JP2004204313A - Lf treating method without adding fluorite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LF (ladle furnace) treating method dissolving such problems as to delay the progresses of deoxidation and desulfurization, extend treating time, lower inclusion absorbing performance of slag and increase inclusion in a steel and generation of clogging to a CC nozzle, in the case of non-adding fluorite. <P>SOLUTION: The slag at the initial stage of the LF treatment is made to become a composition range having low fused point by mixing a complex slag-making agent selecting the composition containing CaO, Al<SB>2</SB>O<SB>3</SB>, Al, SiO<SB>2</SB>and MgO into a ladle during tapping from an electric furnace so as to sufficiently become fused state by forming the slag with the molten steel. Successively, lime, calcium aluminate and deoxidizing agent are added so that the slag keeps in the fused state and high fluidity state and thus, the LF treatment having the same state as the time using the fluorite can be obtained. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

［試験結果］
（試験品Ａ）
（ａ）滓化性、流動性は、従来品と比較して良好であった。
（ｂ）白煙が大量に発生し、電気炉出鋼口の清掃作業や取鍋のクレーン玉がけ等の作業に支障が生じた。
（ｃ）出鋼後、取鍋内でスラグが大きく膨張した。
（ｄ）複合造滓剤1トンに対し、初期投入生石灰４００ｋｇ程度までは、ホタル石を添加せずに滓化可能であった。
【００４０】
（試験品Ｂ：白煙対策）
（ａ）投入時の反応は、現行品よりも大きく、反応時間も長い。Ｍ−Ｓｉを無配合としたことで、白煙は軽減されたが現行品よりは大きかった。
（ｂ）滓化性は良好であった。投入直後の流動性は、従来品より良好であった。
（ｃ）出鋼後、取鍋内でスラグが大きく膨張した。
（ｄ）複合造滓剤1トンに対し、初期投入生石灰４００ｋｇ程度までは、ホタル石を添加せずに滓化可能であった。
【００４１】
（試験品Ｃ：スラグ膨張対策）
（ａ）ＳｉＣとＦ，Ｃを無添加としたことで、スラグ膨張を大幅に軽減できた。
（ｂ）滓化性、流動性は、従来品と同程度であったが、試験品Ａ，Ｂと比較して悪化した。
【００４２】
スラグ膨張対策に効果が確認できたことと、滓化性、流動性等の使用状況は、従来品と同等の結果が得られたことから、試験品Ｃのセミランニング使用を開始した。
【００４３】
セミランニング使用期間中、ＣＣでのノズル閉塞発生やノズル閉塞を予防するためのＣａ−Ｓｉワイヤー添加頻度の増加が問題となった。原因調査の結果、複合造滓剤のＭ−Ａｌ（金属アルミ分）増量が影響している可能性が高いと判断し、再度配合変更を実施した。
【００４４】
（試験品Ｄ：絞り対策）
（ａ）絞りの原因は、複合造滓剤中のＭ−Ａｌと推定し、Ｍ−Ａｌを半減した結果、脱酸力不足のため脱酸材使用量が増加し、Ｃａ―Ｓｉ添加率は低減できなかった。
（ｂ）さらに滓化性、流動性悪く、ＬＦ処理時間は延長した。
【００４５】
（試験品Ｅ：絞り対策及び流動性確保）
上記結果から、最終的に脱酸力を確保した上での絞り対策が必要と判断し、再度ＳｉＣを微粉化して配合（出鋼後のスラグ膨張軽減を狙い、微粉化による反応速度向上を図った）した。また、造滓材使用量が予想以上に増加したことに対応し、スラグの流動性向上も考慮した。
（ａ）ＳｉＣ及びSｉＯ_２増により、滓化性、流動性は大幅に向上した。
（ｂ）ＣＣでの絞り発生頻度およびＣａ―Ｓｉ添加率は、ホタル石使用時と同等のレベルまで低減した。
（ｃ）図２に従来法と試験品Ｅとの脱硫状況のグラフを示す。全体的に本発明の試験品Ｅは、図２に示すように、従来法よりも早い。Ａｌ無添加の低硫黄含有鋼（［Ｓ］≦０．０２０％）においても、本発明方法においては、処理時間を延長することなく処理できている。脱酸力向上と滓化性向上の効果である。
