JPH06271922A - Production of high cleanliness metal by making molten metal drips - Google Patents

Abstract

PURPOSE:To provide a producing method of high cleanliness metal by making molten metal drips. CONSTITUTION:(1) In the producing method of a clean metal by passing the drips 3 of molten metal 9 through molten slag layer in a vessel having the atmospheric pressure adjusted to non-oxidization and absorbing inclusion in the molten metal 9 into the slag 4 to separate and remove the inclusion, before passing through the molten slag layer, the molten metal 9 is made to be fine drips by passing through a refractory-made porous nozzle 2, and also, after changing the form of the inclusion in the molten steel, the molten metal is dropped into the slag layer and made to be the drips to produce the high cleanliness metal. (2) The porous nozzle 2 used is the one having plural holes of 0.5-20mm the inner diameter and 5-100mm the length and <=5% apparent porosity of the refractory material and the composition composed of one or more kinds among 100% oxide of CaO, 100% oxide of SiO2, an oxide containing >=5% CaO and nitride containing >=5% CaO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a highly clean metal by forming droplets of molten metal and detoxifying inclusions in the molten metal.

[0002]

2. Description of the Related Art For example, various means have hitherto been proposed as a method for producing steel requiring high cleanliness.
Typical of these are the following methods.

Flux Blowing Method The most common means for removing inclusions in molten steel is to blow a flux containing CaO as a main component into the molten steel in a container such as a ladle, and to remove the flux and the molten steel. In this method, the inclusions are floated and removed by bringing the inclusions into contact with each other to cause aggregation. In other words, among the deoxidation products that are generated when deoxidizing molten steel and serve as inclusions, it is the most difficult to remove those that contain Al ₂ O ₃ as the main component, so this method is not the main component in the flux. It is characterized in that a certain CaO is combined with Al ₂ O ₃ which is an inclusion to form a low melting point compound, and Al ₂ O ₃ is separated and removed.

Further, the gas used for blowing the flux into the molten steel promotes the stirring of the molten steel and uniformly disperses the blown flux in the molten steel. Therefore, CaO and Al ₂ O
_It also has the effect of further promoting the binding with ₃ .

Gas bubbling method is a widely used method for removing inclusions in molten steel. This also forms a slag layer on the surface of molten steel in a container such as a ladle, stirs the molten steel by blowing gas into the molten steel to levitate the inclusions in the molten steel, and removes the inclusions with the slag on the surface of the molten steel. It is what is absorbed. Although the effect of removing inclusions is inferior to that of the above-mentioned flux blowing method, the treatment operation is extremely simple.

ESR method (electroslag remelting method) This method is known as the most effective method for producing clean steel. In the water-cooled mold, the tip of the steel material to be cleaned that has been made into an electrode shape is immersed in the slag layer that is heated and melted by the electrical resistance of the slag itself, and the steel material itself is continuously remelted by the resistance heat of the slag. The droplets are made into droplets, and the inclusions in the molten steel droplets are discharged to the droplet surface in the process of dropping into the molten slag layer. The inclusions are absorbed in the slag to perform the cleaning process.

Although the processing speed by ESR is extremely small as compared with the above method or method, it can be controlled to some extent by the amount of electric power supplied. Also, since the inclusions (main component: Al ₂ O ₃ ) in molten steel have a high probability of coming into direct contact with the molten slag (main component: CaO), the morphology of inclusions
It is possible to change the morphology from the Al ₂ O ₃ system to the Al ₂ O ₃ —CaO system. Furthermore, in this case, even if the inclusions enter the molten steel again and remain in the treated steel billet, they are harmless as inclusions,
Alternatively, fine inclusions close thereto can be used. Specifically, the particle size of inclusions after being processed by this ESR method is changed to 10 μm or less, and large inclusions (several tens of μm
It is possible to completely remove inclusions having a particle size of about m 2.

Droplet degassing method Molten steel is injected into a vacuum-evacuated container, and the energy in which the gas in the molten steel expands is used to make the molten steel into fine droplets, thereby increasing the reaction surface area and degassing. It promotes. In this method, a large amount of molten steel can be continuously processed at one time.

