Refractory materials for use in line casting, and refractory material components.

Abstract

The invention relates to an improvement in the corrosion resistance and thermal shock resistance of refractory materials based on zircon oxide-carbon and refractory components for line casting. The refractory material under the invention contains free carbon in the amount between 8% and 16% by mass, and the remainder of which is primarily zircon oxide, in which the content of other components besides free carbon and zircon oxide is less than 5% by mass of the total.When the residue after excluding the free carbon component from the refractory material mixture is determined to be 100% by volume, refractory particles with a particle size greater than 0.3 mm account for 5% or more by volume, and refractory particles with a particle size smaller than or equal to 0.045 mm account for between 5% and 40% by volume, and a nearly continuous layer of voids is present around each of the coarse particles, at least one of which is the largest particle size among the refractory particles in the refractory material. The refractory material has a visible porosity of less than or equal to 16%, and a maximum thermal expansion ratio at temperatures up to 1500°C of less than or equal to 0.6%.

Description

Refractories and refractory components for continuous casting

[0001] The present invention relates to a zirconia-carbonaceous material (ZrO ２ The present invention relates to a refractory for continuous casting of steel (carbon-based steel), and to a refractory member such as a nozzle for continuous casting that uses the refractory.

[0002] Zirconia-carbonaceous refractories, including zirconia-graphite refractories, are widely used in powder lines for submerged entry nozzles, which require particularly high corrosion resistance, because zirconia, the main component thereof, has superior corrosion resistance compared to alumina and silica (see, for example, Patent Document 1).

[0003] As described in Patent Document 1, reducing the amount of graphite and increasing the amount of zirconia is effective in improving the corrosion resistance of zirconia-graphite refractories. However, reducing the amount of graphite causes a problem of reduced thermal shock resistance.

[0004] Japanese Patent Application Laid-Open No. 2002-338347

[0005] In recent years, refractory members for continuous casting, such as nozzles for continuous casting, have often been used in a state where they are not preheated sufficiently or at all, and therefore, improvements in corrosion resistance as well as thermal shock resistance are desired.

[0006] The problem to be solved by the present invention is to improve the corrosion resistance and thermal shock resistance of zirconia-carbonaceous refractories and refractory components for continuous casting.

[0007] The present inventors have conducted extensive testing and investigations to improve the corrosion resistance and thermal shock resistance of zirconia-carbonaceous refractories, and have found that it is essential to control the pore morphology inside the refractory while densifying the refractory. They have also found that the particle size distribution (volume ratio) of the refractory particles in the refractory is one of the important control factors for this purpose, and have thus completed the present invention.

[0008] That is, one aspect of the present invention provides the following refractory for continuous casting: A refractory for continuous casting containing 8% by mass or more and 16% by mass or less of a free carbon component, the remainder being a main component of zirconia, and the total content of components other than the free carbon component and the zirconia component being less than 5% by mass, wherein, when the total volume of the components of the refractory excluding the components consisting of free carbon components is taken as 100% by volume, refractory particles having a particle size of more than 0.3 mm account for 5% by volume or more and refractory particles having a particle size of 0.045 mm or less account for 5% by volume or more and 40% by volume or less, at least coarse particles of the largest particle size in the refractory particles are surrounded by a substantially continuous void layer similar to the shape of the coarse particles, and the total thickness of the void layer at the interface between the coarse particles and a carbon-containing matrix structure present at both ends of the substantially continuous void layer is 0.3% to 3.0% of the particle size of the coarse particles, Furthermore, the refractory for continuous casting has an apparent porosity of 16% or less and a maximum coefficient of thermal expansion up to 1500°C of 0.6% or less.

[0009] According to another aspect of the present invention, there is provided a refractory member for continuous casting, in which the refractory for continuous casting of the present invention is disposed in a part or the whole of a portion that comes into contact with molten steel.

[0010] According to the present invention, the corrosion resistance and thermal shock resistance of zirconia-carbonaceous refractories and refractory components for continuous casting can be improved, thereby enabling them to exhibit excellent durability even in an environment in which they are used without preheating.

[0011] 1A and 1B are conceptual diagrams showing the structure of refractory particles as aggregates in the refractory of the present invention and their surroundings, where (a) shows a case where a void layer similar in shape to the particle outline is present around the particle and the particle is located approximately at the center (a typical example of the present invention), and (b) shows a case where a void layer similar in shape to the particle outline is present around the refractory particle and the particle is located unevenly on either side of the inner wall surface of the void layer (an example of uneven distribution that occurs during the preparation of a sample for microscopic observation). A cross-sectional view showing an example of an immersion nozzle, which is one embodiment of a refractory member to which the refractory of the present invention is applied. A cross-sectional view showing another example of an immersion nozzle, which is one embodiment of a refractory member to which the refractory of the present invention is applied. An explanatory diagram showing an example of the installation of a refractory member for continuous casting, in an example of continuous steel casting equipment. A cross-sectional view showing an example of a long nozzle, which is one embodiment of a refractory member to which the refractory of the present invention is applied. A cross-sectional view showing an example of a bottom nozzle, which is one embodiment of a refractory member to which the refractory of the present invention is applied. A cross-sectional view showing another example of a long nozzle, which is one embodiment of a refractory member to which the refractory of the present invention is applied. 1 is a cross-sectional view showing an example of a long stopper, which is one embodiment of a refractory member to which the refractory material of the present invention is applied.

