JP2013188764A - Nozzle for casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent oxidation in a preheating stage of a nozzle for casting by restraining an antioxidant layer, which is arranged on an inner hole surface of the nozzle for casting, from being peeled off in the preheating stage.SOLUTION: In a nozzle 20 for casting, an intermediate layer 2 is provided on a part or the whole of a surface of a nozzle body refractory 1 having an inner hole 5 for allowing the passage of molten steel, and one or more antioxidant layers 3 densified by being vitrified in a temperature range of 400-1,500°C are formed on the outer surface of the intermediate layer 2. The intermediate layer 2 is a refractory in which inorganic fibers are intertwined with one another and coupled together by a carbonaceous binder, and has resistance to heat at 1,000°C or higher. The intermediate layer 2 and the nozzle body refractory 1 configure an integral structure in which matrix organizations of the mutual refractories continue into each other via an interface between them.

Description

  The present invention relates to a casting nozzle used for continuous casting of molten steel.

  Casting nozzles such as immersion nozzles and long nozzles generally have an antioxidant layer having a certain thickness consisting of a vitrification raw material, a binder and pores in order to prevent oxidation in the preheating stage before operation. Is applied to the surface. This anti-oxidation layer is heated above the glass transition temperature during preheating before operation, thereby forming a viscous and dense glass layer, and shielding the external oxidizing gas so that the nozzle body refractory contains carbon. Prevent oxidation.

  Since the casting nozzle has an inner hole for allowing molten steel to pass through and is generally cylindrical, the antioxidant layer is often applied not only to the outer peripheral surface but also to the inner hole surface. When the antioxidant layer applied to the surface of such a casting nozzle is preheated and heated above the glass transition temperature, the vitrification component in the antioxidant layer becomes fluid due to liquefaction or viscosity reduction, The inner pores are aggregated by the surface tension of the glass, and a dense glass layer is formed while contracting in the thickness direction with contraction. In densification, tug-of-war occurs simultaneously in the film plane direction. In the outer periphery of the cylindrical casting nozzle, the stress is released by heating above the glass transition temperature, so that defects such as cracks are unlikely to occur, and the shrinkage direction is also the film thickness direction. For this reason, the antioxidant layer applied to the outer peripheral surface has relatively few defects, and a dense glass layer is formed, so that the antioxidant function is easily exhibited.

  However, since the antioxidant layer applied to the inner hole surface of the cylindrical casting nozzle shrinks in the center direction, that is, the direction in which the circumference is reduced (the direction away from the inner hole surface) with densification, Locally floating portions from the inner hole surface are likely to occur.

  In the production of a casting nozzle, a mold having a core rod is generally filled with a refractory compound containing graphite and molded by CIP, so that the graphite is oriented along the core rod on the inner hole surface. It is easy to expose the inert surface of graphite (the flat surface having a wide flat shape). On the inner hole surface, in addition to the structural factors accompanying the shrinkage of the antioxidant layer as described above, that is, the force that moves toward the center side (space side) of the cylinder is generated, Due to the graphite orientation phenomenon on the inner hole surface, it tends to cause floating and swelling in the preheating stage. If a phenomenon occurs in which the antioxidant layer does not adhere to the inner hole surface of the nozzle body refractory even when locally, the nozzle body refractory is oxidized from the inner hole surface during the preheating stage, causing erosion and wear during casting. It is easy to cause troubles that cause melting.

  Various countermeasures have been taken as countermeasures. For example, in Patent Document 1, the surface of a carbonaceous nozzle body refractory is coated with a slurry-like coating agent composed of oxide fine powder or a binder as an underlayer, and is preliminarily applied by spraying, dipping, brushing, or the like to prevent oxidation. Methods for improving the characteristics have been proposed. However, since this slurry-like coating agent contains a large amount of binder components and moisture in order to obtain fluidity, it often involves a shrinkage phenomenon in the process of removing them. Furthermore, in the case of such an aqueous coating agent, the problem of the wetting defect between the underlayer and the nozzle body refractory occurs when the nozzle body refractory containing carbon, particularly when the graphite content is high and the orientation characteristics are strong. Easily, especially during heating, it appears as a delamination phenomenon of the antioxidant layer. For this reason, management of the coating thickness of the underlayer is an important management item, but it is very difficult to manage the thickness of the coating film due to differences in the porosity of the nozzle body refractory, differences in the graphite content, and the like. As a result, it is difficult to obtain a stable base layer thickness, causing interfacial delamination and intralayer delamination, and cannot necessarily contribute to the stability of the antioxidant property.

By the way, in the casting nozzle, in addition to the above-described reduction in the oxidation prevention function of the inner hole surface, in continuous casting of aluminum killed steel or the like, it occurred due to deoxidation products in molten steel or reoxidation during casting. There is a problem that the operation and steel quality are adversely affected such that alumina or the like adheres to and accumulates on the inner hole surface or the nozzle is blocked. Here, the “alumina etc.” to be attached mainly includes Al ₂ O ₃ component, particles or clusters in the molten steel containing other oxides, metal ingot where the molten steel is solidified, and the like.

  The nozzle clogging is a phenomenon that occurs when alumina or the like reaches the inner hole surface and accumulates. The cause is thought to be that alumina, etc. are attracted to the inner surface by the surface tension due to the solute concentration gradient at the molten steel interface due to carbon or silica contained in the refractory, and at the same time, fine irregularities on the inner surface. It is also considered that so-called micro vortices are generated at the interface with the molten steel, and alumina or the like reaches the inner hole surface and is captured. For this reason, a carbonless material system as a material system in which carbon and silica that are causative components on the refractory side are reduced as much as possible, and a material system in which unevenness on the surface of the refractory is reduced are arranged as a refractory layer on the inner hole side. Have been proposed (for example, Patent Documents 2 to 5).

  However, a casting nozzle having a refractory layer mainly composed of oxide fine particles on the inner hole side has an expansion / shrinkage characteristic that is not close to that of the alumina-graphite-based material or zirconia-graphite-based material on the main body side. Because of the expansion characteristics, random cracks with penetration cracks are likely to occur in the refractory layer on the inner hole side. Furthermore, due to the thermal load during casting, the oxide fine particles are further sintered, the penetration cracks are enlarged, the smoothness of the inner hole surface is lost, and peeling during the casting is likely to occur.

  As a countermeasure for eliminating the occurrence of random cracks, it is conceivable that the thermal expansion characteristic is approximated to the material on the main body side by adding, for example, 10% by mass or more of graphite. However, in such materials containing graphite, exposed graphite dissolves and disappears in a short time due to contact with molten steel, so the surface roughness of the inner hole surface during actual casting is the molten steel of graphite or carbonaceous joints. It increases due to dissolution in the inside, and creates an opportunity for the occurrence of adhesion. Once adhesion occurs, the turbulence of the molten steel flow at the refractory interface increases, and the possibility of progressing to the growth of the alumina adhesion layer or nozzle clogging increases.

