JP2012061516A - Consecutive continuous casting method - Google Patents

Consecutive continuous casting method Download PDF

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JP2012061516A
JP2012061516A JP2010209695A JP2010209695A JP2012061516A JP 2012061516 A JP2012061516 A JP 2012061516A JP 2010209695 A JP2010209695 A JP 2010209695A JP 2010209695 A JP2010209695 A JP 2010209695A JP 2012061516 A JP2012061516 A JP 2012061516A
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molten steel
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JP5429120B2 (en
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Nozomi Yoshihiro
望 吉廣
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Sumitomo Metal Ind Ltd
住友金属工業株式会社
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PROBLEM TO BE SOLVED: To inexpensively manufacture, at high quality, such types of steel that prevents nitrogen from being absorbed in a boundary part of consecutive continuous casting, and, in particular, requires low N in Nb-containing steel or the like which easily generates a surface crack or the like when a nitrogen content is high.SOLUTION: A molten steel weight in a tundish 1 is monitored preliminarily to acquire an immersed state of a lower end of a filling pipe 4 into a molten steel face in the tundish 1, in the consecutive continuous casting. Supply of molten steel is stopped from a ladle 3 under the supply of the molten steel, and supply of Ngas to inside tundish spaces A, B in an inner side of the filling pipe 4 and an outer side of the filling pipe is stopped thereafter to start replacement with Ar gas, when the molten steel in the tundish 1 gets to a prescribed weight capable of securing a replacement time found based on a space volume in the tundish 1 and a replacement speed by the Ar gas. The supply of the molten steel is started in the next ladle 3, and the replacement with the Ngas is started thereafter from the time just after when the lower end of the filling pipe 4 is immersed into the molten steel face with rising-up of the molten steel face in the tundish 1 while the supply of the Ar gas to the space A, B is reduced.

Description

本発明は、炭素鋼、合金鋼、ステンレス鋼など種々の鋼の連続鋳造において、品質を保持しつつコストの低減が可能な連々続鋳造方法に関するものである。   The present invention relates to a continuous casting method capable of reducing costs while maintaining quality in continuous casting of various steels such as carbon steel, alloy steel, and stainless steel.
ここで、連々続鋳造とは、複数の例えば取鍋を順次交換して、タンディッシュへの溶鋼の供給を引継ぎながら連続鋳造することを言う。   Here, continuous casting refers to continuous casting while sequentially replacing a plurality of ladles, for example, and taking over the supply of molten steel to the tundish.
連続鋳造において、タンディッシュ内の溶鋼を空気と遮断することは重要である。空気との遮断が十分でない場合、溶鋼は空気中の酸素と反応して清浄度の悪化を招く。また、タンディッシュ内の溶鋼湯面が乱れると、溶鋼は窒素とも反応して溶鋼中の吸窒の原因となる。以上は、低硫鋼を製造する場合にさらに顕著な傾向を示す。そのため、タンディッシュ内の溶鋼は、ガスシールにより空気と遮断することが一般的に行われている。   In continuous casting, it is important to block the molten steel in the tundish from air. When the insulation with air is not sufficient, molten steel reacts with oxygen in the air and causes deterioration of cleanliness. Further, when the molten steel surface in the tundish is disturbed, the molten steel reacts with nitrogen and causes nitrogen absorption in the molten steel. The above shows a more remarkable tendency when producing low-sulfur steel. Therefore, the molten steel in the tundish is generally cut off from the air by a gas seal.
例えば、タンディッシュ内溶鋼の酸化、吸窒を防止する方法としては、Arガス等の不活性ガスによるシールが良く知られており、実施されている(例えば特許文献1)。しかしながら、Arガス等の不活性ガスは非常に高価であり、製造コストの悪化が問題であった。   For example, as a method for preventing oxidation and nitrogen absorption of molten steel in tundish, sealing with an inert gas such as Ar gas is well known and implemented (for example, Patent Document 1). However, an inert gas such as Ar gas is very expensive, and deterioration of manufacturing cost has been a problem.
