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 a refractory material and refractory component intended for line casting. The refractory material under the invention contains a free carbon component in the amount between 10% and 30% by mass, and the remainder of which: the principal mineral phase consists of one or more components selected from the group including corundum, spinel, and periclase, in which the periclase content is less than 40% by mass; and the total silicon oxide and silicon carbide content is less than 15% by mass.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 occupy more than or equal to 20% by volume, and refractory particles with a particle size smaller than or equal to 0.045 mm occupy between 3% and 30% by volume, in which a nearly continuous layer of pores is present around each of the coarse particles, at least one of which has the largest particle size among the refractory particles in the refractory material, in which the nearly continuous layer of pores has a similar form to the coarse particles. The refractory material has a porosity of less than or equal to 16%, and the maximum thermal expansion ratio at temperatures up to 1500°C is less than or equal to 0.6%.

Description

Refractories and refractory components for continuous casting

[0001] The present invention relates to a refractory for continuous casting and a refractory member such as a nozzle for continuous casting that uses the refractory.

[0002] In Patent Document 1, the present inventors disclosed a refractory for continuous casting that combines excellent corrosion resistance and thermal shock resistance.

[0003] Patent No. 6027676

[0004] The present inventors have produced prototype refractory members using the refractory material disclosed in Patent Document 1 and conducted repeated tests, and have found that further improvements in corrosion resistance and thermal shock resistance are desired. That is, the refractory material disclosed in Patent Document 1 contains 40 mass % or more of magnesia (periclase), and therefore exhibits excellent corrosion resistance against steel types containing basic inclusions such as CaO and MnO, but on the other hand, it exhibits poor corrosion resistance against steel types containing basic inclusions such as SiO ２ It was found that the refractory material disclosed in Patent Document 1 does not have sufficient corrosion resistance for steel types containing acidic inclusions such as magnesium monoxide, magnesium stearate ...

[0005] The problem to be solved by the present invention is to improve the corrosion resistance and thermal shock resistance of refractories and refractory components for continuous casting.

[0006] In view of the above-mentioned disadvantages of containing a large amount of magnesia (periclase), the present inventors decided to limit the content of magnesia (periclase) to less than 40% by mass, and then conducted repeated tests and studies to improve the corrosion resistance and thermal shock resistance. As a result, they found that it is essential to control the pore morphology inside the refractory while densifying the refractory. They also found that the particle size composition (volume ratio) of the refractory particles in the refractory is one of the important control factors, and thus completed the present invention.

[0007] That is, according to one aspect of the present invention, there is provided the following refractory for continuous casting. A refractory for continuous casting containing 10% by mass or more and 30% by mass or less of free carbon components, the remainder of which is a main mineral phase consisting of one or more types selected from corundum, spinel and periclase, the periclase content being less than 40% by mass, and the total content of silica components and silicon carbide components being less than 15% by mass, wherein, when the total volume 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 20% by volume or more and refractory particles having a particle size of 0.045 mm or less account for 3% by volume or more and 30% by volume or less, at least coarse particles with a maximum particle size among the refractory particles in the refractory 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 matrix structure containing carbon present at both ends of the substantially continuous void layer is 0.3% or more and 3.0% or less 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.

[0008] 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.

[0009] According to the present invention, the corrosion resistance and thermal shock resistance of refractories and refractory components for continuous casting can be improved, thereby enabling them to exhibit excellent durability even in an environment where they are used without preheating.

[0010] 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.

[0011] 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.

[0012] The refractory material of the present invention contains a free carbon component of 10% by mass or more and 30% by 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 produced 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 10% by mass, a three-dimensionally continuous carbonaceous matrix is ​​not formed within the refractory structure, and sufficient low-expansion effects cannot be achieved. Furthermore, if the content exceeds 30% by mass, damage to the carbonaceous matrix by molten steel, slag, etc. becomes severe, increasing the amount of refractory wear and reducing corrosion resistance. Furthermore, if graphite or other free carbon components are used in large quantities, moldability is reduced and the refractory's density is impaired, which also reduces corrosion resistance. The content of free carbon components is preferably 15% by mass or more and 25% by mass or less.

[0013] The main mineral phase of the refractory of the present invention is one or more selected from corundum, spinel, and periclase. However, the periclase content is limited to less than 40% by mass. This is because a periclase (magnesia) content of 40% by mass or more results in the above-mentioned disadvantages. The periclase content is preferably 35% by mass or less. Here, in the present invention, the "main mineral phase" refers to the mineral phase that is most abundant among the mineral phases in the refractory. When two or more types of mineral phases are present as the most abundant, all of them are considered to be the main mineral phases. Furthermore, when refractory particles containing multiple mineral phases are included, the "main mineral phase" is determined by adding each of the multiple mineral phases contained in that refractory particle to the same mineral phases contained in other refractory particles.

