JP4023289B2 - Manufacturing method of high cleanliness steel slab by continuous casting - Google Patents

Description

【００４５】
【表２】

【００４６】
連続鋳造を開始してから取鍋の溶鋼量の１／２を鋳込んだ時点にて、タンディッシュ内の溶鋼からサンプルを採取（サンプルの採取位置はタンディッシュノズル2aの直上とした）し、それに含まれる全酸素量（溶存酸素と介在物となって含まれている酸素との合計量、以下、Tot.Ｏと略記する）を分析した。
その結果を表３に示すように、出鋼時に溶鋼にアルミニウムを添加した比較例１〜３、またパッドを使用しなかった比較例４〜６（図８参照）に対して、この発明の方法では、Tot.Ｏの測定値が低下していることがわかる。これは、この発明により、溶鋼清浄度が向上していることを示している。
【００４７】
次に、連続鋳造によって得られた前記スラブを、実際に熱間圧延あるいは冷間圧延に供して薄鋼板を製造した。そして、それらの薄鋼板に含まれる介在物を超音波センサーにより調査した。その調査結果を表３に示す。
比較例の方法で溶製した鋼板は、鋼板中に含まれる介在物量が多いが、この発明を適用して溶製した場合の鋼板は介在物に起因する欠陥が皆無となる結果、歩留りが従来に比べて著しく向上した。
【００４８】
とりわけ、（Ｑ／Ｓ２）×（Ｓ１／Ｓ２）が0.5 〜5.0 の範囲を満足する発明例１〜１１では、Tot.Ｏおよび鋼板中の介在物が一層少なく、より好ましい結果が得られた。
【００４９】
【表３】

【００５０】
【発明の効果】
以上述べたように、この発明では、予備精錬及び一次精錬時の負荷を増大させることなく、タンディッシュ内における溶鋼の短絡流れおよび高速な流れを抑制することにより、介在物に起因した製品欠陥を大幅に低減することが可能となる。従って、介在物含有量に対して最も要求の厳しい缶用鋼板についても、介在物に起因する製缶不良を著しく減少させることが可能となった。
【図面の簡単な説明】
【図１】この発明に従うパッドの好適例を示す図である。
【図２】参考例のパッドを示す図である。
【図３】パッドの形状を変えて実験を行った際の（Ｑ／Ｓ２）×（Ｓ１／Ｓ２）と鋼板の介在物量との関係を示す図である。
【図４】この発明に従うパッドを示す図である。
【図５】この発明に従うパッドを示す図である。
【図６】この発明に従うパッドを示す図である。
【図７】この発明に従うパッドを示す図である。
【図８】従来のタンディッシュの例を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a high cleanliness steel slab, and more particularly to a method for producing a slab from highly purified steel, which is suitable as a raw material for steel plates for cans.
[0002]
[Prior art]
Conventionally, in order to melt high-clean steel, after performing decarburization, dephosphorization, desulfurization, etc. mainly in converters etc. (these processes are often referred to as primary refining), the metal in the molten steel at the time of steel output A deoxidation process was performed using aluminum, and the time until the start of casting thereafter was lengthened to take measures to promote the floating separation of the oxide produced by the deoxidation. In order to lift and remove a large amount of oxide (hereinafter referred to as inclusions) after the primary refining from the molten steel, the so-called secondary refining performed in a vacuum degasser, ladle, etc. It is necessary to increase the amount of stirring gas blown into the steel, extend the secondary refining time, or regulate the casting speed. In addition, a flux with high basicity (CaO / SiO ₂ ) is added to the molten steel so that the inclusions generated in large quantities are once taken into the slag and are not suspended again in the molten steel. Techniques such as increasing the melting point of slag and solidifying it have also been taken.
[0003]
However, increasing the gas flow rate in secondary refining, extending the secondary refining time, or solidifying slag significantly lowers the temperature of the molten steel, so the primary refining in the previous stage increases the molten steel temperature at the time of steel output. There must be. Accordingly, not only does the refining load increase, but also there is a problem that the refining cost is greatly increased by reducing the dephosphorization efficiency due to the high temperature and increasing the wear amount of the refractory lining.
