Refractory for continuous casting and refractory member

Abstract

This invention aims to improve the corrosion resistance and thermal shock resistance of refractory materials and refractory components used in continuous casting. Specifically, the refractory material of this invention contains 10% to 30% by mass of free carbon, and the remaining main mineral phase is composed of one or more minerals selected from corundum, spinel, and periclase, wherein the periclase content is less than 40% by mass, and the combined content of silicon dioxide and silicon carbide is less than 15% by mass. When the portion of the refractory material excluding the free carbon component is taken as 100% by volume, refractory particles with a particle size greater than 0.3 mm account for 20% by volume and refractory particles with a particle size of 0.045 mm or less account for 3% to 30% by volume. Among the refractory particles in this refractory material, at least around the largest coarse particles, there exists a generally continuous void layer with a shape similar to the coarse particles. The apparent porosity of the refractory is less than 16%, and the maximum coefficient of thermal expansion up to 1500°C is less than 0.6%.

Description

Technical Field

[0001] This invention relates to refractory materials for continuous casting and refractory material components such as nozzles for continuous casting using the refractory materials. Background Technology

[0002] The inventors disclosed in Patent Document 1 a refractory for continuous casting that has both excellent corrosion resistance and thermal shock resistance.

[0003] Patent documents

[0004] Patent Document 1: Japanese Patent No. 6027676 Summary of the Invention

[0005] When the inventors were developing and repeatedly testing refractory components using the refractory material disclosed in Patent Document 1, they found that they wanted to further improve the corrosion resistance and thermal shock resistance.

[0006] That is, since the refractory disclosed in Patent Document 1 contains more than 40% by mass of magnesium oxide (pergasse), it exhibits excellent corrosion resistance to steels containing alkaline inclusions such as CaO and MnO, but conversely, it has insufficient corrosion resistance to steels containing acidic inclusions such as SiO2. In addition, it is known that the refractory disclosed in Patent Document 1 will undergo a magnesium oxide-carbon reaction (reaction (1) below) during use, and especially when used repeatedly, the structure will deteriorate and a high elastic modulus will occur, resulting in a decrease in thermal shock resistance.

[0007] MgO (solid) + C (solid) → Mg (gas) + CO (gas) (1)

[0008] In recent years, due to the increasing use of nozzles and other refractory components for continuous casting in a state of insufficient or no preheating, there is a desire to further improve thermal shock resistance.

[0009] The technical problem to be solved by the present invention is to improve the corrosion resistance and thermal shock resistance of refractory materials and refractory components used in continuous casting.

[0010] The inventors, addressing the aforementioned defects caused by excessive magnesium oxide (periacriticite), limited the magnesium oxide (periacriticite) content to less than 40% by mass. Furthermore, through repeated experiments and research to improve corrosion resistance and thermal shock resistance, they discovered that controlling the pore morphology within the refractory while achieving densification is crucial. Moreover, they found that the particle size distribution (volume ratio) of the refractory particles is one of the important control factors, thus leading to the completion of this invention.

[0011] That is, according to one aspect of the present invention, the following refractory for continuous casting can be provided.

[0012] A refractory for continuous casting contains 10% to 30% by mass of free carbon, the remaining main mineral phase being composed of one or more minerals selected from corundum, spinel, and periclase, wherein the periclase content is less than 40% by mass, and the combined content of silicon dioxide and silicon carbide is less than 15% by mass. Its characteristic is that...

[0013] When the portion consisting of free carbon components removed from the composition of the refractory is taken as 100% by volume, refractory particles with a particle size greater than 0.3 mm account for 20% or more by volume, and refractory particles with a particle size of 0.045 mm or less account for 3% or more and 30% by volume.

[0014] In this refractory material, at least around the largest coarse particle, there exists a generally continuous void layer with a shape similar to that coarse particle. Within this generally continuous void layer, the total thickness of the void layer at the interface between the carbon-containing matrix at both ends and the coarse particle is 0.3% to 3.0% relative to the particle size of the coarse particle.

[0015] Furthermore, the apparent porosity is less than 16%, and the maximum coefficient of thermal expansion up to 1500°C is less than 0.6%.

[0016] Furthermore, according to other aspects of the present invention, a refractory component for continuous casting can be provided, wherein the refractory for continuous casting of the present invention is disposed on a portion or entirely of the part in contact with molten steel.

[0017] According to the present invention, the corrosion resistance and thermal shock resistance of refractory materials and refractory components used in continuous casting can be improved. Therefore, excellent durability can be achieved even in environments where they are used without preheating. Attached Figure Description

[0018] Figure 1 This is a schematic diagram showing the structure of the refractory particles used as aggregate in the refractory of the present invention and their surroundings. (a) shows the case where there is a void layer around the refractory particles with a shape similar to the particle outline and the particles are approximately located in the center (a typical example of the present invention). (b) shows the case where there is a void layer around the refractory particles with a shape similar to the particle outline and the particles are located on either side of the inner wall of the void layer (examples such as the off-center distribution produced when preparing a sample for microscopic observation).

[0019] Figure 2 This is a cross-sectional view showing an example of a refractory component in which the refractory of the present invention is applied, namely an impregnation nozzle.

