JP2000233260A - Ingot-making method restraining boiling of molten steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ingot having good surface after ingot-making in a bottom-pouring ingot-making of molten steel. SOLUTION: In the ingot-making method of the molten steel, with which the bottom part of a molten steel pouring tube 1 and the bottom part of bottom-pouring molds 2A, 2B, 2C are communicated through a runner 2R and the molten steel stream 7 flowing down from the bottom part of a ladle 6 is poured from the upper part of the molten steel pouring tube 1 and flows in from the bottom parts of the bottom-pouring molds 2A, 2B, 2C through the runner 2R to make the ingot in the bottom-pouring molds 2A, 2B, 2C, the stream of the molten steel 7M in the inner part of the molten steel pouring tube is made to low speed by forming the inner diameter of the molten steel pouring tube 1 to the large diameter so as to reduce the variation of the molten steel surface caused by gas boiling in the bottom- pouring molds 2A, 2B, 2C and thus, the float-up of the gas G contained in the molten steel 7M is promoted and the gas quantity flowing in the bottom-pouring molds 2A, 2B, 2C is reduced. Alternatively, a sealing body surrounding the molten steel stream 7 between the bottom part of the ladle 6 and the upper part of the molten steel pouring tube 1 is arranged to prevent the development of the gas caused by the entrapment of atmosphere and the atmosphere oxidizing reaction of the components in the molten steel and thus, the gas quantity flowing in the bottom-pouring molds 2A, 2B, 2C is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, a method in which the bottom of one molten steel injection pipe and the bottom of a plurality of casting molds are communicated via a runner, and the molten steel flow flowing down from the bottom of the ladle is provided. A method for suppressing boiling of molten steel suitable for obtaining an ingot by injecting from the upper part of a molten steel injection pipe, flowing from each bottom of the lower casting mold through a runner, and solidifying and ingoting in the lower casting mold. It is about.

[0002]

2. Description of the Related Art Molten steel produced by a converter or an electric furnace is formed into a solidified slab such as a slab or a steel ingot by a continuous casting method of continuous casting or an ingot casting method of batch casting.
Thereafter, it is subjected to slab rolling, and each of such continuous casting method and ingot making method has advantages and disadvantages.

FIGS. 3 and 4 show an example of an ingot-making method for casting molten steel in a batch manner, in which a bottom portion of one molten steel injection pipe 1 arranged at the center of a platen and a plurality (FIG. (In the example shown, 12) Sub casting molds 2A, 2B, 2C, 3A, 3B,
The molten steel flow 7 which is communicated with the bottoms of 3C, 4A, 4B, 4C, 5A, 5B, and 5C through runners 2R to 5R in a plurality of directions (four directions in the illustrated example) and flows down from the bottom of the ladle 6. From the upper part of the molten steel injection pipe 1 and the lower casting molds 2A, 2B, 2C, 3A, 3B, 3C, 4A, 4 through the runners 2R to 5R.
B, 4C, 5A, 5B, and 5C, each of which flows from the bottom and flows into the respective casting molds 2A, 2B, 2C, 3A, 3B, and 3
The ingot is obtained by solidifying and agglomerating inside C, 4A, 4B, 4C, 5A, 5B, 5C.

[0004]

However, in the conventional ingot making method, as shown in FIG. 3, since the flow speed of the molten steel 7M injected into the molten steel injection pipe 1 in the direction of arrow A is high,
The gas G originally contained in the molten steel 7M, or as shown in FIG.
The gas G contained therein passes through the runners 2R to 5R, especially the lower casting molds 2A to 5A close to the molten steel injection pipe 1.
(2B-5B) and flow into the lower casting mold 2A-5
A (2B to 5B) causes boiling and causes fluctuations in the molten metal level, thereby causing the ingot-forming powder 8 as shown in FIG.
Layer state is disturbed, the ingot forming powder 8 is hardly formed between the inner wall surface of the casting mold and the molten steel in the form of a molten thin film, and the surface skin quality of the ingot is deteriorated. There has been a problem that a surface flaw may be generated on the piece.

