JP7099129B2 - Carbon steel thin-walled slab manufacturing equipment, carbon steel thin-walled slab manufacturing method - Google Patents

Description

The present invention relates to a carbon steel thin-walled slab manufacturing apparatus, a carbon steel thin-walled slab manufacturing method, and a carbon steel thin-walled slab.

From the viewpoint of process saving and energy saving, a technique for manufacturing a thin plate close to the final product at the casting stage, that is, near net shape continuous casting is being developed. Of these, Patent Document 1 discloses a double-roll (also referred to as double-drum) type continuous casting method as a promising thin plate-based near-net shape continuous casting. In continuous casting of thin-walled slabs using a twin-roll continuous casting device, molten steel is immersed in a molten steel pool 10 partitioned by a pair of casting rolls 1 rotating in opposite directions as shown in FIG. The thin-walled slab 13 is cast by supplying it from the discharge hole 3.

The solidification structure of low-carbon steel thin-walled slabs cast by the double-roll continuous casting method consists of columnar crystals that grow straight up to the inside of the slabs. The morphology of the solidified structure is strongly influenced by the C concentration in the molten steel and the temperature gradient of the solid-liquid interface during solidification. The larger the value, the easier it is for columnar crystals to grow. Thin-walled slabs with a thickness of several mm manufactured by the double-roll continuous casting method are cold-rolled to the final plate thickness, but unlike the conventional continuous-cast slabs cast with a thickness of about 250 mm, the rolling reduction is large. Cannot be secured. As a result, the direction of solidification structure growth remains on the final thin steel sheet and appears as anisotropy during processing. For example, when deep drawing is performed during can manufacturing, peaks and valleys alternate in the circumferential direction of the can. Then, so-called earrings occur. If these earrings are large, the yield of cans will decrease, and the earrings will come into contact with the mold, leading to can making troubles. At present, it cannot be applied to various applications.

The anisotropy of the thin steel sheet manufactured by the double-roll continuous casting method is due to the columnar crystal structure developed by quenching and solidifying the low-carbon molten steel. Based on this anisotropy expression mechanism, equiaxed crystallization of the solidified structure of low carbon steel is effective in reducing anisotropy.

Depending on the steel type cast by the twin-roll continuous casting method, it is easy to obtain an equiaxed crystal structure without any measures, but the equiaxed crystals generated without positive control are coarse, even if Even if axial crystals are generated, central segregation and porosity are likely to occur.

It has been reported that the method of equiaxed crystallization in the bi-roll continuous casting method is mainly due to the effect of inoculation. In Patent Document 2, Mg is added to low carbon molten steel to modify at least the surface layer of alumina inclusions and titania inclusions into magnesia or alumina magnesia spinel, and these inclusions are used as nuclei for equiaxed crystal formation. A method of equiaxed crystallization of a solidified structure by a twin-roll continuous casting method is disclosed by utilizing it. Further, Patent Document 3 discloses a method for achieving equiaxed crystallization by adding Ti when producing martensitic stainless steel by a double-roll type thin plate casting process.

Patent Document 4 discloses a continuous casting apparatus including a vibrator for applying ultrasonic waves to a solidified surface of a metal in a continuous casting mold. The purpose is to miniaturize the dendrites on the solidified surface by ultrasonic waves. The vibrator has an ultrasonic wave transmitting portion and a dipping portion, and the tip of the dipping portion is arranged at a position within 20 mm from the solidification surface. Further, Patent Document 5 discloses a continuous metal casting method in which ultrasonic vibration is applied to a mold copper plate from the inner surface of a mold during casting to prevent inclusions and bubbles from adhering to the initial solidification shell.

