JP2005179762A - Method for producing extra-low sulfur steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a new extra-low sulfur steel with which even in the case of increasing the stirring power to molten steel, a fixed slag composition having high desulfurizing efficiency can always be kept during desulfurizing treatment and the productivity is high. <P>SOLUTION: When the desulfurizing treatment is applied to the molten steel, this method is the one, in which during desulfurizing treatment, CaO quantity (W<SB>CaO</SB>) satisfying the formula: 1.5(0.037ω+0.28)W<SB>slag</SB>/100≤W<SB>CaO</SB>≤2.0(0.037ω+3.04)W<SB>slag</SB>/100 is charged at least at one time according to stirring power density (ω) into the slag. In the formula, W<SB>CaO</SB>: CaO quantity (kg) charged in the desulfurizing treatment, W<SB>slag</SB>: slag weight (kg) charged at the desulfurizing treatment, ω: stirring power density (watt/ton) and shown with ω=ä0.0285×Q(T+273)/W}log(1+Z/148). Wherein, Q: stirring gas flowing amount (Nl/min ton) per unit weight, T: molten steel temperature (°C) before desulfurizing treatment, W: molten steel weight (ton), Z: molten steel depth (cm). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は、溶鋼の取鍋精錬における脱硫処理に当たり、極低硫鋼を製造する方法に関するものである。   The present invention relates to a method for producing ultra-low sulfur steel in desulfurization treatment in ladle refining of molten steel.

転炉から出鋼した溶鋼は、取鍋精錬炉（Ｌａｄｌｅ Ｆｕｒｍａｃｅ：ＬＦ）でスラグ精錬（脱硫処理等）され、鋼の清浄度が改善される。取鍋精錬によって極低硫鋼を得る方法としては、溶鋼中にフラックスを添加し、溶鋼撹拌時のスラグ組成を、脱硫効率の高いＣａＯ−ＣａＦ₂系、ＣａＯ−Ａｌ₂Ｏ₃系のスラグとする方法が古くから知られており（特許文献１等）；更に取鍋の脱硫能力を一層高める目的で、溶鋼の撹拌力を大きくして溶鋼とスラグの反応性を促進する方法（非特許文献１や非特許文献２）が開示されている。 The molten steel discharged from the converter is slag refined (desulfurization treatment, etc.) in a ladle furnace (LF), and the cleanliness of the steel is improved. As a method of obtaining ultra-low sulfur steel by ladle refining, the flux is added to the molten steel, and the slag composition at the time of stirring the molten steel is changed to CaO-CaF ₂ system and CaO-Al ₂ O ₃ system slag with high desulfurization efficiency. The method of doing this has been known for a long time (Patent Document 1, etc.); for the purpose of further increasing the desulfurization capacity of the ladle, a method of increasing the stirring force of the molten steel and promoting the reactivity of the molten steel and slag (Non-Patent Document) 1 and Non-Patent Document 2) are disclosed.

ところが、溶鋼の撹拌力を大きくすると、溶鋼中に脱酸剤として添加されたＡｌが、脱硫処理中に酸化されて多量のＡｌ₂Ｏ₃が生成される為、スラグの組成が変化してしまい（スラグ中のＡｌ₂Ｏ₃量が増加する）、脱硫能力が低下するという問題がある。 However, when the stirring force of the molten steel is increased, Al added as a deoxidizing agent in the molten steel is oxidized during the desulfurization treatment, and a large amount of Al ₂ O ₃ is generated, so that the composition of the slag changes. (Al ₂ O ₃ content increases in the slag), the desulfurization ability is lowered.

この様な問題を解決すべく、特許文献２には、溶鋼脱硫処理の際、スラグ組成の分析を行いながら脱硫フラックスを少なくとも２回以上に分けて投入する方法が開示されている。しかしながら、この方法は、脱硫処理中に、スラグ組成の分析という新たな工程を付加するものであり、処理効率が低下する他、新たな工程付加に伴う作業負担やコスト増を招き、非効率的である。
特開昭５２−３５７１４号公報 特開昭６０−２２４７１２号公報 電気製鋼 昭和５９年４月発行、第５５巻、第２号、ｐ．９３〜１００ 第７５回特殊鋼部会資料、愛知製鋼株式会社、「ＬＦにおけるガス撹拌の影響について」、昭和５９年１０月２５・２６日、ｐ．１〜２ In order to solve such a problem, Patent Document 2 discloses a method in which a desulfurization flux is charged at least twice while analyzing a slag composition during a molten steel desulfurization process. However, this method adds a new process of analyzing the slag composition during the desulfurization process, which reduces the processing efficiency and increases the work load and cost associated with the addition of the new process, and is inefficient. It is.
JP 52-35714 A JP-A-60-224712 Electric Steelmaking Issued April 1984, Vol. 55, No. 2, p. 93-100 75th Special Steel Division Material, Aichi Steel Corporation, “About the Effect of Gas Stirring in LF”, October 25-26, 1984, p. 1-2