[0020] Figure 3 This is a cross-sectional view showing another example of a refractory component in which the refractory of the present invention is applied, namely an impregnation nozzle.

[0021] Figure 4 This is an example of a continuous casting equipment for steel, and it is an explanatory diagram showing an example of the arrangement of refractory components for continuous casting.

[0022] Figure 5 This is a cross-sectional view showing an example of a long nozzle, which is a form of a refractory component in which the refractory of the present invention is applied.

[0023] Figure 6 This is a cross-sectional view showing an example of a refractory component in which the refractory of the present invention is applied, namely a lower nozzle.

[0024] Figure 7 This is a cross-sectional view showing another example of a refractory component in which the refractory of the present invention is applied, namely a long nozzle.

[0025] Figure 8 This is a cross-sectional view showing an example of a long stopper rod, which is a refractory component in which the refractory of the present invention is applied.

[0026] Symbol Explanation

[0027] 20 - Refractory material of the present invention; 21 - Powder line material (refractory material on the back side); 22 - Difficult-to-adhere material; 22G - Refractory material for ventilation; 22S - Space (gas passage path, accumulator); A - Upper nozzle; B - Sliding nozzle plate; C - Lower nozzle; D - Long nozzle; E - Long stopper rod; F - Impregnated nozzle; G - Refractory material for lining. Detailed Implementation

[0028] As described above, to solve the aforementioned problems, it is important to achieve densification of the refractory while simultaneously controlling the pore morphology within the refractory. Therefore, the inventors have aimed for a refractory structure in which refractory particles with a diameter exceeding 0.3 mm, serving as aggregate, exist independently and discontinuously within a matrix structure containing three-dimensional continuous carbon (hereinafter referred to as "carbonaceous matrix"). Furthermore, among these refractory particles, at least around the largest coarse particles, a generally continuous void layer with a shape similar to that of the coarse particle exists. That is, by employing such a refractory structure, the thermal expansion of the coarse particles, which significantly contributes to the thermal expansion of the refractory, is absorbed by the generally continuous void layer surrounding the particles, resulting in an apparent disappearance of the thermal expansion of the coarse particles. In other words, during heating, while the void layer exists around the coarse particles, the thermal expansion of the refractory is primarily due to the thermal expansion of the three-dimensional continuous carbonaceous matrix portion, thus reducing the thermal expansion of the refractory.

[0029] Furthermore, in this invention, by limiting the volume ratio of refractory particles with a particle size exceeding 0.3 mm (hereinafter referred to as "coarse refractory particles") and refractory particles with a particle size of 0.045 mm or less (hereinafter referred to as "microscopic refractory particles"), densification of the refractory can be achieved, and the pore morphology inside the refractory can be controlled as described above. Therefore, the corrosion resistance and thermal shock resistance of refractory materials and refractory components used for continuous casting can be improved. A detailed explanation follows.

[0030] The refractory of the present invention contains 10% to 30% by mass of free carbon. Here, "free carbon" refers to carbon components consisting of carbon monomers other than compounds such as carbides such as B4C and SiC, excluding unavoidable impurities; it refers to amorphous or quasi-crystalline substances such as graphite formed by heating various organic binders, pitch, tar, and carbon black; and it refers to all carbon components present in the refractory structure, whether in particulate (including fibrous) or non-specifically shaped form, existing in a continuous or discontinuous state.

[0031] When the free carbon content is less than 10% by mass, a three-dimensional continuous carbonaceous matrix cannot be formed within the refractory structure, resulting in insufficient low-expansion effect. Furthermore, when it exceeds 30% by mass, damage to the carbonaceous matrix caused by molten steel, slag, etc., becomes severe, leading to increased refractory melting loss and decreased corrosion resistance. Additionally, the extensive use of graphite and other materials as a source of free carbon reduces formability and impairs the density of the refractory, further reducing corrosion resistance. Preferably, the free carbon content is between 15% and 25% by mass.

[0032] The main mineral phase of the refractory of the present invention is composed of one or more minerals selected from corundum, spinel, and periclase. However, the content of periclase is limited to less than 40% by mass. This is because when the content of periclase (magnesium oxide) is 40% by mass or more, the defects described above will occur. In addition, it is preferable that the content of periclase is 35% by mass or less.

[0033] In this invention, "main mineral phase" refers to the most abundant mineral phase among the mineral phases in the refractory. When there are two or more most abundant mineral phases, they are all considered main mineral phases. Furthermore, when refractory particles contain multiple mineral phases, the "main mineral phase" is determined by combining the multiple mineral phases contained in the refractory particles with the same type of mineral phase contained in other refractory particles.

[0034] In the refractory of the present invention, the combined content of silicon dioxide and silicon carbide is limited to less than 15% by mass. This is because when the combined content of silicon dioxide and silicon carbide is 15% by mass or more, the corrosion resistance will decrease significantly. Furthermore, since silicon carbide has the function of inhibiting the oxidation of free carbon components, it can be appropriately contained in the range of less than 15% by mass; for example, if it is 5% by mass or less, it can exert its oxidation-inhibiting function without substantially reducing the corrosion resistance.

[0035] Next, one of the features of the present invention, namely the particle size distribution (volume ratio) of the refractory particles in the refractory, will be described.