Non-Patent Document 1 discloses that solidified crystals can be finely granulated by applying ultrasonic vibration during solidification in a mold of an Al—Si alloy. In Non-Patent Document 2, when the Al—Si molten metal flows out from the nozzle and solidifies in the mold, an ultrasonic horn is arranged directly above the molten metal suction portion of the nozzle to generate cavitation, thereby causing primary crystal Si particles. It is stated that miniaturization can be achieved. Patent Document 3 describes that graphite in cast iron becomes finer by applying ultrasonic vibration when solidifying cast iron in a mold.

Japanese Unexamined Patent Publication No. 60-137562 Japanese Unexamined Patent Publication No. 2017-131933 Special Table 2013-512347 Gazette Japanese Unexamined Patent Publication No. 2011-212737 Japanese Unexamined Patent Publication No. 2001-25846

"Miniaturization of solidified structure by ultrasonic vibration" Foundry Engineering Vol. 72 (2000) No. 11 pp. 733-738 "Cavitation Phenomenon in Ultrasonic Casting and Its Industrial Use" Iron and Steel Vol. 102 (2016) No. 3, pp. 75-81 "Effects of ultrasonic vibration on solidification of cast iron and other structures" Casting Vol. 67 (1995) No. 5, pp. 325-330

As shown in FIG. 3, in the double-roll continuous casting method, it takes an extremely short time from the start of formation of the solidification shell 12 on the surface of the casting roll 1 to the completion of solidification and the extraction as the thin-walled slab 13. It is not possible to secure the floating removal time of inclusions mixed in the molten metal. Therefore, in the method of performing the inoculation to realize equiaxed crystallization, there is a concern that the cleanliness of the molten steel may be deteriorated. In addition to the inoculation method, low-temperature casting and low-speed casting methods have also been proposed, but these methods have a problem that the nozzle is clogged during casting, the operation is unstable, and the productivity is lowered.

Conventionally, as described above, a technique for miniaturizing a solidified structure by applying ultrasonic vibration during solidification of a molten metal has been known. However, those described in Non-Patent Documents 1 to 3 relate to solidification of Al—Si metal (Non-Patent Document 1 and Non-Patent Document 2) and solidification of cast iron (Non-Patent Document 3), and are related to solidification of steel. It is not about continuous casting. Further, although those described in Patent Documents 4 and 5 relate to continuous casting of steel, Patent Document 4 arranges the tip of an ultrasonic transducer in the immediate vicinity of the solidification surface, and Patent Document 5 describes the mold itself. However, none of them can be applied to the production of carbon steel thin-walled slabs by the double-roll continuous casting method.

In the present invention, in order to solve the above problems in continuous casting by twin-roll type continuous casting, by using a method other than the inoculation method, fine equiaxed crystals are sufficiently formed in the thin-walled slab and operated. A carbon steel thin-walled slab manufacturing device, a carbon steel thin-walled slab manufacturing method, and a carbon steel thin-walled slab that can obtain a fine equiaxed crystal structure with excellent workability and formability while ensuring cleanliness. The purpose is to provide slabs.

That is, the gist of the present invention is as follows.
(1) An apparatus for producing thin-walled carbon steel slabs by double-roll continuous casting, in which molten steel is supplied from a dipping nozzle into a molten steel pool surrounded by twin rolls to perform casting.
A molten steel discharge hole is provided at a position on the side surface of the immersion nozzle to be immersed in the molten steel pool.
It has an ultrasonic oscillator, and the ultrasonic oscillator has an ultrasonic transmitter and a vibration transmission unit.
The ultrasonic vibrator is arranged in a space between the discharge hole and two straight lines drawn perpendicularly to the side surface of the immersion nozzle from both ends of the discharge hole in a plan view, and the vibration tip portion of the vibration transmission unit is provided. Is placed above the upper end of the discharge hole.
A carbon steel thin-walled slab manufacturing apparatus, wherein the vibration tip portion of the vibration transmission portion can be immersed in the molten steel of the molten steel pool.

