KR950002334B1 - Process for the preparation of refractories - Google Patents

Abstract

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Description

Method for manufacturing refractory nozzles for continuous casting

1 and 2 are cross-sectional views showing embodiments of nozzles obtained by the method of the present invention.

* Explanation of symbols for main parts of the drawings

1: Material of the present invention 2: Al ₂ O ₃ -C material

3: ZrO ₃ -C material 4: discharge hole

5: internal study

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an immersion nozzle for use in continuous casting operation of steel, and more particularly, to a continuous casting immersion nozzle refractories in which the alumina adhesion of the nozzle inner hole wall is suppressed and the closing of the inner hole is prevented. It is about a manufacturing method.

Immersion nozzles used for continuous casting of steel are connected to supply molten steel from tundish to mold, and at the same time molten steel during oxidation prevention and injection of molten steel The function of preventing the disturbance of (), the rolling of the slag (slag) and the like is achieved. In addition, it is a member that reduces the non-metallic inclusions in the cast steel and plays an important role in improving the quality.

Immersion nozzles have very strict requirements for anti-spalling, abrasion resistance, corrosion resistance, and the like, and alumina-graphite is widely used as a material satisfying these requirements. In addition, a structure in which a ZrO ₂ -C material having a high corrosion resistance is installed around the powder line portion of the nozzle outer periphery is also widely used.

One of the problems with the immersion nozzle in continuous casting operation is the blockage of the hole in the nozzle due to the adhesion of alumina. Particularly, in aluminum-killed steel and aluminum-silicon-killed steel, non-metallic inclusions such as alumina, which is a deoxidation product in molten steel, adhere to the inner wall of the immersion nozzle, around the discharge hole, and the like. It gradually grows and thickens, and often closes the nozzle. This nozzle clogging reduces the immersion nozzle's useful time and, if the deposit is trapped in the molten steel, causes deterioration of the product.

In order to prevent nozzle clogging, a method of blowing an inert gas such as argon into the nozzle inner cavity surface to prevent adhesion of alumina or the like is widely practiced. However, continuous casting in this method also results in adhesion and growth of non-metallic inclusions such as alumina, which leads to blockage, and also includes a running cost as a preventive measure. In addition, depending on the type of steel, gas blowing itself may be undesirable in a product, and development of a nozzle material which is hard to adhere to alumina has been studied.

As an example of an immersion nozzle material in which alumina adhesion is unlikely to occur, a nozzle made of CaO-C material mainly made of lime clinker and carbon is disclosed in Japanese Patent Laid-Open No. 56-165548. By means of this, lime clinker in the material is a low melting point material such as to react with the alumina to be precipitated in the _{steel, CaO · Al 2 O 3,} 3CaO · Al 2 O 3, because the flow does not stop on the inner wall surface of the nozzle, the nozzle It is said that it is effective for the prevention of occlusion. However, this CaO-C material is easy to produce alumina in steel and the above-mentioned calcium-aluminate, so that the melting rate is large, which is not suitable for long time use such as continuous casting. In addition, since the lime clinker is formulated, there is a drawback that it is easy to extinguish during production, product storage and use.

Japanese Laid-Open Patent Publication No. 59-19075 and Japanese Laid-Open Patent Publication No. 62-288161 propose a continuous casting nozzle made of a raw material obtained by combining calcium zirconate-based clinker and carbon. The former is 40-93% by weight of calcium zirconia-based clinker obtained by mixing 3-35% by weight of calcia in zirconia and calcining at 1600 ° C. or higher, 5-50% by weight of graphite, and silicon metal. ) It is composed of 2-13% by weight.

This nozzle aims at improving the corrosion resistance to mold powder. The latter is a raw material composition of 20-95% by weight of calcium zirconate-based klinger, 5-50% by weight of graphite, and 0-1% by weight of metal silicon. The calcium zirconate-based clinker of this nozzle contains 16-35% by weight of CaO, 0.5-5% by weight of one or two or more of the oxides of Group III and Group IV elements, and CaZrO ₃ as a mineral composition. I am doing it.