[0036] In this invention, the particle size distribution (volume percentage) of the refractory particles in the refractory is characterized in that, when the portion of the constituent consisting of free carbon components removed from the constituent of the refractory is taken as 100 vol%, the coarse refractory particles are 20 vol% or more, and the fine refractory particles are 3 vol% or more and 30 vol% or less.

[0037] Since the volume percentage of coarse refractory particles is less than 20% by volume, the volume percentage of micro or medium-sized refractory particles (described later) increases, thus increasing the number of refractory particles in the refractory. As a result, a refractory structure with continuous refractory particles is formed, leading to high expansion. Consequently, thermal shock resistance decreases. While there is no particular upper limit to the volume percentage of coarse refractory particles, from the viewpoint of consistently ensuring the necessary properties such as strength and corrosion resistance required for continuous casting, it can be, for example, 60% by volume or less. Preferably, the volume percentage of coarse refractory particles is 30% by volume or more, more preferably 40% by volume or more and 60% by volume or less. Furthermore, while there is no particular upper limit to the particle size of coarse refractory particles, again from the viewpoint of consistently ensuring the necessary properties such as strength and corrosion resistance required for continuous casting, it is preferably 3mm or less, more preferably 1mm or less. That is, as coarse refractory particles, in addition to particles with a diameter greater than 0.3 mm and less than 1 mm, the refractory of the present invention may also contain particles with a diameter greater than 1 mm and less than 3 mm. However, it is preferred that the volume percentage of particles with a diameter greater than 1 mm and less than 3 mm is 15% or less when the portion other than the component consisting of free carbon is taken as 100% by volume, and more preferably 0% by volume, that is, it does not contain refractory particles with a diameter greater than 1 mm and less than 3 mm.

[0038] Furthermore, when the volume percentage of the particulate refractory particles is less than 3% by volume, a dense refractory cannot be obtained, and corrosion resistance decreases. On the other hand, when the volume percentage of the particulate refractory particles exceeds 30% by volume, the number of refractory particles in the refractory increases, resulting in a continuous refractory particle structure and high expansion. Consequently, thermal shock resistance decreases. Preferably, the volume percentage of the particulate refractory particles is 5% by volume or more and 15% by volume or less. Additionally, in the refractory of the present invention, the particulate refractory particles are substantially present in a carbonaceous matrix.

[0039] While the volume ratios of coarse (particle size greater than 0.3 mm) and fine (particle size less than 0.045 mm) refractory particles have been described above, the refractory of the present invention appropriately includes medium-sized (particle size greater than 0.045 mm and less than 0.3 mm) refractory particles. The volume ratio is the remaining portion of the volume ratio of coarse refractory particles and fine refractory particles after removing the portion consisting of free carbon components from the composition of the refractory, specifically, preferably 10% to 77% by volume, more preferably 30% to 70% by volume.

[0040] In this invention, the particle size of refractory particles refers to the size of the sieve mesh when sieving refractory particles. For example, refractory particles with a particle size of less than 0.045 mm refer to refractory particles that pass through a sieve with a mesh size of 0.045 mm, 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 a mesh size of 0.3 mm.

[0041] Next, the microstructure of the refractory of the present invention will be described in detail. As described above, the basic microstructure of the refractory of the present invention is as follows: within a three-dimensional continuous carbonaceous matrix, refractory particles with a particle size exceeding 0.3 mm, serving as aggregate, exist independently and discontinuously. Furthermore, among these refractory particles, at least around the largest coarse particle, a generally continuous void layer with a shape similar to that coarse particle exists. Specifically, within this generally continuous void layer, the total thickness of the void layer existing at the interfaces between the carbonaceous matrix and the coarse particle at both ends is 0.3% to 3.0% relative to the particle size of the coarse particle.

[0042] Here, "a roughly continuous void layer" refers to a void shape that, when observed under a microscope in cross-section around the refractory particles used as aggregate, has a magnified shape that is roughly similar to the cross-sectional shape of the particles, and the particles exist inside the voids like bell-shaped balls (see reference). Figure 1 (a) This refers to a structure in which there are no carbon or other structural materials that hinder the thermal expansion of refractory particles within the void layer, and the void layer is uneven or lacks voids, with random portions where refractory particles are in direct contact with each other or with the carbonaceous matrix.

[0043] Furthermore, in the refractory of the present invention, a void layer exists in a "continuous state" around the refractory particles that serve as aggregate. However, when the void layer is verified by microscopic observation, it can be said that the refractory particles exist in a way that is not fixed in space and floats up. Therefore, when a sample is made from the refractory, a portion of the surface of the refractory particles may also be generated that comes into contact with other surrounding refractory particles and carbonaceous matrix (see reference). Figure 1 (b) Therefore, the term "generally continuous" was used to consider the actual conditions during verification. In reality, although a void layer exists overall around the refractory particles, even when a portion of the sample is in contact with other refractory particles or the carbonaceous matrix, such a portion is not in a state of "bonding or adhesion" to the extent that it fixes the refractory particles, as observed, for example under a microscope. That is, through this "generally continuous void layer," the thermal expansion of the refractory particles can be absorbed, thereby achieving low expansion of the refractory.

