JP3827010B2 - LF treatment method without fluorite - Google Patents

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 to which the invention belongs]
The present invention relates to a ladle refining furnace (hereinafter referred to as LF) processing method that is a secondary refining process of molten steel, and more specifically, relates to a LF processing method that can perform the same processing as when using fluorite without adding fluorite.
[0002]
[Prior art]
Conventionally, in LF treatment, as shown in FIG. 1, (1) fluorite, aluminum ash, SiC, etc. are mixed with a slagging agent (quick lime for steel making (hereinafter referred to as quick lime)) into a ladle during electric furnace steelmaking. (2) Add deoxidizer (mixed aluminum, aluminum ash, SiC, fluorite, etc.) into the ladle at the beginning of LF treatment, and (3) Quicklime More fluorite was added depending on the amount added and the state of the slag.
[0003]
The purpose of adding fluorite is to promote quick lime hatching (acceleration of melting by lowering the melting point) and slag fluidity (acceleration of slag and metal reaction). As a result of the addition, molten steel desulfurization and deoxidation are promoted, and processing time is increased. And the inclusion absorption capability of the slag is improved, and the improvement of cleanliness and the prevention of nozzle clogging trouble in the continuous casting (hereinafter referred to as CC) process can be achieved.
[0004]
However, fluorite contains a large amount of fluorine (about 35 to 40% by weight). For this reason, when fluorine is mixed into the steelmaking slag and the steelmaking slag is recycled as a civil engineering material or a soil modifying material, the fluorine is eluted into the surrounding soil. Fluorine is defined as 0.8 mg / liter or less in the water quality standard and soil environment standard of the Basic Environment Law from the viewpoint of protecting human health. In the situation where steelmaking slag is recycled, pollution exceeding these standards is required. It is required not to cause. In addition, the addition of fluorite into the ladle also raises the problem of facilitating melting of the ladle refractory.
[0005]
In order to adhere strictly to the above standards, there are (1) even a very small amount of addition may exceed the standard value depending on the slag composition, and (2) there is a method of adding a fluorine fixing agent into the slag, but long-term stability. However, it is necessary to add no fluorite at present.
[0006]
Thus, when fluorite is not added, (a) it becomes difficult to hatch quicklime, (b) fluidity of slag cannot be secured, (c) the progress of deoxidation and desulfurization is delayed, and the processing time (D) The inclusion absorption capacity of the slag is reduced, and the occurrence of inclusions in the steel and the occurrence of blockage of the CC nozzle increases.
[0007]
The calcium aluminate-based desulfurization agent is conventionally known (see, for example, Patent Document 1), but the patent document merely discloses the contents related to the component change for lowering the melting point of the calcium aluminate itself. The content of the LF processing method itself is not disclosed.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-60832
[Problems to be solved by the invention]
[0010]
The present invention has been made paying attention to such points, and in all the steps (1) to (3) described in paragraph [0002], the above (a) to (d) It is an object of the present invention to provide an LF processing method in which the above problem 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 obtained by hatching with molten steel containing CaO, Al ₂ O ₃ , Al, SiO ₂ and MgO into the ladle in the electric steel discharged from the electric furnace. A composite glaze agent whose composition is selected so as to be sufficiently melted is mixed so that the slag in the initial stage of LF treatment becomes a composition region having a low melting point, and then quick lime, calcium aluminate and a deoxidizer are added to the slag. Is added so as to maintain a molten state and a high fluidity state.
[0012]
The composition of the composite glaze forming agent is preferably selected so that the slag at the initial stage of LF treatment has a melting point of 1500 ° C. or less in the CaO—Al ₂ O ₃ —SiO ₂ phase diagram.
[0013]
Specifically, the composition of the composite glaze-forming agent is CaO 50 to 70% by weight, Al ₂ O ₃ 10 to 20% by weight, Al _{2 to 6} % by weight, SiO ₂ 3 to 10% by weight, and MgO 5 to 10% by weight. (Claim 3).
[0014]
In order to make the slag in the initial stage of LF to be a composition region having a low melting point, it is preferable to add the composite glaze forming agent so as to be a gehlenite region (2CaO.Al ₂ O ₃ .SiO ₂ ). 4).
[0015]
Specifically, the slag composition at the initial stage of the LF treatment may be CaO 35-50% by weight, Al ₂ O ₃ 25-40% by weight, and SiO ₂ 15-35% by weight (Claim 5).
