JP2000301296A - Steel continuously casting method and tundish - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel continuous casting method which can remove even fine oxide in the molten steel and can obtain a cast slab excellent in the cleanliness, and to provide a tundish used for the method. SOLUTION: In this tundish 1, a molten metal receiving part 4 of the molten steel 5 and a molten metal receiving part 5 of the received molten steel into a mold 11 are connected to each other so that the molten steel can flow through a hole type flowing passage 6 opened in the molten metal receiving part 4 and the molten metal supplying part 5, and the hole type flowing passage 6 is inclined downward from the molten metal receiving part 4 to the molten metal supplying part 5. The tundish 1 is used to flow inert gas into the molten steel passing through the hole type flowing passage 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method of steel capable of obtaining a slab excellent in cleanliness with few nonmetallic inclusions and a tundish used in the continuous casting method.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for improved performance of steel materials, and there has been a strong demand for improved cleanliness of steel. In particular, it is required to remove even minute non-metallic inclusions in cast slabs, that is, even minute oxides in molten steel.

In the continuous casting of steel, molten steel in a ladle is first injected into a tundish, and then injected into a mold through an immersion nozzle. Has been done in a variety of ways.

[0004] For example, as a method of removing minute oxides in molten steel in a tundish, a method in which molten steel in a hot water receiving portion is swirled in a horizontal direction has been adopted. The minute oxides gather at the center of the swirling molten steel and enlarge. The enlarged oxide easily floats in the molten steel, so that it floats on the surface of the molten steel, and is removed outside the molten steel system by a flux or the like added to the surface of the molten steel.

In Japanese Patent Application Laid-Open No. 6-597, a tundish is divided into a hot water receiving portion from a ladle and a hot water supply portion to a mold, and a turning magnetic field is externally applied to molten steel in a cylindrical hot water receiving portion to form a molten steel. Has been proposed for turning the camera horizontally.

However, in this method, since the molten steel in the cylindrical hot water receiving portion is swirled in the horizontal direction, a vortex is generated on the surface of the molten steel in the hot water receiving portion. Therefore, slag on the surface of the molten steel, oxides that have floated, and the like are likely to be caught in the molten steel, and the cleanliness of the steel is more likely to deteriorate. In addition, in order to swirl a large volume of molten steel in the hot water receiving section, a large-sized electromagnetic force generator is required, and there is a problem that the equipment becomes excessively large.

In Japanese Patent Application Laid-Open No. Hei 6-31409, a tundish is composed of a hot water receiving portion from a ladle and a hot water supply portion to a mold, and a flow passage of molten steel connecting the hot water receiving portion and the hot water supply portion.
A method of providing a rotating magnetic field applying device outside the flow path of the molten steel has been proposed. By turning the molten steel passing through the flow passage, minute oxides in the molten steel gather at the center of the swirling molten steel and enlarge. The bloated oxide is
It floats in the molten steel in the hot water supply section together with the bubbles of the inert gas blown into the molten steel in the flow passage.

[0008] However, in this method, when the bubbles of the inert gas floating in the molten steel in the hot water supply portion by trapping minute oxides reach the surface of the molten steel in the hot water supply portion, the bubbles are repelled. When the bubbles burst, the fine oxides trapped by the bubbles are likely to be re-engaged in the molten steel. Therefore, the cleanliness of steel tends to worsen rather.

[0009]

As described above, the conventional method for removing minute oxides using a tundish has the following problems. That is, using a tundish having a structure including a method of horizontally rotating molten steel in a tundish hot water receiving portion and a hot water receiving portion, a hot water supply portion, and a flow channel of molten steel connecting these, and an electromagnetic force applying device for the flow channel In the method of swirling molten steel passing inside,
Oxides that have floated on the surface of the molten steel are caught in the molten steel, and the cleanliness of the steel is rather deteriorated. In addition, when turning molten steel in the hot water receiving part of the tundish, a large electromagnetic force generator is required.

[0010] The present invention provides a continuous casting method of steel capable of removing even minute oxides in molten steel at low equipment cost and obtaining a slab excellent in cleanliness, and a tundish used in the continuous casting method. The purpose is to do.

[0011]

The gist of the present invention is to provide a continuous casting method for steel shown in the following (1) and the following (2):
In the tundish shown in (3) and (4).