The nozzle refractory materials which can be seen in Japanese Patent Application Laid-Open No. 59-19075 and Japanese Patent Laid-Open No. 62-288161 are all composed of calcium zirconate-based clinker, graphite, and metal silicon. However, even when a small amount of metal silicon is added, it reacts with C in the material at the time of use to produce β-SiC, thereby improving strength and reducing the diameter of the fine pores, thereby improving corrosion resistance. There is a tendency to deteriorate the spalling resistance by raising. Since this property is likely to be associated with a fatal defect as a nozzle refractory for continuous casting, the addition of metal silicon is undesirable.

In order to express desired corrosion resistance without addition of metal silicon, in the method of the present invention, ZrO ₂ -CaO-C material or ZrO ₂ -CaO- MgO-C material in which ZrO ₂ or MgO is bonded to CaO-C is used. It was possible to reduce adhesion of alumina without reducing corrosion resistance. As the CaO source, fire-extinguishing resistance was obtained by adding 15-31 wt% of CaO to ZrO ₂ and electrolytically melting it into a cubic (equal, equiaxed, ZrO ₂ + ZrCaO ₃ ) form. It was also possible to significantly improve sex.

In the present invention, 15-50% by weight of CaO is added to ZrO ₂ as a basic raw material, and the Cubic ZrO ₂ + ZrCaO ₃ forms formed by electrolysis are arranged in a predetermined particle size, and used as a refractory raw material.

This electrolytic raw material is more excellent in fire resistance than the sintered clinker as a raw material, and a dense structure can be obtained. Thus, even when a refractory material is used, excellent corrosion resistance is obtained.

The present invention reacts CaO in the electrolytic raw material of the nozzle composition with alumina in the molten steel in contact with the nozzle to produce a low melting point product of calcium aluminate. The low-melting point is washed by the flow of molten steel, and the surface is renewed by imparting proper melting loss, thereby preventing the growth of adhered alumina.

As described above, in the present invention, it is conditional to produce a suitable low melting point on the surface of the refractory. Therefore, if excessive melting damage progresses, the solvent resistance is impaired. It becomes important.

In addition, in order to make the strength sufficient without the addition of metal silicon, the present invention uses a pitch of 5-15% by weight (externally added) and 2-6% by weight (externally-added) phenolic resin as a binder to provide high strength. sports come ringseong is excellent, and have gained a refractory material of a thin small, good corrosion resistance, ZrO ₂ -CaO-C-based diameter of the nozzle hole.

In addition, by combining magnesia or B ₄ C (boron carbide) that is grained with the grained ZrO ₂ -CaO-C-based material, the alumina adhesion preventing function can be improved without impairing the corrosion resistance.

Here, the raw material of ZrO ₂ -CaO as the main material is electromelted, and its composition is completely in the form of cubic ZrO ₂ and ZrCaO ₃ . Simply sintering a mixture of ZrO ₂ and CaO at a temperature of about 1600 ° C. may cause free CaO to remain, resulting in insufficient fire resistance. In addition, the amount of CaO component in the electrolytic raw material is 15-31 wt%, the amount of CaO is less than 15 wt%, so that CaO is not sufficiently precipitated from the electrolytic raw material and is produced by reacting with alumina in molten steel. The amount of calcium aluminate is also small, and alumina adhesion cannot be prevented sufficiently. When it exceeds 31% by weight, all of CaO does not react with ZrO ₂ when it is electromelted and does not become ZrCaO ₃ , and free CaO remains to cause fire resistance deterioration. Table 1 shows the comparative results of the fire resistance of various ZrO ₂ -CaO-based raw materials.

TABLE 1

The test of Table 1 is the result of having hold | maintained for 48 hours at the temperature of 35 degreeC, and 90% of humidity (clinker baked at 1600 degreeC for 5 hours).

The electrolytic raw material is pulverized to a particle size of 0.2 mm or less to adjust the particle size. Graphite to be combined with this particle size-adjusted electrolytic raw material is usually used in the form of scale graphite, and 10-50% by weight is added to impart spalling resistance. When the amount of graphite added is less than 10% by weight, a problem occurs in the spalling resistance, and when the amount is more than 50% by weight, the above-mentioned range is preferable because the corrosion resistance is deteriorated.

