JPH0459918A - Method for degassing from molten metal - Google Patents

Abstract

PURPOSE:To efficiently remove gases from a molten metal by inserting iron plate formed with through-holes into a porous material which does not allow the passage of the molten metal but allows the passage of the gases, bringing one surface of the porous material into contact with the molten metal and exposing the other surface to a reduced pressure. CONSTITUTION:A pipe 3 consisting of the porous material sealed at one end is immersed into the molten steel 2 held in a container 1 and the other end of the pipe is connected to a vacuum pump 4 to reduce the pressure in the pipe. Hydrogen 5 generated on the outer side of the pipe in contact with the molten steel is sucked into the pipe in this way and is discharged by the vacuum pump 4. The iron plate are inserted into the porous material to prevent the failure of the porous material at this time. The degassing is executed without degrading the degassing efficiency if the iron plates are formed with the through-holes of >=10% of the total area.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for degassing molten metal.

BACKGROUND OF THE INVENTION Hydrogen, oxygen, nitrogen, and carbon oxide gases are dissolved in molten metal as follows.

H2→2 H(i) 02→20 (2) N2→2 N (3) CO→C+O (4) Here, H2, 02, N2. Co is a gas in a gas, H
lo, N, and C represent gases dissolved in the molten metal.

Therefore, conventional methods for removing gases in molten metal include exposing the molten metal to reduced pressure to remove hydrogen, oxygen, nitrogen, and
A commonly used method is to reduce the amount of each of dissolved hydrogen, dissolved oxygen, dissolved nitrogen, and dissolved carbon by reducing the partial pressure of carbon oxide gas. In this case, gas is generated from inside the molten metal, so the faster the degassing rate is, the more the molten metal will scatter and contaminate the vacuum container and vacuum pump, so it is necessary to clean the vacuum container and vacuum pump. , there were problems such as reduced productivity.

Furthermore, by exposing the molten metal to reduced pressure, the molten metal itself evaporates, resulting in a reduction in the yield of the molten metal. Furthermore, it is necessary to transfer the molten metal from which the gas is to be removed to a dedicated vacuum container, which poses problems such as improving work efficiency.

The present invention was developed to solve these problems and to remove gas from molten metal inexpensively and efficiently.

Means to solve the problem The feature is that it does not allow molten metal to pass through, but
An iron plate with through holes is inserted into a porous material that allows gas to pass through, and one side of the porous material is brought into contact with molten metal.
This is a degassing method in which the gas contained in the molten metal is removed by exposing the other side to reduced pressure.

In the conventional degassing method, the free surface of the molten metal is directly exposed to reduced pressure, so the gas generated inside the molten metal ruptures on the free surface of the molten metal, causing the molten metal to scatter.
This will contaminate the vacuum vessel and vacuum pump. Furthermore, since the free surface of the molten metal is directly exposed to reduced pressure, if the molten metal has a low vapor pressure, the molten metal itself may evaporate. In other words, in the conventional method, various problems occur because the molten metal from which gas is to be removed is directly exposed to a reduced pressure, resulting in a decrease in productivity and yield in the degassing process.

Therefore, in the present invention, various studies have been conducted on methods that do not directly release the gas generated inside the molten metal under reduced pressure. As a result, if the gas generated inside the molten metal is released under reduced pressure through a porous material that does not allow the molten metal to pass through, but allows gas to pass through, it prevents the molten metal from scattering and the molten metal from evaporating in the conventional method. It has been discovered that gas can be removed from molten metal at the same time.

The following is a detailed explanation using the case of removing hydrogen from molten steel as an example. When dehydrogenating molten steel using the conventional method,
A degassing method using a vacuum melting furnace method in which a container containing molten steel is placed in a tank and the tank is depressurized using a vacuum pump to dehydrogenate it, or RH degassing, DH degassing, etc. in which molten steel is sent into a decompression tank A degassing method of dehydrogenation was used. In this case, when the degree of vacuum in the tank or tank is increased, the hydrogen partial pressure decreases, and the amount of equilibrium hydrogen gas dissolved in the molten steel decreases, so that hydrogen gas bubbles are generated from the molten steel. As this hydrogen gas approaches the free surface of the molten steel where the static pressure of the molten steel decreases, its bubble diameter rapidly increases and it leaves the free surface of the molten steel, but when it leaves, it scatters the molten steel.

Furthermore, molten steel normally used industrially contains manganese, and the vapor pressure of manganese is 1@mHg at 1292°C. If the degree of vacuum inside the tank or bath reaches a high vacuum level of 1 mmHz or higher, manganese will not only evaporate and change the molten steel composition, but there is also the risk of contaminating the tank, bath, or vacuum pump with manganese vapor. .

