JP2000126849A - Immersion nozzle for continuous casting and method for continuously casting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the clogging of slit by forming a line crossing orthogonally perpendicular plane to the slit and the inner surface at the bottom of an immersion nozzle as a straight line or a curve bulged diagonally downward, interposing between the straight line rising with the inclination having a specific angle with the slit as the starting point and the inclined straight line having a specific angle or larger reaching the inner surface of the side wall of the same height as a spouting hole with the slit as the starting point. SOLUTION: The immersion nozzle is formed as a bottomed cylindrical state and a right and a left spouting holes 3, 4 are symmetrically positioned at the lower part of the side walls of the cylindrical shape and the slit 5 is arranged between the spouting holes. The line a-f is the straight line with the inclination having 30 deg. to the horizontal line with the slit 5 as the starting point. The line a-g is the straight line with the inclination having >=30 deg. reaching the inner surface of the side walls of the same hight as the right and the left spouting holes 3, 4 with the slit 5 as the starting point. The line a-b is the line crossing the orthogonally perpendicular plane to the slit 5 and the inner surface of the bottom of the immersion nozzle. The line a-b is formed as the straight line or the curve bulged diagonally downward, by interposing between the line a-f and the line a-g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

[0002]

2. Description of the Related Art FIG. 4 is an explanatory view of an example of an immersion nozzle.
(A) is a front view, (B) is a right side view, and (C) is an explanatory view of a cross section taken along an arrow II. The upper end of the immersion nozzle 2 is attached to a tundish, and the lower portion is immersed in a molten metal 1 in a continuous casting mold for use. The immersion nozzle 2 has a bottomed cylindrical shape, and a left discharge hole 3 is formed at a lower portion of the cylindrical side wall.
And a right discharge hole 4 are arranged at symmetrical positions, and one slit 5 is provided at the bottom, one end reaching the right discharge hole 3 and the other end reaching the left discharge hole 4.

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 into the immersion nozzle 2 from the tundish is exclusively discharged from the right discharge hole 3 and the left discharge hole 4. leak. Therefore, the flow rate of the molten metal 6 flowing out of the right discharge hole 3 and the left discharge hole 4 is large. The molten metal stream 6 collides with the side wall of the mold and is separated into an upward flow and a downward flow. When the flow velocity of the molten metal flow 6 is large, the strength of the upward flow is excessive, and the meniscus 9 of the molten metal in the mold is vibrated strongly, so that the casting surface of the slab is damaged. When the flow velocity of the molten metal flow 6 is large, the flow velocity of the descending flow is also excessive,
The descending flow penetrates deeply into the molten metal in the mold, but the descending flow contains inclusions and argon gas bubbles, which will be described in detail later, so that inclusions and argon gas bubbles also penetrate deeply into the molten metal,
It is caught by the solidified shell during infiltration or during floating, resulting in inclusion defects and bubble-like defects in the slab.

In the immersion nozzle of FIG. 4 having the slit 5, the molten metal 7 flows out of the right discharge hole 3 and the left discharge hole 4 and also flows downward from the slit 5 as a downward flow 8. As a result, the flow velocity of the molten metal flow 6 flowing out of the right discharge hole 3 and the left discharge hole 4 becomes slow, and accordingly, the flow velocity of the ascending flow and the descending flow generated from the molten metal flow 6 also becomes slow. The oscillation of the meniscus 9 is reduced, and the inclusions and argon gas bubbles are prevented from deeply penetrating into the molten steel in the mold. For this reason, the immersion nozzle of FIG. 4 is preferable for producing a cast piece having a good casting surface and having few inclusion defects and bubble defects.

[0005] However, according to the knowledge of the present inventors, if no special measures are taken, the immersion nozzle shown in FIG. 4 has a problem that the slit 5 becomes thin or easily closed during casting. 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 agitated by argon gas bubbles to prevent the discharge hole of the immersion nozzle from being blocked. The use of this argon gas can prevent the right discharge hole 3 and the left discharge hole 4 from being blocked.
However, since the slit 5 is a narrow slit, it is difficult to sufficiently prevent the blockage only by blowing argon gas.

In Japanese Patent Application No. 61-14051, the tip is curved in 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. An immersion nozzle similar to that described above is described. However, according to the findings of the present inventors, even in these immersion nozzles whose tips are curved in a hemispherical shape, the width of the slit 5 is narrowed during casting, so that the slit 5
It is difficult to prevent the blockage.

[0007]

The present invention has a bottomed cylindrical shape, in which a left discharge hole 3 and a right discharge hole 4 are arranged symmetrically at a lower portion of a cylindrical side wall, and one end is provided at the bottom with a right discharge hole. It is an object of the present invention to provide an immersion nozzle that has a single slit 5 whose other end reaches the left discharge hole 4 in the hole 3 and that can sufficiently prevent the slit 5 from becoming thin or clogging during casting. And

[0008]

According to the present invention, 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 a line intersecting the vertical surface perpendicular to the slit and the inner surface of the bottom is formed. , A straight line or an obliquely downward direction between a straight line that rises at an inclination of 30 ° with respect to the horizontal from the slit and a straight line that is inclined at an angle of 30 ° or more from the slit and reaches the inner surface of the side wall at the same height as the discharge hole It is an immersion nozzle for continuous casting, characterized in that it has a shape of a bottom inner surface which becomes a curved curve.

(2) A continuous casting method for steel, characterized by casting using the immersion nozzle for continuous casting according to (1), and (3) a continuous casting method according to (1). This is a continuous casting method of steel, characterized in that casting is performed using an immersion nozzle for casting while blowing inert gas into molten steel in the immersion nozzle.

