JP2015193511A - Refractory for casting, nozzle for casting using the same and plate for sliding nozzle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for improving durability of a refractory used for long time use or many time repeating use such as a refractory for casting, especially a nozzle for casting or a plate for sliding nozzle.SOLUTION: There is provided a refractory for casting containing AlOC of 15 to 80 mass%, AlN of 0.5 to 20.0 mass% and the balance refractory components. The refractory for casting has a layer having thickness of 2 to 250 μm on a part or all of particle surface containing AlOC, and the layer has a different structure from particle inside containing AlOC excluding the layer and contains components of Al, N, O and C.

Description

  The present invention relates to a casting refractory used for casting steel, a casting nozzle using the refractory, and a sliding nozzle device (hereinafter referred to as “SN device”) for controlling the flow rate of molten steel. The present invention relates to a nozzle plate.

  In steel casting, a casting nozzle that is a flow path of molten steel discharged from a molten steel container such as a ladle or tundish, or an SN device that controls the flow rate of molten steel is used. The SN device uses a sliding nozzle plate having two or three refractory nozzle holes. The sliding nozzle plates are overlapped under a restrained condition, are slid with a surface pressure applied, and the flow rate of the molten steel is adjusted by adjusting the opening of the nozzle holes.

  From this, the sliding nozzle plate has mechanical strength that can withstand use under restraint conditions, thermal shock resistance against thermal stress during casting, corrosion resistance against components and slag in molten steel, oxidation resistance, and Further, characteristics such as “surface roughness resistance” against “surface roughness” in which the sliding surface serving as the operating surface is worn are required.

  Alumina-carbon refractories are generally used for sliding nozzle plates. For example, refractory materials such as zirconia mullite and alumina zirconia, which have a low thermal expansion coefficient, are used to improve thermal shock resistance. ing. In order to improve the corrosion resistance, the use of high-purity and dense raw materials such as fused alumina that does not easily react with slag, and the optimization of the type and content of carbon are being carried out. In order to ensure the strength of the structure and to improve the wear resistance due to sliding, the structure is made dense by increasing the particle size composition of the raw materials used, and the sliding surface is further polished. Techniques such as improving accuracy are being implemented. Furthermore, non-oxides such as silicon carbide, boron carbide, and aluminum nitride, which are effective for preventing oxidation and improving strength and wear resistance, and metals such as silicon and aluminum are appropriately used.

  For example, in Patent Document 1, an organic binder is added and kneaded into a refractory raw material composition containing aluminum and / or an aluminum alloy in a system mainly composed of an alumina-carbonaceous refractory raw material, and after molding, a nitrogen gas atmosphere In the method for producing a refractory fired at 1000 ° C. or higher and 1400 ° C. or lower, a nitrogen gas atmosphere is set at least when the furnace atmosphere temperature is 300 ° C. or higher, and the oxygen gas concentration in the atmosphere is set when the furnace atmosphere temperature is 1000 ° C. or higher. Refractory material for sliding nozzle plate (hereinafter referred to as “plate refractory material”) characterized by maintaining 100 ppm by volume or less and a total of carbon monoxide gas concentration and carbon dioxide gas concentration at 1.0 volume% or less. A manufacturing method is disclosed. This produces a lot of fine and uniform aluminum nitride in the plate refractory, which prevents the deterioration of the structure caused by digestion caused by the formation of aluminum carbide, suppresses the oxidation of carbon bonds, and improves the surface roughness resistance. Has been.

  In the prior art disclosed in Patent Document 1, by placing AlN in a refractory matrix, oxidation resistance such as FeO resistance is imparted and corrosion resistance is also improved. Reduction of damage can be expected. However, a structure in which AlN is produced using aluminum and / or an aluminum alloy as a starting material is dense and high in strength, but also has a high elastic modulus and a factor in reducing thermal shock resistance.

Therefore, for the purpose of enhancing the thermal shock resistance, Patent Document 1 proposes that at least one of zirconia, zirconia mullite and alumina zirconia is contained in an amount of 4% by mass to 20% by mass as a ZrO ₂ component. Zirconia-based raw materials such as zirconia, zirconia mullite, and alumina zirconia exhibit unique expansion characteristics due to volume changes accompanying the phase transition of zirconia. That is, zirconia belongs to the monoclinic system at room temperature and linearly expands to around 1170 ° C. when the temperature rises, but at a temperature of 1170 ° C. or higher, the phase transition from the monoclinic system to the tetragonal system occurs. The volume shrinks. On the contrary, when the temperature is lowered, volume expansion occurs with the phase transition from the tetragonal system to the monoclinic system. Due to this unique expansion characteristic, microspaces or microcracks are generated around the zirconia-based raw material particles and at the boundary with the matrix, and thermal shock resistance is imparted by reducing the elastic modulus of the refractory. Moreover, since a zirconia-type raw material has a low thermal expansion coefficient compared with an alumina, it contributes to the improvement of a spalling-proof characteristic by reducing the thermal expansion coefficient of a refractory.

  The technique of applying a zirconia-based raw material for the purpose of improving the spalling resistance is widely applied to refractories in general steel casting operations, and is generally used well. However, when the heat load is large due to the large shape of the ladle for a long time, repeated use many times, or in severe conditions such as repeated heating and cooling to a high temperature, the zirconia system in the refractory The raw material repeatedly undergoes phase transition, the microspace or microcrack in the structure expands, and the compactness of the structure is lost, and on the contrary, it becomes a factor that promotes wear due to oxidation and wear.

  Furthermore, when metal aluminum remains in the product in a system in which metal aluminum is used in combination with a zirconia-based raw material-containing system, in long-time casting conditions, in parts that become high-temperature conditions such as near the edge of the nozzle hole, metal Since the oxygen affinity of aluminum itself is strong, zirconia itself is reduced to produce zirconium monoxide, zirconium, and zirconium carbide. These zirconium monoxide, zirconium, and zirconium carbide have a high oxygen affinity and are easily oxidized in an oxidizing atmosphere to produce zirconia. At this time, a vigorous reaction accompanied by volume expansion occurs and a defect occurs in the tissue.

  For these reasons, when casting for a long time or repeated use, the structure deteriorates due to reoxidation of zirconium monoxide, zirconium and zirconium carbide produced by reduction from zirconia to zirconia, resulting in edge defects and sliding surfaces. Damage increases.

