JPH09225603A - Molten steel casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively remove non-metallic inclusions without reinforcing facilities such as the electromagnetic force by setting the depth of a molten steel receiving part of a tundish to the prescribed value. SOLUTION: The depth of a molten steel receiving part 6 of a tundish is >=1500mm. In the molten steel 1 to be poured from a pouring nozzle 2 in the molten steel receiving part 6, relatively large inclusions are floated at high floating speed, and are collided with smaller inclusions and coagulated. Because the molten steel receiving part 6 is deep, coagulation of fine non-metallic inclusions is promoted. Coarse non-metallic inclusions are floated and separated at a transversely long part 7 (its depth is small) provided in series next to the molten steel receiving part 6. When the depth of the molten steel receiving part 6 is >=1500mm, the separation ratio of inclusions of <=50μm in size becomes not less than 50%. The separation ratio is not affected much by the length of the transversely long part 7. The separation ratio is stable even at a non- stationary part in the terminal stage of the ladle or immediately after the ladle change, and steel of excellent quality can be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of casting molten steel for promoting the separation of deoxidation products, non-metallic inclusions such as slag in molten steel.

[0002]

2. Description of the Related Art Conventionally, in continuous casting, when supplying molten metal to a continuous casting mold, the molten steel received in a ladle is first introduced into a tundish, where non-metallic inclusions in the molten steel are separated, and then continuously cast. This tundish is designed to be cast into a casting mold. Various types of weirs are provided in this tundish to promote the separation of non-metallic inclusions (for example, Japanese Patent Laid-Open No. 62-183947), and molten steel in the tundish A technique for extending the residence time of molten steel in the tundish is disclosed by increasing the size of the tundish centered on the extension of the horizontal length of the flow path (for example, Japanese Patent Publication No. 3-147). However, all of these techniques are aimed at levitation separation of relatively large inclusions having a diameter of 50 μm or more, and separation of minute inclusions having a diameter of 50 μm or less, which occupy most of oxygen in non-metallic inclusions, is performed at a floating speed. It is difficult to separate in the tundish due to its small size.

As a method for separating the small inclusions in the tundish, a technique for capturing and separating the inclusions by blowing fine bubbles (for example, Japanese Patent Laid-Open No. 2-115323) or centrifugal separation and turbulence by electromagnetic stirring. A method of separating and combining flow aggregation (for example, JP-A-4-327345).
Gazette). However, with the method of blowing bubbles, it is difficult to separate the fine inclusions because there is no technique for blowing the fine bubbles necessary for capturing the fine inclusions of 50 μm or less. In addition, when the method using electromagnetic stirring is targeted for the separation of oxide-based non-metallic inclusions in molten steel, the area that can be effectively stirred by electromagnetic force is limited. Has a problem that its effect becomes less diluted.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the problems as described above. In a tundish in which molten steel ladle is poured and flows out into a continuous casting mold, 50 μm is used.
An object of the present invention is to provide a method for removing non-metallic inclusions in molten steel for efficiently and economically separating and removing fine non-metallic inclusions of m or less.

[0005]

The gist of the present invention is that in continuous casting of molten steel, the molten steel received in a ladle is
When pouring into a mold for continuous casting through a tundish, by setting the depth of the molten steel receiving portion of the tundish to 1500 mm or more, nonmetallic inclusions are aggregated and coarsened in the tundish. A method for casting molten steel in continuous casting, characterized in that the floating steel is promoted to supply molten steel containing less non-metallic inclusions into a mold.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a conventional horizontally long tundish provided with a weir (hereinafter referred to as a horizontally long tundish). As a result of performing a water model, a fluid analysis simulation, and a numerical simulation of a coagulation separation reaction of nonmetallic inclusions in the horizontal tundish shown in FIG. 1, as shown in FIG.
While it is almost 100% for those with a diameter of 50 μm or more,
It was concluded that the fine non-metallic inclusions having a diameter of 50 μm or less account for at most 20%.

Here, the separation rate of non-metallic inclusions is defined by the non-metallic inclusions of each diameter, and the amount of non-metallic inclusions in the molten steel flowing from the ladle is defined as a and flows out to the mold. Letting b be the amount of non-metallic inclusions in the molten steel, this is the amount showing the ability to remove inclusions in the tundish defined by (ab) / a × 100 (%). That is, non-metallic inclusions having a diameter of 50 μm or less cannot float and separate themselves in the tundish because they have a very low floating speed, but they have an opportunity to float and separate only after they aggregate and become coarse. In the horizontally long tundish, it is shown that the fine nonmetallic inclusions are not sufficiently aggregated.

