JP2014141381A - Zirconia-carbon-containing refractory and immersion nozzle for continuously casting a steel as well as method for manufacturing a zirconia-carbon-containing refractory and method for manufacturing an immersion nozzle for continuously casting a steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zirconia-carbon-containing refractory exhibiting an excellent tolerability as an immersion nozzle for continuously casting a steel.SOLUTION: The provided zirconia-carbon-containing refractory comprises: within the refractory texture thereof, zirconia particles and a carbon matrix material; and at least 78 and no more than 90 mass% of ZrOand at least 5 and no more than 17 mass% of carbon. The zirconia particles comprise, in a case where the total weight of the zirconia particles is defined as 100 mass%, at least 97 mass% of particles having diameters of 75 μm or less and at least 40 mass% of particles having diameters of 45 μm or less. The carbon matrix material has a maximal length of 100 μm or less and an average length of 45 μm and is included within the refractory at a ratio of at least 2 and no more than 15 mass%. The refractory exhibits a strain magnitude fluctuation value confined within 20% in a test method for inducing the rupture of a sample provided by forming the refractory in the shape of a ring by homogeneously compressing the sample from the inner hole thereof.

Description

  The present invention relates to a refractory used for an immersion nozzle or the like used for continuous casting of steel, and in particular, a zirconia-carbon-containing refractory having high corrosion resistance and high thermal shock resistance, and its zirconia-carbon-containing The present invention relates to a continuous casting immersion nozzle provided with a refractory, a method for producing a zirconia-carbon-containing refractory, and a method for producing a steel continuous casting immersion nozzle.

Immersion nozzles used in continuous casting of steel are used to transfer molten steel from the tundish to the mold. The immersion nozzle is used to inject molten steel in a rectified state inside the mold while preventing oxidation of the molten steel by preventing contact between the molten steel and the atmosphere. This prevents slag layers floating on the molten steel surface and non-metallic inclusions present in the molten steel from being mixed into the slab, improving the quality of the slab and improving operational stability. Secured. Generally, a molten glass layer called a mold powder layer exists on the upper surface of the molten steel inside the mold. This mold powder layer contains CaO, SiO ₂ , Na ₂ O, K ₂ O, Al ₂ O ₃ , CaF ₂ , C, and the like. Therefore, it has a strong erosion property with respect to Al ₂ O ₃ , SiO ₂ , C, etc., which are the constituent materials of the immersion nozzle, and causes a problem with the corrosion resistance of the immersion nozzle for a long time operation. Therefore, a material mainly composed of ZrO ₂ having high corrosion resistance with respect to the mold powder is often applied to a portion of the immersion nozzle that comes into contact with the mold powder (hereinafter simply referred to as “powder line”). Furthermore, since it is necessary to ensure thermal shock resistance, a zirconia-carbon-containing refractory material in which a carbon substrate material mainly composed of graphite is added to zirconia raw material particles mainly composed of a ZrO ₂ component as a material for a powder line ( Hereinafter, simply referred to as “zirconia-carbon-containing refractory” is applied.

Improvements in the powder line material, zirconia-carbon-containing refractory, have a direct effect on the life of the nozzle, and various improvements have heretofore been made. In general, it is known that the corrosion resistance is improved by increasing the ZrO ₂ content in the material. However, when the ZrO ₂ content is increased to about 85% by mass or more, the graphite content is relatively reduced, so that the solid lubricity, which is one of the important functions of graphite, is reduced, and CIP (Cold Isostatic Press) The density of the molded body is reduced. As a result, the apparent porosity of the zirconia-carbon refractory increases and the corrosion resistance decreases, or the thermal expansion coefficient and the elastic modulus increase, which increases the risk of cracking due to thermal shock. There was a problem of disturbing. In general, considering the balance between corrosion resistance and thermal shock resistance, the upper limit of the ZrO ₂ content is considered to be about 85% by mass, and about 82% by mass or less is preferable for more stable use. It is considered as a range. In addition, as a raw material containing a ZrO ₂ component to be applied, a crystal structure stabilizer such as CaO, MgO, Y ₂ O ₃ or the like is used with respect to ZrO ₂ from the viewpoint of thermal structural stability during steel receiving. It is common to apply partially stabilized zirconia particles or fully stabilized zirconia particles that contain ˜12% by mass and that exhibit relatively linear thermal expansion characteristics.

  With the recent progress of multi-casting, high productivity, high cleanliness, etc., there is an increasing demand for further extending the life of the immersion nozzle and improving the stability of the nozzle. To meet that need, further improvements in corrosion resistance are required for zirconia-carbon containing refractories for powder lines of immersion nozzles. Under these circumstances, many improvement proposals focusing on the size (particle size) of zirconia particles and the particle size configuration have been proposed as means for improving corrosion resistance. For example, Patent Document 1 includes “Zirconia raw material 70 to 95% by mass, graphite (ordinary scaly graphite, electrode scrap, anthracite, earthy graphite, etc.) 5 to 30% by mass, and the particle size configuration of the zirconia is 45 μm or less. "Zirconia-graphitic refractories" with 70% or more zirconia particles are disclosed.

  In the conventional general zirconia-carbon-containing refractories, when there are many small zirconia particles such as 45 μm or less as described above, it is considered that the dissolution rate of zirconia particles into the molten powder increases and the corrosion resistance decreases. In contrast, Patent Document 1 uses a large amount of fine zirconia particles (45 μm or less). When a large amount of particles smaller than a certain ratio is used, the effect of improving corrosion resistance may be obtained as shown in Patent Document 1.

  On the other hand, without using a large amount of these small zirconia particles (45 μm or less), focusing on the structure of zirconia-carbon-containing refractories under general (general purpose) continuous casting operating conditions, corrosion resistance and heat resistance Proposals have been made to improve both impact properties.

For example, Patent Document 2 states that “in a zirconia-carbon-containing refractory material in which a carbon bond is formed between aggregate particles, the ZrO ₂ component is 80% by mass or more, and a carbon matrix material is contained in the refractory structure. The total volume of the open pore volume and the volume of the carbon matrix material is 42% by volume or less and 25% by volume or more, the pores of 10 μm or more in all the open pores in the refractory structure are 30% or less, and In the carbon substrate material in the zirconia-carbon-containing refractory, the carbon substrate material particles having a maximum length exceeding 45 μm are 60% by mass in the total carbon substrate material excluding the bonded carbon in the zirconia-carbon-containing refractory. A zirconia-carbon-containing refractory, characterized by being less than, has been proposed.

This Patent Document 2 aims to improve the corrosion resistance and improve the thermal shock resistance as well as the means for reducing the dissolution rate in many general molten slags and improving the thermal shock resistance except for the aforementioned Patent Document 1. “The ZrO ₂ component is mainly composed of aggregate particles having a particle size range of 1 mm or less and 0.045 mm or more, and the proportion of ZrO ₂ aggregate particles having a particle size of less than 45 μm is 10% of the total ZrO ₂ aggregate particles. It is preferable to be in the range of mass% to 35 mass%. " That is, this patent document 2 denies the use of a large amount of fine zirconia particles of 45 μm or less shown in the above-mentioned patent document 1, and is an intermediate that is coarse zirconia particles that are relatively difficult to dissolve in the molten mold powder. It is intended to improve the corrosion resistance by adopting a grain structure mainly composed of grains. In Patent Document 2, in addition to the above means, on the premise of a molding method by CIP, “60% by mass of carbon substrate material particles exceeding 45 μm in the total carbon substrate material excluding bonded carbon in the zirconia-carbon-containing refractory”. By making the following, a lubricating function such as zirconia aggregate can be obtained, and as a result, a great improvement effect can be obtained in improving corrosion resistance. Also, “in the graphite raw material having a maximum length of 45 μm or less, the thickness is 10 μm. It is indicated that it is preferable to use a powder containing 40% by mass or more of the following fine graphite powder ”. That is, it is intended to improve the corrosion resistance by densifying the matrix structure.

  However, with these means, as shown in Patent Document 2 itself, the thermal shock resistance is inferior. Therefore, this Patent Document 2 further shows that the thermal shock resistance is remarkably improved by including a carbon substrate material having a fibrous structure having a diameter of 50 nm or less in the bonded carbon in the refractory structure.

JP-A-11-302073 JP 2009-2221031 A

However, in the technique of Patent Document 1, in particular zirconia ZrO ₂ content is high ZrO ₂ content of more than about 85 wt% - increased porosity in the carbon-containing refractory of the refractory material, resulting in corrosion resistance In addition, since the graphite content is relatively decreased, cracks due to thermal shock are likely to occur at a high frequency, and there are still problems in achieving both corrosion resistance and thermal shock resistance. understood.

  For this reason, the application of the technology, which is mainly intended to improve the use of these fine zirconia particles (45 μm or less), depends on a highly controlled production method, and in continuous casting operations such as preheating conditions. It turned out that it is limited to the case where the optimum use conditions, environment, etc. for zirconia-carbon-containing refractories can be strictly controlled. In other words, it has been found that it is often difficult to put it to practical use in the production method of ordinary zirconia-carbon-containing refractories and immersion nozzles and general continuous casting operating conditions.

  In addition, the above-mentioned means in Patent Document 2 provides a certain effect in improving corrosion resistance and thermal shock resistance under general (general purpose) continuous casting operating conditions. However, it is not enough to meet the demands for improved durability and improved thermal shock resistance in the recent high-productivity and clean steel production by multiple continuous casting, and it is compatible with both higher corrosion resistance and thermal shock resistance. It turns out that it is necessary.

  In view of the above problems, the present invention relates to a zirconia-carbon-containing refractory, and has improved both corrosion resistance and thermal shock resistance as compared with the prior art, and has excellent durability, and a zirconia-carbon-containing refractory and its zirconia- It is an object of the present invention to provide a continuous casting immersion nozzle provided with a carbon-containing refractory, a method for producing a zirconia-carbon-containing refractory, and a method for producing a steel continuous casting immersion nozzle.