The inclusions in the droplets are discharged to the surface of the droplets by the action of mutual surface tension (interfacial tension) by making molten steel into fine droplets, and the inclusions are efficiently removed.
Moreover, since smaller inclusions are discharged as the particle size is smaller, various techniques for making the particle size smaller have been proposed and implemented.

[0010] As a method for producing clean steel using such a vacuum drop degassing method and molten slag, for example, Japanese Unexamined Patent Publication No.
In the 263913 publication, the droplets after the inclusions are discharged are dropped into the molten slag layer and passed through the slag, whereby the slag absorbs the inclusions and separates the inclusions from the molten steel. , ESR, and a method for producing clean steel characterized by having the same effect as ESR. With this method, it is possible to make the droplets smaller than in the case of ESR treatment. Therefore, by ejecting finer inclusions and absorbing them in the slag, it is possible to produce steel with higher cleanliness. it can.

Refining method using droplets In a non-oxidizing atmosphere, a high-pressure and high-speed inert gas is blown to the molten metal stream to form fine atomized fine molten metal particles, which are dropped and passed through the molten slag. There is a method of refining in the process (see JP-A-52-42412).

Further, by passing the molten steel through a refractory plate having a large number of pores, the molten steel is made into fine particles and dropped into a molten slag layer such as in a mold in an non-oxidizing atmosphere, and these fine molten steel particles form the slag layer. There is a method in which refining with slag is performed in the process of passing and then casting is performed (see Japanese Patent Application Laid-Open No. 52-143922).

[0013]

Since the above-mentioned method for producing clean steel to be processed in the ladle is to remove inclusions by bringing them into contact with slag, a certain level (for example, oxygen in molten steel) is required. Concentration, that is, total oxygen is about 20ppm)
Although the amount of inclusions can be reduced up to, fine inclusions remain, and it cannot be said to be effective in the case where higher cleanliness is expected.

Therefore, even in these processes, problems in operation such as nozzle clogging due to inclusions and problems such as surface flaws and internal defects in the product cannot be solved. Therefore, it is necessary to adopt another effective method in order to surely reduce the inclusions having an inclusion particle size of less than 50 μm.

The ESR method described above is an effective means in terms of cleaning and control of inclusion morphology, but it is only a batch-wise processing method for each steel material electrode. In addition, it requires a process to make the steel material to be cleaned into the shape of an electrode and melting energy (electric power) to remelt it into droplets. Is.
Even if an attempt is made to improve the processing efficiency by increasing the amount of electric power supplied, since the remelting rate (molten steel dropping rate) is limited, large-scale processing (for example, 50 to 100 kg / sec) is not achieved, and this method It is not possible to produce clean steel in large quantities at.

In the flow drop degassing method described above, as described above, molten steel is injected into a container under vacuum, and the molten steel is made into fine particles by the expansion energy of the gas in the steel or the gas blown into the steel. Therefore, since the droplet diameter is smaller than in the case of the ESR method, the efficiency of removing inclusions is high, and a large amount of molten steel can be processed. However, this method requires an evacuation facility and a vacuum container. Further, from molten steel cleaned under vacuum, to produce a slab using a continuous casting machine in a vacuum state while preventing reoxidation by the atmosphere, in terms of equipment,
There are many problems that must be solved from the operational point of view, and it is quite difficult to realize such a method combining continuous vacuum drop degassing and vacuum continuous casting. drops simply passes the slag layer in a short time by dropwise, only to absorb the inclusions slag, non ductility remaining in the droplets Al ₂
The morphology of O ₃ -based inclusions cannot be changed to ductile inclusions.

Regarding refining of molten steel with a refractory plate having pores, Al ₂ O ₃ -based inclusions adhere to the pores and block the pores, which prevents the molten steel from passing through. It has the drawback that it cannot process a large amount of molten steel.

That is, since the Al ₂ O ₃ -based inclusions have a high melting point and are solid in the molten steel at normal temperature, they do not react with the refractory plate and the pores of the refractory plate at a temperature lower than that of the molten steel. Once in contact with the inner wall, it only adheres to and deposits on the inner wall, and the pores of the refractory plate are closed. As long as the melting point of the inclusion is high, this phenomenon occurs regardless of the type of material of the fireproof plate, although there is a slight difference in the degree.

