JP2002011555A - Method for continuously casting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous casting method of steel by which even fine oxide inclusions is molten steel can be removed and a cast slab having excellent cleanliness is obtained. SOLUTION: A plurality of gas blowing holes 4 are disposed in the width direction of a tundish bottom part which is vertical to the direction connecting a molten steel receiving position at the bottom part of the tundish 3 for receiving the molten steel 16 from the ladle 1 with a hole 5 for supplying the received molten steel into a mold 7. The ratio A/B of the distance A between the gas blowing position having a plurality of gas blowing holes and the molten steel receiving position at the tundish bottom part for receiving the molten steel from the ladle to the distance B between the gas blowing position and the supplying hole of the received molten steel into the mold is regulated within the range of 4/6-6/4. Then, the gas is blown into the molten steel in the tundish under condition of regulating the gas blowing quantity to 5.0-15.0N liter per ton of the molten steel passing through the tundish.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of continuously casting steel to obtain a slab excellent in cleanliness with few nonmetallic inclusions.

[0002]

2. Description of the Related Art In continuous casting of steel, molten steel in a ladle is once injected into a tundish and then fed into a mold through an immersion nozzle. In this tundish, oxides of Al and the like in molten steel are removed by various methods in order to enhance the cleanliness of the steel. In recent years, there has been a growing demand for improving the performance of steel materials in particular, and it has been required to remove even minute oxides in molten steel.

[0003] As a method of removing minute oxides in molten steel in a tundish, an electromagnetic force is applied to the molten steel in the tundish to swirl the molten steel, and the fine oxides are condensed at the center of the swirling molten steel. There is a way to make it bloat. This method utilizes the fact that the oxide in the enlarged molten steel easily floats in the molten steel. However, these methods have problems such as the necessity of excessive facilities such as an electromagnetic force generator and an increase in manufacturing cost.

On the other hand, as an inexpensive method, an inert gas such as Ar is blown into molten steel in a tundish, and oxides of Al and the like in the molten steel are trapped by bubbles of the inert gas to remove these oxides. There is a way to remove it.

For example, Japanese Unexamined Patent Publication No. 9-164455 discloses a method of blowing an inert gas into molten steel from a gas inlet made of a porous refractory (porous plug) provided at the bottom of a tundish hot water receiving portion. Has been proposed. However, the wettability between the molten steel and the porous refractory is poor, and bubbles of the generated inert gas tend to be large. In addition, the time during which molten steel stays in the tundish is short. Therefore, it is difficult to remove even minute oxides in molten steel.

Japanese Unexamined Patent Publication No. Hei 8-117939 discloses a flow of molten steel having a small cross section having irregularities in a flow direction at a position between a falling position of a molten steel from a ladle and a dipping nozzle near a bottom of a tundish. A method has been proposed in which a passage is provided and an inert gas is blown into molten steel from a convex portion in the flow passage. It is stated that the presence of the concave and convex portions reduces the thickness of the boundary layer of the flow of the molten steel, so that the bubbles of the inert gas are miniaturized. However, as the casting time becomes longer, oxides and the like in the molten steel adhere to the concave portion of the flow passage. Therefore, the difference in thickness between the convex and concave portions is reduced, and the bubbles increase with time, making it difficult to remove minute oxides in the molten steel.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a continuous casting method for steel capable of removing minute oxides in molten steel at low equipment cost and manufacturing cost and obtaining a cast having excellent cleanliness. The purpose is to provide.

[0008]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a tank which is perpendicular to a direction connecting a hot water receiving position at the bottom of a tundish for receiving molten steel from a ladle and a hot water supply hole to a casting mold of the molten steel. A plurality of gas injection ports are arranged in the width direction of the dish bottom, a distance A between a gas injection position where the plurality of gas injection ports are arranged and a hot water receiving position of the tundish bottom, the gas injection position and the mold. The ratio A / B to the distance B from the hot water supply hole is set to a value in the range of 4/6 to 6/4, and the amount of gas blown is 5.0 to 15.0 N per molten steel t passing through the tundish. It is a method of continuously casting steel in which gas is blown into molten steel in a tundish under the condition of liter.

