JP3697987B2 - Desulfurization agent for molten steel desulfurization - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、溶鋼脱硫用の脱硫剤に関し、特に清浄度を維持または改善できる溶鋼脱硫用の脱硫剤に関する。
【０００２】
【従来の技術】
鋼中Ｓや非金属介在物は、各種製品欠陥の原因となるためその低減が求められている。特にＳ濃度は１０ppm 以下、鋼種によっては４ppm 以下といった極低域まで低減することが望まれている。
【０００３】
鋼中Ｓの低減は溶鋼段階で主として行われ、その際の脱硫処理方法としては、ＣａＯなどを含有した脱硫剤を溶鋼に吹き込む方法、脱硫剤を減圧下で溶鋼表面に吹き付ける方法、脱硫能力の高いスラグを形成させ不活性ガスなどを溶鋼に吹き込む方法などがこれまでに知られている。
【０００４】
例えば、特開平５−１７１２５３号公報に開示されているＣａＯおよびＣａＦ2 を含有する脱硫剤を溶鋼に吹き込む方法や溶鋼表面に吹き付ける方法は、溶鋼−脱硫剤間の反応界面の面積が大きくなることから極低硫鋼の製造には有利と考えられてきた。
【０００５】
【発明が解決しようとする課題】
しかし、同公報の開示技術でＳ濃度を５ppm 以下とするには大量の脱硫剤と脱酸剤が必要とされ、処理時間も８〜１５分と長時間を要する。従って、短時間で極低硫鋼を得ることが望まれていた。
【０００６】
短時間で極低硫鋼を得るには、脱硫効率を従来以上に向上させる必要がある。脱硫処理時の脱硫反応は、下記化学反応により進行する。
【０００７】
（ＣａＯ）＋［Ｓ］＝（ＣａＳ）＋［Ｏ］
ただし、（ＣａＯ）、（ＣａＳ）：脱硫剤およびスラグ成分
［Ｓ］、［Ｏ］ ：溶鋼中の成分
反応式から明らかなように、溶鋼中の酸素濃度を予め低減すれば、脱硫反応を促進できる。
【０００８】
例えば、特開昭６２−７８１６公報には、脱硫処理に先立ってＡｌ、Ｃａなどの脱酸剤を溶鋼に添加してから脱硫剤を添加するか、脱酸剤と脱硫剤を同時に添加することが有効であることを開示している。
【０００９】
しかし、Ａｌ濃度を高めても脱硫速度を高める効果は小さく、更なる改善が必要であった。
【００１０】
また、特開平１０−１８３２２７公報には、ＣａＯを主原料にした脱硫剤（以下、ＣａＯ系脱硫剤ともいう）にＣａＳｉ合金などの金属Ｃａをさらに含有させた脱硫剤を溶鋼に添加する技術が開示されている。
【００１１】
しかし、この技術は溶鋼中のＳ濃度の低減効果が小さく、しかも介在物が多く生成するため溶鋼の清浄度を悪化させるという問題があった。
【００１２】
一方、脱窒に関しては、ほとんど脱窒効果がないという問題があった。
本発明の目的は、清浄度を維持または改善できる脱硫脱窒用の溶鋼脱硫剤を提供することにある。
【００１３】
【課題を解決するための手段】
前記の通り溶鋼中の酸素濃度を低くするほど脱硫反応が進行し易くなる。
【００１４】
そこで、Ａｌで溶鋼を脱酸した後、ＣａＯ系脱硫剤を減圧下で溶鋼に吹き付ける小規模実験を実施した。
以下にこの実験で得られた知見を示す。
【００１５】
（Ａ）Ａｌで脱酸された溶鋼にＣａＯ系脱硫剤を添加すると、この脱硫剤はＣａＯ主体の組成物からＣａＯとＡｌ2Ｏ3との混合物が主体の組成物（以下、この組成物をＣａＯ−Ａｌ2 Ｏ3 で表す）に変化する。
【００１６】
（Ｂ）ＣａＯとＣａＯ−Ａｌ2 Ｏ3 とでは、ＣａＯ−Ａｌ2 Ｏ3 の脱硫能力（一般にサルファイドキャパシティと呼ばれる）はＣａＯに比べ著しく劣る。
【００１７】
（Ｃ）一方、金属Ｃａを含有したＣａＯ系脱硫剤は金属ＣａがＯおよびＳと強い反応性を有するため、溶鋼中の［Ｏ］および［Ｓ］と反応し易く、ＣａＯとＣａＳとの混合物が主体の組成物（以下、この組成物をＣａＯ−ＣａＳ系介在物で表す）、ＣａＳが主体の組成物（以下、ＣａＳ系介在物で表す）が大量に生成し、清浄度を悪化させる。
