JP3377325B2 - Melting method of high cleanness ultra low carbon steel - Google Patents

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【産業上の利用分野】本発明は、自動車用薄板等に用い
られる高清浄度極低炭素の高清浄度極低炭素鋼、すなわ
ちトータル炭素濃度が３０ｐｐｍ以下であり、固溶した
炭素をＴｉやＮｂで固定した鋼（以下ＩＦ鋼という）の
効率的な溶製方法に関する。BACKGROUND OF THE INVENTION The present invention relates to a high cleanliness ultra-low carbon steel of high cleanliness ultra-low carbon used for thin plates for automobiles, that is, having a total carbon concentration of 30 ppm or less and solid-solved carbon of Ti or Ti. The present invention relates to an efficient melting method of steel fixed with Nb (hereinafter referred to as IF steel).

【０００２】[0002]

【従来の技術】ＩＦ鋼の溶製においては、３０ｐｐｍ以
下という極低炭素材を高い清浄度で高速処理する技術が
必要である。2. Description of the Related Art In the production of IF steel, it is necessary to have a technique for treating extremely low carbon materials of 30 ppm or less at high cleanliness and high speed.

【０００３】極低炭素溶鋼の減圧脱炭方法としては、Ｒ
Ｈ、ＤＨが広く用いられている。しかし、炭素濃度を２
０ｐｐｍ以下に低下させる場合には脱炭速度が低下し、
長時間を要するという問題があった。これを解決するた
めには、通常、ＲＨにおける還流用Ａｒガス流量の増加
や、浸漬管径の増大、あるいはＤＨにおける槽昇降速度
の増加等による溶鋼還流速度の増大といった方法が取ら
れている。しかし、還流用Ａｒガス流量の増加は耐火物
の寿命の低下を招くため限界があり、浸漬管径の増大は
寸法制約上の限界があり、槽昇降速度の増加も溶鋼の追
従性からの限界がある。As a vacuum decarburization method for ultra low carbon molten steel, R
H and DH are widely used. However, if the carbon concentration is 2
When it is reduced to 0 ppm or less, the decarburization rate decreases,
There was a problem that it took a long time. In order to solve this, methods such as increasing the flow rate of Ar gas for reflux in RH, increasing the diameter of the dipping pipe, or increasing the rate of molten steel recirculation by increasing the ascending / descending speed in DH are usually used. However, there is a limit to the increase in the flow rate of the Ar gas for reflux because it shortens the life of the refractory, and there is a limit to the increase in the diameter of the immersion pipe due to dimensional constraints. There is.

【０００４】また、「材料とプロセス」、第３巻（１９
９０）、１６８頁には、ＲＨにおける槽内へのＡｒガス
吹き込みによる反応界面積の増大方法が示されている
が、極低炭素濃度域において効果を得るためには５０Ｎ
Ｌ／（ｔｏｎ・分）以上という大量のガス吹き込みが必
要であり、槽内で激しいスプラッシュを発生させるた
め、操業性を著しく損ねるという問題がある。さらに、
特開昭５７−２００５１４号公報には、ＲＨにおいて環
流用のガスを取鍋の底部より吹き込む方法が示されてい
るが、極低炭素濃度領域で効果を出すために多量のガス
を導入した場合には、浸漬管耐火物下端部に気泡が衝突
するため耐火物損耗が激しいという問題点を有してい
る。Also, "Materials and Processes", Volume 3 (19
90), page 168, a method for increasing the reaction interfacial area by blowing Ar gas into the tank in RH is shown.
It requires a large amount of gas injection of L / (ton · min) or more, and causes a violent splash in the tank, which causes a problem of impairing operability. further,
Japanese Patent Application Laid-Open No. 57-200514 discloses a method of blowing a gas for recirculation from the bottom of a ladle in RH, but when a large amount of gas is introduced in order to exert an effect in an extremely low carbon concentration region. Has a problem that the refractory wear is severe because bubbles collide with the lower end of the refractory in the immersion pipe.

【０００５】ＲＨにおいては、真空槽内で激しく攪拌さ
れている領域は上昇管上部の溶鋼面に過ぎず、他の真空
雰囲気に暴露されている溶鋼面は比較的穏やかな状態で
ある。したがって、処理開始時に浸漬管を浸漬する時点
で真空槽内に混入したスラグは、真空槽表面から内部に
巻き込まれにくいため真空槽外へ排出されにくく、転炉
スラグの影響が排除され得ない。また、脱炭処理後の脱
酸時に生成した酸化物も真空槽内溶鋼表面のスラグに吸
収されるのみで真空槽外には排出されにくい。従って、
処理終了時に復圧した時に圧力が低下して溶鋼表面位置
が低下するにつれて、脱酸生成物を含んだ真空槽内溶鋼
表面のスラグが再び溶鋼中に懸濁される。このため、Ｒ
Ｈは本質的に高清浄度鋼の溶製ができないという問題が
ある。In the RH, the region in the vacuum tank that is vigorously stirred is only the molten steel surface above the rising pipe, and the molten steel surface exposed to the other vacuum atmosphere is in a relatively gentle state. Therefore, since the slag mixed in the vacuum tank at the time of immersing the dip pipe at the start of the process is not easily caught inside the vacuum tank surface, it is difficult to discharge it outside the vacuum tank, and the influence of the converter slag cannot be eliminated. Further, the oxide generated during deoxidation after the decarburization treatment is only absorbed by the slag on the surface of the molten steel in the vacuum tank and is hardly discharged outside the vacuum tank. Therefore,
As the pressure decreases and the molten steel surface position decreases when the pressure is restored at the end of the treatment, the slag on the molten steel surface in the vacuum tank containing the deoxidation product is suspended again in the molten steel. Therefore, R
H has a problem that essentially, high cleanliness steel cannot be melted.

【０００６】これに対して、特開昭５３−６７６０５号
公報には、円筒形の管を浸漬し管内を減圧する減圧精錬
炉が示されているが、この炉では処理中に管内溶鋼と管
外溶鋼とを混合させることを目的として複数回減圧／復
圧を繰り返すため、溶鋼反応表面が高真空下にさらされ
る時間が短く、極低炭素鋼の溶製の場合には長時間を要
するという問題がある。一方、特開昭５１−５５７１７
号公報には、円筒形の管を浸漬し管内を減圧した上で取
鍋底部のポーラスレンガよりＡｒガスを吹き込む減圧精
錬炉が示されている。しかし、これらで示されているよ
うな円筒形の浸漬管に溶鋼を吸い上げ、取鍋底部に設け
たガス吹込み孔から不活性ガスを導入する炉のみでは安
定して極低炭領域まで脱炭することができないため、実
用化には至っておらず、また、この炉を極低炭素鋼や高
清浄度鋼の精錬に使用した例は示されていない。さら
に、この炉のみでは処理中のスプラッシュの発生も安定
して抑制できず、また、転炉スラグを巻き込むため高清
浄度鋼の安定した溶製も難しいという問題がある。On the other hand, Japanese Patent Laid-Open No. 53-67605 discloses a decompression refining furnace in which a cylindrical tube is immersed to reduce the pressure inside the tube. In this furnace, molten steel in the tube and the tube are treated during processing. Since depressurization / re-pressurization is repeated multiple times for the purpose of mixing with external molten steel, the time during which the molten steel reaction surface is exposed to high vacuum is short, and it takes a long time for the production of extremely low carbon steel. There's a problem. On the other hand, JP-A-51-55717
The publication discloses a decompression refining furnace in which a cylindrical tube is immersed to decompress the inside of the tube and then Ar gas is blown from the porous brick at the bottom of the ladle. However, it is possible to stably decarburize to the ultra-low coal area only with a furnace that sucks molten steel into a cylindrical dipping pipe as shown in these and introduces inert gas from the gas injection hole provided at the bottom of the ladle. Since it cannot be done, it has not been put to practical use, and no example of using this furnace for refining extremely low carbon steel or high cleanliness steel is shown. Further, there is a problem that the generation of splash during processing cannot be stably suppressed only by this furnace and that stable melting of high cleanliness steel is difficult because the converter slag is involved.

【０００７】特願平３−１４６５４０号明細書には、直
胴型浸漬管による極低炭素鋼の溶製技術が開示されてい
る。これは、真空下に暴露されている溶鋼表面部分を有
効に攪拌し、実質的な表面積を増大させることが極めて
効果的であるという知見に基づいたもので、吹き込まれ
たガスが真空に暴露されている溶鋼表面に浮上する領域
である気泡活性面を広くとることで極めて効率的な脱炭
を可能としている。しかし、ＩＦ鋼の溶製は単に極低炭
素化するのみでは成し遂げられず、介在物が少ない高清
浄度鋼を同時に溶製する必要があり、この点については
何ら言及されていない。このような直胴型浸漬管を用い
た場合には浸漬管径が大きくなるため、処理開始時に浸
漬管を浸漬する時点で真空槽内に混入するスラグ量は、
たとえば底吹きガスで攪拌しつつ浸漬管を浸漬したとし
てもＲＨよりもはるかに多く、このスラグをすみやかに
浸漬管外に排出しない限り高清浄度鋼は溶製できない。Japanese Patent Application No. 3-146540 discloses a technique for melting ultra-low carbon steel by using a straight body type immersion pipe. This is based on the finding that it is extremely effective to effectively agitate the molten steel surface portion exposed under vacuum and increase the substantial surface area, and the blown gas is exposed to the vacuum. It is possible to achieve extremely efficient decarburization by widening the bubble activation surface, which is the region that floats on the molten steel surface. However, smelting of IF steel cannot be achieved by merely reducing the carbon content to a very low level, and it is necessary to simultaneously smelt high-cleanliness steel with few inclusions, and no mention is made of this point. When such a straight body type immersion pipe is used, the diameter of the immersion pipe becomes large, so the amount of slag mixed in the vacuum tank at the time of dipping the immersion pipe at the start of the treatment is
For example, even if the dipping pipe is dipped while being stirred with a bottom-blown gas, the amount is much higher than that of RH, and high-cleanliness steel cannot be melted unless this slag is promptly discharged to the outside of the dipping pipe.

