JP2020105544A - Molten iron desulfurization method - Google Patents
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本発明は、環境規制上使用が困難なＣａＦ2を用いずに、溶銑段階で行う溶銑脱硫方法に関する。 The present invention relates to a hot metal desulfurization method carried out in the hot metal stage without using CaF 2 which is difficult to use due to environmental regulations.
鉄鋼製品に含有される硫黄分は、強度劣化や材質の磁気特性、加工性などを阻害する悪影響を有することから、製品に応じた濃度以下のものが要求される。製鉄原料の炭材などに含まれる硫黄は高炉出銑後や電気炉還元溶解後などの粗溶銑中に含有され、主に溶鉄の精錬段階において、フラックスやマグネシウムなどの脱硫剤により溶銑脱硫が実施される。更に、転炉吹錬後や電気炉での溶解精錬末期以降の低炭素濃度である溶鋼段階においても、脱酸状態でフラックスを添加する溶鋼脱硫も併せ、後工程の鋳造までに製品規格に対応するように所定の濃度以下に硫黄濃度を低減する処理が実施されている。 Sulfur content contained in steel products has an adverse effect of deteriorating strength, magnetic properties of materials, workability, etc., so that the concentration is required to be not higher than the concentration suitable for the product. Sulfur contained in carbonaceous materials, which is a raw material for iron making, is contained in the crude hot metal after blast furnace tapping and after electric furnace reductive melting, etc. To be done. In addition, even in the molten steel stage where the carbon concentration is low after the end of melting and refining in the electric furnace after converter blowing, molten steel desulfurization that adds flux in the deoxidized state is also included, and it corresponds to the product standard before the casting in the subsequent process. As described above, the treatment for reducing the sulfur concentration to a predetermined concentration or less is performed.
ここで、溶銑段階では溶銑中に炭素を多く含有し、この溶存炭素は溶存硫黄の活量を高めて酸素活量を低下させる作用を有する。したがって、脱硫処理を実施する場合、溶銑段階で実施する溶銑脱硫が効率の良い方法として広く実施されている。このとき、高価な金属マグネシウムを用いることはコスト的な制約があり、脱硫フラックスには、下記（１）式の反応が有効であることから、ＣａＯを多く含むものを用いることが一般的である。
（ＣａＯ）＋［Ｓ］→（ＣａＳ）＋［Ｏ］ ・・・・・（１）式
Here, in the hot metal stage, a large amount of carbon is contained in the hot metal, and this dissolved carbon has an action of increasing the activity of dissolved sulfur and lowering the oxygen activity. Therefore, when performing desulfurization treatment, hot metal desulfurization performed at the hot metal stage is widely performed as an efficient method. At this time, there is a cost limitation in using expensive metallic magnesium, and it is common to use one containing a large amount of CaO as the desulfurization flux because the reaction of the following formula (1) is effective. ..
(CaO)+[S]→(CaS)+[O] (1) Formula
なお、（１）式中の括弧（）は、脱硫フラックス（または精錬スラグ）中の物質を示し、括弧［］は、溶銑中の溶存物質を示す。しかし、ＣａＯの融点は約２５７０℃であるため、溶鉄の精錬を行う際の処理温度ではＣａＯは滓化しない。そこで、ＣａＯの活量を低下させずに液相線温度の低下と粘性低下作用とが著しいＣａＦ2を配合した脱硫フラックスが過去に多く使用されていた。 In addition, the parentheses () in the formula (1) indicate the substances in the desulfurization flux (or the refining slag), and the parentheses [] indicate the dissolved substances in the hot metal. However, since the melting point of CaO is about 2570° C., CaO does not slag at the processing temperature when refining molten iron. Therefore, desulfurization fluxes containing CaF 2 that significantly reduces the liquidus temperature and the effect of decreasing the viscosity without decreasing the activity of CaO have been used in the past.
しかし、脱硫処理後に発生するスラグ中には、ＣａＦ2から起因するフッ素が含有されることから、土木用材料などとしての副産物販売に際して近年の環境基準を満たさない極めて付加価値の低いスラグができてしまう。このため、ＣａＦ2を用いないフラックスを用いた溶銑脱硫処理を行う技術が多く開発されてきた。 However, since fluorine derived from CaF 2 is contained in the slag generated after the desulfurization treatment, it is possible to form a slag with extremely low added value that does not meet the recent environmental standards when selling by-products such as materials for civil engineering. I will end up. Therefore, many techniques have been developed for performing hot metal desulfurization treatment using a flux that does not use CaF 2 .
特許文献１には、製鋼温度でも滓化できるカルシウムアルミネート系フラックスが開示されており、アルミナ（Ａｌ2Ｏ3）を配合することによって液相線温度を低下させ、脱硫能の確保が可能であることが記載されている。この技術を利用する場合、実施例に記載された溶鋼温度（１５５０℃）では、状態図でも明らかなように完全な液相になる。ところが、固相線温度（約１４２０℃以上）よりも低い１３００℃程度で実施される溶銑脱硫では、この技術を利用することによる効果は極めて小さい。したがって、耐火物にダメージを与えて操業阻害が発生しやすく、過剰な加熱によるエネルギーロスを伴う高温溶銑操業にしか適用ができない。 Patent Document 1 discloses a calcium aluminate-based flux that can be slagged even at a steelmaking temperature. By adding alumina (Al 2 O 3 ) to the liquidus temperature, it is possible to secure desulfurization ability. It is stated that there is. When this technique is used, at the molten steel temperature (1550° C.) described in the example, a complete liquid phase is obtained as is apparent from the phase diagram. However, in hot metal desulfurization performed at about 1300° C., which is lower than the solidus temperature (about 1420° C. or higher), the effect of using this technique is extremely small. Therefore, the refractory is liable to be damaged and the operation is likely to be hindered, and it can be applied only to the high temperature hot metal operation accompanied by energy loss due to excessive heating.
従って、ＣａＯ系フラックスにＡｌ2Ｏ3を配合した脱硫剤としては、特許文献２や特許文献３に記載のような、本来、溶銑中には含有されない高価なアルミニウムを合金として添加する操業が提案されている。しかしながら特許文献２に記載の方法では、脱硫処理後のｓｏｌ．Ａｌ濃度を２０−８０ｐｐｍという狭い範囲に制御する必要があることから安定に操業することが難しい。また、特許文献３に記載の方法では、大量の金属アルミニウム合金を必要とするため、高コストな操業になってしまう。 Therefore, the desulfurization agent obtained by blending Al 2 O 3 to CaO-based flux, such as described in Patent Documents 2 and 3, originally, is operated to add an expensive aluminum not contained in the molten iron as an alloy proposed Has been done. However, in the method described in Patent Document 2, sol. It is difficult to operate stably because it is necessary to control the Al concentration within a narrow range of 20-80 ppm. In addition, the method described in Patent Document 3 requires a large amount of metallic aluminum alloy, resulting in high-cost operation.