The gist of the present invention is summarized as follows. The zirconia-carbon-containing refractory according to (1) to (4) below, the immersion nozzle for continuous casting of steel according to (5) below, and the following (6) The manufacturing method of the zirconia-carbon-containing refractory described in 1. and the manufacturing method of the immersion nozzle for continuous casting of steel described in (7) below.
(1) Zirconia-carbon containing zirconia particles and carbon substrate material in the refractory structure, and containing ZrO ₂ as a chemical component in a range of 78% to 90% by mass and carbon in a range of 5% to 17% by mass In refractories,
When the total amount of zirconia particles in the refractory is 100% by mass, the particles having a diameter of 75 μm or less are 97% by mass or more, and the particles having a diameter of 45 μm or less are 40% by mass or more. Contains,
The carbon substrate material has a maximum length of 100 μm or less, an average length of 45 μm or less, and is contained in the refractory in a proportion of 2% by mass or more and 15% by mass or less.
Furthermore, the refractory is divided every 90 ° in the circumferential direction on the same horizontal cross section of the sample in a test method in which the sample is broken by applying uniform pressure from the inner hole of the sample formed in a ring shape. The variation value of the strain amount is within 20%, which is a percentage obtained by dividing the difference between the maximum value and the minimum value of the strain amount at the time of breaking at 4 points by the average value of the strain values at the 4 points. Zirconia-carbon-containing refractory characterized by
(2) The zirconia-carbon-containing refractory according to (1), wherein the ZrO ₂ is contained in an amount of 85% by mass to 90% by mass.
(3) The zirconia-carbon-containing refractory according to (1) or (2), wherein a pore volume ratio of 10 μm or more in a total open pore volume in the refractory structure is 30% or less.
(4) The zirconia-carbon-containing material according to any one of (1) to (3), wherein a fibrous carbon substrate material having a diameter of 50 nm or less is contained in the matrix structure of the refractory. Refractory.
(5) An immersion nozzle for continuous casting of steel, wherein the zirconia-carbon-containing refractory according to any one of (1) to (4) is disposed on a surface in contact with mold powder.
(6) Zirconia-carbon containing zirconia particles and a carbon substrate material in the refractory structure, and containing ZrO ₂ as a chemical component in an amount of 78 to 90% by mass and carbon in an amount of 5 to 17% by mass A method of manufacturing a refractory,
The carbon component is derived from a carbon substrate material and bonded carbon,
At the time of blending the refractory raw material, the carbon substrate material having a maximum length of 100 μm or less and an average length of 45 μm or less is blended so as to be contained in the refractory in a proportion of 2% by mass or more and 15% by mass or less. ,
In addition, when the total amount of zirconia particles to be blended is 100% by mass when blending the refractory raw material, 97% by mass or more of zirconia particles having a diameter of 75 μm or less and 40% by mass or more of zirconia particles having a diameter of 45 μm or less. Zirconia particles are blended so that the ratio of
Further, in the test method in which the refractory is uniformly pressurized from the inner hole of the refractory sample formed in a ring shape and the sample is broken, the refractory sample is cut every 90 ° in the circumferential direction on the same horizontal section of the refractory sample. The variation value of the strain amount, which is a percentage obtained by dividing the difference between the maximum value and the minimum value of the strain amount at the time of breaking at 4 points for each divided position by the average value of the strain amount at the 4 points, is within 20%. Thus, when kneading the blended raw material of the refractory, at least one of adjusting the number of revolutions of the stirring blade of the kneader and adding a solvent, the zirconia-carbon-containing refractory, Production method.
(7) A method for producing an immersion nozzle for continuous casting of steel, characterized in that the zirconia-carbon-containing refractory produced by the production method according to claim 6 is disposed on a surface in contact with mold powder. .

According to the present invention, a zirconia-carbon-containing refractory having both excellent corrosion resistance and thermal shock resistance in a zirconia-carbon-containing refractory having a ZrO ₂ content of 90% by mass or less, and an immersion nozzle for continuous casting are obtained. be able to.

Is a graph showing relationship (Experimental example 1300 ° C.) in the viscosity of the content and the mold powder in the molten mold powder of ZrO _2. A continuum of zirconia particles in which the particles are connected to form a very coarse particle (a so-called “chain” zirconia particle continuum) and a carbon substrate material (example of graphite) outside the continuum. It is a figure which shows the image of a refractory structure | tissue when there exists. It is a figure which shows the image of a refractory structure | tissue in case carbon substrate material (example of graphite) exists so that between zirconia particles may be interrupted | blocked of this invention. It is a photographic image which shows the structure | tissue structure of the zirconia-carbon containing refractory material of this invention manufactured by the 2nd manufacturing method. It is the photographic image which expanded the part of the carbon bond of FIG. It is the TEM photograph image which expanded the part of the carbon bond of FIG. It is a figure which shows an example of the test method which fractures | ruptures a sample by uniformly pressurizing from the inner hole of the sample which formed the refractory material of this invention in the ring shape, and is a figure which shows an example at the time of attaching a sectional view of a ring and a strain gauge It is. It is an image figure (longitudinal direction sectional view) which shows an example at the time of applying a refractory of the present invention to a nozzle for continuous casting in the state where it was immersed in a mold.

The features of the present invention will be described below together with embodiments.
First, the improvement of corrosion resistance will be described.

When partially or completely stabilized zirconia particles come into contact with the mold powder, they are quickly destabilized by the components in the mold powder (especially SiO ₂ , CaF ₂ , Al ₂ O _3, etc.). A so-called fine grain phenomenon occurs that decomposes into monoclinic fine particles. Since the solubility of ZrO _{2 in} the mold powder is low, the zirconia fine particles are hardly dissolved in the mold powder, but suspended in the mold powder in the form of ultrafine particles with a diameter of several μm, and the melt mold according to the volume ratio of the zirconia fine particles. It acts to increase the apparent viscosity of the powder. FIG. 1 illustrates experimental values of the ZrO ₂ content and viscosity in the mold powder.

  In the case of zirconia particles composed mainly of fine zirconia particles, the zirconia particles tend to be finely and rapidly pulverized within a short period of time in contact with the molten mold powder. There is an effect of promoting the production of a highly viscous mold powder in which a large number of zirconia fine particles are suspended in the molten mold powder in the vicinity of the interface, that is, a mold powder film.

  Since the inside of the mold powder film has a high viscosity, mass transfer at the interface between the refractory and the mold powder film is suppressed. Furthermore, the penetration of the mold powder into the refractory structure is suppressed, and the zirconia particles in the deep part of the refractory structure accompanying the penetration of the mold powder as seen in general refractory mainly composed of coarse zirconia particles. Fine graining is suppressed. As a result, the penetration depth of the mold powder inside the refractory is reduced, damage due to the peeling phenomenon of the refractory surface starting from the interface between the osmotic layer and the non-penetrated structure is reduced, and the refractory surface is dissolved uniformly. It becomes a form to lose. That is, the present inventors have found that a high-viscosity mold powder film acts as a protective layer for a zirconia-carbon-containing refractory and can suppress the damage rate of the refractory.

Then, as shown in FIG. 1, the present inventors can obtain the above-described effect when the ZrO ₂ content in the molten mold powder becomes a certain value (8% by mass in this experimental example) or more. Found for the first time.

  As for zirconia particles of a general prior art zirconia-carbon-containing refractory, for example, Patent Document 2 denies the configuration mainly composed of fine particles as described above, and shows that mainly coarse particles are composed. .

When such coarse particles are mainly used, the proportion of fine particles is small and the ZrO ₂ content in the molten mold powder does not exceed a certain value (8% by mass in this experimental example), and zirconia particles are suspended. A turbid high viscosity mold powder film is not formed. The coarse particles are destabilized and refined by the mold powder component that penetrates the outer periphery, and the refractory structure becomes brittle, or the zirconia coarse particles from the refractory structure due to external force due to mold vibration, etc. Is easy to drop off. Moreover, since the thickness falling off at a time is equal to or larger than the size of the coarse particles, the amount of erosion loss is increased. Furthermore, the mold powder is more likely to infiltrate into the space between the coarse zirconia particles due to the disappearance of the fine zirconia particles and the loss of the coarse particles.

When the mold powder is infiltrated in this way, the mold powder causes the zirconia particles to become finer even in the deep part of the refractory structure, so that the above-described particle dropping phenomenon is repeated. In addition, dropping off of coarse particles does not increase the ZrO ₂ content in the mold powder near the interface with the refractory to a certain level or higher, and as a result, does not form a highly viscous mold powder film layer. .

  Then, infiltration of the mold powder into the refractory is not suppressed, and the particles easily fall off from the surface layer of the refractory, and the damage form in the vicinity of the so-called mold powder permeation type interface proceeds continuously. As a result, the corrosion resistance of the refractory is greatly reduced. In this way, a phenomenon in which the wear rate is increased occurs in a particle size configuration mainly composed of large particles and combined with fine particles.

In the initial short time of contact with the mold powder, a high-viscosity mold powder film in which zirconia fine particles with a ZrO ₂ content in the mold powder of a certain value (8% by mass or more in this experimental example) are suspended is rapidly generated. In order to achieve this, the present inventors have found that there is an optimum particle size configuration / range.

That is, the present inventors, as a chemical component, in a zirconia-carbon-containing refractory containing 78% to 90% by mass of ZrO ₂ and 5% to 17% by mass of carbon as a raw material for the ZrO ₂ component. When the total amount of zirconia particles in the refractory is 100% by mass, the proportion of particles having a diameter of 75 μm or less is 97% by mass or more and the proportion of particles having a diameter of 45 μm or less is 40% by mass (100% by mass). Zirconia fine particles having a ZrO ₂ content in the mold powder of a certain value (8% by mass or more in this experimental example) are suspended at the interface between the zirconia-carbon-containing refractory and the mold powder. It was found that a high-viscosity molded powder film can be produced and the corrosion resistance can be improved.

  On the other hand, when the large zirconia particles exceeding 75 μm exceed 3% by mass of the whole zirconia particles, the penetration of the mold powder easily proceeds from the part where the coarse particles are peeled off, and the above-described penetration type damage is caused. It has been found that if the amount of the relatively large particles exceeding 45 μm is more than 60% by mass, it tends to be difficult to produce a highly viscous mold powder film at an early stage.