【０００８】一方、２次精錬炉へ持ち込まれた転炉スラ
グは酸化鉄や酸化マンガン濃度が高いため、脱酸後溶鋼
中に溶解している脱酸元素、例えばＡｌとスラグが反応
し、新たな介在物を生成して鋼の清浄度を低下させると
いう問題がある。これに対しては、特開昭５９−４７３
１４号公報に転炉出鋼時のスラグ流出を抑制するために
出鋼工程の終了間近に半球状の流出防止具を転炉出鋼孔
にあてがう技術が開示されているが、この技術では完全
にはスラグの流出は防止できない。転炉スラグの取鍋内
への流出を完全に防止するため、スラグとともに溶鋼を
も転炉に残留させ廃棄する方法があるが、溶鋼歩留の低
下を招くという問題がある。また、ＤＨでは浸漬管に薄
鋼板製の蓋をした上で取鍋内溶鋼に浸漬する方法が用い
られているが、蓋のコストがかかる上に、浸漬管外部の
取鍋内スラグは改質されないという問題がある。また、
特開昭６０−２１１００９号公報には、転炉出鋼末期に
出鋼孔から排出中のスラグにスラグ還元剤を吹き込んで
スラグを改質した状態で規定量のスラグを取鍋内へ移す
技術が開示されているが、この技術のみでは高清浄度鋼
を製造することはできない。On the other hand, since the converter slag brought into the secondary refining furnace has a high concentration of iron oxide and manganese oxide, the deoxidizing element dissolved in the molten steel, such as Al, reacts with the slag after deoxidation, and There is a problem in that the cleanliness of steel is reduced by the generation of various inclusions. For this, Japanese Patent Laid-Open No. 59-473
Japanese Unexamined Patent Publication No. 14 discloses a technique of applying a hemispherical outflow preventive tool to a converter tapping hole near the end of the tapping step in order to suppress slag outflow when tapping the converter. The outflow of slag cannot be prevented. In order to completely prevent the converter slag from flowing into the ladle, there is a method of leaving the molten steel together with the slag in the converter and discarding it, but there is a problem that the molten steel yield is reduced. Further, in DH, a method is used in which a dipping pipe is covered with a thin steel plate lid and then immersed in molten steel in a ladle. However, in addition to the cost of the lid, the slag in the ladle outside the dipping pipe is modified. There is a problem that is not done. Also,
Japanese Patent Application Laid-Open No. 60-211009 discloses a technique for transferring a specified amount of slag into a ladle in a state where the slag is reformed by blowing a slag reducing agent into the slag being discharged from the tap hole at the end of tapping of the converter. However, it is not possible to produce a high-cleanliness steel by this technology alone.

【０００９】[0009]

【発明が解決しようとする課題】本発明は、「材料とプ
ロセス」、第３巻（１９９０）１６８頁や特開昭５７−
２００５１４号公報に示されたＲＨでの極低炭素鋼溶製
方法における真空槽内に混入したスラグや脱酸生成物が
真空槽外へ排出されにくく、復圧時に脱酸生成物を含ん
だ真空槽内溶鋼表面のスラグが再び溶鋼中に懸濁される
ため、本質的に高清浄度鋼の溶製ができないという問題
点、特開昭５３−６７６０５号公報、特開昭５１−５５
７１７号公報、特願平３−１４６５４０号明細書に示さ
れた直胴型浸漬管を用いた極低炭素鋼溶製方法における
浸漬管内に混入するスラグ量が多く、これを速やかに排
除しない限り高清浄度鋼の溶製ができないという問題点
を解決するとともに、特開昭５９−４７３１４号公報に
示された方法の転炉出鋼時のスラグ流出は完全には防止
できないという問題点、特開昭６０−２１１００９号公
報に示された方法のみでは高清浄度鋼を製造することは
できないという問題点を解決し、直胴型浸漬管によるＩ
Ｆ鋼の溶製方法を提供することを目的とする。DISCLOSURE OF THE INVENTION The present invention is described in "Materials and Processes", Volume 3, (1990) p. 168 and JP-A-57-57.
The slag and deoxidation products mixed in the vacuum tank in the RH ultra-low carbon steel smelting method disclosed in Japanese Patent Publication No. 200514 are difficult to be discharged to the outside of the vacuum tank, and a vacuum containing the deoxidation products at the time of recompression. Since the slag on the surface of the molten steel in the tank is suspended again in the molten steel, it is essentially impossible to produce high-cleanliness steel. JP-A-53-67605 and JP-A-51-55
No. 717 and Japanese Patent Application No. 3-146540, there is a large amount of slag mixed in the dip pipe in the ultra low carbon steel smelting method using the straight body type dip pipe, and unless it is promptly removed. In addition to solving the problem that high cleanliness steel cannot be melted, the problem that the slag outflow at the time of tapping the converter in the method disclosed in Japanese Patent Laid-Open No. 59-47314 cannot be completely prevented. The problem that a high cleanliness steel cannot be produced only by the method disclosed in Japanese Laid-Open Patent Publication No. 60-211009 has been solved, and I by a straight barrel type dipping pipe is solved.
An object of the present invention is to provide a melting method for F steel.

【００１０】[0010]

【課題を解決するための手段】本発明は、取鍋内溶鋼表
面の一部に１個または２個以上の内径の異なる直胴部か
らなる直胴型浸漬管を浸漬し、当該浸漬管内のみを真空
としながら精錬する高清浄度極低炭素鋼の溶製方法にお
いて、浸漬管内溶鋼の浴深Ｈの０．５Ｈよりも深い位置
に設けたガス吹込み孔から０．６〜１５ＮＬ／（ｍｉｎ
・ｔｏｎ）の攪拌用ガスを供給し、かつ、取鍋内径Ｄと
浸漬管内径ｄの比ｄ／Ｄを０．３〜０．８、浸漬管下端
と浸漬管外溶鋼表面との距離Ｓを０．０３Ｈ〜０．３
Ｈ、ガス吹込み孔と浸漬管中心との水平方向の距離Ｌを
０．１ｄ〜０．５ｄ、浸漬管中心と取鍋中心との距離Ｋ
を０．０２Ｄ〜０．１２Ｄとし、取鍋低部からガスを吹
き込んで取鍋内溶鋼の上部にあるスラグを除去した後に
前記浸漬管を浸漬し、スラグを浸漬管外溶鋼表面に２〜
１５ｋｇ／ｔｏｎ存在させた状態で、真空度が７６０〜
３００Ｔｏｒｒの領域では攪拌用ガスを０．６〜２ＮＬ
／（ｍｉｎ・ｔｏｎ）、３００〜１００Ｔｏｒｒの領域
では１．０〜２．５ＮＬ（ｍｉｎ・ｔｏｎ）、１００Ｔ
ｏｒｒ以下の領域では２〜１５ＮＬ／（ｍｉｎ・ｔｏ
ｎ）の範囲で供給することを特徴とする高清浄度極低炭
素鋼の溶製方法である。ここで、ガスとしてはＡｒ、窒
素、ＣＯ、ＣＯ₂ を用いる。直胴型浸漬管は溶鋼浸漬部
から頭部まで単純に円柱とした形状を基本とするが、減
圧により吸い上げられる溶鋼面よりも上部であれば浸漬
管直径を増大させても減少させても全く問題はない。ガ
ス吹込み孔は取鍋底部に設けた多孔質煉瓦、取鍋底部に
設けたパイプ、または浸漬ランスとすることが望まし
い。なお、浸漬ランスとしては垂直形状のインジェクシ
ョンランス、先端をＬ字またはＪ字に近い形状に曲げた
ランスのいずれであっても同等の効果が得られる。According to the present invention, one or two or more straight body type dip pipes having straight body portions having different inner diameters are immersed in a part of the surface of molten steel in a ladle, and only in the dip pipe. In a method for smelting a high-cleanliness ultra-low carbon steel for refining while maintaining the vacuum in a vacuum, 0.6 to 15 NL / (min
・ Ton) stirring gas is supplied, the ratio d / D of the ladle inner diameter D and the immersion pipe inner diameter d is 0.3 to 0.8, and the distance S between the lower end of the immersion pipe and the molten steel surface outside the immersion pipe is 0.03H ~ 0.3
H, the horizontal distance L between the gas injection hole and the center of the immersion pipe is 0.1d to 0.5d, and the distance K between the center of the immersion pipe and the center of the ladle
To 0.02D to 0.12D, and blow gas from the bottom of the ladle.
After removing the slag on the top of the molten steel in the ladle
Immerse the dip pipe, and apply slag to the molten steel surface outside the dip pipe to
With the pressure of 15 kg / ton, the vacuum degree is 760-
In the region of 300 Torr, the stirring gas is 0.6 to 2 NL.
/ (Min · ton), 300-100 Torr area
Then 1.0 to 2.5 NL (min · ton), 100T
2-15 NL / (min · to in the region below orr
It is a method of melting high-cleanliness ultra-low carbon steel, which is characterized in that it is supplied in the range of n) . Here, Ar, nitrogen, CO, or CO ₂ is used as the gas. The straight-body type immersion pipe is basically shaped like a cylinder from the molten steel immersion part to the head, but if it is above the molten steel surface sucked up by depressurization, it does not matter whether the immersion pipe diameter is increased or decreased. No problem. The gas injection hole is preferably a porous brick provided at the bottom of the ladle, a pipe provided at the bottom of the ladle, or an immersion lance. As the immersion lance, the same effect can be obtained regardless of whether it is a vertical injection lance or a lance whose tip is bent into an L-shape or a J-shape.