In addition, since ZrO ₂ and SiO ₂ components are likely to produce FeO and a low melting point material compared to Al ₂ O ₃ , if a large amount of ZrO ₂ -based material is applied, enlargement of the nozzle hole diameter will increase due to melting damage due to oxygen cleaning. When receiving high oxygen steel, there is a problem that wear of the sliding surface increases.

  As described above, conventional material technology in which a material containing zirconia or silica such as alumina zirconia or zirconia mullite is applied to a refractory containing metal aluminum or an alloy containing the same for the purpose of improving thermal shock resistance is a long time. Or, under conditions where repeated heating and cooling are used, there is a limit in durability because surface roughness due to oxidation of the sliding surface and structural deterioration and wear due to reaction with FeO and steel components occur.

On the other hand, Patent Document 2 contains 5 to 95% by mass of Al ₄ O ₄ C as a mineral phase, has a thermal expansion coefficient of 8 × 10 ⁻⁶ / K or less, and a bending strength at room temperature of 10 MPa to 60 MPa. A sliding nozzle plate is shown. Further, Patent Document 3, in an aluminum oxycarbide composition having a crystal of Al 4 _O 4 _C, when viewed the aluminum oxycarbide composition in any cross-section, the cross-sectional area of the Al 4 _O 4 _C crystal An aluminum oxycarbide composition having an average diameter of 20 μm or more when converted into a circle and a refractory containing 15 to 95% by mass of the aluminum oxycarbide composition are shown. Furthermore, these Patent Documents 2 and 3 show that Al ₄ O ₄ C has a low thermal expansion coefficient of about half that of Al ₂ O ₃ and has a high thermal shock resistance effect compared to Al ₂ O _3. ing. In addition, it has been shown that a dense alumina layer is formed on the working surface by reaction with carbon monoxide under high temperature conditions, thereby imparting surface roughness resistance.

  In a conventional technique related to oxidation prevention of a general carbon-containing refractory, a method of adding metal aluminum powder or aluminum-magnesium alloy powder is widely adopted. However, when metallic aluminum or the like changes to carbide or oxide during use, voids are formed in the refractory structure, thereby inhibiting densification. Further, when aluminum carbide or the like is generated, there is a problem that the structure tends to deteriorate due to hydration.

On the other hand, when aluminum oxycarbide (Al ₄ O ₄ C) is used, an effect as an antioxidant can be obtained without generating voids or hydrating. The effect as an antioxidant is that when metallic aluminum is added, as shown in the following formulas 1 and 2, carbon monoxide generated by oxidation in the structure of the refractory is reduced, and alumina and carbon are reduced. It generates, suppresses the disappearance of carbon, and densifies the structure.
2C + O ₂ = 2CO ... Formula 1
_{2Al + 3CO = Al 2 O 3} + 3C ... Equation 2

On the other hand, Patent Document 2 and Patent Document 3 show that the antioxidant effect of a refractory containing Al ₄ O ₄ C can be obtained by the following formula 3.
Al ₄ O ₄ C + 2CO = 2Al ₂ O ₃ + 3C Formula 3

From Formula 2, metallic aluminum (Al) can reduce 1.5 moles of carbon monoxide at 1 mole, whereas Al ₄ O ₄ C reduces 2 moles of carbon monoxide at 1 mole from Formula 3. Stop being able to. When these antioxidant effects are compared by mass, Al ₄ O ₄ C: 5.1% by mass has equivalent antioxidant effect to Al: 1% by mass. Patent Document 4, the effect of improving oxidation resistance and the like by adding _Al 4 _{O 4} C 0.5 to 15 mass% is to be obtained, the _Al 4 _{O 4} C weight Al: 0. The effect is equivalent to the addition of 1 to 2.9% by mass, and the antioxidant effect is insufficient under the use conditions of refractories that are used for a long time or repeatedly.

International Publication No. 2010/071196 JP 2011-104596 A JP 2013-53034 A JP-A-9-29587

  The problem to be solved by the present invention is to improve the durability of a refractory for casting, particularly a refractory that is used for a long time or used repeatedly many times, such as a casting nozzle or a sliding nozzle plate. .

  Here, repeated use refers to, for example, when used in a sliding nozzle plate for a ladle, or after casting where the nozzle hole periphery is at a high temperature condition of 1000 ° C. or higher, such as a condition used in hot rotation even in a tundish. The plate itself is cooled and refers to a use condition in which high-temperature heating and cooling are repeated until the temperature is about 500 ° C. or less until the next casting.

  The multiple use in the case of a ladle refers to a condition in which a plurality of channels (for example, 8 channels or more) are used, and in the case of a hot rotating tundish, it refers to a condition in which 2 casts or more are used.

  When used in a ladle, the long-time use refers to the condition of receiving steel for a long time, for example, the total casting time is about 500 minutes or more, and in the case of hot rotation of the tundish, for example, the condition of 800 minutes or more. Show.

  Such use conditions result in a change in the structure of the refractory material for casting because it is repeatedly heated and cooled and exposed to high temperature conditions for a long time. Therefore, it is a severe use condition in which the wear of the refractory for casting becomes large.

  The present invention is a casting refractory, a casting nozzle, and a sliding nozzle plate described in the following items 1 to 8.

1.
A refractory for casting containing 15% by mass to 80% by mass of Al ₄ O ₄ C, 0.5% by mass to 20.0% by mass of AlN, and the balance comprising a refractory component.

2.
A part or all of the particle surface containing Al ₄ O ₄ C has a layer with a thickness of 2 μm or more and 250 μm or less, and the layer is different from the inside of the particle containing Al ₄ O ₄ C excluding the layer. The refractory material for casting according to 1 above, which has a structure and contains components of Al, N, O, and C.

3.
Al ₄ O ₄ C is a refractory for casting as described in 1 or 2 above, which is contained in particles produced by a melting method.

4).
The size of the Al ₄ O ₄ C and _Al 4 _{O 4} C crystal in the particles comprising the _is Al _{4 O} 4 mean diameter 20μm or more when converted to the cross-sectional area of C crystal in circle, from the 1 4. The refractory material for casting according to any one of 3 above.

5.
5. The refractory material for casting according to any one of 1 to 4 above, which contains 2.0% by mass or more and 8.0% by mass or less of free carbon.

6).
The remaining refractory component is one or more selected from the group consisting of Al ₂ O ₃ , MgO, SiO ₂ , ZrO ₂ , SiC, B ₄ C, BN, Si ₃ N ₄ , metal Al and metal Si, The refractory material for casting according to any one of 1 to 5 above.

