JP3721998B2

JP3721998B2 - Hot metal pretreatment method

Info

Publication number: JP3721998B2
Application number: JP2001068865A
Authority: JP
Inventors: 大輔高橋; 寛野村
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2001-03-12
Filing date: 2001-03-12
Publication date: 2005-11-30
Anticipated expiration: 2021-03-12
Also published as: JP2002266014A

Description

【０００１】
【発明の属する技術分野】
本発明は、溶銑の予備処理方法に係わり、詳しくは、溶銑を転炉で脱炭する前に、予め転炉装入前の溶銑に脱硫及び脱燐を施す技術に関する。
【０００２】
【従来の技術】
製鋼工程においては、高炉から出銑された溶銑が含有する珪素、燐及び硫黄等を、転炉で脱炭吹錬する前に予め除去する所謂「溶銑の予備処理」が普及している。これは、溶銑を事前に予備処理することで、脱炭吹錬の負荷を軽減したり、製鋼トータルコストのミニマム化、あるいは低燐、低硫鋼を安定して溶製するためである。
【０００３】
最近、この溶銑予備処理を導入し、図２に示すような工程からなる新しい製鋼プロセスが注目されている。その製鋼プロセスは、高炉での出銑から製鋼工場までの溶銑移動の間に、高炉鋳床脱珪、脱珪滓の排滓、トピード・カーでの脱硫、脱燐等を行う従来の多段に分割した処理を改め、非常にシンプルなプロセス配置とするばかりでなく、処理場所の集約を図ったものである。また、上記従来の多段分割処理では、高炉出銑から転炉出鋼までの処理時間が長いばかりでなく、トピード・カーを用いるため、スラグ・フォーミングの発生で操業が制約されるという問題があったので、この問題を解消するためでもあった。
【０００４】
ところで、図２に示した溶銑鍋脱硫及び転炉型溶銑脱燐を順次行う溶銑予備処理プロセスでは、脱燐処理中にスラグから溶銑への復硫が起きる恐れがあった。そして、この復硫の程度が予測できないので、特に低硫鋼の溶製に際しては、
１）先の脱硫工程で、復硫分を配慮し、過剰に脱硫する。
２）脱燐に利用する転炉を、常時硫黄含有量の低い溶銑で洗浄してから脱燐を行う
等の対策が必要となる。
【０００５】
しかしながら、これらの対策は、操業上、時間ロスが大きく、生産性を低減する可能性がある。また、復硫を完全に防止できるわけでないので、製品の硫黄規格を満足させるには、脱燐後に再度脱硫をしなければならない恐れもある。
【０００６】
【発明が解決しようとする課題】
本発明は、かかる事情に鑑み、復硫対策を配慮する必要がなく、従来より効率の良い溶銑の予備処理方法を提供することを目的としている。
【０００７】
【課題を解決するための手段】
発明者は、上記目的を達成するため鋭意研究し、その成果を本発明に具現化した。
【０００８】
すなわち、本発明は、転炉装入前の溶銑から脱燐及び脱硫するに際して、予備処理していない溶銑を使用し、まず、反応容器を転炉とした脱燐を行ってから、引き続き溶銑を取鍋に移して機械攪拌式脱硫処理し、該脱硫時の復燐を当該溶銑の脱炭処理時に脱燐処理することを特徴とする溶銑の予備処理方法である。
【０００９】
本発明によれば、製品の硫黄規格に対応した脱硫処理が可能となる。なお、脱硫処理後は、転炉型反応容器に溶銑を移して脱炭処理を行うことで、次工程の二次精錬に移行でき、該転炉型反応容器による脱炭精錬では、燐含有量に応じて調整のための脱燐処理が可能である。
【００１０】
【発明の実施の形態】
以下、発明をなすに至った経緯を交え、本発明の実施の形態について説明する。
【００１１】
従来の方法による取鍋での溶銑脱硫は、脱硫剤にＣａＯを使用すると、脱硫反応は、下記（１）式で表される。
[Ｓ]＋３（ＣａＯ）→（ＣａＳ）＋[Ｏ] （１）
ここで、[ ]は溶銑中の成分、( )はスラグ中の成分であることを示す。
この脱硫処理された溶銑は、除滓後に引き続き転炉に装入され、その中で脱燐処理が行われる（転炉型溶銑脱燐という）。この転炉型溶銑脱燐は、酸素ガスを付加して行われ、脱燐反応は、（２）式で表される。
２[Ｐ]＋３（ＣａＯ）＋５[Ｏ]→（３ＣａＯ・Ｐ₂Ｏ₅）（２）
しかし、先の脱硫処理で生じたスラグの転炉への持ち込み、あるいは転炉内の汚染物質（炉壁付着物等）の作用で、下記（３）式の反応、つまり復硫が同時に起きる。