[0016]
The deoxidizer used in the present invention preferably contains CaO, Al ₂ O ₃ , Al, SiO ₂ and Si (Claim 6).
[0017]
Specifically, the composition of the deoxidizer is CaO 35 to 45% by weight, Al ₂ O ₃ 2 to 20% by weight, Al 20 to 30% by weight, SiO _{2 2 to} 5% by weight, and Si 3 to 10% by weight. (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.
[0019]
The calcium aluminate is preferably a premelt product of the compound form CaO · Al ₂ O ₃ (claim 9).
[0020]
The calcium aluminate preferably contains CaO 45 to 60% by weight, Al ₂ O ₃ 35 to 45% by weight, and SiO ₂ 0 to 10% by weight (claim 10).
[0021]
After the calcium aluminate addition, quick lime is added, and in a state where the fluidity is deteriorated, it is a short time to add the calcium aluminate and the deoxidizer so that the slag is maintained in a molten state and a high fluidity state. (Claim 11).
[0022]
Specifically, the LF-treated final slag composition is preferably CaO 45-60% by weight, Al ₂ O ₃ 25-40% by weight, and SiO ₂ 10-20% by weight (claim 12).
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described.
[0024]
Occurs when fluorite is not added, (a) it becomes difficult to hatch quicklime, (b) fluidity of slag cannot be secured, (c) the progress of deoxidation and desulfurization is delayed, and the processing time Extending (d) Inclusion absorption capacity of slag is reduced, inclusion in steel and CC nozzle clogging increase. To solve the problem, low melting point composition of slag and fluidity improvement in the early stage of LF treatment Accelerated quick lime hatching, promoted deoxidation and desulfurization.
[0025]
First of all, as a substitute for the composite slagging agent containing quicklime or fluorite in conventional operation, it does not contain fluorite but contains CaO, Al ₂ O ₃ , Al, SiO ₂ and MgO, and hatches with molten steel. Then, a new composite iron making agent whose composition is selected so as to be sufficiently melted is added into the ladle in the steel discharged from the electric furnace. The amount of each component of the composition is selected so that the slag at 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]
Specifically, the composition of the composite glaze-forming agent is mainly obtained by increasing the amount of Al ₂ O ₃ and SiO ₂ sources from the conventional one, CaO 50 to 70 wt%, Al ₂ O ₃ : 10 to 20 wt%, Al: 2 to 2 6 wt%, SiO ₂ : 3 to 10 wt%, and MgO: 5 to 10 wt% are preferable.
[0027]
In addition to the above components, M-Si (Si content in the ferrosilicon alloy blended as a deoxidizer): 0 to 3% by weight, SiC: 0 to 5% by weight, F.R. C (fixed carbon content such as coke powder blended as a deoxidizer): About 0 to 5% by weight may be blended.
[0028]
In this way, the composite slagging agent is blended so that the slag at the initial stage of the LF treatment becomes a composition region having a low melting point. 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, it is preferable that the slag composition at the initial stage of the LF treatment is CaO 35 to 50 wt%, Al ₂ O ₃ 25 to 40 wt%, and SiO ₂ 15 to 35 wt%.
[0030]
Then, the LF process is started. When it is determined that 300 kg or more of quick lime needs to be added or when it is determined that the slag has poor fluidity, calcium aluminate is first added. Calcium aluminate, which melts slower than fluorite, can also be easily melted by adding it to a slag in a molten state (a lot of FeO and a low melting point) at the start of treatment. Thereafter, a deoxidizer containing no fluorite is added as necessary. (If the amount of quicklime added is less than 300 kg and the slag fluidity is judged to be good, a deoxidizer that does not contain fluorite is added as needed without adding calcium aluminate. .) The amount added and whether or not added depends 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 with care so that the slag can maintain a molten state. Calcium aluminate and deoxidizer are added so that the melting point of slag is lowered before the quick lime addition is interrupted at the stage where the fluidity has deteriorated and the hatching is poor. The remaining quicklime is then added. It has been experimentally found that by adding the slagging material in this order, it is possible to always maintain a hatched state and a good fluidity, and as a result, desulfurization at the initial stage of processing is promoted.
[0032]
As the deoxidizer used in the present invention, any one used for this purpose can be used, but it contains no fluorite and contains CaO, Al ₂ O ₃ , Al, SiO ₂ and Si. It is preferable to use an agent. This deoxidizer mainly increases the amount of Al ₂ O ₃ and SiO ₂ sources so that the slag has a low melting point and high fluidity after deoxidation.
