JPH07165461A - Baked magnesia-chromium brick and its production - Google Patents

Abstract

PURPOSE:To obtain a baked magnesia-chromium brick having excellent corrosion resistance and slag infiltration resistance and to provide a process for the production of the brick. CONSTITUTION:This baked magnesia-chromium brick contains fine metal particles dispersed in a refractory texture and is obtained by forming a composition composed mainly of 5-70wt.% of chromite and the remaining part of magnesia raw material and baking in a non-oxidizing atmosphere at a high temperature. The baked magnesia-chromium brick contains fine metal particles dispersed in the refractory texture in non-oxidized state and, accordingly, reaction of the fine metal particles with MgO component of the magnesia raw material takes place during use to form a spinel represented by picrochromite. The brick has excellent corrosion resistance and slag infiltration resistance owing to the high melting point, low thermal expansion coefficient, etc., of the spinel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesia-chromic fired brick excellent in corrosion resistance and slag penetration resistance and a method for producing the same.

[0002]

2. Description of the Related Art Magnesia-chromic fired bricks containing a magnesia raw material and chromite as a main aggregate are excellent in corrosion resistance and heat spalling resistance, and are used, for example, as a lining material for a molten steel vacuum degassing furnace. There is. Conventionally, the material improvement has been actively performed. For example, Japanese Patent Laid-Open No. 2-
In Japanese Patent No. 141465, Cr, Fe, Mg, Al, Si
There are examples in which metal powders such as and alloy powders thereof are added. These metal powders and alloy powders are oxidized during the firing step or during use, and the volume expansion at that time fills the voids of the refractory structure to reduce the porosity of the refractory structure, and the lining material for the molten steel vacuum degassing furnace. Contributes to the improvement of corrosion resistance.

Also, the chromium oxide added to the magnesia-chromic fired brick is extremely difficult to sinter. In order to solve this problem, in Japanese Patent Laid-Open No. 62-207757, chromium oxide is used in combination with metallic chromium to form a eutectic, thereby lowering the melting point to improve sintering resistance, corrosion resistance,
Magnesia-chrome fired bricks with excellent slag resistance are introduced.

[0004]

However, in recent years, as the demand for high-grade steel has increased, the secondary refining treatment ratio has increased, and the conventional magnesia-chromic fired bricks have not been able to achieve a sufficient life. Further, in magnesia-chromic fired bricks, damage due to structural spalling is large due to the formation of an altered layer due to the penetration of slag components. Therefore, the present invention provides a magnesia-chrome fired brick which is more excellent in corrosion resistance and slag penetration resistance than conventional materials.

[0005]

[Means for Solving the Problems] The composition of the magnesia-chromic fired brick of the present invention comprises: (1) Sintering a compounded mixture of chromium iron ore of 5 to 70 wt% and the balance of a magnesia raw material as a main material. , Magnesia containing fine metal particles in the refractory structure in a non-oxidized state
Chrome fired brick. (2) Chromite ore 5 to 70 wt%, metal powder 10 wt%
Hereinafter, a magnesia-chromium fired brick in which the remainder is obtained by sintering a composition containing a magnesia raw material as a main material and fine metal particles are mixed in a non-oxidized state in the refractory structure. (3) A method for producing a magnesia-chromic fired brick, in which a mixture containing 5 to 70 wt% of chromite ore and the balance of a magnesia raw material as a main material is molded and then fired at a high temperature in a non-oxidizing atmosphere. (4) Chromite ore 5 to 70 wt%, metal powder 10 wt%
Hereinafter, a method for producing a magnesia-chromic fired brick, in which a composition having the balance of a magnesia raw material as a main component is molded and then fired at a high temperature in a non-oxidizing atmosphere. (5) The method for producing a magnesia-chromic fired brick according to the above (3) or (4), wherein the non-oxidizing atmosphere has an oxygen partial pressure of 10% or less. Is.

[0006]

The function is the same as that of the conventional material, which is obtained by sintering a compound containing chromite ore and a magnesia raw material as main materials. The greatest feature of the present invention is that fine metal particles are mixed in the refractory structure in a non-oxidized state.