また、安価なN2ガスを用いることでArガスの使用量を減らして安価に製造する方法が、特許文献2に記載されている。特許文献2に記載された方法は、タンディッシュ上部より垂下する堰板を用いてタンディッシュ内を受湯部と注湯部に分け、タンディッシュ内溶鋼の安定期には、受湯部はArガスにより、注湯部はN2ガスによりシールすることで、Arガスの使用量を低減するものである。 Further, Patent Document 2 discloses a method of manufacturing at low cost by reducing the amount of Ar gas used by using inexpensive N 2 gas. In the method described in Patent Document 2, the inside of the tundish is divided into a hot water receiving part and a pouring part using a weir plate that hangs down from the upper part of the tundish. The amount of Ar gas used is reduced by sealing the pouring part with N 2 gas.
しかしながら、連々続鋳造において、取鍋からタンディッシュへの溶鋼の供給中にN2ガスからArガスに切り替えても、取鍋交換時における連々続鋳造の境界部では吸窒がしばしば発生し、表面割れ等の品質悪化の要因となっていた。 However, even in continuous continuous casting, even when switching from N 2 gas to Ar gas during the supply of molten steel from the ladle to the tundish, nitrogen absorption often occurs at the boundary of continuous continuous casting when the ladle is replaced. It was a cause of quality deterioration such as cracks.
これは、取鍋交換用のターレットの旋回や、シリンダー用の油圧ホースの設置や取り外し等に時間を要することによって、注入管または取鍋用ロングノズルの下端よりタンディッシュ内の溶鋼湯面が下方になった場合、連々続鋳造での境界部で新たな溶鋼が供給された時に、溶鋼注入流によるたたき込みによって発生する溶鋼湯面の外乱がタンディッシュ内の溶鋼全体に伝播し、タンディッシュ内の溶鋼湯面が変動するためと考えられる。   This is because it takes time to turn the turret for replacing the ladle and to install and remove the hydraulic hose for the cylinder, so that the molten steel surface in the tundish is lowered from the lower end of the injection nozzle or the long nozzle for the ladle. In this case, when new molten steel is supplied at the boundary in continuous casting, the molten steel surface disturbance generated by the squeezing by the molten steel injection flow propagates to the entire molten steel in the tundish, and This is thought to be due to fluctuations in the molten steel surface.
特開昭54−66329号公報JP 54-66329 A 特開昭61−49758号公報JP 61-49758 A
本発明が解決しようとする問題点は、連々続鋳造時に、Arガス等の不活性ガス用いたシールを採用した場合は、Arガス等の不活性ガスが非常に高価であるため、製造コストが悪化するという点である。   The problem to be solved by the present invention is that, when a seal using an inert gas such as Ar gas is employed during continuous casting, the inert gas such as Ar gas is very expensive, so the production cost is low. It is that it gets worse.
一方、タンディッシュ内を堰板により受湯部と注湯部に分け、タンディッシュ内溶鋼の安定期には、受湯部はArガスで、注湯部はN2ガスでシールする場合、取鍋交換時における連々続鋳造の境界部でしばしば吸窒が発生し、品質悪化の要因となるという点である。 On the other hand, if the inside of the tundish is divided into a hot water receiving part and a pouring part by a dam plate, and the hot water receiving part is sealed with Ar gas and the pouring part is sealed with N 2 gas during the stable period of molten steel in the tundish, Nitrogen is often generated at the boundary of continuous casting at the time of pan replacement, which causes quality deterioration.
本発明は、安価なN2ガスを用いてArガスの使用量を減らす場合に、連々続鋳造での取鍋からタンディッシュへの溶鋼の供給中にN2ガスからArガスに切り替えても、取鍋交換時における連々続鋳造の境界部で吸窒が発生しないようにして品質を保持できる連々続鋳造方法を提供するものである。 In the present invention, when reducing the amount of Ar gas used using cheap N 2 gas, even when switching from N 2 gas to Ar gas during the supply of molten steel from the ladle to the tundish in continuous casting, It is an object of the present invention to provide a continuous casting method capable of maintaining quality by preventing nitrogen absorption from occurring at the boundary of continuous casting at the time of ladle replacement.