In the nozzle refractory of the present invention, as a preventive measure against alumina, CaO in the nozzle composition reacts with Al ₂ O ₃ in molten steel to form a low melting point calcium aluminate, and the low melting point is melted and removed. Formation of calcium aluminate, which is a low melting point, generally leads to dissolution. As a countermeasure, it is possible to increase the strength of the material and to reduce the diameter of the thin hole. The addition of metal silicon improves the strength, but its addition is not preferable from the viewpoint of spoiling resistance.

In the present invention, as an external addition to the refractory composition, a pitch of 5 to 15% by weight (preferably 10 to 15% by weight) and phenolic resin to 2 to 6% by weight (preferably 4 to 6% by weight) are added. By this, highly refractory nozzles have been obtained. The pitch used here may be either coal or petroleum, and various softening points may be used over a range of 70 to 450 ° C, but the volatilization amount is preferably 5% or less. The reason for this is that when the volatile content exceeds 5%, in the dissociation of the volatile content during firing, the amount is large, so that the molded body may expand, causing weakening of the composition. The phenol resin is added in an amount of 2 to 6% by weight, but when it is less than 2% by weight, the diameter of the fine pores after firing is about 1 µm, and when it exceeds 6% by weight, the volatile content is large, so that cracks occur during firing. There is a lot of expansion. Therefore, as the addition amount of the phenol resin, the size of the diameter of the fine pores can be made about 0.5 µm by using 4 to 6% by weight, so this range is preferable.

In these additions, a fine powder may be mixed, and then a phenol resin may be added. However, a pitch is added to the ZrO ₂ -CaO electric melt, and the mixture is kneaded while dissolving the pitch at a temperature equal to or higher than the softening point, and then aggregated. It is preferable to use a granule coated with a pitch around and to add a phenol resin after cooling. According to this method, the periphery of each oxide particle is covered with carbon, and the resistance to thermal shock is increased.

Next, the larger the amount of CaO, the greater the effect of preventing nozzle clogging due to alumina adhesion, while increasing the melting loss speed. In the present invention, magnesia may be bonded to an electrolytically melted ZrO ₂ -CaO raw material in addition to the above-described constitution in order to improve the corrosion resistance without lowering the alumina adhesion preventing function. In order to improve the corrosion resistance can be considered to be added to ZrO ₂ in addition to MgO. However, the simple addition of ZrO ₂ improves the corrosion resistance, but is not preferable because it lowers the alumina adhesion preventing function. The addition of MgO improves the corrosion resistance and prevents alumina adhesion from the nozzle pore surface by CO gas generated by the following MgO-C reaction.

MgO (solid) + C (solid) → Mg (gas) + CO (gas)

That is, addition of MgO makes it possible to improve corrosion resistance, suppressing the fall of alumina adhesion prevention function.

The magnesia used herein may be any of electrolytic magnesia, sintered magnesia, and natural magnesia, but is preferably high purity and has a grain size of 0.2 mm or less. The amount of magnesia can be selected according to the melt damage predicted by the conditions of use of the nozzle, and the mixing ratio is 10 to 80% by weight of the electrolytically melted ZrO ₂ -CaO raw material and 10 to 50% by weight of graphite. Magnesia is 10 to 80% by weight, but 30 to 60% by weight is preferred.

In addition, in the production of these nozzles, by adding 0.1 to 3% by weight of boron carbide to the compounding, the strength and the oxidation resistance after firing can be improved. For this reason, the melt loss by the wear of molten steel improves, and also the oxidation resistance with respect to the oxygen in molten steel is improved, and corrosion resistance can be improved. As addition amount of boron carbide, less than 0.1 weight% is too small, On the contrary, when too much, since corrosion resistance deteriorates, the range of 0.1 to 3 weight% is preferable.

In addition to the above conditions, it was confirmed in particular that the granularity of raw materials other than graphite had a great influence on the degree of alumina adhesion and damage resistance. In other words, the surface of the nozzle refractory of the present invention is dense and smooth, so that alumina in molten steel adheres to the surface smoothly, and corrosion resistance is also improved.

