JP2011200911A - Zirconia-carbon-containing refractory and immersion nozzle disposed with the refractory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material combining corrosion resistance and high spalling properties of a zirconia-carbon-containing refractory in a high zirconia region in which the content of ZrOexceeds about 80 mass%, and to provide a nozzle for continuous casting capable withstanding a long time operation in continuous casting by using the material.SOLUTION: The zirconia-carbon-containing refractory wherein a bond by carbon is formed between aggregate particles and the content of zirconia exceeds 80 mass%, contains zirconia and carbon, wherein the ratio of the number of particles having cracks inside the particles to the whole the number of zirconia particles composing the refractory, which can not pass through sieve mesh with a nominal opening of 150 μm of a JIS standard sieve is <25% by a method by observation for the polished cross sections of the particles, the apparent porosity after reduction firing at 1,000°C of the refractory is 12 to 20%, and the ratio of pore size of ≥10 μm in the open pores after the reduction firing at 1,000°C of the refractory is ≤30%.

Description

  The present invention relates to a submerged nozzle used for continuous casting of steel, a zirconia-containing refractory disposed in other nozzles, and a continuous casting nozzle such as a submerged nozzle provided with the refractory and a long nozzle.

  Immersion nozzles used in continuous casting of steel are used to transfer molten steel from the tundish to the mold.

  The immersion nozzle prevents the molten steel from oxidizing by preventing contact between the molten steel and the atmosphere, and at the same time injects the molten steel into the mold in a rectified state. This prevents slag floating on the upper surface of the molten steel and non-metallic inclusions present in the molten steel from being mixed into the molten steel, improving the quality of the steel and ensuring operational stability. .

Generally, a molten glass layer called a mold powder layer exists on the upper surface of the molten steel inside the mold. This molten glass layer contains CaO, SiO ₂ , Na ₂ O, K ₂ O, Al ₂ O ₃ , CaF ₂ , C, and the like.

Such a component of the molten glass layer has a strong erosion property with respect to Al ₂ O ₃ , SiO ₂ , C and the like which are constituent materials of the immersion nozzle. Due to this corrosion resistance, the immersion nozzle causes problems during long-time operation.

Therefore, a zirconia-containing material having high corrosion resistance with respect to molten glass is often applied to a portion of the immersion nozzle that comes into contact with the mold powder (hereinafter, the portion is simply referred to as “powder part”). Moreover, since it is necessary to ensure thermal shock resistance, zirconia-carbon (ZrO ₂ —C) refractory is generally used as a material for the powder part.

  In particular, the improvement of the corrosion resistance of the powder part has a direct effect on the life of the nozzle, so various improvements have been made.

In general, it is known that the corrosion resistance is improved by increasing the ZrO ₂ content in the material. Conventionally, as a material for the powder part, the corrosion resistance is mainly increased by increasing the ZrO ₂ content. We are trying to improve.

  On the other hand, increasing the zirconia content causes an increase in the coefficient of thermal expansion and elastic modulus of the zirconia-carbon-containing refractory, which causes cracks during use and hinders operation. In order to improve the thermal shock resistance, the graphite content should be increased. However, as described above, an increase in the amount of graphite leads to a decrease in corrosion resistance, so the balance between the zirconia content and the graphite content is important.

  In particular, alumina-graphite refractories and alumina-silica-graphite refractories were used for the main body, and zirconia-carbon containing refractories were used for the powder part. For the immersion nozzle, thermal structural stability during steel receiving is important.

From this point of view, ZrO ₂ in zirconia-carbon-containing refractories is partially stabilized aggregate containing 3 to 10% by mass of CaO, MgO, Y ₂ O ₃ etc., which exhibits relatively linear thermal expansion characteristics, and is completely stabilized. It is common to apply aggregate materials. In such a case, since a certain amount of bonded carbon for bonding the aggregates is indispensable, the content of the ZrO ₂ component in the zirconia-carbon-containing refractory used for the powder part is about 86% by mass. It becomes the upper limit.

However, under operating conditions where particularly high thermal shock resistance is required, the content of the ZrO ₂ component as a powder part refractory is 80% by mass or less.

Various attempts have been made to improve both the corrosion resistance and the spalling resistance of the refractories for ZrO ₂ —C used in the powder part having such characteristics and limitations.

  For example, Patent Document 1 discloses a zirconia-graphite material excellent in corrosion resistance, comprising 70 to 95% by mass of a zirconia raw material and 5 to 30% by mass of graphite, and having a zirconia particle size constitution of 45 μm or less and 70% or more of zirconia particles. Refractories are disclosed. This is mainly because zirconia is made into a fine powder having a particle size composition of 45 μm or less, and zirconia is destabilized to be finely divided and dispersed in the slag. The dispersed destabilized zirconia increases the apparent viscosity of the slag. Therefore, it is intended to suppress the infiltration of slag into the refractory, to suppress the refractory melting, and to improve the durability. However, even if the zirconia grains are pulverized as in Patent Document 1, the structure as the refractory structure may be weakened, and the corrosion resistance may be lowered instead. Thus, it cannot be said that the zirconia-graphite refractory and the zirconia-graphite material described in Patent Document 1 sufficiently satisfy both the thermal shock resistance and the corrosion resistance.