[0012] To solve the above problems, it is essential to control the pore morphology within the refractory while densifying it, as described above. Therefore, the inventors aimed to develop a refractory structure in which refractory particles having a particle size of more than 0.3 mm, which serve as aggregates, are present independently and non-contiguous in a three-dimensionally continuous carbon-containing matrix structure (hereinafter referred to as a "carbonaceous matrix"), and at least the largest coarse particles among these refractory particles are surrounded by a substantially continuous void layer similar in shape to the coarse particles. That is, by achieving such a refractory structure, the thermal expansion of the coarse particles, which contributes significantly to the thermal expansion of the refractory, is absorbed by the substantially continuous void layer surrounding the particles, resulting in the apparent disappearance of the thermal expansion of the coarse particles. That is, during the heat-exposure process, while void layers exist around the coarse particles, the thermal expansion of the refractory is mainly due to the thermal expansion of the three-dimensionally continuous carbonaceous matrix, thereby enabling the thermal expansion of the refractory to be reduced. Furthermore, in the present invention, by limiting the volume fraction of refractory particles having a particle size of more than 0.3 mm (hereinafter referred to as "coarse refractory particles") and refractory particles having a particle size of 0.045 mm or less (hereinafter referred to as "fine refractory particles"), it is possible to densify the refractory while controlling the pore morphology inside the refractory as described above, thereby achieving improvements in the corrosion resistance and thermal shock resistance of refractories and refractory components for continuous casting. This will be explained in detail below.

[0013] The refractory material of the present invention contains a free carbon component in an amount of 8 mass % or more and 16 mass % or less. ４The term "free carbon" refers to carbon components consisting of simple carbon components, excluding unavoidable impurities, other than compounds such as carbides of C and SiC. It refers to all carbon components present in the refractory structure, regardless of their shape or structure, such as those formed by heating various organic binders, pitch, tar, and carbon black, whether amorphous or crystalline (e.g., graphite), and whether they are present in the refractory structure in a particulate (including fibrous) or continuous or intermittent form. If the content of free carbon components is less than 8% by mass, a three-dimensionally continuous carbonaceous matrix is ​​not formed within the refractory structure, and sufficient low-expansion effects are not achieved. Furthermore, if the content of free carbon components is less than 8% by mass, moldability is reduced, the density of the refractory is impaired, and corrosion resistance is reduced. On the other hand, if the content exceeds 16% by mass, damage to the carbonaceous matrix by molten steel, slag, etc. becomes severe, increasing the amount of refractory wear and reducing corrosion resistance. The content of free carbon components is preferably 10% by mass or more and 14% by mass or less.

[0014] In the refractory material of the present invention, the remaining main component other than the free carbon component is a zirconia component, and the total content of other components other than the free carbon component and the zirconia component (hereinafter simply referred to as "other components") is less than 5 mass%. That is, the refractory material of the present invention contains more than 79 mass% and 92 mass% or less of the zirconia component. As such, the refractory material of the present invention contains at least 79 mass% of the zirconia component, and therefore has high corrosion resistance from the viewpoint of its basic composition.

[0015] As described above, the refractory of the present invention can contain other components in a total amount of less than 5 mass %, and specifically, the other components can include one or more selected from a magnesia component, a silicon carbide component, a boron carbide component, and a zirconium boride component. The magnesia component reacts with free carbon components and the like in the refractory during the heat-receiving process, and the resulting reaction products inhibit the penetration of molten steel into the refractory, thereby improving corrosion resistance. Furthermore, the silicon carbide component, the boron carbide component, and the zirconium boride component inhibit the oxidation of free carbon components and the like in the refractory. To achieve these effects, the refractory of the present invention can contain one or more selected from a magnesia component, a silicon carbide component, a boron carbide component, and a zirconium boride component in a total amount of less than 5 mass % as the other components. If the total content of these other components exceeds 5 mass %, the content of the zirconia component will decrease relatively, making it impossible to obtain sufficient corrosion resistance.

[0016] Here, the zirconia raw material serving as the source of the zirconia component contains CaO, MgO, Y ２ O ３ The zirconia component in the refractory material of the present invention contains stabilizing components such as CaO, MgO, Y, etc. ２ O ３ In other words, the content of stabilizing components such as CaO, MgO, Y, etc. contained in the zirconia raw material is also included. ２ O ３ The content of stabilizing components such as the above is not included in the content of the other components described above.

