JPH036317A - Method and device for ladle refining - Google Patents

Abstract

PURPOSE:To improve a refining effect by immersing a snorkel having an aperture at the bottom end into the molten metal in a ladle, reducing the pressure in the snorkel and blowing gas from near the bottom end thereof or below. CONSTITUTION:The molten metal 2 is put into the ladle 1 and the snorkel 3 having the aperture 3a at the bottom end is immersed into the molten metal 2. The pressure in the snorkel 3 is reduced and the gas is blown from the position near or below the bottom end of the snorkel 3 in the molten metal 2 to cause the stirring and reflux of the molten metal 2 in the snorkel 3. The degassing reaction is effected on the bath surface to be exposed in vacuum in the snorkel 3 in this way) moreover, the volume of the molten metal 2 housed in or right under the snorkel 3 increases and the greater part of the molten metal 2 is stirred and the sufficient bath depth of the molten metal 2 is obtd. The stirring intensity and reflux rate, therefore, increase and the region where the degassing progresses expands. Sufficient degassing is thus executed in a short period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ladle refining method and apparatus for refining molten metal in a ladle.

[Conventional technology]

Since molten steel produced in a steelmaking furnace in which melting and refining is performed in a converter or the like contains a large amount of gas components, a vacuum treatment method is used to degas the gas under vacuum.

FIG. 5 shows how the vacuum degassing method is carried out using the RH vacuum degassing apparatus. The method uses a ladle (10)
Two immersion tubes (301) filled with molten steel (20) to be treated and placed at the lower end of the vacuum chamber (300) from above.
Soak (302). Then, inert gas such as Ar gas is blown into one of the immersion pipes (301), and the molten steel (20) is
into the vacuum chamber (30) via the immersion tubes (301) (302).
0), and the molten steel (20
) is degassed.

Also, Figure 6 shows how to implement the DH vacuum gas method.
In this method, one immersion tube (301) at the lower end of the vacuum tank (300) is immersed in the molten steel (20), and the molten steel in the ladle (lO) is placed in the vacuum tank 3-1 (300). ) and processes it. If this continues, stirring and circulation of the molten steel (20) in the vacuum chamber (300) will be almost impossible or very small, so in reality, the molten steel (20) in the vacuum chamber (300)
By moving up and down the position of 00), the vacuum chamber (300)
The molten steel (20) in the ladle (lO) is taken in and out of the ladle, and the molten steel (20) is degassed while being stirred.

[Problem that the invention seeks to solve]

These methods have been implemented as the most efficient degassing methods to date;
Since the amount of molten steel that is exposed to vacuum and degassed within the chamber is only about 5 to 10% of the total, the degassing efficiency was not sufficient. In addition, it takes time for the entire molten steel (20) to circulate uniformly between the vacuum tank (300) and the ladle (10), and therefore, it takes time for the entire molten steel (20) to be degassed. However, it took a considerable amount of time, and there were still problems in terms of productivity.

The present invention was devised in view of the above-mentioned problems of the prior art, and aims to provide a new ladle refining method and a device used in this method, thereby further improving the efficiency of refining molten metal. It is something to do.

[Means for solving problems]

Therefore, the present inventors have developed a ladle refining method in which molten metal is degassed under vacuum through the following process.

That is, as shown in FIG. 1(a), molten metal (2) is charged into a ladle (1), and a snorkel (3) having an opening (3a) at the lower end is inserted into the molten metal (2). ).

Then, the pressure inside the snorkel (3) is reduced, and gas is blown into the molten metal (2) from near the lower end of the snorkel (3) or from a position below the lower end, as shown in FIG. 3) Molten metal in (2)
Stir and reflux. This gas injection and snorkel (
The depressurization treatment in 3) may be performed at the same time.

