JP6020603B2 - Method for cleaning molten metal and immersion lance for gas blowing - Google Patents

Description

  The present invention is a method for purifying a molten metal by blowing a gas into a molten metal such as molten steel contained in a ladle and stirring the molten metal to float oxide-based non-metallic inclusions in the molten metal, And it is related with the immersion lance for gas blowing used for it.

Molten steel produced from hot metal by decarburization by oxygen blowing at the converter contains a large amount of dissolved oxygen (oxygen dissolved in the molten steel). In order to remove this dissolved oxygen, Is deoxidized with metallic aluminum or ferrosilicon. By this deoxidation treatment, dissolved oxygen reacts with metallic aluminum, ferrosilicon, etc., and solid oxides such as Al ₂ O ₃ (alumina) and SiO ₂ (silica) are formed.

  If these solid oxides remain in the steel, these oxides can cause quality defects in the steel material as oxide-based non-metallic inclusions. Metal inclusions (hereinafter simply referred to as “inclusions”) are separated and removed. Inclusions have a lower specific gravity than molten steel, and if the molten steel is left in the ladle, the inclusions will float and be separated and removed. The ascent rate is slow. In view of this, a method is widely used in which an inert gas is blown into the molten steel in the ladle to stir the molten steel to promote the floating of inclusions suspended in the molten steel.

  As this method, a method of blowing inert gas from a dipping lance immersed in molten steel in a ladle or a method of blowing inert gas into molten steel from a porous brick installed at the bottom of the ladle It is. However, since the blown gas floats upward in the vertical direction, the gas stirring region is a conical range extending upward with the gas blowing site at the top, and the entire molten steel in the ladle is stirred. It is not possible. That is, there is a problem that the effect of promoting the floating of inclusions can be obtained only in a limited range.

  In order to solve this problem, various methods have been proposed. For example, in Patent Document 1, a dip tube is inserted into the molten steel from above the ladle, and an inert gas is blown from the bottom of the ladle below the dip tube so as to reach the entire molten steel inside the dip tube. A method has been proposed.

JP-A-6-33134

  However, Patent Document 1 has the following problems. That is, in Patent Document 1, the dip tube is immersed in the molten steel in the pan, and this dip tube is an apparatus that is not used in normal secondary refining, and therefore, it is necessary to newly install the dip tube. . Moreover, since only the molten steel existing inside the dip tube is stirred, in order to stir the entire molten steel in the ladle, it is necessary to install a dip tube having a large cross-sectional area. Since a dip tube lifting device is required, the equipment cost increases. Furthermore, since the dip tube is a consumable item, the operation cost of the dip tube is required, which leads to an increase in manufacturing cost.

  The present invention has been made in view of the above circumstances, and the object thereof is to blow a gas into molten metal such as molten steel accommodated in a ladle to stir the molten metal and to include nonmetallic inclusions in the molten metal. In order to clean the molten metal by levitating etc., it is to provide a method for cleaning the molten metal that can rapidly and efficiently purify the molten metal by stirring the molten metal at low cost and efficiently. Moreover, it is providing the immersion lance for gas blowing used for it.

