JP5637630B2 - Refractories for continuous casting and nozzles for continuous casting - Google Patents

Description

  The present invention relates to a refractory material suitably used for an inner hole surface of a continuous casting nozzle, and a continuous casting nozzle using the refractory material.

In continuous casting of steel, Al ₂ O ₃ —SiO ₂ —C quality nozzles with excellent spalling resistance have been widely used in the past, but the fire resistance used for continuous casting with the recent diversification of steel types. The cause of damage and the extent of damage have been strongly influenced by the components supplied from the molten steel side.

In particular, for continuous casting of high oxygen, high Mn and other steels typified by enamel steel, the decarburization action of the refractory by the molten steel, and FeO, MnO, B ₂ O ₃ , SiO ₂ present in the molten steel Oxides such as CaO, etc. (non-metallic inclusions present in the molten steel are collectively referred to as “slag components” hereinafter) are continuously supplied from the molten steel side, resulting in erosion due to a low melting reaction with the refractory. Complex Al ₂ O ₃ —SiO ₂ —MnO—FeO—CaO system and other complex oxides are continuously generated in the refractory interface and in the structure, and flow down with the molten steel, resulting in severe damage to the refractory. come.

  For example, with a pan long nozzle applied for the purpose of oxygen-free casting between a pan and a tundish, damage is caused at the perforated portion where the molten steel collides continuously or at the immersed portion where the molten steel contacts for a long time at the molten steel temperature. There are problems such as severe and extremely short life. The same problem occurs in the immersion nozzle and the lower nozzle in which the same material system is used.

For this reason, as a general method for increasing the damage resistance of the refractory, in the Al ₂ O ₃ —SiO ₂ —C-based material, the carbon content or the slag component is used to prevent structural deterioration due to decarburization. Attempts have been made to reduce or eliminate the amount of SiO ₂ on the refractory side, which can be the main component of low melting with the above. However, although there is a certain effect by reducing SiO ₂ and C, the Al ₂ O ₃ component added as the main aggregate reacts with MnO, FeO, B ₂ O ₃ , SiO ₂ , CaO, etc. Since the melting point is reached, the actual situation is that a sufficient effect is not obtained.

In view of such a situation, a refractory material in which a part or all of the Al ₂ O ₃ aggregate is replaced with an aggregate having a composition that hardly reacts with the slag component has been proposed.

  For example, Patent Document 1 discloses an alumina-magnesia-graphite refractory in which 3 to 60% by mass or less of magnesia having a particle size of 0.02 to 1.0 mm or less is blended with a blend mainly composed of alumina and graphite, or A refractory containing spinel in the refractory has been proposed.

  Patent Document 2 proposes a refractory material in which the entire nozzle or all or a part of the inner hole of the nozzle in contact with molten steel is made of spinel or spinel and periclase as a mineral phase.

  In Patent Document 3, the entire nozzle or the whole or part of the inner hole of the nozzle in contact with the molten steel is spinel 50 to 95% by mass, periclase 0 to 20% by mass, graphite 5 to 30% by mass, unavoidable impurities 3%. An immersion nozzle that is a refractory of less than% spinel-periclase-graphite has been proposed.

  In many cases, these magnesia (periclase) and spinel are selected because they are less likely to produce slag components such as FeO and MnO and low melt than alumina. In particular, the above-mentioned Patent Document 3 shows that spinel and periclase can improve the melt resistance, spalling resistance and the like by forming a dense film of MgO near the surface in contact with the molten steel. Yes.

However, in recent years, as disclosed in Patent Document 4, Nb, V, Cu, etc. are added to the enamel steel in addition to the above slag components in order to improve the nail skipping property, which is one of its characteristics. It has become. In particular, Nb ₂ O ₅ and V ₂ O ₅ promote the low melting of the refractory, and at the same time have a large effect of reducing the surface tension of the slag, so that MnO, FeO, B ₂ O ₃ , SiO ₂ , CaO, etc. When combined with the slag component, a slag having a very strong composition of erosion and permeability (for example, Nb ₂ O ₅ —FeO—MnO—Al ₂ O ₃ —SiO ₂ —CaO system) is generated.

  For this reason, the amount of wear of refractories is larger than before, and even if alumina is simply replaced with the above-mentioned spinel or magnesia (periclase), sufficient durability improvement can be obtained for steel types containing Nb. The present inventors have confirmed that there may be no cases.

The first reason for such poor service life is the high porosity of refractories for continuous casting. Refractories that come into contact with the molten steel of a continuous casting nozzle such as a long nozzle generally have an apparent porosity of 18% or more as a lining material in order to improve spalling resistance (mainly to prevent cracking). % Or less, and it is often used by being integrally formed with the Al ₂ O ₃ -C material of the main body. In addition, other continuous casting nozzles such as a lower nozzle and an immersion nozzle tend to be used. In such a high-porosity structure of the lining material, niobic acid (Nb ₂ O, which is highly erodable and permeable, even if spinel (Al ₂ O ₃ .MgO) or periclase (MgO) aggregates are added. ₅ ) The slag containing ₅ ) easily penetrates into the deep structure through the pores and accelerates the dissolution of the refractory particles.

The second reason lies in the usage environment of refractories for continuous casting in which component systems having high expansion characteristics such as MgO and CaO are difficult to use. In particular, the long nozzle is a member that requires high spalling resistance as compared with other refractory members. This is because the long nozzle is used in a state in which preheating is not sufficient or close to no preheating, unlike an immersion nozzle that is generally preheated by a preheating furnace or a burner. This is because it is often left after use and cooled to near room temperature, and then used again. When a lining material is applied to a long nozzle in such a use environment, a refractory layer to which spinel (Al ₂ O ₃ .MgO) or periclase (MgO) aggregate as the lining material is added is corundum ( Since it has higher thermal expansion than Al ₂ O ₃ ), the possibility of breaking the main body is increased, and volume expansion associated with spinelization in combination with free alumina and free alumina Even in the absence, the formation of a dense and highly elastic layer accompanying the movement of the MgO component in the refractory causes the spalling resistance to be easily impaired, and the durability is not improved.

  For the above reasons, application of a simple MgO-based material is not practical. Therefore, in consideration of the usage environment of the nozzle for continuous casting, proposals have been made to combine spalling resistance and corrosion resistance in the structure and material design.

For example, Patent Document 5 discloses that a part in contact with molten steel is refractory particles such as alumina, spinel, magnesia, mullite, ZrO ₂ -containing clinker, carbon is 10% by mass or less, alkali metal oxide, alkaline earth oxide. By adding 0.5 mass% or more and 8 mass% or less, etc., the refractory layer is imparted with a softening property to the hot refractory layer and the remaining aggregate particle size is adjusted integrally with the main body material. Therefore, a long nozzle has been proposed that suppresses the dissolution of carbon components into molten steel, has excellent spalling resistance and corrosion resistance, and can reduce the occurrence of breakage troubles during repeated use.

  However, even with the long nozzle of Patent Document 5, the spalling resistance as a structure can be ensured. However, especially for the enameled steel to which Nb or the like described above is added, the permeability and the erodibility are very strong. The present inventors have confirmed that the refractory material is greatly damaged due to the influence of the slag of the composition and the durability is not sufficient.

