KR100276310B1 - Refractory material of magnesia castable block - Google Patents

Abstract

PURPOSE: To manufacture a magnesia castable block for use in ladle or tundish for continuous casting, an effective amount of chrome oxide for thermal strength and silica flour having superior drying crack resistance are added to magnesia refractory composition. CONSTITUTION: The magnesia castable block composition comprises 90 to 95wt.% of magnesia clinker, 2 to 5wt.% of silica flour, 30wt.% or less of CaO, 0.3 to 0.7wt.% of sodium hexameta phosphate. In case that 3 to 13wt.% of chrome oxide is additionally added to the magnesia castable block composition for increasing thermal strength, an amount of magnesia clinker is preferably controlled between 78 to 92wt.%.

Description

Refractory composition of magnesia castable block with excellent dry crack resistance

The present invention relates to a fire resistant composition of a magnesia castable block used in a dam block of a ladle or tundish, and more particularly, has excellent hot strength, load softening temperature and spalling resistance, and particularly, dry cracking resistance. A fire resistant composition of this superior magnesia castable block.

In general, dam blocks are used in ladles or continuous casting tundish of the steelmaking process, for example, when molten steel is installed in a tundish and refined in a steelmaking furnace, such as a converter or an electric furnace, is injected into the tundish through the ladle. By suppressing the turbulence of the to prevent the mixing of oxides to the steel or to separate the inclusions in the steel, that is to serve to reduce the physical inclusions.

Such a dam block uses a high alumina precast block or an alumina refractory brick, and a zircon precast block or a magnesia-carbon refractory brick is used when the alumina inclusions are reluctant.

Conventionally, the high alumina precast block mainly used is Al ₂ O ₃ -SiO ₂ system, so it is easy to become an oxygen supply source in molten steel by melting loss, and there is little effect of removing inclusions in molten steel. For this reason, the use of basic dam blocks instead of Al ₂ O ₃ -SiO ₂ dam blocks is required for steel grades requiring cleanliness, and Mg0 quality and Ca0 quality are available. Representative techniques of a method for producing a Ca0 quality dam block are disclosed in Japanese Patent Application Laid-Open Nos. 60-108373, 59-174578, 58-193306, 63-207457. The proposed CaO quality dam block is not suitable for removing alumina inclusions. Although very effective, it is difficult to manufacture a dam block, and because CaO is slaking very easily, there is a problem that cracks are easily generated or easily differentiated during storage in the air, which makes it difficult to put to practical use. On the other hand, MgO quality, which is one of the basic dam blocks, has somewhat lower capturing ability than Ca0 quality, but MgO quality castable blocks have been put to practical use in consideration of ease of manufacture and hydration problems. However, such a magnesia castable block has been limited in its use because of its low hot strength and low load softening temperature. To solve this problem, the present inventors have solved the problem by adding chromium oxide or the like to the Mg0 basic component system. MgO refractory composition is presented in Korean Patent Application No. 95-53574. In the case of the above proposal, the hot strength and the load softening temperature characteristics are excellent, but there is a drawback that the castable block may collapse during drying due to the hydration of the alumina cement added as the magnesia powder or the binder.

Therefore, in order to solve the above problems, the present invention is excellent in hot strength, load softening temperature and spalling resistance by adding silica flower and magnesium oxide, which is a hot cracking enhancement element, to magnesia clinker to prevent dry cracking. It is an object of the present invention to provide a fireproof composition of magnesia castable blocks having excellent suppression force.

Figure 1 (a) is a photograph showing the post-drying state of the magnesia castable block of Comparative Example 1.

Figure 1 (b) is a photograph showing the post-drying state of the magnesia castable block of Comparative Example 2.

Figure 1 (c) is a photograph showing the post-drying state of the magnesia castable block of Comparative Example 5.

Figure 1 (d) is a photograph showing the state after drying of the magnesia castable block of Inventive Example 4.

The present invention for achieving the above object by weight, magnesia clinker: 90-95%; Silica flower: 2-5%; Alumina cement containing less than 30% Ca0 content: 3-5%; Based on the total composition, soda hexametaphosphate 0.3-0.7% based on the total weight The present invention relates to a magnesia fireproof composition having excellent dry crack resistance which is added in the range of.

Furthermore, in weight percent, magnesia clinker: 78-92%; Silica flower: 2-5%; alumina cement containing less than 30% of CaO content: 3-5%; Chromium oxide: 3-13%; magnesia fireproof with excellent dry cracking properties, which is composed by adding hexamethaphosphate in the range of 0.3-0.7% to the total weight of the composition as described above. It relates to a composition.

Hereinafter, the present invention will be described in detail.

Among the fireproof compositions of the present invention, first, the magnesia clinker is preferably used as a main raw material of the fireproof composition in order to maintain a high fire resistance and load softening temperature of the dam block, and to obtain high corrosion resistance against molten steel or slag. It is preferable to contain a large amount of magnesia clinker in order to suppress molten steel inclusions. The addition amount is preferably added at 90-95% by weight (hereinafter referred to as '%') for combination with other additives.

On the other hand, when the refractory composition of the present invention is added to the chromium oxide in 3-13% to improve the hot strength properties, the magnesia clinker is preferably added 78-92%.