[0033]
Specifically, the composition of the deoxidizer is CaO: 35 to 45% by weight, Al ₂ O ₃ : 2 to 20% by weight, Al: 20 to 30% by weight, SiO ₂ : 2 to 5% by weight, and Si: 3 It is preferable to contain 10 to 10 weight%.
[0034]
The calcium aluminate is preferably a premelt product having a melting point of 1400 ° C. or less and a particle size of 35 mm or less and having a compound form of CaO · Al ₂ O _3.
The composition of calcium aluminate should contain CaO 45-60% by weight, Al ₂ O ₃ 35-45% by weight, and SiO ₂ 0-10% by weight.
[0036]
In order to maintain the LF-treated final slag in a molten state and a high fluidity state, the composition is CaO 45-60% by weight, Al ₂ O ₃ 25-40% by weight, and SiO ₂ 10-20% by weight. Is preferred.
[0037]
EXAMPLES Next, although an Example is given and this invention is demonstrated further, this invention is not limited to these Examples.
[0038]
【Example】
Example 1: Examination of composition of composite glaze additive without fluorite added When LF treatment was added without fluorite, the LF treatment load increased. We investigated improvement of fluidity and deoxidizing power. The composite iron making agent having the composition A to E shown in the following table 1 was prepared, and the amount and method of charging were the same as in the past, and added to the ladle during testing in the electric furnace steel and tested immediately after steeling. Slag fluidity, LF initial desulfurization status and CC nozzle clogging occurrence status were confirmed. For comparison, the composite ironing agent conventionally used was also tested in the same manner.
[0039]
[Table 1]

[Test results]
(Test product A)
(A) The hatchability and fluidity were better than those of conventional products.
(B) A large amount of white smoke was generated, which hindered operations such as cleaning the electric steel outlet and the ladle crane work.
(C) The slag expanded greatly in the ladle after steelmaking.
(D) It was possible to hatch without adding fluorite up to about 400 kg of the initial input quick lime with respect to 1 ton of composite glaze.
[0040]
(Test product B: White smoke countermeasures)
(A) The reaction at the time of charging is larger than the current product and the reaction time is longer. By eliminating M-Si, white smoke was reduced, but it was larger than the current product.
(B) The hatchability was good. The fluidity immediately after charging was better than the conventional product.
(C) The slag expanded greatly in the ladle after steelmaking.
(D) It was possible to hatch without adding fluorite up to about 400 kg of the initial input quick lime with respect to 1 ton of composite glaze.
[0041]
(Test product C: slag expansion countermeasure)
(A) Slag expansion could be greatly reduced by adding no SiC, F, and C.
(B) The hatchability and fluidity were similar to those of the conventional products, but deteriorated as compared with the test products A and B.
[0042]
Semi-running test sample C was started because it was confirmed that the slag expansion was effective and the results of use such as hatchability and fluidity were the same as the conventional product.
[0043]
During the semi-running period, the occurrence of nozzle clogging at CC and the increase in the frequency of Ca-Si wire addition to prevent nozzle clogging have become problems. As a result of the cause investigation, it was judged that there was a high possibility that the increase in the amount of M-Al (metal aluminum) in the composite glaze-making agent was affected, and the formulation was changed again.
[0044]
(Test product D: Aperture countermeasure)
(A) The cause of the squeezing is estimated to be M-Al in the composite glaze agent, and 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 Could not be reduced.
(B) Further, hatchability and fluidity were poor, and the LF treatment time was extended.
[0045]
(Test product E: squeezing measures and fluidity)
Based on the above results, it was determined that throttling measures were necessary after ensuring deoxidizing power, and SiC was finely pulverized again to improve the reaction rate by pulverization with the aim of reducing slag expansion after steelmaking. ) Also, in response to the increase in the amount of slagging material used more than expected, the improvement of slag fluidity was also considered.
(A) by SiC and SiO ₂ up, slag formation property, has greatly improved flowability.
(B) The frequency of occurrence of squeezing in CC and the Ca—Si addition rate were reduced to the same level as when fluorite was used.
(C) FIG. 2 shows a graph of the desulfurization status between the conventional method and the test product E. Overall, the test product E of the present invention is faster than the conventional method as shown in FIG. Even in a low sulfur-containing steel containing no Al ([S] ≦ 0.020%), the method of the present invention can be processed without extending the processing time. This is an effect of improving deoxidizing power and hatchability.