7).
Of the remainder, the refractory component of Al ₂ O ₃ , MgO, SiO ₂ , ZrO ₂ contains one or more minerals selected from corundum, mullite, spinel, tetragonal zirconia or orthorhombic zirconia, 1 To refractories for casting according to any one of the above 6.

8).
8. A casting nozzle or a sliding nozzle plate, wherein the casting refractory according to any one of 1 to 7 is partially or entirely disposed.

  The present invention will be described in detail below.

The coefficient of thermal expansion of Al ₄ O ₄ C is 4 × 10 ⁻⁶ / K or less, which is about half that of alumina and has low thermal expansion. Due to this low thermal expansibility, the refractory can have high thermal shock resistance. Moreover, the effect of reducing the coefficient of thermal expansion is higher than that of zirconia-containing raw materials such as alumina zirconia of the prior art. In addition, Al ₄ O ₄ C does not undergo phase transition like zirconia even in a high temperature range and does not exhibit a specific expansion behavior. Therefore, it does not have an effect of reducing the elastic modulus. .

Further, as a result of investigation by the present inventors, the thermal conductivity of Al ₄ O ₄ C is 40 W / m · K (20 ° C.), which is about 30 to 40 W of alumina widely used as a main aggregate in the prior art. / N · K (20 ° C), AlN has a high thermal conductivity of 285 W / m · K (20 ° C). Can be increased. As a result, together with the effect of reducing the thermal expansion coefficient of Al ₄ O ₄ C, it becomes possible to improve the thermal conductivity and to impart high spalling resistance to the refractory.

  In addition, AlN hardly wets slag and has both high corrosion resistance and oxidation resistance. These characteristics can obtain a higher effect than the form in which AlN is arranged in a matrix and is unevenly distributed in the form of particles.

As shown in the following formula 4, AlN immediately reacts with CO gas generated by oxidation of carbon in the refractory on the working surface of the refractory by FeO or the like in the molten steel at the time of use. At that time, alumina and carbon are produced to refine the matrix structure, thereby further improving the corrosion resistance and oxidation resistance of the refractory.
2AlN (s) + 3CO (g) = 2Al ₂ O ₃ (s) + 3C (s) + N ₂ (g) Formula 4

As described above, Al ₄ O ₄ C itself has oxidation resistance, but on the other hand, oxidation proceeds under long-term or repeated use conditions. As the oxidation progresses, the expansibility of the refractory due to its Al ₂ O ₃ formation increases, and the thermal shock resistance decreases, and the refractory tends to crack or break (hereinafter also simply referred to as “deterioration”). . By arranging AlN in the refractory matrix, it is possible to suppress such oxidation of Al ₄ O ₄ C or deterioration of the refractory, while maintaining oxidation resistance, corrosion resistance, wear resistance, etc. In addition, the thermal shock resistance can be maintained.

Similarly, metals having strong oxygen affinity such as aluminum and magnesium and alloys containing these metals and borides generally used as antioxidants in carbon-containing refractories such as boron carbide and boron nitride are similarly oxidized of Al ₄ O ₄ C. There is an effect to suppress. However, when a refractory contains a metal such as aluminum or magnesium and an alloy containing these, sintering proceeds when exposed to high temperature conditions during casting, resulting in a remarkably high elastic modulus and reduced thermal shock resistance of the refractory. Under severe conditions such as repeated casting for a long time with a large shape, edge chipping or the like occurs, and sufficient durability cannot be obtained. Borides such as boron carbide and boron nitride become boron oxide when oxidized, and form a low melting point material such as alumina in a refractory. Therefore, when added in a large amount, wear due to melting damage is large. Become.

  On the other hand, AlN has a high melting point of 2200 ° C. and is stable up to a high temperature and difficult to sinter. In addition, although it has an antioxidant effect, it can be aluminized even when oxidized to oxygen or carbon monoxide, so that high corrosion resistance can be maintained.

As the presence form of AlN, it is also possible to directly apply AlN as a powdery raw material to the matrix portion. Alternatively, Al or an alloy containing Al may be placed in the matrix and fired under a predetermined temperature condition in a nitrogen atmosphere, and then placed in the matrix. Further, as described later, Al 4 _O 4 _C and heat-treated beforehand in nitrogen atmosphere, can be applied that formed a deteriorated layer including AlN on Al 4 _O 4 _C particle surface layer portion. Furthermore, it is possible to form an AlN-containing phase in the matrix or in the aggregate particle surface layer portion by applying an aggregate containing Al ₄ O ₄ C and firing it under a predetermined temperature condition in a nitrogen atmosphere. .

  According to the present invention, the thermal shock resistance can be improved while maintaining the oxidation resistance, corrosion resistance, and wear resistance required for a refractory for casting, and it can be used for a long time or repeatedly. Therefore, the casting nozzle and the sliding nozzle plate using the casting refractory according to the present invention are suitable for a long time or repeated use, and excellent durability can be obtained.

  In particular, under repeated use conditions such as reuse including cooling to a low temperature range, in a system containing a large amount of metal aluminum in the prior art, formation of aluminum carbide and digestion or cracking or collapse due to its hydration reaction occur. May occur. On the other hand, since the refractory for casting of the present invention does not cause a hydration reaction, digestion, cracking or collapse does not occur.

  In a short-time use or a small number of times of use, stable durability can be obtained with less damage than a conventional refractory, a casting nozzle, a sliding nozzle plate, or the like.

Al ₄ O ₄ C needs to be 15 mass% or more and 80 mass% or less. When the content of Al ₄ O ₄ C is less than 15% by mass, the effect of reducing the coefficient of thermal expansion is small and the thermal shock resistance is insufficient. Further, when the content of Al ₄ O ₄ C exceeds 80% by mass, Al ₂ O ₃ conversion due to alteration oxidation of Al ₄ O ₄ C proceeds in an atmosphere containing carbon monoxide that coexists with carbon during casting. However, the elastic modulus becomes remarkably high, and this becomes a factor of reducing the thermal shock resistance.

Furthermore, in one form of the present invention, the surface layer of particles containing Al ₄ O ₄ C has a modified layer, and the raw material used is a raw material containing Al ₄ O ₄ C produced by an electrofusion method, There is substantially no raw material having a content of Al ₄ O ₄ C of 100%, and it necessarily contains impurities such as Al ₂ O ₃ , Al ₂ OC, Al, C, and the balance, Since it contains AlN and free carbon, the content is naturally 80% by mass or less. In addition, Al ₄ O ₄ C itself is a very expensive raw material, and considering the balance between the characteristics and the cost, even if the content exceeds 80% by mass, an effect commensurate with the cost cannot be obtained. In addition, the plate refractory is used when the outer periphery is constrained by a metal band such as iron, or when the outer periphery is constrained by a metal case. Although many cases are used, when the content of Al ₄ O ₄ C is more than 80% by mass, the thermal expansion coefficient becomes remarkably low, and the expansion amount of the outer metal band or metal case is greater. The expansion amount of the plate refractory to be restrained becomes larger, the restraining force of the metal band is reduced, the effect of suppressing cracks is reduced, causing crack expansion, and the refractory is easily detached from the metal case. Occurs. Therefore, the content of Al ₄ O ₄ C is desirably 80% by mass or less.

