JP2012012648A - Method for applying desulfurize-treatment to molten steel - Google Patents
Method for applying desulfurize-treatment to molten steel Download PDFInfo
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本発明は、硫黄濃度が０．００１０質量％以下である極低硫鋼を製造することを目的とし、転炉から出鋼された溶鋼に対して、ＣａＯ含有物質を脱硫剤の主たる構成物質として用いて取鍋内で脱硫処理を施す方法に関する。 The present invention aims to produce an ultra-low-sulfur steel having a sulfur concentration of 0.0010% by mass or less, and a CaO-containing material as a main constituent of a desulfurizing agent for molten steel discharged from a converter. It is related with the method of using and using a ladle in a ladle.
近年、鋼の高付加価値化や鉄鋼材料の使用用途拡大などに伴う材料特性向上のために、高純度鋼製造の要求が増加している。特に、鉄鋼材料の靭性を低下させる元素である硫黄の含有量が少ない極低硫鋼の要求が高い。鉄鋼材料の溶製過程において、脱硫処理は、溶銑段階での脱硫処理と溶鋼段階での脱硫処理とが行われており、通常は、溶銑段階での脱硫処理のみで溶製するが、高級電磁鋼板やラインパイプ用鋼材などの極低硫鋼では、溶銑段階の脱硫処理のみでは十分でなく、溶銑段階での脱硫処理に加えて更に溶鋼段階での脱硫処理が必要となる。 In recent years, there has been an increasing demand for high-purity steel production in order to improve material properties associated with increased added value of steel and expanded use of steel materials. In particular, there is a high demand for ultra-low sulfur steel with a low content of sulfur, which is an element that lowers the toughness of steel materials. In the melting process of steel materials, desulfurization is performed by desulfurization at the hot metal stage and desulfurization at the hot steel stage. Normally, the desulfurization process is performed only by desulfurization at the hot metal stage. For ultra-low sulfur steels such as steel sheets and steel for line pipes, the desulfurization process at the hot metal stage is not sufficient, and a desulfurization process at the molten steel stage is required in addition to the desulfurization process at the hot metal stage.
溶鋼の脱硫処理は、一般に、溶鋼のアーク加熱手段や攪拌手段、更には溶鋼へのフラックス或いは合金粉などの粉体吹き込み手段を有する、ＡＳＥＡ−ＳＫＦ法、ＶＡＤ法、ＬＦ法などの取鍋精錬法によって行われている。これらの脱硫処理方法は、転炉での脱炭精錬によって溶製された溶鋼を収容する取鍋内に脱硫剤を添加し、溶鋼と脱硫剤とを攪拌・混合する或いはアーク加熱することによって脱硫剤を滓化させ、脱硫剤の滓化により形成されたスラグと溶鋼との間でスラグ−メタル間反応を起こさせて溶鋼中の硫黄をスラグ中に移行させるという方法で行われる。脱硫剤としては、ＣａＯ（石灰）を主成分とし、これに脱硫剤の融点降下を目的とするＡｌ2Ｏ3（アルミナ）、ＣａＦ2（蛍石）などを加えた脱硫剤が使用されている。取鍋精錬法による脱硫処理方法で効率的な脱硫反応を起こさせるためには、添加した脱硫剤を早急に滓化させること、及び、攪拌強度を高めて、脱硫剤の滓化により形成されるスラグとメタルとの接触面積を増大させることが重要となる。 The desulfurization treatment of molten steel is generally performed by ladle refining such as ASEA-SKF method, VAD method, and LF method, which has means for arc heating and stirring of molten steel, and also means for blowing powder such as flux or alloy powder into molten steel. It is done by law. In these desulfurization treatment methods, a desulfurization agent is added to a ladle containing molten steel melted by decarburization refining in a converter, and desulfurization is performed by stirring and mixing the molten steel and the desulfurization agent or by arc heating. It is carried out by a method in which the agent is hatched and a slag-metal reaction is caused between the slag formed by the hatching of the desulfurizing agent and the molten steel to transfer sulfur in the molten steel into the slag. As the desulfurizing agent, a desulfurizing agent mainly containing CaO (lime) and added with Al 2 O 3 (alumina), CaF 2 (fluorite) or the like for the purpose of lowering the melting point of the desulfurizing agent is used. . In order to cause an efficient desulfurization reaction in the desulfurization treatment method using the ladle refining method, the added desulfurization agent is rapidly hatched, and the stirring strength is increased and the desulfurization agent is hatched. It is important to increase the contact area between the slag and the metal.
脱硫剤は取鍋内の溶鋼上に上置き添加されることが一般的であり、添加後にアーク加熱で滓化するにしても、また、添加後に溶鋼との攪拌・混合で滓化するにしても、滓化に長時間を要する。そこで、脱硫剤の滓化促進のために、特許文献１には、生石灰、アルミナ及び蛍石との混合品であるフラックスを添加し、その後バブリング処理を行い、脱硫処理後のスラグ組成をＣａＯ／Ａｌ2Ｏ3≧１．５、ＣａＦ2≧５質量％として溶鋼を脱硫する方法が開示されている。しかし、ＣａＦ2を含有する脱硫剤を使用した場合には、生成されるスラグ中のＣａＦ2によって取鍋耐火物が激しく溶損され、取鍋の寿命が大幅に短くなるという問題が生じるのみならず、フッ素の環境への悪影響から、生成したスラブの処分が困難であるという問題がある。 The desulfurizing agent is generally added on top of the molten steel in the ladle. Even after addition, the desulfurizing agent is hatched by arc heating, and after addition, it is hatched by stirring and mixing with the molten steel. However, it takes a long time to hatch. Therefore, in order to promote the hatching of the desulfurizing agent, in Patent Document 1, a flux that is a mixture of quicklime, alumina, and fluorite is added, after which bubbling is performed, and the slag composition after the desulfurization is CaO / A method of desulfurizing molten steel with Al 2 O 3 ≧ 1.5 and CaF 2 ≧ 5 mass% is disclosed. However, when a desulfurizing agent containing CaF 2 is used, the problem that the ladle refractory is severely melted by CaF 2 in the slag to be produced and the life of the ladle is greatly shortened is caused. However, there is a problem that it is difficult to dispose of the generated slab due to the adverse effects of fluorine on the environment.
特許文献２には、滓化促進のために、ＣａＯ−Ａｌ2Ｏ3のプリメルトフラックス（事前に混合均一溶解したもの）またはＣａＯ−Ａｌ2Ｏ3−ＣａＦ2のプリメルトフラックスを脱硫剤として使用する方法が開示されている。しかし、プリメルトフラックスは非常に高価であり、製造コストが上昇するという問題がある。また、ＣａＦ2を含有する脱硫剤では前述した問題が同様に発生する。 In Patent Document 2, in order to promote hatching, a premelt flux of CaO—Al 2 O 3 (mixed and dissolved in advance) or a premelt flux of CaO—Al 2 O 3 —CaF 2 is used as a desulfurization agent. A method of use is disclosed. However, the premelt flux is very expensive, and there is a problem that the manufacturing cost increases. In addition, the above-described problems similarly occur in the desulfurization agent containing CaF 2 .