[0014] In the refractory material of the present invention, the total content of the silica component and the silicon carbide component is limited to less than 15% by mass. This is because if the total content of the silica component and the silicon carbide component is 15% by mass or more, the corrosion resistance will be significantly reduced. Note that the silicon carbide component has the function of inhibiting the oxidation of free carbon components and the like, so it can be appropriately contained within a range of less than 15% by mass. For example, if it is 5% by mass or less, it can exhibit its oxidation inhibitory function without substantially reducing the corrosion resistance.

[0015] 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 account for 20 volume % or more and the fine refractory particles account for 3 volume % to 30 volume %. When the coarse refractory particles account for less than 20 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. The upper limit of the volume ratio of the coarse refractory particles is not particularly limited, but from the viewpoint of consistently ensuring the required properties, such as strength and corrosion resistance, required for a refractory for continuous casting, it can be set to, for example, 60 volume % or less. The volume fraction of the coarse-grained refractory particles is preferably 30% by volume or more, and more preferably 40% 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 less than 1 mm, as well as coarse-grained refractory particles having a particle size of more than 1 mm and less than 3 mm. However, the volume fraction of the coarse-grained refractory particles having a particle size of more than 1 mm and less than 3 mm 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. That is, it does not contain refractory particles having a particle size of more than 1 mm and less than 3 mm.

[0016] Furthermore, if the volume fraction of the fine refractory particles is less than 3% by volume, a dense refractory cannot be obtained, resulting in reduced corrosion resistance. On the other hand, if the volume fraction of the fine refractory particles exceeds 30% by volume, 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. As a result, thermal shock resistance is reduced. The volume fraction of the fine refractory particles is preferably 5% by volume or more and 15% by volume or less. In the refractory of the present invention, the fine refractory particles are basically present in a carbonaceous matrix.

[0017] 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 10 volume% to 77 volume%, and more preferably 30 volume% to 70 volume%.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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 (%)

[0024] 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 preselected coarse particles are calculated by the above method, and the average is used as the MS value of the refractory structure.

[0025] 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.

[0026] The present inventors have confirmed that in a refractory having a main mineral phase consisting of one or more selected from corundum, spinel, and periclase, and a periclase content of less than 40% by mass, 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 coarse particles with the largest particle size. That is, if the MS value is less than 0.3%, a sufficient low-expansion effect cannot be obtained. Furthermore, 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.

[0027] 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 20 volume % or more and the refractory particles having a particle size of 0.045 mm or less to 3 volume % or more and 30 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 composition (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.

[0028] The refractory of the present invention, having the above-mentioned constitution (chemical composition, main mineral phase, 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.

[0029] 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.

[0030] The refractory material of the present invention contains a boron component of B ２ O ３ The boron content is preferably 0.1 mass % or more and 3.0 mass % or less in terms of converted value. The boron component generates fibrous alumina borate and the like in the carbonaceous matrix when the refractory is heated. This densifies and strengthens the carbonaceous matrix, thereby improving the strength of the refractory.

[0031] 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.

[0032] The refractory of the present invention can be produced by a method similar to that used for producing a general refractory having one or more mineral phases selected from corundum, spinel, and periclase, as in the production of samples in the examples described below. For example, a binder is added to a raw material blend containing refractory particles constituting the main mineral phase, 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.

[0033] Next, a refractory component for continuous casting using the refractory of the present invention will be described. Figure 2 shows a longitudinal cross section of an immersion nozzle, one form of refractory component for continuous casting. Figure 2(a) shows an example of an immersion nozzle in which the refractory 20 of the present invention is disposed in a single layer in a portion of the area that comes into contact with molten steel, extending from the surface that comes into contact with the molten steel to the back side. In Figure 2(a), if the refractory 20 of the present invention is also disposed in the powder line material 21, an immersion nozzle in which the refractory of the present invention is disposed in a single layer in the entire area that comes into contact with molten steel, extending from the surface that comes into contact with the molten steel to the back side. A nozzle with a single-layer structure can reduce the risk of cracking and can be manufactured using a simple method. To manufacture such a nozzle with a single-layer structure, 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. While FIG. 2( a) shows a cylindrical example, nozzles such as submerged entry nozzles to which the refractory of the present invention is applied are not limited to cylindrical shapes. For example, as shown in FIG. 2( b), various shapes, such as flat, elliptical, and funnel-shaped (funnel-shaped with an expanded diameter at the top) nozzles primarily used for thin slab casting, are applicable. Furthermore, FIG. 2( c) shows an example of a submerged entry nozzle equipped with the function of blowing gas into molten steel from a portion of the inner bore (the inner bore wall surface) of the submerged entry nozzle shown in FIG. 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 typical alumina-graphite ventilation refractory, or it can be a material that maintains the refractory composition of the present invention while increasing porosity, permeability, etc. Note that the reference symbol 20S in FIG. 2( c) denotes a space, which serves as a gas passageway and a gas pressure accumulation chamber.

