JPS61246313A - Method for protecting lining of apparatus for vacuum-degassing molten steel - Google Patents

Abstract

PURPOSE:To considerably prolong the life of the lining of an apparatus for vacuum-degassing molten steel by leading an inert gas to the rear side of refractory brick contg. carbon as the lining through the iron shell between the end of the degassing of molten steel and the beginning of the next degassing. CONSTITUTION:The iron shell 1 of an apparatus for vacuum-degassing molten steel has been lined with refractory brick 3 contg. carbon with an expansion absorbing layer 2 in-between. An inert gas is led to the rear side of the brick 3 from a gas leading pipe 6 through the shell 1 between the end of the degassing of molten steel and the beginning of the next degassing. The inert gas is diffused by the layer 2 behind the brick 3, so the gas acts uniformly on the whole rear side of the brick 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for protecting the lining of a molten steel vacuum degassing apparatus lined with carbon-containing refractory bricks.

(Conventional technology) Vacuum degassing treatment of molten steel was developed and used for the purpose of eliminating defects in high-grade steel caused by hydrogen, but recently it has been used for the purpose of deoxidation, decarburization, and continuous casting. Its applications, such as the mass processing of ordinary steel and the production of special steel, are rapidly expanding. The most common lining material for vacuum degassing equipment used for this purpose is fired maguro brick. but,
Fired maguro-based bricks absorb slag and form an altered layer, and when temperature fluctuations are applied, cracks occur in this altered layer, causing so-called structural spalling. The lifespan of equipment is shortened due to damage caused by peeling off of the lining.

As a countermeasure to this problem, attempts have been made to use carbon-containing refractory bricks, such as magnesia-carbonaceous bricks, as lining materials that are completely impermeable to slag and do not cause structural spalling.

(Problem to be solved by the invention) However, although carbon-containing refractory bricks have little erosion loss in the early stages of use, erosion rapidly progresses in the later stages of use, and in terms of durability, they end up being no better than conventional fired maguro bricks. It disappears. After researching the reason for this, we found that after vacuum degassing treatment of molten steel,
When the temperature inside the tank decreases while waiting for the next treatment, a joint break occurs on the working surface of the lining, and the air that enters from there is diffused over the entire back surface by the expansion absorption layer provided on the back of the lining. It turns out that this is to oxidize and eliminate the carbon component in the carbon-containing refractory brick. The expansion absorbing layer is generally made of a porous member such as mortar, castable refractory, stamp material, or insulation board, and has a structure that allows air to easily pass through.

Various oxidation prevention technologies for carbon-containing refractory bricks have been proposed, but when used for the lining of vacuum degassing equipment,
In either case, sufficient effects were not obtained0For example, in JP-A No. 5
No. 4-1210 discloses covering carbon-containing bricks for the ceiling of an electric furnace with a metal plate to prevent oxidation. but,
In the case of a vacuum degassing device, unlike when used in an electric furnace, the metal plate is not oxidized during operation and melts and flows out in a metallic state, causing the joints in the lining to open and cause joint erosion.

JP-A-54-163913 proposes a method of preventing oxidation of carbon-containing refractory bricks by adding metal powder, such as Al, Mg, Si, etc., which has a stronger affinity for oxygen than carbon. The amount of these metal powders added is about 3wt% for the lining of converters, etc., but for vacuum degassing equipment, it is about 1wt%.
If it is less than 0wt%, the antioxidant effect is not sufficient; 10wt%
If the amount exceeds %, oxidation will not occur, but since the metal powder is a low melting point substance, the corrosion resistance of the brick will decrease if a large amount is added.

(Means for solving the problem) Since the vacuum degassing equipment is operated in a vacuum, the oxygen concentration is naturally low during operation, and the carbon-containing refractory bricks are not oxidized. Therefore, the molten steel is vacuum degassed. After that, inert gas was introduced into the degassing tank while waiting for the next treatment.

We tried to prevent the lining from oxidizing, but the effect was extremely small. This is because it takes time for the inert gas to spread to the back of the lining where oxidation is a problem.
This is thought to be because air has already entered and cannot be completely replaced with inert gas. Furthermore, this method has the disadvantage that the entire degassing tank must be kept in an inert gas atmosphere, and that a large amount of inert gas is required.