一方、溶鋼攪拌の強化については、攪拌用ガス流量を高めることなく攪拌強度を高める手段として、特許文献３、特許文献４、特許文献５には、フラックスを攪拌用ガスに混入して吹き込む技術が開示されている。しかし、吹き込みガス流量に対してフラックス吹き込み量は限界があり（固気比は５〜３０ｋｇ／ｋｇが限界）、増加可能な攪拌力には限界がある。また、攪拌用ガス流量を増加した場合には、取鍋内の溶鋼湯面の乱れ（揺動）が激しくなり、スプラッシュが発生して地金が蓋に付着する、或いは、電極と溶鋼とで短絡するなどしてアークが安定せず、アーク加熱が困難になるという問題などが発生する。
On the other hand, for strengthening the molten steel stirring,
本発明はこのような事情に鑑みてなされたもので、その目的とするところは、極低硫鋼を製造することを目的として転炉から出鋼された溶鋼に対して、ＣａＯ含有物質を脱硫剤の主たる構成物質として用いて取鍋内で取鍋精錬法による脱硫処理を施すにあたり、ＣａＦ2（蛍石）を脱硫剤の一部として使用しなくても、また、脱硫剤がプリメルトフラックスでなくても、添加した脱硫剤を迅速に滓化させ、効率良く脱硫処理することのできる、溶鋼の脱硫処理方法を提供することである。 The present invention has been made in view of such circumstances, and the object of the present invention is to desulfurize CaO-containing materials from molten steel produced from a converter for the purpose of producing extremely low-sulfur steel. When the desulfurization treatment by ladle refining method is performed in the ladle using it as the main constituent material of the agent, it is not necessary to use CaF 2 (fluorite) as a part of the desulfurization agent. Even if it is not, it is providing the desulfurization processing method of molten steel which can hatch quickly and desulfurize the added desulfurization agent efficiently.
上記課題を解決するための第１の発明に係る溶鋼の脱硫処理方法は、脱硫処理及び脱燐処理の施された溶銑の転炉での脱炭精錬によって得られ、転炉から取鍋に出鋼された溶鋼を、当該溶鋼への攪拌用ガスの吹き込みにより攪拌しながら、取鍋内に添加されたＣａＯ含有物質を脱硫剤として用いて取鍋内で脱硫処理する溶鋼の脱硫処理方法であって、脱硫処理後の取鍋内スラグの組成を、ＳｉＯ2の含有量が５〜１５質量％、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）が１．５〜３．０で、且つＣａＦ2を実質的に含有しない組成に調整することを特徴とする。 The molten steel desulfurization treatment method according to the first invention for solving the above-mentioned problems is obtained by decarburization refining in a converter of hot metal that has been subjected to desulfurization treatment and dephosphorization treatment, and is discharged from the converter to a ladle. This is a desulfurization treatment method for molten steel in which desulfurization treatment is performed in a ladle using the CaO-containing material added to the ladle as a desulfurization agent while stirring the molten steel by blowing a stirring gas into the molten steel. The composition of the slag in the ladle after the desulfurization treatment is such that the content of SiO 2 is 5 to 15% by mass, and [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3 ) is 1. in .5～3.0, and characterized by adjusting the CaF 2 substantially free composition.
第２の発明に係る溶鋼の脱硫処理方法は、第１の発明において、前記［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）を１．８〜２．５に調整することを特徴とする。 The desulfurization treatment method for molten steel according to the second invention is the method according to the first invention, wherein the [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3 ) is 1.8 to 2.5. It is characterized by adjusting to.
第３の発明に係る溶鋼の脱硫処理方法は、第１または第２の発明において、前記攪拌用ガスとともに、Ｃａ合金粉、金属Ｍｇ粉、Ｍｇ合金粉のうちの何れか１種または２種以上を溶鋼中に吹き込むことを特徴とする。 The desulfurization treatment method for molten steel according to the third invention is the first or second invention, in addition to the stirring gas, any one or more of Ca alloy powder, metal Mg powder, and Mg alloy powder. Is injected into molten steel.
第４の発明に係る溶鋼の脱硫処理方法は、第１または第２の発明において、前記脱硫処理の少なくとも一時期において、浸漬ランスからの攪拌用ガスの吹き込みと、底吹きポーラス煉瓦からの攪拌用ガスの吹き込みとを同時に行うことを特徴とする。 The method for desulfurizing a molten steel according to a fourth invention is the method according to the first or second invention, wherein the stirring gas is blown from the immersion lance and the stirring gas from the bottom blown porous brick at least at one time of the desulfurization treatment. It is characterized by simultaneously performing the blowing.
第５の発明に係る溶鋼の脱硫処理方法は、第１ないし第４の発明の何れかにおいて、前記脱硫処理後の取鍋内スラグの組成を、脱硫処理前に取鍋内に添加するＣａＯ含有物質、ＭｇＯ含有物質、金属Ａｌ、Ａｌ2Ｏ3含有物質、ＳｉＯ2含有物質のそれぞれの添加量を制御することによって、上記組成範囲に調整することを特徴とする。 The desulfurization treatment method for molten steel according to the fifth invention is the method according to any one of the first to fourth inventions, wherein the composition of the slag in the ladle after the desulfurization treatment is added to the ladle before the desulfurization treatment. The composition range is adjusted by controlling the amount of each of the substance, MgO-containing substance, metal Al, Al 2 O 3 -containing substance, and SiO 2 -containing substance.
本発明によれば、ＣａＯ含有物質を脱硫剤の主たる構成物質として用いた取鍋精錬法による溶鋼の脱硫処理において、脱硫処理後のスラグ組成を、ＳｉＯ2の含有量が５〜１５質量％になるように調整するので、このＳｉＯ2がＣａＯの滓化促進剤として機能してＣａＯの滓化が促進され、また、脱硫処理後のスラグ組成を、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）が１．５〜３．０になるように調整するので、スラグには高い脱硫能力が確保され、その結果、ＣａＦ2を脱硫剤の一部として使用しなくても、また、脱硫剤がプリメルトフラックスでなくても、効率的に溶鋼の脱硫処理を行うことが実現される。 According to the present invention, in the desulfurization treatment of the molten steel by the ladle refining method using the CaO-containing material as the main constituent material of the desulfurization agent, the slag composition after the desulfurization treatment has a SiO 2 content of 5 to 15% by mass. Therefore, the SiO 2 functions as a CaO hatching accelerator to promote the hatching of CaO, and the slag composition after the desulfurization treatment is changed to [(mass% CaO) + (mass% MgO). )] / (Mass% Al 2 O 3 ) is adjusted so as to be 1.5 to 3.0, so that a high desulfurization capacity is secured in the slag, and as a result, CaF 2 is used as a part of the desulfurizing agent. Even if the desulfurizing agent is not a premelt flux, it is possible to efficiently perform the desulfurization treatment of the molten steel.
以下、本発明を具体的に説明する。先ず、本発明に至った経緯について説明する。 Hereinafter, the present invention will be specifically described. First, the background to the present invention will be described.
本発明者らは、硫黄濃度が０．００１０質量％以下である極低硫鋼を、ＣａＯ含有物質を脱硫剤の主たる構成物質として使用して取鍋精錬法による脱硫処理で溶製するにあたり、ＣａＦ2（蛍石）を脱硫剤の一部として使用しなくても、また、脱硫剤がプリメルトフラックスでなくても、脱硫剤として添加したフラックスを迅速に滓化させ、効率良く脱硫処理することを目的とし、種々試験・研究を重ねた。その結果、脱硫剤として添加したフラックスの滓化促進のためには、フラックスを添加するときの溶鋼の温度、及び、フラックスの組成つまり複数のフラックスが溶解した後に生成されるスラグ組成が重要であることが分った。但し、溶鋼の温度は、転炉からの出鋼時の溶鋼温度によって決まり、むやみに出鋼時の溶鋼温度を高くすることは、転炉耐火物の溶損を増大させ、製造コストの増加を招き得策ではないことから、フラックスの組成について検討することとした。 When the present inventors melt extremely low-sulfur steel having a sulfur concentration of 0.0010% by mass or less by desulfurization treatment using a ladle refining method using a CaO-containing material as a main constituent material of a desulfurization agent, Even if CaF 2 (fluorite) is not used as a part of the desulfurizing agent, and the desulfurizing agent is not a premelt flux, the flux added as the desulfurizing agent is rapidly hatched and efficiently desulfurized. For this purpose, various tests and research were repeated. As a result, in order to promote hatching of the flux added as a desulfurizing agent, the temperature of the molten steel when the flux is added and the composition of the flux, that is, the slag composition that is generated after the plurality of fluxes are dissolved are important. I found out. However, the temperature of the molten steel is determined by the molten steel temperature at the time of steel output from the converter, and increasing the molten steel temperature at the time of steel output unnecessarily increases the melting loss of the converter refractory and increases the production cost. Since this was not an invitation, it was decided to study the flux composition.