(2) A method for manufacturing a carbon steel thin-walled slab using the carbon steel thin-walled slab manufacturing apparatus according to (1) above.
The molten steel is supplied from the immersion nozzle into the molten steel pool surrounded by the twin rolls, the vibration tip of the vibration transmission portion is immersed in the molten steel of the molten steel pool, and ultrasonic vibration is applied to the molten steel in the molten steel pool. A method for manufacturing a carbon steel thin-walled slab, which comprises continuously casting carbon steel thin-walled slabs .
(3) The carbon steel thin wall according to ( 2) above, wherein the ultrasonic transmitter of the ultrasonic transducer generates ultrasonic waves having a frequency of 18 to 25 kHz and an amplitude (pp) of 14 to 50 μm. Method of manufacturing slabs.

The present invention has an ultrasonic oscillator provided with an ultrasonic transmitter and a vibration transmission unit in a twin-roll type continuous casting, and the vibration tip of the vibration transmission unit is immersed in the molten steel of the molten steel pool to form molten steel. Exciting ultrasonic vibrations. As a result, it is possible to sufficiently form fine equiaxed crystals on the thin-walled slab, stabilize the operation, and obtain a fine equiaxed crystal structure having excellent workability and moldability while ensuring cleanliness.

It is a figure which shows an example of the manufacturing apparatus of the thin-walled slab of this invention, (A) is a side sectional view taken along the line AA, (B) (C) is a plan view. It is a figure which shows an example of the manufacturing apparatus of the thin-walled slab of this invention, (A) is a side sectional view taken along the line AA, (B) is a plan view. It is a figure which shows an example of the manufacturing apparatus of a thin-walled slab, (A) is a side sectional view taken along the line AA, (B) is a plan view.

In the continuous casting of double-roll type steel, which is the object of the present invention, as shown in FIG. 3, a region surrounded by a pair of casting rolls 1 (also referred to as a casting drum) and side dams 8 located at both ends thereof. The molten steel pool 10 is filled with molten steel, and the molten steel is supplied from the immersion nozzle 2 into the molten steel pool 10, a solidified shell 12 is formed on the surface of the casting roll, and the two casting rolls 1 are rotated in opposite directions. The thin-walled slab 13 is pulled downward from the gap 9 where the distance between the casting rolls of the book is the shortest. The molten steel is supplied into the molten steel pool 10 from the immersion nozzle 2.

1 (A) and 2 (A) are side sectional views of a double roll portion of a double roll type continuous casting, and FIGS. 1 (B) and 2 (B) are plan views. In FIGS. 1 (B) and 1 (C) and FIG. 2 (B), the surface 31 of the molten steel pool and the edges 32 of the molten steel pool around the surface 31 are shown. The edge 32 of the molten steel pool is located at the boundary between the molten steel pool surface 31 and the casting roll 1 and the boundary between the molten steel pool surface 31 and the side weir 8.

A molten steel discharge hole 3 is provided at a position of being immersed in the molten steel pool 10 on the side surface 20 of the immersion nozzle 2, and the molten steel supplied to the immersion nozzle 2 is discharged from the discharge hole 3 into the molten steel pool 10. The side surface 20 of the immersion nozzle 2 having the discharge hole 3 is arranged parallel to the rotation axis of the casting roll 1. When the molten steel discharge flow 14 discharged from the discharge hole 3 in the direction perpendicular to the side surface 20 reaches the side surface of the casting roll 1, it runs up the surface of the casting roll 1 from there, and when it reaches the vicinity of the molten steel pool surface 31, the molten steel flow 11 changes the flow direction to the left and right (axial direction of the casting roll 1), and forms a flow path that reverses when reaching the vicinity of the side dam 8 (see FIGS. 1 (A) and 3 (B)).

The present invention is intended for a manufacturing apparatus for manufacturing thin-walled slabs of carbon steel. The reason why carbon steel is targeted for casting is that it is conventionally difficult to stably generate fine equiaxed crystals in carbon steel, and the present invention exerts a great effect. Here, the carbon steel means a steel containing 0.001% or more and 0.6% or less of carbon. In particular, the present invention exerts a great effect on low carbon steel having a carbon concentration of 0.05% by mass or less.