[0044] From the perspective of reducing the thermal expansion of refractory materials, the thicker the void layer around the refractory particles, the better. Furthermore, it is preferable that a void layer exists around all refractory particles that serve as aggregates. However, since the void layer around the refractory particles can cause a decrease in the strength of the refractory, it is necessary to adjust the thickness of the void layer while achieving a balance between thermal expansion and strength, damage, etc.

[0045] The ratio of void layer thickness to particle size (void layer thickness ratio per particle: MS value (microspace value)) is such that larger particles have a smaller ratio, and smaller particles have a larger ratio. Therefore, the MS value of the largest coarse particle in a specific refractory particle structure refers to the lower limit of the void layer thickness ratio of each particle in the refractory structure, which can be used to evaluate the approximate thermal shock resistance of the refractory.

[0046] Here, the MS value refers to the ratio of the thickness L of the void layer between the coarse particle and the carbonaceous matrix (the sum of the void layer thicknesses on both sides of the particle is taken as L) to the coarse particle size D, which can be calculated by the following formula.

[0047] MS value = (L / D) × 100 (%)

[0048] Specifically, in this invention, the MS value (%) is calculated by the following method.

[0049] In microscopic observation of the refractory microstructure, ten coarse particles were selected in order of particle size. On the surface of each particle, the largest circle that contacts and encloses its outline was drawn, and an arbitrary line passing through the center of this circle was drawn. Using this line as a reference, three more lines were drawn at 45° intervals passing through the center of the aforementioned circle, for a total of four lines for each particle. Then, on each of these lines, the lengths between the outline points at both ends of the particle were designated as D1, D2, D3, and D4. The total thickness of the void layer at the particle interface on each line was measured as L1, L2, L3, and L4, respectively. Using the values ​​obtained from these four lines, MS1, MS2, MS3, and MS4, calculated using the above formula, were calculated, and the average of these values ​​was taken as the void layer thickness ratio, i.e., the MS value, for one coarse particle. The MS values ​​of the ten pre-selected coarse particles were calculated using the above method, and they were averaged to obtain the MS value of the refractory microstructure.

[0050] Furthermore, the MS value of the refractory structure is evaluated using the ten largest coarse particles selected in descending order of particle size during microscopic observation of the refractory structure because larger particle sizes result in greater changes in volume and length due to expansion, thus having a greater impact on the thermal shock resistance of the refractory. Therefore, the MS value, as an indicator for adjusting and evaluating thermal shock resistance, requires calculation of the largest coarse particles in the refractory structure. Moreover, from the same perspective, in this invention, the aforementioned "generally continuous void layer" needs to exist at least around the ten largest coarse particles selected in descending order of particle size during microscopic observation of the refractory structure.

[0051] The inventors have confirmed that in refractory materials whose main mineral phase is composed of one or more types selected from corundum, spinel, and periclase, and whose periclase content is less than 40% by mass, a low expansion effect is achieved, and the thickness of the void layer around the refractory particles, which achieves a balance in terms of strength, corrosion resistance, and abrasion resistance, is 0.3% to 3.0% based on the MS value calculated for coarse particles with the largest particle size. That is, when the MS value is less than 0.3%, a sufficient low expansion effect cannot be obtained. Furthermore, when the MS value exceeds 3.0%, the strength decreases, and the corrosion resistance and abrasion resistance also decrease. Thus, in this invention, by forming a refractory structure in which, among the refractory particles in the refractory, at least around the largest coarse particle, there exists a generally continuous void layer with a shape similar to that coarse particle, and within this generally continuous void layer, the total thickness of the void layer existing at the interface between the carbonaceous matrix structure at both ends and the coarse particle is 0.3% to 3.0% relative to the particle size of the coarse particle, a refractory structure that can significantly improve thermal shock resistance and achieve a balance in terms of strength, corrosion resistance, and abrasion resistance can be provided.

[0052] This method of controlling MS value involves forming a roughly continuous void layer with a similar shape around at least the largest coarse particles in the refractory material, and controlling the thickness of this void layer, for example, as follows.

[0053] Although controlling the MS value is synonymous with controlling the coefficient of thermal expansion, during heat treatment, larger refractory particles (coarse particles) have greater thermal expansion and a more significant difference in thermal expansion with the carbonaceous matrix. Therefore, a roughly continuous void layer (hereinafter also referred to as "MS") with a similar shape is easily formed around these coarse particles. Conversely, smaller refractory particles have smaller thermal expansion, making it difficult to form a distinct MS. Therefore, by controlling the particle size distribution (volume ratio) of the refractory particles in the refractory, the MS value, i.e., the coefficient of thermal expansion, can be controlled. In this invention, when the portion consisting of free carbon components is removed (100% by volume), by making refractory particles with a particle size greater than 0.3 mm at 20% by volume or more, and refractory particles with a particle size of 0.045 mm or less at 3% by volume or more to 30% by volume, low expansion and its control can be achieved. For example, to achieve lower expansion, one can simply reduce the volume proportion of refractory particles with a diameter of less than 0.045 mm within the aforementioned particle size composition (volume proportion) range to disrupt the continuity of refractory particles in the refractory structure, while increasing the volume proportion of refractory particles with a diameter greater than 0.3 mm, thereby promoting the formation of MS.