一方、特許文献４には、塩基度（ＣａＯ／ＳｉＯ2）が３．５以上と高く、フラックス中のＣａＯ分に対して２〜７質量％のＦｅＯを添加した溶銑脱硫方法が記載されており、その中で、Ａｌ2Ｏ3分を２〜２０質量％含有させる手段の有効性なども記載されている。このような高塩基度フラックスにＡｌ2Ｏ3を含有させて、低融点化を図ることは有効な手段であるが、酸化鉄（ＦｅＯ）はフラックスの粘性を低下させ、サルファイドキャパシティーを高める作用がある。この理由により酸化鉄（ＦｅＯ）濃度が全ＣａＯ濃度の７質量％以下に限定されているために、ＣａＦ2代替作用としての粘性低減、滓化促進効果が不十分である。 On the other hand, Patent Document 4 describes a hot metal desulfurization method in which basicity (CaO/SiO 2 ) is as high as 3.5 or more and 2 to 7 mass% FeO is added to CaO content in the flux. Among them, the effectiveness of the means for containing 2 to 20 mass% of Al 2 O 3 is also described. It is an effective means to make Al 2 O 3 contained in such a high basicity flux to lower the melting point, but iron oxide (FeO) lowers the viscosity of the flux and enhances the sulfide capacity. There is. For this reason, the iron oxide (FeO) concentration is limited to 7% by mass or less of the total CaO concentration, so that the effect of reducing viscosity and promoting slagging as an alternative action of CaF 2 is insufficient.
前述した特許文献１〜４に記載の方法では、溶銑脱硫処理でＣａＦ2を用いないことを前提としているが、高温での溶銑操業を前提としたり、高価な金属Ａｌの使用を伴ったり、ＣａＦ2代替作用として効果が不十分であったりするという課題がある。 In the methods described in Patent Documents 1 to 4 described above, it is premised that CaF 2 is not used in the hot metal desulfurization treatment, but it is premised on the hot metal operation at high temperature, accompanied by the use of expensive metal Al, or CaF 2. 2 There is a problem that the effect is insufficient as an alternative action.
本発明は前述の問題点を鑑み、溶銑段階の処理で、ＣａＦ2を用いることなく、低コストでかつ高温での溶銑操業を回避した反応効率の高い溶銑脱硫方法を提供することを目的とする。 The present invention has been made in view of the above problems, and an object thereof is to provide a hot metal desulfurization method with high reaction efficiency that avoids hot metal operation at low cost and at high temperature without using CaF 2 in the hot metal stage treatment. ..
即ち、本発明の要旨とするところは以下のとおりである。
（１）Ｓｉ濃度が０．３〜１．０質量％の溶銑に対して、ＣａＯ濃度が３５〜６０質量％、（Ａｌ2Ｏ3＋ＳｉＯ2）／（ＣａＯ）が０．５〜０．８、（ＳｉＯ2）≦０．８×（Ａｌ2Ｏ3）、酸化鉄濃度が６質量％以上の条件を満たす精錬スラグを用い、溶銑温度を１２５０〜１３５０℃にて脱硫処理を行うことを特徴とする溶銑脱硫方法。
ここで、括弧（）は、括弧内の物質の精錬スラグ中の濃度（質量％）を表す。
（２）前記脱硫処理後にスラグの除滓処理を実施し、その後、酸素吹錬を実施してＳｉ濃度が０．１質量％未満の溶鉄を得ることを特徴とする上記（１）に記載の溶銑脱硫方法。
（３）酸素吹錬を実施してＣ濃度が１．０質量％未満の溶鋼を得ることを特徴とする上記（２）に記載の溶銑脱硫方法。
（４）前記溶銑脱硫方法を、アーク加熱型電気炉で行うことを特徴とする上記（１）〜（３）のいずれかに記載の溶銑脱硫方法。
That is, the gist of the present invention is as follows.
(1) With respect to the hot metal having a Si concentration of 0.3 to 1.0 mass %, the CaO concentration is 35 to 60 mass %, and (Al 2 O 3 +SiO 2 )/(CaO) is 0.5 to 0.8. , (SiO 2 )≦0.8×(Al 2 O 3 ), using a refining slag satisfying the iron oxide concentration of 6% by mass or more, desulfurization treatment is performed at a hot metal temperature of 1250 to 1350° C. Hot metal desulfurization method.
Here, the parentheses () represent the concentration (mass %) of the substance in the parentheses in the refining slag.
(2) The slag slag treatment is performed after the desulfurization treatment, and then oxygen blowing is performed to obtain molten iron having a Si concentration of less than 0.1% by mass. Hot metal desulfurization method.
(3) The hot metal desulfurization method according to (2), wherein oxygen blowing is performed to obtain molten steel having a C concentration of less than 1.0% by mass.
(4) The hot metal desulfurization method according to any one of (1) to (3), wherein the hot metal desulfurization method is performed in an arc heating type electric furnace.
本発明によれば、溶銑段階の処理で、ＣａＦ2を用いることなく、低コストでかつ高温での溶銑操業を回避した反応効率の高い溶銑脱硫方法を提供することが可能となる。 According to the present invention, it is possible to provide a hot metal desulfurization method with high reaction efficiency, which avoids hot metal operation at high cost at low cost in the hot metal stage treatment without using CaF 2 .
以下、本発明の実施形態について、図１を参照して説明する。
図１は、本実施様態に係る溶銑脱硫方法の例を説明するための図である。図１は、直流電気炉中に型銑と炭材還元ブリケットとを主原料として溶解した溶銑１中から、精錬用フラックス２を用いて脱硫処理を実施している操業を示している。
Hereinafter, an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a diagram for explaining an example of the hot metal desulfurization method according to the present embodiment. FIG. 1 shows an operation in which desulfurization treatment is carried out using a refining flux 2 from hot metal 1 obtained by melting type pig iron and carbonaceous material reducing briquette as a main raw material in a DC electric furnace.
この実施形態における直流電気炉の構造は、上部電極３と下部水冷電極４とによってアーク５を発生して加熱できる構造であり、精錬用フラックス２はホッパー６より炉内に必要量切り出し添加される。
The structure of the DC electric furnace in this embodiment is a structure in which an arc 5 can be generated and heated by the upper electrode 3 and the lower water-cooled electrode 4, and the required amount of the refining flux 2 is cut out from the
また、脱硫処理後の後工程では、酸素ランス７から酸素噴流８を吹き付けて脱炭処理、脱燐処理、および脱炭反応に伴って生じるＣＯボイリングのシール効果を利用した脱窒処理を実施することができる。この際、脱硫によって還元反応で滓化した精錬用フラックスを主成分としたスラグ（以下、精錬スラグと呼ぶ）が酸化反応によって復硫することを抑制するために、脱硫処理が完了した後に炉体９を排滓傾動装置１０で傾動させて除滓孔１１から除滓樋１２を経由してスラグパン１３中に精錬スラグを排滓する方式が採用されている。 Further, in the post-process after the desulfurization treatment, an oxygen jet 8 is blown from the oxygen lance 7 to carry out decarburization treatment, dephosphorization treatment, and denitrification treatment utilizing the sealing effect of CO boiling generated by the decarburization reaction. be able to. At this time, in order to prevent the slag mainly composed of the refining flux that has been slagged by the reduction reaction due to desulfurization (hereinafter referred to as refining slag) from being re-sulfurized by the oxidation reaction, the furnace body after the desulfurization treatment is completed. A method is used in which 9 is tilted by a slag tilting device 10 and the slag slag is discharged from a slag hole 11 through a slag gutter 12 into a slag pan 13.