In addition to performing these treatments, as shown in the same figure (C), the inside of the ladle (1) is sealed and the inner wall of the ladle (1), the snorkel (3) outer wall, and the molten metal (2) bath are separated. It is also possible to pressurize the void surrounded by the surface. This urinary treatment may be performed simultaneously with the immersion of the snorkel (3).

The above treatment constitutes the present invention, and the degassing reaction is carried out on the bath surface exposed to the vacuum inside the snorkel (3), and the degassing reaction is carried out on the bath surface exposed to the vacuum inside the snorkel (3).
) The stirring and reflux of the molten metal (2) in the snorkel (3) is controlled by the reduced pressure inside the snorkel (3).
The amount of molten metal stored inside or directly under the snorkel (3) increases, the stirring reaches most of the molten metal (2), and the bath depth of the molten metal (2) can be sufficiently varied, so the stirring strength increases. is very large, and the amount of reflux is also large. Therefore, the area where degassing progresses is the molten metal (
2) It will spread to the whole area. In this case, the molten metal (2) other than the inner part surrounded by the inner wall of the snorkel (3) and its downward extension becomes a dead zone where it is not stirred, and from the standpoint of refining efficiency, it is desirable that this part be as small as possible. The present inventors have clarified how large this dead zone should be, based on the experimental results of Examples described later. That is, as shown in FIG. 2, the inner wall of the snorkel (3) and its downwardly extending surface, the bottom surface of the ladle (1), and the molten metal (2) in the area surrounded by the bath surface of the molten metal (2) in the snorkel (3). ) volume W□(snorkel (3
) The amount of molten metal W in the inner portion surrounded by the inner wall and its downward extension surface, ) is the total volume W of the molten metal (2) in the ladle (1). (Total amount of molten metal W in ladle (2)),
Snorkel (3) so that W□/Wo≧0.4
The diameter of the snorkel (3), the immersion depth of the snorkel (3), and the ladle (1)
The pressure in the gap surrounded by the inner wall and the snorkel (3), the outer wall and the bath surface of the molten metal (2), and the pressure inside the snorkel (3) are adjusted and controlled.

Furthermore, the gas blown into the molten metal (2) is supplied by a snorkel (
3) A gas blowing port can be provided at the lower end of the inner wall and the gas can be blown from there toward the center in the radial direction, or it can also be introduced from a nozzle installed in advance at the bottom of the ladle. The former case has the advantage of not requiring maintenance or operational management of the nozzle at the bottom of the ladle, and the efficiency of stirring and degassing is also lower than that shown in Figure 1 (b).
) As shown in (c), the flow of molten metal (2) in the snorkel (3) descends at the center of the snorkel (3),
3) Since the circulating flow rises on the side closer to the inner wall surface, the molten metal (2) in the snorkel (3) is sufficiently stirred, and the degassing efficiency is significantly improved.

Furthermore, the gas can be blown from multiple positions on the inner wall of the snorkel, and a large amount of gas can be blown into the snorkel.

Also, when using a gas that is soluble in the molten metal (2) (for example, N2 gas for molten steel) as the blowing gas, the gas blowing position is near the lower end of the snorkel (3) or near the ladle as described above. (1) Since the gas is released from the bottom side, it dissolves well in the molten metal (2). In addition, when the inside of the ladle (1) is pressurized around the outer periphery of the snorkel (3), the molten metal (2) on the lower end side of the snorkel (3) is also under pressure, so the above soluble gas dissolves better. Furthermore, with this blowing, the inside of the snorkel (3) is filled with molten metal (
Since the reflux of 2) occurs, the pressure of the molten metal (2) is reduced as it approaches the bath surface on the vacuum side, and the dissolved gas is generated as fine gas bubbles. The fluttering of the bath surface due to the floating of gas bubbles expands the bath surface area of the molten metal (2) exposed to the vacuum more than when bubbling an inert gas, since the bubbles have a small diameter and are generated in large quantities. Therefore, the degassing efficiency is extremely high.