The carbon steel thin-walled slab manufacturing apparatus of the present invention has an ultrasonic vibrator 4. The ultrasonic vibrator 4 has an ultrasonic transmitter 5 and a vibration transmission unit 6, and one end of the vibration transmission unit 6 is connected to the ultrasonic transmitter 5. The ultrasonic wave is transmitted by the ultrasonic transmitter 5, and the transmitted ultrasonic wave propagates in the vibration transmission unit 6 connected to the ultrasonic transmitter 5 and reaches the tip of the vibration transmission unit 6. The end portion of the vibration transmission portion 6 on the opposite side to the side connected to the ultrasonic transmitter 5 is the vibration tip portion 7. By immersing the vibration tip portion 7 in the molten steel of the molten steel pool 10, ultrasonic vibration can be excited in the molten steel at the tip of the vibration tip portion 7.

In the method for producing carbon steel thin-walled slabs using the carbon steel thin-walled slab manufacturing apparatus of the present invention, molten steel is supplied from a dipping nozzle 2 into a molten steel pool 10 surrounded by two casting rolls 1. The vibration tip portion 7 of the vibration transmission unit 6 is immersed in the molten steel of the molten steel pool 10, and ultrasonic vibration is applied to the molten steel in the molten steel pool 10.

When the vibration tip portion 7 of the vibration transmission unit 6 is immersed in the molten steel of the molten steel pool 10 and ultrasonic vibration is applied to the molten steel in the molten steel pool, cavitation is formed in the molten steel near the vibration tip portion. Is known (see Non-Patent Document 2). Cavitation generated by an ultrasonic vibrator is a phenomenon in which innumerable bubbles are generated by applying ultrasonic vibration to a liquid and collapse under certain conditions.

When cavitation occurs in the molten steel, this cavitation forms fine equiaxed nuclei in the molten steel. If the generated equiaxed crystal core can be maintained and supplied to the center of thickness of the slab during continuous casting, this will generate an equiaxed crystal structure with small anisotropy in the center of thickness of the slab. It is expected to improve the workability and formability of steel sheets. However, when ultrasonic vibration is applied in normal continuous casting, the cooling rate is slow in normal continuous casting, so even if equiaxed crystal nuclei are formed by cavitation due to ultrasonic vibration, the equiaxed crystal nuclei generated thereafter are generated. Is liable to coalesce / grow or redistribute and disappear, so even if ultrasonic vibration is excited in the mold, it is not possible to form a fine equiaxed crystal part in the center of the thickness of the slab. rice field.

On the other hand, it was found for the first time that a fine equiaxed crystal part can be formed in the center of the thickness of the cast thin-walled slab by exciting ultrasonic waves in the molten steel pool in the twin-roll continuous casting method. In the molten steel pool of bi-roll type continuous casting, when equiaxed crystal nuclei are generated in the molten steel by cavitation, they are deposited on the solid-liquid interface in a short time, and before the equiaxed crystal nuclei coalesce / grow or disappear. , It is taken into the slab to be cast, and a fine equiaxed crystal zone is formed in the center of the thickness of the slab. In addition, the cooling rate of the slab after casting is high, and casting becomes possible as fine equiaxed crystals. Further, fine equiaxed crystals are compressed and filled by the twin rolls to suppress central segregation and formation of porosity.

When a fine equiaxed crystal is generated in the molten steel at the tip of the vibration tip by ultrasonic vibration, the range where cavitation occurs is limited to the narrow region at the tip of the vibration tip. Occurrence is also limited to this cavitation area. Therefore, in order to find an advantageous method for forming an equiaxed crystal zone in the slab, the effect was examined by changing the arrangement of the ultrasonic vibrator 4.