AlN is required to be 0.5 mass% or more and 20.0 mass% or less. That is, the refractory of the present invention further contains 0.5% by mass or more and 20.0% by mass of AlN in addition to Al ₄ O ₄ C. By containing AlN having a very high thermal conductivity in combination with Al ₄ O ₄ C having a low thermal expansion coefficient and a low thermal conductivity, the thermal expansion coefficient is low, the thermal conductivity is high, and the thermal shock resistance is further improved. An excellent casting refractory can be obtained. Moreover, AlN has held an antioxidant effect, a matrix or the like, relatively _Al 2 _{O 3} turned into easily _{Al 4 O 4 Al 4 O 4} Al 2 O 3 of C by placing the AlN around the C It is possible to suppress the increase in elastic modulus and thermal expansion coefficient, and to maintain the effect of thermal shock resistance for a long time.

When the content of AlN is less than 0.5% by mass, the effect of increasing the thermal conductivity of the refractory is small. Moreover, the effect which improves the corrosion resistance by the antioxidant effect and wettability improvement with slag is also small. When the content of AlN exceeds 20.0% by mass, the casting time is long, and when the heat load is large, AlN is converted to Al ₂ O ₃ to cause sintering and the like. Moreover, the nitrogen component in AlN elutes into molten steel, the structure deteriorates, and wear increases depending on the use conditions. In addition, if the AlN content is high, the thermal conductivity of the refractory increases significantly, so the temperature of the outer metal band rises under conditions where the outer periphery is restrained with a metal band such as iron. Thus, the expansion amount of the metal band becomes larger than the expansion amount of the refractory to be restrained, the restraining force of the metal band is reduced, the effect of suppressing cracks is reduced, and the cracks are enlarged. Furthermore, after casting, a phenomenon occurs such that the metal band is displaced or detached, making it difficult to reuse or recycle.

In the present invention, it is preferable that a part or all of the particle surface containing Al ₄ O ₄ C has a layer having a thickness of 2 μm to 250 μm. The layer has a structure different from the inside of the particle containing Al ₄ O ₄ C excluding the layer, and contains Al, N, O, and C components.

As a result of investigations by the present inventors, Al ₄ O ₄ C particles or particles of molten raw material containing Al ₄ O ₄ C (in the present invention, these are collectively referred to as “particles containing Al ₄ O ₄ C”). surface portion of.), particularly in the surface layer of _Al 4 _{O 4} C particles, Al, N, O, by disposing the altered layer of 2μm or more in thickness composed mainly of C, long even more, Al ₄ It has been found that the deterioration of O ₄ C can be suppressed and the effect of reducing the thermal expansion coefficient of Al ₄ O ₄ C can be maintained. And as a result of actually analyzing the altered layer of Al ₄ O ₄ C by EPMA, it contains Al, N, O, and C components, and compositions such as AlN, AlON, Al ₂ O ₃ , and Al ₂ OC are used. It was thought to contain. Altered layer formed of these compositions, Al 4 _O 4 _C and the atmosphere is estimated that prevent the direct contact with a surrounding of the Al 4 _O 4 _C. Therefore, it is presumed that there is an effect of suppressing the progress of Al ₄ O ₄ C into Al ₂ O ₃ by reaction with an atmosphere such as oxygen or carbon monoxide.

When the thickness of the deteriorated layer is less than 2 μm, the effect of blocking contact with the atmosphere is small, and the effect of suppressing the progress of Al ₂ O ₃ formation is small. Therefore, when arrange | positioning a deteriorated layer, it is desirable that the thickness is 2 micrometers or more. Further, the altered layer around Al ₄ O ₄ C has high thermal conductivity, and AlN having an oxidation resistance effect has a high effect of suppressing a decrease in thermal conductivity, and at the same time, Al ₄ O ₄ C The effect of suppressing alteration is also high. Therefore, it is more desirable that the altered layer in the surface layer portion of the particles containing Al ₄ O ₄ C contains AlN. This altered layer can be formed by previously heat-treating particles containing Al ₄ O ₄ C under a temperature condition of 1000 ° C. or higher in a non-oxidizing atmosphere such as a nitrogen atmosphere or a carbon monoxide atmosphere. Moreover, after adding other refractory raw materials to particles containing Al ₄ O ₄ C that have not been heat-treated, kneading together with a binder such as a phenol resin, and molding, a nitrogen atmosphere, an Ar atmosphere, a carbon monoxide atmosphere, or the like In a non-oxidizing atmosphere, heat treatment can be performed at a temperature of 1000 ° C. or higher for an appropriate time.

The formation of the altered layer means a change in structure due to the reaction of Al ₄ O ₄ C. However, when the thickness of the altered layer exceeds 250 μm, the volume change is large and the stability of the refractory structure can be ensured. It becomes difficult and causes cracks and weakening of the structure. In addition, when the thickness of the deteriorated layer exceeds 250 μm, it means that the content of Al ₄ O ₄ C is substantially reduced, and a sufficient effect of reducing the coefficient of thermal expansion cannot be secured. There is sex.

Al ₄ O ₄ C is preferably contained in particles produced by an electrofusion method. Al 4 _O 4 _C, in the conventional sintering method poor productivity is practically difficult to industrialization, also to produce a material that can be a dense Al 4 _O 4 _C crystal diameter larger aggregate Is difficult. On the other hand, an electromelting raw material obtained by arc melting (this production method is simply referred to as “melting method” hereinafter, and the raw material produced by this production method is also simply referred to as “electromelting raw material”) is productivity. It is possible to obtain Al ₄ O ₄ C raw material particles having a high and precise arbitrary particle size or crystal diameter.

The size of the _{Al 4 O 4 C Al 4 O} 4 C crystal in the particles containing the, _Al 4 _{O 4} Mean diameter of a circle the cross-sectional area of C crystal (hereinafter, simply "average crystal diameter" It is also preferably 20 μm or more.

