JP2009248094A - Heat insulation method of molten steel - Google Patents
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本発明は、溶鋼を、取鍋からタンディッシュを介してモールドに供給し、鋳片を製造する連続鋳造を行うに際し、モールド内の溶鋼温度のばらつきを低減する溶鋼の保温方法に関する。 TECHNICAL FIELD The present invention relates to a method for keeping molten steel, in which molten steel is supplied from a ladle to a mold via a tundish to reduce variation in molten steel temperature in the mold when performing continuous casting for producing a cast piece.
従来、溶鋼を、取鍋からタンディッシュを介してモールドに供給し、鋳片を製造する連続鋳造が行われているが、鋳造中にモールド内の溶鋼温度が変動している。
ここで、モールド内の溶鋼温度が高い場合は、モールドにおける凝固層の発達が不十分となり、溶鋼が凝固層を破って流出するブレークアウトを起こす可能性があるため、その回避策として鋳造速度を下げざるを得ず、鋳片の生産性が低下する。一方、モールド内の溶鋼温度が低い場合は、浸漬ノズル部で溶鋼が凝固してノズルが閉塞したり、またモールドのメニスカス位置でデッケル（金属塊）が生成する等の不具合が発生し、鋳造中止になる可能性がある。
従って、鋳造中は、モールド内の溶鋼温度の変動を小さくすることが望ましい。
Conventionally, continuous casting in which molten steel is supplied from a ladle to a mold via a tundish to produce a slab is performed, but the molten steel temperature in the mold fluctuates during casting.
Here, when the molten steel temperature in the mold is high, the solidified layer in the mold is not sufficiently developed, and there is a possibility that the molten steel breaks through the solidified layer and flows out. There is no choice but to lower the slab productivity. On the other hand, when the molten steel temperature in the mold is low, the molten steel solidifies at the immersion nozzle and the nozzle closes, and problems such as the formation of deckle (metal lump) at the meniscus position of the mold occur, and casting stops There is a possibility.
Therefore, it is desirable to reduce the fluctuation of the molten steel temperature in the mold during casting.
そこで、溶鋼温度の変動を小さくする方法として、鋳造中の溶鋼温度の低下防止を目的とする以下の方法が提案されている。
例えば、特許文献１には、溶融金属の表面に保温材を添加する方法が開示されている。具体的には、取鍋の保温のため、溶鋼１トンあたり０．３ｋｇの保温材を投入する方法が記載されている。
また、特許文献２には、タンディッシュ内の溶鋼表面に保温材を添加する方法が開示されている。具体的には、タンディッシュ内の溶鋼湯面に、保温材を２．０ｋｇ／ｍ２以上投入することが記載されている。
以上の方法により、溶鋼表面からの熱損失を抑えている。
Therefore, as a method for reducing the fluctuation of the molten steel temperature, the following method for preventing the molten steel temperature from being lowered during casting has been proposed.
For example, Patent Document 1 discloses a method of adding a heat insulating material to the surface of a molten metal. Specifically, a method is described in which 0.3 kg of a heat insulating material is added per ton of molten steel in order to keep the ladle warm.
Patent Document 2 discloses a method of adding a heat insulating material to the molten steel surface in the tundish. Specifically, it is described that 2.0 kg / m 2 or more of a heat insulating material is introduced into the molten steel surface in the tundish.
The heat loss from the molten steel surface is suppressed by the above method.
しかしながら、前記従来の方法には、未だ解決すべき以下のような問題があった。
タンディッシュの耐火物が十分に温まっていない鋳造開始時等の鋳造初期は、溶鋼がタンディッシュを通過する間に熱を奪われるため、モールドには低温の溶鋼が供給される。
また、取鍋内の溶鋼は、取鍋の耐火物に接した部分と浴面から冷却されるが、温度が下がった溶鋼は、密度が上がるため周囲の溶鋼に比べて重くなり、取鍋の下方へ移動する。このため、取鍋内の鍋底付近に位置する溶鋼が低温となり、また浴面付近に位置する溶鋼が高温となって、取鍋の深さ方向に溶鋼の温度分布ができる。従って、鍋底から排出される溶鋼の温度は、鋳造初期に低くなり、この溶鋼が排出された後に一旦上昇するが、溶鋼は熱を放散し続けているため、再度、低下する。
従って、モールド内の溶鋼温度のばらつきを低減するには、タンディッシュの耐火物が十分に温まっていない状態において、取鍋の耐火物の吸熱と溶鋼の浴面からの放熱を適切な範囲に制御する必要がある。
However, the conventional method still has the following problems to be solved.
At the beginning of casting, such as at the start of casting when the refractory of the tundish is not sufficiently warmed, the molten steel is deprived of heat while passing through the tundish, so that low temperature molten steel is supplied to the mold.
Also, the molten steel in the ladle is cooled from the portion of the ladle in contact with the refractory and from the bath surface, but the molten steel that has fallen in temperature becomes heavier than the surrounding molten steel because of its increased density, Move down. For this reason, the molten steel located near the ladle bottom in the ladle becomes low temperature, the molten steel located near the bath surface becomes high temperature, and the temperature distribution of the molten steel can be made in the depth direction of the ladle. Accordingly, the temperature of the molten steel discharged from the bottom of the pan is lowered at the beginning of casting, and once rises after the molten steel is discharged, the molten steel continues to dissipate heat, and thus decreases again.
Therefore, in order to reduce the variation in the molten steel temperature in the mold, the heat absorption of the ladle refractory and the heat dissipation from the molten steel bath surface are controlled within an appropriate range when the tundish refractory is not warm enough. There is a need to.