【００１８】
これらの介在物生成により、溶鋼中の［Ｓ］濃度が低下するため、脱硫剤と溶鋼中の［Ｓ］との反応速度が低下する。
【００１９】
鋼中のＳ濃度とは、溶鋼中の［Ｓ］濃度と介在物に含有されるＳの合計濃度であるが、介在物が溶鋼中に生成すると、溶鋼中の［Ｓ］と脱硫剤との反応速度が前記の通り遅くなるため、結果的に鋼中Ｓ濃度はほとんど低下しないことが判明した。
【００２０】
（Ｄ）以上の知見から、本発明者らは溶鋼中に添加した脱硫剤の組成を変化させずに酸素濃度を低減することが可能となれば、脱硫反応を促進できることに着眼した。
【００２１】
すなわち、脱硫剤中のＣａＯと溶鋼中Ａｌとの反応を抑制するには溶鋼中の金属Ｃａ濃度を適正範囲に制御することによりＣａＯの組成変化を抑制できると着想し、脱硫剤中の金属Ｃａ濃度を適正範囲に制御する試験を以下の方法で実施した。
【００２２】
Ａｌを０．００５〜０．７質量％（以下、単に％で質量％を表す）含有した溶鋼表面に、減圧下でＣａＳｉ合金（金属Ｃａを３０質量％含有；以下単に％で質量％を表す）とＣａＯとを含有した脱硫剤（以下、単に脱硫剤ともいう）を吹き付けた。
【００２３】
ここで、Ａｌ濃度を０．００５〜０．７％としたのは、０．００５％未満では酸素活量低減効果が小さいためであり、また０．７％を超える鋼種が少ないためである。
【００２４】
図１は、溶鋼中の［Ａｌ］濃度が０．０４％一定のときの脱硫剤中の金属Ｃａの配合量と鋼中のＳ濃度および介在物指数との関係を示すグラフである。
【００２５】
なお、介在物指数は処理後の介在物個数を処理前の介在物個数で割った指数を表す。すなわち、指数１は、処理後の介在物個数が処理前の介在物個数と同じ個数であり、１を超えると増加し、１未満で減少していることを示す。
【００２６】
同図に示すように、Ｃａ配合量が低すぎると脱硫反応が進行しない。一方、Ｃａ配合量が高すぎると介在物が多くなり清浄度が悪化し、かつ鋼中のＳ濃度も低下しない。Ｃａ配合量を適正範囲にすると鋼中のＳ濃度を低下でき、介在物指数も上昇しない。すなわち、溶鋼の清浄度は悪化しない。
【００２７】
なお、Ｃａ配合量が高すぎるとＣａと溶鋼中Ｓとの反応が進行し、ＣａＯ−ＣａＳ、ＣａＳ介在物が生成するため、清浄度が悪化し鋼中Ｓ濃度もあまり低下しないものと推定できる。
【００２８】
図２は、溶鋼中の［Ａｌ］濃度が０．０４％一定のときの脱硫剤中の金属Ｃａの配合量と鋼中のＮ濃度との関係を示すグラフである。
同図に示すように、Ｃａ配合量を適正範囲にすると鋼中のＮ濃度を低下できる。
【００２９】
なお、鋼中のＮ濃度を低下できるのは、脱窒阻害元素である溶鋼中のＯおよびＳ濃度が低減できるからと推定できる。
【００３０】
以上のような実験事実に基づいて、さらに溶鋼中のＡｌ濃度を０．００５〜０．７％の範囲で変更し、試験を重ねた結果、図３に示すＡｌ濃度とＣａ配合量との関係を見出した。
【００３１】
図３は、脱硫剤の性能を脱硫剤中のＣａ配合量と溶鋼中のＡｌ濃度との関係で表したグラフである。
【００３２】
同図に示すように、脱硫剤のＣａ配合量と溶鋼中のＡｌ濃度との関係は、３本の直線（ｉ）〜（iii ）で４つの領域に分けることができる。
【００３３】
すなわち、最上部の直線（ｉ）によって、清浄度が悪化し脱硫が困難な領域と、清浄度を改善でき脱硫・脱窒が可能な領域とに分けることができる。
【００３４】
なお、清浄度を改善できるレベルは、前記介在物指数が０．９未満のレベルをいう。
【００３５】
この直線は、下記（ｉ）式で表せる。
（Ｃａ）＝７×［Ａｌ］＋５．１ −−−（ｉ）
ただし、［Ａｌ］：溶鋼中のＡｌ濃度（質量％）、
（Ｃａ）：脱硫剤中の金属Ｃａ濃度（質量％）
