JPH0665626A - Refining method with reduced pressure gas blowing - Google Patents

Abstract

PURPOSE:To improve the contact probability of unrefined molten steel with gas and to shorten the refining time by arranging gas blowing holes facing the bottom part of a ladle and mutually executing the gas blowing. CONSTITUTION:The two gas blowing holes 4-1, 4-2 are arranged so as to face the bottom part of the ladle 1. An immersed tube 3 is arranged into the molten steel 2 in the ladle 1. Pressure in the immersed tube 3 is reduced, and by increasing the gas blowing quantity from the gas blowing hole 4-1, the refining is started. By gas blowing, temporarily, the molten steel stream is stabilized and stagnating parts alpha, beta of the molten steel 2 which does not run into gas bubbles, are formed. After passing the prescribed time, the gas quantity from the gas blowing hole 4-1 is reduced, and the gas blowing quantity from the faced gas blowing hole 4-2 is increased. Then the whole molten steel stream is reversed and the stagnating parts alpha, beta of the molten steel 2 at the time of using the gas blowing hole 4-1 are cancelled. Further, the stream as large block of the molten steel 2 is eliminated, and by developing the fine disturbance, the stirring of the molten steel 2 can be promoted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection decompression refining method for hot metal and molten steel.

[0002]

2. Description of the Related Art Conventionally, in order to remove gas impurities, elements, etc. in molten steel, it is widely used to smelt molten steel by blowing an inert gas such as Ar from a porous brick plug provided at the bottom of a ladle. In addition, a method of further increasing the refining effect by putting the entire ladle in a decompression chamber is also practiced.

Further, in Japanese Patent Application Laid-Open No. 51-55717, a porous brick plug for gas injection is provided, and a molten steel suction port for introducing gas bubbles blown from the bottom and rising in the molten steel is provided to connect to a decompression chamber. It has been proposed to increase the rate of decontamination and extend the life of refractory bricks for refining equipment by means of a gas-injection depressurization refining apparatus for iron and steel.

[0004]

Decontamination of molten steel is promoted by ascending along with gas bubbles and reaching the surface of molten steel in the depressurization refining equipment. However, gas is continuously fed from one place at the bottom of the ladle. In the molten steel refining method of blowing, the molten steel flow becomes a stable large lump at a certain time after the blowing, but a swirling flow and a stagnant zone that do not participate in the upward flow of gas bubbles occur, and until the completion of refining It takes a lot of time.

According to the present invention, the flow of molten steel as a large lump containing a flow not involved in the refining reaction is canceled, fine turbulence is generated, and the flow pattern is reversed to increase the frequency of contact between the molten steel and the blown gas, thereby refining. The present invention provides a gas-blowing decompression refining method that shortens the time required for (1) and reduces the basic unit of refractory material in a ladle.

[0006]

According to the present invention, gas bubbles are blown into molten steel by alternately injecting gas into the molten steel from two gas blowing zones provided opposite to the center of the bottom of a ladle for refining. Is a gas injection depressurization refining method in which the gas is introduced into a dip tube provided in the molten steel surface region and the dip tube is held under reduced pressure, and each gas injection zone has a plurality of gas injection holes.

According to the gas blowing method of the present invention, the amount of gas required for stirring molten steel is blown from one of the gas blowing zones,
When the molten steel flow reaches a steady state, the amount of gas is reduced (zero can be used if zero is possible), and the amount of gas necessary for stirring molten steel is blown from another gas blowing zone.
Similarly, when the molten steel flow reaches a steady state, the amount of gas is reduced and the amount of gas required for stirring molten steel is blown again from the first gas blowing zone. In this way, the gas is alternately blown from the two gas blowing zones.

That is, when the gas is continuously blown from one gas blowing zone, the impurities are removed from the molten steel in the molten steel flow entrained in the rising gas flow, but in the portion not entrained in the rising flow. Decontamination of molten steel in the circulating or stagnant part has not progressed.

This method uses gas injection holes provided at two locations which are almost opposite to the center of the bottom of the ladle, which reduces the amount of gas for agitating molten steel from one location, and the other location. When a predetermined amount of molten steel agitating gas is blown in from above, the molten steel flow pattern reverses, causing a slight disturbance in the molten steel flow, and the molten steel in the part that was circulating or stagnant in other parts becomes an upward gas flow. The molten steel flows together with the molten steel, and the frequency of contact with the molten steel gas in the ladle increases at the same elapsed time as compared with the case where gas is continuously blown from one place.

After a while, a stagnant portion and a circulating portion are similarly generated, but the portions are different from the first portion, and after a predetermined time, the same phenomenon as blowing gas from another gas blowing hole is repeated. become. By alternately blowing the gas for stirring molten steel from these two gas blowing zones, the contact between molten steel in the ladle and the gas, that is, the frequency with which the molten steel is lifted together with the gas to remove impurities from the molten steel Can improve the refining time and reduce the refining time.