脱硫剤として添加するフラックスの組成に関して、前述した従来技術に示すように、フラックスの滓化促進による脱硫反応効率化のための知見が幾つかあるが、従来の知見は滓化促進をＣａＦ2の存在に依存する場合が多い。しかし、ＣａＦ2を使用することは、スラグ中フッ素の環境への溶出が問題であり、ＣａＦ2の使用は避ける必要がある。ＣａＦ2を使用しなくても、滓化が促進されて効率的に脱硫処理することのできるフラックス組成について検討を重ねた結果、ＣａＦ2による融点降下作用に替わって、脱硫処理によって生成される取鍋内スラグに含有される、ＳｉＯ2、ＣａＯ、ＭｇＯ、Ａｌ2Ｏ3の濃度比率を最適に制御し、脱硫処理によって生成するスラグの融点を降下させることが効果的であることが分った。尚、取鍋内スラグは、転炉からの出鋼時の末期に溶鋼とともに転炉から取鍋内に排出される転炉スラグ（＝ＣａＯ−ＭｇＯ−Ａｌ2Ｏ3−ＳｉＯ2系スラグ）を起源としており、脱硫剤としてＣａＯ含有物質を添加した後のスラグ組成もＣａＯ−ＭｇＯ−Ａｌ2Ｏ3−ＳｉＯ2系を基本としている。 Respect to the addition the composition of the flux as a desulfurizing agent, as shown in the prior art described above, although there are several findings for the desulfurization efficiency by slag formation promoting flux, conventional wisdom is the slag formation promoting CaF 2 Often depends on existence. However, the use of CaF 2 has a problem of elution of fluorine in the slag into the environment, and it is necessary to avoid the use of CaF 2 . As a result of repeated studies on a flux composition that can be efficiently desulfurized without using CaF 2 , hatching is promoted and instead of the melting point lowering effect of CaF 2 , It has been found that it is effective to optimally control the concentration ratio of SiO 2 , CaO, MgO, Al 2 O 3 contained in the slag in the pan and lower the melting point of the slag produced by the desulfurization treatment. . In addition, the slag in the ladle is the converter slag (= CaO—MgO—Al 2 O 3 —SiO 2 slag) discharged from the converter into the ladle along with the molten steel at the end of the steel output from the converter. The slag composition after the addition of a CaO-containing substance as a desulfurizing agent is based on the CaO—MgO—Al 2 O 3 —SiO 2 system.
具体的には、フラックスの滓化を促進させる成分としてＳｉＯ2を用いることとした。ＳｉＯ2はＣａＯと反応して低融点化合物を生成する。このＳｉＯ2はＳｉＯ2源をフラックスとして添加してもよいし、出鋼時に溶鋼とともに転炉から取鍋内に流出する転炉スラグに含有されるＳｉＯ2を活用してもよい。但し、ＣａＯ−ＭｇＯ−Ａｌ2Ｏ3−ＳｉＯ2系のスラグにおいて、ＳｉＯ2成分は、スラグの融点を降下させる作用があるが、酸性成分であることから、スラグのサルファイドキャパシティー（硫黄を含有・保持する能力）を低下させ、脱硫反応には不利に作用する。 Specifically, SiO 2 was used as a component for promoting the hatching of the flux. SiO 2 reacts with CaO to form a low melting point compound. For this SiO 2, a SiO 2 source may be added as a flux, or SiO 2 contained in converter slag flowing out from the converter into the ladle together with the molten steel at the time of steel output may be used. However, in CaO—MgO—Al 2 O 3 —SiO 2 -based slag, the SiO 2 component has the effect of lowering the melting point of the slag, but since it is an acidic component, the slag sulfide capacity (containing sulfur)・ The ability to maintain) is reduced, which adversely affects the desulfurization reaction.
そこで、脱硫反応を阻害しない範囲内でＣａＯ−ＭｇＯ−Ａｌ2Ｏ3−ＳｉＯ2系スラグの融点を降下させる作用を発揮できるＳｉＯ2の濃度範囲を検討した結果、ＳｉＯ2が５〜１５質量％の範囲が最適であることが分った。５質量％未満では、融点降下の作用が少なく、一方、１５質量％を超えるとスラグのサルファイドキャパシティーが低下する。 Then, as a result of examining the concentration range of SiO 2 capable of exerting the action of lowering the melting point of CaO—MgO—Al 2 O 3 —SiO 2 slag within a range not inhibiting the desulfurization reaction, SiO 2 is 5 to 15% by mass. The range of was found to be optimal. If it is less than 5% by mass, the effect of lowering the melting point is small. On the other hand, if it exceeds 15% by mass, the sulfide capacity of slag is reduced.
更に、スラグの滓化を妨げることなく、スラグの脱硫能力を確保するためには、ＣａＯ−ＭｇＯ−Ａｌ2Ｏ3−ＳｉＯ2系のスラグにおいて、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）を１．５〜３．０の範囲内に制御する必要があり、好ましくは、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）を１．８〜２．５の範囲内に制御する必要があることが分った。この比が１．５未満の場合には、スラグの融点は降下するものの、脱硫剤として機能するＣａＯ及びＭｇＯが少なくなって効率的な脱硫反応が得られず、一方、３．０を超えるとスラグの融点が高くなり、滓化しにくくなる。尚、Ａｌ2Ｏ3は、ＣａＯ−ＭｇＯ−Ａｌ2Ｏ3−ＳｉＯ2系スラグにおいて融点降下の作用を発揮する。また、ＣａＯ及びＭｇＯはともに塩基性酸化物であり、脱硫能を有するが、ＣａＯの方がＭｇＯに比べて脱硫能が高く、従って、ＭｇＯ濃度を過剰に高くすることは得策ではなく、生成されるＣａＯ−ＭｇＯ−Ａｌ2Ｏ3−ＳｉＯ2系スラグ中の（質量％ＭｇＯ）／（質量％ＣａＯ）を０．１０以下に調整することが好ましい。 Furthermore, in order to ensure the desulfurization ability of slag without hindering the hatching of slag, in the CaO—MgO—Al 2 O 3 —SiO 2 type slag, [(mass% CaO) + (mass% MgO) ] / (Mass% Al 2 O 3 ) must be controlled within the range of 1.5 to 3.0, preferably [(mass% CaO) + (mass% MgO)] / (mass% Al 2 It has been found that O 3 ) needs to be controlled within the range of 1.8 to 2.5. When this ratio is less than 1.5, the melting point of slag is lowered, but CaO and MgO functioning as a desulfurizing agent are reduced and an efficient desulfurization reaction cannot be obtained. The melting point of slag becomes high and it becomes difficult to hatch. Al 2 O 3 exhibits a melting point lowering effect in CaO—MgO—Al 2 O 3 —SiO 2 slag. CaO and MgO are both basic oxides and have a desulfurization ability. However, CaO has a higher desulfurization ability than MgO, and therefore it is not a good idea to make the MgO concentration excessively high. It is preferable to adjust (mass% MgO) / (mass% CaO) in the CaO—MgO—Al 2 O 3 —SiO 2 slag to 0.10 or less.
脱硫反応促進のためには、脱硫剤の組成のみならず、溶鋼の攪拌も重要となる。但し、攪拌用ガスの吹き込み流量を増加すると、湯面の揺動及びスプラッシュが激しくなり、取鍋の上部を覆う蓋への地金付着が発生したり、アーク加熱が安定化しなくなったりする。そこで、このような問題を起こすことなく、溶鋼の攪拌を強化する手段を検討した。その結果、以下の２点が有効であることが分った。 In order to accelerate the desulfurization reaction, not only the composition of the desulfurization agent but also the stirring of the molten steel is important. However, when the flow rate of the stirring gas is increased, the molten metal surface swings and splashes, causing adhesion of the metal to the lid covering the upper portion of the ladle and arc heating becoming unstable. Then, the means to strengthen the stirring of molten steel was examined without causing such a problem. As a result, the following two points were found to be effective.
