JPS6243949B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to casting nozzles such as long nozzles and immersion nozzles used in continuous steel casting. Conventionally, the materials for casting nozzles have mainly been fused silica or alumina-carbon.
The former type of fused siliceous material does not have sufficient corrosion resistance, so its usage is gradually decreasing. On the other hand, the latter alumina-carbonaceous material has excellent corrosion resistance, but has the disadvantage that precipitates from molten steel adhere and accumulate in the nozzle hole, causing blockage of the nozzle hole. It is known to inject Ar/O ₂ gas as a measure to prevent nozzle hole clogging, but manufacturing a nozzle equipped with a nozzle blowing mechanism is complicated and
There were drawbacks such as abnormal erosion at the gas injection point. In order to eliminate the above-mentioned drawbacks of conventional materials, the present inventors first attempted to use magnesia-carbon as a nozzle material. This magnesia-carbonaceous nozzle has already been published in Japanese Patent Publication No. 54-8210 "Immersion Nozzle Composition for Casting" and Ogneupory, No. 11, P22-33,
Nov.1975 "Magnesia Nozzles and Headers"
in Stopperless. Although magnesia has excellent fire resistance and corrosion resistance, it has poor spall resistance, so magnesia alone is not suitable as a nozzle material, but by combining it with carbon, it has improved thermal conductivity and elasticity. Spalling resistance is improved by lowering the ratio, and at the same time, corrosion resistance is further improved by improving the leakage of carbon to molten steel and slag. However, when this material was actually used as a nozzle material, it did not have any significant effects compared to conventional materials in terms of corrosion resistance, hot strength, oxidation resistance, etc.
There was still a lot of room for improvement before it could be put into practical use.
Furthermore, recent continuous casting technology is moving toward multiple casting in which multiple charges are cast using a single nozzle, and there is a stronger desire than ever to extend the service life of the nozzle. Therefore, in order to improve the physical properties of magnesia-carbon nozzles, the present inventors used glasses such as water glass, silicate-alkali glass, sodium phosphate, lead glass, and borosilicate glass, Al, Si, Cr, Ti, etc. In addition to metal powders such as Mg, we conducted repeated experiments with the addition of various additives. Among these, those with glass added have a glass layer covering the refractory particles and carbon particles, which blocks air flow and exhibits an antioxidant effect, but at the same time, corrosion resistance and hot strength are significantly reduced. This is not preferable because it lowers the temperature. Furthermore, although metal powder added had an anti-oxidation effect, when the metal powder came into contact with oxygen or carbon particles, the physical properties suddenly changed, and a decrease in spalling resistance was observed. However, on the other hand, we discovered that products containing boron carbide not only improve oxidation resistance, but also have remarkable effects on corrosion resistance and hot strength that could not be predicted at first by limiting the addition ratio to a specific range.
This completes the present invention. The first invention of the present invention is composed of 90 to 60 parts of magnesia, 10 to 40 parts of carbon, and 0.05 to 0.35 parts of boron carbide in weight proportions.
This is a casting nozzle characterized by comprising: The second invention uses 30 to 90 parts of zirconia and 15 to 90 parts of carbon at the part of the nozzle's outer circumferential surface that comes into contact with the molten steel surface.
A casting nozzle according to claim 1, which is made of 30 parts of refractory material. The addition of boron carbide to carbon-containing refractories is already known from JP-A-55-34664. According to this, in carbon-containing refractories such as mullite-alumina-carbonaceous refractories shown as specific examples, the amount of boron carbide added is 0.4 to 2.0% by weight, but in experiments conducted by the present inventors, magnesia It has become clear that in carbonaceous nozzles, corrosion resistance and hot strength are significantly improved when the addition ratio is limited to 0.35 parts by weight or less. For these reasons, the carbon-containing refractory disclosed in JP-A-55-34664 is not a magnesia-carbon basic refractory but an acidic or neutral refractory such as mullite, alumina, or silica. Next, some of the experiments that led to the present invention will be shown. As shown in Table 1, magnesia-carbon nozzles were manufactured in which the proportions of magnesia clinker, carbon, and binder were kept constant, and only the proportion of boron carbide added was varied, and the physical properties of each were measured. All the formulations shown in Table 1 were thoroughly kneaded with a mixer and then subjected to isostatic press (1000Kg/cm ² )
After molding it into a nozzle shape, it was reduced and calcined at a temperature of 1100°C in a coke breath. Note that the porosity and room temperature bending strength were also measured for those re-fired at 1450°C. Porosity: Based on JIS-R2205. Bending strength: Cut out a 40 x 20 x 150 mm test piece,
Measured over a 100mm span. Oxidation loss: A test piece of 30 x 30 x 30 mm was cut out and heated in an electric furnace at 1450°C for 2 hours, and the difference in weight before and after heating was defined as the oxidation loss. Amount of erosion loss: A test piece cut into a size of 20 x 20 x 150 mm was immersed in molten steel melted in a high frequency furnace for 2 hours, and the dimensions of the erosion loss were measured.