Patent Document 2 discloses that a CaO-stabilized zirconia raw material having a silica content of 0.30% by mass or less is 50 to 90% by mass, a badelite raw material 0 to 30% by mass (however, a CaO-stabilized zirconia raw material and a badelite raw material Dip for continuous casting in which a zirconia-graphite material containing a total amount of 60 to 91% by mass) and 10 to 35% by mass of a graphite raw material is disposed in a portion of the continuous casting immersion nozzle in contact with the molten mold powder. A nozzle is disclosed. This is mainly to reduce the silica content in the CaO-stabilized zirconia particles, thereby suppressing the decomposition reaction of the zirconia particles in the zirconia-graphite material placed in the powder part of the immersion nozzle by the mold powder. is there. However, improvement by only the silica content in the zirconia particles as in Patent Document 2 can be expected to some extent to suppress the dissolution of zirconia particles into the mold powder due to the initial reaction on the surface of the zirconia particles. There is no change in the part where the zirconia grains are exposed to the mold powder that contains a large amount of silica and is in a molten state, and especially contains zirconia that requires high corrosion resistance in the region where the ZrO ₂ content exceeds about 80% by mass. The amount of zirconia-graphitic refractory cannot sufficiently improve corrosion resistance.

Further, Patent Document 3 discloses a zirconia-carbon refractory using electrofused zirconia as a zirconia raw material, and the number of particles in the particle diameter range of 40 μm to 300 μm is 20 in terms of the number of particles. Zirconia-carbon refractories are disclosed that are healthy particles with no cracks and containing no low melt. This indicates that with respect to ZG having a ZrO ₂ content of less than 80% by mass, an increase in the proportion of the fused ZrO ₂ raw material having cracks inside causes a decrease in the corrosion resistance of ZG. However, although Patent Document 3 discloses itself that the corrosion resistance of ZG is lowered, a means for avoiding this is not disclosed. Furthermore, depending on Patent Document 3, it is extremely difficult to use a fused ZrO ₂ raw material having cracks inside against ZG having a ZrO ₂ content of more than 80% by mass in recent years.

Thus, there has not yet been found a sufficiently effective improvement measure for corrosion resistance and thermal shock resistance against ZG having a high ZrO ₂ content of more than 80% by mass, especially in recent years.

JP-A-11-302073 JP-A-8-1293 JP-A-9-142927

The present invention provides a material having both corrosion resistance and high spalling property of zirconia-carbon-containing refractories in a high zirconia region in which the ZrO ₂ content exceeds about 80% by mass, and continuous casting is achieved by using the material. A continuous casting nozzle that can withstand long-term operation.

In the present invention, the corrosion resistance and wear resistance of the zirconia-carbon-containing refractory in the high zirconia region where the ZrO ₂ content exceeds about 80% by mass are other than the purity and mineral composition of the zirconia raw material used in the refractory. In addition, this is based on a novel finding by the present inventor that the form of the zirconia raw material particles has a great influence.

In other words, the influence of the form of the zirconia raw material particles, which greatly affects the corrosion resistance and wear resistance of the refractory containing ZrO ₂ , was designed to maintain a delicate balance between corrosion resistance and thermal shock resistance. The zirconia-carbon-containing refractories containing so-called high ZrO _{2 in} which the content ratio of ZrO ₂ exceeds 80% by mass appears to be large, and among the ZrO ₂ particles, a coarse grain region, that is, a nominal opening of a JIS standard sieve 150 μm It has been found that the influence of the particles that cannot pass through the sieving screen is larger than the influence of the particles passing through the fine particle region, that is, the 150 μm sieving screen.

  In the present invention, the form of particles as a raw material refers to the presence or absence of cracks in the particles, and the crack refers to a space where the zirconia particles are divided within the structure. And the crack of this raw material particle arises during the raw material manufacture.

Moreover, the zirconia particles to be the subject of the present invention are mainly composed of ZrO ₂ , and this zirconia may be any of stabilized, partially stabilized, and unstabilized particles. The stabilizing material may be any component.

Furthermore, the indication relating to the amount of ZrO _{2 in} the present invention refers to the amount that excludes stabilizers such as CaO, MgO, Y ₂ O _{3 and the} like, which contain HfO ₂ that is usually difficult to separate.

  Furthermore, “carbon bond” refers to a structure in which an organic binder is carbonized in a non-oxidizing atmosphere so that particles or the like constituting the refractory are adhered or fixed to each other.

  Hereinafter, the present invention will be described with specific examples of the erosion phenomenon caused by molten mold powder of zirconia-graphitic refractory.

First, the reason why the size of the ZrO ₂ particles differs in the influence of the corrosion resistance of the refractory on the boundary of 150 μm is considered as follows.

