JP2001040411A - Ladle for refining molten steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrically heating type refining ladle, in which mix- stirring force for molten steel can remarkably be strengthed in comparison with the conventional ladle while restraining the disturbance of molten steel surface layer to the minimum, and therefore, the ladle refining time needed for desulfurization, etc., can drastically be shortened or the refining reaching limit, such as the desulfurizing limit, etc., can remarkably be improved. SOLUTION: Plural plugs 3A, 3B are fitted to the ladle for refining and these fitting positions are unevenly positioned to the one side between two parts formed by dividing the bottom part 1B of the ladle 1 for refining into two and also, the relation between the inner diameter (D) of the ladle side wall 1A and the diameter (d) for disposing the plug concentric with the ladle side wall, satisfies d/D=0.50-0.80. Further, the relation between the diameter (d) for disposing the plug and the diameter (A) of the circle passing the center of the electrodes, satisfies d>1.5A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[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 desulfurization and the like, and in particular, a porous plug for gas injection at the bottom (hereinafter simply referred to as a plug). ), And a refining ladle having an electric heating electrode at the top.

2. Description of the Related Art Molten steel refined in a converter is sent to an ingot-making facility such as a continuous casting machine. Before that, so-called secondary casting is performed to reduce impurities such as S or to finely adjust alloy components. Often used for secondary refining. Especially in recent years,
In the case of HIC steel, high-strength steel, etc., so-called single ppm order ultra-low sulfur steel with an S content of 9 ppm or less is increasing, so the ratio of steel subjected to the secondary refining is increasing. .

Ladles for refining are widely used as equipment for such secondary refining. One of them is a ladle having a cylindrical shape as shown in Fig. 1 with a plug for gas injection at the bottom, and an electric current at the top to compensate for the temperature drop of molten steel during secondary refining. Some have heating equipment.
In this type of ladle for refining, molten steel is charged into the ladle for refining and a flux in a molten state is placed thereon.
The molten steel is agitated by the gas blown from the bottom, and the electrodes are immersed in the flux and energized to generate heat by Joule heat, compensating for the temperature drop of the molten steel, or performing refining such as desulfurization while heating more actively. It has become. In this electric heating type refining ladle, it is necessary that stirring by gas is performed as strongly as possible and heating by electric current is controlled.

Normally, this type of electrically heated refining ladle has one plug, and simply increasing the amount of gas blow increases the splash of molten steel, causing ingots to adhere to the water cooling lid of the refining ladle. There is a problem that the operation becomes difficult due to poor current supply or the like. Another problem is that the refining time is relatively long. As a means for solving such a problem, there is a means which does not have an electric heating facility, but a means of using a plurality of plugs disclosed in Japanese Patent Publication No. 63-168253 or Japanese Utility Model Laid-Open No. 2-42738 can be considered. .

[0004]

However, even if these means are used to reduce the amount of gas blown per plug, the molten steel flow rising in the ladle by the gas blow collides at the center of the upper surface. As a result, the central portion of the molten steel surface rises greatly and undulates, so that the molten flux layer existing thereon is disturbed, the current flowing therethrough becomes unstable, and control becomes difficult. Further, the energy loss expended due to the collision of the molten steel flow is large, and the energy used for mixing the molten steel is unlikely to be larger than that of a single plug. Due to these problems, the above-described means cannot be employed as it is.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems in the conventional electric heating type refining ladle, and it has been known that the mixing and stirring power of molten steel can be reduced while minimizing the disturbance of the molten steel surface layer. To propose an energized heating type smelting ladle that can be significantly strengthened compared to the previous one, so that the ladle refining time required for desulfurization etc. can be significantly reduced, or the refining attainment limit such as the desulfurization limit can be significantly improved. With the goal.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the arrangement conditions of the plugs of the electrically heated refining ladle, and have determined that a plurality of plugs are asymmetrical with respect to the center of the ladle. The present invention has been completed by focusing on the advantage of the arrangement. Specifically, the refining ladle for molten steel according to the present invention is a refining ladle provided with a plug for gas injection at the bottom and an electrode for energization and heating at the top, wherein the plug is the ladle for refining. The relationship between the inner diameter (D) of the ladle side wall and the diameter (d) at which the plug is arranged concentrically with the ladle side wall is arranged such that a plurality of the bottom portions are unevenly distributed on one of the two divided portions. /D=0.50 to 0.80, and the diameter (d) at which the plug is arranged
And the diameter (A) of the circle passing through the center of the electrode satisfies d> 1.5A.