FIG. 1 is an explanatory view of an example of an immersion nozzle according to the present invention. FIG. 1 (A) is a view showing a cross section of a lower portion of the immersion nozzle and corresponds to FIG. 4 (C). FIG. 1B is an explanatory view of a vertical cross section taken along a vertical plane perpendicular to the slit 5. FIG.
(A) and ab in FIG. 1 (B) are lines where a vertical plane perpendicular to the slit intersects the inner surface of the bottom of the immersion nozzle of the present invention. Further, a-f in FIG. 1B is a straight line which rises at an inclination of 30 ° with respect to the horizontal from the slit, and a-g is a side wall having the same height as the discharge hole 3 (4) from the slit. Is a straight line having an inclination of 30 ° or more, which reaches the inner surface of. The present invention provides a
-B is an immersion nozzle characterized in that -b is a straight line between af and ag or a curve swelling obliquely downward.

As will be described later, in the present invention, a-b is 30 °.
That is important. Accordingly, a line a-g reaching the inner surface of the side wall having the same height as the discharge hole 3 (4) starting from the slit.
Is important to have a slope of 30 ° or more, and if the a-g is 30 ° or less, the effect of the present invention is small.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors carried out continuous casting using a submerged nozzle having a hemispherical bottom as shown in FIG. 4, and observed the inner surface of the bottom after completion of casting. FIG. 2 is an explanatory diagram thereof.
A large amount of deposit 12 was generated on the inner surface of the hemispherical bottom. The deposit 12 extended to the slit 5 and covered the surface of the slit 5, and a part thereof further reached the outer surface of the slit 5. The present inventors have further investigated and 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 molten steel in the immersion nozzle.

Based on this finding, the present inventors made a test nozzle having the same shape as that of FIG.
This was immersed in a water tank, and water mixed with a tracer of an ion-exchange resin was supplied therein, and 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 is present near 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 flowed above the stagnant portion 10 on the bottom surface.

From these results, it was considered that if the generation of the stagnant portion 10 in FIG. 3 was prevented, the deposit in FIG. 2 was also reduced. Therefore, in FIG. 1B, various test nozzles having different inclination angles of the lines ab were further prepared, and a water model test similar to that described in FIG. 3 was performed. As a result, the test nozzle of FIG. 4 in which the bottom is hemispherical and the inclination angle of a-b is close to 0 degrees has a large stagnation portion 10, but the larger the inclination angle of a-b, the smaller the stagnation portion 10 becomes, It has been found that when a-b is at an inclination angle of 30 ° or more, almost no stagnation occurs.

Based on the results of the water model test, the present inventors assumed that the immersion nozzle of FIG. 4 having a hemispherical bottom portion and that the lines ab in FIG. 1B have inclination angles of 20 °, 30 °, and 40 °. Each of the four types of immersion nozzles was prepared, and was used without blowing argon gas into the immersion nozzle in ordinary continuous casting of molten steel. In each nozzle, the width of the slit 5 is 20
mm. When each immersion nozzle after use was examined, the immersion nozzle of FIG. 4 having a hemispherical bottom portion had two clogging of slits, and almost all of them had narrow slit widths. No slit blockage occurred when the inclination angle was 20 °, but half of the slits had a narrow slit width, and deposits 12 were observed at the bottom. Nozzles with inclination angles of 30 ° and 40 ° did not have any clogging of the slit, the width of the slit tended to slightly widen, and no deposit 12 was generated on the bottom surface of any of the nozzles.

The continuous casting immersion nozzle is likely to be clogged when the molten steel to be injected has a high Al or Ti content. The present inventors continuously cast molten steel having a high Al content and 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 did not close 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 width of the slit from being reduced, it is more preferable to use the immersion nozzle of the present invention and to perform continuous casting while blowing an inert gas into molten steel in the immersion nozzle. Be imagined.

[0017]

When the present invention is practiced, the left discharge hole and the right discharge hole are arranged at the lower part of the cylindrical side wall at the bottom of the cylindrical side wall, and one end is provided at the bottom with the other right discharge hole. Using a continuous casting nozzle provided with one slit 5 whose end reaches the left discharge hole, continuous casting can be performed by sufficiently preventing the slit 5 from becoming thin or clogging during 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 shows deposits on the inner surface of the bottom after use of a conventional immersion nozzle.

FIG. 3 is an explanatory diagram of a water model test of a conventional immersion nozzle.

FIG. 4 is a diagram 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 mold, 2: immersion nozzle, 3: right discharge hole, 4: left discharge hole, 5: slit, 6: molten metal flow from discharge hole, 7: molten metal in immersion nozzle, 8: from slit Downflow, 9: Meniscus of molten metal in mold, 1
0: stagnant swirl, 11: strong water flow towards the slit, 12: deposit at the bottom of the immersion nozzle.

Claims (3)

[Claims] A left discharge hole and a right discharge hole are disposed symmetrically at a lower portion of a cylindrical side wall having a bottom, and one end is provided at a bottom at a right discharge hole and the other end is provided at a left discharge hole. In the immersion nozzle for continuous casting in which a single slit is reached, the shape of the inner surface of the bottom reaching the side wall from the slit, the line where the vertical surface perpendicular to the slit and the inner surface of the bottom intersect, starting from the slit A straight line that rises at a slope of 30 ° from the horizontal and a straight line that slopes 30 ° or more and reaches the inner surface of the side wall at the same height as the discharge hole starting from the slit, or a curve that bulges obliquely downward. An immersion nozzle for continuous casting, characterized by the shape of the bottom inner surface. 2. A continuous casting method for steel, comprising casting using the immersion nozzle for continuous casting according to claim 1. 3. A continuous casting method for steel using the immersion nozzle for continuous casting according to claim 1, wherein the casting is performed while blowing an inert gas into molten steel in the immersion nozzle.