JP3577989B2 - High-speed desulfurization of molten steel - Google Patents
High-speed desulfurization of molten steel Download PDFInfo
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- JP3577989B2 JP3577989B2 JP10267299A JP10267299A JP3577989B2 JP 3577989 B2 JP3577989 B2 JP 3577989B2 JP 10267299 A JP10267299 A JP 10267299A JP 10267299 A JP10267299 A JP 10267299A JP 3577989 B2 JP3577989 B2 JP 3577989B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
【０００１】
【発明の属する技術分野】
本発明は、減圧下における溶鋼の高速脱硫方法に関する。
【０００２】
【従来の技術】
溶鋼中の硫黄（以下、Ｓともいう）は、非金属介在物を形成し製品欠陥を引き起こすこと、介在物の浮上処理を阻害することなどの理由から数多くの鋼種でその低減が求められている。
【０００３】
脱硫処理は、ＣａＯ−Ａｌ２ Ｏ３ 系スラグを溶鋼表面に形成させた後、溶鋼をガス攪拌する方法やＣａＯ系フラックスを溶鋼へ吹き込む方法が知られている。しかし、これらの方法は、脱硫処理のための専用設備が必要であり、設備投資面および保守面から改善が求められている。また、処理時間が長くかかるため全体工程の能率が低下するという問題もあった。これらを改善する目的に、ＲＨ方式などの真空脱ガス装置で脱硫する方法が提案されている。特開平５−１７１２５３号公報には、ＲＨ式真空槽内溶鋼にＣａＯを吹き付ける方法が開示されている。また、特開平６−２０２８号公報には、ＡｌとＣａＯをＲＨ式真空脱ガス装置の取鍋内溶鋼に添加する方法が開示されている。
【０００４】
【発明が解決しようとする課題】
しかし、上記の各方法にはさらに以下の課題があった。
溶鋼中のＳ濃度を約３０ｐｐｍから１０ｐｐｍまで低減するのに９〜１２分、５ｐｐｍ以下まで低減するには１５分以上を要し、真空脱ガス装置では、合金成分調整、昇熱、脱ガスなど複数の処理が順次行われるため、この脱硫処理を加えると真空脱ガス装置における総処理時間は大幅に長くなるという問題がある。
【０００５】
真空脱ガス装置における処理時間が長くなり過ぎると、耐火物寿命低下、エネルギー費用増大などのコストの上昇を招き、生産量も減少する。従って、低硫鋼の安価でかつ大量の供給が困難であった。
【０００６】
本発明の目的は、真空脱ガス装置における脱硫処理時間を短縮できる溶鋼の高速脱硫方法を提供することにある。
【０００７】
【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）溶鋼の脱硫処理には、溶鋼中の酸素濃度を低減した状態で、Ｓと強い親和力を持った物質と反応させることが有効であることが知られている。従って、酸素と強い親和力を持つ物質であるＡｌと、Ｓと強い親和力を持つ物質であるＣａＯを溶鋼に吹き付ける方法が提示されている。
【０００８】
しかし、Ａｌは酸素濃度を低減してＣａＯによる脱硫を促進することができるが、Ｓとの親和力が小さいため、脱硫能が低く、全体処理時間を短縮するという効果を期待できない。
【０００９】
（Ｂ）Ｃａは酸素とＳの両者に強い親和力を有するため、脱硫反応の促進に有利であると考えられる。しかし、Ｃａは沸点が１４４０℃であり、溶鋼温度の１６００℃より低いため、大気圧下でも蒸発するという問題がある。真空脱ガス装置で減圧下にＣａを用いると、Ｃａはさらに蒸発現象が活発になり、脱硫処理効果を期待できない。
【００１０】
（Ｃ）ＣａＯは、それ自体がＳと反応し、ＣａＳを生成させる作用に加えて、Ｃａと溶鋼中のＳとの反応で生成したＣａＳを吸着する作用があることを見いだした。また、Ｃａは酸素濃度を低減して、ＣａＯとＳとの反応を促進させる作用を持つため、ＣａＯとＣａの組み合わせによる溶鋼の脱硫処理は、相乗的に脱硫効率が向上することが期待できる。
【００１１】
（Ｄ）上記知見からＣａとＣａＯとの配合比Ｃａ／ＣａＯ（重量比）を変化させ、脱硫速度の早い配合比を明確化する脱硫試験をＲＨ式真空脱ガス装置で実施した。
【００１２】
図１に、その試験結果を示す。試験条件は、溶鋼量：３００トン、温度：１６２０℃、真空度：１Ｔｏｒｒ、吹き付け速度：溶鋼１トンあたり０．８ｋｇ／ｍｉｎ（以下、ｋｇ／ｔ・ｍｉｎの単位で示す）である。
【００１３】
同図に示すように、配合比Ｃａ／ＣａＯ（重量比）が０．０２〜０．４１の範囲であれば、５分で溶鋼中のＳ濃度は５ｐｐｍ以下になる。
【００１４】
