JP3577988B2 - Manufacturing method of low Al ultra low sulfur steel - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、低Ａｌ極低硫鋼の製造方法、具体的には低Ａｌ鋼の脱硫方法に関する。
【０００２】
【従来の技術】
溶鋼中の硫黄（以下、単にＳともいう）は様々な介在物を形成し、溶接部欠陥や腐食割れ等の原因となり、溶鋼中のＳの低減が鋼材の品質確保の面から必要である。溶鋼中のＳ濃度の低減処理（以下、脱硫処理ともいう）は、主として、転炉処理前の溶銑予備処理あるいは転炉処理終了後の二次精錬で行われるが、Ｓ濃度を１０ｐｐｍ以下まで低減するような極低硫化処理は、溶鋼温度の高い２次精錬で行われている。また、脱硫処理はスラグあるいはフラックス中のＣａＯを用い、ＣａＯ＋Ｓ＝ＣａＳ＋Ｏなる反応を用いて行うため、溶鋼中の酸素濃度が低いほど脱硫は進行する。酸素濃度を低減するにはＡｌ添加による脱酸（以下、Ａｌ脱酸ともいう）が有効であり、極低硫鋼製造時はＡｌ脱酸を行うことが一般的である。
【０００３】
【発明が解決しようとする課題】
ところが、近年、Ａｌ脱酸を行わない極低硫鋼が望まれている。
【０００４】
この理由の第一は、アルミナ介在物による製品欠陥を防止するためである。Ａｌ脱酸を行うと、２Ａｌ＋３Ｏ＝Ａｌ２ Ｏ３ なる反応により、溶鋼中の酸素濃度は低減するが、その代わりにアルミナが生成する。このアルミナの大部分は溶鋼から浮上分離するが一部が非金属介在物となって溶鋼中に残留し、この介在物による欠陥が製品に発生する。
【０００５】
第二の理由は、介在物の形態を良好に保てないからである。すなわち、Ｓｉ−Ｍｎ−Ｏ系あるいはＴｉ−Ｏ−Ｎ系の非金属介在物を用いて鋼材の組織制御する場合、予め溶鋼をＡｌ脱酸すると、Ａｌより脱酸力の弱い、Ｓｉ、ＭｎあるいはＴｉによる前記の有用介在物を生成できなくなるからである。
【０００６】
また、Ａｌ脱酸を行わなければ、脱硫反応が進行しない理由は、酸素濃度が下げられないからである。さらに、Ａｌ脱酸を行わなければ溶鋼表面に存在するスラグ中の低級酸化物濃度（以下、（Ｆｅ＋Ｍｎ）濃度ともいう）も低減できない。
【０００７】
脱硫処理方法として、スラグ−溶鋼間反応を用いる場合、または溶鋼に脱硫フラックスを吹き込む場合のいずれの場合も最終的に溶鋼から除去されたＳはスラグ中へ移行する。スラグ中のＳは、スラグ中の（Ｆｅ＋Ｍｎ）濃度が高いと、スラグ中のＳが溶鋼へ戻るいわゆる復硫が発生し、低硫鋼を得ることができない。
【０００８】
以上の理由から、Ａｌ脱酸を行わずに極低硫鋼を得る精錬技術の確立が望まれていた。しかし、これまでＡｌ脱酸を行わずに極低硫鋼を得る技術はほとんど報告されておらず、実生産で実施された例はなかった。
【０００９】
本発明の目的は、Ａｌ脱酸を行わずに溶鋼中のＳ濃度を５分以内に１０ｐｐｍ以下とすることができる方法を提供することにある。
【００１０】
【課題を解決するための手段】
本発明者等は、各種の試験を重ね以下の知見を得た。
（Ａ）脱硫処理を効率よくおこなう手段として、溶鋼全体の酸素濃度を低減するのではなく脱硫反応が起こる界面付近の酸素濃度のみを低減することが重要である。
【００１１】
溶鋼中のＡｌ濃度は０．０３重量％（以下、単に％で重量％を示す）以上でなければ、溶鋼中の酸素濃度を低減できないが、溶鋼中のＣａ濃度は４ｐｐｍ以上であれば、Ａｌ脱酸と同等の酸素濃度の低減効果がある。また、Ｃａの場合、界面のみに、わずかな量のＣａを供給するようにすれば、溶鋼全体の酸素濃度が低減するおそれがない。
【００１２】
（Ｂ）スラグ中には、一般的に酸化性の強い鉄酸化物、Ｍｎ酸化物が存在しているので、スラグ−溶鋼界面の酸素濃度を低減しても復硫が生じる。従って、スラグで脱硫処理をおこなうのは困難である。この対策として、ＣａＯとＣａを混合したフラックスを溶鋼に供給し、フラックス周辺の酸素濃度を低減することが効果的である。
【００１３】
（Ｃ）ＣａとＣａＯとの混合粉体を単に、取鍋内溶鋼に吹き込めば、吹き込みガスやＣａ蒸気による攪拌作用で、スラグ−溶鋼間の反応が進行し、復硫し、脱硫処理が困難となる。しかし、ＲＨ真空槽内溶鋼表面にＣａとＣａＯとの混合粉体を上吹きで吹き付けるとスラグ−溶鋼間の反応が回避でき、復硫が生じない。