[0009] The fine oxides in molten steel, which are the object of the present invention, mean oxides having a diameter of about 10 µm or less. The hot water receiving position at the bottom of the tundish which receives molten steel from the ladle means a portion where a line extending downward from a nozzle such as a long nozzle provided at the lower portion of the ladle intersects the bottom of the tundish. This means the position of the symbol C shown in FIG. Further, the direction connecting the molten steel receiving position from the ladle to the molten steel supply hole to the casting mold is defined as the longitudinal direction of the tundish, and the direction perpendicular to the longitudinal direction is defined as the width direction of the tundish.

[0010] In order to float and remove minute oxides in molten steel at low equipment and production costs, the method of the present invention employs a plurality of gas injection ports arranged in appropriate regions in the width direction of the bottom of the tundish. Gas is blown into molten steel at an appropriate gas blow rate. Thereby, a circulation flow of two molten steels is formed between the vicinity of the molten steel receiving position from the ladle and the vicinity of the gas injection position, and between the vicinity of the gas injection position and the vicinity of the molten steel supply hole to the mold. You. By forming such a circulating flow of the two molten steels in the tundish, the chances of contact of the minute oxides with each other increase, and it becomes easy to float due to enlargement, and it is easy to be removed outside the molten steel system. Become. In addition, the chance that minute oxides in the molten steel come into contact with bubbles increases, and the effect of removing the oxides thereby increases. This will be described below with reference to the drawings.

FIG. 1 is a schematic view showing a case where a circulating flow of two molten steels is formed in a tundish by applying the method of the present invention. FIG. 1A shows a vertical section in the vertical direction of the tundish longitudinal direction, and FIG. 1B and FIG. 1C.
Is a schematic diagram showing the arrangement of gas inlets arranged in the width direction of the bottom of the tundish, and A1- in FIG.
It is sectional drawing of A2 line. As described later, FIG. 1B shows an example in which a plurality of gas blowing ports are arranged in the entire width of the tundish, and FIG. 1C shows a part of the width.

In FIG. 1, a distance A between a gas blowing position where a plurality of gas blowing ports 4 are arranged in the width direction of the bottom of the tundish 3 and a hot water receiving position at the bottom of the tundish which receives the molten steel 16 from the ladle 1 is shown in FIG. The ratio A / B between the gas injection position and the distance B between the molten steel received from the ladle and the hot water supply hole 5 into the mold 7 is set to 5/5, and the molten steel receiving position from the ladle and the molten steel mold 7 are set.
An example in which a gas blow-in port 4 is provided at an intermediate position of a hot-water supply hole 5 is shown. Here, the distance A means the center-to-center distance between the hot water receiving position of the bottom of the tundish receiving the molten steel from the ladle and the gas blowing position, and the distance B is the hot water supply hole to the molten steel mold and the gas blowing position. Means the distance between centers.

FIG. 1 shows an example in which a lower weir described later is arranged. That is, the lower weir 8 is located near the hot water receiving position between the molten steel receiving position from the ladle and the gas blowing position and near the hot water supplying hole between the gas blowing position and the molten steel casting hole. , 9 are arranged.

In the method of the present invention, molten steel supplied into the tundish 3 via the long nozzle 2 provided at the lower part of the ladle 1 is supplied from a plurality of gas blowing ports 4 arranged in the width direction of the bottom of the tundish. Injected gas bubbles 15
Generates a rising flow 10 that rises from the vicinity of the gas blowing port. Since a plurality of gas blowing ports are arranged in the width direction of the tundish, the upward flow of molten steel is formed over substantially the entire width of the tundish.

