JP2002086250A - Method for continuously casting steel - Google Patents
Method for continuously casting steelInfo
- Publication number
- JP2002086250A JP2002086250A JP2000277001A JP2000277001A JP2002086250A JP 2002086250 A JP2002086250 A JP 2002086250A JP 2000277001 A JP2000277001 A JP 2000277001A JP 2000277001 A JP2000277001 A JP 2000277001A JP 2002086250 A JP2002086250 A JP 2002086250A
- Authority
- JP
- Japan
- Prior art keywords
- molten steel
- immersion nozzle
- tundish
- mold
- sectional area
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
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- Continuous Casting (AREA)
- Casting Support Devices, Ladles, And Melt Control Thereby (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、浸漬ノズル内面へ
の溶鋼中のＡｌの酸化物などの付着の少ない鋼の連続鋳
造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting steel having a small amount of Al oxide or the like in molten steel adhered to the inner surface of an immersion nozzle.
【０００２】[0002]
【従来の技術】Ａｌで脱酸した溶鋼を連続鋳造する際、
溶鋼中のＡｌの酸化物が浸漬ノズル内面に付着するた
め、浸漬ノズル内の溶鋼の流れが阻害される。そのた
め、通常の２つの吐出孔を有する浸漬ノズルを用いる際
に、吐出流が均一にならず、片方の吐出流が弱くなるな
ど、いわゆる鋳型内の溶鋼の流れが片流れになりやす
い。片流れが発生すると、鋳型内の溶鋼の流動が不均一
となり、鋳型内の溶鋼表面に添加したモールドパウダが
溶鋼中に巻き込まれたり、浸漬ノズル内面に付着してい
たＡｌの酸化物などが剥離したものが溶鋼中に巻き込ま
れる。2. Description of the Related Art When continuously casting molten steel deoxidized with Al,
Since the oxide of Al in the molten steel adheres to the inner surface of the immersion nozzle, the flow of the molten steel in the immersion nozzle is hindered. Therefore, when using a normal immersion nozzle having two discharge holes, the flow of so-called molten steel in the mold tends to be one-sided, for example, the discharge flow is not uniform and one of the discharge flows is weak. When one-sided flow occurs, the flow of the molten steel in the mold becomes uneven, mold powder added to the surface of the molten steel in the mold is caught in the molten steel, and oxides of Al and the like attached to the inner surface of the immersion nozzle peeled off Things get caught in the molten steel.
【０００３】このようにして鋳型内の溶鋼中に巻き込ま
れたモールドパウダやＡｌの酸化物などは、鋳型内の凝
固殻に捕捉されて、鋳片表層部に欠陥が発生しやすい。
これら鋳片表層部の欠陥は、その鋳片を素材として熱間
圧延した製品の表面または内部の欠陥の原因となる。[0003] The mold powder and the oxide of Al, etc., which are thus caught in the molten steel in the mold, are trapped by the solidified shell in the mold and tend to cause defects in the surface layer of the slab.
These defects on the surface layer of the slab cause defects on the surface or inside of the product obtained by hot rolling the slab.
【０００４】浸漬ノズル内面に溶鋼中のＡｌの酸化物な
どが付着するのを防止するために、浸漬ノズル内を通過
する溶鋼中に不活性ガスを吹き込む方法が従来から採ら
れている。たとえば、特開平４−３１９０５５号公報に
は、浸漬ノズル内を通過する溶鋼量に応じて、溶鋼中に
吹き込む不活性ガスの量を調整する方法が提案されてい
る。しかし、不活性ガスの吹き込み量によっては、不活
性ガスの気泡が鋳型内の凝固殻に捕捉され、鋳片表層部
に気泡性欠陥が発生する。この鋳片表層部の気泡性欠陥
は製品にまで残存し、製品に表面欠陥が発生しやすい。[0004] In order to prevent the oxide of Al in the molten steel from adhering to the inner surface of the immersion nozzle, a method of blowing an inert gas into the molten steel passing through the immersion nozzle has conventionally been adopted. For example, Japanese Patent Application Laid-Open No. Hei 4-319055 proposes a method in which the amount of inert gas blown into molten steel is adjusted according to the amount of molten steel passing through an immersion nozzle. However, depending on the blowing amount of the inert gas, bubbles of the inert gas are trapped in the solidified shell in the mold, and bubble defects are generated on the surface layer of the slab. This cellular defect on the surface layer of the slab remains in the product, and the product is likely to have surface defects.
【０００５】また、鋳造前の溶鋼中にＣａを添加し、溶
鋼中のＡｌの酸化物を低融点の酸化物とする方法が従来
から採られている。たとえば、特開平９−１９２７９９
号公報には、Ａｌ脱酸後の溶鋼中にＣａを添加し、溶鋼
中のＣａ含有率を１〜５ｐｐｍとする方法が提案されて
いる。しかし、Ｃａを溶鋼中に添加することは、鋳片の
製造コストを増加させるばかりでなく、製品によって
は、Ｃａの添加によって機械的特性が劣化する。[0005] Further, a method of adding Ca to molten steel before casting to convert an oxide of Al in the molten steel into an oxide having a low melting point has conventionally been adopted. For example, Japanese Unexamined Patent Publication No. 9-192799
Japanese Patent Laid-Open Publication No. 2002-210, proposes a method in which Ca is added to molten steel after Al deoxidation to make the Ca content in the molten steel 1 to 5 ppm. However, adding Ca to molten steel not only increases the production cost of cast slabs, but also causes the mechanical properties of some products to deteriorate due to the addition of Ca.
【０００６】さらに、特開平１０−３０５３５５号公報
には、浸漬ノズル内面の材質を溶鋼中のＡｌの酸化物な
どが付着しにくい材質とする方法が提案されている。浸
漬ノズル内面の耐火物の材質をＳｉＯ2 およびＣが少な
いスピネルなどの材質とすることにより、溶鋼中のＡｌ
が酸化されることを抑制し、浸漬ノズル内面に付着する
Ａｌの酸化物を極力少なくする方法である。しかし、こ
れらの耐火物の材質では、通常浸漬ノズルに用いられて
いるアルミナグラファイト質に比べて耐熱衝撃性が劣る
ので、鋳造前の予熱時または鋳造中に浸漬ノズルが破損
しやすい。Furthermore, Japanese Patent Application Laid-Open No. 10-305355 proposes a method in which the material of the inner surface of the immersion nozzle is made of a material to which Al oxide in molten steel is unlikely to adhere. By making the material of the refractory on the inner surface of the immersion nozzle a material such as spinel containing less SiO 2 and C,
Is a method of suppressing oxidation of Al and minimizing the amount of Al oxide adhering to the inner surface of the immersion nozzle. However, these refractory materials are inferior in the thermal shock resistance as compared with the alumina graphite material usually used for the immersion nozzle, so that the immersion nozzle is easily broken at the time of preheating before casting or during casting.
【０００７】その他に、浸漬ノズル内面に段差を設けて
浸漬ノズル内を通過する溶鋼の流速を均一化する方法、
浸漬ノズル本体内部に断熱のための空間または断熱層を
備え、浸漬ノズル内面の温度を高温に維持することによ
りＡｌの酸化物などが浸漬ノズル内面に付着することを
防止する方法などが提案されている。しかし、浸漬ノズ
ル内面への溶鋼中のＡｌの酸化物などの付着を必ずしも
安定して防止できていないのが現状である。Another method is to provide a step on the inner surface of the immersion nozzle to make the flow velocity of the molten steel passing through the immersion nozzle uniform.
A method has been proposed in which a space or a heat insulating layer for heat insulation is provided inside the immersion nozzle body, and the temperature of the inner surface of the immersion nozzle is maintained at a high temperature to prevent oxides of Al and the like from adhering to the inner surface of the immersion nozzle. I have. However, at present, it has not always been possible to stably prevent the adhesion of oxides of Al in the molten steel to the inner surface of the immersion nozzle.
【０００８】上記のような現状に鑑み、安価な方法で、
安定して浸漬ノズル内面への溶鋼中のＡｌの酸化物など
の付着を防止できる方法が望まれている。[0008] In view of the above situation, inexpensive method,
There is a demand for a method capable of stably preventing the adhesion of oxides of Al in molten steel to the inner surface of the immersion nozzle.
