Composite

FIELD: ceramic composites for refractory parts, maintaining under extreme conditions.

SUBSTANCE: Claimed material is sintered under pressure and contains (mass %): hexagonal boron nitride 45-80 and second material 55-20. The second material represents solid aluminum oxide solution in silicium nitride containing 35 % or less of oxygen.

EFFECT: material with low thermal-expansion coefficient, improved rustproof quality and heat resistance.

6 cl, 2 tbl

 

The present invention relates to the creation of new composite (composite) material, and more particularly, to the creation of a sintered during the application of pressure to the material, which contains hexagonal boron nitride and the second material, which contains at least one nitride of the metal. In accordance with another aspect of the present invention, it is proposed a composite material, which is particularly useful for the manufacture of refractory components operating in severe conditions of corrosion and the effects of temperature, such as refractory parts for the metallurgical industry, in particular for the production of steel. In particular, this material is particularly well suited for the manufacture of lateral passes (lateral bounding plates) for the process of casting (casting) stripe (tape).

When one of the types of continuous casting, referred to as a strip casting or pouring with dual rollers, which is used for casting steel strip of a thickness of approximately 2 to 10 mm, lateral constraint of the liquid metal filling the space bounded by the rollers, is provided by plates (passes)which are pressed by means of the appropriate device to the plane of the ends of the rolls. These plates are usually referred to as side walls or lateral passes. Their control panel is the first part, which is designed to enter into contact with liquid metal, made of refractory material, and the periphery of the plates that friction wears away when pressure is applied to the rolls, causes wear and tear of lateral passes. I should say that it is absolutely necessary to maintain perhaps more intimate contact of the lateral passes from the rollers, as the infiltration of liquid metal in the contact region has a detrimental effect on dimensional accuracy spilled strip. In this case, some parts of the strip exposed to the risk of peeling off the main strip and sticking to the rolls. If the adhesion lasts for a complete revolution of the rolls, and when the fragments of the strip edge penetrate into the casting space, it can cause serious damage to the surfaces of the rolls, and as a result, and the actual lanes. In the worst case leaked metal can flow from the machine that requires an immediate stop casting.

These problems can be caused by many reasons, among which we mention the following:

- deformation of the rolls and passes caused enclosed mechanical and thermal stresses, in particular, at the beginning of casting, when set to heat mode;

- gradual (mechanical and chemical) wear passes or rolls, which is not always uniform who throughout their contact area; and

- instant wear passes, caused by the passage of leaked hardened metal.

In connection with the above, there is a need to create a material that combines resistance to mechanical and thermal stresses and has a high resistance to chemical and mechanical wear.

Sintered during the application of pressure polycrystalline mixture of materials already known from U.S. patent 4885264, which describes the materials based on boron nitride, oxides and carbides, in which the fraction of hexagonal boron nitride is approximately from 30 to 85% by weight.

The oxide fraction, which is selected from the group comprising zirconium oxide and magnesium oxide, is from 10 to 50% by weight. Carbide fraction, which is selected from the group comprising silicon carbide, titanium carbide and zirconium carbide, is approximately from 5 to 20% by weight. This material has a density of more than 94% of theoretically possible density (mixture of boron nitride oxide and carbide). In accordance with the U.S. patent 4885264 material is resistant to molten metals, wear-resistant and heat-resistant, and therefore suitable for the manufacture of separators or discontinuous rings, used for horizontal continuous casting of steel and non-ferrous metals.

However, it was found that CH is ate way due to the high coefficient of thermal expansion, this material does not have sufficient heat resistance. Chemical resistance to molten metals is not sufficient.

From U.S. patent 5389587 also known other material, which is a conventional sintered during the application of pressure ceramic material, which contains at least 50% by weight of hexagonal boron nitride and from 1 to 50% by weight of two or more components selected from the group comprising nitride and aluminum oxide and silicon. The mechanical strength of this material is still far from the requirements in the production of steel, for example when making passes.

Thus, there is a need to create a material that combines resistance to mechanical and thermal stresses and has a high resistance to mechanical and chemical wear, particularly high chemical resistance to molten metal.