このため、特許文献１の方法では、溶鋼そのものの保温はできるが、保温材の投入量が少なくなり過ぎ、取鍋の耐火物の吸熱と溶鋼の浴面からの放熱を適切な範囲に制御できていないことから、モールド内の溶鋼温度のばらつきを低減できない。
また、特許文献２の方法は、得られる効果が鋳片品質の向上であり、鋳造中の溶鋼温度のばらつきを低減する効果がない。また、この特許文献２には、保温材の投入量の上限が１００ｋｇ／ｍ２であることが記載されているが、保温材を取鍋内に１００ｋｇ／ｍ２近くも投入すると、保温材の投入量が多くなり過ぎて溶鋼の対流による熱拡散効果が少なくなり、取鍋内の鍋底付近に低温の溶鋼が移動して、溶鋼温度のばらつきを助長する。更に、特許文献２の方法では、タンディッシュ内の溶鋼に保温材を投入しているが、タンディッシュは、上方からロングノズルを介して溶鋼を受け、この溶鋼を下方に配置されたモールドへ浸漬ノズルを介して供給するため、タンディッシュの底に低温の溶鋼が溜まるという現象がなく、取鍋内の溶鋼とは、その深さ方向の温度分布が異なる。
For this reason, in the method of Patent Document 1, although the temperature of the molten steel itself can be maintained, the amount of the heat insulating material input becomes too small, and the heat absorption of the refractory in the ladle and the heat dissipation from the bath surface of the molten steel can be controlled within an appropriate range. Therefore, the variation in molten steel temperature in the mold cannot be reduced.
Moreover, the method of patent document 2 has an effect which is the improvement of slab quality and the effect which reduces the dispersion | variation in the molten steel temperature during casting. Further, in Patent Document 2, it is described that the upper limit of the amount of the heat insulating material is 100 kg / m 2 , but when the heat insulating material is put into the ladle in the vicinity of 100 kg / m 2 , The amount of input increases too much, and the thermal diffusion effect due to the convection of the molten steel decreases, and the low temperature molten steel moves near the bottom of the ladle in the ladle to promote the variation in molten steel temperature. Furthermore, in the method of Patent Document 2, a heat insulating material is introduced into the molten steel in the tundish, but the tundish receives the molten steel from above through a long nozzle and immerses this molten steel in a mold disposed below. Since it is supplied through the nozzle, there is no phenomenon that low temperature molten steel accumulates at the bottom of the tundish, and the temperature distribution in the depth direction is different from the molten steel in the ladle.
本発明はかかる事情に鑑みてなされたもので、モールド内の溶鋼温度の変動を従来よりも低減して、鋳片の生産性の低下と鋳造中止を防止できる溶鋼の保温方法を提供することを目的とする。 The present invention has been made in view of such circumstances, and it is intended to provide a method of keeping molten steel that can reduce a fluctuation in molten steel temperature in a mold as compared with the conventional technique and prevent a reduction in slab productivity and stop of casting. Objective.
前記目的に沿う本発明に係る溶鋼の保温方法は、取鍋で２次精錬が行われた溶鋼を、タンディッシュを介してモールドに供給し、鋳片を製造する連続鋳造を行うに際し、前記２次精錬の終了後に、前記取鍋内の溶鋼の浴面からの放熱が１０ｋＷ／ｍ２以上４０ｋＷ／ｍ２以下の範囲内となるように、該溶鋼の浴面に保温材を配置する。 The method for keeping warm the molten steel according to the present invention, which meets the above-mentioned object, supplies the molten steel, which has been subjected to secondary refining in a ladle, to the mold via a tundish, and performs the above-mentioned 2 After the completion of the next refining, a heat insulating material is disposed on the molten steel bath surface so that the heat radiation from the molten steel bath surface in the ladle is in the range of 10 kW / m 2 to 40 kW / m 2 .
本発明に係る溶鋼の保温方法において、前記保温材はチャーライトであり、前記取鍋内の溶鋼の浴面１ｍ２あたり４ｋｇ以上３０ｋｇ以下配置することが好ましい。
本発明に係る溶鋼の保温方法において、前記保温材はバーミキュライトであり、前記取鍋内の溶鋼の浴面１ｍ２あたり３ｋｇ以上２０ｋｇ以下配置することが好ましい。
本発明に係る溶鋼の保温方法において、前記保温材はヤキモミであり、前記取鍋内の溶鋼の浴面１ｍ２あたり３ｋｇ以上２０ｋｇ以下配置することが好ましい。
In the molten steel thermal insulation method according to the present invention, the thermal insulation material is charlite, and it is preferable that 4 kg or more and 30 kg or less be disposed per 1 m 2 of the molten steel bath surface in the ladle.
In the molten steel heat retaining method according to the present invention, the heat retaining material is vermiculite, and it is preferable to dispose 3 kg or more and 20 kg or less per 1 m 2 of the molten steel bath surface in the ladle.
In the molten steel heat retaining method according to the present invention, the heat retaining material is a firewood, and preferably 3 kg or more and 20 kg or less per 1 m 2 of the molten steel bath surface in the ladle.
本発明に係る溶鋼の保温方法において、前記取鍋に溶鋼を受けてから前記２次精錬の終了までの時間を５０分以上にすることが好ましい。
本発明に係る溶鋼の保温方法において、前記保温材は、少なくとも連続鋳造の開始時に使用する最初の前記取鍋内の溶鋼の浴面に対して配置することが好ましい。
In the heat insulation method for molten steel according to the present invention, it is preferable that the time from when the ladle receives molten steel to the end of the secondary refining be 50 minutes or more.
In the molten steel heat retaining method according to the present invention, it is preferable that the heat retaining material is arranged at least with respect to the molten steel bath surface in the first ladle used at the start of continuous casting.