In the case of molten steel 7M containing Pb, as shown in FIG. 5, the entrained gas in the direction of arrow B causes Pb to oxidize in the atmosphere and generate PbO gas.
bO gas flows through the runners 2R to 5R, especially the molten steel injection pipe 1.
The problem is that, as described above, the surface of the steel slab after the slab rolling may be caused by the flow into the lower casting molds 2A to 5A (2B to 5B) which are close to the above and cause boiling. there were.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is intended to prevent a gas component from reaching a casting mold through a runner as much as possible and to prevent the gas component from flowing into the mold. In this way, it is possible to prevent boiling in the casting mold, which causes fluctuations in the molten metal surface and breaks the layer state of the ingot powder, and prevents the deterioration of the surface skin of the ingot after ingot casting. It is intended to provide a lump method.

[0007]

According to a first aspect of the present invention, there is provided a method for suppressing ingot boiling of molten steel according to the present invention, wherein the bottom of a molten steel injection pipe and the bottom of a lower casting mold are connected via a runner. The molten steel is poured from the bottom of the ladle, and the molten steel flows from the bottom of the ladle. In reducing the fluctuation of the molten steel level due to gas boiling in the mold, the inside diameter of the molten steel injection pipe was increased to slow down the flow of the molten steel inside the molten steel injection pipe and promote the floating of the gas contained in the molten steel. Reducing the amount of gas flowing into the casting mold and / or providing a seal between the bottom of the ladle and the top of the molten steel injection pipe to enclose the molten steel flow, thereby producing gas by entrainment of the atmosphere and atmospheric oxidation of components in the molten steel. To reduce the amount of gas flowing into the casting mold To it, it is characterized in.

Further, in an embodiment of the method for suppressing ingot boiling of molten steel according to the present invention, as described in claim 2, the inner diameter of the molten steel injection pipe is twice to 3 times the outer diameter of the molten steel flow. By making it five times, the flow of the molten steel inside the molten steel injection pipe is slowed down, and the floating of the gas contained in the molten steel is promoted.

[0009] Similarly, in the embodiment of the method for suppressing ingot boiling of molten steel according to the present invention, the molten steel is Pb-containing free-cutting steel, and the bottom of the ladle and the top of the molten steel injection pipe are described. A seal body surrounding the flow of molten steel is provided between them to prevent entrainment of air and generation of PbO gas due to an atmospheric oxidation reaction of Pb in the molten steel.

[0010]

FIG. 1 shows an embodiment of the present invention, in which a bottom portion of a molten steel injection pipe 1 arranged on a surface plate and a plurality of subnotes, for example, as shown in FIG. Mold 2A,
2B, 2C, (3A, 3B, 3C), (4A, 4B, 4
C), the bottom of (5A, 5B, 5C) and runner 2R (3
R, 4R, 5R), the molten steel flow 7 flowing down from the bottom of the ladle 6 is injected from the upper part of the molten steel injection pipe 1, and is poured through the runner 2R (3R, 4R, 5R). Mold 2A, 2
B, 2C, (3A, 3B, 3C), (4A, 4B, 4
C), 7M of molten steel flows from the bottom of (5A, 5B, 5C) and the casting molds 2A, 2B, 2C, (3A, 3
B, 3C), (4A, 4B, 4C), (5A, 5B, 5
In solidifying and agglomerating the inside of C) to form an ingot, the inner diameter of the molten steel injection pipe 1 is increased, for example, so that the inner diameter of the molten steel injection pipe 1 is twice to 3.5 times the outer diameter of the molten steel flow 7. The diameter of the runner 2R (3R, 3R, 3R, 3R, 4R,
5R) via the lower casting molds 2A, 2B, 2C,
(3A, 3B, 3C), (4A, 4B, 4C), (5
A, 5B, 5C), and by maintaining the layered state of the ingot powder 8 without the occurrence of boiling, the ingot powder 8 can be formed between the inner wall of the casting mold and the molten steel. Is formed in the form of a molten thin film.

[0011] By doing so, the surface texture of the ingot can be made good, and it is possible to make it difficult for surface defects to occur in the slab after slab rolling.

