JP2016141871A - Desulfurizing agent for molten steel and desulfurizing method - Google Patents
Desulfurizing agent for molten steel and desulfurizing method Download PDFInfo
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本発明は、環流型真空脱ガス装置にて、Ｆを用いずに効率的かつ安定的に極低硫鋼を溶製することができる溶鋼の脱硫剤、およびその脱硫剤を用いる溶鋼の脱硫方法に関する。 The present invention relates to a desulfurizing agent for molten steel capable of efficiently and stably melting ultra-low sulfur steel without using F in a reflux-type vacuum degassing apparatus, and a method for desulfurizing molten steel using the desulfurizing agent. About.
近年、溶鋼の高純度化に対する要求が高まっており、特にＳに関して、１０ｐｐｍ以下の極低硫鋼を溶製するためには溶銑脱硫だけでは不十分であり、溶鋼段階での脱硫プロセスが必須となる。溶鋼段階での脱硫手法として、例えばＲＨ等の環流型真空脱ガス装置の真空槽内に吸引された溶鋼の表面に、キャリアガスとともにＣａＯを含有する脱硫剤を吹付けて脱硫処理を施す手法が挙げられる。また、左記脱硫処理における溶鋼の脱硫剤の多くはＣａＦ２等のＦを含有している。Ｆは脱硫剤の溶融性および流動性を大きく向上させるため、高脱硫能を発現させるための必須成分の一つであったが、近年では環境ならびに操業の負荷軽減の観点からＦの使用が規制されつつあり、Ｆを使用しない脱硫剤を用いた極低硫鋼溶製技術の開発が望まれている。 In recent years, there has been an increasing demand for high purity of molten steel, and in particular with regard to S, hot metal desulfurization is not enough to produce ultra-low sulfur steel of 10 ppm or less, and a desulfurization process at the molten steel stage is essential. Become. As a desulfurization technique at the molten steel stage, for example, there is a technique in which a desulfurization treatment containing a carrier gas and a desulfurization agent containing CaO is sprayed on the surface of molten steel sucked into a vacuum tank of a recirculating vacuum degassing apparatus such as RH. Can be mentioned. Moreover, most of the desulfurization agents for molten steel in the desulfurization treatment described on the left contain F such as CaF 2 . F has been one of the essential ingredients for developing high desulfurization ability in order to greatly improve the meltability and fluidity of the desulfurization agent. However, in recent years, the use of F has been restricted from the viewpoint of reducing the environmental and operational burdens. Therefore, development of an ultra-low sulfur steel melting technology using a desulfurizing agent that does not use F is desired.
ところで、溶鋼の脱硫を促進させる手法として、脱硫剤の脱硫能の指標であるサルファイドキャパシティの増加、脱硫剤の溶融性および流動性の確保、溶鋼の酸素活量低減等が知られている。また、一般的に脱硫剤中ＣａＯの活量が高いほどサルファイドキャパシティは高位となることが知られている。 By the way, as a technique for promoting desulfurization of molten steel, an increase in sulfide capacity, which is an index of the desulfurization ability of the desulfurizing agent, ensuring meltability and fluidity of the desulfurizing agent, and a reduction in oxygen activity of the molten steel are known. In general, it is known that the higher the activity of CaO in the desulfurizing agent, the higher the sulfide capacity.
Ｆを含有しない脱硫剤として、例えば特許文献１には、ＣａＯ、Ａｌ２Ｏ３およびＳｉＯ２を基本組成として、Ｎａ２Ｏに代表されるアルカリ金属酸化物を配合させることを特徴とする環境保全溶鋼脱硫フラックスが開示されている。これは、アルカリ金属酸化物は脱硫剤のサルファイドキャパシティを増加させ、さらには脱硫剤の粘性を低下させる効果があるため、アルカリ金属酸化物の配合による脱硫反応の大幅な促進を期待したものである。
As a desulfurization agent not containing F, for example,
しかしながら、アルカリ金属酸化物は極めて反応性が高いため、溶鋼温度で容易に蒸発してしまうことに加え、溶鋼中のＡｌにより還元されてＡｌ２Ｏ３が生成する。脱硫剤中のＡｌ２Ｏ３はＣａＯの溶融を促進させるために必要であるが、Ａｌ２Ｏ３が過剰に存在すると脱硫剤のサルファイドキャパシティを大きく低下させるため、アルカリ金属酸化物の配合量によっては脱硫能が寧ろ低下する懸念がある。 However, since alkali metal oxides are extremely reactive, they easily evaporate at the molten steel temperature and are reduced by Al in the molten steel to produce Al 2 O 3 . Al 2 O 3 in the desulfurizing agent is necessary for promoting the melting of CaO. However, if Al 2 O 3 is excessively present, the sulfide capacity of the desulfurizing agent is greatly reduced. Depending on the case, there is a concern that the desulfurization ability may rather decrease.
また、特許文献２には、ＣａＯと、ＣａあるいはＣａ合金を配合した脱硫剤を真空脱ガス装置の真空槽内に吸引された溶鋼に吹付けることを特徴とする溶鋼の減圧下脱硫方法が開示されている。これは、脱硫反応は溶鋼の酸素活量が低位であるほど顕著に生じるため、酸素との親和力が強いＣａを配合させることで脱硫剤周囲を局所的に低酸素活量とし、脱硫反応を促進させるという考えに基づいている。 Patent Document 2 discloses a desulfurization method for molten steel under reduced pressure, characterized by spraying a desulfurization agent containing CaO and Ca or a Ca alloy onto molten steel sucked into a vacuum tank of a vacuum degassing apparatus. Has been. This is because the desulfurization reaction occurs more markedly as the oxygen activity of the molten steel is lower, so by adding Ca that has a strong affinity for oxygen, the desulfurization agent area is locally reduced to promote the desulfurization reaction. Based on the idea of letting
しかしながら、Ｃａは極めて歩留りが悪い事に加え、鋼種によってはＣａを添加できないものもあり、全ての鋼種に適用できるわけではない。 However, in addition to the extremely poor yield of Ca, some steel types cannot add Ca, and are not applicable to all steel types.
さらに、特許文献３には、ＣａＯを主成分とするフラックスに、Ａｌ、Ｃａ、ＳｉおよびＴｉ、ならびにそれらの混合物および合金のうち１種または２種以上を１〜２０質量％含有する脱硫剤を用いることを特徴とする極低硫鋼の製造方法が開示されている。この技術も特許文献２と同様、酸素との親和力が強い元素を配合させて脱硫剤周囲を局所的に低酸素活量とし、脱硫を促進させるというものである。 Furthermore, Patent Document 3 includes a desulfurizing agent containing 1 to 20% by mass of one or more of Al, Ca, Si and Ti, and mixtures and alloys thereof in a flux mainly composed of CaO. A method for producing ultra-low-sulfur steel, characterized by being used, is disclosed. In this technique, similarly to Patent Document 2, an element having a strong affinity for oxygen is blended to locally reduce the desulfurizing agent to have a low oxygen activity, thereby promoting desulfurization.