Further, the method of refining molten steel by high-pressure and high-speed gas blowing has a drawback that when a large amount of molten steel is treated, the refining efficiency is deteriorated because the refining efficiency of the molten steel decreases.

Therefore, a large amount of molten metal is formed into fine droplets under atmospheric pressure in an non-oxidizing atmosphere, and further, Al ₂ O ₃ inclusions do not adhere to a nozzle or the like through which molten steel passes, and have a low melting point with good fluidity. No method has yet been developed for producing clean steel using refractory nozzles that changes the form of ductile inclusions and does not cause excessive melting and damage of the nozzles due to the low melting point inclusions reacting with the nozzles.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to make a metal such as a bearing steel, a steel for a cord wire or a steel for a thin plate, which is required to have high cleanliness. In production, inclusions that are deoxidation products in molten steel that has undergone refining such as deoxidation, prevention of nozzle clogging by high melting point Al ₂ O ₃ inclusions due to refractories and slag, and these inclusions It is an object of the present invention to provide a method suitable for detoxifying the inclusions that become defective in the product together with removing the above.

[0022]

The summary of the present invention is as follows.
It is in the method for producing a highly clean metal of (1) and (2).

(1) In a non-oxidized adjusted atmospheric pressure container, molten metal particles are passed through a molten slag layer, and inclusions in the molten metal are absorbed by the slag to separate and remove inclusions. A method of producing a clean metal by means of which, before passing through the molten slag layer, the molten metal is made into fine droplets through a refractory porous nozzle and the form of inclusions in the molten steel is changed. Then, the method for producing a highly clean metal by forming droplets of a molten metal into the slag layer.

(2) The refractory porous nozzle described in (1) above has a large number of holes having an inner diameter of 0.5 to 20 mm and a length of 5 to 100 mm, and the apparent porosity of the refractory material is 5% or less,
The composition is 100% CaO oxide, 100% SiO ₂ oxide,
2. A droplet nozzle for molten metal according to claim 1, which is a porous nozzle composed of one or more kinds of oxides containing 5% or more of CaO and nitrides containing 5% or more of CaO 2. A method for producing a highly clean metal according to.

Here, "100%" means "high purity" which is usually said, and "nitride" means "a material used as a refractory material".

In order to solve the above problems, the present inventors have
By utilizing the characteristics of both the ESR method and the flow degassing method, the molten metal is made into droplets under atmospheric pressure in a non-oxidizing atmosphere, and the inclusions are discharged to the surface of the droplets, and inclusions are formed by the molten slag. A method of cleaning by absorption and separation and removal of inclusions from molten metal, and a method for realizing harmless inclusions by changing the form of ductile inclusions, etc.
The following new findings were obtained.

Method for making fine droplets of molten metal In a container at atmospheric pressure in which the atmosphere is non-oxidized with Ar gas or the like, the molten metal is made into fine droplets like a shower. Pore diameter of 0.5-20mm, length 5
It is optimal to use a porous nozzle made of refractory material having a diameter of ~ 100 mm, the number of which is determined by the amount of molten metal passed through.

Prevention of Blockage of Porous Nozzle by Inclusion When passing molten metal deoxidized by Al through a porous nozzle, Al ₂ O ₃ -based inclusion, which is a deoxidation product, adheres to the inner wall of the porous nozzle and causes nozzle clogging. Occurs, it becomes impossible to pass the molten metal, and the purpose cannot be achieved. For example, Al
For the treatment of deoxidized steel, a porous nozzle made of Al ₂ O _{3 with} a diameter of φ3 mm × 102 (outer diameter φ50 mm, length 10 mm, apparent porosity 0.2
%), The amount of molten steel passing through is approximately 100 kg due to inclusions.
It becomes impossible to pass by.

FIG. 7A shows Al ₂ after use in this example.
It is a copy drawing of the photograph of the longitudinal section of the porous nozzle made of O ₃ . Figure 7
FIG. 7B is a copy of an enlarged photograph of the circle in FIG. 7A.

The molten steel at this time is carbon steel (sol.Al:0.06
%), The molten steel temperature is 1600 ° C. As shown in the figure, a group-like inclusion of Al ₂ O ₃ having a thickness of about 2 mm adhered to the surface of the porous nozzle, and the pores were completely closed.