In accordance with the present invention one or more of these requirements are implemented through the creation of a composite sintered during the application of pressure to the material, which contains from 45 wt.% and up to 80 wt.% hexagonal boron nitride and from about 55 wt.% up to 20 wt.% the second material, which is a solid solution of alumina in silicon nitride, and the amount of aluminum oxide is W hat, the second material contains not more than 35 wt.% the oxygen.

Found that this material has a relatively low coefficient of thermal expansion and therefore has a high heat resistance. Another characteristic of this material is its low wettability with molten steel, which gives it a higher resistance to molten metal and as a result reduces the chance of curing it began. Finally, it was found that this material has exceptional mechanical wear resistance.

Crystal structure of hexagonal boron nitride is mainly formed by planes, which presumably serve to prevent the spread of cracks. Therefore, the composite material should have a continuous phase of hexagonal boron nitride. Found that for the formation of a continuous phase of hexagonal boron nitride sufficient quantity of at least 45% by weight of hexagonal boron nitride, and mainly from 55% to 70% by weight of hexagonal boron nitride.

The best results were obtained with the application of materials that contain 57.5% by weight of hexagonal boron nitride.

In accordance with a preferred embodiment of the present invention using the Sialon as the second material, with the holding oxygen. Sialon is a well-known material, which is formed by the first letters of its constituent elements Si-Al-O-N, and can be described as a solid solution of alumina in silicon nitride. Conventional chemical formula Sialon matches Si6-zAlzOzN8-zin which z is in the range from 0 to approximately 4,5. In accordance with the present invention z mainly lies in the range from 1 to 4.5, and preferably, from 2 to 3. The oxygen content in the second material should be not less than 2.5%.

It should be borne in mind that the composite material may also contain conventional additives such as oxides of yttrium, magnesium, calcium and/or cerium, which represents the phase of the melt at high temperatures and which are more preferred than the boron oxide.

These additives in the composite material are negligible weight and does not exceed 5% by weight of a mixture of hexagonal boron nitride and the second material.

As starting materials in the manufacture of composite materials in accordance with the present invention mainly uses a powder of hexagonal boron nitride, which has an oxygen content of approximately from 2 to 8% by weight and a specific surface of approximately from 5 to 30 m2/g (measured by BET method), and nitrilotri and oxide powder, with a purity of at least about 95%.

These powders can be uniformly mixed, which is in itself known, in the standard mixing device, while using, if necessary, a binder, followed by sintering under the application of pressure until the density component at least about 94% of theoretical density. During this process, the mixture can be subjected to hot pressing in graphite form, with the application of axial pressure at temperatures from approximately 1500°With up to 1800°With, but mainly at temperatures from approximately 1650°With up to 1750°C, and the pressure is approximately from 10 to 40 MPa, and mostly from approximately 15 to 35 MPa. Alternatively, it may be also conducted by isostatic hot pressing in a vacuum sealed enclosure at temperatures from approximately 1400°With up to 1700°With, but mainly at temperatures from approximately 1500°With up to 1600°C, under pressure of approximately 100 to 300 MPa, and mostly from approximately 100 to 200 MPa in an autoclave for hot pressing using an inert gas as a medium for transmitting pressure. Fittings with the desired dimensions can be obtained by machining obtained from these clicks the zoom bars.

The new composite material in accordance with the present invention will find its primary use as a lateral passes for the casting process of the band, but may also find other applications, which is essential to its exceptional resistance to mechanical and thermal stresses and its excellent chemical and mechanical durability, for example, in metallurgy as a sliding valve sliding gate tundish or bottling bucket.

The new composite material in accordance with the present invention has such excellent characteristics, in particular such erosion resistance and heat resistance that it can be reused as a lateral pass. This is a real breakthrough in the field of casting strip, as hitherto never been able to achieve and even impossible to imagine.

Reuse side of the pass in accordance with the present invention can be carried out with the same side which is in contact with metal, or, alternatively, with reverse side in contact with the metal. Reuse side of the pass in accordance with the present invention can be carried out directly (immediately). However, if the lateral side of the pass, the which was already in contact with molten metal, again must be entered in contact with molten metal, it is necessary to perform adjustment (temperature) this side of the pass.

