickness of the chrome recovered slag The slag drainage of chromium recovered can be stabilized at a high level while suppressing the outflow of slag.
[0038]
In particular, the claims2In the described method for refining crude stainless steel, the basicity of decarburized slag or chromium-recovered slag ((CaO / SiO₂ )_S ) By weight ratio 1.2 ≦ (CaO / SiO₂ )_S By setting it to ≦ 4.5, it is possible to prevent the refractory constituting the smelting furnace from being melted by having an appropriate basicity, and to suppress an increase in the amount of slag, and to improve the chromium recovery rate from the decarburized slag. It is possible to prevent a decrease, a decrease in the removal rate of chromium-recovered slag, and an increase in bullion loss. Also, decarburized slag Al₂ O_Three Content of ((Al₂ O_Three )_S ) 3 wt% ≦ (Al₂ O_Three )_S By setting it to ≦ 23 wt%, it is possible to prevent the refractory constituting the smelting furnace from being melted by having an appropriate basicity, and to impart an appropriate liquid phase ratio and chromium oxide activity. Chromium reduction rate from charcoal slag can be stabilized at a high level. Furthermore, the basicity of the decarburized slag or chromium recovered slag is within the above range, and Al₂ O_Three By setting the content ratio of the refractory within the above range, it is possible to stabilize the chromium reduction rate and the chromium recovery slag rejection rate at a high level while preventing the refractory constituting the smelting furnace from being melted.
[0039]
【The invention's effect】
Claim1, 2In the refining method for the coarsely melted stainless steel described, hot metal is introduced while leaving the decarburized slag having a high Cr content at the end of the finishing refining period in the refining furnace, so that the chromium content in the molten iron and decarburized slag is reduced. Can be recovered at a high reduction rate, and by removing the chromium-recovered slag with a low Cr content at the end of the blowing acid temperature reduction period, the chromium content in the decarburized slag can be removed without discarding it. Can be recovered. Furthermore, by appropriately selecting the weight ratio of the carbonaceous material introduced in the blowing acid temperature reduction reduction period to the decarburized slag or chromium recovered slag, the decarburization slag or chromium recovery slag forming in the blowing acid temperature reduction reduction period is appropriately selected. Thus, abnormal forming and the like can be controlled, and chrome slag can be discharged at a high discharge rate without any metal outflow in the intermediate discharge period. Therefore, an expensive reducing material or the like is not required, and an efficient and stable refining operation can be performed at a low cost.
[0040]
In particular,Carbonate content (V_C ) 3wt% ≦ V by weight with respect to decarburized slag_C Since ≦ 6 wt%, CO gas generated during the blowing acid temperature reduction process can be easily removed from the decarburized slag, and the decarburized slag or chromium has been recovered. Slag forming can be controlled, and the reduction rate of chromium oxide can be maintained at a high level. Also, the carbon content at the end of the blown acid temperature reduction period (V_C ) 0.5wt% ≦ V by weight ratio with respect to decarburized slag_C Since ≦ 3 wt%, the chromium-recovered slag can be discharged efficiently and stably while suppressing the outflow of the metal in the intermediate discharging period.
[0041]
In particular, the claims2In the described method for refining crude stainless steel, the basicity of decarburized slag or chromium-recovered slag ((CaO / SiO₂ )_S ) By weight ratio 1.2 ≦ (CaO / SiO₂ )_S ≦ 4.5 and / or Al of decarburized slag₂ O_Three Content of ((Al₂ O_Three )_S ) 3 wt% ≦ (Al₂ O_Three )_S Since ≦ 23 wt%, it is possible to prevent the refractory constituting the refining furnace from being melted and to reduce chromium oxide in the decarburized slag by having an appropriate basicity in the decarburized slag and chromium-recovered slag. The speed can be maintained at a high level, and an appropriate viscosity can be imparted to prevent a decrease in the rejection rate of the chromium-recovered slag, an increase in metal loss, and an abnormal forming of the decarburized slag.