A refractory layer with a high ZrO ₂ concentration is formed on the working surface of the refractory in contact with the mold powder or slag film (hereinafter referred to as “slag film”) due to the destabilization phenomenon accompanied by the pulverization of zirconia particles. The corrosion resistance is improved by its protective film function. And if the particle | grains of 150 micrometers or more have a crack, molten slag will permeate | transmit the crack in particle | grains, will promote destabilization in a crack part and will collapse particle | grains. Originally, the zirconia component that stays in the vicinity of the working surface by fine graining and contributes to the formation of the protective film and improves the corrosion resistance is dropped into the slag film, so the zirconia concentration at the working interface cannot be increased and the protective film function is lowered.

In addition, when using zirconia particles with cracks in zirconia-carbon refractories, the corrosion resistance and thermal shock resistance decrease.
1. Zirconia particles collapse during use in refractory operation, and easily fall off from the refractory structure, and the detachment part becomes a defect in the refractory structure;
2. An erodible material such as mold powder penetrates into the defective part of the refractory structure, and the defect part of the tissue expands from the penetrated part.
3. The drop-off part becomes a structural defect of the refractory structure, reducing the thermal shock resistance resistance,
4). In addition, erodible substances such as mold powder penetrate into the cracks in the zirconia particles, and promote erosion to disappearance of the zirconia particles themselves.
5. The size of the defect part in the refractory structure due to such dropping or particle disappearance is such that the part present as coarse grains is larger than the part present as fine grains, that is, the defect part is coarse grain. This is thought to be due to a mechanism such as the remarkable size of zirconia and the greater impact on the refractory structure.

  That is, the present invention relates to a zirconia-carbon-containing refractory having a zirconia content exceeding 80 mass% in which a carbon bond is formed between aggregate particles. The zirconia particles that cannot pass through the sieving net of the grain region, that is, the JIS standard sieve having a nominal mesh size of 150 μm are used. When the total number of zirconia particles that cannot pass through a 150 μm sieve screen is 100, the ratio of the number of particles having cracks inside the particles is less than 25%.

  Corrosion resistance and thermal shock resistance gradually decrease as the ratio of the number of particles having cracks inside gradually increases. However, when the ratio is 25% or more, such decrease becomes remarkable. The number ratio of particles with internal cracks varies for each commercial product that is generally available as a zirconia raw material.

  In order to know the ratio of the number of particles having cracks inside, the object refractory is observed with a microscope, the number of particles exceeding 150 μm existing in the visual field area is counted, and the number of particles having cracks is visually counted. Thus, a method for obtaining the ratio of the numbers, that is, a method by observing the polished cross section of the sample can be adopted.

In order to improve the corrosion resistance and thermal shock resistance of the zirconia-carbon-containing refractory in the high zirconia region in which the ZrO ₂ content exceeds about 80% by mass, the present invention, The apparent porosity is 12% or more and 20% or less, and the ratio of the pore diameter of 10 μm or more in the open pores after the 1000 ° C. reduction firing of the refractory is 30% or less.

  This apparent porosity can be measured by the method shown in JIS R 2205. The pores measured as the apparent porosity are the same pores as “open pores” described later, and are pores opened to the outside excluding closed pores (sealed pores) in the tissue. The pores opened to the outside also serve as a direct entry path to a refractory structure such as mold powder.

  If the apparent porosity after reduction firing at 1000 ° C. is less than 12%, the corrosion resistance can be improved, but the thermal shock resistance is lowered, and the possibility that the nozzle breaks in the early stage of casting increases. If the apparent porosity after reduction firing at 1000 ° C. exceeds 20%, the structure becomes too coarse and the fracture resistance becomes small, so that the thermal shock resistance is significantly reduced, and further, the thermal shock resistance is also lowered.

  Note that the carbon after the non-oxidizing atmosphere firing at 1000 ° C. is specified here even if the carbon existing after the non-oxidizing atmosphere firing at 1000 ° C. is exposed to higher temperatures in subsequent operations such as continuous casting. By being in a state to get. That is, even if a carbon component is present after firing in a non-oxidizing atmosphere in a temperature range of less than 1000 ° C., the presence or amount of the carbon component may be unreacted with resin or tar or pitch as a carbon source. Is unstable. Since carbon is in a stable form after firing at 1000 ° C. in a non-oxidizing atmosphere, it can be said that it almost represents an initial state for operation at a temperature of 1000 ° C. or higher.

  Furthermore, when this refractory is applied to an operation in which molten powder exists on the surface of the molten steel in the mold of continuous casting, the pore diameter of the opening pore is 10 μm or more, and the molten powder can easily enter, and 10 μm or more. There is a correlation between the number ratio of pores and the corrosion resistance, and the smaller the volume ratio of pores with a pore diameter of 10 μm or more in the total open pores, the more the corrosion resistance is improved. The present inventors have found that the improvement is remarkable in the following cases.