(1) A molten steel receiving part and a molten steel supply part to the casting mold of the molten steel are connected to each other through a hole-shaped flow passage opening to the molten metal receiving part and the hot water supply part so that the molten steel can flow therethrough. A continuous casting method of steel in which an inert gas is blown into molten steel passing through the hole-shaped flow passage using a tundish in which the hole-shaped flow passage is inclined downward from the hot water receiving portion to the hot water supply portion. .

(2) A tundish used in the continuous casting method of steel according to (1), wherein the hot water receiving portion and the hot water supply portion are connected by a hole-shaped flow passage, and the hole-shaped flow passage is provided. A tundish in which a passage is inclined downward from a hot water receiving section to a hot water receiving section, and the hole-shaped passage has an inert gas injection port.

(3) The tundish as described in (2) above, further comprising an electromagnetic stirrer for applying an electromagnetic force to the molten steel passing therethrough by a swirling magnetic field, outside the hole-shaped passage.

(4) In the bottom of the hot water receiving section, the position corresponding to the extension direction of the hole-shaped flow passage is lower than the bottom on both sides thereof, and the hot water receiving section starts from the lowest position of the bottom of the hot water receiving section. The tundish according to the above (2) or (3), which is inclined upward toward the side wall of the tundish.

The present inventors have solved the above-mentioned problem of the present invention as follows. In the present invention, the minute oxide in the target molten steel means an oxide having a diameter of about 50 μm or less. (A) As a method of preventing entrapment of minute oxides generated due to the bubbles of the inert gas having captured the minute oxides floating in the molten steel and reaching the surface of the molten steel and popping out of the molten steel, the following method is used. A hole-shaped passage having a shape inclined downward from the hot water portion to the hot water supply portion is used. By using the hole-shaped flow passage inclined as described above, the bubble of the inert gas blown into the molten steel from the blow hole provided in the hole-shaped flow passage is not a hot water supply part but a hot water receiving part. It floats in the molten steel in the part. Even if the bubbles of the inert gas trapping the minute oxides burst on the surface of the molten steel in the hot water receiving section, even if the minute oxides trapped in the bubbles get caught in the molten steel in the hot water receiving section, Such oxides are trapped again by the inert gas bubbles in the pore-shaped flow passage. Therefore, the hot water supply section is filled with highly clean molten steel from which minute oxides have been removed.
The cleanliness of the molten steel injected into the mold is also improved.

(B) In order to float fine oxides in the molten steel, the molten steel passing through the hole-shaped passage is swirled,
It is desirable to enlarge the oxide. In the tundish of the present invention, molten steel can be swirled with low equipment cost.

That is, it is preferable to provide an electromagnetic stirrer outside the hole-shaped passage. In this electromagnetic stirrer, a small electromagnetic stirrer may be used because only the molten steel passing through the hole-shaped passage is swirled. As used in the prior art,
There is no need for a large electromagnetic stirrer for swirling the molten steel in the hot water receiving section. Therefore, the molten steel passing through the hole-shaped passage can be swirled at low equipment cost.

Further, the shape of the hot water receiving portion may be a shape inclined upward from the lowest position of the bottom of the hot water receiving portion to the side wall of the hot water receiving portion. The molten steel poured from the ladle into the hot water receiving portion turns vertically in the hot water receiving portion. The molten steel swirling in the vertical direction in the hot water receiver enters the hole-shaped passage while swirling.

If the above-described method is adopted, the molten steel passing through the passage can be swirled at a low equipment cost.

(C) Since the molten steel passing through the hole-shaped flow passage is swirled, slag or the like on the surface of the molten steel in the hot water receiving portion or the hot water supply portion is not involved in the molten steel.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The continuous casting method of the present invention and a tundish used in the method will be described below. FIG.
FIG. 2 is a schematic diagram for explaining a continuous casting method of the present invention and a tundish used in the method.
Fig. 1 shows an example of a box-shaped tundish with a hot water receiving section.
1A is a longitudinal sectional view, and FIG. 1B is a sectional view taken along line A1-A2 in FIG. FIG. 2 is an example of a shape in which the shape of the hot water receiving portion is inclined upward from the lowest position at the bottom of the hot water receiving portion to the side wall of the hot water receiving portion, and is a cross-section taken along line B1-B2 shown in FIG. It is sectional drawing of the hot-water receiving part corresponding to.

