JPH08300141A - Method for improving service life of ladle refractory - Google Patents

Abstract

PURPOSE: To improve the yield of the deoxidizer by forming Al2 O3 on the inner surface of a ladle without heat loss to reduce the erosion of the ladle slag-in. CONSTITUTION: In a vacuum refining equipment where a large diameter immersed tube 2 is immersed in the molten steel in a lade 1, 0.4-1.2 pts.wt. MgO is simultaneously added to the deoxidized Al in terms of pure Al amount in the deoxidization by adding Al after the vacuum decarbonization is achieved to the molten low carbon steel, and the stirring and mixing is achieved with the molten steel flow by the bottom-blowing stirring to form fine Al2 O3 -MO spinel. The service life of the ladle refractory is improved by forming the coating layer on the refractory surface on the inner wall of the ladle 1 by bringing the generated spinel where the molten condition is partly formed by the molten steel heat into contact with the inner wall of the ladle 1, and solidifying it when the generated Al2 O3 -MgO spinel is loaded on the descending flow generated by the bottom-blowing gas and discharged outside from the immersed tube 2. The adhering position of the spinel is adjusted by changing the immersion depth of the large diameter immersed tube 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ladle for refining by receiving molten steel smelted in a converter, an electric furnace or the like, and suppresses melting damage of the refractory formed on the inner wall of the ladle to achieve a long service life. On how to improve.

[0002]

2. Description of the Related Art Ladles have become more severe in terms of refractory damage due to high temperature tapping, molten steel agitation, and longer molten steel residence time in recent years. As a measure to improve the life of ladle refractory, hot spraying of irregular refractory has been proposed.

In Japanese Patent Laid-Open No. 61-232264, the surface of a ladle refractory is Al ₂ O _{3 of} 20 to 30 wt%, FeO <
3% by weight, MgO 7 to 20 and CaO / SiO ₂ = 1.
A method has been proposed in which slag of 5 to 2.5 is coated and the slag adheres favorably to the surface of the refractory as the slag level decreases during casting.

[0004]

However, according to the method described in Japanese Patent Laid-Open No. 61-232264, the floating slag on the ladle surface is partially solidified by cooling in the atmosphere during casting and adheres to the refractory. Is difficult and also during the refining process CaO
When forming a low basicity slag with a weight ratio of / SiO ₂ = 1.5 to 2.5, melting loss of the pan slag line increases.

The problem to be solved by the present invention is that A
By forming l ₂ O ₃ on the inner surface of the ladle, the melting loss of the pot slag-in is reduced and the yield of the deoxidizer is improved.

[0006]

In order to solve the above-mentioned problems, a method for improving the life of a ladle refractory according to the present invention comprises a large-diameter dipping pipe having a ratio of the dipping pipe inner diameter to the ladle inner diameter of 0.3 or more. In a vacuum refining device immersed in molten steel in a ladle, 0.4 to 1.2 parts by weight based on pure Al amount conversion of deoxidized Al at the same time as deoxidation of aluminum after performing vacuum decarburization treatment M
gO was added, and the mixture was agitated and mixed in a molten steel flow by bottom-blown stirring to form minute Al ₂ O ₃ -MgO spinels, and the produced Al ₂ O ₃ -MgO spinel was placed on the downflow generated by the bottom-blown gas. When discharging from the immersion pipe to the outside,
A coating layer is formed on the refractory surface of the inner wall of the ladle by contacting and solidifying the generated spinel, which is partially melted by the heat of molten steel, with the inner wall of the ladle. At this time, the attachment position of the spinel is adjusted by changing the immersion depth of the large diameter immersion pipe.

[0007]

[Operation] In order to extend the pot life in the conventional operation, upgrading of refractory material or repair by hot spraying is mainly used and it is adopted in the actual machine. The temperature drop or the refractory unit price itself becomes expensive and the total cost deteriorates.

The method of the present invention does not require a spray repair machine and deposits oxides conforming to existing spray materials having high fire resistance on the ladle wall.

A stable Al ₂ O ₃ -MgO spinel is effective as a protective deposit on the ladle refractory, and a ladle porous plug was used for the purpose of stirring molten steel in a vacuum refining apparatus with a large diameter immersion tube. Under strong vacuum stirring, Al and MgO were added to the high oxygen content molten steel, and the amount of Al required for deoxidation was determined based on the dissolved oxygen in the molten steel relative to 100 parts by weight of the molten steel, and the Al for deoxidation was converted to pure Al. MgO is 0.4-1.
Add from above in the range of 2 kg / pure Al.

[0010] The added Al and MgO are
Al ₂ O ₃ and MgO oxidized and generated by the heat of oxidation reaction are melt-combined to form a fine Al ₂ O ₃ -MgO spinel, and the Al ₂ O ₃ -MgO spinel melt rolled up by the molten steel stirring flow is efficient. Adheres to the inner wall of the ladle.