(D) As shown in Table 2, compared with the conventional method, the test product E of the present invention was able to significantly reduce the amount of use of the faux-making material (particularly the deoxidizer).
[0046]
The point of improvement of the composite glaze forming agent of the present invention is to increase the amount of Al ₂ O ₃ to improve the hatchability of slag, to lower the melting point, and to reduce the load on LF treatment, M-Al, M -Deoxidizing power is improved 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% Then, it has been confirmed by experiments that the same effect as the product E of the present invention is exhibited.
[0047]
[Table 2]

In addition, the basic unit of the iron making agent is the weight (kg) of the iron making agent required for making the molten steel 1t.
Example 2: Examination of phosphatite-free deoxidizer The test product a (invention product), test product b and test product c having the composition shown in Table 3 were prepared, and LF treatment was performed in the same manner as before. Deoxidation status, desulfurization status, slag hatching status and fluidity were confirmed. For comparison, a conventional deoxidizer containing fluorite was also tested in the same manner.
[0048]
The test product a (the product of the present invention) has the same composition as the conventional product except that calcite is replaced with quicklime, and the test product b has a composition of Al ₂ O ₃ for improving hatchability and fluidity function. As a result, the test product c is a compound containing no carbon (C) as a countermeasure for slag expansion.
[0049]
[Table 3]

[Test results]
In FIG. 3, the graph of the desulfurization transition at the time of test product ac and the conventional product test is shown.
[0050]
(Test product a: Invention product)
(A) The deoxidation situation was almost the same as the case of using a conventional product as judged from the state of slag.
(B) No particular effect of the addition of fluorite was confirmed, and all steel types could be treated in the same manner as conventional products.
(C) No nozzle clogging at CC was confirmed during the test.
(D) There is no problem in use and it is determined that switching to the conventional product is possible.
[0051]
(Test article b)
(A) Although the hatchability and 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 carbon content [C] in molten steel and silicon content [Si] in molten steel was higher than normal, SiC added for the purpose of improving deoxidizing power contributed to deoxidation. It is possible that there is not.
[0052]
(Test product c)
(A) Although the deoxidation status and hatching status were both good, the desulfurization persistence tended to be slightly higher than other test products. However, in steels with no Al added (steel grades with an Al concentration of 0 to 0.050% and no Al added for purposes other than deoxidation), nozzle clogging troubles frequently occur in CC, and Ca-Si wires are added to deal with them. It was an unavoidable situation. Judging from the situation, it is judged that it is difficult to use it for Al-free steel.
[0053]
As described above, the test product “a” was used in the same manner as the conventional product containing fluorite. In particular, in the case of a combined use with a composite glazing additive free of fluorite, it can be treated without addition of fluorite except for some steel types (low sulfur-containing steel types). The composition of the deoxidizer was CaO: 35 to 45% by weight, Al ₂ O ₃ : 2 to 20% by weight, Al: 20 to 30% by weight, SiO ₂ : 2 to 5% by weight, and Si: 3 to 10% by weight. If so, it has been confirmed by experiments that the same effect as that of the test product a of the present invention is exhibited.
[0054]
Example 3: Examination of fluorite substitutes When a low sulfur content steel is treated with LF, when a large amount of quicklime is input, or when a small amount of slag is brought into the LF from an electric furnace, When hatching tends to be insufficient, substitutes with functions similar to fluorite, such as promoting hatching and improving fluidity, are essential. Therefore, the substitutes listed in Table 4 were tested in the same manner as fluorite in the input amount and input method. The slag fluidity immediately after steelmaking, the LF initial desulfurization situation, and the CC nozzle blockage occurrence situation were checked. For comparison, the composite ironing agent conventionally used was also tested in the same manner. The hatching status (hatching speed, quick lime hatching ability, fluidity), the amount of use of the faux-forming agent (quick lime, deoxidizer, fluorite substitute) and desulfurization transition were confirmed. In addition, the substitute used for the test is (a) does not contain fluorine, (b) has a low melting point composition, (c) has a function of promoting quick lime hatching, (d) a function of lowering slag viscosity (improving fluidity) There was a selection condition. The test evaluation results are shown in Table 5 below, and FIG. 4 is a graph showing the desulfurization transition of each test product.
[0055]
[Table 4]

[0056]
[Table 5]

Is better than conventional products, △ is equivalent to conventional products, and × is worse than conventional products.
