JP4364456B2

JP4364456B2 - Method for melting stainless steel

Info

Publication number: JP4364456B2
Application number: JP2001178983A
Authority: JP
Inventors: 健一郎宮本
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2001-06-13
Filing date: 2001-06-13
Publication date: 2009-11-18
Anticipated expiration: 2021-06-13
Also published as: JP2002371313A

Description

【０００１】
【発明の属する技術分野】
本発明は、転炉型精錬容器を用いて一次脱炭精錬で生成したスラグ中のＣｒをＳｉ含有合金で還元を行った後、Ａｌを添加して脱硫し、次いで行う二次脱炭精錬で、Ａｌを添加しないことにより、極低Ａｌ、低Ｓのステンレス溶鋼を溶製するステンレス溶鋼の溶製方法に関する。
【０００２】
【従来の技術】
従来、溶鉄にクロムやニッケルを含有させたステンレス溶鋼を連続鋳造等を用いて鋳片にし、この鋳片に圧延加工を施して製造されたステンレス鋼板は、耐腐食や光沢性に優れているため、油井管や建材等に多く使用されている。
このステンレス鋼板の耐腐食、靱性等の特性は、精錬炉を用いてステンレス溶鋼を溶製する際、ステンレス溶鋼中に含まれるアルミニウム（Ａｌ）に起因した粗大酸化物系介在物が生成し、硫黄は、硫化物を形成するため、ステンレス鋼板の耐腐食が悪くなったり、ステンレス鋼板の靱性が低下する等の問題がある。
この対策として、炭素を０．００５〜０．１質量％で、クロム（Ｃｒ）を１２〜１６質量％、Ａｌを０．００５〜０．２質量％、硫黄（Ｓ）を０．０１５質量％を含むステンレス鋼板が提案されており、この鋼板を用いることにより、Ａｌ脱酸の生成物である粗大介在物を抑制し、しかも、硫化物による腐食及び腐食割れ等の発生を防止する方法が行われている。
【０００３】
【発明が解決しようとする課題】
しかしながら、上記組成のステンレス溶鋼を溶製する際、精錬過程で、ステンレス溶鋼のＡｌ濃度の低減と、脱硫の促進を同じ転炉型精錬炉を用いて極低Ａｌ、低Ｓ濃度のステンレス溶鋼を容易に溶製することができず、更に、精錬時に発生するスラグ中のクロム酸化物（Ｃｒ₂Ｏ₃）の還元回収効率が低くなり、発生スラグの資源化を図ることができない等の問題がある。
【０００４】
本発明はかかる事情に鑑みてなされたもので、ステンレス溶鋼のＡｌ濃度の低減と脱硫の促進を図り極低Ａｌ、低Ｓのステンレス溶鋼の溶製を容易にし、スラグ中のＣｒ₂Ｏ₃濃度を低減して発生スラグの資源化を可能にするステンレス溶鋼の溶製方法を提供することを目的とする。
【０００５】
【課題を解決するための手段】
前記目的に沿う本発明に係るステンレス溶鋼の溶製方法は、転炉型容器に溶銑とフェロクロム合金を装入し、前記溶銑とフェロクロム合金に上吹きランスを用いて吹酸し、前記溶銑とフェロクロム合金の溶解と一次脱炭精錬を行って粗溶鋼を溶製した後、取鍋に前記粗溶鋼を出鋼し、次いで、前記粗溶鋼を二次精錬炉を用いて二次脱炭精錬と脱酸処理を行うステンレス溶鋼の溶製方法において、前記吹酸による前記一次脱炭精錬を行った後に生成したスラグに、シリコンを含有する合金を添加して該スラグ中のＣｒ ₂ Ｏ ₃ 濃度が５質量％以下となるように前記スラグを還元処理した後、前記粗溶鋼中のＡｌ濃度が０．０５〜０．２質量％になるようにＡｌを添加し、前記スラグの塩基度を１．３〜１．８、前記スラグ中のＡｌ ₂ Ｏ ₃ を３〜１０質量％として脱硫処理を行ってから前記取鍋に出鋼することとし、前記還元処理及び前記脱硫処理時の前記粗溶鋼の温度を１５５０℃以上１７００℃未満とし、引き続き行う前記二次精錬炉を用いた二次脱炭精錬における昇熱及び脱酸処理時にＡｌを添加しないで処理を行う。
この方法により、転炉型容器による一次脱炭精錬時に生成したスラグ中に含まれるＣｒ₂Ｏ₃をシリコンを含む還元剤で還元し、Ｃｒを粗溶鋼中に回収でき、更に、粗溶鋼中のＡｌ濃度を０．０５〜０．２質量％にして脱硫処理を行なうので、酸素ポテンシャルを低くして脱硫を促進することができる。
更に、二次脱炭精錬の昇熱期に、Ａｌ昇熱を行うと、スラグ中のＡｌ₂Ｏ₃の濃度が上昇し、わずかにスラグ中のＡｌ₂Ｏ₃が、例えばＳｉ合金等の他の脱酸剤により、還元されて溶鋼中のＡｌ濃度が高くなり、極低Ａｌにすることができない。従って、二次精錬炉による二次脱炭精錬で行う昇熱工程及び二次脱炭精錬を行った後に行う脱酸処理でＡｌを添加しないことにより、最終のステンレス溶鋼のＡｌ含有量を極低Ａｌにし、低Ｓにすることができる。
Ａｌ濃度が０．０５質量％より少ないと、スラグ中の酸素ポテンシャルが高くなり、脱硫反応が悪くなって到達Ｓ濃度が高くなる。一方、Ａｌ濃度が０．２質量％を超えると、脱硫の効果が飽和状態になり、これ以上Ａｌを添加しても合金コストが上昇するだけであり、更に、二次脱炭精錬によりスラグ中のＡｌ₂Ｏ₃濃度が高くなり、極低Ａｌ濃度の溶鋼の溶製が困難になる。
【０００６】