  On the other hand, in Patent Document 6, as a means for preventing nozzle clogging, the refractory constituting at least a part of the inner hole surface of the nozzle and / or the portion in contact with the molten steel has a carbon content of 5% by weight or less and a porosity. It has been proposed to provide a dense layer having a mean particle size of 15 μm or less and an average particle size of 10 μm or less of 0.1 to 1.5 mm or less.

  However, a dense material with such a low carbon content has a high thermal expansibility, and since the stress relaxation capability of the material itself is small, the thermal shock resistance is low and the nozzle is liable to be broken. is there. In this regard, Patent Document 6 discloses that a porous layer having a carbon content of 5% by weight or less and a porosity of more than 15% and not more than 35% at least partially between the dense layer and the nozzle body. A method of mitigating thermal shock by disposing of is disclosed. However, fine oxide particles with an average particle size of 10 μm or less have high surface smoothness at the manufacturing stage, which is advantageous for preventing clogging. As a result, there is a problem that cracks are generated in the layer, exfoliation is promoted, and the blocking prevention effect is lowered. In addition, once the dense layer is peeled off and the porous layer on the back side is exposed, the erosion of the porous layer proceeds at a high speed, and the form of the molten steel flow in the inner hole changes, and the original difficult adhesion property There is a problem that cannot be maintained.

Japanese Patent No. 3763991 Japanese Patent Laid-Open No. 3-243258 JP-A-5-154628 JP-A-8-57601 JP-A-8-57613 JP 10-314905 A

  The main object of the present invention is to prevent the oxidation prevention layer disposed particularly on the inner hole surface of the casting nozzle from peeling off at the preheating stage, and to prevent oxidation at the preheating stage of the casting nozzle.

  Another object of the present invention is to suppress the adhesion of alumina or the like to the inner hole surface of the casting nozzle at the casting stage.

  In order to solve the main problem of the present invention, the layer itself responsible for the antioxidant function should be held without cracking or peeling on the surface of the nozzle body refractory even at a high temperature in the preheating stage. It is essential.

  In the conventional general anti-oxidation layer using the powder as a main component and vitrifying at a certain temperature or higher, a liquid phase is generated at the glass transition point or higher. The liquid phase ratio increases, and as a result, the viscosity of the layer decreases and the flow characteristics also increase. The layer itself in such a state has neither a function of maintaining its shape nor a function of suppressing flow characteristics. Therefore, a crack occurs in the layer due to the surface tension of the layer itself, or a phenomenon that the layer peels or flows away from the surface of the nozzle body refractory, that is, a phenomenon that the antioxidant function is reduced or lost.

  In the present invention, by providing an intermediate layer having a fibrous structure of carbon bonds between the nozzle body refractory and the antioxidant layer, the shrinkage and peeling of the antioxidant layer can be suppressed, and the temperature range above the glass transition point ( In particular, in a high temperature range where the viscosity becomes low enough to flow down), we improve the wetting of the antioxidant layer, provide shape retention during heating, and make it difficult to peel off from the surface of the nozzle refractory. Prevents the loss or loss of the prevention function.

  Specifically, first, a heat resistance of 1000 ° C. or higher, in which inorganic fibers are entangled with each other and bonded by a carbonaceous bonding material between the nozzle body refractory surface and the antioxidant layer to provide shape retention. An intermediate layer having properties is disposed. This intermediate layer has a structure in which inorganic fibers are entangled with each other, and is bonded with a carbonaceous binding material. Strength can be increased. This prevents the layer from being broken to the extent or form that would lead to cracks or delamination.

  The intermediate layer and the nozzle body refractory are configured such that a matrix structure of the refractories is continuous at the interface between them. The carbonaceous bond in the intermediate layer is the same as in the nozzle body refractory, and the carbon remaining after the heat treatment derived from the raw materials such as resin and pitch presses the inorganic fibers together to form a continuous monolithic structure. Therefore, at the interface (junction) between the intermediate layer and the nozzle body refractory, the inorganic fibers and the refractory particles form fine irregularities, and continuous carbon is formed by carbonaceous bonds derived from the same or similar raw materials. In order to form a quality bond, the intermediate layer and the nozzle body refractory adhere well (integrally) physically and chemically. Furthermore, the intermediate layer has a carbonaceous bond around the inorganic fiber and is a structure in which the inorganic fibers are intertwined with each other, unlike the layer mainly composed of fine powder raw material, and the inorganic fibers are in contact with each other. Less frequently. Further, the intermediate layer has a feature that the generation of cracks and peeling is suppressed by the sintering suppressing effect of the carbonaceous bond existing around the inorganic fiber. In addition, since the intermediate layer also has high flexibility due to the structure in which the inorganic fibers are entangled with each other, the effect of suppressing peeling from the nozzle body refractory is extremely high.

As the inorganic fiber, a general inorganic fiber such as Al ₂ O ₃ —SiO ₂ type, Al ₂ O ₃ —SiO ₂ —CaO type, SiO ₂ type, Al ₂ O ₃ type, ZrO ₂ type, etc. Various inorganic fibers can be used regardless of whether they are crystalline or crystalline. However, in order to suppress or prevent the destruction or disappearance of the antioxidant layer, which is the subject of the present invention, it is intended for preheating in a high temperature range of about 1000 ° C. or higher. It is necessary to prepare. The inorganic fibers are inevitably mixed with particulates or short and irregularly shaped fibers generally referred to as “shots”, but the effects of the present invention can be obtained even if such shots are included. .

  Here, the heat resistance of 1000 ° C. or higher means a total amount of liquid phase and molten slag phase (a glass melt composed of a plurality of components) at a temperature of 1000 ° C. (hereinafter, this total amount is simply referred to as “liquid phase amount”). ) Is zero. In other words, it has a characteristic that does not cause cracks or breakage to the extent that it reaches the nozzle body refractory surface through the intermediate layer during preheating.

  In order to independently evaluate the heat resistance of the intermediate layer, for example, a sample of the intermediate layer integrated with the nozzle body refractory is heated to a temperature of 1000 ° C. or higher (an arbitrarily set evaluation temperature range) in a non-oxidizing atmosphere. ), The sample can be observed after heating from the intermediate layer side.

  What is necessary is just to set the thickness of an intermediate | middle layer according to individual operation conditions. In general, the layer of the prior art mainly composed of vitreous material is likely to be peeled off or flowed down due to its surface tension increasing as its thickness increases, or due to its own weight. However, since the intermediate layer of the present invention is mainly composed of a fibrous component and is also a carbonaceous bond, shrinkage and deformation are hardly caused. Therefore, the thickness is not particularly limited, but is preferably about 0.1 mm or more and 10 mm or less from the viewpoint of optimization for obtaining the function, etc., because the molten steel flow at the casting nozzle is not hindered. Moreover, although it changes with manufacturing methods, the range of the said thickness is preferable also from a viewpoint of raising the homogeneity of the structure | tissue of an intermediate | middle layer more in the case of integral molding by CIP.

  In the intermediate layer, the inorganic fibers are integrated with each other while being intertwined with each other by a carbonaceous binder (resin, pitch, etc.). For this reason, the conventional carbon-less material composed of fine powder particles of the prior art, while maintaining the flexibility to the external force of the individual inorganic fibers and the spatial structure between the inorganic fibers, while being fixed to each other Compared to the above, the structural stability, the volume stability, the crack resistance and the peel resistance are very stable, and the heat insulation is excellent. For this reason, the effect which suppresses the heat removal at the early stage of casting, and suppresses adhesion | attachment of a base metal is acquired.