[0054] By combining the above-mentioned composition (chemical composition, main mineral phase, particle size distribution (volume ratio) of refractory particles, and refractory microstructure), the refractory of the present invention can stably possess both a dense structure with an apparent porosity of less than 16% and a low expansion coefficient of less than 0.6% up to 1500°C. Therefore, the corrosion resistance and thermal shock resistance of refractory materials and refractory components used in continuous casting can be improved, and excellent durability can be maintained even in environments where they are used without preheating.

[0055] In this invention, the chemical composition, microstructure, apparent porosity, and coefficient of thermal expansion of the refractory are evaluated primarily on samples heated to 1000°C in a non-oxidizing atmosphere. This is because the goal is to improve analytical accuracy by removing moisture, organic matter, water-based substances, and carbon oxides from the refractory, and by stabilizing the chemical composition through the carbonization of organic binders. Based on this, the heating time is set to the period until the weight change caused by heating disappears. However, if the refractory has already undergone heat treatment at temperatures above 1000°C during its manufacturing process, or at temperatures above 800°C depending on the type of volatile components, the evaluation of the chemical composition, microstructure, apparent porosity, and coefficient of thermal expansion can be performed on the finished product.

[0056] Preferably, the refractory of the present invention contains boron at a concentration of 0.1% to 3.0% by mass (based on B2O3 equivalent). When the refractory is heated, the boron component forms fibrous aluminum borate or the like within the carbonaceous matrix. This densifies and strengthens the carbonaceous matrix, thereby increasing the strength of the refractory.

[0057] Furthermore, the refractory of the present invention may also contain carbon fibers in a carbonaceous matrix. The carbon fibers fill defects such as cracks that occur due to the shrinkage of the carbonaceous matrix, which is caused by the carbonization of organic binder components during heating of the refractory. This achieves densification and strengthening of the carbonaceous matrix, thereby improving the strength of the refractory. From the viewpoint of fully utilizing this strength-enhancing effect of the refractory, it is preferable that the aspect ratio of the carbon fibers is 15 to 200, and preferably that their content is 5% by mass or less.

[0058] Similar to the preparation of the samples in the embodiments described later, the refractory of the present invention can be prepared by the same method as that used for preparing general refractory with one or more main mineral phases selected from corundum, spinel and periclase.

[0059] For example, a binder is added to the raw material formulation containing refractory particles that constitute the main mineral phase, and the mixed clay is adjusted to a state suitable for forming. Then, the clay is formed by CIP (Cold Isostatic Pressing), dried at a temperature below about 300°C, and then heat-treated in a non-oxidizing atmosphere at a temperature between about 800°C and about 1200°C.

[0060] Next, a refractory component for continuous casting using the refractory material of the present invention will be described. Figure 2 The image shows a longitudinal section of a refractory component for continuous casting, namely an impregnation nozzle.

[0061] exist Figure 2 In (a), an example is shown where, in a portion of the area in contact with molten steel, an impregnation nozzle of the refractory 20 of the present invention is arranged as a single layer from the surface in contact with the molten steel to the back side. Figure 2 In (a), if the refractory material 20 of the present invention is also disposed on the powder line material 21 portion, it can become an impregnation nozzle in which the refractory material of the present invention is disposed as a single layer in the entire area of ​​the part in contact with the molten steel, from the surface in contact with the molten steel to the back side. In the case of a nozzle with a single-layer structure, the risk of cracking and the like can be reduced, and in addition, a simple method can be used in manufacturing. In the manufacturing of such a nozzle with a single-layer structure, it is only necessary to fill the target area of ​​the CIP forming mold with the refractory material of the present invention in a single layer using the manufacturing method described above.

[0062] In addition, although Figure 2 (a) shows an example of a cylindrical shape, but nozzles such as impregnation nozzles for refractory materials using the present invention are not limited to such cylindrical shapes, for example, not limited to... Figure 2 (b) shows the shapes of nozzles, including flat, elliptical, and funnel-shaped (funnel-shaped with an expanded upper diameter), which are mainly used for casting thin plates and can be applied to nozzles of various shapes.

[0063] In addition, Figure 2 (c) shows that there is a capability from Figure 2 (a) is an example of an impregnation nozzle that blows gas into molten steel from a portion of its inner bore (inner bore wall). In this example, a highly permeable refractory material (hereinafter referred to as "ventilation refractory") 20G is disposed on 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 can improve porosity and permeability while maintaining the refractory composition of the present invention. Furthermore, Figure 2 In (c), the symbol 20S represents space, which is the passageway for gas and also the gas storage chamber.

[0064] exist Figure 3 The diagram shows an example of an impregnation nozzle in which the refractory material 20 of the present invention is disposed on a portion or entirely of the part in contact with molten steel, and a layer of refractory material (difficult-to-adhere material 22) with a different composition than the refractory material 20 of the present invention is disposed on its inner side, thereby forming multiple layers, and the multiple layers form an integral structure in a state of direct contact with each other. In the manufacture of such a nozzle composed of multiple layers, it is only necessary to, based on the above-described manufacturing method, in the target area within the CIP forming mold, separate the blank for feeding the blank at a position of a predetermined thickness in the radial direction from the surface in contact with the molten steel, fill the inner side (mandrel side) with blank material for refractory material different from the refractory material of the present invention, and fill the back side with blank material for refractory material of the present invention, etc. Thereafter, before forming, it is only necessary to remove the clamps such as the plates used for separation and perform pressure forming.

