JP2000237851A - Immersion nozzle for continuous casting and continuous casting method of steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an immersion nozzle that the clogging of a slit and the drifting phenomenon during casting can be prevented, with respect to the immersion nozzle for continuous casting where arrange are slit is arranged at the bottom part. SOLUTION: Relating to the immersion nozzle 2 for continuous casting where spouting holes 3, 4 symmetrically in the right and the left directions are arranged at the lower part of the side wall and one slit 5 is arranged at the bottom part, the shape of the bottom part 12 is a projecting type upward and the slit width W [mm] and the slit height (h) [mm] have the relation of 2<=h/W<=10, and/or the spouting hole diameter (d) [mm] and the slit width W [mm] have the relation of 0.1<=W/d<=0.5. Further, the continuous casting method is the one using this immersion nozzle. Furthermore, it is more desirable that the casting is executed while executing the inert gas blowing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an immersion nozzle for continuous casting and a method for continuously casting steel.

[0002]

2. Description of the Related Art FIG. 7 is a schematic view showing a conventional immersion nozzle and a flow of molten steel flowing out. The upper end of the immersion nozzle 2 is attached to a tundish (not shown), and the lower portion is used by immersing it in molten steel 1 in a continuous casting mold. The immersion nozzle 2 has a cylindrical shape with a bottom, and a right discharge hole 3 and a left discharge hole 4 are arranged at symmetrical positions below the cylindrical side wall, and molten steel 7 supplied into the immersion nozzle 2 from a tundish is provided. Flows out from the right discharge hole 3 and the left discharge hole 4 as a molten steel flow 6. The molten steel flow 6 collides with the side wall 14 of the mold and is divided into an upward flow 8 and a downward flow 9. As the casting speed increases, the flow velocity of the molten steel flow 6 flowing out of the right discharge hole 3 and the left discharge hole 4 increases. In this case, however, the flow velocity of the upward flow 8 becomes excessive, and the molten steel meniscus 10 in the mold is strongly shaken. In order to move the casting, the casting surface of the casting is damaged, and at the same time, the powder 11 on the molten steel in the casting mold is involved, which causes inclusion defect of the casting. When the flow rate of the molten steel flow 6 is large, the flow velocity of the descending flow 9 is also excessive, and the descending flow penetrates deeply into the molten steel in the mold. Due to the inclusion of bubbles, inclusions and inert gas bubbles also penetrate deeply into the molten steel, and are trapped by the solidified shell during penetration or floating, causing inclusion defects and bubble defects in the slab.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 61-14051 discloses an immersion nozzle shown in FIG. The shape of the bottom of the inner surface of the immersion nozzle is curved in a hemispherical shape, and one slit 5 is arranged so that one end reaches the right discharge hole 3 and the other end reaches the left discharge hole 4. When this immersion nozzle is used, since the molten steel flows out of the slit 5 as well as the right discharge hole 3 and the left discharge hole 4, the flow velocity of the molten steel flow 6 from the right discharge hole 3 and the left discharge hole 4 decreases. Therefore, the swing of the molten steel meniscus 10 in the mold is reduced, and the inclusions and inert gas bubbles are prevented from deeply penetrating into the molten steel in the mold. Therefore, the immersion nozzle of FIG. 9 is suitable for producing a cast piece having a good casting surface and having few inclusion defects and bubble defects.

[0004]

However, according to the knowledge of the present inventors, in the conventional immersion nozzle shown in FIG.
However, there is a problem in that the stencil becomes thinner or is easily clogged.
By blowing the inert gas into the molten steel 7 in the immersion nozzle 2, it is possible to 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 the inert gas.

Further, in the immersion nozzle having the right discharge hole 3 and the left discharge hole 4, depending on the shape of the nozzle, the balance of the amount of molten steel flowing out of the left and right discharge holes is broken, that is, a so-called drift phenomenon occurs. On the side where the molten steel meniscus 10 in the mold is oscillated, the casting surface of the slab is impaired, and at the same time, inclusions and bubbles of inert gas penetrate deeply into the molten steel, and the inclusion defect of the slab There is a problem that this may cause air bubble defects.

An object of the present invention is to provide an immersion nozzle capable of sufficiently preventing the slit 5 from being closed during casting and simultaneously preventing a drift phenomenon.