The adhesion point can be adjusted by changing the immersion depth of the immersion tube. The adhesion Al ₂ O ₃ -MgO spinel causes the ladle refractory to be mechanically abraded by molten steel stirring and chemically affected by the slag in the ladle. Wear is reduced. Further, the deposit works as a heat insulating material for the refractory and suppresses the cooling of the pot, while the temperature drop of the refractory during the pot cooling is made uniform and the expansion accompanying the phase transformation is reduced.

The MgO to be added is effective as a fine MgO source in order to form Al ₂ O ₃ --MgO slag and has a grain size of 5 to 5.
Those having a purity of 90% or more at 30 mm are effective.

[0013]

EXAMPLES The present invention will be specifically described below based on examples. FIG. 1 shows an example of a refining apparatus for carrying out the present invention, where 1 is a ladle and 2 is a large diameter dip tube. The inner diameter of the ladle is 1700 mm, the inner diameter of the large diameter immersion pipe 2 is 1000
It is about mm. If the inner diameter is small (the ratio of the inner diameter of the dipping tube to the inner diameter of the ladle is smaller than 0.3), it is inconvenient because the dipping tube collides with Ar bubbling at the ladle bottom for stirring.
In this case, if it is 1200 mm or more, it cannot be structurally applied because the outer shape of the dip tube coated with the refractory and the inner wall of the ladle will occur.

In the refining apparatus using the large diameter immersion pipe 2 as shown in FIG. 1, molten steel circulation is formed by stirring with an inert gas such as Ar gas from the bottom of the ladle 2.

Al for deoxidation for the purpose of deoxidizing molten steel is added at the end of the treatment in which dissolved oxygen in the molten steel is increased by decarbonization treatment or the like.

In this case, a large amount of heat is generated due to the oxidation reaction between the added deoxidizing Al and the dissolved oxygen.

The present invention utilizes this Al oxidation reaction to melt the additive for protecting the refractory in the ladle and adhere it to the inner wall of the ladle to reduce melting damage of the ladle.

The operation flow is shown in FIG.

In the method of the present invention, the heat of Al oxidation during deoxidation is M
Since it is used for melting gO, it not only suppresses the thermal influence on the dip tube 2, but also has a protective effect on the generated Al ₂ O ₃ —MgO spinel and reduces wear.

The produced Al ₂ O ₃ --MgO spinel rides on the molten steel flow and is discharged to the outside of the dip tube 2. It adheres and suppresses the wear of the ladle refractory.

Al ₂ O ₃ -Mg not adhered to refractory
The O spinel reaches the slag on the ladle 1, but Al ₂ O
_3- MgO spinel is stable and has an effect of suppressing reoxidation after treatment because it blocks slag and molten steel.

Next, after degassing, 1.2 kg / T of Al was added.
On the other hand, in the same manner as in the case of adding 1.4 Kg / T (1.2) of MgO and stirring, 2.0 Kg / T of Al and MgO
Of 0.8 kg / T was added and stirred. As a result, the life of the ladle was extended by about 30%.

[0023]

As described above, the present invention has the following effects.

Since the generated Al ₂ O ₃ and the added MgO are melt-reacted by utilizing the heat of oxidation of Al for deoxidation in the treatment of the high oxygen content molten steel, the Al ₂ O ₃ —MgO spinel is formed, so that there is no heat loss. the al ₂ O ₃ -MgO spinel can be generated.

The fine Al ₂ O ₃ —MgO spinel produced by performing molten steel agitation in the usual process is rolled up by a stirring flow and forms a refractory protective layer in contact with the inner wall of the ladle to form an adhesion layer. .

The refractory protective layer reduced the wear of the ladle refractory and improved the pot life by 30%.

The refractory protective layer acts as a heat insulating material for the ladle refractory, and suppresses refractory spalling by reducing the temperature drop of the ladle and uniformly cooling the refractory itself during cooling of the ladle.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a refining apparatus for carrying out the method of the present invention.

FIG. 2 is an explanatory diagram of an operation flow of the present invention.

[Explanation of symbols]

 1 ladle, 2 dip tube

Claims (2)

[Claims] 1. A vacuum refining apparatus in which a large-diameter dip tube having a ratio of the inner diameter of the dip tube to the inner diameter of the ladle is 0.3 or more is immersed in molten steel in the ladle, and aluminum after vacuum decarburization treatment is performed. At the time of the addition deoxidation, 0.4 to 1.2 parts by weight of MgO is added at the same time with respect to the pure Al amount of deoxidized Al, and the mixture is agitated and mixed by a molten steel flow by bottom blowing agitation to obtain minute Al ₂ O ₃ -MgO
When the spinel is formed and the produced Al ₂ O ₃ —MgO spinel is placed on the downward flow generated by the bottom gas and is discharged to the outside of the dip pipe, the produced spinel partially melted by the heat of molten steel is formed in the ladle. A method for improving the life of a ladle refractory, which comprises forming a coating layer on the surface of the refractory of the ladle inner wall by contacting and solidifying the inner wall. 2. The method for improving the life of a ladle refractory according to claim 1, wherein the attachment position of the spinel is adjusted by changing the immersion depth of the large diameter immersion pipe.