【００１４】
（Ｄ）Ｃａが過剰であれば、Ｃａ脱酸が溶鋼全体におよびＣａ−Ｓ−Ｏ系介在物が生じ、Ａｌ脱酸と同様の問題を生じる。Ｃａが不足であれば、Ｃａ脱酸が不足し、ＣａＯによる脱硫が進行しないという問題が発生する。
【００１５】
以上の知見から、ＣａとＣａＯとの混合粉体の配合比の最適範囲があるはずである。これを確認するため、発明者らはＳｉ脱酸鋼、Ｍｎ脱酸鋼およびＳｉ−Ｍｎ脱酸鋼など複数の非Ａｌ脱酸鋼を対象に、ＲＨ真空槽内で溶鋼表面に各種配合比のＣａ−ＣａＯフラックスを吹き付けた試験を行った。初期の溶鋼中のＳ濃度は４０ｐｐｍである。
【００１６】
図１に試験結果を示す。
同図に示すように、脱硫能は、ＣａとＣａＯとの配合比（重量比Ｃａ／ＣａＯ）と溶鋼中の炭素濃度（以下、単にＣ濃度ともいう）で規定されることが認められた。図中の○印は、溶鋼中の酸素濃度の低下が認められずにＳ濃度が１０ｐｐｍ以下となったことを、△印は、Ｓ濃度が１０ｐｐｍ以下となったが溶鋼中酸素濃度も低減しＣａ−Ｓ−Ｏ系介在物が生成したことを、×印は、酸素濃度が低減せずＳ濃度も１０ｐｐｍ以下に低減しなかったことをそれぞれ示す。
【００１７】
減圧下で、溶鋼中のＣ濃度が高い場合は、溶鋼中のＣが酸素を消費するため、真空槽内溶鋼表面の酸素濃度が低下し、Ｃａ−ＣａＯが吹き付けられた表面の脱硫処理が効率よく進行する。減圧下で溶鋼中のＣ濃度が低い場合は、真空槽内溶鋼表面の酸素濃度が高くなり、Ｃａ配合比が低過ぎると界面酸素濃度を十分に低減できず、脱硫反応が進行しないためＣａ配合比の下限がある。また、Ｃａが過剰であれば、前述のように、Ｃａ脱酸が溶鋼全体におよびＣａ−Ｓ−Ｏ系介在物が生じ、Ａｌ脱酸と同様の問題を生じるためＣａ配合比の上限がある。
【００１８】
上記のように、溶鋼中のＣ濃度に従って真空槽内溶鋼表面にＣａとＣａＯと配合比を適切にして吹き付けることにより、Ａｌ脱酸をせずに極低硫鋼を溶製することが可能となる。
【００１９】
以上の知見に基づいて下記の本発明を完成できた。
ここに本発明は、CaとＣａＯとの重量比を（１）式に従い配合した粉体を溶鋼中の [Ａｌ] 濃度が０．０１重量％未満の真空槽内溶鋼の表面に吹き付けることを特徴とする低Ａｌ極低硫鋼の製造方法である。
【００２０】
−２×［Ｃ］＋０．４５≧（Ｃａ）／（ＣａＯ）
≧−１．９×［Ｃ］＋０．２ （１）
但し、（Ｃａ）：吹き付け粉体中のＣａ重量、
（ＣａＯ）：吹き付け粉体中ＣａＯ重量、
［Ｃ］：溶鋼中の炭素濃度（重量％）。
【００２１】
【発明の実施の形態】
以下、転炉、ＲＨおよび連続鋳造機を順に用いた場合を例に、本発明の実施の形態を説明する。
【００２２】
転炉で脱炭し、溶鋼中のＣ濃度を０．０７％とした溶鋼を取鍋へ出鋼する。出鋼後、取鍋をＲＨへ移動し脱硫処理を開始する。上吹き脱硫処理前に、溶鋼にＳｉ等を添加し酸素ガスを供給する方法で溶鋼の温度を上昇させる昇熱処理を行っても良い。また、上吹き脱硫処理前に、溶鋼に合金成分の添加調整を行ってもよい。上記昇熱処理および／または合金成分の添加調整終了後、ＣａとＣａＯとの重量比を適切な範囲に配合した粉体を減圧下で溶鋼表面に吹き付ける。
【００２３】
ＣａＯにＭｇＯ、Ａｌ２ Ｏ３ 、ＣａＦ２ 等の成分を添加しても良い。しかし、ＣａＯ以外の成分は合計量で４５重量％未満が望ましい。その理由は、４５％以上となるとＣａ、ＣａＯ以外の成分量が増大し、ＣａＯの効果が低減し操業時間の延長あるいは大幅な温度低下を招くおそれがあるからである。ＣａＯ以外の成分量が４５重量％未満であれば、ＣａＯとその他の成分は単なる混合物でも、事前に溶融混合したものであってもよい。
【００２４】
ＣａＯと混合されるＣａは金属Ｃａ、Ｃａ−Ｓｉ合金、Ｃａ−Ｆｅ合金などの合金の形態でも良く製品規格成分に応じて適宜選択できる。
【００２５】
ＣａとＣａＯとの混合物の上吹き速度Ｖは溶鋼トン（ｔ）当り、０．１ｋｇ／ｔ・ｍｉｍ以上、１．５ｋｇ／ｔ・ｍｉｍ以下が望ましい。その理由は、Ｖが０．１ｋｇ／ｔ・ｍｉｍ未満となると操業時間が長くなり、１．５ｋｇ／ｔ・ｍｉｍを超えて高くなると真空槽内スプラッシュが激しくなり、地金付着等の操業に支障が発生するからである。
【００２６】
ＣａとＣａＯの混合物は粒径２ｍｍ以下が望ましく、さらには０．５ｍｍ以下がより望ましい。その理由は、粉体粒径が２ｍｍを超えて大きくなると、混合物と溶鋼との接触面積が低下し、脱硫反応効率が低下するからである。
