JP4221976B2 - Flow control weir of molten metal in tundish - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flow control weir for molten metal in a tundish, which is used for obtaining a continuously cast slab having a particularly high cleanliness in continuous casting of molten metal.
[0002]
[Prior art]
In order to obtain a highly clean slab when continuously casting molten metal, for example, molten steel, a so-called “short circuit flow” in which the molten steel injected into the tundish reaches the mold through the shortest distance. Suppression is considered important. 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.
[0003]
In order to deal with this problem, it is common practice to install an obstacle that hinders short-circuit flow, a so-called lower weir, at the bottom of the tundish. With this lower weir, the molten steel injected from the molten steel pan can be guided to the upper part of 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.
[0004]
In addition to suppressing the short-circuit flow, it is also important to suppress the “high-speed flow” of the molten steel in the tundish in order to obtain a slab having a high cleanliness. That is, if there is a high-speed flow, sufficient time is not obtained until the molten steel injected into the tundish flows into the mold, so that the time for impurities such as non-metallic inclusions existing in the molten steel to float and separate As a result, the molten steel flows into the mold without sufficient impurity removal. In addition, high-speed flow can cause slag and metal turbulence, which can encourage slag entrainment in the molten steel. Therefore, it is also important to suppress this high-speed flow of molten steel.
[0005]
Here, it could not be said that the lower weir installed at the bottom of the tundish had a sufficient effect for suppressing the high-speed flow of molten steel. This is because, by guiding the molten steel injected from the molten steel pan to the upper part in the tundish, a high-speed flow is generated at the slag and metal interface, and as a result, a high-speed circulation flow is generated in the entire tundish. It is.
[0006]
As described above, conventionally, it is difficult to say that the short-circuit flow and the high-speed flow in the tundish are sufficiently suppressed, and the separation of impurities such as non-metallic inclusions in the molten steel is insufficient. there were.
[0007]
On the other hand, Patent Document 1 discloses a collision pad used in a tundish that is designed to suppress turbulent flow of molten metal 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 .
[0008]
This impact pad is intended to redirect the flow of molten metal injected into the tundish back to the incoming flow, decelerating the opposing flows and thereby minimizing turbulence in the tundish And to suppress high-speed flow.
[0009]
However, in the tundish internal collision pad disclosed in the above publication, the outer side wall is endless, so the attenuation of the injection flow from the molten steel pan 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]
Further, since the outer side wall is endless and the internal space is closed, when the supply of the molten metal into the tundish is finished or temporarily stopped, the molten metal is left in the internal space. Since the molten metal solidifies as it is, the collision pad must be recovered. As a result, the collision pad is likely to be disposable.
[0011]
[Patent Document 1]
Japanese Patent No. 2836966
[Problems to be solved by the invention]
Therefore, the present invention advantageously solves the above problem, and appropriately controls the attenuation of the molten metal flow injected into the tundish for each direction of the flow to optimize the molten metal flow in the tundish. By controlling the molten metal in the tundish, the short-circuit flow and high-speed flow of the molten metal in the tundish can be suppressed, and the floating separation of the molten metal in the tundish can be promoted. The purpose is to propose.
[0013]
[Means for Solving the Problems]
This invention is a flow control weir for molten metal in a tundish, which is installed at a portion where a molten metal flow injected from a ladle into a tundish for continuous casting collides with the bottom of the tundish,
A wall (excluding those having through holes) extending upward from the bottom of the tundish only relative to the molten metal flow from directly below the supply nozzle for supplying the molten metal from the molten metal pan to the tundish toward the tundish nozzle And a flow control weir for molten metal in the tundish, characterized by having a hook-shaped portion extending from the upper end of the wall toward the molten metal flow.
[0014]
Here, it is preferable that the height h of the weir wall and the width d of the bowl-shaped portion have a relationship satisfying the following formula.
Record
0.1 ≦ d / h ≦ 1.0
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the flow control weir of the present invention will be specifically described with reference to the drawings. FIG. 1 shows an example in which a flow control weir (hereinafter simply referred to as a weir) according to the present invention is arranged in a tundish, and FIG. 2 shows an example in which a collision weir described in Patent Document 1 is arranged at the same position. Indicates.