As a result of further studies, the inventor of the present invention discovered that oxidation of the back surface of the lining can be effectively prevented by introducing an inert gas to the back surface of the lining after vacuum degassing of the molten steel. A method for protecting the lining of a vacuum degassing equipment for molten steel, which is characterized by introducing an inert gas to the back side of the carbon-containing refractory brick through the iron skin while waiting until the next degassing process is started. be.

Although the specific composition and manufacturing method of the carbon-containing refractory brick lined in the vacuum degassing device are not particularly limited, examples thereof are as follows. First, as the carbon raw material, one or more types selected from, for example, scaly graphite, earthy graphite, pitch coke, electrode scraps, etc. are used. The proportion is preferably 5 wt % or more; if it is less than 5 wt %, the effect of carbon in preventing slag penetration cannot be obtained, and since the proportion of carbon is small, there are few oxidation problems. When combining refractory raw materials other than carbon, examples include magnesia, calcia, dolomite clinker-2 synthetic magdo clinker, and alumina.

Oxide raw materials such as spinel, picrochromite, zirconia, electrofused or sintered maguro, or silicon carbide,
One or more types selected from non-oxide raw materials such as boron carbide are used. Furthermore, if necessary, Alp S
i, Mg.

Add metals such as Fe and Ca, alloys thereof, and others.

The production of carbon-containing refractory bricks involves adding one or more binders, such as phenolic resins, furan resins, and tar pitch, to one or more compounds to remove volatile components and develop the strength of the bricks. Also,
When the binder is a curable resin, this heat treatment causes thermal curing to develop strength. Baked products are further heated to 800℃
that's all.

Carbon bonds are formed from tar or resin bonds by heat treatment at high temperatures, preferably from 900 to 1500"C.The carbon-containing refractory thus obtained can be used to line part or all of a vacuum degassing device. Configure.

The material of the expansion absorbing layer interposed between the iron skin and the carbon-containing refractory bricks is mortar, castable refractories, monolithic refractories such as stamp materials, and heat insulating boards mainly made of ceramic fibers.

The figure shows an example of a vacuum degassing apparatus for carrying out the method of the present invention, in which 1 shows an iron shell, 2 shows an expansion absorption layer, 3 shows a carbon-containing refractory brick, 4 shows a degassing tank, and 5 shows an immersion pipe. . Reference numeral 6 denotes a gas introduction pipe that communicates with the back surface of the carbon-containing refractory brick 3 through the iron shell 1 to introduce an inert gas.

Although not shown in the figure, a permanent brick is generally provided between the carbon-containing refractory brick 3 and the expansion absorbing layer 2 from the viewpoint of operational safety. The material of the permanent brick may be one that does not contain carbon. In this case, the inert gas passes through the joints of the permanent brick and is introduced into the back side of the carbon-containing refractory brick 3. Alternatively, a gas introduction pipe 6 may be provided, and the gas may be introduced directly into the back surface of the carbon-containing refractory brick 3.

In order to make the diffusion of the inert gas smoother in the back surface of the carbon-containing refractory brick 3, for example, a continuous air passage in the circumferential direction may be formed in the expansion absorbing layer 2. For example, there is a method in which a vanishing material such as polyethylene, polystyrene, or polyester is buried in advance at the time of construction and vanishes at high temperatures during furnace operation to form a ventilation path.

In addition, it is more effective if the inert gas introduction pipes 6 are provided at multiple locations on the furnace wall at equal intervals.6 The type of vacuum degassing device to be used is not particularly limited; for example, the RH type, These include the DH type, and the simple degassing type in which the immersion tube and degassing tank are integrated in a straight shape.

The operating method of vacuum degassing equipment is 1, for example, "vacuum degassing method"
May 15, 1978, Published by Refractory Technology Association, P371
As described in 373, the immersion tube installed at the lower end of the degassing tank is immersed in the ladle, the inside of the degassing tank is evacuated, the molten steel is sucked up, and the molten steel is flowed in and scattered to perform the degassing treatment. It will be done. After completing the vacuum degassing process, the immersion tube is conventionally pulled out of the molten steel in the ladle, and the vacuum degassing device is left standing by until the next process.