【００１１】転炉、電気炉等の精錬炉から前記取鍋内に
溶鋼を出鋼する途中または出鋼後に脱酸剤を添加してス
ラグ中の（Ｔ・Ｆｅ）濃度を７％以下に低下させた後、
当該溶鋼表面の一部に前記浸漬管を浸漬することは好ま
しい。なお、脱酸剤としては金属Ａｌ、金属Ａｌを含む
酸化物、Ａｌ合金、Ｓｉ、Ｍｎ、これらを含む合金等を
用いる。A deoxidizing agent is added during or after tapping molten steel from a refining furnace such as a converter or an electric furnace into the ladle to reduce the (T · Fe) concentration in the slag to 7% or less. After letting
It is preferable to immerse the immersion pipe in a part of the surface of the molten steel. As the deoxidizer, metal Al, oxide containing metal Al, Al alloy, Si, Mn, alloy containing these, or the like is used.

【００１２】取鍋低部からガスを吹き込んで取鍋内溶鋼
の上部にあるスラグを除去した後に前記浸漬管を浸漬
し、スラグを浸漬管外溶鋼表面に２〜１５ｋｇ／ｔｏｎ
存在させた状態で、真空度が７６０〜３００Ｔｏｒｒの
領域では攪拌用ガスを０．６〜２ＮＬ／（ｍｉｎ・ｔｏ
ｎ）、３００〜１００Ｔｏｒｒの領域では１．０〜２．
５ＮＬ／（ｍｉｎ・ｔｏｎ）、１００Ｔｏｒｒ以下の領
域では２〜１５ＮＬ／（ｍｉｎ・ｔｏｎ）の範囲で供給
することは好ましい。Gas is blown from the lower part of the ladle to remove the slag at the upper part of the molten steel in the ladle, and then the above dipping pipe is dipped so that the slag is 2 to 15 kg / ton on the surface of the molten steel outside the dipping pipe.
In a state where the vacuum degree is 760 to 300 Torr, the stirring gas is added to 0.6 to 2 NL / (min · to
n), in the region of 300 to 100 Torr, 1.0 to 2.
In the region of 5 NL / (min · ton) or 100 Torr or less, it is preferable to supply in the range of 2 to 15 NL / (min · ton).

【００１３】脱炭処理終了後に１０Ｔｏｒｒ以下の状態
で前記浸漬管の真空排気用弁を閉じ、攪拌用ガスを供給
しながら真空度を大気圧まで復圧する過程で脱酸を行う
ことは好ましい。It is preferable to perform deoxidation in the process of closing the vacuum exhaust valve of the dip tube at a pressure of 10 Torr or less after completion of the decarburization treatment, and returning the vacuum degree to atmospheric pressure while supplying a stirring gas.

【００１４】脱炭処理終了後に前記浸漬管内溶鋼面と浸
漬管下端との距離Ｔを１０００〜２００ｍｍとしながら
１〜５分間保持することは好ましい。After completion of the decarburizing treatment, it is preferable to maintain the distance T between the molten steel surface in the dip pipe and the lower end of the dip pipe at 1000 to 200 mm for 1 to 5 minutes.

【００１５】なお、本発明において真空とは、７００〜
０．０１Ｔｏｒｒと定義する。また、取鍋低部とは、浸
漬管内溶鋼の浴深Ｈの０．５Ｈより深い位置の溶鋼なら
びに取鍋側壁および底部をいう。In the present invention, vacuum means 700 to
It is defined as 0.01 Torr. The lower part of the ladle refers to the molten steel at a position deeper than 0.5H of the bath depth H of the molten steel in the immersion pipe, and the ladle side wall and bottom.

【００１６】[0016]

【作用】図１に本発明の実施態様を模式的に示す。FIG. 1 schematically shows an embodiment of the present invention.

【００１７】直胴型浸漬管２を取鍋１内溶鋼４に浸漬
し、直胴型浸漬管２内のみを真空に引く精錬装置を用い
てＩＦ鋼を溶製するには、処理開始時に低部よりガス
を吹き込み、取鍋１上部にあるスラグ６を除去した後に
浸漬管２を浸漬し、によっても浸漬管２内に混入す
る少量のスラグを真空処理中に浸漬管２外にすみやかに
排出し、脱炭処理後、脱酸時に生成した介在物をすみ
やかに浮上分離し、スラグや雰囲気による酸化を抑制
することが全て重要である。特には従来考えられてい
た以上に重要であり、浸漬管２内に混入する少量のスラ
グを浸漬管２外に完全に排出しない限り脱酸時にスラグ
系の介在物となり、清浄性に大きな影響を与える。スラ
グが微細に***した極めて小さな粒子は排出されにくい
ため微細なスラグ系介在物を生成し、後の工程では浮上
分離できない。特にＩＦ鋼の溶製においては、脱炭を速
やかに進行させるために気泡活性面を広くする必要があ
るが、気泡活性面では激しい攪拌が生じるためスラグが
微細に***し、そのままでは極めて浮上分離しにくい。In order to melt IF steel using a refining device in which the straight barrel type dip tube 2 is dipped in the molten steel 4 in the ladle 1 and only the straight barrel type dip tube 2 is evacuated, a low temperature is required at the start of the treatment. The gas is blown from the part to remove the slag 6 on the upper part of the ladle 1 and then the dipping pipe 2 is dipped, so that a small amount of slag mixed in the dipping pipe 2 is quickly discharged to the outside of the dipping pipe 2 during the vacuum treatment. However, after decarburization, it is all important to promptly float and separate inclusions generated during deoxidation and suppress oxidation due to slag and atmosphere. In particular, it is more important than previously thought, and unless a small amount of slag mixed in the dip tube 2 is completely discharged to the outside of the dip tube 2, it becomes a slag-based inclusion during deoxidation, which greatly affects the cleanability. give. Very small particles of finely divided slag are hard to be discharged, and thus fine slag-based inclusions are generated, which cannot be floated and separated in a later step. Especially in the smelting of IF steel, it is necessary to widen the bubble activation surface in order to accelerate decarburization, but vigorous stirring occurs on the bubble activation surface, so the slag is finely divided, and as it is, it is extremely floated and separated. Hard to do.

【００１８】図２には２個以上の内径の異なる直胴部
２′、２″を有する直胴型浸漬管２を用いる場合を模式
的に示す。（イ）は耐火物構造の安定化を図るため下部
よりも内径の大きい直胴部２′を上部に有する場合、
（ロ）は例えば既設のＤＨやＲＨの上部構造を流用する
ために下部よりも内径の小さい直胴部２′を上部に有す
る場合、（ハ）、（ニ）は（イ）、（ロ）において下部
と上部の中心軸が一致していない場合、（ホ）は内径の
異なる２つの直胴部２′、２″を上部に有する場合を示
す。2 schematically shows a case where a straight barrel type dipping tube 2 having two or more straight barrel portions 2 ', 2 "having different inner diameters is used. (A) shows stabilization of the refractory structure. To have a straight body 2'having a larger inner diameter than the lower part for the sake of illustration,
(B) is a case where the upper part of the existing DH or RH has a straight body part 2'having a smaller inner diameter than the lower part in order to be reused, (c) and (d) are (a) and (b). When the central axes of the lower portion and the upper portion do not coincide with each other in (1), (e) shows a case where two straight body portions 2 ′, 2 ″ having different inner diameters are provided in the upper portion.

【００１９】本発明はまず第１に、浸漬管２内に混入す
る少量のスラグを浸漬管２外に完全に排出させる。この
ため、まず、浸漬管２内溶鋼の浴深Ｈの０．５Ｈよりも
深い位置に設けたガス吹込み孔３から０．６〜１５ＮＬ
／（ｍｉｎ・ｔｏｎ）の攪拌用ガスを供給して、気泡活
性面での激しい攪拌により微細に***し巻き込まれたス
ラグ粒子を浴内で合体粗大化させる。ここで、浸漬管内
溶鋼面は溶鋼比重を７ｇ／ｃｍ² として真空度と取鍋、
浸漬管形状から幾何学的に計算される値である。また、
ガス吹込み孔３は取鍋底部に設けたポーラス煉瓦、小径
パイプを埋め込んだ煉瓦でも、取鍋外部や浸漬管２上部
から挿入した耐火物に覆われたノズルでも構わない。つ
まり、直胴型浸漬管２を取鍋１内溶鋼４に浸漬し、浸漬
管２内のみを真空とする精錬装置で、取鍋低部よりガス
を供給すると、ガス気泡帯の浮上領域（プルームゾー
ン）およびその周囲では激しい乱流攪拌が生じ、巻き込
まれたスラグ粒子が他の粒子と容易に衝突して合体粗大
化できる。このためには、浸漬管２内溶鋼面の浴深Ｈの
０．５Ｈよりも深い位置からガスを供給する必要があ
り、これよりも浅い場合にはプルームゾーンが小さいた
め合体粗大化する量が少なく効果がない。また、ガス流
量が０．６ＮＬ／（ｍｉｎ・ｔｏｎ）よりも少ない場合
は乱流エネルギーが小さいため合体粗大化する量が少な
く、１５ＮＬ／（ｍｉｎ・ｔｏｎ）よりも多い場合はガ
ス気泡による上昇流が極めて強くなるため巻き込まれた
スラグ粒子が極めて細かくなりすぎ、合体粗大化しても
なお浮上可能な大きさに到達しえない。First, the present invention completely discharges a small amount of slag mixed in the dip tube 2 to the outside of the dip tube 2. Therefore, first, from the gas injection hole 3 provided at a position deeper than 0.5H of the bath depth H of the molten steel in the dip pipe 2, 0.6 to 15NL
By supplying a stirring gas of / (min · ton), the slag particles finely divided and entrapped by vigorous stirring on the bubble active surface are aggregated and coarsened in the bath. Here, the molten steel surface in the immersion pipe has a vacuum degree and a ladle with a molten steel specific gravity of 7 g / cm ² .
It is a value calculated geometrically from the shape of the immersion pipe. Also,
The gas injection hole 3 may be a porous brick provided at the bottom of the ladle, a brick having a small diameter pipe embedded therein, or a nozzle covered with a refractory material inserted from the outside of the ladle or from the top of the dipping pipe 2. That is, when the straight barrel type dipping pipe 2 is dipped in the molten steel 4 in the ladle 1 and a gas is supplied from the lower portion of the ladle with a refining device in which only the dipping pipe 2 is evacuated, the floating region (plume of the gas bubble zone) Vigorous turbulent agitation occurs in the zone) and its surroundings, and the entrapped slag particles can easily collide with other particles to form a coarse coalesce. For this purpose, it is necessary to supply the gas from a position deeper than 0.5H, which is the bath depth H of the molten steel surface in the dip pipe 2. If the gas is shallower than this, the plume zone is small and the amount of coalescence coarsening is small. Less effective. Further, when the gas flow rate is less than 0.6 NL / (min · ton), the turbulent flow energy is small and the amount of coalescence coarsening is small, and when it is more than 15 NL / (min · ton), the upward flow due to gas bubbles. Is extremely strong, the entrained slag particles become too fine, and even if the coalescence is coarsened, the size that can be floated cannot be reached.