しかしながら、例えばＡｌ、ＳｉおよびＴｉといったＣａ以外の元素を配合した場合、これらの配合比によっては脱硫剤周囲の局所的な脱酸で生成した酸化物により脱硫剤のサルファイドキャパシティが大きく低下する懸念がある。また、局所脱酸を効率的に発現させるための溶鋼組成や脱硫剤供給速度等の条件が明示されておらず、条件によっては脱硫不良が生じる懸念がある。 However, for example, when elements other than Ca such as Al, Si, and Ti are blended, the sulfide capacity of the desulfurizing agent may be greatly reduced by oxides generated by local deoxidation around the desulfurizing agent depending on the blending ratio. There is. In addition, conditions such as a molten steel composition and a desulfurization agent supply rate for efficiently expressing local deoxidation are not specified, and depending on the conditions, there is a concern that poor desulfurization may occur.
上記したように、Ｆを使用しない脱硫剤および脱硫方法として、Ｆを使用しない代わりにアルカリ金属の酸化物を用いたり、Ｃａを用いたりする方法が知られているが、それらはそれぞれに別の課題を有している。また、Ｃａ以外のＡｌ、ＳｉおよびＴｉといった元素を脱硫剤に配合して溶鋼を局所的に脱酸する方法も知られているが、局所脱酸を効率的に発現させる条件が不明である。したがって、従来の手法では、Ｆを使用せずに安定して極低硫鋼を溶製することは困難であった。そこで本発明は、Ｆを使用せず、かつアルカリ金属の酸化物もＣａも使用せずに、安定的に極低硫鋼を溶製可能な脱硫剤および脱硫方法を提供することを目的とする。 As described above, as a desulfurization agent and a desulfurization method that does not use F, there are known methods in which an alkali metal oxide is used instead of F, or Ca is used. Has a problem. Moreover, although the method of mix | blending elements, such as Al, Si, and Ti other than Ca, with a desulfurization agent and deoxidizing molten steel locally is known, the conditions for expressing local deoxidation efficiently are unknown. Therefore, with the conventional method, it has been difficult to stably produce ultra-low sulfur steel without using F. Accordingly, an object of the present invention is to provide a desulfurization agent and a desulfurization method capable of stably melting an ultra-low sulfur steel without using F and without using an alkali metal oxide or Ca. .
本発明においては、環流型真空脱ガス装置にてＦを使用せずに安定して極低硫鋼を溶製するために、先ず適切な脱硫剤の組成を選定し、その上でその脱硫剤を供給する際の溶鋼組成およびその脱硫剤の供給速度を適切に調整する。本発明に係る要件を満たして脱硫剤を添加することにより、脱硫剤添加時にその周囲で生じる溶鋼の局所脱酸と、その脱酸後の脱硫剤のサルファイドキャパシティの変化とが適切に組み合わされて、溶鋼の脱硫処理に好適な脱硫条件を具現化することができる。 In the present invention, in order to stably melt ultra-low sulfur steel without using F in a reflux type vacuum degassing apparatus, first, an appropriate composition of a desulfurizing agent is selected, and then the desulfurizing agent is selected. The molten steel composition and the supply rate of the desulfurizing agent are appropriately adjusted. By adding the desulfurizing agent satisfying the requirements of the present invention, the local deoxidation of the molten steel generated around the desulfurizing agent and the change in the sulfide capacity of the desulfurizing agent after the deoxidation are appropriately combined. Thus, desulfurization conditions suitable for the desulfurization treatment of molten steel can be realized.
本発明の要旨を、以下に記載の（１）〜（３）に纏めて示す。
（１）質量％で、ＣａＯとＡｌ２Ｏ３が合計で７０％以上、金属ＡｌおよびＡｌ合金のいずれか一方または両方がＡｌ純分の合計で３〜１０％、ＭｇＯおよびＳｉＯ２のいずれか一方または両方が合計で５〜２０％、かつＣａＯ、Ａｌ２Ｏ３およびＡｌの配合量が（１）式を満たし、Ｆを含有しない組成を有することを特徴とする溶鋼の脱硫剤。
The gist of the present invention is summarized in (1) to (3) described below.
(1) By mass%, CaO and Al 2 O 3 are 70% or more in total, and either one or both of metal Al and Al alloy is 3 to 10% in total of pure Al, MgO and SiO 2 A desulfurizing agent for molten steel, wherein one or both are 5 to 20% in total, and the compounding amount of CaO, Al 2 O 3 and Al satisfies the formula (1) and does not contain F.
１．３≦（％ＣａＯ）／｛（％Ａｌ２Ｏ３）＋０．９×（％Ａｌ）｝≦２．０
・・・（１）
（１）式中、（％Ａｌ２Ｏ３）：脱硫剤中Ａｌ２Ｏ３濃度（質量％）、（％Ａｌ）：脱硫剤中Ａｌ濃度（質量％）、（％ＣａＯ）：脱硫剤中ＣａＯ濃度（質量％）である。
1.3 ≦ (% CaO) / {(% Al 2 O 3 ) + 0.9 × (% Al)} ≦ 2.0
... (1)
(1) In the formula, (% Al 2 O 3 ): Al 2 O 3 concentration (% by mass) in the desulfurizing agent, (% Al): Al concentration (% by mass) in the desulfurizing agent, (% CaO): in the desulfurizing agent CaO concentration (% by mass).
（２）環流型真空脱ガス装置の真空槽内に吸引された溶鋼の表面に、上記（１）項に記載の溶鋼の脱硫剤をキャリアガスとともに吹き付けて供給する溶鋼の脱硫方法であって、
前記脱硫剤を吹き付ける前の溶鋼中ｓｏｌ．Ａｌ濃度を０．０１〜０．０７質量％に調整しておくことを特徴とする溶鋼の脱硫方法。
(2) A molten steel desulfurization method in which the molten steel desulfurization agent described in the above (1) is sprayed together with a carrier gas and supplied to the surface of the molten steel sucked into the vacuum tank of the reflux vacuum degassing apparatus,
In the molten steel before spraying the desulfurizing agent, sol. A desulfurization method for molten steel, wherein the Al concentration is adjusted to 0.01 to 0.07 mass%.
