JPS61207506A - Method for protecting lining of vacuum degassing device for molten steel - Google Patents

Abstract

PURPOSE:To decrease the damage of lining refractories of a vacuum degassing device for a molten steel, etc., lined with carbon-contg. refractories and to extend the service life thereof by introducing an inert gas into a degassing vessel in a vacuum state after the degassing treatment of the molten steel. CONSTITUTION:The lining of the degassing vessel of the vacuum degassing device of an RH type, DH type, etc., for the molten steel is executed by stamping and calcining the refractory material prepd. by adding a binder such as phenolic resin, furan resin, pitch or tar to the refractory material consisting of oxide or carbide refractories contg. >=5wt% carbonaceous raw materials such as graphite, pitch coke or electrode scrap and consisting of the balance magnesia, calcia, dolomite clinker, alumina, spinel, zirconia, silicon carbide, boron carbide, etc., and kneading the mixture. The molten steel is refined by the vacuum degassing in such vacuum degassing vessel and thereafter the inexpensive inert gas such as nitrogen is introduced in the degassing vessel, by which the early damage of the refractory lining by the spalling arising from the oxidation of the carbon of the refractory lining is prevented.

Description

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

(Prior art) 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 deoxidizing, decarburizing, and continuous casting. Its applications are rapidly expanding, including mass processing of steel and production of special rust. The most common wear lining for the vacuum degassing equipment used for this purpose is fired maguro bricks. However, fired maguro bricks absorb slabs and form an altered layer, and when humidity fluctuations are applied, this altered layer cracks, causing so-called structural spalling. Gas equipment has a short service life due to damage caused by peeling of the lining.

As a countermeasure to this problem, attempts have been made to use carbon-containing refractories such as magnesia-carbon bricks as lining materials that do not penetrate the slab at all and do not cause structural spalling.

(Problem to be solved by the invention) However, although carbon-containing refractories suffer little erosion 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 different from conventional fired macro bricks. It disappears. When we researched this theory, we found that after vacuum degassing of molten steel, if the temperature inside the tank drops while waiting for the next treatment, cracks will form on the working surface of the lining, and intrusion will occur from there. The air diffuses over the entire back surface of the wear lining through the expansion absorption layer provided between the wear lining and the permanent screw 1~lining, or between the wear lining and the semi-permanent screw 1~lining, and oxidizes and eliminates carbon in the carbon-containing refractory. It turned out to be. The expansion absorbing layer is generally made of a porous material such as mortar, castable material, or stamp material, and has a thickness of 5 to 20 mm, so that air can easily pass through it.

Various anti-oxidation techniques for carbon-containing refractories have been proposed, but when used for the lining of vacuum degassing equipment, sufficient effects have not been obtained. For example, JP-A-54-121
In Publication No.-0, in order to prevent the oxidation of carbon-containing bricks for the ceiling of an electric furnace, the bricks are covered with a metal plate. However, in the case of vacuum degassing equipment, unlike when used in electric furnaces, the metal plate is not oxidized during operation and melts and flows out in a metallic state, and the lining adds to the oxidation of carbon-containing refractories. Methods have been proposed to prevent this. The addition of these metal powders is about 3 wt % in the lining of a converter, etc., but in a vacuum degassing device, if it is less than 10 wt %, the oxidation prevention effect is not sufficient. If the amount exceeds 10 wt%, oxidation will not occur, but since the metal powder is a low melting point substance, corrosion resistance will decrease if a large amount is added.

(Means for Solving the Problems) Since the vacuum degassing apparatus is operated in a vacuum, the oxygen concentration is naturally low during operation, and the carbon-containing refractory is not oxidized.

Therefore, we thought of keeping the interior of the degassing tank in an inert gas atmosphere to prevent oxidation of the lining during the standby period after the vacuum degassing treatment of molten steel and before the next treatment. However,
Simply introducing inert gas during standby had very little effect.

This is because inert gas does not reach the back of the refractory where oxidation is a problem, and when oxidation has already progressed due to air intrusion, if inert gas is introduced into the degassing tank, the back of the lining The present invention was completed after discovering that the oxidation of

That is, the present invention provides a vacuum degassing device lined with a carbon-containing refractory, after completing vacuum degassing treatment of molten steel,
This is a method for protecting the lining of a vacuum degassing apparatus for molten steel, characterized in that an inert gas is introduced into the degassing tank under a vacuum condition to create an inert gas atmosphere inside the degassing tank.

The specific composition and manufacturing method of the carbon-containing refractory lined in the vacuum degassing device are not particularly limited;
The following is an example of this. First, carbon raw materials include, for example, scaly graphite, earthy graphite, pitch coke,
One or more types selected from electrode scraps 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 is no problem of oxidation. 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, Al, Si
tMg.

A shaped refractory is constructed by adding a binder to the above-mentioned mixture, kneading it, and using any method such as casting or stamping. on the other hand.

