JP2004010935A

JP2004010935A - Manufacturing method of molten steel

Info

Publication number: JP2004010935A
Application number: JP2002163806A
Authority: JP
Inventors: Yoshiteru Kikuchi; 菊地　良輝; Fumihiro Washimi; 鷲見　郁宏; Eiju Matsuno; 松野　英寿
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2002-06-05
Filing date: 2002-06-05
Publication date: 2004-01-15
Anticipated expiration: 2022-06-05
Also published as: JP4192503B2

Abstract

【課題】転炉精錬工程において鉄やマンガン等の有価成分のスラグへの損失量を抑制することができると共に、その後の工程で添加される脱酸剤や合金剤の酸化ロスを少なくすることのできる溶鋼の製造方法を提供する。
【解決手段】高炉から出銑された溶銑を予備脱燐処理した後に転炉１にて脱炭精錬して溶鋼を製造する溶鋼の製造方法において、前記予備脱燐処理では、溶銑中の燐濃度を鋼材製品の燐濃度レベルまで低減し、転炉脱炭精錬では、処理溶銑トン当たり２０ｋｇ以下のスラグ量で精錬すると共に、脱炭精錬の後半でＣａＯ源と炭材及び脱酸剤のうちの一種以上とからなる造滓剤７を添加してスラグ６を還元し、脱炭精錬終点の溶鋼中酸素濃度を３００ｐｐｍ以下とする。
【選択図】　　　　　　図１An object of the present invention is to reduce loss of valuable components such as iron and manganese to slag in a converter refining process, and to reduce oxidation loss of a deoxidizing agent and an alloying agent added in a subsequent process. The present invention provides a method for producing molten steel.
Kind Code: A1 Abstract: In a method for producing molten steel, a molten iron produced from a blast furnace is preliminarily dephosphorized and then decarburized and refined in a converter 1 to produce molten steel. In the converter decarburization refining, the refining is carried out with a slag amount of 20 kg or less per ton of treated hot metal, and in the latter half of the decarburizing refining, The slag 6 is reduced by adding one or more kinds of slag-making agents 7, and the oxygen concentration in the molten steel at the end point of the decarburization refining is set to 300 ppm or less.
[Selection diagram] Fig. 1