In the method of the present invention, as shown in FIG. 1A, a tundish in which a hole-shaped flow passage 6 is inclined downward from the hot water receiving portion 4 to the hot water supply portion 5 is used. Inert gas is blown into the molten steel passing through the flow passage. The bubbles 13 of the inert gas blown into the molten steel passing through the hole-shaped flow passage are sheared and refined by the swirling flow A of the molten steel in the vicinity of the injection port 7. The miniaturized bubbles are more likely to capture the minute oxides 14 in the molten steel.

The bubbles 13 of the inert gas capturing fine oxides and the like float in the molten steel in the hot water receiving portion 4 as shown by the flow B of the bubbles of the inert gas in FIG. I do. The oxides in the molten steel that floated on the surface of the molten steel in the hot water receiving section are absorbed by, for example, a flux added to the surface of the molten steel, and removed outside the molten steel system.

The tundish 1 of the present invention has a hot water receiving section 4 into which the molten steel 3 is injected from the ladle 2, a hot water supply section 5 having a function of injecting the molten steel 3 into the mold 11 through the immersion nozzle 12, and a hot water receiving section 5. A hole-shaped passage 6 that connects the unit 4 and the hot water supply unit 5 is provided. In the hole-shaped passage 6, a blow-out port 7 for blowing an inert gas is disposed.

The hole-shaped passage is inclined downward from the hot water receiving portion to the hot water supply portion. This is because bubbles of the inert gas blown into the molten steel in the passage are floated not in the hot water supply part but in the molten steel in the hot water reception part. The angle of the downward inclination is preferably 10 to 70 °. When the angle is less than 10 °, the inert gas bubbles float faster toward the hot water receiving part,
The flow velocity of the molten steel passing through the hole-shaped flow passage toward the hot water supply unit is faster. Therefore, bubbles of the inert gas are carried to the hot water supply unit by the passing molten steel, and float in the molten steel in the hot water supply unit. When the angle exceeds 70 °, the total height of the tundish becomes high, so that the equipment cost increases. 20 ~
60 ° is more desirable.

The flow rate of the molten steel passing through the flow passage and the floating speed of the bubble of the inert gas will be described. For example, the shape of the hole of the hole-shaped flow passage is circular as described later, and its inner diameter is 2 mm.
00mm, when the flow rate of the molten steel passing through is 1.5 t / min,
The average flow velocity of the molten steel passing through this passage is 110 mm /
Seconds. Also, the bubble diameter of the injected inert gas is 1
In the case of a spherical shape of 0 mm, the rising speed Vg at which the bubble rises in the vertical direction is obtained by the Newton's formula below,
540 mm / sec. The inclination angle of the hole-shaped passage is 3
In the case of 0 °, the floating speed of the air bubbles floating in the hole-shaped passage toward the hot water receiving portion is 270 mm / sec.
Therefore, the bubble floating speed Vg 270 mm is higher than the average flow velocity of molten steel 110 mm / sec passing through the hole-shaped flow passage.
Since air / second is faster, air bubbles float toward the hot water receiving part.

Vg = 1.74 × (g × Dg)^0.5 Here, g: 9800 mm / sec by gravity acceleration^Two  Dg: Diameter of gas bubble (mm) The shape of the hole of the hole-shaped flow passage is such that molten steel passing inside turns.
Therefore, a circle is better. At this time, the inner diameter of the hole is
Conditions such as dish capacity, slab size, casting speed, etc.
, But is preferably about 100 to 400 mm. 1
If it is less than 00 mm, it becomes difficult for the molten steel to turn, and
If it exceeds 00 mm, the overall shape of the tundish will be large.
Therefore, equipment costs increase.

The length of the hole-shaped passage is 500-2000.
mm is preferable. If it is less than 500 mm, bubbles of the inert gas may float in the molten steel in the hot water supply unit. 2000
If the diameter exceeds mm, the overall cost of the tundish becomes large, so that the equipment cost increases.

The number of the hole-shaped flow passages is not particularly limited. However, the shape of the bottom of the hot water receiving portion described below is inclined upward from the lowest position of the bottom of the hot water receiving portion to the side wall of the hot water receiving portion. In the case of a planar shape, it is better to have one. This is because the molten steel swirling in the hot water receiving portion is likely to enter the hole-shaped passage while swirling. In the shape of the hot water receiving portion other than the above, the number of hole-shaped passages may be determined according to conditions such as the capacity of the tundish, the size of the slab, and the casting speed.
Up to four hole-shaped passages are preferred.