In order to pass the deoxidized molten metal without blocking the nozzle, the Al ₂ O ₃ -based inclusion having a high melting point is transformed into a low-melting inclusion having good fluidity depending on the material of the porous nozzle. It is better to let them do it. Therefore, the refractory material reacts more easily with Al ₂ O ₃ than with Al ₂ O ₃ itself and becomes a low melting point inclusion (for example, Al ₂ O ₃ -CaO system, Al ₂ O ₃ -SiO ₂ system, etc.). High-purity CaO, high-purity SiO ₂ , oxides containing 5% or more of CaO and CaO 5 which can change the form.
A nitride containing at least% is suitable. Further, the apparent porosity of the refractory material has a certain suitable range.

Inclusion removal By converting the molten metal into fine molten metal droplets, the inclusions in the droplets are formed by the surface tension of the molten metal and the buoyancy of the inclusions, as in the case of the drop degassing method. It is discharged to the surface. In order to separate the inclusions discharged on the surface of the droplets from the molten metal, the molten metal droplets are dropped on the molten slag layer in the same manner as the ESR method, and the low melting point inclusions whose shape is changed when passing through this slag layer. Objects can be absorbed by slag.

[0033]

The method of the present invention will be described in detail with reference to FIG.

FIG. 1 is a schematic vertical sectional view showing an example of an apparatus for carrying out the method of the present invention. Ladle 1 that received molten steel 9
Has a porous nozzle 2 at the bottom thereof for dropping molten steel 9 as molten steel droplets 3. At its bottom, this ladle 1 is connected to a container capable of performing non-oxidative adjustment at atmospheric pressure, that is, a tundish 6 in a sealable manner.
Ar gas is introduced into the tundish 6 to maintain the atmosphere in an unoxidized state. A weir 5 is provided in the tundish 6, and the molten steel 10 after the treatment is communicated and stored under the weir 5, and the weir 5 is the surface of the treated molten steel 10 on the side where the molten steel droplets 3 drop. It has a function of maintaining the molten layer of the slag 4. An immersion nozzle 8 and a mold 7 for continuous casting are provided in the lower part of the tundish 6 on the non-slag storage side.

The ladle 1 which has received the molten steel 9 is conveyed, mounted on the tundish 6 as shown in the drawing, and after the sealing and the atmosphere adjustment are performed, the molten steel 9 is sprayed with the molten steel 9 through the porous nozzle 2. 3 is dropped and passed through the layer of the molten slag 4. The slag 4 in the tundish 6 can be loaded from an input port (not shown) provided on the drip side of the tundish 6.

The molten steel 9 passes through the porous nozzle 2 to form fine molten steel droplets 3, and inclusions in the droplets are discharged to the surface of the droplets by the buoyancy of the inclusions and the surface tension of the molten metal. The inclusions are absorbed by the slag 4 for high cleaning.

Next, the reason for limiting the properties and structure of the refractory material of the porous nozzle as described above will be explained.

As the material of the porous nozzle, high purity CaO,
When a refractory made of high-purity SiO ₂ is used, the Al ₂ O ₃ -based inclusions in the molten steel and the refractory react effectively when the molten steel passes through the porous nozzle, and the Al ₂ O ₃ -CaO-based The morphology can be changed to a low melting point inclusion such as.

The material of the porous nozzle is made of an oxide containing 5% or more of CaO (for example, CaO-MgO, CaO-ZrO ₂ , CaO).
-SiO _2, CaO-MgO -SiO _2, etc.), or a nitride containing 5% or more of CaO (e.g., CaO-BN, CaO-Si 3 etc. N _4), or two of these oxides or nitrides The compounds to be contained above are refractory materials having a CaO content of less than 5%, when there are many Al ₂ O ₃ inclusions in the molten metal,
This is because the CaO is insufficient and the Al ₂ O ₃ inclusions do not react with CaO, and the low melting point Al ₂ O ₃ —CaO inclusions are not formed.
In addition, nitride is an effective refractory material, and B and Si
This is because the nitride also reacts to form B ₂ O ₃ or SiO ₂ and effectively acts on the morphological change to a low melting point inclusion.