【００２７】
上吹き時に使用するランスは、ストレート単孔、ラバール、複数孔、水冷・非水冷などのタイプを問わずに使用できる。ランスと真空槽内溶鋼表面との距離は２０ｃｍ以上２００ｃｍ以下が望ましい。その理由は、２０ｃｍ未満となるとスプラッシュが激しくなるのみでなく、ランス寿命が大幅に低下するからである。２００ｃｍを超えて離れると、粉体を安定して溶鋼に吹き付けることが困難となるからである。
【００２８】
上吹き時の真空度は溶鋼が環流できる範囲であればよいが、１００Ｔｏｒｒ以下が望ましい。その理由は、１００Ｔｏｒｒを超えると環流量が少なくなるため、脱硫速度が低下するからである。
【００２９】
上吹き時間は、２分以上１０分以下が望ましい。その理由は、２分未満であると吹き付けられる絶対粉体量が少なく、十分な精錬効果が得られないからであり、１０分を超えて長くなると、供給粉体量が多くなりすぎ、取鍋スラグ量が過度に増大するからである。
【００３０】
【実施例】
転炉にて溶鋼中のＣ濃度を０．０３％まで脱炭した溶鋼を取鍋へ出鋼した。その後、取鍋をＲＨへ移動した。ＲＨ処理開始後、溶鋼にＳｉを添加し、真空槽内溶鋼に酸素ガスを吹き付け、溶鋼温度を２０℃上昇させた。溶鋼中のＳｉ濃度を０．２％、Ｍｎ濃度を０．７％に調整した後、ＣａとＣａＯとを所定比率に配合した粉体を真空槽内溶鋼に吹き付けた。
【００３１】
上吹き粉体には平均粒径０．２ｍｍのＦｅＣａ（Ｃａ分３０％）とＣａＯとを用い、吹き付け速度は０．６５ｋｇ／（ｔ・ｍｉｎ）、キャリアガスはＡｒ３０００Ｎｌ／ｍｉｎ、真空度は１Ｔｏｒｒとした。
【００３２】
表１に、上吹き粉体の配合比、溶鋼中のＣ濃度と上吹き粉体の適正配合比の範囲、Ａｌ濃度、初期Ｓ濃度、３分後、５分後、７分後、１０分後および１５分後の溶鋼中のＳ濃度を示す。なお、適正配合比の範囲は、下記（１）式から求めた。
【００３３】
−２×［Ｃ］＋０．４５≧（Ｃａ）／（ＣａＯ）
≧−１．９×［Ｃ］＋０．２ （１）
但し、（Ｃａ）：吹き付け粉体中のＣａ重量、
（ＣａＯ）：吹き付け粉体中ＣａＯ重量、
［Ｃ］：溶鋼中の炭素濃度（重量％）。
【００３４】
また、Ｃａ−Ｓ−Ｏ介在物が生成した場合を介在物有無の欄に×、生成しなかった場合を○で示す。
【００３５】
【表１】
表１に示すように、（Ｃａ）／（ＣａＯ）重量比が上記（１）の範囲内であれば、５分以内に溶鋼中のＳ濃度を１０ｐｐｍ以下に低減でき、しかもＣａ−Ｓ−Ｏ介在物の生成を回避できた。
【００３７】
【発明の効果】
本発明によれば、Ａｌ脱酸を行わずに溶鋼中のＳ濃度を５分以内に１０ｐｐｍ以下とし、同時にＣａ−Ｓ−Ｏ系介在物を生成させないことができる。
【図面の簡単な説明】
【図１】脱硫能をパラメーターとしたＣａ／ＣａＯ重量比と溶鋼中の炭素濃度との関係を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a low Al ultra low sulfur steel, specifically, a method for desulfurizing a low Al steel.
[0002]
[Prior art]
Sulfur in molten steel (hereinafter, also simply referred to as S) forms various inclusions and causes weld defects and corrosion cracking. Therefore, it is necessary to reduce S in molten steel from the viewpoint of ensuring the quality of steel materials. The process of reducing the S concentration in molten steel (hereinafter also referred to as desulfurization treatment) is mainly performed by hot metal pretreatment before converter processing or secondary refining after converter processing, but the S