本発明は上記事情に鑑みてなされたものであり、その目的は、溶鋼の撹拌力を高めたとしても、脱硫処理中は常に脱硫効率の高い一定のスラグ組成を維持し得、且つ、生産効率の良い新規な極低硫鋼の製造方法を提供することにある。   The present invention has been made in view of the above circumstances, and its purpose is to always maintain a constant slag composition having a high desulfurization efficiency during the desulfurization process even if the stirring power of the molten steel is increased, and to improve the production efficiency. It is to provide a method for producing a novel ultra-low sulfur steel with good quality.

上記課題を解決し得た本発明に係る極低硫鋼の製造方法は、溶鋼を脱硫処理するに当たり、脱硫処理中に、撹拌動力密度（ω）に応じて少なくとも１回、下式［１］を満足するＣａＯ量（W_CaO）をスラグに投入するところに要旨を有するものである。 The method for producing ultra-low-sulfur steel according to the present invention that has solved the above-described problems is that, when desulfurizing molten steel, during the desulfurization treatment, at least once according to the stirring power density (ω), the following formula [1] The main point is that an amount of CaO (W _CaO ) satisfying the above is introduced into the slag.

1.5（0.037ω＋0.28）W_slag／100≦W_CaO≦2.0（0.037ω＋3.04）W_slag／100
………［１］
式中、
W_CaO ：脱硫処理中に投入するＣａＯ量（ｋｇ），
W_slag：脱硫処理の際、投入したスラグ量（ｋｇ），
ω ：撹拌動力密度（ｗａｔｔ／ｔｏｎ）であり、
ω＝｛0.0285×Ｑ（Ｔ＋273）／Ｗ｝log （1＋Ｚ／148）で表される。 1.5 (0.037ω + 0.28) W _slag / 100 ≦ W _CaO ≦ 2.0 (0.037ω + 3.04) W _slag / 100
……… [1]
Where
W _CaO : CaO amount (kg) input during desulfurization treatment
W _slag : The amount of slag that was input during desulfurization (kg)
ω: stirring power density (watt / ton),
ω = {0.0285 × Q (T + 273) / W} log (1 + Z / 148)

ここで、Ｑ：単位重量当たりの撹拌ガス流量（Ｎｌ／分・ｔｏｎ），
Ｔ：脱硫処理前の溶鋼温度（℃），
Ｗ：溶鋼重量（ｔｏｎ），
Ｚ：溶鋼深さ（ｃｍ）である。 Here, Q: stirring gas flow rate per unit weight (Nl / min · ton),
T: Temperature of molten steel (° C) before desulfurization treatment,
W: Molten steel weight (ton),
Z: Depth of molten steel (cm).

ここで、上記ＣａＯ量（Ｗ_CaO）は、（脱硫処理開始後１分）〜（脱硫処理に要する総時間の１／２）の間に投入することが好ましく、これにより、脱硫率が一層向上する。 Here, the amount of CaO (W _CaO ) is preferably added between (1 minute after the start of the desulfurization process) and (1/2 of the total time required for the desulfurization process), thereby further improving the desulfurization rate. To do.

本発明によれば、生産効率の高い新規な極低硫鋼の製造方法であって、溶鋼の撹拌力を高めたとしても、脱硫処理中は常に脱硫効率の高い一定のスラグ組成が維持されている極低硫鋼の製造方法を提供することができる。   According to the present invention, a novel ultra-low-sulfur steel manufacturing method with high production efficiency, even if the stirring power of molten steel is increased, a constant slag composition with high desulfurization efficiency is always maintained during the desulfurization process. It is possible to provide a method for producing ultra-low sulfur steel.

