JP4209976B2 - Dipping nozzle for continuous casting and method for continuous casting of steel - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
[0002]
[Prior art]
4A and 4B are explanatory views of an example of the immersion nozzle, in which FIG. 4A is a front explanatory view, FIG. 4B is a right side explanatory view, and FIG. The immersion nozzle 2 is used with its upper end attached to a tundish and its lower part immersed in the molten metal 1 in a continuous casting mold. The immersion nozzle 2 has a bottomed cylindrical shape, and a left discharge hole 3 and a right discharge hole 4 are arranged at symmetrical positions at the bottom of a cylindrical side wall, and one end is disposed at the bottom and the other is left discharged at the other end. A single slit 5 reaching the hole 4 is arranged.
[0003]
In the immersion nozzle having the right discharge hole 3 and the left discharge hole 4 but not having the slit 5, the molten metal 7 supplied from the tundish into the immersion nozzle 2 flows out from the right discharge hole 3 and the left discharge hole 4 exclusively. For this reason, the melt flow 6 flowing out from the right discharge hole 3 and the left discharge hole 4 has a high flow velocity. This molten metal flow 6 collides with the side wall of the mold and is divided into an upward flow and a downward flow. When the flow rate of the molten metal flow 6 is large, the strength of the upward flow becomes excessive, and the meniscus 9 of the molten metal in the mold is strongly swung, so that the casting surface of the slab is damaged. Further, when the flow velocity of the molten metal flow 6 is large, the flow velocity of the downward flow becomes excessive, and the downward flow penetrates deeply into the molten metal in the mold, but the downward flow is caused by inclusions, argon gas bubbles described in detail later, and the like. Due to the inclusion, inclusions and argon gas bubbles also penetrate deeply into the molten metal and are held by the solidified shell during the penetration or ascending, resulting in inclusion defects and bubble defects in the slab.
[0004]
In the immersion nozzle of FIG. 4 having the slit 5, the molten metal 7 flows out from the right discharge hole 3 and the left discharge hole 4 and also flows out downward from the slit 5 as a downward flow 8. As a result, the flow rate of the molten metal flow 6 flowing out from the right discharge hole 3 and the left discharge hole 4 becomes gentle, and therefore the flow rate of the upward flow and the downward flow generated from the molten metal flow 6 also becomes gentle. The oscillation of the meniscus 9 is mitigated, and inclusions and argon gas bubbles are prevented from penetrating deeply into the molten steel in the mold. For this reason, the immersion nozzle of FIG. 4 is preferable for producing a slab having a good casting surface and few inclusion defects and bubble defects.
[0005]
However, according to the knowledge of the present inventors, there is a problem in that the slit 5 becomes thin or easily closed during casting in the immersion nozzle of FIG. 4 unless special measures are taken. A method is known in which argon gas is blown into the molten metal 7 in the immersion nozzle 2 and the molten metal 7 is stirred with argon gas bubbles to prevent the discharge holes of the immersion nozzle from being blocked. When this argon gas is used, the right discharge hole 3 and the left discharge hole 4 can be prevented from being blocked. However, since the slit 5 is a narrow slit, it is difficult to sufficiently prevent the clogging by only blowing argon gas.
[0006]
In Japanese Patent Application No. 61-14051, the tip has a hemispherical shape, a slit is formed at the tip, and a pair of molten steel discharge holes are provided at both ends of the slit. Similar immersion nozzles are described. However, according to the knowledge of the present inventors, even in these immersion nozzles whose tip is bent in a hemispherical shape, the width of the slit 5 becomes narrow during casting, and thus the slit 5 is sufficiently prevented from being blocked. It is difficult to do.
[0007]
[Problems to be solved by the invention]
The present invention has a bottomed cylindrical shape, in which the left discharge hole 3 and the right discharge hole 4 are arranged at symmetrical positions at the bottom of the cylindrical side wall, one end at the bottom is the right discharge hole 3 and the other is the left discharge hole. An object of the present invention is to provide an immersion nozzle that can sufficiently prevent the slit 5 from becoming narrow or closed during casting in an immersion nozzle having one slit 5 reaching 4.