In carrying out the above invention,
It is preferable that the plug is installed at a position where a hot water contact portion at the time of receiving steel from the converter is removed.
It is preferable that these are arranged individually. In this case, it is preferable that the two plugs are arranged in a sector having a central angle of 30 to 150 °.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A ladle for refining according to the present invention will be specifically described below with reference to the drawings. FIG. 1 is a side sectional view of an electric heating type refining ladle according to the present invention. As shown here, the electric heating type refining ladle of the present invention comprises a ladle body 1 comprising a cylindrical ladle side wall 1A lined with refractories and a disk-shaped ladle bottom 2B inserted into the bottom thereof. And a water-cooled lid 2 covering the upper part of the main body 1 and graphite electrodes 5A, 5B, 5
C and through the ladle lid 2B, a plurality of
Each of the plugs is composed of the inserted porous plugs 3A and 3B.
The electrodes 5A, 5B, and 5C are immersed freely in a molten flux F floating on the molten steel M that has received the steel, and are energized by a power supply device (not shown) to heat the flux F by Joule heat. In addition, the porous plugs 3A, 3A
B is 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 agitate the molten steel M.

FIG. 2 shows the arrangement of the porous plug 3 of the present invention at the bottom of the ladle, the ladle side wall 1A and the electrodes 5A, 5B, 5C.
FIG. 4 is an explanatory view showing the relationship with FIG. In the present invention, a plurality of plugs 3 are arranged, and they are one of two semi-circles obtained by dividing the ladle bottom 1B into two parts (although any one may be used,
In this case, it is located in a hatched portion). Thus, it is possible to prevent the molten steel flow rising due to the gas blown from the plug 3 from colliding and rising at the center of the upper surface of the steel bath to make the existing state of the flux F unstable. Therefore, the heating by the current flowing from the electrode 5 through the flux F is performed smoothly, and the control is not lost.

A plurality of plugs 3 are arranged in a range separated by concentric circles 11 and 12 with the inner periphery of the ladle side wall 1A. The diameter of the inner boundary 11 of the concentric circle is determined by d / D ≧ 0.50 (1) when the inner diameter of the ladle side is D, while the diameter of the outer boundary 12 of the concentric circle is d /D≦0.80 (2) Thereby, when the molten steel flow rising by the gas blown from the plug 3 reaches the steel bath upper surface,
The flow branches off into a flow descending along the ladle side wall 1A and a flow descending through the relatively center side of the ladle main body 1, so that the molten steel is suitably stirred.

Further, the position of the plug 3 needs to satisfy d> 1.5 A (3) in relation to the diameter A of a circle passing through the center of the electrode 5. This is to prevent the molten steel flow rising by the gas blown from the plug from directly hitting the electrode and abnormally wearing the electrode or preventing the molten steel from being carburized by the electrode graphite.

Therefore, the installation position of the plug 3 on the ladle bottom 1A is one of the half circles obtained by dividing the ladle bottom 1B into two and falls within a range satisfying the conditions of the above equations (1) to (3). By arranging the plug at such a position, it is possible to obtain an agitated flow that is strong and does not disturb the stability of the molten flux layer, as will be described later in Examples.

In the above case, the plurality of plugs 3
Is generally arranged on the same concentric circle as the inner periphery of the ladle side wall 1A, but it is not always necessary to do so.
It is also possible to arrange one part slightly inside and the other part slightly outside in the area delimited by the inside boundary and the outside boundary. Also, there is no need to keep the distance between the plugs uniform. Further, gas pipes for supplying gas to a plurality of plugs can be made 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, the plug should be placed out of the so-called hot water contact portion 13 at the bottom of the ladle, that is, the range where the molten steel directly hits when the molten steel is received from the converter. Is preferred. The position (range) of the hot water contact portion varies depending on operating conditions, and is not necessarily constant. For example, when a case where two plugs are arranged will be described, as shown in FIG.
And the second plug 3B is located at a position approximately 1 / 4D away from the center of the line connecting the ladle suspender 6 with respect to the line connecting the It is good to put in. 2 at a position concentric with the outer periphery of ladle side wall 1A
When arranging the two plugs, the arrangement position of the second plug is approximately 30 to 1 with respect to the arrangement position of the first plug.
It is better to fit within a 50 ° sector.