脱硫のための精錬スラグの組成は、前述の（１）式の反応で高いＣａＯ活量を確保するために、ＣａＯ濃度を３５質量％以上とする。また、良好な滓化を維持するためには一定以上のＡｌ2Ｏ3や酸化鉄などを配合する必要があるため、ＣａＯ濃度は６０質量％以下とする。滓化作用を有するものとしては、Ａｌ2Ｏ3やシリカ（ＳｉＯ2）が液相線温度を低下させるため有効であるが、液相状態では多量のＡｌ2Ｏ3やＳｉＯ2が含まれていると、ＣａＯ活量を低下させる悪影響があるために、適切に上限を規定する必要がある。 As for the composition of the refining slag for desulfurization, the CaO concentration is set to 35% by mass or more in order to secure a high CaO activity in the reaction of the above formula (1). Further, in order to maintain good slag formation, it is necessary to mix a certain amount of Al 2 O 3 or iron oxide, so that the CaO concentration is 60% by mass or less. Al 2 O 3 and silica (SiO 2 ) are effective as slag-forming agents because they lower the liquidus temperature, but in the liquid state, they contain a large amount of Al 2 O 3 and SiO 2. If so, there is an adverse effect of reducing the CaO activity, so it is necessary to properly specify the upper limit.
また、ＦｅＯ、Ｆｅ2Ｏ3、Ｆｅ3Ｏ4などの酸化鉄成分も同様に滓化作用が大きく、酸化鉄は更に、ＣａＦ2に代替するスラグ粘性低下作用と、サルファイドキャパシティーを向上させる作用とがあることが知られている。しかし、酸化鉄自体は精錬スラグの酸素ポテンシャルを上昇させるため、その影響により酸素ポテンシャルの低い溶銑とスラグとの界面酸素ポテンシャルを高めてしまい、（１）式に示される界面化学反応を阻害する悪影響を有する。このため、従来の手段においては高濃度の酸化鉄を含有する精錬スラグを用いた溶銑脱硫処理を効率よく実施することは困難であった。 Further, iron oxide components such as FeO, Fe 2 O 3 , and Fe 3 O 4 also have a large slag-forming effect, and iron oxide further acts to reduce the slag viscosity to substitute for CaF 2 and to improve the sulfide capacity. It is known that However, since iron oxide itself raises the oxygen potential of the refining slag, its effect increases the interfacial oxygen potential between the hot metal and slag with a low oxygen potential, which adversely affects the interfacial chemical reaction shown in equation (1). Have. Therefore, it has been difficult to efficiently carry out the hot metal desulfurization treatment using the refining slag containing a high concentration of iron oxide by the conventional means.
本発明では、滓化作用を有するものとしてＡｌ2Ｏ3を用い、また、Ａｌ2Ｏ3の一部に代えてＳｉＯ2をも併用することにより、従来困難であった高濃度の酸化鉄を含有する精錬スラグにおいても、良好な脱硫処理を可能とする条件を、本発明者の実験研究によって見出した。 In the present invention, Al 2 O 3 is used as one having a slag-forming effect, and SiO 2 is also used in combination in place of a part of Al 2 O 3 , so that a high concentration of iron oxide, which has been difficult in the past, can be obtained. The conditions for enabling a good desulfurization treatment even in the refining slag contained therein have been found by the inventor's experimental research.
精錬スラグにおいて滓化作用を確保するため、（Ａｌ2Ｏ3＋ＳｉＯ2）／（ＣａＯ）（質量濃度比）は０．５〜０．８とする。（Ａｌ2Ｏ3＋ＳｉＯ2）／（ＣａＯ）（質量濃度比）が０．５未満では、ＣａＯの滓化作用が不足してしまい、（Ａｌ2Ｏ3＋ＳｉＯ2）／（ＣａＯ）（質量濃度比）が０．８超では、相対的にＣａＯの比率が小さくなってＣａＯの活量が低下してしまうからである。 In order to secure the slagging action in the refining slag, (Al 2 O 3 +SiO 2 )/(CaO) (mass concentration ratio) is set to 0.5 to 0.8. When (Al 2 O 3 +SiO 2 )/(CaO) (mass concentration ratio) is less than 0.5, the slagging action of CaO is insufficient, and (Al 2 O 3 +SiO 2 )/(CaO) (mass concentration) This is because, when the ratio) is more than 0.8, the ratio of CaO becomes relatively small and the activity of CaO decreases.
また、精錬スラグにおいて、（ＳｉＯ2）≦０．８×（Ａｌ2Ｏ3）とする。精錬スラグ中において、Ａｌ2Ｏ3に対してＳｉＯ2が過剰に含まれていると、精錬スラグ中で網目構造を形成してしまい、それにより流動性が低下し、脱硫効果が低下してしまうからである。 In the refined slag, (SiO 2 )≦0.8×(Al 2 O 3 ). In the refined slag, if SiO 2 is excessively contained with respect to Al 2 O 3 , a network structure will be formed in the refined slag, which will reduce the fluidity and the desulfurization effect. Because.
また、精錬スラグにおいて、滓化作用に加えてサルファイドキャパシティー向上効果を発揮させるために、酸化鉄濃度は６質量％以上とする。ここでいう酸化鉄濃度は、スラグ中の二価の酸化鉄濃度と三価の酸化鉄濃度との合計で規定したものである。このとき、重要になることは、前述の界面の酸素ポテンシャルを低位に維持して（１）式の化学反応を速やかに進行させることである。前述したように、酸化鉄は界面酸素ポテンシャルを高めてしまうが、溶銑中のＳｉ濃度を０．３質量％以上の高濃度に維持することにより、界面酸素ポテンシャルの上昇による悪影響を抑制する効果を発揮する。 Further, in the refining slag, the iron oxide concentration is 6% by mass or more in order to exert the effect of improving the sulfide capacity in addition to the slag-forming effect. The iron oxide concentration here is defined as the total of the divalent iron oxide concentration and the trivalent iron oxide concentration in the slag. At this time, what is important is to maintain the oxygen potential of the above-mentioned interface at a low level and to promptly advance the chemical reaction of the formula (1). As described above, iron oxide increases the interfacial oxygen potential, but by maintaining the Si concentration in the hot metal at a high concentration of 0.3 mass% or more, the effect of suppressing the adverse effect due to the increase in the interfacial oxygen potential can be obtained. Demonstrate.