At this time, if gas is blown into the molten steel under the condition that the amount of gas blown is 5.0 to 15.0 Nl per molten steel t passing through the tundish, the amount of gas bubbles generated becomes appropriate. Also, the force at which the air bubbles float is also appropriate, and the rising speed of the ascending flow of the molten steel is appropriately increased. If the rising speed of the rising flow of molten steel is high within an appropriate range, the rising flow 10
After reaching the vicinity of the molten steel surface, it is divided into a molten steel flow 11 in the ladle direction and a molten steel flow 12 on the opposite side. The molten steel flow 11 toward the ladle changes its direction downward near the lower weir 8 arranged near the hot water receiving position, and a circulation flow 13 of one molten steel is formed. Furthermore, the molten steel flow 12 heading in the opposite direction of the ladle is
The flow becomes downward in the vicinity of the lower weir 9 disposed near the hot water supply hole 5 above the immersion nozzle 6, and a part of the flow flows from the hot water supply hole into the mold through the lower weir 9. However, since the amount of the molten steel going downward before the lower weir 9 is large, one circulation flow 14 of the molten steel is formed. If the amount of gas blown is small, the speed of the ascending flow 10 of the molten steel decreases, and the two circulating flows 13, 1
4 becomes difficult to obtain.

Further, in the method of the present invention, the ratio A / B of the distance A and the distance B is set in the range of 4/6 to 6/4, so that two circulation flows are easily formed. 4/6 ratio A / B
If the value is out of the range of ６/4, it is difficult to form a circulating flow. For example, if the ratio A / B is set to a value smaller than 4/6 and the gas injection position is too close to the molten steel receiving position from the ladle, the rising flow 10 of the molten steel will The molten steel flow 12 is in the opposite direction of the pot. However, since the distance from the position where the rising flow becomes the molten steel flow 12 in the opposite direction of the ladle to the vicinity of the lower weir 9 arranged near the hot water supply hole becomes longer, the molten steel flow 12 in the opposite direction of the ladle flows to the lower weir 9. Before the flow reaches the lower weir 9, it is difficult to form a downward circulating flow. As will be described in detail later, when the lower weir 9 is not provided, the flow of the molten steel flow 12 in the opposite direction of the ladle is weakened before reaching the side wall, and a circulating flow is not easily formed.
Also, for example, when the ratio A / B is set to a value larger than 6/4 and the gas injection position is too close to the vicinity of the hot water supply hole, a downward circulating flow is not easily formed by the lower weir 8. As will be described later in detail, when the lower weir 8 is not provided, the molten steel flow 11 in the opposite direction of the ladle weakens before reaching the side wall, and a circulating flow is hardly formed.

When the two circulating flows 13 and 14 of molten steel are formed in the tundish in this way, the fine oxides in the molten steel are enlarged while circulating, and the enlarged oxides easily float. In addition, oxides in molten steel can be easily removed. Furthermore, while the molten steel circulates, fine oxides in the molten steel are easily captured by the flux or the like added to the surface of the molten steel in the tundish, and are easily removed outside the molten steel system. Further, since there is a region where bubbles float between the two circulating flows, the chance of contact between the bubbles and the minute oxide increases, and the effect of removing the oxides by the bubbles improves.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of the present invention, a distance A between a gas injection position where a plurality of gas injection ports are arranged in the width direction of the tundish bottom and a hot water receiving position at the bottom of the tundish which receives molten steel from a ladle. And the distance B between the gas injection position and the hot water supply hole to the mold of the molten steel received.
/ B is a value in the range of 4/6 to 6/4, and the amount of gas blown is 5.0 per molten steel t passing through the tundish.
１５15.0 N liters (hereinafter referred to as N liters / molten steel t).

The gas injection port may be a porous refractory or a refractory in which a plurality of thin steel tubes having an inner diameter of about 1 mm are embedded. The size of one of the refractories of the gas inlet is not particularly limited, but from the viewpoint of easy handling such as mounting work to the bottom of the tundish, the horizontal cross section is to be a rectangle of about 50 to 100 mm. Is good.