[0034] 3 shows an example of an immersion nozzle in which the refractory material 20 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 20 of the present invention is disposed inside the refractory material 20 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.

[0035] 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 20 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 molten steel flow rate, or as a refractory G for lining the molten steel vessel.

[0036] Figures 5 and 6 show examples of a long nozzle and a bottom nozzle, respectively, in which the refractory material 20 of the present invention is disposed in part or all of the region that comes into contact with molten steel. In Figures 5 and 6, either the inner refractory layer or the backside refractory layer, or both, may be the refractory material 20 of the present invention. Figure 7 shows an example of a long nozzle in which the refractory material 20 of the present invention is disposed in the portion other than the powder line material 21. In Figure 7, the refractory material 20 of the present invention may also be disposed in the portion of the powder line material 21.

[0037] Fig. 8 shows an example of a long stopper in which the refractory material 20 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 20 of the present invention.

[0038] Tables 1 to 6 below show the raw material blends and evaluation results of examples and comparative examples of the present invention. In each table, the "volume percentage of refractory particles" is a volume percentage calculated based on the raw material blend, and this volume percentage is maintained in the produced refractory. That is, the "volume percentage of refractory particles" shown in each table is the same as the volume percentage of refractory particles of each particle size when the refractory constituents excluding the constituents consisting of free carbon components are taken as 100% by volume. In each table, "mineral phase" is shown as the refractory raw material in the raw material blend, and the mineral phases constituting these refractory raw materials are maintained in the produced refractory. Furthermore, in each table, "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."

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The corrosion resistance was evaluated by applying CaO / SiO ２ A 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 2 being set to 100. A corrosion index of less than 100 was deemed to have solved the problem. More specifically, a corrosion index of 90 or less was evaluated as ◯ (excellent), a corrosion index of more than 90 but less than 100 was evaluated as △ (good), and a corrosion index of 100 or more was evaluated as × (poor).

[0043] 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.

[0044] 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 ○; 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 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 ×, the evaluation was × (poor).

[0045]

[0046] 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 15% by mass or more and 25% 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 was below the lower limit of the present invention. Therefore, 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-reducing effect was not obtained, resulting in high expansion and reduced thermal shock resistance. 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.

[0047]

[0048] In Table 2, Examples 6 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 20 vol%, which is the lower limit of the present invention. Compared to Example 7, in which the volume fraction of coarse refractory particles is 30 vol%, the result was high expansion and poor thermal shock resistance. Furthermore, Example 8 is an example in which the upper limit of the particle diameter of the coarse refractory particles is 3 mm. Compared to Example 9, in which the upper limit of the particle diameter of the coarse refractory particles is 1 mm, the result was high apparent porosity and poor corrosion resistance. 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 of the increased number of refractory particles in the refractory, the refractory structure was formed in which the refractory particles were continuously present. This resulted in high expansion and poor thermal shock resistance.

[0049] Similarly, in Table 2, Examples 10, 11, 3, 12, and 13 are examples in which the volume fraction of the fine refractory particles was different, but within the range of the present invention, and the overall evaluation was ○ (excellent) or △ (good), resulting in good results. Among them, Examples 11, 3, and 12, in which the volume fraction of the fine refractory particles was within the preferred range of 5% by mass or more and 15% by mass or less, were overall evaluated as ○ (excellent), resulting in particularly good results. 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 a dense refractory was not obtained, resulting in reduced corrosion resistance. 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, resulting in an increased number of refractory particles in the refractory, resulting in a refractory structure in which the refractory particles were continuously present. This resulted in high expansion and reduced thermal shock resistance.

[0050]

[0051] In Table 3, Examples 3 and 14 to 19 are examples in which the main mineral phases are different, but are within the scope of the present invention, and good results were obtained. In Example 15, the most abundant mineral phases were corundum and spinel, meaning that the main mineral phases were corundum and spinel. In Example 17, the most abundant mineral phases were corundum, spinel, and periclase, meaning that the main mineral phases were corundum, spinel, and periclase. On the other hand, Comparative Example 6 is an example in which the main mineral phase is periclase, but the periclase content exceeds the upper limit of the present invention, resulting in reduced corrosion resistance.