また、中間部の直線（ii）によって清浄度を改善でき脱硫・脱窒が可能な領域と、清浄度を維持でき脱硫・脱窒が可能な領域とに分けることができる。
【００３６】
この直線は、下記（ii）式で表せる。
（Ｃａ）＝５×［Ａｌ］＋１．４ −−−（ii）
さらに、最下部の直線（iii ）によって清浄度を維持でき脱硫・脱窒が可能な領域と、脱硫が困難な領域とに分けることができる。
【００３７】
なお、清浄度を維持できるレベルは、前記介在物指数が０．９〜１．０のレベルをいう。
【００３８】
この直線は、下記（iii ）式で表せる。
（Ｃａ）＝０．９４×［Ａｌ］＋０．３４ −−−（iii ）
これらの（ｉ）〜（iii ）式を基に領域を整理すると、清浄度を少なくとも維持でき脱硫・脱窒が可能な領域は下記（１）式の不等式で表せる。
７×［Ａｌ］＋５．１≧（Ｃａ）≧０．９４×［Ａｌ］＋０．３４ （１）
また、清浄度を改善でき脱硫・脱窒が可能な領域は下記（２）式の不等式で表せる。
７×［Ａｌ］＋５．１＞（Ｃａ）＞５×［Ａｌ］＋１．４ （２）
本発明は、以上の知見に基づいてなされたもので、その要旨は、下記のとおりである。
【００３９】
（１）溶鋼中Ａｌ濃度が０．００５質量％以上０．７質量％以下である溶鋼を脱硫する脱硫剤であって、該脱硫剤がＣａＯおよび金属Ｃａを含有し、該金属Ｃａの含有量が下記（１）式を満足することを特徴とする溶鋼脱硫用の脱硫剤。
７×［Ａｌ］＋５．１≧（Ｃａ）≧０．９４×［Ａｌ］＋０．３４ （１）
ただし、［Ａｌ］：溶鋼中のＡｌ濃度（質量％）、
（Ｃａ）：脱硫剤中の金属Ｃａ濃度（質量％）。
【００４０】
（２）溶鋼中Ａｌ濃度が０．００５質量％以上０．７質量％以下である溶鋼を脱硫する脱硫剤であって、該脱硫剤がＣａＯおよび金属Ｃａを含有し、該金属Ｃａの含有量が下記（２）式を満足することを特徴とする溶鋼脱硫用の脱硫剤。
７×［Ａｌ］＋５．１＞（Ｃａ）＞５×［Ａｌ］＋１．４ （２）
ただし、［Ａｌ］：溶鋼中のＡｌ濃度（質量％）、
（Ｃａ）：脱硫剤中の金属Ｃａ濃度（質量％）。
【００４１】
【発明の実施の形態】
本発明を転炉と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。
【００４２】
転炉処理終了後、溶鋼を取鍋へ出鋼する。取鍋をＲＨ真空脱ガス装置（以下、単にＲＨともいう）へ移動し、真空処理を開始する。
【００４３】
ＲＨ真空槽内に設けた上吹きランスから本脱硫剤を真空槽内溶鋼表面に上吹きする。真空度は環流が維持される程度でよいが、高真空で処理を行うことにより溶鋼攪拌が活発化となり溶鋼の脱硫脱窒が促進されるので望ましい。
【００４４】
本脱硫剤を用いる処理の前後に成分調整、温度調整を実施してもよい。
本脱硫剤を上記上吹きで添加してもよいし、溶鋼中に吹き込んでもよい。
【００４５】
上吹きは、上記の減圧下上吹きの他に不活性ガス雰囲気の大気圧下で上吹きでもよい。またＲＨ処理中に取鍋内への吹き込みを行ってもよい。
溶鋼質量トン当りの脱硫剤量は２ｋｇ〜１０ｋｇが望ましい。
【００４６】
２ｋｇ未満では、脱硫剤が少なすぎて十分に脱硫できない。１０ｋｇを超えて多くなると効果が飽和し経済的ではない。
【００４７】
また、添加速度は溶鋼質量トン当り０．１〜２ｋｇ／min が望ましい。
０．１ｋｇ／min 未満では処理時間が長くなり効率が悪くなるおそれがあり、２ｋｇ／min ）を超えて高いと、溶鋼飛散などの操業上の問題が生じるおそれがある。
【００４８】
本脱硫剤に配合される金属Ｃａ含有物は金属Ｃａの他に、Ｃａ−Ｓｉ、Ｃａ−Ａｌ、Ｆｅ−Ｃａといった合金なども使用できる。
【００４９】
本脱硫剤の主成分はＣａＯであるが、必要に応じてアルミナ、ＣａＦ2 、ＺｒＯ2 、ＭｇＯなどを配合しても良い。
ただし、本脱硫剤中のＣａＯ含有量は２５％以上が望ましい。
【００５０】