  This is because the molten powder penetrates into pores of 10 μm or more that exist even partially, resulting in the partial loss or collapse of the refractory structure including the carbon substrate near the pores. This is probably because the more refractory structures produced, the greater the damage to the refractory structures, and the easier it is to connect them to promote damage to a wide range of refractory structures.

  It should be noted that the volume ratio of pores having a pore diameter of 10 μm or more is 0%, in other words, the pore diameter of all open pores is most preferably less than 10 μm, and it is less likely to adversely affect the physical properties. It is not necessary to provide the lower limit value of the volume ratio of the pores.

  Further, in the present invention, the amount of crystalline free carbon substrate material having a maximum length of 45 μm or less is refractory to all crystalline free carbon substrate materials present in the zirconia-carbon-containing refractory structure. By setting it as 40 mass% or more in a thing, it becomes easy to adjust the refractory whose above-mentioned apparent porosity is 12% or more and 20% or less, and the ratio of the pore diameter of 10 micrometers or more is 30% or less.

  Here, “free carbon” means solid carbon excluding a compound with a metal such as silicon carbide or boron carbide. In addition, “carbon substrate material” refers to all the components of a part of a refractory structure made of free carbon. In other words, regardless of whether the composition is crystalline or amorphous, for example, particles or non-particulate mesh, fiber, etc. composed of free carbon such as graphite, carbon black, etc. It means a continuous structure such as a carbonaceous tissue having a so-called bonding function.

  Therefore, the carbon substrate material in the refractory according to the present invention includes coarse particles or fine particles such as graphitic or amorphous carbon black such as scaly graphite and soil graphite, or a network carbon as a matrix structure having a binding function. Etc.

  The ratio of the apparent porosity and the pore diameter of such a refractory can also be obtained by adjusting the properties of the soil in the molding process or adjusting the molding pressure, as will be described later.

  In addition, the free carbon matrix material particles with a maximum length of 45 μm or less are filled with refractory by making the mass of the free carbon matrix material, which is crystalline within the refractory structure, 40% by mass or more. It is easy to obtain a refractory having the aforementioned apparent porosity and pore diameter ratio.

  In addition, if the free carbon matrix material particles having a maximum length of 45 μm or less are 40% by mass or more based on the total free carbon matrix material being crystalline in the refractory structure, The relative volume fraction and specific surface area of the carbon substrate material will increase. In other words, the contact area between the zirconia particles and the carbon having a bonding function and the carbon substrate material close to an integral structure is increased. This also has the effect of retaining the zirconia particles, which have been reduced in size due to internal cracking and the like, without falling off within the refractory structure.

  The reason why the free carbon substrate material that is crystalline is separated by its maximum length of 45 μm is that if this maximum length exceeds 45 μm, the entanglement between the raw material particles constituting the soil during the molding increases. Therefore, the mutual slip phenomenon is reduced and a relatively coarse structure is likely to be formed. In addition, “free carbon substrate material particles with a maximum length exceeding 45 μm” governing such properties refers to carbonaceous materials among carbon substrate materials, and to natural scaly graphite. Equivalent to.

  The presence of free carbon matrix material particles having a maximum length of 45 μm or less in the zirconia-carbon-containing refractory structure can be easily examined by observing the structure. It can be identified by the following method that it is 40% by mass or more in the free carbon substrate material which is all crystalline in the physical structure.

1. The refractory is heat-treated at 400 ° C. to 500 ° C. in an oxidizing atmosphere for 48 hours or more to remove carbon in the bonded portion (including amorphous single-particle carbon),
2. The carbon substrate raw material exceeding 45 μm is separated from the remainder by sieving,
3. For each of the upper part of the sieve and the lower part of the sieve, the mass of only the free carbon substrate raw material is identified (for example, the upper part of the sieve is heat-treated in an oxidizing atmosphere of 1000 ° C. or more to completely remove the carbon component. The mass of the free carbon substrate material exceeding 45 μm, and the same applies to the lower part of the sieve).
4). Summing the mass of the free carbon substrate raw material above and below the sieve identified in 3 above,
5. The mass of the free carbon substrate raw material at the top of the 3 sieve is divided by the total value obtained by this 4.
The value of 5 can be set as a ratio of free carbon substrate material particles that are crystalline of 45 μm or less, and this ratio can be a determination target (40% or more).

  Therefore, in the present invention, the ratio of the pore diameter of 10 μm or more in the open pores after 1000 ° C. reduction firing of the refractory is set to 30% or less.

  Here, “the ratio of the pore diameter of 10 μm or more” means the ratio between the volume of the pores having a pore diameter of 10 μm or more in the “total opening pores” and the “volume of all opening pores”. R 1655 It can be determined by a method for measuring the pore size distribution of a molded product by mercury porosimetry.

By the way, a zirconia-carbonaceous refractory having zirconia particles having cracks therein is inferior in thermal shock resistance due to the presence of zirconia particles having cracks therein. In addition, the refractory containing the high ZrO ₂ component of the present invention, which has been made dense by the above-mentioned means, is excellent in corrosion resistance, but tends to decrease the thermal shock resistance.