【００２０】次に、合体粗大化したスラグ粒子を浸漬管
２から外部へ流出させる必要がある。このため、浸漬管
２先端と浸漬管２外溶鋼表面との距離Ｓを０．０３Ｈ〜
０．３Ｈ、ガス吹込み孔３と浸漬管２中心との水平方向
の距離Ｌを０．１ｄ〜０．５ｄ、浸漬管２中心と取鍋１
中心との距離Ｋを０．０２Ｄ〜０．１２Ｄとする。直胴
型浸漬管２を取鍋１内溶鋼４に浸漬し、浸漬管２内のみ
を真空とする精錬装置で、取鍋低部よりガスを供給する
場合、Ｌとｄの関係を適正にするとプルームゾーンはガ
ス吹込み孔３を中心として周期的に回転運動を始める。
この回転運動は、溶鋼４の反転流によるプルームゾーン
を曲げようとする運動エネルギーと気泡が垂直方向に上
昇しようとする慣性エネルギーのバランスで生じるもの
であり、このような回転運動をした場合、気泡と酸化物
であるスラグや介在物の比重差や溶鋼４との濡れ性の違
いにより、酸化物は回転運動に完全には追従できず、プ
ルームゾーンから分離され溶鋼４中に残留する割合が高
くなる。この原理を利用しない限りプルームゾーンおよ
びその周囲で合体粗大化したスラグ粒子を浸漬管２外に
流出させることはできず、この原理によりプルームゾー
ンから分離され溶鋼４中に残留したスラグ粒子は溶鋼４
の流れに乗って浸漬管２外に流出することができる。こ
のための最適条件は、図３に示すように、ガス吹込み孔
３と浸漬管２中心との水平方向の距離Ｌを０．１ｄ〜
０．５ｄとすることである。０．１ｄより小さいと回転
運動が起こらないか、起こっても回転角が小さい範囲で
しか運動せず、０．５ｄよりも大きいと溶鋼反転流が強
くなるため常にプルームゾーンが一定方向に曲げられて
回転運動が起こりにくくなり、いずれの場合も合体粗大
化したスラグ粒子は浸漬管２外に流出しにくく脱酸時点
まで残留する。Next, it is necessary to let the coarse coalesced slag particles flow out from the dipping tube 2. Therefore, the distance S between the tip of the immersion pipe 2 and the surface of the molten steel outside the immersion pipe 2 is 0.03H to
0.3H, the horizontal distance L between the gas injection hole 3 and the center of the dip tube 2 is 0.1d to 0.5d, the center of the dip tube 2 and the ladle 1
The distance K from the center is 0.02D to 0.12D. When a straight-body type dip tube 2 is dipped in the molten steel 4 in the ladle 1 and a gas is supplied from the lower part of the ladle with a refining device in which only the dip tube 2 is evacuated, if the relationship between L and d is appropriate. The plume zone periodically starts rotating motion around the gas injection hole 3.
This rotational movement occurs due to the balance between the kinetic energy for bending the plume zone due to the reverse flow of the molten steel 4 and the inertial energy for the bubbles to rise in the vertical direction. Due to the difference in specific gravity of the slag and inclusions that are oxides and the difference in wettability with molten steel 4, the oxide cannot follow the rotary motion completely, and the proportion of the oxide separated from the plume zone and remaining in molten steel 4 is high. Become. Unless this principle is used, the coalesced and coarsened slag particles in the plume zone and its surroundings cannot flow out of the dipping pipe 2, and the slag particles separated from the plume zone and remaining in the molten steel 4 by this principle are the molten steel 4
Can flow out of the dipping tube 2. The optimum condition for this is, as shown in FIG. 3, that the distance L in the horizontal direction between the gas injection hole 3 and the center of the dip tube 2 is 0.1 d.
It is to be 0.5d. If it is smaller than 0.1d, rotational motion does not occur, or even if it occurs, it only moves within a small rotation angle range, and if it is larger than 0.5d, the molten steel reversal flow becomes strong and the plume zone is always bent in a certain direction. As a result, the rotational movement is less likely to occur, and in any case, the coalesced and coarsened slag particles are less likely to flow out of the dip tube 2 and remain until the time of deoxidation.

【００２１】さらに、プルームゾーンから分離され浸漬
管２外に流出したスラグ粒子を効率的に浮上させる必要
がある。これは、浸漬管２下端と浸漬管２外溶鋼表面と
の距離Ｓを０．０３Ｈ〜０．３Ｈ、浸漬管２中心と取鍋
１中心との距離Ｋを０．０２Ｄ〜０．１２Ｄとすること
で成し遂げられる。つまり、一旦、浸漬管２外へ流出し
たスラグ粒子は、再び巻き込まれることなく、すみやか
に浸漬管２外溶鋼表面へ浮上する必要がある。したがっ
て、浸漬管２内の極めて激しい流動とは正反対に、浸漬
管２外部の溶鋼はできる限り静止状態にあることが望ま
しい。このためには、浸漬管２下端と浸漬管２外溶鋼表
面との距離Ｓを適正にする必要がある。Ｓが０．０３Ｈ
よりも小さいと浸漬管２内の極めて激しい流動が浸漬管
２外部の溶鋼にも影響を及ぼし、一旦、浸漬管２外へ流
出したスラグ粒子が再び巻き込まれる確率が高くなり、
スラグ粒子は浸漬管２外に流出しにくく脱酸時点まで残
留する。０．３Ｈよりも大きいと浸漬管２内外の溶鋼の
循環が悪くなるため脱炭速度自体に影響がでる。Ｓを適
正にした上でさらに浸漬管２の中から外へ向かう流動を
強くする必要があり、これには、浸漬管２外部の面積を
広くすることが必要である。これは、浸漬管２と取鍋１
の間隔が小さい場合には、溶鋼４の自由な運動が取鍋１
壁面の影響を受けて妨げられるためと考えられる。しか
し、後記のように浸漬管２の大きさを小さくすると脱炭
特性に多大な悪影響を与えるため、浸漬管２を小さくす
ることはできない。これに対して、本発明では、浸漬管
２の径を小さくしなくても、取鍋１中心に対して適宜偏
芯させて浸漬することで大きな効果が得られる。これ
は、流動の非対称性を最大限に利用したものであり、偏
芯させることにより部分的に取鍋１と浸漬管２の間が広
くあいた領域が生じるため、この領域で浸漬管２の中か
ら外へ向かう強い流動が生じることと、前記のようにプ
ルームゾーンは回転運動をするため、常時ではないにせ
よ必ずこの領域でもプルームゾーンから分離され浸漬管
２外へ向かう流れが生じることとのためである。このた
めには、図４に示すように浸漬管２中心と取鍋１中心と
の距離Ｋを０．０２Ｄ〜０．１２Ｄとする必要がある。
０．０２Ｄよりも小さいと流動の非対称性が小さくなる
ため、浸漬管２の中から外へ向かう強い流動が生じる領
域が部分的にも生じないのでスラグ粒子が排出されにく
く、０．１２Ｄよりも大きいと浸漬管２と取鍋１が接近
しすぎる領域ができ、この領域がほとんど流動しない死
水域となり、脱炭反応を含めた冶金特性が悪化する。Further, it is necessary to efficiently levitate the slag particles separated from the plume zone and flowing out of the dip tube 2. The distance S between the lower end of the dip tube 2 and the surface of the molten steel outside the dip tube 2 is 0.03H to 0.3H, and the distance K between the center of the dip tube 2 and the center of the ladle 1 is 0.02D to 0.12D. It can be achieved. That is, the slag particles that have once flown out of the dip tube 2 need to promptly float to the surface of the molten steel outside the dip tube 2 without being caught again. Therefore, it is desirable that the molten steel outside the dip tube 2 be as stationary as possible, as opposed to the extremely violent flow in the dip tube 2. For this purpose, it is necessary to make the distance S between the lower end of the immersion pipe 2 and the surface of the molten steel outside the immersion pipe 2 appropriate. S is 0.03H
If it is smaller than this, the extremely violent flow in the dip tube 2 affects the molten steel outside the dip tube 2 and the slag particles once flowing out of the dip tube 2 are more likely to be re-engaged,
Slag particles are hard to flow out of the dipping pipe 2 and remain until the time of deoxidation. If it is larger than 0.3H, the circulation of the molten steel inside and outside the dipping pipe 2 is deteriorated, so that the decarburizing rate itself is affected. It is necessary to further increase the flow from the inside of the dip tube 2 to the outside after making S appropriate, and for this purpose, it is necessary to widen the area outside the dip tube 2. This is a dip tube 2 and a ladle 1.
If the space between the two is small, the free movement of the molten steel 4 will cause the ladle 1
It is thought that this is because it is blocked by the influence of the wall surface. However, as will be described later, reducing the size of the dip tube 2 has a great adverse effect on the decarburization characteristics, and therefore the dip tube 2 cannot be made small. On the other hand, in the present invention, even if the diameter of the dipping tube 2 is not reduced, a large effect can be obtained by appropriately eccentrically immersing the ladle 1 in the center. This is because the asymmetry of the flow is used to the maximum extent, and the eccentricity partially creates a wide area between the ladle 1 and the dip tube 2, so that in this area, Between the plume zone and the outside because there is a strong flow outward from the plume zone as described above. This is because. For this purpose, as shown in FIG. 4, the distance K between the center of the dip tube 2 and the center of the ladle 1 needs to be 0.02D to 0.12D.
If it is smaller than 0.02D, the asymmetry of the flow becomes small, so that a region where a strong flow outward from the dip tube 2 does not occur even partially occurs, so that it is difficult for the slag particles to be discharged, and it is more than 0.12D. If it is large, there is a region where the dip tube 2 and the ladle 1 are too close to each other, and this region becomes a dead water region where almost no flow occurs, and the metallurgical properties including the decarburization reaction deteriorate.

