JPH0390271A - Non-calcined brick for sliding nozzle plate - Google Patents

Abstract

PURPOSE:To improve the oxidation resistance of the SN plate by adding carbon fibers of a specific diameter and length, boron carbide and chromium carbide, respectively at specific parts wt., and a binder to the compd. of alumina aggregate, carbon and fine metallic powder, then kneading, molding the mixture and heat treating the molding at a specific temp. CONSTITUTION:The carbonaceous fibers having <=0.2mm diameter and 1 to 1mm length are added at 0.5 to 3 pts.wt., the boron carbide at 0.5 to 3 pts.wt. and the chromium carbide at 0.5 to 10 pts.wt. and phenol resin or pitch as the binder to the compd. contg. the alumina as the refractory aggregate and consisting of the others, such as carbon and fine metallic powder. The mixture composed thereof is kneaded and molded and the molding is heat treated at <=700 deg.C. The powder of a silicone resin having <=1mm grain size is added at 1 to 10 pts.wt. to this molding. The durability of the SN plate is enhanced in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plate brick for a sliding nozzle (hereinafter referred to as SN) device used for controlling the flow rate of molten steel in a steel factory.

[Conventional technology]

When using the SN plate brick, the nozzle hole is approximately 1
It is subjected to the physical and chemical erosion effects of rapid thermal shock and wear caused by the molten steel flow at temperatures of 550 to 1600°C. On the other hand, since the temperature of the outer circumferential portion rises to approximately 400 to 600° C., carbon in the sliding surface portion is likely to be oxidized. The oxidation of carbon weakens the brick structure, causing increased wear and surface roughness when the metal is bitten. In recent years, tundishes have been reused, and along with this, SN plate bricks have also been reused. When reusing the nozzle hole, the base metal adhering to the nozzle hole is dissolved and cleaned using an oxygen jet to remove the metal, so there is a concern that durability may be reduced due to oxidation of the nozzle hole. Thus, it is desired that SN plate bricks have spalling resistance, corrosion resistance, and oxidation resistance.

Conventionally, carbon bond bottom mine bricks are made by adding carbon black, graphite, etc. to aggregates such as alumina and mullite, adding liquid phenol resin or pitch, etc., kneading,
After molding, 10
It is fired at a temperature of 00 to 1400°C.

In recent years, unfired SN plate bricks have been developed to streamline the brick manufacturing process, reduce manufacturing costs, etc., and are being widely used.

Since the structural deterioration of these underground SN plate bricks after oxidation is more pronounced than that of fired products, various studies have been made to improve their oxidation resistance.

For example, ■ Adding BnC'PBN to form a glass layer in the oxidized part (for example, Japanese Patent Publication No. 63-32097); ■ Adding metal aluminum powder, which has a higher affinity for oxygen than carbon (Japanese Patent Publication No. 63-16393). ), etc. are being carried out. In addition, as mentioned above, in areas heated to approximately 500 to 800°C, strength decreases due to carbonization of the binder, and surface roughness is likely to occur due to cracking and wear. Therefore, in order to improve the strength of the brick structure, aluminum Fibers, etc. are added (for example, Japanese Patent Application Laid-Open No. 60-81
068, Japanese Patent Publication No. 61-136966).

[Problem to be solved by the invention]

Unfired SN plate bricks are usually made by adding thermosetting resin such as phenol resin to fire-resistant aggregate as a binder.
After kneading and molding, it is manufactured by heat curing treatment at 150 to 600°C. When using SN plate bricks,
The nozzle hole reaches a high temperature of about 1600°C, and the surrounding area has a relatively low temperature (about 400 to 600°C), creating a significant temperature gradient and causing large thermal stress.

Unfired bricks have the advantage of having a flexible structure against thermal shock and thermal stress, and are excellent in spalling resistance, but on the other hand, unfired bricks containing carbon are susceptible to oxidation of the carbon components in the bricks during use. Disappearance, that is, decarburization, weakens the part and causes noticeable erosion and wear, which significantly reduces the durability of the SN plate.
In the portion heated to 0 to 800° C., strength decreases due to carbonization of the binder, and there is a drawback that cracks due to thermal stress, wear due to contact with base metal, or base metal adhesion are likely to occur.

This invention has been proposed in view of the above-mentioned conventional circumstances, and has the following characteristics:
An object of the present invention is to provide a bottom sliding nozzle plate brick with little metal adhesion.

