WO2023190017A1

WO2023190017A1 - Immersion nozzle, mold, and steel continuous casting method

Info

Publication number: WO2023190017A1
Application number: PCT/JP2023/011462
Authority: WO
Inventors: 周吾森田; 匠川原崎; 智紘田中; 則親荒牧; 章敏松井; 哲郎小谷野; 亮祐千代原; 佳祐佐野
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2022-04-01
Filing date: 2023-03-23
Publication date: 2023-10-05
Also published as: JPWO2023190017A1

Abstract

Provided is a technology for reducing adhesion of inclusions in molten steel to a nozzle, and nozzle erosion, while appropriately controlling a flow of molten steel in a mold. In an immersion nozzle which, when continuous casting of steel is being performed, supplies molten steel from a molten steel storage container into a mold of a continuous caster that performs the continuous casting: an end portion of a nozzle main body, on the side of the immersion nozzle that is immersed into the molten steel in the mold, is closed; one pair of discharge ports having an axis of symmetry along a central axis is provided in each of an upper portion and a lower portion of a part of the nozzle main body that is immersed in the molten steel; and an area of an opening portion of the discharge ports in the lower portion lies in a range of at least 1.0 times and at most 1.6 times an area of the discharge ports in the upper portion. A ratio r/R of an inner diameter r of a flow passage inside the immersion nozzle, from an upper edge of an upper hole of the discharge port to the bottom of a lower edge of the immersion nozzle, to an inner diameter R of the flow passage inside the immersion nozzle, up to the upper edge of the upper hole of the discharge port, is preferably in a range of 0.6 or more to less than 1.0, and the upper portion discharge port and the lower portion discharge port are preferably arranged with an angle θ of 10° or less between discharge directions thereof in a top view.

Description

Immersion nozzle, mold and continuous steel casting method

The present invention relates to a submerged nozzle for injecting molten steel into a mold during continuous steel casting, a mold for a continuous casting machine using the submerged nozzle, and a continuous steel casting method.

When continuously casting steel, a submerged nozzle is immersed in the molten steel in the mold to inject the molten steel. The flow of molten steel in the mold is such that the discharge flow from the left and right discharge ports of the immersion nozzle collides with the inner wall on the shorter side of the mold, and an upward flow rises along the mold inner wall and a downward flow flows downward along the mold inner wall. Divert into streams.

In this case, especially when the discharge flow velocity is high, uneven flow velocity distribution may occur between the upper and lower parts of the discharge port. As a result, the left and right flow rate balance may be disrupted in each of the upward flow and downward flow, or a locally strong discharge flow may occur, resulting in large fluctuations in flow. Such fluctuations become a factor in the generation of defects due to insufficient formation of the solidified shell and the trapping of bubbles and inclusions in the solidified shell.

In order to solve such problems, it is thought that by slowing down the flow of molten steel in the mold and forming a uniform flow, continuous casting that prevents defects due to bubbles and inclusions will become possible. In line with this idea, a four-hole type immersion nozzle (four-hole nozzle) in which molten steel discharge ports are provided in two stages in the vertical direction has been proposed, for example, in the following patent document.

Patent Document 1 discloses a nozzle in which the upper stage discharge opening area is larger than the lower stage discharge opening area in order to reduce the maximum downward flow velocity as much as possible, and a continuous casting method using the nozzle.

International Publication No. 2010/109887

Although the technique described in Patent Document 1 is successful in reducing the downward flow velocity, the flow of molten steel tends to be biased towards the upper and lower discharge ports due to the nature of gravity, resulting in high pressure at the bottom of the nozzle. As a result, stagnation occurs at the bottom of the nozzle, and inclusions may adhere to the inner tube of the immersed nozzle due to a reaction with inclusions present in the molten steel, or the inner tube may be damaged by melting. Furthermore, since the cross-sectional area of each discharge port is relatively small compared to a two-hole nozzle, there is a problem in that adhesion and erosion of the discharge ports disturbs the flow of molten steel and tends to impede operations.