請求項１〜６記載の溶鋼の保温方法は、２次精錬の後に、取鍋内の溶鋼の浴面からの放熱が所定範囲内となるように、取鍋内の溶鋼の浴面に保温材を配置するので、溶鋼の浴面からの放散熱に起因するモールド内の溶鋼温度の変動を従来よりも低減できる。これにより、モールド内の溶鋼温度が高い場合に発生する恐れがあるブレークアウトを回避できるため、鋳造速度を現状より低減するという措置をとる必要がなく、鋳片の生産性を向上できる。また、溶鋼温度が低い場合に発生するノズルの閉塞や、モールドのメニスカスでのデッケルの生成等の不具合を防止でき、連続鋳造を安定に実施できる。
特に、請求項２〜４記載の溶鋼の保温方法は、入手が容易な材料で、モールド内の溶鋼温度の変動を容易に低減でき、経済的である。
The heat insulation method of the molten steel according to claim 1 to 6 is a heat insulating material on the molten steel bath surface in the ladle so that heat radiation from the molten steel bath surface in the ladle is within a predetermined range after secondary refining. Therefore, the fluctuation of the molten steel temperature in the mold due to the heat dissipated from the bath surface of the molten steel can be reduced as compared with the prior art. As a result, breakout that may occur when the molten steel temperature in the mold is high can be avoided, so that it is not necessary to take measures to reduce the casting speed from the current level, and the productivity of the slab can be improved. In addition, problems such as nozzle clogging generated when the molten steel temperature is low and generation of deckle at the meniscus of the mold can be prevented, and continuous casting can be carried out stably.
In particular, the method for keeping warm the molten steel according to claims 2 to 4 is an easily obtainable material, can easily reduce the fluctuation of the molten steel temperature in the mold, and is economical.
請求項５記載の溶鋼の保温方法において、取鍋の耐火物は、溶鋼を取鍋に受ける前に予熱されるが、１６００℃前後の溶鋼温度に対しては低温であり、溶鋼から熱を奪う。そして、時間の経過と共に耐火物の温度が上昇するため、溶鋼から耐火物への吸熱量が次第に減少していく。従って、取鍋の耐火物への吸熱は、溶鋼受入れからの時間が大きく影響する。
ここで、取鍋に溶鋼を受けてから２次精錬の終了までの時間を５０分以上にするので、取鍋の耐火物の吸熱に起因するモールド内の溶鋼温度の変動を従来よりも低減できる。これにより、鋳片の生産性を更に向上でき、しかも連続鋳造をより安定に実施できる。
請求項６記載の溶鋼の保温方法において、取鍋内の溶鋼の浴面からの放散熱と、取鍋の耐火物の吸熱とに起因するモールド内の溶鋼温度の変動は、連続鋳造の開始時に使用する最初の取鍋内の溶鋼で顕著であるので、本発明の効果がより顕著に現れる。
6. The method for keeping warm temperature of molten steel according to claim 5, wherein the refractory of the ladle is preheated before receiving the molten steel in the ladle, but is low with respect to a molten steel temperature of around 1600 ° C. and takes heat from the molten steel. . And since the temperature of a refractory rises with progress of time, the endothermic quantity from molten steel to a refractory gradually decreases. Therefore, the heat absorption to the refractory of the ladle has a great influence on the time from receiving the molten steel.
Here, since the time from receiving the molten steel to the ladle until the end of the secondary refining is set to 50 minutes or more, fluctuation of the molten steel temperature in the mold due to the endothermic heat of the refractory in the ladle can be reduced as compared with the conventional case. . Thereby, the productivity of slab can be further improved and continuous casting can be more stably performed.
In the heat insulation method of the molten steel according to claim 6, the fluctuation of the molten steel temperature in the mold due to the heat dissipated from the bath surface of the molten steel in the ladle and the endothermic heat of the refractory in the ladle is at the start of continuous casting. Since it is remarkable in the molten steel in the first ladle to use, the effect of this invention appears more notably.
続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態につき説明し、本発明の理解に供する。
ここで、図１は本発明の一実施の形態に係る溶鋼の保温方法を適用する取鍋内の溶鋼の深さ方向の温度分布を示す説明図、図２は同取鍋の軸心位置おける溶鋼の深さ方向の温度分布を示す説明図、図３は十分に温まっていないタンディッシュを介して溶鋼をモールドに供給した場合のモールド内の溶鋼温度の変化を示す説明図である。
Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
Here, FIG. 1 is explanatory drawing which shows the temperature distribution of the depth direction of the molten steel in the ladle to which the heat insulation method of the molten steel which concerns on one embodiment of this invention is applied, FIG. 2 is in the axial center position of the ladle FIG. 3 is an explanatory view showing the temperature distribution in the depth direction of the molten steel, and FIG. 3 is an explanatory view showing a change in the molten steel temperature in the mold when the molten steel is supplied to the mold through a tundish that is not sufficiently warmed.
本発明の一実施の形態に係る溶鋼の保温方法は、取鍋（以下、単に鍋ともいう）内の深さ方向の溶鋼の温度分布が、取鍋の耐火物の吸熱と、溶鋼の浴面からの放散熱で決まることを見出し、タンディッシュが十分に温まっていない状態において、取鍋の耐火物の吸熱と溶鋼の浴面の放散熱（以下、放熱ともいう）を適切な範囲にコントロールすることで、モールド内の溶鋼温度の変動を低減する方法である。ここで、モールド内の溶鋼温度の変動とは、１チャージの溶鋼の鋳造開始から鋳造終了まで、モールド内の溶鋼温度を測定した場合の最高温度と最低温度（鋳造開始直後又は鋳造終了直前）の差である。なお、１チャージとは、取鍋１杯分の溶鋼を意味する。 According to one embodiment of the present invention, a method of keeping molten steel has a temperature distribution of molten steel in a depth direction in a ladle (hereinafter also simply referred to as a ladle). It is found that it is determined by the heat dissipated from the heat, and the heat absorption of the refractory in the ladle and the heat dissipated from the bath surface of the molten steel (hereinafter also referred to as heat dissipation) are controlled within an appropriate range when the tundish is not warm enough. By this, it is a method of reducing the fluctuation | variation of the molten steel temperature in a mold. Here, the fluctuation of the molten steel temperature in the mold means the maximum temperature and the minimum temperature (immediately after the start of casting or immediately before the end of casting) when the molten steel temperature in the mold is measured from the start of casting of the molten steel with one charge to the end of casting. It is a difference. One charge means one cup of molten steel.