（３）上記（１）項に記載の溶鋼の脱硫剤を前記溶鋼の表面に吹き付けて供給するに際し、その供給速度を（２）式に示す範囲で調整することを特徴とする、上記（２）項に記載の溶鋼の脱硫方法。 (3) When supplying the molten steel desulfurizing agent described in the above item (1) by spraying on the surface of the molten steel, the supply speed is adjusted within the range shown in the expression (2), The method for desulfurizing molten steel as described in the item).
５ ≦Ｖ×（％Ａｌ）≦１０ ・・・（２）
（２）式中、Ｖ：脱硫剤の供給速度（ｋｇ／ｍｉｎ／ｔｏｎ）、（％Ａｌ）：脱硫剤中Ａｌ濃度（質量％）である。
5 ≦ V × (% Al) ≦ 10 (2)
(2) In the formula, V: supply rate of desulfurization agent (kg / min / ton), (% Al): Al concentration (% by mass) in the desulfurization agent.
本発明者らは、脱硫剤周囲の局所脱酸を実現し得る元素としてＡｌに着目し、脱硫剤中のＡｌ配合量、さらには脱硫剤供給時の溶鋼組成および供給速度を適正に制御することで本課題を解決可能と考えた。 The present inventors pay attention to Al as an element that can realize local deoxidation around the desulfurizing agent, and appropriately control the amount of Al compounded in the desulfurizing agent, and the molten steel composition and supply rate when supplying the desulfurizing agent. I thought that this problem could be solved.
まず、ＣａＯを含む脱硫剤による脱硫反応は、（３）式のようにＣａＯとＳの反応で進行する。 First, a desulfurization reaction with a desulfurization agent containing CaO proceeds by a reaction of CaO and S as shown in equation (3).
ＣａＯ＋Ｓ＝ＣａＳ＋Ｏ ・・・（３）
ただし、ＣａＯは溶鋼温度で固体であるため、脱硫剤にＡｌ２Ｏ３等を含有させることで低融点化し、脱硫反応に寄与する液相を確保する必要がある。
CaO + S = CaS + O (3)
However, since CaO is solid at the molten steel temperature, it is necessary to ensure a liquid phase that contributes to the desulfurization reaction by lowering the melting point by adding Al 2 O 3 or the like to the desulfurization agent.
一方で、脱硫剤中のＡｌによる局所脱酸反応は、脱硫剤周囲の溶存酸素との反応である（４）式、ＣａＯの還元反応である（５）式の２つにより進行する。 On the other hand, the local deoxidation reaction by Al in the desulfurizing agent proceeds by two formulas (4), which is a reaction with dissolved oxygen around the desulfurizing agent, and (5), which is a reduction reaction of CaO.
２Ａｌ＋３Ｏ＝Ａｌ２Ｏ３ ・・・（４）
３ＣａＯ＋２Ａｌ＝３Ｃａ＋Ａｌ２Ｏ３ ・・・（５）
Ａｌ配合による脱硫促進は、上記反応による脱硫剤周囲の低酸素化に加え、Ａｌ２Ｏ３生成によるＣａＯ−Ａｌ２Ｏ３溶融相の形成促進によるものである。しかしながら、上記反応を過剰に生じさせてしまうと脱硫剤のＡｌ２Ｏ３濃度が大きく増加し、サルファイドキャパシティが大きく低下する可能性がある。本発明者らは、脱硫剤中のＣａＯ、Ａｌ２Ｏ３およびＡｌの配合量を（１）式の範囲に制御することで、高脱硫能を維持しながらＡｌによる脱硫促進効果を活用可能であることを見出した。（１）式は、脱硫剤中Ａｌの脱酸反応によるＡｌ２Ｏ３生成量を考慮した、脱硫反応後の脱硫剤のＣａＯおよびＡｌ２Ｏ３の濃度比であり、（％Ａｌ）に係る係数は配合したＡｌの５０％がＡｌ２Ｏ３になると仮定した値である。
2Al + 3O = Al 2 O 3 (4)
3CaO + 2Al = 3Ca + Al 2 O 3 (5)
The desulfurization acceleration by Al blending is due to the promotion of formation of a CaO—Al 2 O 3 melt phase by the generation of Al 2 O 3 in addition to the reduction of oxygen around the desulfurization agent by the above reaction. However, if the above reaction is caused excessively, the concentration of Al 2 O 3 in the desulfurizing agent is greatly increased, and the sulfide capacity may be greatly decreased. The present inventors can utilize the effect of promoting desulfurization by Al while maintaining high desulfurization ability by controlling the blending amount of CaO, Al 2 O 3 and Al in the desulfurization agent within the range of the formula (1). I found out. The formula (1) is a concentration ratio of CaO and Al 2 O 3 of the desulfurization agent after the desulfurization reaction in consideration of the amount of Al 2 O 3 produced by the deoxidation reaction of Al in the desulfurization agent, and relates to (% Al) The coefficient is a value assuming that 50% of the blended Al becomes Al 2 O 3 .
また、本発明者らは、Ａｌ配合による局所脱酸で脱硫剤表面に酸化物が生成し、生成した酸化物により脱硫剤の粗度が増加することによって、溶鋼−脱硫剤間の反応界面積が増大し、脱硫反応速度が大きく増加することを見出した。 In addition, the present inventors generated an oxide on the surface of the desulfurizing agent by local deoxidation by Al compounding, and the generated oxide increases the roughness of the desulfurizing agent, thereby causing a reaction interface area between the molten steel and the desulfurizing agent. And the desulfurization reaction rate was greatly increased.
一般的に脱硫反応を促進させるためには、溶鋼中Ａｌ濃度を高めて低酸素活量として平衡Ｓ濃度を下げることが有効とされてきたが、Ａｌ濃度を過剰に高めてもその効果は飽和するため、上記手法で脱硫反応速度を増加させることで更なる低硫化が可能と考えた。ただし、左記の効果を発現させるためには（４）式反応を促進させる必要があり、添加する脱硫剤の組成を適切化する必要があるとともに、溶鋼中の脱酸元素であるＡｌ濃度の適正化により好適な溶存酸素濃度を調整して確保しておくことが好ましい。 In general, in order to accelerate the desulfurization reaction, it has been effective to increase the Al concentration in molten steel and lower the equilibrium S concentration as a low oxygen activity, but the effect is saturated even if the Al concentration is increased excessively. Therefore, it was considered that further low sulfurization is possible by increasing the desulfurization reaction rate by the above method. However, in order to achieve the effects described on the left, it is necessary to promote the reaction (4), it is necessary to optimize the composition of the desulfurizing agent to be added, and the proper concentration of Al as the deoxidizing element in the molten steel It is preferable to adjust and secure a suitable dissolved oxygen concentration by the conversion.
