JP2008043979A - Continuous casting method for low aluminum steel - Google Patents
Continuous casting method for low aluminum steel Download PDFInfo
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本発明は、低Ａｌ鋼の連続鋳造方法に関し、浸漬ノズルの閉塞を抑制し、かつ介在物欠陥、気泡欠陥ともに少ない鋳片の連続鋳造方法に関するものである。 The present invention relates to a continuous casting method of low Al steel, and relates to a continuous casting method of a slab that suppresses clogging of an immersion nozzle and has few inclusion defects and bubble defects.
一般に、鋼の連続鋳造においては、タンディッシュに収容された溶鋼を、タンディッシュ底部に設けた浸漬ノズルを通して連続鋳造用鋳型へ供給する。 Generally, in continuous casting of steel, molten steel contained in a tundish is supplied to a continuous casting mold through an immersion nozzle provided at the bottom of the tundish.
このとき、タンディッシュ内の溶鋼中にＡｌ2Ｏ3、ＴｉＯ2などの非金属介在物が含まれている場合には、溶鋼中の非金属介在物が浸漬ノズルの壁面に付着し、短期のうちに浸漬ノズル閉塞を引き起こす不具合があった。 At this time, when non-metallic inclusions such as Al 2 O 3 and TiO 2 are contained in the molten steel in the tundish, the non-metallic inclusions in the molten steel adhere to the wall surface of the immersion nozzle, and the short-term There was a problem that caused the immersion nozzle to close.
このため、通常はアルゴンガスや窒素ガスといった不活性ガスを浸漬ノズル内に吹き込んで非金属介在物の付着を防止しており、この点に関する文献としては特許文献１や特許文献２などが知られている。 For this reason, normally, inert gas such as argon gas or nitrogen gas is blown into the immersion nozzle to prevent the adhesion of non-metallic inclusions, and Patent Literature 1 and Patent Literature 2 are known as literature relating to this point. ing.
また、不活性ガスを吹き込むことにより、その気泡が非金属介在物を捕捉したのちに浮上し、結果として鋳片に残存する非金属介在物個数が減少し、介在物欠陥を少なくする効果もある。 In addition, by blowing an inert gas, the bubbles rise after capturing the nonmetallic inclusions, resulting in a reduction in the number of nonmetallic inclusions remaining in the slab and the effect of reducing inclusion defects. .
一方、不活性ガスを吹き込むことにより形成した気泡は、溶鋼が凝固して生成する凝固殻に捕捉され、気泡欠陥の原因となる。気泡欠陥とは凝固殻に捕捉された気泡が原因となって圧延時に線状の疵が生成するもので、製品の外観を著しく損ねる。このため、一定量以上の不活性ガスを吹き込むことは問題がある。 On the other hand, bubbles formed by blowing an inert gas are trapped in a solidified shell formed by solidification of molten steel, which causes bubble defects. The bubble defect is caused by bubbles trapped in the solidified shell, and linear wrinkles are generated during rolling, which significantly impairs the appearance of the product. For this reason, there is a problem in blowing an inert gas of a certain amount or more.
そこで、ノズル閉塞や介在物欠陥と気泡欠陥の両方を防止するため、ガス吹き込み量などの適正化が図られてきた。例えば、特許文献３では連続鋳造の際のスループットおよび鋼中酸素量に基づいて溶鋼に吹き込むべきガスの吹き込み量を予め計算によって求め、得られた結果に従って浸漬ノズルを通過する溶鋼に不活性ガスを吹き込む方法を提案している。この場合、スループットが低下すればガス吹き込み量を下げるとしている。また、特許文献４では、溶鋼の全酸素量Ｔ．Ｏを２６ｐｐｍ以下とし、かつ、Ｔ．Ｏに応じて不活性ガス吹き込み量を決定する方法を提案している。また、特許文献５では、溶鋼中Ｔ．Ｏ、スラグ中Ｔ．Ｆｅに応じて（ガス流量／スループット）比を決定する方法を提案している。
Therefore, in order to prevent both nozzle clogging and inclusion defects and bubble defects, optimization of gas blowing amount and the like has been attempted. For example, in Patent Document 3, the amount of gas to be blown into the molten steel based on the throughput during continuous casting and the amount of oxygen in the steel is calculated in advance, and inert gas is supplied to the molten steel that passes through the immersion nozzle according to the obtained result. Proposes a method of blowing. In this case, if the throughput decreases, the gas blowing amount is decreased. In Patent Document 4, the total oxygen content T.I. O is 26 ppm or less, and T.I. A method of determining the amount of inert gas blown according to O is proposed. Moreover, in
これらの方法は、同一スループットであれば、ひとつの取鍋の溶鋼に対してはガス吹き込み量を一定に規定するものであった。また、基本的にＡｌで脱酸を行う高Ａｌ鋼を対象とするものであった。 In these methods, if the throughput is the same, the amount of gas blown to the molten steel in one ladle is regulated to be constant. Moreover, it was intended for high Al steel that basically undergoes deoxidation with Al.
