JP3721872B2 - Ladle for refining molten steel - Google Patents

Description

[0001]
The present invention relates to a refining ladle suitable for secondary refining of molten steel refined in a converter or the like for the purpose of further desulfurization, and in particular, has a porous plug (hereinafter simply referred to as a plug) for gas injection at the bottom. And an upper part relates to a ladle for refining provided with an electrode for electric heating.
[Prior art]
Molten steel smelted in the converter is sent to an ingot making facility such as a continuous casting machine, but before that, it is used for so-called secondary smelting to reduce impurities such as S or to fine-tune alloy components. Often. In particular, the number of so-called single ppm ultra-low sulfur steels with S content of 9 ppm or less is increasing in recent years in HIC-resistant steel, high-tensile steel, etc. The ratio is increasing.
[0002]
As a secondary refining facility, a refining ladle is widely used. As one of them, there is a plug for gas injection at the bottom of a ladle having a cylindrical shape as shown in FIG. 1, and the upper part is energized to compensate for the temperature drop of the molten steel during secondary refining. Some have heating equipment. In this type of smelting ladle, molten steel is charged into the smelting ladle, a molten flux is placed on the ladle, the molten steel is stirred by the gas blown from the bottom, and the electrode is immersed in the flux.・ Electricity is generated by Joule heat to compensate for temperature drop of molten steel, or refining such as desulfurization is performed while heating more actively. In this energization heating type smelting ladle, it is necessary to perform stirring with gas as strongly as possible and to perform heating with energization controlled.
[0003]
Normally, this type of current heating type smelting ladle has only one plug, and simply increasing the amount of gas blown increases the splash of molten steel, causing adhesion of metal to the water-cooled lid of the smelting ladle and poor conduction. For this reason, there is a problem that it becomes difficult to operate. There is also a problem that the refining time is relatively long. As means for solving such a problem, there may not have electrical heating equipment, the means of using a plurality of plugs disclosed in Japanese Open Sho 63-168253 discloses or real Hei 2-16738, JP- Conceivable.
[0004]
[Problems to be solved by the invention]
However, even if these means are used and the amount of gas blown per plug is reduced, the molten steel flow that has risen in the ladle due to gas blowing collides with the center of the upper surface, and the center of the molten steel rises greatly. As a result, the molten flux layer existing thereon is disturbed, and the current flowing therethrough becomes unstable and difficult to control. Moreover, the energy loss consumed for the collision of the molten steel flow is large, and the energy used for mixing molten steel is less likely to be larger than in the case of a single plug. Because of these problems, it is difficult to adopt the above means as it is.
[0005]
The present invention was made for the purpose of solving the problems in the conventional energization heating type refining ladle. The mixing stirring force of the molten steel is significantly lower than that of the conventional one while minimizing the disturbance of the surface layer of the molten steel. Therefore, it is intended to propose an electric heating type smelting ladle that can greatly reduce the ladle refining time required for desulfurization, etc., or can significantly improve the refining limit such as desulfurization limit. To do.
[0006]
[Means for Solving the Problems]
The present inventors have, in order to solve the above problems, performs studied arrangement condition of the plug of electrically heating type refining ladle, advantageously of placing asymmetrically multiple plug with respect to the center of the ladle bottom This invention was completed paying attention to. Specifically, a ladle for refining molten steel according to the present invention is a refining ladle provided with a plug for gas injection at the bottom , and three current heating electrodes concentrically with the ladle bottom side wall at the top. there are, the plug is more disposed to unevenly distributed on one of the two divided bottom of ladle for the refining, and the inner diameter of the ladle bottom side wall the plug is disposed and (D) and said mounting pan bottom sidewall The relationship with the diameter (d) at which the plugs that are concentric are arranged is:
d / D = 0.50-0.80
And the relationship between the diameter (d) where the plug is disposed and the diameter (A) of a circle passing through the center of the electrode is
d> 1.5A
Is satisfied.
[0007]