（ＣａＳ）＋[Ｏ]→（ＣａＯ）＋[Ｓ] （３）
この復硫量が大きく成分外れとなると、その後に行う転炉での脱炭吹錬では、脱硫が期待できないので、脱炭吹錬前の溶銑段階で再び脱硫処理を行ったり、転炉から出鋼した溶鋼を以降の二次精錬（真空脱ガス処理等）にて予定外の脱硫処理をすることになる。これでは、前記したように、操業上、時間ロスが大きく、生産性を低減してしまう。
【００１２】
そこで、発明者は、（３）式の復硫反応による成分外れを防止するよう、図１に示すように、始めに転炉型脱燐を行い、その後に溶銑鍋脱硫をすることを着想し、この方法を本発明としたのである。このように、脱硫処理と脱燐処理の順番を逆にすると、後で行う溶銑鍋脱硫時に、脱燐処理時に生成して取鍋に持ち込まれたスラグにより、溶鋼への復燐が生じる。しかしながら、その復燐量は、以降に行う転炉での脱炭処理時に起きる脱燐反応で処理可能なので、まったく問題にならないことを確認した。
【００１３】
なお、溶銑鍋での脱硫としては、溶銑中に脱硫剤を添加してからインペラを浸漬して機械攪拌させる機械攪拌式脱硫処理、金属Ｍｇをキャリアガス（不活性ガス）で溶銑中に吹き込む脱硫処理及び焼石灰（ＣａＯ）をキャリアガス（不活性ガス）で溶銑中に吹き込む脱硫処理がある。本発明は、これら３つの処理方法のいずれを採用しても良いが、反応効率の点で機械攪拌式脱硫処理が最も好ましい。
【００１４】
なお、機械攪拌式脱硫は、インペラ脱硫又はＫＲ式脱硫とも呼ばれ、「鉄鋼便覧（第３版）ＩＩ製銑製鋼」の４５２頁に「溶銑の脱硫率と処理コスト比（ＫＲ式脱硫でのコストを１．０とした相対値）との関係」で示されるように、反応効率が非常に良い。この関係を図４に示すが、コストも平均的で好ましい。ただし、この方式による脱硫では、温度降下が大きいが、本発明では、前工程で反応容器を転炉とした脱燐処理を採るため、この脱燐処理で使用される溶銑は予備処理されておらず、転炉で使用する時、熱的余裕度が高く、脱硫での温度降下を見込んだ出鋼温度に調整でき、全処理工程で温度に関して支障をきたすことはない。
【００１５】
【実施例】
本発明に係る溶銑の予備処理法を採用した図１の製鋼プロセスにより、製品の硫黄規格が０．００２４質量％以下の溶鋼を溶製した。
【００１６】
使用した反応容器は、脱硫には収容量が１８０トンの取鍋を、転炉には１８０トンの上底吹き転炉を用いた。なお、転炉は同タイプのものを２基使用し、溶銑の脱燐と脱炭吹錬とを別々に行うようにした。その方が、転炉内の洗浄（付着物除去）が個別に行え、都合が良いからである。
【００１７】
まず、高炉から出銑されたＰ濃度が０．１５０質量％、Ｓ濃度が０．０２００質量％の溶銑を転炉へ装入し、脱燐処理を行った。焼石灰と鉄鉱石を不活性ガスで溶銑に吹き込むと共に、酸素ガスも吹き込んだ。これにより、溶銑中のＰは、０．０１８質量％まで低下した。なお、その際、溶銑中のＳ濃度は、０．０２１質量％であった。
【００１８】
次に、転炉内のスラグを排出し、溶銑を取鍋に移して脱硫処理にかけた。脱硫方法としては、前記した溶銑中に脱硫剤を添加しながらインペラを浸漬して機械攪拌をする方法を採用した。その結果、溶銑中のＰ濃度は、０．０２１質量％、Ｓ濃度は０．００１０質量％となり、脱硫が十分に行われた。
【００１９】
この脱硫処理後の溶銑は、再度転炉に移され、引き続き脱炭吹錬を行い、Ｐ濃度が０．０１５質量％、Ｓ濃度が０．００１４質量％の溶鋼にされた。Ｓ濃度は、脱硫処理後に０．０００４質量％ばかり増加しているが、十分に前記規格を満足する溶鋼が溶製できたことが明らかである。なお、脱硫時には、０．００３質量％程度の復燐があったが、この燐は、転炉での脱炭吹錬中に脱燐されていることも確認できた。
【００２０】
この実施例と同様にして、多数チャージの溶鋼を溶製し、図２に示す従来の方法で溶製した溶鋼の復硫量を調査し、その結果を図３に示す。図３より、本発明に係る溶銑の予備処理方法が優れていることが明らかである。
【００２１】
【発明の効果】
以上述べたように、本発明により、復硫を懸念することなく、従来より効率の良い溶銑の予備処理ができるようになった。
【図面の簡単な説明】
【図１】本発明に係る溶銑の予備処理方法を導入した製鋼プロセスを示す流れ図である。
【図２】従来の予備処理方法を導入した製鋼プロセスを示す流れ図である
【図３】本発明法及び従来法を導入した製鋼プロセスでの復硫量を比較した図である。