現在の連続鋳造においては、生産性を上げ、歩留まりを高める目的から、一回の鋳造で取鍋を数個〜十数個交換する。取鍋を交換する際にはタンディッシュに貯めた溶鋼を消費しつつ鋳造を継続するため、鋳造自体が停止することはなく、連続鋳造機の稼働率を上げることが可能となっている。 In the current continuous casting, several to ten or more ladles are exchanged in one casting for the purpose of increasing productivity and increasing yield. When exchanging the ladle, the casting is continued while consuming the molten steel stored in the tundish, so that the casting itself does not stop and the operating rate of the continuous casting machine can be increased.
発明者らが得た知見によると、同一の取鍋から注入された溶鋼であっても、その部位によって介在物欠陥の発生率が異なる。すなわち、前記特許文献３や特許文献４のように、同一の取鍋溶鋼に対して一定のガス吹き込み量を設定するだけでは、鋳片の全長にわたって介在物欠陥と気泡欠陥、いずれも低位にすることは困難である。 According to the knowledge obtained by the inventors, even with molten steel poured from the same ladle, the incidence of inclusion defects varies depending on the site. That is, as in Patent Document 3 and Patent Document 4, only by setting a constant gas blowing amount for the same ladle molten steel, both inclusion defects and bubble defects are lowered over the entire length of the slab. It is difficult.
さらに、最近では、材質特性などの観点から、Ａｌで脱酸を行わない低Ａｌ鋼の製造が行われている。低Ａｌ鋼ではＡｌの代わりにＳｉやＴｉを用いて脱酸を行う。 Furthermore, recently, from the viewpoint of material properties and the like, low Al steel that is not deoxidized with Al is being manufactured. For low Al steel, deoxidation is performed using Si or Ti instead of Al.
発明者らが得た知見によると、Ａｌで脱酸する鋼と主にＳｉやＴｉで脱酸する鋼では製造する際のＴ．ＯやＴ．Ｆｅが大きくなり、前記特許文献４や特許文献５のような方法でスループットを決定することは難しい。また、Ａｌで脱酸を行わない低Ａｌ鋼では、前記した同一取鍋溶鋼における部位による介在物欠陥発生率の差が非常に大きい。
According to the knowledge obtained by the inventors, the steel that is deoxidized with Al and the steel that is mainly deoxidized with Si or Ti have a T.W. O and T.W. Since Fe becomes large, it is difficult to determine the throughput by the method described in Patent Document 4 and
本発明はかかる事情に鑑みてなされたもので、Ａｌ脱酸を行わない低Ａｌ鋼の製造において、同一の取鍋から注入された溶鋼について、浸漬ノズルの詰まりを抑制したうえで、いずれの部位においても介在物欠陥と気泡欠陥の発生を抑制できる連続鋳造方法を提供することを目的とする。 The present invention has been made in view of such circumstances, and in the production of low Al steel that does not perform Al deoxidation, any part of the molten steel injected from the same ladle is prevented from clogging the immersion nozzle. It aims at providing the continuous casting method which can suppress generation | occurrence | production of an inclusion defect and a bubble defect.