The particle size of aggregates such as Al ₂ O ₃ , ZrO _{2, and} SiO ₂ used in conventional immersion nozzles is usually 1 mm or less, in most cases 0.5 mm or less, and as a refractory, the particle size composition belongs to a thin class. This is being taken. In the present invention, by making the particle size of the ZrO ₂ -CaO electrofusion raw material or magnesia to be blended into 0.2 mm or less, preferably 0.149 mm (100 mesh) or less, a compact and smooth nozzle refractory is obtained. If the nozzle surface is rough and unevenness is severe, nonmetallic inclusions in the molten steel are easily caught and attached, but the smooth surface provides an effect of suppressing physical adhesion. In addition, since the physical properties are also improved by decreasing the particle size of the nozzle refractories, such as small particle size, it is effective in preventing melt loss (mainly due to wear) caused by molten steel. Since graphite itself is flexible, it is not necessary to limit granularity.

Therefore, the method for producing the continuous casting immersion nozzle refractory body of the present invention is electrolytic melting of ZrO ₂ to which 15 to 31% of CaO is added as a weight ratio, and the resulting mineral is composed of an electrolytic raw material consisting of equiaxed ZrO ₂ and ZrCaO ₃ . 50 to 90% by weight and 10 to 50% by weight of graphite were pulverized. The mixture was pulverized and adjusted to a particle size of 0.2 mm or less, and 10 to 50% by weight of graphite was added. The phenol resin of -6 weight% is added, it knead | mixes and press-forms, it is made to dry, and it bakes in a non-oxidizing atmosphere.

In addition, 10 to 80% by weight of the particle size-adjusted electrolytic raw material consisting of the coaxial ZrO ₂ and ZrCaO ₃ described above, 10 to 50% by weight of graphite and 10 to 80% by weight of magnesia particle size adjusted to 0.2 mm or less To this mixture, a pitch of 5 to 15 wt% may be added by external addition, and 2 to 6 wt% phenol resin may be added by external addition, followed by the same. Furthermore, boron carbide is added and blended to the mixture of the particle size adjusted electrolytic raw material and graphite or the mixture of the electrolytic raw material and graphite and magnesia as the above-mentioned equiaxed ZrO ₂ and ZrCaO ₃ , and then mixed. It can also be performed similarly including addition of a binder.

The immersion nozzle obtained by the method of the present invention reacts alumina (Al ₂ O ₃ ) in the molten steel with CaO in the composition material of the immersion nozzle to produce calcium aluminate as follows.

x CaO + y Al ₂ O ₃ → x CaOy Al ₂ O ₃

x CaO · y Al ₂ O ₃ of calcium aluminate, for example a low-melting water such as _{12CaO · 7Al 2 O 3, 3CaO} · Al 2 O 3, standing apart in the molten steel flowing through the nozzle inner hole, improves the pitting wall update In this state, the alumina does not adhere and grow, and nozzle clogging can be prevented.

EXAMPLE

In the following, one specific embodiment of the present invention will be described.

The immersion nozzle was manufactured by the mixing | blending shown in Table 3 using the raw material shown in Table 2. After kneading the required amount of each raw material, it was molded at a pressure of 1200 kg / cm ² by a rubber press, dried at about 260 ° C., and calcined at 1,000 ° C. under a non-oxidizing atmosphere. The physical properties and characteristic values of the obtained nozzle refractory were merged and shown in Table 3.

In addition, the measurement was made with the following method.

(a) spalling test

From the nozzle shape, a cylindrical test piece having an outer diameter of 200 mm and a length of 250 mm was cut out, and then subjected to a 1400 ° C x 1 hr in a vacuum machine. After heating, the mixture was cooled with water and the presence of cracks was observed. (Circle) and a thing with a crack were evaluated by x.

(b) Alumina adhesion test

Cut 20 x 20 x 150 mm specimens and immerse them in a high frequency furnace in which 5 kg of steel was dissolved. Then, 10 g of aluminum was added immediately after immersion, 15 minutes and 30 minutes, and the alumina adhesion thickness after 60 minutes was measured. It was. (Circle) and the thing with 0.5 mm or less of adhesion, (triangle | delta) and the thing with adhesion of 0.5 mm or less were evaluated by x as the thing without adhesion.