[Means to solve the problem]

This invention employs the following means to achieve the above object. That is, 0.5 to 3 parts by weight of carbonaceous fibers with a diameter of 0.2 m or less and a length of 1 to 511 mm and a particle size of 0.044 m or less are added to a mixture consisting of alumina as a refractory aggregate, carbon, and fine metal powder. 0.5 to 3 parts by weight of boron carbide, 0.5 to 10 parts by weight of chromium carbide with a particle size of 0°1 mm or less
Part by weight, phenol resin or pitch is added as a binder, kneaded, molded, and heat treated at 700°C or less. In addition to the above, it is more preferable to add 1 to 10 parts by weight of silicone resin powder having a particle size of 1 fi or less.

[Effect]

The above boron carbide (84G), chromium carbide (Cr=
C, etc.) are added to suppress oxidation of carbon by air.

Here, it is thought that the added boron carbide is easily oxidized, and that the boric acid glass produced covers the oxidized layer and exerts the effect of suppressing the oxidation of the carbon inside. The amount of boron carbide used is 0.5 to 3 parts by weight, more preferably 1 to 3 parts by weight. It is 3 parts by weight. If the amount of boron carbide added is 3 parts by weight or more, the erosion resistance of molten steel will decrease significantly, and if it is less than 0.5 parts by weight, the sufficient effect cannot be achieved.Boron carbide is reactive with oxygen. It is preferable to use fine powder of 0.044 m or less from the viewpoint of increasing the particle size and uniformly dispersing it within the brick to form a glass layer.

Oxidation of chromium carbide becomes significant at temperatures of 1000° C. or higher, and it is thought that chromium carbide exhibits the effect of suppressing oxidation of carbon in bricks. The chromium carbide mentioned above is various, for example trichromium dicarbide (Cr).

C2), heptalomum tricarbide (Crt C3), and tetrachromium carbide (CraC), all of which are effective for this purpose, but the most common is trichromium dicarbide (CriC).
An example of the use of 2) will be described.

That is, trichromium dicarbide is added in an amount of 1 to 10 parts by weight, preferably 1 to 7 parts by weight. If the amount added is 10 parts by weight or more, the brick structure after oxidation will become significantly weakened, resulting in a decrease in the corrosion resistance of molten steel, and if the amount is less than 1 part by weight, the oxidation prevention effect will be reduced. The particle size of chromium carbide is preferably 0.1 MX or less from the viewpoint of increasing reactivity with oxygen.

In order to suppress oxidation, metal powders such as aluminum powder and silicone may be added. Furthermore, these metal powders generate carbides, which strengthen the brick matrix,
It is expected to improve the hot strength of bricks. In other words, by taking advantage of the high oxygen affinity of these metals, oxides of the metal powder are generated during the heating process, and the volumetric expansion when the oxide is generated closes the gaps between particles during molding, thereby achieving densification. This creates high strength while at the same time creating low air permeability through densification. Inside the brick, refractory powder, carbon powder, and metal carbide are formed at the interface between these powders, bonding to each other, blocking ventilation with the outside, and suppressing oxidation of the carbon in the brick.

Furthermore, by adding a silicone resin, the antioxidant effect can be further enhanced. In this case, fibrous silicon oxide (Sil) is produced as a thermal decomposition product when the temperature rises during use.
It is thought that 1) is generated on the surface of the brick in contact with the atmosphere and suppresses the oxidation of carbon in the brick. Furthermore, by adding silicone resin or the like, it is possible to improve the strength of the oxidized layer by promoting sintering by SiO2 in the oxidized structure on the surface of the brick.

The amount of the silicone resin added is 1 to 10 parts by weight, preferably 1 to 7 parts by weight. The amount of silicone resin added is 1
If it is more than 0 parts by weight, the bonding strength of the brick structure due to thermal decomposition of the silicone resin will be significantly reduced at high temperatures when the bricks are used, and if it is less than 1 part by weight, no sufficient effect will be observed.

In the present invention, in addition to the above, boron nitride (BN), silicon carbide (StC), sodium silicate, and sodium silicofluoride that form the glass layer can be added to improve oxidation resistance.

By adding carbonaceous fibers, the mechanical strength of the material can be improved. Also, as mentioned above,
Addition of metal aluminum powder, silicone powder, etc. can improve mechanical strength by forming carbides in the brick matrix.

Here, the carbonaceous fiber used has a diameter of 0.2f.
1 or less, and the length is 5W or less. If the size is larger than this, molding becomes difficult due to its elasticity, so preferably the diameter is 0.1 m or less and the length is 2 to 3 nm. In addition, the amount of this carbonaceous fiber added is 0.5 to 3 parts by weight,
More preferably, it is 1 to 3 parts by weight. If 3 parts by weight or more is added, the entanglement of fibers becomes noticeable during kneading, resulting in segregation and corrosion.