[0004]
Moreover, in patent document 1, the carbon concentration is 0.02 ~ using the primary refining furnace which decarburizes molten steel under atmospheric pressure, and the vacuum degassing apparatus which refines again the molten steel discharged from the primary refining furnace under vacuum. When melting 0.06% by mass of low-carbon molten steel, the carbon concentration in the molten steel is decarburized to 0.02 to 0.05% by mass in the primary refining furnace and carburized at the time of steel extraction. It has been proposed to perform deoxidation treatment by adding a deoxidizer after the concentration of dissolved oxygen is reduced to 0.02 mass% or less by vacuum decarburization and deoxidation in a gas apparatus.
[0005]
However, in the method described in Patent Document 1, carbon must be purposely added at the time of steelmaking, and the refining time is extended. Another problem is that it cannot be applied to ultra-low carbon steel.
[0006]
Here, when continuously casting molten steel, in order to obtain a clean slab, the so-called “short circuit flow” that the molten steel injected into the tundish reaches the mold through the shortest distance is suppressed. It is effective to do. This is to prevent impurities such as non-metallic inclusions present in the injected molten steel from flowing directly into the mold without floating and separating in the tundish. Therefore, it is a common practice to install an obstruction that hinders short-circuit flow, a so-called lower weir, at the bottom of the tundish. By this lower weir, the molten steel injected from the ladle can be guided to the upper part in the tundish, preventing short circuit flow and promoting floating separation of non-metallic inclusions in the molten steel on the molten metal surface Is possible.
[0007]
However, in melting high-clean steel, the lower weir installed at the bottom of the tundish cannot be said to have a sufficient effect. That is, when the molten steel injected from the ladle is guided upward inside the tundish by the lower weir, a high-speed flow is generated at the slag and metal interface, and as a result, a high-speed circulation flow is generated throughout the tundish. Because it becomes.
[0008]
On the other hand, Patent Document 2 discloses a collision pad used in a tundish, which is designed to suppress molten metal turbulence in the tundish. The impact pad has a base with an impact surface and an outer sidewall that surrounds the interior space and extends upward from the base and includes an upper opening for receiving a flow of molten metal. In the pad including an annular inner surface with at least a first portion, the portion extending inward and upward toward the opening, the outer side wall is endless and completely surrounds the internal space . This collision pad is intended to decelerate the opposing flows and suppress high-speed flow.
[0009]
However, in the tundish internal collision pad disclosed in Patent Document 2, since the outer side wall portion is endless, the attenuation of the injection flow from the ladle is made uniform, and the longitudinal direction of the tundish, In other words, the attenuation in the direction where the outlet to the mold is generally present and the direction orthogonal to the longitudinal direction, that is, the direction which is generally orthogonal to the direction where the outlet to the mold is generally orthogonal are always the same. In this case, it cannot be said that the molten steel flow in the tundish is sufficiently controlled, and it is difficult to control the flow of the molten steel in an optimal flow state according to the tundish shape which is generally rectangular. That is, the short-circuit flow and the high-speed flow in the tundish are not sufficiently suppressed.
[0010]
[Patent Document 1]
JP 2001-152238 A [Patent Document 2]
Japanese Patent No. 2836966 [0011]
[Problems to be solved by the invention]
As described above, in the conventional method, it is impossible to industrially manufacture high-clean steel, and the cleanness of the obtained slab was not sufficient.
[0012]
Therefore, the present invention advantageously solves the above problem, and in order to obtain a continuous cast slab having a high cleanliness, thorough slag inclusions that are problematic in the melting stage of clean steel are thoroughly implemented. It aims at proposing about the technique to reduce.