[0057]
CaO ・ SiO ₃ (Wollastonite)
Although the premelt product melts, the hatching rate is so slow that it cannot be compared with fluorite. Regarding the crushed natural minerals, melting was extremely slow, and solidification was confirmed on the slag for a long time. In any case, the same usage as fluorite is difficult.
[0058]
CaO ・ Al ₂ O ₃・ SiO ₂ (Low melting point composition)
If it is introduced in a state where hatching has progressed to some extent, it will melt, but hatching in the initial stage of processing is very slow. Naturally, the progress of desulfurization was slow and the processing time tended to be extended.
[0059]
CaO ・ Al ₂ O ₃ (Calcium aluminate)
In both the fired product and the premelt product, relatively good results were obtained in terms of hatchability and fluidity. The melting rate of the premelt product tended to be slightly faster than that of the fired product. However, in comparison with fluorite, it took some time and temperature to melt completely and obtain fluidity. By adding quick lime at the initial stage of processing, it is possible to cope with it in a relatively short time. Therefore, substitution of fluorite with calcium aluminate is possible.
[0060]
As described above, it was confirmed that by using a composite glaze-forming agent, a deoxidizing agent, and calcium aluminate (preferably a premelt product), LF treatment equivalent to that when using fluorite can be performed without adding fluorite.
[0061]
In the slag by the conventional method, fluorine elution of about 1 to 20 mg / liter was confirmed by the Environmental Agency Notification No. 46 of 1991, but the slag according to the present invention achieved zero fluorine elution.
[0062]
When fluorite is not used in the conventional operation method, a processing time of about 1.5 times that when fluorite is used is required. However, according to the present invention, slag composition control improves slag flowability and improves fluidity. By achieving this, it was possible to secure a deoxidation / desulfurization rate almost the same as when using fluorite, and it was possible to perform treatment in the same amount of time.
[0063]
By promoting hatching at the initial stage of LF treatment and controlling the low melting point area of the slag, the removal of inclusions from the slag was promoted and the melting point of the inclusions was lowered.
[0064]
【The invention's effect】
As described above, according to the present invention, since the LF treatment equivalent to that when using fluorite can be performed without addition of fluorite is solved, it is an extremely innovative invention. . At the same time, when recycling steelmaking slag, it is possible to eliminate the possibility 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 time of use of a conventional composite glaze-forming agent, deoxidizer, quicklime and fluorite.
FIG. 2 is a graph showing the state of desulfurization when a conventional composite glaze is used and when a composite glaze of the present invention is used.
FIG. 3 is a graph showing the desulfurization transition of the reductive deoxidizer of the present invention (test product a), comparative deoxidizers (test products b and c), and conventional products.
FIG. 4 is a graph showing the transition of desulfurization when the calcium aluminate of the present invention and other fluorite substitutes are used.
FIG. 5 is a diagram showing the time of use of the composite glaze agent, deoxidizer, quicklime and calcium aluminate of the present invention.

Claims (12)

A composite iron making agent containing CaO, Al ₂ O ₃ , Al, SiO ₂ and MgO, which has been selected from the composition so as to be sufficiently molten by being hatched with molten steel, in the ladle. Mix so that the slag at the initial stage of the ladle smelting furnace becomes a low melting point composition region, and then keep the lime, calcium aluminate and deoxidizer in a molten state and a high fluidity state. A fluorite-free additive-free LF treatment method characterized by adding. The processing method according to claim 1, wherein the composition of the composite glazing agent is selected so that the slag at 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. 3. The composite iron making agent is CaO 50 to 70% by weight, Al ₂ O ₃ 10 to 20% by weight, Al _{2 to 6} % by weight, SiO ₂ 3 to 10% by weight, and MgO 5 to 10% by weight. Processing method. The processing method according to any one of claims 1 to 3, wherein the composite slagging agent is added so that the slag at the initial stage of the LF treatment is in a 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 processing method according to claim 1, wherein the deoxidizer contains CaO, Al ₂ O ₃ , Al, SiO ₂ and Si. The composition of the deoxidizer contains 35 to 45% by weight of CaO, ₂ to 20% by weight of Al ₂ O _3, 20 to 30% by weight of Al, _{2 to} 5% by weight of SiO ₂ and 3 to 10% by weight of Si. 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 processing method according to claim 1, wherein the calcium aluminate is a premelt product of a compound form 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. The calcium aluminate and the deoxidizer are added so that the slag is maintained in a molten state and a high fluidity state in a state where fluidity is deteriorated after the calcium aluminate is added. The processing method in any one of. 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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