concentration is reduced to 10 ppm or less. Such ultra-low sulfurization treatment is performed in secondary refining with a high molten steel temperature. In addition, since desulfurization treatment is performed using CaO in slag or flux and using a reaction of CaO + S = CaS + O, desulfurization proceeds as the oxygen concentration in the molten steel is lower. Deoxidation by addition of Al (hereinafter, also referred to as Al deoxidation) is effective for reducing the oxygen concentration, and it is general to perform Al deoxidation during the production of extremely low sulfur steel.
[0003]
[Problems to be solved by the invention]
However, in recent years, an ultra low sulfur steel that does not perform Al deoxidation has been desired.
[0004]
The first reason is to prevent product defects due to alumina inclusions. When Al deoxidation is performed, the reaction of 2Al + 3O = Al 2 O 3 reduces the oxygen concentration in the molten steel, but instead generates alumina. Most of the alumina floats and separates from the molten steel, but a part of the alumina remains as nonmetallic inclusions in the molten steel, and defects due to the inclusions occur in the product.
[0005]
The second reason is that the shape of the inclusion cannot be maintained well. That is, when controlling the structure of a steel material using a nonmetallic inclusion of a Si-Mn-O system or a Ti-ON system, if the molten steel is deoxidized in advance with Al, Si, Mn or This is because the above-mentioned useful inclusions cannot be formed by Ti.
[0006]
The reason why the desulfurization reaction does not proceed without Al deoxidation is that the oxygen concentration cannot be reduced. Furthermore, unless Al deoxidation is performed, the lower oxide concentration (hereinafter, also referred to as (Fe + Mn) concentration) in the slag existing on the molten steel surface cannot be reduced.