【table】

[Table] Figures 1 to 4 are graphs showing the correlation between the amount of boron carbide added and the magnesia-carbon refractory based on the results in Table 1. Figure 1 shows the porosity, which is extremely low when the amount of boron carbide added is 0.35 parts by weight or less.
When added in excess of this value, the level gradually increases to a level that is equal to or higher than that without any additive. Figure 2 shows the bending strength at each temperature.At room temperature, even an amount of 0.05 parts by weight is sufficiently effective, and there is almost no change when adding more than 0.35 parts by weight. and gradually decreases. In addition, with regard to hot bending strength at 1450°C, a remarkable effect was observed even with a small amount of addition, and the strength gradually decreased from a peak of 0.1 part by weight. Products refired at the same temperature at 1450°C also have almost the same tendency. The oxidation loss shown in FIG. 3 is effective even when added in an extremely small amount of 0.05 parts by weight, and there is almost no change even if more than that amount is added. The amount of erosion shown in Figure 4 is effective from 0.05 parts by weight.
The least amount is 0.1 to 0.3 parts by weight, and the effect of addition is almost negated if it exceeds 0.35 parts by weight. As is clear from the above results, magnesia
In carbonaceous refractories, even a very small amount of boron carbide, 0.05 parts by weight, is sufficiently effective, and when added to carbon-containing refractories at 0.4% by weight or more, -Conversely, physical properties deteriorate in carbonaceous nozzles. Comprehensive judgment of the above test results revealed that the most effective amount of boron carbide added is 0.05 to 0.35 parts by weight. In addition to the above-mentioned effects, the nozzle of the present invention also has the effect of preventing nozzle clogging, as shown in the examples described below. Possible effects to prevent nozzle clogging are:
During high-temperature operation, the magnesia-carbon nozzle continuously generates gas through the reaction shown below and blows the gas into the nozzle hole, which prevents the accumulation of deposits that can cause nozzle blockage. Because it does. MgO (s) + C (s) → Mg (g) + CO (g) MgO (s) → MgO (g) In this case, the gas is blown out by the reaction of the nozzle material, so it must be done uniformly over the entire surface of the nozzle hole. Therefore, there is no possibility of localized abnormal melting loss caused by blowing gas from a part as in the conventional case. Next, the components constituting the nozzle of the present invention and their proportions will be described. As magnesia, purity is 90% or more, preferably
Use 95% or more sintered or electrofused magnesia clinker, and the proportion shall be 60-90 parts by weight. If it is less than 60 parts by weight, corrosion resistance deteriorates, which is not preferable, and if it exceeds 90 parts by weight, sporin resistance decreases. In addition, since fused magnesia clinker has excellent corrosion resistance, it is more preferable to use sintered magnesia clinker as the coarse particles and fused magnesia as the fine particles. The proportion of carbon is 10 to 40 parts by weight, and the carbon source is exemplified by flaky graphite, earthy graphite, carbon black, pitch, pitch coke, anthracite coke, etc., but the proportion of carbon is 10 to 40 parts by weight. It is preferable to use more than 1 part. If the proportion of carbon is less than 10 parts by weight, spalling resistance decreases, and if it exceeds 40 parts by weight, corrosion resistance deteriorates. The amount of boron carbide is 0.05 to 0.35 parts by weight. If it is less than 0.05 part by weight, no effect will be obtained, and if it exceeds 0.35 part by weight, the amount of expensive boron carbide used will increase, although the improvement in corrosion resistance and hot strength will be slight.
Moreover, this is not preferable because it increases the economic burden. Since this boron carbide is added in a small amount, it is preferable that the purity is 95% or more and the particle size is 50μ or less for uniform dispersion and stable effect. Binders used in nozzle manufacturing include organic binders such as tar, pitch synthetic resin, pulp waste liquid, ethylene glycol, polypropylene, polyvinyl alcohol, CMC, alginates, silicates, and acrylates, or phosphates and silicic acids. Inorganic salts such as salts, sulfates, chlorides, carbonate silica sols can be used. Furthermore, conventional dispersants, peptizers, lubricants, etc. may be added. Among the binders, those with a high residual carbon content, such as tar, pitch, and synthetic resin, also serve as carbon sources. The nozzle of the present invention is mainly composed of the above-mentioned components, and other components such as SiO ₂ and Fe ₂ O ₃ are kept as small as possible because they react with magnesia and cause a decrease in physical properties. Must be less than parts by weight. In addition, silicon carbide, silicon nitride,
A certain amount of carbides or nitrides such as boron nitride may be added, but this will not reduce the effect of the present invention10
Must be less than parts by weight. By the way, it is known that when the lower half of a casting nozzle, such as an immersion nozzle, is immersed in the molten steel in the mold, the parts that come into contact with the molten steel surface on which powder is floating can suffer local melting damage. There is. In conventional alumina-carbon nozzles, this melting loss is particularly severe, and even if other parts are hardly melted, this localized melting loss can end the life of the nozzle. Although the magnesia-carbonaceous nozzle of the present invention has extremely less erosion loss than conventional nozzles, it is still somewhat inferior to the overall erosion loss. If zirconia-carbonaceous refractories are used in the parts that come into contact with the surface of the molten steel, they will exhibit excellent corrosion resistance due to the synergistic effect with the magnesia-carbonaceous material of the main body, and will not block the nozzle, making it smooth and stable. Can be used for casting. FIG. 5 shows an immersion nozzle in which the zirconia-carbonaceous refractory 2 is provided at the part of the nozzle body 1 that comes into contact with the molten steel surface, and FIG. This is an example of applying this technology to a specific location. As described above, the life of the nozzle of the present invention is further extended when the part in contact with the molten steel surface is made of a multilayer structure made of zirconia-carbonaceous refractories. The component ratio of the zirconia-carbonaceous refractory mentioned here is preferably 70 to 30 parts by weight of zirconia and 30 to 15 parts by weight of carbon. Appropriate amounts of one or more of boron, boron oxide, boron nitride, borosilicate glass, lime, dolomite, chromium oxide, etc. may be added. Next, Table 2 shows examples of the present invention and comparative examples. In both Examples and Comparative Examples, the formulations shown in the table were sufficiently kneaded with a mixer, then molded into a submerged nozzle shape using an isostatic press (1000 Kg/cm ² ), and then heated at 1100°C in a coke breeze.
It was reduced and fired at a temperature of . The porosity and bending strength were measured in the same manner as in Table 1 above, and the compressive strength was measured using an Amsler test device. The actual machine test was conducted in a continuous casting operation of aluminum killed steel in a steel pot with a capacity of 200 tons.

