KR20100076113A - Porous refractories and - Google Patents

Abstract

PURPOSE: A porous refractory and a steel manufacturing furnace using the same are provide to improve internal shock resistance property by improving bubbling effects through the control of a fine structure according to pore size and pore adjustment. CONSTITUTION: A porous refractory comprises mullite 70~85 weight%, calcined alumina 5~10 weight%, chromium oxide 1~2 weight%, clay 2~4 weight%, and frit 1~2 weight%. The porous refractory contains zirconia. The particle diameter of the zirconia is 0.01~0.20 mm. The 3~20 weight% of zirconia is contained in the porous refractory.

Description

Porous Refractories and}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous refractory for blowing gas into a molten metal and a steel manufacturing furnace using the same. In particular, the pore size and porosity of the porous refractory may be appropriately adjusted to a fine structure during heating, preheating, and casting. The present invention relates to a gas blowing porous refractory and a steel fabrication furnace using the same, which are suitable for minimizing cracking due to thermal shock and providing resistance to damage and infiltration to physical and chemical reactions.

When manufacturing steel, various refinery furnaces such as tundish and ladle blow bubbles of argon (Ar) and nitrogen (N ₂ ) into the molten steel through porous refractory (firebrick). Non-metallic inclusions, such as impurities, are floated and removed to obtain clean and uniform molten steel.

In addition to the bubbling function of air flow rate and bubble generation ability, the molten steel must withstand chemical and physical erosion by non-metallic inclusions, and thermal shock during preheating or casting. There should be no cracking and no molten steel adhesion or infiltration. The most important bubbling enhancement among the basic properties depends on the pore size.

Referring to Figures 1 to 3 to describe the tundish using a porous refractory for gas blowing in accordance with the prior art, the tundish is the bottom portion such that the porous refractory brick 10 is built on the bottom, molten steel is discharged The top nozzle 11 is installed between the firebricks installed in the wall. A slide nozzle 12 is installed below the top nozzle 11, and a start tube 14 supported by the supporting edge 13 is positioned on the bottom of the top nozzle 11. By being exposed, the molten steel inside the tundish is formed to be discharged downward. Reference numeral 15 is a tundish shell covering the bottom refractory brick 11.

In addition, referring to the ladle using a porous refractory for gas blowing in accordance with the prior art with reference to Figure 4, the outermost side of the ladle 21 is made of a shell (22), the bottom is a refractory chopped to the bottom 24 ) Is provided, and the inside thereof is constructed (reflected) by the refractory material 23. The inner refractory 23 is made of a porous refractory for gas blowing. In addition, the refractory 23 may be formed of a thermal insulation board, a first refractory brick and a second refractory brick in sequence.

On the other hand, the bubbles generated by the gas passing through the pores of the refractory, the larger the size of the inclusions of the inclusion is reduced, but the floating resolution is higher, so the fine structure of the refractory of the optimum size, that is, the appropriate pore size and porosity is required do.

The pore size is determined by the particle size of the porous refractory to be produced and also changes depending on the sintering agent, the firing temperature, the pressing force, and the like. Uniform pore diameter distribution can minimize the problem that the bubble is coalesced when the bubble is formed uniformly.

In order to improve the lifetime of porous bodies, the contents of molten steel should be increased, and this requires low porosity and appropriate pore size. On the other hand, in order to improve the melt damage caused by chemical reactions on molten steel other than physical elements, it is necessary to control the chemical composition. In particular, infiltration of Fe oxide and inclusions by infiltration and oxidation of molten steel results in lowering of breathability due to formation and infiltration of constituents and low melt of the refractory material. Therefore, there is a need for component control for this.

On the other hand, a component having a high melting point for oxygen washing is necessary because the temperature is rapidly increased and the melting of the refractory is made rapidly when used for several times or when the pores are removed by oxygen during the casting or removal of the residue.

Finally, cracks due to heat spalling cause problems of leakage of injected gas, infiltration and leakage of molten steel, and improvement of particle shape, microstructure, and thermal shock by low expandable minerals.