Furthermore, since the gas bubbles float while trapping fine inclusions in the molten metal (2), the inclusion removal efficiency is also excellent. Furthermore, slag refining can be performed by adding flux for desulfurization and dephosphorization into the snorkel (3), which increases stirring and increases the interface area between the molten metal and slag due to fine gas bubbles. The efficiency of removing impurities such as phosphorus is also excellent.

The present inventors have further devised an apparatus most suitable for carrying out the above ladle refining method as fourth and fifth inventions.

That is, the ladle refining apparatus of the fourth invention includes a ladle into which molten metal is charged, a snorkel immersed in the molten metal of the ladle, a pressure reducing device that reduces the pressure inside the snorkel, and a molten metal smelter. The basic feature is that it has a gas blowing device that blows gas into the snorkel to stir and circulate the molten metal inside the snorkel.

Further, the ladle refining device of the fifth invention has the entire configuration of the fourth invention device, and also includes a sealing device that closes the ladle opening, and a pressurizing device that pressurizes the inside of the ladle sealed by the sealing device. It also has the following.

Specific examples of the present invention will be described below.

〔Example〕

The present inventors put 250 tons of molten steel into a ladle with an inner diameter of about 4 m, and performed the following treatment (at this time, the bath depth (Ha) in the ladle was about 2.9 m).

First, a cylindrical snorkel (30) with an inner diameter of about 2.8 m and a height of about 12 m is placed in molten steel (20) as shown in FIG.
The ladle (10) opening was closed with a sealing device (40) made of a truncated conical plate.

The other end of the snorkel (30) is connected to a pressure reducing device (not shown) consisting of a vacuum pump, and the other end is connected to the sealing device (40).
Connect the communication hole (41) provided in a part of the snorkel (') to a pressurizing device (not shown) consisting of a pressure pump.
30) while reducing the pressure inside the ladle (1 torr).
0) Inner wall and snorkel (30) Compressed N2 gas was sent to the gap X surrounded by the outer wall and bath surface and pressurized to 2.5 atm. As a result, the snorkel (30
) The bath depth H from the bottom of the ladle (10) of the outer molten steel (20) decreases to about 0.9 m, and on the contrary, the snorkel (
The molten steel (20) in the snorkel (30) rose to a height of about 4 m above the lower end of the snorkel (30).

Then, Ar gas was blown at a flow rate of 1400 Q/min (in all 7 locations) from 7 locations around the lower end of the snorkel (30) toward its radial center.
The molten steel (20) in 30) is stirred and circulated so that an upward flow forms around the center downward flow as shown in the drawing, and the bath surface of this circulating flow is exposed to vacuum to remove the molten steel (20). did gas.

As a result, melt! The time required for the above treatment to reduce the hydrogen concentration in (20) from 3 ppm to 1 ppm was 10 minutes. This was much shorter than the time (15 minutes) required to process the same amount of molten steel using a conventional RH degasser.

11-12- Furthermore, the present inventors varied the degree of pressurization of the gap X and the degree of depressurization in the snorkel (30) during the above treatment, and immersed the snorkel (30) in the bath. The same degassing treatment as described above was performed on the same quality and amount of molten steel (20) while changing the bath depth H of the molten steel (20) in the ladle (10).

Figure 4 shows the processing time required to reduce the hydrogen content in the molten steel (20) to 1 ppm or less, the inner wall of the snorkel (30) and its downward extension, the bottom of the ladle (10), and the bath surface inside the snorkel (30). The volume W of the molten steel (20) in the area surrounded by and the total molten steel W of the molten steel (20) within the area (10).

What ratio did you use to show it? According to this graph, when W, /Wo exceeds 0.4, the processing time rapidly decreases, and when W1/W, exceeds 0.6, it becomes 10 minutes. This is because in a range where W ) clearly indicates that the amount of molten steel gas processed increases.