[0013]
[Means for Solving the Problems]
In the present invention, after molten steel melted in a converter is put into a ladle without adding aluminum, aluminum is added to the molten steel in a degassing treatment or gas stirring treatment, and then the tundish is once removed from the ladle. When pouring molten steel into the casting mold, then pouring the tundish into a casting mold and producing a slab by a continuous casting method,
A portion of the molten steel flow poured from the ladle into the tundish collides with the bottom of the tundish, a wall that surrounds the collision portion of the molten steel flow and extends upward from the bottom of the tundish; possess a visor-like portion extending toward the surrounding center, and the long side inner wall opposite to the side of the tundish, at least in the wall, the flow control pad to have a notch placed above the flowable control pad A method for producing a high cleanliness steel slab by continuous casting, characterized by receiving a molten steel flow.
[0014]
Here, the flow control pad preferably satisfies the following formula.
Record
0.5 <(Q / S2) × (S1 / S2) <5.0
Here, Q: Molten steel injection speed (m ³ / min)
S1: Area of the upper surface of the flow control pad excluding the buttocks (m ² )
S2: Area of flow control pad bottom surface (m ² )
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Now, the steel targeted in this invention is a steel plate material for cans such as beverage cans and food cans, and this type of steel plate is subjected to high-level forming processing such as drawing processing and ironing processing. It is desired that the content of non-metallic inclusions is reduced to the limit.
[0017]
First, in melting such steel for steel sheets, in the present invention, in the primary refining furnace for decarburizing or dephosphorizing the molten steel under atmospheric pressure, the hot metal is preferably subjected to preliminary dephosphorization treatment in the hot metal phosphorous. Using hot metal stopped until the concentration reaches 0.10% by mass, decarburization treatment is performed so that the carbon concentration in the molten steel becomes 0.02 to 0.05% by mass. It is advantageous to use a converter as the primary smelting furnace. This converter may be any of a top blow converter, a bottom blow converter, and a top bottom converter.
[0018]
Here, at the end of refining in the primary refining furnace (at the time of blowing), the preferred carbon concentration in the molten steel was set to 0.02 to 0.05 mass% if the carbon concentration was 0.05 mass% or less, dissolved in the molten steel This is because the oxygen concentration and the amount of FeO in the slag are increased to a range sufficient to contribute to dephosphorization, and a phosphorus concentration range of 0.020% by mass or less in a normal product steel can be easily achieved. On the other hand, when the carbon concentration is reduced to less than 0.02% by mass, the FeO concentration of the slag becomes too high, and when such slag inevitably flows out into the ladle at the time of steelmaking, the molten steel is reoxidized by this slag, The inclusion concentration may increase after completion of vacuum degassing, and the dissolved oxygen in the molten steel will increase excessively, so the lower limit of the carbon concentration was set to 0.02 mass%.
[0019]
Next, for molten steel that has finished primary refining at an appropriate carbon concentration as described above, aluminum is not added at the time of steel production, but aluminum is added in the subsequent secondary refining to improve cleanliness. I found out that it would have a big impact. This is because if aluminum is added at the time of steel output, the alumina produced in the steel output is easily combined with the slag and then suspended deeply in the molten steel, making it difficult to float.
[0020]
Thereafter, it is even more effective to reduce the dissolved oxygen concentration to 0.02% by mass or less by performing decarburization with a vacuum degassing apparatus. However, even when vacuum degassing is not performed, it is effective to produce steel in a rimmed state, that is, to produce steel without adding dealuminized without adding aluminum.
[0021]
It is also important to prevent reoxidation from the slag. Therefore, in the present invention, at the time of steel extraction from the primary smelting furnace or after steel output, a reducing agent such as metallic aluminum or aluminum slag is added to the slag accompanying the molten steel, such as FeO or MnO in the slag. It is better to reduce the oxidizing component. As a standard of reduction, it is preferable to make FeO in slag 3.0 mass% or less.
[0022]
After that, the molten steel is poured into the tundish from the ladle and then poured into the casting mold from the tundish to produce a slab by the continuous casting method. The molten steel is poured from the ladle into the tundish once. In doing so, it is important to install a flow control pad having a predetermined shape at a portion where the molten steel flow collides with the tundish bottom, and to receive the molten steel flow with this flow control pad. In other words, pouring hot water under the control of the flow control pad and controlling the molten steel flow in the tundish properly is important in realizing the production of continuous cast slabs with highly clean steel. is there.