  Therefore, in the refractory of the present invention, the zirconia-carbon-containing refractory according to the present invention contains a carbon substrate material having a fibrous structure having a diameter of 50 nm or less in the structure of the refractory, and has a thermal shock resistance. Can be remarkably improved.

  The carbon substrate material having a fibrous structure having a diameter of 50 nm or less is present in the refractory structure of the present invention, particularly in the carbon structure (matrix) that bears the binding function, so that the zirconia-carbon-containing refractory can be obtained. Thermal shock resistance can be greatly improved.

  The reason why the thermal shock resistance of the zirconia-carbon-containing refractory can be greatly improved by the structure including the carbon matrix material having a fibrous structure having a diameter of 50 nm or less is considered as follows.

  The structure of the zirconia-carbon-containing refractory is composed of a zirconia particle as an aggregate, a carbon matrix material as an aggregate particle such as graphite, and a carbon structure having a bonding function between the aggregate particles. These zirconia aggregate particles are three-dimensionally configured so as to be surrounded by a carbon structure having a binding function with a carbonaceous aggregate such as graphite. Since the carbon structure responsible for this bonding function is three-dimensionally connected using graphite as a filler, the properties of this structure greatly affect the macro physical properties related to the mechanical stress of the zirconia-carbon containing refractory.

  On the other hand, the carbon bond connecting the aggregate particles is generally formed by non-oxidizing and firing a phenol resin exhibiting a high carbon residue. This carbon is generally called amorphous glassy carbon (hereinafter simply referred to as “glassy carbon”), and has a dense, high elastic modulus and brittle nature.

  A carbon matrix material having a fibrous structure having a diameter of 50 nm or less (hereinafter, simply referred to as “fibrous carbon”) is itself three-dimensionally irregularly oriented, and these fibrous carbons are intertwined in a complicated manner. Distributed throughout the organization. The carbon substrate material having such a structure is a so-called “flexible structure” which itself has a high mechanical deformability and also has a high stress dispersion or stress absorption capability. Accordingly, the carbon bond matrix portion including such a flexible structure also becomes flexible.

  Here, “a fibrous carbon structure having a diameter of 50 nm or less” means a nanoscale ultrafine such as a carbon nanotube (hereinafter simply referred to as “CNT”) or a carbon nanofiber (hereinafter simply referred to as “CNF”). Carbon (fibrous) (structure with an aspect ratio of approximately 3 or more) and its texture.

  Moreover, this fibrous carbon is excellent in tensile strength compared with glassy carbon or other structures of carbon, and functions as a structure reinforcing material. Therefore, this fibrous carbon also increases the fracture toughness of carbon bonds.

  Such fibrous carbon is dispersed and arranged three-dimensionally as fine graphite fine powder or carbon black as filler in a carbon bond matrix so that the carbon bond matrix portion is soft. It becomes a structured and toughened connective structure (hereinafter simply referred to as “fibrous carbon-containing structure”). In other words, by continuously forming a carbon connective structure containing fibrous carbon as a carbon-based fiber filler in the refractory structure between aggregate particles, the refractory is made flexible and tough. The macrophysical properties of the refractory are improved, the elastic modulus and thermal expansion coefficient are reduced, and the strength of the microstructure is also improved, thereby suppressing the occurrence of the starting point of destruction leading to the destruction of the refractory. It is thought that sex can be obtained.

  The thickness of the carbon bonds existing between the carbonaceous fillers in the carbon matrix used in the continuous casting nozzle is on the order of several hundred nm. In order to improve the continuity by a fine fibrous structure, it is considered that the finer the structural unit of the fibrous structure, the better. If it exceeds 50 nm, fine adhesion with the carbon substrate raw material to be a filler is not sufficient, so 50 nm or less is preferable.

The present invention has the following effects.
To a 1, ZrO ₂ content high zirconia content of zirconia exceeds 80 mass% - in the carbon-containing refractories, while using 150μm or zirconia particles cracks are present therein, the corrosion resistance and thermal shock resistance It is possible to ensure a high degree.

  Secondly, the refractory of the present invention can be easily and stably produced by allowing a carbon substrate material having a specific size of 45 μm or less to exist in a zirconia-carbon-containing refractory at a specific ratio or less. In addition, corrosion resistance and thermal shock resistance can be improved.

  Thirdly, it is possible to further improve the thermal shock resistance by disposing a carbon substrate material having a fibrous structure having a diameter of 50 nm or less in a matrix portion mainly composed of carbon.