When the inner diameter of the molten steel injection pipe 1 is enlarged, if the inner diameter of the molten steel injection pipe 1 is smaller than twice the outer diameter of the molten steel flow 7, the flow velocity of the molten steel 7M in the molten steel injection pipe 1 is reduced. It is difficult to effectively reduce the size of molten steel 7
Since it is difficult to expect the promotion of the floating of the gas component in the M, the amount of the gas component flowing to the runner 2R (3R, 4R, 5R) tends to increase, and the inner diameter of the molten steel injection pipe 1 is reduced by the molten steel flow 7
If it is larger than 3.5 times the outer diameter of the molten steel injection pipe 1
This is not preferable because the amount of solidified steel remaining inside the steel tends to increase and the yield tends to decrease.

As shown in FIG. 2, a seal member 9 surrounding the molten steel flow 7 is provided between the bottom (sliding nozzle 6S) of the ladle 6 and the upper part of the molten steel injection pipe 1 so as to entrain the atmosphere and prevent the molten steel from flowing. Prevent gas generation by the atmospheric oxidation reaction of the components, and mold the sub casting molds 2A, 2B, 2C, (3A, 3
B, 3C), (4A, 4B, 4C), (5A, 5B, 5
The amount of gas flowing to C) is reduced.

When the molten steel 7M is a Pb-containing free-cutting steel, a seal 9 is provided to prevent entrainment of atmospheric gas, thereby generating PbO gas by an atmospheric oxidation reaction of Pb contained in the molten steel. Can be prevented, the lower casting molds 2A, 2B, 2C, (3A, 3
B, 3C), (4A, 4B, 4C), (5A, 5B, 5
Gas boiling in C) will be suppressed,
It is possible to improve the surface texture of the ingot made of Pb-containing free-cutting steel.

[0015]

Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to only such an embodiment.

As for the ingot casting apparatus, one having an enlarged inner diameter of the molten steel injection pipe 1 as shown in FIG. 1 and one having a conventional inner diameter as shown in FIG. Using the one provided with the seal member 9 as shown and the one not provided with the seal member (9) as shown in FIG.

The lower casting molds 2A, 2B, 2C, (3
A, 3B, 3C), (4A, 4B, 4C), (5A, 5
B, 5C), the ingot-injected powder 8 was previously charged, and then the under-injected ingot was started.

Then, each of the ingots is subjected to slab rolling, and among these, the ingots formed by the casting molds 2A, 3A, 4A, and 5A closest to the molten steel injection pipe 1 are subjected to slab rolling. When the average percentage of defective surface skin of each steel slab was examined, the results were also shown in Table 1.

[0019]

[Table 1]

As is clear from the results shown in Table 1, P
In the molten steel not containing b, when the sealing body 9 is provided between the bottom of the ladle 6 and the upper part of the molten steel injection pipe 1 with the inner diameter of the molten steel injection pipe 1 as the conventional one, the entrainment of the atmosphere is prevented. It is possible to reduce the gas content in the molten steel, and when the inside diameter of the molten steel injection pipe 1 is enlarged, the flow of the molten steel 7M can be slowed down. 2A, 3A, 4
A, because the flow of gas components into 5A can be suppressed,
The defective rate of the surface skin of the slab after the slab rolling can be reduced, and the defective rate can be further reduced by adopting both the installation of the seal body 9 and the enlargement of the inner diameter of the molten steel injection pipe 1. Met.

Further, although the defective rate of molten steel containing Pb is slightly higher than that of molten steel containing no Pb, the present invention is applied compared to the case where the inner diameter of the conventional molten steel injection pipe 1 is used and the seal member 9 is not provided. In this case, it was possible to considerably reduce the defect rate of surface defects of the slab after slab rolling.

[0022]

According to the method for suppressing ingot ingot of molten steel according to the present invention, as described in claim 1, the bottom of the molten steel injection pipe and the bottom of the casting mold are communicated via a runner, The molten steel flow that flows down from the bottom of the ladle is injected from the upper part of the molten steel injection pipe, flows in from the bottom of the lower casting mold through the runner, and ingots in the lower casting mold. In reducing the fluctuation of the molten steel level due to gas boiling, the inside diameter of the molten steel injection pipe was increased to slow down the flow of the molten steel inside the molten steel injection pipe, to promote the floating of the gas contained in the molten steel, Reducing the amount of flowing gas and / or providing a seal surrounding the molten steel flow between the bottom of the ladle and the top of the molten steel injection pipe to prevent entrainment of the atmosphere and gas generation due to atmospheric oxidation of components in the molten steel; To reduce the amount of gas flowing into the casting mold This makes it possible to suppress the occurrence of gas boiling in the casting mold and to prevent the layer state of the casting powder from being destroyed, thereby melting the casting powder between the inner wall of the casting mold and the molten steel. It is possible to form a uniform film, and it is possible to obtain a remarkably excellent effect that it is possible to improve the surface condition of a steel slab after slab-rolling such an ingot.