溶銑中においては、多量に含有される溶存炭素によって酸素ポテンシャルは低位に維持されているが、例えば脱酸力の強いＡｌを溶銑中に含有させることにより、溶銑中（バルク）の酸素ポテンシャルはさらに低下することが考えられる。また、溶銑中のスラグ／メタル界面付近においては、脱硫反応と並行して、例えば下記（２）式の反応が界面付近で起こり、Ａｌによる酸化ロスが発生して界面酸素ポテンシャルは低下する。
［Ａｌ］※＋（ＦｅＯ）→（Ａｌ2Ｏ3）＋Ｆｅ ・・・・・・（２）
In hot metal, the oxygen potential is maintained at a low level due to a large amount of dissolved carbon. However, for example, by including Al having a strong deoxidizing power in the hot metal, the oxygen potential in the hot metal (bulk) is further increased. It is possible that it will decrease. Further, in the vicinity of the slag/metal interface in the hot metal, for example, the reaction of the following formula (2) occurs in the vicinity of the interface in parallel with the desulfurization reaction, the oxidation loss due to Al occurs, and the interface oxygen potential decreases.
[Al] * +(FeO)→(Al 2 O 3 )+Fe (2)
ここで、（２）式中の［］※は、溶鉄中の均一な合金元素のバルクの濃度ではなく、スラグ／メタル界面近くの濃度境界相で濃度勾配を持った状態における溶銑中のスラグ／メタル界面付近における合金濃度を示す。従って、スラグとメタルとの間の酸素ポテンシャルが非平衡のまま（２）式の反応の進行と共に（１）式の脱硫反応が進行するため、界面の酸素ポテンシャルを規定する［Ａｌ］※は溶銑内のバルク（界面から離れた位置）のＡｌ濃度よりも低位である。 Here, [] * in equation (2) is not the concentration of the uniform alloy element in the molten iron, but the slag in the hot metal in the state where there is a concentration gradient in the concentration boundary phase near the slag/metal interface. The alloy concentration near the metal interface is shown. Therefore, since the desulfurization reaction of the equation (1) proceeds with the progress of the reaction of the equation (2) while the oxygen potential between the slag and the metal is in nonequilibrium, [Al] * that defines the oxygen potential of the interface is hot metal. It is lower than the Al concentration of the bulk inside (position away from the interface).
本発明では、精錬スラグ中に比較的多くの酸化鉄を含有するため、精錬スラグからスラグ／メタル界面へのＦｅＯ供給速度は大きい。一方、溶銑中（バルク）の酸素ポテンシャルは酸化鉄を多く含有する精錬スラグよりも低い非平衡状態であり、その、スラグ／メタル界面にて（２）式は進行する。スラグ／メタル界面では（２）式のＡｌによる酸化ロスが早く進行するために、溶銑内のバルクから濃度境界相を通過して供給されるＡｌが不足し、スラグ／メタル界面での［Ａｌ］※が低位になる。このため、十分に低位な界面酸素ポテンシャルを確保することが困難となり、（１）式の脱硫速度は低下する。従って、溶銑内のバルクからスラグ／メタル界面へＡｌの物質移動が律速せずに（１）式を充分に早く進行させるためには、［Ａｌ］※を高位に維持する必要がある。そのためには、特許文献３に記載の方法のように、高価なアルミ合金を大量に含有させ、溶銑中とスラグ／メタル界面とのＡｌの濃度勾配によって、スラグ／メタル界面へのＡｌの流入を促進させる必要が生じる。しかし、金属Ａｌは溶銑中に元来存在するようなＳｉよりも高価であり、更に、脱酸力がＳｉよりも大幅に強いＡｌを高濃度で操業するのは非効果的であり、コスト的に不利な操業となる。 In the present invention, since the refining slag contains a relatively large amount of iron oxide, the feed rate of FeO from the refining slag to the slag/metal interface is high. On the other hand, the oxygen potential in the hot metal (bulk) is in a non-equilibrium state which is lower than that of the refining slag containing a large amount of iron oxide, and the equation (2) proceeds at the slag/metal interface. At the slag/metal interface, since the oxidation loss due to Al in formula (2) progresses quickly, the Al supplied from the bulk in the hot metal through the concentration boundary phase is insufficient, and [Al] at the slag/metal interface * Is low. For this reason, it becomes difficult to secure a sufficiently low interfacial oxygen potential, and the desulfurization rate of formula (1) decreases. Therefore, in order for the mass transfer of Al from the bulk in the hot metal to the slag/metal interface to proceed in the equation (1) sufficiently quickly without rate control, it is necessary to maintain [Al] * at a high level. For that purpose, as in the method described in Patent Document 3, a large amount of expensive aluminum alloy is contained, and the inflow of Al to the slag/metal interface is caused by the Al concentration gradient between the hot metal and the slag/metal interface. There is a need to promote it. However, metallic Al is more expensive than Si that originally exists in the hot metal, and it is ineffective to operate Al at a high concentration, which has a significantly higher deoxidizing power than Si, which is costly. This is a disadvantageous operation.
一方、Ａｌの代わりにＳｉを添加し、溶銑中において、Ａｌを添加した場合と同等の酸素ポテンシャルにするためには、一般的に、Ａｌよりも１桁以上高い濃度になるようにＳｉを添加する必要がある。精錬スラグ中の酸化鉄濃度が高い場合には精錬スラグからスラグ／メタル界面へ酸化鉄が多く供給されるが、脱硫を促進するよう界面酸素ポテンシャルを低下させるには、必要なマスバランスを評価し、その分だけ溶銑中（バルク）から界面へＳｉを供給する必要がある。このため、溶銑中のスラグ／メタル界面付近におけるＳｉ濃度（［Ｓｉ］※）と溶銑中（バルク）のＳｉ濃度（［Ｓｉ］）との濃度比（［Ｓｉ］※／［Ｓｉ］）は、同一脱酸力に匹敵する量のＡｌを添加した場合のスラグ／メタル界面付近におけるＡｌ濃度（［Ａｌ］※）と溶銑中（バルク）のＡｌ濃度（［Ａｌ］）との濃度比（［Ａｌ］※／［Ａｌ］）よりも高くなる。仮にバルク中の脱酸力がＡｌと同等となるＳｉ濃度とした場合には、Ｓｉを添加した条件では界面酸素ポテンシャルを安定的に低位に維持できるために脱硫促進には極めて有利である。 On the other hand, in order to obtain the oxygen potential equivalent to that in the case of adding Al in the hot metal by adding Si in place of Al, Si is generally added so that the concentration becomes one digit or more higher than that of Al. There is a need to. When the iron oxide concentration in the refining slag is high, a large amount of iron oxide is supplied from the refining slag to the slag/metal interface, but in order to reduce the interfacial oxygen potential to promote desulfurization, the mass balance required is evaluated. Therefore, it is necessary to supply Si from the hot metal (bulk) to the interface. Therefore, the concentration ratio ([Si] * /[Si]) between the Si concentration ([Si] * ) near the slag/metal interface in the hot metal and the Si concentration ([Si]) in the hot metal (bulk) is The concentration ratio of the Al concentration ([Al] * ) near the slag/metal interface and the Al concentration ([Al]) in the hot metal ([Al]) when adding an amount of Al equivalent to the same deoxidizing power ([Al] ] * /[Al]) If the Si concentration is such that the deoxidizing power in the bulk is equal to that of Al, the interfacial oxygen potential can be stably maintained at a low level under the condition of adding Si, which is extremely advantageous for promoting desulfurization.