[0016]
1 and 2, reference numeral 1 is a molten steel pan, 2 is a tundish, 2a is a tundish nozzle, 3 is a molten steel in the tundish, 4 is a molten steel surface of the molten steel in the tundish, and 5 is a continuous casting mold. . FIG. 1 shows that the weir 6 of the present invention is disposed between the bottom of the tundish 2 and the tundish nozzle 2a between the bottom of the supply nozzle 1a for guiding the molten steel 3 from the molten steel pan 1 and the supply nozzle 1a. The molten steel injection flow 7 is converted into flows 8a, 8b, 9a and 9b by the weir 6. That is, 8a and 8b show the flow along the tundish long side, and 9a and 9b show the flow along the tundish short side, respectively.
[0017]
Here, as shown in FIG. 3, the weir 6 surrounds a collision portion of the molten steel flow and extends upward from the bottom of the tundish 2, and a hook-like portion 61 extending toward the injection flow 7 of the wall 60. It has.
[0018]
Now, after the injection flow 7 from the molten steel pan 1 collides with the bottom of the tundish 2, it changes into a flow along the bottom. This molten steel flow collides with the inside of the wall 60 of the weir 6 and further interferes with the injected flow 7 from the molten steel pan 1 by the hook-like portion 61 extending from the upper end of the wall 60 to the molten steel flow of the wall 60 in parallel with the bottom of the tundish 2. You are guided in the direction you want. Due to the interference with the injected flow 7, the molten steel flow induced by the weir 6 becomes a flow 8a whose initial momentum is attenuated.
[0019]
On the other hand, in FIG. 2, the collision pad 10 described in Patent Document 1 is disposed at the same position as in FIG. 1, and the molten steel injection flow 7 from the supply nozzle 1 a flows into the flows 11 a, 11 b, The state converted into 12a and 12b is shown. The flows 11a and 11b are flows in the direction along the tundish length, and the flows 12a and 12b are flows in a direction perpendicular to the tundish length direction.
Also in this case, as in the case of the present invention shown in FIG. 1, the injection flow 7 from the molten steel pan 1 collides with the bottom of the collision pad 10, then changes to a flow along the bottom, and then the collision pad 10. As a result, the molten steel flow is guided in a direction interfering with the pouring flow 7 from the molten steel pan 1 by the hook-shaped protruding portion at the upper end of the side wall. As a result, the molten steel flow is flow 11a, 11b whose initial momentum is attenuated. , 12a and 12b.
[0020]
However, in this conventional collision pad 10, since the flows 11a, 11b, 12a and 12b are subjected to the same attenuation, they are unnecessarily attenuated to the flows 11b, 12a and 12b which are not originally a problem. For this reason, the attenuation of the flow 11a toward the tundish nozzle 2a, which is essentially important, was insufficient.
[0021]
On the other hand, in the weir 6 of the present invention, the flow 8b, 9a and 9b other than toward the tundish nozzle 2a is generated by not providing the hook-shaped portion on the side opposite to the direction other than toward the tundish nozzle 2a. Prevented more than necessary attenuation. As a result, the attenuation in the flows 8b, 9a and 9b other than toward the tundish nozzle 2a which is not originally a problem is suppressed, and the flow 8a toward the tundish nozzle 2a which has been a problem is sufficiently attenuated. Thus, the molten steel flow that finally leads from the molten steel injection flow 7 to the mold 5 is sufficiently damped. Further, the flows 8b, 9a and 9b other than toward the tundish nozzle 2a become an upward flow along the inner wall of the tundish and contribute to promoting the floating separation of impurities by guiding the molten steel to the molten metal surface 4.
[0022]
Thus, by using the weir of the present invention, the short-circuit flow and the high-speed flow are suppressed, and it becomes possible to obtain a molten steel flow in the tundish for obtaining a slab having a high cleanliness.
[0023]
Here, it is preferable that the height h of the weir 6 and the width d of the bowl-shaped portion 61 satisfy the following expression based on the upstream side wall shape of the weir as shown in FIG. .
0.1 ≦ d / h ≦ 1.0
[0024]
That is, when d / h is less than 0.1, there is almost no effect of providing the hook-like portion 61, and the damping effect of the flow 10 toward the tundish nozzle 2a may be inferior. On the other hand, when d / h is> 1.0, the flow along the bottom surface of the tundish does not sufficiently enter the space formed by the upstream side wall and the hook-like portion of the weir 6, and a stagnation portion of the flow is generated. This is not preferable because it is not fully utilized.
[0025]
Further, the height h from the bottom surface of the weir to the bowl-shaped portion shown in FIG. 3 is preferably 30 mm or more. This is because when the length is less than 30 mm, the flow along the bottom surface of the tundish 2 was not able to secure sufficient space for being guided to the injection flow 7 by the upstream side wall of the weir 6 and the bowl-shaped portion 61. This is because the attenuation effect due to the interference between the flow and the injection flow 7 cannot be obtained.