本発明の連々続鋳造方法は、
タンディッシュ内に溶鋼を供給中の鍋から次回の鍋に溶鋼の供給を切り替えながら行う連々続鋳造において、
予めタンディッシュ内の溶鋼重量を監視してタンディッシュ内の溶鋼湯面への注入管下端の浸漬状況を把握しておき、
溶鋼を供給中の鍋からの溶鋼供給の停止後、タンディッシュ内の溶鋼重量が、タンディッシュ内の空間容積とArガスでの置換速度から求められる置換時間を確保できる所定の重量になった時に、注入管の内側および注入管の外側におけるタンディッシュ内空間のN2ガス供給を停止してArガスへの置換を開始し、
次回の鍋の溶鋼の供給の開始後、タンディッシュ内の溶鋼湯面が上昇し、注入管下端が該溶鋼湯面に浸漬した直後から前記空間へのArガスの供給を減少しつつN2ガスへの置換を開始することを最も主要な特徴としている。
The continuous casting method of the present invention is
In continuous casting performed while switching the supply of molten steel from the pot that is supplying molten steel to the next pot in the tundish,
Monitor the weight of the molten steel in the tundish beforehand and know the immersion status of the lower end of the injection pipe to the molten steel surface in the tundish.
When the molten steel weight in the tundish stops after the supply of molten steel from the pan that is supplying molten steel has reached a predetermined weight that can secure the replacement time determined from the space volume in the tundish and the replacement speed with Ar gas. the N 2 gas supply tundish space outside the inner and injection tube of the injection tube to initiate the substitution of Ar gas is stopped,
After the start of the supply of molten steel in the next pan, the molten steel surface in the tundish rises, and the N 2 gas is reduced while the supply of Ar gas to the space is reduced immediately after the lower end of the injection pipe is immersed in the molten steel surface. The most important feature is to start the replacement.
本発明における「所定の重量」とは、予め監視しているタンディッシュ内の溶鋼湯面への注入管の下端が浸漬している状況の溶鋼重量と、タンディッシュ内の溶鋼湯面が注入管の下端と同一レベルになる重量との間で適宜設定される重量である。   The “predetermined weight” in the present invention means the weight of the molten steel in a state where the lower end of the injection pipe is immersed in the molten steel surface in the tundish being monitored in advance, and the molten steel surface in the tundish is the injection pipe. The weight is appropriately set between the lower end of the head and the weight at the same level.
上記本発明の連々続鋳造方法では、鋼の連々続鋳造において、タンディッシュ内の空間に供給するシールドガスを、タンディッシュ内の溶鋼重量に基づいて常に適切に選択して切り替えることができる。   In the continuous continuous casting method of the present invention, in continuous continuous casting of steel, the shielding gas supplied to the space in the tundish can always be appropriately selected and switched based on the molten steel weight in the tundish.
本発明では、鋼の連々続鋳造において、タンディッシュ内の溶鋼重量に基づいて常に適切なタンディッシュ内のシールドガスを選択して切り替えるので、特に窒素が高いと表面割れ等が発生しやすくなるようなNb含有鋼等で低N化が必要となるような鋼種を、高品質で安価に製造することが可能となった。   In the present invention, in continuous continuous casting of steel, since an appropriate shield gas in the tundish is always selected and switched based on the molten steel weight in the tundish, surface cracks and the like are likely to occur particularly when nitrogen is high. It has become possible to manufacture high-quality and low-cost steel grades that require low N in such Nb-containing steels.
本発明の連々続鋳造方法を実施した場合の取鍋とタンディッシュ部の説明図である。It is explanatory drawing of a ladle and a tundish part at the time of implementing the continuous casting method of this invention. 本発明の連々続鋳造方法におけるタンディッシュ内溶鋼重量によるシールドガス制御の一例を示した図で、(a)はタンディッシュ内における溶鋼重量の推移を時系列に示した図、(b)は本発明の連々続鋳造方法の実施時における取鍋交換時に制御するシールドガスの流量と変更手順を(a)図に対応させて示した図、(c)は従来の連々続鋳造方法の実施時における(b)図と同様の図である。It is the figure which showed an example of the shielding gas control by the molten steel weight in a tundish in the continuous casting method of this invention, (a) is the figure which showed transition of the molten steel weight in a tundish in time series, (b) is this The figure which showed the flow volume and change procedure of the shield gas controlled at the time of ladle exchange at the time of implementation of the continuous casting method of the invention corresponding to (a) figure, (c) is at the time of implementation of the conventional continuous casting method (B) It is a figure similar to a figure. 連々続鋳造時に、本発明のシール方法を実施した場合と、従来のシール方法を実施した場合の溶鋼の吸窒例を示した図である。It is the figure which showed the example of nitrogen absorption of the molten steel at the time of implementing the sealing method of this invention at the time of continuous continuous casting, and the case of implementing the conventional sealing method.