The gist of the present invention for solving the above problems is as follows.
[1] In the molten metal cleaning method, the immersion lance is immersed in the molten metal accommodated in the ladle, and the molten metal is stirred by blowing gas into the molten metal from the discharge hole of the immersion lance. A method for cleaning molten metal, characterized in that gases having different blowing pressures are blown from the immersion lance.
[2] Two types of blowing pressures, one blowing pressure less than 8 kgf / cm ² (784.5 kPa), and the other blowing pressure of 8 kgf / cm ² (784.5 kPa) or more. The method for cleaning molten metal according to [1] above.
[3] The gas according to [1] or [2], wherein the gas having a higher blowing pressure is blown at a position below the immersion lance in the vertical direction than the gas having a lower blowing pressure. Method for cleaning molten metal.
[4] The molten metal according to any one of [1] to [3] above, wherein the molten metal is molten steel, and the gas is an inert gas having the same composition. Metal cleaning method.
[5] The above-mentioned [1] to [4], wherein the immersion lance has two positions in the vertical direction for providing discharge holes for blowing gas. The method for cleaning molten metal as described.
[6] A gas blowing immersion lance for blowing the gas into the molten metal to clean the molten metal, and having a plurality of independent flow paths for passing gases having different blowing pressures inside the immersion lance The gas blowing immersion lance is characterized in that each of the flow paths is provided with two or more discharge holes.
[7] The discharge hole is provided on a side surface of the immersion lance, and the gas discharge hole with the higher blowing pressure is located below the gas discharge hole with the lower blowing pressure in the vertical direction of the immersion lance. The gas blowing immersion lance as described in [6] above, which is installed at a position.

  According to the present invention, since gases having different blowing pressures are blown from the immersion lance into the molten metal, a gas having a relatively high blowing pressure has a large distance in the horizontal direction of bubbles in the molten metal, and the blowing pressure is low. The relatively low gas stirs the inside of the agitation region by the gas having a relatively high blowing pressure, which makes it possible to stir the molten metal in a wide range, and to raise the inclusions in the molten metal. As a result, the molten metal can be efficiently cleaned in a short time.

It is the schematic which shows the condition which has given to the molten steel in the ladle the cleaning method of the molten metal by this invention. It is a schematic enlarged view of the A section shown in FIG. It is a figure which shows transition of the total oxygen concentration in the molten steel in gas blowing in comparison with the example of this invention, and a prior art example.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic view showing a situation where a molten metal cleaning method according to the present invention is applied to molten steel in a ladle, and FIG. 2 is a schematic enlarged view of part A shown in FIG. It is sectional drawing cut | disconnected by the surface which passes along the centerline of a road.

  1 and 2, an immersion lance 1 is inserted into the molten steel 3 accommodated in the ladle 2 from above the ladle 2, and an inert gas is blown into the molten steel through the immersion lance 1. A low pressure gas supply pipe 5 and a high pressure gas supply pipe 6 are connected to the immersion lance 1. The low-pressure gas supply pipe 5 is connected to a low-pressure gas flow path 7 installed inside the refractory 1 </ b> A constituting the immersion lance 1, and is installed below the immersion lance 1 through the low-pressure gas flow path 7. The low-pressure gas discharge hole 9 is connected. On the other hand, the high-pressure gas supply pipe 6 is connected to a high-pressure gas flow path 8 installed inside the refractory 1 A constituting the immersion lance 1, and the lower portion of the immersion lance 1 is connected via the high-pressure gas flow path 8. Are connected to the high-pressure gas discharge hole 10.

  That is, the inert gas supplied from the low-pressure gas supply pipe 5 is blown into the molten steel through the low-pressure gas passage 7 and the low-pressure gas discharge hole 9. Separately, the inert gas supplied from the high-pressure gas supply pipe 6 is configured to be blown into the molten steel through the high-pressure gas flow path 8 and the high-pressure gas discharge hole 10.

  In this case, as will be described later, the low-pressure gas discharge hole 10 and the high-pressure gas discharge hole 10 are arranged so that the high-pressure gas discharge hole 10 is located below the immersion lance 1 in the vertical direction with respect to the low-pressure gas discharge hole 9. It is preferable to install. Further, the low-pressure gas flow path 7 and the high-pressure gas flow path 8 are arranged so that the inert gas supplied from the low-pressure gas supply pipe 5 and the inert gas supplied from the high-pressure gas supply pipe 6 are not mixed. The discharge pressure of the inert gas discharged from the high-pressure gas discharge hole 10 is higher than the discharge pressure of the inert gas discharged from the low-pressure gas discharge hole 9. In addition, the inert gas supplied to the low-pressure gas supply pipe 5 is set to have a lower pressure than the inert gas supplied to the high-pressure gas supply pipe 6.

