JP2010189691A - Method for producing high cleanliness aluminum-killed steel - Google Patents

Method for producing high cleanliness aluminum-killed steel Download PDF

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JP2010189691A
JP2010189691A JP2009033997A JP2009033997A JP2010189691A JP 2010189691 A JP2010189691 A JP 2010189691A JP 2009033997 A JP2009033997 A JP 2009033997A JP 2009033997 A JP2009033997 A JP 2009033997A JP 2010189691 A JP2010189691 A JP 2010189691A
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molten steel
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slag
inclusions
mgo
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JP5349074B2 (en
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Hiroaki Matsumoto
弘昭 松元
Hiromi Ota
裕己 太田
Takeshi Mimura
毅 三村
Yuichi Futamura
裕一 二村
Tetsushi Hoshika
哲志 星加
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Kobe Steel Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To produce a steel sheet excellent in a bendability by reducing oxide-based inclusions. <P>SOLUTION: When a ladle-refining process is performed, the time of a gas-stirring is defined as ≥5 min and the slag-thickness under stationaly state, is defined as 260 mm to <400 mm. Further, in the ladle-refining, MgO content in slag is defined as >1.2 kg/ton to <5.0 kg/ton, and the relation between the stirring time (t1) and the MgO content (X) in the slag satisfies t1≤-5X+40, and also satisfies t1≥-5X+20. Furthermore, in a vacuum-degassing refining, a circulating-flowing time of molten steel is made to be 10-40 min and the circulating-flowing quantity is defined as 150-200 ton/min. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

本発明は、高清浄アルミキルド鋼の製造方法に関するものである。   The present invention relates to a method for producing highly clean aluminum killed steel.

従来より、転炉から出鋼した溶鋼に対してガス攪拌による取鍋精錬を行った後、真空脱ガス精錬を行うことで清浄度鋼を製造することは数多く行われている。このような清浄度鋼の製造方法では、鋼中に含まれる酸化系介在物を出来るだけ減少させるような様々な技術が開示されている（例えば、特許文献１〜特許文献３）。
特許文献１では、高清浄度鋼を製造するに当り、転炉または電気炉にて脱炭された後の二次精錬処理において、電磁攪拌のみで溶鋼の攪拌を実施した後に、還流式真空脱ガスを行っている。 2. Description of the Related Art Conventionally, a number of clean steels have been manufactured by performing ladle refining by gas stirring on molten steel produced from a converter and then vacuum degassing refining. In such a method for producing clean steel, various techniques for reducing as much as possible the oxidation inclusions contained in the steel are disclosed (for example, Patent Documents 1 to 3).
In Patent Document 1, in the production of high cleanliness steel, in the secondary refining process after decarburization in a converter or electric furnace, the molten steel is stirred only by electromagnetic stirring, and then the reflux type vacuum degassing is performed. Doing gas.

特許文献２では、真空・減圧精錬装置を用いた溶鋼の精錬方法において、溶鋼にＭｇＯ源を添加して、スラグ中ＭｇＯ濃度を５％以上２０％以下としている。
特許文献３では、取鍋内で、Ｓｉ濃度およびＭｎ濃度を調整するとともに、造滓剤およびＳｉを添加しつつ酸素を吹き付けることにより加熱してＣａＯ−ＳｉＯ2−Ａｌ2Ｏ3−ＭｇＯ 系の組成のスラグを形成し、溶鋼中のＳｉ濃度を０．０５〜０．２重量％に再調整し、予め定められた条件でガスバブリング処理および真空脱ガス処理を行っている。
また、取鍋精錬時におけるスラグ厚が開示されているものとして、特許文献４に開示されているものがある。 In Patent Document 2, in a molten steel refining method using a vacuum / reduced pressure refining apparatus, an MgO source is added to the molten steel so that the MgO concentration in the slag is 5% or more and 20% or less.
In Patent Document 3, in a ladle, as well as adjust the Si concentration and Mn concentration, the oxygen is heated by blowing a CaO-SiO 2 -Al 2 O 3 -MgO based while adding forming agent and Si A slag having a composition is formed, the Si concentration in the molten steel is readjusted to 0.05 to 0.2% by weight, and a gas bubbling process and a vacuum degassing process are performed under predetermined conditions.
Moreover, there exists a thing currently disclosed by patent document 4 as what is disclosed the slag thickness at the time of ladle refining.

特許文献４では、脱炭を主とする精錬炉で精錬した高クロム溶鋼を取鍋に出鋼し、該取鍋内溶鋼を二次精錬するに際し、前記取鍋内溶鋼の浴面上に存在するスラグの量を、平均厚みで３０〜２００ｍｍの範囲となるように調整してから二次精錬を行っている。   In Patent Document 4, when a high chromium molten steel refined in a refining furnace mainly decarburizing is taken out into a ladle and secondarily refined, the molten steel in the ladle is present on the bath surface of the molten steel in the ladle. Secondary refining is performed after adjusting the amount of slag to be in the range of 30 to 200 mm in average thickness.

特開２００６−２３３２５４号公報JP 2006-233254 A 特開２００３−１７１７１４号公報JP 2003-171714 A 特開平１１−０１２６４０号公報Japanese Patent Laid-Open No. 11-012640 特開２００１−２３４２２７号公報JP 2001-234227 A

特許文献１〜特許文献３には、取鍋精錬におけるスラグ中のＭｇＯ濃度が開示され、特許文献４には、スラグの厚みが開示されているものの、スラグ中のＭｇＯ濃度、スラグ厚、溶鋼処理時間を考慮して鋼中に含まれる酸化物系介在物を減少させるという考えは全く開示されておらず、スラグ中のＭｇＯ濃度、スラグ厚、溶鋼処理時間を関係を考慮した上で、酸化物系介在物が少ないアルミキルド鋼を製造するという技術は未だ未開発である。
そこで、本発明は、酸化物系介在物を減少させて曲げ性に優れた鋼板を製造することができる高清浄アルミキルド鋼の製造方法を提供することを目的とする。 Patent Documents 1 to 3 disclose MgO concentration in slag in ladle refining, and Patent Document 4 discloses slag thickness, but MgO concentration in slag, slag thickness, molten steel treatment The idea of reducing the oxide inclusions contained in the steel in consideration of the time is not disclosed at all, and considering the relationship between the MgO concentration in the slag, the slag thickness, and the molten steel processing time, the oxide The technology to produce aluminum killed steel with few inclusions is still undeveloped.
Then, an object of this invention is to provide the manufacturing method of the highly clean aluminum killed steel which can manufacture the steel plate excellent in bendability by reducing an oxide type inclusion.