ここで、前記転炉型容器を用いた前記脱硫処理時のスラグの塩基度を１．３〜１．８、スラグ中のＡｌ₂Ｏ₃を３〜１０質量％以下とすることにより、スラグの脱硫能を高め、しかも、遊離ＣａＯの生成を抑制してスラグの膨張を防止し、スラグの資源化を図ることができる。
スラグの塩基度が１．３より小さいと、スラグの脱硫能が低下し、脱硫反応が悪くなる。一方、スラグの塩基度が１．８を超えると、高塩基度化に伴い遊離ＣａＯが発生し、スラグの膨張が大きく、滓化不良が生じ易くなる。
また、スラグ中のＡｌ₂Ｏ₃濃度が１０質量％を超えると、スラグの脱硫能が低下し、脱硫反応が悪くなる。なお、スラグ中のＡｌ₂Ｏ₃濃度の下限は、スラグの滓化を促進し、脱硫反応を良好にするため、３質量％とする。
【０００７】
更に、前記還元処理を終了した前記スラグ中のＣｒ₂Ｏ₃濃度を５質量％以下にすることにより、スラグ中に含まれる高価なＣｒを還元して粗溶鋼中に回収でき、合金鉄コストを低減することができる。
スラグ中のＣｒ₂Ｏ₃濃度が５質量％を超えると、脱硫処理で添加したＡｌがＣｒ₂Ｏ₃の還元に消費され、スラグ中の酸素ポテンシャルの低下が不十分になり、脱硫反応が低下する。
【０００８】
また、前記還元処理及び前記脱硫処理時の前記粗溶鋼の温度を１５５０℃以上、１７００℃未満とすることにより、スラグの滓化を促進し、脱硫反応を促進し、低Ｓのステンレス粗溶鋼を容易に溶製することができる。
還元処理及び脱硫処理時の粗溶鋼の温度が１５５０℃より低くなると、スラグの滓化に多大の時間を要し、脱硫反応が不利になる。一方、粗溶鋼の温度が１７００℃以上になると、高温度に成り過ぎて精錬炉の耐火物の溶損が増大し、耐火物コストが高くなる。
【０００９】
【発明の実施の形態】
続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態につき説明し、本発明の理解に供する。
図１は本発明の一実施の形態に係るステンレス溶鋼の溶製方法による処理の流れを示す説明図である。
図１に示すように、本発明の一実施の形態に係るステンレス溶鋼の溶製方法によるステンレス溶鋼の脱炭精錬処理は、一次脱炭精錬に用いる転炉型容器の一例である上底吹き転炉１０と、二次脱炭精錬に用いる二次精錬炉の一例である減圧取鍋精錬炉３０を使用している。
上底吹き転炉１０は、溶鉄とフェロクロム合金を入れる炉体１１と、炉口１２の上方に昇降可能に配置して溶鉄とフェロクロム合金に酸素を吹き付ける吹酸ランス１３と、炉体１１の底部から不活性ガスの一例であるアルゴンガスを吹き込んでスラグ１４ａ及び粗溶鋼（ステンレス粗溶鋼ともいう）１５ａを攪拌する底吹きノズル１６と、炉体１１の側上部に出鋼口１７を有している。更に、炉口１２の上方に副原料の一例であるＣａＯやフェロシリコン（Ｆｅ−Ｓｉ）、Ａｌ等を貯蔵するホッパ１８と、ホッパ１８の下方に配置したシュート１９と、脱硫処理を行ったスラグ１４ｂを炉内に残留させて溶製したステンレス粗溶鋼１５ｂを受鋼し、底部に不活性ガスの吹き込みを行うポーラスプラグ２０を有する取鍋２１を備えている。
【００１０】
減圧取鍋精錬炉３０は、上底吹き転炉１０で溶製したステンレス粗溶鋼１５ｂを受鋼した取鍋２１をそのまま用い、この取鍋２１の上に被さる減圧フード３６と、減圧フード３６を貫通して内部とそれぞれ連通する吹酸ランス３１と、図示しないエゼクターに連通した減圧ダクト３２と、途中に遮断弁３４を有するＣａＯや合金鉄等の貯蔵ホッパ３５と接続されたシュート３３を有している。
【００１１】
次に、本発明に係るステンレス溶鋼の溶製方法について上底吹き転炉１０と減圧取鍋精錬炉３０を用いて説明する。
溶鉄とフェロクロム合金を上底吹き転炉１０の炉口１２から炉内に装入し、吹酸ランス（上吹きランス）１３を炉口１２から炉内に下降させ、１５０００〜２５０００Ｎｍ³／（時間）の酸素の吹き付けを行い、同時に、ホッパ１８からＣａＯを添加し、吹酸ランス１３からの吹酸による一次脱炭精錬を行う。
この一次脱炭精錬では、吹酸による昇熱によって、フェロクロム合金が速やかに溶解し、更に、酸素と炭素が反応するいわゆる脱炭反応が促進され、炭素濃度が０．３〜０．８質量％、温度が１５５０℃以上、１７００℃未満のステンレス粗溶鋼１５ａが溶製される。
この一次脱炭精錬の際、添加したＣａＯや溶銑やフェロクロム合金に含まれる珪素（Ｓｉ）、Ａｌ等が酸化され、スラグ１４ａを形成する。
このスラグ１４ａは、一次脱炭精錬の吹酸時に、フェロクロム合金中のＣｒが酸化されたＣｒ₂Ｏ₃を多量に含むため、シリコンを含有する合金の一例であるＦｅ−Ｓｉ合金をホッパ１８から添加し、底吹きノズル１６からステンレス粗溶鋼１５ａ中にアルゴンガスを吹き込んでスラグ１４ａとステンレス粗溶鋼１５ａを攪拌してＣｒ₂Ｏ₃の還元処理を行う。
この還元処理は、スラグ１４ａ中のＣｒ₂Ｏ₃濃度が５質量％以下になるまで行う。
そして、還元処理を終了した後、底吹きノズル１６からアルゴンガスの吹き込みを継続した状態で、Ａｌの一例である金属Ａｌをホッパ１８からシュート１９を介してＡｌ濃度が０．０５〜０．２質量％となるように添加し、スラグ１４ａとステンレス粗溶鋼１５ａを攪拌して脱硫処理を行う。
この脱硫処理直前に、予めスラグ１４ａをサンプリングして分析し、スラグ１４ａの塩基度（ＣａＯ／ＳｉＯ₂）が１．３〜１．８、Ａｌ₂Ｏ₃が１０質量％以下になるように、シュート１９を介して炉内へ添加するＣａＯ量や金属Ａｌ量の調整を行う。
【００１２】