（ｄ）表２に示すように、従来法と比較して、本発明の試験品Ｅは、造滓材使用量（特に脱酸剤）を大幅に低減できた。
【００４６】
本発明の複合造滓剤の改良のポイントは、スラグの滓化性向上を狙ってAｌ_２O_３を増量し、低融点としたことと、ＬＦ処理負荷軽減を目的に、Ｍ−Ａｌ、Ｍ−Ｓｉ及びＳｉＣを増量して脱酸力を向上させたことにある。本発明の複合造滓剤は、ＣａＯ５０〜７０重量％、Aｌ_２O_３：１０〜２０重量％、Aｌ：２〜６重量％、SｉＯ_２：３〜１０重量％及びＭｇＯ：５〜１０重量％であれば、本発明品Ｅと同様の効果を示すことが実験により確認されている。
【００４７】
【表２】

尚、造滓剤原単位とは、熔溶鋼１ｔを造るに要した造滓剤の重量（ｋｇ）
実施例２：ホタル石無添加の脱酸剤の検討
表３に記載の配合の試験品ａ（本発明品）、試験品ｂ及び試験品ｃを調整し、従来と同様にＬＦ処理をし、脱酸状況、脱硫状況、スラグ滓化状況及び流動性を確認した。尚、比較のため従来使用しているホタル石を含有する脱酸剤についても同様にして試験した。
【００４８】
試験品ａ（本発明品）は、ホタル石分を生石灰に置き換えた以外は、従来品と同じ組成にし、試験品ｂは、滓化性、流動性機能向上のためAｌ_２O_３の配合を増加させ、試験品ｃは、スラグ膨張対策のため炭素（Ｃ）無配合としたものである。
【００４９】
【表３】

［試験結果］
図３に、試験品ａ〜ｃと従来品試験時の脱硫推移のグラフを示す。
【００５０】
（試験品ａ：本発明品）
（ａ）脱酸状況は、スラグの状態から判断して従来品使用の場合と同程度であった。
（ｂ）ホタル石無添加化の影響は特に確認されず、全ての鋼種において従来品と同等に処理可能であった。
（ｃ）試験実施中、CCでのノズル閉塞は確認されなかった。
（ｄ）使用上の問題は全く無く、従来品との切替は可能と判断される。
【００５１】
（試験品ｂ）
（ａ）Aｌ_２O_３増量により滓化性やスラグ流動性は良好となったが、脱酸の進行は明らかに従来品より遅かった。通常時と比較して溶鋼中の炭素含有量［C］及び溶鋼中の珪素含有量［Ｓｉ］の歩留まりが高かったことから、脱酸力向上を目的として添加したＳｉＣが脱酸に寄与していないことが考えられる。
【００５２】
（試験品ｃ）
（ａ）脱酸状況、滓化状況は、ともに良好であったが、脱硫の持続性は、他試験品と比較して若干高い傾向にあった。しかし、Ａｌ無添加鋼（鋼中Ａｌ濃度が0〜0.050%で、脱酸目的以外にＡｌを添加しない鋼種）において、ＣＣでノズル閉塞トラブルが頻発し、Ｃａ−Ｓｉワイヤーを添加して対応せざるを得ない状況であった。状況から判断して、Al無添加鋼への使用は困難であると判断する。
【００５３】
以上、試験品ａについてはホタル石含有従来品と遜色ない使用状況であった。特にホタル石無添加の複合造滓剤との併用であれば、一部鋼種（低硫黄含有鋼種）を除きホタル石無添加で処理可能である。脱酸剤の組成は、ＣａＯ：３５〜４５重量％、Aｌ_２O_３：２〜２０重量％、Aｌ：２０〜３０重量％、SｉＯ_２：２〜５重量％及びSｉ：３〜１０重量％であれば、本発明の試験品ａと同様の効果を示すことが実験により確認されている。
【００５４】
実施例３：ホタル石代替品の検討
低硫黄含有鋼をＬＦ処理する場合の様に生石灰投入量が多いときや、電気炉からLFへの持ち込みスラグが少ない場合の様に、複合造滓剤の滓化が不十分となりやすいときには、滓化促進、流動性向上等のホタル石同様の機能を持った代替品が必要不可欠である。そこで表４に記載の代替品について、投入量及び投入方法はホタル石と同様にして試験した。出鋼直後のスラグ流動性、ＬＦ初期脱硫状況及びＣＣノズル閉塞発生状況を確認した。尚、比較のため従来使用している複合造滓剤についても同様にして試験した。滓化状況（滓化速度、生石灰滓化能力、流動性）、造滓剤（生石灰、脱酸剤、ホタル石代替品）使用量及び脱硫推移を確認した。尚、試験に供した代替品は、（ａ）フッ素を含有しない、（ｂ）低融点組成である、（ｃ）生石灰滓化促進機能がある、（ｄ）スラグ粘性低下（流動性向上）機能があることを選定条件とした。 試験の評価結果を次表５に、図４に各試験品の脱硫推移のグラフを示す。
【００５５】
【表４】

【００５６】
【表５】

は従来品より良好、△は従来品と同等、×は従来品より悪い を表す。
【００５７】
ＣａＯ・ＳｉＯ_３（ワラストナイト）
プリメルト品は、溶融はするものの滓化速度は、ホタル石と比較にならないほど遅い。天然鉱物の破砕品に関しては、極めて溶融が遅く、長時間スラグ上に固まりが確認された。いずれもホタル石と同様の使用方法は困難である。
【００５８】
CaO・Al_２O_３・SiO_２（低融点組成混合品）
ある程度滓化が進行した状態で投入すれば溶融するが、処理初期のような状態での滓化は極めて遅い。当然脱硫の進行も遅く、処理時間延長となる傾向にあった。
【００５９】
ＣａＯ・Ａｌ_２Ｏ_３（カルシウムアルミネート）
焼成品、プリメルト品のいずれも、滓化性、流動性は、比較的良好な結果が得られた。溶融速度は、焼成品に比べプリメルト品のほうが若干早い傾向にあった。但し、いずれもホタル石と比べれば、完全に溶融して流動性が得られるのに若干時間と温度を要した。処理初期の生石灰投入前に投入することで、比較的短時間で対応が可能である。よって、カルシウムアルミネートによるホタル石の代用は可能である。