上記課題を解決するために、本発明は以下の構成を要旨とする。
すなわち、（１）溶鋼のＡｌ濃度が１００ｐｐｍ以下の低Ａｌ鋼を鋳造するに当たり、複数個の取鍋を順次交換してタンディッシュに溶鋼を供給し、タンディッシュの底部に設けた浸漬ノズルを通して不活性ガスを吹き込みつつ連続鋳造用鋳型に供給する連続鋳造方法において、取鍋交換部近傍のみガス吹き込み量を増加し、同時に溶鋼のスループットを低下することを特徴とする鋳片の連続鋳造方法である。
また、（２）前記（１）記載の連続鋳造方法において、前鍋の溶鋼量が１／１０になる時点から、後鍋の溶鋼量が８／１０になる時点までの区間の全部もしくは一部を取鍋交換部近傍とし、ガス吹き込み量を増加し、同時に溶鋼のスループットを低下することを特徴とする鋳片の連続鋳造方法である。
また、（３）前記（１）もしくは（２）記載の連続鋳造方法において、取鍋交換部近傍のガス吹き込み量がストランド当たり７．０（ＮＬ／ｍｉｎ）以上であることを特徴とする鋳片の連続鋳造方法である。
また、（４）前記（１）〜（３）記載の連続鋳造方法において、取鍋交換部近傍のストランド当たり溶鋼のスループットが３．３（ｔｏｎ／ｍｉｎ）以下であることを特徴とする鋳片の連続鋳造方法である。
また、（５）前記（１）〜（４）記載の連続鋳造方法において、取鍋交換部近傍以外のガス吹き込み量がストランド当たり１．０〜５．０（ＮＬ／ｍｉｎ）の範囲にあることを特徴とする鋳片の連続鋳造方法である。
In order to solve the above problems, the present invention is summarized as follows.
That is, (1) When casting low Al steel having an Al concentration of 100 ppm or less in molten steel, a plurality of ladles are sequentially replaced to supply the molten steel to the tundish, and are not passed through an immersion nozzle provided at the bottom of the tundish. In a continuous casting method of supplying active gas to a continuous casting mold while blowing an active gas, it is a continuous casting method of a slab characterized by increasing the gas blowing amount only in the vicinity of the ladle replacement part and simultaneously reducing the throughput of molten steel. .
(2) In the continuous casting method according to (1), all or part of a section from the time when the amount of molten steel in the front pan becomes 1/10 to the time when the amount of molten steel in the rear pan becomes 8/10. This is a continuous casting method for a slab characterized in that it is in the vicinity of a ladle exchanging portion, the amount of gas blown is increased, and at the same time the throughput of molten steel is reduced.
(3) In the continuous casting method according to (1) or (2), the gas blowing amount in the vicinity of the ladle replacement part is 7.0 (NL / min) or more per strand. This is a continuous casting method.
(4) In the continuous casting method according to (1) to (3), the slab is characterized in that the throughput of molten steel per strand in the vicinity of the ladle replacement part is 3.3 (ton / min) or less. This is a continuous casting method.
Moreover, (5) In the continuous casting method according to the above (1) to (4), the amount of gas blowing other than the vicinity of the ladle replacement part is in the range of 1.0 to 5.0 (NL / min) per strand. This is a continuous casting method of a slab characterized by the following.
本発明を実施することにより、低Ａｌ鋼における連続鋳造時の浸漬ノズルの詰まりを抑制したうえで、いずれの部位においても介在物欠陥と気泡欠陥の発生を抑制することができる。 By implementing the present invention, clogging of the immersion nozzle during continuous casting in low Al steel can be suppressed, and the occurrence of inclusion defects and bubble defects can be suppressed in any part.
発明者らは、上記の目的を達成すべく調査研究を重ねた結果、同一取鍋の溶鋼であっても、注入開始時と、注入終了時に介在物欠陥が増加することを見出した。 As a result of repeated investigations and studies to achieve the above object, the inventors have found that inclusion defects increase at the start of injection and at the end of injection even for molten steel in the same ladle.
すなわち、注入開始時はタンディッシュの溶鋼量が少なく、周囲に存在する空気からの酸化を受けやすく、溶鋼中の脱酸元素（ＡｌやＴｉやＳｉ）が酸化され、非金属介在物が増加する。 That is, at the start of injection, the amount of molten steel in the tundish is small, and is susceptible to oxidation from the air present in the surroundings, deoxidizing elements (Al, Ti and Si) in the molten steel are oxidized, and nonmetallic inclusions increase. .