前記目的を達成するために、本発明は、次の手段を講じた。
即ち、本発明は、転炉又は電気炉から出鋼した溶鋼に対して２０００ｌ／ｍｉｎ以上４０００ｌ／ｍｉｎ以下にてガス攪拌による取鍋精錬を行った後、真空脱ガス精錬を行うことでアルミキルド鋼を製造する高清浄アルミキルド鋼の製造方法において、前記取鍋精錬の際には、前記ガス攪拌の時間を５分以上とすると共に、静止状態でのスラグ厚を２６０ｍｍ以上４００ｍｍ未満とし、且つ、前記ガス攪拌の時間とスラグ中のＭｇＯ量との関係が式（１）〜式（４）を満たすように精錬し、前記真空脱ガス精錬の際には、溶鋼の還流時間が式（５）を満たすように精錬すると共に、溶鋼の還流量が式（６）を満たすように精錬する点にある。 In order to achieve the above object, the present invention has taken the following measures.
That is, the present invention provides aluminum killed steel by performing vacuum degassing refining after performing ladle refining by gas stirring at 2000 l / min to 4000 l / min with respect to molten steel produced from a converter or electric furnace. In the method for producing highly clean aluminum killed steel, the ladle refining is performed with the gas stirring time of 5 minutes or more, the slag thickness in a stationary state is 260 mm or more and less than 400 mm, and Refining is performed so that the relationship between the gas stirring time and the amount of MgO in the slag satisfies the formulas (1) to (4), and in the vacuum degassing refining, the reflux time of the molten steel is expressed by the formula (5). In addition to refining to satisfy, refining so that the reflux amount of molten steel satisfies the formula (6).

Figure 2010189691
Figure 2010189691

本発明における高清浄アルミキルド鋼の製造方法によれば、酸化物系介在物を減少させて曲げ性に優れた鋼板を製造することができる。   According to the method for producing highly clean aluminum killed steel in the present invention, a steel plate having excellent bendability can be produced by reducing oxide inclusions.

高清浄アルミキルド鋼の製造方法の工程を示した図である。It is the figure which showed the process of the manufacturing method of highly clean aluminum killed steel. 曲げ不良率と介在物の個数との関係図である。It is a related figure of a bending defect rate and the number of inclusions. 取鍋精錬における処理時間（ガス攪拌時間）とスラグ中のＭｇＯ量との関係図である。It is a related figure of the processing time (gas stirring time) in ladle refining, and the amount of MgO in slag.

本発明の高清浄アルミキルド鋼の製造方法について説明する。
以下、本発明の高清浄アルミキルド鋼の製造方法は、図１に示すように、転炉１にて脱炭精錬（一次精錬）次を行った後に、溶鋼を取鍋２に出鋼し、当該溶鋼内にＡｌを投入して脱酸する。そして、脱酸した取鍋２を二次精錬装置３に搬送して当該二次精錬装置３にて精錬し、二次精錬装置３で処理した溶鋼を連続鋳造装置にて鋳造することにより製造する。なお、溶鋼は電気炉から出鋼したものであってもよい。
二次精錬装置３は、ガス攪拌による取鍋精錬を行う取鍋精錬装置５と、還流ガスにより真空脱ガス精錬を行う還流式真空脱ガス装置６とを有している。 The manufacturing method of the highly clean aluminum killed steel of this invention is demonstrated.
Hereinafter, as shown in FIG. 1, the method for producing the highly clean aluminum killed steel of the present invention performs decarburization refining (primary refining) in the converter 1, then discharges the molten steel into the ladle 2, Al is introduced into the molten steel and deoxidized. Then, the deoxidized ladle 2 is transported to the secondary refining device 3 and refined by the secondary refining device 3, and the molten steel treated by the secondary refining device 3 is produced by casting in the continuous casting device. . In addition, the molten steel may be obtained from an electric furnace.
The secondary refining apparatus 3 has a ladle refining apparatus 5 that performs ladle refining by gas stirring, and a recirculation-type vacuum degassing apparatus 6 that performs vacuum degas refining using recirculation gas.

取鍋精錬装置５は、電極加熱式の精錬装置（以降、ＬＦ装置ということがある）であって、溶鋼が装入された取鍋２と、取鍋２の溶鋼内にガスを吹き込む吹き込み装置７と、溶鋼を加熱する電極式加熱装置８と、フラックス等を投入するための供給装置９とを有している。
吹き込み装置７は、取鍋２の底部に設けられてその底部からガスを吹き込むポーラス吹込口１５と、取鍋２の上部からガスを吹き込むランス１６とを備えている。ランス１６の先端には溶鋼内にガスを吹き込むノズルが設けられている。なお、吹き込み装置７は、ポーラス吹込口１５のみを有するものであっても、ランス１６のみを有するものであってもよい。 The ladle refining device 5 is an electrode heating type refining device (hereinafter sometimes referred to as LF device), and a ladle 2 in which molten steel is charged, and a blowing device for blowing gas into the molten steel in the ladle 2 7, an electrode-type heating device 8 for heating molten steel, and a supply device 9 for feeding flux or the like.
The blowing device 7 includes a porous blowing port 15 that is provided at the bottom of the ladle 2 and blows gas from the bottom thereof, and a lance 16 that blows gas from the top of the ladle 2. A nozzle that blows gas into the molten steel is provided at the tip of the lance 16. The blowing device 7 may have only the porous blowing port 15 or only the lance 16.

還流式真空脱ガス装置６は、溶鋼を還流させることで当該溶鋼の脱ガスを行うもの（以降、ＲＨ装置ということがある）であって、溶鋼が装入された取鍋２と、真空状態となって溶鋼内の脱ガスを行う脱ガス槽（真空槽）１０とを有している。ＲＨ装置６の取鍋２は、ＬＦ装置５の取鍋２と同一のものであって、脱ガス槽１０の直下に配置されるようになっている。
脱ガス槽１０の下部には取鍋２内の溶鋼に浸漬させる２本の浸漬管１１が設けられており、この浸漬管１１の一方にはＡｒガス等の不活性ガスを吹き込む吹き込み口（図示省略）が設けられている。脱ガス槽１０の上部には、脱ガス槽１０のガスを排気する排気口１３が設けられている。 The reflux-type vacuum degassing device 6 is for degassing the molten steel by refluxing the molten steel (hereinafter sometimes referred to as an RH device), and a ladle 2 in which the molten steel is charged, and a vacuum state. And a degassing tank (vacuum tank) 10 for degassing the molten steel. The ladle 2 of the RH device 6 is the same as the ladle 2 of the LF device 5 and is arranged immediately below the degassing tank 10.
Two dip pipes 11 to be immersed in the molten steel in the ladle 2 are provided at the lower part of the degassing tank 10, and one of the dip pipes 11 is blown through which an inert gas such as Ar gas is blown (illustrated). (Omitted) is provided. An exhaust port 13 for exhausting the gas in the degassing tank 10 is provided in the upper part of the degassing tank 10.