Ｃａ／ＣａＯ比が０．０２未満であると、Ｓと反応するＣａＯ量は増大するが、Ｃａ絶対量が不足し、Ｃａによる脱硫促進効果が小さくなる。Ｃａ／ＣａＯ比が０．４１を超えて大きくなると、ＣａＯによるＣａ蒸発の抑制効果が小さくなり、Ｃａ蒸発が活発化し、Ｃａの添加効果が減少する。
【００１５】
以上から、ＣａとＣａＯの配合比を適正にすることにより、予想外にも、Ｃａの蒸発を抑え、ＣａとＣａＯの相乗効果により、減圧下でも高速脱硫が可能となるという知見を得て、下記の本発明を完成できた。
【００１６】
ここに本発明は、ＣａとＣａＯとを（１）式に従って配合した脱硫剤を、真空脱ガス装置にて減圧下で真空槽内溶鋼表面に吹き付けることを特徴とする溶鋼の高速脱硫方法である。
０．４１≧Ｃａ／ＣａＯ（重量比）≧０．０２ （１）
【００１７】
【発明の実施の形態】
本発明の実施形態を、転炉とＲＨ式真空脱ガス装置を用いて実施する場合を例に説明する。
【００１８】
転炉処理終了後、溶鋼を取鍋へ出鋼する。出鋼条件によりスラグ中の低級酸化物濃度（以下、（Ｆｅ＋Ｍｎ）濃度ともいう）が高くなる場合は、出鋼時にスラグ改質剤等を用いて、スラグ中の（Ｆｅ＋Ｍｎ）濃度を３％以下とすることが望ましい。取鍋をＲＨ式真空脱ガス装置へ移動し、真空処理を開始する。ＲＨ式真空脱ガス装置では、脱硫処理前に、ＡｌやＳｉ等と酸素ガスを用いて溶鋼昇温処理、成分調整を施しても良い。
【００１９】
脱硫処理時の脱硫剤のＣａ分は、金属Ｃａの他、ＣａＳｉ、ＣａＡｌ、ＦｅＣａ、ＣａＡｌＳｉ等のＣａ合金の形態でも良い。ＣａＯ分は、ＣａＯ単体がよいが、Ａｌ２ Ｏ３ 、ＭｇＯ、ＣａＦ２ などを混合したものでもよい。しかし。ＣａＯ以外の成分は合計で６０％以下が望ましい。その理由は、ＣａＯ以外の成分の合計量が６０％を越えて高くなると、ＣａとＣａＯの相互作用が弱まり、効果が低下するからである。
【００２０】
脱硫剤の構成成分であるＣａとＣａＯは特にプリメルトする必要はなく、単なる混合でよい。溶鋼表面への脱硫剤の吹き付けは、単孔ランス等を使用できる。
【００２１】
溶鋼表面への脱硫剤の吹き付け速度は溶鋼１トン当たり０．１〜１ｋｇ／（ｔ・ｍｉｎ）が望ましい。その理由は、速度が０．１ｋｇ／（ｔ・ｍｉｎ）未満となると処理時間が長くなり、１ｋｇ／（ｔ・ｍｉｎ）を超えて高くなると上吹き時のスプラッシュが激しくなり、真空槽内地金付着などの操業上の問題が発生する。
【００２２】
脱硫剤のキャリヤ−ガスはＡｒ等の不活性ガスが望ましく、その流量は８０００Ｎｌ／ｍｉｎ以下が望ましい。この理由は、溶鋼のスプラッシュ発生の眼界の流量が８０００Ｎｌ／ｍｉｎであるからである。
【００２３】
溶鋼表面への吹き付け処理中の真空度は１００Ｔｏｒｒ以下が望ましく、さらに望ましくは４０Ｔｏｒｒ以下である。その理由は、真空度が１００Ｔｏｒｒを超えて高くなると、ＲＨ式真空脱ガス装置の溶鋼還流が遅くなり、溶鋼攪拌が不十分となり、脱硫反応を阻害するからである。また、真空度を４０Ｔｏｒｒ以下とすると脱硫反応が、さらに促進でき真空脱ガス装置における処理時間が短縮できるからである。
【００２４】
上記条件で、脱硫処理を行った後、必要に応じてさらに合金成分添加、あるいは温度調整を行いＲＨ式真空脱ガス装置での処理を終了する。
【００２５】
【実施例】
転炉で脱炭し、取鍋に出鋼する際、溶鋼３００トンにＡｌを添加して脱酸すると同時に、スラグにＡｌ含有炭酸カルシウムを添加してスラグ中の（Ｆｅ＋Ｍｎ）濃度を１．４％とした。その後、取鍋をＲＨ式真空脱ガス装置に移動し、真空処理を開始した。
【００２６】
真空処理開始後、溶鋼にＡｌを添加し、真空槽内溶鋼表面に酸素ガスを吹き付けて溶鋼温度を１５９５℃から１６２０℃に昇温させた。昇温処理後成分調整を行い、真空度１Ｔｏｒｒで単孔ランスを使用して溶鋼表面への脱硫剤の吹き付け処理を実施した。吹き付け速度は０．７ｋｇ／（ｔ・ｍｉｎ）とし、Ａｒガスをキャリヤ−ガスとして５０００Ｎｌ／ｍｉｎ使用した。
表１に、脱硫剤の吹き付け処理前の溶鋼成分を示す。
【００２７】
【表１】
表２に、使用した脱硫剤の重量比（Ｃａ／ＣａＯ）と試験結果を示す。
【００２９】
【表２】
表２に示すように、脱硫剤の重量比（Ｃａ／ＣａＯ）が０．０２〜０．４１の範囲であれば、５分でＳ濃度は５ｐｐｍ以下とすることができたのに対し、０．０２未満、あるいは０．４１を超えると処理時間が１５分でも１０ｐｐｍ前後の値しか得られなかった。
【００３１】
【発明の効果】
本発明によれば、真空脱ガス装置における脱硫処理時間を大幅に短縮できる。
【図面の簡単な説明】
【図１】脱硫剤のＣａ／ＣａＯ重量比と脱硫速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 high-speed desulfurization method for molten steel under reduced pressure.
[0002]
[Prior art]