The present invention has been made to solve the above problems, and aims to provide a technology that reduces the adhesion of inclusions in the molten steel to the nozzle and melting damage of the nozzle while appropriately controlling the flow of molten steel in the mold. .

In order to solve the above problems, the inventors studied the pressure distribution inside the nozzle in order to optimize the opening area ratio of the upper and lower discharge ports of a porous immersion nozzle and the flow rate of each discharge port, and as a result, they arrived at the present invention. did.

The immersion nozzle according to the present invention for solving the above problems is a immersion nozzle that supplies molten steel from a molten steel storage container into a mold of a continuous casting machine that performs continuous casting when continuously casting steel. , the end of the nozzle main body of the immersion nozzle on the side that is immersed in the molten steel in the mold is closed, and the upper and lower parts of the part of the nozzle main body that are immersed in the molten steel are each provided with 1 1/2 increments with the central axis as the axis of symmetry. It has a pair of discharge ports, and the opening area of the discharge port in the lower section is in the range of 1.0 times or more and 1.6 times or less as compared to the opening area of the discharge port in the upper section. do.

In addition, the immersion nozzle according to the present invention is
a. In the flow path inside the submerged nozzle, the ratio r/R of the internal diameter r from the upper end of the discharge port upper hole to the bottom of the lower end of the submerged nozzle to the inner diameter R to the upper end of the discharge port upper hole is in the range of 0.6 or more and less than 1.0. thing,
b. The discharge direction of the discharge port in the upper stage portion and the discharge port in the lower stage portion are arranged at an angle θ of 10° or less when viewed from above;
etc. may be a more preferable solution.

Further, the mold according to the present invention is a mold for a continuous casting machine having any of the above-mentioned immersion nozzles, and has an index K that affects the fluctuation of the melt level expressed by the following equation (1) of 0.09 to 0. As in the range of 14,
It is characterized by being configured.
K ² =(L ² +W ² /4)/TP ² (1)
Here, L is the distance [m] from the meniscus to the upper end of the discharge port upper hole of the immersion nozzle,
W is the distance between the short sides of the mold at the meniscus position [m],
TP is the mass of molten steel passing per unit time [t/min].

The mold according to the present invention includes a DC coil that is installed on the outside of the long side of the mold above the discharge port of the immersion nozzle, and is capable of applying a magnetic field in which a DC magnetic field and an AC magnetic field are superimposed to the molten steel in the mold; an electromagnetic stirring device having an AC coil; and an electromagnetic brake device having a DC coil installed outside the long side of the mold below the discharge port of the immersion nozzle and capable of applying a DC magnetic field to the molten steel in the mold. provision may be a more preferable solution.

Further, in the continuous casting method of steel according to the present invention, when continuously casting steel using any of the above-mentioned immersion nozzles, the melt level fluctuation index K shown by the above equation (1) is 0.09 to 0.0. It is characterized in that it is adjusted to fall within a range of 14.

The method for continuous casting of steel according to the present invention is as follows:
c. The molten steel in the mold above the discharge port of the immersion nozzle immersed in the molten steel in the mold is applied with a DC magnetic field having a magnetic flux density of 0.1 to 0.8T and an alternating current magnetic field having a magnetic flux density of 0.03 to 0.1T. applying a magnetic field with a superimposed magnetic field, and applying a DC magnetic field having a magnetic flux density of 0.1 to 0.8 T to the molten steel in the mold below the discharge port;
d. Adjust the ratio Q _Ar /TP of the Ar gas flow rate Q _Ar [NL/min] to the mass of molten steel passing TP [t/min] to be 2.0 or more and 5.0 or less, and let Ar flow in from the upper nozzle. thing,
etc. may be a more preferable solution.

According to the immersion nozzle and continuous casting machine of the present invention, by making the lower discharge opening area larger than the upper discharge opening area of the porous immersion nozzle, the flow stagnates at the bottom of the nozzle and a high-pressure part is formed. Steel can be continuously cast without any negative pressure being formed near the discharge port. Therefore, it is possible to prevent adhesion and nozzle erosion due to the reaction between the nozzle refractory and inclusions, and is expected to have the effect of reducing the risk of hindering operations. The immersion nozzle of the present invention is suitable for use in a continuous steel casting method.