上底吹き転炉１０を用いた還元処理は、ステンレス粗溶鋼１５ａ及びスラグ１４ａの温度を１５５０℃以上、１７００℃未満にして底吹きノズル１６からアルゴンガスを吹き込んで攪拌し、しかも、Ｆｅ−Ｓｉ合金を添加しているので、スラグ１４ａの滓化が良好になり、スラグ１４ａ中のＣｒ₂Ｏ₃の還元反応が促進される。
還元されたＣｒは、ステンレス粗溶鋼１５ａ中に回収され、スラグ１４ａ中に残留するＣｒ₂Ｏ₃濃度として５質量％（Ｃｒ換算で質量％）以下にすることができる。
還元処理の後に行う脱硫処理は、ステンレス粗溶鋼１５ａに、金属Ａｌを添加しその濃度を０．０５〜０．２質量％にするので、スラグ１４ａ中の酸素ポテンシャルを十分に低減し、温度を１５５０℃以上、１７００℃未満にし、しかも、底吹きノズル１６からアルゴンガスを吹き込んで攪拌するので、脱硫反応が促進されて到達Ｓ濃度を低くすることができる。
更に、スラグ１４ａ中のＣｒ₂Ｏ₃の濃度を５質量％以下にしているので、添加した金属Ａｌが、Ｃｒ₂Ｏ₃との酸化反応による消耗を少なくし、しかも、スラグ１４ａ中のＡｌ₂Ｏ₃の増加を抑制して、スラグ１４ａ中の酸素ポテンシャルを効率良く低減でき、脱硫反応を安定して促進することができる。
この還元処理と脱硫処理を行ったステンレス粗溶鋼１５ｂは、脱硫処理によってＳ濃度が０．０００５〜０．００１質量％の低Ｓ濃度になり、炉体１１の傾転によって出鋼口１７から取鍋２１に出鋼し、図示しない搬送手段により減圧取鍋精錬炉３０による処理場所まで移動する。
また、スラグ１４ｂは、残留するＣｒ₂Ｏ₃の濃度が５質量％以下、ＣａＯ／ＳｉＯ₂が１．３〜１．８、Ａｌ₂Ｏ₃が３〜１０質量％となり、膨張の無い良質スラグとして、図示しない排滓鍋に炉口１２から排滓され、冷却、破砕等の処理後、路盤材や土木埋め立て材等の資源として有効利用される。
【００１３】
次に、減圧取鍋精錬炉３０では、ステンレス粗溶鋼１５ｂを入れた取鍋２１の上を覆って、減圧フード３６を載置し、シュート３３の遮断弁３４を開いて貯蔵ホッパ３５からＣａＯ等の副原料を取鍋２１内に投入し、吹酸ランス３１を下降して吹酸を開始し、同時に、エゼクターを作動して減圧ダクト３２から取鍋２１の内部を１００〜０．２ｔｏｒｒに減圧して昇熱し、炭素濃度が０．０１〜０．０５質量％となるまで二次脱炭精錬を行った。
二次脱炭精錬の終了後、Ａｌの添加を行わないで、ステンレス粗溶鋼１５ｂを脱酸処理した。
【００１４】
この吹酸ランス３１からの酸素の吹き付けによって、前記脱硫処理で金属Ａｌを添加した際、溶鋼ステンレス粗溶鋼１５ｂ中に付加されたＡｌを確実に酸化し、二次脱炭精錬で生成したスラグ１４ｃにＡｌ₂Ｏ₃として吸収させ、更に、脱酸処理でＡｌを使用しないので、ステンレス溶鋼１５ｃへのＡｌの付加が防止できる。更に、ステンレス粗溶鋼１５ｂ中に残留したＡｌは、減圧取鍋精錬炉３０を用いた二次脱炭精錬時に酸化されてＡｌ₂Ｏ₃となり、そのＡｌ₂Ｏ₃生成量は、極めて僅少であるため、スラグ１４ｃの組成中のＡｌ₂Ｏ₃濃度は、差ほどの変化が無く、脱酸処理時にスラグ１４ｃ中のＡｌ₂Ｏ₃が還元されない利点があり、相乗した作用によって、Ａｌ濃度が０．００１〜０．００２質量％の極低Ａｌのステンレス溶鋼１５ｃを溶製することができた。
そして、炭素濃度が０．０１〜０．０５質量％、極低Ａｌ、低Ｓ濃度のステンレス溶鋼１５ｃは、連続鋳造等を用いて鋳片にし、所定のサイズに切断され、圧延等の加工が施されて鋼板や型鋼等が製造される。
【００１５】
【実施例】
次に、本発明に係るステンレス溶鋼の溶製方法の実施例について説明する。
上底吹き転炉（転炉型容器）に溶銑とＦｅ−Ｃｒを装入し、吹酸ランスを炉内に下降させて酸素を吹き付けて昇熱処理を行ない、炭素濃度が０．３〜０．８質量％になるまで一次脱炭精錬を行ってステンレス粗溶鋼を溶製した。
更に、ステンレス粗溶鋼を溶製する際、脱硫処理時のＡｌ濃度、及びスラグ組成（ＣａＯ／ＳｉＯ₂、Ａｌ₂Ｏ₃濃度）、還元処理終了時のＣｒ₂Ｏ₃濃度、還元脱硫処理時の温度を変化させて還元処理及び脱硫処理を行った。そして、脱硫時Ｓ分配（（％Ｓ）／〔％Ｓ〕）、二次精錬時極低Ａｌ化のコントロール性、転炉耐火物溶損状況、脱硫後スラグの資源化、総合評価について調査した。その結果を表１に示す。
実施例１及び実施例２は、転炉脱硫時のＡｌ濃度、転炉脱硫時スラグ組成、還元処理終了時Ｃｒ₂Ｏ₃濃度、還元脱硫処理時の温度のいずれもが、本発明の範囲を満たす場合であり、脱硫時Ｓ分配をそれぞれ５５０、６７０に高くでき、二次精錬時極低Ａｌ化のコントロール性も良く、転炉耐火物溶損を小さくでき、脱硫後スラグの資源化が可能となり、総合評価として良い（○）結果が得られた。
実施例３は、転炉脱硫時のＡｌ濃度が下限値である０．０５質量％、実施例４は、転炉脱硫時のＡｌ濃度が上限値である０．２０質量％にした場合であり、脱硫時Ｓ分配を、それぞれ４２０、５７０に高くでき、二次精錬時極低Ａｌ化のコントロール性も良く、転炉耐火物溶損を小さくでき、脱硫後スラグの資源化が可能となり、総合評価として良い（○）結果が得られた。
実施例５は、転炉脱硫時スラグ組成（ＣａＯ／ＳｉＯ₂）を下限値である１．３、実施例６は、転炉脱硫時スラグ組成（ＣａＯ／ＳｉＯ₂）を上限値である１．８にした場合であり、脱硫時Ｓ分配を、それぞれ３２０、７５０にでき、二次精錬時極低Ａｌ化のコントロール性も良く、転炉耐火物溶損を小さくでき、脱硫後スラグの資源化が可能となり、総合評価として良い（○）結果が得られた。