The particles are dense, as the particle size including the _Al 4 _{O 4} C is large, and _Al 4 as _{O 4} average crystal size of _Al 4 _{O 4} C in the particles containing C is large, high temperature, even under oxidizing conditions The contact area with oxygen and carbon monoxide is reduced, and it becomes possible to suppress the oxidation of Al ₄ O ₄ C and the formation of Al ₂ O ₃ and maintain a healthy particle and refractory structure for a long time. Further, it is possible to maintain the low thermal expansion property of the refractory and to maintain the thermal shock resistance of the refractory at a high level.

If the average crystal size of Al ₄ O ₄ C is less than 20 μm, the thermal expansion rate is low due to the alteration of Al ₄ O ₄ C under particularly severe use conditions in which the long-term heat load is large and oxidation or Al ₂ O ₃ formation is likely to proceed. The effect cannot be maintained, and sintering is likely to proceed, and wear such as edge chipping is likely to occur due to a decrease in thermal shock resistance. However, the effects of the present invention can be obtained even when the average crystal diameter of Al ₄ O ₄ C is less than 20 μm in cases other than the particularly severe use conditions.

The other main component in the Al ₄ O ₄ C raw material is corundum (alumina), which also indicates the stability of Al ₄ O ₄ C in the particles and the high thermal shock resistance of the refractory containing the same. This contributes to maintaining the properties, oxidation resistance, corrosion resistance, and the like.

Free carbon is preferably contained in an amount of 2.0% by mass or more and 8.0% by mass or less. Free carbon, the presence to cover or surround the periphery of the raw material containing Al 4 _O 4 _C, excessive formation or other affected layer oxidation of the surface of the raw material containing Al 4 _O 4 _C, other There is an effect of suppressing the progress of excessive sintering between the constituent raw materials and the like. As a result, the stability of Al ₄ O ₄ C in particles containing Al ₄ O ₄ C and the high thermal shock resistance, oxidation resistance, corrosion resistance, etc. of the refractory containing the same are maintained for a longer time. can do.

If the free carbon is less than 2.0% by mass, the effect of maintaining the stability of such Al ₄ O ₄ C and a refractory containing the same, or the effect of suppressing sintering, etc. is small, and thereby the thermal shock The effect of maintaining the properties and the like may be reduced. Moreover, the effect which suppresses the infiltration of slag may become small, and the tendency for the wear by slag infiltration and melt | dissolution on an operation surface to become large may arise.

  If free carbon exceeds 8.0% by mass, elution of free carbon components into the molten steel and a tendency to increase structure deterioration due to oxidation increase, wear on the working surface increases, and good durability is obtained. It may be difficult to do.

  This free carbon source can be attributed to phenolic resin applied as a binder, and all carbon substrate materials other than compounds, whether crystalline or amorphous, such as graphite, coke, anthracite, pitch, carbon black, etc. Furthermore, when impregnating a refractory with tar, pitch or the like, a carbon component after impregnation or heat treatment is also included.

The remainder of the refractory component is one or more selected from the group consisting of Al ₂ O ₃ , MgO, SiO ₂ , ZrO ₂ , SiC, B ₄ C, BN, Si ₃ N ₄ , metal Al, and metal Si. can do.

In addition, when a zirconia-containing raw material such as zirconia mullite or alumina zirconia, which is generally applied to a sliding nozzle plate, is applied, since it contains ZrO ₂ and SiO ₂ components, the erodibility to FeO is reduced. Furthermore, Al ₄ O ₄ C has the property of reducing SiO ₂ , ZrO _2, etc., and when exposed to high temperatures for a long time in the presence of these, ZrO ₂ and SiO ₂ components are reduced and ZrC is reduced. A phenomenon such as generation or disappearance as SiO gas may occur, which may be a factor for promoting wear of the refractory.

Since the ZrO ₂ component may cause collapse of the refractory structure as described above, it cannot be used in a large amount and is preferably a small amount of about 3.0% by mass or less. On the other hand, when tetragonal zirconia or monoclinic zirconia is dispersed in part as the ZrO ₂ component, the thermal shock resistance may be improved. In particular, by utilizing the unique expansion behavior of monoclinic zirconia, it is effective in improving the thermal shock resistance by reducing the elastic modulus. In addition, since these minerals do not contain a low-melting component such as CaO as a stabilizer, there is no wear due to deterioration of the refractory structure due to the CaO component during use.

The SiO ₂ component disappears as a gas, and since the SiO ₂ component itself has low corrosion resistance against FeO or the like, when it is contained, the function of a sintering aid or the like is expected to be about 3.0% by mass or less. It is preferable to keep it in a small amount. Further, when it is contained as mullite, a phenomenon such as disappearance as gas hardly occurs, and since the thermal expansion property of mullite itself is small, it is effective for further reducing the thermal expansion property as a refractory.

When MgO component is contained as periclase, depending on the amount of MgO component, in addition to its high thermal expansibility itself, it produces a spinelation reaction with Al ₂ O ₃ produced from Al ₄ O ₄ C at high temperatures. The thermal shock resistance may be lowered due to the extremely large thermal expansion coefficient or residual expansion coefficient. On the other hand, when the MgO component is contained as spineled particles, there is no such problem as an extremely high coefficient of thermal expansion, which is effective for improving the corrosion resistance against FeO or the like.

Al ₂ O ₃ component (corundum) is difficult to reduce even when coexisting with metals, AlN, etc., is thermally stable, hardly reacts with Al ₄ O ₄ C, and has an excellent balance between corrosion resistance and thermal shock resistance .

For these reasons, it is desirable that the remainder of the refractory component is mainly Al ₂ O ₃ as corundum, Al ₂ O ₃ as spinel, or MgO.

  In addition to the above, it is possible to contain clay minerals, glassy materials, etc. as the oxide component, but in order to suppress a decrease in corrosion resistance, etc., the amount may be limited to about 5.0% by mass or less. preferable.

  The balance is mainly carbide, boride, nitride, etc. for the purpose of improving corrosion resistance and infiltration resistance to slag, etc., and mainly Al, Si, Mg, etc. for the purpose of improving oxidation resistance and strength, etc. The metal can be contained. However, carbon raw materials, carbides, borides, nitrides, non-oxides such as Al, Si, and Mg, and metals easily wet and react with molten steel. Therefore, if the content of these non-oxides and metals is large, the wear of the sliding surface in contact with the molten steel may increase when casting for a long time or repeated use.