[0017] The contents of the above-mentioned components in the refractory material of the present invention can basically be determined by ICP emission spectroscopy. ２ O ３ It is not possible to distinguish between the stabilizing components such as CaO, MgO, Y contained in the zirconia raw material and the other components mentioned above. ２ O ３ The contents of stabilizing components such as CaO, MgO, Y, etc. can be determined in advance, and the amounts of CaO, MgO, Y, etc. contained in the zirconia raw material can be determined from the values ​​determined by ICP emission spectroscopy.２ O ３ The contents of other components can be determined by subtracting the contents of stabilizing components such as

[0018] Next, we will explain the particle size distribution (volume ratio) of the refractory particles in the refractory, which is one of the features of the present invention. In the present invention, the particle size distribution (volume ratio) of the refractory particles in the refractory is characterized in that, when the total volume of the refractory excluding the free carbon component is taken as 100 volume %, the coarse refractory particles are 5 volume % or more and the fine refractory particles are 5 volume % to 40 volume %. When the coarse refractory particles are less than 5 volume %, the volume ratio of the fine refractory particles or the medium refractory particles described below increases relatively, resulting in an increase in the number of refractory particles in the refractory. As a result, the refractory structure becomes one in which the refractory particles are continuously present, resulting in high expansion. This reduces thermal shock resistance. While there is no particular upper limit to the volume ratio of the coarse refractory particles, it can be set to, for example, 60 volume % or less from the viewpoint of stably ensuring the required properties, such as strength and corrosion resistance, required for a refractory for continuous casting. The volume fraction of the coarse-grained refractory particles is preferably 10% by volume or more, and more preferably 10% by volume or more and 60% by volume or less. The upper limit of the particle size of the coarse-grained refractory particles is not particularly limited, but from the viewpoint of stably ensuring the required properties, such as strength and corrosion resistance, required of a refractory for continuous casting, it is preferably 3 mm or less, and more preferably 1 mm or less. That is, the refractory of the present invention may contain coarse-grained refractory particles having a particle size of more than 0.3 mm and 1 mm or less, as well as coarse-grained refractory particles having a particle size of more than 1 mm and 3 mm or less. However, the volume fraction of the coarse-grained refractory particles having a particle size of more than 1 mm and 3 mm or less is preferably 15% by volume or less, and more preferably 0% by volume, when the total volume of the refractory excluding the component consisting of free carbon components is taken as 100% by volume. This means that the refractory does not contain refractory particles having a particle size of more than 1 mm and 3 mm or less.

[0019] Furthermore, if the volume fraction of the fine refractory particles is less than 5 vol%, sufficient corrosion resistance cannot be obtained. On the other hand, if the volume fraction of the fine refractory particles exceeds 40 vol%, the number of refractory particles in the refractory increases, resulting in a refractory structure in which the refractory particles are continuously present, resulting in high expansion. This reduces thermal shock resistance. Furthermore, if the volume fraction of the fine refractory particles exceeds 40 vol%, the formability decreases, the density of the refractory is impaired, and as a result, the corrosion resistance decreases. The volume fraction of the fine refractory particles is preferably 10 vol% or more and 30 vol% or less. In the refractory of the present invention, the fine refractory particles are basically present in a carbonaceous matrix.

[0020] While the volumetric proportions of coarse-grained (grain size exceeding 0.3 mm) and fine-grained (grain size equal to or less than 0.045 mm) refractory particles have been described above, the refractory of the present invention also appropriately contains medium-grained refractory particles (grain size exceeding 0.045 mm and equal to or less than 0.3 mm). The volumetric proportion is the remainder of the volumetric proportions of the coarse-grained refractory particles and the fine-grained refractory particles, when the total volume of the refractory components excluding the components made of free carbon components is taken as 100 volume%, and specifically, is preferably 90 volume% or less, and more preferably 25 volume% to 85 volume%.

[0021] Here, in the present invention, the particle size of refractory particles refers to the size of the sieve openings when the refractory particles are sieved and separated. For example, refractory particles with a particle size of 0.045 mm or less refer to refractory particles that pass through a sieve with 0.045 mm openings, and refractory particles with a particle size of more than 0.3 mm refer to refractory particles that do not pass through a sieve with 0.3 mm openings.

[0022] Next, the structure of the refractory of the present invention will be described in detail. The basic structure of the refractory of the present invention is a refractory structure in which refractory particles having a particle size of more than 0.3 mm that serve as aggregates are present independently and not contiguous in a three-dimensionally continuous carbonaceous matrix, as described above, and at least the largest coarse particles among these refractory particles have approximately continuous void layers around them that are similar in shape to the coarse particles. Specifically, this is a refractory structure in which the total thickness of the void layers at the interfaces between the carbonaceous matrix and the coarse particles at both ends of the approximately continuous void layers is 0.3% to 3.0% of the particle size of the coarse particles.