As the refractory for the hole-shaped passage, a general refractory such as high alumina, magnesia, and zirconia may be used.

A blow-in port 7 for blowing an inert gas is provided in the hole-shaped passage. The blowing port may be a porous refractory or a refractory in which a thin steel tube is embedded. The blow-in port is preferably provided between the opening of the hole-shaped flow passage to the hot water receiving portion and the vicinity of the intermediate position of the length. When the gas is brought closer to the hot water supply unit, bubbles of the blown inert gas are easily dispersed in the molten steel in the hot water supply unit. Ar gas or the like can be used as the inert gas.

An electromagnetic stirring device 8 is preferably provided outside the hole-shaped passage 6. If the molten steel passing through the hole-shaped flow passage is swirled by operating the electromagnetic stirring device, the molten steel 3 passing through is more easily swirled.

The shape of the hot water receiving portion may be a shape inclined upward from the lowest position at the bottom of the hot water receiving portion to the side wall of the hot water receiving portion. Then, the molten steel passing through the hole-shaped passage is more likely to turn. This is because the molten steel poured from the ladle into the hot water receiving portion turns vertically in the hot water receiving portion and enters the hole-shaped passage while turning.

When a tundish having a shape inclined upward from the lowest position of the bottom of the hot water receiving portion to the side wall of the hot water receiving portion is used, as shown in FIG.
It is preferable to immerse the ladle long nozzle 9 in the molten steel and to inject the molten steel in the ladle between the side wall of the ladle and the extending direction of the passage. When using a tundish other than the above-described shape, an injection pipe may be used instead of the ladle long nozzle 9.

A lower weir 10 may be provided at the bottom of each of the hot water receiving section 4 and the hot water supply section 5. In the hot water receiving section, an upper weir may be provided at the upper part, or a lower weir and an upper weir may be provided at the bottom and the upper part, respectively. By providing the upper weir above the hot water receiving portion, it is possible to prevent oxides and the like floating on the molten steel surface together with bubbles from spreading over the entire molten steel surface of the hot water receiving portion. When it spreads over the whole, the oxide is easily entangled in the molten steel again.

[0037]

(Example 1) Test No. of the present invention example. Test No. 1 of Comparative Example 2 and No. In No. 3, an extremely low carbon steel having a carbon content of about 0.001% by weight was formed using a vertical bending type slab continuous casting machine to a thickness of 250 mm and a width of 1000 mm.
Was cast at a speed of 2.0 m / min.

Test No. In Example 1, a tundish having one hole-shaped passage having the apparatus configuration shown in FIG. 1 was used.
The hole diameter of the hole-shaped passage is 200 mm and the length is 1500 mm
A downward inclination of 60 ° was provided from the hot water receiving section toward the hot water supply section. The output is 30 outside the hole-shaped passage.
800 m near the center of the flow path through a 0 kW electromagnetic stirrer
m. In addition, the inlet of the inert gas made of a porous refractory is provided at three places in the longitudinal direction and in the circumferential direction at a position 400 mm from the center of the hole-shaped passage and the hot water supply side from the center and the middle thereof. 4 locations at 90 ° pitch, total 12
It was arranged in three places. Ar gas was blown in at a flow rate of 500 cm ³ / sec in total.

Test No. In Test No. 2, only the inclination of the hole-shaped passage was horizontal, A tundish different from the tundish used in 1 was used. The other conditions are as follows: Same as 1 Test No. In No. 3, a conventional box-shaped tundish in which the hot water receiving portion and the hot water supply portion were integrated was used. There is no inlet for inert gas.

From the inside of the ladle before the start of continuous casting and the inside of the mold after the casting operation such as casting speed is stabilized, a diameter of 30 mm
A molten steel sample having a capacity of 100 mm in length was collected by the bomb method, and the total oxygen content was analyzed. In addition, the surface layer 1 of the obtained slab
A sample of 1 kg was taken from a position except for 0 mm, nonmetallic inclusions were extracted by an electrolytic method (slime extraction method), and the nonmetallic inclusions were classified by particle size using filters of various sizes. And the particle size distribution was determined.

The obtained slab was rolled into a hot-rolled steel strip having a thickness of 4.5 mm, wound up into a coil, pickled, and examined for the occurrence of surface defects in the coil. The coil in which the surface defect was generated was regarded as a surface defect generating coil, the total weight of the surface defect generating coil was obtained, and the value obtained by dividing by the weight of all the investigated coils was defined as the surface defect generation rate. Test No. Test No. 3 with the surface defect occurrence rate of No. 3 as an index 1.0. 1 and test no.
2 were evaluated. Table 1 shows the test conditions and test results.