実施例７は、転炉脱硫時スラグ組成（Ａｌ₂Ｏ₃濃度）を上限値である１０質量％、実施例８は、転炉脱硫時スラグ組成（Ａｌ₂Ｏ₃濃度）を４．９質量％にした場合であり、脱硫時Ｓ分配を、それぞれ４３０、４１０にでき、二次精錬時極低Ａｌ化のコントロール性も良く、転炉耐火物溶損を小さくでき、脱硫後スラグの資源化が可能となり、総合評価として良い（○）結果が得られた。
実施例９は、還元脱硫処理時の温度を１５５０℃に、実施例１０は、還元脱硫処理時の温度を１６９９℃にした場合であり、脱硫時Ｓ分配を、それぞれ３３０、６４０にでき、二次精錬時極低Ａｌ化のコントロール性も良く、転炉耐火物溶損を小さくでき、脱硫後スラグの資源化が可能となり、総合評価として良い（○）結果が得られた。
【００１６】
【表１】

【００１７】
これに対し、比較例１は、転炉脱硫時のＡｌ濃度が０．０２質量％と低くなった場合であり、脱硫時Ｓ分配が３０と極めて悪くなり、低Ｓ化を図るため二次脱炭精錬の負荷が増し、総合評価として悪い（×）結果となった。
比較例２は、転炉脱硫時のＡｌ濃度が０．３２質量％と高くなった場合であり、二次精錬時極低Ａｌ化のコントロール性が悪く、ステンレス溶鋼中のＡｌ濃度を極低Ａｌ濃度にすることができず、総合評価として悪い（×）結果となった。
【００１８】
以上、本発明の実施の形態を説明したが、本発明は、上記した形態に限定されるものでなく、要旨を逸脱しない条件の変更等は全て本発明の適用範囲である。
例えば、脱硫処理の際に添加するＡｌは、金属Ａｌの他に、Ｆｅ−Ａｌ、アルミドロス等のＡｌ合金を用いることができる。
更に、二次脱炭精錬炉としては、一般的に減圧精錬装置として用いられているＤＨ、ＲＨ、ＶＯＤ等を用いることができる。
【００１９】
【発明の効果】
請求項１記載のステンレス溶鋼の溶製方法においては、転炉型容器に溶銑とフェロクロム合金を装入し、溶銑とフェロクロム合金に上吹きランスを用いて吹酸し、溶銑とフェロクロム合金の溶解と一次脱炭精錬を行って粗溶鋼を溶製した後、取鍋に粗溶鋼を出鋼し、次いで、粗溶鋼を二次精錬炉を用いて二次脱炭精錬と脱酸処理を行うステンレス溶鋼の溶製方法において、吹酸による一次脱炭精錬を行った後に生成したスラグに、シリコンを含有する合金を添加してスラグを還元処理した後、粗溶鋼中のＡｌ濃度が０．０５〜０．２質量％になるようにＡｌを添加して脱硫処理を行ってから取鍋に出鋼し、引き続き行う二次精錬炉を用いた二次脱炭精錬における昇熱及び脱酸処理時にＡｌを添加しないで処理を行うので、ステンレス溶鋼のＡｌ濃度を低減し、脱硫を促進して、極低Ａｌ、低Ｓのステンレス溶鋼の溶製を低コストで工業的に安定して生産可能にする。しかも、脱炭精錬で発生したスラグ路盤材や土木埋め立て材等の資源として活用することができる。
【００２０】
特に、転炉型容器を用いた脱硫処理時のスラグの塩基度を１．３〜１．８、スラグ中のＡｌ₂Ｏ₃を３〜１０質量％にするので、極低Ａｌ、低Ｓのステンレス溶鋼を安定して溶製でき、しかも、遊離ＣａＯに起因する膨張を安定して抑制し、スラグの資源化を促進することができる。
【００２１】
また、還元処理を終了したスラグ中のＣｒ₂Ｏ₃濃度を５質量％以下にするので、高価なＣｒを還元して粗溶鋼中に回収でき、合金鉄コストを低減することができる。
【００２２】
更に、還元処理及び脱硫処理時の粗溶鋼の温度を１５５０℃以上、１７００℃未満とするので、スラグの滓化を促進し、脱硫反応を促進し、低Ｓのステンレス粗溶鋼を容易に溶製することができ、滓化が促進されてスラグ中の遊離ＣａＯを抑制してスラグを安定して資源として活用することができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係るステンレス溶鋼の溶製方法による処理の流れを示す説明図である。
【符号の説明】
１０：上底吹き転炉（転炉型容器）、１１：炉体、１２：炉口、１３：吹酸ランス、１４ａ：スラグ、１４ｂ：スラグ、１４ｃ：スラグ、１５ａ：ステンレス粗溶鋼、１５ｂ：ステンレス粗溶鋼、１５ｃ：ステンレス溶鋼、１６：底吹きノズル、１７：出鋼口、１８：ホッパ、１９：シュート、２０：ポーラスプラグ、２１：取鍋、３０：減圧取鍋精錬炉（二次精錬炉）、３１：吹酸ランス、３２：減圧ダクト、３３：シュート、３４：遮断弁、３５：貯蔵ホッパ、３６：減圧フード[0001]
BACKGROUND OF THE INVENTION
In the present invention, after reduction of Cr in slag produced by primary decarburization refining using a converter-type refining vessel with an Si-containing alloy, Al is added to desulfurize, and then secondary decarburization refining is performed. Further, the present invention relates to a method for producing a molten stainless steel in which a very low Al, low S molten stainless steel is produced by adding no Al.