【００６０】
以上、複合造滓剤、脱酸剤及びカルシウムアルミネート（好ましくはプリメルト品）を使用することによって、ホタル石無添加で、ホタル石使用時と同等のLF処理ができることが確認された。
【００６１】
従来法によるスラグでは、平成３年環境庁告示第４６号法により１〜２０ｍｇ／リットル程度のフッ素溶出が確認されたが、本発明によるスラグでは、フッ素溶出ゼロを達成した。
【００６２】
従来の操業方法でホタル石不使用にすると、ホタル石使用時の１．５倍程度の処理時間が必要になるが、本発明によれば、スラグ組成コントロールによりスラグの低融点化流動性向上を達成したことにより、ホタル石使用時とほぼ同等の脱酸・脱硫速度を確保することができ、同等の時間での処理が可能となった。
【００６３】
LF処理初期の滓化促進とスラグの低融点領域コントロールにより、スラグへの介在物浮上除去の促進、介在物の低融点化が図られ、CCでのノズル閉塞トラブルが解消できた。
【００６４】
【発明の効果】
以上述べた如く、本発明によれば、ホタル石無添加でホタル石使用時と同等のＬＦ処理ができるという従来解決できなかった課題を解決したものであるから、極めて画期的な発明である。それと共に、製鋼スラグをリサイクルする場合にも、フッ素溶出基準が土壌環境基準を超える恐れをなくすことができる。
【図面の簡単な説明】
【図１】従来の複合造滓剤、脱酸剤、生石灰及びホタル石の使用時期を示す図である。
【図２】従来の複合造滓剤を使用した場合と本発明の複合造滓剤を使用した場合との脱硫状況を示すグラフである。
【図３】本発明の還元脱酸剤（試験品ａ）、比較脱酸剤（試験品ｂ及びｃ）及び従来品との脱硫推移を示すグラフである。
【図４】本発明のカルシウムアルミネートと他のホタル石代替品とを使用した場合の脱硫推移を示すグラフである。
【図５】本発明の複合造滓剤、脱酸剤、生石灰およびカルシウムアルミネートの使用時期を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ladle refining furnace (hereinafter referred to as LF) processing method as a secondary refining process for molten steel, and more particularly, to a LF processing method capable of performing the same processing as when using fluorite without the addition of fluorite.
[0002]
[Prior art]
Conventionally, in the LF treatment, as shown in FIG. 1, (1) fluorite, aluminum ash, SiC, etc. are mixed with a slag-making agent (quick lime for steelmaking (hereinafter, quick lime)) into a ladle during tapping of an electric furnace. (2) Briquette is added to the ladle at the beginning of LF treatment, and (3) Briquette is mixed with aluminum, aluminum ash, SiC, fluorite, etc., and (3) quicklime Fluorite was further added depending on the amount added and the state of the slag.
[0003]
The purpose of adding fluorite is to promote quick lime slag (promotion of melting by lowering the melting point) and slag fluidity (promotion of slag-metal reaction). As a result of the addition, desulfurization and deoxidation of molten steel are promoted, and treatment time is increased. As a result, the ability to absorb inclusions of the slag is improved, thereby improving the cleanliness and preventing the nozzle clogging trouble in the continuous casting (hereinafter, CC) process.