In the method of the present invention, a plurality of refractories at the gas blowing ports are arranged in the width direction of the bottom of the tundish. At this time, it is preferable to arrange the gas inlets so that the total length in the tundish width direction of the arranged gas inlets is 50% or more of the total width of the bottom of the tundish. It is preferable to arrange them evenly in the width direction. FIG. 1B shows an example in which the gas blowing ports are arranged over the entire width of the tundish. FIG. 1C shows an example in which the gas blowing ports are arranged evenly at about 60% of the length of the entire width. 50 of full width length
%, It is difficult to form a circulating flow due to the upward flow of molten steel. It is more preferable to arrange a gas blowing port over the entire width of the tundish and blow the gas. A more uniform updraft is obtained over the entire width of the tundish.

The ratio A / B of the distance A to the distance B is 4/6 to 6
By circulating gas from a plurality of inlets arranged at the bottom of the tundish within the range of / 4, two circulating flows of molten steel are formed in the tundish. Ratio A / B
Is less than 4/6 or more than 6/4, as described above, when the upward flow of molten steel reaches the molten steel surface and becomes the molten steel flow in the ladle direction or the opposite direction of the ladle, the molten steel flow Is weak, so that a circulating flow is hardly formed. A more preferable range of the ratio A / B between the distance A and the distance B is 4.5 / 5.5.
5.5 / 4.5.

The distance between the molten steel receiving position from the ladle and the gas blowing position at the bottom of the tundish is 0.3.
It is desirable to set it to about 3.0 m. At a short distance of less than 0.3 m, the flow of molten steel supplied from a long nozzle or the like provided at the lower part of the ladle reaches the inert gas blowing position because the flow of the molten steel is too fast.
An upward flow of molten steel is unlikely to be formed. When the length is longer than 3.0 m, it is difficult to form a circulating flow over the entire area in the tundish, and the tundish becomes large, which is not economical.

The ratio A / B of the distance A and the distance B is set to a value within an appropriate range as described above, and the gas blowing amount is 5.0 to 1
5.0N liter / t of molten steel. With the blowing amount in this range, the force of the bubble of the blown gas rises,
In the vicinity of the gas injection port, an upward flow of molten steel is likely to be formed.

If it is less than 5.0 Nl / t of molten steel, an upflow of the molten steel is hardly formed in the vicinity of the gas injection port. 1
If it exceeds 5.0 Nl / molten steel t, the molten steel surface in the tundish fluctuates up and down due to gas bubbles, and it becomes easy for the flux added on the molten steel to be entangled in the molten steel. Flux and the like entrained in the molten steel are easily brought into the molten steel in the mold,
It tends to remain as non-metallic inclusions in the slab. As the gas to be blown, an inert gas such as a nitrogen gas or an Ar gas can be used.

In FIG. 1A described above, an example in which the lower weir is arranged has been described. However, the formation of two circulating flows in the case where the lower weir is not arranged will be described with reference to a part of FIG. I do. The upward flow 10 of the molten steel is formed by the force of the gas bubbles 15 blown from the gas blowing ports 4 arranged in the width direction of the bottom of the tundish to float. After reaching the vicinity of the molten steel surface, the ascending flow 10 is divided into a molten steel flow 11 in the ladle direction and a molten steel flow 12 on the opposite side. The molten steel flow 11 toward the ladle changes its direction downward near the hot water receiving position or near the tundish side wall, and a circulating flow of one molten steel is formed. Furthermore, the molten steel flow 12 heading in the opposite direction of the ladle is
The flow is downward in the vicinity of the tundish side wall, and a part of the flow flows from the hot water supply hole into the mold. However, since the amount of molten steel flowing in the direction of the gas injection port is large, a circulating flow of one molten steel is formed. In this way, two circulating flows are formed.