本発明者らは、「溶鋼の撹拌力を大きくして脱硫処理すると、多量のＡｌ₂Ｏ₃が生成する為、処理中にスラグ組成（脱硫効率の高いスラグ組成）が変化してしまい、脱硫能が低下する」という問題を解決するに当たり、非特許文献２の如く脱硫処理中にスラグ組成の分析をわざわざ行わなくとも、生産性良く簡易に、最適な脱硫スラグ組成を長時間維持し得る極低硫鋼の製造方法を提供すべく、鋭意検討してきた。その結果、溶鋼の撹拌力（溶鋼の撹拌動力密度ω）と、溶鋼の脱硫処理中に生成するアルミナ増加量（ΔＡｌ₂Ｏ₃）とは、一定の関係式を満たしていること；当該関係式に基づき、ΔＡｌ₂Ｏ₃のバラツキをも考慮して定められるＣａＯ量（Ｗ_CaO）であって、脱硫能の高いスラグ組成を長時間維持し得るＣａＯ量をスラグに投入すれば、ΔＡｌ₂Ｏ₃に伴うスラグ組成のズレ（変化）を簡便に是正し得ること：従って、溶鋼の撹拌力（ω）を高めた場合であっても、該溶鋼の撹拌力に応じて、脱硫効率の高いスラグ組成を維持し得るＣａＯ量を予め算出しておくことが可能となり、脱硫処理中にスラグ組成をチェックするといった手間も不要で、生産性の高い極低硫鋼の製造方法を提供できることを見出し、本発明を完成した。 The inventors of the present invention have stated that “When desulfurization treatment is performed by increasing the stirring force of molten steel, a large amount of Al ₂ O ₃ is generated, so the slag composition (slag composition having high desulfurization efficiency) changes during the treatment, and desulfurization is performed. In order to solve the problem of “decrease in performance”, it is possible to maintain the optimum desulfurized slag composition for a long period of time easily and with good productivity without performing a slag composition analysis during desulfurization treatment as in Non-Patent Document 2. In order to provide a method for producing low-sulfur steel, intensive studies have been conducted. As a result, the stirring power of molten steel (stirring power density ω of molten steel) and the amount of increase in alumina (ΔAl ₂ O ₃ ) generated during the desulfurization treatment of molten steel satisfy a certain relational expression; the basis, a CaO amount determined in consideration of the variation in _{ΔAl 2 O 3 (W CaO)} , the amount of CaO can maintain a high slag composition desulfurization ability long if put into slag, ΔAl ₂ O _The slag composition deviation (change) associated with ₃ can be easily corrected: Therefore, even when the stirring power (ω) of the molten steel is increased, the slag having a high desulfurization efficiency is obtained according to the stirring power of the molten steel. It becomes possible to calculate in advance the amount of CaO that can maintain the composition, and it is unnecessary to check the slag composition during the desulfurization process, and it can be found that a method for producing a highly productive ultra-low sulfur steel can be provided. The present invention has been completed.

以下、本発明に到達した実験経緯に基づき、本発明法を詳細に説明する。   Hereinafter, the method of the present invention will be described in detail based on the experimental background that has reached the present invention.

一般に取鍋精錬脱硫処理の際、脱硫能を高める目的で溶鋼撹拌を行うと、脱酸剤の目的で鋼中に添加されたＡｌの一部は、周囲の雰囲気、またはスラグ（取鍋スラグ）中のＦｅＯやＭｎＯ等によって酸化されてアルミナ（Ａｌ₂Ｏ₃）となり、スラグに取り込まれる為、脱硫処理の際、スラグ中のＡｌ₂Ｏ₃濃度が増加する。その結果、脱硫処理前には、脱硫効率の高いスラグ組成であっても、脱硫処理中に、Ａｌ₂Ｏ₃濃度の増加に伴ってスラグ組成が変化してしまい、脱硫能力が低下する様になる。 In general, during the ladle refining desulfurization treatment, when molten steel is stirred for the purpose of enhancing the desulfurization ability, a part of Al added to the steel for the purpose of deoxidizer is the ambient atmosphere or slag (ladder slag) Since it is oxidized by FeO, MnO, etc. in the inside to become alumina (Al ₂ O ₃ ) and taken into the slag, the concentration of Al ₂ O ₃ in the slag increases during the desulfurization treatment. As a result, even if the slag composition has high desulfurization efficiency before the desulfurization treatment, the slag composition changes with the increase of the Al ₂ O ₃ concentration during the desulfurization treatment, and the desulfurization capacity is lowered. Become.