FIG. 1 is a longitudinal cross-sectional view of a submerged nozzle according to an embodiment of the present invention. FIG. 7 is a cross-sectional view of a submerged nozzle according to another embodiment of the present invention, showing the positional relationship between upper and lower discharge ports. It is a graph showing the relationship between the maximum pressure inside the immersion nozzle and the ratio of the cross-sectional area of the upper discharge port to the cross-sectional area of the lower discharge port. It is a graph showing the relationship between the minimum pressure near the discharge port and the ratio of the cross-sectional area of the upper discharge port to the cross-sectional area of the lower discharge port. It is a graph showing the relationship between the normalized maximum pressure inside the immersion nozzle and the ratio r/R of the inner diameter of the immersion nozzle. FIG. 6 is an explanatory diagram of the positional relationship of the discharge ports of the immersion nozzle that affects the floating of Ar bubbles in a mold for a continuous casting machine according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be specifically described. Note that each drawing is schematic and may differ from the actual drawing. Furthermore, the following embodiments are intended to exemplify devices and methods for embodying the technical idea of the present invention, and the configuration is not limited to the following. That is, the technical idea of the present invention can be modified in various ways within the technical scope described in the claims.

[Immersion nozzle]
FIG. 1 is a longitudinal sectional view showing the tip shape of a multi-hole immersion nozzle according to an embodiment of the present invention. During continuous casting of steel, molten steel is injected by dipping such a submerged nozzle into the molten steel in a mold. This embodiment has a total of four discharge ports, two pairs of upper and lower pairs, with the center axis 4 as the axis of symmetry, and is a so-called four-hole immersion nozzle.

In this embodiment, the cross-sectional area of the lower discharge port 2 is set to be 1.0 times or more and 1.6 times or less the cross-sectional area of the upper discharge port 1. The reason is explained below.

In general, attention is focused on how to obtain a damping effect on the discharge flow velocity and reduce defects in slabs in a porous immersion nozzle having discharge ports in upper and lower stages.

However, the inventors found that the flow of molten steel tends to be biased toward the lower stage due to the influence of gravity. As a result, it was found that the pressure at the bottom 3 of the immersion nozzle inner tube increases, making it easier to form a stagnation part, and that negative pressure is more likely to be created near the discharge port. As a result of both, a reaction between the inclusions in the molten steel and the immersed nozzle refractory is induced, which causes inclusions to adhere to the immersed nozzle and erosion of the nozzle refractory, making stable operation difficult. I found out.

First, in a submerged nozzle having an upper discharge port 1 and a lower discharge port 2, by making the opening area of the lower discharge port 2 greater than or equal to the opening area of the upper discharge port 1, the gap between the upper and lower discharge ports is It was decided to rectify the flow and reduce the stagnation area (stagnation area) formed at the bottom 3 of the immersion nozzle. In the stagnation area, the flow of molten steel is determined by the size of the stagnation area, the balance between the discharge port area of the upper and lower stages, and the internal diameter of the nozzle body around the discharge port. Since these factors also affect the "continuity" of the molten steel flow field, it is difficult to predict the influence of each factor individually.

Therefore, in order to control the formation of stagnation caused by local high pressure areas and negative pressure areas by balancing the sizes of the upper and lower discharge ports, the influence of the ratio of the area of the upper and lower discharge ports on the stagnation is The evaluation was done using numerical calculations.

In addition, the aforementioned stagnation area at the bottom of the nozzle is created by forcing a part of the molten steel flow to collide with the refractory existing between the upper and lower discharge ports, and forcibly guiding the molten steel flow to the upper stage discharge port. We thought that it would be possible to control this, and conducted numerical calculations to examine the effect that changes in the inner diameter of the nozzle body around the discharge port have on the stagnation area.