[0052] Similarly, in Table 3, Examples 20 to 22 are examples in which a refractory raw material (refractory particles) containing multiple mineral phases was used, but these examples were within the scope of the present invention and yielded favorable results. In Table 3, an alumina-zirconia raw material, a zirconia-mullite raw material, and a mullite raw material were used as the refractory raw materials containing multiple mineral phases, and the contents of the mineral phases in each raw material were as follows: Alumina-zirconia raw material: 60 mass % corundum, 40 mass % zirconia Zirconia-mullite raw material: 50 mass % zirconia, 35 mass % corundum, 15 mass % silica Mullite raw material: 60 mass % corundum, 40 mass % silica As described above, in the present invention, when a refractory particle containing multiple mineral phases is included, the "main mineral phase" is determined by adding each of the multiple mineral phases contained in that refractory particle to the same mineral phases contained in the other refractory particles. For example, in Example 21, 65% by mass of the zirconia-mullite raw material contains 65 x 0.35 = 22.75% by mass of corundum, and when this is added to the 11.2% by mass of corundum in the corundum raw material, the total mass of the raw material blend is 33.95% by mass. Note that 65% by mass of the zirconia-mullite raw material contains 65 x 0.5 = 32.5% by mass of zirconia, but the content of zirconia in this raw material blend is less than the content of corundum, so the main mineral phase of Example 21 is corundum.

[0053] On the other hand, in Table 3, the main mineral phase of Comparative Example 7 is zirconia contained in the zirconia-mullite raw material, which is outside the range of the present invention. Furthermore, in Comparative Example 7, the total content of the silica component and the silicon carbide component in the refractory exceeds the upper limit of the present invention. Therefore, the corrosion resistance was reduced. Furthermore, the main mineral phase of Comparative Example 8 is corundum, which is within the range of the present invention, but the total content of the silica component and the silicon carbide component in the refractory exceeds the upper limit of the present invention. Therefore, the corrosion resistance was reduced.

[0054]

[0055] In Table 4, Examples 3, 23, and 24 are examples in which the contents (total) of the silica component and silicon carbide component in the refractory are different, but are within the range of the present invention, and the overall evaluation was ○ (excellent) or △ (good), thereby obtaining good results. On the other hand, Comparative Example 9 is an example in which the contents (total) of the silica component and silicon carbide component in the refractory exceed the upper limit value of the present invention, and the corrosion resistance was reduced. Note that, by comparing Example 3 with Examples 23 and 24, it is clear that the contents (total) of the silica component and silicon carbide component in the refractory are preferably 5 mass% or less, and that it is particularly preferable to reduce the content of the silica component.

[0056]

[0057] The examples shown in Table 5 are examples in which the amount and type of additives added are different, but are within the scope of the present invention, and the overall evaluation was ○ (excellent) or △ (good), and good results were obtained. ２ O ３ Examples 26, 3, and 27 to 30, which contained 0.1% by mass or more and 3.0% by mass or less in terms of converted value, were given an overall rating of ○ (excellent), and particularly good results were obtained.

[0058]

[0059] The examples shown in Table 6 are examples in which the aspect ratio and content of the carbon fiber differ, but are within the scope of the present invention, and the overall evaluation was ○ (excellent) or △ (good), and good results were obtained. Among them, Examples 32, 3, and 33, in which the aspect ratio of the carbon fiber was 15 to 200 and the content was limited to 5 mass% or less, were overall evaluated as ○ (excellent), and particularly good results were obtained.

[0060] 20 Refractory of the present invention 21 Powder line material (refractory on the back side) 22 Hard-to-adhere material 22G Ventilation refractory 22S Space (gas passage path, 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 10% to 30% by mass of free carbon components, the remainder of which is a main mineral phase consisting of one or more types selected from corundum, spinel and periclase, the periclase content being less than 40% by mass, and the total content of silica and silicon carbide components being less than 15% by mass, wherein, when the total volume of the refractory excluding the free carbon components is taken as 100%, refractory particles having a particle size of more than 0.3 mm account for 20% by volume or more and refractory particles having a particle size of 0.045 mm or less account for 3% to 30% by volume, 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 carbon-containing matrix structure 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 30% by volume or more, and the refractory particles having a particle size of 0.045 mm or less account for 5% by volume or more and 15% by volume or less.

3. Boron component B ２ O ３ The refractory for continuous casting according to claim 1 or 2, containing 0.1 mass % or more and 3.0 mass % or less in terms of a converted value.

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

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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