JPH0459917A - Method for degassing from molten metal - Google Patents

Abstract

PURPOSE:To efficiently remove gases from a molten metal by bringing one surface of a porous material which does not allow the passage of the molten metal but allows the passage of the gases into contact with the molten metal and fludizing a gas which does not contain the gaseous components to be removed on the surface of the porous material while 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. Refractories which are usually used for treating the molten steel and have 10 to 30% porosity suffice as the porous material. The degassing speed is further improved if the gas 7 which does not contain the gaseous components to be removed is fluidized on the surface of the porous material exposed to the reduced pressure. The volume of the gas to be fluidized is sufficient at about 1 to 2l/min per 1 ton of the molten steel.

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.

N7→2 H(1) 02→20 (2) N2→2 N (3) CO→C+O(4) Here, H2,02, H, co represent the gas in the gas, Hl
o, 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, the molten metal from which the gas is to be removed needs to be transferred to a dedicated vacuum container, resulting in problems such as poor workability.

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
One side of the porous material that allows gas to pass through is brought into contact with molten metal, and the other side is exposed to reduced pressure, while flowing a gas that does not contain the gas component to be removed onto the surface of the porous material exposed to reduced pressure. This is a degassing method that removes gases contained in molten metal.

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 inside the tank or vessel is increased, the hydrogen partial pressure decreases and the equilibrium concentration of hydrogen gas dissolved in the molten steel decreases, so 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. Further, molten steel normally used industrially contains manganese, and the vapor pressure of manganese is 1 mHg at 1282°C. The degree of vacuum inside the tank or tank is 1m■
When the degree of vacuum is higher than Hg, manganese not only evaporates and changes the composition of the molten steel, but also there is a risk of contaminating the inside of the tank, the tank, or the vacuum pump with manganese vapor.

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

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.

At this time, we have discovered that the descaling rate can be further improved by flowing a gas 7 that does not contain the gas component to be removed onto the surface of the porous material exposed to reduced pressure via a gas supply vibro. be. This is because even if you try to suck the hydrogen generated outside the pipe by lowering the hydrogen partial pressure on the inside surface of the pipe with the vacuum pump 4, the hydrogen partial pressure on the inside surface of the vibrator will not be effectively reduced due to the pressure loss inside the pipe. It is thought that this is because the degassing rate was improved because the hydrogen partial pressure on the surface inside the vibrator was effectively lowered by flowing a small amount of gas 7. The amount of gas to be fluidized is approximately 1 to 2 liters per ton of molten steel, and any type of gas is fine as long as it does not contain the gas to be removed, but it is usually a matter of safety and versatility. Considering this, argon gas should be used.

Example 1 The porous pipe shown in Table 1 with its lower end closed was heated with a burner for 20 minutes to reach a surface temperature of 300°C, and then
20 kg of molten steel adjusted to the composition shown in Table 2 in a melting furnace.
C. The porous pipe was immersed in water, and while 0.1 liter/layer of argon was flowing through the porous pipe, the pressure inside the porous pipe was reduced to 1*mHg using a vacuum pump, and dehydrogenation treatment was performed for 30 minutes. The surface of the molten steel was sealed with argon at 1 atm. The initial hydrogen content of molten steel was 6.3 ppm, but after the treatment Q, the hydrogen content decreased to 9 ppm. Incidentally, no molten steel was observed to be scattered from the molten steel surface.

Comparative Example 1 The porous pipe 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.
c) Immerse the inside of the porous pipe with a vacuum pump to 1 mm) without allowing argon to flow into the porous pipe.
The pressure was reduced to 100%, and dehydrogenation treatment was performed for 30 minutes. The surface of the molten steel was sealed with argon at 1 atm. Initial hydrogen 88-3p
The p of molten steel decreased to 1.8 Pp■ after the treatment. Incidentally, no molten steel was observed to be scattered from the molten steel surface.

Effects of the Invention According to the present invention, compared to conventional degassing methods, molten metal can be easily and reliably degassed without scattering of molten metal, and accurate degassing can be performed on an industrial scale. This made it possible to obtain excellent effects such as:

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a method of implementing the present invention. 1... Container, 2... Molten steel, 3... Pipe, 4-...
Battle vacuum pump, 5...hydrogen, 6...-gas supply vibe, 7...gas.

Claims (1)

[Claims] One side of the porous material that does not allow the molten metal to pass through, but allows the gas to pass through, is brought into contact with the molten metal, and the other side is exposed to a reduced pressure, while the gas components that are to be removed are placed on the surface of the porous material exposed to reduced pressure. A degassing method characterized in that gas contained in molten metal is removed by flowing a gas that does not contain molten metal.