In the double-roll type continuous casting method, the molten steel discharged from the discharge hole 3 of the immersion nozzle 2 runs up the roll once and then moves in the direction of the side weir 8 as shown in FIGS. 1 (A) and 3 (B). It was found that it flowed and then reversed at the side weir 8. Therefore, in a plan view, it is a space between the discharge hole 3 and the two straight lines 22 drawn perpendicularly to the side surface 20 of the immersion nozzle from both ends of the discharge hole until the casting roll 1 is reached (FIG. 1 (B). When the ultrasonic transducer 4 was installed in the region A) of), it was found that the fine equiaxed crystals also flowed along with the flow of the discharge flow 14 and were uniformly distributed in the width direction. At the same time, by arranging the vibration tip portion 7 of the vibration transmission portion 6 above the upper end of the discharge hole 3, the cavitation portion can be arranged in the discharge flow 14 from the discharge hole 3, which is the most excellent. Can exert the effect. Hereinafter, the above-mentioned arrangement of the ultrasonic vibrator 4 is referred to as "arrangement (A)".

When the ultrasonic vibrator 4 is arranged in the arrangement (A) and ultrasonic vibration is applied, fine equiaxed crystals are directly generated in the discharge flow 14 from the discharge hole 3 of the immersion nozzle 2, so that the discharge flow 14 is solid. It becomes a liquid coexistence state. As a result, since the discharged molten steel contains fine equiaxed crystals, its viscosity increased, and it was possible to suppress the run-up of the molten steel to the roll. The run-up of the molten steel to the roll causes the molten metal pool to fluctuate, causing cracks on the surface of the slab. Therefore, it is possible to prevent cracking on the surface of the slab by applying ultrasonic vibration in the arrangement (A).

As shown in FIG. 1 (C), the position of the ultrasonic vibrator is located at a position outside the region A, although it is a space between the side surface 20 where the discharge hole of the immersion nozzle is provided and the casting roll. When arranged in the region B) (installation (B)), a part of the formed equiaxed crystal nuclei moves along with the molten steel flow, which contributes to the formation of the equiaxed crystal zone of the slab, but the arrangement (A). The effect was weaker than that in the case of the arrangement (A), and the equiaxed crystal ratio at the center of the plate width was lower than that in the case of the arrangement (A).

As shown in FIG. 2, when the ultrasonic vibrator is arranged on the side of the nozzle (the side of the side surface 21 having no discharge hole 3) (region C) (referred to as arrangement (C)), ultrasonic vibration is applied. Although it is effective in forming the equiaxed crystal zone of the slab, the flow of the equiaxed crystal is further suppressed by the reversal flow, and the equiaxed crystal ratio is arranged in the center of the plate thickness and near the side dam (B). It was lower. For this reason, it is desirable to install the ultrasonic transducer 4 in the region A in front of the nozzle discharge hole in order to uniformly disperse the equiaxed crystals.

In promoting the formation of equiaxed crystals by cavitation in the molten steel at the tip of the vibration tip portion 7 of the ultrasonic vibrator 4, there are suitable conditions for the ultrasonic transmitter of the ultrasonic vibrator. That is, it is preferable that the ultrasonic transmitter generates ultrasonic waves having a frequency of 18 to 25 kHz and an amplitude (pp) of 14 to 50 μm. As a result of the test in which the frequency was set to 18 kHz or more and 25 kHz or less, fine equiaxed crystals were generated in the implementation range. It is preferable that the amplitude (pp) is 14 μm or more because the amount of equiaxed crystals produced is small and the product becomes anisotropy when the amplitude (pp) is less than 14 μm. It is preferable that the amplitude (pp) is 50 μm or less because if the amplitude (pp) is more than 50 μm, scum floating on the molten steel surface is involved, which leads to product defects. The amplitude (pp) means the set value of the ultrasonic transmitter.

