JPH0348151B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is based on MgO-C (magnesia carbon).
MgO-, which has high accuracy in the intermediate and high temperature range, is useful as a refractory, more specifically as a steelmaking furnace lining material, etc.
This relates to C refractories. With the recent development of steelmaking technology, refractories used in steelmaking furnaces are required to withstand increasingly severe conditions. For example, a typical example is the bottom blowing converter method, and MgO-C bricks have recently been widely used as a useful refractory for this method. These MgO-C bricks have excellent corrosion resistance and spalling resistance for use in steelmaking furnaces (converters, degassing ladles, etc.), but they are usually lined as unfired bricks. Therefore, it does not develop strength until it is heated at high temperatures for a long time, and the strength is insufficient especially during the process from intermediate to high temperatures.As a result, corrosion resistance decreases and cracking due to mechanical stress occurs, which deteriorates its characteristics. The reality is that they are not being fully utilized. In view of these points, and as a result of various studies, the present invention has been developed to reduce the strength loss that tends to occur at intermediate to high temperatures in the temperature range of 500 to 1500℃.
This problem was solved by adding a combination of additives that easily form ceramic bonds, and the problem was successfully improved in the entire area. That is, in the present invention, the borax component is Na ₂ O.
0.1-3% as 2B ₂ O ₃ , ultrafine powder Al ₂ O ₃ of 20μ or less
The gist is a MgO-C refractory containing 0.5 to 5% of MgO-C. It should be noted that although there have been proposals in the past to try adding Al ₂ O ₃ and B ₂ O ₃ components which can become borax components to MgO-C bricks, these results are not fully satisfactory. No results have been obtained. For example, JP-A No. 56-92160 discloses a magnesia-alumina-carbon brick and discloses that 5 to 35% of Al ₂ O ₃ is added.
Al ₂ O ₃ does not disclose the present invention in terms of quantity or particle size, and there is no addition of borax component at all, so the object of the present invention cannot be achieved in any way. In particular, the formation of spinel bond by the reaction between Al ₂ O ₃ and MgO occurs at a temperature of 1300° C. or higher, so no strength is developed up to this temperature, and if there is too much Al ₂ O ₃ , corrosion resistance decreases. In addition, MgO-
Although it is disclosed that a compound containing boron is added to C bricks, there is no indication that it is added as borax, and it is not intended to improve intermediate to high temperature strength, which is the purpose of the present invention.
The addition of Al ₂ O ₃ is also not disclosed at all, and the object of the present invention cannot be achieved in any way. Furthermore, since boron alone requires a reaction temperature of 950°C or higher with MgO, strength cannot be developed up to this temperature. Furthermore, at high temperatures, the compound of B ₂ O ₃ and MgO liquefies and flows, so it does not develop strength at high temperatures (1400°C or higher), which poses a problem in use. The present invention has succeeded in bringing about objects and effects not seen in such disclosures, and will be explained in detail below. In the MgO-C refractory of the present invention, first,
Suitable examples of MgO (magnesia) include calcined magnesia clinker and fused magnesia clinker, and magnesite and other materials normally used as raw materials for MgO refractories.C carbon materials include natural graphite, artificial graphite, and coke. , carbon black, or other commonly used materials may be used. In the present invention, the ratio of MgO and C can be applied over a wide range depending on the purpose and usage of the refractory, that is, it can be selected within the range of 95 to 5% of each other, but corrosion resistance, oxidation resistance, wear resistance etc.
From the point of view of conventional comprehensive evaluation of MgO-C refractories, the former is preferably about 95 to 50% and the latter about 5 to 50%. At least the following two types of additives are blended into the refractory of the present invention with respect to such main raw materials. First, one is the borax component, which is considered to act as a component that forms strength in the intermediate temperature range up to about 1000° C. in the present invention. That is, Na ₂ O 2B ₂ O ₃ is generated up to about 1000℃ and exists around MgO particles,
B ₂ O ₃ and MgO react, 3MgO・B ₂ O ₃ (melting point 988
℃) and 2MgO・B ₂ O ₃ (melting point: 1313℃), which is thought to generate strength. In this way, in the present invention, Na ₂ O・2B ₂ O ₃
A component that generates and reacts with MgO at intermediate temperatures, that is, a borax component, is necessary and essential, and even if the B ₂ O ₃ component or the Na ₂ O component is present alone, it is not effective. There is no. The most suitable borax component is hydrated or anhydrous sodium borate.