[0004]
However, fluorite contains a large amount of fluorine (about 35 to 40% by weight). For this reason, fluorine is mixed into steelmaking slag, and when steelmaking slag is recycled as a civil engineering material or a soil modifying material, fluorine is eluted into the surrounding soil. From the viewpoint of protecting human health, fluorine is specified as 0.8 mg / liter or less in the water quality environmental standard and the soil environmental standard of the Basic Environmental Law, and in the situation where steelmaking slag is recycled, pollution exceeding these standards is considered. It is required not to cause. In addition, when fluorite is added to the ladle, there is also a problem that the ladle refractory is promoted to be melted.
[0005]
In order to adhere to the above standards, there are (1) even if a very small amount is added, depending on the composition of the slag, and (2) a method of adding a fluorine fixing agent to the slag. However, it is necessary to make fluorite free.
[0006]
However, when fluorite is not added, (a) it becomes difficult to make quicklime slag, (b) the fluidity of slag cannot be ensured, (c) the progress of deoxidation and desulfurization is delayed, and the processing time is reduced. And (d) the inclusion absorption capacity of the slag is reduced, and the inclusions in steel and the occurrence of CC nozzle clogging are increased.
[0007]
Calcium aluminate-based desulfurizing agents are conventionally known (for example, see Patent Literature 1), but this patent literature only discloses the content of a component change for lowering the melting point of calcium aluminate itself. , LF processing itself is not disclosed.
[0008]
[Patent Document 1]
JP, 2002-60832, A
[Problems to be solved by the invention]
[0010]
The present invention has been made in view of such a point, and in all of the steps (1) to (3) described in paragraph [0002], fluorite is not added, and the above (a) to (d) It is an object of the present invention to provide an LF processing method in which the problem described above does not occur.
[0011]
[Means for Solving the Problems]
The invention according to claim 1 of the present invention that meets the above-mentioned object is characterized in that, during the tapping of an electric furnace, slag is formed into a ladle with molten steel containing CaO, Al ₂ O ₃ , Al, SiO ₂ and MgO. A composite slag-making agent having a composition selected so as to be in a sufficiently molten state is mixed so that the slag in the early stage of the LF treatment has a low melting point composition region, and then quicklime, calcium aluminate and a deoxidizing agent are mixed with the slag. Is added so as to maintain a molten state and a high fluidity state.
[0012]
The composition of the composite slag-making agent is preferably selected so that the slag in the initial stage of the LF treatment has a melting point of 1500 ° C. or lower in a CaO—Al ₂ O ₃ —SiO ₂ phase diagram (claim 2).
[0013]
The composition of the composite slag-making agent is, specifically, 50 to 70% by weight of CaO, 10 to 20% by weight of Al2O3, _{2 to} 6% by weight of Al, _{3 to} 10% by weight of SiO2 and _{5 to} 10% by weight of MgO. Is preferable (claim 3).
[0014]
In order to make the slag in the early stage of the LF treatment into a composition region with a low melting point, it is preferable to add the composite slag-making agent so as to be in a gehlenite region (2CaO.Al ₂ O ₃ .Sio ₂ ). 4).
[0015]
LF treatment early slag composition, specifically, CaO35～50 wt%, Al ₂ O ₃ 25 to 40 wt%, amount may be SiO ₂ 15 to 35 wt% (claim 5).
[0016]
The deoxidizing agent used in the present invention preferably contains CaO, Al ₂ O ₃ , Al, SiO ₂ and Si (Claim 6).
[0017]
Wherein the composition of an acid acceptor Specifically, CaO35～45 wt%, Al ₂ O ₃ 2 to 20 wt%, Al20～30 wt%, to the SiO ₂ 2 to 5% by weight and Si3~10 wt% Is good (claim 7).
[0018]
The calcium aluminate having a melting point of 1400 ° C. or less and a particle size of 35 mm or less is preferably used (claim 8).
[0019]
The calcium aluminate is preferably a premelt product of the compound form CaO.Al ₂ O ₃ (Claim 9).
[0020]
The composition of the calcium aluminate, CaO45～60 wt%, Al ₂ O ₃ 35 to 45% by weight, and preferably those containing _SiO 2 0 wt% (claim 10).
[0021]
After the calcium aluminate is added, quick lime is added, and the calcium aluminate and the deoxidizer are added in a state where the fluidity is deteriorated so that the slag is maintained in a molten state and a high fluidity state in a short time. (Claim 11).
[0022]
The LF treatment final slag composition Specifically, CaO45～60 wt%, Al ₂ O ₃ 25 to 40 wt%, preferably in a SiO ₂ 10 to 20% by weight (claim 12).
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described.