  On the outer surface side of the intermediate layer, one or a plurality of antioxidant layers that are vitrified and densified in a temperature range of 400 ° C. to 1500 ° C. are formed. This antioxidant layer mainly has a function of protecting the intermediate layer, that is, preventing oxidation of the carbonaceous connective tissue in the intermediate layer structure. The carbonaceous connective tissue starts to oxidize at about 400 ° C., and it becomes easier to oxidize as the temperature increases, the time increases, and the airflow increases. The preheating temperature of a general casting nozzle is about 600 ° C. to about 1000 ° C., but the preheating conditions vary greatly depending on individual operating conditions such as equipment, preheating method, atmosphere and air flow, and preheating time. Since the temperature of the molten steel is about 1500 ° C., the maximum temperature at the time of preheating may be about 1500 ° C. including a local high temperature portion such as a burner direct fire.

  Therefore, the antioxidant layer is vitrified in a temperature range arbitrarily set according to individual conditions from 400 ° C. to 1500 ° C., and is dense enough to block the oxidizing gas such as oxygen and water vapor. The composition may be such that As this antioxidant layer, a plurality of layers having different compositions may be arranged so as to be vitrified and densified in stages according to different temperatures.

The composition showing such a function is a glass in which a glass forming material such as SiO ₂ and B ₂ O ₃ and an alkali metal oxide, an alkaline earth metal oxide and other glass modifiers are set (desired). What is necessary is just to select and mix | blend according to crystallization temperature. As long as this purpose is met, the composition may contain Al ₂ O ₃ , ZrO ₂ components and the like for the purpose of adjusting the viscosity of the glass.

  When the antioxidant layer having the above function is disposed on the outer surface of the intermediate layer, there is an effect of maintaining the antioxidant layer and improving adhesion as a molten glass layer. This is because the intermediate layer, which is in a good adhesive state with the nozzle body refractory, does not contain graphite that impedes the wetting of the glass, and is a structure mainly composed of inorganic fibers, and has fine irregularities on the surface layer. Therefore, even when the antioxidant layer is a molten glass layer, the wettability with the intermediate layer is good and the physical adhesion is good, so that defects such as peeling are unlikely to occur. This is thought to be because it is easy to maintain the antioxidant layer as the glass layer.

  For this reason, by providing an intermediate layer, the anti-oxidation layer peels off or swells from the surface of the nozzle body refractory, as typically seen in the prior art, and the nozzle body refractory is oxidized at a high temperature. The phenomenon can be reduced.

  The thickness of the antioxidant layer may be set according to individual operating conditions, and there is no particular reason for limiting it. However, the anti-oxidation layer of the present invention may be about 0.3 mm or less up to about 2 mm because peeling or the like is less likely to occur even when the thickness is larger than the prior art due to the characteristics of the contact portion with the intermediate layer described above. It can adjust suitably in the range of thickness. The upper limit of the thickness depends on the degree of dense structure of the intermediate layer. In the case of a dense intermediate layer having an apparent porosity of about 15% or less, the maximum thickness of the antioxidant layer may be about 1 mm (average thickness is about 0.6 mm), and is preferable. In the case of a relatively coarse structure where the apparent porosity of the intermediate layer exceeds 15%, the maximum thickness can be reduced to about 2 mm. This is because the components of the antioxidant layer that have become vitrified and have low viscosity penetrate into the open pores of the intermediate layer. If the maximum thickness exceeds 2 mm, there is a risk that a crack will occur before vitrification and a part that will be partially destroyed or dropped will occur. In addition, if a rapid vitrification occurs, a part will flow down. There is a fear. The lower limit of the thickness is 0.1 to 0.2 mm in combination with the presence of the intermediate layer when the smoothness of the surface of the intermediate layer is extremely high, when the preheating temperature is extremely low, or when the preheating time is extremely short. Although an antioxidant function can be obtained even at a degree, it is preferably 0.3 mm or more because the effect lacks stability. Therefore, the total of the antioxidant layer of the present invention is preferably 0.3 mm or more and 2 mm or less, and more preferably 1 mm or less when the intermediate layer is dense.

  The intermediate layer and the antioxidant layer described above are suitable for the inner hole surface where there are many problems such as peeling in the prior art, but may be applied to surfaces other than the inner hole surface of the casting nozzle (nozzle body refractory). it can.

The means for solving the main problems of the present invention are summarized as follows.
(1) An intermediate layer is provided on a part or all of the surface of the nozzle body refractory having an inner hole for allowing molten steel to pass, and the outer surface of the intermediate layer is vitrified in a temperature range of 400 ° C to 1500 ° C to be dense. One or more anti-oxidation layers are formed, and the intermediate layer is a refractory material in which inorganic fibers are entangled with each other and bonded by a carbonaceous binder, and has a heat resistance of 1000 ° C. or higher. The casting nozzle in which the intermediate layer and the nozzle body refractory form an integral structure in which the matrix structure of the refractories is continuous at the interface between them (Claim 1).
(2) The casting nozzle according to (1), wherein the intermediate layer has a thickness of 0.1 mm to 10 mm and the antioxidant layer has a thickness of 0.3 mm to 2 mm.

  Since the above-mentioned antioxidant layer is a glass layer, it flows down by the molten steel flow and disappears after the start of casting. On the other hand, the intermediate layer may be caused to flow down by the molten steel flow after the start of casting or disappear, or may remain. When the intermediate layer is eliminated, a method of adjusting the ratio of the liquid phase at 1550 ° C. in a range exceeding 50 mass% and up to about 90 mass% can be adopted. The carbon component as the carbonaceous binder in the intermediate layer does not need to be particularly limited because it hardly affects the disappearance of the intermediate layer after the start of casting, but in order to maintain the shape retention of the intermediate layer, and In order to make the continuous connective structure with the nozzle body refractory more uniform, the amount of the carbonaceous binder is preferably less than or equal to that of the nozzle body refractory. Further, from the viewpoint of enhancing the effect of suppressing the sintering of inorganic fibers in the intermediate layer, it is advantageous that the carbon amount of the intermediate layer is large, but if the amount of bonded carbon increases, the flexibility of the intermediate layer tends to decrease. is there. Specifically, from the viewpoints of both the matrix structure and the sintering of the inorganic fibers, the carbon amount of the intermediate layer is 10% by mass when the amount of the carbonaceous binder of the nozzle body refractory is 100% by mass. The upper limit amount is appropriately determined in consideration of factors such as the shape of the nozzle and the balance of flexibility in an optimal range, i.e., within a range equal to or less than the amount of the carbonaceous binder in the nozzle body refractory. What is necessary is just to select and about 50 mass% or less is still more preferable. For example, when the amount of the general carbonaceous binder of the nozzle body refractory is about 1% by mass or more and about 5% by mass, it is preferably about 0.1% by mass or more and about 5% by mass or less, depending on the amount. More preferable is about 5% by mass or less.