この様な問題を解決するに当たり、本発明者らはまず、脱硫処理中に生成するＡｌ₂Ｏ₃増加量（ΔＡｌ₂Ｏ₃）に着目し、溶鋼の撹拌力ω（溶鋼の撹拌動力密度）を変化させた場合における、ΔＡｌ₂Ｏ₃の変化について調べた。ΔＡｌ₂Ｏ₃に着目したのは、これにより、処理中に増加するスラグ中のＡｌ₂Ｏ₃生成量（ΔＷ_Al2O3）が定まるからである。 In solving such problems, the inventors first focused on the amount of increase in Al ₂ O ₃ (ΔAl ₂ O ₃ ) generated during the desulfurization process, and the stirring power ω of the molten steel (stirring power density of the molten steel). The change in ΔAl ₂ O ₃ was investigated when the value was changed. The reason for paying attention to ΔAl ₂ O ₃ is that this determines the amount of Al ₂ O ₃ produced (ΔW _Al2O3 ) in the slag that increases during processing.

このうちωは、下式で表され、K. Nakanishi, T. Fuji : Iron and steel making, 1975, vol.2, p193に掲載されている既知の式を適用した。   Of these, ω is represented by the following formula, and a known formula published in K. Nakanishi, T. Fuji: Iron and steel making, 1975, vol.

ω＝｛０．０２８５×Ｑ（Ｔ＋２７３）／Ｗ｝・ｌｏｇ（１＋Ｚ／１４８）
ここで、Ｑ：単位重量当たりの撹拌ガス流量（Ｎｌ／分・ｔｏｎ），
Ｔ：脱硫処理前の溶鋼温度（℃），
Ｗ：溶鋼重量（ｔｏｎ），
Ｚ：溶鋼深さ（ｃｍ）である。 ω = {0.0285 × Q (T + 273) / W} · log (1 + Z / 148)
Here, Q: stirring gas flow rate per unit weight (Nl / min · ton),
T: Temperature of molten steel (° C) before desulfurization treatment,
W: Molten steel weight (ton),
Z: Depth of molten steel (cm).

その結果を図１に示す。   The result is shown in FIG.

図１より、ΔＡｌ₂Ｏ₃とωは、下記の回帰式［２］を満足することが分った。 From FIG. 1, it was found that ΔAl ₂ O ₃ and ω satisfy the following regression equation [2].

ΔＡｌ₂Ｏ₃（％）＝（０．０３７×ω）＋１．６６ ……………［２］
但し、バラツキ（１σ＝１．３８）を考慮すると、最終的にΔＡｌ₂Ｏ₃とωは、下記の回帰式［３］（上限）と、下記の回帰式［４］（下限）の範囲を満足することが分かった。 ΔAl ₂ O ₃ (%) = (0.037 × ω) +1.66 …………… [2]
However, in consideration of variation (1σ = 1.38), ΔAl ₂ O ₃ and ω finally have a range of the following regression equation [3] (upper limit) and the following regression equation [4] (lower limit). I was satisfied.

ΔＡｌ₂Ｏ₃（％）＝（０．０３７×ω）＋３．０４ ……………［３］
ΔＡｌ₂Ｏ₃（％）＝（０．０３７×ω）＋０．２８ ……………［４］
換言すれば、ΔＡｌ₂Ｏ₃とωは、下記関係式［５］を満足するものである。 ΔAl ₂ O ₃ (%) = (0.037 × ω) +3.04 (3)
ΔAl ₂ O ₃ (%) = (0.037 × ω) +0.28 …………… [4]
In other words, ΔAl ₂ O ₃ and ω satisfy the following relational expression [5].

（０．０３７×ω）＋０．２８≦ΔＡｌ₂Ｏ₃（％）≦（０．０３７×ω）＋３．０４
……………［５］
次いで、この様にして得られるΔＡｌ₂Ｏ₃と、脱硫効率に最適なスラグ組成（既知）と、脱硫処理中に増加するスラグ中のＡｌ₂Ｏ₃量［ΔＷ_Al2O3（ｋｇ）］に基づき、最終的に本発明で規定する上記関係式［１］；即ち、脱硫効率に最適なスラグ組成とする為の、撹拌動力密度（ω）と、脱硫処理中に投入すべきＣａＯ量［Ｗ_CaO（ｋｇ）］との関係式を、以下の様にして決定した。 (0.037 × ω) + 0.28 ≦ ΔAl ₂ O ₃ (%) ≦ (0.037 × ω) +3.04
…………… [5]
Next, based on ΔAl ₂ O ₃ obtained in this way, the optimal slag composition for desulfurization efficiency (known), and the amount of Al ₂ O ₃ in the slag that increases during the desulfurization treatment [ΔW _Al2O3 (kg)], The above relational expression [1] finally defined in the present invention; that is, the stirring power density (ω) and the amount of CaO to be charged during the desulfurization treatment [W _CaO ( kg)] was determined as follows.