[0007]

The present invention provides (1) a molten metal 1
A left discharge hole 4 and a right discharge hole 3 are symmetrically arranged with respect to the center of the nozzle cross section at the lower part of the side wall of the immersion nozzle. One slit 5 with one end reaching the right discharge hole and the other end reaching the left discharge hole
Is arranged in the continuous casting immersion nozzle, the shape of the bottom portion 12 is an upward convex shape, and the slit width W [m
m] and a slit height h [mm] satisfying a relationship of 2 ≦ h / W ≦ 10. (2) A dipping nozzle for casting a molten metal 1 into a mold. In the immersion nozzle 2, a left discharge hole 4 and a right discharge hole 3 are arranged at a lower portion of a side wall of the immersion nozzle at positions symmetrical with respect to the center of the nozzle cross section. In the continuous casting immersion nozzle having one slit 5 reaching the left discharge hole at the end, the discharge hole diameter d [mm] and the slit width W
[3] An immersion nozzle for continuous casting, wherein [mm] satisfies the relationship of 0.1 ≦ W / d ≦ 0.5, and (3) an immersion nozzle 2 for casting the molten metal 1 into a mold. At the bottom of the side wall of the immersion nozzle, a left discharge hole 4 and a right discharge hole 3 are arranged symmetrically with respect to the center of the nozzle cross section. In the continuous casting immersion nozzle provided with one slit 5 reaching the hole, the discharge hole diameter d [mm] and the slit width W [m
m] satisfies the following relationship: 0.1 ≦ W / d ≦ 0.5. (1) A gas injection hole is provided in the immersion nozzle 2 for the continuous casting according to (1). (1)-characterized in that
An immersion nozzle for continuous casting according to (3). Also,
(5) A continuous casting method for steel, characterized by casting using the continuous casting immersion nozzle according to any one of (1) to (4), and (6) the method according to (4). A continuous casting method for steel, wherein an inert gas is blown into the immersion nozzle for casting using the continuous casting immersion nozzle.

The shape of the discharge hole may be elliptical or the like in addition to the circle. The equivalent diameter of the discharge hole is the diameter of a circle having the same area as the area of the discharge hole.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of an immersion nozzle according to the present invention, and FIG. 1 (a) is a view showing a cross section of a lower portion of the immersion nozzle by a horizontal plane. FIG. 1B is an explanatory view of a vertical section taken along a vertical plane parallel to the slit 5. FIG.
FIG. 4C is an explanatory view of a vertical section taken by a vertical roll perpendicular to the slit 5. In the figure, d is the discharge hole diameter [mm], and W
Is a slit width [mm], and h is a slit height [mm]. The shape of the bottom of the immersion nozzle according to the present invention is convex upward, but may be a shape such as a chevron above.

The present inventors performed continuous casting using a conventional type of immersion nozzle shown in FIG. 9 in which the inner surface shape of the immersion nozzle bottom 12 was hemispherical, and observed the inner surface of the bottom after completion of the casting. FIG. 8 is an explanatory view showing that a large amount of deposits 13 were generated on the inner surface of the hemispherical bottom. The deposit 13 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. In addition, this deposit 13
This also occurred when continuous casting was performed by blowing an inert gas into the molten steel in the immersion nozzle.

[0011] Based on this finding, the present inventors based on FIG.
A test nozzle having the same shape as the above was made of a transparent plastic, immersed in a water tank, an inert gas was introduced from above, and the behavior of bubbles of the inert gas was investigated. According to this water model test, the bubbles of the inert gas are mainly
In addition, almost no inert gas bubbles flowed out of the left discharge hole 4 and flowed out of the slit 5.

From these results, it is considered that, for example, if the shape of the immersion nozzle is changed to increase the amount of the inert gas bubble discharged from the slit 5, the deposit 13 shown in FIG. 8 is also reduced. They manufactured the test nozzle shown in FIG. 1 and performed the same water model test as described above. At this time, the shape of the bottom portion is as shown in FIGS. 2A and 2B, and the slit height h [mm] and the slit width W are used.
[Mm] was changed variously, and the test was performed. FIG. 3 shows the ratio (h / h) of the slit height h [mm] to the slit width W [mm].
The relationship between W) and the number of bubbles discharged from the slit 5 is shown. h / W is 2.0 or more and 10.0 or less and slit 5
It is considered that the number of bubbles discharged from the nozzle is increased, and that the h / W is set in this range, it is possible to prevent the slit 5 from being closed. Incidentally, in the conventional immersion nozzle shown in FIG. 9, h / W was 1.5.