一方、注入終了時には取鍋内のスラグが溶鋼とともに注入され、懸濁することでスラグ中のＦｅＯやＭｎＯが溶鋼中の脱酸元素（ＡｌやＴｉやＳｉ）と反応し、非金属介在物が生成することで介在物欠陥が増加する。 On the other hand, at the end of pouring, the slag in the ladle is poured together with the molten steel and suspended so that FeO and MnO in the slag react with deoxidizing elements (Al, Ti and Si) in the molten steel, and non-metallic inclusions are formed. Inclusion defects are increased by the generation.
このような現象は、複数個の取鍋を交換しつつ連続鋳造を行う際には必ず発生しうる現象であり、完全に抑制することは難しい。 Such a phenomenon is a phenomenon that can always occur when performing continuous casting while exchanging a plurality of ladles, and is difficult to completely suppress.
さらに、このような現象に対して鋳造する鋼種の影響を調査したところ、Ａｌを多量添加するＡｌ脱酸鋼ではその影響が小さいが、Ａｌをほとんど添加せず、主にＳｉやＴｉで脱酸する鋼ではその影響が大きいことを見出した。 Furthermore, when investigating the influence of the cast steel type on such a phenomenon, Al deoxidized steel to which a large amount of Al is added has little effect, but Al is hardly added and deoxidation is mainly performed with Si or Ti. It was found that the effect of steel is great.
その理由としては、Ａｌ脱酸鋼の場合には、空気やスラグからの酸化を受けた際にＡｌ2Ｏ3が生成するが、この非金属介在物自体は比較的凝集合体、浮上分離しやすいため、鋳造中に大部分が浮上してしまい、鋳片内に残りにくいことからその影響は小さい。一方、Ａｌをほとんど含まず、主にＳｉやＴｉで脱酸した鋼の場合、空気やスラグからの酸化を受けた際にＳｉＯ2やＴｉＯ2が生成するが、これら非金属介在物は凝集合体、浮上分離しにくく、非金属介在物が鋳片内に残りやすいことから悪影響が大きい。 The reason for this is that, in the case of Al deoxidized steel, Al 2 O 3 is generated when it is oxidized from air or slag, but this nonmetallic inclusion itself is relatively agglomerated and easily separated by floating. For this reason, most of the surface is floated during casting and is less likely to remain in the slab. On the other hand, in the case of steel that contains almost no Al and is mainly deoxidized with Si or Ti, SiO 2 and TiO 2 are formed when oxidized from air or slag, but these non-metallic inclusions are aggregated coalesced It is difficult to float and separate, and the non-metallic inclusions are likely to remain in the slab, so the adverse effect is great.
このような低Ａｌ鋼における鍋交換部の介在物欠陥を抑制する方法について熟考した結果、当該部分のみ不活性ガス流量を増加し、気泡による介在物の除去を促進することに思い至った。さらに、ガス吹き込み量を増やすと気泡欠陥が増加するため、当該部位のみスループットを低下し、気泡の浮上を促進することで、鋳片に残留する気泡個数を低減することを考えた。 As a result of careful consideration about the method for suppressing the inclusion defect in the pan replacement part in such a low Al steel, the inventors came up with the idea of increasing the inert gas flow rate only in this part and promoting the removal of inclusions by bubbles. Furthermore, since the bubble defects increase when the gas blowing amount is increased, it was considered that the number of bubbles remaining in the slab is reduced by reducing the throughput only at the relevant part and promoting the rising of the bubbles.
すなわち、本発明の主旨は、溶鋼のＡｌ濃度が１００ｐｐｍ以下の低Ａｌ鋼を鋳造するに当たり、複数個の取鍋を順次交換してタンディッシュに溶鋼を供給し、タンディッシュの底部に設けた浸漬ノズルを通して不活性ガスを吹き込みつつ連続鋳造用鋳型に供給する連続鋳造方法において、取鍋交換部近傍のみガス吹き込み量を増加し、同時に溶鋼のスループットを低下することである。 That is, the gist of the present invention is to provide a molten steel to the tundish by sequentially replacing a plurality of ladles when casting a low Al steel having an Al concentration of 100 ppm or less in the molten steel, and a dipping provided at the bottom of the tundish. In a continuous casting method in which an inert gas is blown into a continuous casting mold while blowing an inert gas through a nozzle, the gas blowing amount is increased only in the vicinity of the ladle replacement part, and at the same time the throughput of the molten steel is lowered.