溶鋼の脱硫処理に最適なスラグ組成は概ね、ＣａＯ：Ａｌ₂Ｏ₃＝１．５〜２：１であることが知られている。即ち、脱硫処理中に増加するスラグ中のＡｌ₂Ｏ₃量［ΔＷ_Al2O3（ｋｇ）］と、当該Ａｌ₂Ｏ₃量の増加に伴い、脱硫処理中に投入すべきＣａＯ量［Ｗ_CaO（ｋｇ）］は、
１．５×ΔＷ_Al2O3≦Ｗ_CaO≦２×ΔＷ_Al2O3 …………［６］
の関係を満足すれば良い。 It is known that the optimum slag composition for the desulfurization treatment of molten steel is generally CaO: Al ₂ O ₃ = 1.5-2: 1. That is, the amount of Al ₂ O ₃ in the slag that increases during the desulfurization treatment [ΔW _Al2O3 (kg)] and the amount of CaO that should be input during the desulfurization treatment with the increase in the amount of Al ₂ O ₃ [W _CaO (kg ]]
1.5 × ΔW _Al2O3 ≦ W _CaO ≦ 2 × ΔW _Al2O3 ………… [6]
Satisfy the relationship.

ここで、ΔＷ_Al2O3［脱硫処理中に増加するスラグ中のＡｌ₂Ｏ₃量（ｋｇ）］と、ΔＡｌ₂Ｏ₃［脱硫処理中に生成するＡｌ₂Ｏ₃増加量（％）］の関係は、
ΔＷ_Al2O3＝ΔＡｌ₂Ｏ₃×Ｗ_slag／１００ ……………［７］
式中、Ｗ_slag：スラグ量（ｋｇ）
で表されることから、この関係式［７］を前述の関係式［６］に代入すると、
１．５×（ΔＡｌ₂Ｏ₃×Ｗ_slag／１００）≦Ｗ_CaO≦
２×（ΔＡｌ₂Ｏ₃×Ｗ_slag／１００） …………［８］
となる。 Here, the relationship between ΔW _Al2O3 [the amount of Al ₂ O ₃ in slag increasing during desulfurization (kg)] and ΔAl ₂ O ₃ [the amount of increase in Al ₂ O ₃ generated during desulfurization (%)] is ,
ΔW _Al2O3 = ΔAl ₂ O ₃ × W _slag / 100 …………… [7]
In the formula, W _slag : Slag amount (kg)
When this relational expression [7] is substituted into the above-mentioned relational expression [6],
1.5 × (ΔAl ₂ O ₃ × W _slag / 100) ≦ W _CaO ≦
2 × (ΔAl ₂ O ₃ × W _slag / 100) ………… [8]
It becomes.

この関係式［８］に、前述の式［５］を代入すると、
１．５×［０．０３７×ω＋０．２８］×Ｗ_slag／１００≦Ｗ_CaO≦
２×［０．０３７×ω＋３．０４］₃×Ｗ_slag／１００……………［１］
となり、本発明で規定する式［１］が得られる。 Substituting the above equation [5] into this relational equation [8],
1.5 × [0.037 × ω + 0.28] × W _slag / 100 ≦ W _CaO ≦
2 × [0.037 × ω + 3.04] ₃ × W _slag / 100 ………… [1]
Thus, the formula [1] defined in the present invention is obtained.

即ち、脱硫処理中に、上記範囲のＣａＯ量（Ｗ_CaO）をスラグに投入すれば、ΔＡｌ₂Ｏ₃によるスラグ組成のズレを修正することができるので、脱硫効率の高いスラグ組成を長時間、維持することができ、脱硫効率に優れた極低硫鋼の製造方法を提供することができる（後記する実施例で確認している）。 That is, if a CaO amount (W _CaO ) in the above range is introduced into the slag during the desulfurization treatment, the deviation of the slag composition due to ΔAl ₂ O ₃ can be corrected. It can be maintained, and a method for producing an ultra-low sulfur steel excellent in desulfurization efficiency can be provided (confirmed in Examples described later).