[0023]
Therefore, a tundish flow control pad according to the present invention will be specifically described below with reference to the drawings.
FIG. 1 shows an example in which flow control pads (hereinafter simply referred to as pads) according to the present invention are arranged in a tundish.
In Fig. 1, number 1 ladle, 2 tundish, 2a is tundish nozzle, 3 molten steel in the tundish, the molten metal surface of the tundish molten steel 4, 5 as a template.
[0024]
First, FIG. 1 shows that the pad 6 of the present invention is disposed on the bottom surface of the tundish 2 just below the supply nozzle 1a for guiding the molten steel 3 from the ladle 1 and the molten steel injection flow 7 from the supply nozzle 1a is provided. The state converted into flows 8 and 9 by the pad 6 is shown. That is, 8 indicates the flow in the tundish long side direction, and 9 indicates the flow in the tundish short side direction.
[0025]
Now, after the injection flow 7 from the ladle 1 collides with the bottom part of the pad 6, it changes into the flow along a bottom part. This molten steel flow collides with the inner side of the wall 60 of the pad 6 and is further shown in detail in FIGS. 4 to 7, and further extends toward the center of the wall 60 in parallel with the bottom of the tundish 2 at the upper end of the wall 60. 61 is guided in a direction that interferes with the injection flow 7 from the ladle 1. Due to the interference with the injection flow 7, the molten steel flow induced by the pad 6 becomes the flows 8 and 9 whose initial momentum is attenuated. As a result, the flow 8 is damped uniformly compared to the case without the pad, and the molten steel moves in the tundish with sufficient time for the inclusions to float and separate while facing the tundish nozzle 2a. Will be. Since the flow 9 rises along the tundish wall, there are more opportunities for the molten steel containing inclusions to come into contact with the tundish flux on the bath surface 4, and the absorption of inclusions into the tundish flux is promoted. The Thus, cleaning of the molten steel is achieved in the tundish.
The flow 8 is particularly important, and if the flow 8 is strong, the downflow leading to the tundish outlet side becomes strong and the inclusion floating is hindered.
On the other hand, the flow 9 is less important than the flow 8, but a certain amount of the flow becomes an upward flow and helps to raise the inclusions. However, if the flow becomes too strong, a part of the flow 9 merges with the flow 8 and strengthens the flow 8, thereby inhibiting inclusion floating.
[0026]
Similarly, in FIG. 2, as a reference example, a pad 10 different from that shown in FIG. 1 is arranged on the bottom surface of the tundish 2 immediately below the supply nozzle 1 a that guides the molten steel 3 from the ladle 1. The molten steel injection stream 7 from la was converted to streams 11 and 12 by the impact pad 10. This flow 11 is a flow in the tundish longitudinal direction, and the flow 12 is a flow in a direction orthogonal to the tundish longitudinal direction. Also in this case, as in the case shown in FIG. 1, the injection flow 7 from the ladle 1 collides with the bottom of the collision pad 10, then changes to a flow along the bottom, and then collides with the side wall of the collision pad 10. Furthermore, as a result of being guided in a direction interfering with the pouring flow 7 from the ladle 1 by the hook-like protruding portion at the upper end of the side wall, the molten steel flow becomes flows 11 and 12 whose initial momentum is attenuated. As a result, steel cleaning is achieved by the same action as described above. However, in this case, the flows 11 and 12 are attenuated equally, and the inherently more important flow 11 cannot be preferentially attenuated, so that the effect is less than the configuration of FIG.
[0027]
Furthermore, with regard to the pad according to the present invention described above, the influence of its shape on the cleaning of the steel was examined, and the relationship between the capacity (shape) of the tundish pad and the amount of molten steel cast greatly affected the cleanliness. It turned out to give.