It shows a ZrO ₂ raw material particles having a crack inside the particles. ZrO ₂ raw material particles having no cracks inside the particles are shown. It shows an enlarged photograph of a cross section after the corrosion test of the refractory blended with 150μm or more ZrO ₂ raw material particles having a crack inside the particles. It shows an enlarged photograph of a cross section after the corrosion test of the refractory blended with 150μm or more ZrO ₂ raw material particles having no crack inside the particles. The enlarged photograph of the carbonaceous connective structure of the refractory which does not contain the carbonaceous fibrous structure of diameter 50nm or less of this invention is shown. The enlarged photograph (TEM image) of the carbonaceous fibrous part of the carbonaceous connective structure in which the carbonaceous fibrous structure of diameter 50nm or less of the refractory material of this invention is contained in the structure | tissue of an amorphous carbon is shown. Figure a shows a carbonaceous connective tissue ratio of about 20% (area ratio), b shows a carbonaceous connective tissue ratio (area ratio), and c shows a carbonaceous connective tissue. Each of which is substantially filled with a fibrous structure.

  The refractory of the present invention is manufactured by the following method.

  First, zirconia particles having a size exceeding 150 μm in the raw material of zirconia particles are 25% by mass with respect to the total amount of the raw material with cracks shown in FIG. 1 and the raw material without cracks shown in FIG. Prepare.

  When the refractory material of the present invention is applied to an immersion nozzle for continuous casting, the prepared zirconia raw material particles are mixed with other raw materials such as graphite to produce a clay, and then molded, dried and fired with CIP , Adopt the manufacturing method by general process such as processing.

  In order to adjust the apparent porosity after reduction firing at 1000 ° C. to 12% or more and 20% or less, the molding pressure is adjusted in the molding process. When the pressure during molding is increased, densification, that is, the porosity tends to decrease, and when it is lowered, roughening, that is, the porosity tends to increase. Moreover, although it can also adjust by adjusting the wet state of the earth soil used for this shaping | molding, since the defect in a structure | tissue will arise easily when this adjustment width | variety is enlarged, the adjustment method by a pressure is more preferable.

  The size of the zirconia raw material grains constituting the refractory according to the present invention can be classified into groups of several levels, and the mixing ratio of each group for each classified size can be changed. For example, when the adjustment is made in the direction close to the closest packing, the structure of the refractory obtained by the configuration tends to be dense, and in the opposite direction, the structure of the refractory tends to become coarse.

FIG. 3 shows an enlarged photograph of a cross section after an erosion test of a refractory compounded with 150 μm or more ZrO ₂ raw material particles having cracks inside the particles. If the ZrO ₂ raw material particles (aggregate) of 150 μm or more have cracks, molten slag penetrates into the cracks in the aggregate, promotes destabilization at the cracks, and collapses the aggregate. Originally, the zirconia component that stays in the vicinity of the working surface due to the finer grain and contributes to the formation of the protective film and improves the corrosion resistance is dropped into the slag film, so that the protective film function cannot be increased without increasing the zirconia concentration at the working interface. descend.

FIG. 4 shows an enlarged photograph of a cross section after an erosion test of a refractory containing 150 μm or more ZrO ₂ raw material particles having no cracks inside the particles. Due to the destabilization phenomenon accompanied by the fine graining phenomenon of ZrO ₂ aggregate, a refractory layer having a high ZrO ₂ concentration is formed on the working surface in contact with the slag film, and the corrosion resistance is improved by its protective film function.

  In order to make the free carbon substrate material having a maximum length of 45 μm or less in a crystalline state into 40% by mass or more, addition of fine graphite is most preferable. When the same amount is added, compared to coarse graphite, the addition of fine graphite increases the amount of graphite that exists between the zirconia particles, so it is possible to reduce internal friction during molding and prevent the pore diameter from becoming coarse.

  In addition, carbon black with excellent solid lubricating performance can be used alone or in combination. In the case of use in combination with fine graphite, it is preferably about 0.5 mass% or more and about 5 mass% or less. If the amount is less than 0.5% by mass, the effect of improving the solid lubricity caused by using carbon black is poor. If the amount exceeds 5% by mass, the refractory structure tends to be rough and may cause lamination. start.

  As the carbon black, it is preferable to use monospherical particles, but it is also possible to use a bunch of grapes (so-called cluster-like) carbon black in which aggregates are developed.

  In order to incorporate a carbon substrate material having a carbonaceous fibrous structure having a diameter of 50 nm or less into a refractory containing zirconia and carbon, for example, the following method can be employed.

  First, when the refractory of the present invention is 100% by mass, it is about 0.01% by mass to 1.0% by mass (with respect to the carbon content of the matrix portion, the carbon content is 100% by mass). (Occasionally 0.3 mass% to 12.5 mass% or less) Fibrous carbonaceous raw material with a diameter of 50 nm or less is used to produce an organic material containing a solution that forms a refractory carbonaceous binder during the production of the soil. Examples thereof include a method of dispersing in a fine carbonaceous raw material such as resin, pitch or tar, or carbon black.

  Second, when the refractory of the present invention is 100% by mass, it is about 0.03% by mass to 0.3% by mass (with respect to the carbon content of the matrix portion, the carbon content is 100% by mass). As a transition metal (sometimes about 0.3% to 6.0% by mass), organic resin containing a solution that forms a refractory carbonaceous binder, pitch, tar, etc., fine particles such as carbon black The mixture is dispersed and mixed in a carbonaceous raw material, and the kneaded clay is formed by CIP or the like, and heat-treated in a non-oxidizing atmosphere at 600 to 1200 ° C., preferably 900 to 1100 ° C.