Sulfur in molten steel (hereinafter, also referred to as S) is required to be reduced in many types of steels because it forms nonmetallic inclusions and causes product defects, and hinders the levitation treatment of inclusions. .
[0003]
Desulfurization, after forming a CaO-Al 2 O 3 based slag molten steel surface, a method of blowing molten steel into the molten steel a method and CaO-type flux and stirring gas are known. However, these methods require dedicated equipment for desulfurization treatment, and improvements are required in terms of capital investment and maintenance. Further, there is a problem that the efficiency of the entire process is reduced due to the long processing time. For the purpose of improving these, a method of desulfurizing with a vacuum degassing device such as an RH method has been proposed. JP-A-5-171253 discloses a method of spraying CaO onto molten steel in an RH type vacuum chamber. Japanese Patent Application Laid-Open No. 6-2028 discloses a method of adding Al and CaO to molten steel in a ladle of an RH type vacuum degassing apparatus.
[0004]
[Problems to be solved by the invention]
However, each of the above methods has the following problems.
It takes 9 to 12 minutes to reduce the S concentration in molten steel from about 30 ppm to 10 ppm, and 15 minutes or more to reduce it to 5 ppm or less. In vacuum degassing equipment, adjustment of alloy components, heating, degassing, etc. Since a plurality of treatments are sequentially performed, there is a problem that adding this desulfurization treatment significantly increases the total treatment time in the vacuum degassing apparatus.
[0005]
If the processing time in the vacuum degassing device becomes too long, costs such as shortening of the refractory life and increase in energy cost are caused, and the production amount is also reduced. Therefore, it has been difficult to supply low-sulfur steel inexpensively and in large quantities.
[0006]
An object of the present invention is to provide a high-speed desulfurization method for molten steel capable of shortening a desulfurization treatment time in a vacuum degassing apparatus.
[0007]
[Means for Solving the Problems]
The present inventors have conducted various tests and obtained the following findings.