[0065] As nozzles for continuous casting of refractory materials to which the present invention can be applied or suitable for application, in addition to impregnation nozzles, examples include gating nozzles (including upper nozzles, open nozzles, etc.), intermediate nozzles, and flow control nozzles (especially internal orifices, etc.).

[0066] exist Figure 4The diagram shows an example of a continuous casting apparatus for steel. On the left side of the same figure, a structure is shown where the nozzle section, serving as the flow path for molten steel when discharging from a molten steel container, is composed of multiple nozzles. In this structure, the immersion nozzle F is an externally mounted type. The refractory material 20 of the present invention can be applied not only to the immersion nozzle F, but also to part or the entire portion of the contact area with molten steel at various nozzles such as the upper nozzle A, sliding nozzle plate B, lower nozzle C, and long nozzle D of such a structure composed of multiple nozzles for continuous casting. Furthermore, it can also be applied to so-called internally mounted immersion nozzles with a structure that integrates the nozzle section serving as the discharge path. Figure 4 On the right side), so-called open nozzles that are not immersed in molten steel, etc. Furthermore, it can also be used as a stopper E located above the nozzle section for controlling or opening / closing the molten steel flow, or as a refractory lining G for molten steel containers.

[0067] exist Figure 5 and Figure 6 The image shows an example where a long nozzle and a lower nozzle of the refractory material 20 of the present invention are respectively arranged on part or the whole of the part in contact with molten steel. Figure 5 and Figure 6 In the present invention, either or both of the inner refractory layer and the back refractory layer can be the refractory material 20.

[0068] In addition, Figure 7 The image shows an example of using the refractory material 20 of the present invention to construct a long nozzle other than the powder wire material 21 portion. Additionally, in... Figure 7 Alternatively, the refractory material 20 of the present invention can be disposed on the powder line material 21 portion.

[0069] exist Figure 8 The image shows an example of a long stopper rod in which the refractory material 20 of the present invention is disposed in part or entirely at the portion in contact with molten steel. Figure 8 In this invention, either or both of the top end of the long stopper rod and the base end other than the top end can be the refractory material 20.

[0070] Example

[0071] Tables 1 to 6 below show the raw material formulations and evaluation results of embodiments and comparative examples of the present invention. Furthermore, in each table, the "volume ratio of refractory particles" is a volume ratio calculated based on the raw material formulation, but this volume ratio is maintained in the manufactured refractory. That is, 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 100% of the constituents of the refractory is taken as the portion consisting of free carbon components removed from the constituents of the refractory. In addition, in each table, "mineral phase" refers to the refractory raw materials in the raw material formulation, but the mineral phases constituting these refractory raw materials are maintained in the manufactured refractory. Furthermore, in each table, "additive" refers to a boron source, and the amount added is expressed as an external addition amount of 100% by mass relative to the raw material formulation other than "additive".

[0072] In each of the examples shown in the table, an organic binder, namely phenolic resin, was added to the raw material formulation to adjust the mixed clay to a state suitable for molding. After molding the clay by CIP, it was cured and dried at 300°C, followed by heat treatment at 1000°C in a non-oxidizing atmosphere to obtain the refractory materials of each example.

[0073] The chemical composition of the obtained refractory was analyzed, the microstructure was observed, and the results were used for evaluation tests.

[0074] The chemical composition analysis was conducted according to the method of Japanese Industrial Standard JIS R2216.

[0075] In the observation of the microstructure, after the resin is impregnated into the refractory microstructure, a mirror surface is polished by mechanical grinding. The MS value is then obtained by microscopic observation using the above method, and the continuity of the void layer is observed.

[0076] As an evaluation of refractory materials, the apparent porosity, maximum coefficient of thermal expansion up to 1500℃, corrosion resistance, and thermal shock resistance were evaluated, and a comprehensive evaluation was conducted based on these evaluation results.

[0077] Apparent porosity was determined according to the method of Japanese Industrial Standard JIS R2205.

[0078] The coefficient of thermal expansion is measured up to 1500°C according to the method of Japanese Industrial Standard JISR2207-3, and the maximum coefficient of thermal expansion up to 1500°C is evaluated.

[0079] The corrosion resistance was evaluated by immersing prism specimens (20×20×180mm) of refractory materials from each example in a crucible containing approximately 30mm of synthetic slag with a CaO / SiO2 mass ratio adjusted to 1.0, on the surface of low-carbon steel melted at 1550°C. After removal, the melting loss at the steel-slag interface was measured, and the degree of melting loss was compared. Specifically, the melting loss of each example refractory was converted into a melting loss index, with the melting loss of Comparative Example 2 set as 100. A melting loss index less than 100 was considered an effective solution to the problem. More specifically, a melting loss index of 90 or less was rated as 0 (excellent), more than 90 but less than 100 as △ (good), and more than 100 as × (poor).