[0023] Here, the term "substantially continuous void layer" means that, when observed through a microscope in cross section around a refractory particle serving as aggregate, the void outline is enlarged to a shape substantially similar to the outline of the particle cross section, and particles are present inside the voids like bell balls (see FIG. 1(a)). That is, the void layer does not have a structure in which carbon or other structures that hinder the thermal expansion of the refractory particle are present, and the void layer is non-uniform or has no voids, and there are no random areas where the refractory particles are in direct contact with each other or with the carbonaceous matrix. In the refractory of the present invention, the void layer is present all around the refractory particle serving as aggregate, i.e., in a "continuous state." However, when attempting to verify this through microscope observation, since the refractory particles are present as if floating in space, as it were, some of the surfaces of the refractory particles may be in contact with other surrounding refractory particles or the carbonaceous matrix when preparing a sample from the refractory (see FIG. 1(b)). Therefore, the term "substantially continuous" is used in consideration of the actual situation in the verification. Although a void layer is actually present all around the refractory particle, for example, when inspecting a sample under a microscope, even if some parts are in contact with other refractory particles or the carbonaceous matrix, these parts are not in a "bonded or adhered" state to the extent that they fix the refractory particle. In other words, such a "substantially continuous void layer" absorbs the thermal expansion of the refractory particle, thereby making it possible to achieve low expansion of the refractory.

[0024] From the viewpoint of reducing the thermal expansion of the refractory, the thicker the void layer around the refractory particles, the better, and it is preferable that void layers exist around all of the refractory particles serving as aggregate. However, since the void layers around the refractory particles cause a decrease in the strength of the refractory, it is necessary to adjust the thickness of the void layer while balancing the thermal expansion with the strength, damage, etc.

[0025] The ratio of the void layer thickness to the particle size (void layer thickness ratio per particle: MS value (microspace value)) is smaller for larger particles and larger for smaller particles. Therefore, specifying the MS value of the coarse particle with the largest particle size among the refractory particles specifies the lower limit of the void layer thickness ratio per particle in the refractory structure, making it possible to roughly evaluate the thermal shock resistance of the refractory.

[0026] Here, the MS value is the ratio of the thickness L of the void layer between the coarse particle and the carbonaceous matrix (the sum of the thicknesses of the void layers on both sides of the particle is L) to the diameter D of the coarse particle, and is calculated using the following formula: MS value = (L / D) x 100 (%)

[0027] Specifically, in the present invention, the MS value (%) is calculated by the following method. In observing the microscopic structure of a refractory, 10 coarse particles are selected in descending order of particle size. The largest circle tangent to and encompassing the outline of each particle is drawn on the surface of each particle, and an arbitrary line is drawn through the center of the circle. Furthermore, using the largest circle as a reference, three more lines are drawn at 45° intervals through the center of the circle, for a total of four lines per particle. The lengths between the outline points at both ends of the particle on each of the lines are then measured as D1, D2, D3, and D4. Furthermore, the sums of the thicknesses of the void layers present at the particle interfaces at both ends on each line are measured as L1, L2, L3, and L4, respectively. Using the values ​​obtained for these four lines, MS1, MS2, MS3, and MS4 calculated by the above formula are calculated, and the average of these values ​​is calculated as the void layer thickness ratio, i.e., the MS value, of one coarse particle. The MS values ​​of 10 pre-selected coarse particles are calculated by the above method, and the average is used as the MS value of the refractory structure.

[0028] The reason why the MS value of the refractory structure is evaluated using the largest coarse particle in size, i.e., the 10 largest particles selected in descending order of particle size in microscopic observation of the refractory structure, is that the larger the particle size, the greater the change in volume and length due to expansion, which has a greater effect on the thermal shock resistance of the refractory. Therefore, the MS value, which serves as an index for adjusting and evaluating thermal shock resistance, must be calculated for the largest coarse particle in the refractory structure. From the same perspective, the above-mentioned "substantially continuous void layer" in the present invention must be present around at least the largest coarse particle in size, i.e., the 10 largest coarse particles selected in descending order of particle size in microscopic observation of the refractory structure.

[0029] The present inventors have confirmed that in a refractory containing 8% by mass or more and 16% by mass or less of a free carbon component, with the remainder being primarily zirconia, the thickness of the void layer around the refractory particles, which has a low-expansion effect and is well-balanced in terms of strength, corrosion resistance, and wear resistance, is 0.3% or more and 3.0% or less in terms of MS value calculated for the largest coarse particle size. That is, if the MS value is less than 0.3%, a sufficient low-expansion effect cannot be obtained. On the other hand, if the MS value exceeds 3.0%, the strength decreases, and the corrosion resistance and wear resistance also decrease. In this way, in the present invention, a refractory structure is formed in which a substantially continuous void layer similar in shape to the shape of the coarse particle is present around at least the largest coarse particle of the refractory particles in the refractory, and the total thickness of the void layer at the interface between the coarse particle and a carbon-containing matrix structure present at both ends of this substantially continuous void layer is 0.3% to 3.0% of the particle size of the coarse particle, thereby making it possible to significantly improve thermal shock resistance and to provide a refractory that is well-balanced in terms of strength, corrosion resistance, and wear resistance.