  In addition, one of the reasons for setting the standard value of the particle diameter in the present invention as the above value is to perform a test using raw materials obtained by sieving using standard sieves of various openings of JIS standards, This is because the above-mentioned value was obtained from the results of a comparative study on the presence or absence of the action effect, and the mesh sizes of the standard sieves that exist intermittently (150 μm, 125 μm, 106 μm, 100 μm, 90 μm, 75 μm, 63 μm, 53 μm, 45 μm, 38 μm, 32 μm, 25 μm, etc.).

  Therefore, when the total amount of zirconia particles in the refractory is 100% by mass, if the zirconia particles having a diameter of 75 μm or less are less than 97% by mass, the above-described penetration type damage is likely to proceed, and the diameter is Even if the zirconia particles having a diameter of 75 μm or less are 97% by mass or more, if the ratio of the zirconia particles having a diameter of 45 μm or less is less than 40% by mass, a high-viscosity mold powder film cannot be promptly produced, and fire resistance It becomes difficult to form a protective layer on the object surface.

  As a result, the erosion rate on the surface of the refractory becomes non-uniform, and the mold powder is locally infiltrated into the tissue from the surface erosion mode on the entire working surface with the appropriate particle size. It tends to be a molten mold powder infiltration type erosion mode with the thickness infiltrating or collapsing part on the refractory operating surface.

  The zirconia fine particles of less than 10 μm contribute to the early and stable formation of a highly viscous slag layer in the vicinity of the contact surface of the refractory with the mold powder. However, the fine particles of less than 10 μm tend to be sintered during the casting of steel in the refractory structure, and also have a strong particle size region that tends to aggregate and be unevenly distributed. When the content of the fine particles of less than 10 μm exceeds 20% by mass, the tendency to reduce the thermal shock resistance of the refractory becomes strong. Therefore, there is a possibility that the strength in the refractory and the uniformity of the structure may be impaired, and the content of zirconia fine particles of less than 10 μm may be limited to 20% by mass or less when the total amount of zirconia particles is 100% by mass. preferable.

  Configuring the particle size of the zirconia particles as described above also means that the movement speed is controlled so that the zirconia particles move stepwise into the mold powder in the formation of the mold powder film.

  The relative speed of movement into the mold powder increases as the diameter of the zirconia particles decreases, and decreases as the diameter increases. Ideally, particles with a diameter of more than 75 μm should not contain particles with a diameter of more than 75 μm because they are not only difficult to move into the mold powder, but often fall off and form defects in the refractory structure. It is. However, it is not realistic to classify strictly at 75 μm for the production of refractory. Actually, particles with a diameter exceeding 75 μm are mixed in a ratio of several percent or less, but 97 mass of zirconia particles with a diameter of 75 μm or less are mixed. If there is less than 3% by mass of zirconia particles having a diameter of 75% or more, that is, a diameter exceeding 75 μm, there is no problem. The present inventors have found that such a mixing ratio does not impair the effect for solving the problems of the present invention.

  The reason for this is that in the present invention, a highly viscous mold powder film is stably and continuously formed on the surface of the refractory by the particle size constitution of particles having a diameter of 75 μm or less, and a small amount of particles having a local diameter exceeding 75 μm. This is because the mold powder film covers and protects the defective portion even if a drop-off portion is generated. Further, since the highly viscous mold powder film is present on the surface of the refractory, dropping of particles having a diameter exceeding 75 μm itself is suppressed to some extent.

  Therefore, it is not necessary to strictly specify the upper limit of the size of particles having a diameter exceeding 75 μm, but in order to minimize the tissue defect portion, it should be as close to 75 μm as possible, for example, about 200 μm or less. Is preferred.

  Furthermore, in the present invention, partially stabilized or fully stabilized zirconia particles that are generally inferior in corrosion resistance to unstabilized zirconia can be used as the type of zirconia particles. This is because these zirconia particles in the refractory form a highly viscous protective layer, that is, a mold powder film, within a short time with the mold powder. Rather, it is preferable to use partially stabilized or fully stabilized zirconia particles because the molded powder film can be formed quickly and the thermal shock resistance as a refractory is also improved.

The upper limit of the content of the ZrO ₂ component is 90 mass%, the ZrO ₂ component is more than 90 wt%, relative proportions of carbon substrate material which may comprise becomes too small, among the advantages of the present invention This is because the effect of crack resistance is impaired.

Moreover, the reason why the ZrO ₂ component is 78% by mass or more is that, as the ZrO ₂ component content decreases, the carbon substrate material that is vulnerable to erosion increases in place of the ZrO ₂ component. This is because the corrosion resistance is greatly reduced.

The carbon content in the refractory is in a mutually complementary relationship with the zirconia content (the carbon content is basically the remaining amount of the zirconia particles). In the present invention, the carbon content is A range of 5 mass% or more and 17 mass% or less is a favorable range. Here, the content of the ZrO ₂ component is an amount that includes HfO ₂ that is not easily separated and excludes stabilizing materials such as CaO, MgO, and Y ₂ O ₃ . Moreover, a particle diameter says the magnitude | size which passes the sieve net | network provided with the opening corresponding to each particle diameter according to JISZ8801. “Structure” refers to the relationship between pores and particles of various shapes and sizes in a refractory product (JIS R2001). Further, in the present invention, the “diameter” represents the size of the particle, but is not necessarily limited to a geometrically spherical shape, and passes through a sieve mesh having an opening as described above. The size when the maximum size of the sieving net is regarded as a sphere or a circle for convenience.

  In addition, the content rate of each chemical component prescribed | regulated in this invention means the content rate of each chemical component in the refractory material before using for operation as a product fundamentally. In confirming whether the proportion of each chemical component of the refractory is within the appropriate range, at least a part of the refractory is sampled and heat-treated in a non-oxidizing atmosphere at 1000 ° C. Each chemical component analysis is preferably performed on the sample. The reason is that if the refractory has undergone a heat treatment of less than 1000 ° C. (eg, when baked at less than 1000 ° C. during production), the volatile components remain, and the presence form in the heat treatment conditions of less than 1000 ° C. This is because, for example, when there is a possibility that different components exist, an accurate chemical component composition may not be evaluated. When there is no such variation factor, it is not necessary to specify the heat treatment temperature or the like.

Further, the ZrO ₂ content is a value measured by a fluorescent X-ray method (JIS-R2216). ZrO ₂ in the present invention is a numerical value containing HfO ₂ . About carbon, it is the value measured by the method (JIS-R2011) which measures the density | concentration of the carbon monoxide and carbon dioxide which generate | occur | produce by carrying out high temperature combustion, flowing oxygen through a sample as an infrared absorption amount.

  Next, improvement in thermal shock resistance will be described.

  Corrosion resistance can be improved by making the zirconia particle size configuration and range as described above. However, in the case of such a zirconia-carbon-containing refractory mainly composed of fine zirconia particles such as that of the present invention and Patent Document 1, coarse zirconia particles are used in a system in which coarse graphite is mainly used as a carbon source. Compared to the general zirconia-carbon-containing refractory used, the thermal shock resistance tends to be greatly reduced.

When a large amount of fine zirconia particles (especially 45 μm or less) is used, the number of points where the zirconia particles directly contact each other (hereinafter also referred to as “direct contact”) increases, and when the number of direct contacts increases, the zirconia particles continuously The present inventors have found that the behavior is increased and the behavior of a single or continuous solid coarse particle is exhibited. (Such a continuous and integral structure is hereinafter referred to as a “chain”.)
FIG. 2 shows a continuum of such zirconia particles Z in which the particles are connected to form a very coarse particle (a continuum of so-called “chain-like” zirconia particles), and a carbon substrate material outside the continuum. It is a figure which shows the image of a refractory structure | tissue in case G (example of graphite) exists.

  The chain portion between the zirconia particles hardly causes internal strain or the like. As a result, a high thermal expansion coefficient or a high elastic modulus is exhibited as a refractory during preheating or operation, and the thermal shock resistance is lowered.

  That is, the chain part of fine zirconia particles that are in direct contact with each other in the structure has poor mutual solid lubricity and high homogeneity composed mainly of fine particles, so the stress relaxation ability between the particles is small and apparent. The volume ratio of zirconia particles having an extremely large diameter corresponding to the chain length is increased. The physical properties such as expansion characteristics and elastic modulus of the zirconia particles having an extremely large diameter corresponding to the chain length are almost shown as they are. Furthermore, the change in physical properties during casting is also remarkable, and the direct contact state of oxides, especially fine powders, in the refractory structure containing carbon in a reducing atmosphere is the temperature during casting. At the level, there is a significant change in physical properties (higher strength, higher elastic modulus, higher expansion coefficient, etc.) due to the sintering phenomenon, etc., leading to a decrease in thermal shock resistance. This makes stable operation of continuous casting difficult.

  Furthermore, since the zirconia particles are difficult to slip each other during molding by CIP, it becomes difficult to obtain a dense structure due to a decrease in the density of the molded body, or there is a lot of variation in the filling degree of the molded body structure. There is also. This leads to non-uniformity of the refractory structure, high porosity, generation of defects (fragile parts, etc.) in the structure, etc., which may reduce the corrosion resistance and further reduce the thermal shock resistance. ing. For these reasons, even if a large amount of fine zirconia is applied easily for high corrosion resistance, the corrosion resistance decreases and the risk of cracking also increases, so that high corrosion resistance and thermal shock resistance are improved or stable operation is improved. It becomes difficult to satisfy the requirements at the same time.

This phenomenon caused by the chain of the so-called zirconia particles, especially zirconia ZrO ₂ content is high ZrO ₂ content of more than about 85 wt% - becomes pronounced in carbon-containing refractories.

  This problem can be solved by including, in the zirconia particles having the above-described configuration, a carbon substrate material having a shape with a maximum length of 100 μm or less and an average length of 45 μm or less in an amount of 2% by mass to 15% by mass. The present inventors have found out.