  FIG. 5 shows an enlarged photograph of a carbonaceous connective structure of a refractory containing no carbonaceous fibrous structure having a diameter of 50 nm or less according to the present invention, and a, b, and c in FIG. The enlarged photograph of the carbonaceous fibrous part of the carbonaceous connective tissue containing the carbonaceous fibrous structure of diameter 50nm or less is shown.

  As a method of observing the carbonaceous connective structure in the refractory structure, for example, the refractory structure is pulverized with a mortar and dispersed in a dispersion such as water, and the supernatant liquid after settling is scooped with a TEM observation grid. , It can be observed by immobilization. In FIG. 6, a, b, and c are TEM images obtained by observing a carbonaceous connective structure including a carbon fibrous structure of 50 nm or less. The carbon fibrous structure has a small proportion (about 20%) of the carbon fibrous structure when attention is paid to the area in the field of view in the TEM image as shown in FIG. This refers to a material that contains the same degree of amorphous and fibrous structure, and one that is almost entirely filled with a fibrous structure as shown in FIG.

  As can be seen in these enlarged photographs, there are the following differences between them. In the case of FIG. 5 which does not contain a carbonaceous fibrous structure, it is a homogeneous and glass-like structure, and a structure having a deformable structure or deformation that allows flexibility to the structure is allowed. There are no voids. On the other hand, in the case of FIGS. 6A, 6B and 6C, which are carbonaceous connective structures including a carbon fibrous structure having a diameter of 50 nm or less, a fibrous structure rich in deformability that provides flexibility to the structure. Are irregular three-dimensional arrangements, and voids or the like that allow deformation of the joint structure can be seen around the fibrous structure.

  By including such a carbon fibrous structure, it is possible to improve thermal shock resistance. Incidentally, it is technically difficult to directly and accurately identify the mass of a carbon fibrous structure having a diameter of 50 nm or less. Therefore, as described above, if the existence can be confirmed by observing the processed structure indirectly, the effect of improving the thermal shock resistance can be expected.

  The transition metal dispersed in the fine carbonaceous raw material described above may be liquid or powder, and may be in any form such as an alloy state or a compound state. Further, the transition metal in the refractory obtained by the heat treatment may be in any form such as a metal state including an alloy or a compound state.

Table 1 shows the chemical composition of the ZrO ₂ raw material particles used in Examples I to Example H shown below, and the ratio of cracked particles for each particle size. In the table, raw material A is a type with a high crack mixing rate, and raw material B is a type with a low crack mixing rate.

  Tables 2 to 5 of the following examples show the mixing ratio of the aggregate of the test material, the graphite raw material of 45 μm or less, the chemical composition of the test material, and the physical characteristics and chemical characteristics.

The evaluation of the meltability was carried out in a predetermined zirconia graphite prism sample (20 × 20) in a crucible (inner diameter: 150 mm) in which a molding powder was floated about 30 mm on the surface of low carbon steel melted at 1550 to 1570 ° C. in the atmosphere. X160 mm) was immersed for 120 minutes and pulled up, and the maximum amount of erosion at the (molten steel / molten powder) interface was compared. A molten powder having a CaO / SiO ₂ weight ratio of 1.0 was used.

The corrosion resistance evaluation index in the table is that the ratio of ZrO ₂ raw material particles having cracks in the particles is the smallest in Example i, that is, the relationship with the number ratio of ZrO ₂ raw material particles having cracks in the particles. It is an index in which the degree of erosion of Example 4, which is an example having the highest corrosion resistance, is 100.

Incidentally, the corrosion resistance evaluation index is about 120 when the ZrO ₂ component is 80% by mass and the number ratio of ZrO ₂ raw material particles having cracks in the particles is about 7% (same as in Example 4). Therefore, if the corrosion resistance evaluation index is 120 or less, it can be determined that the effect of the present invention is obtained, and can be regarded as a level that exhibits the function as the high corrosion resistance ZG material.

  In addition, the spalling test method is to raise a cylindrical sample (outer diameter 150 / inner diameter 100 mm × height 80 mmh) whose end face is closed with a lid made of the same material to a predetermined temperature, and into the sample from the lid side. It was immersed in water so that water did not enter, was subjected to thermal shock, and the limit ΔT was confirmed by the presence or absence of cracks.

  It has been found that a material exhibiting thermal shock resistance that does not cause cracking in a water cooling test at 1250 ° C. or higher by this test method has a thermal shock resistance level at which there is no problem in actual operation. Therefore, the thermal shock resistance level that can be stably used in an actual furnace needs to be cleared to 1250 ° C. by water-cooled spalling.