本発明では、連々続鋳造での取鍋からタンディッシュへの溶鋼の供給中にN2ガスからArガスに切り替えても、取鍋交換時における連々続鋳造の境界部で吸窒が発生しないようにするという目的を、タンディッシュ内の溶鋼重量に基づいてシールドガスを選択して切り替えることによって実現した。 In the present invention, even when switching from N 2 gas to Ar gas during the supply of molten steel from the ladle to the tundish in continuous casting, nitrogen absorption does not occur at the boundary of continuous casting during ladle replacement. This was achieved by selecting and switching the shielding gas based on the molten steel weight in the tundish.
以下、本発明の連々続鋳造方法を、発明成立に至るまでの考え方と共に、図1〜図3を用いて説明する。   Hereinafter, the continuous casting method of the present invention will be described with reference to FIGS.
溶鋼内における窒素含有量の増加は、鋳込み初期や取鍋交換時の非定常部(以下、単に非定常部と言う。)で発生しやすく、連続鋳造の定常部では問題とならない。
これは、非定常部では、以下に説明する状態となっていることに起因する。
The increase in the nitrogen content in the molten steel is likely to occur in the unsteady part at the beginning of casting or when replacing the ladle (hereinafter simply referred to as unsteady part), and does not cause a problem in the steady part of continuous casting.
This is because the unsteady portion is in the state described below.
すなわち、取鍋からタンディッシュへの溶鋼の供給(以下、給湯という。)が完了すると、給湯ノズルを閉鎖して当該取鍋を移動退避する間もタンディッシュから鋳型への給湯は継続され、次の取鍋がタンディッシュ上に移動して給湯を開始するまで減少し続ける。   That is, when the supply of molten steel from the ladle to the tundish (hereinafter referred to as hot water supply) is completed, the hot water supply from the tundish to the mold is continued while the hot water nozzle is closed and the ladle is moved and retracted. It continues to decrease until the ladle moves over the tundish and begins to supply hot water.
その後、次の取鍋による給湯を開始した後に、溶鋼湯面を定常鋳込みでの所定の重量に短時間で到達するよう、初期は比較的大きな流量で給湯を開始するので、タンディッシュ内の溶鋼重量が大きく変動してタンディッシュ内の溶鋼の湯面変動が発生し、十分置換されていない空気中の窒素を溶鋼が吸収する。   After that, after starting hot water supply with the next ladle, hot water supply is started at a relatively large flow rate so that the molten steel surface reaches the predetermined weight in steady casting in a short time. The weight fluctuates greatly and the molten steel surface level of the molten steel in the tundish is generated, and the molten steel absorbs nitrogen in the air that has not been sufficiently replaced.
連続鋳造の定常部と非定常部でシールドガスを変更するのみでは前記のように非定常部で吸窒が発生しており、発明者らは、吸窒発生部位(連々続鋳造の境界部にあたるスラブ)とタンディッシュ重量との間に相関が見られることを見出した。   Nitrogen is generated in the unsteady part as described above only by changing the shielding gas between the steady part and the unsteady part of the continuous casting. It was found that there is a correlation between the slab) and the tundish weight.
また、タンディッシュ内のガス分析を行った結果、ガスを置換するまでに時間が掛かることが分かった。   In addition, as a result of gas analysis in the tundish, it was found that it takes time to replace the gas.
さらに、発明者らが吸窒発生部位とタンディッシュ重量との相関を調査したところ、タンディッシュ重量が少ない場合、注入管との溶鋼湯面の位置関係も吸窒量に影響していることを見出した。   Furthermore, the inventors investigated the correlation between the site of nitrogen absorption and the tundish weight, and found that when the tundish weight is small, the positional relationship of the molten steel surface with the injection pipe also affects the nitrogen absorption amount. I found it.