Similarly, from the water model experiment and the numerical simulation of the reaction of agglomeration / coarsening, when there is no forced convection due to electromagnetic stirring or the like, the agglomeration of non-metallic inclusions in the tundish is mainly due to Stokes agglomeration. I obtained the knowledge that it will occur. Stokes agglomeration refers to an agglomeration mechanism in which, when a relatively large inclusion in molten steel floats at a higher levitation speed, it collides with an inclusion having a relatively small levitation speed and agglomerates. That is, the separation rate of minute non-metallic inclusions in the horizontal tundish is low because the relatively large non-metallic inclusions float up in a short path in the initial stage due to the small bath depth. This is because the frequency of collision with inclusions is reduced, and the chance of coarsening small non-metallic inclusions is kept low.

From this finding, for the separation of minute non-metallic inclusions, in the tundish where the relatively large non-metallic inclusions remain, the part near the molten steel receiving part from the ladle where the bath depth is large Therefore, the inventors have come to the idea that the provision of the can promote the aggregation of minute non-metallic inclusions.

According to the method for producing clean steel having less non-metallic inclusions of the present invention having the above-mentioned structure, a small non-metal which cannot be normally removed in a large bath depth region of the tundish receiving portion. The inclusions can be separated and removed by coarsening using Stokes aggregation. Therefore, in continuous casting in which molten metal is poured from the ladle to the tundish, clean molten steel with a small amount of non-metallic inclusions can be supplied to the mold not only in the steady part but also at the end of the pot pouring or immediately after the pan is replaced.

[0011]

EXAMPLE FIG. 3 shows an example of a block diagram of a tundish capable of casting a clean steel having less non-metallic inclusions according to the present invention. In the example of FIG. 3, by increasing the bath depth of the injection part 6, the agglomeration of fine inclusions by Stokes agglomeration is promoted, and a horizontally elongated part 7 having a small bath depth is provided in series with this to increase the coarse nonmetallic inclusion. Floating separation of objects. In FIG. 3, when the bath depth (H1) of the injection part and the length (L1) of the laterally long part were changed under various conditions shown in FIG. 4, the removal rate of inclusions was actually measured. As shown, the separation rate of inclusions of 50 μm or less is such that H1 is 1 regardless of changes in L1.
A high value of almost 50% or more was obtained at 500 mm or more. This means that, by increasing the bath depth of the pouring portion, the aggregation of fine non-metallic inclusions was promoted.

Further, in the case of a relatively large nonmetallic inclusion having a size of 100 μm or more in FIG. 4B, the separation rate is L1.
When L1 is smaller than 2000 mm, the separation rate is smaller than that in the conventional horizontally long tundish when the value of H1 is larger than 1500 mm.
This is because the fine inclusions aggregated and coarsened in the pouring part could not be completely floated and separated because the laterally long part was short. Therefore, also in the example of the method for producing clean steel according to the present invention having the configuration shown in FIG. 3 for obtaining molten steel with less non-metallic inclusions, increasing the length of the laterally elongated portion can reduce coarse non-metallic inclusions. Although it is a necessary element for floating separation, the effect of the present invention can be obtained even if it is replaced with another coarse nonmetallic inclusion separation technology already disclosed, for example, a nonmetallic inclusion separation technology using bubbles as an alternative. Not lost

[0013]

As described above, according to the method for producing clean steel of the present invention, which obtains molten steel with less non-metallic inclusions, the cause of defects in the steel sheet can be achieved without excessive facility enhancement such as electromagnetic force. It is possible to effectively remove the non-metallic inclusions, which can produce stable and high-quality steel products not only in the steady pouring part, but also in the non-steady part at the end of the ladle or immediately after the pan is replaced.

[Brief description of drawings]

FIG. 1 is a view showing an example of a conventional horizontal tundish.

FIG. 2 is a diagram showing a result of a simulation calculation of a separation rate of inclusions in the conventional tundish of FIG.

FIG. 3 is a diagram showing an example of a tundish for obtaining clean steel according to the present invention.

FIG. 4 is a view showing a relationship between a bath depth of a tundish pouring portion and a tundish length inclusion separation rate.

[Explanation of symbols]

 1 Molten Steel 2 Injection Nozzle 3 Refractory Weir 4 Conventional Horizontal Tundish 5 Outflow Nozzle 6 Pouring Part (Aggregation Area of Small Inclusions) 7 Horizontal Length (Floating Area of Coarse Inclusions)

Claims (1)

[Claims] 1. In continuous casting of molten steel, when the molten steel received in a ladle is cast into a mold for continuous casting through a tundish, the depth of the molten metal receiving portion of the tundish is set to 1500 mm or more. By doing so, the non-metallic inclusions are aggregated and coarsened in the tundish,
A method for casting molten steel in continuous casting, characterized in that the molten steel containing less non-metallic inclusions is supplied into a mold by promoting floating separation.