１つの手段は、攪拌用ガスとともにＣａ合金粉、金属Ｍｇ粉、Ｍｇ合金粉のうちの何れか１種または２種以上を溶鋼に吹き込む方法である。この金属粉を吹き込む方法は、攪拌用ガスとともに、金属粉を含有しない、酸化物、フッ化物などからなるフラックスを吹き込む方法と比較しても、更なる脱硫率の向上が得られる。これは、攪拌用ガスとともに酸化物、フッ化物などからなるフラックスを吹き込む方法では、フラックスによる攪拌強化の効果とフラックスによる脱硫効果とが得られるが、攪拌用ガスとともにＣａ合金粉、金属Ｍｇ粉、Ｍｇ合金粉のうちの何れか１種または２種以上を吹き込む方法では、金属粉による攪拌強化の効果と金属粉による脱硫効果とが得られ、更に、金属粉から発生するＣａガス或いはＭｇガスによる攪拌増加効果が得られるからである。 One means is a method in which any one or two or more of Ca alloy powder, metal Mg powder, and Mg alloy powder are blown into the molten steel together with the stirring gas. This method of blowing metal powder can further improve the desulfurization rate as compared with a method of blowing a flux made of oxide, fluoride, or the like that does not contain metal powder together with the stirring gas. This is because the method of blowing a flux composed of oxide, fluoride, etc. together with the stirring gas provides the effect of stirring strengthening by the flux and the effect of desulfurization by the flux, but together with the stirring gas, Ca alloy powder, metallic Mg powder, In the method of blowing any one or more of the Mg alloy powders, the effect of strengthening the stirring by the metal powder and the effect of desulfurization by the metal powder can be obtained. This is because an effect of increasing stirring can be obtained.
他の１つの手段は、ガス攪拌の吹き込み位置を分散させて、合計の攪拌ガス吹き込み流量を増加させる方法である。具体的には、取鍋内溶鋼の攪拌を、取鍋底部に配置した羽口或いはポーラス煉瓦からのガス吹き込みと、浸漬ランスからのガス吹き込みと、で行うように構成し、脱硫処理の少なくとも一時期において、取鍋底部に配置した羽口或いはポーラス煉瓦からのガス吹き込みと浸漬ランスからのガス吹き込みとを同時に行う方法である。この方法により、それぞれの部位からの吹き込み流量は、吹き込み位置が一箇所の場合に比較して少なくなっても、溶鋼に吹き込まれる単位時間あたりの合計の攪拌ガス流量は大幅に増加し、攪拌力が増加して効率的な脱硫処理を行うことが可能となる。 Another means is a method of increasing the total stirring gas blowing flow rate by dispersing the gas stirring blowing positions. Specifically, the molten steel in the ladle is agitated by gas blowing from a tuyere or porous brick placed at the bottom of the ladle and gas blowing from an immersion lance, and at least one time of desulfurization treatment In this method, gas blowing from a tuyere or porous brick arranged at the bottom of the ladle and gas blowing from an immersion lance are performed simultaneously. By this method, even if the blowing flow rate from each part is smaller than that in the case of one blowing position, the total stirring gas flow rate per unit time blown into the molten steel is greatly increased, and the stirring force is increased. This increases the efficiency of the desulfurization process.
本発明は、これらの検討結果に基づきなされたものであり、以下、本発明の具体的な実施方法を説明する。 The present invention has been made based on these examination results, and a specific method for carrying out the present invention will be described below.
高炉から出銑された溶銑を溶銑鍋やトピードカーなどの溶銑搬送用容器で受銑し、次工程の脱炭精錬を行う転炉に搬送する。通常、この搬送途中で、溶銑に対して脱硫処理や脱燐処理などの溶銑予備処理が施されており、本発明は、極低硫鋼を製造する技術であることから、脱硫処理を実施する。また、極低硫鋼の成分規格上からは脱燐処理が必要でない場合でも、転炉出鋼後の脱硫処理における転炉スラグからの復燐を防止するために、脱燐処理を実施する。 The hot metal discharged from the blast furnace is received in a hot metal transfer container such as a hot metal ladle or topped car, and transferred to a converter for decarburization and refining in the next process. Usually, hot metal pretreatment such as desulfurization treatment or dephosphorization treatment is performed on the hot metal during the conveyance, and the present invention is a technique for producing ultra-low sulfur steel, and therefore desulfurization treatment is performed. . Moreover, even if dephosphorization is not necessary due to the component specifications of the ultra-low sulfur steel, the dephosphorization is performed in order to prevent rephosphorization from the converter slag in the desulfurization after the converter steel.
脱硫処理及び脱燐処理の施された溶銑に対して転炉で脱炭精錬を実施し、得られた溶鋼を取鍋に出鋼する。転炉での脱炭精錬は、溶銑には既に脱硫処理及び脱燐処理が施されているので、少量の生石灰（ＣａＯ）及び少量のドロマイト（ＭｇＣＯ3−ＣａＣＯ3）或いは焼成ドロマイト（ＭｇＯ−ＣａＯ）をフラックスとして使用し、炉内にスラグ（「転炉スラグ」と呼ぶ）を形成させる。この転炉スラグは、溶銑の脱燐反応を促進させる役割を担うが、溶銑が既に予備脱燐処理されていることから、主たる役割は、吹錬中の鉄スプラッシュの発生防止及び転炉内張り耐火物の溶損抑制である。出鋼の末期、溶鋼に混入して転炉スラグが取鍋内に流出するので、これを防止するために、通常実施されるスラグ流出防止対策を実施する。スラグ流出防止対策を実施しても、転炉スラグの完全な流出防止は困難であり、取鍋には或る程度の量の転炉スラグが溶鋼に混入して流出する。出鋼後、溶鋼に混入して流入した転炉スラグを取鍋から除去してもよいが、転炉スラグ中のＳｉＯ2成分が、脱硫剤としてその後に添加されるＣａＯ含有物質の滓化に寄与することから、除去しなくてもよい。 The desulfurized and dephosphorized hot metal is decarburized and refined in a converter, and the resulting molten steel is taken out into a ladle. Decarburization refining in a converter furnace, since already desulfurized and dephosphorization treatment is applied to molten iron, a small amount of quicklime (CaO) and a small amount of dolomite (MgCO 3 -CaCO 3) or burnt dolomite (MgO-CaO ) As a flux to form slag (referred to as “converter slag”) in the furnace. This converter slag plays a role in promoting the dephosphorization reaction of hot metal, but since the hot metal has already been subjected to preliminary dephosphorization treatment, the main roles are to prevent the occurrence of iron splash during blowing and to protect the furnace lining from fire. It is the suppression of melting of objects. Since the converter slag flows out into the ladle at the end of the steel output, the slag outflow prevention measures that are usually implemented will be implemented. Even if slag outflow prevention measures are implemented, it is difficult to completely prevent the converter slag from flowing out, and a certain amount of converter slag enters the ladle and flows out of the molten steel. After steeling out, the converter slag that flows into the molten steel may be removed from the ladle, but the SiO 2 component in the converter slag is used to hatch the CaO-containing material that is subsequently added as a desulfurizing agent. It does not have to be removed because it contributes.