本発明者らは、溶鋼温度の調査や熱流体解析を行い、溶鋼の温度変動に影響する因子について検討を行った。その検討結果を述べながら、本発明に至った経緯を説明する。
まず、取鍋内の深さ方向の溶鋼の温度分布について、実態に基づき熱流体解析を行った結果について、図１、図２を参照しながら説明する。この図１、図２は、内径：４ｍ、深さ：４ｍの一般的な取鍋を使用し、この取鍋の耐火物の温度を９００℃に設定して１６００℃の溶鋼を受けた場合の解析結果である。なお、溶鋼深さは３．５ｍとした。
図１、図２に示すように、取鍋の溶鋼には、その深さ方向に温度分布（取鍋の底位置：１５６０℃、湯面位置：１５９５℃）が生じており、実際の取鍋でも温度差が生じていることが推定された。また、種々の条件で熱流体解析を行った結果、浴面からの放散熱と取鍋の耐火物の吸熱が、取鍋内の溶鋼の温度分布に大きく影響することが分かった。
The inventors of the present invention investigated the molten steel temperature and analyzed the thermal fluid, and examined the factors that affect the temperature fluctuation of the molten steel. The background that led to the present invention will be described while describing the examination results.
First, the temperature distribution of the molten steel in the depth direction in the ladle will be described with reference to FIG. 1 and FIG. This FIG. 1 and FIG. 2 show a case where a general ladle having an inner diameter of 4 m and a depth of 4 m is used, and the temperature of the refractory of the ladle is set to 900 ° C. and 1600 ° C. molten steel is received. It is an analysis result. The molten steel depth was 3.5 m.
As shown in FIGS. 1 and 2, the molten steel of the ladle has a temperature distribution in the depth direction (bottom position of the ladle: 1560 ° C., surface position: 1595 ° C.), and the actual ladle However, it was estimated that there was a temperature difference. In addition, as a result of thermal fluid analysis under various conditions, it was found that the heat dissipated from the bath surface and the endothermic heat of the refractory in the ladle have a great influence on the temperature distribution of the molten steel in the ladle.
続いて、図１、図２に示した取鍋内の深さ方向の溶鋼の温度分布の解析結果を使って、取鍋の底から排出される溶鋼の温度を計算し、この溶鋼を、十分に温まっていないタンディッシュ（耐火物の表面温度：１０００℃）を経由してモールドに供給した場合のモールド内の溶鋼温度を計算した結果について説明する。
図３に示す計算結果より、モールド内の溶鋼温度は、鋳造初期が低く、一旦温度が上がった後は再び低下するという変化を示すことが分かる。
このことから、取鍋、タンディッシュ、及びモールドの各々において、以下に示すような現象が起こっていると推定される。
Subsequently, using the analysis result of the temperature distribution of the molten steel in the depth direction in the ladle shown in FIGS. 1 and 2, the temperature of the molten steel discharged from the bottom of the ladle is calculated. The result of calculating the molten steel temperature in the mold when supplied to the mold via a tundish (refractory surface temperature: 1000 ° C.) that is not warmed to the temperature will be described.
From the calculation results shown in FIG. 3, it can be seen that the molten steel temperature in the mold shows a change in which the initial casting is low and then once again rises.
From this, it is presumed that the following phenomenon occurs in each of the ladle, the tundish, and the mold.
（１）鋳造初期（鋳造時間：０時間）は、鍋底付近にある低温の溶鋼が排出され、更にタンディッシュの耐火物も溶鋼の熱を吸熱するため、モールド内の溶鋼温度が低くなる。
（２）鋳造中期（鋳造時間：０．５時間程度）は、取鍋から排出される溶鋼の温度が上がり、タンディッシュの耐火物も溶鋼で温められるため、モールド内の溶鋼温度が、一旦上昇する。
（３）鋳造末期（鋳造時間：０．５時間を超え１．７５時間程度）は、取鍋内の溶鋼が放熱を続けているため、取鍋内の溶鋼の温度が低下しモールド内の溶鋼温度が再び低下する。
(1) In the initial stage of casting (casting time: 0 hour), the low-temperature molten steel near the pan bottom is discharged, and the tundish refractory also absorbs the heat of the molten steel, so the molten steel temperature in the mold is lowered.
(2) In the middle of casting (casting time: about 0.5 hour), the temperature of the molten steel discharged from the ladle rises, and the tundish refractory is also heated by the molten steel, so the molten steel temperature in the mold rises once To do.
(3) At the end of casting (casting time: more than 0.5 hours and about 1.75 hours), the molten steel in the ladle continues to dissipate heat, so the temperature of the molten steel in the ladle decreases and the molten steel in the mold The temperature drops again.