(A) It is known that in desulfurization treatment of molten steel, it is effective to react with a substance having a strong affinity with S while reducing the oxygen concentration in the molten steel. Therefore, a method has been proposed in which Al, a substance having a strong affinity for oxygen, and CaO, a substance having a strong affinity for S, are sprayed on molten steel.
[0008]
However, Al can promote the desulfurization by CaO by reducing the oxygen concentration, but has a low affinity for S, so that the desulfurization ability is low and the effect of shortening the entire treatment time cannot be expected.
[0009]
(B) Since Ca has a strong affinity for both oxygen and S, it is considered to be advantageous for promoting the desulfurization reaction. However, since Ca has a boiling point of 1440 ° C. and is lower than the molten steel temperature of 1600 ° C., there is a problem that it evaporates even under atmospheric pressure. When Ca is used under reduced pressure in a vacuum degassing apparatus, the evaporation phenomenon of Ca becomes more active, and the effect of desulfurization treatment cannot be expected.
[0010]
(C) It has been found that CaO itself has a function of reacting with S to generate CaS and a function of adsorbing CaS generated by the reaction between Ca and S in molten steel. Further, since Ca has an effect of reducing the oxygen concentration and promoting the reaction between CaO and S, desulfurization treatment of molten steel by a combination of CaO and Ca can be expected to synergistically improve desulfurization efficiency.
[0011]
(D) From the above findings, a desulfurization test was carried out with an RH-type vacuum degassing apparatus in which the mixing ratio of Ca and CaO, Ca / CaO (weight ratio), was changed to clarify the mixing ratio with a high desulfurization rate.
[0012]
FIG. 1 shows the test results. The test conditions are as follows: molten steel amount: 300 tons, temperature: 1620 ° C., degree of vacuum: 1 Torr, spraying speed: 0.8 kg / min per ton of molten steel (hereinafter, indicated in units of kg / t · min).
[0013]
As shown in the figure, when the mixing ratio Ca / CaO (weight ratio) is in the range of 0.02 to 0.41, the S concentration in the molten steel becomes 5 ppm or less in 5 minutes.
[0014]
If the Ca / CaO ratio is less than 0.02, the amount of CaO reacting with S increases, but the absolute amount of Ca becomes insufficient, and the effect of Ca to promote desulfurization decreases. When the Ca / CaO ratio becomes larger than 0.41, the effect of suppressing Ca evaporation by CaO becomes small, Ca evaporation becomes active, and the effect of adding Ca decreases.
[0015]
From the above, it was unexpectedly obtained that by appropriately adjusting the mixing ratio of Ca and CaO, the evaporation of Ca was suppressed, and the synergistic effect of Ca and CaO enabled high-speed desulfurization even under reduced pressure. The present invention described below has been completed.
[0016]
Here, the present invention is a high-speed desulfurization method for molten steel, characterized by spraying a desulfurizing agent in which Ca and CaO are blended according to the formula (1) to the surface of molten steel in a vacuum tank under reduced pressure by a vacuum degassing device. .
0.41 ≧ Ca / CaO (weight ratio) ≧ 0.02 (1)
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described by taking as an example a case where the present invention is implemented using a converter and an RH type vacuum degassing apparatus.
[0018]
After the completion of the converter processing, the molten steel is tapped into the ladle. When the lower oxide concentration (hereinafter also referred to as (Fe + Mn) concentration) in the slag becomes higher due to tapping conditions, the (Fe + Mn) concentration in the slag is 3% or less by using a slag modifier at tapping. It is desirable that The ladle is moved to the RH-type vacuum degasser, and vacuum processing is started. In the RH type vacuum degassing apparatus, before the desulfurization treatment, the temperature of the molten steel may be raised and the components may be adjusted using Al, Si or the like and oxygen gas.
[0019]
The Ca content of the desulfurizing agent at the time of the desulfurization treatment may be in the form of Ca alloy such as CaSi, CaAl, FeCa, CaAlSi, in addition to metallic Ca. The CaO content is preferably CaO alone, but may be a mixture of Al 2 O 3 , MgO, CaF 2 and the like. However. Components other than CaO are desirably 60% or less in total. The reason is that when the total amount of components other than CaO exceeds 60%, the interaction between Ca and CaO is weakened, and the effect is reduced.
[0020]
Ca and CaO, which are constituent components of the desulfurizing agent, do not need to be particularly pre-melted, and may be simply mixed. A single hole lance or the like can be used to spray the desulfurizing agent onto the surface of the molten steel.