[0024]
When fluorite is not added, (a) it becomes difficult to make quicklime slag, (b) fluidity of slag cannot be secured, (c) the progress of deoxidation and desulfurization is delayed, and the processing time is reduced. (D) Inclusion in slag decreases, absorption of inclusions in steel increases, and the occurrence of CC nozzle clogging increases. To solve the problem, low melting point composition of slag in the early stage of LF treatment and improvement of fluidity To promote quicklime slag formation, deoxidation and desulfurization.
[0025]
First of all, as a substitute for the complex slag-making agent containing lime or fluorite in the conventional operation, it does not contain fluorite but contains CaO, Al ₂ O ₃ , Al, SiO ₂ and MgO, and is slagged with molten steel. A new composite slag agent, the composition of which has been selected so as to be in a sufficiently molten state, is added to the ladle during tapping in an electric furnace. The amounts of each component in the above composition are selected so that the slag in the initial stage of the LF treatment has a melting point of 1500 ° C. or less in the CaO—Al ₂ O ₃ —SiO ₂ phase diagram.
[0026]
More specifically, the composition of the composite slag-making agent mainly includes an increased amount of the Al ₂ O ₃ and SiO ₂ sources as compared with the conventional ones, 50 to 70% by weight of CaO, 10 to 20% by weight of Al ₂ O ₃ , and Al: 2 to 2%. It is preferable to be 6% by weight, 3-10% by weight of SiO ₂ and 5-10% by weight of MgO.
[0027]
In addition to the above components, M-Si (Si content in a ferrosilicon alloy compounded as a deoxidizing agent): 0 to 3% by weight, SiC: 0 to 5% by weight, C (fixed carbon content of coke powder or the like blended as a deoxidizing agent): about 0 to 5% by weight may be blended.
[0028]
The composite slag is mixed in this manner so that the slag in the early stage of the LF treatment has a low melting point composition region. In the present invention, the composition region having a low melting point is a gehlenite region (2CaO.Al ₂ O ₃ .Sio ₂ ).
[0029]
Specifically, LF processing initial slag composition, CaO35～50 wt%, Al ₂ O ₃ 25 to 40 wt%, preferably used so that a SiO ₂ 15 to 35 wt%.
[0030]
Then, the LF processing is started. If it is determined that 300 kg or more of quicklime needs to be added or if the slag has poor fluidity, calcium aluminate is added first. Calcium aluminate, which melts slower than fluorite, can be easily melted by adding it to a slag in a molten state (a lot of FeO and a low melting point) at the beginning of the treatment. Thereafter, a deoxidizer containing no fluorite is added as needed. (If the amount of quicklime is less than 300 kg and the fluidity of the slag is judged to be good, a deoxidizer containing no fluorite is added from the beginning without adding calcium aluminate as necessary. )) The amount and the presence or absence of addition depend on the amount of slag in the ladle, the oxygen concentration in the molten steel, and the degree of desulfurization.
[0031]
Thereafter, quick lime is added while paying attention so that the state of the slag can be maintained in a molten state. At a stage where the fluidity has deteriorated, the addition of quicklime is interrupted, and calcium aluminate or a deoxidizing agent is added so that the melting point of the slag is reduced before the slag formation becomes defective. Thereafter, the remaining quicklime is added. Experiments have shown that by adding the slag forming material in such an order, a slagging state and a good fluidity state can always be maintained, and as a result, desulfurization in the early stage of the treatment is promoted.
[0032]
As the deoxidizing agent used in the present invention, any deoxidizing agent used for this purpose can be used. However, the deoxidizing agent containing CaO, Al ₂ O ₃ , Al, SiO ₂ and Si without fluorite is used. Preferably, an agent is used. This deoxidizing agent mainly increases the amount of Al ₂ O ₃ and SiO ₂ sources as compared with the conventional one so that the slag has a low melting point and a high fluidity after deoxidation.
[0033]
The composition of an acid acceptor Specifically, CaO: 35 to 45 wt%, Al ₂ O _3: 2~20 wt%, Al: 20 to 30 wt%, SiO _2: 2 to 5 wt% and Si: 3 It preferably contains from 10 to 10% by weight.
[0034]
The calcium aluminate is preferably a pre-melt product having a melting point of 1400 ° C. or less, a particle size of 35 mm or less, and a compound form of CaO.Al ₂ O _3.
The composition of the calcium aluminate, CaO45～60 wt%, Al ₂ O ₃ 35 to 45 wt%, and is good to to contain _SiO 2 0% by weight.
[0036]
The To maintain LF process final slag in a molten state and highly liquid state, the composition is, CaO45～60 wt%, Al ₂ O ₃ 25 to 40% by weight, SiO ₂ 10 to 20 wt% Is preferred.
[0037]
Next, the present invention will be further described with reference to examples, but the present invention is not limited to these examples.