【０００９】[0009]
【発明が解決しようとする課題】本発明は、浸漬ノズル
内面への溶鋼中のＡｌの酸化物などの付着を、安価な方
法で安定して防止でき、得られた鋳片を素材とする熱間
圧延した製品において、モールドパウダ、Ａｌの酸化
物、気泡などによる鋳片表層部の欠陥に起因する製品の
表面または内部の欠陥の発生を防止できる鋼の連続鋳造
方法を提供することを目的とする。SUMMARY OF THE INVENTION According to the present invention, it is possible to stably prevent the adhesion of Al oxide or the like in molten steel to the inner surface of a submerged nozzle by an inexpensive method. It is an object of the present invention to provide a continuous casting method of steel capable of preventing the occurrence of surface or internal defects of a product caused by defects in a surface layer portion of a slab due to defects of mold powder, oxides of Al, bubbles, etc. I do.
【００１０】[0010]
【課題を解決するための手段】本発明の要旨は、浸漬ノ
ズルを用いてタンディッシュから鋳型内に溶鋼を供給す
る連続鋳造方法において、下記（イ）式で定義されるタ
ンディッシュの出口の開口断面積Ｓ（ｍ2 ）と浸漬ノズ
ル内の溶鋼が上方から下方に通過する部分の横断面積Ａ
（ｍ2 ）とが下記（ロ）式を満足する浸漬ノズルを用
い、下記（ハ）式で定義される浸漬ノズル内部の溶鋼ヘ
ッド指数Ｈ（ｍ）が下記（ニ）式を満足する条件で鋳造
し、かつ、浸漬ノズル内を通過する溶鋼中に単位時間に
吹き込む不活性ガス量Ｗ（ｍ3 (Normal)／ｓ）が下記
（ホ）式を満足する条件で鋳造する鋼の連続鋳造方法に
ある。 Ｓ＝Ｑ／｛ρ×（２ｇｈ）1/2 ｝ ・・・(イ) ２＜Ａ／Ｓ＜５ ・・・(ロ) Ｈ＝(２ｇ)-1×(ρｃ)-2×(Ｑ／Ａ)2 ・・・(ハ) ０．０８＜Ｈ＜０．５ ・・・(ニ) １×１０-6 ＜Ｗ／Ｑ＜ ５×１０-6 ・・・(ホ) ここで、Ｑ：単位時間に浸漬ノズル内を通過する溶鋼流
量(ｋｇ／ｓ) ρ：溶鋼の密度(ｋｇ／ｍ3) ｇ：重力加速度(ｍ／ｓ2) ｈ：タンディッシュ内部の溶鋼の深さ(ｍ) ｃ：流路係数(−) 上記（イ）式はエネルギ保存の法則から求まる式で、こ
の式で定義されるタンディッシュの出口の開口断面積Ｓ
とは、タンディッシュから浸漬ノズル内に溶鋼を供給す
るためのタンディッシュの出口の開口断面積を意味す
る。すなわち、（イ）式の右辺の分子は単位時間当たり
の鋳型内への溶鋼の供給流量で、分母はタンディッシュ
内の溶鋼の深さがｈ、すなわち、溶鋼の損失ヘッドｈの
際の溶鋼の流速を意味する。したがって、単位時間当た
りの鋳型内への溶鋼の供給流量を溶鋼の損失ヘッドｈの
際の溶鋼の流速で除した上記（イ）式の右辺は、タンデ
ィッシュの出口の開口断面積を意味する。たとえば、鋳
造速度を変更して鋳型内への溶鋼の供給流量Ｑを変化さ
せる際には、この断面積Ｓは変化する。SUMMARY OF THE INVENTION The gist of the present invention is to provide a continuous casting method for supplying molten steel from a tundish into a mold using an immersion nozzle, wherein an opening of an outlet of the tundish defined by the following formula (a) is provided. Cross-sectional area S (m 2 ) and cross-sectional area A of the portion where molten steel in the immersion nozzle passes from above to below
(M 2 ) using an immersion nozzle that satisfies the following equation (b) under the condition that the molten steel head index H (m) inside the immersion nozzle defined by the following equation (c) satisfies the following equation (d) A continuous casting method for steel that is cast and cast under conditions that the amount of inert gas W (m 3 (Normal) / s) blown into the molten steel per unit time passing through the immersion nozzle satisfies the following formula (e). It is in. S = Q / {ρ × (2gh) 1/2・ ・ ・ (A) 2 <A / S <5 (B) H = (2g) −1 × (ρc) −2 × (Q / A) 2 ... (c) 0.08 <H <0.5 (d) 1 × 10 -6 <W / Q <5 × 10 -6 (e) where Q: Flow rate of molten steel passing through immersion nozzle per unit time (kg / s) ρ: density of molten steel (kg / m 3 ) g: acceleration of gravity (m / s 2 ) h: depth of molten steel inside tundish (m) c: Channel coefficient (-) The above equation (a) is an equation obtained from the law of conservation of energy, and the opening cross-sectional area S of the outlet of the tundish defined by this equation is
Means the opening cross-sectional area of the outlet of the tundish for supplying molten steel from the tundish into the immersion nozzle. That is, the numerator on the right side of the equation (a) is the supply flow rate of the molten steel into the mold per unit time, and the denominator is the depth h of the molten steel in the tundish, ie, the molten steel at the loss head h of the molten steel. Means flow velocity. Therefore, the right side of the above equation (a), which is obtained by dividing the supply flow rate of the molten steel into the mold per unit time by the flow velocity of the molten steel at the loss head h of the molten steel, means the opening cross-sectional area of the outlet of the tundish. For example, when changing the casting speed to change the supply flow rate Q of molten steel into the mold, the cross-sectional area S changes.
【００１１】また、上記（ハ）式で定義される浸漬ノズ
ル内部の溶鋼ヘッド指数Ｈ（ｍ）とは、浸漬ノズル内部
に形成された溶鋼表面の高さと鋳型内の溶鋼表面の高さ
との差を意味する。浸漬ノズル内を通過する溶鋼流量、
浸漬ノズルの横断面積などを適正な条件とすることによ
り、タンディッシュの出口から流入してくる溶鋼は、浸
漬ノズル内部に形成された溶鋼表面上に落下する。その
際、上記（ハ）式は、上記（イ）式と同じくエネルギ保
存の法則から求まり、（イ）式と相違する点は、式中に
流路係数ｃを付与している点である。この流路係数ｃ
は、一般にベルヌーイの式で取り扱われている速度ヘッ
ド修正係数の逆数を意味する。The molten steel head index H (m) inside the immersion nozzle defined by the above equation (c) is the difference between the height of the molten steel surface formed inside the immersion nozzle and the height of the molten steel surface in the mold. Means Molten steel flow through the immersion nozzle,
By setting the cross-sectional area of the immersion nozzle or the like to an appropriate condition, the molten steel flowing from the outlet of the tundish falls on the molten steel surface formed inside the immersion nozzle. At this time, the above equation (c) is obtained from the law of conservation of energy similarly to the above equation (a), and the difference from the equation (a) is that the flow path coefficient c is added to the equation. This channel coefficient c
Means the reciprocal of the velocity head correction factor generally treated in Bernoulli's equation.
【００１２】ここで、溶鋼の密度ρの値として７０００
（ｋｇ／ｍ3 ）、重力加速度ｇの値として９．８（ｍ／
ｓ2 ）を用いることができる。また、浸漬ノズル内部の
溶鋼の鋳型内の溶鋼中への吐出する流れは、乱流として
取り扱うのがよいので、流路係数ｃとして０．９を用い
ることができる。Here, the value of the density ρ of the molten steel is 7000
(Kg / m 3 ), and 9.8 (m / m 3 )
s 2 ) can be used. Further, the flow of the molten steel in the immersion nozzle into the molten steel in the mold is preferably handled as a turbulent flow, so that a flow path coefficient c of 0.9 can be used.
【００１３】図１は、タンディッシュ内および浸漬ノズ
ル内の溶鋼の状況を示す模式図である。図１（ｂ）は、
図１（ａ）におけるＡ１−Ａ２線の断面を拡大した図で
ある。タンディッシュ２の出口の開口断面積Ｓ（前述の
（イ）式で定義する断面積）、浸漬ノズル１内の溶鋼１
０が通過する部分の横断面積Ａ、タンディッシュ内部の
溶鋼の深さｈ、および浸漬ノズル内部の溶鋼ヘッド指数
Ｈなどを模式的に示す。符号３はスライデイングゲー
ト、符号４は吐出孔、符号８はメニスカス、符号９はモ
ールドパウダ、符号１１は鋳型、および符号１２は凝固
殻を示す。FIG. 1 is a schematic diagram showing the state of molten steel in a tundish and an immersion nozzle. FIG. 1 (b)
FIG. 2 is an enlarged view of a cross section taken along line A1-A2 in FIG. The cross-sectional area S of the opening of the outlet of the tundish 2 (the cross-sectional area defined by the above-mentioned formula (A)), the molten steel 1 in the immersion nozzle 1
The cross-sectional area A of the portion through which 0 passes, the depth h of the molten steel inside the tundish, and the molten steel head index H inside the immersion nozzle are schematically shown. Reference numeral 3 denotes a sliding gate, reference numeral 4 denotes a discharge hole, reference numeral 8 denotes a meniscus, reference numeral 9 denotes a mold powder, reference numeral 11 denotes a mold, and reference numeral 12 denotes a solidified shell.