[Table] The mechanism by which the nozzle of the present invention shows good results with the addition of a small amount of boron carbide is not clear, but as is clear from the physical property values and actual test results in Table 2,
All of the nozzles of the examples of the present invention have remarkable effects on corrosion resistance and hot strength, and also have the effect of preventing clogging of the nozzle hole, which magnesia-carbon nozzles originally have, and contact with the molten steel surface. In addition, since boron carbide is an extremely expensive raw material, it is economically advantageous that the effect can be obtained with a small addition amount as in the present invention. In comparison, Comparative Examples 1, 2, and 3 contain boron carbide in an amount equivalent to that of the present invention, and other components are not satisfied, and Comparative Example 4 has other components equivalent to those of the present invention. Both Nos. 5 and 6 suffered from melting damage and cracking, making it impossible to cast smoothly. As described above, since the magnesia-carbon nozzle of the present invention has a long service life, it is of great value for continuous casting technology, which has recently become increasingly prone to multiple casting.

[Brief explanation of the drawing]

Figures 1, 2, 3 and 4 are graphs showing changes in the amount of boron carbide added and physical properties in a magnesia-carbon nozzle, and Figures 5 and 6 are examples of embodiments of the nozzle of the present invention. FIG. 1: Nozzle body, 2: Zirconia-carbonaceous refractory.

Claims (1)

[Claims] 1. 90 to 60 parts of magnesia and 10 to 60 parts of carbon by weight
40 parts, and 0.05 to 0.35 parts of boron carbide. 2. The casting nozzle according to claim 1, wherein the portion of the outer peripheral surface of the nozzle that comes into contact with the molten steel surface is made of a refractory material consisting of 30 to 90 parts of zirconia and 15 to 30 parts of carbon.