JPH09104915A - Refractory lining of rh degassing chamber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the refractory linings of an RH degassing chamber having a long life. SOLUTION: The refractory linings of the RH degassing chamber are formed by lining part or the whole of the chamber with magnesia carbon bricks having <=5mm thickness of the oxidation decarburized layers after exposure for four hours in an atm. atmosphere of 1400 deg.C or the refractory linings of the RH degassing chamber are formed by lining part or the whole of the chamber with magnesia carbon bricks formed by covering the >=1 surfaces of the bricks with metallic plates or metallic foil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a refractory lining for a tank of an RH degassing facility used for iron and steel refining.

[0002]

2. Description of the Related Art With the recent tightening of steel composition, the importance of RH degassing equipment (hereinafter referred to as RH) has increased significantly.
Refining operations are demanding for refractory linings. In particular, when flux is added to molten steel in an RH degassing tank (hereinafter referred to as RH tank) during refining, the wear of the lining refractory material is greatly accelerated. Moreover, since the life of the lining refractory material has a great influence on the steel refining cost, the lining refractory material is required to have an even longer life in order to manufacture an inexpensive steel product. Further, in order to improve productivity by matching with converters and continuous casting and achieving a production plan in accordance with the plan, a stable tank life, that is, a life of lining refractory is expected.

Conventionally, magro bricks have been widely used as refractory linings for RH tanks. This is because the magro brick can be stably used under high temperature and vacuum conditions, and has relatively high corrosion resistance against the ladle slag that enters the RH tank when it is immersed in the molten steel of the ladle. Directly-bonded bricks, which are fired bricks based on sintered magnesia clinker and natural chrome ore, are mainly used as magro bricks. But,
When particularly high durability is required, a semi-ribbon brick is also used in which magnesia and chrome ore are once melted in an electric furnace and then solidified, and this is crushed to use together with an electro-fused magcro clinker.

[0004]

The refractory lining for the RH tank is required to have a stable and long life as described above. However, the lined magcro brick is mainly worn by the following mechanism, and it is not easy to achieve a long life.

One of the wear mechanisms of magro bricks is a phenomenon in which the bricks are cracked by thermal shock caused by repeated operation and standby of the tank, which causes cracks in the bricks. This is also called thermal spalling, or simply spalling or spalling.

On the other hand, the ladle slag that has entered the tank from the ladle or the like melts or infiltrates the brick. The part where the slag has infiltrated becomes an altered layer, and easily peels off when subjected to thermal shock. The exfoliation of the slag infiltration layer is called structural spalling or simply structural spall. In particular, magcro bricks easily form an altered layer due to the infiltration of slag,
There is a drawback that structural spalling is likely to occur, which often determines the life of the refractory lining.

By the way, there is magnesia carbon brick as a brick that is hard to infiltrate slag and is resistant to thermal spalling. An example of application of magnesia carbon bricks to an RH tank is the invention described in JP-A-63-74596. In the present invention, a magnesia carbon brick containing a metal is used as a refractory lining for an RH tank. However, when the present invention is carried out, there is a problem in that magnesia carbon brick, which is a refractory lining, is oxidatively decarburized during drying, preheating, or during operation, and sufficient durability and life cannot be obtained. Here, the oxidative decarburization is mainly observed on the working surface and the back surface of the brick because the carbon component in the brick is oxidized and disappeared by oxygen contained in the atmosphere.

When using magnesia carbon bricks for refractory linings in RH tanks, measures against oxidative decarburization that occur on the back surface of the bricks are also found in the literature. For example, refractories (19
87) vol.39, P.273-281 describes an example in which a flexible and contractible magnesia board is used for the back surface of a magnesia carbon brick. However, even this measure cannot block oxygen sufficiently because the porosity of magnesia board is high, and it cannot be said that a sufficient effect can be obtained in all cases.

[0009]

[Means for Solving the Problems] Magnesia carbon brick is an excellent brick which is difficult for slag to infiltrate and is resistant to thermal spalling. In order to use this as a refractory for RH tank lining, it was judged that the oxidative decarburization had to be suppressed. As a countermeasure, first of all, it is necessary to select an appropriate brick material in order to suppress oxidative decarburization on the operating side, and to prevent oxidative decarburization on the rear side, an appropriate oxidative decarburization is required. The present inventors obtained the present invention by proceeding with research in consideration of the need to treat preventive measures.

That is, according to the present invention, the refractory lining of an RH degassing tank in which a magnesia carbon brick having an oxidative decarburized layer thickness of 5 mm or less after being exposed in an air atmosphere of 1400 ° C. for 4 hours is lined partially or entirely. Alternatively, it is a refractory lining for an RH degassing tank in which a magnesia carbon brick in which one or more sides of a brick is covered with a metal plate or a metal foil is partially or entirely lined.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION First, an exposure test method for a magnesia carbon brick will be described. The test piece is a cylinder with a diameter of about 50 mm and a height of about 50 mm, and the axis of the cylinder is parallel to the pressing axis during brick molding. The electric furnace used at that time has a volume of 0.008 m per one test piece.
^{At least 3} (8 liters), and the atmosphere is the atmosphere. It is desirable to be able to supply air from the outside into the electric furnace. The heating element shall be a material that can withstand use in the atmosphere.