２５％未満では脱硫性能が低下するおそれがある。
本脱硫剤の粒径は、０．００１〜３ｍｍが望ましい。
【００５１】
その理由は、０．００１ｍｍ未満では質量が小さく溶鋼中に侵入しないおそれがあり、３ｍｍを超えると反応界面の面積が減少し脱硫性能が低下するおそれがあるからである。
【００５２】
【実施例】
転炉で脱炭した溶鋼を、取鍋内に出鋼し、取鍋をＲＨ真空脱ガス装置に移動し、真空処理を開始した。
【００５３】
真空処理開始後、溶鋼にＡｌを添加し、溶鋼中のＡｌ濃度を確認した後、脱硫剤中の金属Ｃａの配合量を決定し、真空槽内溶鋼表面に脱硫剤を吹き付けた。
なお、金属Ｃａは金属Ｃａを３０質量％含有するＦｅ−Ｃａ合金を用いた。
【００５４】
ＲＨ真空槽の真空度は、約３００Ｐａ、脱硫剤の吹き付け速度は溶鋼質量トン当り１ｋｇ／min 、吹き付け時間は８分とした。なお、脱硫剤のキャリヤ−ガスとしてＡｒガスを用いた。
表１に試験結果を示す。
【００５５】
【表１】
なお、表中の介在物指数は、前記の通り処理後の介在物個数を処理前の介在物個数で割った指数を表す。
【００５７】
また、表中のＣａの配合量評価は、前記（１）式で示される範囲のＣａの配合量：○を、前記（２）式で示される範囲のＣａの配合量：◎の評価とした。
【００５８】
［Ｓ］濃度は、処理後の溶鋼中の［Ｓ］濃度が５ppm 以下：○を、５ppm を超える溶鋼中の［Ｓ］濃度：×とした。
【００５９】
［Ｎ］濃度は、処理後の溶鋼中の［Ｎ］濃度が２０ppm 以下：○を、２０ppm を超える溶鋼中の［Ｎ］濃度：×とした。
【００６０】
介在物指数０．９〜１．０は介在物個数が処理前と変化してないと判断でき、○（介在物個数維持）を、０．９未満は介在物個数を低減できたとして◎を、
１．０超は介在物個数が増加したとして×をそれぞれつけて評価した。
【００６１】
総合評価の◎は、［Ｓ］濃度が５ppm 以下であり、［Ｎ］濃度が２０ppm 以下であり、さらに介在物指数が０．９未満であることを示す。
【００６２】
総合評価の○は、［Ｓ］濃度が５ppm 以下であり、［Ｎ］濃度が２０ppm 以下であり、さらに介在物指数が０．９〜１．０であることを示す。
。
【００６３】
総合評価の×は、［Ｓ］濃度が５ppm 超、または［Ｎ］濃度が２０ppm 超、または介在物個数が１．０超のいずれかに該当する場合であることを示す。
【００６４】
表１に示すように、前記（１）式で示される範囲の金属Ｃａ配合量の脱硫剤で吹き付け処理を行うと、介在物個数を増加させることなく、［Ｓ］濃度および［Ｎ］濃度を低下できた。
【００６５】
また、前記（２）式で示される範囲の金属Ｃａ配合量の脱硫剤で吹き付け処理を行うと、介在物個数を低減でき、さらに［Ｓ］濃度および［Ｎ］濃度を低下できた。
【００６６】
【発明の効果】
本発明の溶鋼脱硫用の脱硫剤により、清浄度を維持または改善しながら溶鋼の脱硫脱窒ができる。
【図面の簡単な説明】
【図１】溶鋼中の［Ａｌ］濃度が０．０４％一定のときの脱硫剤中の金属Ｃａの配合量と鋼中のＳ濃度および介在物指数との関係を示すグラフである。
【図２】溶鋼中の［Ａｌ］濃度が０．０４％一定のときの脱硫剤中の金属Ｃａの配合量と鋼中のＮ濃度との関係を示すグラフである。
【図３】ＣａＯ系脱硫剤の性能を脱硫剤のＣａ配合量と溶鋼中のＡｌ濃度との関係で表したグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a desulfurization agent for molten steel desulfurization, and more particularly to a desulfurization agent for molten steel desulfurization that can maintain or improve cleanliness.