以下、本発明の高清浄アルミキルド鋼の製造方法について詳しく説明する。
図１に示すように、高清浄アルミキルド鋼の製造方法では、まず、転炉１にて溶鋼の脱炭処理行う。そして、転炉１から溶鋼を取鍋２に出鋼し、取鍋２内にＡｌを投入することによって溶鋼を脱酸する。その後、溶鋼が装入された取鍋２をＬＦ装置５に搬送し、ＬＦ装置５の吹き込み装置７によって溶鋼内にＡｒガスを２０００ｌ／ｍｉｎ以上４０００ｌ／ｍｉｎ以下の範囲で溶鋼内に吹き込んでいる。
なお、ＬＦ装置５による取鍋精錬では、電極式加熱装置８でアーク放電することにより溶鋼上のスラグを滓化させると共に、様々な合金を溶鋼に投入することで成分調整を行う。また、この取鍋精錬では、上述した処理を行うと共に、主に溶鋼に対する脱硫や酸素低減を行う。 Hereafter, the manufacturing method of the highly clean aluminum killed steel of this invention is demonstrated in detail.
As shown in FIG. 1, in the method for producing highly clean aluminum killed steel, first, molten steel is decarburized in a converter 1. Then, the molten steel is taken out from the converter 1 into the ladle 2 and the molten steel is deoxidized by introducing Al into the ladle 2. Thereafter, the ladle 2 charged with molten steel is conveyed to the LF device 5, and Ar gas is blown into the molten steel in the range of 2000 l / min to 4000 l / min by the blowing device 7 of the LF device 5. .
In the ladle refining by the LF device 5, the slag on the molten steel is hatched by arc discharge with the electrode type heating device 8, and the components are adjusted by introducing various alloys into the molten steel. Moreover, in this ladle refining, while performing the process mentioned above, desulfurization with respect to molten steel and oxygen reduction are mainly performed.

取鍋精錬では、ガスによる攪拌（ガス攪拌）の時間を５分以上とすると共に、静止状態でのスラグ厚を２６０ｍｍ以上４００ｍｍ未満とし、且つ、ガス攪拌の時間とスラグ中のＭｇＯ量との関係が式（１）〜式（４）を満たすように精錬している。   In ladle refining, the time of gas agitation (gas agitation) is 5 minutes or more, the slag thickness in a stationary state is 260 mm or more and less than 400 mm, and the relationship between the gas agitation time and the amount of MgO in the slag Is refined so as to satisfy formulas (1) to (4).

Figure 2010189691
Figure 2010189691

一般的に、一次精錬後に行われるＡｌによる脱酸では、２Ａｌ＋３Ｏ→Ａｌ2Ｏ3の反応が進み、取鍋精錬前の溶鋼中にＡｌ2Ｏ3が不可避的に多量に存在することになる。
また、取鍋精錬中では、スラグにはＭｇＯが含まれていることから、ＭｇＯ→Ｍｇ＋Ｏの反応により、溶鋼内にＭｇが溶け出すことになる。ここで、取鍋精錬では、溶鋼中に溶け出したＭｇと、Ａｌによる脱酸等により溶鋼中に含まれるＡｌ2Ｏ3とが、３Ｍｇ＋４Ａｌ2Ｏ3→３ＭｇＯ・Ａｌ2Ｏ3＋２Ａｌの反応により、スピネル（ＭｇＯ・Ａｌ2Ｏ3）が生成することになる。取鍋精錬中に生成するスピネル（ＭｇＯ・Ａｌ2Ｏ3）は、介在物の一種であり、溶鋼中には出来るだけ少ないことが望ましいが、スピネル（ＭｇＯ・Ａｌ2Ｏ3）は、アルミナ（Ａｌ2Ｏ3）に比べて、真空脱ガス精錬時に除去し易いという利点がある。そこで、本発明では、取鍋精錬において出来る限りアルミナよりもスピネルを生成させて、最終的には、真空脱ガス精錬にてスピネルを除去することにより、アルミナやスピネルといった介在物を極力減らすようにしている。即ち、本発明では、取鍋精錬においてスピネルを制御することにより、介在物の少ないアルミキルド鋼を製造することとしている。 Generally, in the deoxidation with Al performed after the primary refining, the reaction of 2Al + 3O → Al 2 O 3 proceeds, and a large amount of Al 2 O 3 is inevitably present in the molten steel before ladle refining.
Further, during ladle refining, MgO is contained in the slag, and therefore Mg is dissolved into the molten steel by the reaction MgO → Mg + O. Here, in ladle refining, Mg dissolved in the molten steel and Al 2 O 3 contained in the molten steel due to deoxidation by Al, etc. are caused by a reaction of 3Mg + 4Al 2 O 3 → 3MgO · Al 2 O 3 + 2Al. Spinel (MgO.Al 2 O 3 ) is generated. The spinel (MgO.Al 2 O 3 ) produced during ladle refining is a kind of inclusions, and it is desirable that the molten steel contains as little as possible, but the spinel (MgO · Al 2 O 3 ) is made of alumina ( Compared to Al 2 O 3 ), there is an advantage that it is easy to remove during vacuum degassing. Therefore, in the present invention, spinel is produced as much as possible in ladle refining as much as possible, and finally, spinel is removed by vacuum degassing refining so as to reduce inclusions such as alumina and spinel as much as possible. ing. That is, in the present invention, aluminum killed steel with few inclusions is manufactured by controlling spinel in ladle refining.

さて、上述したように、取鍋精錬において、ガス攪拌の時間が５分未満であって非常に短いと、スラグ中から溶鋼内にＭｇが溶け出すという反応時間が短いため、溶鋼中にＭｇが非常に少なくなってしまう（反応が進まない）。そのため、スラグから溶鋼中に溶け出したＭｇと、溶鋼中に含まれるＡｌ2Ｏ3との反応によるスピネルの生成が少なくなる可能性がある。そこで、様々な実験等により、取鍋精錬におけるガス攪拌の時間は、５分以上としている。
一方で、取鍋精錬中に、ガス攪拌の時間が十分にあったとしても、スラグ中に含まれるＭｇＯ量が少ないと、アルミナとの反応が進まず、スピネルがあまり生成されない可能性がある。そこで、様々な実験等により、取鍋精錬におけるスラグ中のＭｇＯ量は、式（４）を満たす必要がある。 As described above, in ladle refining, if the gas stirring time is less than 5 minutes and is very short, the reaction time that Mg dissolves into the molten steel from the slag is so short that Mg is contained in the molten steel. It becomes very little (the reaction does not progress). Therefore, there is a possibility that the generation of spinel due to the reaction between Mg melted into the molten steel from the slag and Al 2 O 3 contained in the molten steel may be reduced. Therefore, the gas stirring time in the ladle refining is set to 5 minutes or more by various experiments.
On the other hand, even if there is sufficient gas stirring time during ladle refining, if the amount of MgO contained in the slag is small, the reaction with alumina may not proceed and spinel may not be generated much. Therefore, through various experiments, the amount of MgO in the slag in ladle refining needs to satisfy formula (4).

ここで、スラグ中のＭｇＯ量は、溶鋼１ｔｏｎ当たりのスラグ中のＭｇＯ量であり、単位は、ｋｇ／ｔｏｎである。ＭｇＯ量は、溶鋼１ｔｏｎ当たりのスラグ量とスラグ中のＭｇＯ濃度を乗じて算出する［Ｘ＝スラグ量（ｋｇ／ｔｏｎ）×スラグ中ＭｇＯ濃度（質量％）÷１００］。
また、様々な実験等により、ガス攪拌の時間が５分以上であり、スラグ中のＭｇＯ量が式（４）を満たしている場合であっても、スピネルの生成には、ガス攪拌の時間とスラグ中のＭｇＯ量との関係が式（２）を満たす必要がある。 Here, the amount of MgO in the slag is the amount of MgO in the slag per ton of molten steel, and the unit is kg / ton. The amount of MgO is calculated by multiplying the amount of slag per ton of molten steel by the MgO concentration in the slag [X = slag amount (kg / ton) × MgO concentration in slag (mass%) ÷ 100].
Further, according to various experiments and the like, even when the gas stirring time is 5 minutes or more and the amount of MgO in the slag satisfies the formula (4), the time for gas stirring is The relationship with the amount of MgO in the slag needs to satisfy the formula (2).

