JPH0354160A - Refractory - Google Patents

Abstract

PURPOSE:To obtain refractory useful for making low porosity of magnesium chromium refractory for lining of vacuum vessel by adding metal aluminum powder to main ingredient of magnesia.chromium refractory main ingredient. CONSTITUTION:The refractory obtained by adding 1-20wt.% metal aluminum powder to a main ingredient of magnesia.chromium. The above-mentioned refractory can be used as burned brick when burned after press molding and as unburned brick in case of only press molding and can be used as amorphous refractory directly or by adding proper binder. When refractory containing metal aluminum is burned, the metal aluminum is not often sufficiently oxidized in the center part according to selected burning conditions and the metal aluminum is kept in a form of metal in the central part and has coarse structure, low corrosion resistance and low strength. Oxidizing agent is preferably added to the refractory before burning in order to remove unoxidized part. As the oxidizing agent, Fe2O3 or Fe3O4 are preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a refractory material suitable as a lining material for molten metal containers, particularly vacuum containers.

[Conventional technology]

In the steelmaking process, degassing is performed using DH and RH equipment to remove impurities after refining in a converter. The refractory for lining these vacuum containers is required to be a material that is particularly stable under high-temperature vacuum conditions.

In general, refractories containing silica as a main component are unsuitable for this purpose because they tend to dissociate under high-temperature vacuum conditions, but magnesia, spinel, chromium m, and the like are stable and suitable for this purpose. Among these, burnt-out type magnesia, magnesia spinel, and magnesia chromite refractories are particularly suitable from the viewpoint of wear resistance against molten steel flow.

Among them, magnesia chromium bricks are slag and
It has excellent spalling resistance and is resistant to chemical attack due to reaction with molten steel and thermal shock due to temperature changes.

Magnesia chromium refractory materials can be roughly divided into two types, direct bond and bond, based on their raw material structure.

Direct Bond uses high-purity magnesia clinker as the magnesia source and natural chromite as the chromium source, and presses or shapes these compounds.
It is fired at a high temperature of 1800°C or higher.

On the other hand, Ribondo is a mixture of magnesia clinker and low-impurity electrofused maguro, which is obtained by melting and cooling the magnesia clinker and chromium ore in an electric furnace and then pulverizing them, followed by burning.

By the way, porosity is one of the factors that influences corrosion resistance. In other words, foreign substances such as slag and molten steel enter the bricks through the pores, and react with some of the bricks to produce low-melting materials, and are easily worn and damaged by the slag flow. .

In the case of magnesia chromium bricks, regardless of direct bonding or ribbon bonding, as a means of controlling porosity,
Conventionally, it has been customary to adjust the particle size composition to obtain a close-packed particle size composition, fill it using a high-pressure press, and then sinter it at an extremely high temperature to promote sintering.

At that time, in order to fill the pores, promote sintering, and reduce the porosity, it is disclosed in JP-A-62-207757 that chromium oxide powder and metallic chromium are used together.
Addition of alumina powder has also been carried out, but the current lower limit of porosity is 14% in the case of direct bonding and 12% in the case of ribbon bonding.

Furthermore. In order to reduce the porosity within the brick structure, there is an improvement in the pressing ability when forming bricks, and even ultra-high temperature burning.
Both have economic limits.

[Problem to be solved by the invention]

The problem to be solved by the present invention is to establish an economical means for reducing the porosity of magnesia-chromium refractories for lining containers for molten metal, especially vacuum containers.

[Means to solve the problem]

The fireproof material of the present invention is basically composed of magnesia. The above object was achieved by adding 1 to 20% by weight of metallic aluminum powder to the main component, which is a mixture of one or more of electrofused maguro, spinel, and chromite, including magnia or electrofused maguro.

[Effect]

The refractory material of the present invention is produced by constructing a material uniformly mixed with metallic aluminum in an oxidizing atmosphere by burning or unburning, oxidizing the metal during use, and then reacting with magnesia.
The aim is to lower the porosity by filling the pores by utilizing the volumetric expansion at that time.

On the other hand, it is described in Japanese Patent Publication No. 60-2269 that aluminum powder is blended with magnesia carbon, but this is added to suppress carbon oxidation, and the expansion caused by oxidation fills the pores. This is fundamentally different from the present invention, which aims at densification.

The reduction in porosity of magnesia/chromium direct bonded bricks containing aluminum metal will be explained based on the attached diagram that schematically shows the reduction in porosity.

Fig. 1 shows the filling state after the material of the present invention has been pressed and shaped, and Fig. 2 shows the state after the material has been burned.

As shown in FIG. 1, after press molding, fine grained metal aluminum powder 3 is uniformly dispersed between magnesia rL1 and chromite 2.

By firing this material in an air atmosphere, the metal aluminum powder 3 is oxidized, and fine-grained spinel 4 containing chromium oxide as a solid solution is newly produced (Fig. 2). At this time,
Since the volume is expanded by about 1.3 times, the pores 5 are filled. Furthermore, since the pores 5 are filled, the overall strength is also improved.

Although the case of magnesia-chromium burnt bricks has been explained above, the reduction of porosity can be similarly achieved in the case of other large burnt-resistant materials due to the oxidation of metal aluminum and the volume expansion caused by the reaction with magnesia. can.