[0002]
[Prior art]
Conventionally, stainless steel sheets produced by rolling stainless steel with molten iron containing chromium or nickel into continuous slabs and then rolling the slabs are excellent in corrosion resistance and gloss. It is often used for oil well pipes and building materials.
The properties of this stainless steel sheet, such as corrosion resistance and toughness, are due to the formation of coarse oxide inclusions caused by aluminum (Al) contained in the molten stainless steel when the molten stainless steel is melted using a refining furnace. Since sulfide is formed, there is a problem that the corrosion resistance of the stainless steel plate is deteriorated and the toughness of the stainless steel plate is lowered.
As a countermeasure, a-carbon with 0.005 to 0.1 wt%, chromium (Cr) 12 to 16 wt%, 0.005 wt% of Al, 0.015 mass sulfur (S) A stainless steel plate that contains 50 % is proposed. By using this steel plate, a coarse inclusion that is a product of Al deoxidation is suppressed, and corrosion and corrosion cracking due to sulfide are prevented. Has been done.
[0003]
[Problems to be solved by the invention]
However , when melting molten stainless steel with the above composition, during the refining process, the Al concentration of the molten stainless steel is reduced and the desulfurization is promoted by using the same converter type refining furnace to produce a very low Al and low S concentration stainless molten steel. There is a problem that it cannot be melted easily, and the reduction and recovery efficiency of chromium oxide (Cr ₂ O ₃ ) in the slag generated during refining is low, and the generated slag cannot be recycled. is there.
[0004]
The present invention has been made in view of such circumstances, and facilitates the melting of stainless steel with extremely low Al and low S by reducing the Al concentration of stainless steel and promoting desulfurization, and the Cr ₂ O ₃ concentration in the slag. An object of the present invention is to provide a method for producing molten stainless steel that reduces the amount of slag and enables the generation of slag resources.
[0005]
[Means for Solving the Problems]
The method for melting stainless steel according to the present invention in accordance with the above-described object is to insert hot metal and a ferrochrome alloy into a converter type vessel, and blown acid into the hot metal and the ferrochrome alloy using an upper blowing lance, and the hot metal and ferrochrome. After melting the alloy and performing primary decarburization and refining the crude molten steel, the crude molten steel is put out into a ladle, and then the crude molten steel is subjected to secondary decarburization refining and desorption using a secondary refining furnace. In the smelting method of molten stainless steel that performs acid treatment, an alloy containing silicon is added to the slag generated after the primary decarburization refining with the blowing acid , and the Cr ₂ O ₃ concentration in the slag is 5 After reducing the slag so as to be less than or equal to mass% , Al is added so that the Al concentration in the crude molten steel is 0.05 to 0.2 mass%, and the basicity of the slag is 1.3. -1.8, ₃ to 10 Al ₂ O ₃ in the slag And the mass% and that tapped into the ladle after performing desulfurization treatment, the reducing treatment and the temperature of the crude molten steel during the desulfurization process is less than 1550 ° C. or higher 1700 ° C., subsequently performing secondary refining The treatment is performed without adding Al during the heating and deoxidation treatment in the secondary decarburization refining using a furnace.
By this method, Cr ₂ O ₃ contained in the slag generated during the primary decarburization refining by the converter type vessel can be reduced with a reducing agent containing silicon, and Cr can be recovered in the crude molten steel. Since the desulfurization treatment is performed at an Al concentration of 0.05 to 0.2 % by mass , the oxygen potential can be lowered to promote desulfurization.
Furthermore, if Al heating is performed during the heat-up period of secondary decarburization refining, the concentration of Al ₂ O ₃ in the slag increases, and a slight amount of Al ₂ O ₃ in the slag, for example, other than Si alloy By the deoxidizer, the Al concentration in the molten steel is increased and cannot be made extremely low Al. Therefore, by not adding Al in the heat-up process performed in the secondary decarburization refining in the secondary refining furnace and the deoxidation treatment performed after the secondary decarburization refining, the Al content of the final stainless steel melt is extremely low. Al and low S can be achieved.
When the Al concentration is less than 0.05 % by mass , the oxygen potential in the slag is increased, the desulfurization reaction is deteriorated, and the ultimate S concentration is increased. On the other hand, if the Al concentration exceeds 0.2 % by mass , the effect of desulfurization becomes saturated, and even if Al is added more than this, the alloy cost only rises. The Al ₂ O ₃ concentration of the steel becomes high, and it becomes difficult to produce molten steel with an extremely low Al concentration.
[0006]
Here, by the slag salts Motodo during desulfurization 1.3-1.8, and the Al ₂ O ₃ in the slag 3-10 wt% or less with the converter-type vessel, the slag In addition, the desulfurization ability of the slag can be increased, and the production of free CaO can be suppressed to prevent the expansion of the slag, thereby making it possible to recycle the slag.
If the basicity of the slag is less than 1.3, the desulfurization ability of the slag is lowered and the desulfurization reaction becomes worse. On the other hand, when the basicity of the slag exceeds 1.8, free CaO is generated along with the increase in basicity, the expansion of the slag is large, and hatching defects tend to occur.
On the other hand, when the Al ₂ O ₃ concentration in the slag exceeds 10 % by mass , the desulfurization ability of the slag is lowered and the desulfurization reaction is deteriorated. The lower limit of the Al ₂ O ₃ concentration in the slag is 3 % by mass in order to promote hatching of the slag and improve the desulfurization reaction.
[0007]
Furthermore, the reduction treatment More and child the Cr ₂ O ₃ concentration in the slag ended 5 wt% or less, can be recovered in a reduced crude molten steel expensive Cr contained in slag, ferroalloys Cost can be reduced.
When the Cr ₂ O ₃ concentration in the slag exceeds 5 % by mass , the Al added in the desulfurization process is consumed for the reduction of Cr ₂ O ₃ , and the oxygen potential in the slag is insufficiently reduced, resulting in a decrease in the desulfurization reaction. To do.