Description

【０００１】
【発明の属する技術分野】
本発明は、高炉から出銑された溶銑を用い、この溶銑中の不純物成分を除去して鋼材製品の要求する溶鋼を製造する方法に関するものである。
【０００２】
【従来の技術】
高炉で製造された溶銑から鋼材製品を製造するには、製鋼精錬工程を経る必要がある。この製鋼精錬工程では、溶銑に含まれる不純物成分を除去した上で、鋼材製品の材料特性上要求される組成への調整が行われる。溶銑に含まれる不純物成分としては、４ｍａｓｓ％以上含有される炭素の他、燐、硫黄等があり、又、鋼材製品の要求成分としては、強度や靭性を高めるマンガンや珪素等がある。
【０００３】
炭素や燐の不純物成分を除去するために、溶銑を転炉に装入し、この溶銑に大量の酸素を供給して不純物成分を酸化除去する酸化精錬が行われる。この酸化精錬においては脱炭反応や脱燐反応に伴って鉄も酸化され、酸化鉄を大量に含有するスラグが生成されるため、生成したスラグのみならず溶鋼の酸化度も高くなる。その結果、転炉炉内では鉄やマンガン等の有価成分のスラグへの損失量が多くなる上に、その後の工程で添加される脱酸剤や合金剤の酸化ロスも多くなり、脱酸剤や合金剤の歩留まり低下の原因になっている。
【０００４】
それ故、スラグの酸化度を上昇させないようにするため、脱炭精錬終期の送酸速度を減少させることが行われてきたが、送酸速度を下げると酸素ジェットによる攪拌効率も下がるのでスラグの酸化度を下げる効果に限界があり、更に、送酸速度を下げることによる排ガス回収効率の低下や吹錬時間の延長と云った新たな問題が発生する。
【０００５】
又、炭素及び燐を同時に除去していた従来の転炉精錬方法に対し、最近は燐を事前の溶銑段階で除去（予備脱燐処理）することが行われている。その結果、転炉における脱炭精錬工程では、脱燐のための媒溶剤は不要となり、少ないスラグ量で吹錬することが可能になった。しかし、転炉脱炭精錬終点での鉄やマンガン歩留を高くするためには、反応原理からスラグとメタル（溶鋼）とでの分配比率を大きくすることが必要であり、単にスラグ量を低減しただけでは、転炉内における鉄やマンガンの損失量を減少させること、並びに、その後の工程における脱酸剤や合金剤の酸化ロスを減少させることは自ずと限界があった。
【０００６】
更に、スラグの酸素ポテンシャルを低下するために、吹錬中にコークス等の炭材を炉内に投入・添加することが従来から提案されているが、部分的にはメタル中の酸素やスラグ中の酸素と反応するものの、効率的にメタル中の溶解酸素やスラグ中の酸化鉄を下げるまでには至らなかった。この場合、スラグとの接触反応界面積を増加させ、効率を高めるために炭材を細かくしなけらばならず、効率的な添加が難しいことも問題であった。又、炭材に含まれる窒素や硫黄が鋼材の成分に悪影響を来すこともあり、添加量も限られる。このようなことから、炭材は操業を安定化させるためのスラグフォーミングに用いられるのが主体であり、炭材添加によりスラグ中の鉄やマンガン酸化物を還元するには限界があった。
【０００７】
【発明が解決しようとする課題】
本発明は上記事情に鑑みなされたもので、その目的とするところは、転炉精錬工程において鉄やマンガン等の有価成分のスラグへの損失量を抑制することができると共に、その後の工程で添加される脱酸剤や合金剤の酸化ロスを少なくすることのできる溶鋼の製造方法を提供することである。
【０００８】
【課題を解決するための手段】
上記課題を解決するための本願第１の発明に係る溶鋼の製造方法は、高炉から出銑された溶銑を予備脱燐処理した後に転炉にて脱炭精錬して溶鋼を製造する溶鋼の製造方法において、前記予備脱燐処理では、溶銑中の燐濃度を鋼材製品の燐濃度レベルまで低減し、転炉脱炭精錬では、処理溶銑トン当たり２０ｋｇ以下のスラグ量で精錬すると共に、脱炭精錬の後半でＣａＯ源と炭材及び脱酸剤のうちの一種以上とからなる造滓剤を添加してスラグを還元し、脱炭精錬終点の溶鋼中酸素濃度を３００ｐｐｍ以下とすることを特徴とする。
【０００９】
第２の発明に係る溶鋼の製造方法は、第１の発明において、前記予備脱燐処理後の溶銑中燐濃度を０．０２ｍａｓｓ％以下とすることを特徴とし、第３の発明に係る溶鋼の製造方法は、第１の発明又は第２の発明において、前記転炉脱炭精錬におけるスラグ量を処理溶銑トン当たり１０ｋｇ以下とすることを特徴とし、第４の発明に係る溶鋼の製造方法は、第１の発明ないし第３の発明の何れかにおいて、前記造滓剤の一部又は全部を上吹きランス或いは浴面下の羽口を通じて添加することを特徴とし、第５の発明に係る溶鋼の製造方法は、第１の発明ないし第４の発明の何れかにおいて、前記ＣａＯ源を生石灰、石灰石、焼成ドロマイト、未焼成ドロマイトのうちの一種以上とすることを特徴とする。
【００１０】
又、第６の発明に係る溶鋼の製造方法は、第１の発明ないし第５の発明の何れかにおいて、前記炭材を土壌黒鉛、人造黒鉛、プラスチックの製造工程或いは加工工程で発生するプラスチック廃材、プラスチック製品の使用後発生する廃棄プラスチックのうちの一種以上とすることを特徴とし、第７の発明に係る溶鋼の製造方法は、第１の発明ないし第６の発明の何れかにおいて、前記脱酸剤をアルミドロス、アルミニウム、鉄−珪素合金、金属珪素、珪素合金のうちの一種以上とすることを特徴とし、第８の発明に係る溶鋼の製造方法は、第１の発明ないし第７の発明の何れかにおいて、前記造滓剤のＣａＯ源の割合を、１０ｍａｓｓ％から９０ｍａｓｓ％とすることを特徴とし、第９の発明に係る溶鋼の製造方法は、第１の発明ないし第８の発明の何れかにおいて、前記脱炭精錬終点における溶鋼中酸素濃度と溶鋼中炭素濃度とで計算されるＣＯ分圧を０．７以下とすることを特徴とする。
【００１１】
本発明では、転炉脱炭精錬の後半でＣａＯ源と炭材及び脱酸剤のうちの一種以上とからなる造滓剤を添加する。造滓剤中の炭材及び脱酸剤は、メタル中の溶解酸素やスラグ中の酸化鉄或いはマンガン酸化物等との反応に消費される。同時に添加されるＣａＯによるスラグ脱酸がＣＯ生成反応に優先して進行し、溶解酸素との平衡関係を更に改善する方向及び維持する方向に作用するので、溶融メタル中の酸素濃度の低減化、並びに、スラグ中の酸化鉄含有量の低減化を安定して達成することができる。炭材や脱酸剤のみの添加では、溶解酸素やスラグ中酸化鉄の一時的な低減は可能なものの安定化は困難であるが、ＣａＯ源を同時に添加することにより安定化が達成される。
【００１２】
【発明の実施の形態】
以下、本発明の実施の形態を説明する。高炉から出銑された溶銑は高炉鋳床を経由して溶銑鍋に注湯され、溶銑鍋内に貯留される。この溶銑鍋を脱燐処理場まで搬送し、溶銑の予備脱燐処理を施す。
【００１３】
酸素ガス等の気体酸素源及び鉄鉱石やミルスケール等の固体酸素源を溶銑に供給して溶銑の予備脱燐処理を行い、予備脱燐処理後の溶銑中燐濃度を鋼材製品の燐濃度レベルまで、具体的には０．０３０ｍａｓｓ％以下まで低減する。
【００１４】
この予備脱燐処理では、溶銑のガス攪拌等を付与し更に生石灰等によりＣａＯ分を添加して処理される。この予備脱燐処理は、溶銑鍋のみならず、酸素源や副原料の添加及び溶銑の攪拌機能を備えた設備ならば行うことができ、例えば、溶銑鍋と同様な溶銑搬送容器であるトーピードカーでも当然良く、又、転炉等の脱燐専用の容器に移し替えて行っても良い。脱燐処理時、スラグの過酸化を防止するために適正な攪拌を行う必要があり、一般にはガス攪拌が行われる。
【００１５】
特に、安定して脱燐処理を行うには、スラグ量を極力少なくする必要があり、少ないスラグ量でも十分に脱燐させるため、脱燐能の高いスラグを生成する必要がある。これには、スラグの塩基度（ＣａＯ／ＳｉＯ_２）を高めることが効果的であり、スラグの塩基度を高める観点から事前に溶銑中の珪素を除去（「脱珪処理」という）しておくことが好ましい。事前に溶銑中珪素濃度を０．２ｍａｓｓ％以下まで脱珪しておけば、少ないＣａＯの添加でスラグの塩基度を３以上に高めることができる。予備脱燐処理後、生成したスラグを溶銑鍋から取り除き、溶銑を次工程の転炉脱炭精錬に供する。
【００１６】
尚、次工程の転炉脱燐精錬におけるスラグ量を少なくするためには、予備脱燐処理後の溶銑中燐濃度を下げるほど望ましく、この観点から、予備脱燐処理後の溶銑中燐濃度が０．０２ｍａｓｓ％以下となるまで脱燐処理することが好ましい。溶銑の燐濃度が０．０２ｍａｓｓ％以下であれば、製品の燐規格にもよるが、転炉脱炭精錬における媒溶剤の添加量を溶銑トン当たり５ないし１０ｋｇ（以下「ｋｇ／Ｔ」と記す）以下とし、生成スラグ量を１０ないし２０ｋｇ／Ｔ以下にすることができる。転炉脱炭精錬におけるスラグ量が少ないほど、鉄やマンガン等の有価成分のスラグへの損失量を抑制することができ、鉄やマンガンの歩留まりが向上する。
【００１７】
このようにして予備脱燐処理を施した溶銑を転炉内に装入し、上吹きランス等から酸素を供給して転炉脱炭精錬を行う。図１に、本発明による転炉脱炭精錬を実施する際に用いた転炉設備の１例を示す。図１において、１は転炉、２は上吹きランス、３は原料投入装置、４は底吹き羽口、５は溶銑、６はスラグ、７はＣａＯ源と炭材及び脱酸剤のうちの一種以上とからなる造滓剤である。図１に示すような酸素を上吹きして攪拌用ガスを底吹きする精錬方法を複合吹錬という。
【００１８】
上吹きランス２は、その中央部に粉体若しくは粒体の造滓剤７をＡｒ等の不活性ガスを搬送用ガスとして溶銑５に吹き付け投射するための通路と、その外側に酸素を溶銑５に吹き付けるための通路と、更にその外側に上吹きランス２を冷却するための冷却水が往復するための通路との四重管構造になっており、上吹きランス２から酸素を供給して脱炭精錬を行う。そして、この脱炭精錬の後半に、上吹きランス２又は原料投入装置３を介して造滓剤７を転炉１内に投入する。この場合、脱炭精錬の後半とは、酸素を供給する期間の中間点よりも後半部分の期間を意味する。粉状若しくは粒状の造滓剤７は、底吹き羽口４から吹き込むようにすることもできる。
【００１９】