[0030] A method for controlling the MS value, i.e., a method for forming a substantially continuous void layer similar in shape to the largest coarse particle among the refractory particles in the refractory and controlling the thickness of the void layer, is as follows. Controlling the MS value is synonymous with controlling the thermal expansion coefficient. However, during heat treatment, larger refractory particles (coarse particles) have a greater amount of thermal expansion, resulting in a significant difference in thermal expansion from the carbonaceous matrix. This makes it easier for a substantially continuous void layer (hereinafter also referred to as "MS") similar in shape to form around the coarse particle. Meanwhile, smaller refractory particles have a smaller amount of thermal expansion, making it more difficult to form a distinct MS. Therefore, controlling the particle size composition (volume fraction) of the refractory particles in the refractory makes it possible to control the MS value, i.e., the thermal expansion coefficient. In the present invention, when the portion excluding constituents consisting of free carbon components is taken as 100 volume %, low expansion and its control can be achieved by setting the refractory particles having a particle size of more than 0.3 mm to 5 volume % or more and the refractory particles having a particle size of 0.045 mm or less to 5 volume % or more and 40 volume % or less. For example, if lower expansion is desired, the volume fraction of refractory particles having a particle size of 0.045 mm or less can be reduced within the above particle size configuration (volume fraction) range to break the continuity of the refractory particles in the refractory structure, and at the same time, the volume fraction of refractory particles having a particle size of more than 0.3 mm can be increased to promote the formation of MS.

[0031] The refractory of the present invention, having the above-mentioned constitution (chemical composition, particle size constitution (volume ratio) of the refractory particles, and refractory structure), can stably achieve both high density with an apparent porosity of 16% or less and low expansion with a maximum thermal expansion coefficient of 0.6% or less up to 1500°C. This makes it possible to improve the corrosion resistance and thermal shock resistance of refractories and refractory components for continuous casting, and to demonstrate excellent durability even in an environment in which they are used without preheating.

[0032] In the present invention, the chemical composition, refractory structure, apparent porosity, thermal expansion coefficient, etc. of a refractory are basically evaluated for a sample "after heating in a non-oxidizing atmosphere at 1000°C." The reason for this is to improve analytical accuracy by removing components such as moisture, organic matter, hydrates, and carbonate compounds from the refractory and stabilizing the chemical composition of the refractory by carbonizing the organic binder components. For this reason, the heating time is determined as the time until no weight change due to heating occurs. However, if the refractory has already been heat-treated at a temperature of 1000°C or higher during its manufacturing process, or if it has been heat-treated at a temperature of 800°C or higher depending on the type of volatile component, it is possible to evaluate the chemical composition, refractory structure, apparent porosity, thermal expansion coefficient, etc. of the product after manufacturing.

[0033] The refractory of the present invention may also contain carbon fibers in the carbonaceous matrix. The carbon fibers fill defects such as cracks that occur as the carbonaceous matrix shrinks due to carbonization of the organic binder component during heating of the refractory. This densifies and strengthens the carbonaceous matrix, improving the strength of the refractory. From the viewpoint of fully demonstrating this effect of improving the strength of the refractory, the aspect ratio of the carbon fibers is preferably 15 to 200, and the content of the carbon fibers is preferably 5 mass% or less.

[0034] The refractory of the present invention can be produced by a method similar to that for producing general zirconia-carbonaceous refractories, as well as the preparation of samples in the examples described below. For example, a binder is added to a raw material blend containing zirconia raw material, graphite, etc., and the kneaded clay is adjusted to a state suitable for molding. The clay is molded by CIP (Cold Isostatic Pressing), dried at a temperature of about 300°C or less, and then heat-treated in a non-oxidizing atmosphere at about 800°C to about 1200°C.

[0035] Next, a refractory member for continuous casting using the refractory of the present invention will be described. Figure 2 shows a longitudinal cross section of an immersion nozzle (SEN), one form of refractory member for continuous casting. Figure 2(a) shows an example of an SEN in which the refractory 21 of the present invention is applied to a powder line. While Figure 2(a) shows a cylindrical example, nozzles such as SENs to which the refractory of the present invention is applied are not limited to such cylindrical shapes. For example, as shown in Figure 2(b), nozzles such as SENs to which the refractory of the present invention is applied can be applied to nozzles of various shapes without being limited to the shape of the nozzle. For example, as shown in Figure 2(b), a flat, elliptical, or funnel-shaped (funnel-shaped with an expanded diameter at the top) shape, which is primarily used for casting thin slabs, can be used. Furthermore, Figure 2(c) shows an example of an SEN equipped with the function of blowing gas into molten steel from a portion of the inner bore (wall surface of the inner bore) of the SEN shown in Figure 2(a). In this example, a highly permeable refractory (hereinafter referred to as "ventilation refractory") 20G is disposed in a portion of the inner bore. The material of this ventilation refractory 20G can be a general alumina-graphite ventilation refractory, or it can be a material that has increased porosity, permeability, etc. while maintaining the refractory composition of the present invention. Reference numeral 20S in FIG. 2(c) denotes a space, which is a gas passage path and also serves as a gas pressure accumulation chamber. Reference numeral 20 in FIG. 2 denotes a material for the main body. This also applies to FIG. 3 and FIG. 5 to FIG. 8, which will be described later.