[0007]
Regardless of whether a desulfurization treatment method uses a reaction between slag and molten steel or a case where a desulfurization flux is blown into the molten steel, S finally removed from the molten steel moves into the slag. If the S in the slag has a high (Fe + Mn) concentration in the slag, so-called resulfurization in which the S in the slag returns to the molten steel occurs, and a low-sulfur steel cannot be obtained.
[0008]
For the above reasons, it has been desired to establish a refining technique for obtaining extremely low sulfur steel without performing Al deoxidation. However, there has been almost no report on a technique for obtaining an ultra-low sulfur steel without performing Al deoxidation, and there has been no example of actual production.
[0009]
An object of the present invention is to provide a method capable of reducing the S concentration in molten steel to 10 ppm or less within 5 minutes without performing Al deoxidation.
[0010]
[Means for Solving the Problems]
The present inventors have conducted various tests and obtained the following findings.
(A) As a means for efficiently performing the desulfurization treatment, it is important to reduce only the oxygen concentration near the interface where the desulfurization reaction occurs, instead of reducing the oxygen concentration in the entire molten steel.
[0011]
The oxygen concentration in the molten steel cannot be reduced unless the Al concentration in the molten steel is 0.03% by weight (hereinafter simply referred to as% by weight), but if the Ca concentration in the molten steel is 4 ppm or more, It has the same effect of reducing oxygen concentration as deoxidation. Further, in the case of Ca, if a small amount of Ca is supplied only to the interface, there is no possibility that the oxygen concentration of the entire molten steel is reduced.
[0012]
(B) Since slag generally contains iron oxide and Mn oxide having strong oxidizability, resulfurization occurs even if the oxygen concentration at the slag-molten steel interface is reduced. Therefore, it is difficult to perform desulfurization treatment with slag. As a countermeasure, it is effective to supply a flux in which CaO and Ca are mixed to molten steel to reduce the oxygen concentration around the flux.
[0013]
(C) If the mixed powder of Ca and CaO is simply blown into the molten steel in the ladle, the reaction between the slag and the molten steel proceeds due to the stirring action by the blown gas or Ca vapor, and resulfurization is difficult, and desulfurization treatment is difficult. It becomes. However, when the mixed powder of Ca and CaO is sprayed on the surface of the molten steel in the RH vacuum chamber by upward blowing, a reaction between the slag and the molten steel can be avoided, and resulfurization does not occur.
[0014]
(D) If Ca is excessive, Ca deoxidation occurs in the entire molten steel and Ca—S—O-based inclusions are generated, causing the same problem as Al deoxidation. If Ca is insufficient, there is a problem that Ca deoxidation is insufficient and desulfurization by CaO does not progress.
[0015]
From the above findings, there should be an optimum range of the mixing ratio of the mixed powder of Ca and CaO. In order to confirm this, the present inventors targeted a plurality of non-Al deoxidized steels such as Si deoxidized steel, Mn deoxidized steel and Si-Mn deoxidized steel, and applied various mixing ratios to the molten steel surface in an RH vacuum chamber. The test which sprayed Ca-CaO flux was performed. The initial S concentration in the molten steel is 40 ppm.
[0016]
FIG. 1 shows the test results.
As shown in the figure, it was recognized that the desulfurization ability was defined by the compounding ratio of Ca and CaO (weight ratio Ca / CaO) and the carbon concentration in the molten steel (hereinafter, also simply referred to as C concentration). In the figure, a circle indicates that the oxygen concentration in the molten steel was reduced to 10 ppm or less without a decrease in the oxygen concentration in the molten steel, and a triangle indicates that the oxygen concentration in the molten steel was reduced even when the S concentration was 10 ppm or less. The x mark indicates that Ca-SO-based inclusions were formed, and the X mark indicates that the oxygen concentration did not decrease and the S concentration did not decrease to 10 ppm or less, respectively.