この転炉脱炭精錬では、予め鋼材製品の燐濃度レベルまで予備脱燐処理を施しているので、酸素吹錬時に生成する酸化鉄の薄め剤として若しくは浴面からの粒滴の飛散や放熱を抑制するために少量のカバー用スラグ６は必要であるが、本発明における転炉脱炭精錬では脱燐反応の必要性がほとんどないため、スラグ６を形成する媒溶剤の量は、脱燐反応に規定されずにマンガン鉱石中の脈石等から持ち来される酸化珪素（ＳｉＯ_２）分の塩基度調整分のみの少量で良い。即ち、２０ｋｇ／Ｔ以下の少ないスラグ量で十分である。
【００２０】
前述したように、予備脱燐処理にて溶銑中燐濃度を０．０２ｍａｓｓ％以下まで脱燐しておけば、鋼材製品の燐濃度レベルまで燐濃度が低下しているので、スラグ６の脱燐能が不要であり、媒溶剤の添加は１０ｋｇ／Ｔ以下にでき、マンガン鉱石の使用量にもよるが、マンガン鉱石を添加しても生成スラグ量を２０ｋｇ／Ｔ以下にすることが可能である。又、スラグ組成の変動も問題ないため、炉内へのスラグ残留操業等で繰り返しスラグ６を使用し、新規に供給する媒溶剤をなくすることもできる。
【００２１】
転炉精錬工程では、上吹きランス２からの送酸により脱炭が進行し同時に酸化鉄も生成して溶湯温度が上昇する。酸素吹錬の前期から中期にかけては塩基度調整分の生石灰が媒溶剤として添加され、又、必要に応じて単体のマンガン鉱石が添加される。添加されたマンガン鉱石は溶融し、溶銑中炭素による還元が進行する。
【００２２】
吹錬中期から後期においては、溶銑５中の炭素の酸化速度に遅滞が見られると共に、スラグ６への酸化鉄の蓄積が始まる、このスラグ６の酸化度の上昇に応じてマンガンの還元も停止し、マンガンはメタルとスラグ６とに分配され、スラグ６中には、酸化鉄（ＦｅＯ）とマンガン酸化物（ＭｎＯ）が残留する。このような脱炭反応の進行と共にメタル中の溶解酸素は上昇し、溶銑５で数ｐｐｍから数十ｐｐｍであった酸素濃度が、脱炭精錬終点の低炭素溶鋼では数百ｐｐｍまでになる。
【００２３】
複合吹錬において、底吹きガス量や攪拌強度等によりメタル中炭素とメタル中酸素との関係は様々であるが、一般的には［ｍａｓｓ％Ｃ］×［ｍａｓｓ％Ｏ］の濃度積は、平衡状態における約０．００２３に対して０．８から１．２程度の範囲を示す。転炉精錬におけるこのようなメタル中酸素の挙動から、酸素濃度の上昇が開始する臨界炭素濃度以降で、造滓剤７を添加することが有効である。一般的には、臨界炭素濃度は０．２ｍａｓｓ％から０．５ｍａｓｓ％程度であり、吹錬中のこの濃度近傍以降に造滓剤７を添加することとする。酸素吹錬の終了間近或いは酸素吹錬終了後に添加することも可能である。
【００２４】
ＣａＯ源と、炭材及び脱酸剤の一種以上とからなる造滓剤７は、塊状まま或いは粒状・粉状のどちらでも用いることができる。添加方法は、原料投入装置３による上置き投入の他、上吹きランス２による投射法による添加もできる。造滓剤７は炭素やアルミニウム等の還元剤を含むので、搬送用ガスを用いて添加する場合にはＡｒ等の不活性ガスを搬送用ガスとして用いることが好ましい。造滓剤７の形態や添加法は、一種に限らず、同時に併用も可能である。
【００２５】
造滓剤７を構成する原料であるＣａＯ源としては、基本的には何でも使えるが、経済性を考え、通常転炉精錬で用いられる生石灰やＭｇＯ分を含む焼成ドロマイトを使うことが好ましい。石灰石や未焼成ドロマイトも炉内での吸熱を伴う脱炭酸化が操業に影響しない場合には問題なく使うことができる。
【００２６】
造滓剤７を構成する原料である炭材も基本的には何でも使えるが、経済性を考え、プラスチックの製造工程或いは加工工程で発生するプラスチック廃材や、含プラスチック製品を使用後発生する廃棄プラスチックを使うことが好ましい。後者の場合、含プラスチック製品中のプラスチック分以外の混入が好ましくない場合、事前に分別や粉砕による分離を行うことができる。石炭やコークスを用いることにより硫黄、窒素等の不純物が問題となる場合には、これらに替わって土壌黒鉛や人造黒鉛等を用いることができる。
【００２７】
造滓剤７を構成する原料である脱酸剤としては、強脱酸元素であるＡｌ成分を含有する、金属アルミニウムやアルミ合金若しくはアルミドロス等の低純度アルミニウム品を使うことが好ましい。その他、成分や経済性で問題なければ珪素やマグネシウム等の強脱酸元素及びその含有品を使うことができる。珪素含有金属としては金属珪素、鉄−珪素合金等がある。
【００２８】
造滓剤７を添加し、造滓剤７中のＣ、Ａｌ、Ｓｉ成分によりスラグ６中の酸化鉄（主にＦｅＯ）やマンガン酸化物を還元すると共に、溶鋼中の酸素を部分的に低下させる。更に、同時に添加されるＣａＯ分がスラグ６のＦｅＯや溶鋼の酸素に作用し効率的に脱酸を進行させることができる。炭材や脱酸剤のみの添加では、メタル中溶解酸素やスラグ中酸化鉄の一時的な低減は可能なものの安定化は困難であるが、ＣａＯ源を同時に添加することにより安定化が達成される。但し、ＣａＯ源添加による安定化を効率的に進行させるには、炭材及び脱酸剤の反応サイト近傍へのＣａＯ源の添加や、ＣａＯ源自体を微粉化することが好ましく、従って、炭材及び脱酸剤と混合したものを用い、これを上吹きランス２から投射したり底吹き羽口４からインジェクションしたりすることが望ましい。この場合、メタル及びスラグ６と造滓剤７との反応を促進する上で、スラグ量は２０ｋｇ／Ｔ以下とすることが有効である。
【００２９】
造滓剤７は、ＣａＯ源の配合比率が１０ｍａｓｓ％〜９０ｍａｓｓ％の範囲内となるように炭材及び脱酸剤を配合する。この範囲を外れる場合には、ＣａＯ分と炭材又は脱酸剤との配合比率が片寄り、スラグ６を還元するためには大量の造滓剤７が必要になるためである。上記の範囲を外れる場合には、ＣａＯ分及び炭材又は脱酸剤のどちらかが過剰に添加されることになる。又、造滓剤７の添加量は、炭材又は脱酸剤が０．３ｋｇ／Ｔ以上、ＣａＯ源が１ｋｇ／Ｔ以上であれば十分である。
【００３０】
ＣａＯ源の配合比率が１０ｍａｓｓ％〜９０ｍａｓｓ％の範囲内であり、炭材又は脱酸剤が０．３ｋｇ／Ｔ以上、ＣａＯ源が１ｋｇ／Ｔ以上となるように造滓剤７を添加することで、［ｍａｓｓ％Ｃ］×［ｍａｓｓ％Ｏ］の濃度積は、平衡状態での約０．００２３に対して安定して０．７以下となる。
【００３１】
鉄−マンガン合金や珪素−マンガン合金等のマンガン合金の使用量は、吹錬中に添加されたマンガン源のメタル中への歩留りで決まる脱炭精錬終点のマンガン濃度と製品のマンガン規格との差分で決まる。製品の種類等にもよるが、吹錬途中で高くなったスラグ６中のマンガンを造滓剤７の添加により還元回収する点から判断して、マンガン源がマンガン純分で２ｋｇ／Ｔ以上添加される場合に本発明を適用することが好ましい。
【００３２】
このようにして溶銑５を脱燐処理し更に脱炭精錬することにより、鉄やマンガン等の有価成分のスラグ６への損失量を抑制することができると共に、その後の工程で添加される脱酸剤や合金剤の酸化ロスを少なくすることのできる。その結果、鉄やマンガン更には脱酸剤や合金剤の歩留まりが向上し、製造コストの大幅な削減を達成することが可能となる。
【００３３】
【実施例】
高炉から出銑された溶銑に対し、高炉鋳床での脱珪処理、転炉での予備脱燐処理、転炉での脱炭精錬処理の一連の処理を施した試験操業（試験Ｎｏ．１〜１２）を説明する。
【００３４】
高炉鋳床での脱硅時、塊状の酸化鉄を１１ｋｇ／Ｔの原単位で上置き添加した。高炉鋳床から溶銑鍋への落下硫の攪拌により、溶銑中珪素濃度は０．１４ｍａｓｓ％まで低下した。その後の溶銑鍋内での送酸脱珪処理により、溶銑中珪素濃度は０．０６ｍａｓｓ％まで低下した。
【００３５】
生成したスラグを排滓後、溶銑を図１に示す転炉と同一仕様の転炉に装入して予備脱燐処理を施した。この予備脱燐処理では合計８ｋｇ／Ｔの生石灰と蛍石とを添加し、上吹きランスから１１Ｎｍ^３／Ｔの酸素を供給して行い、処理後の溶銑中燐濃度を０．０１０〜０．０２８ｍａｓｓ％まで低下させた。
【００３６】
予備脱燐処理が施された溶銑を一旦取鍋（装入鍋）に出湯し、図１に示す別の転炉に溶銑を装入し、脱炭精錬を施した。用いた転炉は２５０トン容量であり、脱炭精錬では、炉底部の底吹き羽口から０．１Ｎｍ^３／ｍｉｎ・Ｔの窒素若しくはＡｒを供給して溶銑を攪拌しつつ、上吹きランスからの送酸を行った。混入する珪酸に対しスラグの塩基度調整を考慮して生石灰を媒溶剤として添加した。媒溶剤としての生石灰の添加量は、溶銑の燐濃度が０．０１２　ｍａｓｓ％以下では３ｋｇ／Ｔの一定量とし、溶銑の燐濃度に応じて９ｋｇ／Ｔまで増加させた。上吹きランスからの送酸速度は、吹錬初期から１１分までは３．０Ｎｍ^３／ｍｉｎ・Ｔ、１１分以降は２．０Ｎｍ^３／ｍｉｎ・Ｔで行った。脱炭精錬の終点時は溶鋼中炭素濃度が０．０５ｍａｓｓ％の時点を基準とし、溶鋼中酸素濃度に及ぼす終点炭素濃度の影響を調査するために炭素濃度が０．０８ｍａｓｓ％及び０．１２ｍａｓｓ％の場合も実施した。溶鋼温度は１６３０℃から１６４５℃に制御した。
【００３７】
造滓剤を構成するＣａＯ源として生石灰を用い、炭材として土壌黒鉛及びプラスチックを用い、脱酸剤として金属アルミニウムを５０ｍａｓｓ％含有するアルミドロスを用い、生石灰に炭材又は脱酸剤を配合して造滓剤を作製し、添加量を１．３〜６．８ｋｇ／Ｔの範囲で変更した。添加法は、上吹きランスを介して連続的に投射する方法と、所定配合の生石灰及び炭材を事前に造粒した塊状造滓剤を原料投入装置により連続的に上置き投入する方法で行った。添加速度は、投射法及び上置き投入法共に溶鋼トン当たり毎分１．５〜２．０ｋｇで実施した。
【００３８】
又、比較のために造滓剤を添加しない場合（試験Ｎｏ．１３〜１５）に加え、造滓剤として炭材単体（試験Ｎｏ．１６）、アルミドロス単体（試験Ｎｏ．１７）及び生石灰単体（試験Ｎｏ．１８）の場合や、予備脱燐処理後の溶銑中燐濃度が高く、転炉脱炭精錬工程においても脱燐の必要が生じ、大量の媒溶剤の添加によりスラグ量が増加した場合（試験Ｎｏ．１９，２０）も実施した。各試験操業の操業条件及び操業結果を表１に示す。尚、表１に示すＣａＯは生石灰、Ｃは土壌黒鉛、Ａｌ灰はアルミドロス、ＰＬはプラスチックを表示している。
【００３９】
【表１】