尚、ＣａＯ量（Ｗ_CaO）の投入時期は、（脱硫処理開始後１分）〜（脱硫処理に要する総時間の１／２）の間とすることが推奨され、これにより、脱硫効率を高めることができる。ここで、脱硫処理後１分よりも前（例えば脱硫開始前、脱硫処理と同時等）にＣａＯを投入すると、スラグの融点が高くなって、脱硫処理に効率的な液相スラグ組成となるのに長時間要してしまう。一方、ＣａＯの投入時期が遅くなると、スラグ中のＡｌ₂Ｏ₃が増加した状態、即ち、脱硫効率が低下したスラグで脱硫処理する状態が長くなり、脱硫効率が低下する為、その上限を、（脱硫処理に要する総時間の１／２）とするのが好ましい。ここで、本発明における「脱硫処理に要する総時間（ｔとする）」は、下記［９］式により定めた。 It is recommended that the CaO amount (W _CaO ) input time be between (1 minute after the start of the desulfurization process) and (1/2 of the total time required for the desulfurization process), thereby increasing the desulfurization efficiency. be able to. Here, when CaO is introduced before 1 minute after the desulfurization treatment (for example, before the start of the desulfurization, simultaneously with the desulfurization treatment, etc.), the melting point of the slag becomes high, and the liquid phase slag composition becomes effective for the desulfurization treatment. Takes a long time. On the other hand, when the CaO charging time is delayed, the state in which Al ₂ O ₃ in the slag is increased, that is, the state of desulfurization treatment with slag having reduced desulfurization efficiency is lengthened, and the desulfurization efficiency is decreased. (1/2 of the total time required for the desulfurization treatment) is preferable. Here, the “total time (denoted by t) required for the desulfurization treatment” in the present invention is determined by the following equation [9].

ｔ（分）＝３８２９×ΔS＋１０８−９．７×Ｑ ……………［９］
式中、
ΔS（質量％）
＝［脱硫処理前（ＬＦ投入前）の鋼中Ｓ量］−［脱硫処理後の目標鋼中Ｓ量］
Ｑ ：単位重量当たりの撹拌ガス量（Ｎｌ／分・ｔｏｎ）
脱硫処理に要する時間（ｔ）は、概ね、ΔＳとＱの関係で決定されることが知られており、本発明では、種々の基礎実験を通じて上式［９］を決定した。 t (minutes) = 3829 × ΔS + 108−9.7 × Q (9)
Where
ΔS (mass%)
= [S content in steel before desulfurization treatment (before LF introduction)]-[S content in target steel after desulfurization treatment]
Q: Stirring gas amount per unit weight (Nl / min · ton)
It is known that the time (t) required for the desulfurization treatment is generally determined by the relationship between ΔS and Q. In the present invention, the above formula [9] is determined through various basic experiments.

また、ＣａＯの投入回数は、好ましくは上記投入時期の間に、少なくとも１回とする。即ち、本発明では、上記関係式［１］に基づいて定められるＣａＯ量（Ｗ_CaO）を、上述した好ましい投入時期の間に、１回で投入しても良いが、或いは、当該ＣａＯ量（Ｗ_CaO）を、２回、３回、４回等と分けて投入しても良い。尚、その上限は特に限定しないが、生産効率や作業負荷等を考慮すると、上限を３回とすることが好ましく、最も好ましくは１回である。 Further, the number of CaO injections is preferably at least once during the above injection period. That is, in the present invention, the CaO amount (W _CaO ) determined based on the relational expression [1] may be charged once during the above-described preferable charging time, or alternatively, the CaO amount ( W _CaO ) may be added in two, three, four, etc. The upper limit is not particularly limited, but considering the production efficiency, work load, etc., the upper limit is preferably 3 times, and most preferably 1 time.

尚、本発明における撹拌動力密度（ω）の範囲は特に限定されず、溶鋼の脱硫処理に当たり、通常採用される溶鋼撹拌条件の範囲であれば全て本発明で定める式［Ｉ］を適用することができる。   In addition, the range of the stirring power density (ω) in the present invention is not particularly limited, and the formula [I] defined in the present invention is applied to all the molten steel stirring conditions normally employed in the desulfurization treatment of molten steel. Can do.

以上、本発明に係る極低硫鋼の製造方法について記載した。尚、本発明の製造方法は、上述した様に脱硫処理中に、溶鋼の撹拌力に応じて上記関係式［１］で定められるＣａＯ量を投入するところに特徴があるのであって、使用する取鍋精錬炉は特に限定されない。従って、後記する実施例に記載の通り、加熱精錬装置を備えた取鍋精錬を用いて脱硫処理しも良いし、或いは、当該加熱装置を有しない（即ち、溶鋼撹拌のみ行う）簡易式溶鋼処理設備を備えた取鍋精錬を用いても良い。   The manufacturing method of the ultra-low sulfur steel according to the present invention has been described above. The production method of the present invention is characterized in that the amount of CaO defined by the above relational expression [1] is charged according to the stirring force of the molten steel during the desulfurization treatment as described above. The ladle refining furnace is not particularly limited. Therefore, as described in the examples described later, desulfurization treatment may be performed using a ladle refining equipped with a heating refining device, or a simple molten steel treatment not having the heating device (that is, performing only molten steel stirring). Ladle refining with equipment may be used.