ここで、スラグ中から溶鋼内へ溶け出したＭｇが多く、溶鋼中のＭｇＯ濃度が高くなってしまうと、溶鋼中のＭｇと溶鋼中のＡｌ2Ｏ3との反応によりスピネルが生成されるという反応よりも、溶鋼中のＭｇと溶鋼中のＯとが反応するという現象（Ｍｇ＋Ｏ→ＭｇＯ）が支配的になってしまう。そこで、溶鋼中のＭｇが多くなり、スピネルが生成されるという現象よりも、ＭｇＯが生成されるという現象を抑制するために、様々な実験により、スラグ中のＭｇＯ量は式（３）を満たす必要がある。
また、スラグ中のＭｇＯ量が式（３）を満たした場合であっても、ガス攪拌時間が長いと溶鋼中に溶出するＭｇ量が多くなるという傾向がある。そこで、様々な実験により、スラグ中のＭｇＯ量と、ガス攪拌の時間との関係を整理すると、スラグ中のＭｇＯ量と、ガス攪拌時間との関係は式（１）を満たす必要がある。 Here, if there is a lot of Mg dissolved into the molten steel from the slag and the MgO concentration in the molten steel becomes high, spinel is generated by the reaction between Mg in the molten steel and Al 2 O 3 in the molten steel. A phenomenon (Mg + O → MgO) in which Mg in molten steel reacts with O in molten steel becomes more dominant than reaction. Therefore, in order to suppress the phenomenon that MgO is generated rather than the phenomenon that Mg in the molten steel increases and spinel is generated, the amount of MgO in the slag satisfies Equation (3) by various experiments. There is a need.
Even if the amount of MgO in the slag satisfies the formula (3), if the gas stirring time is long, the amount of Mg eluted in the molten steel tends to increase. Therefore, when the relationship between the amount of MgO in the slag and the gas stirring time is arranged by various experiments, the relationship between the amount of MgO in the slag and the gas stirring time needs to satisfy Expression (1).

このように、取鍋精錬では、スラグから溶鋼に溶け出すＭｇと、溶鋼中のアルミナとを用いてスピネルを生成させている。また、スピネルを生成させる際には、スラグから溶け出すＭｇのバランスやＭｇの反応度合いも考え、スラグ中に含まれるＭｇＯ量とガス攪拌の時間との関係も考慮している。
さて、取鍋精錬におけるガス攪拌では、そのガスの流量（Ａｒガスの流量）が２０００ｌ／ｍｉｎ以上４０００ｌ／ｍｉｎ以下であって強攪拌である。Ａｒガスを溶鋼内に吹き込む前の溶鋼の静止状態におけるスラグ厚みが２６０ｍｍ未満であると、Ａｒガスを溶鋼内に吹き込んだ際（最大４０００ｌ／ｍｉｎのとき）に、スラグが取鍋の縁側（外側）に寄ってしまい溶鋼がスラグにより覆われずに、溶鋼の湯面が空気に触れてしまう虞がある。即ち、溶鋼の静止時においてスラグ厚みが２６０ｍｍ未満であると、溶鋼を強攪拌した際に溶鋼と大気中の酸素とが反応してＡｌ2Ｏ3が生成して介在物を増加させてしまうという虞がある。そこで、Ａｒガスを溶鋼に吹き込んでも、溶鋼が表面に現れないようにするために、スラグ厚を２６０ｍｍ以上確保する必要がある。 Thus, in ladle refining, spinel is generated using Mg that melts from molten slag into molten steel and alumina in the molten steel. Moreover, when producing | generating a spinel, the balance of Mg melt | dissolved from slag and the reaction degree of Mg are also considered, and the relationship between the amount of MgO contained in slag and the time of gas stirring is also considered.
In the gas stirring in the ladle refining, the gas flow rate (Ar gas flow rate) is 2000 l / min to 4000 l / min and is strong stirring. When the slag thickness in a stationary state of the molten steel before blowing Ar gas into the molten steel is less than 260 mm, when Ar gas is blown into the molten steel (at a maximum of 4000 l / min), the slag is on the edge side (outside) ) And the molten steel is not covered with slag, and the molten steel surface may come into contact with the air. That is, when the molten steel is stationary, the slag thickness is less than 260 mm, and when the molten steel is vigorously stirred, the molten steel reacts with oxygen in the atmosphere to generate Al 2 O 3 and increase inclusions. There is a fear. Therefore, even if Ar gas is blown into the molten steel, it is necessary to ensure a slag thickness of 260 mm or more so that the molten steel does not appear on the surface.

一方で、スラグ厚が４００ｍｍ以上になると、スラグの流動化が低下するために、スラグ−メタル反応が不十分となって、スラグ中のＭｇが溶出し難くなる。
上述したように、取鍋精錬の際には、スピネルを制御するために、ガス攪拌の時間を５分以上とすると共に、静止状態でのスラグ厚を２６０ｍｍ以上４００ｍｍ未満とし、且つ、ガス攪拌の時間とスラグ中のＭｇＯ量との関係が式（１）〜式（４）を満たすように精錬している。
次に、取鍋精錬が終了すると、溶鋼が装入された取鍋２をＲＨ装置６に搬送する。そして、ＲＨ装置６では、浸漬管１１を取鍋２内の溶鋼に浸漬し、吹き込み口から不活性ガスを吹き込むと共に、排気口１３から脱ガス槽１０のガスを排気して脱ガス槽１０内を略真空状態して溶鋼を脱ガス槽１０と取鍋２との間で循環させることで、真空脱ガス精錬（還流式脱ガス精錬）を行う。 On the other hand, when the slag thickness is 400 mm or more, fluidization of the slag is lowered, so that the slag-metal reaction becomes insufficient, and Mg in the slag becomes difficult to elute.
As described above, during ladle refining, in order to control the spinel, the gas stirring time is set to 5 minutes or more, the slag thickness in a stationary state is set to 260 mm or more and less than 400 mm, and gas stirring is performed. Refinement is performed so that the relationship between time and the amount of MgO in the slag satisfies the formulas (1) to (4).
Next, when the ladle refining is completed, the ladle 2 charged with molten steel is conveyed to the RH device 6. In the RH device 6, the dip tube 11 is dipped in the molten steel in the pan 2, and an inert gas is blown from the blowing port, and the gas in the degassing tank 10 is exhausted from the exhaust port 13. Is evacuated and the molten steel is circulated between the degassing tank 10 and the ladle 2 to perform vacuum degassing refining (reflux degassing refining).