【００４０】
試験Ｎｏ．１３〜１５では、脱炭精錬終点の溶鋼中酸素濃度は炭素濃度に応じて３００ｐｐｍ以下になる場合もあったが、スラグの鉄酸化物濃度（Ｔ．Ｆｅ）は何れも１４ｍａｓｓ％程度と高い値であった。試験Ｎｏ．１６〜１８では、スラグ及びメタルの還元が不足し、脱炭精錬終点の溶鋼中酸素濃度は３００ｐｐｍ以上と高く、且つ、スラグの鉄酸化物濃度（Ｔ．Ｆｅ）も１２ｍａｓｓ％以上と高い値であった。試験Ｎｏ．１９．２０では、スラグ量が多いために造滓剤添加の効果が発揮されず、脱炭精錬終点の溶鋼中酸素濃度は３００ｐｐｍ以上と高く、且つ、スラグの鉄酸化物濃度（Ｔ．Ｆｅ）も１２ｍａｓｓ％以上と高い値であった。
【００４１】
これに対して、予め予備脱燐処理して溶銑燐濃度を０．０３０ｍａｓｓ％以下とすると共にＣａＯ源と炭材とを含む造滓剤又はＣａＯ源と脱酸剤とを含む造滓剤を脱炭精錬の後半で添加して脱炭精錬終点の溶鋼中酸素濃度を３００ｐｐｍ以下とした試験Ｎｏ．１〜１２では、スラグ中の鉄酸化物濃度（Ｔ．Ｆｅ）は９ｍａｓｓ％未満であり、スラグ中の酸化鉄の減少即ちスラグ酸化度の低減が達成された。又、次工程で添加される脱酸用アルミニウムの歩留まりは高く４０％以上であった。
【００４２】
表１には示していないが、鉄と同様にマンガンの損失も少なくすることが可能であり、脱炭精錬終点の溶鋼中のマンガン濃度を高くできる上に、燐の上昇量も問題なく、更に発生スラグ量も少なくすることができた。尚、表１の備考欄には、本発明の範囲内の試験には本発明例と表示し、それ以外の試験には比較例と表示した。
【００４３】
【発明の効果】
本発明によれば、鉄やマンガン等の有価成分のスラグへの損失量を抑制することができると共に、その後の工程で添加される脱酸剤や合金剤の酸化ロスを少なくすることのでき、その結果、鉄やマンガン更には脱酸剤や合金剤の歩留まりが向上し、製造コストの大幅な削減を達成することができ、工業上有益な効果がもたらされる。
【図面の簡単な説明】
【図１】本発明による脱炭精錬を実施する際に用いた転炉設備の１例を示す図である。
【符号の説明】
１　転炉
２　上吹きランス
３　原料投入装置
４　底吹き羽口
５　溶銑
６　スラグ
７　造滓剤[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for producing molten steel required by steel products by using hot metal tapped from a blast furnace and removing impurity components in the hot metal.
[0002]
[Prior art]
In order to produce steel products from hot metal produced in a blast furnace, it is necessary to go through a steelmaking refining process. In this steelmaking refining process, after the impurity components contained in the hot metal are removed, the steel product is adjusted to a composition required in terms of material properties. Impurities contained in the hot metal include phosphorus and sulfur in addition to carbon contained at 4 mass% or more, and required components of steel products include manganese and silicon which increase strength and toughness.
[0003]
In order to remove impurity components such as carbon and phosphorus, hot metal is charged into a converter, and a large amount of oxygen is supplied to the hot metal to perform oxidation refining for oxidizing and removing the impurity components. In this oxidative refining, iron is also oxidized in accordance with the decarburization reaction and the dephosphorization reaction, and slag containing a large amount of iron oxide is generated. Therefore, not only the generated slag but also the degree of oxidation of molten steel increases. As a result, the amount of valuable components such as iron and manganese to the slag increases in the converter furnace, and the oxidation loss of the deoxidizing agent and alloying agent added in the subsequent process increases, and the deoxidizing agent increases. And the yield of alloying agents is reduced.
[0004]
Therefore, in order to prevent the degree of oxidation of the slag from increasing, the acid supply rate at the end of the decarburization refining has been reduced. There is a limit to the effect of lowering the degree of oxidation, and further, a new problem such as a reduction in exhaust gas recovery efficiency or an increase in blowing time due to a reduction in the acid feed rate occurs.
[0005]
In contrast to the conventional converter refining method in which carbon and phosphorus have been simultaneously removed, recently, phosphorus has been removed (preliminary dephosphorization treatment) in a hot metal stage in advance. As a result, in the decarburization refining process in the converter, a solvent for dephosphorization was not required, and it was possible to blow with a small amount of slag. However, to increase the yield of iron and manganese at the end of converter decarburization refining, it is necessary to increase the distribution ratio between slag and metal (molten steel) from the reaction principle, and simply reduce the amount of slag. There is naturally a limit in reducing the loss of iron and manganese in the converter and reducing the oxidation loss of the deoxidizing agent and the alloying agent in the subsequent steps only by doing so.
[0006]
Furthermore, in order to reduce the oxygen potential of the slag, it has been conventionally proposed to add and add a carbon material such as coke into the furnace during the blowing, but partially, oxygen or metal in the metal or slag is added. However, it did not reach the point where the dissolved oxygen in the metal and the iron oxide in the slag were efficiently reduced. In this case, in order to increase the area of the contact reaction interface with the slag and to increase the efficiency, the carbon material must be finely divided, and it is also difficult to efficiently add the carbon material. Further, nitrogen and sulfur contained in the carbonaceous material may adversely affect the components of the steel material, and the amount of addition is limited. For this reason, the carbon material is mainly used for slag forming to stabilize the operation, and there is a limit in reducing iron and manganese oxide in the slag by adding the carbon material.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress loss of valuable components such as iron and manganese to slag in a converter refining process, and to add them in a subsequent process. An object of the present invention is to provide a method for producing molten steel capable of reducing the oxidation loss of a deoxidizing agent or an alloying agent.
[0008]
[Means for Solving the Problems]
The method for producing molten steel according to the first invention of the present application for solving the above-mentioned problems is a method for producing molten steel in which molten iron produced from a blast furnace is preliminarily dephosphorized and then decarburized and refined in a converter to produce molten steel. In the method, in the preliminary dephosphorization treatment, the phosphorus concentration in the hot metal is reduced to the phosphorus concentration level of the steel product, and in the converter decarburization refining, the refining is performed with a slag amount of 20 kg or less per ton of the treated hot metal, and In the latter half of the process, the slag is reduced by adding a CaO source and a slag-making agent comprising one or more of a carbon material and a deoxidizing agent, and the oxygen concentration in the molten steel at the end point of the decarburization refining is set to 300 ppm or less. I do.
[0009]
A method for producing molten steel according to a second invention is characterized in that, in the first invention, the phosphorus concentration in the hot metal after the preliminary dephosphorization treatment is set to 0.02 mass% or less. The production method according to the first invention or the second invention, characterized in that the amount of slag in the converter decarburization refining is set to 10 kg or less per ton of treated hot metal. In any one of the first invention to the third invention, a part or the whole of the slag-making agent is added through a top blowing lance or a tuyere below a bath surface, and the molten steel according to the fifth invention is added. The method of manufacturing according to any one of the first to fourth inventions, wherein the CaO source is at least one of quicklime, limestone, calcined dolomite, and uncalcined dolomite.
[0010]
A method for producing molten steel according to a sixth aspect of the present invention is the method according to any one of the first to fifth aspects, wherein the carbonaceous material is a plastic waste material generated in a process of manufacturing or processing soil graphite, artificial graphite or plastic. According to a seventh aspect of the present invention, there is provided the method for producing molten steel according to any one of the first to sixth aspects, wherein the method comprises producing at least one of waste plastics generated after use of a plastic product. The acid agent is at least one of aluminum dross, aluminum, iron-silicon alloy, metallic silicon, and silicon alloy. The method for producing molten steel according to the eighth invention is characterized in that the method according to the first to seventh inventions In any one of the inventions, the method of producing a molten steel according to the ninth invention is characterized in that a ratio of the CaO source in the slag-making agent is from 10 mass% to 90 mass%. In any of the invention is characterized in that the CO partial pressure of 0.7 or less which is calculated by the oxygen concentration and molten steel in the carbon concentration in molten steel in the decarburization refining endpoint.
[0011]
In the present invention, a slag-making agent composed of a CaO source and one or more of a carbonaceous material and a deoxidizer is added in the latter half of the converter decarburization refining. The carbonaceous material and the deoxidizer in the slag-making agent are consumed in the reaction with dissolved oxygen in the metal and iron oxide or manganese oxide in the slag. Since the slag deoxidation by CaO added at the same time proceeds in preference to the CO generation reaction and acts in the direction of further improving and maintaining the equilibrium relationship with the dissolved oxygen, the reduction of the oxygen concentration in the molten metal, In addition, the reduction of the iron oxide content in the slag can be stably achieved. Addition of only a carbonaceous material or a deoxidizer can temporarily reduce dissolved oxygen and iron oxide in slag, but is difficult to stabilize, but stabilization is achieved by adding a CaO source at the same time.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described. Hot metal poured from the blast furnace is poured into the hot metal pot via the blast furnace casting bed and stored in the hot metal pot. The hot metal pot is transported to a dephosphorization treatment plant, where a preliminary dephosphorization treatment of the hot metal is performed.