本発明者らの実験研究の結果、高濃度の酸化鉄を含有する精錬スラグでは、溶銑中のＳｉ濃度が０．３質量％以上の条件において、良好な脱硫処理を実施できることを知見した。上記の理由から、本発明において規定される、精錬スラグの組成及び溶銑中Ｓｉ濃度は、フラックスを添加したり成分を調整したりした後のスラグの滓化が完了した時点から、所定の脱硫処理が完了するまでの間に維持すべき範囲である。 As a result of the experiments conducted by the present inventors, it has been found that the refining slag containing a high concentration of iron oxide can carry out a good desulfurization treatment under the condition that the Si concentration in the hot metal is 0.3 mass% or more. For the above reasons, the composition of the smelting slag and the Si concentration in the hot metal defined in the present invention are determined by a predetermined desulfurization treatment from the time when the slag slag after the addition of the flux or the adjustment of the components is completed. This is the range that should be maintained until the completion of.
但し、精錬スラグの組成及び溶銑中Ｓｉ濃度が一部の間規定範囲外であっても、反応速度は低下するものの脱硫反応は進行する。また、完全滓化前の精錬スラグの組成域や、溶銑中のＳｉ濃度が０．３質量％未満になる処理末期での脱硫反応進行時間を区分することは困難である。そこで、本発明では、脱硫処理全体のうち、６割以上のＳ濃度低下分で、精錬スラグの組成及び溶銑中Ｓｉ濃度が前述の条件を満たしていればよい。 However, even if the composition of the refining slag and the Si concentration in the hot metal are out of the specified range for some time, the desulfurization reaction proceeds although the reaction rate decreases. Further, it is difficult to distinguish the composition range of the refining slag before complete slagging and the desulfurization reaction progress time at the end of the treatment when the Si concentration in the hot metal is less than 0.3% by mass. Therefore, in the present invention, the composition of the refining slag and the Si concentration in the hot metal should satisfy the above-mentioned conditions with a decrease in S concentration of 60% or more of the entire desulfurization treatment.
また、前述したように、溶銑中のＳｉ濃度の下限値を０．３質量％としたのは、スラグ／メタル界面での界面酸素ポテンシャルを低下させて（１）式の反応を速やかに進行させるために最低限のＳｉ濃度を確保しなければならないからである。一方、溶銑中のＳｉ濃度の上限値は、１．０質量％とする。溶銑中のＳｉ濃度が１．０質量％を超える操業を実施するためには、通常大量の合金シリコンを必要とし、コストが多くかかってしまう。また、溶銑中のＳｉ濃度が１．０質量％を超えると、溶鋼を製造するまでに酸化によってＳｉＯ2が多く生成され、その分スラグ量が過剰になって操業制約になる場合が多い。 Further, as described above, the lower limit of the Si concentration in the hot metal is set to 0.3% by mass so that the interfacial oxygen potential at the slag/metal interface is lowered and the reaction of the formula (1) proceeds rapidly. This is because it is necessary to secure the minimum Si concentration. On the other hand, the upper limit of the Si concentration in the hot metal is 1.0% by mass. In order to carry out the operation in which the Si concentration in the hot metal exceeds 1.0% by mass, a large amount of alloy silicon is usually required, resulting in a high cost. Further, when the Si concentration in the hot metal exceeds 1.0 mass %, a large amount of SiO 2 is produced by the oxidation until the molten steel is produced, and the slag amount becomes excessive by that amount, which often imposes operational restrictions.
なお、溶銑中のＳｉ濃度を０．３〜１．０質量％に確保する場合、安価型銑に比較的多く含まれるような原料中に予め不可避的に含有されているＳｉや、電気炉でアーク溶解中に浮遊する酸化物中のＳｉＯ2が高温アーク部などで炭素によって還元されたＳｉを含めることができる。そのため、フェロシリコンなどの合金の添加量を削減でき、さらには後工程で過剰のＳｉを酸化除去して、熱裕度を確保することもできる。 When securing the Si concentration in the hot metal to 0.3 to 1.0% by mass, Si which is inevitably contained in advance in a raw material that is contained in a relatively large amount in inexpensive pig iron or an electric furnace is used. SiO 2 in the floating oxide during arc melting can include Si reduced by carbon, such as at high temperature arc parts. Therefore, it is possible to reduce the amount of addition of an alloy such as ferrosilicon, and it is also possible to oxidize and remove excess Si in a subsequent step to secure a thermal margin.
また、脱硫処理中の処理温度は１２５０〜１３５０℃とする。脱硫処理中の温度が１２５０℃未満では、滓化性や精錬スラグの流動性が悪化して反応速度が十分ではなくなり、反応効率が著しく低下してしまう。また、脱硫処理中の温度が１３５０℃を超えると、炉内の耐火物の損傷が大きくなり炉の寿命が大きく低下してしまう。しかしながら、１３５０℃を超えると吸熱反応である（１）式の反応自体が早くなり、本発明の規定範囲外であっても同等の脱硫速度を発現することが可能である。 The treatment temperature during the desulfurization treatment is 1250 to 1350°C. If the temperature during the desulfurization treatment is less than 1250°C, the slagging property and the fluidity of the refining slag are deteriorated, the reaction rate becomes insufficient, and the reaction efficiency remarkably decreases. Further, if the temperature during the desulfurization treatment exceeds 1350° C., the refractory in the furnace will be greatly damaged and the life of the furnace will be greatly reduced. However, if the temperature exceeds 1350° C., the reaction itself of the formula (1), which is an endothermic reaction, becomes faster, and it is possible to exhibit an equivalent desulfurization rate even if it is outside the specified range of the present invention.