【図４】溶銑の脱硫率と処理コスト比（ＫＲ法でのコストを１．０としている）との関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot metal pretreatment method, and more particularly, to a technique for desulfurizing and dephosphorizing hot metal before charging the converter before decarburizing the hot metal in the converter.
[0002]
[Prior art]
In the steelmaking process, so-called “hot metal pretreatment” in which silicon, phosphorus, sulfur, and the like contained in the hot metal discharged from the blast furnace are removed in advance before decarburization blowing in the converter is widespread. This is because the hot metal is pre-treated in advance to reduce the decarburization blow load, to minimize the total cost of steelmaking, or to stably produce low phosphorus and low sulfur steel.
[0003]
Recently, a new steelmaking process consisting of the steps shown in FIG. The steelmaking process is a conventional multi-stage process in which blast furnace casting floor desiliconization, desiliconization slag, desulfurization in a topped car, dephosphorization, etc. are performed during the hot metal transfer from the blast furnace to the steel factory. In addition to revising the divided processing to make a very simple process arrangement, the processing locations are consolidated. In addition, the conventional multi-stage splitting process has a problem that not only the processing time from the blast furnace tapping to the converter tapping steel is long, but also the operation is restricted due to the occurrence of slag forming because a topped car is used. Therefore, it was also to solve this problem.
[0004]
By the way, in the hot metal preliminary treatment process in which the hot metal ladle desulfurization and the converter type hot metal dephosphorization shown in FIG. 2 are sequentially performed, there is a possibility that slag to hot metal may be sulfurized during the dephosphorization treatment. And since the degree of this sulfurization cannot be predicted, especially when melting low-sulfur steel,
1) In the previous desulfurization process, the desulfurization is taken into account and excessive desulfurization is performed.