さらに、局所脱酸反応の駆動力は単位時間当たりのＡｌ供給量、すなわちＡｌ供給速度に依存する。Ａｌ供給速度は下記（６）式で表され、脱硫剤中Ａｌ濃度が変数として含まれることから、高い脱硫能を安定して得るためには、Ａｌの配合量が少ない脱硫剤は配合量が多いものと比較して供給速度を大きくするよう調整することが一層好ましい。
ＶＡｌ＝Ｖ×（％Ａｌ）／１００ ・・・（６）
ここで、（６）式中、ＶＡｌ：Ａｌ供給速度（ｋｇ／ｍｉｎ／ｔｏｎ）、Ｖ：脱硫剤の供給速度（ｋｇ／ｍｉｎ／ｔｏｎ）である。
Furthermore, the driving force of the local deoxidation reaction depends on the Al supply amount per unit time, that is, the Al supply rate. The Al supply rate is expressed by the following formula (6), and since the Al concentration in the desulfurizing agent is included as a variable, in order to stably obtain a high desulfurizing ability, a desulfurizing agent with a small amount of Al has a compounding amount. It is more preferable to adjust so as to increase the supply speed as compared with many.
V Al = V × (% Al) / 100 (6)
Here, in the formula (6), V Al : Al supply rate (kg / min / ton) and V: desulfurization agent supply rate (kg / min / ton).
上記の考え方から、本発明者らは、（２）式で表されるＶ×（％Ａｌ）には適正範囲が存在する知見を得て、上記本発明（３）を完成させた。 From the above idea, the present inventors have obtained the knowledge that an appropriate range exists in V × (% Al) represented by the formula (2), and completed the present invention (3).
本発明によれば、Ｆを使用することなく、さらには設備の増設を行うことなく、適切な組成に調整した脱硫剤を用いることによって、安定して極低硫鋼を溶製することが可能になる。さらに、脱硫剤供給時の溶鋼組成および供給速度を適正化することによって、本発明に係る脱硫剤の溶鋼低硫化効果を一層効果的に発揮することができるようになる。 According to the present invention, ultra-low sulfur steel can be stably melted by using a desulfurizing agent adjusted to an appropriate composition without using F and without adding equipment. become. Furthermore, by optimizing the molten steel composition and the supply rate at the time of supplying the desulfurizing agent, the molten steel low-sulfurizing effect of the desulfurizing agent according to the present invention can be more effectively exhibited.
以下に本発明について説明する。以下に説明する環流型真空脱ガス装置とは、一般的にＲＨと呼称される真空槽を有する溶鋼処理装置であり、環流処理とは、環流型真空脱ガス装置にて溶鋼を環流させる処理のことを指す。また、「局所脱酸反応」とは、配合したＡｌにより脱硫剤近傍で生じる上記（４）、（５）式に示す脱酸反応を指すものである。 The present invention will be described below. The recirculation-type vacuum degassing apparatus described below is a molten steel processing apparatus having a vacuum tank generally called RH, and the recirculation process is a process of recirculating molten steel with a recirculation-type vacuum degassing apparatus. Refers to that. The “local deoxidation reaction” refers to the deoxidation reaction represented by the above formulas (4) and (5) generated in the vicinity of the desulfurizing agent by the blended Al.
（本発明に係る脱硫剤組成）
以下、本発明に係る脱硫剤組成について説明する。
(Desulfurization agent composition according to the present invention)
Hereinafter, the desulfurization agent composition according to the present invention will be described.
［ＣａＯとＡｌ２Ｏ３が合計で７０質量％以上］
ＣａＯは（３）式の脱硫反応に必要不可欠であり、かつＡｌ２Ｏ３は脱硫剤の液相の確保に必要である。したがって、ＣａＯとＡｌ２Ｏ３が少なすぎると脱硫剤の脱硫能が大きく低下する懸念があり、これらが合計で脱硫剤の全質量に対して７０質量％以上含有されている必要がある。
[CaO and Al 2 O 3 total 70% by mass or more]
CaO is indispensable for the desulfurization reaction of the formula (3), and Al 2 O 3 is necessary for securing the liquid phase of the desulfurizing agent. Therefore, there is a concern that the desulfurization capacity of when the CaO and Al 2 O 3 is too small desulfurizing agent is greatly reduced, it is necessary that these are contained more than 70% by weight relative to the total weight of the desulfurizing agent in total.
［金属ＡｌおよびＡｌ合金のいずれか一方または両方がＡｌ純分の合計で３〜１０質量％］
本発明において、「金属Ａｌ」とは純度が９９．９％以上のＡｌを表す。「Ａｌ合金」としては、例えば、Ａｌ濃度が３０〜６０質量％のＦｅＡｌが挙げられる。本発明においては金属Ｃａを使用しないため、ＣａＡｌ等は対象外である。また、「Ａｌ純分の合計」は、金属ＡｌやＡｌ合金の質量も脱硫剤の全質量中に含まれているために、金属ＡｌやＡｌ合金に含まれるＡｌの合計質量が脱硫剤の全質量に対して占める比率を質量％で表す。
[Any one or both of metal Al and Al alloy is a total of 3 to 10% by mass of pure Al]
In the present invention, “metal Al” represents Al having a purity of 99.9% or more. Examples of the “Al alloy” include FeAl having an Al concentration of 30 to 60% by mass. In the present invention, metal Ca is not used, so CaAl or the like is excluded. In addition, since “total Al content” includes the mass of metal Al or Al alloy in the total mass of the desulfurization agent, the total mass of Al contained in the metal Al or Al alloy is the total mass of the desulfurization agent. The ratio with respect to the mass is expressed by mass%.
脱硫剤中のＡｌは上記局所脱酸反応を生じさせるために必要であるが、３質量％未満の配合では効果が表れないため、少なくとも３質量％以上配合させる必要がある。一方で、Ａｌを１０質量％を超えて配合させても局所脱酸反応の効果が飽和することに加え、Ａｌ２Ｏ３が溶鋼−脱硫剤界面に過剰に濃化して脱硫反応を阻害してしまう懸念があるため、１０質量％を上限とする。 Al in the desulfurizing agent is necessary for causing the above-mentioned local deoxidation reaction. However, since the effect is not exhibited when the amount is less than 3% by mass, it is necessary to add at least 3% by mass. On the other hand, even if Al is added in an amount exceeding 10% by mass, the effect of the local deoxidation reaction is saturated, and Al 2 O 3 is excessively concentrated at the molten steel-desulfurization agent interface to inhibit the desulfurization reaction. Therefore, the upper limit is 10% by mass.