[0042]

[Table 1]

Test No. of the present invention example. 1, the total oxygen content of 41 ppm in the molten steel in the ladle was 17 p in the molten steel in the mold.
pm and the test No. of the comparative example. 2 and No. Compared to No. 3, it was confirmed that the cleanliness of the molten steel was significantly improved in the tundish. FIG. 3 is a diagram showing a distribution of nonmetallic inclusions in a slab by particle size. FIG.
From Test No. In No. 1, it can be seen that there are few minute nonmetallic inclusions having a size of about 50 μm in the slab. This is the effect of removing minute oxides in the molten steel in the tundish. In addition, the occurrence of surface defects on the rolled steel strip was determined by the test N
o. The index of 1 was 0.08, indicating a good product surface quality condition.

(Example 2) Test No. Test No. 4 of Comparative Example 5 and No. 5 In No. 6, low carbon steel having a carbon content of about 0.06% by weight was cast on a slab having a thickness of 100 mm and a width of 1000 mm at a speed of 3.0 m / min using a vertical bending type slab continuous casting machine.

Test No. In No. 4, a tundish having one hole-shaped flow passage having the device configuration shown in FIG. 2 and having a shape inclined upward from the lowest position of the bottom of the hot water receiving portion to the side wall of the hot water receiving portion was used. Hole diameter of hole-shaped flow passage is 200m
m, the length was 1200 mm, and a downward inclination of 30 ° was provided from the hot water receiving section toward the hot water supply section. The inlet of the inert gas made of a porous refractory is placed at three places in the longitudinal direction and 120 ° in the circumferential direction at the center of the hole-shaped flow passage and at a position 400 mm from the center to the hot water supply side and in the middle thereof. 3 on the pitch
And 9 places in total. Ar gas 160c in total
The air was blown at a flow rate of m ³ / sec.

Test No. In Test No. 5, only the inclination of the hole-shaped passage was horizontal. A tundish different from the tundish used in No. 4 was used. The other conditions are as follows: Same as 4. Test No. In No. 6, a conventional box-shaped tundish in which a hot water receiving portion and a hot water supply portion were integrated was used. There is no inlet for inert gas.

Test No. 4-No. In No. 6, the total oxygen content of the molten steel in the ladle and the molten steel in the mold was investigated by the method described above. In addition, diameter 30mm collected by the bomb method,
The surface of the cross section of the molten steel sample having a length of 100 mm is polished, and the magnification of 100 times and, if necessary, 4 times with an optical microscope.
The number of nonmetallic inclusions having a size of 10 μm or more was examined by size at a magnification of 00 times. The maximum length of non-metallic inclusions in the form of clusters and blocks was regarded as the diameter of the inclusions, and the diameter of spherical inclusions was regarded as the diameter of the inclusions.

Further, the obtained slab was rolled into a hot-rolled steel strip having a thickness of 3.5 mm, pickled, and the surface defect occurrence rate of a coil wound with the steel strip was examined. Test No. Test No. 6 using the surface defect occurrence rate of No. 6 as an index 1.0. 4 and test no. 5 were evaluated. Table 2 shows the test conditions and test results.

[0049]

[Table 2]

Test No. of the present invention example In Test No. 4, the total oxygen content of the molten steel in the mold was significantly lower than that of the molten steel in the ladle. 5 and No. 5 Compared to 6,
The remarkable improvement in the cleanliness of the molten steel in the tundish was confirmed. FIG. 4 is a diagram illustrating the number of nonmetallic inclusions in a slab by size using an optical microscope. From FIG. In No. 4, it can be seen that there are few minute nonmetallic inclusions having a size of about 50 μm in the slab. This is the effect of removing minute oxides in the molten steel in the tundish. In addition, the occurrence of surface defects on the rolled steel strip was determined by the test N
o. The index of No. 4 was 0.05, indicating a good product surface quality condition.

Example 3 Test No. of the present invention example Test No. 7 of Comparative Example 8 and No. In No. 9, Cr and N were obtained using a curved billet continuous caster having a circular cross section.
Austenitic stainless steels having an i content of 18 and 8% by weight were cast into billets having a diameter of 230 mm at a speed of 1.0 m / min.