Thus, continuous casting of molten steel with inclusions in steel of complex oxide such as Nb ₂ O ₅ —FeO—MnO—Al ₂ O ₃ —SiO ₂ —CaO system having strong erosion property due to low melting reaction with refractory However, a refractory for continuous casting and a nozzle for continuous casting that have excellent spalling resistance and excellent infiltration resistance and corrosion resistance have not been provided so far. In particular, in a molten steel (especially enameled steel) containing 50 ppm or more of oxygen in the molten steel and 10 ppm or more of Nb, it is in a situation where a plurality of charges (the amount of molten steel in the molten steel pan is one charge) cannot be cast.

International Publication No. 99/38818 Japanese Patent Laid-Open No. 10-305355 JP-A-11-320047 International Publication No. 2007/55400 JP 2006-130555 A

The problem to be solved by the present invention is a complex oxide-based inclusion in steel (corrosion resistance) that is highly erosive for refractories such as Nb ₂ O ₅ —FeO—MnO—Al ₂ O ₃ —SiO ₂ —CaO. Even in continuous casting of molten steel containing a strong slag component), particularly enameled steel containing oxygen of 50 ppm or more and Nb of 10 ppm or more, it has high infiltration resistance and corrosion resistance against the slag component etc. An object of the present invention is to provide a refractory for continuous casting and a nozzle for continuous casting which are also provided with poling properties (including thermal shock resistance and resistance to crushing cracks, the same shall apply hereinafter).

The “molten steel with complex oxide inclusions (strongly erosive slag component) such as Nb ₂ O ₅ —FeO—MnO—Al ₂ O ₃ —SiO ₂ —CaO” is represented by enamel steel. High oxygen-high Mn content steel is mentioned.

The continuous casting refractory according to the present invention has 10% by volume of particles having a size of 0.045 mm or less when the part excluding the component composed of a free carbon component from the refractory component is 100% by volume. Particle size composition of 50 volume% or less, particles larger than 0.045 mm and 0.21 mm or less in 40 volume% (including zero), particles larger than 0.21 mm in 40 volume% or more and 90 volume% or less When the total of particles having a size of 0.045 mm or less in the refractory and the free carbon component is 100% by mass, the free carbon component is 3.0% by mass or more and 35.0% by mass or less, The total of SiO ₂ component and CaO component in terms of oxide is a chemical composition of 0.4% by mass or more and 5.0% by mass or less, excluding the free carbon component, SiO ₂ component and CaO component, 0 .045mm or more The remainder of the size of the particles have an average molar ratio of total particles _{(Al 2} O 3 / MgO) corundum is mineral composition of 1.05 or more 2.35 or less _(Al 2 _{O 3)} and spinel (Al ₂ O ₃ .MgO) including a particle group, and a portion excluding particles having a size of 0.045 mm or less and a free carbon component is composed of corundum (Al ₂ O ₃ ) and spinel (Al ₂ O ₃ · MgO), or both.

  The continuous casting nozzle of the present invention is a continuous casting nozzle in which the continuous casting refractory of the present invention is arranged in a part or all of the inner hole surface of the nozzle. The thickness of the refractory is not less than a value obtained by adding 2 mm to the value obtained by multiplying the damage rate of the continuous casting refractory by the set use time.

  Hereinafter, the present invention will be described in detail.

  In solving the above-mentioned problems, investigations were made on a molten steel (especially enameled steel) containing about 50 ppm or more of oxygen and about 10 ppm or more of Nb, which requires the highest infiltration resistance and corrosion resistance. If it is a refractory that can solve the above-mentioned problems with respect to such molten steel, it is relatively more resistant to infiltration against molten steel containing oxygen, Nb, etc. lower than this level, compared to the case with respect to the molten steel. Corrosion resistance is obtained.

The present invention protects the inside of a refractory by quickly forming a thin and thin spinel layer on the working surface and in the refractory having pores in the inside thereof on the side in contact with the molten steel. This is based on the knowledge that the infiltration property and the melting loss can be reduced. That is, in the present invention, a thin and dense protective layer is formed on the working surface in contact with the molten steel by the rapid formation of the secondary spinel layer, and Nb ₂ O ₅ —MnO—SiO ₂ — suspended in enamel steel or the like. A remarkable improvement in corrosion resistance can be obtained even for highly permeable slag containing FeO or the like (inclusion composition), and this effect can be obtained without impairing the thermal shock resistance as a continuous casting nozzle. This is very different from the prior art.

  In order to promptly generate a secondary spinel layer on the surface of the refractory having pores, the present inventors particularly important the chemical composition and mineral composition in the particle size range of 0.045 mm or less constituting the refractory. I found something. This will be specifically described below.

First, in order to extract enamel characteristics (foam resistance / spot resistance, adhesion, and resistance to tearing), the oxygen concentration in molten steel is generally 50 ppm or more, and alloy elements such as Mn, Si, Nb, V, B, etc. Is added in a predetermined amount. Therefore, it is considered that some of these alloy elements are present as oxides in the molten steel, and in particular, (MnO), (SiO ₂ ), (Nb ₂ O ₅ ) that affect the refractory melting loss. , (V ₂ O ₅ ), (B ₂ O ₃ ) [() means slag] or the like is fused with (FeO) present in the steel to lower the melting oxide (hereinafter referred to as “low melting point in steel”). It is also called “slag”). Among these, (Nb ₂ O ₅ ) and (V ₂ O ₅ ) have the action of lowering the surface tension of the slag phase and promoting low melting, so that the slag phase containing these oxides penetrates into the refractory structure. The composition has strong properties and meltability.

The above complex oxides are thought to be suspended in the molten steel as low melting non-metallic inclusions, which first come into contact with the refractory surface together with the molten steel flow. On the other hand, the carbon present in the refractory dissolves quickly into the molten steel by contact with the molten steel, so that the oxide phase is exposed in the surface layer. As a result, oxide particles having different particle sizes come into contact with the low melting point slag fine particles suspended in the molten steel. Since the low melting point slag in steel and the refractory surface are the same oxides, the wettability is very good, and Al ₂ O ₃ and MgO are brought into contact with the refractory surface and the pores of the refractory. It penetrates into the tissue while dissolving the aggregate containing refractory, and the erosion of the refractory proceeds. As a result, the composition of the low-melting-point slag in steel changes sequentially in such a way as to absorb Al ₂ O ₃ and MgO components.

The inventors of the present invention focused on the feature that particles are dissolved more rapidly in the slag as the particle size is finer, and studied to accelerate the formation of the secondary spinel phase by changing the chemical composition, mineral composition, etc. in the fine particle region. It was. Here, the secondary spinel phase, a spinel particles without added during refractory material formulation, the Al 2 _{O 3, MgO} component in the slag as the raw material, Al ₂ O ₃ freshly crystallized from slag , Refers to a phase grown as an MgO-based spinel crystal.

As a result of the examination, it was found that the refractory structure before being subjected to casting must satisfy the following three requirements in order to quickly generate the secondary spinel phase.

(Requirement 1) When the total of particles having a size of 0.045 mm or less and a free carbon component in the refractory is 100% by mass, the components of SiO ₂ and CaO in terms of oxide are 0.4 in total. It should be contained in the range of mass% to 5.0 mass%.

(Requirement 2) When the total of particles having a size of 0.045 mm or less and a free carbon component in the refractory is 100% by mass, the free carbon component is 3.0% by mass or more and 35.0% by mass or less. Contain.