[0038]
【Example】
Example 1: Examination of composition of fluorite-free composite slag-making agent When LF treatment is performed without fluorite, the LF treatment load increases. The improvement of fluidity and the improvement of deoxidizing power were studied. The composite slag-making agents having compositions A to E shown in the following Table 1 were prepared, and the amount and method of addition were the same as before, and the test was conducted by adding the material into the ladle during tapping of an electric furnace. The slag fluidity, LF initial desulfurization status, and CC nozzle clogging occurrence status were confirmed. For comparison, the same test was carried out for the conventional composite slag-making agent.
[0039]
[Table 1]

[Test results]
(Test A)
(A) The slagging property and fluidity were better as compared with the conventional product.
(B) A large amount of white smoke was generated, which hindered the work of cleaning the tap hole of the electric furnace and the work of ladle crane dangling.
(C) After tapping, the slag expanded significantly in the ladle.
(D) Up to about 400 kg of initially added quicklime with respect to 1 ton of the composite slag-making agent, slag could be formed without adding fluorite.
[0040]
(Test B: White smoke countermeasures)
(A) The reaction at the time of introduction is larger than that of the current product, and the reaction time is longer. By not including M-Si, white smoke was reduced but was larger than the current product.
(B) The slag property was good. The fluidity immediately after introduction was better than the conventional product.
(C) After tapping, the slag expanded significantly in the ladle.
(D) Up to about 400 kg of initially added quicklime with respect to 1 ton of the composite slag-making agent, slag could be formed without adding fluorite.
[0041]
(Test C: Slag expansion countermeasures)
(A) By not adding SiC and F and C, slag expansion could be greatly reduced.
(B) The slagging property and fluidity were almost the same as those of the conventional product, but deteriorated as compared with the test products A and B.
[0042]
The semi-running use of the test sample C was started because the effect was confirmed as a measure against slag expansion, and the results of use such as slagging property and fluidity were equivalent to those of the conventional product.
[0043]
During the semi-running use period, an increase in the frequency of Ca-Si wire addition for preventing nozzle clogging and nozzle clogging in CC has become a problem. As a result of investigating the cause, it was determined that there was a high possibility that the increase in the amount of M-Al (metal aluminum component) in the composite slag-making agent was affected, and the formulation was changed again.
[0044]
(Test D: Measure against drawing)
(A) The cause of squeezing is presumed to be M-Al in the composite slag-making agent. As a result of halving M-Al, the amount of deoxidizing material used increases due to insufficient deoxidizing power, and the Ca-Si addition rate is reduced. Could not be reduced.
(B) Further, slagging property and fluidity were poor, and the LF treatment time was prolonged.
[0045]
(Specimen E: squeezing measures and ensuring fluidity)
From the above results, it was concluded that it was necessary to take measures against squeezing after securing the deoxidizing power in the end, and the SiC was again pulverized and compounded (to reduce the slag expansion after tapping, and to improve the reaction speed by pulverization). Was). In addition, in response to an increase in the amount of slag material used more than expected, consideration was given to improving the fluidity of slag.
(A) By increasing SiC and SiO ₂ , slagging property and fluidity were greatly improved.
(B) The frequency of squeezing and the Ca-Si addition rate in CC were reduced to the same level as when fluorite was used.
(C) FIG. 2 is a graph showing the state of desulfurization between the conventional method and the test sample E. Overall, the test article E of the present invention is faster than the conventional method, as shown in FIG. In the method of the present invention, even low-sulfur-containing steel without addition of Al ([S] ≦ 0.020%) can be processed without prolonging the processing time. This is the effect of improving the deoxidizing power and the slag property.
(D) As shown in Table 2, the test article E of the present invention was able to significantly reduce the amount of slag-making material used (particularly, the deoxidizing agent) as compared with the conventional method.
[0046]
The point of improvement of the composite slag-making agent of the present invention is to increase the amount of Al ₂ O ₃ to lower the melting point in order to improve slag slagging properties, and to reduce M-Al, M -It is to improve the deoxidizing power by increasing the amount of Si and SiC. Composite slag agent of the present invention, CaO50～70 wt%, Al ₂ O _3: 10~20 wt%, Al: 2 to 6 wt%, SiO _2: 3 to 10 wt% and MgO: 5 to 10 wt% It has been confirmed by experiments that the same effect as that of the product E of the present invention is exhibited.
[0047]
[Table 2]

The basic unit of the slag-making agent is the weight (kg) of the slag-making agent required to produce 1 t of molten steel.
Example 2: Examination of a deoxidizer without fluorite The test product a (the product of the present invention), the test product b and the test product c having the composition shown in Table 3 were prepared, and subjected to LF treatment in the same manner as before. Deoxidation status, desulfurization status, slag residue status, and fluidity were confirmed. For comparison, the same test was carried out for a conventionally used deoxidizer containing fluorite.