In carrying out the above invention, it is preferable that the plug is installed at a position where the hot water contact portion is removed when receiving steel from the converter, and that two plugs are arranged. It is preferable. In this case, the two plugs are preferably arranged in a sector region having a central angle of 30 to 150 °.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the ladle for refining according to the present invention will be specifically described with reference to the drawings. FIG. 1 is a cross-sectional side view of an electrically heated refining ladle according to the present invention. As shown here, electrically heating type refining ladle of the present invention, the ladle body with refractory consists disk-shaped preparative pan bottom 1 B which is fitted at its bottom a cylindrical ladle sidewalls 1A lined 1 and three electrodes 5A, 5B made of graphite that are arranged concentrically with a ladle bottom side wall through a water-cooled lid 2 that covers the top of the main body 1 and that can be adjusted vertically within the main body. 5C and the ladle (2 in this case) a plurality of bottom 1B through inlaid porous plug 3A, made of 3B. The electrodes 5A, 5B, and 5C are immersed in a molten flux F floating on the molten steel M that has received steel, and are energized by a power supply device (not shown) to heat the flux F by Joule heat. The porous plugs 3A and 3B are connected to the gas pipes 4A and 4B, and an inert gas such as argon is fed into the molten steel M from the bottom to stir the molten steel M.
[0009]
FIG. 2 is an explanatory diagram showing the arrangement of the porous plug 3 of the present invention at the bottom of the ladle in relation to the ladle side wall 1A and the electrodes 5A, 5B, 5C. In the present invention, a plurality of plugs 3 are arranged, but they are unevenly distributed in one of the half circles obtained by dividing the ladle bottom 1B into two (whichever is free, but in this case, the hatched portion). Arranged. As a result, it is possible to avoid the molten steel flow rising by the gas blown from the plug plug 3 from colliding at the center portion of the upper surface of the steel bath and rising and destabilizing the presence state of the flux F. Therefore, the heating by the current flowing from the electrode 5 through the flux F is performed smoothly and does not become uncontrollable.
[0010]
A plurality of plugs 3 are arranged in a range partitioned by 11 and 12 which are concentric circles with the inner periphery of the bottom of ladle side wall 1A. The diameter of the concentric circle of the inner boundary 11, when the inner diameter of the side wall of the ladle bottom and is D,
d / D ≧ 0.50 (1)
While the diameter of the outer boundary 12 of the concentric circle is
d / D ≦ 0.80 (2)
Determined by. As a result, when the molten steel flow rising by the gas blown from the plug 3 reaches the upper surface of the steel bath, it branches into a flow descending along the ladle side wall 1A and a flow descending through the relatively central side of the ladle body 1. And stirring of molten steel comes to be performed suitably.
[0011]
Further, the position of the plug 3 is related to the diameter A of a circle passing through the center of the electrode 5.
d> 1.5A (3)
Need to be satisfied. This is to prevent the molten steel flow rising by the gas blown from the plug from directly contacting the electrode and abnormally damaging the electrode, or preventing the molten steel from being carburized by the electrode graphite.
[0012]
Therefore, the installation position of the plug 3 on the ladle bottom 1A is one of the semicircles obtained by dividing the ladle bottom 1B into two, and is in a range that satisfies the conditions of the above expressions (1) to (3). By disposing the plug at such a position, as will be shown later in Examples, it is possible to obtain a stirring flow that is strong and does not disturb the stability of the molten flux layer.
[0013]
In the above case, the plurality of plugs 3 are generally arranged on the same concentric circle with the inner periphery of the ladle side wall 1A, but it is not always necessary to do so, and the inner boundary and the outer boundary. It is also possible to arrange one side slightly inside and the other side slightly outside in the partitioned area. Further, it is not necessary to make the distance between the plugs uniform. Furthermore, gas pipes for supplying gas to the plurality of plugs can be independent, and the amount of gas ejected from each plug can be controlled independently. Thereby, the stirring state in the ladle can be controlled in a more preferable direction.
[0014]
In addition to the above basic conditions, it is preferable that the plug is disposed at a position where a so-called hot water contact portion 13 at the bottom of the ladle, that is, a range where the molten steel directly hits when receiving the molten steel from the converter, is removed. The position (range) of the hot water contact portion varies depending on the operating conditions and is not necessarily constant. However, for example, a case where two plugs are arranged will be described. As shown in FIG. The second plug 3B is placed at a position approximately 1 / 4D away from the center of the line connecting the ladle hangers 6 with respect to the line. It is good. When two plugs are arranged concentrically with respect to the outer periphery of the ladle side wall 1A, the arrangement position of the second plug is approximately 30 to 150 ° with respect to the arrangement position of the first plug. It is better to be within the range.
[0015]
[Example 1]