【００２２】ところで、脱炭反応の速度を増大させるた
めには、物質移動速度の増加ではなく、反応表面積の増
加が最も重要な要因となる。気泡が浮上し表面で破泡す
るという一連の経過を考えると、気泡が溶鋼との密度差
により浮上した後、表面で破裂し、次いで周囲の溶鋼表
面が波立つという過程をとる。このうち、気泡が表面で
破裂した瞬間が最も大きな表面積を形成し、その後周囲
に生成される波では表面積はほとんど増加されない。一
方、気泡が浮上することにより形成される最表面での上
向きの流れの速度はガス吹込み速度や攪拌エネルギーに
影響されるが、それは液滴を高くまで飛散させる運動エ
ネルギーを与えるものであり、個々の気泡が表面で破裂
した瞬間の自由表面の形態には大きくは影響しない。し
たがって、個々の気泡が表面で破裂する時に形成する自
由表面はほぼ一定であり、反応容器全体の表面積を有効
に増大させるためには、表面で破裂する気泡の数を多く
することが重要となる。このためには、気泡の合体を可
能な限り抑制できるように、広い面積にわたって気泡を
浮上させることが必要となり、気泡活性面の大きさが重
要となる。気泡活性面を最大限に利用し、極低炭素域ま
で効率的に脱炭させるためには、図５に示すように、取
鍋内径Ｄと浸漬管内径ｄの比ｄ／Ｄを０．３〜０．８と
することが必要である。ｄ／Ｄが０．３よりも小さいと
気泡活性面が小さいため脱炭が効率的には進行せず、
０．８よりも大きいと浸漬管内の溶鋼量が増加するため
浸漬管２内溶鋼表面の取鍋底からの高さが低くなり、気
泡活性面が小さくなり脱炭反応速度が低下するととも
に、ガス吹込み深さが小さくなるためスラグ粒子の合体
粗大化も起こり難くなる。By the way, in order to increase the rate of the decarburization reaction, not the increase in the mass transfer rate but the increase in the reaction surface area is the most important factor. Considering a series of processes in which bubbles float and break on the surface, the bubbles rise due to the difference in density from the molten steel, then burst on the surface, and then the surrounding molten steel surface undulates. Of these, the largest surface area is formed at the moment when the bubbles burst on the surface, and the surface area is hardly increased by the waves generated around the surface. On the other hand, the velocity of the upward flow at the outermost surface formed by floating bubbles is affected by the gas blowing velocity and stirring energy, which gives kinetic energy to fly droplets to a high level, It does not significantly affect the morphology of the free surface at the moment each bubble bursts at the surface. Therefore, the free surface formed when individual bubbles burst at the surface is almost constant, and it is important to increase the number of bubbles burst at the surface in order to effectively increase the surface area of the entire reaction vessel. . For this purpose, it is necessary to float the bubbles over a large area so that coalescing of the bubbles can be suppressed as much as possible, and the size of the bubble active surface is important. In order to utilize the air bubble active surface to the maximum and to efficiently decarburize to the extremely low carbon region, as shown in FIG. 5, the ratio d / D of the ladle inner diameter D and the dipping pipe inner diameter d is 0.3. It is necessary to set to 0.8. If d / D is less than 0.3, decarburization does not proceed efficiently because the bubble active surface is small.
When it is larger than 0.8, the amount of molten steel in the dip pipe increases, so that the height of the molten steel surface in the dip pipe 2 from the ladle bottom becomes low, the bubble activation surface becomes small, the decarburization reaction rate decreases, and the gas blowing rate decreases. Since the embedding depth becomes smaller, coalescence coarsening of slag particles is less likely to occur.

【００２３】脱炭反応はｄ／Ｄを適正にするだけでな
く、上記各条件を適正とし、浸漬管２内からスラグをす
みやかに排出することにより格段に効率的となる。これ
は、脱炭反応は主に気泡活性面で起こるが、スラグ粒子
が充分に排出されない場合には、常時気泡活性面に溶鋼
中に懸濁したスラグ粒子が上昇してくるため、予想以上
にスラグの影響を受けるためである。極低炭素域の脱炭
反応では、溶鋼の酸素濃度と炭素濃度により（１）式数
１で求められる平衡ＣＯ分圧Ｐ_COと雰囲気真空度の差が
小さくなっているため、少量のスラグでもスラグによる
静圧が存在すれば極めて反応が進行しにくくなるため
と、粘性の高いスラグが存在しているため気泡が自由表
面で破裂する時に形成する飛散粒子のサイズが大きくな
り、スラグが無い場合に比べて自由表面積が増加できな
いためである。これは、後述するように、高清浄度化す
るためスラグを改質すると鋼中の酸素濃度が低下した場
合でも高い脱炭速度を維持できるという点で極めて重要
である。The decarburization reaction is not only effective in adjusting d / D, but also in appropriate conditions, and the slag is promptly discharged from the dip pipe 2 to be remarkably efficient. This is because the decarburization reaction mainly occurs on the bubble activated surface, but if the slag particles are not sufficiently discharged, the slag particles suspended in the molten steel rise on the bubble activated surface at all times, so it is more than expected. This is because it is affected by slag. In the decarburization reaction in the extremely low carbon region, the difference between the equilibrium CO partial pressure _PCO and the atmospheric vacuum degree obtained by the equation (1) according to the oxygen concentration and the carbon concentration of the molten steel is small, so even a small amount of slag can be obtained. When static pressure due to slag is present, the reaction is extremely difficult to proceed.Because of the presence of highly viscous slag, the size of the scattered particles that form when the bubbles burst on the free surface is large, and there is no slag. This is because the free surface area cannot be increased compared to. This is extremely important in that a high decarburization rate can be maintained even if the oxygen concentration in the steel is reduced by modifying the slag for high cleanliness, as will be described later.

【００２４】[0024]

【数１】 [Equation 1]

【００２５】減圧脱炭時のスラグの浸漬管２への混入を
より効率的に抑制するには、取鍋低部よりガスを吹き込
み、取鍋１内溶鋼上部にあるスラグ６を除去した後に浸
漬管２を浸漬した上で、スラグを浸漬管２外溶鋼表面に
２〜１５ｋｇ／ｔｏｎ存在させた状態で、真空度が７６
０〜３００Ｔｏｒｒの領域では攪拌用ガスの供給速度を
０．６〜２ＮＬ（ｍｉｎ・ｔｏｎ）、３００〜１００Ｔ
ｏｒｒの領域では１．０〜２．５ＮＬ（ｍｉｎ・ｔｏ
ｎ）、１００Ｔｏｒｒの以下の領域では２〜１５ＮＬ
（ｍｉｎ・ｔｏｎ）の範囲に調節することが重要であ
る。つまり、処理開始時に浸漬管２内にスラグ６を混入
させないために、取鍋低部よりガスを吹き込み、取鍋１
上部にあるスラグ６を除去した後に浸漬管２を浸漬する
が、真空度に応じてガス供給量を制御しない場合には、
一旦浸漬管２外に排除されたスラグ６が再び浸漬管２内
に入り込む。これは、攪拌用ガスのプルームゾーンが回
転している間に瞬間的に一部の気泡が浸漬管２外に漏れ
だし、この漏れだした気泡により浸漬管２外のスラグ６
が強く攪拌され、一部が溶鋼４内部に懸濁するためであ
る。そこで、あらゆる条件で気泡が浸漬管２外に漏れだ
さない条件を詳細に検討したところ、真空度に応じて適
正範囲にガス流量を制御すればよいことが明らかになっ
た。上記の各真空度での適正流量範囲よりも多い場合に
は気泡の漏れだしが生じ、適正流量範囲よりも少ない場
合には混合が悪くなるため脱炭特性が悪化し、さらに、
スラグ粒子の合体粗大化も進行しにくくなる。In order to more effectively suppress the mixing of slag into the dipping pipe 2 during decarburization under reduced pressure, gas is blown from the lower part of the ladle to remove the slag 6 on the molten steel upper part in the ladle 1 and then dipping. After immersing the pipe 2, with the slag existing on the surface of the molten steel outside the dipping pipe 2 in the amount of 2 to 15 kg / ton, the degree of vacuum is 76
In the range of 0 to 300 Torr, the stirring gas supply rate is 0.6 to 2 NL (min · ton), 300 to 100 T
In the area of orr, 1.0 to 2.5 NL (min · to
n), 2 to 15 NL in the area below 100 Torr
It is important to adjust the range to (min · ton). In other words, in order to prevent the slag 6 from being mixed in the dipping pipe 2 at the start of the treatment, gas is blown from the lower part of the ladle to remove the slag 6.
Although the dip pipe 2 is dipped after removing the slag 6 at the upper part, if the gas supply amount is not controlled according to the degree of vacuum,
The slag 6 once removed outside the dip tube 2 enters the dip tube 2 again. This is because while the stirring gas plume zone is rotating, some air bubbles leak out of the dip tube 2 instantaneously, and the leaked air bubbles cause the slag 6 outside the dip tube 2 to leak.
Is strongly stirred and a part is suspended inside the molten steel 4. Therefore, a detailed study of conditions under which air bubbles do not leak out of the dipping tube 2 under all conditions has revealed that the gas flow rate may be controlled within an appropriate range according to the degree of vacuum. If the flow rate is higher than the appropriate flow rate range at each vacuum level, air bubbles will leak out, and if the flow rate is lower than the proper flow rate range, the decarburization characteristics will deteriorate due to poor mixing.
It also becomes difficult for the slag particles to coalesce and coarsen.