真空脱ガス精錬では、溶鋼の還流時間が式（５）を満たすように精錬すると共に、溶鋼の還流量が式（６）を満たすように精錬している。溶鋼の還流量（溶鋼還流量）は、単位時間当たりに還流する溶鋼量であって、溶鋼還流速度とも言う。溶鋼還流量は、「桑原達朗ら：鉄と鋼、73(1987）,S176」に示されている式（７）を用いて算出した。   In the vacuum degassing refining, refining is performed so that the reflux time of the molten steel satisfies the equation (5), and the recirculation amount of the molten steel satisfies the equation (6). The reflux amount of molten steel (molten steel reflux amount) is the amount of molten steel that is refluxed per unit time, and is also referred to as the molten steel reflux rate. The molten steel reflux amount was calculated using the equation (7) shown in “Tatsuro Kuwahara et al .: Iron and Steel, 73 (1987), S176”.

Figure 2010189691
Figure 2010189691

真空脱ガス精錬では、取鍋精錬にて生成したスピネル等を、溶鋼を還流しながら真空引きすることによって除去している。真空脱ガス精錬において、溶鋼の還流時間が１０分未満であると、スピネル等の介在物の浮上する時間（除去する時間）が不十分であるため、溶鋼内に多くの介在物が残ってしまう。
一方で、真空脱ガス精錬において、溶鋼の還流時間が４０分を超えると、スピネル等の介在物を除去する時間は十分であるものの、逆に、脱ガス槽１０に付着した付着物や耐火物の溶損によって、溶鋼内の介在物が増加するという傾向にある。 In vacuum degassing refining, spinel and the like produced by ladle refining are removed by evacuating the molten steel while refluxing. In the vacuum degassing refining, if the reflux time of the molten steel is less than 10 minutes, the time for removing inclusions such as spinel (the time for removal) is insufficient, so that many inclusions remain in the molten steel. .
On the other hand, in the vacuum degassing refining, if the reflux time of the molten steel exceeds 40 minutes, the time for removing inclusions such as spinel is sufficient, but on the contrary, the deposits and refractories attached to the degassing tank 10 There is a tendency that inclusions in the molten steel increase due to the melting loss.

したがって、真空脱ガス精錬では、溶鋼内のスピネル等の介在物を十分に除去する時間を確保しつつ、脱ガス槽１０に付着した付着物や耐火物の影響により溶鋼内の介在物を増加させない時間、即ち、式（５）を満たす還流時間にて精錬する必要がある。
真空脱ガス精錬において、溶鋼還流量が１５０ｔｏｎ／ｍｉｎ未満であると、溶鋼の還流度合いが弱いので、スピネル等の介在物が十分に浮上せず、溶鋼内に多くの介在物が残ってしまう。一方で、真空脱ガス精錬において、溶鋼還流量が２００ｔｏｎ／ｍｉｎより超えると、溶鋼の還流度合いが強くスピネル等の介在物を十分に浮上させることができるが、脱ガス槽１０に付着した付着物や耐火物の溶損による介在物の増加が顕著になり、溶鋼内に多くの介在物が残ってしまう。 Therefore, vacuum degassing refining does not increase inclusions in the molten steel due to the influence of deposits and refractories attached to the degassing tank 10 while ensuring sufficient time to remove inclusions such as spinel in the molten steel. It is necessary to refine at the time, that is, the reflux time satisfying the formula (5).
In the vacuum degassing refining, if the molten steel recirculation amount is less than 150 ton / min, the recirculation degree of the molten steel is weak, so that inclusions such as spinel do not sufficiently float and many inclusions remain in the molten steel. On the other hand, in the vacuum degassing refining, when the molten steel recirculation amount exceeds 200 ton / min, the molten steel recirculation degree is strong, and inclusions such as spinel can sufficiently float, but the deposits adhered to the degassing tank 10 Increase of inclusions due to melting of refractories and refractories becomes remarkable, and many inclusions remain in the molten steel.

したがって、真空脱ガス精錬では、溶鋼内のスピネル等の介在物を十分に除去することのできる溶鋼還流量で還流すると共に、その溶鋼還流量が強すぎないようにする必要がある。即ち、真空脱ガス精錬では、式（６）を満たす還流時間にて精錬する必要がある。
表１及び表２は、本発明の高清浄アルミキルド鋼の製造方法を実施した実施例と、本発明の高清浄アルミキルド鋼の製造方法を実施しなかった比較例とを示したものである。 Therefore, in vacuum degassing refining, it is necessary to recirculate at a molten steel reflux amount that can sufficiently remove inclusions such as spinel in the molten steel, and to prevent the molten steel reflux amount from being too strong. That is, in vacuum degassing refining, it is necessary to perform refining at a reflux time that satisfies the formula (6).
Tables 1 and 2 show examples in which the manufacturing method of the highly clean aluminum killed steel of the present invention was performed and comparative examples in which the manufacturing method of the highly clean aluminum killed steel of the present invention was not performed.

Figure 2010189691
Figure 2010189691

Figure 2010189691
Figure 2010189691

実施例及び比較例における条件について説明する。
実施例や比較例で製造した高清浄アルミキルド鋼は、９８０ＭＰａ級のハイテン鋼であって、その化学成分は、質量％で、Ｃ：０．００５〜０．５００％、Ｓｉ：０．００５〜２．０００％、Ｍｎ：０．１０〜３．００％、Ｐ：０．００５〜０．１００％、Ｓ：０．００１〜０．０２０％、Ａｌ：０．０１〜０．１０％である。
真空脱ガス精錬後は、連続鋳造にて半製品（スラブ）とし、熱延、酸洗、冷延、焼鈍を行った後に板厚１．４ｍｍの冷延板とした。連続鋳造、熱延、酸洗、冷延、焼鈍、圧延は、この鋼種（９８０ＭＰａ級のハイテン鋼）を製造する当業者の常法通りに行った。 The conditions in the examples and comparative examples will be described.
The high-clean aluminum killed steel manufactured in the examples and comparative examples is a high-tensile steel of 980 MPa class, and its chemical composition is mass%, C: 0.005 to 0.500%, Si: 0.005 to 2 0.000%, Mn: 0.10 to 3.00%, P: 0.005 to 0.100%, S: 0.001 to 0.020%, Al: 0.01 to 0.10%.
After vacuum degassing and refining, a semi-finished product (slab) was obtained by continuous casting, and after hot rolling, pickling, cold rolling and annealing, a cold rolled plate having a thickness of 1.4 mm was obtained. Continuous casting, hot rolling, pickling, cold rolling, annealing, and rolling were carried out in the same manner as those skilled in the art of producing this steel type (980 MPa grade high-tensile steel).

実施例や比較例においては、介在物の低減度合いを評価するために、取鍋精錬後と製品（冷延板）とで、アルミナ介在物個数、スピネル介在物、ＭｇＯ介在物を測定した。取鍋精錬後は、ディスクサンプルを採取し、介在物を測定した。製品では板厚１．４ｍｍの冷延板の表面を測定した。
これらの介在物（アルミナ介在物個数、スピネル介在物、ＭｇＯ介在物）は、ＥＰＭＡ（電子プローブ・マイクロアナライザー）で計測した。使用したＥＰＭＡは日本電子社製「ＪＸＡ−８０００」シリーズで、測定条件は加速電圧２０ｋＶ、Ｘ線種はＫ線、ビーム径は２μｍとし、ＥＤＳ検出器による組成分析を行った。 In Examples and Comparative Examples, the number of alumina inclusions, spinel inclusions, and MgO inclusions were measured after ladle refining and in the product (cold rolled sheet) in order to evaluate the degree of inclusion reduction. After ladle refining, a disk sample was taken and the inclusions were measured. For the product, the surface of a cold-rolled sheet having a thickness of 1.4 mm was measured.
These inclusions (the number of alumina inclusions, spinel inclusions, and MgO inclusions) were measured with EPMA (Electron Probe Microanalyzer). The EPMA used was “JXA-8000” series manufactured by JEOL Ltd., the measurement conditions were an acceleration voltage of 20 kV, the X-ray type was K-ray, the beam diameter was 2 μm, and composition analysis was performed using an EDS detector.