  Sifting at the time of raw material blending, the carbon substrate material has a maximum length of 100 μm or less (sieving with a 100 μm sieve and collects the undersieving), and further has a fine shape with an average length of 45 μm or less (multistage The average particle size is adjusted by sieving with the refractory material, and the refractories to be manufactured can have the same maximum length and average length, and the number of carbon substrate materials themselves is increased. High dispersibility can be obtained. That is, high dispersibility can be obtained even between zirconia particles having a large number of particles because of the fine particle structure. In addition, when sieving with a sieve having a certain mesh (for example, x μm), the maximum particle size under the sieve is defined as the same as the size of the sieve (x μm).

  Stated from the viewpoint of the structure of this dispersed state, the maximum length is 100 μm or less in the zirconia secondary particles formed by agglomerating adjacent zirconia single particles or zirconia single particles in the refractory structure. In other words, a carbon substrate material having an average length of 45 μm or less is present. At that time, since carbon (bonded carbon) as a binder derived from an organic binder is also present in the refractory structure, the carbon matrix material forms a carbonaceous matrix structure together with the bonded carbon.

  Here, the carbon substrate material length means a size that passes through a sieving net having openings corresponding to each particle diameter according to JIS Z8801.

  In other words, the continuous arrangement of zirconia secondary particles (secondary particles and single particles) between adjacent zirconia particles in the refractory structure is blocked by direct contact between the zirconia particles, and the zirconia particles are coarsened by chaining and agglomeration. In other words, it is a structure in which a carbon matrix material composed of a carbon substrate material and bonded carbon is present in a form that inhibits or suppresses the above. Thereby, lubricity arises between zirconia particles, mutual sintering etc. are suppressed, and each zirconia particle comes to show the behavior as a discontinuous single particle. As a result, it is possible to suppress an increase in the coefficient of thermal expansion as a refractory, to suppress an increase in elastic modulus due to sintering of fine particles during operation, and to improve thermal shock resistance. As a result, it can contribute to stable operation.

  That is, a carbon substrate material having a maximum length of 100 μm or less and an average length of 45 μm or less is included in the zirconia particle group (secondary particle and single particle group) in an amount of 2% by mass to 15% by mass. Thus, the carbon substrate material between the zirconia particles (secondary particles and single particles) to the extent that the problem of the present invention can be solved by inhibiting or suppressing the coarsening of the zirconia particles due to chain formation and aggregation. A blocking state can be obtained (see FIG. 3, Z in the figure is secondary particles or single particles of zirconia, G is a carbon matrix material (bonded carbon is present in the surroundings but not shown)). In addition, even if there are some continuous parts (including several secondary particle groups) in part and zirconia particles that greatly exceed 75 μm are present, the periphery is blocked. Therefore, the continuity blocking effect necessary for solving the problem can be obtained.

  If the maximum length of the carbon matrix material exceeds 100 μm, and if the average length exceeds 45 μm, the dispersion of the carbon matrix material between the zirconia particles may be insufficient, or the lubricating effect between the zirconia particles may be increased. The risk is that the refractory structure is reduced and the refractory structure becomes non-uniform, resulting in a rough portion, that is, a defect. If the carbon substrate material content is less than 2% by mass, coarsening due to chaining or agglomeration of zirconia particles cannot be suppressed, and if it exceeds 15% by mass, the amount of binder is relatively reduced, so uniform kneading. Therefore, the carbon substrate material having a maximum length of 100 μm or less and an average length of 45 μm or less is contained in an amount of 2 to 15% by mass.

In addition, in the case of a zirconia-carbon-containing refractory having a high ZrO ₂ content, the volume ratio of the carbon matrix material is extremely small relative to the zirconia particles, and therefore the carbon matrix material needs to be highly dispersible, The substrate material preferably has an average thickness of 5 μm or less.

  The average thickness can be measured by adding graphite to the resin, and then allowing it to settle, curing the resin, forming a horizontally oriented precipitation layer at the bottom of the resin layer, cutting this in the vertical direction, and then polishing. The thickness of each graphite is actually measured with a microscope, and the average value is calculated. The measured number is preferably 50 points or more in order to reduce variation.

  By reducing the average thickness to 5 μm or less, the number of individuals can be greatly increased. In the refractory that assumes the above-mentioned zirconia particle size configuration, the carbon matrix material is dispersed between the zirconia particles, and the chain It is possible to inhibit or suppress the coarsening of the zirconia particles due to the formation and aggregation. Furthermore, the presence of a plurality of carbon substrate materials in a superimposed manner can further improve the lubricating effect between the zirconia particles, and can further improve the uniformity and denseness of the refractory structure.

  Specific examples of the carbon substrate material include particulate materials such as graphite powder such as scaly graphite and soil graphite, and amorphous or crystalline carbon black, and these may be used alone or in combination. Is possible. The carbon substrate material does not include carbon-bonded carbon as a binder-derived binder.

  These particulate carbon substrate materials coexist with bonded carbon, but the coexistence form does not necessarily have to be integrated with bonded carbon in the refractory structure, and there may be a separate and independent part.

  In the conventional general zirconia-carbon-containing refractory technology, graphite having a large particle size of about 100 μm to 1000 μm is used as a carbon substrate material for contributing to such thermal shock resistance. Necessary and small particle length graphite of 100 μm or less has been considered undesirable. In particular, the thermal shock resistance is lowered by making the zirconia particles mainly composed of fine particles, and it is considered that the thermal shock resistance is synergistically reduced by making the carbon substrate material graphite as small as the particle length. There were many.

  On the other hand, a carbon substrate material having a maximum length of 100 μm or less and an average length of 45 μm or less applied to the zirconia-carbon-containing refractory of the present invention is generally zirconia for the purpose of improving thermal shock resistance. It is a finer shape than the scaly graphite having a diameter used as a part of the carbon-containing refractory.

  However, the means for coexisting small carbon substrate particles with the small zirconia particles of the present invention overturns the technical idea that has been denied in the past, but at the same time improves not only corrosion resistance but also thermal shock resistance. Succeeded in getting.

  As described above, it is preferable that the carbon substrate material and the bonded carbon are uniformly present between all of the zirconia single particles or the zirconia secondary particles formed by agglomerating the zirconia single particles. Of course, due to problems in the production of earthen earth for refractory production and molding, the carbon matrix material does not exist uniformly between the particles, and some zirconia particles become coarse in some parts. There is. In other words, the degree of some defects appears as variations in the homogeneity of the tissue structure, which is indirectly specified by a method for evaluating the homogeneity of the tissue structure described later (method shown in Japanese Patent No. 3459029). be able to.

  Next, a method for evaluating the homogeneity of the tissue structure will be described.

  In order to improve the thermal shock resistance of the refractory, the present inventors have found that the homogeneity of the above-described structure is an important factor. If the refractory structure lacks homogeneity even by the above-mentioned means, in other words, if there are different parts of the refractory structure with a certain difference or more, a stress is applied to the relatively fragile part. Concentrates and breaks down easily from the site as a starting point.

  Therefore, it is a further constituent requirement that the refractory of the present invention has a certain homogeneity. This homogeneity refers to the structure of the zirconia particles and the carbon matrix material (especially graphite) that has no dispersibility and alignment, or the homogeneity of the carbon matrix material that blocks the continuity between the zirconia particles and the particles. In other words, the dispersibility can be said.

The present invention has found a method for quantitatively evaluating the homogeneity of the refractory of the present invention described above.
That is, a sample (cylindrical test piece) in which the refractory is formed in a ring shape is taken from the zirconia-carbon-containing refractory region arranged in the powder line of the immersion nozzle, and is uniformly pressurized from the inner hole side. It was found that the homogeneity of the structure of the zirconia-carbon-containing refractory of the present invention can be quantitatively shown by a test method (a method shown in Japanese Patent No. 3459029) for breaking a sample.

This test method will be described in detail.
The variation value representing the homogeneity of the refractory structure in the present invention is the circumferential direction 90 ° in the horizontal section generated on the outer surface side by the internal pressure from the inner hole side of the sample processed into a ring shape of the refractory. The amount of strain in the circumferential direction at four points of the pitch is measured, and is expressed by Equation 1.
B = (εmax−εmin) / εave × 100% (1)
Here, B: Dispersion value of strain amount εmax: Maximum value of each measured strain value εmin: Minimum value of each measured strain value εave: Average value of each measured strain value

  The strain amount in the present invention is measured by a strain gauge method (FIG. 7). The strain gauge 6 to be affixed to the outer peripheral portion of the cylindrical test piece 5 is a single-axis gauge and a gauge length of 30 mm. A total of four points are affixed at a 90 ° pitch on the outer periphery of the same horizontal section at the center of the sample height direction. When the pressure is uniformly applied in the direction 7, it is calculated by the above formula from the measurement results of the strain amount at four points when the cylindrical test piece 5 is broken.

  Note that the sample formed into a ring shape may be cut out from the refractory material into a ring shape by boring or the like. The cut ring shape is not particularly limited as long as it is a thick cylindrical shape (the ratio r / t of the average radius r between the inner radius and the outer radius to the wall thickness t is smaller than 10).

  In the zirconia-graphite-containing structure, zirconia particles are present in a dispersed form in a so-called carbonaceous matrix composed of graphite or the like and bonded carbon. In the structure after carbonization by heat treatment in a non-oxidizing atmosphere, the zirconia particles and the carbonaceous matrix do not have a strong bond due to differences in oxide and non-oxide, differences in thermal expansion coefficient, and the like. The present inventors confirmed that the macroscopic physical properties of the zirconia-graphite-containing refractory material greatly depend on the dispersion / existence state of the continuous carbonaceous matrix portion and zirconia particles in the structure, and the homogeneity of the structure was confirmed. By pursuing, it has been confirmed that there is a significant improvement effect in terms of thermal shock resistance during operation, and the present invention has been achieved.

  That is, in a structure where the dispersion state of the carbonaceous matrix is constant and the arrangement of zirconia and graphite is almost uniform, when the internal pressure is applied to the inner surface of the ring-shaped sample, the strain amount of the material generated on the outer surface is the same. If it is a cross section, every measurement point becomes a substantially constant value. On the other hand, in the case of a structure in which graphite, zirconia, bonding components, and the like are biased, variations in each strain amount are caused by measurement under the same conditions.