【００２６】さらに、浸漬管２外に流出したスラグ粒子
は、浸漬管２外にあらかじめ存在しているスラグ６に吸
収される必要がある。このためには、スラグ６を浸漬管
２外溶鋼表面に２〜１５ｋｇ／ｔｏｎ存在させた状態で
処理すればよい。２ｋｇ／ｔｏｎよりも少ないと脱炭処
理中に浸漬管２外に流出したスラグ粒子やその後の脱酸
時に生成した酸化物粒子が浸漬管２外にあらかじめ存在
しているスラグ６に充分に吸収されえず、再び溶鋼４内
部へ混入する確率が残るため清浄度が上がらない。ま
た、浸漬管２外溶鋼表面が充分スラグ６に被覆されてい
ないため温度低下が大きく、大気からの窒素吸収が大き
いという問題も生じる。１５ｋｇ／ｔｏｎよりも多いと
浸漬管２耐火物を激しく溶損するという問題を生じる。Furthermore, the slag particles flowing out of the dip tube 2 need to be absorbed by the slag 6 existing outside the dip tube 2 in advance. For this purpose, the slag 6 may be treated in the state where the slag 6 is present on the surface of the molten steel outside the dipping pipe 2 in an amount of 2 to 15 kg / ton. If it is less than 2 kg / ton, the slag particles flowing out of the dip tube 2 during the decarburization process and the oxide particles generated during the subsequent deoxidation are sufficiently absorbed by the slag 6 existing in advance outside the dip tube 2. First of all, the cleanliness cannot be improved because there is a possibility that the molten steel 4 will be mixed again. Further, since the surface of the molten steel outside the dip pipe 2 is not sufficiently covered with the slag 6, there is a problem that the temperature drop is large and the absorption of nitrogen from the atmosphere is large. If it is more than 15 kg / ton, there is a problem that the refractory of the dip tube 2 is severely melted.

【００２７】本発明は第２に、脱酸後の転炉スラグによ
る酸化反応を完全に抑制する。これは、精錬炉からの出
鋼中または出鋼後に脱酸剤を添加してスラグ中の（Ｔ・
Ｆｅ）濃度を７％以下に低下させることで成し遂げられ
る。このように（Ｔ・Ｆｅ）濃度を低下させるために
は、出鋼時や出鋼後に取鍋スラグにＡｌを添加する方法
が採られるが、このようにするとスラグを脱酸する以上
に溶鋼中の酸素濃度が低下し、脱炭が進行しにくくなる
のが一般的である。しかし、上記各条件を適正とした直
胴型浸漬管２を取鍋１内溶鋼に浸漬し、浸漬管２内のみ
を真空に引く処理を実施した場合には、広い気泡活性面
が確保できる上に、真空に暴露された表面からスラグを
完全に排除できるため、極めて脱炭が進行しやすい。但
し、脱炭時間をより短縮するために、適宜酸素を付与す
ることは可能であり、その場合には、上吹きランスによ
る酸素供給が最も容易である。Secondly, the present invention completely suppresses the oxidation reaction by the converter slag after deoxidation. This is due to the addition of a deoxidizer during tapping from the refining furnace or after tapping (T ・
This is achieved by reducing the Fe) concentration to below 7%. In order to lower the (T / Fe) concentration in this way, a method of adding Al to the ladle slag at the time of tapping or after tapping is adopted, but this method is more effective than deoxidizing the slag in molten steel. It is general that the oxygen concentration of the is decreased and decarburization becomes difficult to proceed. However, when the straight-body type immersion pipe 2 with the above-mentioned respective conditions being appropriate is immersed in the molten steel in the ladle 1 and a process of drawing only the inside of the immersion pipe 2 to a vacuum is performed, a wide bubble active surface can be secured. In addition, since slag can be completely removed from the surface exposed to vacuum, decarburization is extremely easy to proceed. However, in order to further shorten the decarburization time, it is possible to appropriately add oxygen, and in that case, the oxygen supply by the top blowing lance is the easiest.

【００２８】本発明は第３に、脱酸生成物を浮上分離さ
せる。これは、直胴型浸漬管２を取鍋１内溶鋼に浸漬
し、浸漬管２内のみを真空に引く精錬装置の任意の真空
度で攪拌混合処理が可能な特性を活かしたものである。
つまり、脱炭処理後に脱酸剤を添加した以降は、スラグ
粒子よりもはるかに微細な脱酸生成物の浮上分離が重要
となるため、上記の脱炭時の乱流攪拌を利用した合体粗
大化等では対処できず、浸漬管２内から管外へ向かうマ
クロ的な流れを作る必要がある。しかし、取鍋低部から
ガスを供給し続ける限り上昇流が大きく、浸漬管２内の
脱酸生成物が一旦下方へ移動し、続いて浸漬管２投影面
より外周部へ移動し、最後に浸漬管２外表面へ浮上する
という一連の過程を効率的にとることは困難である。ま
た、取鍋低部からのガスの供給を停止した場合には、乱
流攪拌を利用した合体粗大化がほとんど起こらない上
に、脱酸生成物は上方へ浮上するのみであり、浸漬管２
内で生成した脱酸生成物は浸漬管２内表面に浮上するも
のの、そこにはスラグは存在しないため吸収、安定化さ
れない。この相反する問題を解決するには、脱炭処理終
了後に浸漬管２の真空排気用弁を閉じ、攪拌用ガスを供
給し続けた状態で脱酸を行えばよい。具体的には、脱炭
処理終了後に１０Ｔｏｒｒ以下の状態で浸漬管２の真空
排気用弁を閉じ、攪拌用ガスを供給しながら真空度を大
気圧まで復圧する過程で脱酸剤を添加するもので、脱酸
剤は真空度が２００Ｔｏｒｒまで復圧するまでに投入す
ることが望ましい。これにより攪拌用ガスと自然なリー
クガスにより次第に真空度が低下するため、溶鋼ヘッド
が次第に下がり、攪拌用ガスを供給したままでもマクロ
的な下降流が形成される。さらに、浸漬管２内溶鋼ヘッ
ドの低下に対応して浸漬管２外溶鋼ヘッドが上昇するた
め、浸漬管２外ではマクロ的な上昇流が生成する。その
ため、浸漬管２内の脱酸生成物がマクロ的な下降流に乗
って一旦下方へ移動し、続いて浸漬管２投影面より外周
部へ移動し、最後にマクロ的な上昇流に乗って浸漬管２
外表面へ浮上するという一連の過程を効率的に進めるこ
とができる。また、浸漬管２内の雰囲気は攪拌用ガスと
自然なリークガスにより決まるため、攪拌用ガスとして
Ａｒ等の非酸化性ガスを用いた場合には非酸化性雰囲気
となるため合金歩留まりが向上するとともに、再酸化の
悪影響や窒素吸収も回避される。The present invention thirdly floats the deoxidized product. This is because the straight-body type immersion pipe 2 is immersed in the molten steel in the ladle 1 and the stirring and mixing process can be performed at an arbitrary vacuum degree of the refining device for drawing only the immersion pipe 2 into a vacuum.
In other words, after adding the deoxidizing agent after the decarburizing treatment, the floating separation of the deoxidizing product, which is much finer than the slag particles, is important. However, it is necessary to create a macroscopic flow from the inside of the immersion pipe 2 to the outside of the pipe. However, as long as gas is continuously supplied from the lower part of the ladle, the ascending flow is large, and the deoxidation product in the dip tube 2 once moves downward, then moves from the projection surface of the dip tube 2 to the outer peripheral part, and finally It is difficult to efficiently take the series of steps of floating to the outer surface of the immersion tube 2. Further, when the gas supply from the lower part of the ladle is stopped, coalescence coarsening using turbulent agitation hardly occurs, and the deoxidized product only floats upward.
Although the deoxidation product generated inside floats on the inner surface of the dip tube 2, it is not absorbed or stabilized because there is no slag therein. In order to solve this contradictory problem, the vacuum exhaust valve of the dip tube 2 is closed after the decarburization treatment is completed, and deoxidation may be carried out while the stirring gas is continuously supplied. Specifically, after the decarburization treatment is completed, the vacuum exhaust valve of the dip tube 2 is closed under 10 Torr or less, and the deoxidizer is added in the process of returning the vacuum degree to the atmospheric pressure while supplying the stirring gas. Then, it is desirable to add the deoxidizer before the pressure is restored to a vacuum degree of 200 Torr. As a result, the degree of vacuum is gradually lowered by the stirring gas and the natural leak gas, so that the molten steel head is gradually lowered, and a macroscopic downward flow is formed even while the stirring gas is supplied. Furthermore, since the molten steel head outside the immersion pipe 2 rises in response to the decrease in the molten steel head inside the immersion pipe 2, a macroscopic upward flow is generated outside the immersion pipe 2. Therefore, the deoxidation product in the dip tube 2 rides on the macroscopic downward flow and once moves downward, then moves from the projection surface of the dip tube 2 to the outer peripheral portion, and finally rides on the macroscopic upward flow. Dip tube 2
It is possible to efficiently proceed with a series of processes of ascending to the outer surface. Further, since the atmosphere in the dip tube 2 is determined by the stirring gas and the natural leak gas, when a non-oxidizing gas such as Ar is used as the stirring gas, the atmosphere becomes a non-oxidizing atmosphere and the alloy yield is improved. The adverse effects of reoxidation and nitrogen absorption are also avoided.