また、使用するフラックスの種類や量等も特に限定されず、取鍋精錬に通常使用されるもの（ＣａＯ−Ａｌ₂Ｏ₃系、ＣａＯ−ＣａＦ₂系、ＣａＯ−Ａｌ₂Ｏ₃−ＣａＦ₂系等）を適宜選択すれば良い。 Also, the type and amount of the flux to be used are not particularly limited, and those usually used for ladle refining (CaO—Al ₂ O ₃ series, CaO—CaF ₂ series, CaO—Al ₂ O ₃ —CaF ₂ series) Etc.) may be selected as appropriate.

以下、実施例を挙げて本発明を更に詳細に説明するが、下記実施例は本発明を限定する性質のものではなく、前・後記の主旨に適合し得る範囲で適当に変更して実施することも可能であり、それらはいずれも本発明の技術的範囲に包含される。   Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and are implemented with appropriate modifications within a range that can meet the gist of the preceding and following descriptions. All of which are within the scope of the present invention.

本実施例では、取鍋加熱精錬装置を用いて以下の脱硫精錬を行った。まず、溶銑を２４０トン転炉で一次精錬した後、該転炉から取鍋へ出鋼し、更に転炉から持ち込まれるスラグを除滓する。その後、所定量のフラックス（ＣａＯ６４％、Ａｌ₂Ｏ₃２８％、ＭｇＯ８％）３４００ｋｇを取鍋に投入し、表１に記載の条件に基づいてＮｏ．１〜１１の溶鋼を脱硫処理した。その結果を表１に示す。尚、本実施例では、Ｗ_slagは３４００ｋｇ、Ｚは２００ｃｍ、Ｗは２４０ｔｏｎであり、脱硫処理後の鋼中Ｓ量が０．００１％になるまでの脱硫時間を測定した。 In the present Example, the following desulfurization refining was performed using the ladle heating refining apparatus. First, after the hot metal is first refined in a 240-ton converter, steel is removed from the converter to a ladle, and slag brought from the converter is removed. Thereafter, 3400 kg of a predetermined amount of flux (CaO 64%, Al ₂ O ₃ 28%, MgO 8%) was placed in a ladle. 1-11 molten steel was desulfurized. The results are shown in Table 1. In this example, W _slag was 3400 kg, Z was 200 cm, and W was 240 ton, and the desulfurization time until the S amount in the steel after desulfurization was 0.001% was measured.

表１の結果より、以下の様に考察することができる。   From the results in Table 1, it can be considered as follows.

まず、Ｎｏ．１〜５は、本発明で定める式［１］に規定するＣａＯ量（Ｗ_CaO）を、本発明の好ましい投入時期（脱硫処理開始後１分後から、脱硫処理に要する総時間の１／２までの間）に投入した本発明例であり、いずれも脱硫処理時間は６０分以下と、短時間に極低硫鋼を製造することができる。このうちＮｏ．４は、Ｗ_CaOを２回に分けて投入した例であるが、他の件発明と同程度の、優れた脱硫効率を有していることが分かる。 First, no. 1 to 5 represents the CaO amount (W _CaO ) defined in the formula [1] defined in the present invention at a preferable charging time of the present invention (one minute after the start of the desulfurization treatment, ½ of the total time required for the desulfurization treatment In all of the examples of the present invention, the desulfurization treatment time is 60 minutes or less, and extremely low sulfur steel can be produced in a short time. Of these, No. _No. 4 is an example in which W _CaO was added in two portions, and it can be seen that it has excellent desulfurization efficiency comparable to other inventions.

尚、表１には、本発明で定める式［１］の範囲のうち、ワンポイントについてのみ実施した結果を示したが、これに限定されず、当該式［１］の範囲の任意の点においても優れた脱硫効率が得られることを実験により確認している（表１には示さず）。   Table 1 shows the result of the implementation of only one point in the range of the formula [1] defined in the present invention. However, the present invention is not limited to this, and at any point in the range of the formula [1]. It was confirmed by experiments that excellent desulfurization efficiency was obtained (not shown in Table 1).