As shown in FIG. 2, the arrangement positions of the upper and

lower discharge ports

1 and 2 are set to have an angular difference θ (°) in the nozzle circumferential direction, and are preferably shifted by a maximum of 10°. It is preferable that the lower discharge ports 2 are arranged to face the short sides of the mold so that the molten steel projecting direction is parallel to the long sides of the mold, and the upper discharge ports 1 are offset in the circumferential direction. Even if alumina or other substances adhere to the inside of the nozzle, the flow from the upper discharge port 1 will collide with the long sides of the mold, which can be expected to suppress the effect of the molten steel flow directly colliding with the molten metal surface. . As a result, the influence on the hot water level can be kept to a low level. On the other hand, if the shifting angle is too large, the molten steel flow collides with the long side surfaces of the mold, causing the molten steel flow to be deflected, and there is a risk that fluctuations in the molten steel level will increase due to the upward flow. The angle difference θ is more preferably more than 1° and less than 10°, and even more preferably more than 3° and less than 10°.

<Analysis 1>
First, the immersion nozzle has a straight shape with an inner diameter R of 150 mm, and has an upper discharge port and a lower discharge port having openings with the shapes shown in Table 1. Four-hole immersion nozzles numbered 1 to 5 were subjected to numerical calculations. The general-purpose thermal fluid analysis solution STAR-CCM+ was used for the analysis, and the steady-state total pressure distribution was determined under the conditions that the pressure near the outlet side of the discharge port was 0 and the maximum flow velocity in the nozzle was 3.0 m/s. evaluated. In Table 1, "vertical" represents the vertical direction, and "horizontal" represents the horizontal direction.

Among the analysis results in Table 1, the relationship between the maximum pressure inside the immersion nozzle and the ratio SL/SU of the cross-sectional area of the upper discharge port 1 to the cross-sectional area of the lower discharge port 2 is shown in the graph of FIG. Here, the cross-sectional area of the upper discharge port 1 is SU, and the cross-sectional area of the lower discharge port 2 is SL. As shown in FIG. 3, as SL/SU increases, that is, as the cross-sectional area of the lower discharge port 2 increases relative to the cross-sectional area of the upper discharge port 1, the maximum pressure tends to decrease. It is thought that the division will be dissolved. In particular, when SL/SU was 1.0 or more, a large pressure reduction effect was obtained.

Furthermore, among the analysis results in Table 1, the relationship between the minimum pressure near the discharge port and the ratio SL/SU of the cross-sectional area of the upper discharge port 1 to the cross-sectional area of the lower discharge port 2 is shown graphically in FIG. . As shown in FIG. 4, as SL/SU increases, the minimum pressure in the vicinity of the discharge port decreases, and in particular, at a value exceeding 1.6, the pressure becomes negative. Inclusions in the molten steel tend to collect in negative pressure areas, and this also induces a reaction between the inclusions in the molten steel and the immersed nozzle refractory, as in the stagnation area, causing the inclusions to adhere to the immersed nozzle and the nozzle refractory. It is thought that this may cause melting and damage to objects. Therefore, SL/SU is set to 1.6 or less.

<Analysis 2>
Next, for a submerged nozzle with SL/SU of 1.0, in the flow path inside the nozzle, the ratio r/ The relationship between R and maximum pressure was analyzed. The analysis results are shown in Table 2. Here, the maximum pressure inside the nozzle when r/R is 1.0 was normalized to 1.0. The relationship between the normalized maximum pressure and the inner diameter ratio r/R is shown graphically in FIG.

From the results in Table 2 and FIG. 5, it can be seen that there is an optimal range for the inner diameter ratio r/R. The normalized maximum pressure is the smallest when the inner diameter ratio is about 0.7, and the normalized maximum pressure becomes large even if it is smaller or larger. In particular, when r/R was 0.5, the normalized maximum pressure exceeded 1.0. This is thought to be because the proportion of the area where the molten steel flow hits the refractory between the upper and lower discharge ports has increased, creating a new high-pressure area and a dangerous area for the formation of stagnation. Therefore, the inner diameter ratio r/R is preferably 0.6 or more and less than 1.0. The normalized maximum pressure can be suppressed to less than 1.0. Preferably, r/R is 0.9 or less.