この方法を実施することにより、多少の生産性低下はあるものの、低Ａｌ鋼の取鍋交換部近傍の介在物欠陥、気泡欠陥ともに抑制することが可能となる。 By implementing this method, although there is a slight reduction in productivity, it is possible to suppress both inclusion defects and bubble defects in the vicinity of the ladle replacement part of low Al steel.
なお、この場合、低Ａｌ鋼とはＳｉ脱酸鋼やＴｉ脱酸鋼などのほか、Ｔｉ脱酸やＳｉ脱酸を実施した後、ＣａやＭｇやＲＥＭなどを用いて介在物を改質した鋼種も含まれる。 In this case, low Al steel is Si deoxidized steel, Ti deoxidized steel, etc., and after Ti deoxidation and Si deoxidation, inclusions were modified using Ca, Mg, REM, etc. Steel types are also included.
図１には、不活性ガスを吹き込まない条件での鋳造時間と取鍋重量および鋳片の介在物量の関係を示す。前鍋の溶鋼量が１／１０になる時点から、後鍋の溶鋼量８／１０になる時点までの区間で特に介在物量の増加が顕著である。すなわち、この区間の全部もしくは一部でガス吹き込み量を増加し、スループットを低下するにより、必要な効果を得ることができる。 FIG. 1 shows the relationship between the casting time, ladle weight and the amount of inclusions in the slab under the condition where the inert gas is not blown. The increase in the amount of inclusions is particularly remarkable in the section from the time when the amount of molten steel in the front pan becomes 1/10 to the time when the amount of molten steel in the rear pan becomes 8/10. That is, the required effect can be obtained by increasing the gas blowing amount in all or part of this section and decreasing the throughput.
図２にはガス吹き込み量と介在物欠陥の関係を示す。取鍋交換部近傍では介在物欠陥が多いため、ガス吹き込み量を増やす必要があり、ストランド当たり７．０（ＮＬ／ｍｉｎ）以上あると好ましい。一方、取鍋交換部近傍以外ではガス吹き込み量が少なくても問題なく、ストランド当たり１．０（ＮＬ／ｍｉｎ）以上あれば良い。 FIG. 2 shows the relationship between the gas blowing amount and the inclusion defect. Since there are many inclusion defects in the vicinity of the ladle exchange part, it is necessary to increase the amount of gas blowing, and it is preferable that there are 7.0 (NL / min) or more per strand. On the other hand, there is no problem even if the gas blowing amount is small except in the vicinity of the ladle exchange part, and it is sufficient if it is 1.0 (NL / min) or more per strand.
図３にはストランド当たり溶鋼のスループットと気泡欠陥の関係を示す。溶鋼のスループット３．３（ｔｏｎ／ｍｉｎ）以下であればガス吹き込み量が多くても気泡欠陥はほとんどない。従って、取鍋交換部ではスループットを３．３（ｔｏｎ／ｍｉｎ）以下に低下することが必要である。取鍋交換部以外では、スループット３．３（ｔｏｎ／ｍｉｎ）以下にすることも可能であるが、例えば生産性を向上する目的でスループット５．０（ｔｏｎ／ｍｉｎ）にするためにはストランド当たりガス吹き込み量５．０（Ｌ／ｍｉｎ）以下にすれば良い。 FIG. 3 shows the relationship between the throughput of molten steel per strand and bubble defects. As long as the throughput of molten steel is 3.3 (ton / min) or less, there is almost no bubble defect even if the gas blowing amount is large. Therefore, it is necessary to reduce the throughput to 3.3 (ton / min) or less in the ladle exchange unit. Other than the ladle exchanging section, it is possible to reduce the throughput to 3.3 (ton / min) or less. For example, in order to increase the throughput to 5.0 (ton / min) for the purpose of improving productivity, The gas blowing amount may be 5.0 (L / min) or less.