  By the way, if the intermediate layer disappears after the start of casting, the nozzle body refractory comes into direct contact with the molten steel. For steel grades such as aluminum killed steel and other steels with strong adhesion such as components derived from molten steel, they adhere to the inner surface of the nozzle refractory and the nozzle is blocked (hereinafter, these are also collectively referred to as “nozzle blocking”). May provoke. After the disappearance of the intermediate layer, the surface (inner hole surface) of the nozzle body refractory may be more uneven as compared with the core rod liner surface during CIP molding (particularly in the case of integral molding described later). Tend).

  Therefore, the present invention takes measures to solve the main problem of the present invention, and in order to solve the secondary problem of the present invention, the intermediate layer is left after the start of casting, There is also provided a casting nozzle having a function in which the remaining intermediate layer itself suppresses or prevents the adhesion phenomenon of alumina or the like during casting.

  The present inventor can solve the problem of nozzle clogging due to adhesion of alumina or the like by solving the above-mentioned intermediate layer with high density and smoothness (solving the secondary problem of the present invention). I found out.

As described above, nozzle clogging is a phenomenon that occurs when alumina or the like reaches the inner hole surface and accumulates. One of the causes is considered that so-called micro vortices are generated at the interface due to the unevenness of the refractory surface (inner hole surface), and alumina or the like reaches the inner hole surface and is captured. For the purpose of preventing adhesion of alumina or the like to the inner hole surface of a casting nozzle, a refractory material called a carbonless material mainly composed of an oxide fine powder system has been widely applied in the prior art. The graphite raw material in the refractory produces a surface tension gradient accompanying the carbon concentration gradient in the vicinity of the molten steel interface, and at this time, the graphite easily dissolves into the molten steel. It has the effect of promoting the adhesion of etc. Therefore, in these material systems, carbon raw materials such as graphite, which generally cause adhesion of alumina or the like, are not added, but oxide raw materials as particles and raw materials mainly composed of Al ₂ O ₃ and MgO components Since it is configured, the coefficient of thermal expansion also increases.

  On the other hand, the present inventor has found that the surface roughness Rmax of the intermediate layer is 20 μm or less, thereby having a remarkable effect of suppressing adhesion of alumina or the like.

  The intermediate layer of the present invention does not generate cracks in the preheating stage or the casting stage, and can maintain smoothness and soundness by entanglement between the inorganic fibers. In addition, the smoothness and denseness of the intermediate layer can be easily changed by adjusting the diameter of the inorganic fiber, the molding method, and the like. The intermediate layer having a surface roughness Rmax of 20 μm or less suppresses the generation of so-called micro vortices at the interface with the molten steel, thereby suppressing adhesion of alumina or the like.

The present inventors, Al ₂ O ₃ result components were tested by changing the surface roughness of the samples containing even refractory high above 98 wt% Al ₂ O ₃ ingredient content, surface It has been found that just by setting the roughness Rmax to 20 μm or less, the adhesion of alumina or the like is remarkably reduced, and when Rmax exceeds 20 μm, the adhesion of alumina or the like is increased.

  Note that the surface roughness of the intermediate layer is determined by observing a cross-sectional structure in a direction perpendicular to the outer surface of the intermediate layer with a microscope or the like, and at least 10 points in the field of view of the top surface of the unevenness adjacent to the outer surface. What is necessary is just to set it as the maximum value of the dimensional difference of a bottom part.

  As described above, the intermediate layer of the present invention has a carbonaceous binder around each inorganic fiber, and has a structure in which fibrous inorganic materials are entangled with each other. And since this structure brings about the effect of suppressing sintering by carbon, the effect of reducing physical contact between oxides, the effect of developing high flexibility, etc., it is difficult to sinter and hardly enter a molten state. Therefore, it is difficult to cause cracks and breakage, and has a high ability to relax against internally generated stress due to expansion and external mechanical stress. Therefore, the ability to maintain macro smoothness as the inner pore surface on the surface of the intermediate layer of the present invention is extremely high as compared with a layer made of a conventional finely divided oxide.

From these facts, in the present invention, the structure mainly composed of aggregate particles of the prior art is hardly difficult to adopt because it does not cause destruction due to thermal shock or the like. For example, Al ₂ O ₃ , MgO component system For example, even if the component material itself has a high thermal expansibility, even if the content is close to 100% by mass, for example, if the tissue structure is mainly composed of the inorganic fiber of the present invention, thermal shock and continuous thermal stress Because the risk of destruction by is extremely small, it can be adopted.

  In order to obtain such an intermediate layer having a surface roughness Rmax of 20 μm or less, the maximum diameter of the inorganic fibers constituting the layer needs to be 20 μm or less. This is because if the structure is such that the fibrous constituents are randomly entangled with each other, the surface roughness Rmax of the structure inevitably has a portion that is larger than the diameter of the constituent fibers.

As the inorganic fiber, as described above, a general inorganic fiber, for example, Al ₂ O ₃ —SiO ₂ type, Al ₂ O ₃ —SiO ₂ —CaO type, SiO ₂ type, Al ₂ O ₃ type, ZrO ₂ type, etc. Various inorganic fibers can be used regardless of whether they are amorphous or crystalline. However, in order to reduce or prevent such adhesion of alumina or the like, it is necessary to select a component having a liquid phase ratio of about 50% or less at a molten steel temperature of about 1550 ° C. and a material having a mineral composition. When the ratio of the liquid phase exceeds 50%, the viscosity of the intermediate layer is remarkably reduced, the wear due to the molten steel flow increases, and it becomes difficult to maintain the smoothness as the inner hole surface in contact with the molten steel, such as alumina. Adhesion tends to occur.

  However, only in terms of solving the main problem of the present invention (maintaining the anti-oxidation function during preheating), the ratio of the liquid phase need not be 50% or less, and can be used in a range exceeding 50%. Is possible. Here, the “ratio of liquid phase” (also referred to as “liquid phase ratio”) means the mass ratio of the liquid phase when the entire composition is 100% by mass, and includes the slag phase. This can be obtained directly from the phase diagram, but if the component system is complex due to the inclusion of alkali metal components, alkaline earth metal components, etc., the ratio is calculated using general thermodynamic equilibrium calculation software. Can be requested.

  The intermediate layer for preventing the adhesion of alumina or the like can be applied to any part such as an inner hole surface including a discharge hole of an immersion nozzle as long as it is a part where the adhesion of alumina or the like is likely to occur. Moreover, what is necessary is just to determine the range to apply arbitrarily according to the place and state in which adhesion of alumina or the like is likely to occur in individual operations.

The means for solving the secondary problems of the present invention are summarized as follows.
(3) The intermediate layer formed on a part or all of the inner hole surface of the nozzle body refractory has a surface roughness Rmax of 20 μm or less and a liquid phase ratio at 1550 ° C. of 50% by mass. The casting nozzle according to (1) or (2), which is the following (Claim 3).