そこで、発明者らは、通常、ロードセル等で計量されて知り得るタンディッシュ内の溶鋼重量の情報を基に、タンディッシュ内の溶鋼湯面と注入管の浸漬状況を把握した上で、該注入管の内側と外側のタンディッシュ内の空間領域を把握できることが分かった。   Therefore, the inventors usually grasp the molten steel surface in the tundish and the immersion state of the injection tube based on the information on the molten steel weight in the tundish that can be known by being measured by a load cell or the like, and then perform the injection. It was found that the spatial area in the tundish inside and outside the tube could be grasped.
本発明は、前記把握した遮断状況をもとに、それらの空間領域をシールするシールドガス種、シールドガス流量を変更することにより吸窒を防止する連々続鋳造方法を提案するものである。   The present invention proposes a continuous casting method for preventing nitrogen absorption by changing the shielding gas type and shielding gas flow rate for sealing those space regions based on the grasped shut-off state.
すなわち、本発明の連々続鋳造方法は、図1に示すように、タンディッシュ1内に溶鋼2を供給中の取鍋3から次の取鍋に給湯を切り替えながら行う連々続鋳造において、以下のようにしてタンディッシュ1内の溶鋼2を空気と遮断するのである。   That is, as shown in FIG. 1, the continuous casting method of the present invention is the following in continuous casting performed while switching hot water from a ladle 3 that is supplying molten steel 2 into the tundish 1 to the next ladle. In this way, the molten steel 2 in the tundish 1 is shielded from air.
例えばロードセルにより予めタンディッシュ1内の溶鋼2の重量を監視してタンディッシュ1内の溶鋼湯面への注入管4の下端の浸漬状況を把握しておく。   For example, the weight of the molten steel 2 in the tundish 1 is monitored in advance by a load cell to grasp the state of immersion of the lower end of the injection tube 4 into the molten steel surface in the tundish 1.
取鍋3からの給湯の停止後、タンディッシュ1内の溶鋼2の容積とArガスでの置換速度から求められるタンディッシュ1内の溶鋼重量が所定の重量になった時に、注入管4の内側におけるタンディッシュ1内の空間A、および注入管4の外側におけるタンディッシュ1内の空間BのN2ガス供給を停止してArガスへの置換を開始する。 After the hot water supply from the ladle 3 is stopped, when the molten steel weight in the tundish 1 obtained from the volume of the molten steel 2 in the tundish 1 and the replacement speed with Ar gas reaches a predetermined weight, the inside of the injection pipe 4 The N 2 gas supply in the space A in the tundish 1 and the space B in the tundish 1 outside the injection tube 4 is stopped, and replacement with Ar gas is started.
次の取鍋3の給湯を開始した後、タンディッシュ1内の溶鋼湯面が上昇し、注入管4の下端が該溶鋼湯面に浸漬した直後から、前記空間AおよびBへのArガスの供給を減少しつつN2ガスへの置換を開始する。なお、図1中の5は浸漬ノズル、6は鋳型である。 After the next hot water supply of the ladle 3 is started, the molten steel surface in the tundish 1 rises and immediately after the lower end of the injection pipe 4 is immersed in the molten steel surface, the Ar gas is introduced into the spaces A and B. Start replacing N 2 gas while reducing supply. In FIG. 1, 5 is an immersion nozzle and 6 is a mold.
次に本発明の連々続鋳造方法の効果を確認するために実施した結果について説明する。
炭素含有量が0.2〜0.6質量%の溶鋼を、短辺寸法が227mm、長辺寸法が950〜1250mmの湾曲型のスラブ連続鋳造機にて連続鋳造中の定常部の溶鋼重量を38tonに維持したタンディッシュを用いて連続鋳造を実施した。その際、取鍋からタンディッシュへの溶鋼注入には、注入管を使用した。
Next, the results carried out to confirm the effect of the continuous casting method of the present invention will be described.
Molten steel with a carbon content of 0.2 to 0.6% by mass is measured with a curved slab continuous casting machine having a short side dimension of 227 mm and a long side dimension of 950 to 1250 mm. Continuous casting was performed using a tundish maintained at 38 tons. At that time, an injection tube was used for pouring molten steel from the ladle into the tundish.