At the bottom of the tundish, at least a region between the molten steel receiving position from the ladle and the gas injection position or a region between the gas injection position and the molten steel supply hole for the molten steel received from the ladle is a lower weir. It is desirable to arrange. that time,
The height of the lower weir is 70 to 8 times the height of the molten steel in the tundish.
It is desirable to set it to 0%. As described above, the circulation flow is likely to be formed more effectively. The material of these lower weirs is
The same refractory material as the other tundish portions can be used. For example, refractories such as ordinary high alumina, magnesia, and zirconia materials may be used.

As the nozzle provided at the lower part of the ladle, a long nozzle dipped in molten steel in a tundish is preferably used. At this time, it is preferable that the ejection hole of the long nozzle has one downward hole. When a long nozzle is used, the molten steel supplied from the ladle does not directly act on the molten steel flow formed near the surface of the molten steel in the tundish, and the molten steel flows are stabilized.

Although FIG. 1 shows an example in which only one strand is used, the method of the present invention can be applied to a tundish having two or more strands.

[0029]

EXAMPLE Using a vertical bending type continuous casting machine, a low carbon steel having a C content of 0.05% by mass was formed to a thickness of 200 mm and a width of 120 mm.
A 0 mm cross section was cast into a rectangular slab at a speed of 1.2 m / min. One heat is about 80t.

The shape of the tundish is an ordinary box shape,
Its inner size is 800mm wide, 1250mm high,
The length was 2500 mm. The capacity is about 18t. The distance between the molten steel receiving position from the ladle and the hot water supply hole to the mold at the bottom of the tundish was 2000 mm. The distance between the hot water receiving position or the hot water supply hole and the adjacent side wall was the same. The depth of the molten steel was adjusted to be constant at 1000 mm.

In the test for disposing a gas inlet at the bottom of the tundish, a normal high alumina porous refractory inlet was used. One porous refractory had a square horizontal cross section and a side of 50 mm, and these blowing ports were arranged as follows. That is, the distance A between the gas injection position where a plurality of gas injection ports are arranged in the width direction of the tundish and the hot water receiving position at the bottom of the tundish that receives the molten steel from the ladle, and the gas injection position and the mold of the molten steel received. A / B with the distance B between the hot water supply hole
Was changed in position in the range of 3/7 to 7/3 and arranged. In the width direction of the tundish, the gas injection ports are arranged uniformly in the width direction of the tundish so that the total length of the gas injection ports is 30%, 50%, or the entire width of the entire width of the tundish. .

An Ar gas was used as the gas to be blown, and the amount of the blown gas was changed in the range of 5.0 to 15.0 Nl / t of molten steel for the test. In some tests, Ar gas was not blown.

In some tests, at the bottom of the tundish,
In the vicinity of the hot water receiving position between the molten steel receiving position from the ladle and the gas blowing position, and near the hot water supplying portion between the gas blowing position and the hot water supply hole to the molten steel casting mold, respectively, Weirs were placed. The distance between the hot water receiving position and the lower weir, and the distance between the lower weir and the hot water supply hole were each 300 mm. The height of the lower weir is 80 times the height of the molten steel in the tundish.
% Was set to 800 mm.

After the casting operation such as the casting speed was stabilized, a molten steel sample having a diameter of 30 mm and a length of 100 mm was collected by the bomb method in the vicinity of the hot water receiving portion in the tundish and in the mold. The cross section of the obtained sample was polished to 40
The number of oxides having a size of 5 μm or more, that is, nonmetallic inclusions was examined for each particle size by an optical microscope at 0 × magnification. The value obtained by dividing the number of oxides in the molten steel in the mold by the number of oxides in the molten steel in the vicinity of the receiving part in the tundish was determined for each particle size, and expressed as a reduction ratio of the oxides in the molten steel. Therefore, the smaller the value of the oxide reduction ratio, the more effectively the oxide was removed.

Further, the flow analysis of the molten steel in the tundish was performed based on each test condition such as the shape of the tundish, the conditions for blowing Ar gas, and the casting speed. In the flow analysis of molten steel, energy conservation equation, momentum conservation equation, mass conservation equation, gas bubble kinetic equation,
And the transport equation of the distribution density of bubbles was coupled, and the turbulence model was analyzed using a κ-ε model.