[0008]
Further, the reduction treatment and the temperature of the crude molten steel during the desulfurization process 1550 ° C. or higher, more and child and less than 1700 ° C., to promote the slag formation of the slag and promote the desulfurization reaction, a low S Stainless crude Molten steel can be easily produced.
If the temperature of the crude molten steel during the reduction treatment and the desulfurization treatment is lower than 1550 ° C., it takes a long time to hatch the slag, and the desulfurization reaction becomes disadvantageous. On the other hand, when the temperature of the crude molten steel is 1700 ° C. or higher, the temperature becomes too high, the melting loss of the refractory in the smelting furnace increases, and the refractory cost increases.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
FIG. 1 is an explanatory view showing a flow of processing by a method for melting molten stainless steel according to an embodiment of the present invention.
As shown in FIG. 1, the decarburization and refining treatment of molten stainless steel by the method for melting stainless steel according to an embodiment of the present invention is an upper bottom blow rolling that is an example of a converter type vessel used for primary decarburization refining. A furnace 10 and a reduced pressure ladle refining furnace 30 which is an example of a secondary refining furnace used for secondary decarburization refining are used.
The top-bottom blowing converter 10 includes a furnace body 11 in which molten iron and a ferrochrome alloy are placed, a blown acid lance 13 that is disposed so as to be movable up and down above the furnace port 12 and blows oxygen to the molten iron and ferrochrome alloy, and a bottom portion of the furnace body 11. A bottom blowing nozzle 16 that stirs slag 14a and coarse molten steel (also referred to as stainless coarse molten steel) 15a by blowing argon gas, which is an example of an inert gas, and a steel outlet 17 on the upper side of the furnace body 11. Yes. Furthermore, a hopper 18 that stores CaO, ferrosilicon (Fe—Si), Al, and the like, which are examples of auxiliary materials, above the furnace port 12, a chute 19 disposed below the hopper 18, and a slag that has undergone desulfurization treatment There is provided a ladle 21 having a porous plug 20 for receiving a stainless crude molten steel 15b made by melting 14b remaining in the furnace and blowing an inert gas at the bottom.
[0010]
The reduced pressure ladle refining furnace 30 uses the ladle 21 that has received the stainless coarse molten steel 15b melted in the top bottom blowing converter 10 as it is, and the reduced pressure hood 36 that covers the ladle 21 and the reduced pressure hood 36 are provided. A blown acid lance 31 that passes through and communicates with the inside, a decompression duct 32 that communicates with an ejector (not shown), and a chute 33 that is connected to a storage hopper 35 such as CaO or iron alloy having a shut-off valve 34 in the middle. ing.
[0011]
Next, a method for melting stainless steel molten steel according to the present invention will be described using the top-bottom blow converter 10 and the reduced pressure ladle refining furnace 30.
Molten iron and a ferrochrome alloy are charged into the furnace from the furnace port 12 of the top-bottom blowing converter 10, and the blown acid lance (upper blowing lance) 13 is lowered into the furnace from the furnace port 12 to 15000 to 25000 Nm ³ / (hour At the same time, CaO is added from the hopper 18, and primary decarburization refining with the blowing acid from the blowing acid lance 13 is performed.
In this primary decarburization refining, the ferrochrome alloy is rapidly dissolved by the heating by blown acid, and further, so-called decarburization reaction in which oxygen and carbon react is promoted, and the carbon concentration is 0.3 to 0.8 mass%. The stainless coarse molten steel 15a having a temperature of 1550 ° C. or higher and lower than 1700 ° C. is melted.
During this primary decarburization refining, added CaO, hot metal, silicon (Si), Al, etc. contained in the ferrochrome alloy are oxidized to form slag 14a.
Since this slag 14a contains a large amount of Cr ₂ O ₃ in which Cr in the ferrochrome alloy is oxidized at the time of blowing acid for primary decarburization refining, an Fe—Si alloy, which is an example of an alloy containing silicon, is taken from the hopper 18. Then, argon gas is blown into the stainless coarse molten steel 15a from the bottom blowing nozzle 16, and the slag 14a and the stainless coarse molten steel 15a are stirred to reduce Cr ₂ O ₃ .
This reduction treatment is performed until the Cr ₂ O ₃ concentration in the slag 14a becomes 5 % by mass or less.
Then, after the reduction process is completed, in a state in which the argon gas is continuously blown from the bottom blowing nozzle 16, the metal Al, which is an example of Al, has an Al concentration of 0.05 to 0.2 from the hopper 18 through the chute 19. It adds so that it may become mass%, and the slag 14a and the stainless coarse molten steel 15a are stirred and a desulfurization process is performed.
Immediately before the desulfurization treatment, the slag 14a is sampled and analyzed in advance, so that the basicity (CaO / SiO ₂ ) of the slag 14a is 1.3 to 1.8, and Al ₂ O ₃ is 10 % by mass or less. The amount of CaO added to the furnace through the chute 19 and the amount of metal Al are adjusted.
[0012]
In the reduction treatment using the top-bottom blow converter 10, the temperature of the stainless steel coarse molten steel 15a and the slag 14a is set to 1550 ° C. or higher and lower than 1700 ° C., and argon gas is blown from the bottom blowing nozzle 16 and stirred. Since the alloy is added, hatching of the slag 14a is improved, and the reduction reaction of Cr ₂ O ₃ in the slag 14a is promoted.
The reduced Cr is recovered in the stainless coarsely molten steel 15a, and the Cr ₂ O ₃ concentration remaining in the slag 14a can be reduced to 5 % by mass ( % by mass in terms of Cr) or less.
In the desulfurization treatment performed after the reduction treatment, metal Al is added to the stainless crude molten steel 15a to make the concentration 0.05 to 0.2 % by mass , so that the oxygen potential in the slag 14a is sufficiently reduced, and the temperature is increased. Since 1550 ° C. or more and less than 1700 ° C. and argon gas is blown from the bottom blowing nozzle 16 and stirred, the desulfurization reaction is promoted and the ultimate S concentration can be lowered.