  When the segregation phenomenon of the blending occurs in the CIP molding mold during molding, for example, when the compound after mixing (yes earth) is filled into the CIP molding mold, the continuity of the carbonaceous matrix portion is locally Therefore, since the zirconia has a relatively large or continuous portion, the tissue state is unevenly distributed, or the local carbon state matrix is abundant. Arise. Thus, the dispersion state of the carbonaceous matrix can be indirectly grasped by the variation value of the strain amount measured at each point, and the quantitative evaluation of the structure becomes possible.

  For such a segregation phenomenon, when there is a sufficient carbonaceous matrix, for example, when the zirconia content is less than about 80%, the amount of carbonaceous matrix is relatively large, so the variation in strain amount is relatively high. It is not a small and big problem, and for this reason, operational stability is also high. On the other hand, when the amount of zirconia is about 80% or more, the carbonaceous matrix portion is about 17% by volume or less. Therefore, the uneven distribution phenomenon of the carbonaceous matrix is caused by local defects (grains or surfaces) of the zirconia particles. The risk of serious operational troubles such as breakage is increased. In particular, in the region of 85% or more, the influence is remarkable. For example, on the aggregated surface of zirconia, in addition to local changes in physical properties such as low strength, high elasticity, and high expansion due to the lack of the carbonaceous matrix portion. The oversintering phenomenon between oxides during operation is likely to occur, the corrosion resistance and thermal shock resistance of the refractory are likely to be lowered, and the operation stability is significantly impaired.

When the zirconia-carbon-containing refractory structure of the present invention was evaluated using the variation value of the strain amount at the time of sample breakage as an index, there is a strong correlation between the variation value and the thermal expansion amount, and the smaller the variation value is, It was discovered that the coefficient of thermal expansion at the product stage was small and the decrease in thermal shock resistance after heat load was small. In particular, when the ZrO ₂ content is 85% by mass or more, this tendency is remarkable, and when the variation value is 20% or less, the amount of thermal expansion at the product stage and the rate of increase in elastic modulus before and after the thermal load are small. The present inventors have confirmed that the thermal shock resistance is extremely excellent, that is, the corrosion resistance and the thermal shock resistance of the refractory containing a high ZrO ₂ content mainly composed of fine powder of the present invention can be compatible.

When the variation value of the strain amount exceeds 20%, it indicates that the structure is highly non-uniform, and when subjected to operation as a zirconia-carbon-containing refractory, there is a high possibility of causing "cracking". Become. In particular, in the zirconia-carbon-containing refractory mainly composed of fine powder having a ZrO ₂ content ratio of 85% by mass or more and a particle having a diameter of 75 μm or less of 97% by mass or more, the homogeneity of the structure has an influence on the thermal shock resistance. It was large and the knowledge that it was necessary to suppress the variation value within 20% was obtained.

  Next, the pore volume ratio will be described.

  In order to suppress the penetration phenomenon of the molten mold powder, to form a mold powder film as a protective layer on the surface of the high-refractory refractory, and to form a erosion that progresses uniformly on the refractory surface, further refractory The present inventors have found that the pore size of the object is an important factor. That is, by setting the pore volume ratio of 10 μm or more in the total open pore volume in the refractory structure to 30% or less, infiltration of the molten mold powder into the refractory structure can be reduced, and better corrosion resistance. It was confirmed by an experiment that

  In the general prior art, if the zirconia particles become finer, the internal resistance during molding increases and the open pore volume tends to increase, which leads to a decrease in corrosion resistance. Therefore, setting this range is particularly important.

  By blocking between adjacent zirconia particles having a diameter exceeding about 10 μm in the above-mentioned refractory structure with a carbon substrate material having a maximum length of 100 μm or less and an average length of 45 μm or less, such zirconia particles are separated. The lubricity is improved, and the effect of improving the densification in the molding stage by CIP and the uniformity of the refractory structure can be obtained. By this means and pressure adjustment at the time of CIP molding, it becomes easy to make the pore volume ratio of 10 μm or more in the total open pore volume in the refractory structure 30% or less. By these, it can contribute not only to the improvement of thermal shock resistance but also to further improvement of corrosion resistance.

Next, further improvement of thermal shock resistance will be described.
In the present invention, improvement has been promoted focusing on the quality of bonded carbon.

  Bound carbon exists between particles constituting a refractory, specifically, particles as a main component such as zirconia and carbon substrate material particles such as graphite, and these particles are bonded to each other and 3 in the refractory structure. It is thought that a dimensional carbonaceous network is being developed. Therefore, it is presumed that the bonded carbon as a continuous carbon matrix part in the refractory structure has a great influence on the macro physical properties of the refractory. For this reason, the thermal shock resistance described above can be further improved by changing the quality of the bonded carbon portion.

  In the present invention, the carbon fiber structure having a diameter of 50 nm or less is contained in the bonded carbon portion, thereby succeeding in reducing the elastic modulus.

  That is, in the present invention, it has been confirmed that it is practically effective that the carbon fibrous structure contains a fibrous carbon substrate material having a diameter of 50 nm or less. When the diameter exceeds 50 nm, effects such as lowering the elastic modulus associated with the soft tissue unique to the fibrous tissue are reduced.

  The fibrous carbon substrate material having a diameter of 50 nm or less increases the effect of making the carbonaceous matrix a flexible structure as the diameter is smaller. However, the smaller the diameter of the carbon substrate material, the easier it is to dissolve into the molten steel or it is oxidized. Therefore, the lower limit of the diameter is preferably set as appropriate.

  In addition, since this physical property improving effect is brought about by the presence of carbon having a fibrous structure, the shape of the carbon is fibrous, that is, a fibrous carbon substrate material having an aspect ratio (length / diameter) of approximately 10 or more ( Carbon fiber structure), and a soft structure having a nano-level space between the carbon fibers is preferable. Further, the carbon fiber is preferably graphitic.

  The carbon fibrous structure containing soft tissue inside becomes low elasticity compared to a continuous structure of amorphous carbon derived from a resin such as general phenol, and in terms of macroscopic physical properties as a refractory, Low elastic modulus can be achieved. Thereby, the thermal shock resistance can be further improved.

The ratio of the carbon substrate material of 100 μm or less converted into the refractory as a product can be evaluated as follows, for example.
1. The target refractory is oxidized and fired at about 350 ° C. to 550 ° C. for 5 to 120 hours, and the bonded carbon that is oxidized in the low temperature range is lost. Thereby, the refractory is powdered.
2. The refractory in powder form containing zirconia aggregate particles is classified with a sieve having an opening of 100 μm using the JIS Z8801 sieve, and is divided into a powder on the sieve and a powder on the sieve.
3. The amount of carbon in each powder is measured. From the measured carbon content on the sieve, it is confirmed that the maximum length of the carbon substrate material is 100 μm or less.
4). The amount of carbon under the sieve is divided by the amount obtained by subtracting the weight reduced in 1 from the total amount of the refractory before evaluation.

  Furthermore, classification is performed even with a sieve having an opening of 45 μm, and the amount of carbon in the passed powder (under the sieve) is measured (carbon amount A). The amount of carbon is the amount of carbon under the sieve having an opening of 100 μm ( From the proportion of the carbon content B), it is determined that the average particle size is 45 μm or less.

Furthermore, the particle size constitution of the zirconia particles in the refractory of the present invention can be evaluated as follows. Above 1. After this treatment, heat treatment is further performed at 800 to 1000 ° C. in an oxidizing atmosphere to remove carbon as CO or CO ₂ , and the remaining refractory powder is sieved with a 75 μm sieve. Sieving with 45 μm sieve. The weight of the remaining refractory powder, the weight of 75 μm under the sieve, and the weight of 45 μm under the sieve are weighed, and the weight of the remaining refractory powder with respect to the weight of 75 μm under the sieve and 45 μm. The mass% under the sieve is calculated, and the ratio of 75 μm or less and the ratio of 45 μm or less are evaluated.

  For evaluation of the point that a fibrous carbon substrate material having a diameter of 50 nm or less is contained in the matrix structure of the refractory, the fibrous carbon substrate material is confirmed by an SEM photograph, and the thickness of the fiber is determined. A method of measuring the thickness and confirming 50 nm or less can be used.

  Next, a method for producing a zirconia-carbon-containing refractory according to the first embodiment of the present invention (hereinafter simply referred to as “first production method”) will be described.

  The zirconia-carbon-containing refractory and the immersion nozzle of the present invention can be basically a method according to the usual method for producing a zirconia-carbon-containing refractory and an immersion nozzle.

  As a first step, a refractory raw material is mixed and kneaded to obtain a molding earth.

Any of CaO, MgO, Y ₂ O _{3 and the} like can be used as a stabilizing material for partially stabilized or fully stabilized zirconia particles as a raw material for the ZrO ₂ component. In particular, it is most preferable to use CaO-stabilized zirconia having a relatively large stabilizing effect with a small amount of addition, from the viewpoint of increasing the content of ZrO ₂ while increasing the thermal shock resistance.

  Further, the mixing ratio of the raw materials in the mixing and kneading may be determined by calculating back the known chemical components of the respective raw materials so as to obtain the chemical component composition of the refractory of the present invention.

  Moreover, what is necessary is just to mix | blend what a zirconia raw material classify | categorized into the predetermined particle size so that it may become a predetermined ratio regarding a particle size. That is, sieving at the time of blending the raw materials may be performed so that a predetermined particle size is included in a predetermined ratio. In addition, when sieving with a sieve having a certain mesh (for example, x μm), the maximum particle size under the sieve is defined as the same as the size of the sieve (x μm).

  The zirconia particles constituting the refractory according to the present invention contain 97% by mass or more of particles having a diameter of 75 μm or less, and 45 μm or less when the total amount of zirconia particles in the refractory is 100% by mass. In order to reduce the size of the particles having a ratio of 40% by mass or more but exceeding 75 μm as close to 75 μm as possible, for example, about 200 μm or less, for example, the zirconia raw material is sieved using a 75 μm sieve. However, it is preferable to use the one collected under the sieve, and most of them are 75 μm or less, and even if zirconia particles having a large aspect ratio are present, zirconia particles exceeding 200 μm are rarely mixed.