〔Effect of the invention〕

According to the ladle refining method and apparatus thereof of the present invention detailed above, the ratio of the amount of molten metal in the snorkel where the degassing reaction proceeds is greater than that of the molten metal in the vacuum chamber of the conventional RH degassing device. The ratio is very high compared to the amount, and it is also possible to strongly stir the molten metal inside the snorkel,
The efficiency of degassing inclusion removal and slag refining has improved,
This means that the processing time can be shortened.

[Brief explanation of the drawing]

Figure 1 (a), (b), and (c) are explanatory diagrams showing the basic steps of the first and second invention methods, and Figure 2 is smelting with as little molten metal remaining in the dead zone in the ladle during processing as possible. A detailed explanatory diagram of the third invention that aims to improve efficiency. FIG. 3 is a sectional view schematically showing the ladle refining apparatus used in the embodiment of the present invention. FIG. A graph showing the correlation between the volume ratio of molten steel in the ladle and the refining processing time, Fig. 5 is a sectional view showing the schematic structure of a conventional RH vacuum degassing device, and Fig. 6 is a schematic structure of the same <DH degassing device. FIG. In the figure, (1) and (10) are ladle, (2) is molten metal, and (
20) is molten steel, (3) (30) is snorkel, (40
) indicates a sealing device, and (300) indicates a vacuum chamber. 15-7 2nd Figure 0 Figure □□□□□ --- Vl/, /W. Figure 0 Figure

Claims (7)

[Claims] (1) Charge molten metal into a ladle, immerse a snorkel with an opening at the lower end into the molten metal, further reduce the pressure inside the snorkel, and insert or remove the molten metal from near the lower end of the snorkel. A ladle refining method characterized by blowing gas from a position below the lower end and causing the gas to float in the molten metal in the snorkel, thereby stirring and circulating the molten metal. (2) In the ladle refining method described in the preceding paragraph, the ladle refining method is characterized in that the interior of the ladle is sealed and a gap surrounded by the inner wall of the ladle, the outer wall of the snorkel, and the molten metal bath surface is pressurized. (3) In the ladle refining method described in the preceding paragraph, the step of sealing the interior of the ladle and pressurizing the gap surrounded by the inner wall of the ladle, the outer wall of the snorkel, and the molten metal bath surface is carried out simultaneously with the immersion of the snorkel. A ladle refining method according to claim 2, which is characterized by: (4) In the ladle refining method according to claims 1 to 3, the volume of molten metal in a portion surrounded by the snorkel inner wall, its downward extension surface, the ladle bottom surface, and the molten metal bath surface in the snorkel. The diameter of the snorkel, the immersion depth of the snorkel, and the void area surrounded by the inner wall of the ladle, the outer wall of the snorkel, and the molten metal bath surface so that W_1 satisfies the following conditions with respect to the volume W_0 of the entire molten metal in the ladle. A ladle refining method characterized by adjusting the pressure inside the snorkel as well as the pressure inside the snorkel. W_1/W_0≧0.4 (5) In the ladle refining method according to claims 1 to 4, a gas soluble in the molten metal is used as the gas blown into the molten metal. A ladle refining method according to items 1 to 4 of the scope. (6) a ladle into which molten metal is charged, a snorkel having an opening at the lower end and immersed in the molten metal of the ladle, and a pressure reducing device for reducing the pressure inside the snorkel;
A ladle refining device comprising: a gas blowing device for blowing gas into the molten metal from near the lower end of the snorkel or from a position below the lower end to stir and circulate the molten metal in the snorkel. (7) A ladle into which molten metal is charged, a snorkel having an opening at its lower end and immersed in the molten metal of the ladle, a sealing device for closing the opening of the ladle, and the sealing device. a pressurizing device that pressurizes the inside of the ladle, which is hermetically sealed; a depressurizing device that reduces the pressure inside the snorkel; A ladle refining device characterized by having a gas blowing device for stirring and circulating molten metal.