JP5166302B2 - Continuous casting nozzle - Google Patents

Description

  The present invention relates to a continuous casting nozzle used for continuous casting of molten steel, in particular, continuous casting of aluminum killed steel.

  In recent years, aluminum killed steel cast as high-grade steel such as thin plates has become more stringent in quality, and upper nozzles, plates, lower nozzles, immersion nozzles, etc. used when pouring into molds from tundish in continuous casting Many efforts have been made to prevent alumina from adhering to the inner hole of the continuous casting nozzle.

  Alumina adhering to the inner hole of the continuous casting nozzle coalesces into large inclusions, which are taken together with the molten steel flow into the slab and become defects in the slab, reducing the quality. Further, when alumina or the like is deposited in the inner hole, the nozzle hole becomes narrow, so that the continuous casting nozzle has a short life.

  As an example of a measure for preventing the alumina from adhering to the inner hole of the continuous casting nozzle, a technique is adopted in which argon gas is blown into the molten steel from the inner surface of the nozzle to physically prevent the alumina from adhering. However, in this method, if the amount of argon gas blown is too large, bubbles are taken into the slab and become pinholes, resulting in slab defects. Therefore, there is a restriction on the amount of gas blown in, so that it cannot be a sufficient measure.

  As another effective means for preventing the adhesion of alumina, application of a refractory containing CaO can be mentioned. CaO reacts with the adhered alumina to form a low-melting substance, and this reaction product is easily flowed by the molten steel flow, so that the adhesion of alumina can be suppressed. There is dolomite clinker as a typical refractory aggregate containing CaO, and by placing a refractory containing dolomite clinker as an inner hole in the inner hole of the nozzle for continuous casting, adhesion of alumina is suppressed, that is, difficult adhesion Can increase the sex. The continuous casting nozzle is generally formed by separately forming a sleeve-shaped inner hole body and a continuous casting nozzle body, and heat-treating the respective molded bodies, and then the inner hole of the continuous casting nozzle body. In this method, a sleeve-like inner hole body is inserted into the gap, and a mortar or the like is interposed in the gap to join.

  For example, Patent Document 1 discloses that the average particle size of a CaO-MgO clinker is set to the graphite content in a refractory for continuous casting that prevents adhesion of alumina mainly composed of graphite and a CaO-MgO clinker (dolomite clinker). It is described that, by controlling together, oxidation of graphite during preheating is prevented, thereby improving the difficulty adhesion more effectively. In Examples, 5 to 35% by mass of graphite of 0.5 mm or less is used.

  On the other hand, in Patent Document 2, the composition is composed of dolomite clinker and magnesia clinker, and the mass% of particles of 1 mm or less in the particle size configuration of dolomite clinker is WD, and the mass% of particles of 1 mm or less in the particle size configuration of magnesia clinker is When WM is set, the ratio of WD / WM is 0.5 or more and 15 or less. Further, when the content mass% of the CaO component is W1 and the content mass% of the MgO component is W2, the ratio of W1 / W2 is 0.00. A continuous casting nozzle is disclosed in which a refractory obtained by adding a binder to a compound of 33 to 3.0 and kneading, molding, and heat-treating is disposed at least in contact with molten steel.

  The magnesia clinker fine powder is moderately dispersed in the dolomite clinker fine powder to reinforce the grain boundaries between the dolomite clinker, and the magnesia clinker dispersed from the dolomite clinker is integrated to provide excellent corrosion resistance. It is said that a layer can be formed.

JP 2004-323265 A International Publication No. 05/087406 Pamphlet

  In the refractory for continuous casting disclosed in Patent Document 1, since the dolomite clinker originally melts due to the adhesion of alumina, there is no problem of clogging due to the adhesion of alumina, but there is a problem that the lifetime is short because the melting damage is extremely large. Furthermore, dolomite clinker has a problem of thermal shock resistance because of its extremely large thermal expansion. For this reason, in the case of Patent Document 1 in which graphite is combined with this dolomite clinker, the deterioration of corrosion resistance due to the further dissolution of graphite into the molten steel is further increased, and the actual use is limited to special applications with a large amount of alumina adhesion. The general alumina adhesion problem cannot be solved. On the other hand, if the content of CaO is reduced by using a magnesia clinker together in order to give priority to corrosion resistance, the service life is reduced due to nozzle clogging due to alumina adhesion.