It is known in the art to add metal powder to produce magnesia-chromic fired bricks. However, unless it is unfired brick or amorphous refractory, the metal powder is oxidized in the firing process. As described in Japanese Patent Application Laid-Open No. 2-141465, the effect of unfired brick and amorphous refractory containing metal powder is described. However, unfired bricks and amorphous refractories do not have the aggregate and matrix sintered like fired bricks,
Corrosion resistance is not improved even when the MgO component of the magnesia raw material and the metal powder are not sufficiently reacted during use and the metal powder remains as compared with the case of baked bricks.

[0008] On the other hand, it was found that the fired bricks and the magnesia-chromium fired bricks in which fine metal particles were mixed in the refractory structure in a non-oxidized state were remarkably excellent in corrosion resistance. It is considered that this is because the fine metal particles react with the MgO component of the magnesia raw material in a high temperature atmosphere on the operating surface to generate spinel represented by picromchromite (MgO.Cr ₂ O ₃ ). Picrochromite has excellent corrosion resistance and slag penetration resistance due to its characteristics such as high melting point and low thermal expansion.

In order to obtain a material in which fine metal particles are mixed in a non-oxidized state in the refractory structure, there is, for example, the following method. That is, firing is performed in a non-oxidizing atmosphere.
In the production of carbonaceous fired bricks, firing may be performed in a non-oxidizing atmosphere to prevent oxidation of carbon components. However, in conventional magnesia-chromic fired bricks, etc., fired in the atmosphere without special operation, that is,
Firing is performed in an oxidizing atmosphere.

As the non-oxidizing atmosphere, it is desirable that the oxygen partial pressure of the gas in contact with the brick surface during firing is 10% or less. The method of setting a non-oxidizing atmosphere during firing is not particularly limited. For example, there are methods such as vacuum atmosphere, introduction of an inert gas, and covering with a oxidative member, an air blocking member, or the like, but it may be performed by any means in consideration of equipment, cost, and the like.

The brick material of the present invention contains chromite. Chromite contains Cr oxide, Fe oxide and the like. Then, by firing in a non-oxidizing atmosphere, Cr oxides, Fe oxides, etc. are reduced, and fine metal particles are generated.

A specific amount of metal powder may be added to the brick composition of the present invention. By firing in a non-oxidizing atmosphere,
The metal powder remains as it is without being oxidized. The above-mentioned metal from chromite is mainly formed in and around the chromite grains, but the added metal powder permeates into the magnesia raw material together with the matrix part and is more uniformly mixed in the refractory structure.

In order to make the effect of the present invention remarkable, it is desirable that the total area occupied by the fine metal particles per 10 × 10 mm is 0.01 mm ² or more in the cross-sectional structure of the refractory. FIG. 1 is a photomicrograph of a magnesia-chromic fired brick, FIG. 1 is an example of the present invention, and FIG.
Indicates the cross-sectional structure of the comparative example product. In FIG. 1, the white parts surrounded by the horizontal line group in the product of the present invention are fine metal particles. In fact, it has a metallic sheen. In the conventional product shown in FIG. 2, the presence of the metal fine particles cannot be confirmed.

If the brick of the present invention is to be mass-produced by firing in a non-oxidizing atmosphere, for example, the surface of the brick may be partially oxidized and the metal powder may be oxidized at that portion. In the brick of the present invention, it is needless to say that the fine metal particles are mixed in the entire structure, but an oxide layer may be present if it is a part. However, in order to obtain the effect of the present invention, it is desirable that the structure in which the fine metal particles are mixed is 70% or more in volume with respect to the entire brick.

Since the metal powder reacts with the slag component to form a low-melting point substance, it is a cause of deterioration in corrosion resistance according to the common general technical knowledge. However, in the brick of the present invention, the magnesia raw material from the vicinity of the operating surface is used during use. It reacts with the MgO component to form spinel and improves the corrosion resistance.

