JPH0767603B2 - Immersion nozzle for continuous casting - Google Patents

Description

TECHNICAL FIELD The present invention relates to an immersion nozzle that suppresses adhesion and growth of inclusions on the inner wall of the immersion nozzle and prevents generation of defects due to oxide inclusions in continuous casting. It is a thing.

[Prior Art] The adhesion of inclusions to the inner wall of the immersion nozzle in continuous casting increases with the passage of time, not only restricting the operation time, but also deoxidizing products in molten steel of several microns coarsen, Often induces product defects. Regarding the adhesion to the inner wall of the immersion nozzle, the material of the immersion nozzle has a great influence, and, for example, the inclusion of inclusions is hardly recognized in the immersion nozzle made of fused silica. However, the molten siliceous dipping nozzle reacts with Mn in steel and melts, causing operational troubles and causing problems with the quality of the slab. Therefore, in general continuous casting of aluminum killed steel, an immersion nozzle made of alumina graphite or a combination material of alumina graphite and zirconia is used. When an alumina graphite immersion nozzle is used, the adhesion, sintering, and growth of oxide-based inclusions proceed rapidly, so by blowing argon gas as an inert gas into the immersion nozzle for cleaning,
This progress is suppressed. Furthermore, recently, the material of the immersion nozzle has been studied. For example, as a measure against thermal shock at the start of casting,
Although 30% of SiO ₂ is mixed, it becomes SiO ₂ (s) + C (s) → SiO (g) + CO (g) under a strong reducing atmosphere during casting, Si is gasified and this is in the steel. Becomes an oxygen source to
The material of the immersion nozzle is changed from SiO ₂ to SiC and carbon because it may generate inclusions and induce the adhesion and growth of inclusions. Alternatively, for zirconia-based immersion nozzles, recently, zirconia-based immersion nozzles are often used because of their low thermal conductivity and difficulty in adhering deoxidized products. FIG. 6 is a sectional view of a conventional immersion nozzle 1 passing through the centers of two discharge holes 2, and FIG. 6A is a plan sectional view of the immersion nozzle 1 passing through the centers of two discharge holes 2.
(B) is a vertical sectional view (AA ') of the immersion nozzle 1 passing through the centers of the two discharge holes 2 in (A) of FIG. 6, and (C) is the two discharges of (B) in FIG. A vertical cross section (BB ') of a vertical cross section (AA') of the immersion nozzle 1 passing through the center of the hole 2.
Is. The alumina adhesion thickness 4 on the inner wall side 3 of the molten metal flow passage 4 after the use of the immersion nozzle 1 is 40 mm from the upper end of the discharge hole 2 of the immersion nozzle 1 and the vertical sectional view A-A 'and the vertical sectional view B-
It was measured at B '. The results of using alumina graphite and zirconia as the material of the immersion nozzle 1 will be described. 7th
The figure is a graph showing the relationship between the casting time and the alumina adhesion thickness on the inner wall side of the molten metal flow passage after the use of the immersion nozzle. The ○ and △ marks are alumina graphite nozzles, and ● and ▲
The mark is a zirconia nozzle. The ◯ mark and the ● mark are vertical cross-sectional views AA ′ of the immersion nozzle 1, and the Δ marks and ▲ marks are vertical cross-sectional views BB ′ of the immersion nozzle 1. FIG. 8 is a graph showing the relationship between the in-pipe flow velocity in the nozzle and the alumina adhesion thickness on the inner wall side of the molten metal flow passage after the use of the immersion nozzle. The in-pipe flow velocity shown here is the average flow velocity obtained by dividing the molten metal passage amount (m ³ / sec) by the immersion nozzle internal cross-sectional area (m ² ). In FIG. 8, in the vertical sectional view AA ′ of the immersion nozzle 1, the alumina deposition thickness decreases due to the increase in the pipe flow velocity, but in the vertical sectional view BB ′, there is a clear correlation between the pipe flow velocity and the alumina deposition thickness. Can't be seen. The reason for this is that although the molten metal passage amount should increase and the flow velocity in the pipe should naturally increase, a vertical sectional view B- of the immersion nozzle 1
In the downstream region of B ', there is a deceleration region near the wall due to a sudden cross-sectional change due to the discharge hole, and since the flow velocity does not change with a slight increase in the amount of molten metal passing through, alumina in the molten metal is discharged from the flow and the deceleration region. This is because they entered and grew there. FIG. 9 is a graph showing the relationship between the amount of argon gas blown from the upper part of the immersion nozzle and the alumina adhesion thickness. As is clear from FIGS. 7, 8 and 9, in the longitudinal sectional view AA ′ of the discharge hole 2 of the immersion nozzle 1, the material of the immersion nozzle 1 is changed to zirconia, the flow velocity of the molten metal in the immersion nozzle 1 is increased. And the amount of argon gas blown from the upper part of the immersion nozzle is reduced, the alumina deposition thickness is reduced. On the other hand, in the vertical sectional view BB ′ of the discharge hole 2 of the immersion nozzle 1, Zirconia material, immersion nozzle 1
Even if the flow velocity of the molten metal in the inside is increased or the amount of argon gas blown from the upper part of the immersion nozzle is increased, the alumina adhesion thickness is hardly reduced, so that an unexpected defect often occurs in the product.