  The continuous casting nozzle of Patent Document 2 is superior in corrosion resistance to the refractory material of Patent Document 1, but since the graphite raw material is hardly used in the blend, the expansion is very large and the thermal shock resistance is poor. For this reason, a special structure for absorbing expansion is required, and there is a problem that the cost is higher than that of a conventional immersion nozzle.

  As described above, continuous casting nozzles such as immersion nozzles containing dolomite clinker in the inner hole have a problem of short life due to the contradictory relationship between difficult adhesion and corrosion resistance, and only under special conditions. It was used.

  Therefore, an object of the present invention is to enable a continuous casting nozzle containing an inner hole body to contain dolomite clinker so that it can be provided with a balance between difficult adhesion, corrosion resistance and thermal shock resistance.

  The continuous casting nozzle of the present invention is a continuous casting nozzle in which an organic binder is added to a refractory raw material composition, kneaded, and an inner hole body obtained by heat treatment after molding is disposed in the inner hole of the nozzle body for continuous casting. The refractory raw material composition is 10% by mass or less (including 0) of dolomite clinker having a particle size of more than 1 mm, 20 to 90% by mass of particle having a particle size of more than 0.1 mm and 1 mm or less, and a particle size of 0.1 mm or less. Characterized by comprising less than 15% by mass (including 0), 3-20% by mass of graphite having an aspect ratio of 10 or more and a particle size of 500 μm or less, and the balance being a magnesia clinker having a particle size of 1 mm or less. To do.

  In addition, the particle size as used in the field of this invention is shown with the sieve opening (mm) in a JIS standard sieve. For example, a raw material particle having a particle size of 1 mm or less is a raw material particle that has passed through a sieve when the sieve opening is sieved with a 1 mm sieve. In the present invention, 0.1 mm has a sieve opening of 0.105 mm.

In the present invention, it is preferable to use a magnesia clinker having a particle size of 150 μm or less and a SiO ₂ content of less than 6 mass% (including 0).

  Moreover, it is preferable that the mass ratio of CaO / MgO in a refractory raw material mixture shall be 0.3-1.2, and the total amount of MgO and CaO shall be 70-97 mass%.

  Furthermore, it is preferable that the adhesion / melting speed of the inner hole body is within ± 15 μm / min in the rotating test in molten steel.

  The present invention will be described in detail below.

  FIG. 1 shows a schematic diagram of the inner hole structure of the continuous casting nozzle of the present invention. In FIG. 1, a dolomite clinker 1 has a textured structure in which graphite 2 and magnesia clinker 3 are arranged by carbon bonds around them. In use, the alumina in the molten steel and the dolomite clinker 1 come into contact with each other on the surface of the refractory (working surface 4), so that a calcium-aluminate (CA) low melt is formed on the surface of the dolomite clinker 1. Is done.

  In general, alumina in molten steel dissolves up to about 50% as a CA-based low melt with respect to the total amount of the dolomite clinker component and the alumina component dissolved therein at the molten steel temperature, and the dolomite clinker becomes completely liquid phase. This CA-based low-melt material has a low viscosity in the vicinity of a working surface with a high alumina concentration, so a part of it flows out by the molten steel flow, but a part of it is diffused and accumulated in the refractory structure from the dolomite clinker. .

  As a result of various experiments, the present inventors have found that the presence of graphite 2 around the dolomite clinker 1 as shown in FIG. 1 has the effect of controlling the penetration of the CA-based low melt into the refractory deep. did. As a result, by focusing attention on the form of the graphite, the particle size of the dolomite clinker and the magnesia clinker, etc., it was possible to provide a high level of good adhesion, corrosion resistance and thermal shock resistance.

  That is, by using high aspect ratio graphite having a small thickness and a large area, graphite can be uniformly dispersed in the structure with a small amount of graphite used. Therefore, the deterioration of the corrosion resistance due to the use of graphite is suppressed, and the graphite coated around the dolomite clinker becomes a wall against the penetration of the CA-based low melted material into the structure. For this reason, since the inner pore body can always keep the optimum concentration range of the CA-based low-melted product in the vicinity of the surface thereof, the hard adhesion is maintained. In addition, a magnesia clinker having a high corrosion resistance with respect to the CA-based low melted product is used with a particle size of 1 mm or less, more preferably 150 μm or less, and the amount of dolomite clinker with a particle size of 0.1 mm or less is suppressed to less than 15% by mass. Further, by combining with graphite having a higher aspect ratio, diffusion in the refractory structure of the CA-based low melt can be optimized, and corrosion resistance can be improved while maintaining difficult adhesion. In addition, if the use of a dolomite clinker having a particle size of 0.1 mm or less is supplemented with a magnesia clinker, the amount of a dolomite clinker having a particle size of 0.1 mm or less can be made zero.