[0026]
Moreover, as shown in FIG. 4, it is also possible to make the inner side of the bowl-shaped part 61 from the wall 60 of the weir 6 continue with a curved surface. At this time, as the curved surface to be applied, it is advantageous from the viewpoint of the production surface of the weir 6 and the durability that the curved surface conforms to the radius of curvature corresponding to the width d of the bowl-shaped portion 61.
[0027]
As described above, the application of the weir 6 of the present invention to the one-strand type tundish has been illustrated, but for example, as shown in FIG. 5, it is also possible to apply to the two-strand type tundish. The effect of the weir 6 at that time is as described above.
[0028]
【Example】
Using the weir 6 shown in FIG. 1, a continuous cast slab was manufactured under the following conditions.
<Basic conditions>
・ Tundish capacity: 20ton
-Number of strands: 1 strand-Molten steel injection speed: 2.2 ton / min
・ Tundish shape: Bottom width 0.8 m, molten steel depth 1.0 m
<Execution conditions of this invention>
d: 80mm
h: 200 mm
d / h = 0.4
[0029]
Further, as Comparative Example 1 according to the prior art, a continuous cast slab was manufactured under the basic conditions described above using the pad shown in FIG.
Furthermore, as Comparative Example 2 out of the preferred conditions, a continuous cast slab was manufactured using the weir shown in FIG. 6 under the basic conditions described above. That is, the weir 13 shown in FIG. 6 does not have a hook-like portion.
[0030]
Here, reference numeral 14a in FIG. 6 is a flow toward the tundish nozzle 2a, and similarly reference numerals 14b, 15a and 15b are other flows.
<Execution conditions of Comparative Example 2>
The specifications of the weir used in Comparative Example 2 are as follows.
d: 0 mm
h ': 300 mm
d / h ′ = 0
[0031]
The results obtained by examining the occurrence rate of defects in the cold-rolled coil due to inclusions were obtained by hot-rolling and cold-rolling continuous cast slabs obtained according to the invention examples and comparative examples 1 and 2. As shown in FIG.
Here, the defect occurrence rate is expressed in% of the total length of defects caused by inclusions with respect to the total length of the cold-rolled coil.
As shown in the figure, in comparison with Comparative Example 1, the inventive example was able to significantly reduce product defects caused by inclusions.
Moreover, in the comparative example 2, the product defect resulting from the inclusion increased significantly compared with the invention example, indicating that the scope of the present invention is appropriate.
[0032]
【The invention's effect】
Thus, according to the present invention, the short-circuit flow and the high-speed flow in the tundish are suppressed, and product defects caused by inclusions can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a view showing a preferred example of a tundish weir according to the present invention.
FIG. 2 is a view showing a conventional collision weir.
FIG. 3 is a view showing a tundish weir according to the present invention.
FIG. 4 is a view showing a tundish weir according to the present invention.
FIG. 5 is a view showing a tundish weir according to the present invention.
FIG. 6 is a diagram showing a comparative example of a tundish weir.
FIG. 7 is a diagram showing a comparison of defect rates of continuous cast slabs when continuous casting is performed using each weir.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Molten ladle 2 Tundish 2a Tundish nozzle 3 Molten steel in tundish 4 Molten surface of molten steel in tundish 5 Mold 6 Weir 7 Injection flow from molten ladle
8a Flow of molten steel
8b Flow of molten steel
9a Flow of molten steel
9b Molten steel flow
10 collision pads
11a Flow of molten steel
11b Flow of molten steel
12a Flow of molten steel
12b Flow of molten steel
13 weir
14a Flow of molten steel
14b Flow of molten steel
15a Flow of molten steel
15b Flow of molten steel

Claims (2)

A flow control weir for molten metal in the tundish, which is installed at a portion where the molten metal flow injected from the ladle into the tundish for continuous casting collides with the bottom of the tundish,
A wall (excluding those having through holes) extending upward from the bottom of the tundish only relative to the molten metal flow from directly below the supply nozzle for supplying the molten metal from the molten metal pan to the tundish toward the tundish nozzle And a flow control weir for molten metal in the tundish, characterized by having a hook-shaped portion extending from the upper end of the wall toward the molten metal flow. 2. The flow control weir for molten metal in a tundish according to claim 1, wherein the height h of the weir wall and the width d of the bowl-shaped portion satisfy the following formula.
0.1 ≦ d / h ≦ 1.0

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