  It is preferable that the inert gas supplied to the low-pressure gas supply pipe 5 and the inert gas supplied to the high-pressure gas supply pipe 6 have the same composition. As a matter of course, the inert gas supplied to the low-pressure gas supply pipe 5 and the inert gas supplied to the high-pressure gas supply pipe 6 may be inert gases having different compositions. As the inert gas to be used, a rare gas such as argon gas or helium gas, or a non-oxidizing gas such as nitrogen gas can be used.

  The low-pressure gas discharge hole 9 and the high-pressure gas discharge hole 10 face the horizontal direction, and the inert gas is discharged in the horizontal direction. In FIG. 2, the discharge direction of the low-pressure gas discharge hole 9 and the high-pressure gas discharge hole 10 is the horizontal direction, but the discharge direction is not limited to the horizontal direction and is within an angle range of ± 45 ° from the horizontal direction. Anything can be used. However, from the viewpoint of efficiently stirring the molten steel 3, it is preferable that the distance in the horizontal direction of the bubbles in the molten steel is increased, and therefore the discharge direction is the largest in the horizontal direction of the bubbles. The horizontal direction is preferably. In FIG. 2, the low-pressure gas discharge hole 9 and the high-pressure gas discharge hole 10 both have two outlets on the same straight line, but may have three or more outlets. Absent.

  The cross-sectional area of the low-pressure gas discharge hole 9 and the cross-sectional area of the high-pressure gas discharge hole 10 are appropriately set according to the flow rate of the inert gas, and basically the low-pressure gas discharge hole 9. And the cross-sectional area of the high-pressure gas discharge hole 10 are the same, and the flow rate of the inert gas is the same for the low-pressure gas discharge hole 9 and the high-pressure gas discharge hole 10. As a matter of course, as long as the discharge pressure of the inert gas discharged from the high-pressure gas discharge hole 10 is higher than the discharge pressure of the inert gas discharged from the low-pressure gas discharge hole 9, the cross-sectional area and inertness are increased. There may be a difference in the gas flow rate.

Before the inert gas is blown into the molten steel 3, the molten steel 3 is deoxidized with metallic aluminum. Al ₂ O ₃ is formed in the molten steel by deoxidation treatment with metallic aluminum. A deoxidizing agent such as ferrosilicon, ferromanganese, or silicomanganese may be used in combination when deoxidizing with metallic aluminum. Moreover, in order to make the slag 4 efficiently absorb inclusions in the molten steel that floats, a CaO-based or MgO-based flux may be added to the slag 4 in advance to adjust the composition of the slag 4. Further, in order to further promote the absorption of the inclusions that have floated, the converter slag that has flowed into the ladle 2 during steel removal from the converter is removed, and then the flux is added to absorb the inclusions that float. An excellent synthetic slag may be formed.

By blowing an inert gas from the immersion lance 1, the molten steel 3 is stirred, and the floating of inclusions such as Al ₂ O ₃ floating in the molten steel is promoted. The floated inclusions are absorbed by the slag 4 existing on the molten steel, and the cleaning of the molten steel 3 proceeds.

  The inert gas blown from the low-pressure gas discharge hole 9 has a relatively low blow pressure, that is, discharge pressure, so that the distance of bubbles in the molten steel in the horizontal direction is small. The molten steel 3 in the vicinity of is stirred. On the other hand, the inert gas blown from the high-pressure gas discharge hole 10 has a relatively high blown pressure, that is, a discharge pressure, so that the arrival distance of bubbles in the molten steel in the horizontal direction is large, that is, in the horizontal direction. The molten steel 3 located at a position away from the immersion lance 1 is stirred. In this case, the high-pressure gas discharge hole 10 for blowing the inert gas having a relatively high pressure is disposed below the immersion lance 1 in the vertical direction with respect to the low-pressure gas discharge hole 9. The inert gas blown from the hole 10 and the inert gas blown from the low-pressure gas discharge hole 9 do not collide with each other, and each agitates the molten steel 3 efficiently.