更に、脱硫処理を完了した後に引き続き、同一炉で脱炭処理や脱燐処理等を実施することによって、固定費の低い操業を行ってもよい。そのために、上記脱硫処理を実施した後にスラグを排出し、その後に、図１の酸素ランス７から酸素を溶銑面に吹き付けて酸素吹錬を実施し、Ｓｉ濃度が０．１質量％未満の範囲に脱珪することによって熱裕度を向上させることができる。また、炭素、燐の酸化除去による精錬を実施することもできる。また、スラグを排滓する場合には、図１に示すような排滓孔を有する電気炉の傾動排滓方式を採用したり、転炉や電気炉の炉口からの傾動排滓（ドラッガー使用など適宜可能）、ＶＳＤ式吸引排滓などを採用したり、適宜排滓方式は選定できる。 Furthermore, after the desulfurization treatment is completed, a decarburization treatment, a dephosphorization treatment, or the like may be continuously performed in the same furnace to perform an operation with a low fixed cost. Therefore, after performing the desulfurization treatment, the slag is discharged, and then oxygen is blown from the oxygen lance 7 of FIG. 1 onto the hot metal surface to perform oxygen blowing, and the Si concentration is within a range of less than 0.1 mass %. The thermal tolerance can be improved by desiliconizing. It is also possible to carry out refining by oxidizing and removing carbon and phosphorus. When slag is discharged, a tilting slag system of an electric furnace having a slag hole as shown in Fig. 1 is adopted, or tilting slag (using a dragger) from a furnace of a converter or an electric furnace is used. Etc.), a VSD type suction slag, etc. can be adopted, and a slag method can be selected appropriately.
なお、溶銑中のＳｉ濃度が０．１質量％以上の状態では、供給した酸素の殆どが脱珪処理に使用されて、脱炭やそれに伴う低窒素化、脱燐などの処理が実質できない。したがって、脱珪処理を行う場合には、同一炉でＳｉ濃度が０．１質量％未満の範囲にまで脱珪した溶鉄を製造することが好ましい。 When the Si concentration in the hot metal is 0.1% by mass or more, most of the supplied oxygen is used for desiliconization treatment, and decarburization and accompanying reduction of nitrogen and dephosphorization cannot be substantially performed. Therefore, when performing the desiliconization treatment, it is preferable to produce molten iron desiliconized to a Si concentration of less than 0.1 mass% in the same furnace.
特にアーク加熱型電気炉で実施する場合には、スラグの排滓後の脱珪処理により熱裕度を確保できるため、熱源としての電気エネルギーを大幅に削減することが可能であり、さらにＣ濃度が１．０質量％未満の溶鋼を製造する際には、スラグ中のＳｉＯ2のフォーミング効果によって外部空気に起因する窒素のピックアップを回避し、通常の電気炉操業では困難とされる、脱炭吹錬時の低窒素化操業を可能にするため、電気炉操業で酸素吹錬によりＣ濃度が１．０質量％未満の溶鋼を製造することが好ましい。 Especially when it is carried out in an arc heating type electric furnace, the thermal tolerance can be secured by the desiliconization treatment after the slag slag is removed, so that it is possible to significantly reduce the electric energy as a heat source, and further the C concentration. When producing molten steel with less than 1.0 mass%, decarburization, which is difficult in normal electric furnace operation, avoids nitrogen pickup due to external air due to the forming effect of SiO 2 in slag. In order to enable a nitrogen-reducing operation during blowing, it is preferable to produce molten steel with a C concentration of less than 1.0 mass% by oxygen blowing in an electric furnace operation.
以上のように本実施形態では、図１に示したような直流電気炉で溶銑の脱硫処理を行う例について説明した。一方、本発明は、直流電気炉以外にも、トーピードカーや溶銑鍋を用いた機械攪拌、三相交流や高周波型各種電気炉等を用いても実施可能であり、高炉溶銑や、溶融還元法、各種スクラップ溶解法などによって製造された溶鉄やそれらの混合物で、一般的には炭素を２．０質量％以上含有する溶鉄を対象にして実施することができる。 As described above, in the present embodiment, an example of performing desulfurization treatment of hot metal in the DC electric furnace as shown in FIG. 1 has been described. On the other hand, the present invention, in addition to the DC electric furnace, mechanical stirring using a torpedo car or a hot metal ladle, can also be carried out using a three-phase AC or various high-frequency type electric furnace, blast furnace hot metal, smelting reduction method, Molten iron produced by various scrap melting methods or the like, or a mixture thereof can be generally used for molten iron containing 2.0% by mass or more of carbon.
次に、本発明の実施例について説明するが、この条件は、本発明の実施可能性及び効果を確認するための一条件例であり、本発明は、この実施例の記載に限定されるものではない。本発明は、本発明の要旨を逸脱せず、本発明の目的を達成する種々の手段にて実施することができる。 Next, an example of the present invention will be described, but this condition is an example of a condition for confirming the practicability and effect of the present invention, and the present invention is limited to the description of this example. is not. The present invention can be implemented by various means for achieving the object of the present invention without departing from the spirit of the present invention.
（第１の実験）
３ＭＶＡの直流電気炉で４ｔ／ｃｈの溶銑を製造し、直流電気炉を傾動させて溶解時に発したスラグの除滓を行い、不可避的に残留するスラグのみ存在する状態とした。次いで、フラックスを添加してアーク加熱を行い、精錬スラグを生成させて、脱硫処理を行った。フラックスはＬＦ造塊滓を主成分としたものを用い、酸化鉄としてはヘマタイトを主成分とした鉄鉱石を用い、比較例も含めて実験水準毎にフラックスの組成を調整し、精錬スラグの組成を調整した。フラックスの組成を調整する際には、必要に応じてアルミナ煉瓦屑、生石灰、硅砂を用いた。また、フラックスの組成を調整する際に予め３ｍｍアンダーに粉砕した混合品を実験水準毎に使用した。フラックス添加前の溶銑の成分は、質量％でＣ：３．０〜３．７％、Ｓｉ：０．５〜０．６％、Ｍｎ：０．０５％未満、Ｐ：０．０８〜０．１３％で、Ｓ：０．０５％±０．０１％であった。
(First experiment)
4 t/ch of hot metal was manufactured in a 3 MVA direct current electric furnace, and the direct current electric furnace was tilted to remove slag generated during melting, so that only the slag remaining inevitably existed. Next, flux was added and arc heating was performed to generate refining slag, and desulfurization treatment was performed. The LF slag was used as the main component of the flux, and the iron ore containing hematite as the main component was used as the iron oxide. The composition of the slag was adjusted by adjusting the composition of the flux for each experimental level, including comparative examples. Was adjusted. When adjusting the composition of the flux, alumina brick scraps, quicklime, and silica sand were used as needed. Further, when adjusting the composition of the flux, a mixed product which was crushed to 3 mm under in advance was used for each experimental level. The components of the hot metal before the addition of the flux are C: 3.0 to 3.7%, Si: 0.5 to 0.6%, Mn: less than 0.05%, and P: 0.08 to 0. At 13%, S: 0.05% ± 0.01%.
添加したフラックスの量はいずれも３０ｋｇ／ｃｈで、フラックス添加後の処理時間は１２分で、処理前後と処理開始後７分とで溶銑温度を消耗型熱電対で測定した。溶銑温度は、１２１０〜１３４０℃の範囲で調整し、実験を行った。 The amount of the added flux was 30 kg/ch, the treatment time after the addition of the flux was 12 minutes, and the hot metal temperature was measured by a consumable thermocouple before and after the treatment and 7 minutes after the treatment was started. The hot metal temperature was adjusted in the range of 1210 to 1340° C. and the experiment was conducted.