From the analysis results of the flow state of the molten steel, the molten steel supplied into the tundish becomes an upward flow near the gas injection port, and then the upward flow of the molten steel flows in the ladle direction and on the opposite side. It was evaluated whether or not two circulating flows were formed in the tundish by being divided into a molten steel flow. Evaluation ○ indicates that two strong circulating flows are formed, and evaluation △ indicates that two circulating flows are formed.
When the flow was weak, the evaluation x was made when the circulation flow was not formed. Table 1 shows the test conditions and test results.

[0037]

[Table 1] Test No. of the present invention example. 1 to No. In 4, the value of the ratio A / B for the gas injection position is set to 4/6 or 6/4,
5.0Nl / Molten steel t or 1 from full width
The gas was blown into the molten steel at a blowing gas amount of 5.0 Nl / t of molten steel.

In these tests, the reduction ratio of oxides in molten steel having a size exceeding 50 μm was 0.05 to 0.14, and the oxides in the molten steel floated to effectively move out of the molten steel system. Removed. Fine oxides in molten steel of less than 10 μm were also effectively removed outside the molten steel system at a reduction ratio of 0.27 to 0.45. The flow analysis results of the molten steel also confirmed that two strong circulating flows were formed.

Test No. of the present invention example 5 and No. 5 In No. 6, the value of the ratio A / B with respect to the gas injection position was set to 5/5, and Ar gas was blown into the molten steel from the entire width at a blowing gas amount of 5.0 Nl / molten steel t or 15.0 Nl / molten steel t.

In these tests, the reduction ratio of oxides in molten steel having a size exceeding 50 μm was 0.02 or 0.10.
The oxides in the molten steel floated and were effectively removed outside the molten steel system. Even small oxides in the molten steel of less than 10 μm were effectively removed outside the molten steel system at a reduction ratio of 0.25 or 0.40. Furthermore, the flow analysis results of the molten steel also confirmed that two strong circulating flows were formed. The test No. described above. 1 to No. The result that was better than 4 was that the value of the ratio A / B with respect to the gas injection position was 5/5.
This is an effect of 5.

Test No. of the present invention example 7 and No. 7 In No. 8, the value of the ratio A / B with respect to the gas injection position was set to 5/5, and Ar gas was blown into the molten steel from the entire width at a blowing gas amount of 5.0 Nl / molten steel t or 15.0 Nl / molten steel t. In both cases, a lower weir was placed at the bottom of the tundish.

In these tests, the reduction ratio of oxides in molten steel having a size exceeding 50 μm was 0.02 or 0.08.
The oxides in the molten steel floated and were more effectively removed outside the molten steel system. Fine oxides in the molten steel of less than 10 μm were also removed more effectively outside the molten steel system at a reduction ratio of 0.19 or 0.35. Furthermore, the flow analysis results of the molten steel also confirmed that two strong circulating flows were formed. The test No. described above. 5 and No. 5 The result that was better than 6 was the effect of disposing the lower weir at the bottom of the tundish.

Test No. of the present invention example. In No. 9, the gas was blown only from a position corresponding to 30% of the entire width of the tundish with respect to the gas blowing position. Other test conditions are test N
o. Same as 6. The reduction ratio of oxide in molten steel having a size exceeding 50 μm is 0.26, and the reduction ratio of minute oxide in molten steel of less than 10 μm is 0.50, which has an oxide removing effect. The effect is shown in Test No. 1 to No.
It was a little smaller than 8. In the flow analysis results of molten steel,
Although two circulating flows were formed, it was confirmed that the flows were slightly weak, which was an analysis result supporting the test results.

Test No. of Comparative Example In No. 10, Ar gas was not blown into the molten steel. The reduction ratio of minute oxides in the molten steel of less than 10 μm was 0.98, which was hardly levitated or removed. In the flow analysis of the molten steel, no circulating flow was formed.