2) It is necessary to take measures such as dephosphorization after the converter used for dephosphorization is always washed with hot metal having a low sulfur content.
[0005]
However, these measures have a large time loss in operation and may reduce productivity. Further, since it is not possible to completely prevent resulfurization, it may be necessary to desulfurize again after dephosphorization in order to satisfy the sulfur specification of the product.
[0006]
[Problems to be solved by the invention]
In view of such circumstances, an object of the present invention is to provide a hot metal pretreatment method that is more efficient than conventional methods and does not require consideration of sulfidation measures.
[0007]
[Means for Solving the Problems]
The inventor diligently studied to achieve the above object, and the results were embodied in the present invention.
[0008]
That is, in the present invention, when dephosphorizing and desulfurizing the hot metal before charging the converter, the hot metal that has not been pretreated is used. First, after dephosphorization using the reaction vessel as a converter, The hot metal pretreatment method is characterized in that it is transferred to a ladle and subjected to mechanical stirring desulfurization treatment, and the dephosphorization at the time of desulfurization is dephosphorization treatment at the time of decarburization treatment of the hot metal .
[0009]
According to the present invention, it is possible to perform a desulfurization treatment corresponding to a sulfur standard of a product. After the desulfurization treatment, the hot metal is transferred to the converter reactor and decarburized, so that it can be transferred to the secondary refining of the next step. Depending on the condition, dephosphorization treatment for adjustment is possible.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the following, an embodiment of the present invention will be described with reference to the background to the invention.
[0011]
In hot metal desulfurization in a ladle according to a conventional method, when CaO is used as a desulfurizing agent, the desulfurization reaction is represented by the following formula (1).
[S] +3 (CaO) → (CaS) + [O] (1)
Here, [] indicates a component in hot metal, and () indicates a component in slag.
The desulfurized hot metal is subsequently charged into the converter after demetalization, and dephosphorization is performed therein (referred to as converter-type hot metal dephosphorization). This converter type hot metal dephosphorization is performed by adding oxygen gas, and the dephosphorization reaction is represented by the formula (2).
2 [P] +3 (CaO) +5 [O] → (3CaO · P ₂ O ₅ ) (2)
However, the reaction of the following formula (3), that is, resulfurization occurs simultaneously by bringing the slag generated in the previous desulfurization process into the converter or by the action of contaminants (furnace wall deposits etc.) in the converter.
(CaS) + [O] → (CaO) + [S] (3)
If this amount of desulfurization is large and out of the components, decarburization blown in the converter that is performed afterwards cannot be expected to be desulfurized. Unscheduled desulfurization treatment will be performed on the molten steel by subsequent secondary refining (vacuum degassing treatment, etc.). In this case, as described above, time loss is large in operation, and productivity is reduced.
[0012]
In view of this, the inventor has conceived to perform converter-type dephosphorization first, followed by hot metal ladle desulfurization, as shown in FIG. This method is the present invention. Thus, when the order of the desulfurization treatment and the dephosphorization treatment is reversed, at the time of the hot metal ladle desulfurization performed later, the slag generated during the dephosphorization treatment and brought into the ladle causes rephosphorization to the molten steel. However, it was confirmed that the amount of recovered phosphorus is not a problem at all because it can be processed by the dephosphorization reaction that occurs during the decarburization process in the converter to be performed later.
[0013]
In addition, as desulfurization with hot metal ladle, mechanical stirring type desulfurization treatment in which a desulfurizing agent is added to hot metal and then impeller is immersed and mechanically stirred, metal Mg is blown into hot metal with carrier gas (inert gas) There is a treatment and desulfurization treatment in which burned lime (CaO) is blown into hot metal with a carrier gas (inert gas). In the present invention, any of these three treatment methods may be adopted, but the mechanical stirring type desulfurization treatment is most preferable in view of reaction efficiency.