  According to the present invention, since the antioxidant layer is disposed on the surface of the nozzle body refractory through the intermediate layer, the occurrence of cracks and peeling of the antioxidant layer in the preheating stage can be remarkably suppressed. Thereby, the oxidation of the surface of the nozzle body refractory, particularly the inner hole surface, in the preheating stage can be remarkably prevented over a long period of time.

  In addition, the intermediate layer of the present invention is not limited to the oxidation prevention effect in the preheating stage, and the nozzle body is increased in viscosity or solid particles due to thermal shock caused by molten steel of the nozzle body refractory in the early stage of casting or the initial temperature drop. It can also contribute to protecting the nozzle body refractory surface from molten steel flow that causes mechanical shock and wear on the refractory surface.

  Furthermore, since the intermediate layer of the present invention has a structure in which inorganic fibers are entangled with each other, the thermal conductivity is lower than that of the nozzle body refractory. Is suppressed, and the effect of suppressing the adhesion of the metal is also obtained.

At the same time, the effect of reducing the risk of destruction by relaxing the thermal shock to the nozzle body refractory can be obtained. Therefore, the content ratio of Al ₂ O ₃ component, MgO component, etc. that are difficult to adopt due to the high risk of breaking due to thermal shock due to the high thermal expansion of the nozzle body refractory, although it has high corrosion resistance and high adhesion prevention The possibility of applying even a high material can be expanded.

  The intermediate layer of the present invention can be eliminated by the molten steel flow after the start of casting by adjusting the chemical composition and structure, and can be arbitrarily adjusted to remain. Thereby, the molten steel flow in the nozzle being cast can be matched with a desired flow form, or the state of the nozzle surface can be held in a desired state (including adjustment of the holding time) with a high degree of freedom. .

  In addition, by setting the surface roughness of the intermediate layer to Rmax 20 μm or less, even in operation conditions where alumina adheres to the inner hole surface during casting or nozzle clogging is likely to occur, such as casting of aluminum killed steel, Adhesion or nozzle clogging can be significantly suppressed or prevented.

  In addition, it is extremely difficult to adopt a material system containing a high proportion of a component having a high thermal expansion property in the conventional structure mainly composed of aggregate particles. In the present invention, a structure such as a special stress relaxation part (such as a space) is required in the object, but in the present invention, this can be simply placed on the surface of the nozzle body refractory and with strong adhesiveness. . This not only significantly suppresses or prevents adhesion of alumina or the like or nozzle clogging, but also provides high corrosion resistance and high wear resistance without risk of destruction.

  In order to obtain the effect of preventing adhesion of alumina or the like by the intermediate layer, it is necessary to leave the intermediate layer at least for a fixed (arbitrary) time in the initial stage of casting, but the residual time is arbitrarily adjusted by the liquid phase ratio and the like. Can handle a wide range of operating conditions.

It is an example of this invention, Comprising: It is a cross-sectional image figure which shows the example which applied the intermediate | middle layer and the antioxidant layer to the inner-hole surface (a discharge hole surface is included) of an immersion nozzle. It is a cross-sectional image figure which shows the structure of the intermediate | middle layer of this invention, an antioxidant layer, and a nozzle main body refractory. It is the image figure to which the A section of FIG. 2 was expanded. It is a photograph which shows the structural example of the intermediate | middle layer of this invention, an antioxidant layer, and a main body refractory (before an oxidation test). It is a photograph which shows the structural example of the intermediate | middle layer of this invention, an antioxidant layer, and a main body refractory (after an oxidation test). It is a schematic diagram which shows the adhesion test apparatus used by Example AC. It is a schematic diagram which shows the apparatus which measures the compression shear strength between an inner-hole side refractory layer and an outer peripheral side refractory layer.

  FIG. 1 shows an example of a casting nozzle according to the present invention. The casting nozzle shown in FIG. 1 is an immersion nozzle, and the nozzle body refractory 1 is made of, for example, an alumina-silica-graphite material. The nozzle body refractory 1 has an inner hole 5 through which molten steel passes, and the molten steel is discharged from the discharge hole 6. A zirconia-graphite refractory 4 is disposed in the powder line portion of the nozzle body refractory 1. In such an immersion nozzle 20, in the example of FIG. 1, the intermediate layer 2 and the antioxidant layer 3 of the present invention are applied to the inner hole surface (including the discharge hole surface) of the immersion nozzle 20.

  FIG. 2 is a cross-sectional image view showing the structure of the intermediate layer 2 and the antioxidant layer 3 and the nozzle body refractory 1 of the present invention, and FIG. 3 is an enlarged image view of part A of FIG. The main body refractory 1 shown in FIGS. 2 and 3 is composed of graphite 9 and a matrix 11 as aggregates, and an intermediate layer 2 and an antioxidant layer 3 are disposed on the surface of the main body refractory 1. The intermediate layer 2 is made of a refractory material in which inorganic fibers 10 are entangled with each other and bonded together by a carbonaceous binder, and the intermediate layer 2 and the nozzle body refractory material 1 are mutually connected at the interface (reference numeral 7). The refractory matrix structure forms a continuous and integral structure. The antioxidant layer 3 formed on the outer surface of the intermediate layer 2 is made of a material that is vitrified and densified in a temperature range of 400 ° C. to 1500 ° C.

  4 and 5 show an actual structure example of the intermediate layer 2 and the antioxidant layer 3 and the main body refractory 1 of the present invention. FIG. 4 shows the state before the oxidation test, and FIG. 5 shows the state after the oxidation test. The initial thickness of the antioxidant layer 3 is 0.6 mm. In addition, the code | symbol 11 in FIG. 4 shows a part of structure | tissue where the matrix continued including the structure | tissue where the carbon bond of the interface 7 vicinity was continuous.

  Next, the manufacturing method of the casting nozzle of the present invention will be described.

  The casting nozzle of the present invention can be produced in the same process as a general casting nozzle except for the following CIP molding-related points. First, an example of simultaneous integral molding by CIP of an intermediate layer (part relating to a material made of inorganic fibers) will be described.

  Molding that uses a sheet-like or pipe-like material in which a resin or pitch forming a carbonaceous binder is coated or impregnated on the surface of each individual inorganic fiber and the inorganic fibers are intertwined with each other at the time of CIP molding. By wrapping around a core rod, it is arranged on the core rod surface, that is, as an intermediate layer on the inner hole surface side. Next, the space between the outer layer and the rubber mold is filled with a refractory material for the nozzle body refractory containing resin or pitch. Then, it pressurizes by CIP and obtains a simultaneous integral molding. The pressure at the time of CIP molding may be a pressure for manufacturing a general casting nozzle of about 50 MPa to about 150 MPa, for example.

  Thereby, the intermediate | middle layer in which the inorganic fiber became entangled in part or all (the range set arbitrarily) of the inner-hole surface which contacts the molten steel of a casting nozzle can be formed. At the same time, at the interface between the nozzle body refractory surface and the intermediate layer, an integral structure in which the matrix structure of the refractories is continuous can be obtained. This is because the particles in the earth for the refractory material for the nozzle body are arranged in a spatial manner while forming a concavo-convex state with each other, and the same carbonaceous binder is formed with each other. Alternatively, since the same kind of resin or pitch is added, they are integrated with each other, and after heat treatment, a matrix structure in which carbonaceous bonds are continuous is formed.