  The aspect ratio of graphite is 10 or more, preferably 13 or more. When the aspect ratio is less than 10, the covering effect is reduced, and the effect of preventing the penetration of the CA-based low-melting product into the refractory deep portion becomes insufficient, so that the difficult adhesion is lowered. However, when the particle size (area) of graphite having an aspect ratio of 10 or more is too large, the dispersibility is deteriorated, so the particle size is set to 500 μm or less. When the particle size exceeds 500 μm, the coating becomes insufficient due to segregation, and the hard adhesion is reduced.

  Further, when the graphite having an aspect ratio of 10 or more is more than 20% by mass, not only the corrosion resistance is lowered, but also the diffusion of the CA-based low melt into the refractory structure is reduced, and the graphite covering property around the dolomite clinker is reduced. Since it increases too much, the alumina concentration in the dolomite clinker in the vicinity of the working surface easily rises, accompanied by an excessive increase in the liquid phase ratio, and the tendency of erosion increases. Conversely, if the amount of graphite having an aspect ratio of 10 or more is less than 3% by mass, the effect of suppressing the penetration of the CA-based low-melted product into the refractory deep by graphite disappears. Although the phase ratio is not increased and the corrosion resistance is excellent, the blocking prevention effect and the thermal shock resistance are reduced. (The optimum liquid phase ratio in terms of operation is estimated to be 30 to 80%.)

  In the inner hole used for the continuous casting nozzle of the present invention, the refractory raw material composition is mainly composed of raw material particles having a particle size of 1 mm or less. In the present invention, during use, alumina adhesion is prevented by reacting alumina in molten steel with CaO in dolomite clinker near the surface of the inner pore to produce a CA-based low melt. For this reason, if the porosity of the refractory becomes too high, the CA-based low melted product tends to penetrate deeper into the refractory. In addition, when raw material particles such as dolomite clinker and magnesia clinker become too coarse, they fall off in the vicinity of the surface of the refractory during use, or the corrosion resistance decreases due to excessive segregation caused during production. Therefore, by reducing most of the raw material particles (over 90% by mass) to a particle size of 1 mm or less, the above problem can be improved and the corrosion resistance is improved. This is presumed to be because when the raw material particles are small, even if dropping or segregation occurs, the damage is small and the influence is reduced. The raw material particles having a particle size exceeding 1 mm can be used within a range that does not adversely affect the corrosion resistance at a practical level as long as it is 10% by mass or less.

The particle size of the magnesia clinker used is 1 mm or less, but is preferably 150 μm or less, more preferably 10 μm or more and 150 μm or less in consideration of dispersion in the matrix. If it exceeds 150 μm, formation of a magnesia-rich corrosion-resistant layer is inhibited, and the effect of improving corrosion resistance is lowered. If it is less than 10 μm, magnesia clinker is easily digested. In order to improve the corrosion resistance of the magnesia-rich layer, it is also possible to use a magnesia clinker fine powder having a high SiO ₂ content of 6% by mass or less (including 0). When SiO ₂ is more than 6 wt%, the corrosion resistance improving effect is lowered.

  In the inner pore body containing dolomite clinker, the smaller the CaO / MgO mass ratio in the refractory raw material composition, the less CaO amount and the more alumina inclusions are attached. The erosion loss increases and the service life is reduced. However, since the refractory and the molten steel flow are in vigorous contact under actual use conditions, the influence of the molten steel flow is very large on the difficulty adhesion and the corrosion resistance. Therefore, as a result of performing a rotation test in molten steel in which the inventor conducted an evaluation test under the condition that the refractory for the inner hole body is in contact with the molten steel flow, the mass ratio of CaO / MgO is 0.3 to 1.2. In addition, it was found that high adhesion and corrosion resistance can be satisfied at the same time. That is, if it is less than 0.3, adhesion of alumina inclusions becomes excessive, and if it exceeds 1.2, the corrosion resistance decreases.