Furthermore, since the concentration of Cr ₂ O ₃ in the slag 14a is 5 % by mass or less, the added metal Al reduces the consumption due to the oxidation reaction with Cr ₂ O ₃ , and Al ₂ in the slag 14a. The increase in O ₃ can be suppressed, the oxygen potential in the slag 14a can be reduced efficiently, and the desulfurization reaction can be promoted stably.
The stainless steel crude molten steel 15b subjected to the reduction treatment and the desulfurization treatment has a low S concentration of 0.0005 to 0.001 % by mass due to the desulfurization treatment. The steel is put into the pot 21 and moved to a processing place by the reduced pressure ladle refining furnace 30 by a conveying means (not shown).
The slag 14b has a residual Cr ₂ O ₃ concentration of 5 % by mass or less, CaO / SiO ₂ of 1.3 to 1.8, and Al ₂ O _{3 of 3} to 10 % by mass . As described above, the waste is discharged from a furnace port 12 to a discharge pot (not shown), and is effectively used as a resource such as a roadbed material and a civil engineering landfill after processing such as cooling and crushing.
[0013]
Next, in the pressure reduction ladle refining furnace 30, the pressure reduction hood 36 is placed on the ladle 21 containing the stainless steel coarse molten steel 15b, the shut-off valve 34 of the chute 33 is opened, and the storage hopper 35 transfers CaO or the like. The auxiliary raw material is taken into the ladle 21, the blowing acid lance 31 is lowered to start blowing acid, and at the same time, the ejector is operated to depressurize the ladle 21 from the decompression duct 32 to 100 to 0.2 torr. Then, the temperature was raised and secondary decarburization refining was performed until the carbon concentration became 0.01 to 0.05 mass% .
After the completion of the secondary decarburization refining, the stainless crude molten steel 15b was deoxidized without adding Al.
[0014]
When metal Al is added by the desulfurization treatment by blowing oxygen from the blown acid lance 31, the slag 14c generated by secondary decarburization refining is ensured by oxidizing Al added to the molten stainless steel crude molten steel 15b. the absorbed as Al ₂ O _3, further uses no Al in deoxidation treatment can prevent the addition of Al to the stainless molten steel 15c. Furthermore, the Al remaining in the stainless crude molten steel 15b is oxidized during the secondary decarburization refining using the reduced pressure ladle refining furnace 30 to become Al ₂ O ₃ , and the amount of Al ₂ O ₃ produced is extremely small. Therefore, the Al ₂ O ₃ concentration in the composition of the slag 14c does not change as much as the difference, and there is an advantage that the Al ₂ O ₃ in the slag 14c is not reduced during the deoxidation treatment. 0.001 to 0.002 mass% of ultra-low Al molten stainless steel 15c could be produced.
Then, the molten stainless steel 15c having a carbon concentration of 0.01 to 0.05 mass% , extremely low Al, and low S concentration is formed into a slab using continuous casting or the like, cut into a predetermined size, and processed such as rolling. It is applied to produce steel plates, mold steels and the like.
[0015]
【Example】
Next, the Example of the melting method of the molten stainless steel based on this invention is described.
The top bottom blowing converter (converter type vessel) is charged with hot metal and Fe-Cr, the blown acid lance is lowered into the furnace, oxygen is blown, and the heat treatment is performed, and the carbon concentration is 0.3-0. Primary decarburization refining was performed until 8 mass% , and stainless steel was melted.
In addition, when melting stainless steel, the Al concentration at the time of desulfurization and slag composition (CaO / SiO ₂ , Al ₂ O ₃ concentration), the Cr ₂ O ₃ concentration at the end of the reduction treatment, Reduction treatment and desulfurization treatment were performed while changing the temperature. And we investigated S distribution at the time of desulfurization ((% S) / [% S]), controllability of extremely low Al at the time of secondary refining, converter refractory erosion status, recycling of slag after desulfurization, and comprehensive evaluation. . The results are shown in Table 1.
In Examples 1 and 2, the Al concentration at the time of converter desulfurization, the slag composition at the time of converter desulfurization, the Cr ₂ O ₃ concentration at the end of the reduction treatment, and the temperature at the time of reduction desulfurization treatment all fall within the scope of the present invention. In this case, the S distribution during desulfurization can be increased to 550 and 670, respectively, the control of ultra-low Al during secondary refining is good, the refractory refractory melt damage can be reduced, and slag can be recycled after desulfurization. Thus, a good (◯) result was obtained as a comprehensive evaluation.
Example 3 is the case where the Al concentration at the time of converter desulfurization is 0.05 % by mass which is the lower limit, and Example 4 is the case where the Al concentration at the time of converter desulfurization is 0.20 % by mass which is the upper limit. , S distribution during desulfurization can be increased to 420 and 570, respectively, and the controllability of ultra-low Al during secondary refining is good, converter refractory melting damage can be reduced, and slag can be recycled after desulfurization. Good (◯) results were obtained for evaluation.
In Example 5, the slag composition at the time of converter desulfurization (CaO / SiO ₂ ) is 1.3, which is the lower limit, and in Example 6, the slag composition at the time of converter desulfurization (CaO / SiO ₂ ) is the upper limit. 8 and S distribution during desulfurization can be set to 320 and 750, respectively, and the control of ultra-low Al during secondary refining is good, converter refractory refractory erosion can be reduced, and slag can be recycled after desulfurization. As a result, a good (○) result was obtained as a comprehensive evaluation.
In Example 7, the slag composition (Al ₂ O ₃ concentration) at the time of converter desulfurization was 10 % by mass , and in Example 8, the slag composition (Al ₂ O ₃ concentration) at the time of converter desulfurization was 4.9 masses. % , S distribution during desulfurization can be set to 430 and 410, respectively, and control of extremely low Al during secondary refining is good, converter refractory refractory melting damage can be reduced, and slag can be recycled after desulfurization As a result, a good (○) result was obtained as a comprehensive evaluation.
In Example 9, the temperature during reductive desulfurization treatment is 1550 ° C., and in Example 10, the temperature during reductive desulfurization treatment is 1699 ° C., and the S distribution during desulfurization can be set to 330 and 640, respectively. The control of the ultra-low Al at the time of the next refining is also good, the refractory melting of the converter refractory can be reduced, and the slag can be recycled after desulfurization.