[0002]
[Prior art]
Since S in steel and non-metallic inclusions cause various product defects, their reduction is required. In particular, it is desired to reduce the S concentration to an extremely low range of 10 ppm or less, and depending on the steel type, 4 ppm or less.
[0003]
Reduction of S in steel is mainly performed in the molten steel stage, and as a desulfurization process at that time, a method of blowing a desulfurizing agent containing CaO or the like into the molten steel, a method of blowing a desulfurizing agent on the surface of the molten steel under reduced pressure, A method of forming a high slag and blowing an inert gas into molten steel has been known so far.
[0004]
For example, the method of blowing a desulfurization agent containing CaO and CaF 2 disclosed in JP-A-5-171253 into molten steel or the method of blowing it onto the molten steel increases the area of the reaction interface between the molten steel and the desulfurization agent. It has been considered advantageous for the production of ultra-low sulfur steel.
[0005]
[Problems to be solved by the invention]
However, a large amount of a desulfurizing agent and a deoxidizing agent are required to reduce the S concentration to 5 ppm or less with the disclosed technique of the publication, and the processing time is as long as 8 to 15 minutes. Therefore, it has been desired to obtain ultra-low sulfur steel in a short time.
[0006]
In order to obtain ultra-low sulfur steel in a short time, it is necessary to improve the desulfurization efficiency more than before. The desulfurization reaction during the desulfurization process proceeds by the following chemical reaction.
[0007]
(CaO) + [S] = (CaS) + [O]
However, (CaO), (CaS): desulfurization agent and slag component [S], [O]: As is clear from the component reaction formula in the molten steel, the desulfurization reaction is promoted by reducing the oxygen concentration in the molten steel in advance. it can.
[0008]
For example, in Japanese Patent Laid-Open No. 62-7816, a deoxidizer such as Al or Ca is added to molten steel before desulfurization, or a desulfurizer is added, or a deoxidizer and a desulfurizer are added simultaneously. Is disclosed to be effective.
[0009]
However, even if the Al concentration is increased, the effect of increasing the desulfurization rate is small, and further improvement is necessary.
[0010]
Japanese Patent Laid-Open No. 10-183227 discloses a technique for adding to a molten steel a desulfurization agent containing CaO as a main raw material (hereinafter also referred to as a CaO-based desulfurization agent) and further containing a metal Ca such as a CaSi alloy. It is disclosed.
[0011]
However, this technique has a problem in that the effect of reducing the S concentration in the molten steel is small, and more inclusions are produced, which deteriorates the cleanliness of the molten steel.
[0012]
On the other hand, there has been a problem that denitrification has almost no denitrification effect.
An object of the present invention is to provide a molten steel desulfurization agent for desulfurization and denitrification that can maintain or improve cleanliness.
[0013]
[Means for Solving the Problems]
As described above, the lower the oxygen concentration in the molten steel, the easier the desulfurization reaction proceeds.
[0014]
Then, after deoxidizing the molten steel with Al, a small-scale experiment was conducted in which a CaO-based desulfurizing agent was sprayed onto the molten steel under reduced pressure.
The knowledge obtained in this experiment is shown below.
[0015]
(A) When a CaO-based desulfurizing agent is added to molten steel deoxidized with Al, this desulfurizing agent is a composition mainly composed of CaO and a mixture of CaO and Al 2 O 3 (hereinafter referred to as this composition). (Represented by CaO—Al 2 O 3 ).
[0016]
(B) With CaO and CaO-Al 2 O 3 , the desulfurization capacity of CaO—Al 2 O 3 (generally called sulfide capacity) is significantly inferior to CaO.
[0017]
(C) On the other hand, since the CaO-based desulfurization agent containing metal Ca has a strong reactivity with O and S, the metal Ca easily reacts with [O] and [S] in the molten steel, and is a mixture of CaO and CaS. The composition mainly composed of (hereinafter, this composition is represented by CaO-CaS inclusions) and the composition mainly composed of CaS (hereinafter, represented by CaS inclusions) are produced in large amounts, thereby deteriorating the cleanliness.
[0018]
Since these inclusions are produced, the [S] concentration in the molten steel is lowered, and the reaction rate between the desulfurizing agent and [S] in the molten steel is lowered.
[0019]
The S concentration in the steel is the total concentration of [S] in the molten steel and S contained in the inclusions. If the inclusions are generated in the molten steel, the S concentration in the molten steel and the desulfurizing agent Since the reaction rate was slow as described above, it was found that the S concentration in the steel hardly decreased as a result.