［ＣａＯ、Ａｌ２Ｏ３およびＡｌ濃度の関係：（１）式］
上記したように、（１）式は脱硫剤中Ａｌの脱酸反応によるＡｌ２Ｏ３生成量を考慮した、脱硫反応後のＣａＯ／Ａｌ２Ｏ３濃度比である。ＣａＯ−Ａｌ２Ｏ３系スラグは、１８７３ＫにおいてＣａＯ／Ａｌ２Ｏ３濃度比がおよそ１．３以上でＣａＯ飽和組成（ＣａＯ活量＝１）となり、高脱硫能が維持される。しかしながら、ＣａＯ／Ａｌ２Ｏ３濃度比が１．３を下回るとＣａＯ活量が著しく低下してしまうことから、（１）式の下限は１．３とした。一方で、ＣａＯ／Ａｌ２Ｏ３濃度比が高すぎると脱硫反応に寄与する液相量が大きく低下してしまうことから、（１）式の上限は２．０とする必要がある。
[Relationship between CaO, Al 2 O 3 and Al concentration: Formula (1)]
As described above, the formula (1) is the CaO / Al 2 O 3 concentration ratio after the desulfurization reaction in consideration of the amount of Al 2 O 3 produced by the deoxidation reaction of Al in the desulfurization agent. The CaO—Al 2 O 3 -based slag has a CaO saturated composition (CaO activity = 1) at a CaO / Al 2 O 3 concentration ratio of about 1.3 or more at 1873K, and maintains a high desulfurization ability. However, when the CaO / Al 2 O 3 concentration ratio is less than 1.3, the CaO activity is significantly reduced, so the lower limit of the formula (1) is set to 1.3. On the other hand, if the CaO / Al 2 O 3 concentration ratio is too high, the amount of liquid phase that contributes to the desulfurization reaction is greatly reduced, so the upper limit of the formula (1) needs to be 2.0.
［ＭｇＯおよびＳｉＯ２のいずれか一方または両方が合計で５〜２０質量％］
上記脱硫剤は、脱硫剤の溶解を促進するため、ＭｇＯおよびＳｉＯ２のいずれか一方または両方を合計で、脱硫剤の全質量に対して５〜２０質量％含有する。これらの成分は、適度に含有させることによって脱硫剤の溶解を促進するものであって、本発明に係る脱硫剤の組成範囲においては５〜２０質量％程度含有させることが適当である。この濃度が５質量％未満では脱硫剤の溶解促進効果を十分に発揮することができない。一方、２０質量％を超えるとＣａＯやＡｌ２Ｏ３およびＡｌという、本発明に係る脱硫剤としての基本的成分の濃度が低下してしまい、脱硫能が低下する。ＭｇＯとＳｉＯ２との配合比は特に限定されないが、ＳｉＯ２は脱硫剤のサルファイドキャパシティを低下させる成分であることから、１５：５〜１０：１０であることが望ましい。
[Any one or both of MgO and SiO 2 is 5 to 20% by mass in total]
In order to promote dissolution of the desulfurizing agent, the desulfurizing agent contains either one or both of MgO and SiO 2 in a total amount of 5 to 20% by mass with respect to the total mass of the desulfurizing agent. These components promote the dissolution of the desulfurizing agent by appropriately containing them, and it is appropriate to contain about 5 to 20% by mass in the composition range of the desulfurizing agent according to the present invention. If this concentration is less than 5% by mass, the effect of promoting the dissolution of the desulfurizing agent cannot be sufficiently exhibited. On the other hand, if it exceeds 20% by mass, the concentration of basic components as the desulfurization agent according to the present invention, such as CaO, Al 2 O 3 and Al, is lowered, and the desulfurization ability is lowered. The mixing ratio of MgO and SiO 2 is not particularly limited, but it is preferably 15: 5 to 10:10 because SiO 2 is a component that lowers the sulfide capacity of the desulfurizing agent.
なお、本発明で使用する脱硫剤は環境ならびに操業の負荷軽減の観点からＦを含有しないほか、本発明に係る背景技術の説明に記載した従来技術の問題点を回避する観点から、アルカリ金属の酸化物や金属Ｃａを含まない。 In addition, the desulfurizing agent used in the present invention does not contain F from the viewpoint of reducing the environmental and operational load, and from the viewpoint of avoiding the problems of the prior art described in the background art description of the present invention, Does not contain oxide or metal Ca.
但し、不純物として、Ａｌを合金で添加する場合におけるＦｅ等の合金成分を脱硫剤の全質量に対して１０質量％以下含むことがあるほか、ＣａＯ、Ａｌ２Ｏ３、ＭｇＯおよびＳｉＯ２の原材料から混入することがある酸化鉄やＴｉＯ２等の成分を１質量％以下含有する。したがって、本発明に係る脱硫剤の必須成分であるＣａＯ、Ａｌ２Ｏ３、ＭｇＯ、ＳｉＯ２およびＡｌの５成分の合計濃度は、脱硫剤の全質量に対して８９質量％以上となる。
However, in the case where Al is added as an impurity as an impurity, an alloy component such as Fe may be contained in an amount of 10% by mass or less based on the total mass of the desulfurizing agent, and raw materials of CaO, Al 2 O 3 , MgO and SiO 2 is contains iron oxide and components such as
（本発明に係る脱硫剤を吹き付ける前の溶鋼組成）
次に、以上の様な組成の脱硫剤を溶鋼に吹付ける前の溶鋼組成について説明する。
(The molten steel composition before spraying the desulfurization agent according to the present invention)
Next, the molten steel composition before spraying the desulfurizing agent having the above composition on the molten steel will be described.
［ｓｏｌ．Ａｌ：０．０１〜０．０７質量％］
上記したように、Ａｌ配合による局所脱酸反応で脱硫剤表面の粗度を増加させ、脱硫反応速度を向上させる観点からは、適度に溶存酸素を調整して確保しておくことが好ましいと考えられる。一般的にｓｏｌ．Ａｌ濃度が高いほど溶存酸素が低位となり、脱硫に有利とされているが、ｓｏｌ．Ａｌ濃度を増加させすぎると局所脱酸に利用される溶存酸素が著しく低下することから、０．０７質量％を上限、望ましくは０．０５質量％を上限とすることが好ましい。一方で、ｓｏｌ．Ａｌ濃度が少なすぎると溶存酸素が大きく増加し、脱硫反応が停滞する懸念があることから０．０１質量％を下限とすることが好ましい。
[Sol. Al: 0.01 to 0.07% by mass]
As described above, from the viewpoint of increasing the roughness of the surface of the desulfurizing agent by the local deoxidation reaction by Al blending and improving the desulfurization reaction rate, it is preferable to appropriately adjust and ensure dissolved oxygen. It is done. In general, sol. The higher the Al concentration, the lower the dissolved oxygen, which is advantageous for desulfurization. If the Al concentration is increased too much, the dissolved oxygen used for local deoxidation is significantly reduced, so 0.07% by mass is the upper limit, preferably 0.05% by mass. On the other hand, sol. If the Al concentration is too low, dissolved oxygen will increase greatly, and there is a concern that the desulfurization reaction will stagnate, so it is preferable to set 0.01% by mass as the lower limit.