タンディッシュ内の溶鋼重量に基づいて実施したシールドガスの制御方法の一例を図2に示す。   An example of the shielding gas control method implemented based on the molten steel weight in the tundish is shown in FIG.
図2(a)はタンディッシュ内における溶鋼重量の推移を時系列に示した図である。また、図2(b)は、本発明の連々続鋳造方法の実施時における取鍋交換時に制御するシールドガス(ArガスおよびN2ガス)の流量と変更手順(ロジック)を図2(a)に対応させて示した図である。 Fig.2 (a) is the figure which showed the transition of the molten steel weight in a tundish in time series. FIG. 2B shows the flow rate and change procedure (logic) of the shield gas (Ar gas and N 2 gas) controlled at the time of ladle replacement when the continuous casting method of the present invention is performed. It is the figure shown corresponding to.
また、図2(c)は従来の連々続鋳造方法の実施時における図2(b)と同様の図を示した図である。図2(c)に示すように、従来は、吸窒防止のため、取鍋による給湯が終了した後から次回の取鍋が開口するまでの間、注入管4の内側におけるタンディッシュ1内の空間A、および注入管4の外側におけるタンディッシュ1内の空間Bともに、N2ガスからArガスに全量交換していた。 Moreover, FIG.2 (c) is the figure which showed the same figure as FIG.2 (b) at the time of implementation of the conventional continuous casting method. As shown in FIG. 2 (c), conventionally, in order to prevent nitrogen absorption, the hot water in the tundish 1 inside the injection pipe 4 is maintained after the hot water supply by the ladle is finished until the next ladle opens. Both the space A and the space B in the tundish 1 outside the injection tube 4 were completely exchanged from N 2 gas to Ar gas.
これに対して、本発明では、図2(a)に示すように、連続鋳造中の定常部でタンディッシュ内の溶鋼重量が38tonと十分な場合は、タンディッシュ内は吸窒が発生しないために、図2(b)に示すように、シールドガスは安価なN2ガスを使用する。 On the other hand, in the present invention, as shown in FIG. 2 (a), when the molten steel weight in the tundish is sufficient at 38 tons in the steady part during continuous casting, no nitrogen absorption occurs in the tundish. In addition, as shown in FIG. 2B, an inexpensive N 2 gas is used as the shielding gas.
定常部でのN2ガス流量は、図2(b)に示すように、注入管の内側の給湯空間領域(以下、A部という。)に30Nm3/hr、注入管の外側のタンディッシュの本体空間領域(以下、B部という。)に30Nm3/hrの流量で注入した。 As shown in FIG. 2 (b), the N 2 gas flow rate in the stationary part is 30 Nm 3 / hr in the hot water supply space area inside the injection pipe (hereinafter referred to as part A), and the tundish outside the injection pipe It inject | poured into the main body space area | region (henceforth B part) with the flow volume of 30 Nm < 3 > / hr.
前回の取鍋から次回の取鍋に交換する際の非定常部で、前回の取鍋の給湯が完了した後、タンディッシュ内の溶鋼重量が減少する。そして、図2(a)に示すように、タンディッシュ内の溶鋼重量が32tonより少なくなると、A部及びB部をN2ガスからArガスに切替える。 In the unsteady part when changing from the previous ladle to the next ladle, the molten steel weight in the tundish decreases after the hot water supply of the previous ladle is completed. Then, as shown in FIG. 2 (a), when the molten steel weight in the tundish is less than 32Ton, it switches the parts A and B from the N 2 gas to the Ar gas.
タンディッシュ内の雰囲気をN2ガスからArガスに置換を始め、さらにタンディッシュ内の溶鋼重量が低下して29tonに達し、溶鋼湯面が注入管下端よりも下方になった時点で、図2(a)に示すように、吸窒対策としてArガスの流量を設定値から全開に増加し、図2(b)に示すように、A部は全開流量の120Nm3/hrとした。また、B部は80Nm3/hrとした。 When the atmosphere in the tundish is replaced with N 2 gas by Ar gas, the molten steel weight in the tundish decreases to 29 tons, and the molten steel surface is below the lower end of the injection pipe. As shown in (a), the flow rate of Ar gas was increased from the set value to full open as a measure against nitrogen absorption, and as shown in FIG. 2 (b), the A portion was set to 120 Nm 3 / hr of the full open flow rate. Moreover, B part was 80 Nm < 3 > / hr.