On the other hand, in the present invention, after the vacuum degassing treatment, an inert gas is introduced into the back surface of the carbon-containing refractory brick 3 through the iron shell 1 while waiting until the next degassing treatment is started.

The type of inert gas used here is 1. For example, nitrogen gas, argon gas, etc. can be used, but nitrogen gas is preferable from a cost perspective. It is preferable that the pressure on the back side of the refractory brick 3 is always kept at a positive pressure with respect to atmospheric pressure.

(Function) After finishing the gas treatment of molten steel, when inert gas is introduced through the steel shell 1, the inert gas diffuses in the expansion absorption layer 2, which is a porous member, and spreads over the entire back surface of the carbon-containing refractory brick 3. Even if air has already invaded the back surface of the carbon-containing refractory bricks 3, the air is discharged into the degassing tank through the joints of the carbon-containing refractory bricks 3 by introducing an inert gas.

(Effects) According to the present invention, by directly introducing an inert gas into the back surface of the carbon-containing refractory brick, it is possible to quickly and reliably prevent oxidation. Moreover, the inert gas is diffused by the expansion absorption layer provided on the back surface and acts uniformly on the entire back surface of the carbon-containing refractory brick. Furthermore, since the inert gas is introduced into a limited area, that is, the back surface of the lining, the amount of inert gas used is small and the time required for introduction is short.

Therefore, when carbon-containing refractory bricks are used as a lining, the phenomenon of rapid erosion of the lining at the end of use is eliminated, and the effect of carbon-containing refractory bricks, such as preventing slab penetration, can be fully exerted, and the implementation described below As is clear from the example data, the life of the lining of the vacuum degasser is significantly improved.

(Example) Next, examples of the present invention will be shown, but the present invention is not limited thereto.

The carbon-containing refractory bricks used for lining on each side were made of flaky graphite 3
0 wt%, the balance being magnesia clinker.

As a binder, 5 wt% of a phenolic resin with a fixed carbon content of 45% and a viscosity of 300 cps was added, and after cross-wiring and molding, 2
This is a magnesia-carbonaceous brick obtained by drying at 50°C for 24 hours.

Further, the vacuum degassing device was an RH type.

Example - From the inside of the iron shell, a 30 mm thick insulation board made of siliceous fibers (in the longitudinal direction of thick bricks)
It was lined with magnesia bricks of 230m+i, alumina castable refractories of 30+am thick, and carbon-containing refractory bricks of 300I (thick in the length direction of the bricks). After the molten steel is gas-treated, it is passed through the steel shell and attached to the back of the carbon-containing refractory.
Nitrogen gas was introduced at a flow rate of Q/min.

Comparative Example 1: In the lining structure shown in the example, after degassing the molten steel, 600 Q/min was placed in the degassing tank.
Nitrogen gas was introduced at a flow rate of .

Comparative Example 2: In the lining structure shown in the example, after degassing the molten steel, no inert gas was introduced, and the operation was carried out in the conventional manner.

Each side performs the above operations three times in accordance with the operation of the vacuum degassing equipment.
The oxidation resistance and wear rate of the lining are shown in the 0-order table, which was repeated 00 times.

*l; After 200 operations, the furnace was stopped and the thickness of the oxidized layer of the carbon-containing refractory brick was measured.

[Brief explanation of the drawing]

The figure is a partial sectional view of a vacuum degassing device for explaining the present invention. 1; Iron skin 4; Degassing tank 2F Expansion absorption layer 5; Immersion pipe 3; Carbon-containing refractory brick 6
; Gas introduction pipe patent applicant Harima Refractory Brick Co., Ltd. Engraving of drawings (no change in content) Procedural amendment (voluntary) April 19, 1985 1, Indication of case Patent application No. 592' of 1985? 7
No. 2, Name of the invention ES Method for protecting the lining of a 1/4 vacuum degassing device 3, Relationship with the case of the person making the amendment Patent applicant 4, All drawings subject to the amendment も・-71

Claims (1)

[Claims] In a vacuum degassing device in which carbon-containing refractory bricks are lined inside the steel shell with an expansion absorbing layer, after the degassing process of molten steel is completed, during the waiting period before starting the next degassing process, the steel shell is A method for protecting the lining of a molten steel vacuum degassing device, characterized by introducing an inert gas to the back side of a carbon-containing refractory brick.