Based on the results of the water model test, the present inventors have proposed a dip nozzle having a hemispherical bottom and an h / W of 1.5 as shown in FIG. 9 and a dip nozzle having the shape shown in FIG. The width W is 15-30 [mm] and the h / W is 1.0 to 1
Ten pieces each of which was changed to 5.0 were manufactured, and argon gas was blown into the immersion nozzle as an inert gas at a rate of 5 [L / min] in continuous casting of ordinary molten steel, and a carbon concentration of 30 ppm was used. Ultra low carbon steel 125
0t was cast. After casting, slit 5 of the immersion nozzle
Obstruction was observed. FIG. 4 shows the types of immersion nozzles,
The relationship between the number of closed lines is shown. As a result, in the conventional immersion nozzle having a hemispherical bottom as shown in FIG. 9, there were seven nozzles in which the slits 5 were obstructed, and the remaining slits were thin. In the immersion nozzle having the shape shown in FIG.
Is 2.0 or more and 10.0 or less, the ratio of the number of the slits 5 closed is 5 or less, and none of the slits 5 is closed in the range of 2.5 to 8.0. Therefore, the slit width W [m
m] and slit height h [mm] are 2.0 ≦ h / W ≦ 1
0.0 must be satisfied, and preferably 2.5 ≦ h / W ≦ 8.0.

The conventional immersion nozzle shown in FIG. 9 has a semicircular bottom inner surface shape, whereas the immersion nozzle of the shape shown in FIG. This is because bubbles are more likely to reach the slit portion by eliminating the stagnation portion of the molten metal at the nozzle bottom.

Next, the present inventors made an immersion nozzle having the shape shown in FIG. 1 from a transparent plastic, immersed it in a water tank, supplied water to the inside, and set the discharge hole diameter d [mm]. The right discharge hole 3 at that time by changing the slit width W [mm]
And the flow velocity of the water flowing out of the left discharge hole 4 was measured, and the drift phenomenon was evaluated. The drift phenomenon is based on the absolute value of the difference between the flow velocity of the water flowing out of the right discharge hole 3 and the flow velocity of the water flowing out of the left discharge hole 4. Was evaluated by the value (deviation index) divided by the sum of the flow velocities. FIG. 5 shows the ratio of the discharge hole diameter d to the slit width W (W /
The relation between d) and the drift index is shown. W / d of 0.1 or more,
It is understood that the drift phenomenon can be suppressed by setting it to 0.5 or less. By the way, in the conventional immersion nozzle shown in FIG. 9, W / d was 0.3.

Based on the results of the water model test, the present inventors have found that the immersion nozzle having the shape shown in FIG. 1 has a slit width W of 15-30 [mm] and h / W of 3.0. ,
Those with W / d varied from 0.05 to 0.8 were manufactured, and 5 [L / min] of argon gas was used as an inert gas in the immersion nozzle in normal continuous casting of molten steel.
Was used while being blown in at a rate of 1250 t to cast 1250 t of ultra-low carbon steel having a carbon concentration of 30 ppm. The obtained slab was hot-rolled and cold-rolled by a conventional method, and the number of surface defects of the cold-rolled steel sheet was measured. FIG. 6 shows the ratio of the discharge hole diameter d to the slit width W (W /
The relation between d) and the number of surface defects is shown. As a result, the number of defects considered to have occurred due to the drift phenomenon was W / d of 0.1.
As described above, although it decreases at 0.5 or less, W / d is 0.2 or more,
At 0.4 or less, it was further reduced. Therefore, the discharge hole diameter d [mm] and the slit width W [mm] are 0.1 ≦ W / d ≦
The relationship 0.5 must be satisfied, and preferably the relationship 0.2 ≦ W / d ≦ 0.4.