【００１４】本発明者らは、前述の課題を下記および
の知見を基に、の対策を採ることにより解決した。 図２は、浸漬ノズル内面に付着物が付着する状況を示
す模式図である。符号５は、浸漬ノズル１内へのタンデ
ィッシュの出口近傍で、たとえば、スライディングゲー
ト３近傍に付着した付着物、符号６は、浸漬ノズルの胴
部に付着した付着物、符号７は、吐出孔４近傍に付着し
た付着物である。符号１０は溶鋼、符号１１は鋳型、お
よび符号１２は凝固殻を示す。The present inventors have solved the above-mentioned problems by taking the following measures based on the following and findings. FIG. 2 is a schematic diagram showing a situation in which deposits adhere to the inner surface of the immersion nozzle. Reference numeral 5 denotes an adhering substance adhering near the exit of the tundish into the immersion nozzle 1, for example, near the sliding gate 3, reference numeral 6 denotes an adhering substance adhering to the body of the immersion nozzle, and reference numeral 7 denotes a discharge hole. 4 is a deposit attached to the vicinity. Reference numeral 10 denotes molten steel, reference numeral 11 denotes a mold, and reference numeral 12 denotes a solidified shell.
【００１５】通常の２つの吐出孔を有する浸漬ノズルを
用いる際に、吐出流が均一にならず、鋳型内の溶鋼の流
れに片流れが発生するのは、吐出孔４近傍の付着物７が
多く形成されている場合に発生しやすい。２つの吐出孔
近傍のそれぞれの付着物の大きさは異なることが多いの
で、２つの吐出孔からのそれぞれの吐出流の流速や方向
が同じにならず、いわゆる片流れが発生するのである。
片流れが発生すると、モールドパウダや浸漬ノズル内面
に付着していたＡｌの酸化物などが剥離したものを鋳型
内の溶鋼中に巻き込んだりしやすいのは前述の通りであ
る。When an ordinary immersion nozzle having two discharge holes is used, the discharge flow is not uniform, and one-sided flow occurs in the flow of the molten steel in the mold because there are many deposits 7 near the discharge holes 4. It is easy to occur when it is formed. Since the size of each attached matter near the two discharge holes is often different, the flow rates and directions of the respective discharge flows from the two discharge holes are not the same, so that a so-called one-sided flow occurs.
As described above, when the one-sided flow occurs, the powder from which Al oxide or the like adhering to the inner surface of the mold powder or the immersion nozzle has peeled off is likely to be involved in the molten steel in the mold.
【００１６】吐出孔近傍に付着物が形成されるのは、
吐出孔から流出する直前の溶鋼の圧力が高い場合に、吐
出孔上方の溶鋼の流れに渦流が発生しやすいためであ
る。渦流が発生すると、溶鋼中のＡｌの酸化物などが浸
漬ノズル内面と接する機会が多くなるので、Ａｌの酸化
物などが浸漬ノズル内面に付着しやすくなる。以下に渦
流が発生する状況を、さらに説明する。The reason why the deposit is formed in the vicinity of the discharge hole is as follows.
This is because when the pressure of the molten steel immediately before flowing out of the discharge hole is high, a vortex easily occurs in the flow of the molten steel above the discharge hole. When the eddy current occurs, the oxides of Al and the like in the molten steel often come into contact with the inner surface of the immersion nozzle, so that the oxides of Al and the like easily adhere to the inner surface of the immersion nozzle. The situation in which a vortex is generated will be further described below.
【００１７】本発明者らは、浸漬ノズル内の溶鋼の流動
および吐出流の流動を調査するため、縮尺１／１の水モ
デル実験を行った。縮尺１／１モデルを用いることによ
り、レイノズル数およびフルード数を同時に、実際の溶
鋼系と同じにできるという利点がある。その結果、吐出
孔上方で渦流が発生しやすいのは、浸漬ノズル内が溶鋼
で充満し、吐出孔から流出する直前の溶鋼の圧力とし
て、タンディッシュ内の溶鋼の深さが作用する場合に相
当することがわかった。その際、吐出孔から流れ出た溶
鋼の圧力は、鋳型内の溶鋼表面と吐出孔との高さの差に
相当する圧力にまで急激に低下する。そのため、吐出孔
上方で吐出孔内への溶鋼の吸い込みが発生し、吐出孔上
方において渦流が発生する。The present inventors conducted a 1 / 1-scale water model experiment in order to investigate the flow of molten steel and the flow of discharge flow in the immersion nozzle. By using the 1/1 scale model, there is an advantage that the number of Reynolds nozzles and the number of fluids can be simultaneously made the same as in an actual molten steel system. As a result, swirl is likely to occur above the discharge hole when the inside of the immersion nozzle is filled with molten steel and the depth of the molten steel in the tundish acts as the pressure of the molten steel immediately before flowing out of the discharge hole. I found out. At that time, the pressure of the molten steel flowing out of the discharge hole rapidly decreases to a pressure corresponding to a difference in height between the surface of the molten steel in the mold and the discharge hole. Therefore, the molten steel is sucked into the discharge hole above the discharge hole, and a vortex flows above the discharge hole.
【００１８】浸漬ノズル内が溶鋼で充満せず、タンディ
ッシュの出口から流入してくる溶鋼が、浸漬ノズル内部
に形成された溶鋼表面上に落下する場合には、吐出孔か
ら流出する直前の溶鋼の圧力は、浸漬ノズル内部の溶鋼
表面と鋳型内の溶鋼表面との高さの差に相当する程度で
ある。したがって、吐出孔から流出する直前の溶鋼の圧
力と吐出孔から流れ出た溶鋼の圧力との差は小さいの
で、吐出孔上方での吐出孔内への溶鋼の吸い込み、およ
び渦流の発生は防止される。When the inside of the immersion nozzle is not filled with the molten steel and the molten steel flowing from the outlet of the tundish falls on the surface of the molten steel formed inside the immersion nozzle, the molten steel immediately before flowing out of the discharge hole is formed. Is equivalent to the difference in height between the molten steel surface inside the immersion nozzle and the molten steel surface inside the mold. Therefore, since the difference between the pressure of the molten steel immediately before flowing out of the discharge hole and the pressure of the molten steel flowing out of the discharge hole is small, suction of the molten steel into the discharge hole above the discharge hole and generation of a vortex are prevented. .
【００１９】本発明の方法では、前述の（イ）式で定
義されるタンディッシュの出口の開口断面積Ｓ（ｍ2 ）
と浸漬ノズル内の溶鋼が上方から下方に通過する部分の
横断面積Ａ（ｍ2 ）とが前述の（ロ）式を満足する浸漬
ノズルを用いる。かつ、前述の（ハ）式で定義される浸
漬ノズル内部の溶鋼ヘッド指数Ｈ（ｍ）が前述の（ニ）
式を満足する条件で鋳造する。In the method of the present invention, the opening cross-sectional area S (m 2 ) of the outlet of the tundish defined by the above-mentioned equation (A) is used.
An immersion nozzle is used in which the cross-sectional area A (m 2 ) of the portion where the molten steel in the immersion nozzle passes from above to below satisfies the above formula (b). In addition, the molten steel head index H (m) inside the immersion nozzle defined by the above formula (c) is calculated by the above (d).
Cast under conditions that satisfy the formula.