  The total of MgO and CaO in the refractory raw material composition is more preferably 70 to 97% by mass. If it is less than 70% by mass, the carbon component coming from the graphite and the binder component becomes too much, which is advantageous in terms of thermal shock resistance, but damage due to contact between the molten steel and carbon becomes severe, resulting in a problem of melting loss. On the other hand, if it exceeds 97% by mass, it will be advantageous in terms of resistance to erosion, but the carbon component will decrease, so that the concentration phenomenon on the operating surface of the alumina component supplied from the steel will be less likely to occur. There is a problem in that the phase ratio is lowered and adhesion is likely to occur. The amount of MgO and CaO can be controlled by the use ratio of dolomite clinker and magnesia clinker.

  As described above, the inner porous body containing dolomite clinker is in violent contact between the refractory and the molten steel flow under actual use conditions, and therefore the influence of the molten steel flow is very large on the difficulty adhesion and the corrosion resistance. Therefore, as a result of performing a rotation test in molten steel in which the present inventor conducted an evaluation test under the condition that the refractory for the inner hole is in contact with the molten steel flow, it is excellent when the adhesion / melting speed is within ± 15 μm / min. It was found that it exhibits poor adhesion and corrosion resistance. If the adhesion / melting speed is less than −15 μm / min (if the melting speed is greater than 15 μm / min), the life may be shortened or the inclusions may become defective in the product due to melting. When the erosion rate is higher than 15 μm / min, it tends to be clogged due to adhesion, resulting in a short life.

  According to the present invention, it is possible to obtain a continuous casting nozzle having a good balance of difficult adhesion, corrosion resistance and thermal shock resistance as compared with a continuous casting nozzle using a conventional dolomite-carbonaceous refractory as an inner hole. . For this reason, the lifetime of the nozzle for continuous casting improves.

It is a schematic diagram of the inner-hole body structure | tissue of the nozzle for continuous casting of this invention. It is explanatory drawing which shows the outline of the rotation test method in molten steel. It is explanatory drawing which shows the measuring point of the adhesion and erosion rate in the rotation test method in molten steel. It is a longitudinal cross-sectional view of the immersion nozzle used for the test in a real furnace.

  The continuous casting nozzle of the present invention is manufactured by separately forming the continuous casting nozzle body and the inner hole body, and arranging the inner hole body in the inner hole of the continuous casting nozzle body after heat treatment. The heat treatment may be performed at a low temperature of 100 ° C. to 800 ° C. enough to cure the binder, but may be performed at a high temperature of 800 ° C. to 1300 ° C. at which carbon bonds are formed. As described above, the inner hole body referred to in the present invention refers to a refractory formed separately from the continuous casting nozzle body because it is disposed in the inner hole of the continuous casting nozzle body. In order to arrange the inner hole body in the inner hole of the continuous casting nozzle body, an expansion allowance is provided in order to prevent damage to the continuous casting nozzle body due to thermal expansion of the inner hole body. This expansion allowance can be arranged by employing a known method such as a mortar joint or space.

  As described above, by arranging the preformed inner hole body in the continuous casting nozzle body, the expansion allowance can be ensured reliably. As a result, it is possible to reliably prevent the continuous casting nozzle main body from being split by the thermal expansion of the inner hole body, and to obtain a continuous casting nozzle excellent in thermal shock resistance. Furthermore, even when the inner hole body contains a raw material that reacts with the nozzle body for continuous casting to reduce the durability, the inner hole body is separated by an expansion allowance such as mortar, so that there is an effect of suppressing the reaction.

  In the continuous casting nozzle of the present invention, the proportion of the inner hole body arranged in the inner hole of the continuous casting nozzle body is 50% or more, more preferably, in terms of the area ratio of the total area of the inner holes of the continuous casting nozzle body. 80% or more is more preferable in terms of the effect of preventing occlusion. If it is less than 50%, the blocking prevention effect is insufficient.

  As the mortar used when joining the inner hole body to the nozzle body for continuous casting, a MgO component having a mass strength of 50% by mass or more and an adhesive strength of 0.01 Mpa or more at normal temperature and hot temperature can be used. The joint thickness between the nozzle main body and the inner hole can be 3 mm or less, more preferably 2 mm or less. Thus, by using an appropriate mortar, it is possible to more reliably prevent peeling of the inner pore body during use.

  The dolomite clinker used as the refractory raw material composition of the inner pore body of the present invention is a refractory raw material mainly composed of CaO and MgO, and is generally used as a raw material for refractories such as dolomite bricks. Any raw material can be used without problems. For example, in addition to dolomite clinker obtained by heat-treating natural dolomite mainly composed of about 60% by mass of CaO and about 40% by mass of MgO, a synthetic dolomite clinker prepared in an arbitrary composition using artificial raw materials can be used.