転炉出鋼後の３００ｔｏｎの溶鋼をＲＨ真空脱ガス装置にて脱炭処理し、この溶鋼をいくつかの方法で脱酸した。この処理を各実施例について５回行い、合計１５００ｔｏｎの溶鋼を２ストランドスラブ連続鋳造装置にて鋳造し、鋳片を製造した。 The 300 ton molten steel after the converter steel was decarburized with an RH vacuum degassing apparatus, and this molten steel was deoxidized by several methods. This process was performed five times for each example, and a total of 1500 ton of molten steel was cast with a two-strand slab continuous casting apparatus to produce a slab.
このとき、取鍋交換部近傍、およびそれ以外の定常部のガス吹き込み量と溶鋼のスループットをいくつか変化させて鋳造を実施した。このとき、取鍋交換部とは前鍋の溶鋼量が１／１０になる時点から、後鍋の溶鋼量が８／１０になる時点までの区間とし、それ以外を定常部とした。 At this time, casting was carried out by changing the amount of gas blown in the vicinity of the ladle exchanging portion and other steady portions and the throughput of the molten steel. At this time, the ladle exchange part was defined as a section from the time when the amount of molten steel in the front pan became 1/10 to the time when the amount of molten steel in the rear pan became 8/10, and the rest as the steady part.
連続鋳造終了後にタンディッシュノズルおよび浸漬ノズルを観察した。さらに、上記鋳片を定法に従って熱間圧延、冷間圧延を実施し、冷延板を製造した。この冷延板の非金属介在物起因、気泡起因の表面欠陥を評価した。 After the end of continuous casting, the tundish nozzle and the immersion nozzle were observed. Furthermore, the said slab was hot-rolled and cold-rolled according to the usual method, and the cold rolled sheet was manufactured. The surface defects caused by non-metallic inclusions and bubbles caused by this cold-rolled sheet were evaluated.
このとき得られた鋼板の成分、および取鍋交換部近傍と定常部のストランド当たりガス吹き込み量と溶鋼のスループット、さらに成績として冷延板の表面性状、ノズル閉塞状況を、表１中に示す。表１において、Ｎｏ．１〜１１が本発明例であり、Ｎｏ．１２〜１９が比較例である。以下の本発明例、比較例の説明において示すＮｏ．は表１のＮｏ．に対応している。 Table 1 shows the components of the steel sheet obtained at this time, the amount of gas blown per strand in the vicinity of the ladle exchange part and the steady part, the throughput of the molten steel, and the surface properties of the cold-rolled sheet and the nozzle blockage as results. In Table 1, no. 1 to 11 are examples of the present invention. 12 to 19 are comparative examples. No. shown in the description of the present invention examples and comparative examples below. No. in Table 1. It corresponds to.
（本発明例１）（Ｎｏ．１）
ＲＨ真空脱ガス装置にて脱炭処理後Ｃ濃度を０．００１５質量％に調整した。金属Ａｌを添加後、溶鋼中溶存酸素濃度を２００ｐｐｍまで低下させ、その後金属Ｔｉを用いてＴｉ脱酸を行い、さらにミッシュメタル合金を添加した。このようにして溶製した溶鋼を取鍋交換部近傍のガス吹き込み量７（ＮＬ／ｍｉｎ）、溶鋼のスループット３．３（ｔ ｏｎ／ｍｉｎ）、定常部のガス吹き込み量５（ＮＬ／ｍｉｎ）、溶鋼のスループット５．５（ｔ ｏｎ／ｍｉｎ）の条件で鋳造した。
(Invention Example 1) (No. 1)
The C concentration was adjusted to 0.0015% by mass after decarburization with an RH vacuum degasser. After adding metal Al, the dissolved oxygen concentration in molten steel was reduced to 200 ppm, Ti Ti was then deoxidized using metal Ti, and a misch metal alloy was further added. The molten steel thus melted in the ladle exchanging portion near the gas blowing rate 7 (NL / min), the molten steel throughput 3.3 (ton / min), the steady portion gas blowing rate 5 (NL / min) Casting was performed under conditions of a molten steel throughput of 5.5 (ton / min).