ＥＰＭＡで観測された介在物の組成がＣａＯ−Ａｌ2Ｏ3−ＳｉＯ2−ＭｇＯの４元系換算において、Ａｌ2Ｏ3≧６０％、ＭｇＯ＜１０％を含有するものをアルミナ介在物とし、Ａｌ2Ｏ3≧６０％、１０％≦ＭｇＯ＜４０％を含有するものをスピネル介在物とし、Ａｌ2Ｏ3＜６０％、ＭｇＯ≧４０％を含有するものをＭｇＯ介在物とした。
これらの介在物において、介在物の大きさが５μｍ以上であるものの個数を測定した。測定では、信頼性を確保するために３０００ｍｍ2以上観測し、１ｃｍ2当たりの個数を介在物個数とした。 In the quaternary conversion of CaO—Al 2 O 3 —SiO 2 —MgO, the composition of inclusions observed by EPMA is Al 2 O 3 ≧ 60%, and MgO <10% contains alumina inclusions. Those containing Al 2 O 3 ≧ 60%, 10% ≦ MgO <40% were used as spinel inclusions, and those containing Al 2 O 3 <60% and MgO ≧ 40% were used as MgO inclusions.
Of these inclusions, the number of inclusions having a size of 5 μm or more was measured. In the measurement, 3000 mm 2 or more was observed in order to ensure reliability, and the number per 1 cm 2 was defined as the number of inclusions.

また、製品の曲げ不良率を調査した。具体的には、折り畳み曲げ加工を模擬した曲げ試験にて加工性を調査した。この曲げ試験では、信頼性を確保するために１つのサンプルに対して１００枚の試験を実施した。曲げ試験においては、試験片サイズを１．４×４０×７５ｍｍ(圧延方向に垂直方向の試験片で、割れ方向は圧延方向と同じ方向)とし、80tプレス機(ＡＩＤＡ製８０ｔｏｎクランクプレス：ＮＣ１−８０)にて、ストローク長さを１６０ｍｍ、ストローク数を４０ｒｐｍ、限界曲げＲより大きいＲ＝２ｍｍにて曲げ試験を行った。曲げ試験では、目視にて加工部（試験部位）の観察し、割れを発見後ＳＥＭ／ＥＤＸにて介在物に起因した割れかどうかを観察した。そして、１００枚のサンプルに対して介在物に起因した割れをカウントして、不良率（曲げ不良率）を求めた。不良率（％）＝（介在物割れ／１００枚）×１００になる。   In addition, the bending defect rate of the product was investigated. Specifically, workability was investigated by a bending test simulating folding bending. In this bending test, 100 tests were performed on one sample in order to ensure reliability. In the bending test, the test piece size was 1.4 × 40 × 75 mm (a test piece perpendicular to the rolling direction and the cracking direction was the same as the rolling direction), and an 80 t press machine (AITON 80 ton crank press: NC1- 80), a bending test was performed at a stroke length of 160 mm, a stroke number of 40 rpm, and R = 2 mm larger than the limit bending R. In the bending test, the processed part (test site) was visually observed, and after finding the crack, it was observed by SEM / EDX whether the crack was caused by inclusions. And the crack resulting from the inclusion was counted with respect to 100 samples, and the defect rate (bending defect rate) was calculated | required. Failure rate (%) = (inclusion crack / 100 sheets) × 100.

表１及び表２に示すように、比較例１、２では、取鍋精錬時において、ガス攪拌による流量（Ａｒガス流量）が、２０００ｌ／ｍｉｎ未満であるため、取鍋精錬時にスピネルの生成が進まず、最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去したとしても、アルミナ介在物個数が多くなり、曲げ不良率も０％にすることができなかった（総合評価「×」）。
比較例３、４では、取鍋精錬時において、ガス攪拌の時間（表中、処理時間）が５分未満であるため、取鍋精錬時にスピネルの生成が進まず、最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去したとしても、アルミナ介在物個数が多くなり、曲げ不良率も０％にすることができなかった（総合評価「×」）。 As shown in Table 1 and Table 2, in Comparative Examples 1 and 2, since the flow rate by gas stirring (Ar gas flow rate) is less than 2000 l / min during ladle refining, spinel is generated during ladle refining. Even if all the spinel inclusions were removed after vacuum degassing and refining, the number of alumina inclusions increased and the bending failure rate could not be reduced to 0% (overall evaluation “×”). ).
In Comparative Examples 3 and 4, since the time of gas stirring (treatment time in the table) is less than 5 minutes during ladle refining, spinel formation does not proceed during ladle refining, and finally vacuum degassing Even if all the spinel inclusions were removed after refining, the number of alumina inclusions increased, and the bending failure rate could not be reduced to 0% (overall evaluation “×”).

比較例５、６では、取鍋精錬時において、静止時のスラグ厚（表中、スラグ厚）が２６０ｍｍ未満であるため、取鍋精錬時にアルミナを増加させてしまうという結果となり、最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去したとしても、アルミナ介在物個数が多くなり、曲げ不良率も０％にすることができなかった（総合評価「×」）。
比較例７、８では、取鍋精錬時において、静止時のスラグ厚が４００ｍｍを超えているため、取鍋精錬時にスピネルの生成が進まず、最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去したとしても、アルミナ介在物個数が多くなり、曲げ不良率も０％にすることができなかった（総合評価「×」）。 In Comparative Examples 5 and 6, when ladle refining, since the slag thickness at rest (in the table, slag thickness) is less than 260 mm, the result is that alumina is increased during ladle refining, and finally, Even if all the spinel inclusions were removed after vacuum degassing, the number of alumina inclusions increased, and the bending failure rate could not be reduced to 0% (overall evaluation “×”).
In Comparative Examples 7 and 8, when ladle refining, the slag thickness at rest exceeds 400 mm, so spinel formation does not proceed during ladle refining, and finally, spinel inclusions after vacuum degassing refining Even when all of these were removed, the number of alumina inclusions increased, and the bending failure rate could not be reduced to 0% (overall evaluation “×”).