Test No. 7, a tundish having one hole-shaped communication channel having the device configuration shown in FIG. 1 was used.
The hole-shaped flow passage had a hole diameter of 150 mm and a length of 600 mm, and had a downward inclination of 10 ° from the hot water receiving portion toward the hot water supply portion. Outside the hole-shaped passage, the output is 200
A kW electromagnetic stirring device was provided along the entire length of the flow path. In addition, one injection port for inert gas made of porous refractory is provided at one location 200 mm from the center of the hole-shaped passage toward the hot water supply side, and four locations at 90 ° pitch in the circumferential direction, for a total of four locations. And Ar gas was blown in at a total flow rate of 50 cm ³ / sec.

Test No. In Test No. 8, only the inclination of the hole-shaped flow passage was horizontal. A tundish different from the tundish used in No. 7 was used. Other conditions are as follows: Same as 7. Test No. 9
Used a conventional box-shaped tundish in which a hot water receiving section and a hot water supply section were integrated. There is no inlet for inert gas.

Test No. 7-No. In No. 9, the total oxygen content of the molten steel in the ladle and the molten steel in the mold was investigated by the method described above. Further, the obtained slab was rolled into a seamless steel pipe having an outer diameter of 32 mm and a thickness of 3 mm, and the incidence of defects on the inner surface of the steel pipe was examined. Test No. Test No. 9 with the defect occurrence rate of No. 9 as an index 1.0. 7 and test no. 8 were evaluated. Table 3 shows the test conditions and test results.

[0055]

[Table 3]

Test No. of the present invention example In Test No. 7, the total oxygen content of the molten steel in the mold was significantly lower than that of the molten steel in the ladle. 8 and No. Compared to 9,
The remarkable improvement in the cleanliness of the molten steel in the tundish was confirmed. In addition, the state of occurrence of defects on the inner surface of the rolled steel pipe was determined in Test No. The index of No. 7 was 0.10, and a steel pipe having good inner surface quality was obtained.

[0057]

According to the continuous casting method of the present invention and the tundish of the present invention used in the method, even fine oxides in molten steel can be removed at low equipment cost and a cast piece excellent in cleanliness can be obtained. Is possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a continuous casting method of the present invention and a tundish used in the method.

FIG. 2 is a schematic diagram for explaining the tundish of the present invention, and is a diagram of an example of a tundish which is inclined upward from the bottom to the side wall of the hot water receiving portion.

FIG. 3 is a diagram showing the number of nonmetallic inclusions of a slab by size according to the slime extraction method.

FIG. 4 is a diagram showing the number of non-metallic inclusions of a slab by size using an optical microscope.

[Explanation of symbols]

1: Tundish 2: Ladle 3: Molten steel 4: Hot water receiving part 5: Hot water supply part 6: Hole-shaped flow passage 7: Inlet 8: Electromagnetic stirrer 9: Ladle long nozzle 10: Lower dam 11: Mold 12: Immersion nozzle 13: Bubbles of inert gas 14: Fine oxides in molten steel A: Swirling flow of molten steel B: Flow of bubbles of inert gas

Claims (4)

[Claims] A molten metal receiving part and a molten steel supply part to a casting mold of the molten steel are connected through a hole-shaped flow passage opening to the molten metal receiving part and the hot water supply part so that the molten steel can flow therethrough. A steel characterized in that an inert gas is blown into molten steel passing through the hole-shaped flow passage using a tundish whose hole-shaped flow passage is inclined downward from the hot water receiving portion to the hot water supply portion. Continuous casting method. 2. A tundish for use in the continuous casting method of steel according to claim 1, wherein the hot water receiving portion and the hot water supply portion are connected by a hole-shaped flow passage, and the hole-shaped flow passage is formed by: A tundish characterized by being inclined downward from a hot water receiving portion to a hot water receiving portion, and having an inlet for an inert gas in the hole-shaped passage. 3. The tundish according to claim 2, further comprising an electromagnetic stirrer for applying an electromagnetic force to the molten steel passing therethrough by a swirling magnetic field, outside the hole-shaped passage. 4. A bottom portion of the hot water receiving portion, the position corresponding to the extension direction of the hole-shaped passage is lower than the bottom portions on both sides thereof, and the lowest position of the bottom portion of the hot water receiving portion extends from the lowest position of the hot water receiving portion. The tundish according to claim 2 or 3, wherein the tundish is inclined upward toward the side wall.