  The inorganic fibers are compressed with high pressure by CIP, so that the pores in the initial fibrous material disappear, and the dense intermediate layer in which the inorganic fibers are intertwined with each other and the fibers are pressure-bonded with a resin or the like. Form. As a characteristic of isostatic pressing by CIP, the forming stress increases greatly as the core rod in the mold is approached. As a result, the surface layer on the core rod liner side is most easily densified.

  The apparent porosity of the intermediate layer is preferably 15% or less, and more preferably 5% or less. When the apparent porosity of the intermediate layer exceeds 15%, this antioxidant layer is formed when the antioxidant layer formed on the intermediate layer surface, that is, the layer of the glassy antioxidant is reduced in viscosity beyond the vitrification transition temperature. Will penetrate into the structure of the intermediate layer excessively, and if the preheating exceeds the design conditions (assumed temperature, time, etc.) of the antioxidant layer and is exposed to high temperatures for a long time, the intermediate layer will be oxidized. This is because there is a risk of being invited.

  The raw material of the inorganic fiber is not particularly limited as long as it is an aggregate of fibers, and can be appropriately selected without being limited to a specific form such as a sheet form, a blanket form, or a molded product.

  Compared to general refractory compounds containing graphite with excellent solid lubricating ability, inorganic fiber materials are mainly composed of fibrous (including columnar) components, so that moldability, that is, propagation of pressure and Homogeneous filling is greatly reduced. Therefore, the core rod liner part at the time of molding is relatively easily densified, but when the fibrous structure layer is thick, the porosity tends to increase as it is closer to the nozzle body refractory side (away from the core rod liner). It becomes. In consideration of such homogeneity, the thickness as the intermediate layer is preferably 0.1 mm or more and 10 mm or less because a good fibrous refractory structure can be formed. This range and the optimum thickness can be adjusted and changed by the pressure, time, etc. during CIP. If it is thicker than 10 mm, the porosity of the intermediate layer in contact with the nozzle body refractory becomes too high, and adhesion failure and strength reduction at this portion tend to occur. The intermediate layer made of an inorganic fibrous structure integrally formed in this range is from a portion with a relatively high porosity on the side in contact with the nozzle body refractory to a portion with a relatively low porosity on the core rod side. There is no noticeable difference and integration with continuous porosity gradient without extreme change. As a result, internal defects such as cracks and peeling are less likely to occur in the intermediate layer.

  The intermediate layer can be obtained by integrally molding by the above-mentioned CIP method, or by molding inorganic fibers coated or impregnated with resin or pitch in a separate process into a sheet or pipe, and the material after the molding The surface of the casting nozzle (nozzle body refractory) manufactured separately by a general method using a binder that forms a carbonaceous bond such as resin or pitch as an adhesive (not only the inner hole surface but also the inner hole surface) It can also be formed by sticking to any nozzle surface). However, the strength, denseness, etc. of bonding with the surface of the nozzle body refractory are better when obtained by the CIP simultaneous molding method and are more economical, and it is preferable to adopt the CIP simultaneous molding method.

  The casting nozzle formed in this way can form an antioxidant layer on the surface through a heat treatment process such as drying and firing and a processing process in the same manner as a general casting nozzle. The antioxidant layer only needs to satisfy the requirement of vitrification and densification in the temperature range of 400 ° C. to 1500 ° C., and it is possible to apply a material and a forming process mainly composed of a general vitrification component. it can. As a general method for forming the anti-oxidation layer, it is possible to immerse the anti-oxidation material in a mud-like soil bath, spray the soil, or apply with a brush or the like. it can. A general method can be similarly applied to subsequent steps such as drying.

  This is because the core rod liner side inner hole surface portion of the intermediate layer made of inorganic fibrous structure is relatively dense and smooth, so when using the graphite raw material in the prior art This is because a healthy smooth surface mainly composed of oxide can be obtained. Therefore, when an antioxidant layer composed of a glassy raw material is applied to the surface, no special treatment is required and it can be applied directly. In addition, since the intermediate layer has a dense fibrous structure not only on the surface but also on the whole, cracks and peeling hardly occur, and naturally it does not propagate or expand. As a result, the occurrence of defects at the interface between the antioxidant layer and the intermediate layer is extremely small, and the antioxidant layer vitrifies and wets the surface of the intermediate layer satisfactorily (with a uniform thickness, distribution, etc.). Since it maintains stably, it becomes possible to maintain the antioxidant function in the preheating process.

  The antioxidant applied to the antioxidant layer having an antioxidant function on the surface of the intermediate layer is a refractory containing a glass raw material, a vitrification raw material, a binder component and the like. These are formed into a film at a temperature range of about 400 ° C. or higher where the oxidation of carbonaceous components in the intermediate layer and the nozzle body refractory starts (ie, liquefaction accompanying partial or complete vitrification and pores accompanying low viscosity, etc.) This phenomenon protects the carbonaceous components inside the refractory from oxidizing gas.

Specific examples of such glass-based refractory compositions include various silicon compounds such as SiO ₂ and B ₂ O ₃ , boron compounds, alkali metal oxides that are glass modifiers, and alkaline earth materials. Examples thereof include a metal oxide and the like, and a raw material already having a glass structure, a raw material containing the various components that vitrify in a predetermined temperature range, and the like can be appropriately used. Furthermore, in addition to the above functions, for the purpose of adjusting the viscosity of the glass and the like, these compositions may contain raw materials containing various Al ₂ O ₃ components, raw materials containing various ZrO ₂ components, and the like.

  The temperature range showing the antioxidant function is from 400 ° C. to 1500 ° C. The preheating temperature (including distribution), time, preheating atmosphere (oxygen partial pressure, etc.), etc. vary depending on individual operating conditions. Because. In other words, the composition of the antioxidant may be such that the gas containing oxygen can be shut off at a temperature or the like arbitrarily set according to individual conditions. Specifically, for example, when the preheating time in an oxidizing atmosphere of a temperature range of about 400 ° C. to about 700 is long, a borosilicate composition having a high boron content is used. If the preheating time in an oxidizing atmosphere in a higher temperature range is longer without being exposed, a silicic acid-based composition with a low content of boron or alkali metal oxide components is required (however, a precise balance design is required) It is. Furthermore, a plurality of antioxidant layers having these different design conditions (compositions) may be arranged hierarchically.

  An intermediate layer having a surface roughness Rmax of 20 μm or less can be easily obtained by simultaneously forming the nozzle body refractory as described above. Even when the intermediate layer is molded in a separate step, it can be obtained by adjusting the molding pressure.

  The preparation methods of the samples of Examples A to D shown below are as follows.

  An inorganic fiber sheet consisting of predetermined components (described in the following examples) and having a thickness of 1 mm and a maximum fiber diameter of 15 μm is immersed in a solution-like phenol resin (resin content: 5% by mass), and then dried at 60 ° C. An inorganic fiber sheet was prepared in advance by coating the periphery of all the fibers in the layer with a phenol resin component.