[0008]
[Means for Solving the Problems]
In the above immersion nozzle, (1) the shape of the inner surface of the bottom reaching the side wall from the slit is such that the line intersecting the vertical surface perpendicular to the slit and the inner surface of the bottom is horizontal with respect to the slit as a starting point. A straight line between a straight line rising at a 30 ° inclination and a straight line having an inclination of 30 ° or more reaching the inner surface of the side wall at the same height as the discharge hole starting from the slit, or an inner surface of the bottom that forms a downwardly bulging curve It is an immersion nozzle for continuous casting characterized by its shape.
[0009]
(2) A continuous casting method of steel, characterized by casting using the immersion nozzle for continuous casting described in (1), and (3) for continuous casting described in (1). It is a continuous casting method of steel characterized by casting while blowing an inert gas into the molten steel in the immersion nozzle using an immersion nozzle.
[0010]
FIG. 1 is an explanatory view of an example of an immersion nozzle according to the present invention, and FIG. 1 (A) is a diagram showing a cross section of the lower part of the immersion nozzle, corresponding to FIG. FIG. 1B is an explanatory view of a longitudinal section by a vertical plane knee perpendicular to the slit 5. 1A and 1B, ab is a line where a vertical plane perpendicular to the slit intersects with the inner surface of the bottom of the immersion nozzle of the present invention. Further, af in FIG. 1B is a straight line that rises at an inclination of 30 ° with respect to the horizontal starting from the slit, and ag is a side wall having the same height as the discharge hole 3 (4) starting from the slit. It is a straight line with an inclination of 30 ° or more that reaches the inner surface of. The present invention is a submerged nozzle characterized in that ab is a straight line between af and ag or a curve that swells obliquely downward.
[0011]
As will be described later, in the present invention, it is important that ab is 30 ° or more. Therefore, it is important that the line ag reaching the inner surface of the side wall at the same height as the discharge hole 3 (4) starting from the slit has an inclination of 30 ° or more. The effect of the invention is small.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors performed continuous casting using the immersion nozzle described in FIG. 4 having a hemispherical bottom, and observed the inner surface of the bottom after completion of the casting. FIG. 2 is an explanatory diagram showing that a large amount of deposits 12 were generated on the inner surface of the hemispherical bottom. This deposit 12 extended to the slit 5, covered the surface of the slit 5, and part of the deposit 12 further reached the outer surface of the slit 5. As a result of further investigation, the present inventors have found that this deposit is a high alumina deposit. The deposit 12 was also generated when continuous casting was performed by blowing argon gas into the molten steel in the immersion nozzle.
[0013]
Based on this knowledge, the inventors made a test nozzle of the same shape as in FIG. 2, made of transparent plastic, immersed in a water tank, and supplied with water mixed with an ion exchange resin tracer inside, The flow of water around the slit 5 was investigated. FIG. 3 shows the result. According to this water model test, a weak swirl flow 10 exists in the vicinity of the bottom surface, but becomes a stagnant portion, and a strong water flow 11 toward the slit 5 does not exist. That is, the strong water flow 11 toward the slit 5 mainly flows above the stagnation portion 10 on the bottom surface.
[0014]
From this result, it was considered that if the occurrence of the stagnation portion 10 in FIG. 3 is prevented, the deposits in FIG. 2 are also reduced. For this reason, in FIG. 1B, various test nozzles having different inclination angles of line ab were further created, and the same water model test as described in FIG. 3 was performed. As a result, the clogged portion 10 is large in the test nozzle of FIG. 4 where the bottom is hemispherical and the ab tilt angle is close to 0 degrees, but the staggered portion 10 becomes smaller when the ab tilt angle is increased. It has been found that when ab is an inclination angle of 30 ° or more, almost no stagnation occurs.