Example I In this example I, raw materials A and B shown in Table 1 were mixed at a predetermined ratio, and the raw materials were prepared by changing the ratio of crack-containing particles in the particle size range of 150 μm or more (indicated as +150 μm in the table). This is the result of evaluating the corrosion resistance and thermal shock resistance.

  Table 2 shows the test materials and results.

  In the case of Comparative Examples 1 to 3 in which the crack mixing ratio in the particle size range of 150 μm or more exceeded 25%, the corrosion resistance was significantly lowered. In addition, Examples 1 to 4 satisfy the condition that the crack mixing ratio in a particle size region of 150 μm or more is 25% or less.

  In addition, if the corrosion resistance evaluation index is 120 or less, it is a level that exhibits a function as a high corrosion resistance ZG material. In addition, the thermal shock resistance level that can be stably used in an actual furnace must be cleared to 1250 ° C. by water-cooled spalling. If it is this thermal shock resistance level, it can be stably used as an immersion nozzle without cracking.

Example B This example B shows the test results in which the apparent porosity is substantially constant and the ratio of the pore diameter of 10 μm or more after firing is changed by changing the ratio of the graphite raw material of 45 μm or less.

  Table 3 shows the test materials and test results. Examples 4, 5, 6 and 7 in the same table are the same evaluation indices and are between 85 and 115, and passed, but in the case of Comparative Example 4, it is 123 and the pore diameter ratio is 32%. Decline in corrosion resistance was seen and it was rejected.

Example C This Example C is a test result obtained by changing the carbon bond structure to a bond form including a carbon fibrous structure.

  Table 4 shows the samples and the results. The carbon fibrous structure of Example 8 in the table has an area ratio in the visual field in the TEM image as shown in FIG. Based on Example 5, the carbon bond structure was changed to a bond form containing a carbon fibrous structure. There was no change in corrosion resistance, and the thermal shock resistance was improved by using a carbon fiber structure for the bonds.

  From this result, it is considered that the thermal shock resistance is further improved when the area ratio in the field of view in the TEM image of the carbon fibrous structure in the structure of the carbon bond portion is increased as shown in FIG.

Example D This Example D shows an example in which the ratio of crack-containing particles of zirconia particles having a size of less than 150 μm (denoted as −150 μm in the table) is increased.

  Table 5 shows the test materials and test results. In Example 9 shown in the table, the ratio of crack-containing particles having a zirconia particle size was increased based on Example 4. There was no significant change in both corrosion resistance and thermal shock resistance as seen in Table 3. This shows that the particle size range to be managed as zirconia raw material particles is 150 μm or more.

Example E This Example E investigated the effect of apparent porosity.

  Table 6 shows the test materials and test results. The effect of apparent porosity was investigated by changing the plasticity at the time of molding of the formulation of Example 8 in the table, specifically changing the properties of the soil.

  When the apparent porosity exceeded 20%, the thermal shock resistance did not change greatly, but the corrosion resistance decreased and the test was rejected. On the other hand, in Comparative Example 6 having an apparent porosity of 11.5%, the corrosion resistance was very excellent, but a decrease in the thermal shock resistance was observed and the test was rejected.

  The refractory material of the present invention can be used as a refractory material used for functional parts such as various kilns or nozzles used in the steelmaking and steelmaking processes. In particular, it is suitable as a refractory for a mold powder part of an immersion nozzle used for molten steel injection between a tundish and a mold for continuous casting.

  Moreover, it is suitable also as a refractory material arrange | positioned in the area | region which contacts the molten slag in a tundish of what is called a long nozzle used in order to discharge | emit molten steel from a molten steel ladle to a tundish.

Claims (5)

In a zirconia-carbon-containing refractory in which the content of zirconia in which carbon bonds are formed between aggregate particles exceeds 80% by mass,
Percentage of the number of particles having cracks inside the particles by the method of observing the polished cross section of the particles with respect to the total number of zirconia particles in which the zirconia particles constituting the refractory cannot pass through a sieve screen having a nominal aperture of 150 μm of a JIS standard sieve Is less than 25%,
The apparent porosity of the refractory after 1000 ° C. reduction firing is 12% or more and 20% or less,
And,
A refractory containing zirconia and carbon having a pore diameter ratio of 10 μm or more in open pores after reduction firing of the refractory at 1000 ° C. of 30% or less.   In the refractory structure containing zirconia and carbon, the free carbon matrix material particles having a maximum length of 45 μm or less are free carbon that is all crystalline in the refractory structure. The refractory containing zirconia and carbon according to claim 1, which is 40% by mass or more based on the substrate material.   The zirconia and carbon according to claim 1 or 2, wherein the refractory structure containing zirconia and carbon contains a carbon substrate material having a carbonaceous fibrous structure having a diameter of 50 nm or less. Refractory.   A nozzle for continuous casting in which the refractory according to any one of claims 1 to 3 is disposed in a region in contact with molten powder in a mold.   A nozzle for continuous casting in which the refractory according to any one of claims 1 to 3 is disposed in a region in contact with the molten slag in the tundish.