  Examples of the magnesia clinker that can be used in the present invention include electrofused magnesia clinker and sintered magnesia clinker that are generally used for refractories. The purity of the magnesia clinker is not particularly limited, but is preferably 95% by mass or more, more preferably 98% by mass or more.

  In the present invention, graphite having an aspect ratio of 10 or more is used. As graphite having an aspect ratio of 10 or more, expanded graphite can be used. Expanded graphite is a natural scaly graphite that has been acid-treated and then heat-treated to expand the interlayer of graphite. A graphite having an aspect ratio of 20 or more is obtained. Moreover, it may be crushed to reduce the thickness and use a high aspect ratio. Also, natural scaly graphite can be used if it has an aspect ratio of 10 or more, more preferably 13 or more. Natural scaly graphite has an aspect ratio that differs depending on the production area and the crushing treatment after mining, but can be used if the aspect ratio is 10 or more, more preferably 13 or more. Besides these, soil graphite can also be used. Further, in the graphite having an aspect ratio of 10 or more, the thickness is more preferably 20 μm or less. The thinner one is because the coating effect of dolomite clinker is high with a small amount of use. In addition, graphite having a small thickness is more excellent in corrosion resistance. As the aspect ratio of the graphite, an average value obtained by randomly measuring 20 points of the (maximum length / maximum thickness) ratio of the cross section of the graphite particles in the 20-fold field of view by microscopic observation of the graphite cross section was used.

The refractory raw material composition of the inner pore body of the present invention includes 10% by mass (including 0) of dolomite clinker having a particle size of more than 1 mm, 20 to 90% by mass of particles having a particle size of more than 0.1 mm and 1 mm or less, It contains less than 15% by weight (including 0) of 0.1 mm or less, 3-20% by weight of graphite having an aspect ratio of 10 or more and a particle size of 500 μm or less, and the balance comprising magnesia clinker having a particle size of 1 mm or less. Further, a magnesia clinker having a particle size of 150 μm or less and a SiO ₂ content of 6% by mass or less (including 0) can be used.

  However, in addition to these refractory raw materials, metals, boron carbide, etc. that are usually used as refractory raw materials for continuous casting are used for the purpose of reinforcing the connective structure, improving corrosion resistance, improving thermal shock resistance, or preventing oxidation. A borate, a carbide such as silicon carbide, a nitride such as silicon nitride, zircon, zirconia, silica, alumina, alumina magnesia spinel, pitch, tar, and carbon black may be contained in an amount of 5% by mass or less. it can.

  In addition, as an organic binder used by this invention, it is preferable to use what produces | generates a carbon bond by heating, A phenol resin, a furan resin, a pitch, etc. can be used. As the phenol resin or furan resin, a resin whose viscosity is adjusted by diluting with a solvent can be used. The pitch can be used with no problem, either liquid or powder.

  The above refractory raw materials are weighed so as to have the blending ratio of the present invention to obtain a refractory raw material mixture, and an organic binder such as a phenol resin is added to the refractory raw material mixture, kneaded, molded, and heat treated. The inner hole used for the continuous casting nozzle of the invention can be obtained. The inner hole body is generally cylindrical, but an inner hole body obtained by dividing the cylinder into a plurality of parts can also be formed. For forming, CIP, friction press, oil press or the like can be used. Regarding the heat treatment, the heat treatment can be performed at 1500 ° C. or less, but more preferably, the thermal shock resistance during use is sufficiently obtained by heat treatment at 800 ° C. to 1300 ° C. in a non-oxidizing atmosphere. The inner hole body obtained by the heat treatment is disposed in the inner hole of the continuous casting nozzle body to obtain the continuous casting nozzle of the present invention.

  Furthermore, it is more preferable that the inner hole body of the present invention has an adhesion / melting loss rate within ± 15 μm / min in the evaluation by a rotating test in molten steel. The molten steel rotation test is a test method in which a test piece is rotated in molten steel in which alumina is present, and it is possible to evaluate difficult adhesion, corrosion resistance, and thermal shock resistance at the same time. Inner pores with an adhesion / melting rate within ± 15 μm / min are used for steels with many inclusions that tend to cause nozzle clogging compared to conventional dolomite alone or inner pores containing dolomite and graphite. However, it is possible to prevent the nozzle from being blocked for a long period of time, and to have a long-life inner-hole body that satisfies the corrosion resistance without excessive melting loss.

  The characteristic that the adhesion / melting speed of the inner pores is within ± 15 μm / min can be obtained by using the refractory raw material composition disclosed in the present invention and producing it by the above-mentioned production method.