Using an electric heating type smelting ladle having the specifications shown in FIG. 3, many ladle smelting for desulfurization was performed while blowing argon gas of 0.0026 Nm ³ / min / t-steel per plug. . The target steel was Al killed steel. A desulfurization agent having a composition of CaO: 50%, Al ₂ O ₃ : 30%, SiO ₂ : 8%, MgO: 12% (weight ratio) was used at 22.0 kg / t-steel. As a comparative example (conventional method), an electrically heated refining ladle provided with one plug was used. The desulfurizing agent was the same as in the present invention example, and the amount of gas blown was smaller than that of the present invention .
[0016]
When steel with a pre-treatment S concentration (weight ratio) of 30 ppm was treated using the apparatus of the present invention, desulfurization proceeded according to the curve of (1) shown in FIG. On the other hand, in the comparative example, it progressed according to the curve of (2). From these curves, when the steel concentration of 30 ppm before treatment was treated for 60 minutes, the reached S concentration was compared to 10 ppm in the conventional method, but 6 ppm when using the apparatus of the present invention. Further, the processing time required to reduce the S concentration to 10 ppm required 60 minutes in the conventional method, but was 33 minutes when the apparatus of the present invention was used.
[0017]
FIG. 5 is a relationship diagram between the pre-treatment S concentration and the post-treatment S concentration when steel having various pre-treatment S concentrations is treated for 60 minutes under the same conditions as described above. As shown here, when the apparatus of the present invention was used, a desulfurization rate of about 80% was achieved. On the other hand, in the conventional example, the desulfurization rate was only about 65%.
[0018]
In the present invention example, the amount of gas blown was larger than that in the conventional example, but there was no swell of the molten steel directly below the electrode or disturbance of the flux layer, and the current heating could be performed smoothly. In addition, the occurrence of splash and the accompanying bullion to the water-cooled lid were not observed.
[0019]
[Example 2]
Using the same energization heating type refining ladle as in Example 1, ladle refining was performed on Al killed steel for the purpose of obtaining ultra-low desulfurized steel. The operating conditions were such that the argon gas blowing rate was increased to 0.0033 Nm ³ / min / t-steel per plug, and the desulfurization agent usage was 27.0 kg / t-steel. As a result, the average desulfurization rate after 30 minutes treatment reached 88%, and the S concentration before treatment of 30 ppm was able to reach 3 ppm S concentration after 30 minutes treatment. In this case as well, no disturbance of the flux layer or occurrence of splash was observed directly under the electrode that hinders the electric heating.
[0020]
【The invention's effect】
By using the current heating type smelting ladle according to the present invention, extremely strong molten steel stirring can be performed without causing disturbance of the slag layer directly under the electrode. Thereby, the secondary refining process such as desulfurization can be quickly performed while smoothly controlling the energization heating, and the desulfurization time can be shortened and the limit can be reduced.
[Brief description of the drawings]
FIG. 1 is a side sectional view of an electrically heated refining ladle according to the present invention.
FIG. 2 is an explanatory view showing the arrangement of the porous plug at the bottom of the ladle in relation to the ladle side wall and the electrode.
FIG. 3 is a layout view showing the specifications of the energization heating type smelting ladle used in the examples.
FIG. 4 is a relationship diagram between a desulfurization treatment time and an S concentration in steel when the apparatus of the present invention is used.
FIG. 5 is a relationship diagram between the pre-treatment S concentration and the post-treatment S concentration when the apparatus of the present invention is used.
[Explanation of symbols]
1: Ladle body 1A: Ladle side wall 1B: Ladle bottom 2: Water-cooled lids 3A, 3B: Porous plugs 4A, 4B: Gas piping 5A, 5B, 5C: Heating electrode 6: Suspension 11: Concentric inner boundary 12: Concentric outer boundary 13: Hot water contact portion M: Molten steel F: Molten flux D: Inner diameter of ladle side wall d: Diameter of concentric circle where plug is arranged A: Diameter of circle passing through center of electrode

Claims (3)

A refining ladle having a plug for gas blowing at the bottom , and three current heating electrodes concentrically with the ladle bottom side wall at the top ,
A plurality of the plugs are arranged in a unevenly distributed manner on one side of the bottom of the smelting ladle divided into two parts, and
Relationship between the diameter of said plug plug is an inner diameter (D) and said mounting pan bottom side wall and concentric ladle bottom side wall disposed is disposed (d) is,
d / D = 0.50-0.80
And the relationship between the diameter (d) where the plug is disposed and the diameter (A) of a circle passing through the center of the electrode is
d> 1.5A
A ladle for refining molten steel characterized by satisfying       The ladle for refining molten steel according to claim 1, wherein the plug is installed at a position from which a hot water contact portion is removed during steel receiving.       The ladle for refining molten steel according to claim 1 or 2, wherein two plugs are arranged.

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