取鍋内に所定の組成のＣａＯ−ＭｇＯ−Ａｌ2Ｏ3−ＳｉＯ2系の脱硫用スラグを形成するべく、フラックスとして、ＣａＯ含有物質、ＭｇＯ含有物質、Ａｌ2Ｏ3含有物質、ＳｉＯ2含有物質を取鍋内に添加する。但し、前述したように、ＭｇＯはＣａＯに比較して脱硫能が低いので、ＭｇＯ含有物質は添加しなくても構わない。また、溶鋼の脱酸及びスラグの還元（スラグ中のＦｅ酸化物及びＭｎ酸化物の還元）のために、取鍋内に金属Ａｌを添加する。これらの物質は、ＡＳＥＡ−ＳＫＦ法、ＶＡＤ法、ＬＦ法の何れかの方法により脱硫処理を実施する後工程の設備で添加してもよいが、ＣａＯの滓化を促進させる観点から、転炉から取鍋への出鋼時または出鋼直後に取鍋内に添加することが好ましい。 To form a CaO-MgO-Al 2 O 3 -SiO 2 based desulfurization slag of a predetermined composition in the ladle, as a flux, CaO-containing material, MgO-containing substance, Al 2 O 3 containing materials, SiO 2 content Add material into pan. However, as described above, since MgO has a lower desulfurization ability than CaO, the MgO-containing material may not be added. Moreover, metal Al is added in a ladle for deoxidation of molten steel and reduction of slag (reduction of Fe oxide and Mn oxide in slag). These substances may be added in the post-process equipment for performing desulfurization treatment by any of the ASEA-SKF method, VAD method, and LF method. From the viewpoint of promoting the hatching of CaO, the converter It is preferable to add to the ladle at the time of steel extraction from the ladle to immediately after the steel extraction.
ＣａＯ含有物質、ＭｇＯ含有物質、金属Ａｌ、Ａｌ2Ｏ3含有物質、ＳｉＯ2含有物質の添加量は、取鍋内に流出した転炉スラグの質量及び成分組成を加味し、この転炉スラグを含めて添加されるフラックスが滓化した後に取鍋内に生成されるスラグの組成が、ＳｉＯ2含有量＝５〜１５質量％で、且つ、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）＝１．５〜３．０となるように、好ましくは［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）＝１．８〜２．５となるように、ＣａＯ含有物質、ＭｇＯ含有物質、金属Ａｌ、Ａｌ2Ｏ3含有物質、ＳｉＯ2含有物質のそれぞれの添加量を定める。この場合に、生成されるスラグの（質量％ＭｇＯ）／（質量％ＣａＯ）が０．１０以下になるようにそれぞれの添加量を定めることが、より好ましい。そして、これらの物質を、定めた添加量だけ取鍋内に添加する。金属Ａｌは添加した全量がＡｌ2Ｏ3になるわけではなく、溶鋼中にも溶解して残る。従って、予め試験によって溶鋼に溶解する溶解Ａｌ分とスラグ中のＡｌ2Ｏ3になる分との比率を求めておき、それに基づき金属Ａｌの添加量を設定する。ＣａＦ2は添加しない。尚、本発明において、「脱硫処理後の取鍋内スラグの組成を、ＣａＦ2を実質的に含有しない組成に調整する」とは、ＣａＦ2などのフッ素化合物をＣａＯの滓化促進剤として使用しないで脱硫処理後のスラグ組成を調整することであり、使用するＣａＯ含有物質やＡｌ2Ｏ3含有物質などに不可避的に混入して持ち来たされるフッ素が脱硫処理後のスラグに存在しても、ＣａＦ2を実質的に含有しないスラグと定義する。 The addition amount of CaO-containing material, MgO-containing material, metal Al, Al 2 O 3- containing material, and SiO 2 -containing material takes into account the mass and composition of the converter slag that has flowed into the ladle. The composition of the slag produced in the ladle after the added flux hatches is SiO 2 content = 5 to 15% by mass and [(mass% CaO) + (mass% MgO)] / (Mass% Al 2 O 3 ) = 1.5 to 3.0, preferably [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3 ) = 1.8 The addition amount of each of the CaO-containing material, MgO-containing material, metal Al, Al 2 O 3 -containing material, and SiO 2 -containing material is determined so as to be ˜2.5. In this case, it is more preferable to determine each addition amount so that (mass% MgO) / (mass% CaO) of the slag to be generated is 0.10 or less. Then, these substances are added to the ladle in a predetermined amount. The total amount of added metal Al does not become Al 2 O 3 but remains dissolved in the molten steel. Therefore, the ratio between the dissolved Al content that dissolves in the molten steel and the amount that becomes Al 2 O 3 in the slag is determined in advance, and the amount of metal Al added is set based on the ratio. CaF 2 is not added. Incidentally, used in the present invention, "the composition of the ladle slag after the desulfurization treatment is adjusted to a composition containing no CaF 2 substantially" and the fluorine compound such CaF 2 as a slag formation accelerators CaO Without adjusting the slag composition after desulfurization treatment, fluorine brought in unavoidably mixed with the CaO-containing material or Al 2 O 3- containing material used is present in the slag after desulfurization treatment. Even so, it is defined as a slag substantially free of CaF 2 .
添加するＣａＯ含有物質としては、生石灰（ＣａＯ）、石灰石（ＣａＣＯ3）、消石灰（Ｃａ(ＯＨ)2）、ドロマイト（ＭｇＣＯ3−ＣａＣＯ3）、焼成ドロマイト（ＭｇＯ−ＣａＯ）などを使用し、ＭｇＯ含有物質としては、マグネシアクリンカー（ＭｇＯ）、ドロマイト（ＭｇＣＯ3−ＣａＣＯ3）、焼成ドロマイト（ＭｇＯ−ＣａＯ）などを使用する。Ａｌ2Ｏ3含有物質としては、アルミドロス（金属Ａｌを２０〜７０質量％含有、残部の主成分はＡｌ2Ｏ3）、ボーキサイト（Ａｌ2Ｏ3・２Ｈ2Ｏ）、仮焼アルミナ（Ａｌ2Ｏ3）などを使用する。アルミドロスは金属Ａｌの代替にもなる。ＳｉＯ2含有物質としては、珪砂（ＳｉＯ2）、珪灰石（ＣａＯ−ＳｉＯ2）などを使用する。 As the CaO-containing substance to be added, quick lime (CaO), limestone (CaCO 3 ), slaked lime (Ca (OH) 2 ), dolomite (MgCO 3 —CaCO 3 ), calcined dolomite (MgO—CaO), etc. are used. the content material, magnesia clinker (MgO), dolomite (MgCO 3 -CaCO 3), or the like is used calcined dolomite (MgO-CaO). Examples of the Al 2 O 3 -containing material include aluminum dross (containing 20 to 70% by mass of metallic Al, the main component of the balance being Al 2 O 3 ), bauxite (Al 2 O 3 .2H 2 O), calcined alumina (Al 2 O 3 ) or the like is used. Almidros can also replace Al metal. As the SiO 2 -containing substance, quartz sand (SiO 2 ), wollastonite (CaO—SiO 2 ) or the like is used.
この場合、取鍋内に流出した転炉スラグの質量が多い場合には、ＳｉＯ2含有物質の添加を必要としないことも起こり得る。また、ＭｇＯ含有物質は、ＭｇＯ含有物質を添加しなくても、スラグ組成が［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）＝１．５〜３．０、好ましくは１．８〜２．５となるならば、添加しなくてもよい。 In this case, when the mass of the converter slag flowing out into the ladle is large, it may not be necessary to add the SiO 2 -containing material. Further, the MgO-containing material has a slag composition of [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3 ) = 1.5 to 3.0 without adding an MgO containing substance. If it is preferably 1.8 to 2.5, it may not be added.
次いで、溶鋼を収容した取鍋を、ＡＳＥＡ−ＳＫＦ法、ＶＡＤ法、ＬＦ法の何れかの方法により脱硫処理を実施する設備に搬送し、溶鋼の脱硫処理を実施する。本発明では、脱硫処理をＬＦ設備で実施する場合を例として説明する。図１に、本発明を実施する際に用いたＬＦ設備の側面概略図を示す。図１において、１はＬＦ設備、２は取鍋、３は昇降式の蓋、４はアーク加熱用の電極、５、６は浸漬ランス、７、８は底吹きポーラス煉瓦、９は溶鋼、１０はスラグ、１１は原材料投入シュート、１２はＡｒガス導入管である。 Next, the ladle containing the molten steel is transported to a facility for desulfurization treatment by any one of the ASEA-SKF method, the VAD method, and the LF method, and the desulfurization treatment of the molten steel is performed. In the present invention, a case where the desulfurization process is performed in an LF facility will be described as an example. FIG. 1 shows a schematic side view of an LF facility used in carrying out the present invention. In FIG. 1, 1 is an LF facility, 2 is a ladle, 3 is an elevating lid, 4 is an electrode for arc heating, 5 and 6 are immersion lances, 7 and 8 are bottom blown porous bricks, 9 is molten steel, 10 Is a slag, 11 is a raw material charging chute, and 12 is an Ar gas introduction pipe.