なお、本発明ではＡｌによる溶鋼の局所脱酸に着目し、併せて溶鋼中の好ましいＡｌ濃度を上記のように定めているが、Ｓｉも溶鋼を脱酸する。そこで、もしＳｉをＡｌと共に溶鋼に含有させるなら、０．１０質量％以下とすることが好ましい。０．１０質量％を超えて含有されるとＳｉ脱酸がＡｌ脱酸よりも優勢となり、Ａｌによる局所脱酸反応が活用できなくなる懸念がある。 In the present invention, attention is focused on local deoxidation of the molten steel with Al, and a preferable Al concentration in the molten steel is determined as described above, but Si also deoxidizes the molten steel. Therefore, if Si is contained in the molten steel together with Al, the content is preferably 0.10% by mass or less. If the content exceeds 0.10% by mass, Si deoxidation is dominant over Al deoxidation, and there is a concern that local deoxidation reaction by Al cannot be utilized.
また、ＴｉもＳｉと同様に溶鋼の脱酸剤として利用されることがあるが、０．０３質量％を超えて含有されるとＴｉ脱酸がＡｌ脱酸よりも優勢となり、Ａｌによる局所脱酸反応が活用できなくなる懸念がある。このため、Ｔｉ濃度の上限は０．０３質量％以下とすることが好ましい。 Ti may also be used as a deoxidizer for molten steel in the same way as Si. However, if it is contained in an amount exceeding 0.03% by mass, Ti deoxidation becomes dominant over Al deoxidation, and local deoxidation by Al is caused. There is concern that the acid reaction cannot be used. For this reason, it is preferable that the upper limit of Ti concentration shall be 0.03 mass% or less.
（処理条件）
次に、本発明における脱硫処理方法について説明する。
(Processing conditions)
Next, the desulfurization processing method in this invention is demonstrated.
本発明において、溶鋼を環流型真空脱ガス装置（ＲＨ）にて環流処理している最中に、ＲＨ真空槽内に挿入した上吹きランスから粉状の脱硫剤をキャリアガスとともに溶鋼表面に吹き付ける操業を例にとる。但し、本発明に係る脱硫剤の添加は、ＲＨを用いる溶鋼の環流処理中に限られないことは当然である。適度な溶鋼撹拌を伴う処理であれば、本発明に係る脱硫剤の添加効果を発揮することができる。 In the present invention, a powdered desulfurization agent is sprayed onto the surface of the molten steel together with a carrier gas from an upper blowing lance inserted into the RH vacuum tank while the molten steel is being refluxed by a circulating vacuum degassing apparatus (RH). Take operation as an example. However, as a matter of course, the addition of the desulfurizing agent according to the present invention is not limited to during the recirculation treatment of molten steel using RH. If it is the process accompanied by moderate molten steel stirring, the addition effect of the desulfurization agent which concerns on this invention can be exhibited.
ＲＨを用いて環流処理している最中に本発明に係る脱硫剤を添加する場合には、先ず転炉等の精錬容器から取鍋に出鋼する際に、副原料や合金鉄、Ａｌ等を適宜投入して溶鋼の脱酸、成分調整を行い、その後環流型真空脱ガス装置を用いて環流処理を開始する。 When adding the desulfurizing agent according to the present invention during the recirculation treatment using RH, first, when steeling from a refining vessel such as a converter to a ladle, auxiliary materials, alloy iron, Al, etc. Is appropriately added to perform deoxidation and component adjustment of the molten steel, and then the reflux treatment is started using a reflux-type vacuum degassing apparatus.
本発明においては脱硫剤吹き付け前のｓｏｌ．Ａｌ濃度を０．０１〜０．０７質量％に調整することが好ましいため、出鋼時のＡｌ添加はこの濃度を意識して行うと良い。但し、このｓｏｌ．Ａｌ濃度は、ＲＨでの環流処理の開始後に、溶鋼にＡｌを添加したり、酸素を吹き付けたりして調整することができる。Ａｌと同様な観点から、Ｓｉ濃度やＴｉ濃度も、それぞれ０．１０質量％以下、０．０３質量％以下の範囲に止めておくことが好ましい。 In the present invention, the sol. Since it is preferable to adjust the Al concentration to 0.01 to 0.07% by mass, the addition of Al at the time of steelmaking is preferably performed with this concentration in mind. However, this sol. The Al concentration can be adjusted by adding Al to the molten steel or blowing oxygen after the start of the reflux treatment with RH. From the same viewpoint as Al, it is preferable to keep the Si concentration and the Ti concentration within the ranges of 0.10% by mass or less and 0.03% by mass, respectively.
これらの溶鋼脱酸元素の濃度は、転炉からの出鋼時の溶鋼中Ｃ％が分かれば、操業経験に基づいて容易に調整することができる。 The concentration of these molten steel deoxidizing elements can be easily adjusted based on operational experience if C% in the molten steel at the time of steel removal from the converter is known.
好ましくは以上の様な成分調整を行った後、溶鋼の環流処理を継続しながら脱硫剤の吹き付けを開始する。このとき、（２）式に示す指標Ｖ×（％Ａｌ）が５以上１０以下となる条件で吹付けを行うことが一層好ましい。 Preferably, after adjusting the components as described above, spraying of the desulfurizing agent is started while continuing the reflux treatment of the molten steel. At this time, it is more preferable to perform the spraying under the condition that the index V × (% Al) shown in the formula (2) is 5 or more and 10 or less.
この好ましい条件は、上記した本発明に係る脱硫剤を用いて、後述する効果の確認方法に則り、２５０ｔｏｎの溶鋼を環流型脱ガス装置にて調査して把握した結果である。脱硫剤吹付け中の溶鋼温度を１６４０〜１６８０℃とし、脱硫剤吹付け前の溶鋼中ｓｏｌ．Ａｌ濃度を０．０１〜０．０７質量％、かつＳ濃度を０．００２６〜０．００３５質量％、脱硫剤吹付け量を溶鋼１ｔ当たりで４〜７ｋｇとした条件で、脱硫剤供給速度Ｖおよび脱硫剤中Ａｌ濃度（％Ａｌ）を変えて脱硫処理実験を行った結果を、図１に示す。 This preferable condition is a result obtained by investigating 250 ton of molten steel using a reflux type degassing apparatus in accordance with a method for confirming the effect described later using the desulfurizing agent according to the present invention. The molten steel temperature during spraying of the desulfurizing agent is set to 1640 to 1680 ° C., and the sol. Desulfurization agent supply rate V under the conditions that the Al concentration is 0.01 to 0.07 mass%, the S concentration is 0.0026 to 0.0035 mass%, and the desulfurization agent spraying amount is 4 to 7 kg per ton of molten steel. FIG. 1 shows the results of desulfurization treatment experiments performed by changing the Al concentration (% Al) in the desulfurizing agent.