(Requirement 3) The remainder of particles having a size of 0.045 mm or less excluding the free carbon component, SiO ₂ component and CaO component is the average molar ratio of the entire particle group (Al ₂ O ₃ / MgO) Is composed of particles composed of corundum (Al ₂ O ₃ ) and spinel (Al ₂ O ₃ .MgO) having a mineral composition of 1.05 to 2.35.

  When the refractory satisfies the above requirements 1 to 3, the secondary spinel layer can be quickly formed at the contact interface between the refractory and the molten steel during continuous casting (while the molten steel passes). It becomes possible.

  Details of each requirement will be described below.

  The present inventors have found that chemical components, mineral compositions, etc. in the particle size range of 0.045 mm or less in the refractory are important as conditions for promptly generating secondary spinel. The reason why the chemical composition, mineral composition, etc. in the particle size range of 0.045 mm or less in this refractory material is important is that this particle size range is the particle size corresponding to the matrix part mainly connecting the coarse particles, and further the reactivity By forming a liquid phase structure in the high-fine powder matrix part, the secondary spinel phase that connects the particles with a size exceeding 0.045 mm is crystallized in the slag phase of the working surface, so that only on the working surface This is because a dense layer of thin secondary spinel can be formed quickly.

In order to generate a liquid phase structure during continuous casting, the portion of fine particles or the like that is 0.045 mm or less excluding the free carbon component (that is, more than 0.045 mm from the entire refractory component other than the free carbon component) When the total amount of sized particles (hereinafter also referred to as “coarse and medium grain portions”) and free carbon components (not limited to 0.045 mm or less) is 100% by mass, A total of 0.4 mass% or more and 5.0 mass% or less of the components of SiO ₂ and CaO in terms of oxide are present in this particle size range (requirement 1). This aims at promoting the formation of a secondary spinel layer on the working surface (molten steel contact surface) and improving the spalling resistance as a refractory.

SiO ₂ has a function of dissolving a low-reactivity MgO component in the spinel phase as a free MgO component once in slag to enhance the reactivity and facilitating movement in a refractory structure as Mg (g) described later. Fulfill. SiO ₂ can be added in the form of an oxide or in the form of a non-oxide such as SiC or Si ₃ N ₄ .

CaO fulfills the function of preferentially reacting with the components of corundum and spinel particles, particularly the Al ₂ O ₃ component, to generate a small amount of liquid phase. The liquid phase produced by this CaO also facilitates the movement of the MgO component.

Further, by allowing these SiO ₂ and CaO to be dispersed in the structure of a part such as fine particles of 0.045 mm or less, a slight (thin) Al ₂ O ₃ —MgO—SiO ₂ —CaO is present in the structure. In addition to reducing the generated stress value due to the refractory particle size configuration described later, the generated stress value due to its own thermal expansion and elastic modulus can be reduced in a constrained refractory placement environment. The effect of reducing the risk of pushing cracks due to the inner hole material of the refractory body can be obtained.

During continuous casting, a certain amount of Al ₂ O ₃ component or MgO component contained in corundum or spinel of fine powder particles in a portion such as fine particles of 0.045 mm or less is a (SiO ₂ —CaO) -based liquid It dissolves in the phase structure and forms a liquid phase containing the fine particle component. Thereby, the Al ₂ O ₃ component and the MgO component in the spinel particles, which are particularly thermodynamically stable phases, are once converted into a (SiO ₂ —CaO—Al ₂ O ₃ —MgO) -based slag phase. This mechanism facilitates the movement of the MgO component in the tissue.

On the other hand, in the working surface portion in contact with the molten steel, the working surface, particularly 0, can be obtained by contacting and sequentially reacting with complex oxide slag (inclusions) such as Nb ₂ O ₅ —MnO—SiO ₂ —FeO in the steel. The Al ₂ O ₃ and MgO components of the particles constituting the refractory having a thickness of 0.045 mm or less are further dissolved in the liquid phase structure, and the amount of liquid phase in the highly reactive portion such as the fine particles is increased.

At this time, if the total amount of SiO ₂ and CaO is more than 5% by mass, the fire resistance of the refractory structure is lowered and the corrosion resistance is lowered, and it is not preferable. Since the amount of liquid phase to be reduced is reduced, there is a problem that a dense layer due to the secondary spinel phase cannot be generated quickly.

In this way, the liquid phase component is preliminarily present in the fine powder region of the refractory, and contact with the complex oxide slag (inclusions) such as Nb ₂ O ₅ —MnO—SiO ₂ —FeO existing in the molten steel. Through the process of reacting, an SiO ₂ —CaO-based liquid phase structure in which an Al ₂ O ₃ component and an MgO component are dissolved from corundum and spinel is sequentially generated inside the refractory. This facilitates the movement of the MgO component in the thermodynamically stable spinel inside the refractory. In addition, on the operating surface, particularly dissolution of Al ₂ O ₃ and MgO components in the slag proceeds in a portion such as fine particles, and it is considered that a large amount of slag phase having a high Al ₂ O ₃ or MgO component content is generated in the vicinity of the operating surface. It is done.

Here, the average molar ratio (Al ₂ O ₃ / MgO) of corundum and spinel as chemical components in a particle size range of 0.045 mm or less needs to be an alumina-rich composition of 1.05 to 2.35. .

The first reason is that the Al ₂ O ₃ component in spinel particles of 0.045 mm or less selectively reacts with the CaO component to facilitate the decomposition of the particles, and promotes liquid phase generation around the spinel particles. Because. The second reason is that the average molar ratio (Al ₂ O ₃ / MgO) in the slag on the operation surface is adjusted in advance to an alumina-rich composition, so that the MgO component that moves from the inside of the refractory structure through the pores This is for the purpose of increasing the concentration of (MgO) in the slag near the working surface (see below). Since the spinel phase is a thermodynamically stable phase, the continuous supply of the (MgO) component to the slag phase causes the formation of a new high-melting-point and dense secondary spinel phase (crystallization) from the slag. Will happen. The composition of the secondary spinel phase generated on the operating surface changes greatly depending on the supply amount of (MgO), and when the MgO component is sufficiently supplied from the inside of the refractory, the secondary spinel phase rich in MgO is operating. Produced in the matrix part of the nearby refractory, it is considered to increase the corrosion resistance of the refractory.

At this time, if the average molar ratio of the chemical component (Al ₂ O ₃ / MgO) initially set to 0.045 mm or less is smaller than 1.05, the formation of the secondary spinel phase is not sufficient, and is larger than 2.35. Although secondary spinel is generated, the low melting component remains and tends to cause erosion.

In addition, in the case where metal Al is present, the chemical components Al ₂ O ₃ and MgO of 0.045 mm or less for calculating the above average molar ratio can be converted into oxides and added. . This is because even if metal Al is present, it is oxidized during casting to alumina as corundum.

  Further, usable oxide particles of 0.045 mm or less are particles containing corundum and spinel as minerals.

The corundum may be a single-composition particle or may be present in a spinel particle mixed with spinel to form an integral particle structure. Corundum is preferable because it easily forms a slag phase with SiO ₂ or CaO added as a slag component and contributes to densification of the matrix portion.

  The use of spinel particles is mainly preferred from the following three points. The first point is that the coefficient of thermal expansion is lower than that of MgO, and the spalling resistance can be maintained and improved. The second point is that the spinel particles are thermodynamically stable, and the influence of low viscosity on the slag phase is small. In addition, a part of the dissolved MgO component increases the reactivity with carbon. It is in the point which makes easy the movement to the working surface side of a component. The third point is that the absorption capacity of FeO in the slag is excellent and the penetration of the slag phase is not promoted.