[0020]
(D) From the above knowledge, the present inventors have focused on the fact that the desulfurization reaction can be promoted if the oxygen concentration can be reduced without changing the composition of the desulfurizing agent added to the molten steel.
[0021]
That is, in order to suppress the reaction between CaO in the desulfurizing agent and Al in the molten steel, it was conceived that the change in the composition of CaO can be suppressed by controlling the concentration of metallic Ca in the molten steel within an appropriate range. The test which controls a density | concentration to an appropriate range was implemented with the following method.
[0022]
On a molten steel surface containing Al in an amount of 0.005 to 0.7% by mass (hereinafter simply expressed as%), a CaSi alloy (containing 30% by mass of metal Ca; hereinafter simply expressed as% by mass) under reduced pressure. ) And CaO were sprayed (hereinafter also simply referred to as a desulfurizing agent).
[0023]
Here, the reason why the Al concentration is set to 0.005 to 0.7% is that when the content is less than 0.005%, the effect of reducing the oxygen activity is small, and because there are few steel types exceeding 0.7%.
[0024]
FIG. 1 is a graph showing the relationship between the amount of metallic Ca in the desulfurizing agent, the S concentration in steel and the inclusion index when the [Al] concentration in molten steel is constant 0.04%.
[0025]
The inclusion index represents an index obtained by dividing the number of inclusions after treatment by the number of inclusions before treatment. That is, an index of 1 indicates that the number of inclusions after treatment is the same as the number of inclusions before treatment, and increases when it exceeds 1 and decreases when it is less than 1.
[0026]
As shown in the figure, the desulfurization reaction does not proceed if the Ca content is too low. On the other hand, if the Ca content is too high, inclusions increase, the cleanliness deteriorates, and the S concentration in the steel does not decrease. When the Ca content is within an appropriate range, the S concentration in the steel can be reduced, and the inclusion index does not increase. That is, the cleanliness of the molten steel does not deteriorate.
[0027]
If the Ca content is too high, the reaction between Ca and S in molten steel proceeds and CaO-CaS and CaS inclusions are produced. Therefore, it can be estimated that the cleanliness is deteriorated and the S concentration in the steel does not decrease so much. .
[0028]
FIG. 2 is a graph showing the relationship between the amount of metallic Ca in the desulfurizing agent and the N concentration in the steel when the [Al] concentration in the molten steel is constant 0.04%.
As shown in the figure, the N concentration in the steel can be reduced when the Ca content is within an appropriate range.
[0029]
In addition, it can be estimated that the N concentration in the steel can be reduced because the O and S concentrations in the molten steel, which is a denitrification inhibiting element, can be reduced.
[0030]
Based on the experimental facts as described above, the Al concentration in the molten steel was further changed in the range of 0.005 to 0.7%, and as a result of repeated tests, the relationship between the Al concentration and the Ca content shown in FIG. I found.
[0031]
FIG. 3 is a graph showing the performance of the desulfurizing agent in terms of the relationship between the Ca content in the desulfurizing agent and the Al concentration in the molten steel.
[0032]
As shown in the figure, the relationship between the Ca content of the desulfurizing agent and the Al concentration in the molten steel can be divided into four regions by three straight lines (i) to (iii).
[0033]
That is, the uppermost straight line (i) can be divided into a region where cleanliness is deteriorated and desulfurization is difficult, and a region where cleanliness can be improved and desulfurization / denitrification can be performed.
[0034]
In addition, the level which can improve a cleanliness means the level whose said inclusion index is less than 0.9.
[0035]
This straight line can be expressed by the following equation (i).
(Ca) = 7 × [Al] +5.1 −−− (i)
However, [Al]: Al concentration in molten steel (mass%),
(Ca): Metal Ca concentration (% by mass) in the desulfurization agent
Moreover, the straight line (ii) in the middle part can be divided into a region where the cleanliness can be improved and desulfurization / denitrification can be performed, and a region where the cleanliness can be maintained and desulfurization / denitrification can be performed.
[0036]
This straight line can be expressed by the following equation (ii).
(Ca) = 5 × [Al] +1.4 −−− (ii)
Furthermore, the lowermost straight line (iii) can be divided into a region where cleanliness can be maintained and desulfurization / denitrification can be performed, and a region where desulfurization is difficult.
[0037]
In addition, the level which can maintain cleanliness means the level whose said inclusion index is 0.9-1.0.
[0038]
This straight line can be expressed by the following formula (iii).
(Ca) = 0.94 × [Al] +0.34 −−− (iii)
If the regions are arranged based on these equations (i) to (iii), the region where the cleanliness can be maintained and desulfurization / denitrification can be performed can be expressed by the following inequality (1).