As the chromite ore and the magnesia raw material used in the production of the brick of the present invention, the same refractory materials as conventional materials can be used. Chromite is, for example, Turkish chromite, machine rock chromite, Japan chromite, transval chromite, or the like. The constituent components of chromite ore react with the MgO component of the magnesia raw material to generate a spinel structure, and have the action of firmly binding the aggregates. The proportion of chromite in the total composition is 5 to 70 wt%, preferably 20 to 60 wt%. If it is less than 5% by weight, the tissue bonding function of chromite is insufficient and the corrosion resistance is poor. When it exceeds 70 wt%, the proportion of the magnesia raw material decreases accordingly and the corrosion resistance deteriorates. Specific examples of the magnesia-based raw material include sintered or electrofused magnesia and magnesia-chromium.

The magnesia-chromic fired brick of the present invention is more preferably added with metal powder from the viewpoint of improving the corrosion resistance. When metal powder is added, the content of the metal powder is 10 wt% or less, and the lower limit is preferably 1 wt% in order to fully exert the effect of adding metal powder. If it exceeds 10 wt%, the reaction between the fine metal particles and the magnesia raw material becomes remarkable during the use of brick, and the expansion due to this reaction becomes large. For this reason, the open pores of the brick structure increase, and the corrosion resistance decreases.

Specific examples of the metal powder include Cr, Fe, Al and S.
It is one or more selected from i, Mg, Ni and alloys thereof. Examples of alloys include Al-Si, Al-Mg, F
Examples include e-Cr, Fe-Si, Fe-Ni, and Ni-Cr. In addition to the above aggregates and metal powders, chromium oxide, picrochromite, zircon, zirconia, carbon, carbides, nitrides, borides, and the like may be added in appropriate amounts within a range that does not impair the effects of the present invention. What is good is similar to the production of conventional magnesia-chromic fired bricks.

Molding is no different from normal brick making methods.
An organic, inorganic or organic-inorganic composite binder is added, and after kneading, pressure is applied by a friction press, an oil press or the like. The firing temperature is, for example, 1600 to 19
Set to 00 ° C. It is preferable to take a sufficient holding time so that no unbaked portion remains.

[0020]

EXAMPLES Examples of the present invention and comparative examples will be described below. Tables 1 and 2 show examples of the present invention, comparative examples, and test results thereof.

[0021]

[Table 1]

[0022]

[Table 2]

In each example, 4 wt% of a phenol resin as an external additive was added to the composition shown in Tables 1 and 2 as a binder,
After kneading, pressure molding was performed into a normal shape by a friction press. Baking was performed in a tunnel kiln at 1800 ° C. for 3 hours to obtain a test brick. Examples 1-7, Comparative Examples 1-3
Was fired in a non-oxidizing atmosphere, and Comparative Examples 4 and 5 were fired in an oxidizing atmosphere. Using the test bricks thus obtained, the amount of fine metal particles mixed, corrosion resistance, and slag penetration resistance were tested.

Amount of fine metal particles mixed: cut perpendicular to the longest direction of the brick. The area of the fine metal particles contained in a 10 × 10 mm square was determined based on the micrograph of the central structure of the cut surface. A reflection microscope was used to confirm the presence or absence of the fine metal particles, but it can also be confirmed by means such as X-ray diffraction and EPMA point analysis.

Corrosion resistance: Performed by the rotary erosion method. A weight ratio of slag (CaO / SiO ₂ = 3): steel 6: 4 was added to the erosion agent, and the drum was rotated to 1700.
After heating in a burner at ℃ × 30 minutes, drain the erosion agent,
Allow to air cool for minutes. After repeating this 10 times, the erosion size was measured.

Slag permeation resistance: 10 times from the operating surface of the test bricks whose corrosion resistance was measured by the rotary erosion method.
The mm portion was sampled and subjected to chemical analysis. This allows
The degree of penetration of CaO and SiO ₂ was compared.

In Comparative Example 1 in which the amount of chromite in the compound is less than the range of the present invention, the corrosion resistance is poor because the texture bonding of chromite is weak. Conversely, the amount of chromite in the formulation is
In Comparative Example 2 in which the content is larger than the range of the present invention, the ratio of the magnesia raw material is reduced, the reaction between the MgO component of the magnesia raw material and chromite is small, the spinel formation is small, and the corrosion resistance is poor.