On the other hand, a method of adding MgO (periclase) fine powder to a particle size range of 0.045 mm or less in advance is also conceivable. In general, the MgO component is difficult to form a low-melting-point compound even in contact with a slagging component present in steel, and is preferable in terms of corrosion resistance. However, in the refractory having open pores, the slag phase penetrates into the structure through the open pores, and the dissolution into the slag in which the MgO component penetrates into the pores as Mg ions gradually proceeds. Bring about As a result, the refractory containing MgO has a deeper penetration of slag than the Al ₂ O ₃ refractory. In particular, when a large amount of FeO component in the slag is present in the form of Fe ions, carbonaceous bonds that connect the particles disappear (C + (FeO) → CO (g) + Fe). As a result, damage due to dropping off of the aggregate particles tends to proceed, and improvement in durability cannot be expected. On the other hand, a thermodynamically stable spinel phase has a smaller slag viscosity reducing effect than MgO particles. Furthermore, the use of MgO (periclase) is unfavorable because MgO itself has a larger coefficient of thermal expansion than alumina and spinel, and is disadvantageous in terms of spalling resistance when considering the usage environment of long nozzles.

Moreover, in the part (coarse grain and middle grain part) excluding particles having a size of 0.045 mm or less and free carbon components, of corundum (Al ₂ O ₃ ) and spinel (Al ₂ O ₃ .MgO) Either one or both are used. Since the aggregate dissolution rate is slow at the coarse and medium grain portions, the corrosion resistance against slag or the like is not impaired to the extent that the durability of the refractory of the present invention is determined by either spinel particles or corundum. They are also effective in maintaining and improving spalling resistance.

  The secondary spinel formation mechanism will be described in more detail by the reaction formula.

The SiO ₂ component coexisting with the MgO component dissolved in the spinel or in the slag phase in the matrix part causes the reactions shown in the following (formula 1) and (formula 2) in the presence of carbon. On the surface (working surface) where the refractory is in contact with the molten steel, since the molten steel is flowing, a negative pressure region is formed, so the gas components generated by the reactions of (Equation 1) and (Equation 2) Moves to the working surface through the pores in the refractory structure. Furthermore, the gas components of SiO (g) and Mg (g) generated in (Expression 1) and (Expression 2) generate MgO (s) and Si (l) in the middle of movement or in the vicinity of the working surface (Expression 3). MgO (s) produced in the vicinity of the working surface is a composite oxide slag (for example, steel inclusion slag Nb ₂ O ₅ —MnO—SiO ₂ —FeO and fine powder aggregate component) in which fine powder is dissolved on the refractory working surface. The mixture) is absorbed by the phase and increases the MgO concentration of the slag (Equation 4). Further, the produced Si (l) is dissolved in the molten steel. If the activity of MgO in the working surface slag exceeds 1, MgO will crystallize in the solid phase in the slag. At this time, spinel Al ₂ O ₃ .MgO (secondary spinel), which is a thermodynamically more stable compound that binds to the alumina component abundantly present in the slag, rather than MgO being produced as a simple substance (periclase) in the slag. Phase). Therefore, the secondary spinel phase is generated and grown from the slag present in the matrix portion (Formula 5).
MgO (s) + C → Mg (g) + CO (g) (Formula 1)
SiO ₂ (s) + C → SiO (g) + CO (g) (Formula 2)
Mg (g) + SiO (g) → MgO (s) + Si (l) (Formula 3)
MgO (s) → (MgO) (Formula 4)
(MgO) + (Al ₂ O ₃ ) → Al ₂ O ₃ .MgO (S) (Formula 5)

Through the above process, the nucleation and growth in the slag phase or particles constituting the refractory in contact with the slag phase centering on the matrix part connecting the particles constituting the refractory on the active surface side. The next spinel phase is generated and a dense layer is formed. In addition, macroscopically, the MgO component is unevenly distributed in the structure. That is, a region having a large MgO component is formed on the secondary spinel phase generation side on the working surface side, and a layer having a relatively large amount of Al ₂ O _{3 and a} small amount of MgO is formed below the region. In other words, the surface layer becomes a structure rich in MgO.

  Here, as the amount of carbon in the above reaction, when the total of particles having a size of 0.045 mm or less and the total amount of free carbon components in the refractory is 100% by mass, the free carbon components are 3. It is necessary to be 0 to 35.0% by mass, preferably 5 to 15% by mass. The free carbon component is not a compound bonded to other components such as SiC, but is mainly composed of carbon and particulate carbonaceous powder (graphite, carbon black) that connect refractory components such as particles. Etc.).

  The free carbon component is an essential component for accelerating the reactions of the above (formula 1) and (formula 2), and has the effect of preventing the penetration of slag and the like and improving the spalling resistance.

  As a free carbon component, a resin having a high fixed carbon such as phenol resin, furan resin, polyacrylonitrile resin, pitch, and tar added for the purpose of imparting moldability and strength during kneading (hereinafter also referred to as “bond carbon”). Can be used. In addition to the bond carbon, any one or more of carbon powder such as graphite having graphite and anthracite, carbon powder having no crystallinity, and carbon powder having a mixed structure thereof may be used in combination. Bond carbon alone may be used to improve corrosion resistance and wear resistance. These are preferably used in a powder of 0.045 mm or less in order to make the refractory structure stable and strong in a reducing atmosphere, but further enhance the expression of properties such as contributing to improved spalling resistance. Therefore, it is also possible to use a size of more than 0.045 mm and 1 mm or less.

  When the free carbon component is less than 3.0% by mass, the reaction progress of the above (formula 1) and (formula 2) or the supply of the MgO component to the slag layer on the working surface side is delayed, and the dense layer on the working surface Formation becomes difficult. Further, if it is more than 35.0% by mass, it is preferable in terms of the progress of the reactions of the above (formula 1) and (formula 2), but since it easily dissolves and disappears by contact with molten steel, the working surface is fireproof with many pores. The structure becomes a physical structure, and the contact area by the complex oxide from the molten steel side or the penetration into the inside of the structure increases, so that the erosion rate increases and the risk of reducing the corrosion resistance increases.

  Due to the presence of the dense layer generated by the mechanism as described above, it is possible to suppress the intrusion of the complex oxide (slag) from the molten steel side having a strong permeability and erodibility and to protect the refractory structure.

By the way, from the viewpoint of spalling resistance, the continuous casting nozzle is generally made of a low expansion Al ₂ O ₃ —SiO ₂ —C system or Al ₂ O ₃ —C having excellent spalling resistance. System materials (hereinafter, these are also referred to as “AG materials”) are applied. In many cases, the material of the present invention is disposed in a contact portion with molten steel, for example, a part of or the entire region of the inner hole surface from the viewpoint of improving corrosion resistance. In this case, there is a risk of mechanical damage such as the lining material cracking the main body material due to the difference in physical properties between the main body material and the material arranged on the inner hole surface (hereinafter also referred to as “lining material”). May increase.

  With regard to this mechanical damage, it is considered that the risk of the occurrence can be reduced or reduced by reducing the generated stress value of the lining material up to the casting temperature range. The inventors focused on reducing this generated stress value and made intensive studies.