And, as described in claim 2,
By making the inner diameter of the molten steel injection pipe 2 to 3.5 times the outer diameter of the molten steel flow, the flow of the molten steel inside the molten steel injection pipe is slowed to promote the floating of the gas contained in the molten steel. A remarkably excellent effect is achieved in that the generation of gas boiling in the casting mold can be effectively suppressed.

Still further, as described in claim 3, the molten steel is a Pb-containing free-cutting steel, and a seal is provided between the bottom of the ladle and the top of the molten steel injection pipe to enclose the flow of the molten steel to entrain the atmosphere. And PbO by atmospheric oxidation reaction of Pb in molten steel
By preventing the generation of gas, a remarkably excellent effect that it is possible to effectively suppress the occurrence of gas boiling in the sub casting mold even in the sub casting ingot of molten steel containing Pb which is easily oxidized in the atmosphere. Brought.

[0025]

[Brief description of the drawings]

FIG. 1 is a basic explanatory diagram showing an embodiment of a method for suppressing ingot boiling of molten steel according to an embodiment of the present invention.

FIG. 2 is a partial explanatory view showing another embodiment of the method for suppressing ingot boiling of molten steel according to the present invention.

FIG. 3 is a basic explanatory diagram showing a conventional underflow lump method according to a conventional example.

FIG. 4 is an explanatory plan view showing an example of the arrangement of a casting mold in the casting method;

FIG. 5 is a partial explanatory view showing a conventional method of making an ingot under lump.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molten steel injection pipe 2A, 2B, 2C Undercasting mold sharing runners 2R Runners 3A, 3B, 3C Undercasting mold sharing runners 3R Runners 4A, 4B, 4C Underrunner sharing runners Casting mold 4R Runner 5A, 5B, 5C Lower casting mold that shares runner with each other 5R Runner 6 Ladle 7 Molten steel flow 7M Molten steel 8 Ingot powder 9 Seal body

Claims (3)

[Claims] 1. A bottom of a molten steel injection pipe and a bottom of a casting mold are communicated via a runner, and a molten steel flow flowing down from a bottom of a ladle is injected from an upper portion of the molten steel injection pipe, and the casting mold is passed through a runner. In order to reduce the fluctuation of the molten steel level due to gas boiling in the sub casting mold in the ingot casting method of molten steel that flows from the bottom of the casting pipe and ingots in the casting mold, the inside diameter of the casting pipe is increased by increasing the inner diameter of the casting pipe. Slowing the flow of molten steel inside to promote the levitation of gas contained in the molten steel to reduce the amount of gas flowing into the casting mold and / or to reduce the flow of molten steel between the bottom of the ladle and the top of the molten steel injection pipe A method of suppressing boiling of molten steel, comprising: providing a seal body surrounding a flow to prevent entrainment of air and gas generation due to an atmospheric oxidation reaction of components in the molten steel to reduce the amount of gas flowing into a sub casting mold. 2. The flow rate of the molten steel in the molten steel injection pipe is reduced by setting the inner diameter of the molten steel injection pipe to be twice to 3.5 times the outer diameter of the molten steel flow, so that the gas contained in the molten steel rises. The method for suppressing ingot boiling of molten steel according to claim 1, wherein the ingot is promoted. 3. The molten steel is a Pb-containing free-cutting steel, and a seal is provided between the bottom of the ladle and the top of the molten steel injection pipe so as to enclose the flow of the molten steel, and PbO gas is generated by entrainment of the atmosphere and an atmospheric oxidation reaction of Pb in the molten steel. The method according to claim 1 or 2, wherein boiling of molten steel is suppressed.