From these, the oxides by the use condition to the rest, free of carbon, carbides or nitrides, borides, metallic Al, it is desirable to include a metal Si or metal Mg or their alloys, Al ₄ O The total content of ₄ C, AlN, Al ₂ O ₃ and MgO (MgO is present as spinel) is desirably 85% by mass or more.

The total content of Al ₄ O ₄ C, AlN and Al ₂ O ₃ , or the total content of Mg ₄ (although MgO is present as spinel) added to Al ₄ O ₄ C, AlN, Al ₂ O ₃ is 85 mass In the case of less than%, other carbides, borides, nitrides, metals, oxide components and the like are relatively increased, and the content of Al ₄ O ₄ C, AlN, which is the object of the present invention, is high. It becomes difficult to maintain the effects of thermal shock resistance, oxidation wear resistance, and corrosion resistance at a level for a long time.

  A method for producing a refractory according to the present invention will be described using a sliding nozzle plate as an example.

The sliding nozzle plate to which the refractory material of the present invention is applied can be obtained by a general method for manufacturing a sliding nozzle plate. That is, a raw material composed of aggregate particles mainly composed of Al ₄ O ₄ C, AlN, Al ₂ O ₃ , MgO (MgO is present as spinel), carbon matrix aggregate, and other refractory components is predetermined. A step of mixing at a particle size constitution / mixing ratio, a step of adding and kneading an organic binder that forms a carbon bond such as a phenol resin, a step of forming into a predetermined sliding nozzle plate shape, a step of drying and heat treatment, It is a manufacturing method including processing steps such as the surface.

  In addition to the case where AlN is contained as the raw material particles as described above, a manufacturing method is adopted in which metallic aluminum is contained in the earth and the molded body, and then converted to AlN using a nitriding reaction in a nitrogen atmosphere. Is also possible.

  These detailed conditions can be optimized by any design according to individual conditions. The heat treatment is more preferably a non-oxidizing atmosphere and an inert gas atmosphere.

The refractory samples used in Examples A to G below are kneaded by adding an organic binder to an electromelting raw material containing Al ₄ O ₄ C, an alumina raw material, metallic aluminum, a carbonaceous raw material and other refractory aggregates. Obtained by a manufacturing method including a step of forming a refractory with an oil press, a step of drying, and a heat treatment step at a temperature of about 1400 ° C. in a nitrogen atmosphere.

Al ₄ O ₄ C, Al ₂ O ₃ (corundum), AlN and BN in the obtained refractory are quantified by the internal standard method by X-ray diffraction, and the phase without the standard sample is determined from the profile by the Reedveld method. Quantification was performed. Free carbon (also referred to as “FC”), total carbon, SiC, Si, and Al were quantified according to JIS-R-2011. Other oxides such as ZrO ₂ and SiO ₂ were quantified by a fluorescent X-ray analyzer according to JIS-R-2016. B ₄ C was quantified according to JIS-R-2015. Si ₃ N ₄ was quantified according to JIS-R-1603.

The maximum particle diameter of the Al ₄ O ₄ C-containing raw material particles in the refractory and the thickness of the altered layer on the particle surface were determined by visually observing the structure with a reflection microscope. The maximum particle size was determined as the maximum particle size in a visual field observed visually 10 times under a microscope. Similarly, the thickness of the deteriorated layer was determined as the maximum thickness in a visual field observed visually at 10 times under a microscope. The component of this altered layer was qualitatively determined by EPMA. In particular, nitrogen was difficult to quantify, and was judged to be qualitatively indicated by ○.

Al ₄ O ₄ C-containing size of _Al 4 _{O 4} C crystal in the raw material particles, the microscopic observation of the _Al 4 _{O 4} C-containing raw material particles, to greater than the area of half of the entire, large Al sectional area _The cross-sectional areas were accumulated in order from the ₄ O ₄ C crystals, and the accumulated cross-sectional areas of the respective products were expressed as average values of the respective diameters when converted into circles.

And the predetermined | prescribed shape was cut out from the obtained refractory material, and the following evaluation was performed.
-Bulk specific gravity: According to JIS-R-2205.
-Apparent porosity: According to JIS-R-2205.
-Thermal expansion coefficient: Conforms to JIS-R-2207.

Furthermore, the following thermal shock resistance evaluations A and B were performed as evaluations after repeated repeated use, which was the subject of the present invention.
Thermal shock resistance evaluation A: The heat-treated sample was immersed in a hot metal at 1600 ° C. for 3 minutes and then air-cooled repeatedly 5 times, and the degree of cracking was evaluated.
-Thermal shock resistance evaluation B: A metal band was wound around a refractory prototyped in the shape of a sliding nozzle plate, the inner hole was heated with a burner, and the state of cracks generated, band displacement, etc. were evaluated.

Furthermore, as an evaluation of oxidation resistance, the remaining amount of Al ₄ O ₄ C after oxidation was evaluated. Specifically, a sample after heat treatment at 1500 ° C. for 3 hours in a coke breeze was evaluated by an X-ray diffraction method, and the Al ₄ O ₄ C content was quantified by a Reedveld method, and the Al ₄ O ₄ C before and after the heat treatment was quantified. From the content of, the residual ratio of Al ₄ O ₄ C was calculated.

  In addition, as an evaluation of corrosion resistance, an erosion test was performed by immersing the sample in a high-frequency induction furnace in which SS400 and a mill scale were melted at 1600 ° C. for 3 hours. This is mainly to evaluate FeO resistance, and was evaluated by a value obtained by indexing the maximum amount of melting loss of Comparative Example 1 shown in Table 1 described later as 100. It shows that it is excellent in corrosion resistance (FeO resistance), so that this index | exponent is small.

[Example A]
Example A is an example in which the content of Al ₄ O ₄ C in the refractory was investigated. Table 1 shows the configuration and results of each example.

Comparative Example 1 the _{Al 4 O 4} Al 2 O ₃ contained no C mainly was typical example of the prior art. It can be seen that the coefficient of thermal expansion tends to become significantly smaller as the content of Al ₄ O ₄ C increases. In Comparative Example 2 having an Al ₄ O ₄ C content of 13% by mass, although the thermal expansion coefficient is lower than that of Comparative Example 1 of the prior art, the thermal shock resistance after the heat treatment is not sufficient. Although the corrosion resistance of Comparative Example 2 is equivalent to that of Example 1, the thermal shock resistance is not sufficient in consideration of repeated use for a long time.