[0016]
[Table 1]

[0017]
On the other hand, Comparative Example 1 is a case where the Al concentration during converter desulfurization is as low as 0.02 % by mass , and the S distribution during desulfurization is extremely low (30). The load of charcoal refining increased, and the overall evaluation was bad (×).
Comparative Example 2 is a case where the Al concentration at the time of converter desulfurization was as high as 0.32 % by mass , and the controllability of ultra-low Al during secondary refining was poor, and the Al concentration in the molten stainless steel was very low Al. The concentration could not be achieved, and the result was poor (×) as a comprehensive evaluation.
[0018]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and all changes in conditions and the like that do not depart from the gist are within the scope of the present invention.
For example, as the Al added during the desulfurization treatment, an Al alloy such as Fe—Al or aluminum dross can be used in addition to the metal Al.
Furthermore, as the secondary decarburization refining furnace, DH, RH, VOD or the like generally used as a vacuum refining apparatus can be used.
[0019]
【The invention's effect】
In the melting method of claim 1 Symbol placement of stainless molten steel was charged with converter type vessel hot metal and ferrochromium alloy, and吹酸with lance above the hot metal and ferrochromium alloys, dissolution of the molten iron and ferrochromium alloy And first decarburization refining to melt the crude molten steel, then the crude molten steel is taken out to the ladle, and then the crude molten steel is subjected to secondary decarburization refining and deoxidation treatment using a secondary refining furnace In the molten steel smelting method, an alloy containing silicon is added to the slag generated after primary decarburization refining with blown acid, and after the slag is reduced, the Al concentration in the crude molten steel is 0.05 to After adding desulfurization treatment to add 0.2 % by mass , the steel is taken out in a ladle and subsequently subjected to heating and deoxidation treatment in secondary decarburization refining using a secondary refining furnace. Since the treatment is performed without adding A, stainless steel A Reduced concentration, to promote desulfurization, very low Al, to industrially stably can produce ingot of low S stainless molten steel at low cost. In addition, it can be used as resources such as slag roadbed material and civil engineering landfill material generated by decarburization refining.
[0020]
In particular, the slag salt Motodo during desulfurization process using a converter type vessel 1.3-1.8, since it the Al ₂ O ₃ in the slag 3-10 wt%, very low Al, low S In addition, it is possible to stably melt molten stainless steel, and it is possible to stably suppress expansion caused by free CaO and promote resource utilization of slag.
[0021]
Further , since the Cr ₂ O ₃ concentration in the slag after the reduction treatment is set to 5 % by mass or less, expensive Cr can be reduced and recovered in the crude molten steel, and the iron alloy cost can be reduced.
[0022]
Furthermore , since the temperature of the crude molten steel at the time of the reduction treatment and the desulfurization treatment is set to 1550 ° C. or higher and lower than 1700 ° C., the hatching of slag is promoted, the desulfurization reaction is promoted, and the low-S stainless coarse molten steel is easily produced. The hatching is promoted and free CaO in the slag is suppressed, and the slag can be stably utilized as a resource.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram showing a flow of processing by a method for melting molten stainless steel according to an embodiment of the present invention.
[Explanation of symbols]
10: Top-bottom blowing converter (converter type vessel), 11: Furnace body, 12: Furnace port, 13: Blown acid lance, 14a: Slag, 14b: Slag, 14c: Slag, 15a: Stainless steel coarse molten steel, 15b: Stainless steel coarse molten steel, 15c: Stainless steel molten steel, 16: Bottom blowing nozzle, 17: Steel outlet, 18: Hopper, 19: Chute, 20: Porous plug, 21: Ladle, 30: Vacuum ladle refining furnace (secondary refining Furnace), 31: blown acid lance, 32: decompression duct, 33: chute, 34: shutoff valve, 35: storage hopper, 36: decompression hood

Claims

転炉型容器に溶銑とフェロクロム合金を装入し、前記溶銑とフェロクロム合金に上吹きランスを用いて吹酸し、前記溶銑とフェロクロム合金の溶解と一次脱炭精錬を行って粗溶鋼を溶製した後、取鍋に前記粗溶鋼を出鋼し、次いで、前記粗溶鋼を二次精錬炉を用いて二次脱炭精錬と脱酸処理を行うステンレス溶鋼の溶製方法において、
前記吹酸による前記一次脱炭精錬を行った後に生成したスラグに、シリコンを含有する合金を添加して該スラグ中のＣｒ ₂ Ｏ ₃ 濃度が５質量％以下となるように前記スラグを還元処理した後、前記粗溶鋼中のＡｌ濃度が０．０５〜０．２質量％になるようにＡｌを添加し、前記スラグの塩基度を１．３〜１．８、前記スラグ中のＡｌ ₂ Ｏ ₃ を３〜１０質量％として脱硫処理を行ってから前記取鍋に出鋼することとし、前記還元処理及び前記脱硫処理時の前記粗溶鋼の温度を１５５０℃以上１７００℃未満とし、引き続き行う前記二次精錬炉を用いた二次脱炭精錬における昇熱及び脱酸処理時にＡｌを添加しないことを特徴とするステンレス溶鋼の溶製方法。Hot metal and ferrochrome alloy are charged into a converter-type vessel, and the hot metal and ferrochrome alloy are blown using a top lance, and the molten iron and ferrochrome alloy are melted and primary decarburization refining to produce crude molten steel. Then, in the smelting method of molten stainless steel, the crude molten steel is taken out in a ladle, and then the crude molten steel is subjected to secondary decarburization refining and deoxidation treatment using a secondary refining furnace,
An alloy containing silicon is added to the slag produced after the primary decarburization refining with the blowing acid, and the slag is reduced so that the Cr ₂ O ₃ concentration in the slag is 5% by mass or less. Then, Al is added so that the Al concentration in the crude molten steel is 0.05 to 0.2 % by mass , the basicity of the slag is 1.3 to 1.8, and Al ₂ O in the slag is added. ₃ and 3-10 wt% and that tapped into the ladle after performing desulfurization treatment, and the reduction treatment and the desulfurization treatment the crude molten steel temperature 1550 ° C. or higher 1700 below ° C. of at continued A method for producing a molten stainless steel, characterized in that Al is not added during heating and deoxidation treatment in secondary decarburization refining using the secondary refining furnace.