[0017]
When the C concentration in the molten steel is high under reduced pressure, the C in the molten steel consumes oxygen, so the oxygen concentration on the surface of the molten steel in the vacuum tank decreases, and desulfurization of the surface sprayed with Ca-CaO is efficient. Progress well. When the C concentration in the molten steel is low under reduced pressure, the oxygen concentration on the surface of the molten steel in the vacuum tank increases, and when the Ca mixing ratio is too low, the interfacial oxygen concentration cannot be reduced sufficiently, and the desulfurization reaction does not proceed, so the Ca mixing There is a lower limit on the ratio. Further, if Ca is excessive, as described above, Ca deoxidation occurs in the entire molten steel and Ca-SO-based inclusions occur, and the same problem as Al deoxidation occurs, so there is an upper limit of the Ca compounding ratio. .
[0018]
As described above, it is possible to melt ultra-low sulfur steel without deoxidizing Al by spraying the molten steel surface in the vacuum chamber at an appropriate mixing ratio of Ca and CaO according to the C concentration in the molten steel. Become.
[0019]
The present invention described below has been completed based on the above findings.
The present invention here, the spraying in a weight ratio (1) [Al] concentration inside the vacuum chamber of molten steel below 0.01 wt% surface soluble in steel powder formulated in accordance with formula of Ca and CaO This is a method for producing a low-Al ultra-low sulfur steel, which is a feature.
[0020]
−2 × [C] + 0.45 ≧ (Ca) / (CaO)
≧ −1.9 × [C] +0.2 (1)
However, (Ca): Ca weight in sprayed powder,
(CaO): CaO weight in sprayed powder,
[C]: Carbon concentration in molten steel (% by weight).
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with an example in which a converter, an RH, and a continuous casting machine are used in order.
[0022]
Decarburization is performed in a converter, and the molten steel with the C concentration in the molten steel set to 0.07% is discharged to a ladle. After tapping, the ladle is moved to RH to start desulfurization. Before the top blowing desulfurization treatment, a heat treatment for increasing the temperature of the molten steel by a method of adding Si or the like to the molten steel and supplying oxygen gas may be performed. Before the top-blown desulfurization treatment, the addition of alloy components to the molten steel may be adjusted. After the completion of the heat treatment and / or the adjustment of the addition of the alloy component, a powder in which the weight ratio of Ca and CaO is blended in an appropriate range is sprayed on the molten steel surface under reduced pressure.
[0023]
Components such as MgO, Al 2 O 3 and CaF 2 may be added to CaO. However, components other than CaO are desirably less than 45% by weight in total. The reason is that when the content is 45% or more, the amount of components other than Ca and CaO increases, and the effect of CaO decreases, which may lead to an increase in operation time or a significant temperature drop. As long as the amount of components other than CaO is less than 45% by weight, CaO and other components may be mere mixtures or those previously melt-mixed.
[0024]
Ca to be mixed with CaO may be in the form of an alloy such as metallic Ca, a Ca—Si alloy, or a Ca—Fe alloy, and may be appropriately selected according to the product specification component.
[0025]
The upper blowing speed V of the mixture of Ca and CaO is preferably 0.1 kg / t · mim or more and 1.5 kg / t · mim or less per ton (t) of molten steel. The reason is that when V is less than 0.1 kg / t · mim, the operation time becomes long, and when V exceeds 1.5 kg / t · mim, the splash in the vacuum chamber becomes severe, which hinders the operation such as adhesion of metal. Is generated.
[0026]
The mixture of Ca and CaO preferably has a particle size of 2 mm or less, more preferably 0.5 mm or less. The reason is that when the powder particle size becomes larger than 2 mm, the contact area between the mixture and the molten steel decreases, and the desulfurization reaction efficiency decreases.
[0027]
The lance used at the time of top blowing can be used irrespective of straight single hole, Laval, multiple holes, water-cooled / non-water-cooled type. The distance between the lance and the surface of the molten steel in the vacuum chamber is preferably 20 cm or more and 200 cm or less. The reason is that when it is less than 20 cm, not only the splash becomes severe, but also the lance life is greatly reduced. If the distance exceeds 200 cm, it is difficult to stably spray the powder on the molten steel.
[0028]
The degree of vacuum at the time of top blowing may be within a range in which the molten steel can be circulated, but is desirably 100 Torr or less. The reason is that when the pressure exceeds 100 Torr, the ring flow rate decreases, and the desulfurization rate decreases.