That is, a wide area of the molten steel 3 is efficiently stirred by the inert gas blown from the low-pressure gas discharge hole 9 and the inert gas blown from the high-pressure gas discharge hole 10, thereby cleaning the molten steel 3. Is achieved in a short time. In this case, in order to separate the trajectories of both gases, the pressure (discharge pressure) of the inert gas blown from the low-pressure gas discharge hole 9 is set to less than 8 kgf / cm ² (784.5 kPa), and the high-pressure gas discharge hole 10 It is preferable that the pressure (discharge pressure) of the inert gas blown from the air is 8 kgf / cm ² (784.5 kPa) or more (1 kgf / cm ² = 98.0665 kPa).

This is because, by setting the pressure (discharge pressure) of the inert gas blown from the high-pressure gas discharge hole 10 to 8 kgf / cm ² (784.5 kPa), the bubble of the blown inert gas is generally used. This is because it reaches about ½ of the radius of the ladle 2 having a large size and a wide area of the molten steel 3 is stirred. The arrival distance L _H of the bubbles discharged from the low-pressure gas discharge hole 9 and the high-pressure gas discharge hole 10 can be calculated by the following equation (1).

L _H = 3.7 × d _n × F _r ^1/3 (1)
However, in (1), L _H the reach distance (m), the d _n diameters of the discharge holes (m), F _r is the Froude number (dimensionless) is calculated by the following equation (2) The

F _r = ρ _g × V _o ² / [d _n × g × (ρ _L −ρ _g )] (2)
However, in the formula (2), ρ _g is the density of inert gas (kg / m ³ ), ρ _L is the density of molten metal such as molten steel (kg / m ³ ), and V _o ² is inert from the discharge hole. discharge flow rate of gas (m / s), g is gravitational acceleration (m / s ^2), the d _n is the diameter of the discharge hole (m).

The pressure difference between the pressure of the inert gas blown from the low-pressure gas discharge hole 9 (discharge pressure) and the pressure of the inert gas blown from the high-pressure gas discharge hole 10 (discharge pressure) is 3 kgf / cm ² (294.2 kPa). ), More preferably 4 kgf / cm ² (392.3 kPa) or more. By doing in this way, an inert gas bubble reaches the whole ladle, and stirring of molten steel 3 is promoted.

  The lower limit value of the pressure of the inert gas blown from the low-pressure gas discharge hole 9 (discharge pressure) and the pressure of the inert gas blown from the high-pressure gas discharge hole 10 (discharge pressure) are calculated by the following equation (3). What is necessary is just to make it more than the static pressure of molten metals, such as molten steel.

P = ρ _L × g × H (3)
In Equation (3), P is the static pressure (Pa) of the molten metal, ρ _L is the density of molten metal such as molten steel (kg / m ³ ), g is the acceleration of gravity (m / s ² ), and H is the molten metal. The distance (m) from the position of the metal surface to the discharge hole of the immersion lance (discharge hole for low pressure gas or discharge hole for high pressure gas).

For example, when the distance between the discharge hole of the immersion lance and the molten steel surface is 2.5 m, since the density of the molten steel 3 is 7000 kg / m ³ , the discharge pressure of the inert gas is 1.75 kgf / cm ² (171 .6 kPa) or more. The upper limit of the pressure (discharge pressure) of the inert gas blown from the high-pressure gas discharge hole 10 may be about 15 kgf / cm ² (1471.0 kPa).

  As described above, according to the present invention, gases having different blowing pressures are blown from the immersion lance 1 into the molten metal, so that the gas having a relatively high blowing pressure reaches the bubbles in the horizontal direction in the molten metal. A gas having a large distance and a relatively low blowing pressure stirs the inside of the agitation region with a gas having a relatively high blowing pressure, which makes it possible to stir the molten metal in a wide range. The floating of the inclusions is promoted, and the molten metal can be efficiently cleaned in a short time.