In Examples 1 to 3 in which the content of Al ₄ O ₄ C is 15% by mass to 80% by mass, both the thermal shock resistance and the corrosion resistance are improved. On the other hand, in Comparative Example 3 in which the Al ₄ O ₄ C content is 83% by mass, the thermal expansion coefficient is greatly reduced and the corrosion resistance is further improved as compared with Comparative Example 1 of the prior art. The thermal shock resistance after heat treatment tends to decrease. This is thought to be due to the fact that the mass change of Al ₄ O ₄ C due to heat treatment increases and the elastic modulus increases. Moreover, in the thermal thermal shock resistance evaluation B in which a plate-shaped inner hole heating test is performed, the metal band is displaced, and the thermal shock resistance tends to be reduced due to the influence. From these results, it is understood that the Al ₄ O ₄ C content needs to be 15% by mass or more and 80% by mass or less.

[Example B]
Example B is an example in which the content of AlN in the refractory was investigated. Table 2 shows the configuration and results of each example.

In Example B, all examples and comparative examples were based on a refractory containing 20% by mass of Al ₄ O ₄ C. In Comparative Example 4 which does not contain AlN and is mainly composed of Al ₄ O ₄ C and Al ₂ O ₃ , the thermal shock resistance evaluation A does not provide sufficient thermal shock resistance. This is considered to be because the Al ₄ O ₄ C content after the heat treatment is lowered, the effect of reducing the thermal expansion coefficient is reduced, and the elastic modulus is increased due to the alteration of Al ₄ O ₄ C.

  In contrast, in Examples 4 to 6 in which the AlN content is in the range of 0.5 to 20% by mass, the thermal shock resistance is improved and the corrosion resistance is also improved as the AlN content is increased. Thus, it can be seen that it has sufficient durability against conditions such as repeated use.

In Comparative Example 5 in which the content of AlN is excessive as 21% by mass, the corrosion resistance is good, but in the thermal shock resistance evaluation A, the thermal shock resistance tends to decrease. This is presumably because AlN was converted to Al ₂ O ₃ after the heat treatment, resulting in sintering. Further, in Comparative Example 5, the thermal shock resistance evaluation B caused the band to shift and the crack expanded.

  From these results, it is understood that the AlN content needs to be 0.5 mass% or more and 20 mass% or less.

[Example C]
Example C is an example in which the thickness of the altered layer on the surface of Al ₄ O ₄ C particles was investigated. Table 3 shows the configuration and results of each example.

In Example C, all examples were based on a refractory containing Al ₄ O ₄ C in an amount of 15% by mass or more and AlN in an amount of 2% by mass or more. In Example 7 in which the thickness of the altered layer on the surface of the Al ₄ O ₄ C particles is 0.5 μm, the thermal shock resistance is slightly lowered in the thermal shock resistance evaluation A. This is presumably because the residual amount of Al ₄ O ₄ C after heat treatment is as small as 10% by mass.

In Examples 8 to 10 in which the thickness of the altered layer on the surface of the Al ₄ O ₄ C particles is in the range of 2 to 250 μm, all of the corrosion resistance evaluation, the thermal shock resistance evaluation A, and the thermal shock resistance evaluation B have good results. Show.

On the other hand, in Example 11 where the thickness of the altered layer on the surface of the Al ₄ O ₄ C particles is as thick as 300 μm, the cracks tend to be slightly larger in the evaluation by the thermal shock resistance evaluation A. This is because the thickness of the altered layer on the surface of Al ₄ O ₄ C particles before heat treatment is as thick as 300 μm, and the heat treatment further increases the mass change of Al ₄ O ₄ C, resulting in a large volume change due to alteration. Therefore, it is considered that the thermal shock resistance has decreased.

From these results, it can be seen that the thickness of the altered layer on the surface of the Al ₄ O ₄ C particles is more preferably 2.0 μm or more and 250 μm or less.

[Example D]
Example D is an example in which the production method of the Al ₄ O ₄ C-containing raw material and the crystal particle diameter of Al ₄ O ₄ C were investigated. Table 4 shows the configuration and results of each example.

Examples 12 to 15 are all based on a refractory containing 20% by mass of Al ₄ O ₄ C and 2% by mass of AlN and 2 μm in the altered layer thickness of Al ₄ O ₄ C. As a result, 4% by mass of free carbon, 1% by mass of SiO ₂ , 0.5% by mass of SiC, and 0.5% by mass of B ₄ C are contained.

In Example 12 in which the Al ₄ O ₄ C-containing raw material was produced by a sintering method and the average diameter of the Al ₄ O ₄ C crystals was as fine as 5 μm, the thermal shock resistance evaluation A was slightly large in cracks. Tend to be. This is presumably because the residual amount of Al ₄ O ₄ C after heat treatment is as small as 10% by mass.

Further, although the Al ₄ O ₄ C-containing raw material is manufactured by the arc melting method, Example 13 in which the average diameter of the Al ₄ O ₄ C crystals is as fine as 5 μm is cracked in the thermal shock resistance evaluation A. Tends to be slightly larger. This is also considered to be because the residual amount of Al ₄ O ₄ C after heat treatment is as small as 10% by mass.

In Example 14 and Example 15 in which the Al ₄ O ₄ C-containing raw material is manufactured by the arc melting method and the average diameter of the Al ₄ O ₄ C crystals is 20 μm or more, both materials have a thermal shock resistance evaluation A The result is good with small cracks.

From the above, it can be seen that the Al ₄ O ₄ C-containing raw material is produced by an arc melting method, and the average diameter of Al ₄ O ₄ C crystals in the Al ₄ O ₄ C-containing raw material is more preferably 20 μm or more. .

[Example E]
Example E is an example in which the amount of free carbon in the refractory was investigated. Table 5 shows the configuration and results of each of these examples.

Examples 15 to 18 all contain 20% by mass of Al ₄ O ₄ C and 2% by mass of AlN, respectively, and are based on a refractory having an altered layer thickness of Al ₄ O ₄ C of 2 μm. And 1% by mass of free carbon, SiO ₂ , 0.5% by mass of SiC, and 0.5% by mass of B ₄ C. In addition, in all cases, the Al ₄ O ₄ C-containing raw material is manufactured by an arc melting method, and an Al ₄ O ₄ C crystal having an average diameter of 20 μm or more is used.

  In Example 16 having a free carbon content of 1.5% by mass, both the results of thermal shock resistance evaluations A and B tend to be somewhat cracked. This is thought to be because the amount of free carbon is small and the effect of suppressing sintering is small.

  In Examples 16 to 17 in which the free carbon content is 2 to 8% by mass, both the results of the thermal shock resistance evaluations A and B are good, and the corrosion resistance is also good.