[0042]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
Here, FIGS. 1 (A) to 1 (E) are explanatory views showing the operating state of an upper bottom blow converter to which a method for refining a stainless coarse molten steel according to an embodiment of the present invention is applied, and FIG. 2 is a blowing acid. It is a characteristic view which shows the relationship between the content rate of the carbonaceous material in the decarburization slag in the temperature reduction period, and the forming height of the decarburization slag. More specifically, FIG. 1 (A) is an explanatory view showing a state in which hot metal is put into an upper bottom blowing converter to which a method for refining a stainless coarse molten steel according to an embodiment of the present invention is applied, and FIG. 1 (B). Is an explanatory view showing a blowing acid temperature-increasing reduction period of the upper bottom blowing converter, FIG. 1 (C) is an explanatory view showing an intermediate discharge period of the upper bottom blowing converter, and FIG. 1 (D) is an upper bottom blowing converter. Explanatory drawing which shows the finishing refining period of FIG. 1, FIG.1 (E) is explanatory drawing which shows the steeling period of the same bottom blow converter.
[0043]
As shown in FIGS. 1 (A) to 1 (E), the upper-bottom blow converter 10 is formed in a substantially symmetric shape by stacking refractory bricks and the like. In one embodiment of the present invention, an upper bottom blow converter 10 of hot metal receiving steel amount 175 tons was used. Moreover, although not shown in figure, the upper bottom blow converter 10 employ | adopts a trunnion ring system or a trunnion ring-less system etc., and is a predetermined direction, ie, the clockwise direction and counterclockwise direction in FIG. It is held so that it can tilt (or turn). Further, the upper bottom blow converter 10 is formed with a receiving port 10a for introducing hot metal described later. Further, decarburization refining is performed on the side wall portion below the receiving port 10a of the upper bottom blow converter 10, that is, on the right side wall portion of the upper bottom blow converter 10 in FIG. A steel outlet 10b for producing the molten steel is formed. In addition, a plurality of gas supply ports 10c are formed at the bottom of the upper bottom blow converter 10, and a gas supply tube 10d is attached to the gas supply ports 10c. Further, a ladle 11 is disposed in the vicinity of the receiving port 10a of the upper bottom blowing converter 10 so as to be close to (or laterally movable) the upper bottom blowing converter 10. A lance 12 for supplying an oxidizing gas such as oxygen is disposed at the upper part of the receiving port 10a of the upper bottom blow converter 10 so as to be movable up and down. Although not shown in the drawing, a sub lance for measuring the component of hot metal (or molten steel) or slag, measuring the temperature, or the like is also arranged in the vicinity of the lance 12.
[0044]
Then, the refining method of the stainless rough molten steel which concerns on one embodiment of this invention using this top bottom blow converter 10 is demonstrated.
First, an appropriate amount of aluminum dross containing 30 wt% of metal Al as a reducing material is added while leaving the decarburized slag 13 generated in the final refining period of the precharge in the upper bottom blow converter 10. Next, as shown in FIG. 1 (A), the upper bottom blow converter 10 is tilted counterclockwise toward the ladle 11, and the inside of the upper bottom blow converter 10 is moved from the ladle 11 through the receiving port 10a. In addition to charging the hot metal 14 for the next charge, a charging agent (or called flux) such as lime or fluorite is charged.
[0045]
Next, the content of carbonaceous materials such as powdered coke (V_C) 3 wt% ≦ V by weight ratio with respect to decarburized slag 13_CWhile adding while continuously charging so as to be in the range of ≦ 6 wt%, as shown in FIG. 1 (B), the tip of the lance 12 is brought into the upper bottom blow converter 10 through the receiving port 10a. It is lowered and oxygen is supplied from the lance 12. With such top blowing acid, the hot metal 14 and the decarburized slag 13 are heated, and the chromium oxide in the decarburized slag 13 is reduced into the hot metal 14 by the reaction shown in the formula (2). Chromium is recovered in the hot metal 14. In addition, by setting the content rate of the carbonaceous material within the above range, the CO gas generated by the carbon combustion reaction such as the formulas (1) and (2) is accumulated, and bubbles are appropriately generated in the decarburized slag 13. As a result, abnormal defoaming of the decarburized slag 13 and the like were suppressed, and the decarburized slag 13 was appropriately formed.