  FIG. 2 shows an outline of the rotating test method in molten steel. In FIG. 2, a state in which a holder 11 holding four test samples 10 at the lower part is immersed in molten steel 13 in a crucible 12 is shown.

  There are four test samples 10 in the shape of a rectangular parallelepiped, which are respectively fixed to the lower four surfaces of the rectangular column holder 11. This test sample 10 is inserted through a mortar into a recess provided in a square column holder 11, and can be removed by pulling it out after the test. The upper part of the holder is connected to a rotating shaft (not shown), and is held rotatably about the longitudinal axis as a rotating shaft.

  The holder 11 has a square shape with a side of 40 mm in the horizontal cross section with respect to the longitudinal axis, the length in the longitudinal direction is 160 mm, and is made of zirconia carbonaceous refractory. The test sample 10 has an exposed portion from the holder 11 having a length of 20 mm, a width of 20 mm, and a length L of 25 mm. Further, the lower end surface of the test sample 10 is attached at a position 10 mm above the lower end surface of the holder. The crucible 12 is made of a cylindrical refractory having an inner diameter of 130 mm and a depth of 190 mm. The immersion depth of the holder 11 is 50 mm or more. The crucible 12 is housed in a high frequency induction furnace 14. Although not shown, the upper surface can be covered.

  In the rotating test in molten steel, the test sample 10 is preheated by holding it on the molten steel 13 for 5 minutes, and then the test sample 10 is immersed in the molten molten steel 13 (low carbon aluminum killed steel). Rotate at an average peripheral speed of 1 m / sec. During the test, the oxygen concentration is maintained in the range of 10 to 50 ppm by adding aluminum into the molten steel 13, and the temperature is maintained in the range of 1550 to 1600 ° C. After 3 hours, the sample is pulled up and the adhesion / melting speed (μm / min) of the test sample 10 is measured.

  As shown in FIG. 3B, the adhesion / melting speed is measured by removing the test sample 10 after the test from the holder and cutting it along a horizontal plane with respect to the rotation axis. On the cut surface, the lengths of six locations are measured and averaged at a pitch of 3 mm from the end surface 10a toward the rotation axis direction. The length of the test sample 10 before the test is similarly measured and averaged as shown in FIG. The average value before the test (mm) −the average value after the test (mm) is divided by the test time of 180 minutes to calculate the adhesion / melting speed (mm / min). When it is negative, it is a tendency of erosion, and when it is positive, it is an adhesion tendency.

  Tables 1 to 6 show the composition of the refractory raw material of the refractory for the inner hole disposed in the continuous casting nozzle of the present invention and the test results thereof. Dolomite clinker with a CaO content of 60% by mass and MgO content of 40% by mass as a dolomite clinker, an electrofused magnesia clinker with a MgO content of 98% by mass as magnesia clinker, scaly graphite as graphite, phenol as an organic binder Resins were used and these were uniformly kneaded, and then a quality measurement sample was molded with a friction press and heat-treated at 1000 ° C. in a non-oxidizing atmosphere. The fired refractory for the inner hole body after firing was cut into a predetermined shape and subjected to an evaluation test. As the phenolic resin, a liquid resin whose viscosity was adjusted by adding a solvent was used, and the addition amount was set to an appropriate amount based on the fact that the kneaded product had a softness suitable for molding. The CaO / MgO ratio and the total amount of MgO and CaO were calculated according to the blending ratio from the respective chemical analysis results of the raw materials used.

  The test in the actual furnace was applied to the immersion nozzle 20 shown in FIG. In FIG. 4, a cylindrical product having a thickness of 25 mm and heat-treated was used as an inner hole body 22, which was adhered to the inner hole of the immersion nozzle body 21 made of alumina carbonaceous material with a mortar 23. At this time, the inner hole body 22 was arranged on the entire surface of the inner hole excluding the discharge port 24 of the immersion nozzle (100% in area ratio). The joint thickness by the mortar 23 was 2.5 mm. As the mortar 23, magnesia mortar having an MgO component of 80% by mass, an adhesive strength at room temperature of 0.5 Mpa, and a compressibility at normal temperature (a compressibility of the mortar layer at a pressure of 2.5 MPa) is 55%. used. The molten steel used for casting is a low carbon aluminum killed steel, and one casting is about 300 t for one ladle.