以上に述べた解析結果から、取鍋の耐火物の吸熱と取鍋内の溶鋼の浴面の放散熱がモールド内の溶鋼温度のばらつきに影響していることが推定された。そこで、取鍋の耐火物の吸熱と溶鋼の浴面の放散熱を適切な範囲にコントロールする方法について、以下に説明する。
転炉で処理された溶鋼は、取鍋に受けて２次精錬（例えば、真空脱ガス装置による精錬）が行われた後、タンディッシュを介してモールドに供給される。ここで、取鍋に溶鋼を受けてから２次精錬が終了するまでの時間を、５０分以上とするのが好ましい。
取鍋の耐火物は、溶鋼の受入れ前に予熱されるが、１６００℃前後の溶鋼温度に対しては低温であり、溶鋼から熱を奪う。そして、時間の経過と共に耐火物の温度が上昇するため、溶鋼から耐火物への吸熱量が次第に減少していく。
従って、耐火物への吸熱は、溶鋼受入れからの時間が大きく影響する。
From the analysis results described above, it was inferred that the heat absorption of the refractory in the ladle and the heat dissipated from the bath surface of the molten steel in the ladle had an effect on the dispersion of the molten steel temperature in the mold. Therefore, a method for controlling the heat absorption of the refractory in the ladle and the dissipated heat of the molten steel bath to an appropriate range will be described below.
The molten steel processed in the converter is received in a ladle and subjected to secondary refining (for example, refining by a vacuum degassing apparatus), and then supplied to a mold through a tundish. Here, it is preferable that the time from when the molten steel is received in the ladle to the end of the secondary refining be 50 minutes or more.
Although the refractory in the ladle is preheated before receiving the molten steel, the temperature is low with respect to the molten steel temperature around 1600 ° C., and heat is taken away from the molten steel. And since the temperature of a refractory rises with progress of time, the endothermic quantity from molten steel to a refractory gradually decreases.
Therefore, the heat absorption to the refractory greatly affects the time from receiving molten steel.
そこで、上記したように、２次精錬終了までの時間を５０分以上（好ましくは、６０分以上）とすることにより、耐火物の吸熱を適正な範囲に抑えることができる。なお、２次精錬終了までの時間を規定したのは、２次精錬では鍋底からのバブリング等により溶鋼が撹拌されているため、鍋内の溶鋼温度が均一であり、鍋内の深さ方向の溶鋼の温度分布の形成には、２次精錬終了した後の取鍋の耐火物の吸熱が問題となるからである。
一方、２次精錬終了までの時間が長くなるに伴い、耐火物の吸熱を適正な範囲に抑えることができるため、その上限については規定していない。しかし、２次精錬終了までの時間が長くなるに伴い、時間の経過と共に溶鋼の温度が低下するため、転炉で溶鋼の温度を更に高める必要がある。これにより、転炉での熱エネルギーコストの上昇や、溶鋼の生産性の低下を招く恐れがあるため、上限を１２０分（好ましくは、１００分）とすることが好ましい。
上記したことから、２次精錬終了までの時間を５０分以上とするのが好ましいが、特に規定する必要はなく、通常の操業で要する時間（例えば、４０分程度）でもよい。
Therefore, as described above, by setting the time until the end of the secondary refining to 50 minutes or more (preferably 60 minutes or more), the endothermic heat of the refractory can be suppressed to an appropriate range. The time until the end of the secondary refining is specified because the molten steel is stirred by bubbling from the bottom of the pan in the secondary refining, so the temperature of the molten steel in the pan is uniform and the depth in the pan This is because the heat absorption of the refractory in the ladle after the secondary refining is a problem in forming the temperature distribution of the molten steel.
On the other hand, as the time until the end of the secondary refining becomes longer, the endothermic heat of the refractory can be suppressed to an appropriate range, so the upper limit is not specified. However, as the time until the end of secondary refining becomes longer, the temperature of the molten steel decreases with the passage of time, so it is necessary to further increase the temperature of the molten steel in a converter. This may increase the thermal energy cost in the converter and reduce the productivity of the molten steel, so the upper limit is preferably set to 120 minutes (preferably 100 minutes).
From the above, it is preferable to set the time until the end of secondary refining to 50 minutes or more, but it is not necessary to specify in particular, and it may be a time required for normal operation (for example, about 40 minutes).
２次精錬が終了した直後に、取鍋内の溶鋼の浴面（表面）に保温材を投入し配置する。
この溶鋼の浴面への保温材の配置は、取鍋内の溶鋼の浴面からの放熱が１０ｋＷ／ｍ２以上４０ｋＷ／ｍ２以下の範囲内となるように行う。ここで、取鍋内の溶鋼の浴面からの放熱が１０ｋＷ／ｍ２未満の場合、放熱が少な過ぎて溶鋼の対流による熱拡散が少なくなるため、取鍋の底部に低温の溶鋼が溜まり、鋳造初期のモールド内の溶鋼温度が著しく低くなる。一方、放熱が４０ｋＷ／ｍ２を超える場合、放熱が多過ぎて溶鋼の熱拡散が起こるが、溶鋼の温度低下が著しくなる。このため、取鍋の耐火物の吸熱と溶鋼の浴面からの放熱を適切な範囲に制御できす、モールド内の溶鋼温度のばらつきを低減できなくなる。
そこで、取鍋内の溶鋼の浴面からの放熱が１０ｋＷ／ｍ２以上４０ｋＷ／ｍ２以下（好ましくは、下限を１５ｋＷ／ｍ２、更には２０ｋＷ／ｍ２、上限を３５ｋＷ／ｍ２、更には３０ｋＷ／ｍ２）の範囲内となるように行う。
Immediately after the secondary refining is completed, a heat insulating material is introduced and placed on the bath surface (surface) of the molten steel in the ladle.