このＬＦ設備１において、走行台車（図示せず）に積載された、溶鋼９を収容する取鍋２を蓋３の直下の所定位置に配置し、蓋３を下降させて取鍋２の上端部に密着させ、その状態でＡｒガス導入管１２からＡｒガスを供給して取鍋２と蓋３とで囲まれる空間をＡｒガス雰囲気とする。取鍋内にＣａＯ含有物質、ＭｇＯ含有物質、金属Ａｌ、Ａｌ2Ｏ3含有物質、ＳｉＯ2含有物質が予め添加されていない場合には、及び、これらの添加量が不足する場合には、この状態で、原材料投入シュート１１を介して取鍋内にこれらのフラックス及び金属Ａｌを投入する。
In this LF facility 1, a ladle 2 that accommodates molten steel 9 loaded on a traveling carriage (not shown) is disposed at a predetermined position directly below the
次いで、必要に応じて電極４に通電してアークを発生させ、溶鋼９を加熱するとともに添加したフラックスを滓化させた後、溶鋼９に浸漬ランス５或いは浸漬ランス６を浸漬させ、浸漬ランス５、浸漬ランス６、または、底吹きポーラス煉瓦７，８のうちの少なくとも一箇所から溶鋼９に攪拌用ガスとしてＡｒガスを吹き込み、溶鋼９を攪拌する。溶鋼９を攪拌することによりフラックスが溶鋼９と混合され、フラックスの滓化が進行してスラグ１０が生成される。生成したスラグ１０は、溶鋼９の攪拌により溶鋼９と攪拌・混合され、溶鋼９とスラグ１０との間でスラグ−メタル間反応が発生し、溶鋼中の硫黄がスラグ中に移行する脱硫反応が発生する。
Then, if necessary, the electrode 4 is energized to generate an arc, the molten steel 9 is heated, and the added flux is hatched. Then, the immersion lance 5 or the immersion lance 6 is immersed in the molten steel 9, and the immersion lance 5 Then, Ar gas is blown into the molten steel 9 from at least one of the immersion lance 6 or the bottom blown
この場合、脱硫反応を促進させる観点から、前述したように、浸漬ランス５，６からＡｒガスとともに、Ｃａ合金粉、金属Ｍｇ粉、Ｍｇ合金粉のうちの何れか１種または２種以上を溶鋼中に吹き込むこと、或いは、脱硫処理の少なくとも一時期において、浸漬ランス５，６からの攪拌用ガスの吹き込みと、底吹きポーラス煉瓦７，８からの攪拌用ガスの吹き込みとを同時に行うことが好ましい。Ｃａ合金粉としては、Ｃａ−Ｓｉ合金粉、Ｃａ−Ａｌ合金粉などを使用し、Ｍｇ合金粉としては、Ｍｇ−Ａｌ−Ｚｎ合金粉、Ｍｇ−Ｓｉ−Ｆｅ合金粉などを使用する。これら金属粉の粒径は、吹き込み添加が可能である限り特定する必要はないが、反応界面積を確保する観点から最大粒径を１ｍｍ以下とすることが好ましい。
In this case, from the viewpoint of promoting the desulfurization reaction, as described above, one or more of Ca alloy powder, metal Mg powder, and Mg alloy powder is molten steel together with Ar gas from the immersion lances 5 and 6. It is preferable to blow in the inside or to blow the stirring gas from the immersion lances 5 and 6 and to blow the stirring gas from the bottom blown
溶鋼９の硫黄濃度が０．００１０質量％以下になったなら、溶鋼９へのＡｒガスの吹き込みを停止して脱硫処理を終了する。脱硫処理が終了した時点で、溶鋼９の温度が目標温度よりも低い場合はアーク加熱を実施し、また、溶鋼９の成分が目標の範囲にない場合には、原材料投入シュート１１を介して成分調整用の合金鉄や金属を投入する。脱硫処理終了後は、必要に応じてＲＨ真空脱ガス装置などで脱ガス精錬を実施した後、連続鋳造機でスラブ鋳片に鋳造する。
When the sulfur concentration of the molten steel 9 becomes 0.0010% by mass or less, the blowing of Ar gas into the molten steel 9 is stopped and the desulfurization process is ended. When the temperature of the molten steel 9 is lower than the target temperature at the time when the desulfurization treatment is completed, arc heating is performed, and when the component of the molten steel 9 is not within the target range, the component is supplied via the raw
以上説明したように、本発明によれば、ＣａＯ含有物質を脱硫剤の主たる構成物質として用いた取鍋精錬法による溶鋼９の脱硫処理において、脱硫処理後のスラグ組成を、ＳｉＯ2の含有量が５〜１５質量％になるように調整するので、ＳｉＯ2がＣａＯの滓化促進剤として機能してＣａＯの滓化が促進され、また、脱硫処理後のスラグ組成を、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）が１．５〜３．０になるように調整するので、スラグ１０には高い脱硫能力が確保され、その結果、ＣａＦ2を脱硫剤の一部として使用しなくても、また、脱硫剤がプリメルトフラックスでなくても、効率的に溶鋼９の脱硫処理を行うことが実現される。
As described above, according to the present invention, in the desulfurization treatment of the molten steel 9 by the ladle refining method using the CaO-containing material as the main constituent material of the desulfurization agent, the slag composition after the desulfurization treatment is changed to the content of SiO 2 . Therefore, SiO 2 functions as a CaO hatching accelerator to promote the hatching of CaO, and the slag composition after desulfurization treatment is [[mass% CaO ) + (Mass% MgO)] / (mass% Al 2 O 3 ) is adjusted so as to be 1.5 to 3.0, so that a high desulfurization capacity is ensured in the
尚、上記説明はＬＦ設備で本発明を実施した例であるが、ＡＳＥＡ−ＳＫＦ設備及びＶＡＤ設備においても、上記に準じて本発明を適用することができる。 In addition, although the said description is an example which implemented this invention with LF equipment, this invention can be applied according to the above also in ASEA-SKF equipment and VAD equipment.
高炉から出銑された溶銑に対して脱珪処理、脱硫処理、脱燐処理を行ったのち、この溶銑を転炉に装入して脱炭精錬を実施し、炭素濃度が０．０５〜０．０９質量％、硫黄濃度が０．００３〜０．００４質量％、燐濃度が０．００４〜０．０１０質量％の約２５０トンの溶鋼を得た。出鋼末期に溶鋼に混入して取鍋へ流出する転炉スラグを除去しないことを前提とし、転炉から取鍋への出鋼時に、出鋼流に脱酸用の金属Ａｌと、脱硫用フラックルとして、生石灰、軽焼ドロマイト、アルミドロスとを添加した。この場合、金属Ａｌ、生石灰、軽焼ドロマイト、アルミドロスの添加量は、過去の実績に基づいて転炉スラグの取鍋への流出量を推定し、転炉内のスラグ組成が、ＳｉＯ2含有量＝５〜１５質量％、且つ、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）＝１．５〜３．０の範囲内になるように、計算によって求めた。出鋼後、取鍋へ流出した転炉スラグを徐滓せず、金属Ａｌ、生石灰、軽焼ドロマイト、アルミドロスの添加された取鍋を図１に示すＬＦ設備に搬送した。 The hot metal discharged from the blast furnace is subjected to desiliconization treatment, desulfurization treatment, and dephosphorization treatment. Then, the hot metal is charged into a converter and subjected to decarburization refining, and the carbon concentration is 0.05-0. About 250 tons of molten steel having 0.09 mass%, a sulfur concentration of 0.003 to 0.004 mass%, and a phosphorus concentration of 0.004 to 0.010 mass% was obtained. Assuming that the converter slag mixed in the molten steel and flowing into the ladle at the end of the steel output is not removed, when the steel is output from the converter to the ladle, the deoxidation metal Al and desulfurization As flack, quick lime, light-burned dolomite, and aluminum dross were added. In this case, the addition amount of metal Al, quicklime, light-burned dolomite, and aluminum dross was estimated based on past results, the amount of outflow to the ladle of the converter slag, and the slag composition in the converter contained SiO 2 By calculation so that the amount is in the range of 5 to 15% by mass and [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3 ) = 1.5 to 3.0. Asked. After the steel was removed, the ladle slag that had flowed into the ladle was not gradually removed, and the ladle added with metal Al, quicklime, light-burned dolomite, and aluminum dross was conveyed to the LF facility shown in FIG.