なお、図2(b)中のArガス流量増速度は、タンディッシュ内をArガスで置換するために予めArガスに切り替えておく必要があり、そのA部、B部の容積と置換速度から決定した。   Note that the Ar gas flow rate increase rate in FIG. 2 (b) needs to be switched to Ar gas in advance in order to replace the inside of the tundish with Ar gas. Were determined.
そして、連々続鋳造開始後、すなわち次回の取鍋を開口して給湯を開始した後、図2(a)に示すように、タンディッシュ重量が増加して30tonに達し、注入管下端よりもタンディッシュ溶鋼湯面が上になった時点でArガスの流量を例えば全開から設定値まで低下させ30Nm3/hrとする。 Then, after starting continuous casting, that is, after opening the next ladle and starting hot water supply, the tundish weight increased to 30 tons as shown in FIG. When the molten steel surface of the dish is turned up, the flow rate of Ar gas is reduced from, for example, full open to a set value to 30 Nm 3 / hr.
さらに、図2(a)に示すよううに、タンディッシュ内の溶鋼重量が33tonとなり、吸窒の可能性がなくなるタンディッシュ内の定常部の溶鋼重量38tonまで増加するとき、タンディッシュ内のシールドガスを、図2(b)に示すように、ArガスからN2ガスに変化させ30Nm3/hrとした。 Further, as shown in FIG. 2 (a), when the molten steel weight in the tundish becomes 33 tons and the molten steel weight in the steady portion in the tundish where the possibility of nitrogen absorption disappears increases to 38 tons, the shielding gas in the tundish As shown in FIG. 2B, the gas was changed from Ar gas to N 2 gas to 30 Nm 3 / hr.
なお、図2(b)中のArガス流量減少速度は、そのA部、B部の容積と置換速度から決定し、注入管下端に接触した時点でArガスの切替えを開始し、その後注入管内の湯面が安定したところでArガスからN2ガスに変更した。 In addition, the Ar gas flow rate decreasing speed in FIG. 2B is determined from the volume of the A part and B part and the replacement speed, and switching of Ar gas is started when it contacts the lower end of the injection pipe. When the molten metal surface became stable, the gas was changed from Ar gas to N 2 gas.
上記のように、タンディッシュのシールドガスのArガスからN2ガスへの切替えを、タンディッシュ内溶鋼重量の変化に応じて実施することで、表面品質、特に窒素が高いと表面割れ等が発生しやすくなるようなNb含有鋼等で低N化が必要となるような鋼種を安価かつ高品質に製造することが可能となる。 As described above, switching from Ar gas to N 2 gas of the tundish shielding gas according to changes in the molten steel weight in the tundish causes surface cracks, especially surface cracks when nitrogen is high. Therefore, it is possible to produce a steel type that requires N reduction, such as Nb-containing steel, which can be easily manufactured at low cost and high quality.
どのような溶鋼重量になった時にシールドガスの種類、流量を変更するのかは、タンディッシュ内の容積とシールドガス流量から算出したタンディッシュ内の置換時間に、溶鋼重量の減少速度または増加速度を乗算して算出した。   The type and flow rate of the shield gas that changes when the molten steel weight is reached is determined by the rate of decrease or increase in the molten steel weight based on the displacement time in the tundish calculated from the volume in the tundish and the flow rate of the shield gas. Calculated by multiplication.
上記手順(ロジック)を連々続鋳造の取鍋交換時における非定常部に実施して、シールドガス種の変更と流量変更時期を決定し、タンディッシュ内溶鋼のシールを行った。図2(b)に示した本発明方法と、図2(c)に示した従来方法におけるタンディッシュ内溶鋼の吸窒例を図3に示すが、従来方法の場合35ppmの吸窒量であったものが本発明方法を採用することで2ppmまで減少することができた。   The above procedure (logic) was performed on the unsteady part when changing the ladle for continuous casting, the change of shield gas type and the flow rate change time were determined, and the molten steel in the tundish was sealed. An example of nitrogen absorption of molten steel in tundish in the method of the present invention shown in FIG. 2 (b) and the conventional method shown in FIG. 2 (c) is shown in FIG. Can be reduced to 2 ppm by adopting the method of the present invention.