Furthermore, when actually continuously casting steel, if a submerged nozzle is used, an inert gas such as Ar gas can be mixed into the molten steel through the upper nozzle. By doing so, the molten steel receives the effect of the buoyancy of the bubbles, and the formation of a high-pressure portion at the bottom 3 of the immersion nozzle can be alleviated.

However, if the amount of inert gas mixed in is excessive, the buoyancy of the flow after coming out of the immersion nozzle to the meniscus in the mold for casting steel will increase, causing large fluctuations in the metal level, which will hinder operations. becomes. Therefore, there is an appropriate range of blown gas amount.

[template]
Furthermore, in the continuous casting method using the above-mentioned immersion nozzle, Ar gas or the like is blown into the nozzle in order to suppress nozzle clogging due to adhesion of alumina or the like inside the nozzle. In particular, air bubbles flowing out of the upper discharge port 1 along with the molten steel may become a factor in fluctuations in the molten metal level due to their levitation. FIG. 6 is an enlarged conceptual diagram of a cross-section of a mold 20 for a continuous casting machine. In FIG. 6, the locus of bubble levitation is shown by an arrow marked with the symbol Ar. Further, the rising position of the bubbles is related to the diagonal length √(L ² +W ² /4) from the upper discharge port 1 to the meniscus position on the short side of the mold and the mass TP of molten steel passing per unit time. According to the inventors' studies, by setting the index K, which affects the hot water level fluctuation, expressed by the following equation (1), to be in the range of 0.09 to 0.14, the hot water level fluctuation can be significantly suppressed. It turns out. In order to satisfy the relationship of equation (1) below, it is necessary to control the change in the distance between the short sides 8 of the mold, control the casting speed that affects the mass of molten steel passing through, that is, control the slab withdrawal speed, and control the immersion depth of the immersion nozzle 10. It is preferable to do the following. Since the distance between the short sides 8 of the mold is fixed at the required slab width, it is preferable to adjust the immersion depth of the immersion nozzle 10 or the casting speed.
K ² =(L ² +W ² /4)/TP ² (1)
Here, L is the distance [m] from the meniscus 5 to the upper end of the discharge port upper hole of the immersion nozzle,
W is the distance [m] between the short sides 8 of the mold at the meniscus 5 position;
TP is the mass of molten steel passing per unit time [t/min].

(Example 1)
The present invention is configured as described above, and the feasibility and effects of the present invention will be further explained below using Examples.
When casting using this nozzle with a vertical bending continuous casting machine, the nozzle configuration and casting method described in Table 3 were used. As an indicator of operational stability in Table 3, an eddy current sensor was installed directly above the mold surface at the center of the thickness, which was located from the short side to the center of the width by 1/4 of the distance W between the short sides of the mold (casting width). The eddy current sensor measured changes in the hot water level over time. At that time, processing No. The magnitude of the hot water level fluctuation of each treatment was expressed as an index, with the magnitude of the hot water level fluctuation of A1 set as 100. The average value of the first and second half of casting was used for evaluation as an index indicating operational stability. Note that the upper and lower stage discharge ports were both opened in the direction opposite to the short sides, and the center of the discharge flow was parallel to the long sides of the mold.

From the results in Table 3, all of the invention examples had better results than the comparative examples. Comparing samples with the same Ar gas amount ratio Q _Ar /TP blown from the upper nozzle, processing No. 1 with the inner diameter ratio r/R in an appropriate range. A2 and A4 are processing Nos. in which the inner diameter ratio r/R is 1.0. The results were better than A1 and A3, respectively. Comparing samples with the same inner diameter ratio r/R, processing No. 1 with the Ar gas amount ratio Q _Ar /TP blown from the upper nozzle in an appropriate range. A3 and A4 are respectively processed No. The results were better than A1 and A2. Among them, treatment No. A4 showed the lowest average hot water level variation index and exhibited high operational stability.