In this regard, the conventional refractory material lacks thermal shock resistance, so that cracks are initially generated when receiving molten steel, and the generated cracks continue to increase during molten steel casting, so that the concentration of gas is concentrated into cracks, making uniform gas blowing difficult. have.

In addition, such uneven injection of gas causes alumina inclusions present in molten steel to be attached to valves and plates for valves in various steel making furnaces during casting, which causes the plate and nozzle holes to be closed and casting is stopped.

In order to solve the problems as described above, it provides a porous refractory made of a new chemical composition and improved the spalling resistance, thermal shock resistance and the like of the porous body and a steel manufacturing furnace using the same.

Porous refractory material according to the present invention for achieving the above object,

In a porous refractory comprising mullite (3Al ₂ O ₃ · 2SiO ₂ ), calcined alumina (Al ₂ O ₃ ), chromium oxide (Cr ₂ 0 ₃ ), clay, and frit, the particle diameter is 0.01 to 0.20. zirconia (ZrO ₂ ) in mm.

The zirconia is preferably contained in 3 to 20% by weight. More preferably the zirconia is contained in 10 to 15% by weight.

In addition, the mullite has a diameter of 0.2 to 1.0mm and 70 to 85% by weight, the zirconia has a diameter of 0.01 to 0.2mm and 10 to 15% by weight, the calcined alumina is 5 to 10% by weight, the chromium oxide is Most preferably, 1 to 2% by weight, 2 to 4% by weight of clay, and 1 to 2% by weight of frit.

In addition, in the steel production according to the present invention, the non-metallic inclusions are removed by blowing gas into the molten steel using the aforementioned porous refractory material and bubbling.

According to the present invention as described above, by appropriately adjusting the particle diameter and the like to select the appropriate chemical composition containing zirconia and to strengthen the inter-particle bonding strength, the bubbling effect is improved by controlling the microstructure according to the pore size and porosity control In addition to this, a porous refractory and steel manufacturing furnace having improved solvent resistance, spalling resistance, and thermal shock resistance is obtained.

Hereinafter, the present invention will be described in detail. In describing the present invention, detailed descriptions of related well-known functions or configurations are omitted in order not to obscure the gist of the present invention.

The porous refractory according to the present invention contains mullite (3Al ₂ O ₃ · 2SiO ₂ ), calcined alumina (Al ₂ O ₃ ), chromium oxide (Cr ₂ 0 ₃ ), clay, frit, and zirconia (ZrO 2). do.

Mullite is an aluminum silicate mineral (3Al ₂ O ₃ · 2SiO ₂ ) rarely found in nature and is produced when baking raw materials of aluminum silicate and is the most important component of ceramic products, ceramics, high temperature insulators and refractory materials. In the present invention, the mullite preferably has a particle diameter of 0.2 to 1.0 mm. This is to ensure the pore size, porosity, and handling strength in terms of the overall particle size of the porous refractory.

The composition weight ratio is controlled by the amount of zirconia used, but the mullite is preferably contained in an amount of 70 to 85% by weight in comparison with the amount of zirconia described later. This represents the remaining weight percentage except for alumina, clay, chromium and zirconia added as an auxiliary material.

Zirconia has a chemical formula of ZrO ₂ and is also called zirconium oxide. It is a silvery white hard rare metal element produced from zircon deposits. Zirconia has a high refractive index and a high melting point, and thus has high corrosion resistance. It is insoluble in water and soluble in sulfuric acid and hydrofluoric acid. It is used as a heat-resistant material because it withstands sudden changes in temperature. In the present invention, the zirconia is used to improve the thermal shock resistance, the particle size of 0.01 to 0.2 mm in consideration of the pore size, porosity, mechanical properties to a size smaller than the particle size of the mullite is used. The greater the amount of the zirconia used, the better the thermal shock resistance, but preferably 10 to 15% by weight in consideration of the mechanical strength of the porous body. If it is less than 10% by weight, there is no enhancement effect of heat shock resistance, and if it exceeds 15% by weight, the strength is lowered.