【００２９】さらに、脱炭処理終了後に浸漬管２内溶鋼
面と浸漬管２下端との距離Ｔを１０００〜２００ｍｍと
しながら１〜５分間保持することにより、尚一層効率的
に脱酸生成物の浮上分離が可能となる。浸漬管２内溶鋼
面と浸漬管２下端との距離Ｔを１０００ｍｍよりも大き
くすると浸漬管２内の脱酸生成物が浸漬管２外に流出し
にくくなり、２００ｍｍよりも小さくすると攪拌ガスに
よる揺動で浸漬管２内に外部から空気が巻き込まれる。
保持時間が１分よりも短いと浸漬管２内の脱酸生成物が
浸漬管２外に充分に流出できる時間がなく、５分よりも
長いと温度低下が激しく実際的ではない。保持する状態
としては、脱炭処理終了後に浸漬管２の真空排気用弁を
閉じ、攪拌用ガスを供給しながら真空度を大気圧まで復
圧させる一連の過程の中で、脱酸剤を添加した後、３０
０Ｔｏｒｒ以下の任意の真空度で保持することが望まし
い。Further, by maintaining the distance T between the molten steel surface in the dip pipe 2 and the lower end of the dip pipe 2 after the decarburization treatment for 1 to 5 minutes, the deoxidized product can be more efficiently produced. Float separation is possible. If the distance T between the molten steel surface in the dip tube 2 and the lower end of the dip tube 2 is larger than 1000 mm, the deoxidized product in the dip tube 2 will not easily flow out of the dip tube 2, and if it is smaller than 200 mm, it will be shaken by stirring gas. Dynamically, air is drawn into the dip tube 2 from the outside.
If the holding time is shorter than 1 minute, the deoxidation product in the dip tube 2 will not have enough time to flow out of the dip tube 2, and if it is longer than 5 minutes, the temperature drop will be severe and impractical. The state of holding is to add a deoxidizing agent in a series of processes in which the vacuum exhaust valve of the dipping pipe 2 is closed after the decarburization treatment is completed and the vacuum degree is restored to the atmospheric pressure while supplying the stirring gas. After doing, 30
It is desirable to hold at an arbitrary vacuum degree of 0 Torr or less.

【００３０】[0030]

【実施例】以下の実施例は、３５０トンの転炉出鋼溶鋼
を用いて、図１に示した形状の真空精錬炉で実施した。
いずれの場合も、処理前の炭素濃度は２５０〜４５０ｐ
ｐｍであり、処理後の〔Ｃ〕が１０〜３０ｐｐｍの範囲
で（２）式数２により求めた脱炭速度定数κと、脱酸後
の全酸素濃度〔Ｔ・Ｏ〕を評価した。攪拌用ガスとして
はＡｒを用いた。EXAMPLES The following examples were carried out in a vacuum refining furnace having the shape shown in FIG. 1, using 350 tons of molten steel discharged from a converter.
In any case, the carbon concentration before treatment is 250 to 450 p.
pm, the decarburization rate constant κ obtained by equation (2) and the total oxygen concentration [T · O] after deoxidation were evaluated in the range of [C] after treatment of 10 to 30 ppm. Ar was used as the stirring gas.

【００３１】[0031]

【数２】 κ＝（ｌｎ〔％Ｃ〕₁ −ｌｎ〔％Ｃ〕₂ ）／△ｔ …（２） ここで、〔％Ｃ〕₁ は実験開始時の炭素濃度 〔％Ｃ〕₂ は実験終了時の炭素濃度 △ｔは実験時間（分）## EQU2 ## κ = (ln [% C] ₁ −ln [% C] ₂ ) / Δt (2) where [% C] ₁ is the carbon concentration at the start of the experiment [% C] ₂ is the experiment At the end, the carbon concentration Δt is the experiment time (minutes)

【００３２】表１には、種々の大きさの浸漬管や、種々
の位置に攪拌用ポーラス煉瓦のガス吹込み孔を設置した
取鍋、浸漬吹込み用ランスを用いて、吹込み深さ、ガス
供給量、ｄ／Ｄ、Ｓ／Ｈ、Ｌ／ｄ、Ｋ／Ｄを変化させた
結果を示す。Ｈは浸漬管内溶鋼の浴深（ｍ）、Ｑはガス
供給量（ＮＬ／（ｍｉｎ・ｔｏｎ））、Ｄは取鍋内径
（ｍ）、ｄは浸漬管内径（ｍ）、Ｓは浸漬管下端と浸漬
管外溶鋼表面との距離（ｍ）、Ｌはガス吹込み孔と浸漬
管中心との水平方向の距離（ｍ）、Ｋは浸漬管中心と取
鍋中心との距離（ｍ）を表す。尚、本実施例で用いた真
空精錬炉と同一の排気能力を有するＲＨの場合に、κは
０．１８（１／分）、〔Ｔ・Ｏ〕は２４ｐｐｍであっ
た。Table 1 shows the immersion depths of the immersion pipes of various sizes, the ladle in which the gas injection holes of the stirring porous brick are installed at various positions, and the immersion blow lance. The results obtained by changing the gas supply amount, d / D, S / H, L / d, and K / D are shown. H is the depth of molten steel in the immersion pipe (m), Q is the gas supply amount (NL / (min · ton)), D is the ladle inner diameter (m), d is the immersion pipe inner diameter (m), and S is the lower end of the immersion pipe. And the surface of the molten steel outside the immersion pipe (m), L is the horizontal distance (m) between the gas injection hole and the center of the immersion pipe, and K is the distance (m) between the center of the immersion pipe and the center of the ladle. . Incidentally, in the case of RH having the same exhaust capacity as the vacuum refining furnace used in this example, κ was 0.18 (1 / min) and [TO] was 24 ppm.

【００３３】[0033]

【表１】 [Table 1]

【００３４】表２は、転炉からの出鋼中に脱酸剤を添加
してスラグを改質した後に、本発明例１の条件で処理し
た結果を示す。Table 2 shows the results of treating under the conditions of Inventive Example 1 after modifying the slag by adding a deoxidizing agent during tapping from the converter.

【００３５】[0035]

【表２】 [Table 2]

【００３６】表３は、転炉スラグ量を変化させ、本発明
例２４の条件で処理した結果を示す。Table 3 shows the results of processing under the conditions of Inventive Example 24 while changing the converter slag amount.

【００３７】[0037]

【表３】 [Table 3]

【００３８】表４は、真空度と攪拌ガス流量の関係を変
化させ、本発明例２４の条件で処理した結果を示す。Table 4 shows the results of processing under the conditions of Inventive Example 24 while changing the relationship between the degree of vacuum and the flow rate of stirring gas.

【００３９】[0039]

【表４】 [Table 4]

【００４０】表５は、脱炭処理後脱酸剤添加時の復圧方
法を変化させ、本発明例２４の条件で処理した結果を示
す。Table 5 shows the results of treating under the conditions of Inventive Example 24 while changing the pressure restoration method when the deoxidizing agent was added after the decarburizing treatment.

【００４１】[0041]

【表５】 [Table 5]

【００４２】表６は、脱炭処理終了後、約１Ｔｏｒｒで
真空排気弁を閉じ、攪拌用Ａｒを供給し続けた状態で１
００Ｔｏｒｒまで復圧した時点で脱酸し、そのままの状
態を続けて５００〜７６０Ｔｏｒｒまで復圧した時点で
一定圧力に保持し、浸漬管内溶鋼面と浸漬管下端との距
離を一定値にした状態で所定時間保持し、本発明例２４
の条件で処理した結果を示す。Table 6 shows that after the decarburization treatment was completed, the vacuum exhaust valve was closed at about 1 Torr and the stirring Ar was continuously supplied.
When the pressure is restored to 00 Torr, it is deoxidized, and the state is continuously maintained. When the pressure is restored to 500 to 760 Torr, the pressure is kept constant, and the distance between the molten steel surface in the immersion pipe and the lower end of the immersion pipe is kept constant. Inventive Example 24
The results of processing under the conditions of are shown.

【００４３】[0043]

【表６】 [Table 6]

【００４４】[0044]

【発明の効果】本発明により、ＩＦ鋼を極低炭素領域ま
で脱炭速度を低下させることなく高い生産性で効率的に
溶製することが可能となる。EFFECTS OF THE INVENTION According to the present invention, it becomes possible to efficiently produce IF steel with high productivity without lowering the decarburization rate to an extremely low carbon region.