なお、図3に示した吸窒量は、スラブより鋳片表層55mm(鋳片厚さの1/4の箇所)から20×20mm角のサンプルを採取し、ガスクロマトグラフィーにより分析を行った結果である。   In addition, the nitrogen absorption amount shown in FIG. 3 is a result of analyzing a sample of 20 × 20 mm square from a slab from a slab surface layer of 55 mm (1/4 of the slab thickness) and gas chromatography. It is.
本発明は上記の例に限らず、請求項に記載された技術的思想の範疇であれば、適宜実施の形態を変更しても良いことは言うまでもない。   The present invention is not limited to the above example, and it goes without saying that the embodiments may be changed as appropriate within the scope of the technical idea described in the claims.
例えば、上記の例では、取鍋からタンディッシュへの給湯部に注入管を用いたものについて説明したが、取鍋用ロングノズルを用いた場合もロングノズルの下端から外れた場合には同様の吸窒現象が発生するので、同様に適用できる。   For example, in the above example, an explanation has been given of the use of the injection pipe in the hot water supply part from the ladle to the tundish, but the same applies when the ladle long nozzle is removed from the lower end of the long nozzle. Since a nitrogen absorption phenomenon occurs, it can be similarly applied.
また、上記のタンディッシュ内のシールドガスの選択・切り替えは、シーケンサーにより自動で変更することにより行うことが望ましいが、作業者が手動で行っても良いことは言うまでもない。   In addition, it is desirable that the shield gas in the tundish should be selected and switched by automatically changing it with a sequencer, but it goes without saying that it may be performed manually by an operator.
また、タンディッシュへの溶鋼の供給は取鍋に限らず、どのような鍋(容器)を用いて行っても良い。   The supply of molten steel to the tundish is not limited to a ladle, and any pan (container) may be used.
1 タンディッシュ
2 溶鋼
3 取鍋
4 注入管
A 注入管の内側におけるタンディッシュ内の空間
B 注入管の外側におけるタンディッシュ内の空間
DESCRIPTION OF SYMBOLS 1 Tundish 2 Molten steel 3 Ladle 4 Injection pipe A Space in tundish inside injection pipe B Space in tundish outside injection pipe

Claims (1)

  1. タンディッシュ内に溶鋼を供給中の鍋から次回の鍋に溶鋼の供給を切り替えながら行う連々続鋳造において、
    予めタンディッシュ内の溶鋼重量を監視してタンディッシュ内の溶鋼湯面への注入管下端の浸漬状況を把握しておき、
    溶鋼を供給中の鍋からの溶鋼供給の停止後、タンディッシュ内の溶鋼重量が、タンディッシュ内の空間容積とArガスでの置換速度から求められる置換時間を確保できる所定の重量になった時に、注入管の内側および注入管の外側におけるタンディッシュ内空間のN2ガス供給を停止してArガスへの置換を開始し、
    次回の鍋の溶鋼の供給の開始後、タンディッシュ内の溶鋼湯面が上昇し、注入管下端が該溶鋼湯面に浸漬した直後から前記空間へのArガスの供給を減少しつつN2ガスへの置換を開始することを特徴とする連々続鋳造方法。
    In continuous casting performed while switching the supply of molten steel from the pot that is supplying molten steel to the next pot in the tundish,
    Monitor the weight of the molten steel in the tundish beforehand and know the immersion status of the lower end of the injection pipe to the molten steel surface in the tundish.
    When the molten steel weight in the tundish stops after the supply of molten steel from the pan that is supplying molten steel has reached a predetermined weight that can secure the replacement time determined from the space volume in the tundish and the replacement speed with Ar gas. the N 2 gas supply tundish space outside the inner and injection tube of the injection tube to initiate the substitution of Ar gas is stopped,
    After the start of the supply of molten steel in the next pan, the molten steel surface in the tundish rises, and the N 2 gas is reduced while the supply of Ar gas to the space is reduced immediately after the lower end of the injection pipe is immersed in the molten steel surface. The continuous casting method characterized by starting the replacement with.
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