  In addition to the above three requirements for improving the corrosion resistance and the stress relaxation effect due to the liquid phase in the refractory structure of the present invention, by adding the following “Requirement 4”, the corrosion resistance is excellent and the spalling resistance is also excellent. It is possible to realize a continuous casting nozzle.

(Requirement 4) When a part excluding a constituent composed of a free carbon component from a constituent of a refractory is defined as 100% by volume, particles having a size of 0.045 mm or less are 10% by volume to 50% by volume. Particles having a size larger than 0.045 mm and 0.21 mm or less are 40 volume% or less (including zero), and particles larger than 0.21 mm are 40 volume% or more and 90 volume% or less. (This is shown in the figure and is in the range of FIG. 1.)

  As described above, the largest number of particles (coarse particles) larger than 0.21 mm, the next most particles (fine particles) of 0.045 mm or less (including the same proportion as the coarse particles), and 0.045 mm It is possible to increase the porosity in the refractory structure by reducing the number of particles (medium particles) of 0.21 mm or less to a maximum, that is, a so-called gap particle size configuration. This facilitates the movement of particles in the tissue (ie, the rearrangement of particles and voids. This can also be expressed as local “buckling” when focusing on the tissue surface). It is possible to reduce the stress value generated. If the particle size is outside the above range, the rearrangement of the particles becomes difficult, so the maximum generated stress value increases, and the risk of pushing cracks increases. The larger the inner diameter of the continuous casting nozzle and the thinner the wall, the easier it is to break. In the general nozzle shape used for continuous casting, the maximum generated stress value needs to be 10 MPa or less at the maximum from the result of the molten steel injection test. Is almost gone.

  In addition, regarding the particle size constitution as an element of such spalling resistance, the constitution of the free carbon component is excluded from the constitution of the refractory mainly for the following reason. The mechanical stress generated in the refractory of the continuous casting nozzle is greatly affected by the structural relationship between solid particles such as oxides, which are small in deformation (nearly none). This is because it is possible to evaluate the spalling resistance clearly and most effectively by excluding the elements other than the relationship between the particles. The elements other than the interrelationship between the particles are graphite, which is a carbon component, and other particulate carbon (described later). These have a great influence (improvement effect) on the spalling resistance. In the specification, it is a relative ratio excluding the carbon component.

  It becomes possible to set it as the maximum generated stress value of 10 MPa or less by setting it as the said particle size structure. When particles having a size of 0.045 mm or less are less than 10% by volume, particles having a size greater than 0.21 mm are more than 90% by volume, and particles having a size greater than 0.045 mm and 0.21 mm or less are 40% by volume. In the case of exceeding, the particles having a size of 0.045 mm or less in the refractory are difficult to uniformly disperse, and due to the uneven distribution, distortion that can serve as a starting point of destruction of the refractory tends to occur in the refractory structure. When particles having a size of 0.045 mm or less exceed 50% by volume, and when particles larger than 0.21 mm are less than 40% by volume, the refractory structure becomes close to a unitary structure, and stress dispersion or fracture occurs. As a result, there are relatively few coarse grains that serve to prevent the occurrence of cracks and the spread of breakage, and the stress propagates over a wide range, making breakage easier.

Here, the “maximum generated stress value” is obtained from the result of measuring a measurement sample made of a lining material using a generated stress test apparatus. The measurement method of the maximum generated stress value is as follows.
(1) A cylindrical refractory having an outer diameter of 50 mm and a height of 50 mm is used as a measurement sample and set in an electric furnace capable of creating a non-oxidizing atmosphere.
(2) An initial load of 0.2 MPa is applied to the sample by a push bar fixed from above and below.
(3) After setting the sample, the temperature is raised to 1500 ° C. while measuring the temperature with a thermocouple set near the sample.
(4) Due to the thermal expansion of the sample as the temperature rises, stress corresponding to the thermal expansion amount and elastic modulus of the sample is transmitted to the fixed push rod.
(5) The generated stress is measured by reading this stress with a load cell for each temperature and plotted.
(6) The maximum value of the generated stress is defined as the maximum generated stress.

  It is possible to obtain a continuous casting refractory and a continuous casting nozzle that have high infiltration resistance and corrosion resistance against slag components derived from molten steel and also have spalling resistance. In particular, in continuous casting of molten steel (typically enameled steel) containing about 50 ppm or more oxygen and about 10 ppm or more of Nb in molten steel, the conventional refractories such as alumina and alumina containing no carbon are used. In addition, extremely excellent infiltration resistance and corrosion resistance can be obtained. Furthermore, as a single substance, it is possible to obtain better infiltration resistance and corrosion resistance than MgO (periclase) refractories, which are conventionally said to have higher corrosion resistance to slag and the like than the alumina and the like.

  With these effects, it is possible to provide a continuous casting refractory and a continuous casting nozzle that can withstand multiple charges (the amount of molten steel in the molten steel pan is 1 charge) or continuous casting for a longer time than before.

It is a figure which shows the range of a particle size structure when the structure except the free carbon component of the refractory of this invention is 100 volume%. It is sectional drawing which shows the example of the long nozzle which installed the refractory material of this invention in the whole inner-hole surface. It is sectional drawing which shows the example of the immersion nozzle which installed the refractory material of this invention in the inner-hole surface whole surface. It is sectional drawing which shows the example of the lower nozzle which installed the refractory of this invention in the whole inner-hole surface.

  The refractory material of the present invention and a method for producing a continuous casting nozzle using the same will be described.

As a raw material of SiO ₂ when converted into an oxide, amorphous silica, crystalline silica, metal Si, SiC, or the like can be used. Since Si increases the strength and elastic modulus after heat treatment and decreases the thermal shock resistance, the amount of Si added is 100% by mass of the total of particles having a size of 0.045 mm or less and free carbon components in the refractory. It is preferable to limit the amount to 0.5% by mass or less.

  As CaO raw materials when converted to oxides, CaO-based compounds that contain Ca carbonate and hydroxide, become CaO after heat treatment at about 1000 ° C or higher, calcium silicate (Portland cement, etc.) are used. can do.

These raw materials of SiO ₂ and CaO have a particle size of 0.045 mm or less, but are preferably as small as possible (fine powder) in order to improve the dispersibility in the refractory structure.

  As alumina particles and spinel particles, any raw material having a mineral composition with the above-described components and molar ratio can be used regardless of the production method such as the sintering method and the electrofusion method.

  The particle shape used for each part such as fine particles, coarse particles and medium particles may be either crushed particles or non-crushed particles, but the particles used for fine particles (0.045 mm or less) are crushed particles. Is preferable because of its high reactivity.

  As the carbon component of particulate (aggregate particles), graphite aggregate with developed hexagonal surface crystals such as scale-like graphite, earth-like graphite particles, artificial graphite, or amorphous carbon such as so-called carbon black The use of fine particles is preferred. In particular, the use of naturally occurring scaly graphite is most preferable from the viewpoint of spalling resistance. The carbon content in the graphite aggregate is preferably 90.0% by mass or more (including 100% by mass excluding inevitable impurities). The reason is that the purity is less than 90.0% by mass, which leads to a high elastic modulus of the refractory structure due to a sintering reaction between impurities or impurities and other raw material particles. It is because it falls.

  As described above, these graphite aggregates are added as fillers between carbonaceous connective tissues, thereby increasing the strength of the structure, increasing the thermal conductivity, and decreasing the coefficient of thermal expansion. Can improve sex. In addition, the presence of carbon, including the binder, uniformly dispersed between the oxides and the like has an effect of suppressing the oxide sintering and the low melting reaction, and can stabilize the quality during casting.