7 × [Al] + 5.1 ≧ (Ca) ≧ 0.94 × [Al] +0.34 (1)
Further, the region where the cleanliness can be improved and desulfurization / denitrification can be performed can be expressed by the following inequality (2).
7 × [Al] +5.1>(Ca)> 5 × [Al] +1.4 (2)
The present invention has been made based on the above findings, and the gist thereof is as follows.
[0039]
(1) A desulfurizing agent for desulfurizing molten steel having an Al concentration in molten steel of 0.005 mass% to 0.7 mass% , wherein the desulfurizing agent contains CaO and metallic Ca, and the content of the metallic Ca Satisfies the following formula (1), a desulfurization agent for molten steel desulfurization.
7 × [Al] + 5.1 ≧ (Ca) ≧ 0.94 × [Al] +0.34 (1)
However, [Al]: Al concentration in molten steel (mass%),
(Ca): Metal Ca concentration (% by mass) in the desulfurization agent.
[0040]
(2) A desulfurization agent for desulfurizing molten steel having an Al concentration in the molten steel of 0.005 mass% or more and 0.7 mass% or less, the desulfurization agent containing CaO and metal Ca, and the content of the metal Ca Satisfies the following formula (2): A desulfurization agent for desulfurization of molten steel.
7 × [Al] +5.1>(Ca)> 5 × [Al] +1.4 (2)
However, [Al]: Al concentration in molten steel (mass%),
(Ca): Metal Ca concentration (% by mass) in the desulfurization agent.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
The case where the present invention is carried out using a converter and an RH vacuum degassing apparatus will be described as an example.
[0042]
After the converter process, the molten steel is taken out into a ladle. The ladle is moved to an RH vacuum degasser (hereinafter also simply referred to as RH), and vacuum processing is started.
[0043]
The desulfurizing agent is sprayed on the surface of the molten steel in the vacuum chamber from an upper spray lance provided in the RH vacuum chamber. The degree of vacuum may be such that the reflux is maintained, but it is desirable because the treatment with high vacuum activates the stirring of molten steel and promotes desulfurization and denitrification of the molten steel.
[0044]
Component adjustment and temperature adjustment may be performed before and after the treatment using the present desulfurizing agent.
The desulfurizing agent may be added by top blowing or may be blown into molten steel.
[0045]
The top blow may be a top blow under an atmospheric pressure of an inert gas atmosphere in addition to the above-described top blow under reduced pressure. Moreover, you may blow in the ladle during RH process.
The amount of the desulfurizing agent per ton of molten steel is desirably 2 kg to 10 kg.
[0046]
If it is less than 2 kg, there are too few desulfurization agents and it cannot fully desulfurize. When the amount exceeds 10 kg, the effect is saturated and it is not economical.
[0047]
The addition rate is desirably 0.1 to 2 kg / min per ton of molten steel.
If it is less than 0.1 kg / min, the treatment time may be long and the efficiency may be deteriorated. If it exceeds 2 kg / min), operational problems such as molten steel scattering may occur.
[0048]
The metal Ca-containing material blended in the present desulfurizing agent may be an alloy such as Ca—Si, Ca—Al, Fe—Ca, etc. in addition to the metal Ca.
[0049]
The main component of the present desulfurizing agent is CaO, but alumina, CaF 2 , ZrO 2 , MgO or the like may be blended as necessary.
However, the CaO content in the present desulfurizing agent is preferably 25% or more.
[0050]
If it is less than 25%, the desulfurization performance may be lowered.
The particle size of the desulfurizing agent is preferably 0.001 to 3 mm.
[0051]
The reason is that if it is less than 0.001 mm, the mass is small and it may not enter the molten steel, and if it exceeds 3 mm, the area of the reaction interface may decrease and the desulfurization performance may deteriorate.
[0052]
【Example】
The molten steel decarburized in the converter was put into the ladle, the ladle was moved to the RH vacuum degassing device, and vacuum treatment was started.
[0053]
After the vacuum treatment was started, Al was added to the molten steel, and after confirming the Al concentration in the molten steel, the amount of metal Ca in the desulfurizing agent was determined, and the desulfurizing agent was sprayed on the surface of the molten steel in the vacuum chamber.
In addition, the metal Ca used the Fe-Ca alloy containing 30 mass% of metal Ca.
[0054]
The degree of vacuum of the RH vacuum tank was about 300 Pa, the spraying speed of the desulfurizing agent was 1 kg / min per ton of molten steel, and the spraying time was 8 minutes. Ar gas was used as a carrier gas for the desulfurization agent.