[0013]
A gaseous oxygen source such as oxygen gas and a solid oxygen source such as iron ore and mill scale are supplied to the hot metal to perform a pre-phosphorus dephosphorization treatment, and the phosphorus concentration in the hot metal after the preliminary dephosphorization treatment is determined as the phosphorus concentration level of the steel product. , Specifically, to 0.030 mass% or less.
[0014]
In this preliminary dephosphorization treatment, the molten iron is subjected to gas agitation or the like, and is further treated by adding CaO using quicklime or the like. This preliminary dephosphorization treatment can be performed not only in a hot metal ladle but also in a facility having a function of adding an oxygen source or an auxiliary material and stirring hot metal.For example, in a torpedo car that is a hot metal transfer vessel similar to a hot metal ladle. Naturally, it may be transferred to a container for exclusive use of dephosphorization such as a converter. During the dephosphorization treatment, it is necessary to perform appropriate stirring to prevent peroxidation of the slag, and gas stirring is generally performed.
[0015]
In particular, in order to stably perform the dephosphorization treatment, it is necessary to reduce the amount of slag as much as possible, and to sufficiently dephosphorize even a small amount of slag, it is necessary to generate slag having a high dephosphorization ability. For this purpose, it is effective to increase the basicity of the slag (CaO / SiO ₂ ). From the viewpoint of increasing the basicity of the slag, silicon in the hot metal is removed in advance (referred to as “silicon removal treatment”). Is preferred. If the silicon concentration in the hot metal is previously desiliconized to 0.2 mass% or less, the basicity of the slag can be increased to 3 or more by adding a small amount of CaO. After the preliminary dephosphorization treatment, the generated slag is removed from the hot metal pot, and the hot metal is subjected to the next step of converter decarburization refining.
[0016]
In order to reduce the amount of slag in the converter dephosphorization refining in the next step, it is desirable to lower the phosphorus concentration in the hot metal after the preliminary dephosphorization treatment. It is preferable to perform the dephosphorization treatment until the content becomes 0.02 mass% or less. If the phosphorus concentration in the hot metal is 0.02 mass% or less, the amount of the solvent added in the converter decarburization refining is 5 to 10 kg per ton of hot metal (hereinafter referred to as “kg / T”), depending on the phosphorus standard of the product. ) And the amount of produced slag can be reduced to 10 to 20 kg / T or less. As the amount of slag in converter decarburization refining is smaller, the amount of loss of valuable components such as iron and manganese to slag can be suppressed, and the yield of iron and manganese is improved.
[0017]
The hot metal thus preliminarily dephosphorized is charged into a converter, and oxygen is supplied from a top blowing lance or the like to perform converter decarburization refining. FIG. 1 shows an example of converter equipment used when performing converter decarburization refining according to the present invention. In FIG. 1, 1 is a converter, 2 is a top blowing lance, 3 is a raw material charging device, 4 is a bottom blowing tuyere, 5 is hot metal, 6 is slag, 7 is a CaO source, a carbon material and a deoxidizer. It is a slag-making agent consisting of one or more types. A refining method in which oxygen is blown upward and a stirring gas is blown downward as shown in FIG. 1 is called composite blowing.
[0018]
The upper blowing lance 2 has a passage through which a powdery or granular slagging agent 7 is sprayed onto the hot metal 5 by using an inert gas such as Ar as a carrier gas and projected to the central portion thereof, and oxygen is supplied outside the hot metal 5 by the hot metal 5. And a passage through which cooling water for cooling the upper lance 2 reciprocates is provided outside. Perform charcoal refining. Then, in the latter half of the decarburization refining, the slag-making agent 7 is charged into the converter 1 via the upper blowing lance 2 or the raw material charging device 3. In this case, the latter half of the decarburization refining means the latter half of the period of the oxygen supply period from the middle point. The powdery or granular slag-making agent 7 may be blown from the bottom blowing tuyere 4.
[0019]
In this converter decarburization refining, preliminary dephosphorization treatment has been performed up to the phosphorus concentration level of the steel product, so that it is used as a thinner for iron oxide generated during oxygen blowing or scattering and heat radiation of droplets from the bath surface. Although a small amount of the cover slag 6 is required to suppress this, the converter decarburization refining according to the present invention hardly requires a dephosphorization reaction. The amount of silicon oxide (SiO ₂ ) brought from gangue or the like in the manganese ore, which is not specified, may be a small amount of only the basicity adjustment amount. That is, a small slag amount of 20 kg / T or less is sufficient.
[0020]
As described above, if the phosphorus concentration in the hot metal is reduced to 0.02 mass% or less by the preliminary dephosphorization treatment, the phosphorus concentration is reduced to the phosphorus concentration level of the steel product. No manganese ore is required, and the amount of slag produced can be reduced to 20 kg / T or less even if manganese ore is added, depending on the amount of manganese ore used. . Further, since there is no problem in fluctuation of the slag composition, the slag 6 can be repeatedly used in the operation of remaining slag in the furnace and the like, and the solvent newly supplied can be eliminated.
[0021]
In the converter refining process, the decarburization proceeds due to the supply of acid from the upper blowing lance 2, and at the same time, iron oxide is generated, and the temperature of the molten metal rises. From the first to middle stages of oxygen blowing, quick lime for basicity adjustment is added as a solvent, and if necessary, simple manganese ore is added. The added manganese ore is melted, and the reduction by the carbon in the hot metal proceeds.
[0022]
In the middle to late stages of blowing, the oxidation rate of carbon in the hot metal 5 is delayed, and the accumulation of iron oxide in the slag 6 starts, and the reduction of manganese is stopped in accordance with the increase in the degree of oxidation of the slag 6. Then, manganese is distributed to the metal and the slag 6, and iron oxide (FeO) and manganese oxide (MnO) remain in the slag 6. As the decarburization reaction proceeds, the dissolved oxygen in the metal rises, and the oxygen concentration from several ppm to several tens ppm in the hot metal 5 becomes several hundred ppm in the low carbon molten steel at the end point of the decarburization refining.
[0023]
In composite blowing, the relationship between carbon in metal and oxygen in metal varies depending on the amount of bottom blown gas, stirring intensity, etc., but in general, the concentration product of [mass% C] × [mass% O] is: The range is about 0.8 to 1.2 with respect to about 0.0023 in the equilibrium state. From the behavior of oxygen in the metal in the converter refining, it is effective to add the slag-making agent 7 after the critical carbon concentration at which the oxygen concentration starts to increase. Generally, the critical carbon concentration is about 0.2 mass% to 0.5 mass%, and the slag-making agent 7 is added near this concentration during blowing. It is also possible to add near the end of oxygen blowing or after the end of oxygen blowing.
[0024]
The slag-making agent 7 composed of a CaO source and one or more of a carbon material and a deoxidizing agent can be used either as a lump or in a granular or powder form. As an addition method, in addition to the top-loading by the raw material charging device 3, the addition by the projection method using the upper blowing lance 2 can be performed. Since the slag-making agent 7 contains a reducing agent such as carbon or aluminum, it is preferable to use an inert gas such as Ar as a carrier gas when adding using a carrier gas. The form and addition method of the slag-making agent 7 are not limited to one type, and may be used simultaneously.
[0025]