  In order to allow carbon to exist in such a uniformly dispersed state, it is possible to use a graphite aggregate having a particle size of 1 mm or less. From the viewpoint of the homogeneity of the structure and the movement of the MgO component in the structure. Is more preferably 0.045 mm or less.

  These graphite aggregates may not be used for improving corrosion resistance, but when the total of particles having a size of 0.045 mm or less and a free carbon component is 100% by mass. , And can be used in combination within the range of 35.0 mass% or less including bond carbon. As a lining material, in addition to promoting the formation of secondary spinel phase by promoting the movement of MgO component in the structure, it also enhances the function of adjusting the amount of expansion with the main body material (improving yield and thermal spalling properties). Objective.

  These raw material particles are mixed to make a uniform particle mixture. And, to this particle mixture, a binder such as a phenolic resin, pitch, and tar as a carbonaceous raw material (free carbon component) that bears the connective tissue is appropriately selected and added, and kneaded uniformly to form a clay for molding. Get. The raw material used as the binder may be powder or liquid, but it is important to adjust the plasticity of the soil in accordance with the properties of the soil suitable for molding.

  Next, an example is described about the manufacturing method of the nozzle for continuous casting which installed the refractory material obtained from the said refractory material of this invention in the inner-hole side layer.

  Separately from the refractory clay of the present invention, an outer layer, that is, a clay for the main body of the nozzle for continuous casting is prepared (a general manufacturing method may be used). Next, a step of providing a plurality of spaces partitioned to a predetermined size for forming the inner hole side layer and the outer peripheral side layer in the molding mold, and each space in the molding mold were produced exclusively for each. Yes. Adjacent soil is directly contacted, such as by filling it with soil and removing the partition of the space.

  These directly contacted soils are simultaneously pressed by a CIP device to be integrally formed. The obtained molded body is heat-treated at 600 ° C. or higher and 1300 ° C. or lower in a non-oxidizing atmosphere or in an oxidizing atmosphere with the surface subjected to an antioxidant treatment. Prior to the heat treatment step, an independent heat treatment step may be included at a temperature lower than the above temperature for the purpose of removing volatile components and curing the resin. Finally, processing or the like is appropriately performed in the same manner as in the manufacture of a normal continuous casting nozzle.

  The basic operation / working method of each process described above, the apparatus to be used, and the like may be the same as those of a general continuous casting nozzle manufacturing method.

  In addition, about the manufacturing method of the nozzle for continuous casting using the refractory material of this invention, it is not restricted to the integral manufacturing method with another material as the above-mentioned inner-hole side layer, (1) As a cylindrical molded object A method in which the manufactured tubular body is attached to the inner hole of the separately manufactured main body part and fixed with mortar or the like, and (2) the nozzle main body part and the inner hole side layer part are molded as a single body by the material of the present invention. The method of doing can be employed.

  Here, when the refractory according to the present invention is disposed in a part or all of the inner hole surface of the continuous casting nozzle, the thickness of the refractory is damaged to slag in the tundish of the refractory. It is necessary to be equal to or greater than a value obtained by adding 2 mm to a value obtained by multiplying the speed (mm / unit time) by the set use time. The damage rate and set usage time are determined by the specific fluctuating conditions (molten steel amount, slag composition, temperature, casting speed, etc.) for each individual operation. It is necessary to set a value obtained by multiplying the required casting time for the entire amount of molten steel (for one charge) by an integer (that is, a predetermined number of charges).

  The refractory material of the present invention is characterized in that a liquid phase is formed in the structure, and the presence of this liquid phase exhibits a stress relaxation function, while deformation or peeling occurs due to a mechanical external force or the like. It can be a cause. The reason why 2 mm is added to the thickness of the refractory layer of the present invention is to prevent this deformation and peeling. Conditions for the phenomenon of deformation and peeling are not constant, but in the case of a lining structure with a diameter of about 50 to 150 mm, when the thickness of the refractory layer of the present invention is approximately 2 mm or more, it is almost Since we have gained experience that it does not occur, we decided to add 2 mm.

  Note that, as described above, the refractory according to the present invention is arranged as an inner hole side layer only on the inner hole surface of the continuous casting nozzle as described above. However, the present invention can be used not only for the inner hole side layer but also for other parts, for example, the aforementioned “main part” and the entire continuous casting nozzle.

  In addition, as an example in the case of arranging a part of the inner hole surface of the continuous casting nozzle, in the long nozzle, only the upper side centering on the large portion of wear near the lower nozzle of the ladle, in the lower nozzle, In the immersion nozzle, the wear near the top part of the molten steel in the mold is almost the same as the center of the high wear part near the sliding nozzle and the part near the joint with the immersion nozzle. It can be installed only in a region centered on a large part.

  FIGS. 2-4 shows the example of the nozzle for continuous casting which has arrange | positioned the refractory material of this invention in the inner-hole surface whole surface. 2 shows the long nozzle 11, FIG. 3 shows the immersion nozzle 12, and FIG. 4 shows the lower nozzle 13. In the drawings, reference numeral 1 is a refractory layer of the main body, reference numeral 2 is an inner hole, reference numeral 3 is a refractory layer (lining) of the present invention, and reference numeral 4 is a zirconia-graphitic layer (of the refractory layer of the main body ( For mold powder part).

  Regarding the refractory and continuous casting nozzle of the present invention, examples obtained by experiments in a test room and examples used for continuous casting operations in actual equipment will be described below.

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

  In Examples A to E, the tests of “Evaluation 1 to 4” 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. The sample was produced by a method according to the method described in the method for producing a refractory according to the present invention.

<Test conditions for evaluation 1>
In a molten steel of 1550 to 1570 ° C. ([O]: 100 ppm, [Nb]: 20 ppm, [Mn]: 200 ppm), a rod-like refractory sample (□ 20 × 160 mm, apparent porosity after firing at 1000 ° C. in a non-oxidizing atmosphere is 25 % Sample) was held for 30 minutes after being immersed for 100 mm and pulled up, and the structure (presence or absence of secondary spinel layer) on the refractory operating surface after cooling was observed, and the results were as follows: ○, Δ and × evaluated. ○ and Δ indicate that the effect was recognized.
○: Secondary spinel layer only (no melt, coalesced with coarse and medium grains to form a dense layer)
Δ: Secondary spinel layer formed from melt (residual melt)
×: No secondary spinel formation with melt only

<Test conditions for evaluation 2>
The same molten steel as described above was prepared, and a propeller-shaped rod-shaped test sample (□ 20 × 40 mm) was immersed in a molten steel at 1550 to 1570 ° C. at a rotational speed of 200 rpm for 120 minutes and then pulled up. It was evaluated by the numerical value divided by the molten steel wear resistance (1550 ° C.-120 minutes).

The evaluation is as follows, and “◯” and “Δ” indicate that the effect was recognized. Note that “melting steel wear resistance” is the presence or absence of apparent wear, and is not limited to damage caused by a mechanical “wear phenomenon” mechanism in a narrow sense. It also includes losses.
○: <15 μm / min
Δ: 15-30 μm / min
×:> 30 μm / min

<Test conditions for evaluation 3>
As described in the “maximum generated stress value” part. This maximum generated stress value is 10 MPa or less, which means that the effect was recognized.