The carbon steel thin-walled slab having a thickness of 5 mm or less of the present invention can be produced by applying the method for producing a carbon steel thin-walled slab using the carbon steel thin-walled slab manufacturing apparatus of the present invention. The obtained carbon steel thin-walled slab is characterized by having an equiaxed crystal ratio of 20% or more and an equiaxed crystal average particle size of 0.1 mm or less. The reason why the thickness of the slab is 5 mm or less is that the effect of the near net shape continuous casting can be fully exerted. The equiaxed crystal ratio of 20% or more and the equiaxed crystal average particle size of 0.1 mm or less are made possible for the first time by the present invention for slabs of such quality. This is because by ensuring the axial crystal ratio and the equiaxed crystal average particle size, a fine equiaxed crystal structure having excellent workability and moldability while ensuring cleanliness can be obtained.

Using a twin-roll casting apparatus (see FIGS. 1 and 2) having a pair of casting rolls 1 having a roll width of 1000 mm and a roll diameter of 1200 mm, 60 tons of steel was cast to produce a slab having a thickness of 2 mm. At the time of casting, the casting speed was set to 0.9 m / s. The ultrasonic vibrator 4 has an ultrasonic transmitter 5 and a vibration transmission unit 6. The vibration transmission unit 6 has a cylindrical shape with a diameter of 50 mm. The vibration tip portion 7 of the vibration transmission portion 6 was immersed in the molten steel pool 10, and ultrasonic waves were applied to the molten steel. The vibration tip portion 7 was installed so as to match the height of the upper end of the discharge hole 3 of the immersion nozzle 2. The positions of the ultrasonic transducers 4 are arranged in the regions A, B, and C in a plan view, and are arranged (A) (see FIG. 1 (B)) and arranged (B) (see FIG. 1 (C), respectively). ), Arrangement (C) (see FIG. 2B). The amplitude (pp) of the ultrasonic oscillator indicates the set value of the ultrasonic oscillator.

A slab sample is collected from the 1/2 width part (position 400 to 600 mm from the width end face) and 1/4 width part (position 100 to 300 mm from the width end face) of the cast thin-walled slab, and equiaxed crystals are collected. The rate, equiaxed grain size, isoaxial crystalliteity in the width direction, porosity, scum entrainment, and slab surface cracking were evaluated.
Measurement of equiaxed crystal ratio: The cross section of the slab in the 1/2 width part was etched with picric acid to reveal the solidified structure, and the slab sample was calculated as the equiaxed crystal zone area / plate observation surface area × 100 (%). ..
Measurement of equiaxed crystal grain size: A solidified structure was revealed by etching the cross section of a slab of 1/2 thick part with picric acid, and the equivalent circle diameter of 20 typical equiaxed crystals was calculated and used as the average grain size. ..
Width uniformity of equiaxed crystal ratio: The cross section of the slab in the 1/2 width part and the 1/4 width part is picric acid etched to reveal the solidified structure, and the equiaxed crystal ratio is measured. %) Was evaluated as ⊚ if the difference was less than 15 points, ◯ if the difference was 15 to 30 points, and Δ if the difference was more than 30 points.
Porosity: Observe the cross section of the slab in the 1/2 width part and the 1/4 width part with an optical microscope, and if porosity of 0.2 mm or more occurs in the major axis, "Porosity" is "Yes" and the major axis is 0.2 mm. If there is no above porosity, it is set to "None".
Scum entrainment :: Observe the cross section of the slab in the 1/2 width part and the 1/4 width part with an optical microscope, and if there is an oxide-based foreign substance with a diameter equivalent to 0.5 mm or more, "Yes". If not, it was "None".
Fragment surface cracks: Observe the slab cross sections of 1/2 width and 1/4 width with an optical microscope, and if cracks of 0.5 mm or more that continue to the surface occur, there is a slab surface crack. If it is less than 0.5 mm, it is set as "None".