  The investigation of difficult adhesion and corrosion resistance was conducted by a rotating test in molten steel and a dipping test in molten steel. The rotating test in molten steel was performed by the method described above. Further, in the immersion test in molten steel, which is a static evaluation, the rotation was stopped and the same test as in the molten steel rotation test was performed. In the rotation test in molten steel, the result of the comparison with the adhesion and erosion rate of the immersion nozzle in which the refractory for the inner body manufactured under almost the same conditions was placed in the inner hole was tested. It has been found that the speed is preferably within ± 15 μm / min, more preferably within ± 10 μm / min. In Tables 1 to 6, the case of erosion is indicated by minus (−), and the case of adhesion is indicated by plus (+). In addition, the adhesion / melting loss rate was evaluated as ◯ when the rate was ± 15 μm / min or less, Δ when the rate was more than ± 15 to ± 25 μm / min, and x when the rate was more than ± 25 μm / min.

  Table 1 shows the results of investigating the influence of graphite aspect ratio on adhesion. By changing the graphite brand, graphite having an aspect ratio of 1 to 35 was selected, and a test sample was prepared and evaluated by the method described above. As for the aspect ratio of graphite, 20 points of (maximum length / maximum thickness) ratio of the cross section of graphite particles in a 20-fold field of view were randomly measured and average values were used.

  In Table 1, Examples 1 and 2 have an aspect ratio of graphite within the range of the present invention (10 or more), and Comparative Examples 1 to 3 have an aspect ratio of graphite outside the range of the present invention (less than 10). is there.

In Examples 1 and 2, the adhesion / melting rate was balanced by increasing the aspect ratio, and a good state was shown. (It is considered that the coverage of the dolomite clinker with graphite is increased, and the CA-based low melted product generated on the operating surface side is likely to stay, and although the melt resistance is exhibited, the adhesion preventing effect is exhibited.) When granular graphite having an aspect ratio of 1 was used, the adhesion rate in a rotating test in molten steel was 35 μm / min, indicating an adhesion tendency. Adhesion was also observed at an aspect ratio of 3 in Comparative Example 2 and an aspect ratio of 5 in Comparative Example 3. (CA-based low melted product (CaO-Al ₂ O ₃ -based melt) generated by the reaction between the alumina component and the CaO component in steel is easy to penetrate into the material because the dolomite clinker particles are not sufficiently covered with the graphite particles. Therefore, it is thought that the fact that the liquid phase ratio on the operation side was reduced promoted the adhesion of alumina.)

  Table 2 shows the results of investigating the influence of graphite particle size on adhesion. Test samples were prepared and evaluated in the same manner as in Table 1.

  In Table 2, Examples 1 and 3 have a graphite particle size within the range of the present invention (500 μm or less), and Comparative Examples 4 to 7 have a graphite particle size outside the range of the present invention (over 500 μm).

  Example 1 is good because the melt speed is small in the rotating test in molten steel. Example 3 is an example in which the amount of CaO is smaller than that in Example 1 and the CaO / MgO ratio is 0.3. Unlike Example 1, although it tends to adhere, the adhesion rate is small and good. On the other hand, in Comparative Example 4, when the graphite particle size was coarsened, adhesion tendency was observed. Further, in Comparative Example 5, when coarse graphite having a small aspect ratio was used, adhesion tendency was further increased. It is thought that the decrease in the coverage of graphite around the dolomite clinker promoted the penetration of the CA-based low melted material into the tissue and promoted the adhesion. Comparative Examples 6 and 7 showed the results when the CaO / MgO ratio was 0.3, which was the same as that of Example 3. However, the CaO / MgO ratio showed a tendency to adhere as in the case of the CaO / MgO ratio of 0.8 (Comparative Examples 4 and 5). .

  Table 3 shows the results of investigating the influence of the amount of graphite used on the adhesion. Test samples were prepared and evaluated in the same manner as in Table 1.

  In Table 3, Examples 1, 4, and 5 have graphite usage in the range of the present invention (3 to 20% by mass), and Comparative Examples 8 and 9 have graphite usage outside the range of the present invention. It is.

  In Examples 1, 4, and 5, the adhesion and the melting loss were well balanced and good. On the other hand, in Comparative Example 8 in which the amount of graphite was 25% by mass, the melting loss was large. This is thought to be due to a decrease in corrosion resistance due to an increase in graphite. Moreover, it became an adhesion tendency in the comparative example 9 which does not contain graphite at all.