比較例９、１０では、取鍋精錬時において、スラグ中のＭｇＯ量が１．２ｋｇ／ｔｏｎ未満であるため、取鍋精錬時にスピネルの生成が進まず、最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去したとしても、アルミナ介在物個数が多くなり、曲げ不良率も０％にすることができなかった（総合評価「×」）。
比較例１１、１２では、取鍋精錬時において、スラグ中のＭｇＯ量が５．０ｋｇ／ｔｏｎを超えているため、取鍋精錬時にスピネルの生成が進まず、ＭｇＯの生成が進んでしまい、最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去したとしても、ＭｇＯ介在物個数が多くなり、曲げ不良率も０％にすることができなかった（総合評価「×」）。 In Comparative Examples 9 and 10, since the amount of MgO in the slag is less than 1.2 kg / ton during ladle refining, spinel formation does not proceed during ladle refining, and finally spinel after vacuum degassing refining. Even if all the inclusions were removed, the number of alumina inclusions increased, and the bending defect rate could not be reduced to 0% (overall evaluation “×”).
In Comparative Examples 11 and 12, since the amount of MgO in the slag exceeds 5.0 kg / ton during ladle refining, the generation of spinel does not proceed during ladle refining, and the production of MgO proceeds. In particular, even when all the spinel inclusions were removed after vacuum degassing, the number of MgO inclusions increased and the bending failure rate could not be reduced to 0% (overall evaluation “×”).

比較例１３、１４では、取鍋精錬時において、ガス攪拌の時間（ｔ１）と、スラグ中のＭｇＯ量（Ｘ）との関係が、ｔ１≧−５Ｘ＋２０を満たしていないため、ガス攪拌の時間に比べてスラグ中のＭｇＯ量が少なく、アルミナからスピネルへの組成制御が進まず、最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去したとしても、アルミナ介在物個数が多くなり、曲げ不良率も０％にすることができなかった（総合評価「×」）。
比較例１５〜１７では、取鍋精錬時において、ガス攪拌の時間（ｔ１）と、スラグ中のＭｇＯ量（Ｘ）との関係が、ｔ１≦−５Ｘ＋４０を満たしていないため、ガス攪拌の時間に比べてスラグ中のＭｇＯ量が多く、スピネルが生成される前にＭｇＯへの組成変化してしまい、最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去したとしても、ＭｇＯ介在物個数が多くなり、曲げ不良率も０％にすることができなかった（総合評価「×」）。 In Comparative Examples 13 and 14, at the time of ladle refining, the relationship between the gas stirring time (t1) and the amount of MgO in the slag (X) does not satisfy t1 ≧ −5X + 20. Compared to the amount of MgO in the slag, the composition control from alumina to spinel does not proceed. Finally, even if all the spinel inclusions are removed after vacuum degassing refining, the number of alumina inclusions increases and bending occurs. The defect rate could not be reduced to 0% (overall evaluation “×”).
In Comparative Examples 15 to 17, during the ladle refining, the relationship between the gas stirring time (t1) and the amount of MgO in the slag (X) does not satisfy t1 ≦ −5X + 40. Compared to the amount of MgO in the slag, the composition changes to MgO before spinel is generated, and even if all the spinel inclusions are removed after vacuum degassing, the number of MgO inclusions The bending defect rate could not be reduced to 0% (overall evaluation “×”).

比較例１８、１９では、真空脱ガス精錬において、溶鋼の還流時間（表中、処理時間）が１０分未満と短いために、取鍋精錬時に生成したスピネルを十分に除去することができず、曲げ不良率も０％にすることができなかった（総合評価「×」）。
比較例２０、２１では、真空脱ガス精錬において、溶鋼の還流時間が４０分よりも長いために、脱ガス槽１０に付着した付着物や耐火物の溶損の影響により溶鋼内の介在物を逆に増加させてしまうという結果になった。最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去したとしても、アルミナ介在物個数が多くなり、曲げ不良率も０％にすることができなかった（総合評価「×」）。 In Comparative Examples 18 and 19, in the vacuum degassing refining, since the reflux time of molten steel (in the table, the processing time) is as short as less than 10 minutes, the spinel generated during ladle refining cannot be sufficiently removed, The bending failure rate could not be reduced to 0% (overall evaluation “×”).
In Comparative Examples 20 and 21, in the vacuum degassing refining, since the reflux time of the molten steel is longer than 40 minutes, inclusions in the degassing tank 10 and inclusions in the molten steel are removed due to the influence of refractory erosion. On the other hand, it resulted in increasing. Finally, even if all the spinel inclusions were removed after vacuum degassing, the number of alumina inclusions increased and the bending failure rate could not be reduced to 0% (overall evaluation “×”).

比較例２２、２３では、真空脱ガス精錬において、溶鋼還流量が１５０ｔｏｎ／ｍｉｎ未満であり、溶鋼の還流する度合いが弱いために、介在物の凝固集合体（介在物が固まったもの）の分離浮上や除去が進まなかった。最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去することができず、曲げ不良率も０％にすることができなかった（総合評価「×」）。
比較例２４、２５では、真空脱ガス精錬において、溶鋼還流量が２００ｔｏｎ／ｍｉｎを超えてしまい、溶鋼の還流する度合いが強すぎるために、脱ガス槽１０に付着した付着物や耐火物の溶損物を溶鋼内に取り込んでしまい、溶鋼内の介在物を逆に増加させてしまうという結果になった。最終的に、真空脱ガス精錬後にスピネルの介在物を全て除去したとしても、アルミナ介在物個数が多くなり、曲げ不良率も０％にすることができなかった（総合評価「×」）。 In Comparative Examples 22 and 23, in the vacuum degassing refining, the molten steel recirculation amount is less than 150 ton / min, and the degree of recirculation of the molten steel is weak, so that the solidified aggregates of inclusions (thinned inclusions solidified) are separated. Ascent and removal did not progress. Finally, all the inclusions of the spinel could not be removed after vacuum degassing and the bending failure rate could not be reduced to 0% (overall evaluation “×”).
In Comparative Examples 24 and 25, in the vacuum degassing refining, the molten steel recirculation amount exceeded 200 ton / min, and the degree of recirculation of the molten steel was too strong, so that the deposits and refractory adhering to the degassing tank 10 were dissolved. As a result, the damaged material was taken into the molten steel, and the inclusions in the molten steel were increased. Finally, even if all the spinel inclusions were removed after vacuum degassing, the number of alumina inclusions increased and the bending failure rate could not be reduced to 0% (overall evaluation “×”).

実施例２６〜３８では、取鍋精錬時において、ガス攪拌の時間は５分以上であり、静止状態でのスラグ厚は２６０ｍｍ以上４００ｍｍ未満である。また、実施例２６〜３８では、取鍋精錬時において、スラグ中のＭｇＯ量が１．２ｋｇ／ｔｏｎ以上５．０ｋｇ／ｔｏｎ以下であり、ガス攪拌の時間（ｔ１）とスラグ中のＭｇＯ量（Ｘ）との関係がｔ１≦−５Ｘ＋４０を満たすとと共に、ｔ１≧−５Ｘ＋２０を満たしている。
加えて、実施例２６〜３８では、真空脱ガス精錬において、溶鋼の還流時間は、１０分以上４０分以下であり、溶鋼還流量も１５０ｔｏｎ／ｍｉｎ以上２００ｔｏｎ／ｍｉｎ以下である。 In Examples 26 to 38, during ladle refining, the gas stirring time is 5 minutes or more, and the slag thickness in a stationary state is 260 mm or more and less than 400 mm. In Examples 26 to 38, the amount of MgO in the slag was 1.2 kg / ton or more and 5.0 kg / ton or less at the time of ladle refining, the gas stirring time (t1) and the amount of MgO in the slag ( X) satisfies t1 ≦ −5X + 40 and satisfies t1 ≧ −5X + 20.
In addition, in Examples 26 to 38, in the vacuum degassing refining, the reflux time of the molten steel is 10 minutes or more and 40 minutes or less, and the molten steel reflux amount is 150 ton / min or more and 200 ton / min or less.