[0048]
Test product a (the product of the present invention) had the same composition as the conventional product except that the fluorite was replaced with quicklime, and test product b contained Al ₂ O ₃ in order to improve slagging and fluidity functions. The test sample c was made without carbon (C) to prevent slag expansion.
[0049]
[Table 3]

[Test results]
FIG. 3 shows graphs of the test products a to c and the transition of desulfurization at the time of testing the conventional product.
[0050]
(Test product a: product of the present invention)
(A) The state of deoxidation was about the same as that of the conventional product, judging from the state of the slag.
(B) The effect of no fluorite addition was not particularly confirmed, and all steel types could be treated similarly to conventional products.
(C) No nozzle blockage at CC was observed during the test.
(D) There is no problem in use, and it is determined that switching to the conventional product is possible.
[0051]
(Test product b)
(A) Although the slagging property and the slag fluidity were improved by increasing the amount of Al ₂ O ₃ , the progress of deoxidation was clearly slower than the conventional product. Since the yield of the carbon content [C] in the molten steel and the silicon content [Si] in the molten steel was higher than usual, the SiC added for the purpose of improving the deoxidizing power contributed to the deoxidation. It is not possible.
[0052]
(Test product c)
(A) Both the deoxidation status and the slagging status were good, but the durability of desulfurization tended to be slightly higher than other test products. However, in Al-free steel (a steel type in which the Al concentration in the steel is 0 to 0.050% and Al is not added for purposes other than deoxidation), nozzle clogging troubles frequently occur at CC, and a Ca-Si wire is added to respond. It was inevitable. Judging from the situation, it is judged that it is difficult to use Al-free steel.
[0053]
As described above, the use condition of the test product a was comparable to that of the conventional product containing fluorite. In particular, if it is used in combination with a composite slag-making agent without fluorite, it can be treated without fluorite except for some steel types (low-sulfur-containing steel type). The composition of the deoxidizing agent, CaO: 35 to 45 wt%, Al ₂ O _3: 2~20 wt%, Al: 20 to 30 wt%, SiO _2: 2 to 5 wt% and Si: 3 to 10 wt% It has been confirmed by experiments that the same effect as that of the test sample a of the present invention is exhibited.
[0054]
Example 3: Examination of fluorite substitutes When the amount of quick lime is large as in the case of LF treatment of low sulfur content steel or when the amount of slag brought in from the electric furnace to the LF is small, the use of composite slag forming agents is considered. When slagging is likely to be insufficient, a substitute having the same function as fluorite such as accelerating slagging and improving fluidity is indispensable. Therefore, the substitutes described in Table 4 were tested in the same manner as in the case of fluorite in the amount and method of introduction. Slag fluidity immediately after tapping, LF initial desulfurization status, and CC nozzle blockage occurrence status were confirmed. For comparison, the same test was carried out for the conventional composite slag-making agent. The state of slag formation (slag formation rate, quick lime slag forming ability, fluidity), the amount of slag-forming agent (quick lime, deoxidizing agent, fluorite replacement) and desulfurization transition were confirmed. The substitutes used in the test were (a) no fluorine, (b) low melting point composition, (c) quick lime slag promotion function, and (d) slag viscosity reduction (fluidity improvement) function. Was selected as a selection condition. The evaluation results of the test are shown in Table 5 below, and FIG. 4 is a graph showing the transition of desulfurization of each test sample.
[0055]
[Table 4]

[0056]
[Table 5]

Indicates better than conventional product, Δ indicates equivalent to conventional product, and x indicates worse than conventional product.
[0057]
CaO ・ SiO ₃ (Wollastonite)
Although the premelt product melts, the slagging rate is as slow as that of fluorite. For the crushed product of natural minerals, melting was extremely slow, and solidification on slag was confirmed for a long time. In any case, it is difficult to use the same method as fluorite.
[0058]
CaO ・ Al ₂ O ₃・ SiO ₂ (low melting point composition mixture)
If it is charged in a state where slagging has progressed to some extent, it melts, but slagging in a state such as the initial stage of processing is extremely slow. Naturally, the progress of desulfurization was slow, and the processing time tended to be prolonged.
[0059]
CaO.Al ₂ O ₃ (calcium aluminate)
Both the calcined product and the pre-melt product showed relatively good results in terms of slagging property and fluidity. The melting rate of the pre-melt product tended to be slightly faster than that of the fired product. However, compared to fluorite, it took some time and temperature to completely melt and obtain fluidity. By putting it in before the quick lime feeding in the early stage of the treatment, it is possible to respond in a relatively short time. Therefore, it is possible to substitute fluorite with calcium aluminate.