In the case of shaped refractories, for example, a binder such as phenol resin, furan resin, or tar pitch is added, and after cross-wiring and molding, in the case of unfired products, heat treatment is performed at 100 to 400 °C, which is the binder. Removes the volatile content in the tar or resin and develops the strength of the refractory. Furthermore, when the binder is a curable resin, thermal curing occurs and strength is developed.

The fired product is further heated to 800°C or higher, preferably 900-15°C.
Carbon bonds are formed from tar or resin bonds by heat treatment to a high temperature of 00°C.

The carbon-containing refractory thus obtained forms part or all of the lining of the vacuum degassing device. The type of vacuum degassing equipment to be applied is not particularly limited, and the operating method of the vacuum degassing equipment is, for example, the "Vacuum degassing method" published by the Refractory Technology Association, May 15, 1970, P371-3.
As described in 73, 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 and scattered to perform vacuum degassing treatment. will be held. 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, the immersion tube is not pulled up immediately, but the lower end of the immersion tube is closed with molten steel, and the degassing tank introduces an inert gas under a vacuum condition. After creating an inert gas atmosphere inside, pull up the immersion tube.

Examples of the inert gas introduced into the degassing tank include nitrogen.

Although argon or the like can be used, nitrogen is preferable from the viewpoint of cost 1. Inert gas introduction [The position of J is not particularly limited; for example, in the case of an RH type vacuum gas tank, in order to circulate the molten steel, oxygen is blown in from the argon gas blowing conduit installed in the immersion pipe. If the side wall of the lower tank is equipped with a lining for blowing, the air can also be blown through the lining. A separate inlet for blowing inert gas may be provided, but in this case, the blockage caused by slabs or molten steel during vacuum degassing treatment must be sealed in the degassing tank by covering it, or the inert gas A more complete inert gas atmosphere can be maintained by continuously introducing gas to maintain a positive pressure. The degree of vacuum when introducing inert gas is 300 r
n m I (although the effect is recognized even at about g, it is preferable) is not more than Om m Hg.

(Function) In a vacuum degassing device, oxidation of the carbon-containing refractory that is the lining of the vacuum degassing device can be prevented. In vacuum degassing equipment, oxidation is a problem on the back side of carbon-containing refractories, but since the degassing tank introduces inert gas under vacuum conditions,
The inert gas instantly passes through small gaps such as the 1" bottom or cracks of the inner lining, spreads to the back side of the lining, and prevents oxidation of the back side.

(Example) Next, an example of the present invention will be shown, but the present invention is limited to this example.
, it is not something that will be done.

The carbon-containing refractories used for the lining on each side were scale graphite 20
wt%, the balance consisting of magnesia clinker,
As a binder, 45% fixed carbon and 11% phenolic resin with a viscosity of 300 cps were added, and after kneading and molding,
This is a magnesia-carbonaceous brick obtained by drying at 250°C for 24 hours.

Nitrogen gas was introduced from the existing oxygen blowing panel provided on the side wall of the lower tank. During standby, the pressure inside the degassing tank was maintained at a nitrogen gas atmosphere of 1.05 atm.

Comparative Example 1; After vacuum degassing of the molten steel, the immersion tube was pulled out from the molten steel in the ladle, and after the inside of the degassing tank was returned to atmospheric pressure, the existing oxygen installed on the side wall of the lower tank was removed. Nitrogen gas was introduced through the blowing line. During standby, the pressure inside the degassing tank was maintained at a nitrogen gas atmosphere of 1.05 atm.

Comparative Example 2: After the molten steel was vacuum degassed, the operation was carried out in the conventional manner without introducing any inert gas.

On each side, the above-mentioned operation was repeated 300 times in accordance with the operation of the vacuum degassing equipment. The oxidation resistance and wear rate of the lining on each side is shown in the table.

*1; After 200 operations, the furnace was stopped and the thickness of the oxidized layer on the lining was measured.

(Effects) According to the present invention, it is possible to solve the problem of backside oxidation that occurs when a carbon-containing gas is used for the lining of a vacuum degassing device, and the lining is rapidly eroded at the end of use. The phenomenon disappears.

Therefore, the effects of the carbon-containing refractory, such as preventing penetration of slack, can be fully exhibited, and as is clear from the results of the examples, the life of the lining is greatly extended.

The present invention is achieved only when the inert gas is introduced into the degassing tank under a vacuum condition, but since a vacuum condition can be created by using the operation of a vacuum degassing device, the present invention It can be carried out using existing equipment as is.

Note that similar effects were obtained when the lining was made of a carbon-containing refractory other than those shown in the examples.

Claims (1)

[Claims] In vacuum degassing equipment lined with carbon-containing refractories,
Lining protection for molten steel vacuum degassing equipment, characterized in that after vacuum degassing of molten steel is completed, an inert gas is introduced into the degassing tank under vacuum conditions to create an inert gas atmosphere inside the degassing tank. Method.