Calcined alumina (calcined alumina) (Al ₂ O ₃ ) is an ultra-fine alumina having a large specific surface area and showing excellent sinterability and reactivity, and is alumina made by calcining aluminum hydroxide. In the present invention, the calcined alumina is used to reinforce the matrix of the porous body, and preferably contains 5 to 10 wt% of particles having a particle diameter of 10 μm or less. This is to enhance the sinterability of the porous body, if less than 5% by weight, the effect is weak, if more than 10% by weight problems in the composition of the particle size.

Chromium oxide (Cr ₂ O ₃ ) is added to improve the content line, which inhibits the formation of low melt by the reaction of Fe oxide and non-metallic inclusions to form compounds of high melting point and high viscosity, Suppresses local loss.

Clay is added to enhance the formability and sinterability of the porous body, it is preferable that the clay particles having a diameter of 44um or less is contained in 2 to 4% by weight. If it is less than 2% by weight, the sinterability is insufficient, and if it exceeds 4% by weight, the thermal shock resistance is lowered due to excessive sintering.

Fret refers to a molten glass raw material such as, for example, glassy lye of porcelain, and is sintered at a relatively low temperature with mullite and zirconia, which are the main components of the porous refractory material of the present invention. Its resistance to molten steel wear is significantly improved.

Next will be described a specific embodiment of the porous refractory according to the present invention contained in the above weight% range.

In the following description of the embodiment, the 'strength degradation rate (%)' is a strength of the specimen by measuring the bending strength after repeated heating at 1400 ° C. and cooling at room temperature using a specimen of a certain size. The degree of deterioration is compared and expressed as a percentage, and is calculated by the following equation.

Equation: Strength deterioration rate (%) = (Bending Strength Value after Thermal Shock / Initial Bending Strength Value) × 100

Here, when the strength degradation rate is high, it means that the heat spalling resistance is low, and in this case, the crack progresses rapidly, thereby deteriorating the uniformity of gas injection.

Incidentally, the thickness of the inclusions (molten steel 180 minutes casting) attached to the immersion nozzle after the application of the furnace is referred to as 'inclusion thickness (mm)'.

In addition, in the following examples, the calcined alumina has a particle diameter of 0.2 mm or less and is contained in 5 wt%, and chromium oxide is 44 μm or less and contains 1 wt%. In addition, clay has a particle diameter of 44 um or less and is contained at 3% by weight, and frit has a particle diameter of 44 um or less and is contained at 1% by weight.

On the other hand, the zirconia has a particle diameter of 0.2 mm or less, and the content thereof is 3% by weight (Example 1), 20% by weight (Example 2), 10% by weight (Example 3), 15% by weight (Example 4). ), And the content of mullite having a particle diameter of 0.2 to 1.0 mm was also 87% by weight (Example 1), 70% by weight (Example 2), 80% by weight (Example 3), 75% by weight. It was changed to% (Example 4).

In addition, a comparative sample containing no zirconia was prepared for comparison with the above examples, wherein the diameters of the particles were the same as the above examples, and the composition ratio was 90% by weight of mullite and 5% by weight of calcined alumina. , 1% by weight of chromium oxide, 3% by weight of clay, and 1% by weight of frit.

Table 1 below is a table comparing the physical properties and properties of the refractory composition of the porous refractory prepared by the above embodiments and the comparative sample.

TABLE 1

When analyzing the strength deterioration rate in [Table 1], compared to the comparative sample does not contain zirconia, there is a slight difference depending on the content of zirconia in each of the embodiments containing zirconia, but the strength deterioration rate is further reduced It can be seen that the fire resistance is improved. In particular, when the zirconia content is 10% by weight, it can be confirmed that the strength deterioration rate is the smallest.