In Comparative Example 3 in which the amount of the metal powder in the composition is more than the range of the present invention, the reaction between the fine metal particles and the MgO component of the magnesia raw material becomes vigorous during use, and the brick structure is caused by the expansion due to this reaction. Deteriorates and the corrosion resistance is poor. Further, Comparative Examples 4 and 5 were fired in an oxidizing atmosphere and had no fine metal particles, so that they did not react with the MgO component of the magnesia raw material and thus had poor corrosion resistance. On the other hand, the magnesia-chrome fired brick according to the embodiment of the present invention has excellent corrosion resistance and at the same time excellent slag penetration resistance.

Actual machine test: Among the magnesia-chromic fired bricks manufactured in the actual machine shape by substantially the same method as shown in the above-mentioned Example, Example 2, Example 4, Example 6,
Regarding Comparative Example 1 and Comparative Example 4, actually, the RH type vacuum degassing furnace was built on the inner lining of the lower tank and operated.

Melt rate of 1.5 in Comparative Example 1 and Comparative Example 4,
1.2, the second, the fourth, and the sixth examples have a value of 0.
The results were as small as 8, 0.6, and 0.6, showing good results. The penetration amount of the slag component of 10 mm from the operating surface was less than half of the values of Example 2, Example 4, and Example 6 as compared with Comparative Example 1 and Comparative Example 4, showing good slag penetration resistance. . As a result, although not shown in the table, about twice the durability was obtained.

In the RH type vacuum degassing furnace, the construction site in the actual machine test is a site where the damage due to the recirculation of molten steel is remarkable. As is clear from this test result, the magnesia-chromic fired brick obtained by the present invention exhibited a sufficient effect even in an actual machine. R as an example of actual machine test
Although the case where it was performed in the lower tank of the H type vacuum degassing furnace was described, the same effect was obtained also in the DH type vacuum degassing furnace, the CAS apparatus and the like.

[0032]

EFFECTS OF THE INVENTION In the magnesia-chromic fired brick produced by the present invention, fine metal particles are mixed in the majority of the brick, which is excellent in corrosion resistance as compared with the conventional magnesia-chrome fired brick. . Further, it has excellent resistance to slag penetration, and can suppress the formation of an altered layer due to slag penetration, which is a major cause of damage to magnesia-chromic fired bricks, and can solve structural spalling. As a result, the durability is about twice as high as that of the conventional product, and the economical effect is great.

[Brief description of drawings]

1 is a drawing of a micrograph of the structure of Example 4. FIG.

2 is a drawing of a micrograph of the structure of Comparative Example 5. FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Yamamoto 1-3-1 Niihama, Arai-machi, Takasago, Hyogo Prefecture Harima Ceramics Co., Ltd.

Claims (5)

[Claims] 1. A magnesia-chromium material comprising 5 to 70 wt% of chromite, the remainder being a mixture of a magnesia raw material as a main material, sintered, and fine metal particles mixed in a non-oxidized state in a refractory structure. Fired bricks. 2. Chromite ore 5 to 70 wt%, metal powder 10
A magnesia-chromic fired brick, which is obtained by sintering a mixture containing wt% or less and the remainder being a magnesia raw material as a main material, and in which fine metal particles are mixed in a non-oxidized state in the refractory structure. 3. A method for producing a magnesia-chromic fired brick, which comprises firing a high-temperature firing in a non-oxidizing atmosphere after molding a compounding mixture containing 5-70 wt% of chromite ore and the balance being a magnesia raw material. 4. Chromite 5 to 70 wt%, metal powder 10
Magnesia which is not more than wt% and whose remainder is magnesia-based raw material as a main material and is then fired at high temperature in a non-oxidizing atmosphere
Method for producing chrome fired brick. 5. The method for producing a magnesia-chromic fired brick according to claim 3, wherein the non-oxidizing atmosphere has an oxygen partial pressure of 10% or less.