[0021]
The spraying rate of the desulfurizing agent to the molten steel surface is desirably 0.1 to 1 kg / (t · min) per ton of molten steel. The reason is that when the speed is less than 0.1 kg / (t · min), the processing time becomes long, and when the speed exceeds 1 kg / (t · min), the splash at the time of top blowing becomes severe, and the metal in the vacuum chamber adheres. And other operational problems.
[0022]
The carrier gas of the desulfurizing agent is desirably an inert gas such as Ar, and the flow rate is desirably 8000 Nl / min or less. The reason for this is that the flow rate in the eye field where the splash of molten steel occurs is 8000 Nl / min.
[0023]
The degree of vacuum during the spraying process on the molten steel surface is preferably 100 Torr or less, and more preferably 40 Torr or less. The reason is that when the degree of vacuum is higher than 100 Torr, the reflux of molten steel in the RH type vacuum degassing device becomes slow, the stirring of molten steel becomes insufficient, and the desulfurization reaction is hindered. Further, when the degree of vacuum is set to 40 Torr or less, the desulfurization reaction can be further promoted, and the processing time in the vacuum degassing apparatus can be shortened.
[0024]
After the desulfurization treatment is performed under the above conditions, alloy components are added or the temperature is adjusted as necessary, and the treatment in the RH type vacuum degassing device is completed.
[0025]
【Example】
When decarbonizing in a converter and tapping into a ladle, Al is added to 300 tons of molten steel to deoxidize, and at the same time, Al-containing calcium carbonate is added to the slag to reduce the (Fe + Mn) concentration in the slag to 1.4. %. Thereafter, the ladle was moved to an RH-type vacuum degassing device, and vacuum processing was started.
[0026]
After the start of the vacuum treatment, Al was added to the molten steel, and oxygen gas was blown onto the surface of the molten steel in the vacuum chamber to raise the temperature of the molten steel from 1595 ° C to 1620 ° C. After the heating treatment, the components were adjusted, and a desulfurizing agent was sprayed on the surface of the molten steel using a single-hole lance at a degree of vacuum of 1 Torr. The spray speed was 0.7 kg / (t · min), and Ar gas was used as a carrier gas at 5000 Nl / min.
Table 1 shows the components of the molten steel before the desulfurizing agent is sprayed.
[0027]
[Table 1]
Table 2 shows the weight ratio (Ca / CaO) of the desulfurizing agent used and the test results.
[0029]
[Table 2]
As shown in Table 2, when the weight ratio of the desulfurizing agent (Ca / CaO) was in the range of 0.02 to 0.41, the S concentration could be reduced to 5 ppm or less in 5 minutes. When it was less than 0.02 or more than 0.41, a value of only about 10 ppm was obtained even when the treatment time was 15 minutes.
[0031]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the desulfurization processing time in a vacuum degassing apparatus can be shortened significantly.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the Ca / CaO weight ratio of a desulfurizing agent and the desulfurization rate.
Claims (1)
０．４１≧Ｃａ／ＣａＯ（重量比）≧０．０２ （１）A high-speed desulfurization method for molten steel, comprising spraying a desulfurizing agent in which Ca and CaO are blended according to the formula (1) to the surface of molten steel in a vacuum tank under reduced pressure by a vacuum degassing device .
0.41 ≧ Ca / CaO (weight ratio) ≧ 0.02 (1)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10267299A JP3577989B2 (en) | 1999-04-09 | 1999-04-09 | High-speed desulfurization of molten steel |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
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| JP10267299A JP3577989B2 (en) | 1999-04-09 | 1999-04-09 | High-speed desulfurization of molten steel |
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| JP2000297318A JP2000297318A (en) | 2000-10-24 |
| JP3577989B2 true JP3577989B2 (en) | 2004-10-20 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP3577988B2 (en) * | 1999-04-09 | 2004-10-20 | 住友金属工業株式会社 | Manufacturing method of low Al ultra low sulfur steel |
| JP2007270178A (en) * | 2006-03-30 | 2007-10-18 | Sumitomo Metal Ind Ltd | Method for manufacturing extra-low sulfur steel |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH05287356A (en) * | 1992-04-06 | 1993-11-02 | Sumitomo Metal Ind Ltd | Ladle refining method |
| 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 |
| 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 |
| JP3577988B2 (en) * | 1999-04-09 | 2004-10-20 | 住友金属工業株式会社 | Manufacturing method of low Al ultra low sulfur steel |
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