【００２０】そのため、浸漬ノズル内が溶鋼で充満せ
ず、タンディッシュの出口から流入してくる溶鋼が浸漬
ノズル内部に形成された溶鋼表面上に落下するので、吐
出孔から流出する直前の溶鋼の圧力は、浸漬ノズル内部
の溶鋼表面と鋳型内の溶鋼表面との高さの差に相当する
程度で小さく、吐出孔から流れ出た溶鋼の圧力との差は
小さくなるので、吐出孔上方での渦流は発生しにくい。
渦流が発生しにくいので、浸漬ノズル内面に溶鋼中のＡ
ｌの酸化物などが付着しにくい。Therefore, the interior of the immersion nozzle is not filled with the molten steel, and the molten steel flowing from the outlet of the tundish falls on the surface of the molten steel formed inside the immersion nozzle. The pressure is small enough to correspond to the height difference between the molten steel surface inside the immersion nozzle and the molten steel surface in the mold, and the difference between the pressure of the molten steel flowing out of the discharge hole and the eddy current above the discharge hole is small. Is unlikely to occur.
Since eddy currents are unlikely to occur, A
l oxides and the like hardly adhere.
【００２１】さらに、本発明の方法では、浸漬ノズル内
を通過する溶鋼中に単位時間に吹き込む不活性ガス量Ｗ
（ｍ3 (Normal)／ｓ）が前述の（ホ）式を満足するよ
う、つまり、通過する溶鋼量に対して適正な量の不活性
ガスを吹き込むので、浸漬ノズル内面への溶鋼中の酸化
物の付着を防止でき、さらに、鋳型内の凝固殻に不活性
ガスの気泡が捕捉されることも防止できる。Further, according to the method of the present invention, the amount W of inert gas blown per unit time into the molten steel passing through the immersion nozzle
Since (m 3 (Normal) / s) satisfies the above-mentioned equation (e), that is, an appropriate amount of inert gas is blown with respect to the amount of molten steel passing therethrough. It is possible to prevent the adhesion of objects and to prevent the bubbles of the inert gas from being trapped in the solidified shell in the mold.
【００２２】[0022]
【発明の実施の形態】本発明の方法は、Ａｌで脱酸さ
れ、溶鋼中にＡｌの酸化物が存在する溶鋼の連続鋳造に
適用するのに好適である。ただし、Ａｌで脱酸された溶
鋼に限定しない。本発明の方法は、Ｔｉ、Ｚｒなどの酸
化物、その他の硫化物、窒化物などが溶鋼中に存在する
溶鋼の連続鋳造に対しても効果的である。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention is suitable for application to continuous casting of molten steel which is deoxidized with Al and contains oxides of Al in the molten steel. However, it is not limited to molten steel deoxidized with Al. The method of the present invention is also effective for continuous casting of molten steel in which oxides such as Ti and Zr, other sulfides and nitrides are present in the molten steel.
【００２３】本発明の方法は、広幅の鋳片、すなわちス
ラブ鋳片を鋳造する際に適用するのに好適である。この
ような鋳片を鋳造する際、たとえば２つの吐出孔からの
それぞれの吐出流の流速や方向が不均一で、いわゆる片
流れが発生すると、鋳型内の溶鋼の流動が不均一とな
り、モールドパウダや浸漬ノズル内に付着していた酸化
物が剥離したものを鋳型内の溶鋼中に巻き込みやすいか
らである。鋳片幅が広いほど、このような吐出流の片流
れの影響を受けやすいので、鋳片幅が１０００ｍｍ以上
の場合に、本発明の方法を適用するのが好ましく、さら
には、１２００ｍｍ以上の場合に、本発明の方法を適用
するのがより好ましい。The method of the present invention is suitable for application in casting a wide slab, that is, a slab slab. When casting such a slab, for example, if the flow velocity and direction of each discharge flow from the two discharge holes are non-uniform, so-called one-sided flow occurs, the flow of molten steel in the mold becomes non-uniform, and mold powder and The reason for this is that the oxide that has adhered to the immersion nozzle and that has been peeled off is easily rolled into molten steel in the mold. The wider the slab width is, the more easily the slab of the discharge flow is affected by such a flow, so that the method of the present invention is preferably applied when the slab width is 1000 mm or more, and further, when the slab width is 1200 mm or more. More preferably, the method of the present invention is applied.
【００２４】浸漬ノズルの吐出孔の数は２つ以上の偶数
であるのが好ましい。本発明の方法は、いわゆるスラブ
鋳片を鋳造する場合を対象とするのが好ましいので、浸
漬ノズルの吐出孔の数は、通常用いられている２つでも
よいし、または４つなど、２以上の偶数であるのがよ
い。それらの内の半数ずつの吐出孔からの吐出流は、鋳
型の互いに反対方向にある短辺方向にそれぞれほぼ向い
ておればよい。これらの吐出孔の合計の断面積は、浸漬
ノズル内部の溶鋼が通過する部分の横断面積Ａの２〜３
倍であることが好ましい。また、２．２〜２．６倍であ
ることが、より好ましい。The number of discharge holes of the immersion nozzle is preferably an even number of two or more. Since the method of the present invention is preferably intended for casting a so-called slab slab, the number of discharge holes of the immersion nozzle may be two or more commonly used, or two or more such as four. Should be an even number. The discharge flow from each half of the discharge holes may be substantially directed to the short sides of the mold opposite to each other. The total cross-sectional area of these discharge holes is 2 to 3 times the cross-sectional area A of the part through which molten steel passes inside the immersion nozzle.
Preferably it is twice. More preferably, it is 2.2 to 2.6 times.
【００２５】浸漬ノズル内の溶鋼が上方から下方に通過
する部分の横断面形状は、とくに限定しないが、円形が
好ましい。さらに、浸漬ノズルの上部から下部にかけ
て、その内径が一定であることが好ましい。ただし、浸
漬ノズルの製造上の都合から、通常、上部から下部にか
けて、５〜１０ｍｍ程度、内径が小さくなっている。こ
のように、内径を変化させている場合には、最小の内径
の部分に相当する横断面積を、前述の横断面積Ａとすれ
ばよい。The cross section of the portion of the immersion nozzle through which molten steel passes from above to below is not particularly limited, but is preferably circular. Further, it is preferable that the inner diameter is constant from the upper part to the lower part of the immersion nozzle. However, for convenience in manufacturing the immersion nozzle, the inner diameter is generally reduced from the upper part to the lower part by about 5 to 10 mm. As described above, when the inner diameter is changed, the cross-sectional area corresponding to the portion having the minimum inner diameter may be set as the above-described cross-sectional area A.
【００２６】本発明の方法では、前述の（イ）式で定義
されるタンディッシュの出口の開口断面積Ｓに対する浸
漬ノズル内の溶鋼が上方から下方に通過する部分の横断
面積Ａの比Ａ／Ｓは、２を超えて、５未満の値とする。In the method of the present invention, the ratio A / of the cross-sectional area A of the portion where the molten steel in the immersion nozzle passes from above to below with respect to the opening cross-sectional area S of the outlet of the tundish defined by the above-mentioned equation (A). S is a value exceeding 2 and less than 5.
【００２７】比Ａ／Ｓの値が５以上では、タンディッシ
ュの出口の開口断面積、すなわち、浸漬ノズル内に供給
される溶鋼の横断面積に比べて浸漬ノズル内の横断面積
が大きいので、溶鋼は特定方向の浸漬ノズル内壁に沿っ
た流れとなりやすい。したがって、吐出流の強さが吐出
孔によって異なりやすく、吐出流が不均一となり、鋳型
内の溶鋼の流れが片流れとなりやすい。極端な場合に
は、鋳型内の溶鋼表面を浸漬ノズルを境に左右で表現す
れば、左右のどちらかの側の溶鋼表面、すなわち、湯面
レベルが高くなる現象が発生する。比Ａ／Ｓの値が２以
下では、浸漬ノズル内の溶鋼が通過する横断面積が比較
的に小さいので、浸漬ノズル内を溶鋼がほぼ充満して落
下する。そのため、吐出孔から流出する直前の溶鋼にタ
ンディッシュ内の溶鋼の深さに相当する溶鋼ヘッドが作
用するので、前述のとおり、吐出孔上方において渦流が
発生し、浸漬ノズル内面に溶鋼中のＡｌの酸化物などが
付着しやすい。When the value of the ratio A / S is 5 or more, the cross-sectional area of the opening of the outlet of the tundish, that is, the cross-sectional area of the molten steel supplied to the submerged nozzle is larger than that of the molten steel. Tends to flow along the inner wall of the immersion nozzle in a specific direction. Therefore, the strength of the discharge flow tends to vary depending on the discharge holes, the discharge flow becomes non-uniform, and the flow of molten steel in the mold tends to be one-sided. In an extreme case, if the surface of the molten steel in the mold is expressed by the left and right sides of the immersion nozzle, a phenomenon occurs in which the surface of the molten steel on one of the left and right sides, that is, the molten metal level becomes high. When the value of the ratio A / S is 2 or less, since the cross-sectional area through which the molten steel passes through the immersion nozzle is relatively small, the molten steel falls almost completely inside the immersion nozzle. Therefore, the molten steel head corresponding to the depth of the molten steel in the tundish acts on the molten steel immediately before flowing out of the discharge hole, and as described above, a vortex is generated above the discharge hole, and the Al in the molten steel is formed on the inner surface of the immersion nozzle. Oxide easily adheres.