転炉スラグの取鍋への流出量は、流出した転炉スラグの厚みを測定することで推定可能であり、転炉スラグの成分と流出量、及び、出鋼中に添加した金属Ａｌ、生石灰、軽焼ドロマイト、アルミドロスの添加量から、転炉内スラグのＣａＯ、ＭｇＯ、Ａｌ2Ｏ3、ＳｉＯ2の含有量を算出した。算出されたスラグ組成が、ＳｉＯ2含有量＝５〜１５質量％で、且つ、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）＝１．５〜３．０の範囲内でないときには、ＬＦ設備において、不足するフラックスを添加した（本発明例）。また、比較例として、スラグ中のＳｉＯ2含有量、及び、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）を上記範囲外に変化させた脱硫処理も実施した。スラグ中のＳｉＯ2含有量の調整には珪砂を使用した。本発明例及び比較例ともにＣａＦ2は添加しなかった。 The amount of converter slag outflow to the ladle can be estimated by measuring the thickness of the outflow converter slag, the converter slag components and outflow amount, and the metal Al and quicklime added to the steel output. The contents of CaO, MgO, Al 2 O 3 and SiO 2 in the slag in the converter were calculated from the addition amounts of light-burned dolomite and aluminum dross. The calculated slag composition is SiO 2 content = 5-15% by mass, and [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3 ) = 1.5-3. When it was not within the range of 0, insufficient flux was added in the LF facility (Example of the present invention). In addition, as a comparative example, desulfurization treatment in which the content of SiO 2 in slag and [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3 ) is changed outside the above range is also performed. did. Silica sand was used to adjust the SiO 2 content in the slag. CaF 2 was not added in both the inventive examples and the comparative examples.
電極をスラグに浸漬させてアーク加熱を行いながら、浸漬ランスから２０００ＮＬ／ｍｉｎのＡｒガスを溶鋼中に吹き込んで溶鋼を攪拌し、約２０分間脱硫処理を行った。 While the electrode was immersed in the slag and performing arc heating, 2000 NL / min Ar gas was blown into the molten steel from the immersion lance and the molten steel was stirred, and desulfurized for about 20 minutes.
表１に各脱硫試験における処理後のスラグ組成（化学分析値）、脱硫処理前後の溶鋼中硫黄濃度（化学分析値）、脱硫率を示す。評価の欄は、脱硫率が８０％以上で処理後の硫黄濃度が０．０００８質量％以下の試験は◎印、処理後の硫黄濃度が０．００１０質量％以下で脱硫率が７０％以上の試験は○印、脱硫率が７０％未満の試験は×印で評価した。また、表１の備考欄には、本発明の範囲内の試験は「本発明例」、それ以外は「比較例」として表示した。尚、脱硫率は、脱硫処理前後の溶鋼中硫黄濃度の差分を脱硫処理前の溶鋼中硫黄濃度に対して百分率で表示した値である。 Table 1 shows the slag composition (chemical analysis value) after treatment in each desulfurization test, the sulfur concentration (chemical analysis value) in the molten steel before and after the desulfurization treatment, and the desulfurization rate. In the column for evaluation, a test in which the desulfurization rate is 80% or more and the sulfur concentration after treatment is 0.0008% by mass or less is marked by ◎, and the sulfur concentration after treatment is 0.0010% by mass or less and the desulfurization rate is 70% or more. The test was evaluated with a circle mark, and the test with a desulfurization rate of less than 70% was evaluated with a mark x. Further, 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 cases are indicated as “comparative examples”. The desulfurization rate is a value obtained by displaying the difference in sulfur concentration in the molten steel before and after the desulfurization treatment as a percentage with respect to the sulfur concentration in the molten steel before the desulfurization treatment.
脱硫処理後のスラグ組成を、ＳｉＯ2含有量＝５〜１５質量％、且つ、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）＝１．５〜３．０の範囲内に調整した本発明例では、脱硫処理後の溶鋼中硫黄濃度は０．００１０質量％以下であり、７０％以上の脱硫率が得られた。特に、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）＝１．８〜２．５の範囲内とする試験Ｎo.１、２、４では高い脱硫率が得られた。但し、試験Ｎo.１０は、スラグ中の（質量％ＭｇＯ）／（質量％ＣａＯ）が０．１４０であり、その他の条件は試験Ｎo.１と同等であったものの、試験Ｎo.１に比べて脱硫率が低下した。この結果から、生成するスラグ中の（質量％ＭｇＯ）／（質量％ＣａＯ）を０．１０以下に調整することが好ましいことが確認できた。 The slag composition after the desulfurization treatment, SiO 2 content = 5-15 wt%, and, [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3) = 1.5~3 . In the present invention example adjusted within the range of 0, the sulfur concentration in the molten steel after the desulfurization treatment was 0.0010% by mass or less, and a desulfurization rate of 70% or more was obtained. In particular, in tests No. 1, 2 , and 4 in which [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3 ) = 1.8 to 2.5, a high desulfurization rate is obtained. Obtained. However, in test No. 10, (mass% MgO) / (mass% CaO) in the slag was 0.140, and other conditions were the same as test No. 1, but compared with test No. 1. As a result, the desulfurization rate decreased. From this result, it was confirmed that it was preferable to adjust (mass% MgO) / (mass% CaO) in the slag to be generated to 0.10 or less.
一方、比較例では、何れの試験も脱硫処理後の溶鋼中硫黄濃度を０．００１０質量％以下まで脱硫することはできなかった。 On the other hand, in the comparative example, in any test, the sulfur concentration in the molten steel after the desulfurization treatment could not be desulfurized to 0.0010% by mass or less.
高炉から出銑された溶銑に対して脱珪処理、脱硫処理、脱燐処理を行ったのち、この溶銑を転炉に装入して脱炭精錬を実施し、炭素濃度が０．０５〜０．０９質量％、硫黄濃度が０．００３〜０．００５質量％、燐濃度が０．００４〜０．０１０質量％の約２５０トンの溶鋼を得た。出鋼末期に溶鋼に混入して取鍋へ流出する転炉スラグを除去しないことを前提とし、転炉から取鍋への出鋼時に、出鋼流に脱酸用の金属Ａｌと、脱硫用フラックルとして、生石灰、軽焼ドロマイト、アルミドロスとを添加した。この場合、金属Ａｌ、生石灰、軽焼ドロマイト、アルミドロスの添加量は、過去の実績に基づいて転炉スラグの取鍋への流出量を推定し、転炉内のスラグ組成が、ＳｉＯ2含有量＝５〜１５質量％、且つ、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）＝１．５〜３．０の範囲内になるように、計算によって求めた。出鋼後、取鍋へ流出した転炉スラグを徐滓せず、金属Ａｌ、生石灰、軽焼ドロマイト、アルミドロスの添加された取鍋を図１に示すＬＦ設備に搬送した。 The hot metal discharged from the blast furnace is subjected to desiliconization treatment, desulfurization treatment, and dephosphorization treatment. Then, the hot metal is charged into a converter and subjected to decarburization refining, and the carbon concentration is 0.05-0. About 250 tons of molten steel having 0.09 mass%, a sulfur concentration of 0.003 to 0.005 mass%, and a phosphorus concentration of 0.004 to 0.010 mass% was obtained. Assuming that the converter slag mixed in the molten steel and flowing into the ladle at the end of the steel output is not removed, when the steel is output from the converter to the ladle, the deoxidation metal Al and desulfurization As flack, quick lime, light-burned dolomite, and aluminum dross were added. In this case, the addition amount of metal Al, quicklime, light-burned dolomite, and aluminum dross was estimated based on past results, the amount of outflow to the ladle of the converter slag, and the slag composition in the converter contained SiO 2 By calculation so that the amount is in the range of 5 to 15% by mass and [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3 ) = 1.5 to 3.0. Asked. After the steel was removed, the ladle slag that had flowed into the ladle was not gradually removed, and the ladle added with metal Al, quicklime, light-burned dolomite, and aluminum dross was conveyed to the LF facility shown in FIG.