Thus, the present invention is also related to improvements in the casting of the strip, at which the lateral limit of the liquid metal filling the space bounded by the rollers, is provided by the side of the passes, which are pressed to the plane of the ends of the rolls. This improvement of the casting process the strip is to re-use the same side of the pass and/or other previously used side of the pass.

Hereinafter the present invention will be described in more detail with examples of its implementation.

Examples

Were prepared following powder mixture:

In examples 1-5 in accordance with the present invention the second material is a nitride of silicon containing oxygen is introduced in the form of aluminum oxide or magnesium oxide. In these examples use the Sialon with z=2, obtained by means of known methods, such as solid of reaction of silicon nitride, aluminum oxide or the recovery of carbon a mixture of oxides of silicon and aluminum in an ammonia atmosphere. In the Sialon add 3% by weight MgO, which allows you to get 11.45 per cent of oxygen in the second mother of the Le.

In examples 3 and 4 in the Sialon add to 4.1% by weight of yttrium oxide (Y2O3).

TABLE 1
ExampleThe boron nitride

(% by weight)
The second material (% by weight)MgO (% by weight Sialon)Y2About3(% by weight Sialon)
1505030
2653530
3505031
4653531
5of 57.542,530

For comparison we have also prepared powder mixture which contains 50% by weight of hexagonal boron nitride, 40% by weight of zirconium dioxide (ZrO2) and 10% by weight of silicon carbide (example C1).

Powder mixtures prepared in accordance with examples 1-5 and C1, were subjected to hot pressing at a temperature of 1650°and at a pressure of 20 MPa. Table 2 shows the results obtained for the materials according to examples 1-5 and C1.

TABLE 2
ExampleThe coefficient of thermal expansion (10-6To-1)R factor (ΔT necessary for the early formation of cracks) (°)Wettability (compared to stainless steel at 1550°)
12,5488from 130 to 150°
22,55879-
31,75915-
42,0529-
51,85596from 130 to 150°
C13,3337from 100 to 110°

From the comparison of examples 1-5 example C1 is clear that the material in accordance with the present invention has a very low coefficient of thermal expansion and therefore has excellent resistance to thermal stresses. It also follows from the values of R factor representing resistance, which is calculated by the formula:

R=σ(1-ν)/εα,

in which σ is the modulus of bending (MOR), ν displays the Poisson's ratio, ε represents the young's modulus, and α is the coefficient of thermal expansion. The values of R indicate that the material in accordance with this what their invention can withstand the temperature difference Δ T, which are 2-3 times higher than ΔT able to lead to the formation of cracks in the well-known materials. Values specialisti show that material in accordance with the present invention poorly wetted by the molten steel, which is also confirmed when exposed to a sample of material with a drop of molten stainless steel at a temperature of 1550°C in argon atmosphere. After removing drops of stainless steel observed the formation of a zone of interaction with a depth of 250 μm on the material of example C1, while in the case of material in accordance with the present invention (example 5) observed the formation of a zone of interaction depth of only 50 microns.

1. Composite material, sintered during the application of pressure, which contains from 45 to 80 wt.% hexagonal boron nitride and from 55 to 20 wt.% the second material, which is a solid solution of alumina in silicon nitride, and the amount of aluminum oxide is such that the second material contains not more than 35 wt.% the oxygen.

2. A composite material according to claim 1, characterized in that it contains from 55 to 70 wt.% hexagonal boron nitride.

3. A composite material according to claim 1, characterized in that the second material contains at least 2.5% oxygen.

4. A composite material according to claim 1, characterized in that the second material is formed from Sialon (Si6-z/sub> AlzOzN8-z), where z is chosen in the range from 1 to 4.5.

5. A composite material according to claim 4, wherein z is chosen in the range from 2 to 3.

6. Plate side of the pass containing a composite material according to one of claims 1 to 5.



 

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Composite // 2243955

FIELD: ceramic composites for refractory parts, maintaining under extreme conditions.

SUBSTANCE: Claimed material is sintered under pressure and contains (mass %): hexagonal boron nitride 45-80 and second material 55-20. The second material represents solid aluminum oxide solution in silicium nitride containing 35 % or less of oxygen.

EFFECT: material with low thermal-expansion coefficient, improved rustproof quality and heat resistance.

6 cl, 2 tbl

FIELD: chemistry.

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1 tbl, 1 ex

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