FIG. 10 is a cross-sectional view of a conventional immersion nozzle that passes through the centers of two discharge holes 2 and has a slit nozzle installed at the bottom.
(A) is a plane cutaway view of the immersion nozzle passing through the centers of the two discharge holes, and (b) is a vertical cross-sectional view (AA 'of FIG. 10) showing the immersion nozzle passing through the centers of the two discharge holes. ), (C) is the 10th
The vertical cross-sectional view (BB ') of the immersion nozzle passing through the centers of the two discharge holes in (B) of the drawing, which is taken at a right angle in the vertical cross-sectional view (AA').
FIG. As a countermeasure against this, a method of blowing argon gas into the molten metal through a slit nozzle 16 from the entire bottom surface 11 of the immersion nozzle 1 as shown in FIG.

[Problems to be Solved by the Invention] However, according to this method, although the alumina adhesion thickness of the vertical cross section (BB ') of the immersion nozzle 1 passing through the centers of both discharge holes 2 is reduced, such a wide range is achieved. A large amount of argon gas is required to blow the argon gas more uniformly from the region. In addition, it is necessary to blow argon gas from the upper part of the immersion nozzle 1 as described above (if the blowing is not carried out, alumina adheres at the upper part of the immersion nozzle 1).
The blowing amount is 6 to 10 Nl / min, and a total of 12 to 20 Nl / min is required. If the amount of blown-in argon gas is too large, surface defects such as slag slagging and blowing will occur. Fig. 11 shows an example in which a porous body is provided at the molten steel injection port in the upper tundish of the immersion nozzle 1 and argon gas is blown. In this case, a part of the amount of argon floats in the tundish, but 2 to 5 ton / FIG. 4 is a graph showing the relationship between the amount of argon gas blown into the molten metal and the number of blows on the surface of the slab when casting was performed at min. As is clear from this figure, the blow number increases in proportion to the blowing amount of the argon gas. Argon gas blowing amount 5N
When it was less than 1 / min, there was a problem that alumina adhered to the inside of the immersion nozzle 1 during casting and the nozzle was clogged.

The present invention has been made in view of such circumstances,
Norokami of slab, depending on the method of blowing argon gas
The purpose is to prevent alumina adhesion in the immersion nozzle without increasing surface defects such as blowing.

[Means and Actions for Solving the Problem] The immersion nozzle for continuous casting according to the present invention is a immersion nozzle for injecting the molten metal in a tundish into a mold, which is offset by 90 degrees from two discharge holes in the inner wall of the immersion nozzle body. A gas outflow portion provided at a position in the height range of 0 to +100 mm between the upper end level of the gas outflow portion and the upper end level of the discharge hole on the molten metal inlet side, and the gas connected to the gas outflow portion. It is characterized by comprising a flow passage and a gas supply means for supplying gas to the gas flow passage. In the above, the gas outflow portion is a portion in which a gas blown into the inner wall of the immersion nozzle or a gas permeable layer is provided.

And, the total gas blowing amount is not changed from 5 to 10 Nl / min, and it is shifted by 90 degrees from the two discharge holes of the immersion nozzle, and the gap between the gas outflow upper end level and the melt inlet side upper end level of the discharge hole is 0. Provide a gas outlet that is located in the +100 mm height range. Here, the reason why the interval between the upper end level of the gas outlet and the upper end level of the discharge hole on the molten metal inlet side is limited is
This is because when the thickness is less than 0 mm or more than 100 mm, the alumina adhesion thickness increases. As a result, it is possible to prevent alumina from adhering to the inner wall of the immersion nozzle without causing surface defects such as slagging and blow of the slab.