As a CaO source, which is a raw material constituting the slag-making agent 7, basically any material can be used. However, in view of economy, it is preferable to use calcined lime or a calcined dolomite containing MgO, which is usually used in converter refining. Limestone and unfired dolomite can also be used without any problem if the endothermic decarboxylation in the furnace does not affect the operation.
[0026]
Basically, any carbon material can be used as a raw material of the slag-making agent 7. However, in consideration of economical efficiency, plastic waste generated in a plastic manufacturing process or a processing process or waste plastic generated after using a plastic-containing product is used. It is preferable to use In the latter case, if mixing other than the plastic component in the plastic-containing product is not preferred, separation by separation or pulverization can be performed in advance. When impurities such as sulfur and nitrogen become problematic by using coal or coke, soil graphite or artificial graphite can be used instead of these.
[0027]
As the deoxidizing agent as a raw material constituting the slag-making agent 7, it is preferable to use a low-purity aluminum product such as metal aluminum, an aluminum alloy, or aluminum dross, which contains an Al component that is a strongly deoxidizing element. In addition, a strong deoxidizing element such as silicon or magnesium and its containing product can be used if there is no problem in the components and economy. Examples of the silicon-containing metal include metal silicon and an iron-silicon alloy.
[0028]
The slag forming agent 7 is added to reduce iron oxide (mainly FeO) and manganese oxide in the slag 6 by the C, Al, and Si components in the slag forming agent 7 and partially reduce oxygen in the molten steel. Let it. Furthermore, the CaO component added simultaneously acts on the FeO of the slag 6 and the oxygen of the molten steel, so that the deoxidation can proceed efficiently. With the addition of only carbonaceous materials and deoxidizers, it is possible to temporarily reduce dissolved oxygen in metal and iron oxide in slag, but stabilization is difficult, but stabilization is achieved by simultaneously adding a CaO source. You. However, in order to efficiently advance the stabilization by the addition of the CaO source, it is preferable to add the CaO source to the vicinity of the reaction site of the carbonaceous material and the deoxidizing agent, or to pulverize the CaO source itself. It is desirable to use a mixture of the mixture and a deoxidizing agent, which is projected from the upper blowing lance 2 or injected from the lower blowing tuyere 4. In this case, in order to promote the reaction between the metal and the slag 6 and the slag-making agent 7, it is effective to set the slag amount to 20 kg / T or less.
[0029]
The slag-making agent 7 contains a carbon material and a deoxidizing agent such that the compounding ratio of the CaO source is in the range of 10 mass% to 90 mass%. If the ratio is out of this range, the mixing ratio of the CaO component and the carbon material or the deoxidizing agent is uneven, and a large amount of the slag-making agent 7 is required to reduce the slag 6. If it is out of the above range, the CaO component and either the carbon material or the deoxidizer will be added in excess. The amount of the slag-making agent 7 is sufficient if the carbon material or the deoxidizing agent is 0.3 kg / T or more and the CaO source is 1 kg / T or more.
[0030]
Adding the slag-making agent 7 so that the mixing ratio of the CaO source is in the range of 10 mass% to 90 mass%, the carbon material or the deoxidizing agent is 0.3 kg / T or more, and the CaO source is 1 kg / T or more. Then, the concentration product of [mass% C] × [mass% O] stably becomes 0.7 or less with respect to about 0.0023 in the equilibrium state.
[0031]
The amount of manganese alloys used, such as iron-manganese alloys and silicon-manganese alloys, is determined by the difference between the manganese concentration at the end of decarburization refining, which is determined by the yield of the manganese source added during blowing, and the manganese standard for the product. Is determined. Although it depends on the type of product, it is judged from the point that manganese in the slag 6 that has become high during blowing has been reduced and recovered by the addition of the slag-making agent 7, and the manganese source is added at 2 kg / T or more in pure manganese. In this case, it is preferable to apply the present invention.
[0032]
By dephosphorizing the hot metal 5 and further decarburizing and refining it in this way, the amount of loss of valuable components such as iron and manganese to the slag 6 can be suppressed, and the deoxidation added in the subsequent process Oxidation loss of the agent or alloying agent can be reduced. As a result, the yield of iron and manganese, as well as the deoxidizing agent and the alloying agent, is improved, and it is possible to achieve a significant reduction in manufacturing costs.
[0033]
【Example】
A test operation (Test No. 1) in which a series of treatments of hot metal poured from a blast furnace, such as desiliconization treatment in a blast furnace cast bed, preliminary dephosphorization treatment in a converter, and decarburization refining treatment in a converter, were performed. 12) will be described.
[0034]
At the time of desiliconization in the blast furnace cast floor, massive iron oxide was added at a unit rate of 11 kg / T. The silicon concentration in the hot metal was reduced to 0.14 mass% by the stirring of the dropping sulfur from the blast furnace cast floor to the hot metal pot. The silicon concentration in the hot metal was reduced to 0.06 mass% by the subsequent acidification and desiliconization in the hot metal pot.
[0035]
After discharging the generated slag, the hot metal was charged into a converter having the same specifications as the converter shown in FIG. 1 and subjected to a preliminary dephosphorization treatment. In this preliminary dephosphorization treatment, a total of 8 kg / T of quicklime and fluorite are added, and 11 Nm ³ / T of oxygen is supplied from the top blowing lance to carry out the treatment. It decreased to 028 mass%.
[0036]
The hot metal that had been subjected to the preliminary dephosphorization treatment was once poured into a ladle (a charging pan), charged with the hot metal in another converter shown in FIG. 1, and subjected to decarburization refining. The converter used had a capacity of 250 tons. In the decarburization refining, nitrogen or Ar of 0.1 Nm ³ / min · T was supplied from the bottom blowing tuyere at the bottom of the furnace, and the molten iron was stirred from the top blowing lance. Was sent. Quick lime was added as a solvent to the mixed silicic acid in consideration of the basicity adjustment of the slag. The amount of quicklime added as a medium solvent was a fixed amount of 3 kg / T when the phosphorus concentration of the hot metal was 0.012 mass% or less, and was increased to 9 kg / T according to the phosphorus concentration of the hot metal. Oxygen-flow-rate from the top blowing lance, from the blow initial up to 11 minutes 3.0Nm ³ / min · T, 11 minutes later was carried out at 2.0Nm ³ / min · T. At the end point of the decarburization refining, the carbon concentration in the molten steel is 0.05 mass% as a reference. In order to investigate the influence of the end carbon concentration on the oxygen concentration in the molten steel, the carbon concentration is 0.08 mass% and 0.12 mass%. Was also carried out. The molten steel temperature was controlled from 1630 ° C to 1645 ° C.
[0037]
Using quicklime as a CaO source constituting the slag forming agent, using soil graphite and plastic as a carbon material, using aluminum dross containing 50 mass% of metallic aluminum as a deoxidizing agent, and blending a carbon material or a deoxidizing agent into quicklime. A slag-making agent was prepared by using the method described above, and the amount added was changed in a range of 1.3 to 6.8 kg / T. The addition method is carried out by a method of continuously projecting through a top blowing lance and a method of continuously placing a mass slag forming agent obtained by previously granulating quicklime and carbonaceous material of a predetermined blend by a raw material charging device. Was. The addition rate was 1.5 to 2.0 kg per minute per ton of molten steel for both the projection method and the top-loading method.
[0038]
For comparison, in addition to the case where no slag-making agent was added (Test Nos. 13 to 15), carbonaceous material alone (Test No. 16), aluminum dross alone (Test No. 17) and quicklime alone were used as slag-making agents. In the case of (Test No. 18) and the high phosphorus concentration in the hot metal after the preliminary dephosphorization treatment, dephosphorization was required in the converter decarburization refining process, and the amount of slag increased due to the addition of a large amount of a solvent. Cases (Test Nos. 19 and 20) were also performed. Table 1 shows the operation conditions and operation results of each test operation. In Table 1, CaO indicates quick lime, C indicates soil graphite, Al ash indicates aluminum dross, and PL indicates plastic.
[0039]
[Table 1]