[0036] 3 shows an example of an immersion nozzle in which the refractory material 21 of the present invention is disposed in part or all of the area that comes into contact with molten steel, and a layer of a refractory material (non-adhesive material 22) of a different composition from the refractory material 21 of the present invention is disposed inside the refractory material 21 of the present invention, forming a multi-layer structure in which the multi-layer structure is in direct contact with each other. To manufacture such a multi-layer nozzle, the manufacturing method described above is used as a base, but a cavity for introducing a moldable material is partitioned in the target area of ​​the CIP mold at a position of a predetermined radial thickness from the surface that comes into contact with the molten steel, and the inside (the core rod side) of the cavity is filled with a moldable material for a refractory material different from the refractory material of the present invention, and the back side is filled with a moldable material for the refractory material of the present invention. The plate or other jig used for the partition is then removed before molding, and the nozzle is then pressure-molded.

[0037] In addition to submerged entry nozzles, continuous casting nozzles to which the refractory of the present invention can be applied or to which it is suitable include tundish nozzles (including upper nozzles, open nozzles, etc.), intermediate nozzles, and flow rate control nozzles (especially inner bores, etc.). Figure 4 shows an example of the configuration of a continuous steel casting facility. The left side of the figure shows an example of an external submerged entry nozzle F, which is a structure consisting of multiple nozzles and serves as a molten steel flow path when discharging molten steel from a molten steel vessel. The refractory 21 of the present invention can be applied not only to the submerged entry nozzle F, but also to some or all of the portions of various nozzles that come into contact with molten steel, such as the upper nozzle A, sliding nozzle plate B, lower nozzle C, and long nozzle D, of such a structure consisting of multiple continuous casting nozzles. It can also be applied to so-called insert-type submerged entry nozzles (shown on the right side of Figure 4 ), which have a structure with an integrated nozzle portion serving as a discharge path, and so-called open nozzles that are not submerged in molten steel. Furthermore, it can also be used as a stopper E located above the nozzle portion to control or open / close the flow rate of molten steel, or as a refractory G for lining the molten steel vessel.

[0038] Figures 5 and 6 show examples of a long nozzle and a bottom nozzle, respectively, in which the refractory 21 of the present invention is disposed in part or all of the area that comes into contact with molten steel. In Figures 5 and 6, either the inner refractory layer or the backside refractory layer, or both, can be the refractory 21 of the present invention. Figure 7 also shows an example of a long nozzle in which the powder line is formed from the refractory 21 of the present invention. Note that if the refractory 21 of the present invention is disposed in areas other than the powder line in Figure 7, the immersion nozzle will have the refractory of the present invention disposed in a single layer over the entire area that comes into contact with molten steel, from the surface that comes into contact with molten steel to the backside. A single-layer nozzle can reduce the risk of cracking and can be manufactured easily. To manufacture such a single-layer nozzle, the refractory clay of the present invention is simply filled in a single layer in the target area of ​​a CIP mold, based on the manufacturing method described above.

[0039] Fig. 8 shows an example of a long stopper in which the refractory material 21 of the present invention is disposed in a part or all of the portion that comes into contact with molten steel. In Fig. 8, either or both of the tip end portion and the base end portion other than the tip end portion of the long stopper can be made of the refractory material 21 of the present invention.

[0040] The following Tables 1 to 6 show the raw material blends and evaluation results of Examples and Comparative Examples of the present invention. In each table, the "volume ratio of refractory particles" is a volume ratio calculated based on the raw material blend, and this volume ratio is maintained in the produced refractory. In other words, the "volume ratio of refractory particles" shown in each table is the same as the volume ratio of refractory particles of each particle size when the portion of the refractory components excluding components made of free carbon components is set to 100 volume %.

[0041] The raw material composition of each example shown in each table was mixed with phenolic resin, an organic binder, to prepare a kneaded clay suitable for molding. The clay was molded by CIP, cured and dried up to 300°C, and then heat-treated at 1000°C in a non-oxidizing atmosphere to obtain the refractory material of each example.

[0042] The chemical components of the obtained refractories were analyzed, and the microstructural state was observed and subjected to evaluation tests. The analysis of the chemical components was carried out according to JIS R2216. For the observation of the microstructural state, the refractory structure was impregnated with resin and then mechanically polished to produce a mirror surface, and the MS value was determined by the above-mentioned method through microscopic observation, and the continuity of the void layer was also observed. The refractories were evaluated for apparent porosity, maximum thermal expansion coefficient up to 1500°C, corrosion resistance, and thermal shock resistance, and an overall evaluation was carried out based on these evaluation results.

[0043] The apparent porosity was measured in accordance with JIS R 2205. The thermal expansion coefficient was measured up to 1500°C in accordance with JIS R 2207-3, and the maximum thermal expansion coefficient up to 1500°C was evaluated.

[0044] The corrosion resistance was evaluated by applying CaO / SiO ２A rectangular columnar sample (20 × 20 × 180 mm) of the refractory material of each example was immersed for 60 minutes in a crucible containing approximately 30 mm of floating synthetic slag, the mass ratio of which was adjusted to 1.0. After being pulled out, the amount of corrosion at the molten steel-molten slag interface was measured, and the extent of corrosion was compared. Specifically, the amount of corrosion of the refractory material of each example was converted into a corrosion index, with the amount of corrosion in Comparative Example 1 being set at 100. A corrosion index of less than 100 was deemed to have solved the problem. More specifically, a corrosion index of 94 or less was evaluated as ◯ (excellent), a corrosion index of more than 94 but less than 100 was evaluated as △ (good), and a corrosion index of 100 or more was evaluated as × (poor).