【００２８】本発明の方法では、前述の（ハ）式で定義
される浸漬ノズル内部の溶鋼ヘッド指数Ｈの値は、０．
０８ｍを超えて、０．５ｍ未満とする。In the method of the present invention, the value of the molten steel head index H inside the immersion nozzle defined by the above-mentioned equation (c) is 0.1.
More than 08m and less than 0.5m.
【００２９】Ｈの値が０．５ｍ以上では、吐出孔から流
出する直前の溶鋼の圧力が大きくなるので、吐出孔上方
において渦流が発生しやすい。Ｈの値が０．０８ｍ以下
では、浸漬ノズル内径を極端に大きくしたり、または鋳
造速度を極端に遅くする場合に相当し、浸漬ノズル内に
供給される溶鋼の量が少ない。そのため、溶鋼から浸漬
ノズルへの熱供給量が減少するので、浸漬ノズルの温度
が低下し、浸漬ノズル内面に地金が付着しやすくなる。
極端な場合には、浸漬ノズル詰まりが発生し、鋳造の継
続が困難となる。When the value of H is 0.5 m or more, the pressure of the molten steel immediately before flowing out of the discharge hole becomes large, so that a vortex is easily generated above the discharge hole. When the value of H is 0.08 m or less, it corresponds to the case where the inner diameter of the immersion nozzle is extremely increased or the casting speed is extremely slowed down, and the amount of molten steel supplied into the immersion nozzle is small. As a result, the amount of heat supplied from the molten steel to the immersion nozzle decreases, so that the temperature of the immersion nozzle decreases, and the metal becomes more likely to adhere to the inner surface of the immersion nozzle.
In an extreme case, clogging of the immersion nozzle occurs, making it difficult to continue casting.
【００３０】本発明の方法では、単位時間に浸漬ノズル
内を通過する溶鋼流量Ｑ（ｋｇ／ｓ）に対し、これら溶
鋼中に単位時間に吹き込む不活性ガス量Ｗ（ｍ3 (Norma
l)／ｓ）の比Ｗ／Ｑ（ｍ3 (Normal)／ｋｇ）は、１×１
０-6ｍ3 (Normal)／ｋｇを超えて、５×１０-6ｍ3 (Nor
mal)／ｋｇ未満とする。In the method of the present invention, the amount of inert gas W (m 3 (Norma) which is blown into the molten steel per unit time with respect to the flow rate Q (kg / s) of the molten steel passing through the immersion nozzle per unit time.
l) / s), the ratio W / Q (m 3 (Normal) / kg) is 1 × 1
0 Beyond -6 m 3 (Normal) / kg , 5 × 10 -6 m 3 (Nor
mal) / kg.
【００３１】比Ｗ／Ｑが５×１０-6ｍ3 (Normal)／ｋｇ
以上では、不活性ガスの量が多すぎるため、不活性ガス
の気泡が鋳型内の凝固殻に捕捉されやすい。また、極端
な場合には、鋳型内の溶鋼表面が波立ちやすく、モール
ドパウダを鋳型内の溶鋼中に巻き込みやすくなり、鋳型
内の凝固殻にモールドパウダが付着しやすい。また、１
×１０-6ｍ3 (Normal)／ｋｇ以下では、浸漬ノズル内面
に溶鋼中の酸化物が付着しやすい。The ratio W / Q is 5 × 10 −6 m 3 (Normal) / kg
In the above, since the amount of the inert gas is too large, bubbles of the inert gas are easily captured by the solidified shell in the mold. In an extreme case, the surface of the molten steel in the mold is easily wavy, the mold powder is easily entangled in the molten steel in the mold, and the mold powder is easily attached to the solidified shell in the mold. Also, 1
If it is less than × 10 −6 m 3 (Normal) / kg, the oxide in the molten steel tends to adhere to the inner surface of the immersion nozzle.
【００３２】浸漬ノズル内を通過する溶鋼中に不活性ガ
スを吹き込む位置は、タンディッシュ底部で浸漬ノズル
への開口部近傍、スライディングゲートおよび浸漬ノズ
ルのうちの少なくとも１箇所から吹き込むのがよい。The position where the inert gas is blown into the molten steel passing through the immersion nozzle is preferably blown from at least one of the sliding gate and the immersion nozzle near the opening to the immersion nozzle at the bottom of the tundish.
【００３３】[0033]
【実施例】２ストランドを有する垂直曲げ型連続鋳造機
を用い、Ｃ含有率が０．００１〜０．００３質量％の極
低炭素鋼を、厚さ２７０ｍｍ、幅１２００ｍｍまたは１
６００ｍｍの鋳片に１．３〜１．６ｍ／分の速度で鋳造
した。タンディッシュ内の溶鋼の深さは０．９６〜２．
２ｍとした。EXAMPLE Using a vertical bending type continuous casting machine having two strands, an ultra-low carbon steel having a C content of 0.001 to 0.003 mass% was prepared with a thickness of 270 mm and a width of 1200 mm or 1 mm.
It was cast at a speed of 1.3 to 1.6 m / min on a 600 mm slab. The depth of molten steel in the tundish is 0.96 to 2.
It was 2 m.
【００３４】浸漬ノズルは、アルミナグラファイト質の
耐火物とし、通常の下向き３０°の２孔を有するノズル
とした。１つの吐出孔の断面積は０．００８ｍ2 、溶鋼
が通過する部分の有効高さは９３０ｍｍでそれぞれ一定
とし、溶鋼が上方から下方に通過する部分の内径を７０
〜１２０ｍｍで変更して試験した。浸漬ノズル下端部の
鋳型内の溶鋼中への浸漬深さは２５０〜３００ｍｍとし
た。The immersion nozzle was a refractory made of alumina graphite, and was a normal nozzle having two holes of 30 ° downward. The cross-sectional area of one discharge hole is 0.008 m 2 , the effective height of the portion through which molten steel passes is 930 mm, which is constant, and the inner diameter of the portion through which molten steel passes downward from above is 70 mm.
The test was performed with a change of 〜120 mm. The immersion depth of the lower end of the immersion nozzle into the molten steel in the mold was 250 to 300 mm.
【００３５】スライディングゲートから、Ａｒガスを６
７×１０-6〜５００×１０-6ｍ3 (Normal)／ｓ（約４〜
３０リットル(Normal)／分）の量で浸漬ノズル内を通過
する溶鋼中に吹き込んだ。Ar gas is supplied from the sliding gate to 6
7 × 10 -6 to 500 × 10 -6 m 3 (Normal) / s (about 4 to
30 liters (Normal) / min) was blown into the molten steel passing through the immersion nozzle.
【００３６】１ヒート約２８０ｔの溶鋼を、４ヒート連
続して鋳造し、鋳造後に浸漬ノズルを回収した。回収し
た浸漬ノズルを縦断し、吐出孔近傍の付着物の発生の有
無と、その付着厚さを調査した。Approximately 280 tons of molten steel per heat was cast continuously for 4 heats, and the immersion nozzle was recovered after the casting. The collected immersion nozzle was traversed longitudinally, and the presence or absence of deposits near the discharge holes and the thickness of the deposits were investigated.
【００３７】得られた鋳片の表面を酸素ガスで、いわゆ
るスカーフィングすることにより、モールドパウダの巻
き込みに起因する鋳片表層部のノロカミ疵、または縦割
れ疵などを目視で調査した。The surface of the obtained slab was subjected to so-called scarfing with an oxygen gas to visually inspect the surface layer portion of the slab for noro-kami flaws or vertical crack flaws due to entrainment of mold powder.