Further, the refractory material of the present invention can be used as a fired brick if it is press-shaped and then fired, or as an unburnt brick if only press-formed, and can be used as it is or as a monolithic refractory by adding a suitable binder. When unburnt bricks or monolithic refractories are used, a series of reactions occur during use, reducing the porosity.

By the way, when a refractory material containing metallic aluminum is burned in this way, depending on the burning conditions, the metallic aluminum may not be sufficiently oxidized in the central part during burning. In this part, aluminum metal remains in the form of metal, with a coarse structure, low corrosion resistance, and low strength.

In order to eliminate unoxidized parts, an oxidizing agent can be added before burning. The oxidizing agent needs to be stable before firing, oxidize the metal during firing, and not have a large adverse effect on the corrosion resistance of the refractory, nor cause any harm to the firing furnace. Fe20s and Fe30 meet these points.

These oxidize other metals during annealing, and themselves are F
It takes the form of e○ and diffuses into magnesia, etc. If the amount added is controlled, it is unlikely to have a major adverse effect on the corrosion resistance of refractories. Moreover, it does not have any adverse effect on the kiln.

If the amount of metal aluminum powder added exceeds 20%, cracks may occur due to volumetric expansion during firing or use, and in some cases, molten metal aluminum may ooze out during heating. In addition, if the amount added is less than 1%, it is difficult to separate the metal aluminum powder uniformly.
And the effect of densification is small. Therefore, the appropriate amount to add is 1 to 2
It is 0%.

Further, the particle size of the metal aluminum powder is preferably about 500 μm or less, which does not reduce the reaction.

The main ingredients are magnesia and spinel. The chrome ore or electrofused maguro may be of a quality within the range normally used. In other words, in the case of magnesia, Mg○〉90
%, in the case of spinel, IJg○・Al20,>90%, in the case of chromite, Mg○・Crz○3>50%, and in the case of fused maguro, impurities other than Mg○ and Cr203 are 30% or less. It is desirable that the chromium oxide powder and the alumina powder each have a purity of 80% or more and a particle size of 500 μm or less.

Metallic aluminum powder can be used as a diluent for uniform dispersion of metals other than aluminum (e.g.
iron. An alloy or mixture containing magnesium, chromium, etc.) may also be used.

If the amount of Fear3 and Fe3C)+ grains added is less than 1%, there will be no effect, and if it is added in excess of 50%, it will adversely affect the corrosion resistance of the refractory. Therefore, the appropriate amount to add is 1 to 50%.
It is. Further, the particle size is desirably 500 μm or less since it is necessary to react efficiently with the metal. Regarding purity, it is desirable that impurities other than iron oxides be about 20% or less from the viewpoint of preventing the formation of unnecessary low melting point substances.

〔Example〕

Example 1 Table 1 shows the effect of adding metallic aluminum to magnesia-chromium direct bond bricks.

From the same table, it can be seen that when the amount of aluminum added is 1 to 20% by weight, it is possible to reduce the porosity, improve the hot strength, and improve the corrosion resistance.

Table 1 Example 2 Table 2 shows the effect of adding metal aluminum to magnesia spinel bricks.

From the same table, it can be seen that when the amount of aluminum added is 1 to 20% by weight, it is possible to reduce the porosity, improve the hot strength, and improve the corrosion resistance.

Table 2 Example 3 Table 3 shows the effect of adding 20 Fe to magnesia-chromium direct bond bricks containing 20% by weight of metallic aluminum.

From the same table, it can be seen that when the amount of Peso3 added is 1 to 50% by weight, it is possible to sufficiently oxidize metal aluminum and obtain good quality without deteriorating corrosion resistance.

Table 3 Example 4 Table 4 shows the effect of adding Fe2O3 to magnesia spinel bricks containing 20% by weight of metallic aluminum.

From the same table, it can be seen that when the amount of Few○3 added is 1 to 50% by weight, metal aluminum can be sufficiently oxidized and good quality can be obtained without deterioration of corrosion resistance.

Table 4 [Effects of the Invention] The refractory material of the present invention can exhibit the following effects.

(1) When mixed with magnesia, chromium, and other refractories, the porosity of the refractories can be significantly reduced without impairing their properties.

(2) A very dense structure is obtained, and the hot strength is significantly improved.

(3) Slag encroachment is suppressed due to the reduction in porosity and the resulting effect of spinel growing in the grain boundaries, and corrosion resistance is significantly improved.

[Brief explanation of drawings]

The drawings are schematic diagrams of porosity reduction of magnesia/chromium direct bonded bricks containing aluminum metal, with Figure 1 showing the bricks after press forming and Figure 2 after firing. 1: Magnesia grains 2: Chromite 3: Aluminum powder 4: Spinel 5: Pores

Claims (4)

[Claims] 1. A refractory material characterized by adding 1 to 20% by weight of metallic aluminum powder to a magnesia/chromium refractory main component. 2. A refractory material in which 1 to 50% by weight of one or a mixture of two of Fe_2O_3 grains and Fe_3O_4 grains is added to the magnesia-chromium refractory main component according to claim 1. 3. A refractory material in which the magnesia-chromium refractory main component according to claim 1 is a mixture of one or more of fused magna, spinel, and chromite. 4. A refractory material in which the magnesia-chromium refractory main component according to claim 1 is added with 1 to 20% by weight of alumina powder.