The silica flour (silica flour) improves the fluidity, and the calcium silicate compound (CaO-SiO _2- ) is reacted with potassium hydroxide (Ca (OH) ₂ ), which is formed together with the alumina cement as a hydrate. H ₂ O-based) is added to play a role of suppressing the crack of the magnesia castable block, the addition amount is preferably 2-5%. The reason is that when the silica flower is used in less than 2% by weight, the magnesia castable block is collapsed due to hydration of alumina cement and magnesia powder during drying, so that it cannot be used as a refractory structure. This is because the hot characteristic of the film, i.e., the hot strength and the load softening temperature, decreases.

On the other hand, the silica flower appears to be involved in the mathematical suppression of magnesia powder, but the exact suppressing mechanism is not known.

The alumina cement is preferably used that contains less than 30% by weight of CaO content, because the use of alumina cement containing a large amount of CaO content lowers the hot strength and load softening temperature due to the generation of low melting point material . Such alumina cement acts as a curing agent and binder in the magnesia castable block. When the amount of alumina cement added is less than 3%, the alumina cement has a weak curing function as a curing agent and a binder. If it is used more than%, it is preferable to add it in the range of 3-6% because the corrosion resistance is lowered due to a large amount of low melting point material and the hot strength and load softening temperature are lowered.

The hexametaphosphate is commercially available commercial industrial powder, which provides fluidity to the magnesia influx and is added to express strength at room temperature. When 0.3-0.7% is used with respect to the total amount of the composition, Good flowability of influent, no problem in construction.

On the other hand, the present invention is added to the chromium oxide powder in order to further improve the hot strength characteristics of the refractory composition as described above, when the chromium oxide powder is added to react with magnesia during hot use to produce spinel (MgCr ₂ O ₄ ) and magnesia Forms a solid solution, increases the strength and heat softening temperature in the heat, and also increases the thermal shock resistance. If the added amount is less than 3% by weight, the hot strength is not sufficiently expressed, and the softening amount of chromium oxide is low, so the load softening temperature is lowered. And spinel to form, which can over-expand and collapse when used in hot. In addition, the production of large amounts of spinel may cause loosening of the refractory tissue, which may reduce the effect of slag infiltration. Therefore, chromium oxide is preferably added in the range of 3-13%.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

To the refractory composition shown in Table 1, 0.5% of sodium hexamethane phosphate and 7% of water were added to the entire refractory composition, and formed into 100 × 150 × 100 mm, and then demoulded and dried. It is shown in Table 1 below to investigate.

At this time, the specimen for measuring the physical properties was molded into a size of 40mm × 40mm × 160mm and cured in a constant temperature and humidity chamber maintained at 25 ° C. for 24 hours, and then dried at 110 ° C. for 24 hours to measure its characteristics. The specimen for temperature measurement was measured by coboring a specimen dried to a size of 60 × 60 × 60mm to a size of 50φmm × 50mm to measure the load softening temperature. On the other hand, the relative after drying of the blocks of Comparative Examples (1, 2, 5) and Inventive Example (4) in Table 1 are shown in the photograph.

TABLE 1

As shown in Table 1 and Figure 1, Comparative Example 1 (Fig. 1 (a)) is not added to the silica flower was not possible to manufacture because the block is collapsed when drying the castable block. Comparative Example 2 (Fig. 1 (b)) is the content of the silica flower exceeds the scope of the present invention, there is an improvement than the addition of the silica flower, but cracks existed after block drying. In Comparative Example 3, a large amount of silica flower was added, and a low melting point material was excessively produced, resulting in a sharp drop in hot strength and load softening temperature.

In Comparative Example 4, the content of the alumina cement was out of the range of the present invention, and the dry strength was weak, which may cause a problem when the dried body of the castable block was applied. Comparative Example 5 (Fig. 1 (c)) is the addition of chromium oxide to the magnesia clinker and when the silica flower is not added, the castable block collapsed in the same manner as in Comparative Example 1.

On the other hand, horse name 4 (Fig. 1 (d)) is added to the silica flower 2% by weight compared to Comparative Example 5 there was no cracking or collapse even after drying the castable block. On the other hand, in the case of the invention example (4) to which the chromium oxide was added, it was found that the hot bending strength was improved by about 5-3 kg / cm ² as compared to the invention example (1-3) to which the chromium oxide was not added.

As described above, the present invention can provide a magnesia castable block having excellent hot strength and excellent dry cracking resistance by adding silica flower and chromium oxide to the magnesia refractory composition, and the provided block is a steelmaking process. There is a useful effect that can be applied to the tundish of ladle or continuous casting.

Claims (2)

By weight, magnesia clinker: 90-95%; Silica flower: 2-5%; Alumina cement containing less than 30% of CaO content: 3-5%; based on the composition, and the hexamethaphosphate is 0.3-0.7% based on the total weight Magnesia refractory composition with excellent dry crack resistance, characterized in that the composition is added in the range of. By weight, magnesia clinker: 78-92%; Silica flower: 2-5%; alumina cement containing less than 30% of CaO content: 3-5%; Chromium oxide: 3-13%; has a good dry crack resistance, characterized in that the composition is added to the composition of 0.3 to 0.7% hexametaphosphate in the range of 0.3 to 0.7% based on the total weight Magnesia fireproof composition.