  In addition, this invention is not limited to the range of the said description, A various change is possible. For example, in the above description, two types of inert gas, high pressure and low pressure, are used, but the present invention is implemented by independently blowing inactive gases whose pressures are controlled to three or more. be able to.

By adopting the molten metal cleaning method shown in FIG. 1, about 300 tons of molten steel accommodated in the ladle was subjected to a cleaning process. The molten steel to be treated is carbon steel having a carbon concentration of 0.45% by mass, and the inclusion to be cleaned is Al ₂ O ₃ . The inner diameter of the ladle used was 4 m, the immersion depth of the immersion lance from the molten steel surface was 2.5 m, and the argon gas blowing flow rate from the immersion lance was 400 NL / min. Here, “NL” is normal liters. The used immersion lance has two outlets for the low-pressure gas discharge hole and two for the high-pressure gas discharge hole. The blowing pressure from the low-pressure gas discharge hole, that is, the discharge pressure is 6.5 kgf / cm ² ( 637.4 kPa), the blowing pressure from the high-pressure gas discharge hole, that is, the discharge pressure was 9.5 kgf / cm ² (931.6 kPa), and the blowing flow rate was 200 NL / min (invention example).

For comparison, an immersion lance having four radial outlets is used, the blowing pressure, that is, the discharge pressure is set to 6.5 kgf / cm ² (637.4 kPa), and the argon gas blowing flow rate is set to 400 NL / A method (conventional example) of purging molten steel by blowing argon gas under the condition of min was also carried out.

  The transition of the total oxygen concentration in the molten steel during gas blowing was compared between the inventive example and the conventional example. In FIG. 3, the result of having compared transition of the total oxygen concentration in the molten steel in gas blowing with the example of this invention and a prior art example is shown. Here, total oxygen is the sum of dissolved oxygen in molten steel and oxygen in the form of oxides.

  As shown in FIG. 3, it was confirmed that by applying the present invention, the total oxygen concentration in the molten steel can be rapidly reduced as compared with the conventional example.

DESCRIPTION OF SYMBOLS 1 Immersion lance 2 Ladle 3 Molten steel 4 Slag 5 Low pressure gas supply pipe 6 High pressure gas supply pipe 7 Low pressure gas flow path 8 High pressure gas flow path 9 Low pressure gas discharge hole 10 High pressure gas discharge hole

Claims (4)

In the molten metal cleaning method, in which the immersion lance is immersed in the molten metal accommodated in the ladle, the gas is blown into the molten metal from the discharge hole of the immersion lance, and the molten metal is stirred , the cross-sectional area of all the discharge holes , The gas blowing position from the discharge hole is different , the gas blowing position of the higher blowing pressure, the position of the lower dip of the immersion lance than the gas blowing position of the lower blowing pressure, A method for cleaning molten metal, characterized by blowing from the immersion lance. The said blowing pressure is made into 2 types, One blowing pressure shall be less than 8 kgf / cm < ² > (784.5 kPa), and the other blowing pressure shall be 8 kgf / cm < ² > (784.5 kPa) or more, It is characterized by the above-mentioned. 2. The method for cleaning molten metal according to 1. The method for cleaning a molten metal according to claim 1 or 2 , wherein the molten metal is molten steel, and the gas is an inert gas having the same composition. An immersion lance for gas blowing that blows gas into the molten metal to clean the molten metal, and has a plurality of independent flow paths for passing gases having different blowing pressures inside the immersion lance. Two or more discharge holes are provided on the side surface of the immersion lance with the same cross-sectional area of all of the discharge holes provided in each flow path, and the gas discharge holes having a higher blowing pressure However, the immersion lance for gas blowing is characterized in that it is installed at a position below the immersion lance in the vertical direction with respect to the gas discharge hole having a lower blowing pressure .

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