図１に示した結果から、本発明に係る脱硫剤を用いることによって、以下に（７）式で示す脱硫効果の指標（脱硫ｋ値）を０．１７以上にできることが確認された。さらに、脱硫剤吹付け前の溶鋼中ｓｏｌ．Ａｌ濃度を０．０１〜０．０７質量％にした上で、先に（２）式で示した指標Ｖ×（％Ａｌ）が５〜１０の範囲では、その脱硫ｋ値を０．２０以上と一層高くすることができると分かった。 From the results shown in FIG. 1, it was confirmed that by using the desulfurizing agent according to the present invention, the desulfurization effect index (desulfurization k value) represented by the following formula (7) can be 0.17 or more. Further, the sol. When the Al concentration is set to 0.01 to 0.07% by mass and the index V × (% Al) previously indicated by the formula (2) is in the range of 5 to 10, the desulfurization k value is 0.20 or more. I found that it could be even higher.
この（２）式指標が５を下回ると、Ａｌ供給量が不足して局所脱酸反応が効率的に活用できておらず、Ｓが十分に低減できなかったと考えられる。そこで、（２）式指標の下限は５とした。一方、（２）式指標が１０を上回ると、局所脱酸反応が過剰に生じて脱硫剤周囲にＡｌ２Ｏ３が濃化し、Ｓが十分に低減できなかったと考えられる。そこで、（２）式指標Ｖ×（％Ａｌ）の上限は１０とした。 When this (2) type | formula index is less than 5, Al supply amount is insufficient, local deoxidation reaction cannot be utilized efficiently, and it is thought that S could not be reduced sufficiently. Therefore, the lower limit of the formula (2) index is set to 5. On the other hand, when the formula (2) index exceeds 10, it is considered that local deoxidation reaction occurs excessively, Al 2 O 3 is concentrated around the desulfurizing agent, and S cannot be sufficiently reduced. Therefore, the upper limit of the formula (2) index V × (% Al) is set to 10.
（効果の確認方法）
本発明の効果は、（７）式で表される脱硫ｋ値によって判断した。
(How to check the effect)
The effect of the present invention was judged by the desulfurization k value represented by the formula (7).
脱硫ｋ値＝ｌｎ（［％Ｓ］脱硫剤前／［％Ｓ］脱硫剤後）／脱硫剤原単位・・・（７）
ここで、（７）式中、［％Ｓ］脱硫剤後：脱硫剤吹付け後の溶鋼中Ｓ濃度（質量％）、［％Ｓ］脱硫剤前：脱硫剤吹付け前の溶鋼中Ｓ濃度（質量％）である。本発明において、脱硫剤吹付け直前および直後に採取した溶鋼サンプルから得られたＳ濃度に基づいて上記脱硫ｋ値を算出し、脱硫ｋ値が０．１７以上であった場合を発明の効果があり、さらに０．２０以上であった場合を顕著に効果が得られたと判断した。
Desulfurization k value = ln ([% S] before desulfurization agent / after [% S] desulfurization agent ) / desulfurization agent basic unit (7)
Here, in the formula (7), after [% S] desulfurizing agent : S concentration (mass%) in the molten steel after spraying the desulfurizing agent, [% S] before desulfurizing agent: S concentration in the molten steel before spraying the desulfurizing agent. (Mass%). In the present invention, the desulfurization k value is calculated based on the S concentration obtained from the molten steel sample taken immediately before and immediately after the desulfurization agent spraying, and the effect of the invention is obtained when the desulfurization k value is 0.17 or more. In addition, it was judged that the effect was remarkably obtained when it was 0.20 or more.
まず、転炉から２５０ｔの溶鋼を出鋼し、その最中からＲＨ真空脱ガス装置にて脱硫剤を吹き付けるまでの段階で、副原料や合金鉄、Ａｌ等を適宜投入して溶鋼の脱酸、成分調整を行い、以下の表１に示す組成の溶鋼を得た。次に、成分調整を終え、溶鋼温度を１６４０〜１６８０℃に調整した溶鋼に対し、表１に記載の脱硫剤を溶鋼に吹き付けて、脱硫処理を開始した。脱硫剤に配合したＡｌ源には微粉を除いた金属Ａｌ粉を主として用いたが、一部ではＦｅＡl粉も混合して用いた。このときの脱硫剤供給速度Ｖ、脱硫剤吹付け前後のＳ濃度、（２）式指標および脱硫ｋ値を併せて表２に記載する。 First, 250t of molten steel is discharged from the converter, and from the middle of the process until the desulfurization agent is sprayed by the RH vacuum degassing apparatus, auxiliary materials, alloy iron, Al, etc. are appropriately added to deoxidize the molten steel. The components were adjusted to obtain molten steel having the composition shown in Table 1 below. Next, the component adjustment was completed, and the desulfurization agent shown in Table 1 was sprayed on the molten steel with respect to the molten steel whose molten steel temperature was adjusted to 1640 to 1680 ° C., and desulfurization treatment was started. As the Al source blended in the desulfurizing agent, metallic Al powder excluding fine powder was mainly used, but in part, FeAl powder was also mixed and used. Table 2 shows the desulfurization agent supply rate V, the S concentration before and after spraying the desulfurization agent, the formula (2) index, and the desulfurization k value.
Ｃｈ．Ｎｏ．１〜６は、本発明に係る脱硫剤の組成を満たすようにして溶鋼に吹き付けた結果である。いずれのＣｈ．Ｎｏ．においても、前記した脱硫ｋ値は０．１７以上であって、脱硫剤添加を終えた後の溶鋼中Ｓ濃度は１２ｐｐｍ以下となっていた。中でも、Ｃｈ．Ｎｏ．１〜３は、脱硫剤吹付け前の溶鋼組成をｓｏｌ．Ａｌ：０．０１〜０．０７質量％の範囲内とし、かつ、（２）式指標を５〜１０の範囲内に制御した結果、脱硫ｋ値を０．２０以上にすることができた。 Ch. No. 1 to 6 are results of spraying molten steel so as to satisfy the composition of the desulfurizing agent according to the present invention. Any Ch. No. The desulfurization k value described above was 0.17 or more, and the S concentration in the molten steel after the addition of the desulfurizing agent was 12 ppm or less. Among them, Ch. No. 1 to 3 show the molten steel composition before spraying the desulfurizing agent. As a result of controlling Al: in the range of 0.01 to 0.07 mass% and controlling the formula (2) index in the range of 5 to 10, the desulfurization k value could be made 0.20 or more.