It is added as Na ₂ B ₄ O ₇ (Na ₂ O・2B ₂ O ₃ ), but in some cases, the Na ₂ O component and the B ₂ O ₃ component are mixed separately and the Na ₂ O・It is also possible to generate 2B ₂ O ₃ . The blending ratio of this borax component is 0.1 to 3% as Na ₂ O 2B ₂ O ₃ in the MgO-C refractory (excluding when carbon binder described later is blended),
It is preferably 0.2 to 2%. This is because if the amount is too small, the purpose cannot be achieved, and on the other hand, since these compounds are low melting point components, it is better to use as little as possible within the range that the purpose can be achieved. Another essential component in the present invention is Al ₂ O ₃ ultrafine powder, which is considered to act as a component that develops strength in a high temperature range of about 1500°C in the present invention. That is, in the 1500°C region, by existing around MgO particles, it reacts with MgO to form spinel (MgO・Al ₂ O ₃ ), and this spinel becomes MgO
This seems to be because it forms a strong joint for the -C refractories. In this invention, high temperature
Is it because it is necessary that the reaction between MgO and Al ₂ O ₃ progresses easily, that is, the spinel formation reaction becomes easy?
It has been found that it is desirable to blend Al ₂ O ₃ as an ultrafine powder that is as active as possible. That is, as a result of various studies, it has been confirmed that the strength can be improved to the extent that the purpose can be achieved by blending with ultrafine powder of 20μ or less, and particularly preferably, the majority of it is 5μ or less. It has been found that blending as an ultrafine powder also contributes to the formability and compactness of refractories. The blending ratio of this Al ₂ O ₃ fine powder is 0.5 to 5% by weight in the MgO-C refractory (excluding the carbon binder), and preferably 1 to 4%. This is because if the amount is too high, the amount of spinel (MgO・Al ₂ O ₃ ) generated will increase, which will reduce the corrosion resistance against slag and molten steel, and will also increase the volume expansion associated with spinelization, which is undesirable. If the amount is too small, the formation of spinel bonds will be insufficient.
This is because it becomes difficult to obtain high-temperature strength. It should be noted that the purity of Al ₂ O ₃ should be as high as possible, as a large amount of impurities will cause a decrease in corrosion resistance.
99.5% or higher is good. The refractory of the present invention can be produced by adding a suitable binder to the particle size-adjusted main raw materials and essential components, thoroughly kneading the mixture, and then molding and drying the mixture in a conventional manner. In this case, as a binder, this kind of MgO-C
Resins such as phenolic resins, furan resins, silicone resins, etc., which are carbon binders well known as binders for refractories, or resinous pitches may be used, and the amount of these compounds is usually 0.5 to 10% by weight. . The refractory of the present invention is useful as an unfired refractory that has just been subjected to a drying treatment up to about 500°C as a heat treatment after normal forming, but it can also be used as an amorphous refractory. Although it is rare, it can also be used as a fired refractory that is molded or shaped into an amorphous shape, hardened, and then fired. In this way, the refractory of the present invention improves the strength, which was previously lacking, without impairing the characteristics of MgO-C refractories, compared to, for example, conventional MgO-C bricks.
It is possible to increase the temperature by about twice as much at temperatures up to about 1,000℃ and about three times in the high temperature range of about 1,500℃, making it extremely useful as a lining material for steelmaking furnaces, etc. The value is enormous. The present invention will now be explained with reference to Examples. Example After thoroughly kneading the raw materials in the proportions (parts by weight) shown in Table 1, 80/70×150× under a pressure of 1000 Kg/cm ² or more
After molding to a size of 230 mm, it was dried at 400°C for 5 hours to obtain an unfired brick.

【table】 The various properties obtained are shown in Table 2.

【table】

【table】

Claims (1)

[Claims] 1% by weight, with borax component as Na ₂ O.2B ₂ O ₃
A MgO-C refractory containing 0.1 to 3% and 0.5 to 5% of ultrafine Al ₂ O ₃ of 20μ or less. 2 Borax component: 0.2-2%, ultrafine powder Al ₂ O ₃ : 1-4
% of the refractory according to claim 1. 3. The refractory according to claim 1 or 2, wherein the ultrafine powder Al ₂ O ₃ has a particle size of 5 μ or less. 4. The refractory according to claim 1, which contains 0.5 to 10% by weight of carbon binder. 5 The ratio of MgO and C is MgO50 to 95 in weight%.
%, C50 to 5%. 6. The refractory according to claim 1 or 5, wherein the MgO-C refractory is an unfired regular or amorphous refractory.