That is, in a non-oxidizing atmosphere container, high melting point and non-ductile A in molten steel produced by Al deoxidation
The l ₂ O ₃ -based inclusions collide with the inner wall of the nozzle in the process of passing through the porous nozzle having pores, and react with the above-mentioned nozzle material to become fluid low-melting-point inclusions. Not generated, the molten steel passes through a porous nozzle with pores.

Therefore, the smaller the pores of the nozzle,
The probability that the Al ₂ O ₃ -based inclusions in the molten metal will collide with the inner walls of the nozzle pores will increase, and the reaction efficiency of the transformation of the high melting point non-ductile Al ₂ O ₃ -based inclusions into the low melting point inclusions will be promoted. To be done.

However, the Al ₂ O ₃ -based inclusions react with the nozzle refractory material to form low-melting-point inclusions, which flow out together with the molten steel droplets, causing the nozzle refractory material to melt. But,
Since this erosion should not be excessive, use a highly dense refractory material with an apparent porosity of 5% or less and minimize the reaction layer at the interface of the porous nozzle with which the molten metal contacts as a preventive measure. Therefore, the melting loss of the nozzle is reduced.

When the apparent porosity of the refractory exceeds 5%, the reaction with the inclusions proceeds through the pores (between the particles constituting the refractory), and the melting loss progresses while the refractory particles are removed. Therefore, the amount of melting damage of the nozzle refractory increases. Therefore, the apparent porosity of the refractory material is set to 5% or less.

The number of pores of the porous nozzle can be appropriately set according to the throughput, but the pore diameter is limited to φ 0.5 to 20 mm. If the pore diameter is less than φ0.5 mm and the molten metal head (static pressure) in the ladle is about 50 mm or less, the surface tension of the nozzle refractory and molten metal cannot be overcome and the molten metal cannot pass through. . On the other hand, when the diameter exceeds 20 mm, the probability that the inclusions collide with the inner wall of the nozzle decreases, and the reaction efficiency decreases.

The length of the pores is 5 to 200 mm. If the pore length is less than 5 mm, the strength of the porous nozzle against the static pressure of the molten metal cannot be obtained, and the reaction efficiency is low. on the other hand,
Above 200 mm, the pressure loss becomes too large and molten metal does not pass through.

The pore spacing of the nozzles is determined by the relationship with the strength of the porous nozzle with respect to the molten metal head in the ladle. That is, it depends on three factors: the refractory material selected, the nozzle length (thickness), and the molten metal head. This interval has no practical problem as long as it can maintain the strength of the porous nozzle, and does not significantly affect the cleanliness of the molten metal.

The outer diameter of the porous nozzle is determined by whether or not the nozzle having the pore size, the number and the length according to the processing speed can withstand the molten metal head. Since the reaction between the inclusions and the refractory material in the nozzle is promoted by the collision with the inner wall of the pore, the outer diameter itself of the porous nozzle has little relation to the reaction efficiency and the cleanliness of the molten metal.

By the above means, it is possible to prevent nozzle clogging and excessive melting loss, and to make molten metal into fine molten metal droplets. As an example, Al deoxidized sol.Al:0.05
%, Temperature: 1600 ℃ molten steel of carbon steel, diameter φ3mm × 102
One porous nozzle (outer diameter φ50 mm, length 30 mm, material: CaO
(Apparent porosity 1%), SiO ₂ (apparent porosity 2%), 30% Ca
O-MgO-SiO ₂ (apparent porosity 5%) and 10% CaO-BN
(Apparent porosity 0.2%)] was used to treat 1800 kg. Of these, the states of the porous nozzles after the use of the former three are shown in FIGS. 2, 3 and 4.

[0049] Figure 2 in the case of CaO, FIG. 3 is a replication view photograph showing a longitudinal section of the nozzle in the case when the SiO ₂ and 4 of 30% CaO-MgO -SiO _2. As shown in the figure, only the entrance corners of the pores were melted and rounded, but the Al ₂ O _{3 group} inclusions as shown in FIG. 7 (a) did not adhere at all. The same was true for the above 10% CaO-BN.