[0046]
Next, when chromium oxide in the decarburized slag 13 is reduced to produce chromium-recovered slag 13a having a Cr content of 3 wt% or less, as shown in FIG. The blow furnace 10 is tilted counterclockwise in the direction opposite to the steel outlet 10b, and a part or most of the chromium recovered slag 13a is discharged. In addition, the content rate (V_C) 0.5 wt% ≦ V in weight ratio with respect to the chrome recovered slag 13a_CBy setting it to ≦ 3 wt% or less, it is possible to form a chromium recovered slag 13a having a sufficient thickness while preventing a decrease in the viscosity of the chromium recovered slag 13a. As a result, the chromium recovered slag 13a could be efficiently and stably discharged while suppressing the outflow of the metal. In addition, the hot metal 14 is the molten steel 14a which Cr content rate increased by collect | recovering the chromium in the decarburization slag 13. FIG.
[0047]
Next, as shown in FIG. 1 (D), a ferrochrome alloy or flux is added into the upper bottom blowing converter 10 through the receiving port 10a, and further, as described above, top blowing acid is performed. Carburized and refined. Thereby, the slag 13b is newly produced | generated on the molten steel 14a. Next, when molten steel 14b having a predetermined composition and a predetermined temperature is generated, as shown in FIG. 1 (E), the upper bottom blow converter 10 is tilted clockwise toward the steel outlet 10b, and this discharge is performed. The molten steel 14b is extracted from the steel port 10b. Note that the Cr content of the decarburized slag 13 was 11 wt% to 19 wt%. Here, the generated decarburized slag 13 is left in the upper bottom blow converter 10 as it is.
[0048]
By repeating the above operation, stainless steel is refined by multiple charges. During the refining operation, the basicity of the decarburized slag 13 or the chromium recovered slag 13a ((CaO / SiO₂)_S) By weight ratio 1.2 ≦ (CaO / SiO₂)_SSince it was within the range of ≦ 4.5, there was no refractory damage of the refractory constituting the upper-bottom blow converter 10, and it was possible to prevent a reduction in the waste rate due to a decrease in the viscosity of the chromium recovered slag 13a. Furthermore, Al of the decarburized slag 13₂O_ThreeContent of ((Al₂O_Three)_S) 3 wt% ≦ (Al₂O_Three)_SSince it was within the range of ≦ 23 wt%, there was no refractory damage of the refractory constituting the upper bottom blow converter 10, and further, promotion of the chromium reduction rate and abnormal formation of the decarburized slag 13 could be prevented.
[0049]
Next, the confirmation test of the refining method of the stainless coarse molten steel which concerns on one embodiment of this invention was done. The results will be described below.
(Experimental Examples 1-6)
First, the decarburization refining of stainless coarsely molten steel was performed 6 charges using the method for refining stainless coarsely molten steel according to one embodiment of the present invention (test numbers 1 to 6). Here, the weight ratio of the carbonaceous material in the decarburized slag during the blowing acid temperature rising reduction period in each charge, the basicity ((CaO / SiO₂)_S) And Al₂O_ThreeThe content was as shown in Table 1.
[0050]
[Table 1]

[0051]
In addition, the Cr reduction rate (kg / min / T) during blown acid warming reduction period in each charge, the presence or absence of abnormal decarburization slag forming, the removal rate (%) of chromium recovered slag during the intermediate elimination period, and the ground The amount of gold loss (kg / T) and the refractory melt damage after completion of refining for each charge were examined. The results are shown in Table 1. Note that the Cr reduction rate refers to the amount of Cr reduction per unit time in the blowing acid temperature rising reduction period. Moreover, the amount of metal loss means the weight of the molten iron (or molten steel) discharged together with the chromium-recovered slag in the intermediate discharging period.
[0052]
Further, the rejection rate is obtained by the following equation (6). That is,
Exclusion rate (%) = V_sd/ (V_sd+ V_sr(6)
However, V_sd： Chromium recovered slag discharged from the top-bottom blow converter
V_sr: Weight of chromium recovered slag remaining in the top bottom blowing converter
It is.