[0045] The thermal shock resistance was evaluated by a test in which a cylindrical sample (outer diameter / inner diameter (inner hole diameter) / height = 130 / 55 / 300 mm) was subjected to a thermal shock test by pouring molten iron at 1600°C into the inner hole of the sample at room temperature. After the test, the horizontal cross section was cut at 50 mm intervals and checked for the presence or absence of cracks. The test was then evaluated as ○ (excellent) when no cracks were observed, △ (good) when microcracks were observed, and × (poor) when cracks were observed.

[0046] The overall evaluation was rated as ○ (excellent) when, in the structural state, the MS value was within the range of the present invention (0.3% or more and 3.0% or less), the continuity of the void layer was almost continuous, the apparent porosity was within the range of the present invention (16% or less), and the maximum thermal expansion coefficient up to 1500°C was within the range of the present invention (0.6% or less), and the corrosion resistance was rated as ○ and the thermal shock resistance was rated as ○; △ (good) when, in the structural state, the MS value was within the range of the present invention (0.3% or more and 3.0% or less), the continuity of the void layer was almost continuous, the apparent porosity was within the range of the present invention (16% or less), and the maximum thermal expansion coefficient up to 1500°C was within the range of the present invention (0.6% or less), and either the corrosion resistance or the thermal shock resistance was rated as △; and × (poor) when, in the structural state, the continuity of the void layer was partially continuous, the apparent porosity was more than 16%, the maximum thermal expansion coefficient up to 1500°C was more than 0.6%, and the corrosion resistance was rated as × or the thermal shock resistance was rated ×.

[0047]

[0048] In Table 1, Examples 1 to 5 are examples in which the free carbon component (hereinafter referred to as "FC") content in the refractory differs. However, the content is within the range of the present invention. The refractory exhibited low apparent porosity, excellent corrosion resistance, and excellent thermal shock resistance. Overall evaluations of ○ (excellent) or △ (good) were obtained, resulting in favorable results. Among these, Examples 2 to 4, in which the FC content was within the preferred range of 10% by mass or more and 14% by mass or less, were overall evaluated as ○ (excellent), resulting in particularly favorable results. In contrast, Comparative Example 1 is an example in which the FC content is below the lower limit of the present invention. A three-dimensionally continuous carbonaceous matrix was not formed within the refractory structure, and the continuity of the void layers around the coarse particles was impaired, resulting in a "partially continuous" structure. Therefore, a sufficient expansion reduction effect was not obtained, resulting in high expansion and reduced thermal shock resistance. Furthermore, due to moldability issues, a dense refractory was not obtained, and corrosion resistance also decreased. On the other hand, Comparative Example 2 is an example in which the FC content exceeded the upper limit of the present invention, resulting in reduced corrosion resistance.

[0049]

[0050] In Table 2, Examples 6, 3, and 7 to 9 have different volume fractions of coarse refractory particles, but are within the range of the present invention. The overall evaluation was ○ (excellent) or △ (good), and favorable results were obtained. Note that Example 6 is an example in which the volume fraction of coarse refractory particles is 5% by volume, which is the lower limit of the present invention. Compared to other Examples in which the volume fraction of coarse refractory particles is 10% by volume or more, Example 6 exhibited high expansion and poor thermal shock resistance. Furthermore, Example 6 also exhibited high apparent porosity and poor corrosion resistance compared to other Examples. On the other hand, Comparative Example 3 is an example in which the volume fraction of coarse refractory particles is below the lower limit of the present invention. As a result, the number of refractory particles in the refractory increased, resulting in a refractory structure in which the refractory particles were continuously present. Although the continuity of the void layer was "almost continuous," the refractory structure had an MS value below the lower limit of the present invention. This resulted in high expansion and poor thermal shock resistance.

[0051]

[0052] In Table 3, Examples 10, 11, 3, 12 to 14 are examples in which the volume fraction of the fine refractory particles was different, but within the range of the present invention. The overall evaluation was ○ (excellent) or △ (good), and good results were obtained. Among them, Examples 11, 3, 12, and 13, in which the volume fraction of the fine refractory particles was within the preferred range of 10% by mass or more and 30% by mass or less, were overall evaluated as ○ (excellent), and particularly good results were obtained. In contrast, Comparative Example 4 is an example in which the volume fraction of the fine refractory particles was below the lower limit of the present invention, and corrosion resistance was reduced. On the other hand, Comparative Example 5 is an example in which the volume fraction of the fine refractory particles was above the upper limit of the present invention. As a result, the number of refractory particles in the refractory increased, resulting in a refractory structure in which the refractory particles were continuously present. Although the continuity of the void layer was "almost continuous," the refractory structure had an MS value below the lower limit of the present invention. This resulted in high expansion and reduced thermal shock resistance. Furthermore, due to problems with formability, dense refractories could not be obtained, and corrosion resistance also decreased.