これに対し、Ｎｏ．６〜７は、Ｗ_CaOの投入量は本発明で定める式［１］を満足しているが、ＣａＯの投入時期が本発明の好ましい範囲を外れている参考例であり、Ｎｏ．７（脱硫処理に要する総時間の１／２以降）では脱硫処理時間が６３分と、本発明例に比べて若干長くなった。また、Ｎｏ．６（脱硫処理と同時に投入）の脱硫処理時間は５５分であり、Ｎｏ．６と同じ撹拌力（Ｑ）で脱硫処理したＮｏ．２の脱硫処理時間（４３分）に比べて、１０分以上も長くなった。 In contrast, no. Nos. 6 to 7 are reference examples in which the input amount of W _CaO satisfies the formula [1] defined in the present invention, but the input timing of CaO is out of the preferred range of the present invention. 7 (after 1/2 of the total time required for the desulfurization treatment), the desulfurization treatment time was 63 minutes, which was slightly longer than that of the present invention example. No. No. 6 (added simultaneously with the desulfurization treatment) has a desulfurization treatment time of 55 minutes. No. 6 subjected to desulfurization treatment with the same stirring force (Q) as in No. 6. Compared with the desulfurization treatment time of 2 (43 minutes), it was longer than 10 minutes.

また、Ｎｏ．８〜９は、ＣａＯ量を添加しない従来例；Ｎｏ．１０〜１１は、Ｗ_CaOが本発明で定める式［１］上限を超える比較例であり、いずれも脱硫処理時間は７０分以上と長時間を要している。 No. Nos. 8 to 9 are conventional examples in which no CaO amount is added; Nos. 10 to 11 are comparative examples in which W _CaO exceeds the upper limit of the formula [1] defined by the present invention, and all of them require a long time of 70 minutes or more for the desulfurization treatment time.

溶鋼の撹拌動力密度ωと、ΔＡｌ₂Ｏ₃との関係を示すグラフである。A stirring power density ω of the molten steel is a graph showing the relationship between ΔAl ₂ O _3.

Claims (2)

溶鋼を脱硫処理するに当たり、
脱硫処理中に、撹拌動力密度（ω）に応じて少なくとも１回、下式［１］を満足するＣａＯ量（W_CaO）をスラグに投入することを特徴とする極低硫鋼の製造方法。
1.5（0.037ω＋0.28）W_slag／100≦W_CaO≦2.0（0.037ω＋3.04）W_slag／100
………［１］
式中、
W_CaO ：脱硫処理中に投入するＣａＯ量（ｋｇ），
W_slag：脱硫処理の際、投入したスラグ量（ｋｇ），
ω ：撹拌動力密度（ｗａｔｔ／ｔｏｎ）であり、
ω＝｛0.0285×Ｑ（Ｔ＋273）／Ｗ｝log （1＋Ｚ／148）で表される。
ここで、Ｑ：単位重量当たりの撹拌ガス流量（Ｎｌ／分・ｔｏｎ），
Ｔ：脱硫処理前の溶鋼温度（℃），
Ｗ：溶鋼重量（ｔｏｎ），
Ｚ：溶鋼深さ（ｃｍ）である。 In desulfurizing molten steel,
A method for producing an ultra-low sulfur steel, characterized in that, during the desulfurization treatment, an amount of CaO (W _CaO ) satisfying the following formula [1] is introduced into the slag at least once according to the stirring power density (ω).
1.5 (0.037ω + 0.28) W _slag / 100 ≦ W _CaO ≦ 2.0 (0.037ω + 3.04) W _slag / 100
……… [1]
Where
W _CaO : CaO amount (kg) input during desulfurization treatment
W _slag : The amount of slag that was input during desulfurization (kg)
ω: stirring power density (watt / ton),
ω = {0.0285 × Q (T + 273) / W} log (1 + Z / 148)
Here, Q: stirring gas flow rate per unit weight (Nl / min · ton),
T: Temperature of molten steel (° C) before desulfurization treatment,
W: Molten steel weight (ton),
Z: Depth of molten steel (cm). 前記ＣａＯ量（Ｗ_CaO）は、（脱硫処理開始後１分）〜（脱硫処理に要する総時間の１／２）の間に投入するものである請求項１に記載の脱硫方法。 The desulfurization method according to claim 1, wherein the CaO amount (W _CaO ) is charged between (1 minute after the start of the desulfurization treatment) and (1/2 of the total time required for the desulfurization treatment).

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