鋳造終了後のタンディッシュノズルおよび浸漬ノズルには付着物はほとんどみられなかった。また冷延板には非金属介在物起因、気泡起因の表面欠陥は全く認められなかった。 There was almost no deposit on the tundish nozzle and the immersion nozzle after casting. Further, no surface defects caused by non-metallic inclusions and bubbles were observed on the cold-rolled sheet.
（本発明例２）（Ｎｏ．２〜９）
ＲＨ真空脱ガス装置にて脱炭処理した後の溶鋼を、表１に示すようにＴｉ脱酸、Ｔｉ−Ｃａ脱酸、Ｔｉ−ＲＥＭ脱酸から選択して脱酸した。このようにして溶製した溶鋼を、取鍋交換部近傍、および定常部のガス吹き込み量と溶鋼のスループットを表１に示すように変化させて鋳造した。
(Invention Example 2) (No. 2 to 9)
As shown in Table 1, the molten steel after the decarburization treatment by the RH vacuum degassing apparatus was selected from Ti deoxidation, Ti-Ca deoxidation, and Ti-REM deoxidation to be deoxidized. The molten steel thus melted was cast by changing the amount of gas blown in the vicinity of the ladle exchange part and the steady part and the throughput of the molten steel as shown in Table 1.
鋳造終了後のタンディッシュノズルおよび浸漬ノズルには付着物はほとんどみられなかった。また冷延板には非金属介在物起因、気泡起因の表面欠陥は全く認められなかった。 There was almost no deposit on the tundish nozzle and the immersion nozzle after casting. Further, no surface defects caused by non-metallic inclusions and bubbles were observed on the cold-rolled sheet.
（本発明例３）（Ｎｏ．１０、１１）
転炉にて溶鋼を脱炭処理し、出鋼時にＳｉもしくはＴｉを添加して脱酸を実施した。その後、ＲＨ真空脱ガス装置で成分調整を行ったのち、取鍋交換部近傍、および定常部のガス吹き込み量と溶鋼のスループットを定めて鋳造した。
(Invention Example 3) (No. 10, 11)
The molten steel was decarburized in a converter, and deoxidation was performed by adding Si or Ti at the time of steel output. Thereafter, the components were adjusted with the RH vacuum degassing apparatus, and then cast in the vicinity of the ladle exchange part, the gas blowing amount in the stationary part, and the throughput of the molten steel.
鋳造終了後のタンディッシュノズルおよび浸漬ノズルには付着物はほとんどみられなかった。また冷延板には非金属介在物起因、気泡起因の表面欠陥は全く認められなかった。 There was almost no deposit on the tundish nozzle and the immersion nozzle after casting. Further, no surface defects caused by non-metallic inclusions and bubbles were observed on the cold-rolled sheet.
（比較例１）（Ｎｏ．１２〜１５）
ＲＨ真空脱ガス装置にて脱炭、脱酸処理した後の溶鋼を、取鍋交換部近傍、定常部ともに同一のガス吹き込み量（２〜５（ＮＬ／ｍｉｎ））とし、溶鋼のスループットだけを変化して（取鍋交換部近傍：３．３（ｔｏｎ／ｍｉｎ）、定常部：５．０〜６．０（ｔｏｎ／ｍｉｎ））鋳造した。
(Comparative example 1) (No. 12-15)
The molten steel after decarburization and deoxidation treatment in the RH vacuum degassing apparatus is set to the same gas injection amount (2 to 5 (NL / min)) in the vicinity of the ladle exchange part and the stationary part, and only the molten steel throughput is achieved. The casting was carried out by changing (near ladle replacement part: 3.3 (ton / min), stationary part: 5.0 to 6.0 (ton / min)).
鋳造終了後のタンディッシュノズルおよび浸漬ノズルには付着物はほとんどみられなかった。冷延板の表面性状を観察したところ、取鍋交換部で介在物起因の欠陥が観察された。 There was almost no deposit on the tundish nozzle and the immersion nozzle after casting. When the surface properties of the cold-rolled sheet were observed, defects due to inclusions were observed at the ladle replacement part.