[0015]

Example 1 Using an electrically heated refining ladle having the specifications shown in FIG. 3, 0.0026 Nm ³ / min / t-steel per plug
Ladle refining for the purpose of desulfurization was performed while blowing argon gas. The target steel was Al-killed steel. A desulfurizing 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), a conventional energization heating type refining ladle provided with one plug was used. The desulfurizing agent was the same as that of the present invention, and the gas blowing amount was as follows.

When a steel having an S concentration (weight ratio) of 30 ppm before treatment was treated using the apparatus of the present invention, desulfurization proceeded according to the curve shown in FIG. On the other hand, in the comparative example, it progressed according to the curve. From these curves,
A comparison of the ultimate S concentration when the steel having a concentration of 30 ppm was treated for 60 minutes was 10 ppm in the conventional method and 6 ppm in the case of using the apparatus of the present invention. In addition, S concentration is 10ppm
In the conventional method, the processing time required for lowering the temperature was 60 minutes, but in the case of using the apparatus of the present invention, it was 33 minutes.

FIG. 5 is a graph showing the relationship between the S concentration before treatment and the S concentration after treatment when steel having various S concentrations before treatment is treated under the same conditions as above for 60 minutes. As shown here, when the apparatus of the present invention was used, a desulfurization rate of about 80% was achieved. In contrast, in the conventional example, the desulfurization rate was only about 65%.

In the present invention, although the gas injection amount was larger than that of the conventional example, there was no swelling of the molten steel immediately under the electrode or the disturbance of the flux layer, and the electric heating could be performed smoothly. In addition, no splash was generated and no metal was attached to the water-cooled lid.

[0019]

Example 2 Ladle refining was performed on Al-killed steel in order to obtain ultra-low desulfurized steel using the same electrically heated refining ladle as in Example 1. The operating conditions were such that the blowing rate of argon gas was increased to 0.0033 Nm ³ / min / t-steel per plug, and the amount of desulfurizing agent used was 27.0 kg / t-steel. As a result, the average desulfurization rate after the treatment for 30 minutes reached 88%, and the steel having the S concentration of 30 ppm before the treatment was able to have the S concentration of 3 ppm after the treatment for 30 minutes. Even in this case, no disturbance of the flux layer or generation of a splash immediately below the electrode, which hinders electric heating, was observed.

[0020]

According to the present invention, by using the electric heating type refining ladle, extremely strong stirring of molten steel can be performed without causing disturbance of the slag layer immediately below the electrode. Thereby, the secondary refining process such as desulfurization can be performed promptly while the electric heating is smoothly controlled, so that 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 electric heating type refining ladle according to the present invention.

FIG. 2 is an explanatory diagram showing an arrangement of a porous plug at a ladle bottom in relation to a ladle side wall and electrodes.

FIG. 3 is a layout diagram showing the specifications of an electrically heated refining ladle used in an example.

FIG. 4 is a diagram showing the relationship between the desulfurization treatment time and the S concentration in steel when the apparatus of the present invention is used.

FIG. 5 is a diagram showing the relationship between the S concentration before processing and the S concentration after processing when the apparatus of the present invention is used.

[Explanation of symbols]

 1: Ladle main body 1A: Ladle side wall 1B: Ladle bottom 2: Water cooling lid 3A, 3B: Porous plug 4A, 4B: Gas pipe 5A, 5B, 5C: Heating electrode 6: Hanger 11: Inner boundary of concentric circle 12: Outer boundary of concentric circle 13: Hot metal contact part 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 the center of electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koji Yamaguchi 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Pref. F-term in Kawasaki Steel Works, Mizushima Works (Reference)

Claims (3)

[Claims] 1. A refining ladle having a gas blowing plug at a bottom portion and an electric heating electrode at an upper portion, wherein the plug is unevenly distributed on one of two parts of a bottom portion of the refining ladle. The relationship between the inner diameter (D) of the ladle side wall and the diameter (d) at which the plug concentric with the ladle side wall is arranged satisfies d / D = 0.50 to 0.80. And the diameter (d) at which the plug is located
And a diameter (A) of a circle passing through the center of the electrode satisfies d> 1.5A. 2. The ladle for refining molten steel according to claim 1, wherein the plug is installed at a position where a hot water contact portion at the time of receiving the steel is removed. 3. A ladle for refining molten steel according to claim 1, wherein two plugs are arranged.