The heat insulating material is arranged on the bath surface of the molten steel so that the heat radiation from the bath surface of the molten steel in the ladle is in the range of 10 kW / m 2 to 40 kW / m 2 . Here, when the heat dissipation from the bath surface of the molten steel in the ladle is less than 10 kW / m 2 , since the heat dissipation is too small and the thermal diffusion due to the convection of the molten steel is reduced, low temperature molten steel accumulates at the bottom of the ladle, The molten steel temperature in the mold at the beginning of casting becomes extremely low. On the other hand, when the heat dissipation exceeds 40 kW / m 2 , there is too much heat dissipation and thermal diffusion of the molten steel occurs, but the temperature drop of the molten steel becomes significant. For this reason, the dispersion | variation in the molten steel temperature in a mold which can control the heat absorption of the refractory of a ladle and the heat radiation from the bath surface of a molten steel to an appropriate range cannot be reduced.
Therefore, the heat radiation from the bath surface of the molten steel in the ladle is 10 kW / m 2 or more and 40 kW / m 2 or less (preferably, the lower limit is 15 kW / m 2 , further 20 kW / m 2 , the upper limit is 35 kW / m 2 , Is performed within a range of 30 kW / m 2 ).
なお、上記した放熱を満足する保温材としては、例えば、チャーライト、バーミキュライト、又はヤキモミを使用することが好ましい。このチャーライトとバーミキュライトは粒状のものである。また、ヤキモミとは、例えば、焼きもみがら（粉状）、又は焼きもみがらの造粒物（粒状）である。
投入された保温材は、溶鋼の浴面全体を覆う。なお、浴面を覆った保温材の厚みは、その全体に渡って均一の厚みであることが好ましいが、均一でなくてもよい。
ここで、保温材に、チャーライト、バーミキュライト、又はヤキモミを使用する場合、浴面からの放熱が１０ｋＷ／ｍ２以上４０ｋＷ／ｍ２以下となるように、各材料の熱伝導率とかさ密度から、その使用量を規定できる。
In addition, it is preferable to use, for example, charlite, vermiculite, or fir fir as a heat insulating material that satisfies the above-described heat dissipation. The charlite and vermiculite are granular. Yakifomi is, for example, grilled chaff (powder) or a granulated product (granular) of grilled chaff.
The added heat insulating material covers the entire bath surface of the molten steel. In addition, the thickness of the heat insulating material covering the bath surface is preferably uniform throughout, but may not be uniform.
Here, when using charlite, vermiculite, or fir fir for the heat insulating material, the heat conductivity and bulk density of each material are set so that the heat radiation from the bath surface is 10 kW / m 2 or more and 40 kW / m 2 or less. The amount of use can be defined.
具体的には、保温材にチャーライトを使用する場合、溶鋼の浴面１ｍ２あたり４ｋｇ以上３０ｋｇ以下（好ましくは、下限を７ｋｇ、上限を１０ｋｇ）配置する。なお、チャーライトは、熱伝導率：０．５Ｗ／（ｍ・Ｋ）以上３．０Ｗ／（ｍ・Ｋ）以下、かさ密度：５３０ｋｇ／ｍ３である。
また、保温材にバーミキュライトを使用する場合は、溶鋼の浴面１ｍ２あたり３ｋｇ以上２０ｋｇ以下（好ましくは、下限を６ｋｇ、上限を８ｋｇ）配置する。なお、バーミキュライトは、熱伝導率：０．３Ｗ／（ｍ・Ｋ）以上２．０Ｗ／（ｍ・Ｋ）以下、かさ密度：１６０ｋｇ／ｍ３である。
そして、保温材にヤキモミを使用する場合は、溶鋼の浴面１ｍ２あたり３ｋｇ以上２０ｋｇ以下（好ましくは、下限を６ｋｇ、上限を８ｋｇ）配置する。なお、ヤキモミは、熱伝導率：０．２Ｗ／（ｍ・Ｋ）以上３．０Ｗ／（ｍ・Ｋ）以下、かさ密度：１４０ｋｇ／ｍ３である。
Specifically, when charlite is used for the heat insulating material, 4 kg or more and 30 kg or less (preferably, the lower limit is 7 kg and the upper limit is 10 kg) per 1 m 2 of the molten steel bath surface. Charlite has a thermal conductivity of 0.5 W / (m · K) to 3.0 W / (m · K) and a bulk density of 530 kg / m 3 .
In addition, when vermiculite is used as the heat insulating material, 3 kg or more and 20 kg or less (preferably the lower limit is 6 kg and the upper limit is 8 kg) per 1 m 2 of the molten steel bath surface. Vermiculite has a thermal conductivity of 0.3 W / (m · K) to 2.0 W / (m · K) and a bulk density of 160 kg / m 3 .
And when using a firewood for a heat insulating material, 3 kg or more and 20 kg or less (preferably a lower limit is 6 kg and an upper limit is 8 kg) per 1 m < 2 > of molten steel bath surface. In addition, a firewood has a thermal conductivity of 0.2 W / (m · K) to 3.0 W / (m · K) and a bulk density of 140 kg / m 3 .
上記した保温材は、連続鋳造の開始時に使用する最初の取鍋内の溶鋼、即ち加熱手段（例えば、ガスバーナー）で予熱されたタンディッシュを使用する連続鋳造の開始時の１チャージ目の溶鋼の浴面に対して配置することが好ましい。なお、２チャージ目以降の溶鋼の浴面に対して、保温材を配置してもよい。
このように、溶鋼の浴面に保温材を配置した取鍋を、連続鋳造設備のタンディッシュまで搬送し、取鍋の耐火物の吸熱と溶鋼の浴面の放散熱を適切な範囲にコントロールした溶鋼を、取鍋の底に取り付けたロングノズルを介してタンディッシュ内へ供給する。そして、この溶鋼を、タンディッシュを介してモールドに供給し、鋳片を製造する連続鋳造を行うことで、モールド内の溶鋼温度の変動を従来よりも低減でき、その結果、モールド内の溶鋼温度が高い場合の鋳片の生産性の低下と、溶鋼温度が低い場合の鋳造中止を防止できる。
The above-mentioned heat insulating material is molten steel in the first ladle used at the start of continuous casting, that is, molten steel of the first charge at the start of continuous casting using tundish preheated by a heating means (for example, a gas burner). It is preferable to arrange it with respect to the bath surface. In addition, you may arrange | position a heat insulating material with respect to the bath surface of the molten steel after the 2nd charge.