In addition, when analyzing the heat spalling resistance in [Table 1], when the zirconia is contained in less than 10% by weight in Example 1, there is no heat spalling resistance, and also in Example 2 more than 15% by weight of zirconia If contained, it can be confirmed that there is no heat spalling resistance. When the zirconia is contained in 10 to 15% by weight, as in Example 3 and Example 4, it can be confirmed that the heat-span resistance. Here, the presence or absence of heat spalling resistance depends on the strength deterioration rate, and if the strength deterioration rate is 10% or less, it is determined that there is heat spalling resistance.

In addition, when analyzing the thickness of inclusion inclusions in [Table 1], in Example 1 and Example 2 it can be confirmed that the thickness is smaller than the comparative sample, in the case of Examples 1 and 2, heat spalling resistance Without this, the effect is not remarkable. However, it can be confirmed that in Example 3 and Example 4, the thickness thereof is significantly smaller than that of the comparative sample, thereby greatly improving the fire resistance characteristics.

Comparing the above fire resistance characteristics, Example 1 and Example 2 does not significantly improve the adhesion thickness of the inclusions due to the lack of heat-span resistance, the strength degradation rate is greatly improved to 15 to 30%, the present invention containing zirconia The fire resistance properties of the fire resistant composition were improved, and in particular, as shown in Examples 3 and 4, when the content of zirconia was 10 to 15% by weight, the inclusion thickness was 8 to 10 mm due to heat spalling resistance. At the same time it can be confirmed that the strength degradation rate is also significantly improved to 5 to 10%.

Therefore, as shown in the above embodiment, the present invention contains zirconia in an appropriate size and an appropriate weight percent, so that the strength deterioration rate is excellent, or the strength deterioration rate and heat spalling resistance are excellent, so that it is uniform even during long time casting. The gas can be blown and the adhesion of inclusions to a nozzle can be suppressed.

Porous refractory materials as described above can be used as refractory materials in various steel fabrications, for example, tundishes or ladles. 1 to 3 can be used to manufacture a tundish using the porous refractory according to the present invention instead of the conventional refractory (firebrick) 10, and also in accordance with the present invention instead of the conventional refractory 23 in Figure 4 Porous refractory can be used to prepare ladles. Of course, this is only an example, and the porous refractory according to the present invention may be used in all furnaces for steel fabrication using porous refractory. Steel fabrication using the porous refractory according to the present invention is excellent in the strength degradation rate, or excellent strength degradation rate and heat-span resistance, it is possible to uniform gas blowing even during long time steel casting.

As described above, the porous refractory and the steel production furnace using the same have been described, but the present invention is not limited by the embodiments disclosed herein, and various modifications are made by those skilled in the art within the technical scope of the present invention. Of course it can be done.

1 is a partially enlarged view showing a tundish using a conventional gas blowing porous refractory,

Figure 2 is a partial cutaway cross-sectional view showing the entire interior of the conventional tundish refractory,

3 is a cross-sectional view showing a cross section viewed from A-A of FIG.

4 is a cross-sectional view showing a ladle using a porous gas for refractory gas of the prior art.

Claims (5)

In a porous refractory including mullite (3Al ₂ O ₃ · 2SiO 2), calcined alumina (Al ₂ O ₃ ), chromium oxide (Cr ₂ 0 ₃ ), clay, and frit, Porous refractory containing zirconia (ZrO2) having a particle diameter of 0.01 to 0.20 mm. The method according to claim 1, Porous refractory containing 3 to 20% by weight of the zirconia. The method according to claim 1, Porous refractory containing 10 to 15% by weight of the zirconia. The method according to claim 1, The mullite has a diameter of 0.2 to 1.0mm and 70 to 85% by weight, the zirconia has a diameter of 0.01 to 0.2mm and 10 to 15% by weight, the calcined alumina is 5 to 10% by weight, the chromium oxide is 1 to Porous refractory containing 2% by weight, 2 to 4% by weight of clay, and 1 to 2% by weight of frit. In the steel manufacturing furnace to remove non-metallic inclusions by blowing gas into the molten steel through the porous refractory, bubbling, The porous refractory is to steel production using the porous refractory of any one of claims 1 to 4.

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