The inventors sought the conditions for effectively attenuating the injection flow with the pad as described above. The molten steel injection rate from the nozzle 1a was Q (m ³ / min), and the area of the opening on the upper surface of the pad was S1. When (m ² ) and the bottom area of the pad is S 2 (m ² ), it has been conceived that it can be arranged by the parameter (Q / S 2) × (S 1 / S 2). Note that the area S1 of the upper surface opening of the pad refers to a hatched portion in FIG. 1B or FIG. 2B, that is, a planar projection area of the opening. Further, the pad bottom area S2 refers to a portion surrounded by a dotted line in FIG. 1B or FIG. 2B, that is, an area of a bottom surface inside the pad.
[0028]
Here, (Q / S2) is a value obtained by dividing the molten steel injection rate by the bottom area of the pad, and represents a measure of the average linear flow velocity of molten steel that collides with the pad and reverses upward. On the other hand, (S1 / S2) is the area ratio of the pad upper surface opening to the pad bottom area, and represents how much the molten steel flow spreading on the bottom surface is throttled after inversion, that is, a measure of the damping ratio of the molten steel flow. . Therefore, (Q / S2) × (S1 / S2) obtained by multiplying the damping ratio (S1 / S2) by (Q / S2) representing the strength of the molten steel reversal flow is the molten steel flow velocity after being attenuated by the pad. Can be thought of as a measure of
[0029]
The inventors decided to evaluate the cleanliness of the obtained steel with respect to this parameter (Q / S2) × (S1 / S2) by performing continuous casting under various conditions.
FIG. 3 shows the results of summarizing the relationship between the parameter (Q / S2) × (S1 / S2) and the quality (cleanness) relating to the pad capacity and the molten steel casting amount.
The quality was determined by detecting inclusions of 30 μm or more with an ultrasonic sensor for the obtained cold-rolled sheet, and indicated as defect density, which is the number of inclusions per unit area.
[0030]
As can be seen from FIG. 3, the quality of the pad of any shape in FIGS. 1 and 2 is particularly good when (Q / S2) × (S1 / S2) is in the range of 0.5 to 5.0. I understand.
The reason for this is that the molten steel flow generated in the pad according to the pouring amount is attenuated by the padding, the short-circuit flow and the high-speed flow are suppressed, and the molten steel flow in the tundish to obtain a clean slab. It is interpreted that it can be obtained.
[0031]
When (Q / S2) × (S1 / S2) ≦ 0.5, the reason for the increase in inclusions is not clear, but if Q is too small, the temperature of the molten steel decreases and the inclusion floats in the tundish and in the mold. This is presumably because the molten steel injected into the tundish does not sufficiently flow into the pad when S1 / S2 is too small, and a molten steel flow that cannot be controlled by the pad occurs.
[0032]
On the other hand, if (Q / S2) × (S1 / S2) ≧ 5.0, the inclusion increases because the outflow flow Q generated in the pad is large, the pad bottom surface S2 is too small, or the damping ratio is sufficient. It is presumed that the short circuit flow and the high-speed flow damping effect due to the padding cannot be obtained, and the molten steel flow in the tundish for obtaining a clean slab cannot be obtained.
[0033]
Further, when the results shown in FIG. 3 are examined in detail, the pad of FIG. 1 having a notch is more effective in improving the cleanliness, particularly when the pads having the shapes shown in FIGS. 1 and 2 are compared. Recognize. This is because, in the pad 10 shown in FIG. 2, since the flow 11 and the flow 12 are subjected to the same attenuation, unnecessary attenuation is applied to the flow 12 in the direction perpendicular to the longitudinal direction of the tundish, which is not a problem. This is because the attenuation of the flow 11 in the longitudinal direction of the tundish, which is inherently important, is insufficient as compared with the case of the pad of FIG.