The inorganic fiber sheet is wound around the core part for CIP molding a predetermined number of times (multi-layer structure), set in a rubber mold, and then an alumina-silica-graphite material (Al ₂ O ₃ : 55 mass) which is a refractory for the nozzle body. %, SiO ₂ : 15% by mass, C: 27% by mass) and zirconia-graphite material (ZrO ₂ : 82% by mass, C: 13% by mass) in the space outside the inorganic fiber sheet. Filled.

  This was pressure-molded with CIP, and the molded body was cured at 150 ° C. and carbonized at 1200 ° C., and had a matrix structure in which the nozzle body refractory and carbonaceous bonds were continuous on the inner side of the casting nozzle. In addition, a casting nozzle having an intermediate layer of a fibrous structure in which the contact surface with the refractory body of the nozzle body is intertwined with irregularities was produced. As samples, a plurality of types having different intermediate layer thicknesses were produced.

  As a comparative example, a sample not provided with an inorganic fibrous layer (intermediate layer) was also prepared and subjected to an oxidation test and an adhesion test such as alumina.

  The oxidation test method and evaluation criteria are as follows.

  About 0.6 mm of antioxidant containing glass frit with an effective temperature range (range where oxidation does not occur) 900 ° C. to 1500 ° C. on the outer surface of each sample (surface opposite to the nozzle body refractory bonding side) The “antioxidation layer” was formed by coating.

  Rapid heating was performed with a gas flame so that the surface of the sample inner hole (antioxidation layer) was 1300 ° C., and after the surface of the sample inner hole reached 1300 ° C., the surface was held at 1300 ° C. for 6 hours. About the sample cooled after the said heating, the external appearance of the intermediate | middle layer and the state of the cut surface were observed. The case where the nozzle body refractory was not oxidized was evaluated as ◯ (passed), and the case where the nozzle body refractory was oxidized was evaluated as x (failed).

  Alumina adhesion test methods and evaluation criteria are as follows.

  As shown in FIG. 6, in a high-frequency induction furnace, a sample (sample) was immersed in a molten steel, held for a certain time while rotating in the immersed state, cooled after completion of the immersion rotation, and the cross section was observed. . The sample shape is 20 mm □ × 30 mm in length, and a sample in which an intermediate layer is placed on the 20 mm × 20 mm surface part at the front end in the length direction is arranged so that the intermediate layer part is on the outermost peripheral side, and four on the rotating shaft Set / times.

The conditions are as follows.
Molten steel type: Low-carbon aluminum killed steel Immersion rotation time: Maximum 120 min
Oxygen concentration in steel: approx. 83ppm at start → end <1ppm
Molten steel temperature: 1550-1570 ° C
Rotation speed: 200rpm

The evaluation was classified into the following ranks according to the degree of adhesion rate of alumina or the like to the intermediate layer.
・> ± 30 μm / min. : × (Fail)
+10 μm / min. ~ + 30 μm / min. : △ (Passed. Good.)
--10 μm / min. ~ -30 μm / min. : △ (Passed. Good.)
・ <± 10 μm / min. : ○ (Pass. Best.)
Here, “+” means that there is adhesion, and “−” means that there is a reduction (partial disappearance of the sample due to melting damage or the like).

[Example A]
Example A is an example in which the thickness of the intermediate layer was changed to evaluate the oxidation and adhesion of alumina and the like.

In this Example A, the inorganic fibers of the intermediate layer used were components of Al ₂ O ₃ = 47% by mass, SiO ₂ = 52% by mass, and Na ₂ O = 0.2% by mass.

  Table 1 shows the configuration of the sample and the evaluation results.

  In each of Examples 1 to 5 in which the thickness of the intermediate layer was changed from 1 mm to 10 mm, in the oxidation test, the intermediate layer remained in a substantially healthy state and there was no oxidation of the nozzle body refractory. ) ”. In the evaluation of the adhesion test such as alumina, it was “◯ (pass)” (melting tendency). In Example 6 in which the thickness of the intermediate layer was 11 mm, both evaluations of the oxidation test and the adhesion test such as alumina were “◯ (passed)”, but a part of the sample after the oxidation test was found to be peeled off. (There was no oxidation of the nozzle body refractory surface). From these results, it can be seen that the thickness of the intermediate layer is preferably 10 mm or less.

  On the other hand, in Comparative Example 1 in which the intermediate layer was not disposed, the oxidation prevention layer was swollen (peeled from the surface of the nozzle body refractory) in the evaluation of the oxidation test, and the nozzle body refractory was oxidized to indicate “× (failure). ) ”. Further, the adhesion of alumina and the like was large, and this was also “x (failed)”.

  The intermediate layer of the example had a surface roughness Rmax of 8 μm, and the inner surface of the comparative example 1 had a surface roughness Rmax of 120 μm.

[Example B]
Example B is an example in which the influence of the surface roughness Rmax of the intermediate layer in the case where the intermediate layer remains is investigated by evaluation of an oxidation test and an adhesion test such as alumina. The surface roughness Rmax was changed by changing the diameter of the inorganic fibers constituting the intermediate layer. The thickness of the intermediate layer was 3 mm, the same as in Example 3. Moreover, the inorganic fiber of the same layer system as Example A was used for the inorganic fiber of the intermediate | middle layer.

  Table 2 shows the configuration of the sample and the evaluation results.

  In each of Examples 7 to 9 where the surface roughness Rmax of the intermediate layer was changed from 8 μm to 20 μm, the intermediate layer remained in a substantially healthy state in the oxidation test, and the nozzle body refractory was not oxidized. The evaluation of “○ (pass)” was also made, and the evaluation of the adhesion test for alumina and the like was also “○ (pass)”.

  On the other hand, in Example 10 in which the surface roughness Rmax of the intermediate layer was 22 μm, the evaluation was “◯ (pass)” in the evaluation of the oxidation test, but the adhesion was increased in the evaluation of the adhesion test such as alumina. (Passed, but “OK”) ”.

  From these results, although the surface roughness Rmax of the intermediate layer is 22 μm in the pass region, there is a possibility that the adhesion of alumina or the like may further increase depending on the operating conditions such as a longer casting time. It can be seen that the roughness Rmax is preferably 20 μm or less.

[Example C]
Example C is an example in which the influence of the ratio of the liquid phase of the intermediate layer in the case where the intermediate layer remains is investigated by evaluation of an oxidation test and an adhesion test such as alumina. The ratio of the liquid phase is as follows: Al ₂ O ₃ component is about 99% by mass fiber, Al ₂ O ₃ component is 50% by mass, SiO ₂ component is 50% by mass, and the fiber is mainly composed of alkali metal oxide. The entire intermediate layer excluding the carbon component was adjusted by mixing so as to have a liquid phase ratio set for each sample.

In addition, the preparation example by this method is shown next.
Liquid phase ratio 15% by mass: Al ₂ O ₃ = 47% by mass, SiO ₂ = 52, Na ₂ O = 0.2% by mass
Liquid phase ratio 30% by mass: Al ₂ O ₃ = 47% by mass, SiO ₂ = 52, Na ₂ O = 0.4% by mass
Liquid phase ratio 50% by mass: Al ₂ O ₃ = 46% by mass, SiO ₂ = 51, Na ₂ O = 3% by mass
Liquid phase ratio 60% by mass: Al ₂ O ₃ = 45% by mass, SiO ₂ = 49, Na ₂ O = 6% by mass

  Table 3 shows the configuration of the sample and the evaluation results.