  As a raw material for a carbon substrate material having a maximum length of 100 μm or less and an average length of 45 μm or less, in addition to scaly graphite, one kind of earthy graphite, artificial graphite, carbon black or the like is used alone, or a plurality of kinds are combined. Can be used. When using one of these alone, scaly graphite rich in solid lubricity and stress relaxation ability of the fine powder raw material itself is most preferable.

  As the graphite, scaly graphite having a carbon purity of 90% by mass or more, earthy graphite, or the like can be used. In order to obtain a carbon substrate material having an average length of 45 μm or less, the graphite raw material can be pulverized if necessary and classified by a sieve mesh of about 300 mesh. Further, as described above, the graphite raw material having a maximum length of 100 μm or less and an average length of 45 μm or less is preferably subjected to processing such as pulverization at the raw material stage so that the average thickness becomes 5 μm or less.

  This graphite pulverization process is performed, for example, by pulverizing a graphite material having a length of 500 μm and a thickness of several tens of μm with an apparatus having a pressurizing function or a pulverizing function, and classifying the pulverized material to a predetermined size. Can be obtained. In order to obtain a shape having an average thickness of 5 μm or less, a maximum length of 100 μm or less, and an average length of 45 μm or less, time, pressure, speed, etc. may be adjusted according to the characteristics of the processing machine used.

  As the carbon black, general amorphous carbon black or graphitized carbon black having improved crystallinity can be used.

For the purpose of imparting oxidation resistance or improving the strength, metal powders of Al, Mg, Si, carbide powders such as SiC and B ₄ C, and nitride powders such as BN are separately provided (mass of each raw material, etc. In addition to the total ratio, if the total component of the zirconia-carbonaceous refractory as a product is 100% by mass, the total amount is in the range of about 2% by mass or less (depending on the fluctuation conditions of oxidation in individual operations) May be adjusted accordingly), and may be blended in an appropriate amount in the soil.

  An organic binder is added to the mixture of the raw material particles and kneaded to obtain a soil. The organic binder can be any one of a phenol resin, tar, or pitch, or a mixture in which these are arbitrarily combined. These organic binders form carbon bonds after firing. In order to adjust characteristics such as the wet state of the soil during molding, an organic liquid that does not form a carbon bond may be used in combination.

  For mixing and kneading, general mixers used for mixing and kneading refractories can be used. In particular, it is preferable to use a mixing or kneading apparatus having a high stirring speed, such as a so-called high-speed mixer, in order to increase the dispersibility of the carbon substrate material and keep the variation value of the strain amount within 20%.

  As a second step, the clay prepared in the first step is filled into a forming mold made of an elastic body and a metal core rod covering the outside, and formed by CIP.

  Note that the pressure and the like at the time of molding can be appropriately adjusted to optimum conditions according to the individual design conditions of the molded body such as the structure and size of the molded body, and the compactness and porosity.

  Further, the fine zirconia particles containing 97% by mass or more of particles having a diameter of 75 μm or less, the ratio of the particles having a diameter of 45 μm or less being 40% by mass or more, and a maximum length of 100 μm or less and an average length of 45 μm or less. In the kneading operation of the fine carbon substrate material, since all the aggregates are fine powders, agglomeration phenomenon between particles is likely to occur, and further, aggregation of the binder is likely to occur. Therefore, the kneading conditions are optimized in order to improve the dispersibility of the zirconia powder and the binder and to make the variation value of the strain amount 20% or less. Specifically, in order to increase the shearing force on the compound and prevent the phenomenon of aggregation between particles from occurring, the rotational speed of the stirring blade is increased, and a solvent is added to improve the resin coating property. By taking measures such as lowering the resin viscosity during the kneading process, etc., and performing sufficient kneading (e.g., increasing the time), it is possible to reduce the strain variation value to 20% or less. Become. For example, ethylene glycol can be used as the solvent. In optimizing the manufacturing conditions, the present invention has acquired an evaluation means called a variation value of the strain amount, and therefore, it is possible to determine a manufacturing method in which the variation value of the strain amount is actually 20% or less by feedback through the variation value evaluation. It becomes possible.

  When kneading the refractory compounding raw material, the adjusting method such as the rotation speed of the mixing blade and the stirring blade of the kneading machine depends on the conditions regarding the use conditions and effects specific to the arbitrarily selected mixing machine and kneading machine. Thus, the operation may be performed so as to obtain higher uniformity. In other words, what is necessary is just to follow the method of the general unit operation for each mixing machine and kneading machine.

  The addition of the solvent is related to the operation of each individual kneader, but in accordance with the change in properties according to the time of the soil (operation stage), uniform dispersion, and then the addition of a uniform shearing force, etc. What is necessary is just to determine suitably according to each manufacturing machine and manufacturing conditions in order to perform.

  As a third step, the molded body is fired in a non-oxidizing atmosphere.

  The maximum firing temperature in the firing step can be about 600 ° C. to about 1200 ° C. Before the firing at the maximum temperature, it is preferable to add a drying step at a temperature of about 150 ° C. to 250 ° C. in order to remove the solvent and moisture or to promote the development of the strength of the binder.

  As a fourth step, the sintered compact is subjected to a surface treatment as necessary, and an antioxidant is applied as necessary (according to individual operations).

A manufacturing method for reducing the pore volume ratio of 10 μm or more in the total open pore volume in the refractory structure to 30% or less will be described. As described above, the use of a carbon substrate material having a maximum length of 100 μm or less and an average length of 45 μm or less between adjacent zirconia particles having a diameter exceeding about 10 μm in the refractory structure, By adjusting the pressure or the like, the ratio of particles having a size of less than 10 μm in the ZrO ₂ particles is set to 20% by mass or less, whereby the pore volume ratio of 10 μm or more in the total open pore volume in the refractory structure is set to 30%. % Or less.

  Next, a manufacturing method in the case of containing a zirconia-carbon-containing refractory according to the second embodiment of the present invention, that is, a carbon substrate material having a fibrous structure having a diameter of 50 nm or less (hereinafter simply referred to as “second manufacturing method”). ).

  The basic production method is the same as the first production method. However, in the second production method, as a raw material having a fibrous structure having a diameter of 50 nm or less in the mixing or kneading step for obtaining the soil. Carbon substrate materials, or transition metals or transition metal salts can be blended into the refractory raw material or organic binder.

  Hereinafter, the case where the transition metal or the transition metal salt is contained will be described with respect to the difference from the first production method.

  The refractory material of the present invention containing a carbon matrix material having a fibrous structure with a diameter of 50 nm or less is obtained by blending a carbon matrix material having a fibrous structure with a diameter of 50 nm or less in the raw material itself, It can also be obtained by blending a fine transition metal or transition metal salt of 1000 nm or less in the refractory material and heat-treating it. The former method is not practical because the former carbon matrix material raw material having a fibrous structure with a diameter of 50 nm or less is extremely expensive. Therefore, it is preferable to produce the latter method, that is, a method of blending a transition metal or a transition metal salt as described in Patent Document 2 into a soil in the form of fine particles having a particle size of 1000 nm or less. The temperature and time of the heat treatment may be appropriately adjusted so that a fibrous structure having a diameter of 50 nm or less is obtained.

  A carbon structure having a fibrous structure having a diameter of 50 nm or less is generated and developed in a portion where a fine particle transition metal or transition metal salt having a particle diameter of 1000 nm or less is in contact with a carbon component. This contacting carbon component is not in the form of particles, and the carbon that forms the connective tissue is more reactive. Therefore, in order to blend the fine particles of transition metal or transition metal salt having a particle diameter of 1000 nm or less into the soil, it can be mixed and kneaded as a powder in another refractory raw material composition. In order to improve dispersibility, it is preferable to blend and disperse in advance in the organic binder as the previous raw material.

  That is, an organic binder made of any one of phenol resin, tar, pitch, etc., or a mixture of these, and a colloidal transition metal in which fine particles having a particle size of 1000 nm or less are dispersed in a solvent. It is preferable to add and knead a mixed solution with a transition metal salt solution (hereinafter simply referred to as “transition metal solution”) to an admixture of other refractory raw materials.

  As the transition metal, Ni, Co, Fe, Ti, Zr, Cr, or Pt can be used. In particular, Ni, Co, Fe, and Cr are preferably used from the viewpoint of high effect as a catalyst in the synthesis reaction of an extremely fine carbon fibrous structure such as CNT (carbon nanotube).

  The blending ratio of the transition metal solution is the total amount of the residual transition metal amount, i.e., the product in terms of solid content after carbonization of the powder part and organic binder before kneading of the zirconia particles, carbon substrate material, antioxidant, etc. When the refractory in a state after heat treatment in a non-oxidizing atmosphere at 100 ° C. is 100% by mass, the transition in the transition metal solution is such that the ratio of the residual transition metal amount is 0.5% by mass or less. It is preferable to adjust the concentration and addition amount of the metal amount. If it exceeds 0.5% by mass, there is a risk of reducing the oxidation resistance and strength of the refractory.

  The subsequent steps are the same as those in the first manufacturing method.

  The zirconia-carbon-containing refractory of the present invention manufactured by the second manufacturing method as described above has a structure as shown in FIGS. 4 and 5, the structure of the zirconia-carbon-containing refractory is formed by carbonization of zirconia coarse particles (coarse particles of zirconia aggregates) 1, carbon bonding portions including graphite particles (an organic binder including graphite particles). And a transition metal-containing nanoparticle 4 dispersed in the matrix structure 2 (the transition metal-containing nanoparticle 4 is a microscope shown in FIGS. 4 and 5). The field magnification is too small to visually confirm that it exists in the matrix structure 2).

  FIG. 6 shows a TEM photograph in which the carbon bond portion of FIGS. 4 and 5 is enlarged. In the carbon in the matrix structure 2, many ultrafine carbon fibrous structures 3 having a diameter of about 20 nm are observed around the transition metal-containing nanoparticles 4.