[0050] having the composition as appropriate porosity as such nozzle _{materials, CaO, SiO 2, CaO-} MgO -SiO 2 and
When CaO-BN is used, the inclusion morphology is Al ₂ O ₃ -CaO system, and the melting point of this inclusion is obvious from the Al ₂ O ₃ -CaO system phase diagram, depending on the ratio of Al ₂ O ₃ and CaO. As you can see, it drops to about 1400 ℃.

The molten metal passes through the porous nozzle having the above-mentioned pores to form fine droplets, and the inclusions in the fine molten metal are efficiently discharged to the surface of the droplets.
FIG. 5 and FIG. 6 are copy diagrams of scanning electron micrographs of the surface of the droplets showing the comparison of this example.

FIG. 5 shows the spherical Al ₂ O ₃ —Ca discharged on the surface of the droplet when the CaO porous nozzle shown in FIG. 2 is used.
As for the O inclusions, FIG. 6 shows the cluster-like Al ₂ O discharged onto the surface of the droplet when the Al ₂ O ₃ porous nozzle shown in FIG. 7 is used.
_{The three} inclusions are shown respectively.

It is necessary that the molten slag to be used has such a property that the molten metal can easily pass therethrough and that the inclusions can be easily absorbed, and the composition has good wettability with Al ₂ O ₃ -based inclusions and easily reacts. Select one. For example, CaO-CaF ₂ -Al ₂ O
₃ series slag can be mentioned.

[0054]

EXAMPLE The following experiment was conducted using the apparatus shown in FIG.

Deoxidized with Al having the chemical composition shown in Table 1 at 1600 ° C.
2000 kg of molten steel and a porous nozzle under the following conditions were used.

[0056]

[Table 1]

Porous Nozzle: Material: High-purity, high-density CaO (apparent porosity: 1%) High-purity, high-density SiO ₂ (apparent porosity: 2%) High-density 30% CaO-MgO -SiO ₂ (apparent porosity: 5%) High density 10% CaO-BN (apparent porosity: 0.5%) Pore: Diameter φ3mm, number 102, spacing 2.5mm Outer diameter: φ50mm Length: 30mm Atmosphere Molten steel was passed through a porous nozzle at a rate of 420 kg / min into a tundish adjusted to a medium oxygen concentration of 0.1% or less and a preheating temperature of 1200 ° C, and was injected as fine droplets. The molten slag having the composition shown in Table 2 was used as the slag in the tundish, and fine particle droplets were dropped on this. Continuous casting was performed by blocking with a weir so that the molten slag did not flow into the mold.

[0058]

[Table 2]

In the comparative example, a single-hole nozzle (material: alumina graphite) having a diameter of 30 mm and the same cross-sectional area as the total pore cross-sectional area of the above-mentioned porous nozzle was used, and no molten slag was used. If you want to.

The evaluation was performed by a method of comparing the reduction rate of total oxygen and the total number of inclusions and the average size of inclusions before and after the treatment. Furthermore, the change in inclusion morphology before and after the treatment was also investigated. The results are shown in Tables 3 to 6.

[0061]

[Table 3]

[0062]

[Table 4]

[0063]

[Table 5]

[0064]

[Table 6]

As shown in Table 3, the total oxygen value of the CaO porous nozzle was 42 ppm in the molten steel in the ladle before the treatment.
In the treated tundish, it decreased to 9ppm, and the reduction rate reached about 80%. To 10ppm from 44ppm similarly in SiO ₂ made of porous nozzle, similarly to 11ppm from 45ppm is a porous nozzle made of CaO -MgO -SiO _2, similarly to 10ppm from 46ppm is a porous nozzle made of CaO-BN, The decrease rate was about 80% in each case.

On the other hand, as shown in Table 4, in the comparative examples, without slag, the total oxygen value after the treatment decreased only to 30 ppm, and the reduction rate remained at 26.8%. Similarly, with slag, it decreased only to 38.0 ppm, and the rate of decrease was 8.4%.

As is clear from Table 5, when the total number of inclusions is compared, the reduction rate of the inclusions after the treatment is 77 in the present invention.
~ 83%, which is a significant decrease.