In this way, the ladle in which the heat insulating material is arranged on the molten steel bath surface is conveyed to the tundish of the continuous casting equipment, and the heat absorption of the refractory in the ladle and the heat dissipated from the molten steel bath surface are controlled within an appropriate range. Molten steel is fed into the tundish through a long nozzle attached to the bottom of the ladle. Then, by supplying this molten steel to the mold through a tundish and performing continuous casting to produce a slab, fluctuations in the molten steel temperature in the mold can be reduced as compared with the conventional case. It is possible to prevent slab productivity from being lowered when the temperature is high and to stop casting when the molten steel temperature is low.
次に、本発明の作用効果を確認するために行った実施例について説明する。
モールド内の溶鋼温度のばらつきは、実際に取鍋の耐火物の吸熱と溶鋼の浴面の放散熱を変えて鋳造を行い、モールド内の溶鋼温度を連続的に測定して調査した。
ここで、取鍋の耐火物の吸熱状態は、取鍋に溶鋼を受鋼してから２次精錬が終了するまでの時間を変化させることで調査した。また、溶鋼の浴面の放散熱は、事前に熱伝導率とかさ密度を測定した保温材の投入量を変えることで変化させた。そして、モールド内の溶鋼温度のばらつきは、１チャージの溶鋼の鋳造開始から鋳造終了まで、モールド内の溶鋼温度を測定した場合の最高温度と最低温度の差であり、この差を溶鋼温度のばらつきとして評価した。
Next, examples carried out for confirming the effects of the present invention will be described.
The variation of the molten steel temperature in the mold was investigated by actually changing the heat absorption of the refractory in the ladle and the dissipated heat of the molten steel bath surface, and continuously measuring the molten steel temperature in the mold.
Here, the endothermic state of the refractory in the ladle was investigated by changing the time from the receiving of molten steel to the ladle until the end of secondary refining. Moreover, the heat dissipated on the bath surface of the molten steel was changed by changing the input amount of the heat insulating material whose thermal conductivity and bulk density were measured in advance. The variation in the molten steel temperature in the mold is the difference between the maximum temperature and the minimum temperature when the molten steel temperature in the mold is measured from the start to the end of casting of the molten steel with one charge, and this difference is the variation in the molten steel temperature. As evaluated.
なお、試験に際しては、内径４ｍ、深さ４ｍの取鍋を、その耐火物の内面の温度が９００℃になるまでガスバーナーで予熱した後、３５０トンの溶鋼を受入れ、２次精錬を行った。そして、２次精錬が終了した溶鋼の浴面に保温材に投入し配置した後、この取鍋を連続鋳造設備に移送して、ガスバーナーで１０００℃程度に予熱された容量３０トンのタンディッシュを経て、モールドに溶鋼を供給し、鋳造を開始した。
まず、保温材として粒状のチャーライトを使用し、その投入量を変えて鋳造を行ったときのモールド内の溶鋼温度のばらつきを測定した結果を、表１に示す。
In the test, a ladle having an inner diameter of 4 m and a depth of 4 m was preheated with a gas burner until the temperature of the inner surface of the refractory reached 900 ° C., and 350 tons of molten steel was received and subjected to secondary refining. . After the secondary refining is finished, the heat insulating material is placed on the bath surface of the molten steel, the ladle is transferred to a continuous casting facility, and the tundish with a capacity of 30 tons is preheated to about 1000 ° C. with a gas burner. Then, molten steel was supplied to the mold and casting was started.
First, Table 1 shows the results of measuring the variation in the molten steel temperature in the mold when casting was performed by using granular charlite as a heat insulating material and changing the amount of the charged charlite.
この表１中の浴面放散熱（溶鋼の浴面の放熱）は、チャーライトの投入量とかさ密度から得られるチャーライトの厚さと、チャーライトの熱伝導率から算出したものである。
また、表１中の評価（合否）は、改善割合（溶鋼温度のばらつきの改善割合）と、温度降下（２次精錬終了からの温度降下）の双方が良好な結果を「○」とし、それ以外を「×」とした。
ここで、改善割合は、現状の比較例１の保温材投入量における溶鋼温度のばらつきと比較して、そのばらつき割合が１０％以上改善したものを合格とした。
また、温度降下は、（２次精錬終了時の取鍋内の溶鋼温度）と（１チャージ鋳造完了直前の溶鋼温度）との差を求め、２次精錬終了からの温度降下が７０℃以下のものを合格とした。これは、２次精錬終了からの温度降下があまりにも大きい場合、モールド内の溶鋼温度の下限を確保するため、２次精錬終了時の溶鋼温度を高くする必要があるが、取鍋の耐火物の溶損を早めてその寿命を短くすることに起因する。
The heat dissipated on the bath surface in Table 1 (heat dissipation on the bath surface of molten steel) is calculated from the thickness of charlite obtained from the amount of charlite input and the bulk density, and the thermal conductivity of charlite.
In addition, the evaluation (pass / fail) in Table 1 indicates that the improvement ratio (improvement ratio of variation in molten steel temperature) and the temperature drop (temperature drop after the completion of secondary refining) are both good, and Except for “×”.
Here, the improvement rate was determined to be acceptable when the variation rate was improved by 10% or more as compared with the variation in molten steel temperature in the heat insulating material input amount of the present Comparative Example 1.