[0015]
Based on the results of the water model test, the present inventors have four types of immersion nozzles of FIG. 4 whose hemisphere is the bottom and inclination angles of 20 °, 30 °, and 40 ° of line ab in FIG. 10 immersion nozzles were prepared, and used without blowing argon gas into the immersion nozzle in normal continuous casting of molten steel. In any nozzle, the width of the slit 5 is 20 mm. Each immersion nozzle after use was investigated. The immersion nozzle shown in FIG. 4 having a hemispherical bottom had two slits clogged, and most of the slits were narrow. When the inclination angle was 20 °, no slit blockage occurred, but half of the slits had a narrow slit width, and deposits 12 were observed at the bottom. The nozzles with inclination angles of 30 ° and 40 ° did not have clogging of the slits, the width of the slits tended to be slightly widened, and no deposit 12 was generated on the bottom surface of any nozzle.
[0016]
The continuous casting immersion nozzle is easily clogged when the Al content and Ti content of the molten steel to be injected are high. The present inventors continuously cast molten steel having a high Al content and / or a high Ti content by using the above immersion nozzle in which the line ab in FIG. 1B has an inclination angle of 30 °. The slit of the immersion nozzle was not blocked in any case. However, when argon gas was not blown into the immersion nozzle, deposits 12 were generated at the bottom of the nozzle. On the other hand, when argon gas was blown into the immersion nozzle, there was no deposit 12 at the bottom of the nozzle. From this result, in order to sufficiently prevent the slit width from being narrowed, it is more preferable to use the immersion nozzle of the present invention and perform continuous casting while blowing an inert gas into the molten steel in the immersion nozzle. Contemplating.
[0017]
【The invention's effect】
When the present invention is implemented, it is a bottomed cylindrical shape, the left discharge hole and the right discharge hole are arranged at symmetrical positions at the bottom of the cylindrical side wall, one end is the right discharge hole and the other is the left discharge hole at the bottom. By using a continuous casting nozzle provided with a single slit 5 reaching the diameter, it is possible to sufficiently prevent the slit 5 from becoming thin or clogged during casting and to perform continuous casting.
[Brief description of the drawings]
FIG. 1 is an explanatory view of an example of an immersion nozzle of the present invention.
FIG. 2 is a view showing deposits on the inner surface of the bottom after using a conventional immersion nozzle.
FIG. 3 is an explanatory view of a water model test of a conventional immersion nozzle.
FIG. 4 is a view showing an example of a conventional immersion nozzle having left and right discharge holes at the bottom and a slit at the bottom.
[Explanation of symbols]
1: molten metal in the mold, 2: immersion nozzle, 3: right discharge hole, 4: left discharge hole, 5: slit, 6: molten metal flow from the discharge hole, 7: molten metal in the immersion nozzle, 8: from the slit Downward flow, 9: meniscus of molten metal in the mold, 10: stagnant swirling flow, 11: strong water flow toward the slit, 12: deposit on the bottom of the immersion nozzle.

Claims (3)

A bottomed cylinder with a left discharge hole and a right discharge hole located symmetrically at the bottom of the cylindrical side wall, one slit reaching the right discharge hole and the other reaching the left discharge hole at the bottom The shape of the inner surface of the bottom reaching the side wall from the slit is a line where the vertical plane perpendicular to the slit intersects the inner surface of the bottom with respect to the horizontal starting from the slit. The shape of the inner surface of the bottom which is a straight line between the straight line rising with an inclination of ° and the straight line with an inclination of 30 ° or more reaching the inner surface of the side wall at the same height as the discharge hole starting from the slit, or a curve that bulges diagonally downward An immersion nozzle for continuous casting, characterized in that A continuous casting method of steel, wherein the casting is performed using the immersion nozzle for continuous casting according to claim 1. A continuous casting method for steel, characterized by using the immersion nozzle for continuous casting according to claim 1 and performing casting while blowing an inert gas into the molten steel in the immersion nozzle.

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