（比較例２）（Ｎｏ．１６、１７）
ＲＨ真空脱ガス装置にて脱炭、脱酸処理した後の溶鋼を、取鍋交換部近傍、定常部ともに同一の溶鋼スループット（３．５〜５．０（ＮＬ／ｍｉｎ））とし、ガス吹き込み量だけを変化して（取鍋交換部近傍：７（Ｌ／ｍｉｎ）、定常部：４〜５（Ｌ／ｍｉｎ））鋳造した。
(Comparative example 2) (No. 16, 17)
The molten steel after decarburization and deoxidation treatment in the RH vacuum degassing apparatus has the same molten steel throughput (3.5 to 5.0 (NL / min)) in the vicinity of the ladle exchange part and the steady part, and gas is injected. Only the amount was changed (the vicinity of the ladle exchange part: 7 (L / min), the stationary part: 4 to 5 (L / min)) and cast.
鋳造終了後のタンディッシュノズルおよび浸漬ノズルには付着物はほとんどみられなかった。冷延板の表面性状を観察したところ、取鍋交換部で気泡起因の欠陥が観察された。 There was almost no deposit on the tundish nozzle and the immersion nozzle after casting. When the surface properties of the cold-rolled sheet were observed, defects due to bubbles were observed at the ladle replacement part.
（比較例３）（Ｎｏ．１８）
ＲＨ真空脱ガス装置にて脱炭、脱酸処理した後の溶鋼を、取鍋交換部近傍、定常部ともに同一の溶鋼スループット（５．０（ＮＬ／ｍｉｎ））、ガス吹き込みなしで鋳造した。
(Comparative Example 3) (No. 18)
The molten steel after decarburization and deoxidation treatment by the RH vacuum degassing apparatus was cast in the vicinity of the ladle exchange part and the steady part with the same molten steel throughput (5.0 (NL / min)) and no gas blowing.
鋳造終了後のタンディッシュノズルおよび浸漬ノズルには大量の付着物が観察された。冷延板の表面性状を観察したところ、取鍋交換部、定常部ともに介在物起因の欠陥が観察された。 A large amount of deposits were observed on the tundish nozzle and the immersion nozzle after completion of the casting. When the surface properties of the cold-rolled sheet were observed, defects due to inclusions were observed in both the ladle changing part and the steady part.
（比較例４）（Ｎｏ．１９）
ＲＨ真空脱ガス装置にて脱炭、脱酸処理した後の溶鋼を、取鍋交換部近傍、定常部ともに同一の溶鋼スループット（４、０（ＮＬ／ｍｉｎ））、同一のガス吹き込み量（１０（ＮＬ／ｍｉｎ））で鋳造した。
(Comparative Example 4) (No. 19)
The molten steel that has been decarburized and deoxidized by the RH vacuum degassing apparatus has the same molten steel throughput (4, 0 (NL / min)) and the same gas blowing amount (10 (NL / min)).
鋳造終了後のタンディッシュノズルおよび浸漬ノズルには付着物はほとんどみられなかった。冷延板の表面性状を観察したところ、取鍋交換部、定常部ともに気泡起因の欠陥が観察された。 There was almost no deposit on the tundish nozzle and the immersion nozzle after casting. When the surface properties of the cold rolled sheet were observed, defects due to bubbles were observed in both the ladle changing part and the steady part.
以上、本発明の実施の形態を説明したが、本発明は、上記した形態に限定されるものでなく、要旨を逸脱しない条件の変更等は全て本発明の適用範囲である。例えば、鋳型に溶鋼を注湯した際、電磁撹拝装置を用いて鋳型内の溶鋼を撹拝することができる。更に、ガスの吹き込みは、浸漬ノズルのポーラス耐火物からの吹き込み、浸漬ノズルの上流側に設けたタンディッシュに取付けた上ノズル等から行うことができ、ポーラス耐火物と浸漬ノズルから併用して吹き込むこともできる。 Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and all changes in conditions and the like that do not depart from the gist are within the scope of the present invention. For example, when molten steel is poured into a mold, the molten steel in the mold can be stirred using an electromagnetic stirring device. Further, the gas can be blown from the porous refractory of the immersion nozzle or from the upper nozzle attached to the tundish provided upstream of the immersion nozzle, and blown in combination from the porous refractory and the immersion nozzle. You can also.
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