【００３８】得られた鋳片を素材として４〜５ｍｍの厚
さの鋼帯に熱間圧延し、その後酸洗した後、冷間で厚さ
０．８〜１．０ｍｍの鋼帯に圧延した。製品鋼帯の表面
疵発生状況を目視により調査した。表面疵が発生した部
分は切断し、その合計の量を冷間圧延量で除して、製品
疵発生率として評価した。試験条件を表１に、試験結果
を表２にそれぞれ示す。The obtained slab was hot-rolled into a steel strip having a thickness of 4 to 5 mm as a raw material, then pickled, and then cold-rolled into a steel strip having a thickness of 0.8 to 1.0 mm. . The occurrence of surface flaws on the product steel strip was visually inspected. The portion where the surface flaw was generated was cut, and the total amount was divided by the amount of cold rolling to evaluate as a product flaw occurrence rate. Table 1 shows the test conditions, and Table 2 shows the test results.
【００３９】[0039]
【表１】 [Table 1]
【表２】 試験Ｎｏ．１およびＮｏ．２では、鋳片幅１６００ｍｍ
とし、鋳造速度は１．６ｍ／分とした。また、試験Ｎ
ｏ．３では、鋳片幅１２００ｍｍとし、鋳造速度は１．
３ｍ／分とした。これらの試験では、タンディッシュ内
部の溶鋼の深さｈを１．８ｍまたは２．０ｍとし、タン
ディッシュの出口の開口断面積Ｓを１１．２×１０-4〜
１９．４×１０-4ｍ2 とし、浸漬ノズル内の溶鋼が通過
する部分の横断面積Ａを４７．８×１０-4ｍ2 または６
３．６×１０-4ｍ2 とすることにより、比Ａ／Ｓを２．
６０〜４．２６として試験した。これらの比Ａ／Ｓの値
は、本発明の方法で規定する条件の範囲内の値である。
また、鋳片幅に対応した上記の鋳造速度としたので、単
位時間に浸漬ノズル内を通過する溶鋼流量Ｑは４９．１
４ｋｇ／ｓまたは８０．６４ｋｇ／ｓとなり、前述の
（ハ）式で定義される浸漬ノズル内部の溶鋼ヘッド指数
Ｈは０．１３６ｍ〜０．３６５ｍとなった。これら溶鋼
ヘッド指数Ｈの値は、本発明の方法で規定する条件の範
囲内の値である。さらに、浸漬ノズル内を通過する溶鋼
中に単位時間に吹き込む不活性ガス量Ｗを２００×１０
-6〜３３３×１０-6ｍ3 (Normal)／ｓとしたので、単位
時間に浸漬ノズル内を通過する溶鋼流量Ｑに対する溶鋼
中に単位時間に吹き込む不活性ガス量Ｗの比Ｗ／Ｑは
３．１０×１０-6〜４．１３×１０-6ｍ3 (Normal)／ｋ
ｇとなった。これら比Ｗ／Ｑの値は、本発明の方法で規
定する条件の範囲内の値である。[Table 2] Test No. 1 and No. In 2, slab width 1600mm
And the casting speed was 1.6 m / min. Test N
o. In No. 3, the slab width was 1200 mm and the casting speed was 1.
3 m / min. In these tests, the depth h of the molten steel inside the tundish was set to 1.8 m or 2.0 m, and the opening cross-sectional area S at the outlet of the tundish was set to 11.2 × 10 −4 or less .
19.4 × 10 −4 m 2, and the cross-sectional area A of the portion through which molten steel passes in the immersion nozzle is 47.8 × 10 −4 m 2 or 6
By setting the ratio to 3.6 × 10 −4 m 2 , the ratio A / S is set to 2.
Tested as 60-4.26. These values of the ratio A / S are values within the range of the conditions defined by the method of the present invention.
Further, since the casting speed was set to the above-mentioned casting speed corresponding to the slab width, the flow rate Q of molten steel passing through the immersion nozzle per unit time was 49.1.
It became 4 kg / s or 80.64 kg / s, and the molten steel head index H inside the immersion nozzle defined by the above formula (c) was 0.136 m to 0.365 m. These values of the molten steel head index H are values within the range defined by the method of the present invention. Further, the amount W of inert gas blown per unit time into molten steel passing through the immersion nozzle is set to 200 × 10
-6 to 333 × 10 -6 m 3 (Normal) / s, the ratio W / Q of the amount W of inert gas blown per unit time into molten steel to the flow rate Q of molten steel passing through the immersion nozzle per unit time is as follows. 3.10 × 10 -6 to 4.13 × 10 -6 m 3 (Normal) / k
g. These values of the ratio W / Q are values within the range defined by the method of the present invention.
【００４０】試験Ｎｏ．１では、浸漬ノズル内面には、
付着物は発生していなかった。試験Ｎｏ．２およびＮ
ｏ．３では、吐出孔近傍に２ｍｍまたは３ｍｍの厚さで
付着物が認められたが、極わずかな厚さであった。ま
た、これらの試験では、鋳片表面にノロカミ疵などは認
められず、鋳造作業も順調であった。さらに、製品疵発
生率は０．１〜０．３％と少なく、良好な結果であっ
た。Test No. In 1, the inner surface of the immersion nozzle
No deposit was generated. Test No. 2 and N
o. In No. 3, the deposit was observed at a thickness of 2 mm or 3 mm near the discharge hole, but the thickness was extremely small. Also, in these tests, noroka flaws and the like were not found on the surface of the slab, and the casting operation was well. Further, the product flaw occurrence rate was as small as 0.1 to 0.3%, which was a good result.
【００４１】試験Ｎｏ．４では、浸漬ノズル内を通過す
る溶鋼中に単位時間に吹き込む不活性ガス量Ｗを５００
×１０-6ｍ3 (Normal)／ｓと多くし、また、試験Ｎｏ．
５では、この不活性ガス量Ｗを６７×１０-6ｍ3 (Norma
l)／ｓと少なくして試験した。その他の試験条件は、試
験Ｎｏ．１またはＮｏ．２とほぼ同じ条件とした。Ｎ
ｏ．４では、単位時間に浸漬ノズル内を通過する溶鋼流
量Ｑに対する溶鋼中に単位時間に吹き込む不活性ガス量
Ｗの比Ｗ／Ｑは６．２０×１０-6ｍ3 (Normal)／ｋｇと
なり、Ｎｏ．５では、この比Ｗ／Ｑは０．８３×１０-6
ｍ3 (Normal)／ｋｇとなった。これら比Ｗ／Ｑの値は、
本発明の方法で規定する条件の上限または下限を、それ
ぞれ外れる値であった。これら試験での比Ａ／Ｓの２．
４６および溶鋼ヘッド指数Ｈの０．３６５ｍの値は、本
発明の方法で規定する条件の範囲内の値であった。Test No. In No. 4, the amount W of inert gas blown per unit time into the molten steel passing through the immersion nozzle is set to 500.
× 10 −6 m 3 (Normal) / s.
5, the amount W of this inert gas is 67 × 10 −6 m 3 (Norma
l) / s. Other test conditions are as follows: 1 or No. The conditions were almost the same as those in 2. N
o. In No. 4, the ratio W / Q of the amount W of inert gas blown into the molten steel per unit time to the flow rate Q of molten steel passing through the immersion nozzle per unit time is 6.20 × 10 −6 m 3 (Normal) / kg, No. 5, the ratio W / Q is 0.83 × 10 -6
m 3 (Normal) / kg. The values of these ratios W / Q are:
The values deviated from the upper and lower limits of the conditions defined by the method of the present invention, respectively. 1. The ratio A / S in these tests
The value of 46 and the molten steel head index H of 0.365 m were within the range defined by the method of the present invention.
【００４２】試験Ｎｏ．４では、溶鋼中に単位時間に吹
き込む不活性ガス量が多かったので、浸漬ノズルの吐出
孔近傍に厚さ１ｍｍの付着物しか発生していなかった。
しかし、不活性ガスの吹き込み量が多いので、鋳造中に
鋳型内の湯面レベルが大きく変動したため、鋳片表面に
ピンホール疵およびノロカミ疵が多く発生した。さら
に、製品には、鋳片表面のピンホール疵またはノロカミ
疵に起因する線状疵が多く発生し、製品疵発生率は２．
３％で悪かった。試験Ｎｏ．５では、不活性ガスの吹き
込み量が少ないため、２ヒート目の途中で浸漬ノズル詰
まりが発生し、鋳造速度を低下させて鋳造していたが、
鋳造速度低下による鋳片品質の劣化が予測されたので、
鋳造を中止した。回収した浸漬ノズル内面には、厚さ１
５ｍｍの付着物が発生していた。鋳片表面には、ノロカ
ミ疵が多く発生していた。浸漬ノズル詰まりで、鋳型内
の溶鋼の流動が安定せず、片流れなどにより湯面レベル
変動が発生したためである。鋳片表面のノロカミ疵に起
因する製品疵が多く発生し、製品疵発生率は５．７％で
悪かった。Test No. In No. 4, since the amount of the inert gas blown into the molten steel per unit time was large, only the deposit having a thickness of 1 mm was generated near the discharge hole of the immersion nozzle.