【図面の簡単な説明】[Brief description of drawings]

【図１】本発明の実施態様を模式的に示す図である。FIG. 1 is a diagram schematically showing an embodiment of the present invention.

【図２】本発明の実施態様を模式的に示す図である。FIG. 2 is a diagram schematically showing an embodiment of the present invention.

【図３】処理後の全酸素濃度に及ぼすガス吹込み孔と浸
漬管中心との水平方向の距離Ｌと浸漬管内径ｄの比の影
響を示す図である。FIG. 3 is a diagram showing the influence of the ratio of the horizontal distance L between the gas injection hole and the center of the immersion pipe and the immersion pipe inner diameter d on the total oxygen concentration after the treatment.

【図４】処理後の全酸素濃度に及ぼす浸漬管中心と取鍋
中心との距離Ｋと取鍋内径Ｄの比の影響を示す図であ
る。FIG. 4 is a diagram showing the effect of the ratio of the distance K between the center of the dip tube and the center of the ladle and the inner diameter D of the ladle on the total oxygen concentration after the treatment.

【図５】脱炭速度に及ぼす取鍋内径Ｄと浸漬管内径ｄの
比の影響を示す図であり、●はＳ／Ｈ＝０．１、Ｌ／ｄ
＝０．２、Ｋ／Ｄ＝０．０７とした本発明例、○は比較
例を示す。FIG. 5 is a diagram showing the effect of the ratio of the ladle inner diameter D and the dip tube inner diameter d on the decarburization rate, where ● represents S / H = 0.1 and L / d.
= 0.2, K / D = 0.07 of the present invention, and ◯ indicates a comparative example.

【符号の説明】[Explanation of symbols]

１ 取鍋 ２ 直胴型浸漬管 ２′ 直胴部 ２″ 直胴部 ３ ガス吹込み孔 ４ 溶鋼 ５ Ａｒガス ６ スラグ ａ−ａ′ 浸漬管中心線 ｂ−ｂ′ 取鍋中心線 ｃ−ｃ′ ガス吹込み孔中心線 Ｄ 取鍋内径 ｄ 浸漬管内径 Ｈ 浸漬管内溶鋼の浴深 Ｓ 浸漬管下端と浸漬管外溶鋼表面との距離 Ｌ ガス吹込み孔と浸漬管中心との水平方向の距
離 Ｋ 浸漬管中心と取鍋中心との距離 Ｔ 浸漬管内溶鋼面と浸漬管下端との距離1 Ladle 2 Straight Body Type Immersion Pipe 2'Straight Body 2 "Straight Body 3 Gas Injection Hole 4 Molten Steel 5 Ar Gas 6 Slag aa 'Immersion Pipe Center Line b-b' Ladle Center Line c-c ′ Gas injection hole center line D Ladle inner diameter d Immersion pipe inner diameter H Immersion pipe molten steel bath depth S Distance between bottom of immersion pipe and surface of molten steel outside immersion pipe L Horizontal distance between gas injection hole and immersion pipe center K Distance between center of immersion pipe and center of ladle T Distance between molten steel surface in immersion pipe and lower end of immersion pipe

───────────────────────────────────────────────────── フロントページの続き (72)発明者 宮本 健一郎 東京都千代田区大手町二丁目６番３号 新日本製鐵株式会社内 (56)参考文献 特開 平６−116624（ＪＰ，Ａ) 特開 平６−228629（ＪＰ，Ａ) 特開 平６−299227（ＪＰ，Ａ) 特開 平５−339623（ＪＰ，Ａ) 特開 平６−212243（ＪＰ，Ａ) (58)調査した分野(Int.Cl.⁷，ＤＢ名) C21C 7/10 C21C 7/068 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenichiro Miyamoto 2-6-3 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Steel Co., Ltd. (56) Reference JP-A-6-116624 (JP, A) Kaihei 6-228629 (JP, A) JP 6-299227 (JP, A) JP 5-339623 (JP, A) JP 6-212243 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) C21C 7/10 C21C 7/068

Claims (3)

(57)【特許請求の範囲】(57) [Claims] 【請求項１】 取鍋内溶鋼表面の一部に１個または２個
以上の内径の異なる直胴部からなる直胴型浸漬管を浸漬
し、当該浸漬管内のみを真空としながら精錬する高清浄
度極低炭素鋼の溶製方法において、浸漬管内溶鋼の浴深
Ｈの０．５Ｈよりも深い位置に設けたガス吹込み孔から
０．６〜１５ＮＬ／（ｍｉｎ・ｔｏｎ）の攪拌用ガスを
供給し、かつ、取鍋内径Ｄと浸漬管内径ｄの比ｄ／Ｄを
０．３〜０．８、浸漬管下端と浸漬管外溶鋼表面との距
離Ｓを０．０３Ｈ〜０．３Ｈ、ガス吹込み孔と浸漬管中
心との水平方向の距離Ｌを０．１ｄ〜０．５ｄ、浸漬管
中心と取鍋中心との距離Ｋを０．０２Ｄ〜０．１２Ｄと
し、取鍋低部からガスを吹き込んで取鍋内溶鋼の上部に
あるスラグを除去した後に前記浸漬管を浸漬し、スラグ
を浸漬管外溶鋼表面に２〜１５ｋｇ／ｔｏｎ存在させた
状態で、真空度が７６０〜３００Ｔｏｒｒの領域では攪
拌用ガスを０．６〜２ＮＬ／（ｍｉｎ・ｔｏｎ）、３０
０〜１００Ｔｏｒｒの領域では１．０〜２．５ＮＬ／
（ｍｉｎ・ｔｏｎ）、１００Ｔｏｒｒ以下の領域では２
〜１５ＮＬ／（ｍｉｎ・ｔｏｎ）の範囲で供給すること
を特徴とする高清浄度極低炭素鋼の溶製方法。1. A high cleanliness method in which one or two or more straight body type immersion pipes having different internal diameters are immersed in a part of the surface of molten steel in a ladle, and refining is performed while only the immersion pipe is evacuated. In the melting method of ultra-low carbon steel, a stirring gas of 0.6 to 15 NL / (min · ton) is supplied from a gas injection hole provided at a position deeper than 0.5H of the bath depth H of the molten steel in the immersion pipe. And the ratio d / D of the inner diameter D of the ladle and the inner diameter d of the immersion pipe is 0.3 to 0.8, and the distance S between the lower end of the immersion pipe and the surface of the molten steel outside the immersion pipe is 0.03H to 0.3H, The horizontal distance L between the gas injection hole and the center of the immersion pipe is 0.1d to 0.5d, and the distance K between the center of the immersion pipe and the center of the ladle is 0.02D to 0.12D.
Then, blow gas from the bottom of the ladle to the top of the molten steel in the ladle.
After removing a certain slag, immerse the dipping pipe,
2 to 15 kg / ton was present on the surface of the molten steel outside the immersion pipe
In the state, the vacuum degree is disturbed in the range of 760 to 300 Torr.
Stirring gas is 0.6 to 2 NL / (min · ton), 30
In the range of 0 to 100 Torr, 1.0 to 2.5 NL /
(Min · ton), 2 in the area below 100 Torr
The method for melting high-cleanliness ultra-low carbon steel is characterized in that it is supplied in the range of 15 NL / (min · ton) . 【請求項２】 精錬炉から前記取鍋内に溶鋼を出鋼する
途中または出鋼後に脱酸剤を添加してスラグ中の（Ｔ・
Ｆe ）濃度を７％以下に低下させた後、当該溶鋼表面の
一部に前記浸漬管を浸漬する場合に、取鍋低部からガス
を吹き込んで取鍋内溶鋼の上部にあるスラグを除去した
後に前記浸漬管を浸漬し、スラグを浸漬管外溶鋼表面に
２〜１５ｋｇ／ｔｏｎ存在させた状態で、真空度が７６
０〜３００Ｔｏｒｒの領域では攪拌用ガスを０．６〜２
ＮＬ／（ｍｉｎ・ｔｏｎ）、３００〜１００Ｔｏｒｒの
領域では１．０〜２．５ＮＬ（ｍｉｎ・ｔｏｎ）、１０
０Ｔｏｒｒ以下の領域では２〜１５ＮＬ／（ｍｉｎ・ｔ
ｏｎ）の範囲で供給することを特徴とする請求項１記載
の高清浄度極低炭素鋼の溶製方法。2. A deoxidizer is added during or after tapping molten steel from the refining furnace to the inside of the ladle.
When the Fe) concentration is reduced to 7% or less and then the immersion pipe is immersed in a part of the surface of the molten steel, gas from the bottom of the ladle is used.
To remove the slag on the top of the molten steel in the ladle
After that, immerse the dip pipe and apply slag to the surface of the molten steel outside the dip pipe.
2 to 15 kg / ton, the degree of vacuum is 76
In the range of 0 to 300 Torr, the stirring gas is 0.6 to 2
NL / (min · ton), 300-100 Torr
In the area, 1.0 to 2.5 NL (min · ton), 10
In the region of 0 Torr or less, 2 to 15 NL / (min · t
on) in a range of 1.), the method for smelting a high cleanliness ultra-low carbon steel according to claim 1. 【請求項３】 脱炭処理終了後に１０Ｔｏｒｒ以下の状
態で前記浸漬管の真空排気用弁を閉じ、攪拌用ガスを供
給しながら真空度を大気圧まで復圧する過程で脱酸を行
うことを特徴とする請求項１または２記載の高清浄度極
低炭素鋼の溶製方法。3. The deoxidation is performed in the process of closing the vacuum exhaust valve of the dip tube at a pressure of 10 Torr or less after the decarburization treatment and returning the vacuum degree to atmospheric pressure while supplying a stirring gas. The method for producing a high cleanliness ultra-low carbon steel according to claim 1 or 2 .