[0040]
Test No. In the case of 13 to 15, the oxygen concentration in the molten steel at the end point of the decarburization refining was sometimes 300 ppm or less according to the carbon concentration, but the iron oxide concentration (T.Fe) of the slag was as high as about 14 mass% in all cases. Met. Test No. In 16-18, the reduction of slag and metal is insufficient, the oxygen concentration in molten steel at the end point of decarburization refining is as high as 300 ppm or more, and the iron oxide concentration (T.Fe) of slag is as high as 12 mass% or more. there were. Test No. In 19.20, the effect of adding the slag-making agent was not exhibited due to the large amount of slag, the oxygen concentration in the molten steel at the end of decarburization refining was as high as 300 ppm or more, and the iron oxide concentration (T.Fe) of the slag was large. Was also as high as 12 mass% or more.
[0041]
On the other hand, a pre-dephosphorization treatment is performed in advance to reduce the hot metal phosphorus concentration to 0.030 mass% or less and to remove a slag-making agent containing a CaO source and a carbon material or a slag-making agent containing a CaO source and a deoxidizing agent. Test No. 2 was added in the latter half of coal refining to reduce the oxygen concentration in molten steel at the end point of decarburization refining to 300 ppm or less. In Nos. 1 to 12, the iron oxide concentration (T.Fe) in the slag was less than 9 mass%, and a reduction in iron oxide in the slag, that is, a reduction in the degree of slag oxidation was achieved. Also, the yield of aluminum for deoxidation added in the next step was as high as 40% or more.
[0042]
Although not shown in Table 1, it is possible to reduce the loss of manganese in the same manner as iron, to increase the manganese concentration in the molten steel at the end of decarburization refining, and to increase the amount of phosphorus without any problem. The amount of generated slag could be reduced. In the remarks column of Table 1, tests within the scope of the present invention are indicated as examples of the present invention, and other tests are indicated as comparative examples.
[0043]
【The invention's effect】
According to the present invention, the amount of loss of valuable components such as iron and manganese to the slag can be suppressed, and the oxidation loss of the deoxidizing agent and the alloying agent added in the subsequent step can be reduced, As a result, the yield of iron and manganese, as well as the deoxidizing agent and the alloying agent, is improved, and it is possible to achieve a significant reduction in manufacturing cost, which brings about an industrially beneficial effect.
[Brief description of the drawings]
FIG. 1 is a diagram showing one example of converter equipment used when performing decarburization refining according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Converter 2 Top blowing lance 3 Raw material charging device 4 Bottom blowing tuyere 5 Hot metal 6 Slag 7 Slag forming agent