(Example 2)
Processing No. of Example 1. Table 4 shows the melt level fluctuation index when processing was carried out under the conditions of A1 using a submerged nozzle whose upper discharge port was inclined at an angle θ in the nozzle circumferential direction with respect to the short side of the mold. Process No. where the angle θ is 3 to 10 degrees. In C2 to C4, processing No. Improvement in hot water level fluctuation was seen compared to A1. Processing No. In C5, the fluctuation of the hot water level increased slightly. This is thought to be due to the fact that by tilting the discharge port too much toward the long side, the influence of the reversed flow that collides with the long side and reaches the molten metal surface increases.

(Example 3)
Processing No. of Example 1. Table 5 shows the melt level level fluctuation index when processing was carried out under A4 conditions using a submerged nozzle whose upper discharge port was inclined by 7° in the nozzle circumferential direction with respect to the short side of the mold. Processing No. In D1, processing No. Improvement in hot water level fluctuation was seen compared to A4.

(Example 4)
Fluctuations in the level of hot water when using the continuous casting machine of Example 1, using immersion nozzles with different opening area ratios SL/SU of the upper and lower discharge ports, and variously changing the K value in equation (1) above. The index is shown in Table 6. Note that the immersion nozzle inner diameter ratio r/R was 1.00, and the Ar gas amount ratio Q _Ar /TP blown from the upper nozzle was 1.50. When the K value is in the range of 0.09 to 0.14, the improvement in hot water level fluctuation is remarkable. On the other hand, if the K value is too small, the effect of suppressing molten metal level fluctuation is small due to the influence of whether the mass of molten steel passing through is too large, the casting width is too narrow, or the nozzle immersion depth is too shallow. Furthermore, if the K value is too large, the effect of suppressing molten metal level fluctuation is small due to the influence of whether the mass of passing molten steel is too small, the casting width is too wide, or the nozzle immersion depth is too deep. The inventors believe that maintaining an appropriate deceleration distance of the molten steel flow discharged from the immersion nozzle is effective in suppressing fluctuations in the molten metal level.

(Example 5)
The mold of the continuous casting machine of Example 1 was equipped with an electromagnetic stirring device in the upper part and an electromagnetic brake device in the lower part as shown in FIG. The electromagnetic stirring device in the upper part applied an alternating current magnetic field superimposed on a direct current magnetic field. The electromagnetic brake device in the lower section applied a DC magnetic field. Note that the immersion nozzle inner diameter ratio r/R was 1.00, and the Ar gas amount ratio Q _Ar /TP blown from the upper nozzle was 1.50. Processing No. F01 is the processing No. of Example 4. Equivalent to E11. Table 7 shows the various processing conditions and the hot water level fluctuation index. Processing No. For F02 to F10, the hot water level fluctuation level index was reduced by applying a magnetic field compared to when no magnetic field was applied. On the other hand, treatment No. In F02, the DC magnetic field in the lower stage was too weak, the DC magnetic field in the upper stage was too strong, and the AC magnetic field in the upper stage was too weak, and although it was better than when no magnetic field was applied, it promoted fluctuations in the melt level. In addition, processing No. In F10, the DC magnetic field in the lower stage was too weak, the DC magnetic field in the upper stage was too strong, and the AC magnetic field in the upper stage was too strong, and although it was better than when no magnetic field was applied, it promoted fluctuations in the melt level. In addition, processing No. In F11, although a magnetic field was applied, the discharge port area ratio SL/SU of the upper and lower stages was outside the range of the present invention, so the hot water level fluctuation index deteriorated. Therefore, it is preferable to apply a DC magnetic field with a magnetic flux density of 0.1 to 0.8 T in the lower electromagnetic brake device. In the upper electromagnetic stirring device, it is preferable to apply a magnetic field in which an alternating current magnetic field having a magnetic flux density of 0.03 to 0.1 T is superimposed on a direct current magnetic field having a magnetic flux density of 0.1 to 0.8 T. It was found that by appropriately combining electromagnetic stirring and electromagnetic brake, it was possible to further improve the level fluctuation.

In this specification, the unit of volume "L" means 10 ^-3 m ³ , the unit of mass "t" means metric ton = 10 ³ kg, and the symbol for the volume of gas "N" represents the volume at a temperature of 0° C. and a pressure of 101,325 Pa, which are standard conditions.