[0014]
Mechanical stirring desulfurization is also referred to as impeller desulfurization or KR desulfurization, and “Steels Manual (Third Edition) II Steel Making” on page 452, “Desulfurization rate of hot metal and treatment cost ratio (for KR desulfurization) The reaction efficiency is very good, as shown by “Relationship with the relative value (cost is 1.0)”. This relationship is shown in FIG. 4, and the cost is average and preferable. However, in the desulfurization by this method, the temperature drop is large, but in the present invention, since the dephosphorization process using the reaction vessel as a converter is adopted in the previous process, the hot metal used in this dephosphorization process is not pretreated. In addition, when used in a converter, the thermal margin is high and the temperature can be adjusted to allow for a temperature drop during desulfurization, and there is no problem with temperature in all processing steps.
[0015]
【Example】
By the steelmaking process of FIG. 1 employing the hot metal pretreatment method according to the present invention, molten steel having a product sulfur specification of 0.0024% by mass or less was melted.
[0016]
The reaction vessel used was a ladle having a storage capacity of 180 tons for desulfurization, and a 180 ton top-bottom blowing converter for the converter. Two converters of the same type were used, and hot metal dephosphorization and decarburization blowing were performed separately. This is because cleaning (debris removal) in the converter can be performed individually and is convenient.
[0017]
First, hot metal having a P concentration of 0.150% by mass and an S concentration of 0.0200% by mass discharged from a blast furnace was charged into a converter and subjected to dephosphorization treatment. Burnt lime and iron ore were blown into the hot metal with inert gas, and oxygen gas was also blown. Thereby, P in molten iron fell to 0.018 mass%. At that time, the S concentration in the hot metal was 0.021% by mass.
[0018]
Next, the slag in the converter was discharged, the hot metal was transferred to a ladle and subjected to a desulfurization treatment. As the desulfurization method, a method was adopted in which the impeller was immersed in the hot metal and mechanical stirring was performed while adding a desulfurizing agent. As a result, the P concentration in the hot metal was 0.021 mass%, the S concentration was 0.0010 mass%, and desulfurization was sufficiently performed.
[0019]
The molten iron after the desulfurization treatment was transferred again to the converter and subsequently decarburized and blown to obtain molten steel having a P concentration of 0.015 mass% and an S concentration of 0.0014 mass%. Although the S concentration has increased by 0.0004 mass% after the desulfurization treatment, it is clear that molten steel that sufficiently satisfies the above-mentioned standards has been produced. In addition, at the time of desulfurization, there was about 0.003% by mass of recovered phosphorus. It was also confirmed that this phosphorus was dephosphorized during decarburization blowing in the converter.
[0020]
In the same manner as in this example, molten steel with a large number of charges was melted, the amount of sulfurization of the molten steel melted by the conventional method shown in FIG. 2 was investigated, and the results are shown in FIG. FIG. 3 clearly shows that the hot metal pretreatment method according to the present invention is excellent.
[0021]
【The invention's effect】
As described above, according to the present invention, the hot metal pretreatment can be performed more efficiently than before without worrying about resulfurization.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a steelmaking process in which a hot metal pretreatment method according to the present invention is introduced.
FIG. 2 is a flowchart showing a steelmaking process in which a conventional pretreatment method is introduced. FIG. 3 is a diagram comparing the amount of resulfurization in the steelmaking process in which the method of the present invention and the conventional method are introduced.
FIG. 4 is a diagram showing the relationship between the hot metal desulfurization rate and the treatment cost ratio (the cost in the KR method is 1.0).

Claims

In that dephosphorization and desulfurization from Tenro charged previous hot metal, using the hot metal that is not pretreated, first, the reaction vessel after performing dephosphorization was a converter, subsequently transferred to the hot metal in the ladle machine A hot metal pretreatment method, characterized by performing a stirring type desulfurization treatment and dephosphorizing the dephosphorization at the time of desulfurization at the time of decarburization treatment of the hot metal.