処理後に溶銑サンプルとスラグサンプルとを汲み上げ、そこから鉄製サンプラーでサンプルを採取して組成を分析し、その分析値を実験後結果として整理した。また、フラックスを添加してから２分後にも精錬スラグのサンプルを採取した結果、各実験において２分後のサンプルと処理後のスラグの液相部とにおいて成分に大きな差異は認められず、滓化進行に変化は認められなかった。主な実験結果の一覧を表１に示す。脱硫率が８０％以上であったものを発明の効果が得られたものとして評価した。なお、表中の酸化鉄濃度（質量％）とは、サンプル中の２価、３価として存在するそれぞれＦｅＯ、Ｆｅ2Ｏ3、およびＦｅ3Ｏ4の酸化鉄濃度の合計値である。また、表中の下線は、本発明の範囲から外れた条件であることを示している。 After the treatment, a hot metal sample and a slag sample were pumped up, a sample was taken from the sample with an iron sampler to analyze the composition, and the analyzed values were arranged as the results after the experiment. Further, as a result of collecting the samples of the refined slag even 2 minutes after the addition of the flux, no significant difference was observed in the components between the sample after 2 minutes and the liquid phase part of the treated slag in each experiment. No change was observed in the progression. Table 1 shows a list of the main experimental results. When the desulfurization rate was 80% or more, the effect of the invention was evaluated. The iron oxide concentration (mass %) in the table is the total value of the iron oxide concentrations of FeO, Fe 2 O 3 and Fe 3 O 4 , which are present as divalent and trivalent in the sample. The underline in the table indicates that the condition is outside the scope of the present invention.
実施例１は、本実験の基本条件であり脱硫後の溶銑中Ｓ濃度が０．００７１質量％であり、脱硫率は８０％を超え、目標としていた０．０１質量％以下の良好な脱硫特性を確認することができた。実施例２及び３は、ＣａＯ濃度を変更した水準であるが、本発明の滓化促進作用は充分であることが確認でき、脱硫処理も良好で脱硫後の溶銑中Ｓ濃度はそれぞれ０．００６５、０．００８５質量％であった。 Example 1 is the basic condition of the present experiment, the S concentration in the hot metal after desulfurization is 0.0071% by mass, the desulfurization rate exceeds 80%, good desulfurization characteristics of 0.01% by mass or less targeted I was able to confirm. In Examples 2 and 3, the CaO concentration was changed, but it was confirmed that the slag formation promoting effect of the present invention was sufficient, the desulfurization treatment was also good, and the S concentration in the hot metal after desulfurization was 0.0065 each. Was 0.0085 mass %.
実施例４は、滓化作用のあるＳｉＯ2の比率を高めた水準であるが、Ａｌ2Ｏ3との比率が規定の範囲内であり、脱硫後の溶銑中Ｓ濃度が０．００８４質量％と結果も良好であった。実施例５は、酸化鉄濃度を本発明の規定範囲下限付近で実施したものであるが、脱硫後の溶銑中Ｓ濃度が０．００８４質量％と良好な脱硫処理を実施することができた。 Example 4 is a level in which the ratio of SiO 2 having a slag-forming effect is increased, but the ratio with Al 2 O 3 is within the specified range, and the S concentration in the hot metal after desulfurization is 0.0084% by mass. And the result was also good. Although Example 5 was carried out near the lower limit of the specified range of the present invention, the S concentration in the hot metal after desulfurization was 0.0084% by mass, and a good desulfurization treatment could be carried out.
一方、比較例１は、規定より酸化鉄濃度が低い操業の結果であったが、酸化鉄量が低いため、精錬スラグの粘性低減作用が低かった。また、サルファイドキャパシティーが不足していたため、脱硫後の溶銑中Ｓ濃度が０．０１２１質量％であり、脱硫率は８０％に到達せず、目標としていた０．０１質量％以下を達成できなかった。比較例２は、溶銑中Ｓｉ濃度を規定より下げた操業であったが、界面酸素ポテンシャルが十分に低下させることができなかったため、脱硫後のＳ濃度が０．０１３１質量％であり、脱硫率は８０％に到達せず、目標としていた０．０１質量％以下を達成できなかった。 On the other hand, Comparative Example 1 was the result of the operation in which the iron oxide concentration was lower than the regulation, but the amount of iron oxide was low, and therefore the viscosity reducing action of the smelting slag was low. Further, since the sulfide capacity was insufficient, the S concentration in the hot metal after desulfurization was 0.0121% by mass, the desulfurization rate did not reach 80%, and the target 0.01% by mass or less could not be achieved. It was Comparative Example 2 was an operation in which the Si concentration in the hot metal was lower than the specified value, but the interfacial oxygen potential could not be lowered sufficiently, so the S concentration after desulfurization was 0.0131% by mass, and the desulfurization rate was Did not reach 80%, and the target 0.01 mass% or less could not be achieved.
比較例３は、ＣａＯ濃度が規定より高い操業で、滓化不良によって規定時間内での脱硫が不十分であったため、脱硫率は８０％に到達せず、脱硫後の溶銑中Ｓ濃度が０．０１４２質量％であった。比較例４はＣａＯ濃度が規定値以下で、比較例５は（Ａｌ2Ｏ3＋ＳｉＯ2）／（ＣａＯ）が規定値以上の操業で、いずれもＣａＯの活量が低かったため、脱硫率は８０％に到達せず、脱硫後の溶銑中Ｓ濃度が０．０１４４質量％であった。 In Comparative Example 3, the operation in which the CaO concentration was higher than the specified value, and the desulfurization within the specified time was insufficient due to poor slag formation, so the desulfurization rate did not reach 80%, and the S concentration in the hot metal after desulfurization was 0. It was 0.0142% by mass. In Comparative Example 4, the CaO concentration was not more than the specified value, and in Comparative Example 5, the operation was such that (Al 2 O 3 +SiO 2 )/(CaO) was not less than the specified value, and since the activity of CaO was low, the desulfurization ratio was 80. %, the S concentration in the hot metal after desulfurization was 0.0144% by mass.