1 Upper discharge port 2 Lower discharge port 3 Bottom 4 Central axis 5 Hot water surface (meniscus)
6 Electromagnetic stirring device 7 Electromagnetic brake device 8 Short side of the mold 10 Immersion nozzle 20 Mold (for continuous casting machine) R Inner diameter from the upper end of the discharge port upper hole r Inner diameter from the upper end of the discharge port upper hole to the bottom of the lower end of the immersion nozzle W Meniscus Distance between the short sides of the mold at the position L Distance from the meniscus to the upper end of the upper discharge hole of the immersion nozzle

Claims

A immersed nozzle that supplies molten steel from a molten steel storage container into a mold of a continuous casting machine that performs the continuous casting when continuously casting steel, the nozzle on the side of the immersed nozzle that is immersed in the molten steel in the mold. The ends of the main body are closed, and each of the upper and lower parts of the nozzle main body that is immersed in the molten steel has a pair of discharge ports with the central axis as an axis of symmetry,
The immersion nozzle, wherein the opening area of the discharge port in the lower stage is in a range of 1.0 times or more and 1.6 times or less as compared to the opening area of the discharge port in the upper stage.
In the flow path inside the submerged nozzle, the ratio r/R of the internal diameter r from the upper end of the discharge port upper hole to the bottom of the lower end of the submerged nozzle to the inner diameter R to the upper end of the discharge port upper hole is in the range of 0.6 or more and less than 1.0. , The submerged nozzle according to claim 1.
The immersion nozzle according to claim 1 or 2, wherein the discharge direction of the discharge port of the upper stage portion and the discharge port of the lower stage portion are arranged at an angle θ of 10° or less when viewed from above.
A mold for a continuous casting machine having a submerged nozzle according to any one of claims 1 to 3,
So that the index K, which affects the fluctuation of the hot water level as shown by the following formula (1), is in the range of 0.09 to 0.14.
It is composed of a mold.
K 2 =(L 2 +W 2 /4)/TP 2 (1)
Here, L is the distance [m] from the meniscus to the upper end of the discharge port upper hole of the immersion nozzle,
W is the distance between the short sides of the mold at the meniscus position [m],
TP is the mass of molten steel passing per unit time [t/min].
an electromagnetic stirring device having a DC coil and an AC coil, which are installed outside the long side of the mold above the discharge port of the immersion nozzle, and can apply a magnetic field in which a DC magnetic field and an AC magnetic field are superimposed to the molten steel in the mold;
an electromagnetic brake device having a DC coil installed outside the long side of the mold below the discharge port of the immersion nozzle and capable of applying a DC magnetic field to the molten steel in the mold;
The mold according to claim 4, comprising:
When continuously casting steel using the immersion nozzle according to any one of claims 1 to 3, the melt level fluctuation index K shown by the following formula (1) is in the range of 0.09 to 0.14. Continuous casting method for steel.
K 2 =(L 2 +W 2 /4)/TP 2 (1)
Here, L is the distance [m] from the meniscus to the upper end of the upper hole of the discharge port,
W is the distance between the short sides of the mold at the meniscus position [m],
TP is mass of molten steel passing per unit time [t/min]
It is.
The molten steel in the mold above the discharge port of the immersion nozzle immersed in the molten steel in the mold is applied with a DC magnetic field having a magnetic flux density of 0.1 to 0.8T and an alternating current magnetic field having a magnetic flux density of 0.03 to 0.1T. 7. The continuous steel casting method according to claim 6, wherein a magnetic field with a superimposed magnetic field is applied, and a DC magnetic field having a magnetic flux density of 0.1 to 0.8 T is applied to the molten steel in the mold below the discharge port.
Adjust the ratio Q Ar /TP of the Ar gas flow rate Q Ar [NL/min] to the mass of molten steel passing TP [t/min] to be 2.0 or more and 5.0 or less, and let Ar flow in from the upper nozzle. , The continuous casting method of steel according to claim 6 or 7.