[0053]
(Experimental examples 7 to 11)
Next, the carbon content in the decarburization slag during the blowing acid temperature reduction period, the carbon content in the decarburization slag at the end of the blowing acid temperature reduction period, and the decarburization during the blowing acid temperature reduction period Slag basicity and Al₂O_ThreeEach of the contents was changed, and decarburization and refining of the stainless crude molten steel was performed 5 times (test numbers 7 to 11). Specifically, the carbonaceous material in the decarburized slag in the blowing acid temperature reduction period is less than 3 wt% by weight ratio (Test No. 7), and the carbonaceous material in the decarburized slag in the blowing acid temperature reduction period is weight ratio. In the decarburized slag at the end of the blowing acid heating and reducing period, the carbon material in the decarburized slag at the end of the blowing acid heating and reducing period exceeds 3 wt% by weight (test number 8) In the decarburization slag in the blowing acid temperature reduction period, the basic material of the decarburization slag in the blowing acid temperature reduction period is less than 1.2 (test number 9). The decarburization slag in the blowing acid temperature-reduction period is made to be less than 3 wt% in weight ratio and the basicity of the decarburization slag in the blowing acid temperature-reduction period exceeds 4.5 (test number 10). The weight ratio of the carbon material is less than 3 wt%, and the weight ratio of the carbon material at the end of the blowing acid heating and reducing period is less than 0.5%. Al of decarburization in the slag of the reduction period₂O_ThreeExcept for the content rate exceeding 23 wt% (Test No. 11), the Cr reduction rate (kg / min / T) and decarburization slag abnormality during the blowing acid temperature increase and reduction period were the same as in Experimental Examples 1 to 6. The presence or absence of forming, the removal rate of chromium recovered slag in the intermediate elimination period (%), the amount of metal loss (kg / T), and the refractory melt damage after the refining for each charge were examined. The results are shown in Table 1.
[0054]
As can be seen from Table 1, when the carbonaceous material in the decarburized slag during the blowing acid temperature rising reduction period is less than 3 wt% (test number 7), the decarburization of the CO gas generated by the carbon combustion reaction It was found that abnormal decarburization of decarburized slag occurred during the blowing acid heating and reducing period due to insufficient separation from slag. As a result, it was confirmed that the carbonaceous material in the decarburized slag during the blowing acid temperature rising reduction period is preferably 3 wt% or more by weight.
[0055]
Further, as is apparent from Table 1, the carbonaceous material in the decarburized slag in the blowing acid temperature-reduction period is less than 3 wt% by weight, and the chromium recovered slag at the end of the blowing acid temperature-reduction period When the carbon material exceeds 3 wt% by weight (test number 8), the slag thickness during the intermediate evacuation period of the chromium-recovered slag is insufficient due to the suppression of forming by the carbon material, resulting in a decrease in the evacuation rate and the metal I found out that Ross was inviting. As a result, the carbon material in the decarburized slag in the blowing acid temperature reduction period is 3 wt% or more in weight ratio, and the carbon material in the chromium-recovered slag at the end of the blowing acid temperature reduction period is 3 wt% in weight ratio. It was confirmed that it was good to be less than%.
[0056]
Further, as is apparent from Table 1, the carbonaceous material in the decarburized slag in the blowing acid temperature-programmed reduction period is less than 3 wt% in weight ratio, and the basicity of the decarburized slag in the blowing acid temperature-programmed reduction period is 1 When the ratio was less than 2 (test number 9), it was found that refractory erosion due to low basicity slag was in progress. As a result, the carbonaceous material in the decarburized slag during the blowing acid temperature reduction process is 3 wt% or more in weight ratio, and the basicity of the decarburized slag during the blowing acid temperature reduction period is 1.2 or more. It was confirmed to be good.