  An example in which the zirconia-carbon-containing refractory of the present invention is applied to a nozzle for continuous casting of molten steel is shown in FIG. The figure is an image (longitudinal sectional view) showing a state in which the continuous casting nozzle 10 is immersed in molten steel 14 in the mold. In the continuous casting nozzle 10, the zirconia-carbon-containing refractory 11 is at least, It is necessary to apply to the part which contacts the mold powder 12 which exists in the upper surface of the molten steel 14 in a mold. By doing so, the high-viscosity mold powder film 13 can be formed in the contact portion, and excellent durability can be obtained.

  Examples of the zirconia-carbon-containing refractory and continuous casting immersion nozzle according to the present invention obtained by experiments in a test room will be described below.

  The test conditions and evaluation methods of Examples A to D shown below are as follows.

  As carbon substrate materials, graphite A, B, C, D, F, G, H, and carbon black shown in Table 1 were prepared. In Table 1, numerical values that deviate from the scope of the present invention are underlined. The same applies to Tables 2 to 6 below.

  The sample was produced by a method according to the method described in the method for producing a refractory according to the present invention. That is, an organic binder is added to the mixture of raw material particles and kneaded to obtain a soil. The organic binder forms a carbon bond after firing and becomes a bonded carbon. For mixing and kneading, among general mixers used for mixing and kneading refractories, laboratory-scale very common dry-type mixers and kneaders (high-speed mixers) were used. This soil was formed into a sample shape by CIP. This molded body was fired at 1200 ° C. in a non-oxidizing atmosphere. Regarding the rotation speed of the mixing blades of the mixer and kneader, a sample is prepared using the blended raw material within the scope of the present invention, and feedback for optimizing the manufacturing method is performed by evaluating the variation value of the strain amount. The manufacturing method in which the value was 20% or less was determined.

  In Examples A to D, the tests of “Evaluation 1 to 3” described below are performed for each sample, and whether or not all the setting criteria for each result are satisfied is regarded as a comprehensive evaluation. It was set as the Example which can be used as a nozzle for casting and can solve the subject of this invention.

  In addition, about the zirconia raw material which restrict | limited the ratio of 10 micrometers or less in the Example to 20 mass% or less, the particle | grains with many ratios of 10 micrometers or less are obtained by classifying and processing a zirconia raw material microparticles | fine-particles beforehand with a test machine, and each example It mix | blended in the ratio shown in.

<Test conditions for evaluation 1>
Evaluation 1 is an evaluation of corrosion resistance. The corrosion resistance was evaluated by measuring a predetermined zirconia-carbonaceous refractory prism sample (20 mm) in a crucible (inner diameter: 150 mm) by floating a mold powder on the surface of low carbon steel melted at 1550 to 1570 ° C. in the atmosphere in the atmosphere. X20x160mm) was immersed for 120 minutes and pulled up, and the amount of erosion between materials was compared by measuring the erosion dimension at the (molten steel / mold powder) interface after cooling. As the mold powder, one having a CaO / SiO ₂ mass ratio of about 1.0 was used, and a new powder was exchanged every 30 minutes. The obtained amount of erosion mm was described in the table as the erosion index with the erosion amount of Example 1 being 100. The smaller the number, the smaller the amount of erosion and the better the corrosion resistance. As an evaluation, it was judged that a meltability index of 120 or less could be used from the absolute value of the amount of damage, and the following evaluation criteria were used.
○: Good (index with Example 1 as 100: ≦ 120)
×: Inferior = Not applicable (index with Example 1 as 100: 120 <˜ ≦ 150)
XX: Defect (Index with Example 1 as 100: 150 <)

<Test conditions for evaluation 2>
Evaluation 2 is an evaluation of thermal shock resistance.
Thermal shock was applied at the following two levels for a sample formed by CIP into an outer shape of 115 mm × inner diameter of 60 mm × height of 50 mm and processed in a non-oxidizing atmosphere at 1000 ° C.
After reduction firing at level 1.1000 ° C (product stage), water cooling after holding at 1200 ° C for 1 h Level 2.1500 ° C after heating for 10 hrs (assuming the end of casting), after holding at 1200 ° C for 1 h, water cooling level 1 and level 2 respectively The structure | tissue in the refractory working surface after cooling was observed, and the result was evaluated as (circle) and (x) as follows as thermal shock resistance.
◯: No cracking ×: The case where no cracking occurred at both crack generation level 1 and level 2 was defined as “acceptable thermal shock resistance”.
When heated for 10 hours at 1500 ° C. of level 2, the thermal condition inside the refractory sample is in a steady state, which approximates the condition during long-time operation.

In the following [Example E], the following Level 3 evaluation was also performed.
Level 3. Number of occurrences of cracking (endurance number) when the level 2 is repeated
○: No cracking for 2 cycles or more ×: Cracking occurred in less than 2 cycles

<Test conditions for evaluation 3>
Evaluation 3 is the evaluation of the homogeneity of the structure (the variation value of the 4-point strain amount).
This is the above-mentioned method according to Japanese Patent No. 3459029, which is an outer diameter of 140 mm × an inner diameter of 100 mm × a height of 70 mm, and a strain gauge (single gauge, gauge length at a 90 ° pitch in a horizontal section half of the sample height direction. 30 mm) is applied to the four circumferential positions of the zirconia-carbonaceous refractory sample by applying pressure uniformly from the inner wall surface side, and reading the values of the strain gauges applied to the four locations at the time of the sample break. The variation value was quantified. The sample was treated in a non-oxidizing atmosphere at 1000 ° C. The sample is not limited to the above shape, and the same measurement can be performed by cutting a ring shape of a thick cylinder by machining from an actual nozzle-like refractory.
○: Good (variation value of strain amount ≤ 20%)
X: Average range of general zirconia-carbonaceous refractories. (20% <Distortion variation value ≦ 30%)
Xx: Defect (component segregation is large) (30% <strain variation value)

[Example A]
Example A shows an example in which the influence of the zirconia particle diameter and particle size constitution is mainly investigated. Furthermore, the example in the case of containing a fibrous carbon structure of 50 nm or less is also shown.

Table 2 shows the configuration of each sample and the evaluation results. In the raw material addition amount display in Table 2, the total of CaO-stabilized ZrO ₂ and the carbon substrate material is displayed as 100% by mass, and crystalline carbon is displayed as an external addition amount with respect to 100%. The “carbon substrate material content in the refractory” is 100% by mass of the entire refractory, and the carbon substrate material content in the refractory is expressed by mass%. “Graphite type” in “Carbon substrate material” in Table 2 indicates which graphite in Table 1 was used, “Graphite addition amount” indicates the addition amount of the graphite species, and “Carbon black” indicates Table 1 The amount of carbon black added is shown. The same applies to Tables 3-6.

  In Example 1, Example 2, and Example 4, graphite G was used as the graphite seed, the average length of graphite / average thickness = 40/2 (maximum length of 100 μm or less), and zirconia particles of 75 μm or less. The above evaluations 1 to 3 were performed by changing the zirconia particle size ratio of 45 μm or less. By using the graphite, the structure became dense and the pore volume ratio of 10 μm or more became 30% or less, and all of evaluations 1 to 3 of corrosion resistance, thermal shock resistance, and structure homogeneity were good results.

  On the other hand, in the comparative example 1 which reduced the zirconia particle size ratio of 45 micrometers or less to 35 mass%, all of evaluation 1-3 of evaluation 1-3 failed.

  In addition, the thermal shock resistance (Evaluation 2) is good in Comparative Example 2 containing 10% by mass of zirconia particles exceeding 45 μm (in this example, 150 μm at the maximum) in the same manner as in Example 4 except for the zirconia particle size ratio of 45 μm or less. Although it was a pass level, although not significant, the corrosion resistance (Evaluation 1) and the homogeneity of the structure (Evaluation 3) were lowered.

  As described above, when the zirconia particles having a diameter of 75 μm or less are less than 97% by mass, there is a portion where the generation of the mold powder film as a high-viscosity protective film cannot be quickly obtained, and the thickness is uneven. Due to expansion, etc. due to the formation of a portion of the refractory that has infiltrated or collapsed in the refractory working surface, and the zirconia particles exceeding 75 μm locally form pores and voids in the refractory structure mainly composed of fine powder. This is thought to be due to the non-uniform physical properties and behavior of the tissue.

  In addition to these examples, the zirconia particle size ratio of 45 μm or less was the same as that of Example 4, and the molding pressure was increased (in this example, increased by 50%), and the pore diameter ratio of 10 μm or more was reduced ( In this example, 12%) According to Example 5, the influence of the pore diameter ratio of 10 μm or more was investigated. In Example 5, all of the evaluations 1 to 3 are good, and it can be seen that the corrosion resistance (evaluation 1) and the homogeneity of the structure (evaluation 3) are further improved.

  On the other hand, in Comparative Example 1 and Comparative Example 2 that were rejected as described above, both of the pore diameter ratios of 10 μm or more exceeded 30% of Example 4, which is the highest among the examples that passed.

  From the results of Example 5, Comparative Example 1 and Comparative Example 2, it can be seen that the pore diameter ratio of 10 μm or more is preferably 30% or less.

  From the above, it is considered that such a zirconia particle having a diameter exceeding 75 μm is an inevitable proportion in practical production (according to a general production method, it is considered to be about several percent in the refractory. It can be seen that mixing at a ratio of about% does not have a detrimental adverse effect to the extent that the problem of the present invention cannot be solved.

  Furthermore, in Example 3, which contains the zirconia particle size ratio of 45 μm or less and the other configurations as in Example 4 and contains a fibrous carbon structure of 50 nm or less, all of Evaluations 1 to 3 are good, and corrosion resistance (Evaluation 1 ) And the homogeneity of the tissue (Evaluation 3) are further improved. Since the results of thermal shock resistance (Evaluation 2) here are good in both Example 2 and Example 3, the difference regarding the existence effect of the fibrous carbon structure of 50 nm or less cannot be directly recognized. Since the homogeneity (Evaluation 3) is further improved, it can be indirectly observed that the thermal shock resistance is improved.