〔Example〕

The blending ratio of bricks in the examples and comparative examples of the present invention was
Shown in the upper column of the table. For trial production of bricks, each compound was kneaded with the addition of phenol resin or pitch. In addition, to prevent lamination during molding,
The potting soil using phenol resin was heat treated in a hot air dryer maintained at 60°C so that the volatile content became the value shown in Table 1. When pitch is used as pine powder, kneading is carried out by heating the blended raw materials from the bottom of the mixer with a burner and maintaining it at about 120°C, so that the volatile content measurement value becomes the value shown in Table 1. I made it.

For molding, a 500 ton friction press was used to mold an SN plate for a tandem dish. The molded bricks using phenol resin were held at 180° C. for 1 day to undergo a hardening treatment. The molded bricks using pitch were buried in coke pleat and heat treated at 500°C for 5 hours.

The quality characteristics of the SN plate produced in this way were determined as follows.
Shown in the middle column of the table. Note that the physical property values were determined by the usual method for refractories. Characteristic values were measured in the following manner.

■Thickness of oxidized layer: Two specimens of 30x30x30 were cut out from a prototype brick, and the specimens were placed in an electric furnace in an air atmosphere maintained at a predetermined temperature and heat-treated for 3 hours. The thickness of the oxidized layer was measured at the cut surface at the center of the height during the heating test.

■Amount of wear: Two specimens each measuring 30 x 30 x 30 m+ were cut out from a trial brick, placed in a rotary furnace heated by an oxygen-propane burner maintained at a predetermined temperature, and rotated while heating for 1 hour. The amount of wear was measured from the volume change of the specimen before and after wear.

The volume of the specimen was measured by the mercury displacement method.

■ Molten steel corrosion resistance index: 16 when the sample is lined in a high frequency furnace
After conducting a molten steel erosion test at 50°C for 3 hours, the center of the sample was cut in the longitudinal direction and the erosion area on the cut surface was measured.The erosion area of Comparative Example 1 was set as 100 and the relative erosion area between each sample was The value was determined and used as the molten steel corrosion resistance index.

Three cents each of the trial bricks of Comparative Example 1 and Examples 1 to 9 were used in actual machines as SN plates for tundishes. When using the actual machine, one charge (hereinafter abbreviated as ch) is defined as one charge of molten steel (approximately 280 tons) poured into the mold.
ch. After continuous injection, the slag was discharged, the nozzle hole was cleaned with an oxygen jet, and 5 channels of continuous reuse casting were performed (total of 10 channels of casting).

After use, the container was collected and observed, and as a result, it was found to be in a damaged state as shown in the lower column of Table 1. As a result, it was possible to suppress erosion of the inner surface of the nozzle and the edges of the nozzle hole, oxidation of the sliding surface, and metal entrapment, and to reduce surface roughness. In all cases, the occurrence of cracks was relatively small and did not become the main reason for the scrapping of the SN plates.

It can be said that a product with less erosion damage on the nozzle inner surface and nozzle hole edge, and less oxidation and surface roughness on the sliding surface can be cast many times, and from this point of view, Examples 1 to 9 are better than conventional products. It is judged that durability has improved.

(Left below) [Effects of the Invention] As described above, the SN plate of the present invention is produced by adding carbon fiber, boron carbide, or chromium carbide to the conventional carbon-containing non-burning bottom material, or by adding silicone resin powder. By adding phenol resin or pitch as a binder, it was possible to improve the oxidation resistance.

As a result, it was possible to reduce melting damage on the nozzle inner surface and the nozzle hole edge, to prevent metal from getting caught in the sliding surface, to reduce surface roughness, and to improve durability.

Claims (2)

[Claims] (1) A mixture of alumina as a refractory aggregate, carbon, and fine metal powder, with a diameter of 0.2 mm or less and a length of 1 to 5 mm.
0.5 to 3 parts by weight of carbonaceous fiber of mm, 0.5 to 3 parts by weight of boron carbide, 0.5 to 10 parts by weight of chromium carbide, and phenol resin or pitch as a binder, kneaded, and molded. , an unfired sliding nozzle plate brick characterized by being heat-treated at 700°C or less. (2) 1 to 10 silicone resin powders with a particle size of 1 mm or less
The unfired sliding nozzle plate brick according to claim 1, wherein the unfired sliding nozzle plate brick is added in an amount by weight.