The present invention is a degassing method in which the gas contained in the molten metal is removed by contacting one side of a porous material that does not allow the molten metal to pass through but allows the gas to pass through, and the other side is placed under reduced pressure. It is.

A method of removing hydrogen from molten steel according to the present invention will be explained with reference to FIG. A pipe 3 made of a porous material with one end sealed is immersed in molten steel 2 held in a container 1, and the other end of the pipe is connected to a vacuum pump 4 to reduce the pressure inside the pipe. As a result, hydrogen 5 generated on the outside of the pipe in contact with the molten steel is sucked into the inside of the pipe and exhausted by the vacuum pump 4. As the porous material, a refractory material normally used for processing molten steel with a porosity of 10 to 30% is sufficient.

However, at this time, the porous material may break and molten steel may scatter, which may impede productivity and safety. As a result of various studies to solve these problems,
It has been found that inserting an iron plate into the porous material can prevent breakage of the porous material. However, usually RH
It has been found that when a reinforcing plate, which is used in a immersion tube with a vacuum system, is used, the efficiency of degassing through a porous material, which is the basis of the present invention, is greatly reduced by the reinforcing plate.

Therefore, we conducted various experiments to increase the strength of porous materials without reducing the degassing efficiency, and the results showed that if there are 105 or more through holes in the total area of the iron plate, the degassing efficiency can be improved. It has been found that gas can be degassed without deterioration, and as the percentage of through-holes increases, qualitatively the strength tends to decrease, although this is also affected by the conditions of use, according to the inventors' experience. In this case, if the through hole was up to 60%, no breakage occurred due to insufficient strength.

Example 1 A porous vibrator shown in Table 1 with its lower end closed was heated with a burner for 20 minutes to bring the surface temperature to 300°C, and then
20 kg of molten steel adjusted to the composition shown in Table 2 in a melting furnace.
Immerse the C layer and pump the inside of the porous vibrator to 1 mmH with a vacuum pump.
The pressure was reduced to 1.5 g, and dehydrogenation treatment was performed for 30 minutes.

To reinforce the porous vibrator, a through hole with a diameter of 5 mm was opened in a 3 m thick iron plate by 10% of the total area of the iron plate and was installed at the center of the thickness of the porous vibrator. The surface of the molten steel was sealed with 1% argon, and the experiment was conducted five times.
．． It decreased to 13-2.0 ppm.

Note that no breakage of the porous vibrator occurred.

Comparative Example 1 The porous vibrator shown in Table 1 with its lower end closed was heated with a burner for 20 minutes to bring the surface temperature to 300°C, and then
20 kg of molten steel adjusted to the composition shown in Table 2 in a melting furnace.
Immerse in the C layer and pump the inside of the porous vibrator with a vacuum pump to 1 mmH.
The pressure was reduced to 1.5 g, and dehydrogenation treatment was performed for 30 minutes.

To reinforce the porous pipe, a through hole with a diameter of 5 mm was opened in a 3-layer iron plate by 5% of the total area of the iron plate, and this was installed at the center of the thickness of the porous vibe. The surface of the molten steel was sealed with argon at 1 atm, and the experiment was conducted five times.
It decreased only to 8 to 6.3 pp■. Note that no breakage of the porous vibrator occurred.

Comparative Example 2 The porous vibrator shown in Table 1 with its lower end closed was heated with a burner for 20 minutes to bring the surface temperature to 300°C, and then
2 to the molten steel adjusted to the composition shown in Table 2 in a 0kg melting furnace.
0c■ Soak the cod in the porous pipe with a vacuum pump for 1 g.
The pressure was reduced to 100%, and dehydrogenation treatment was performed for 30 minutes.

It was not used to reinforce porous pipes.

The surface of the molten steel was sealed with argon at 1 atm.

This experiment was conducted five times, and two of them broke during the experiment. The dehydrogenation status of the experiment that did not break was that the initial hydrogen was 6.2
~7.5pp layer of molten steel becomes 1.8~2.0ppm after treatment
According to the present invention, compared to conventional degassing methods, molten metal can be easily and reliably degassed without scattering, and it can be carried out accurately on an industrial scale. It is possible to obtain excellent effects such as degassing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of a method of implementing the present invention. 1-φ・container, 2・kai・molten steel, 3.6...vibrator, 4
...Vacuum pump, 5...Hydrogen.

Claims (1)

[Claims] By inserting an iron plate with through holes inside a porous material that does not allow molten metal to pass through, but allows gas to pass through, one side of the porous material is brought into contact with the molten metal, and the other side is exposed to reduced pressure. A degassing method characterized by removing gas contained in molten metal.