  In Examples 11 to 13 in which the liquid phase ratio was changed from 15% by mass to 50% by mass, the intermediate layer remained in a substantially healthy state in the oxidation test and the nozzle body refractory was not oxidized. The evaluation was “◯ (pass)”, and the evaluation of the adhesion test for alumina and the like was also “◯ (pass)”.

  On the other hand, in Example 14 in which the ratio of the liquid phase of the intermediate layer was 60% by mass, the evaluation was “◯ (pass)” in the evaluation of the oxidation test, but the reduction amount was large in the evaluation of the adhesion test such as alumina. It became "x (failed)".

  From these results, it is understood that the ratio of the liquid phase of the intermediate layer when the intermediate layer remains is preferably 50% by mass or less.

  If there is no need to leave the intermediate layer during casting, the intermediate layer will not be greatly deformed or disappear at the preheating temperature according to the individual operating conditions (no oxidation of the nozzle refractory occurs) What is necessary is just to be below the liquid phase ratio. Further, depending on the operating conditions such as a short casting time and a low molten steel temperature, it can be used even if the liquid phase ratio exceeds 50 mass%.

[Example D]
Example D is an example in which the influence of the apparent porosity of the intermediate layer in the case where the intermediate layer remains is investigated by evaluation of an oxidation test and an adhesion test such as alumina. The apparent porosity was made mainly by changing the pressure applied when forming the intermediate layer. Further, the structure of the intermediate layer was based on Example 11.

  Table 4 shows the configuration of the sample and the evaluation results.

  In each of Examples 15 to 17 in which the apparent porosity of the intermediate layer was changed from 4% to 15%, the intermediate layer remained in a substantially healthy state in the oxidation test, and there was no oxidation of the nozzle body refractory. The evaluation was “◯ (passed)”, and the evaluation of the adhesion test for alumina and the like was also “◯ (passed, almost no adhesion)”.

  On the other hand, in Example 18 in which the apparent porosity of the intermediate layer was 18%, the evaluation was “◯ (pass)” in the evaluation of the oxidation test, but the adhesion was increased in the evaluation of the adhesion test such as alumina. (Passed, but “OK”) ”. Further, Comparative Example 2 in which the apparent porosity of the intermediate layer was set to 25% (this is an example that can solve the main problem of the present invention, that is, the antioxidant function. Here, the comparative example is only related to adhesion of alumina or the like. In the evaluation of the oxidation test, “○ (passed)” was obtained, but in the evaluation of the adhesion test of alumina or the like, the adhesion was significantly larger than that of Example 18, and “x (failed)” was obtained. It was. This is also a result of the surface roughness Rmax being 22 μm in Example 18 and 33 μm in Comparative Example 2.

  From these results, the apparent porosity of the intermediate layer is also related to the surface roughness, but although 18% is in the pass region, the adhesion of alumina and the like further increases depending on the operating conditions such as a longer casting time. Since there is a possibility, it turns out that it is preferable to make it 15% or less.

[Example E]
Example E is an example in which the influence of the joining mode between the intermediate layer and the nozzle body refractory was investigated.

  In Example 19, the composition of the intermediate layer was the same as that in Example 4, and the nozzle body refractory was simultaneously and integrally formed by CIP.

In Comparative Example 3 and Example 20, the composition of the intermediate layer is the same as that of Example 4, but in Example 20, the intermediate layer obtained by press molding separately from the nozzle body refractory was independently CIP-molded nozzle body refractory. And bonded to each other. In Comparative Example 3, a general mortar composed of about 70% by mass of Al ₂ O ₃ component and about 30% by mass of SiO ₂ component was used in a thickness of 1 mm, and Example 20 was the same as that used for the intermediate layer. A liquid phenolic resin is applied and adhered.

About these samples, hot compressive shear strength was evaluated as adhesive strength. The hot compressive shear strength Sh (MPa) is obtained by using a sample of a tubular refractory structure having a structure in which an intermediate layer is embedded in the outer nozzle body refractory as shown in FIG. The entire sample is heated to 1000 ° C. in a furnace in a nitrogen gas atmosphere and held until the temperature is stabilized. In this state, only the intermediate layer is moved at a moving speed of 0.001 to 0.01 mm / sec. It compresses, the maximum load P (N) and displacement are measured, and it can obtain | require by following Formula.
Sh = P / A
Here, A represents the area (m ² ) of the contact portion between the intermediate layer and the nozzle body refractory.

  In this measurement of compressive shear strength, the sample can be obtained by cutting out from the product (actual shape) or can be produced exclusively, but it is difficult to measure when the intermediate layer is particularly thin, such as 1 mm or less. The following shape is measured as a standard.

  That is, the nozzle body refractory had an inner diameter of 65 mm, an outer diameter of 105 mm, the intermediate layer had an inner diameter of 55 mm and an outer diameter of 65 mm, and the intermediate layer was pressurized from above (the shear direction with respect to the bonded portion) with the vertical facing surface as the bonding surface.

  Table 5 shows the configuration of the sample and the evaluation results.

  The adhesive strength was 0.6 MPa in Comparative Example 2 where mortar was used for joining, whereas Example 19 of CIP integral molding showed extremely strong adhesiveness of 18 MPa. Example 20, which was molded separately and coated with phenol resin and adhered, showed 3 MPa, which was significantly lower than Example 19, but showed significantly stronger adhesion to Comparative Example 3.

DESCRIPTION OF SYMBOLS 1 Nozzle body refractory 2 Intermediate layer 3 Antioxidation layer 4 Zirconia-graphite refractory 5 Inner hole 6 Discharge hole 7 Interface (joint part) of main body refractory and intermediate layer
8 Interface between intermediate layer and antioxidant layer 9 Graphite 10 Inorganic fiber 11 Matrix 20 Casting nozzle (immersion nozzle)

Claims (3)

Oxidation comprising an intermediate layer on part or all of the surface of the nozzle body refractory having an inner hole for passing molten steel, and vitrifying and densifying the outer surface of the intermediate layer in a temperature range of 400 ° C. to 1500 ° C. One or more prevention layers are formed,
The intermediate layer is a refractory in which inorganic fibers are entangled with each other and bonded by a carbonaceous binder, and has a heat resistance of 1000 ° C. or higher.
The casting nozzle in which the intermediate layer and the nozzle body refractory form an integral structure in which the matrix structure of the refractories is continuous at the interface.   The casting nozzle according to claim 1, wherein the intermediate layer has a thickness of 0.1 mm to 10 mm, and the antioxidant layer has a thickness of 0.3 mm to 2 mm.   The intermediate layer formed on a part or all of the inner hole surface of the nozzle body refractory has a surface roughness Rmax of 20 μm or less and a liquid phase ratio at 1550 ° C. of 50% by mass or less. The casting nozzle according to claim 1 or 2.