Table 1 shows the cast molten steel components (unit: mass%), and Table 2 shows the casting conditions and casting results.

Examples 1 to 5, 10 to 11 are examples of the present invention. Among them, Examples 1 to 5 have an arrangement (A) in which the ultrasonic amplitude is in the preferable range of the present invention and the arrangement position of the ultrasonic vibrator is a suitable position, and the equiaxed crystal ratio and the equiaxed crystal grain size. , The uniformity of the equiaxed crystal ratio in the width direction was good. As a result, all of porosity generation, scum entrainment, and slab surface cracking were "none", and the best results could be obtained.

In Reference Examples 6 to 9, the arrangement position of the ultrasonic transducer is out of the optimum position (arrangement (A)), and although the equiaxed crystal ratio and equiaxed crystal grain size are obtained with good results, the equiaxed axis is obtained. The uniformity in the width direction of the crystal ratio was not as good as in Examples 1 to 5 above. In addition, slab cracking occurred due to the run-up of molten steel on the roll.

In Example 10, the ultrasonic amplitude was out of the lower limit of the preferable range of the present invention, the effect of improving the equiaxed crystal ratio and the equiaxed crystal grain size was slightly low, and porosity was observed. In Example 11, the ultrasonic amplitude was out of the upper limit of the preferable range of the present invention, and although the porosity and the surface cracking of the slab were good, scum entrainment was observed.

Comparative Examples 1 and 2 are cases where ultrasonic vibration is not applied. Comparative Example 1 had an equiaxed crystal ratio of 0%, and Comparative Example 2 had an equiaxed crystal ratio of 4%, and had a substantially columnar crystal structure. Although some equiaxed crystal structure was formed, the structure was non-uniform in the width direction. Porosity occurred without filling with equiaxed crystals. Fragment cracking occurred due to the run-up of molten steel on the roll.

1 Casting roll 2 Immersion nozzle 3 Discharge hole 4 Ultrasonic oscillator 5 Ultrasonic transmitter 6 Vibration transmission part 7 Vibration tip part 8 Side dam 9 Gap part 10 Molten steel pool 11 Molten steel flow 12 Solidified shell 13 Cast piece 14 Discharge flow 20 Side 21 Side 22 Straight 31 Molten steel pool surface 32 Edge of molten steel pool surface

Claims (3)

A carbon steel thin-walled slab manufacturing device by double-roll continuous casting, in which molten steel is supplied from a dipping nozzle into a molten steel pool surrounded by double-rolls for casting.
A molten steel discharge hole is provided at a position on the side surface of the immersion nozzle to be immersed in the molten steel pool.
It has an ultrasonic oscillator, and the ultrasonic oscillator has an ultrasonic transmitter and a vibration transmission unit.
The ultrasonic vibrator is arranged in a space between the discharge hole and two straight lines drawn perpendicularly to the side surface of the immersion nozzle from both ends of the discharge hole in a plan view, and the vibration tip portion of the vibration transmission unit is provided. Is placed above the upper end of the discharge hole.
A carbon steel thin-walled slab manufacturing apparatus, wherein the vibration tip portion of the vibration transmission portion can be immersed in the molten steel of the molten steel pool. A method for manufacturing a carbon steel thin-walled slab using the carbon steel thin-walled slab manufacturing apparatus according to claim 1.
The molten steel is supplied from the immersion nozzle into the molten steel pool surrounded by the twin rolls, the vibration tip of the vibration transmission portion is immersed in the molten steel of the molten steel pool, and ultrasonic vibration is applied to the molten steel in the molten steel pool. A method for manufacturing a carbon steel thin-walled slab, which comprises continuously casting carbon steel thin-walled slabs. The production of a carbon steel thin-walled slab according to claim 2, wherein an ultrasonic wave having a frequency of 18 to 25 kHz and an amplitude (pp) of 14 to 50 μm is generated by the ultrasonic transmitter of the ultrasonic transducer. Method.

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