[0080] The evaluation of thermal shock resistance was conducted by using a cylindrical sample (outer diameter / inner diameter (inner hole diameter) / height = 130 / 55 / 300 mm), and pouring molten iron at 1600°C into the inner hole of the sample at room temperature, thus subjecting the refractory material to thermal shock. After the test, horizontal sections were cut at 50 mm intervals and inspected for cracks. Cases with no observed cracks were rated ○ (Excellent), cases with micro-cracks were rated △ (Good), and cases with confirmed cracks were rated × (Poor).

[0081] The overall evaluation is as follows: A case where the MS value in the microstructure is within the range of this invention (0.3% to 3.0%), the continuity of the void layer is substantially continuous, the apparent porosity is within the range of this invention (16% or less), and the maximum coefficient of thermal expansion up to 1500°C is within the range of this invention (0.6% or less), with a corrosion resistance rating of 0 and a thermal shock resistance rating of 0 is evaluated as ○ (Excellent). A case where the MS value in the microstructure is within the range of this invention (0.3% to 3.0%), the continuity of the void layer is substantially continuous, the apparent porosity is within the range of this invention (16% or less), and the maximum coefficient of thermal expansion up to 1500°C is within the range of this invention (0.6% or less), and either the corrosion resistance or thermal shock resistance rating is △ is evaluated as △ (Good). A case where the continuity of the void layer in the microstructure is partially continuous, the apparent porosity exceeds 16%, the maximum coefficient of thermal expansion up to 1500°C exceeds 0.6%, and either the corrosion resistance rating is × or the thermal shock resistance rating is × is evaluated as × (Poor).

[0082] (Table 1)

[0083]

[0084] In Table 1, Examples 1 to 5 are examples with different contents of free carbon (hereinafter referred to as "FC") in the refractory. However, within the scope of the present invention, they exhibit low apparent porosity, excellent corrosion resistance, and excellent thermal shock resistance, and are rated as ○ (excellent) or △ (good) overall, yielding good results. Among them, Examples 2 to 4, with an FC content in the preferred range of 15% by mass to 25% by mass, are rated as ○ (excellent) overall, yielding particularly good results.

[0085] In contrast, Comparative Example 1, where the FC content is below the lower limit of the present invention, failed to form a three-dimensional continuous carbonaceous matrix within the refractory structure. The continuity of the void layer surrounding the coarse particles was compromised, resulting in "partial continuity." Consequently, a sufficient low-expansion effect was not achieved, leading to high expansion and decreased thermal shock resistance. On the other hand, Comparative Example 2, where the FC content exceeds the upper limit of the present invention, resulted in decreased corrosion resistance.

[0086] (Table 2)

[0087]

[0088] In Table 2, Examples 6 to 9 are examples with different volume ratios of coarse refractory particles, but within the scope of the present invention, the overall evaluation is ○ (excellent) or △ (good), indicating good results. Furthermore, Example 6 is an example where the volume ratio of coarse refractory particles is the lower limit of the present invention, i.e., 20% by volume. Compared to Example 7, where the volume ratio of coarse refractory particles is 30% by volume, this results in high expansion, leading to poorer thermal shock resistance. Additionally, Example 8 is an example where the upper limit of the coarse refractory particle size is 3 mm. However, compared to Example 9, where the upper limit of the coarse refractory particle size is 1 mm, the apparent porosity increases, resulting in poorer corrosion resistance.

[0089] On the other hand, Comparative Example 3 is an example where the volume ratio of coarse refractory particles is lower than the lower limit of the present invention. As a result, the number of refractory particles in the refractory increases, resulting in a refractory structure in which refractory particles exist continuously. Therefore, it becomes highly expandable and its thermal shock resistance decreases.

[0090] Similarly, in Table 2, Examples 10, 11, 3, 12, and 13 are examples with different volume ratios of refractory particles, but within the scope of the present invention, they are rated as ○ (excellent) or △ (good), indicating good results. Among them, Examples 11, 3, and 12, which have a preferred volume ratio of refractory particles of 5% to 15% by mass, are rated as ○ (excellent), indicating particularly good results.

[0091] Conversely, Comparative Example 4 is an example where the volume ratio of the refractory particles is lower than the lower limit of the present invention, resulting in an inability to obtain a dense refractory and a decrease in corrosion resistance. On the other hand, Comparative Example 5 is an example where the volume ratio of the refractory particles exceeds the upper limit of the present invention. As a result, the number of refractory particles in the refractory increases, resulting in a refractory structure with continuous refractory particles. Therefore, it becomes highly expandable and its thermal shock resistance decreases.

[0092] (Table 3)

[0093]

[0094] In Table 3, Examples 3 and Examples 14 to 19 are examples with different main mineral phases, but good results can be obtained within the scope of the present invention. Furthermore, in Example 15, the most abundant mineral phases are corundum and spinel, therefore the main mineral phases are corundum and spinel. In addition, in Example 17, the most abundant mineral phases are corundum, spinel, and periclase, therefore the main mineral phases are corundum, spinel, and periclase.

[0095] 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 a decrease in corrosion resistance.