[Example B]
Example B is a case where the particle size constitution ratio of the zirconia particles of 45 μm or less of the present invention is provided, and further shows an example in which the influence of the ratio of particles having a size of less than 10 μm is investigated.

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

  The evaluation of Example 6 in which the proportion of particles having a size of less than 10 μm is 10% by mass and Example 7 in which 20% by mass is good are good. However, Example 8 in which the proportion of particles having a size of less than 10 μm is 25% by mass shows a tendency that the thermal shock resistance after heating at Level 2 of Evaluation 2, that is, 1500 ° C., is slightly inferior. From this, it can be seen that the proportion of particles having a size of less than 10 μm is preferably 20% by mass or less. Furthermore, by setting the ratio of the zirconia particles having a size of less than 10 μm to 20% by mass or less, the ratio of the pore volume of 10 μm or more to the total open pore volume in the refractory structure can be set to 30% or less. .

[Example C]
Example C shows an example in which graphite A, B, C, D, F, G, H, and carbon black are used as the carbon substrate material, and the influence of the particle size constitution of the carbon substrate material is investigated. That is, an example in which the influence of the maximum particle length, the average particle length, and the average thickness of the carbon substrate material is investigated is shown. Here, the investigation was conducted mainly on graphite processed into a predetermined shape.

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

  In Examples 9 to 13 in which graphite D, F, G, and H are used and the maximum particle length of graphite is 100 μm or less and the average particle length is 45 μm or less, all of evaluations 1 to 3 show excellent results. Yes.

  In Comparative Example 6 and Comparative Example 7 in which graphite A was used and the average particle length of graphite was 300 μm (the maximum particle length exceeded 100 μm), all of Evaluations 1 to 3 were inferior. In particular, in Comparative Example 7 in which the proportion of zirconia particles having a diameter of 75 μm or less is 80% by mass of less than 97% by mass, the corrosion resistance is significantly reduced.

  Using Graphite C, the average particle length of graphite is 50 μm (the maximum particle length is also greater than 100 μm), Comparative Example 4 is used, and graphite B is used, and the average particle length of graphite is 80 μm (the maximum particle length is also greater than 100 μm). In Comparative Example 5, all of Evaluations 1 to 3 are better than Comparative Examples 6 and 7, but are inferior results. It can be seen that the worse the average particle length exceeds 45 μm, the worse the degree of any of the evaluations 1 to 3.

  In particular, in Comparative Example 7 in which the zirconia particles having a diameter of 75 μm or less in this system are less than 97% by mass, the reason why any of the evaluations 1 to 3 is significantly reduced is basically the same as described in Comparative Example 5 above. Furthermore, the drop of large zirconia particles (in this example, 150 μm) exceeding 75 μm and the drop of large carbon matrix material are likely to cause local deep damage in the refractory structure. It is conceivable that the thermal expansion destroyed the structure around the particles, and that the carbon matrix material was not uniformly present between the zirconia particles, making it difficult to sufficiently block the continuity between the zirconia particles.

[Example D]
Example D shows an example in which the influence of the content ratio of the ZrO ₂ component and the content ratio of the carbon component was investigated. All chemical components are values after heat treatment in a non-oxidizing atmosphere at 1000 ° C. Here, the zirconia particles and the graphite particles were replaced, and the ZrO ₂ component content ratio and the carbon component content ratio were changed for investigation.

  In all the examples and comparative examples, the zirconia particles have a ratio of 75 μm or less at 100 mass% and a ratio of 45 μm or less at 60 mass%, and the graphite has a maximum particle length of 100 μm or less and an average particle length of 45 μm or less. Graphite F having an average particle thickness of 5 μm or less was applied.

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

Each of Examples 14 to 18 in which ZrO ₂ was changed from 78 mass% to 90 mass%, carbon was changed from 5 mass% to 17 mass%, and the graphite amount was changed from 2 mass% to 15 mass% was evaluated as 1 All of -3 show excellent results. On the other hand, in Comparative Example 8 containing 91% by mass of ZrO ₂ and 4% by mass of carbon, all of the evaluations 1 to 3 show inferior results. From these facts, it is understood that the lower limit is 5% by mass of the carbon component amount and 2% by mass of the graphite amount.

[Example E]
Example E is an example in which the variation value of the strain amount exceeds 20% in the <Evaluation 3> test in which the refractory is uniformly pressed from the inner hole of the sample formed in a ring shape to break the sample. In this example, the mixture of the same raw material composition as Example 2 shown in Example A is manufactured under conditions that deliberately deviate from the optimum condition range grasped for each mixer and kneader. did. In this example, a very common dry mixer and kneader (high-speed mixer) equipment on a laboratory scale was used.

  In this experiment, by shortening the predetermined kneading time (30 minutes), the dispersibility of the resin was lowered and the variation value was increased. The results are shown in Comparative Example 9 and Comparative Example 10 in Table 6.

  In Table 6, Example 19 is a case where the kneading time was shortened by 10%, but the dispersion value increased to 20% compared to Example 2, and the number of times of endurance at the level 3 of thermal shock resistance evaluation was from 5 cycles. Reduced to 2 cycles. However, it is practical and can be used.

  On the other hand, the case where the kneading time for a predetermined time was further reduced by 30% is shown in Comparative Example 9, but the pore volume of 10 μm or more, Evaluation 1, and Evaluation 2 were the same as Example 2. However, the variation value of Evaluation 3 was 23%, exceeding 20%. Furthermore, the number of times of endurance of the level 1, level 2 and level 3 in the thermal shock resistance evaluation was significantly reduced.

  Furthermore, in the case of Comparative Example 10 in which the kneading time was shortened by 50%, the variation value was greatly increased to 32%, and accordingly, the thermal shock resistance was significantly reduced.

  As described above, by suppressing the variation value to 20% or less, the binder and particles have a uniformly dispersed structure, so that a fragile portion that becomes a starting point of destruction is less likely to exist in the refractory structure. This leads to stability and quality improvement.

  The refractory of the present invention can be used for an immersion nozzle used for pouring molten steel from a tundish to a mold. Since the refractory of the present invention is particularly excellent in corrosion resistance and thermal shock resistance, even if it is used under conditions where the preheating temperature is slightly low (for example, a low temperature of about 600 ° C.), it is less damaged. Excellent durability can be obtained.

Z zirconia particles (image)
G Carbon substrate material (image)
1 Coarse zirconia particle 2 Carbon bond including graphite particle (matrix structure)
3 Ultrafine carbon fibrous structure having a diameter of about 20 nm 4 Transition metal-containing nanoparticles 5 Cylindrical specimen 6 Strain gauge 7 Pressure direction 10 Dipping nozzle for continuous casting 11 Zirconia-carbon-containing refractory 12 Mold powder 13 High viscosity Mold powder film 14 Molten steel in mold

Claims (7)

In a zirconia-carbon-containing refractory material having zirconia particles and a carbon substrate material in a refractory structure, and containing ZrO ₂ as a chemical component of 78% by mass to 90% by mass and carbon of 5% by mass to 17% by mass. ,
When the total amount of zirconia particles in the refractory is 100% by mass, the particles having a diameter of 75 μm or less are 97% by mass or more, and the particles having a diameter of 45 μm or less are 40% by mass or more. Contains,
The carbon substrate material has a maximum length of 100 μm or less, an average length of 45 μm or less, and is contained in the refractory in a proportion of 2% by mass or more and 15% by mass or less.
Further, the refractory is divided every 90 ° in the circumferential direction on the same horizontal cross section of the sample in a test method in which the refractory is uniformly pressed from the inner hole of the sample formed in a ring shape to break the sample. The variation value of the strain amount is within 20%, which is a percentage obtained by dividing the difference between the maximum value and the minimum value of the strain amount at the time of breaking at 4 points by the average value of the strain values at the 4 points. Zirconia-carbon-containing refractory characterized by _2. The zirconia-carbon-containing refractory according to claim 1, wherein the zirconia-carbon-containing refractory according to claim 1 contains the ZrO ₂ in an amount of 85 mass% to 90 mass%.   The zirconia-carbon-containing refractory according to claim 1 or 2, wherein a pore volume ratio of 10 µm or more in a total open pore volume in the refractory structure is 30% or less.   The zirconia-carbon-containing refractory according to any one of claims 1 to 3, wherein the matrix structure of the refractory contains a fibrous carbon substrate material having a diameter of 50 nm or less.   An immersion nozzle for continuous casting of steel, wherein the zirconia-carbon-containing refractory according to any one of claims 1 to 4 is disposed on a surface in contact with mold powder. A zirconia-carbon-containing refractory material having zirconia particles and a carbon substrate material in a refractory structure, and containing ZrO ₂ as a chemical component of 78% by mass to 90% by mass and carbon of 5% by mass to 17% by mass. A manufacturing method comprising:
The carbon component is derived from a carbon substrate material and bonded carbon,
At the time of blending the refractory raw material, the carbon substrate material having a maximum length of 100 μm or less and an average length of 45 μm or less is blended so as to be contained in the refractory in a proportion of 2% by mass or more and 15% by mass or less. ,
In addition, when the total amount of zirconia particles to be blended is 100% by mass when blending the refractory raw material, 97% by mass or more of zirconia particles having a diameter of 75 μm or less and 40% by mass or more of zirconia particles having a diameter of 45 μm or less. Zirconia particles are blended so that the ratio of
Further, in the test method in which the refractory is uniformly pressurized from the inner hole of the refractory sample formed in a ring shape and the sample is broken, the refractory sample is cut every 90 ° in the circumferential direction on the same horizontal section of the refractory sample. The variation value of the strain amount, which is a percentage obtained by dividing the difference between the maximum value and the minimum value of the strain amount at the time of breaking at 4 points for each divided position by the average value of the strain amount at the 4 points, is within 20%. Thus, when kneading the blended raw material of the refractory, at least one of adjusting the number of revolutions of the stirring blade of the kneader and adding a solvent, the zirconia-carbon-containing refractory, Production method.   A method for producing an immersion nozzle for continuous casting of steel, wherein the zirconia-carbon-containing refractory produced by the production method according to claim 6 is disposed on a surface in contact with mold powder.