The test method is to place a test piece in a furnace at room temperature and raise the temperature in the furnace at a temperature rising rate of 10 ° C. per minute. 1
After reaching 400 ° C, hold at 1400 ° C for 4 hours. After that, the test piece is taken out of the furnace and allowed to cool to room temperature in the atmosphere. After cooling, the cylinder test piece is cut perpendicular to the axis of the cylinder at half its height. On the circular cut surface at this time, the thickness of the white or gray oxidative decarburized layer was measured at four positions with the central angle of the circle at 90 °, using calipers or the like,
The obtained four values were averaged to obtain the oxidative decarburized layer thickness.

There is a close relationship between the result of the exposure test of the magnesia carbon brick and the wear rate of the magnesia carbon brick lined in the RH tank. FIG. 1 illustrates this relationship. That is, using different brands of magnesia carbon bricks as samples, the exposure test results and actual R
H Investigate the relationship of the wear rate when partially tensioned to the lower tank,
Figure 1 was created. At that time, the partial tension is R of 350t capacity.
H Side wall of the lower tank. In FIG. 1, the abscissa plots the oxidative decarburization layer thickness by the exposure test, and the ordinate plots the wear rate. Here, as the wear rate, 1 for the conventionally used magcro direct bond brick is used.
00 was displayed as an index. The larger the value, the larger the wear rate, and the smaller the value, the smaller the wear rate. From this, it can be seen that the wear rate in actual RH can be suppressed low if the thickness of the oxidized decarburized layer by the exposure test is 5 mm or less.

As described above, as the magnesia carbon brick having an oxidative decarburization layer thickness of 5 mm or less in the exposure test, metals such as Al, Si, Mg and Ca, alloys composed of two or more of these metals, Carbon content 2 with various boride, various carbides, or various glasses added
Approximately 20% by weight of magnesia carbon brick can be mentioned. However, it may not always be possible to reduce the thickness of the oxidative decarburized layer by the exposure test to 5 mm or less simply by adjusting the amounts of the above-mentioned additives. The particle size composition of the carbon source such as magnesia clinker and scaly graphite, the manufacturing conditions such as binder selection, kneading, molding, and drying are also important factors. A magnesia carbon brick with a coal layer thickness of 5 mm or less can be obtained.

Further, in order to suppress the oxidative decarburization on the back surface of the magnesia carbon brick to realize a long life of the lining, the portion on the back surface or joint of the brick where the oxidative decarburization occurs is a metal plate or a metal foil. Cover with. Since the metal plate or metal foil blocks the flow path of oxygen to the brick,
Oxidative decarburization of bricks can be suppressed. This method is much more reliable than the method using high porosity magnesia board.

Various types of heat-resistant steels or heat-resistant alloys are ideal as the material of the metal plate or metal foil. However, general steel, stainless steel, and alloy steel can also be used. The thickness must be determined in consideration of the part to be used and the resistance to oxidative decarburization and strength of the metal. Considering handling and durability, 0.1 to 2 mm is suitable.

As a method of covering the surface of the brick with a metal plate or a metal foil, a method of sticking it with an inorganic or organic adhesive, a method of covering the brick with a box-shaped metal plate or a metal foil, a metal plate or foil at the time of brick molding There is a method of molding along with the inner surface of the mold and molding with the kneaded clay.

[0018]

【Example】

[Example 1] 1% by weight and 4% by weight of Al and Al-Mg powder were added, respectively, and a magnesia carbon brick having an oxidative decarburization layer thickness of 3 mm in an exposure test at C = 15% by weight was used in an RH tank having a capacity of 350 t. Was lined on the side wall of the lower tank.
Other parts such as the bottom of the upper and lower tanks were lined with magcro direct bond bricks as before. In addition, no measures were taken to prevent oxidative decarburization on the back side.

As a result, the average wear rate measured at a position half the height of the side wall is reduced by about 25% in the case of a normal magcro direct bond brick, and the life of the tank, that is, the life of the refractory lining is improved by about 20%. The effect of lining a magnesia carbon brick appeared. However, when investigating the magnesia carbon bricks after use, the back side was oxidized and decarburized to a depth of about 20 mm and turned white or gray,
It was tattered.

[Embodiment 2] A box of heat-resistant steel plate having a thickness of 0.5 mm is formed on the side surface of the same brick as that used in Embodiment 1, one third of the back surface side and the back surface. The attached one was lined on the side surface of the lower tank of the RH as in the case of Example 1.

As a result, the average wear rate measured at a position half the height of the side surface was reduced by about 30% and the life of the tank was improved by about 25% as compared with the case of a normal magcro direct bond brick. No oxidative decarburized layer was observed on the back side of the used magnesia carbon brick.

[0022]

Industrial Applicability According to the present invention, it is possible to prolong the life of refractory linings in the RH tank, which contributes to the reduction of steel production costs and the improvement of productivity.

[Brief description of the drawings]

FIG. 1 shows the relationship between the oxidative decarburized layer thickness and the wear rate in the RH lower tank after exposing a test piece to an air atmosphere at 1400 ° C. for 4 hours. Note that the wear rate is 10 in the case of magcro direct bond brick, which has been used in the conventional RH lower tank.
It was set to 0.

Claims (2)

[Claims] 1. A refractory lining for an RH degassing tank in which part or all of a magnesia carbon brick having an oxidative decarburization layer thickness of 5 mm or less after being exposed to an air atmosphere at 1400 ° C. for 4 hours is lined. 2. A refractory lining for a RH degassing tank in which a magnesia carbon brick whose one or more surfaces are covered with a metal plate or a metal foil is lined partially or entirely.