[0053]

[0054] In Table 4, Example 3 and Examples 15 to 18 are examples in which different types of zirconia raw materials were used. The zirconia raw materials used in each example are as follows: Example 3: 4 mass% CaO partially stabilized zirconia (the same applies to the examples in Tables 1 to 3, and Tables 5 and 6 described below). Example 15: 6 mass% CaO partially stabilized zirconia. Example 16: 6 mass% MgO partially stabilized zirconia. Example 17: 8 mass% Y ２ O ３ Partially stabilized zirconia Example 18: 90 mass% of 4 mass% CaO partially stabilized zirconia and 10 mass% of unstabilized zirconia were contained in 100 mass% of zirconia raw material. As described above, in the refractory material of the present invention, the content of the zirconia component is adjusted to include CaO, MgO, Y, and the like. ２ O ３ The content of stabilizing components such as zirconia component (ZrO ２) are added together. Example 3 and Examples 15 to 18 are all within the scope of the present invention, and the overall evaluation was ○ (excellent) or △ (good), and good results were obtained. Note that Examples 15 and 16 contain a zirconia component (ZrO ２ ) contains CaO and MgO, but ZrO which excludes CaO and MgO ２ Since the amount of Y was small, the corrosion resistance was rated as △ (good). ２ O ３ Since it has high corrosion resistance, the corrosion resistance was rated as excellent.

[0055]

[0056] Although each example shown in Table 5 contains carbon fiber, it is within the scope of the present invention and was evaluated as either ○ (excellent) or △ (good), resulting in favorable results. Among them, Example 19, in which the aspect ratio of the carbon fiber was 15 to 200 and the content was limited to 5 mass% or less, was evaluated as ○ (excellent) and showed particularly favorable results.

[0057]

[0058] In Table 6, Examples 21 to 23 are examples containing "other components," but the content (total) of these components was less than 5 mass %, which was within the range of the present invention, and good results were obtained. In contrast, Comparative Examples 6 to 12 contained the content (total) of other components of 5 mass % or more, and the corrosion resistance was reduced. In addition, B was used as the other component. ４ In Comparative Example 8 containing 5 mass % or more of the C component, B ４ From component C to B ２ O ３ A large amount of liquid phase components was generated, and these liquid phase components penetrated into the void layer around the refractory particles, causing the void layer to lose its continuity and become "partially continuous." This resulted in high expansion and reduced thermal shock resistance. In addition, other components included B ４ Even in Comparative Example 11, which contains a total of 5 mass % or more of the C component and the MgO component, a large amount of liquid phase components is generated during the heat-receiving process, and the liquid phase components penetrate into the void layer around the refractory particles, causing the void layer to lose its continuity and become "partially continuous." This results in high expansion and a decrease in thermal shock resistance. In Comparative Example 12, ZrB２ B produced from the ingredients ２ O ３ The reaction between the boron component and the MgO component promoted sintering of the entire structure, increasing the elastic modulus and decreasing the thermal shock resistance. In Table 6, "additives" are boron component sources, and their amounts are shown as outer percentages based on 100% by mass of the raw material blend other than the "additives."

[0059] 20 Main body material 21 Refractory material of the present invention 22 Hard-to-adhere material 22G Ventilation refractory 22S Space (gas passageway, pressure accumulator) A: Upper nozzle B: Sliding nozzle plate C: Lower nozzle D: Long nozzle E: Long stopper F: Submerged nozzle G: Lining refractory

Claims

1. A refractory for continuous casting containing 8% by mass or more and 16% by mass or less of free carbon components, the remainder being mainly zirconia components, and the total content of components other than the free carbon components and the zirconia components being less than 5% by mass, wherein, when the volume of the components of the refractory excluding the components consisting of free carbon components is taken as 100% by volume, refractory particles having a particle size of more than 0.3 mm are 5% by volume or more and refractory particles having a particle size of 0.045 mm or less are 5% by volume or more and 40% by volume or less, at least coarse particles of the largest particle size in the refractory particles are surrounded by a nearly continuous void layer similar to the shape of the coarse particles, and the total thickness of the void layer at the interface between the coarse particles and a matrix structure containing carbon present at both ends of this nearly continuous void layer is 0.3% to 3.0% of the particle size of the coarse particles, Furthermore, the refractory for continuous casting has an apparent porosity of 16% or less and a maximum coefficient of thermal expansion up to 1500°C of 0.6% or less.

2. A refractory for continuous casting according to claim 1, wherein the refractory particles having a particle size of more than 0.3 mm account for 10% by volume or more, and the refractory particles having a particle size of 0.045 mm or less account for 10% by volume or more and 30% by volume or less.

3. A refractory for continuous casting according to claim 1 or 2, wherein the matrix structure contains carbon fibers having an aspect ratio of 15 to 200, and the content of said carbon fibers is 5 mass % or less.

4. A refractory for continuous casting according to any one of claims 1 to 3, wherein the other components are one or more selected from the group consisting of magnesia components, silicon carbide components, boron carbide components and zirconium boride components.

5. A refractory member for continuous casting, in which the refractory for continuous casting according to any one of claims 1 to 4 is arranged in part or all of the area that comes into contact with molten steel.

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