As shown in Table 6, the reduction rate of the total number of inclusions was about 16% without the slag in the comparative example, and was increased by 4.7% with the slag. As described above, in each of the comparative examples, the effect of reducing the total number of inclusions is not observed.

The average size of the inclusions ranges from 52 to 55 μm (max is 300 μm) before the treatment in both the inventive examples and the comparative examples, and from 8.5 to 10.5 μm (max is 25 μm) after the treatment of the inventive examples. To 35 μm (without slag) and 61 μm (with slag) in the comparative example, which is very small.

The form of inclusions before treatment is about
While 98% is a community-like inclusions of non-ductile Al ₂ O ₃ system, the form of inclusions after treatment, either in the present invention example about 93-96% of the total inclusions Al ₂ O ₃ - It was changed to a CaO-based spherical ductile inclusion. On the other hand, after the treatment without slag in the comparative example, 37% of all the inclusions were spherical ductile inclusions of Al ₂ O ₃ -CaO system, but the inclusions increased after the treatment than before treatment. However, since it has grown, it is presumed that the slag is entrained in the molten steel by the injection flow from the ladle. Therefore, although the morphology of inclusions may have some effect, it has no effect on the cleaning of steel.

[0071]

According to the method of the present invention, the high melting point, non-ductile, cluster-like Al ₂ O ₃ -based inclusions in the molten metal are converted into low melting point spherical particles.
After changing the morphology to Al ₂ O ₃ -CaO-based ductile inclusions, the molten metal is made into fine droplets and the inclusions are discharged onto the surface of these droplets. Inclusions can be absorbed in slag to remove the inclusions, and a large amount of highly clean metal can be produced.

Since the inclusions of which the form has changed are low-melting inclusions having good fluidity, the nozzles will not be blocked by the inclusions. Even if inclusions remain in the molten metal, they are very fine and ductile inclusions, so they are harmless in products.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is a copy of a photograph of a vertical cross section of a nozzle showing an example after using a porous nozzle made of CaO 2.

FIG. 3 is a copy of a photograph of a vertical cross section of a nozzle showing an example after using a porous nozzle made of SiO ₂ .

FIG. 4 is a copy of a photograph of a vertical cross section of a nozzle showing an example after using a porous nozzle made of CaO—MgO—SiO ₂ .

FIG. 5 is a copy of a scanning electron micrograph showing an example of Al ₂ O ₃ —CaO based spherical inclusions discharged to the surface of steel droplets when a CaO porous nozzle is used.

FIG. 6 is a copying diagram of a scanning electron micrograph showing an example of a cluster-like Al ₂ O ₃ -based inclusion discharged onto the surface of steel droplets when an Al ₂ O ₃ porous nozzle is used.

FIG. 7 is a diagram showing an example after using a porous nozzle made of Al ₂ O ₃ . (a) is a copy of a photograph of a vertical cross section of a nozzle when it is blocked by an Al ₂ O ₃ -based inclusion. (b) is a copy of the enlarged photograph of the circle in (a).

[Explanation of symbols]

1: Ladle, 2: Porous nozzle, 3: Molten steel droplets, 4: Slag, 5: Weir, 6: Tundish, 7: Mold,
8: Immersion nozzle, 9: Molten steel, 10: Molten steel after treatment

Claims (2)

[Claims] 1. A non-oxidation-controlled atmospheric pressure container,
A method for producing clean metal by passing droplets of molten metal through a molten slag layer, absorbing inclusions in the molten metal by the slag, separating and removing inclusions, and passing through the molten slag layer. Before, while the molten metal is made into fine droplets through a refractory porous nozzle, after changing the form of inclusions in the molten steel, the molten metal particles characterized by being dropped into the slag layer A method for producing a highly clean metal by dripping. 2. The refractory porous nozzle according to claim 1 has a large number of holes having an inner diameter of 0.5 to 20 mm and a length of 5 to 100 mm, and the refractory material has an apparent porosity of 5%. The composition is as follows: 100% CaO oxide, 100% SiO ₂ oxide, Ca
A droplet nozzle for molten metal according to claim 1, which is a porous nozzle made of one kind or two or more kinds of oxides containing 5% or more of O 2 and nitrides containing 5% or more of CaO 2. A method for producing a highly clean metal according to.