[Embodiment] An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view of an immersion nozzle according to an embodiment of the present invention, (a) is a plan sectional view including two gas outflow parts for blowing in argon, and (b) is the two sectional views of (a) of FIG. A vertical sectional view (A-A ') of the immersion nozzle passing through the center of the discharge hole,
(C) is a view showing a vertical cross-sectional view (BB ') in the direction perpendicular to the vertical cross-sectional view (AA') of the immersion nozzle passing through the centers of the two discharge holes in (b) of FIG. . Reference numeral 1 is an immersion nozzle, 2 is a discharge hole, 11 is the bottom of the immersion nozzle, 12 is a gas outlet, 13 is a gas flow passage, 14 is a gas supply pipe, and 15 is a gas supply means.

The discharge hole 2 of the immersion nozzle 1 has a round shape, and has a pool shape at the bottom of the immersion nozzle. The immersion nozzle 1 is made of a refractory material, and has two discharge holes 2 facing each other at the bottom thereof. Argon gas is introduced from the gas supply means 15 into the gas flow passage 13 through the gas supply connection pipe 14, and the argon gas is discharged from the gas flow outlet portion 12 connected to the gas flow passage 13.

(Example 1) Molten metal was supplied to a submerged nozzle 1 from a tundish (not shown), and a mold (not shown) was provided from two discharge holes 2 facing each other.
Injected inside. Then, when an argon gas of about 2 Nl / min is supplied from the gas supply means 15, it is guided to the gas flow passage 13 through the gas supply connection pipe 14 and further connected to the gas outflow portion 12. Bubbles are blown into the molten metal from the two gas outflow portions 12 on the inner wall of the immersion nozzle 1. At this time, from the conventional argon blowing position and from the tundish inlet,
Argon of 5 to 8 Nl / min is blown in to prevent the thickness of alumina adhered to the inner wall over the upper part of the immersion nozzle 1. The total flow rate of argon blown into the melt of the nozzle is 5
Since it is up to 10 Nl / min, it is possible to prevent the alumina adhesion thickness in the vicinity of the gas outflow portion 12 without increasing the number of blows on the surface of the slab as shown in FIG. The range of the gas outlet 12 is 30 mm ×
It is 100 mm. The diameter of the discharge hole is 800Φ.

Regarding the blowing position of the gas outflow portion 12, the upper end level of the gas outflow portion 12 of the nozzle and the upper end level of the discharge hole 2 were set to the same level.

As a result, the alumina adhesion thickness was reduced to 1/3.

(Example 2) Next, the blowing position of the gas outflow portion was changed and the relationship of the alumina adhesion thickness was investigated. The interval between the upper end of the discharge hole on the molten metal inlet side and the upper end of the gas outflow portion was changed within the range of −30 to +150 mm in the height direction. FIG. 2 is a sectional view of the immersion nozzle showing a level in which the blowing position of the gas outflow portion is changed.
In (a), the distance between the upper end of the gas outlet 12 of the nozzle and the upper end of the discharge hole 2 is 30 mm downward. (B) is the same level as the upper end of the gas outlet 12 of the nozzle and the upper end of the discharge hole 2. In (c), the distance between the upper end level of the gas outlet 12 of the nozzle and the upper end level of the discharge hole 2 is 30 mm upward. In (d), the distance between the upper end level of the gas outlet 12 of the nozzle and the upper end level of the discharge hole 2 is 100 mm upward. (E) shows that the distance between the upper end level of the gas outlet 12 of the nozzle and the upper end level of the discharge hole 2 is 150 mm above.

FIG. 3 is a graph showing the relationship between the difference in the blowing position of the gas outflow portion shown in FIG. 2 and the alumina adhesion thickness. As is clear from this figure, when the distance between the upper end level of the discharge hole on the molten metal inlet side and the upper end level of the gas outlet portion is in the range of −0 to +100 mm in the height direction, the alumina adhesion thickness is small.