その結果、実施例２６〜３８では、取鍋精錬時においてスピネルを十分に生成して、真空脱ガス精錬時にスピネルを全て除去することができ、アルミナ介在物も非常に少なく、曲げ不良率を０％にすることができた（総合評価「○」）。
図２は、比較例及び実施例において、介在物個数の合計（アルミナ介在物個数＋スピネル介在物の個数＋ＭｇＯ介在物の個数）と、曲げ不良率との関係をまとめたものである。
図２及び表１、表２に示すように、取鍋精錬時においてスピネルを十分に生成した後、真空脱ガス精錬時にスピネルを全て除去し、アルミナ介在物も非常に少なくして、介在物個数の合計を２．０個／ｃｍ2以下にするような実施例２６〜３８を行う、即ち、上述した本発明の条件を満たすような操業を行うと、曲げ不良率を０％にすることができる。一方で、介在物個数の合計が２．０個／ｃｍ2以下にできないような比較例１〜２５、即ち、上述した本発明の条件を外れるような操業では、曲げ不良率を０％にすることはできなかった。 As a result, in Examples 26 to 38, spinel can be sufficiently generated during ladle refining, and all spinel can be removed during vacuum degassing refining, and there are very few alumina inclusions, and the bending failure rate is 0. % (Comprehensive evaluation “◯”).
FIG. 2 summarizes the relationship between the total number of inclusions (the number of alumina inclusions + the number of spinel inclusions + the number of MgO inclusions) and the bending defect rate in the comparative examples and examples.
As shown in Fig. 2 and Tables 1 and 2, after spinel is sufficiently generated during ladle refining, all spinel is removed during vacuum degassing refining, and the number of inclusions is reduced to a very low level. When performing Examples 26 to 38 that make the total of 2.0 pieces / cm 2 or less, that is, performing an operation that satisfies the above-described conditions of the present invention, the bending defect rate may be reduced to 0%. it can. On the other hand, in Comparative Examples 1 to 25 in which the total number of inclusions cannot be reduced to 2.0 pieces / cm 2 or less, that is, operations that do not satisfy the above-described conditions of the present invention, the bending defect rate is set to 0%. I couldn't.

なお、スラグ中のＭｇＯ量と、取鍋精錬におけるガス攪拌時間（処理時間）をまとめると、図３に示すようになる。図３に示した「×」が比較例であり、「○」が実施例である。
図３に示した４つの直線が、本発明に示した式（１）〜式（４）の条件となる。
以上、取鍋精錬の際には、ガス攪拌の時間を５分以上とすると共に、静止状態でのスラグ厚を２６０ｍｍ以上４００ｍｍ未満とし、且つ、ガス攪拌の時間とスラグ中のＭｇＯ量との関係が式（１）〜式（４）を満たすように精錬し、真空脱ガス精錬の際には、溶鋼の還流時間が式（５）を満たすように精錬すると共に、溶鋼の還流量が式（６）を満たすように精錬することによって、鋼中の酸化物系介在物（アルミナ介在物、スピネル介在物、ＭｇＯ介在物）が減少して、曲げ性に優れた鋼板を製造することができる。 In addition, when the amount of MgO in slag and the gas stirring time (processing time) in ladle refining are put together, it comes to show in FIG. “X” shown in FIG. 3 is a comparative example, and “◯” is an example.
The four straight lines shown in FIG. 3 are the conditions of the equations (1) to (4) shown in the present invention.
As described above, in ladle refining, the gas stirring time is 5 minutes or more, the slag thickness in a stationary state is 260 mm or more and less than 400 mm, and the relationship between the gas stirring time and the amount of MgO in the slag Is refined so as to satisfy the formula (1) to formula (4), and in the vacuum degassing refining, the reflux time of the molten steel is refined so as to satisfy the formula (5), and the reflux amount of the molten steel is expressed by the formula ( By refining to satisfy 6), the oxide inclusions (alumina inclusions, spinel inclusions, MgO inclusions) in the steel are reduced, and a steel sheet having excellent bendability can be produced.

なお、今回開示された実施の形態はすべての点で例示であって制限的なものではないと考えられるべきである。本発明の範囲は上記した説明ではなくて特許請求の範囲によって示され、特許請求の範囲と均等の意味及び範囲内でのすべての変更が含まれることが意図される。アルミキルド鋼は、上述したように、転炉１の出鋼時にＡｌを投入することによって脱酸するものであっても、二次精錬時にＡｌを投入して脱酸するようなものであってもよい。また、取鍋精錬では、電磁攪拌により溶鋼を攪拌するようなＡＳＥＡ−ＳＫＦは対象としていない。また、本発明の製造方法では、溶鋼をＳｉによりキルドしたシリコンキルド鋼は含まない。   The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. As described above, the aluminum killed steel may be deoxidized by introducing Al when steel is output from the converter 1, or may be deoxidized by adding Al during secondary refining. Good. Moreover, in ladle refining, ASEA-SKF which stirs molten steel by electromagnetic stirring is not made into object. Further, the production method of the present invention does not include silicon killed steel obtained by killing molten steel with Si.

１ 転炉
２ 取鍋
３ 二次精錬装置
５ 取鍋精錬装置
６ ＲＨ装置 1 Converter 2 Ladle 3 Secondary refining equipment 5 Ladle refining equipment 6 RH equipment

Claims (1)

転炉又は電気炉から出鋼した溶鋼に対して２０００ｌ／ｍｉｎ以上４０００ｌ／ｍｉｎ以下にてガス攪拌による取鍋精錬を行った後、真空脱ガス精錬を行うことでアルミキルド鋼を製造する高清浄アルミキルド鋼の製造方法において、
前記取鍋精錬の際には、前記ガス攪拌の時間を５分以上とすると共に、静止状態でのスラグ厚を２６０ｍｍ以上４００ｍｍ未満とし、且つ、前記ガス攪拌の時間とスラグ中のＭｇＯ量との関係が式（１）〜式（４）を満たすように精錬し、
前記真空脱ガス精錬の際には、溶鋼の還流時間が式（５）を満たすように精錬すると共に、溶鋼の還流量が式（６）を満たすように精錬することを特徴とする高清浄アルミキルド鋼の製造方法。
Figure 2010189691
 Highly clean aluminum killed steel that produces aluminum killed steel by performing vacuum degassing refining after performing ladle refining by gas stirring at 2000 l / min to 4000 l / min for molten steel produced from a converter or electric furnace In the steel manufacturing method,
In the ladle refining, the gas stirring time is 5 minutes or more, the slag thickness in a stationary state is 260 mm or more and less than 400 mm, and the gas stirring time and the amount of MgO in the slag Refined so that the relationship satisfies the formulas (1) to (4),
In the vacuum degassing refining, a high clean aluminum kill characterized by refining so that the reflux time of the molten steel satisfies the formula (5) and refining so that the reflux amount of the molten steel satisfies the formula (6) Steel manufacturing method.
Figure 2010189691
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