An example of the present invention will be described below with reference to the drawings.
In FIG. 1, 1 is a ladle, 2 is molten steel, 3 is a dipping pipe, 4 is Ar piping, 4-1 and 4-2 are Ar blowing holes, 5 is a vacuum pump system, and 6-1 and 6-2 are It is a control valve.

At the bottom of the ladle 1 of the present invention, two Ar blowing holes 4-1 and 4-2 are provided facing each other as shown in FIG. is there. The number of each of the gas injection holes provided at the two locations may be plural.

In the present invention, the immersion pipe 3 is provided in the molten steel 2 in the ladle, and the inside of the immersion pipe is decompressed by the vacuum pump system 5. Before refining, Ar is blown into both Ar blowing holes 4-1 and 4-2 in an amount necessary to prevent molten steel from being inserted. Ar blow hole 4-
Refining was started by increasing the amount of Ar blown from 1
Blowing is performed alternately.

That is, the molten steel flow is temporarily stabilized by Ar blowing from the Ar blowing hole 4-1 and stagnant portions α and β of molten steel that do not encounter Ar bubbles are formed, but Ar blowing is performed at a predetermined time. When the Ar amount in the injection hole 4-1 is reduced and the Ar injection amount from the opposite injection hole 4-2 is increased, the entire molten steel flow is reversed and the molten steel at the time of using the injection hole 4-1 is The stagnant part is resolved.

Further, the flow of the molten steel as a large lump is canceled out, and fine turbulence is generated to promote the stirring of the molten steel. Blow-out hole 4-
The Ar amount of 2 is reduced, and the Ar amount of the blowing hole 4-1 is increased. The shape of the gas injection hole is multiple pipe, single pipe,
Porous bricks, slits, etc. are appropriately adopted.

In the present invention, in the case of fine pores, the blowing gas can be made zero because the molten steel does not enter the inside of the pores due to the surface tension of the molten steel, but when the pore diameter is large,
Adopt a method of continuously blowing a small amount of gas to prevent the injection of molten steel into the gas injection hole.For example, when using a small-diameter pipe injection pipe, the molten steel depth and Although it depends on the inner diameter of the pipe, a gas injection amount of about 10 to 50 Nl / min is required per pipe. By repeating the above, refining is completed in a shorter time than the conventional method.

FIG. 3 shows another example of the present invention. In this example, the blowing holes 4-1 and 4-2 are set as one zone, and the blowing holes 4-3 and 4-4 are opposed to each other. It is also useful in the case of multiple injection holes in one zone.

[0018]

[Examples] Table 1 shows a method and a refining effect of decarburizing and refining a molten steel ladle having a molten steel treatment amount of 175 tons under reduced pressure.

[0019]

[Table 1]

Porous plugs for injecting Ar are provided at two opposing positions on the bottom of the ladle located in the inner wall of the dipping pipe of the decarburizing and refining equipment used in the method of the present invention. As shown in FIG.
With a blowing rate of 200 Nl / min / ke, the C concentration in the molten steel is 300 pp by alternately switching the two blowing locations every minute.
It was possible to reduce m to 10 ppm in 10 minutes. Since a porous plug was used in this experimental example, the amount of Ar blown was nearly zero while Ar was blown at 200 Nl / min / ke from the other porous plug.

For comparison, as shown in Table 1 of the conventional method, when a porous plug for injecting Ar is provided at one place at the bottom of the ladle, the C concentration in the molten steel is 300 ppm to 10 pp.
Ar at 200 Nl / min / ke constant to reduce m to 1
I had to blow for 5 minutes.

When a pipe with an inner diameter of 3 mm was used, 30 Nl / min / ke Ar was blown to prevent molten steel from being inserted while the other pipe was being blown with 200 Nl / min / ke, but the same effect was obtained. It was With the method of the present invention, the decarburization rate was increased by 1.5 times compared with the conventional method, and the refining time was greatly reduced to 2/3.

[0023]

EFFECTS OF THE INVENTION By providing gas blowing holes facing the bottom of a ladle and alternately blowing gas, the contact probability between unrefined molten steel and Ar, for example, is improved, and the refining time is greatly shortened. be able to.

As a result, in the present invention, the refractory basic unit of the ladle is reduced, and the refractory basic unit of 0.6 kg / t-steel in the conventional method is 0.5 kg / t-in the present method. We were able to reduce to steel. As other effects, we were able to confirm the secondary effects of reducing the amount of refining gas used and reducing the basic unit of refractory in the converter by lowering the tapping temperature of the converter.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the present invention.

FIG. 2 is a partial explanatory view of the present invention.

FIG. 3 is a partial explanatory diagram of another example of the present invention.

FIG. 4 is a diagram of an embodiment of the present invention.

Claims (2)

[Claims] 1. Immersion in which gas bubbles are alternately blown into the molten steel from two gas blowing zones facing the center of the bottom of the ladle for refining, and gas bubbles rising in the molten steel are provided in the molten steel surface area. A gas blowing decompression refining method, which comprises introducing the dipping tube into a tube and holding the dipping tube under reduced pressure. 2. The gas injection decompression refining method according to claim 1, wherein the gas injection zone has a plurality of gas injection holes.