  Table 4 shows the relationship between magnesia clinker and dolomite clinker particle size, digestion resistance and adhesion rate. Test samples were prepared in the same manner as in Table 1, and a 20 × 20 × 20 mm sample was left in an environment of 30 ° C. and 80% relative humidity for 14 days to measure the change in weight and compare digestion resistance. In Table 4, the weight increase index is a numerical value obtained by indexing the weight increase rate of each sample with the weight change rate ΔW (%) of the test sample of Example 1 being 100.

  In Table 4, in each example, the particle size of magnesia clinker and dolomite clinker is within the range of the present invention, and Comparative Example 10 is outside the range.

  From Table 4, it can be seen that as the magnesia clinker becomes finer, the weight increase increases and the digestion tends to be easier, but the adhesion and erosion rate decreases and the corrosion resistance improves. It can also be seen that the smaller the amount of dolomite clinker used is 0.1 mm or less, the better the adhesion is.

  Any of the examples shown in Table 4 can be used without problems in practical use. On the other hand, Comparative Example 10 in which a dolomite clinker having a diameter of 0.1 mm or less is outside the scope of the present invention has a large melting loss and also has low digestion resistance.

  Table 5 shows the results of preparing magnesia clinker of the same particle size with different silica contents and comparing the deposition rate. Although the melting rate tends to increase as the silica content increases, any of the examples shown in Table 5 can be used without problems in practical use.

  Table 6 shows the effect of the CaO / MgO ratio. In Table 6, Examples 17, 18, 12, 19, and 20 have a CaO / MgO ratio in the preferred range of the present invention (0.3 to 1.2), and all have a good balance between adhesion and melting loss. It was good. In Example 16, the CaO / MgO ratio was 1.5, and the evaluation in the stationary system (immersion test in molten steel) was good with little erosion and adhesion, but the evaluation of the rotating system (rotation in molten steel) In the test, the melting rate is slightly large (can be used in practical use). In Comparative Example 11 and Comparative Example 12, the CaO / MgO ratio is 0.2 and 0.1, but adhesion occurs in any evaluation of the stationary system and the rotating system.

  As the characteristics required for the difficult-to-adhere material, it is necessary that balance between melting and adhesion is small and the CaO / MgO ratio is in the range of 0.3 to 1.2 from the results of Table 6. Under the molten steel flow velocity (evaluation of the rotating system), there is little melting loss and adhesion, and it can be said that there are few occurrences of alumina clogging and inclusion problems.

  In addition, when the immersion nozzle is used in an actual tundish and cast with low carbon aluminum killed steel, it can be used 8 times without clogging the nozzle in the middle of Example 12 and 7 times similarly in Example 19. There was no abnormality in the quality of the product steel. On the other hand, the use of Comparative Example 11 was stopped for the third time due to adhesion, and Comparative Example 12 was stopped for the first time.

DESCRIPTION OF SYMBOLS 1 Dolomite clinker 2 Graphite 3 Magnesia clinker 4 Working surface 10 Test sample 10a End surface of test sample 11 Holder 12 Crucible 13 Molten steel 14 High frequency induction furnace 20 Immersion nozzle 21 Immersion nozzle body 22 Inner hole body 23 Mortar 24 Discharge port

Claims (4)

A continuous casting nozzle in which an inner binder obtained by adding an organic binder to a refractory raw material composition and kneading and heat-treating after molding is disposed in the inner bore of the nozzle body for continuous casting,
The refractory raw material composition is 10% by mass or less (including 0) of dolomite clinker having a particle size of more than 1 mm, 20 to 90% by mass of a particle having a particle size of more than 0.1 mm and 1 mm or less, and a particle size of 0.1 mm or less. Of 15 to 15 mass% (including 0), 3 to 20 mass% of graphite having an aspect ratio of 10 or more and a particle size of 500 μm or less, and the remainder being a magnesia clinker having a particle size of 1 mm or less. The continuous casting nozzle according to claim 1, wherein a magnesia clinker having a particle size of 150 μm or less and a SiO ₂ content of 6 mass% or less (including 0) is used.   The nozzle for continuous casting according to claim 1 or 2, wherein a mass ratio of CaO / MgO in the refractory raw material composition is 0.3 to 1.2, and a total amount of MgO and CaO is 70 to 97 mass%. .   4. The evaluation according to claim 1, 2, or 3, wherein the adhesion / melting loss rate of the inner hole body is within ± 15 μm / min in an evaluation by a rotating test in molten steel in which a specimen is rotated in molten steel in which alumina is present. Nozzle for continuous casting.