However, since the amount of the inert gas blown was large, the level of the molten metal in the mold fluctuated significantly during casting, so that many pinhole flaws and noroka flaws were generated on the slab surface. In addition, many linear flaws are generated on the product due to pinhole flaws or noro flaws on the slab surface.
3% was bad. Test No. In No. 5, since the amount of inert gas blown was small, clogging of the immersion nozzle occurred in the middle of the second heat, and casting was performed at a reduced casting speed.
Since the deterioration of the slab quality due to the lower casting speed was predicted,
The casting was stopped. Thickness 1
A deposit of 5 mm was generated. Many norokami flaws occurred on the slab surface. This is because the flow of the molten steel in the mold was not stabilized due to the clogging of the immersion nozzle, and the level of the molten metal level occurred due to one-sided flow. Many product flaws were generated due to noro-kami flaws on the slab surface, and the product flaw occurrence rate was poor at 5.7%.
【００４３】試験Ｎｏ．６では、タンディッシュ内の溶
鋼深さｈを０．９６ｍと浅くすることにより、比Ａ／Ｓ
を１．８０と小さくして試験した。その他の試験条件
は、試験Ｎｏ．１またはＮｏ．２とほぼ同じ条件とし
た。この比Ａ／Ｓの値は、本発明の方法で規定する条件
の下限を外れる値であった。指数Ｗ／Ｑ３．１０×１０
-6ｍ3 (Normal)／ｋｇおよび溶鋼ヘッド指数Ｈ０．３６
５ｍのそれぞれの値は、本発明の方法で規定する条件の
範囲内の値であった。Test No. In No. 6, the molten steel depth h in the tundish was made as shallow as 0.96 m, so that the ratio A / S
Was reduced to 1.80 and tested. Other test conditions are as follows: 1 or No. The conditions were almost the same as those in 2. The value of the ratio A / S was outside the lower limit of the condition specified by the method of the present invention. Index W / Q 3.10 × 10
-6 m 3 (Normal) / kg and molten steel head index H 0.36
Each value of 5 m was within the range of the conditions defined by the method of the present invention.
【００４４】試験Ｎｏ．６では、タンディッシュの出口
の開口断面積に対して、浸漬ノズル内径が小さいため、
浸漬ノズル内が溶鋼で充満し、吐出孔上方において渦流
が発生したものと推定され、浸漬ノズル詰まりが発生
し、鋳造後の浸漬ノズル内面には、厚さ８ｍｍの付着物
が発生していた。また、浸漬ノズル詰まりにより、鋳型
内に溶鋼に片流れが発生したため、湯面レベル変動が大
きかった。そのため、鋳片表面には、ノロカミ疵が多く
発生した。鋳片表面のノロカミ疵に起因する製品疵が多
く発生し、製品疵発生率は３．２％で悪かった。Test No. In No. 6, since the inner diameter of the immersion nozzle is smaller than the opening cross-sectional area of the outlet of the tundish,
It was presumed that the inside of the immersion nozzle was filled with molten steel and a vortex was generated above the discharge hole, the immersion nozzle was clogged, and a deposit of 8 mm in thickness was generated on the inner surface of the immersion nozzle after casting. In addition, since the immersion nozzle clogging caused a one-sided flow of the molten steel in the mold, the level of the molten metal level was large. For this reason, many slime flaws were generated on the slab surface. Many product flaws were generated due to noro-kami flaws on the slab surface, and the product flaw occurrence rate was as bad as 3.2%.
【００４５】試験Ｎｏ．７では、タンディッシュ内の溶
鋼深さｈを２．２ｍと深くすること、および浸漬ノズル
の内径を大きくし、浸漬ノズル内の溶鋼が通過する部分
の横断面積Ａを６３．６×１０-4ｍ2 と大きくすること
により、比Ａ／Ｓを５．１６と大きくして試験した。そ
の他の試験条件は、試験Ｎｏ．３とほぼ同じ条件とし
た。この比Ａ／Ｓの値は、本発明の方法で規定する条件
の上限を外れる値であった。指数Ｗ／Ｑ２．９４×１０
-6ｍ3 (Normal)／ｋｇおよび溶鋼ヘッド指数Ｈ０．１０
２ｍのそれぞれの値は、本発明の方法で規定する条件の
範囲内の値であった。Test No. In No. 7, the depth h of the molten steel in the tundish is increased to 2.2 m, the inner diameter of the immersion nozzle is increased, and the cross-sectional area A of the portion through which the molten steel passes in the immersion nozzle is 63.6 × 10 −4. The test was performed by increasing the ratio A / S to 5.16 by increasing the ratio to m 2 . Other test conditions are as follows: The conditions were almost the same as those of No. 3. The value of the ratio A / S was outside the upper limit of the condition specified by the method of the present invention. Index W / Q 2.94 × 10
-6 m 3 (Normal) / kg and molten steel head index H0.10
Each value of 2 m was within the range of the conditions defined by the method of the present invention.
【００４６】試験Ｎｏ．７では、タンディッシュの出口
の開口断面積に対して、浸漬ノズル内径が大きいので、
鋳造後の浸漬ノズル内面の付着物の厚さは３ｍｍであっ
たものの、浸漬ノズル内を通過する溶鋼は特定方向の浸
漬ノズル内壁に沿った流れとなり、そのため、鋳型内の
溶鋼に片流れが発生した。そのため、湯面レベル変動が
大きくなり、鋳片表面にノロカミ疵が発生した。鋳片表
面のノロカミ疵に起因する製品疵が発生し、製品疵発生
率は１．８％であった。Test No. 7, the inner diameter of the immersion nozzle is larger than the opening cross-sectional area of the outlet of the tundish.
Although the thickness of the deposit on the inner surface of the immersion nozzle after casting was 3 mm, the molten steel passing through the immersion nozzle flowed along the inner wall of the immersion nozzle in a specific direction, and therefore, a single flow occurred in the molten steel in the mold. . As a result, the level change of the molten metal surface became large, and the surface of the slab had nookami flaws. Product flaws caused by noro-kami flaws on the slab surface occurred, and the product flaw occurrence rate was 1.8%.
【００４７】試験Ｎｏ．８では、浸漬ノズル内径を１２
０ｍｍと大きくしたので、浸漬ノズル内部の溶鋼ヘッド
指数Ｈは０．０６５ｍと小さくなった。その他の試験条
件は、試験Ｎｏ．１またはＮｏ．２とほぼ同じ条件とし
た。この溶鋼ヘッド指数Ｈの値は、本発明の方法で規定
する条件の下限を外れる値である。指数Ｗ／Ｑ２．４８
×１０-6ｍ3 (Normal)／ｋｇおよび比Ａ／Ｓ４．７６の
それぞれの値は、本発明の方法で規定する条件の範囲内
の値であった。Test No. 8, the inner diameter of the immersion nozzle is 12
Since it was increased to 0 mm, the molten steel head index H inside the immersion nozzle was reduced to 0.065 m. Other test conditions are as follows: 1 or No. The conditions were almost the same as those in 2. The value of the molten steel head index H is a value outside the lower limit of the condition specified by the method of the present invention. Index W / Q 2.48
Each value of × 10 -6 m 3 (Normal) / kg and the ratio A / S 4.76 was within the range of the conditions specified by the method of the present invention.
【００４８】試験Ｎｏ．８では、浸漬ノズル内径を極端
に大きくしたので、浸漬ノズル内に供給される溶鋼の量
が少なくなり、浸漬ノズルの温度が低下したので、浸漬
ノズル内面に地金が多く付着した。そのため、３ヒート
目の途中で、浸漬ノズル詰まりが著しく発生し、鋳造速
度を低下させて鋳造していたが、結局、鋳造を中止し
た。回収した浸漬ノズル内面には、厚さ１８ｍｍの地金
が付着していた。鋳片表面には、ノロカミ疵が発生して
いた。浸漬ノズル詰まりで、鋳型内の溶鋼に片流れが発
生し、湯面レベル変動が発生したためである。鋳片表面
のノロカミ疵に起因する製品疵が多く発生し、製品疵発
生率は４．３％で悪かった。Test No. In No. 8, since the inner diameter of the immersion nozzle was extremely increased, the amount of molten steel supplied into the immersion nozzle was reduced, and the temperature of the immersion nozzle was lowered, so that much metal was attached to the inner surface of the immersion nozzle. Therefore, during the third heat, clogging of the immersion nozzle occurred remarkably, and casting was performed at a reduced casting speed. However, casting was eventually stopped. 18 mm thick metal was adhered to the inner surface of the recovered immersion nozzle. Norokami flaws were found on the slab surface. This is because clogging of the immersion nozzle caused a one-sided flow in the molten steel in the mold, causing a change in the level of the molten metal. Many product flaws were generated due to noro-kami flaws on the slab surface, and the product flaw occurrence rate was as poor as 4.3%.