転炉スラグの取鍋への流出量は、流出した転炉スラグの厚みを測定することで推定可能であり、転炉スラグの成分と流出量、及び、出鋼中に添加した金属Ａｌ、生石灰、軽焼ドロマイト、アルミドロスの添加量から、転炉内スラグのＣａＯ、ＭｇＯ、Ａｌ2Ｏ3、ＳｉＯ2の含有量を算出した。算出されたスラグ組成が、ＳｉＯ2含有量＝５〜１５質量％で、且つ、［（質量％ＣａＯ）＋（質量％ＭｇＯ）］／（質量％Ａｌ2Ｏ3）＝１．５〜３．０の範囲内でないときには、ＬＦ設備において、不足するフラックスを添加した。スラグ中のＳｉＯ2含有量の調整には珪砂を使用した。ＣａＦ2は全ての試験において添加しなかった。 The amount of converter slag outflow to the ladle can be estimated by measuring the thickness of the outflow converter slag, the converter slag components and outflow amount, and the metal Al and quicklime added to the steel output. The contents of CaO, MgO, Al 2 O 3 and SiO 2 in the slag in the converter were calculated from the addition amounts of light-burned dolomite and aluminum dross. The calculated slag composition is SiO 2 content = 5-15% by mass, and [(mass% CaO) + (mass% MgO)] / (mass% Al 2 O 3 ) = 1.5-3. When it was not within the range of 0, insufficient flux was added in the LF facility. Silica sand was used to adjust the SiO 2 content in the slag. CaF 2 was not added in all tests.
電極をスラグに浸漬させてアーク加熱を行いながら、浸漬ランスまたは底吹きポーラス煉瓦から７００〜３５００ＮＬ／ｍｉｎのＡｒガスを溶鋼中に吹き込んで溶鋼を攪拌し、脱硫処理を行った（試験Ｎo.１８〜２５）。また、一部の試験では、浸漬ランスから吹き込むＡｒガスとともにＣａ合金粉と金属Ｍｇ粉とを同時に吹き込む試験（試験Ｎo.２６〜２８）、及び、生石灰粉を同時に吹き込む試験（試験Ｎo.２９）を実施した。攪拌ガスとともに吹き込む粉体の吹き込み速度は２５ｋｇ／ｍｉｎとした。更に、浸漬ランスから２０００ＮＬ／ｍｉｎのＡｒガスを吹き込みながら、底吹きポーラス煉瓦から７００、１５００ＮＬ／ｍｉｎのＡｒガスを吹き込む試験（試験Ｎo.３０〜３１）も実施した。 While the electrode was immersed in the slag and arc heating was performed, 700-3500 NL / min Ar gas was blown into the molten steel from an immersion lance or bottom blown porous brick, and the molten steel was stirred to perform desulfurization treatment (Test No. 18). ~ 25). Further, in some tests, a test in which Ca alloy powder and metal Mg powder are simultaneously blown together with Ar gas blown from the immersion lance (test No. 26 to 28), and a test in which quick lime powder is simultaneously blown (test No. 29). Carried out. The blowing speed of the powder blown with the stirring gas was 25 kg / min. Furthermore, while blowing 2000 NL / min Ar gas from the immersion lance, a test (test Nos. 30 to 31) was conducted in which 700 and 1500 NL / min Ar gas was blown from the bottom blown porous brick.
表２に各脱硫試験における溶鋼の攪拌方法、脱硫処理前後の溶鋼中硫黄濃度、脱硫処理時間、脱硫率を示す。 Table 2 shows the molten steel stirring method, the sulfur concentration in the molten steel before and after the desulfurization treatment, the desulfurization treatment time, and the desulfurization rate in each desulfurization test.
攪拌用ガスの吹き込み箇所を一箇所とし、且つ、ガス吹き込み流量を２７００ＮＬ／ｍｉｎ以上に増加させた試験Ｎo.２１、２２、２５ではスプラッシュが激しく、蓋への地金付着が発生した。攪拌用ガスの吹き込み箇所が一箇所であっても、ガス吹き込み流量が２０００ＮＬ／ｍｉｎ以下の場合には、蓋への地金付着は見られなかった。 In the test Nos. 21, 22, and 25 in which the stirring gas was blown into one place and the gas blowing flow rate was increased to 2700 NL / min or more, the splash was intense and adhesion of the metal to the lid occurred. Even if the stirring gas was blown into one location, no adhesion of the metal to the lid was observed when the gas blowing flow rate was 2000 NL / min or less.
これに対して、浸漬ランスと底吹きポーラス煉瓦とから同時に吹き込んだ試験Ｎo.３０、３１では、ガス吹き込み流量が２７００ＮＬ／ｍｉｎ以上であっても蓋への地金付着は見られず、短時間の脱硫処理で高い脱硫率が得られた。 On the other hand, in the tests No. 30 and 31, which were blown simultaneously from the immersion lance and the bottom blown porous brick, even when the gas blowing flow rate was 2700 NL / min or more, no adhesion of the metal to the lid was observed and the time was short. A high desulfurization rate was obtained by this desulfurization treatment.
即ち、攪拌用ガスの吹き込み位置を分散させることで、激しいスプラッシュを起こさずにガス吹き込み流量を増加することが可能となり、溶鋼の攪拌が強化されて高い脱硫率が得られることが分った。 That is, it has been found that by dispersing the stirring gas blowing position, the gas blowing flow rate can be increased without causing severe splash, and the stirring of the molten steel is strengthened to obtain a high desulfurization rate.
また、浸漬ランスからＡｒガスとともにＣａ合金粉と金属Ｍｇ粉とを同時に吹き込んだ試験Ｎo.２６〜２８では、生石灰を吹き込んだ試験Ｎo.２９よりも更に短時間で高い脱硫率が得られ、極めて効率良く脱硫処理できることが確認できた。 Moreover, in the test No. 26 to 28 in which Ca alloy powder and metal Mg powder were simultaneously blown together with Ar gas from the immersion lance, a higher desulfurization rate was obtained in a shorter time than in the test No. 29 in which quick lime was blown. It was confirmed that the desulfurization treatment can be performed efficiently.
試験Ｎo.１８〜３１は、脱硫処理後のスラグ組成が本発明の範囲内であり、脱硫処理後の溶鋼中硫黄濃度は全ての試験で０．００１０質量％以下を達成した。 In Test Nos. 18 to 31, the slag composition after the desulfurization treatment was within the scope of the present invention, and the sulfur concentration in the molten steel after the desulfurization treatment achieved 0.0010% by mass or less in all tests.
１ ＬＦ設備
２ 取鍋
３ 蓋
４ 電極
５ 浸漬ランス
６ 浸漬ランス
７ 底吹きポーラス煉瓦
８ 底吹きポーラス煉瓦
９ 溶鋼
１０ スラグ
１１ 原材料投入シュート
１２ Ａｒガス導入管
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