[0029]
The upper blowing time is desirably from 2 minutes to 10 minutes. The reason is that if it is less than 2 minutes, the amount of the absolute powder to be sprayed is small, and a sufficient refining effect cannot be obtained. This is because the amount of slag increases excessively.
[0030]
【Example】
In the converter, the molten steel decarbonized to a C concentration of 0.03% in the molten steel was discharged to a ladle. Thereafter, the ladle was moved to RH. After the start of the RH treatment, Si was added to the molten steel, and oxygen gas was sprayed on the molten steel in the vacuum chamber to raise the temperature of the molten steel by 20 ° C. After adjusting the Si concentration in the molten steel to 0.2% and the Mn concentration to 0.7%, a powder in which Ca and CaO were mixed in a predetermined ratio was sprayed on the molten steel in the vacuum chamber.
[0031]
FeCa (Ca content 30%) and CaO having an average particle diameter of 0.2 mm are used for the upper blowing powder, the spraying speed is 0.65 kg / (t · min), the carrier gas is Ar 3000 Nl / min, and the degree of vacuum is 1 Torr. And
[0032]
Table 1 shows the blending ratio of the top blown powder, the range of the C concentration in the molten steel and the proper blending ratio of the top blown powder, the Al concentration, the initial S concentration, after 3 minutes, after 5 minutes, after 7 minutes, and after 10 minutes. The S concentration in the molten steel after and after 15 minutes is shown. The range of the proper compounding ratio was determined from the following equation (1).
[0033]
−2 × [C] + 0.45 ≧ (Ca) / (CaO)
≧ −1.9 × [C] +0.2 (1)
However, (Ca): Ca weight in sprayed powder,
(CaO): CaO weight in sprayed powder,
[C]: Carbon concentration in molten steel (% by weight).
[0034]
Moreover, the case where Ca-SO inclusions were generated is indicated by x in the column of the presence or absence of inclusions, and the case where they were not generated is indicated by ○.
[0035]
[Table 1]
As shown in Table 1, when the (Ca) / (CaO) weight ratio is within the range of the above (1), the S concentration in the molten steel can be reduced to 10 ppm or less within 5 minutes, and Ca—S—O The generation of inclusions was avoided.
[0037]
【The invention's effect】
According to the present invention, the S concentration in the molten steel can be reduced to 10 ppm or less within 5 minutes without performing Al deoxidation, and Ca-SO-based inclusions can not be generated at the same time.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the Ca / CaO weight ratio and the carbon concentration in molten steel using desulfurization ability as a parameter.
Claims (1)
−２× [Ｃ] ＋０．４５≧（Ca）／（CaＯ）
≧−１．９× [Ｃ] ＋０．２ （１）
但し、（Ca）：吹き付け粉体中のCa重量、
（CaＯ）：吹き付け粉体中CaＯ重量、
[Ｃ] ：溶鋼中の炭素濃度（重量％）。Low Al electrode and the weight ratio of the Ca and CaO powder formulated according (1) is [Al] concentration soluble in steel, characterized in that spraying on the surface of the vacuum tank molten steel is less than 0.01 wt% Manufacturing method of low sulfur steel.
-2 × [C] + 0.45 ≧ (Ca) / (CaO)
≧ −1.9 × [C] +0.2 (1)
However, (Ca): Ca weight in sprayed powder,
(CaO): CaO weight in sprayed powder,
[C]: Carbon concentration (% by weight) in molten steel.
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| JP5525939B2 (en) * | 2010-07-02 | 2014-06-18 | 大阪鋼灰株式会社 | Lime-based flux and its manufacturing method |
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| JPH06322431A (en) * | 1993-05-10 | 1994-11-22 | Sumitomo Metal Ind Ltd | Method for desulfurizing and denitriding molten steel |
| JP3412269B2 (en) * | 1994-08-15 | 2003-06-03 | 住友金属工業株式会社 | Manufacturing method of extremely low sulfur steel |
| JPH10102134A (en) * | 1996-09-25 | 1998-04-21 | Sumitomo Metal Ind Ltd | Method for desulfurizing molten steel |
| JP3463573B2 (en) * | 1998-08-31 | 2003-11-05 | 住友金属工業株式会社 | Manufacturing method of ultra clean ultra low sulfur steel |
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