Test No. of Comparative Example 11 and No. 12
Then, the value of the ratio A / B with respect to the gas injection position is 3/7.
Or tested as 7/3. These values are out of the conditions defined by the method of the present invention. In addition, from the entire width, 5.0 N l / mol of steel t or 15.0 N
The gas was blown at a rate of 1 liter / t of molten steel. These values of the blown gas amount are values outside the conditions defined by the method of the present invention.

In these tests, the reduction ratio of oxides in molten steel having a size exceeding 50 μm was 0.30 or 0.35.
And the effect of removing oxides in the molten steel was small. Further, the reduction ratio of minute oxides in the molten steel of less than 10 μm was 0.78 or 0.85, and was hardly removed outside the molten steel system. In the flow analysis results of molten steel, two circulating flows were formed, but it was confirmed that the flows were weak, and the analysis results supported the test results.

Test No. of Comparative Example 13 and No. 14
Then, the value of the ratio A / B with respect to the gas injection position is 5/5
And This value is a value within the range defined by the method of the present invention. In addition, Ar gas was blown into the molten steel from the entire width at a blowing gas amount of 2.5 N l / t molten steel or 20.0 N l / t molten steel t. These values are out of the conditions defined by the method of the present invention.

Test No. 1 with a small gas injection amount of 2.5 Nl / t of molten steel. In No. 13, the reduction ratio of the oxide in the molten steel having a size exceeding 50 μm was 0.35, and the effect of removing the oxide in the molten steel was small. Furthermore, 10 μm
The reduction ratio of minute oxides in the molten steel less than 0.85 was hardly removed outside the molten steel system. The results of the flow analysis of the molten steel also confirmed that a circulating flow was not formed because the amount of gas blown was small.

The gas blowing rate is 20.0 Nl /
Test No. In No. 14, the reduction ratio of oxides in each molten steel by the particle size was 0.80 to 1.20, and the large oxides in the molten steel supplied into the tundish resulted in an increase. . The flow analysis results of molten steel confirmed that a circulating flow was formed,
The amount of gas blown was too large and the flux on the molten steel surface in the tundish was involved in the molten steel, resulting in a bad result.

[0050]

According to the method of the present invention, even minute oxides in molten steel can be removed at low equipment cost and production cost, and a cast piece excellent in cleanliness can be obtained.

[Brief description of the drawings]

FIG. 1 shows the application of the method of the present invention to a 2
It is a schematic diagram which shows the case where the circulation flow of two molten steels is formed.

[Explanation of symbols]

1: Ladle 2: Long nozzle 3: Tundish 4: Gas inlet 5: Hot water supply hole 6: Immersion nozzle 7: Mold 8: Lower weir 9: Lower weir 10: Upflow 11: Molten steel flow toward ladle 12 : Molten steel flow on the opposite side 13: Circulating flow 14: Circulating flow 15: Bubbles 16: Molten steel A: Distance between hot metal receiving position from ladle at ladle bottom and gas blowing position B: Tundish bottom The distance between the gas injection position and the hot water supply hole to the mold of the molten steel that has been received C: The receiving position at the bottom of the tundish that receives molten steel from the ladle

Claims (1)

[Claims] 1. A gas blowing port is provided in a width direction of a bottom of a tundish, which is a direction perpendicular to a direction connecting a hot water receiving position of a bottom of a tundish for receiving molten steel from a ladle and a hot water supply hole to a casting mold of the received molten steel. A distance A between a gas injection position where a plurality of gas injection ports are arranged and a hot water receiving position at the bottom of the tundish, a distance B between the gas injection position and a hot water supply hole to the mold, and Ratio A / B of 4 /
The value is in the range of 6 to 6/4, and the amount of gas blown is 5.0 to 15.0 per molten steel t passing through the tundish.
A continuous casting method for steel, wherein gas is blown into molten steel in a tundish under a condition of N liters.