  In Example 18 in which the free carbon content is 9.0% by mass, both the results of the thermal shock resistance evaluations A and B are good, but the corrosion resistance tends to decrease due to the excess of free carbon. is there.

  From the above, it can be seen that the free carbon content is more preferably in the range of 2.0 to 8.0 mass%.

[Example F]
Example F is an example in which components other than Al ₄ O ₄ C, Al ₂ O ₃ , AlN, and free carbon were investigated. Table 6 shows the configuration and results of each of these examples.

All the materials of Examples 19 to 22 contain 20% by mass of Al ₄ O ₄ C and 2% by mass of AlN, respectively, and are based on a refractory having an altered layer thickness of 2 μm of Al ₄ O ₄ C. As a component, 4% by mass of free carbon, 0.5% by mass of SiC, and 0.5% by mass of B ₄ C are contained. In any of the materials, the Al ₄ O ₄ C-containing raw material is manufactured by an arc melting method, and the average diameter of Al ₄ O ₄ C crystals is 20 μm or more.

Example 19 containing 3% by mass of the ZrO ₂ component and 3% by mass of the SiO ₂ component each contained mullite and monoclinic zirconia as the main mineral phase in addition to Al ₄ O ₄ C and corundum. However, the results of thermal shock resistance evaluations A and B are both good and the corrosion resistance is also good.

Example 20 containing 3% by mass of MgO and 1% by mass of SiO ₂ component contains spinel as a main mineral phase in addition to Al ₄ O ₄ C and corundum, but thermal shock resistance evaluation A Both the results of B and B are good, and the corrosion resistance is also good.

Example 21 containing 3% by mass of the ZrO ₂ component, 3% by mass of the SiO ₂ component, 0.5% by mass of the Si ₃ N ₄ component, and 0.5% by mass of the BN component is the main mineral phase. Although it contains mullite and monoclinic zirconia in addition to Al ₄ O ₄ C and corundum, both the results of thermal shock resistance evaluations A and B are good and the corrosion resistance is also good.

Example 22 containing 3% by mass of ZrO ₂ component, 3% by mass of SiO ₂ component, 1.0% by mass of metal Si component, and 1.0% by mass of gold Al component, respectively, _Although it contains mullite and monoclinic zirconia in addition to ₄ O ₄ C and corundum, both the results of thermal shock resistance evaluations A and B are good, and the corrosion resistance is also good.

From the above, as components other than Al ₄ O ₄ C, Al ₂ O ₃ , AlN and free carbon, Al ₂ O ₃ , MgO, SiO ₂ , ZrO ₂ , SiC, B ₄ C, BN, Si ₃ N ₄ or metal Si etc. can be contained. Further, any mineral of corundum, mullite, spinel, tetragonal zirconia or orthorhombic zirconia can be contained as the mineral phase of the remaining oxide component.

[Example G]
Example G shows the results of use in an actual furnace as a sliding nozzle plate for a ladle. Table 7 shows the configuration and evaluation of each example.

  In place A indicated by the actual furnace use result A in Table 7, a test was performed and evaluated as a sliding nozzle plate having an inner hole diameter of 93 mm with a ladle of 320 tons. 1ch is a casting time of about 40 minutes on average, and usually about 9ch is used. In place A, the used sliding nozzle plate is collected, a ring-shaped refractory is inserted into the inner hole, and the sliding surface is polished to regenerate the plate refractory. Use result A (reproduction use) shows the result.

  In the place B shown by the actual furnace use result B in Table 7, the test was carried out and evaluated as an SN plate having an inner hole diameter of 75 mm with a 200-ton ladle. 1ch is an average casting time of about 100 minutes, and usually about 6ch is used.

Comparative Example 6 and Comparative Example 7 are general Al ₂ O ₃ —ZrO ₂ —C based materials that have been conventionally used.

  In the place A indicated by the actual furnace use result A, 9 ch of Comparative Example 6 was used, but the surface roughness of the sliding surface was large and unsatisfactory. Although 9 ch of Comparative Example 7 was also used, the edge portion of the nozzle inner hole was missing and was in a malfunction. In Example 23 of the present invention, 11 ch was used, and the appearance after use was also good with slight cracks.

  Similarly, 7 ch of the sliding nozzle plate that was regenerated and used in the A place was used in Comparative Example 6, but the sliding surface was so rough that good results could not be obtained. Comparative Example 7 (Material B) had a large crack after use and could not be regenerated. In contrast, Example 21 was used well for 10 ch.

  In the place B indicated by the actual furnace use result B, 6ch of Comparative Example 6 was used, but the surface roughness of the sliding surface was large and unsatisfactory. Although 6 ch of Comparative Example 7 was also used, the edge chipping occurred and was unsatisfactory. On the other hand, Example 23 was used in 8ch, and the state after use was good with few cracks.

Claims (8)

A refractory for casting containing 15% by mass to 80% by mass of Al ₄ O ₄ C, 0.5% by mass to 20.0% by mass of AlN, and the balance comprising a refractory component. A part or all of the particle surface containing Al ₄ O ₄ C has a layer with a thickness of 2 μm or more and 250 μm or less, and the layer is different from the inside of the particle containing Al ₄ O ₄ C excluding the layer. The refractory for casting according to claim 1, which has a structure and contains Al, N, O and C components. The refractory material for casting according to claim 1 or 2, wherein Al ₄ O ₄ C is contained in particles produced by a melting method. Al ₄ O ₄ size of _Al 4 _{O 4} C crystal in particles containing C _is at 20μm or more in average diameter when converted to the cross-sectional area of the Al _{4 O} 4 C crystal in circle claim 1 The refractory for casting according to claim 3.   The refractory material for casting according to any one of claims 1 to 4, comprising free carbon in an amount of 2.0 mass% to 8.0 mass%. The remaining refractory component is one or more selected from the group consisting of Al ₂ O ₃ , MgO, SiO ₂ , ZrO ₂ , SiC, B ₄ C, BN, Si ₃ N ₄ , metal Al and metal Si, The casting refractory according to any one of claims 1 to 5. The refractory component of Al ₂ O ₃ , MgO, SiO ₂ , ZrO ₂ among the balance includes one or more minerals selected from corundum, mullite, spinel, tetragonal zirconia or orthorhombic zirconia. The refractory material for casting according to any one of claims 1 to 6.   A casting nozzle or a sliding nozzle plate, wherein the casting refractory according to any one of claims 1 to 7 is disposed in part or in whole.