Also, the temperature drop is the difference between (the molten steel temperature in the ladle at the end of the secondary refining) and (the molten steel temperature just before the completion of the 1 charge casting) and the temperature drop from the end of the secondary refining is 70 ° C or less. Things were accepted. If the temperature drop from the end of secondary refining is too large, it is necessary to increase the molten steel temperature at the end of secondary refining in order to secure the lower limit of the molten steel temperature in the mold. This is caused by shortening the life of the steel by accelerating its melting.
表１に示すように、取鍋に溶鋼を受けてから２次精錬終了までの時間を５０分とした場合、モールド内の溶鋼の浴面の放散熱が１０〜４０ｋＷ／ｍ２のときに、溶鋼温度のばらつきが低減すると共に、２次精錬からの温度降下を７０℃以下に抑えることができることを確認できた。
なお、ここでは、保温材としてチャーライトを使用しているが、溶鋼温度のばらつきを低減するためには、投入量を４〜３０ｋｇ／ｍ２とすることが望ましい。
このほか、保温材としてバーミキュライトとヤキモミを使用した場合についても、それぞれ鋳造を行ったが、いずれの場合も浴面放散熱が１０〜４０ｋＷ／ｍ２のときに、溶鋼温度のばらつきが小さくなるという結果を得た。このときの最適な保温材投入量は、バーミキュライトの場合３〜２０ｋｇ／ｍ２、ヤキモミの場合３〜２０ｋｇ／ｍ２であった。
As shown in Table 1, when the time from the receiving of molten steel to the ladle to the end of secondary refining is 50 minutes, when the heat dissipated on the surface of the molten steel in the mold is 10 to 40 kW / m 2 , It was confirmed that the variation in molten steel temperature was reduced and the temperature drop from secondary refining could be suppressed to 70 ° C. or less.
Here, charlite is used as the heat insulating material, but in order to reduce the variation in molten steel temperature, it is desirable that the input amount be 4 to 30 kg / m 2 .
In addition, when vermiculite and yakimomi were used as heat insulating materials, casting was performed, but in any case, when the heat dissipation from the bath surface was 10 to 40 kW / m 2 , the variation in molten steel temperature was reduced. The result was obtained. The optimum heat insulating material input amount at this time was 3 to 20 kg / m 2 for vermiculite and 3 to 20 kg / m 2 for Yakimomi.
次に、取鍋に溶鋼を受けてから２次精錬終了までの時間を４０分とした場合に、保温材として粒状のチャーライトを使用し、その投入量を変えて鋳造を行ったときのモールド内の溶鋼温度のばらつきを測定した結果を、表２に示す。なお、改善割合は、現状の比較例４の保温材投入量における溶鋼温度のばらつきと比較して、そのばらつき割合が１０％以上改善したものを合格とした。 Next, when the time from receiving the molten steel in the ladle to the end of the secondary refining is 40 minutes, the mold is used when casting is performed using granular charlite as a heat insulating material and changing its input amount. Table 2 shows the results of measuring the dispersion of the molten steel temperature. In addition, the improvement rate made the thing which the variation rate improved 10% or more compared with the variation in the molten steel temperature in the heat insulating material input amount of the present comparative example 4 as the pass.
この場合も、モールド内の溶鋼の浴面の放散熱が１０〜４０ｋＷ／ｍ２の範囲にあるときに、溶鋼温度のばらつきが低減されており、本発明の効果が確認された。但し、溶鋼を受けてから２次精錬終了までの時間を５０分とした場合（表１）に比べ、溶鋼温度のばらつきの絶対値が大きいことから、溶鋼温度のばらつきを低減するためには、溶鋼を受けてから２次精錬終了までの時間を５０分以上とすることが望ましいことが確認された。
なお、ここでも、保温材としてチャーライトを使用しているが、溶鋼温度のばらつきを低減するためには、投入量を４〜３０ｋｇ／ｍ２とすることが望ましい。また、保温材としてバーミキュライトとヤキモミを使用した場合についても、それぞれ鋳造を行ったが、いずれの場合も浴面放散熱が１０〜４０ｋＷ／ｍ２のときに、溶鋼温度のばらつきが小さくなるという結果を得た。
Also in this case, when the heat dissipated on the bath surface of the molten steel in the mold was in the range of 10 to 40 kW / m 2 , the variation in molten steel temperature was reduced, and the effect of the present invention was confirmed. However, since the absolute value of the variation in molten steel temperature is larger than when the time from receiving the molten steel to the end of secondary refining is 50 minutes (Table 1), in order to reduce the variation in molten steel temperature, It has been confirmed that it is desirable to set the time from the receipt of molten steel to the end of secondary refining to 50 minutes or more.
Here, too, charlite is used as a heat insulating material, but in order to reduce variations in molten steel temperature, it is desirable that the input amount be 4 to 30 kg / m 2 . In addition, when vermiculite and yakimomi were used as the heat insulating materials, casting was performed, respectively, but in each case, when the heat radiated from the bath surface was 10 to 40 kW / m 2 , the variation in molten steel temperature was reduced. Got.
以上、本発明を、実施の形態を参照して説明してきたが、本発明は何ら上記した実施の形態に記載の構成に限定されるものではなく、特許請求の範囲に記載されている事項の範囲内で考えられるその他の実施の形態や変形例も含むものである。例えば、前記したそれぞれの実施の形態や変形例の一部又は全部を組合せて本発明の溶鋼の保温方法を構成する場合も本発明の権利範囲に含まれる。 As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the configuration described in the above embodiment, and the matters described in the scope of claims. Other embodiments and modifications conceivable within the scope are also included. For example, the case where the molten steel heat retaining method of the present invention is configured by combining some or all of the above-described embodiments and modifications is also included in the scope of the right of the present invention.
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