Table 1 shows the test results.
[0055]
[Table 1]
The inclusion index in the table represents an index obtained by dividing the number of inclusions after treatment by the number of inclusions before treatment as described above.
[0057]
In addition, the amount of Ca contained in the table was evaluated in terms of the amount of Ca contained in the range represented by the formula (1): ○ and the amount of Ca contained in the range represented by the formula (2): ：. .
[0058]
As for the [S] concentration, the [S] concentration in the molten steel after the treatment was 5 ppm or less: ○, and the [S] concentration in the molten steel exceeding 5 ppm was taken as x.
[0059]
As for the [N] concentration, the [N] concentration in the molten steel after the treatment was 20 ppm or less: ◯, and the [N] concentration in the molten steel exceeding 20 ppm: x.
[0060]
Inclusion index of 0.9 to 1.0 can be judged that the number of inclusions has not changed from that before the treatment, and ○ (maintenance of the number of inclusions) is less than 0.9. ,
When the number of inclusions exceeded 1.0, the number of inclusions was increased, and each was evaluated with a cross.
[0061]
The 総 合 in the overall evaluation indicates that the [S] concentration is 5 ppm or less, the [N] concentration is 20 ppm or less, and the inclusion index is less than 0.9.
[0062]
In the overall evaluation, ◯ indicates that the [S] concentration is 5 ppm or less, the [N] concentration is 20 ppm or less, and the inclusion index is 0.9 to 1.0.
.
[0063]
The x in the comprehensive evaluation indicates that the [S] concentration exceeds 5 ppm, the [N] concentration exceeds 20 ppm, or the number of inclusions exceeds 1.0.
[0064]
As shown in Table 1, when spraying with a desulfurizing agent having a metallic Ca content in the range represented by the above formula (1), the [S] concentration and the [N] concentration are increased without increasing the number of inclusions. I was able to decrease.
[0065]
Moreover, when the spray treatment was performed with a desulfurizing agent having a metallic Ca content within the range represented by the formula (2), the number of inclusions could be reduced, and the [S] concentration and [N] concentration could be further reduced.
[0066]
【The invention's effect】
With the desulfurization agent for molten steel desulfurization of the present invention, desulfurization and denitrification of molten steel can be performed while maintaining or improving the cleanliness.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the amount of metallic Ca in a desulfurizing agent, the S concentration in steel and the inclusion index when the [Al] concentration in molten steel is constant 0.04%.
FIG. 2 is a graph showing the relationship between the amount of metallic Ca in the desulfurizing agent and the N concentration in steel when the [Al] concentration in molten steel is constant 0.04%.
FIG. 3 is a graph showing the performance of a CaO-based desulfurizing agent in relation to the Ca content of the desulfurizing agent and the Al concentration in the molten steel.
Claims (2)
７×［Ａｌ］＋５．１≧（Ｃａ）≧０．９４×［Ａｌ］＋０．３４ （１）
ただし、［Ａｌ］：溶鋼中のＡｌ濃度（質量％）、
（Ｃａ）：脱硫剤中の金属Ｃａ濃度（質量％）。A desulfurization agent for desulfurizing molten steel having an Al concentration in a molten steel of 0.005 mass% or more and 0.7 mass% or less, the desulfurization agent containing CaO and metal Ca, and the content of the metal Ca is the following ( 1) A desulfurization agent for molten steel desulfurization characterized by satisfying the formula:
7 × [Al] + 5.1 ≧ (Ca) ≧ 0.94 × [Al] +0.34 (1)
However, [Al]: Al concentration in molten steel (mass%),
(Ca): Metal Ca concentration (% by mass) in the desulfurization agent.
７×［Ａｌ］＋５．１＞（Ｃａ）＞５×［Ａｌ］＋１．４ （２）
ただし、［Ａｌ］：溶鋼中のＡｌ濃度（質量％）、
（Ｃａ）：脱硫剤中の金属Ｃａ濃度（質量％）。A desulfurization agent for desulfurizing molten steel having an Al concentration in a molten steel of 0.005 mass% or more and 0.7 mass% or less, the desulfurization agent containing CaO and metal Ca, and the content of the metal Ca is the following ( 2) A desulfurizing agent for molten steel desulfurization characterized by satisfying the formula:
7 × [Al] +5.1>(Ca)> 5 × [Al] +1.4 (2)
However, [Al]: Al concentration in molten steel (mass%),
(Ca): Metal Ca concentration (% by mass) in the desulfurization agent.
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| LAPS | Cancellation because of no payment of annual fees |