<Test conditions for evaluation 4>
The refractory of the present invention is arranged (lined) as an integral structure on the inner hole side (AG: φ120 / φ70 mm) on the AG main body (Al ₂ O ₃ : 68 mass%, C: 27 mass%, SiC: 5 mass%). , Inner lining: φ70 / φ50mm) Hot metal at 1600 ° C was poured into an inner hole with a height of 300mm and a thermal shock was applied from the inner hole, and the occurrence of pushing cracks by this pouring method was evaluated with ○ and × as follows did. ○ means that the effect was recognized.
○: No crack,
×: Occurrence of pushing crack

[Example A]
Example A mainly investigated the effect of the mineral composition and Al ₂ O ₃ / MgO molar ratio of the remainder of particles having a size of 0.045 mm or less, excluding free carbon components, SiO ₂ components and CaO components. It is an example.

  Table 1 shows the configuration of each sample and the evaluation results. In Table 1 and Tables 2 to 5 shown later, the blending design is indicated by the volume ratio of the particles, but the same particle size configuration as that of the blending design is maintained even in the manufactured refractory. In each table, “FC” indicates a free carbon component.

Examples (Examples 1 to 4) in which the remaining mineral composition is a case where corundum and spinel coexist and Al ₂ O ₃ / MgO molar ratio is 1.05 to 2.35 are all evaluated. You can see that it meets the criteria.

  Comparative Example 1 is an example in which not only the fine particle portion of 0.045 mm or less but also all oxide particles are periclase magnesia, and Comparative Example 2 is also the same in which all oxide particles are periclase magnesia particles and spinel particles. As an example, in these comparative examples, the formation of secondary spinel is not particularly observed, the penetration of slag into the structure is observed, and the wear resistance of the molten steel is low. Furthermore, the maximum generated stress increases and the spalling resistance is inferior.

  From these facts, it can be seen that magnesia, which is a periclase, needs not to exist.

Moreover, in Comparative Example 3 and Comparative Example 4, which are cases of only spinel containing no corundum, the formation of secondary spinel is seldom observed, and the molten steel wear resistance is low. Furthermore, even if the components of SiO ₂ and CaO are added, the maximum generated stress is still large and the spalling resistance is inferior.
This shows that the presence of corundum is necessary.

In Comparative Example 5 and Comparative Example 6 in which the Al ₂ O ₃ / MgO molar ratio exceeds 2.35, the generation state of the secondary spinel layer in Evaluation 1 is deteriorated, and the wear resistance of the molten steel in Evaluation 2 is reduced. Recognize. This is considered to be because when the Al ₂ O ₃ / MgO molar ratio exceeds 2.35, corundum becomes relatively excessive, and low melt production with the slag component increases.

[Example B]
Example B is an example of investigating the relationship between the particle size distribution and the coexistence of corundum and spinel. That is, the effects of the presence or absence of corundum and spinel in the fine particle portion of 0.045 mm or less, the medium particle portion of more than 0.045 mm and 0.21 mm or less, and the coarse particle portion of more than 0.21 mm were investigated. .

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

  In addition to Example 3 described above, corundum and spinel coexist in the fine particle part, and Example 5 in which the medium particle part and the coarse particle part are composed of corundum. The medium particle part and the coarse particle part are spinel. All of the constructed examples 6 gave good results.

  However, in Comparative Example 7 and Comparative Example 8 in which the fine-grained portion is composed only of corundum and the middle-grained portion or coarse-grained portion is coexistence of corundum and spinel, and in Comparative Example 9 where spinel does not coexist, both are secondary spinel. Formation was not observed, and slag penetration into the structure was observed, resulting in poor molten steel wear resistance.

  This shows that corundum and spinel need to coexist in a fine particle portion of 0.045 mm or less. It can also be seen that good results can be obtained even if the medium grain portion or the coarse grain portion is composed of only one of corundum and spinel.

[Example C]
Example C is an example in which the influence of the particle size configuration was investigated. That is, when the part excluding the free carbon component from the refractory composition is defined as 100% by volume, a fine particle part of 0.045 mm or less, a medium grain part of more than 0.045 mm and 0.21 mm or less, 0.21 mm The effect of the coarse-grained portion exceeding the above and the relative volume ratio of each on the properties of the refractory is investigated.

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

  The proportion of the fine-grained portion is 10% by volume or more and 50% by volume or less, the proportion of the medium-grained portion is 40% by volume or less (including zero), and the proportion of the coarse-grained part is 40% by volume or more and 90% by volume or less. In Example 2 (the same is true for each example in Table 1) and Examples 7 to 13, although there was a slight difference in the production state of secondary spinel, good results were obtained in the overall evaluation.

  On the other hand, in Comparative Example 10, Comparative Example 13 and Comparative Example 14 in which the proportion of the fine particles was less than 10% by volume, the secondary spinel formation state and the molten steel wear resistance or the resistance to crushing cracking were inferior.

  In Comparative Example 11 in which the proportion of the fine-grained portion exceeds 50% by volume and Comparative Example 12 in which the coarse-grained portion is smaller than 40% by volume, the result of inferior press cracking resistance is obtained, and the comparative example in which the proportion of the coarse-grained portion exceeds 90% by volume No. 14 resulted in poor secondary spinel formation and molten steel wear resistance.

  In addition, in all of Example 12 in which only the maximum particle diameter of Example 2 (maximum particle diameter is 1.0 mm) was set to 2.0 mm and Example 13 in which 3.0 mm was set to 3.0 mm, all evaluations were good results. Got. Rather, the larger the maximum particle size, the better the secondary spinel formation.

  From these, the proportion of fine particles is 10% by volume or more and 50% by volume or less, the proportion of medium particles is 40% by volume or less (including zero), and the proportion of coarse particles is 40% by volume or more and 90% by volume or less. It can be seen that it is necessary to have a grain size configuration of Further, it can be seen that the maximum particle size is not affected by the above-described evaluations of the refractory of the present invention, and that at least the investigated 3.0 mm is good. Therefore, it can be determined that the maximum particle size is not limited to 3.0 mm as long as the size is acceptable for a structure such as the size of a continuous casting nozzle.

[Example D]
Example D is an example in which the influence of the amount of the free carbon component when the total of the particles having a size of 0.045 mm or less and the free carbon component in the refractory is 100% by mass is investigated.

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

  Example 14 in which the free carbon component is composed of only bond carbon and is 3.0% by mass, and particulate carbon (graphite) is added to bond carbon, resulting in 8% by mass, 10% by mass, and 20% by mass. In the case of Example 2, Example 15, Example 16, and Example 17, which is the case of 35% by mass, good results with excellent resistance to wear of molten steel and resistance to crushing cracks as well as the state of secondary spinel formation It became.

On the other hand, in the comparative example 15 which is a case where the free carbon component is composed of only bond carbon and is 2.5% by mass, the secondary spinel formation state falls within the standard, but the molten steel wear resistance is inferior. As a result.
This is thought to be because a uniform or sufficient reducing atmosphere could not be formed inside the refractory structure, and because there was too little carbon contributing to bonding, destruction (including fine ones) occurred inside the structure. It is done.