The reason for this will be described with reference to FIGS. 4 and 5. FIG. 4 is a sectional view of a conventional immersion nozzle, (a) is a plan sectional view of the immersion nozzle, and (b) is a vertical sectional view taken along line XX ′ of (a) of FIG. In FIG. 4 (a), the circles indicate the flow velocity in the pipe in the discharge hole direction (XX-X '), and the triangles indicate the direction shifted by 90 degrees from the discharge hole (Y-).
Y ') is the flow velocity in the pipe. The measurement points of the in-pipe flow velocity are a and e for the vicinity of the inner wall of the immersion nozzle, c for the center of the immersion nozzle, and b and d for the vicinity of the inner wall of the immersion nozzle and the center of the immersion nozzle. The straight line AA ′ in FIG. 4B is the upper end of the discharge hole 2, and the straight line BB ′ is 30 mm from the upper end of the discharge hole 2.
In this position, the straight line C-C 'is 150 mm from the upper end of the discharge hole 2. FIG. 5 is a graph showing the relationship of the flow velocity distribution in the pipe for each measurement position in FIG. (A) of FIG.
Is the flow velocity distribution in the pipe of the straight line AA 'in FIG. 4 (b), and FIG. 5 (b) is the flow velocity distribution in the pipe of the straight line BB' in FIG. 4 (b). (C) is the straight line C- in FIG.
It is a flow velocity distribution in the pipe of C'section. As is clear from this figure, the flow velocity in the pipe in the discharge hole direction (XX ′) is straight line A−.
Although it does not change much at A ', straight line BB', and straight line CC ', the flow velocity distribution in the pipe in the direction (Y-Y') deviated by 90 degrees from the discharge hole is shown in Figs. The flow distribution state has a deceleration region as shown by a dotted line in a part shown in b). This becomes remarkable when the distance from the upper end (inside) of the discharge hole is 30 mm or less. On top of that, a flow distribution state as shown in FIG.
Therefore, it is effective to blow gas into the range and clean the side wall to prevent the adhesion of alumina.

That is, when the interval between the upper end level of the discharge hole on the molten metal inlet side and the upper end level of the gas outlet portion is in the range of −0 to +100 mm in the height direction, the alumina adhesion thickness is small.

As a result, the alumina deposition thickness was reduced to 1/3 to 1/5.

[Effects of the Invention] According to the present invention, the gap between the upper end level of the melt inlet side and the upper end level of the gas outflow portion of the discharge holes is 0 degrees, which is offset by 90 degrees from the two discharge holes. Since argon flows from the gas outlet provided in a position in the height direction of up to +100 mm, the stagnation of that portion is eliminated and the alumina adhesion thickness is reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an immersion nozzle according to an embodiment of the present invention, FIG. 2 is a sectional view of the immersion nozzle showing a level in which the blowing position of the gas outflow portion is changed, and FIG. 3 is shown in FIG. FIG. 4 is a graph showing the relationship between the difference in the blowing position of the gas outflow portion and the thickness of the deposited alumina, FIG. 4 is a cross-sectional view of a conventional immersion nozzle, and FIG. 5 shows the relationship of the flow velocity distribution inside the pipe for each measurement position in FIG. FIG. 6 is a cross-sectional view of a conventional immersion nozzle that passes through the centers of two discharge holes, and FIG. 7 shows the relationship between the casting time and the alumina deposition thickness on the inner wall side of the molten metal flow passage after the immersion nozzle is used. Fig. 8 is a graph showing the relationship between the flow velocity in the nozzle and the thickness of the alumina deposit on the inner wall of the molten metal flow passage after the immersion nozzle is used. Fig. 9 is the amount of argon gas blown from the upper part of the immersion nozzle. Graph showing the relationship between the thickness and the alumina adhesion thickness Fig. 10 is a cross-sectional view of a conventional immersion nozzle that passes through the center of two discharge holes, with a slit nozzle installed at the bottom, and Fig. 11 shows argon gas from the molten steel injection port in the upper tundish of the immersion nozzle to melt argon gas. It is a graph which shows the relationship between the blow-in amount and the number of blows on the surface of the slab. 1 ... Immersion nozzle, 2 ... Discharge hole, 11 ... Bottom of immersion nozzle, 12 ... Gas outflow part, 13 ... Gas flow passage, 14 ... Gas supply connection pipe, 15 ... Gas supply means.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takashi Mori Marunouchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Issei Okimoto 1-21-2 Marunouchi Chiyoda-ku, Tokyo Yukio Numasawa (56) References Japanese Steel Pipe Co., Ltd. References JP 59-47053 (JP, A) JP 59-190456 (JP, U)

Claims (1)

[Claims] 1. A submerged nozzle for injecting the molten metal in a tundish into a mold, which is offset by 90 degrees from the two discharge holes in the inner wall of the main body of the immersion nozzle, and has a gas outflow upper end level and a melt inlet side upper end. A gas outflow portion provided at a position in a height range of 0 to +100 mm, a gas flow passage connected to the gas outflow portion, and a gas supply for supplying gas to the gas flow passage. Means, and the gas outflow means is not provided in the peripheral surface other portion at the height position of the inner wall where the gas outflow portion is provided, the immersion nozzle for continuous casting.