[0034]
On the other hand, in the pad 6 shown in FIG. 1, by providing the notch 62 on the side facing the long side of the tundish, the flow 9 in the direction orthogonal to the length of the tundish is attenuated more than necessary. As a result, the flow 8 in the tundish longitudinal direction is sufficiently damped. As a result, the molten steel flow finally connected from the molten steel injection flow 7 to the mold 5 can be sufficiently damped. Furthermore, the flow 9 in a direction orthogonal to the tundish longitudinal direction becomes an upward flow along the inner wall of the tundish long side, and contributes to guiding the molten steel to the molten metal surface 4 and promoting the floating separation of impurities.
[0035]
Here, the opening width d of the notch 62 provided in the pad 6 is set to a value satisfying the following formula based on the inner shape of the pad as shown in FIGS. Is preferred.
0.01 ≦ d / {L1- (2 × t1)} ≦ 0.5
Here, L1: the tundish longitudinal distance of the inner wall of the pad t1: the length of the pad bowl-shaped portion in the tundish longitudinal direction
That is, when d / {(L1- (2 × t1)} is less than 0.01, the effect of providing the above-described notch is almost lost, and the tundish in the longitudinal direction of the tundish is the same as the pad illustrated in FIG. However, if d / {(L1 (2 × t1)} exceeds 0.5, the flow out of the notch will be excessive. The length of the pad hook-shaped portion in the direction perpendicular to the tundish length is not preferable because a part of the slag and the metal may be disturbed and a part of the slag may be entrained. t2 is not particularly required as long as it does not collide with the molten steel injection flow (melting downstream) from the ladle, but it is preferable to set t2 equal to t1.
[0037]
Further, the height h from the bottom surface of the pad to the bowl-shaped portion shown in FIGS. 3 to 6 is preferably 30 mm or more. This is because if it is less than 30 mm, the flow along the bottom of the pad is guided to the injection flow by the inner wall and the bowl-shaped portion of the pad, so that sufficient space cannot be secured, and the attenuation effect due to interference with the injection flow It is because it cannot be obtained.
[0038]
When the pad according to the present invention is arranged on the bottom surface of the tundish 2, it is preferable to arrange the pad 6 with a slight gap between the inner wall of the long side of the tundish 2 as shown in FIG. That is, forming the molten steel upward flow 9 along the long side inner wall of the tundish 2 through this gap is advantageous for controlling the molten steel flow. It is recommended that this gap be 150mm or less.
[0039]
The pad according to the present invention is not limited to the rectangular pad described above, and may be a pad having a circular planar shape as shown in FIG. 7, for example. Also in the case of this circular shape, the same effect as described above can be obtained by providing the notch 62 on the side facing the long side of the tundish 2.
[0040]
In such a circular pad, the opening width d of the notch 62 described above should satisfy the following equation.
0.01 ≦ d / {L3- (2 × t3)} ≦ 0.5
Here, L3: the maximum distance in the tundish longitudinal direction of the inner wall of the pad t3: the length in the tundish longitudinal direction of the upper part of the pad ridge
Further, in the pad shown in FIG. 7, the wall 60 to the bowl-shaped portion 61 are continuous with a curved surface. However, in the rectangular pad shown in FIGS. May be continuous with a curved surface.
[0042]
【Example】
As an example according to the present invention (Invention Examples 1 to 15 in Table 1) and a reference example , hot metal having a phosphorus concentration of about 0.10% by hot metal pretreatment was used in a bottom blow converter with a production capacity of 260 tons. The refined molten steel was produced without adding aluminum. The molten steel temperature at the time of steelmaking during primary refining was in the range of 1600 to 1620 ° C.
[0043]
Next, a deoxidizer was added onto the slag on the molten steel bath surface in the ladle, and the iron oxide in the slag was reduced to 2.0 mass%. Thereafter, this molten steel was subjected to vacuum treatment (some molten steel was deoxidized after decarburization, and other molten steel was deoxidized), and then aluminum was added to the molten steel for final deoxidation treatment. The molten steel thus melted was transported to a continuous casting machine and poured into a mold through a tundish to perform continuous casting. The Tan the dish, the pad 10 having a shape reference example shown in FIG. 2, Invention Examples 1 to 15 the pad 6 of the shape shown in FIGS. 4, 5 and 6 were respectively installed. The tundish has a tundish capacity: 50 tons and a number of strands: 2.