Claims

In the method for producing molten steel, in which molten iron from a blast furnace is preliminarily dephosphorized and then decarburized and refined in a converter to produce molten steel, the preliminarily dephosphorizing treatment includes determining the phosphorus concentration in the molten iron by the phosphorus of the steel product. In the converter decarburization refining, the refining is performed with a slag amount of 20 kg or less per ton of treated hot metal, and in the latter half of the decarburization refining, it consists of a CaO source and one or more of a carbonaceous material and a deoxidizer. A method for producing molten steel, wherein a slag is reduced by adding a slag-making agent, and the oxygen concentration in the molten steel at the end point of decarburization refining is adjusted to 300 ppm or less.

The method for producing molten steel according to claim 1, wherein the phosphorus concentration in the hot metal after the preliminary dephosphorization treatment is set to 0.02 mass% or less.

3. The method for producing molten steel according to claim 1, wherein an amount of slag in the converter decarburization refining is set to 10 kg or less per ton of treated hot metal. 4.

The method for producing molten steel according to any one of claims 1 to 3, wherein a part or all of the slag-making agent is added through an upper blowing lance or a tuyere below a bath surface.

The method for producing molten steel according to any one of claims 1 to 4, wherein the CaO source is at least one of quick lime, limestone, calcined dolomite, and unfired dolomite.

4. The method according to claim 1, wherein the carbon material is at least one of soil graphite, artificial graphite, plastic waste generated in a plastic manufacturing or processing step, and waste plastic generated after use of a plastic product. 5. The method for producing molten steel according to any one of 5.

7. The production of molten steel according to claim 1, wherein the deoxidizing agent is at least one of aluminum dross, aluminum, iron-silicon alloy, metallic silicon, and silicon alloy. Method.

The method for producing molten steel according to any one of claims 1 to 7, wherein the ratio of the CaO source in the slag-making agent is from 10 mass% to 90 mass%.

The CO partial pressure calculated by the oxygen concentration in molten steel and the carbon concentration in molten steel at the end point of the decarburization refining is set to 0.7 or less, according to any one of claims 1 to 8, wherein Method of producing molten steel.