[0096] Similarly, in Table 3, Examples 20 to 22 are examples of refractory materials (refractory particles) containing multiple mineral phases, but good results can be obtained within the scope of the present invention. Furthermore, in Table 3, alumina-zirconia raw materials, zirconium-mullite raw materials, and mullite raw materials were used as refractory materials containing multiple mineral phases, but the mineral phase content of each raw material is as follows.

[0097] Alumina and zirconia raw materials: 60% by mass of corundum, 40% by mass of zirconia

[0098] Zircon-mullite raw material: Zirconium oxide 50% by mass, Corundum 35% by mass, Silica 15% by mass

[0099] Mullite raw material: 60% corundum, 40% silica

[0100] As described above, in this invention, when refractory particles containing multiple mineral phases are included, the "main mineral phase" is determined by combining the multiple mineral phases contained in the refractory particles with the same mineral phases contained in other refractory particles. For example, in Example 21, 65% by mass of the zircon mullite raw material contains 65 × 0.35 = 22.75% by mass of corundum. If this is combined with the 11.2% by mass of corundum in the corundum raw material, the total content in the raw material formulation is 33.95% by mass. Furthermore, although 65% by mass of the zircon mullite raw material contains 65 × 0.5 = 32.5% by mass of zirconium oxide, since the zirconium oxide content in this raw material formulation is less than the corundum content mentioned above, the main mineral phase in Example 21 is corundum.

[0101] On the other hand, in Table 3, the main mineral phase of Comparative Example 7 is zirconium oxide contained in the zircon-mullite raw material, which is outside the scope of the present invention. Furthermore, in Comparative Example 7, the combined content of silica and silicon carbide in the refractory exceeds the upper limit of the present invention. Therefore, corrosion resistance decreases.

[0102] Furthermore, although the main mineral phase of Comparative Example 8 was corundum, which is within the scope of the present invention, the combined content of silica and silicon carbide in the refractory exceeded the upper limit of the present invention. Therefore, corrosion resistance decreased.

[0103] (Table 4)

[0104]

[0105] In Table 4, Examples 3, 23, and 24 are examples where the total content of silica and silicon carbide in the refractory varies, but within the scope of the present invention, the overall evaluation is ○ (excellent) or △ (good), indicating good results. On the other hand, Comparative Example 9 is an example where the total content of silica and silicon carbide in the refractory exceeds the upper limit of the present invention, resulting in decreased corrosion resistance.

[0106] Furthermore, through comparison of Example 3 with Examples 23 and 24, it is preferred that the content (total) of silicon dioxide and silicon carbide in the refractory is 5% by mass or less, and it is particularly preferred to reduce the content of silicon dioxide.

[0107] (Table 5)

[0108]

[0109] The embodiments shown in Table 5 are examples of different amounts and types of additives, but within the scope of the present invention, the overall evaluation is ○ (excellent) or △ (good), indicating good results. Among them, Examples 26, 3, and 27 to 30, which contain 0.1% to 3.0% boron by mass (converted to B2O3), have an overall evaluation of ○ (excellent), indicating particularly good results.

[0110] (Table 6)

[0111]

[0112] The embodiments shown in Table 6 are examples of different aspect ratios and contents of carbon fibers, but within the scope of the present invention, the overall evaluation is ○ (excellent) or △ (good), and good results can be obtained. Among them, the overall evaluation of Embodiments 32, 3, and 33, in which the aspect ratio of carbon fibers is more than 15 and less than 200 and the content of carbon fibers is limited to less than 5% by mass, is ○ (excellent), and particularly good results can be obtained.

Claims

1. A refractory for continuous casting, comprising 10% to 30% by mass of free carbon, wherein the remaining main mineral phase is composed of one or more minerals selected from corundum, spinel, and periclase, wherein the periclase content is less than 40% by mass, and the combined content of silicon dioxide and silicon carbide is less than 15% by mass, characterized in that... When the portion consisting of free carbon components removed from the composition of the refractory is taken as 100% by volume, refractory particles with a particle size greater than 0.3 mm account for 20% or more by volume, and refractory particles with a particle size of 0.045 mm or less account for 3% or more and 30% by volume. In this refractory material, at least around the largest coarse particle, there exists a generally continuous void layer with a shape similar to that coarse particle. Within this generally continuous void layer, the total thickness of the void layer at the interface between the carbon-containing matrix at both ends and the coarse particle is 0.3% to 3.0% relative to the particle size of the coarse particle. Furthermore, the apparent porosity is less than 16%, and the maximum coefficient of thermal expansion up to 1500°C is less than 0.6%.

2. The refractory for continuous casting according to claim 1, characterized in that, The refractory particles with a diameter greater than 0.3 mm account for more than 30% by volume, and the refractory particles with a diameter less than 0.045 mm account for more than 5% by volume and less than 15% by volume.

3. The refractory for continuous casting according to claim 1 or 2, characterized in that, It contains boron content of more than 0.1% by mass and less than 3.0% by mass, based on the B2O3 conversion value.

4. The refractory for continuous casting according to any one of claims 1 to 3, characterized in that, The matrix contains carbon fibers with an aspect ratio of 15 to 200, and the content of the carbon fibers is less than 5% by mass.

5. A refractory component for continuous casting, characterized in that, The refractory for continuous casting as described in any one of claims 1 to 4 is disposed on a portion or the entire part of the part in contact with the molten steel.

Images