Further, in Comparative Example 16, which is a case where the free carbon component is composed of bond carbon and particulate carbon (graphite) and is 35.5% by mass, the production state of the secondary spinel falls within the standard, but the resistance is reduced. The result was inferior molten steel wear.
This is because the area where the free carbon component comes into contact with the molten steel increases, the amount of dissolution in the molten steel increases, and the relative balance with the secondary spinel part, which is highly resistant to molten steel, is broken. Conceivable. Therefore, the result was less than the required wear resistance of the molten steel for the refractory of the present invention.

  From these facts, when the total of particles having a size of 0.045 mm or less in the refractory and the free carbon component is 100% by mass, the free carbon component is 3.0% by mass or more and 35.0% by mass. When it contains below, it turns out that not only the production | generation state of a secondary spinel and the resistance to pushing cracks are excellent, but also the abrasion resistance of molten steel is good.

[Example E]
Example E is the influence of the total amount of SiO ₂ component and CaO component in terms of oxide when the total of particles having a size of 0.045 mm or less and free carbon component in the refractory is 100% by mass. This is an example of investigation.

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

Example 18 in which the total amount of SiO ₂ component and CaO component is 0.4% by mass, Example 19 in the case of 1.0% by mass, Examples 2 and 3 in the case of 2.0% by mass In the case of Example 20, Example 21, Example 22, and Example 23, which is the case of 5.0% by mass, the production state of secondary spinel as well as the resistance to molten steel wear Also, good results with excellent resistance to crushing cracks were obtained.

Moreover, the total amount of the SiO ₂ component and the CaO component is the same as 3.0% by mass, and the example 21 is the case of Example 21 where the relative composition ratio is 1: 9, and Example 22 is the case of 9: 1. In either case, the total amount of these, the SiO ₂ component and the CaO component is the same as 3.0% by mass, and good results are obtained that are not different from Example 20 in which the relative constituent ratio is 1: 1. It was.

On the other hand, in Comparative Example 17 in which the total amount of the SiO ₂ component and the CaO component is 0.3% by mass, the secondary spinel generation state and the molten steel wear resistance are within the standard, but the press resistance is reduced. The result was inferior in crackability.
This is presumably because the total amount of the SiO ₂ component and the CaO component was relatively insufficient to decompose spinel, and the stress relaxation ability was also lowered because the liquid phase amount was small.

In Comparative Example 18 the total amount of SiO ₂ component and CaO component is the case of 5.2 wt%, generation state of the secondary spinel, resulted in solvent steel wear resistance are poor.
This is presumably because the total amount of the SiO ₂ component and the CaO component is relatively large, the liquid phase amount is excessive, and the refractory structure is weakened.

From these, when the total of particles having a size of 0.045 mm or less in the refractory and the free carbon component is 100% by mass, the total amount of the SiO ₂ component and the CaO component is 0.4% by mass or more. In the case of 5.0 mass% or less, it turns out that all of the production | generation state of secondary spinel, resistance to a press crack, and abrasion resistance of a molten steel are favorable. Furthermore, it can be seen that the relative proportions of the SiO ₂ component and the CaO component do not affect the properties of the refractory of the present invention.

[Example F]
Example F is an example in which the refractory of the present invention was applied to a continuous casting nozzle and subjected to actual operation.

  The operating conditions are as follows: molten steel: oxygen content in molten steel 100 ppm, Nb content 20 ppm, Mn content 150 pppm, carbon content 50 ppm enamel steel, molten steel temperature (within tundish): about 1530 ° C. to about 1570 C., casting time: 240 minutes (2 charges). The nozzles for continuous casting of Examples 24-26 and Comparative Examples 19-21 shown below were subjected to actual operation.

(Example 24)
It is the example which has arrange | positioned the refractory material of the said Example 2 to the whole inner-hole surface of the long nozzle shown in FIG.

(Example 25)
It is the example which has arrange | positioned the refractory material of the said Example 13 to the whole inner-hole surface of the lower nozzle of a tundish shown in FIG.

(Example 26)
It is the example which has arrange | positioned the refractory material of the said Example 12 in the inner-hole surface whole surface except the discharge hole of the immersion nozzle shown in FIG.

(Comparative Example 19)
It is the example which has arrange | positioned the refractory material of the said comparative example 2 to the whole inner-hole surface of the long nozzle shown in FIG.

(Comparative Example 20)
5 is an example in which the refractory material of Comparative Example 2 is disposed on the entire inner surface of the lower nozzle of the tundish shown in FIG.

(Example 21)
It is the example which has arrange | positioned the refractory material of the said comparative example 2 in the inner-hole surface whole surface except the discharge hole of the immersion nozzle shown in FIG.

  As a result of continuous casting in actual operation, the maximum wear rate in Example 24 was significantly reduced to 68 as an index with Comparative Example 19 being 100, compared to Comparative Example 19. Also, no destruction was seen. The long nozzle of Comparative Example 19 could not be used with a plurality of continuous charges, but it was confirmed that the continuous casting nozzle of Example 24 could be used with a plurality of continuous charges.

  In Example 25, compared to Comparative Example 20, the maximum wear rate was greatly reduced to 52, which is an index with Comparative Example 20 being 100. Also, no destruction was seen.

  In Example 26, compared to Comparative Example 21, the maximum wear rate was greatly reduced to 70, which is an index with Comparative Example 21 being 100. Also, no destruction was seen.

  As described above, in all the examples, the durability was greatly improved as compared with the comparative example (conventional continuous casting nozzle).

  The refractory material of the present invention can be used for a long nozzle used for pouring from a ladle to a tundish, an upper and lower nozzle for a sliding nozzle, an immersion nozzle used for pouring from a tundish to a mold, and the like. Since the refractory of the present invention is particularly excellent in spalling 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.

DESCRIPTION OF SYMBOLS 1 Refractory layer of main body 2 Inner hole 3 Refractory layer (lining) of this invention
4 Of the refractory layers of the main body, a zirconia-graphite layer (for mold powder)
11 Long nozzle 12 Immersion nozzle 13 Lower nozzle

Claims (2)

When the volume of the refractory component excluding the component composed of a free carbon component is defined as 100% by volume, particles having a size of 0.045 mm or less are 10% by volume to 50% by volume, 0.045mm. Particles having a particle size of 40% by volume or less (including zero) larger than 0.21 mm in size and 40% by volume or more and 90% by volume or less of particles greater than 0.21 mm,
When the total of particles having a size of 0.045 mm or less in the refractory and the free carbon component is 100% by mass, the free carbon component is 3.0% by mass or more and 35.0% by mass or less. The total of the SiO ₂ component and the CaO component in the chemical composition is 0.4 mass% or more and 5.0 mass% or less,
The remainder of the particles having a size of 0.045 mm or less excluding the free carbon component, the SiO ₂ component and the CaO component has an average molar ratio (Al ₂ O ₃ / MgO) of the entire particle group of 1.05. It is configured to include particles composed of corundum (Al ₂ O ₃ ) and spinel (Al ₂ O ₃ .MgO) having a mineral composition of 2.35 or less,
Continuous casting in which a portion excluding particles having a size of 0.045 mm or less and a free carbon component is composed of one or both of corundum (Al ₂ O ₃ ) and spinel (Al ₂ O ₃ .MgO). Refractories for use.   The refractory for continuous casting according to claim 1, wherein the refractory for continuous casting is a nozzle for continuous casting arranged in a part or all of the inner hole surface of the nozzle, and the thickness of the refractory for continuous casting is the continuous casting. A continuous casting nozzle that is equal to or greater than the value obtained by multiplying the damage rate of the refractory by a set usage time plus 2 mm.

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