[0060]
As described above, it was confirmed that the use of the composite slag-making agent, the deoxidizing agent, and the calcium aluminate (preferably, a pre-melt product) can perform the same LF treatment without the addition of fluorite as when using fluorite.
[0061]
In the slag by the conventional method, fluorine elution of about 1 to 20 mg / liter was confirmed by the Environment Agency Notification No. 46 of 1991, but the slag according to the present invention achieved zero fluorine elution.
[0062]
If fluorite is not used in the conventional operation method, a treatment time about 1.5 times longer than when fluorite is used is required. However, according to the present invention, the slag composition is controlled to lower the melting point and improve the fluidity of the slag. By achieving this, it was possible to secure a deoxidation / desulfurization rate almost equal to that when using fluorite, and it was possible to perform treatment in the same time.
[0063]
By promoting the slagging at the beginning of LF treatment and controlling the low melting point region of the slag, the floating removal of inclusions in the slag was promoted, the melting point of the inclusions was reduced, and the nozzle blockage problem in CC was eliminated.
[0064]
【The invention's effect】
As described above, according to the present invention, it is possible to achieve a LF treatment equivalent to that of using fluorite without the use of fluorite, which was a conventionally unresolved problem. . At the same time, when recycling steelmaking slag, it is possible to eliminate the risk that the fluorine elution standard exceeds the soil environmental standard.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing the use periods of conventional composite slag-making agents, deoxidizing agents, quicklime and fluorite.
FIG. 2 is a graph showing desulfurization states when a conventional composite slag is used and when a composite slag is used according to the present invention.
FIG. 3 is a graph showing the change in desulfurization of the reduced deoxidizer of the present invention (test product a), the comparative deoxidizers (test products b and c), and the conventional product.
FIG. 4 is a graph showing the transition of desulfurization when the calcium aluminate of the present invention and another fluorite substitute are used.
FIG. 5 is a diagram showing the use time of the composite slag-making agent, deoxidizing agent, quicklime and calcium aluminate of the present invention.

Claims (12)

During the tapping of the electric furnace, a compound slag forming agent containing CaO, Al ₂ O ₃ , Al, SiO ₂ and MgO and having a composition selected so as to form a slag with molten steel and to be in a sufficiently molten state is introduced into the ladle. Mixing so that the slag in the ladle refining furnace process is in a low melting point composition region, and then quick lime, calcium aluminate and a deoxidizing agent so that the slag is maintained in a molten state and a high fluidity state. A LF-free LF treatment method characterized by adding LF. The LF processing initial slag, such that the melting point of 1500 ° C. or less in CaO-Al ₂ O ₃ -SiO ₂ phase diagram, the processing method according to claim 1, wherein selecting the composition of the composite slag agent. Said composite slag agents, CaO50～70 wt%, Al ₂ O ₃ 10 to 20 wt%, Al2～6 wt%, according to claim 1 or 2 wherein the SiO ₂ 3 to 10 wt% and MgO5~10 wt% Processing method. The LF processing initial slag, the treatment method according to claim 1, adding the composite slag agent so that the gehlenite region _{(2CaO · Al 2 O 3 ·} SiO 2). The LF processing initial slag composition, CaO35～50 wt%, Al ₂ O ₃ 25 to 40 wt%, processing method according to claim 1 is a SiO ₂ 15 to 35 wt%. The treatment method according to claim 1, wherein the deoxidizing agent contains CaO, Al ₂ O ₃ , Al, SiO ₂ and Si. The composition of the deoxidizing agent, CaO35～45 wt%, Al ₂ O ₃ 2 to 20 wt%, Al20～30 wt%, according to claim 6 which contains SiO ₂ 2 to 5% by weight and Si3~10 wt% Processing method. The processing method according to claim 1, wherein the calcium aluminate has a melting point of 1400 ° C. or less and a particle size of 35 mm or less. The treatment method according to any one of claims 1 to 8, wherein the calcium aluminate is a pre-melt product in a compound form of CaO · Al ₂ O ₃ . The composition of the calcium aluminate, CaO45～60 wt%, Al ₂ O ₃ 35~45 processing method according to claim 1 containing wt% and _SiO 2 0% by weight. 11. The calcium aluminate and a deoxidizing agent are added after the calcium aluminate is added so as to maintain the slag in a molten state and a high fluidity state in a state where the fluidity is deteriorated. The processing method according to any one of the above. The LF processing final slag composition, CaO45～60 wt%, Al ₂ O ₃ 25 to 40 wt%, processing method according to any one of claims 1 to 11 is a SiO ₂ 10 to 20 wt%.

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