[0017]

According to the immersion nozzle of the present invention, it is possible to sufficiently prevent the slit from being closed during casting by determining the discharge hole diameter, the slit width, and the slit height to appropriate levels, and Continuous casting can be performed while reducing surface defects due to the drift phenomenon.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an example of an immersion nozzle of the present invention,
(A) is an explanatory view of a cross section by a horizontal plane below the immersion nozzle, (b) is an explanatory view of a vertical section taken by a vertical plane parallel to the slit 5, (c) is a vertical view perpendicular to the slit 5 It is explanatory drawing of the longitudinal cross section by surface rolling.

2A and 2B are diagrams illustrating the shape of the bottom of a nozzle used in a water model experiment, wherein FIG. 2A is a diagram of a submerged nozzle having a flat bottom, and FIG. 2B is a diagram of a submerged nozzle having a curved bottom. .

FIG. 3 shows the ratio of the slit height h to the slit width W (h / W).
FIG. 7 is a diagram showing a relationship between the number of bubbles discharged from the slit 5 and the number of bubbles.

FIG. 4 is a diagram showing the relationship between the type of immersion nozzle and the number of closed slits 5;

FIG. 5 shows the ratio (W / d) between the discharge hole diameter d and the slit width W;
It is a figure which shows the relationship of a drift index.

FIG. 6 shows the ratio (W / d) between the discharge hole diameter d and the slit width W;
It is a figure which shows the relationship of the number of surface defects.

FIG. 7 is a schematic view showing a conventional immersion nozzle and a flow of molten steel flowing out.

FIG. 8 shows deposits on the inner surface of the bottom after use of a conventional immersion nozzle.

FIG. 9 is a side 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 steel, 2: immersion nozzle, 3: right discharge hole, 4: left discharge hole, 5: slit, 6: molten steel flow from the discharge hole, 7: molten steel in the immersion nozzle, 8: ascending flow near the side wall, 9: Downflow near the side wall, 10: Meniscus of molten steel in the mold, 11: Cast powder, 12: Bottom of immersion nozzle, 13: Deposit near the bottom of immersion nozzle, 14: Side wall

Continued on the front page (72) Inventor Takehiko Fuji 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation Technology Development Division (72) Inventor Eiichi Takeuchi 20-1 Shintomi Futtsu-shi Technology Development Nippon Steel Corporation Headquarters F term (reference) 4E004 FB06 HA01 4E014 DB04

Claims (6)

[Claims] 1. An immersion nozzle for casting a molten metal into a mold, wherein a left discharge hole and a right discharge hole are arranged at lower portions of side walls of the immersion nozzle at symmetrical positions with respect to the center of the nozzle cross section.
At the bottom, one end is in the right discharge hole, the other end is a continuous casting immersion nozzle in which one slit reaching the left discharge hole is arranged,
The shape of the bottom is upward and convex, and the slit width W
An immersion nozzle for continuous casting, wherein [mm] and a slit height h [mm] satisfy a relationship of 2 ≦ h / W ≦ 10. 2. An immersion nozzle for casting a molten metal into a mold, wherein a left discharge hole and a right discharge hole are arranged at lower portions of side walls of the immersion nozzle at symmetrical positions with respect to the center of the nozzle cross section.
At the bottom, one end is in the right discharge hole, the other end is a continuous casting immersion nozzle in which one slit reaching the left discharge hole is arranged,
An immersion nozzle for continuous casting, wherein a discharge hole diameter d [mm] and a slit width W [mm] satisfy a relationship of 0.1 ≦ W / d ≦ 0.5. 3. An immersion nozzle for pouring a molten metal into a mold, wherein a left discharge hole and a right discharge hole are arranged at lower portions of side walls of the immersion nozzle at symmetrical positions with respect to the center of the nozzle cross section.
At the bottom, one end is in the right discharge hole, the other end is a continuous casting immersion nozzle in which one slit reaching the left discharge hole is arranged,
2. The immersion nozzle for continuous casting according to claim 1, wherein the discharge hole diameter d [mm] and the slit width W [mm] satisfy a relationship of 0.1 ≦ W / d ≦ 0.5. 4. The immersion nozzle for continuous casting according to claim 1, wherein a gas blowing hole is provided in the immersion nozzle. 5. A continuous casting method for steel, comprising casting using the continuous casting immersion nozzle according to any one of claims 1 to 4. 6. A continuous casting method for steel, wherein an inert gas is blown into the immersion nozzle for casting using the immersion nozzle for continuous casting according to claim 4.