(c) molten steel erosion test

The test piece (50 x 50 x 50 mm) immersed in the molten steel of the high frequency furnace was subjected to a vibration of 1500 cycles per minute with a vibrating device at 1600 占 폚 x 1 hr. Maintained. Melt loss amount (mm) was measured.

(d) other

It was set as the normal refractory test method based on JIS.

NO.1-4 are by this invention, and NO.5-9 is a comparative example.

NO.1 and 2 are cases where the CaO content in the ZrO ₂ to CaO electrolytic melts is different, No. 3 is the addition of boron carbide, and No. 4 is the combination of ZrO ₂ -CaO electrolytic melt and magnesia.

No. 5 is a nozzle refractories of a conventional ZrO ₂ -C material, No. 6 is a ZrO ₂ -CaO electro-melt, but the addition of metal silicon, NO. 7 is a metal oxide in NO. 6 except, NO. 8 is a particle size of the ZrO ₂ -CaO electrolytic melt that is 0.5 mm or less, rougher than Example No. 2 of the present invention, and No. 9 is prepared by adding magnesia to contrast with No. 4 in the present invention.

Considering these results, Comparative Example No. 5 using conventional zirconia that does not contain CaO has many alumina adhesions.

Comparative Example No. 6 in which metal silicon was added to No. 7 is inferior in spobling resistance. The comparative example which does not use pitch and a phenol resin together shows the tendency which is inferior to corrosion resistance. On the contrary, the present invention showed excellent results.

Particularly, in Nos. 1 to 4 of the examples of the present invention, the particle size of the ZrO ₂ -CaO electric melting raw material and the magnesia was 0.15 mm or less. Therefore, even in the case of prolonged alumina adhesion, even in comparison with the comparative example (No. 2 and No. .8, No.4 and No.9) Alumina adhesion was not confirmed, and the result of the erosion test was good, and the effect of reducing the granularity was obtained.

Moreover, in actual nozzle manufacture, although the whole may be made into the material which concerns on this invention, you may make it as shown to FIG. 1 or 2 in consideration of cost, etc. That is, the material 1 of the present invention is disposed in all or a part of the inner cavities 5 and the discharge holes 4, and the remaining part is disposed in the conventional Al ₂ O ₃ -C material 2, in particular in the powder line part. Likewise, the conventional ZrO ₂ -C material (3) was applied.

As another example, as shown in FIG. 2 with respect to No. 3, the inventive material 1 was disposed in the inner cavity 5 at a thickness of 10 mm.

The nozzle was subjected to a practical test as a immersion nozzle between tundish-molds.

As a result, even if the material of Comparative Example No. 5 was closed by alumina occlusion as the use of the 5th charge, it was the 8th order even when any of Nos. 1 to 4 according to the present invention. It was obtained that alumina occlusion did not occur even if the aji was completely cast.

TABLE 2

TABLE 3

The continuous casting immersion nozzle refractories containing the electrolytic melt of zirconia containing CaO of the present invention as a main raw material are more resistant to alumina adhesion than nozzle refractories made of conventional alumina-carbon, zirconia-carbon, or lime-carbonaceous refractories. It shows excellent properties in all of the effects, spalling resistance and fire resistance.

Claims (2)

ZrO ₂ with 15 to 31% CaO added as a weight ratio was electromelted to obtain a mineral of ZrO ₂ + ZrCaO ₂ in equiaxed crystal system, which was then ground and adjusted to a particle size of 0.2 mm or less. In the first step, 50 to 90% by weight of the minerals mentioned above and 10 to 50% by weight of graphite are mixed, and 5 to 15% by weight of pitch and 2 to 6% by weight of phenolic resin ( continuous process comprising a second process of adding a phenol resin to obtain a calcined raw material, followed by a third process of kneading, press molding, and drying the calcined raw material in a non-oxidizing atmosphere. Method for producing a crude immersion nozzle refractory. The method for producing a continuous casting immersion nozzle refractory according to claim 1, wherein boron carbide (B ₄ C) is added in an amount of 0.1 to 3% by weight based on the mixture in the aforementioned second step.

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