Ｃｈ．Ｎｏ．３と５では、Ａｌ源として金属ＡｌとＦｅＡｌとを併用したが、脱硫に関する違いは特に認められなかった。 Ch. No. In 3 and 5, metal Al and FeAl were used in combination as the Al source, but no particular difference regarding desulfurization was observed.
Ｃｈ．Ｎｏ．７〜１２には、比較のために、脱硫剤組成が請求項１に記載の範囲を外れていたものを使用した結果を示す。
Ch. No. 7 to 12 show the results of using a desulfurizing agent composition outside the scope of
Ｃｈ．Ｎｏ．７は、脱硫剤中ＣａＯおよびＡｌ２Ｏ３濃度の合計が７０質量％を下回っていたため、脱硫反応に寄与するＣａＯおよびＡｌ２Ｏ３の量が不足して、脱硫ｋ値が０．１５４と本発明の効果の目安とする０．１７以上に届かなかったと考えられる。 Ch. No. No. 7, since the total concentration of CaO and Al 2 O 3 in the desulfurizing agent was less than 70% by mass, the amount of CaO and Al 2 O 3 contributing to the desulfurization reaction was insufficient, and the desulfurization k value was 0.154. It is thought that it did not reach 0.17 or more, which is a standard for the effect of the present invention.
Ｃｈ．Ｎｏ．８は、脱硫剤中Ａｌ濃度が３質量％を下回っており、局所脱酸反応を有効に活用できなかったため、発明の効果が得られなかったものである。 Ch. No. In No. 8, since the Al concentration in the desulfurizing agent was less than 3% by mass and the local deoxidation reaction could not be effectively used, the effect of the invention could not be obtained.
Ｃｈ．Ｎｏ．９は、脱硫剤中Ａｌ濃度が１０質量％を上回っており、局所脱酸反応でＡｌ２Ｏ３が過剰に生成したことで脱硫反応が阻害され、発明の効果が得られなかったものである。 Ch. No. In No. 9, the Al concentration in the desulfurization agent exceeded 10% by mass, and the desulfurization reaction was inhibited by the excessive generation of Al 2 O 3 by the local deoxidation reaction, and the effects of the invention were not obtained. .
Ｃｈ．Ｎｏ．１０は、（１）式指標が１．３を下回っており、脱硫剤のＣａＯ活量、すなわちサルファイドキャパシティが大きく低下してしまったため、発明の効果が得られなかったものである。 Ch. No. In No. 10, the formula (1) index is less than 1.3, and the CaO activity of the desulfurization agent, that is, the sulfide capacity, has been greatly reduced, so the effect of the invention was not obtained.
Ｃｈ．Ｎｏ．１１は、（１）式指標が２．０を上回っており、脱硫剤のサルファイドキャパシティは確保されていたものの、反応に寄与する液相量が不足していたため発明の効果が得られなかったものである。 Ch. No. 11, the index of the formula (1) exceeded 2.0, and although the sulfide capacity of the desulfurizing agent was ensured, the effect of the invention was not obtained because the amount of liquid phase contributing to the reaction was insufficient. Is.
Ｃｈ．Ｎｏ．１２は、脱硫剤中ＭｇＯおよびＳｉＯ２濃度の合計が５質量％を下回っていたため、脱硫剤の溶解が遅れて発明の効果が得られなかったものである。 Ch. No. No. 12, since the total concentration of MgO and SiO 2 in the desulfurizing agent was less than 5% by mass, dissolution of the desulfurizing agent was delayed and the effects of the invention were not obtained.
Claims (3)
１．３≦（％ＣａＯ）／｛（％Ａｌ２Ｏ３）＋０．９×（％Ａｌ）｝≦２．０
・・・（１）
（１）式中、（％Ａｌ２Ｏ３）：脱硫剤中Ａｌ２Ｏ３濃度（質量％）、（％Ａｌ）：脱硫剤中Ａｌ濃度（質量％）、（％ＣａＯ）：脱硫剤中ＣａＯ濃度（質量％）である。 In mass%, CaO and Al 2 O 3 total 70% or more, either one or both of metal Al and Al alloy is 3 to 10% in total Al pure, one or both of MgO and SiO 2 5 to 20% in total, and the blending amount of CaO, Al 2 O 3 and Al satisfies the formula (1) and has a composition not containing F, a desulfurizing agent for molten steel.
1.3 ≦ (% CaO) / {(% Al 2 O 3 ) + 0.9 × (% Al)} ≦ 2.0
... (1)
(1) In the formula, (% Al 2 O 3 ): Al 2 O 3 concentration (% by mass) in the desulfurizing agent, (% Al): Al concentration (% by mass) in the desulfurizing agent, (% CaO): in the desulfurizing agent CaO concentration (% by mass).
前記脱硫剤を吹き付ける前の溶鋼中ｓｏｌ．Ａｌ濃度を０．０１〜０．０７質量％に調整しておくことを特徴とする溶鋼の脱硫方法。 A desulfurization method for molten steel, in which a desulfurizing agent for molten steel according to claim 1 is sprayed together with a carrier gas onto the surface of the molten steel sucked into a vacuum tank of a reflux type vacuum degassing apparatus,
In the molten steel before spraying the desulfurizing agent, sol. A desulfurization method for molten steel, wherein the Al concentration is adjusted to 0.01 to 0.07 mass%.
５ ≦Ｖ×（％Ａｌ）≦１０ ・・・（２）
（２）式中、Ｖ：脱硫剤の供給速度（ｋｇ／ｍｉｎ／ｔｏｎ）、（％Ａｌ）：脱硫剤中Ａｌ濃度（質量％）である。 When the desulfurizing agent for molten steel according to claim 1 is supplied by spraying on the surface of the molten steel, the supply speed is adjusted within the range indicated by the formula (2). Desulfurization method.
5 ≦ V × (% Al) ≦ 10 (2)
(2) In the formula, V: supply rate of desulfurization agent (kg / min / ton), (% Al): Al concentration (% by mass) in the desulfurization agent.
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| JP2005344129A (en) * | 2004-05-31 | 2005-12-15 | Jfe Steel Kk | Method for refining molten steel |
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