【００４９】試験Ｎｏ．９では、浸漬ノズル内径を７０
ｍｍと小さくしたので、浸漬ノズル内部の溶鋼ヘッド指
数Ｈは０．５６３ｍと大きくなった。また、指数Ａ／Ｓ
は１．９８と小さな値となった。その他の試験条件は、
試験Ｎｏ．１またはＮｏ．２とほぼ同じ条件とした。こ
の溶鋼ヘッド指数Ｈの値は、本発明の方法で規定する条
件の上限を外れる値である。また、この比Ａ／Ｓの値
は、本発明の方法で規定する条件の下限を外れる値であ
る。指数Ｗ／Ｑ２．４８×１０-6ｍ3 (Normal)／ｋｇの
値は、本発明の方法で規定する条件の範囲内の値であっ
た。Test No. In No. 9, the inner diameter of the immersion nozzle was 70
mm, the molten steel head index H inside the immersion nozzle was increased to 0.563 m. The index A / S
Was a small value of 1.98. Other test conditions are
Test No. 1 or No. The conditions were almost the same as those in 2. The value of the molten steel head index H is a value outside the upper limit of the condition specified by the method of the present invention. Further, the value of the ratio A / S is a value outside the lower limit of the condition defined by the method of the present invention. The value of the index W / Q 2.48 × 10 −6 m 3 (Normal) / kg was within the range defined by the method of the present invention.
【００５０】試験Ｎｏ．９では、浸漬ノズル内径を小さ
くして浸漬ノズル内部の溶鋼ヘッド指数Ｈを大きくした
ため、吐出孔から流出する直前の溶鋼の圧力が大きくな
り、吐出孔上方において渦流が発生した。そのため、浸
漬ノズル詰まりが発生し、鋳型内の溶鋼に片流れが発生
した。そのため、湯面レベル変動が大きくなり、鋳片表
面にノロカミ疵が発生した。鋳片表面のノロカミ疵に起
因する製品疵が発生し、製品疵発生率は２．８％であっ
た。Test No. In No. 9, since the inner diameter of the immersion nozzle was reduced and the molten steel head index H inside the immersion nozzle was increased, the pressure of the molten steel immediately before flowing out of the discharge hole was increased, and a vortex was generated above the discharge hole. As a result, clogging of the immersion nozzle occurred, and one-sided flow occurred in the molten steel in the mold. As a result, the level change of the molten metal surface became large, and the surface of the slab had nookami flaws. Product flaws caused by noro flaws on the slab surface occurred, and the product flaw occurrence rate was 2.8%.
【００５１】[0051]
【発明の効果】本発明の方法の適用により、浸漬ノズル
内面への溶鋼中のＡｌの酸化物などの付着を、安価な方
法で安定して防止でき、得られた鋳片を素材とする熱間
圧延した製品において、モールドパウダ、Ａｌの酸化
物、気泡などによる鋳片表層部の欠陥に起因する製品の
表面欠陥または内部欠陥の発生を防止できる。According to the method of the present invention, it is possible to stably prevent the adhesion of Al oxide or the like in the molten steel to the inner surface of the immersion nozzle by an inexpensive method. In the cold-rolled product, it is possible to prevent surface defects or internal defects of the product due to defects in the surface layer of the slab due to mold powder, oxides of Al, bubbles, and the like.
【図１】タンディッシュ内および浸漬ノズル内の溶鋼の
状況を示す模式図である。FIG. 1 is a schematic diagram showing the state of molten steel in a tundish and an immersion nozzle.
【図２】浸漬ノズル内面に付着物が付着する状況を示す
模式図である。FIG. 2 is a schematic diagram showing a situation in which a deposit adheres to an inner surface of a immersion nozzle.
１：浸漬ノズル ２：タンディッシ
ュ ３：スライディングゲート ４：吐出孔 ５：スライディングゲート近傍に付着した付着物 ６：浸漬ノズルの胴部に付着した付着物 ７：吐出孔近傍に付着した付着物 ８：メニスカス ９：モールドパウ
ダ １０：溶鋼 １１：鋳型 １２：凝固殻 Ｓ：タンディッシュの出口の開口断面積 Ａ：浸漬ノズル内の溶鋼が通過する部分の横断面積 ｈ：タンディッシュ内部の溶鋼の深さ Ｈ：浸漬ノズル内部の溶鋼ヘッド指数1: Immersion nozzle 2: Tundish 3: Sliding gate 4: Discharge hole 5: Deposit adhering near sliding gate 6: Deposit adhering to body of immersion nozzle 7: Deposit adhering near discharge hole 8: Meniscus 9: Mold powder 10: Molten steel 11: Mold 12: Solidified shell S: Cross-sectional area of the opening of the outlet of the tundish A: Cross-sectional area of the part through which the molten steel passes in the immersion nozzle h: Depth of the molten steel inside the tundish H : Index of molten steel head inside immersion nozzle
Claims (1)
型内に溶鋼を供給する連続鋳造方法であって、下記
（イ）式で定義されるタンディッシュの出口の開口断面
積Ｓ（ｍ 2 ）と浸漬ノズル内の溶鋼が上方から下方に通
過する部分の横断面積Ａ（ｍ2 ）とが下記（ロ）式を満
足する浸漬ノズルを用い、下記（ハ）式で定義される浸
漬ノズル内部の溶鋼ヘッド指数Ｈ（ｍ）が下記（ニ）式
を満足する条件で鋳造し、かつ、浸漬ノズル内を通過す
る溶鋼中に単位時間に吹き込む不活性ガス量Ｗ（ｍ 3 (N
ormal)／ｓ）が下記（ホ）式を満足する条件で鋳造する
ことを特徴とする鋼の連続鋳造方法。 Ｓ＝Ｑ／｛ρ×（２ｇｈ）1/2 ｝ ・・・(イ) ２＜Ａ／Ｓ＜５ ・・・(ロ) Ｈ＝(２ｇ)-1×(ρｃ)-2×(Ｑ／Ａ)2 ・・・(ハ) ０．０８＜Ｈ＜０．５ ・・・(ニ) １×１０-6 ＜Ｗ／Ｑ＜ ５×１０-6 ・・・(ホ) ここで、Ｑ：単位時間に浸漬ノズル内を通過する溶鋼流
量(ｋｇ／ｓ) ρ：溶鋼の密度(ｋｇ／ｍ3) ｇ：重力加速度(ｍ／ｓ2) ｈ：タンディッシュ内部の溶鋼の深さ(ｍ) ｃ：流路係数(−)1. Casting from a tundish using an immersion nozzle
A continuous casting method for supplying molten steel in a mold, comprising:
The opening cross section of the outlet of the tundish defined by equation (a)
Product S (m Two ) And the molten steel in the immersion nozzle
Cross-sectional area A (mTwo ) Satisfies the following expression (b)
Immersion nozzle defined by the following formula (c)
The molten steel head index H (m) inside the pickling nozzle is expressed by the following formula (d).
Casting under conditions that satisfy
Amount of inert gas W (m Three (N
ormal) / s) is cast under the condition satisfying the following formula (e).
A continuous casting method for steel. S = Q / ｛ρ × (2gh)1/2 ｝ (A) 2 <A / S <5 (b) H = (2g)-1× (ρc)-2× (Q / A)Two (C) 0.08 <H <0.5 (D) 1 × 10-6 <W / Q <5 × 10-6 (E) Here, Q: molten steel flow passing through the immersion nozzle per unit time
Amount (kg / s) ρ: Density of molten steel (kg / mThree) g: Gravitational acceleration (m / s)Two) h: Depth of molten steel inside tundish (m) c: Channel coefficient (-)
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| JP2014184462A (en) * | 2013-03-22 | 2014-10-02 | Nippon Steel & Sumitomo Metal | Continuous casting method of extra-low-carbon steel slab |
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