[0057]
Further, as is apparent from Table 1, the carbonaceous material in the decarburized slag in the blowing acid temperature-programmed reduction period is less than 3 wt% in weight ratio, and the basicity of the decarburized slag in the blowing acid temperature-programmed reduction period is 4 When exceeding .5 (Test No. 10), it was found that due to the increase in the amount of slag, the reduction rate of the chrome slag recovered during the intermediate elimination period and the loss of bullion were increased. As a result, the carbonaceous material in the decarburized slag in the blowing acid temperature reduction reduction period is 3 wt% or more in weight ratio, and the basicity of the decarburization slag in the blowing acid temperature reduction reduction period is 4.5 or less. It was confirmed to be good.
[0058]
Further, as is apparent from Table 1, the weight ratio of the carbonaceous material in the decarburized slag during the blowing acid temperature reduction reduction period is less than 3 wt%, and the weight ratio of the carbonaceous material at the end of the blowing acid temperature reduction reduction period is Al in decarburized slag in the dehydration slag during blowing acid temperature reduction process₂O_ThreeWhen the content ratio of Al exceeds 23 wt% (Test No. 11), Al₂O_ThreeIt was found that abnormal forming occurred due to the increase in the viscosity of decarburized slag with the increase in the content rate, and further the refractory melt was promoted. As a result, the carbonaceous material in the decarburized slag during the blowing acid temperature reduction period is 3 wt% or more in weight ratio, and Al in the decarburized slag during the blowing acid temperature reduction period₂O_ThreeIt was confirmed that the content of the slag was 23 wt% or less.
[0059]
As mentioned above, although embodiment of this invention was described, this invention is not limited to these embodiment, The change of the conditions etc. which do not deviate from a summary are all the application scopes of this invention.
[Brief description of the drawings]
FIG. 1 (A) is an explanatory view showing a state in which hot metal is put into an upper-bottom blow converter to which a method for refining crude stainless steel according to an embodiment of the present invention is applied.
(B) It is explanatory drawing which shows the blowing acid temperature rising reduction period of the same bottom blowing converter.
(C) It is explanatory drawing which shows the intermediate waste period of the same bottom blow converter.
(D) It is explanatory drawing which shows the finishing refining period of the same bottom blow converter.
(E) It is explanatory drawing which shows the steel output period of the same bottom blow converter.
FIG. 2 is a characteristic diagram showing the relationship between the weight ratio of the carbonaceous material in the decarburized slag and the forming height of the decarburized slag during the blowing acid temperature reduction reduction period.
[Explanation of symbols]
10 Upper bottom blowing converter 10a Receiving port
10b Steel outlet 10c Gas supply port
10d Gas air pipe 11 Ladle
12 Lance 13 Decarburization slag
13a Chrome recovered slag 13b Slag
14 Hot metal 14a Hot metal or molten steel
14b Molten steel

Claims

While the decarburized slag generated in the final refining period of the previous charge in the refining furnace is left in the decarburized slag containing chromium oxide, the hot metal of the next charge is added and the carbon material is added to the refining furnace and the oxidizing gas is added. Recovery process of reducing the chromium oxide in the decarburized slag into the molten iron, and recovery of chromium obtained by reducing the chromium oxide into the molten metal in the heated acid temperature reducing period An intermediate discharge period for discharging spent slag, and the finishing refining period for decarburizing and refining while melting the ferrochrome alloy in the molten iron remaining in the refining furnace in the intermediate discharge period ,
In addition, the carbon content (V _C ) 3 wt% ≦ V _{C in} weight ratio with respect to the decarburized slag ≦ 6 wt%, and the content of the carbonaceous material at the end of the blowing acid temperature reduction period (V _C ) 0.5 wt% ≦ V _{C in} weight ratio with respect to the chromium recovered slag A method for refining stainless steel roughly molten steel characterized by ≦ 3 wt% .

The basicity ((CaO / SiO ₂ ) _S ) of the decarburized slag or the chromium-recovered slag is 1.2 ≦ (CaO / SiO ₂ ) _S ≦ 4.5 by weight ratio and / or the decarburized. the content of Al ₂ O ₃ slag _{_{_{((Al 2 O 3) S}}} ) 3wt% ≦ a _{_{_{(Al 2 O 3) S ≦}}} 23wt% and refining method according to claim 1, wherein the stainless crude molten steel.