比較例６は、滓化作用のあるＳｉＯ2のＡｌ2Ｏ3に対する比率が規定より高い条件であったが、精錬スラグの粘性が高く、精錬スラグ中にＣａＳとして吸収された硫黄分の物質移動律速によって反応効率が低く、脱硫率は８０％に到達せず、脱硫後の溶銑中Ｓ濃度が０．０１２１質量％であった。比較例７は処理温度が規定以下であり、吸熱反応の脱硫処理には不十分な条件であったため、脱硫率は８０％に到達せず、脱硫後の溶銑中Ｓ濃度が０．０１１０質量％であった。 In Comparative Example 6, the ratio of SiO 2 having a slag forming effect to Al 2 O 3 was higher than the regulation, but the viscosity of the smelting slag was high, and the mass transfer of the sulfur content absorbed as CaS in the smelting slag was performed. The reaction efficiency was low due to rate control, the desulfurization rate did not reach 80%, and the S concentration in the hot metal after desulfurization was 0.0121% by mass. In Comparative Example 7, the treatment temperature was not more than the specified value and the conditions were not sufficient for the desulfurization treatment of the endothermic reaction, so the desulfurization rate did not reach 80%, and the S concentration in the hot metal after desulfurization was 0.0110% by mass. Met.
（第２の実験）
第１の実験の実施例１の基本条件とほぼ同一の条件で脱硫処理を行い、溶銑中Ｓ濃度が０．００７１質量％の溶銑を得た。その後、直流電気炉を傾動してその溶銑を残したまま脱硫スラグを排滓した。そして、８０Ｎｍ3／ｈ・ｔの送酸速度でランスから酸素を供給して酸素吹錬を実施した。酸素吹錬により、溶銑中Ｓｉ濃度を０．１質量％未満の状態とすることができ、その後、脱炭、脱燐、脱窒効果が認められ、吹錬終了後、Ｃ濃度が０．１質量％未満、Ｐ濃度が０．０３質量％以下、Ｎ濃度が０．００２５質量％未満の溶鋼を得ることができ、Ｓ濃度は０．００７１質量％のまま変動はなかった。一方、比較のため、脱硫後のスラグを排滓せずに同様の条件で酸素吹錬を実施した。この例では、吹錬終了までに復硫してＳ濃度が０．０３質量％を超えてしまい、高品位溶鋼の製造には適さなかった。
(Second experiment)
Desulfurization treatment was performed under substantially the same conditions as in Example 1 of the first experiment to obtain hot metal having an S concentration of 0.0071 mass% in the hot metal. Then, the direct current electric furnace was tilted, and the desulfurization slag was discharged while leaving the hot metal. Then, oxygen blowing was performed by supplying oxygen from the lance at an acid transfer rate of 80 Nm 3 /h·t. Oxygen blowing can bring the Si concentration in the hot metal to a state of less than 0.1% by mass. After that, decarburization, dephosphorization, and denitrification effects are observed, and after the blowing, the C concentration is 0.1%. It was possible to obtain molten steel with less than mass%, P concentration of 0.03 mass% or less, and N concentration of less than 0.0025 mass%, and the S concentration remained unchanged at 0.0071 mass%. On the other hand, for comparison, oxygen blowing was carried out under the same conditions without discharging the slag after desulfurization. In this example, the sulfur content was increased by the end of blowing and the S concentration exceeded 0.03 mass %, which was not suitable for the production of high-grade molten steel.
酸素吹錬の初期においては、溶銑中Ｓｉ濃度は０．３質量％以上であったが、脱珪による発熱分が熱裕度として作用したため、溶銑中Ｓｉ濃度が＜０．１質量％の状態で酸素吹錬を開始する操業と比較して、スクラップ配合比率を全処理量の５％以上増加させることができることが確認した。 In the initial stage of oxygen blowing, the Si concentration in the hot metal was 0.3 mass% or more, but the heat generation due to desiliconization acted as a thermal margin, so the Si content in the hot metal was <0.1 mass%. It was confirmed that the scrap blending ratio can be increased by 5% or more of the total amount of treatment compared with the operation of starting oxygen blowing.
また、吹錬中にＣＯボイリングに伴って進行する脱窒反応は、溶銑中のＳ濃度が高いと大きく阻害されるが、本発明によって得られた低硫溶銑は、Ｓ濃度が十分下げられている。また、脱硫後に溶銑中に残留するＳｉは脱珪によって酸化してＳｉＯ2となるため、脱燐時には、ＣａＯ系脱燐剤とともに良好な滓化性を有する。さらに、脱炭時にＣＯが発生することによってフォーミングが生じ、このフォーミングによって溶鉄表面が覆われ、大気中の窒素の吸着を防止することができる。従来の電気炉操業では４０ｐｐｍ以下の低窒素溶鋼を製造することが困難とされていたが、上述した作用により２５ｐｐｍの低窒素化を実現できた。 Further, the denitrification reaction that progresses with CO boiling during blowing is largely inhibited when the S concentration in the hot metal is high, but the low sulfur hot metal obtained by the present invention has a sufficiently reduced S concentration. There is. In addition, since Si remaining in the hot metal after desulfurization is oxidized by desiliconization to become SiO 2 , it has a good slag forming property together with the CaO-based dephosphorizing agent during dephosphorization. Further, when CO is generated during decarburization, forming occurs, and the surface of the molten iron is covered by this forming, so that adsorption of nitrogen in the atmosphere can be prevented. Although it has been difficult to produce a low-nitrogen molten steel of 40 ppm or less in the conventional electric furnace operation, it has been possible to achieve a nitrogen reduction of 25 ppm by the above-described action.
本発明によれば、蛍石を添加した操業のようなスラグの副産物価値を損なう操業とはならず、また、高価な金属Ａｌの大量使用を必要とせず、耐火物の損耗をも抑えて安価で効率の良い溶銑脱硫を実施することができる。また、造塊滓などの安価な脱硫材の効率的な利用が可能になるなど、工業的利用価値の高い操業の実施が可能になる。 ADVANTAGE OF THE INVENTION According to this invention, it does not become an operation which spoils the by-product value of slag like the operation which added the fluorite, it does not require large-scale use of expensive metal Al, and also suppresses the wear of a refractory material and is cheap. Thus, hot metal desulfurization can be performed efficiently. In addition, it becomes possible to efficiently use inexpensive desulfurization materials such as ingots and slags, and to carry out operations with high industrial utility value.
１ 溶銑
２ 精錬用フラックス
３ 上部電極
４ 下部水冷電極
５ アーク
６ ホッパー
７ 酸素ランス
８ 酸素噴射
９ 炉体
１０ 排滓傾動装置
１１ 除滓孔
１２ 除滓樋
１３ スラグパン
1 Hot Metal 2 Refining Flux 3 Upper Electrode 4 Lower Water-Cooled Electrode 5
Claims (4)
ここで、括弧（）は、括弧内の物質の精錬スラグ中の濃度（質量％）を表す。 With respect to the hot metal having a Si concentration of 0.3 to 1.0% by mass, the CaO concentration is 35 to 60% by mass, (Al 2 O 3 +SiO 2 )/(CaO) is 0.5 to 0.8, and (SiO 2 2 )≦0.8×(Al 2 O 3 ), using a refining slag satisfying an iron oxide concentration of 6% by mass or more, desulfurization treatment is performed at a hot metal temperature of 1250 to 1350° C. Desulfurization method.
Here, the parentheses () represent the concentration (mass %) of the substance in the parentheses in the refining slag.
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