Moreover, as a comparative example (Comparative Examples 1 to 3 in Table 1), except that aluminum was added to the molten steel when the steel was discharged from the converter, the same treatment as in the present invention was performed, and casting was performed using the same tundish. It was.
Further, as other comparative examples (Comparative Examples 4 to 6 in Table 1), the same treatment as that of the present invention was performed except that the pad was not used in the tundish and the conventional type weir was used.
Details of each operating condition are as shown in Tables 1 and 2.
[0044]
[Table 1]

[0045]
[Table 2]

[0046]
At the time when half of the molten steel amount in the ladle was cast after starting continuous casting, a sample was collected from the molten steel in the tundish (the sample collection position was directly above the tundish nozzle 2a), The total amount of oxygen contained therein (the total amount of dissolved oxygen and oxygen contained as inclusions, hereinafter abbreviated as Tot.O) was analyzed.
As shown in Table 3, the results of Comparative Example 1 to 3 in which aluminum was added to molten steel at the time of steel extraction, and Comparative Examples 4 to 6 (see FIG. 8) in which no pad was used were used. Then, it can be seen that the measured value of Tot. This has shown that the molten steel cleanliness is improving by this invention.
[0047]
Next, the slab obtained by continuous casting was actually subjected to hot rolling or cold rolling to produce a thin steel plate. And the inclusion contained in those thin steel plates was investigated with the ultrasonic sensor. The survey results are shown in Table 3.
The steel sheet melted by the method of the comparative example has a large amount of inclusions contained in the steel sheet, but the steel sheet when melted by applying the present invention has no defects due to inclusions, resulting in a conventional yield. Compared to
[0048]
In particular, Inventive Examples 1 to 11 where (Q / S2) × (S1 / S2) satisfies the range of 0.5 to 5.0, Tot.O and inclusions in the steel sheet were further reduced, and more preferable results were obtained.
[0049]
[Table 3]

[0050]
【The invention's effect】
As described above, the present invention eliminates product defects caused by inclusions by suppressing the short-circuit flow and high-speed flow of molten steel in the tundish without increasing the load during preliminary refining and primary refining. It can be greatly reduced. Therefore, even for steel plates for cans that are the most demanding with respect to inclusion content, it has become possible to significantly reduce can-making defects due to inclusions.
[Brief description of the drawings]
FIG. 1 shows a preferred example of a pad according to the present invention.
FIG. 2 is a diagram showing a pad of a reference example .
FIG. 3 is a diagram showing the relationship between (Q / S2) × (S1 / S2) and the amount of inclusions in a steel plate when an experiment was conducted with the pad shape changed.
FIG. 4 shows a pad according to the present invention.
FIG. 5 shows a pad according to the present invention.
FIG. 6 shows a pad according to the present invention.
FIG. 7 shows a pad according to the present invention.
FIG. 8 is a diagram illustrating an example of a conventional tundish.

Claims (2)

After the molten steel melted in the converter is put into the ladle without adding aluminum, aluminum is added to the molten steel in the degassing process or gas stirring process, and then the molten steel is poured into the tundish from the ladle. Hot water, then poured into the casting mold from the tundish to produce a slab by a continuous casting method,
A portion of the molten steel flow poured from the ladle into the tundish collides with the bottom of the tundish. possess a visor-like portion extending toward the surrounding center, and the long side inner wall opposite to the side of the tundish, at least in the wall, the flow control pad to have a notch placed above the flowable control pad A method for producing a high cleanliness steel slab by continuous casting, characterized by receiving a molten steel flow. The method for producing a highly clean steel slab according to claim 1, wherein the flow control pad satisfies the following formula.
0.5 <(Q / S2) × (S1 / S2) <5.0
Here, Q: Molten steel injection speed (m ³ / min)
S1: Area of the upper surface of the flow control pad excluding the buttocks (m ² )
S2: Area of bottom surface of flow control pad (m ² )

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